draft-ietf-rmt-pi-norm-revised-06.txt   draft-ietf-rmt-pi-norm-revised-07.txt 
Reliable Multicast Transport (RMT) B. Adamson Network Working Group B. Adamson
Working Group NRL Internet-Draft Naval Research Laboratory
Internet-Draft C. Bormann Intended status: Standards Track C. Bormann
Expires: 31 July 2008 Universitaet Bremen TZI Expires: April 27, 2009 Universitaet Bremen TZI
M. Handley M. Handley
UCL University College London
J. Macker J. Macker
NRL Naval Research Laboratory
NACK-Oriented Reliable Multicast (NORM) Protocol October 24, 2008
draft-ietf-rmt-pi-norm-revised-06
NACK-Oriented Reliable Multicast Protocol
draft-ietf-rmt-pi-norm-revised-07
Status of this Memo Status of this Memo
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This Internet-Draft will expire on July 31, 2008. This Internet-Draft will expire on April 27, 2009.
Copyright Notice
Copyright (C) The IETF Trust (2008).
Abstract Abstract
This document describes the messages and procedures of the Negative- This document describes the messages and procedures of the Negative-
acknowledgment (NACK) Oriented Reliable Multicast (NORM) protocol. ACKnowledgment (NACK) Oriented Reliable Multicast (NORM) Protocol.
This protocol is designed to provide end-to-end reliable transport of This protocol is designed to provide end-to-end reliable transport of
bulk data objects or streams over generic IP multicast routing and bulk data objects or streams over generic IP multicast routing and
forwarding services. NORM uses a selective, negative acknowledgment forwarding services. NORM uses a selective, negative acknowledgment
mechanism for transport reliability and offers additional protocol mechanism for transport reliability and offers additional protocol
mechanisms to allow for operation with minimal "a priori" mechanisms to allow for operation with minimal a priori coordination
coordination among senders and receivers. A congestion control among senders and receivers. A congestion control scheme is
scheme is specified to allow the NORM protocol to fairly share specified to allow the NORM protocol to fairly share available
available network bandwidth with other transport protocols such as network bandwidth with other transport protocols such as Transmission
Transmission Control Protocol (TCP). It is capable of operating with Control Protocol (TCP). It is capable of operating with both
both reciprocal multicast routing among senders and receivers and reciprocal multicast routing among senders and receivers and with
with asymmetric connectivity (possibly a unicast return path) between asymmetric connectivity (possibly a unicast return path) between the
the senders and receivers. The protocol offers a number of features senders and receivers. The protocol offers a number of features to
to allow different types of applications or possibly other higher allow different types of applications or possibly other higher level
level transport protocols to utilize its service in different ways. transport protocols to utilize its service in different ways. The
The protocol leverages the use of FEC-based repair and other IETF protocol leverages the use of FEC-based repair and other IETF
reliable multicast transport (RMT) building blocks in its design. reliable multicast transport (RMT) building blocks in its design.
Table of Contents Requirements Language
1. Introduction and Applicability. . . . . . . . . . . . . . . . . . 5 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
1.1. NORM Delivery Service Model. . . . . . . . . . . . . . . . . . 6 NOT","SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
1.2. NORM Scalability . . . . . . . . . . . . . . . . . . . . . . . 8 this document are to be interpreted as described in [RFC2119].
1.3. Environmental Requirements and Considerations. . . . . . . . . 9
2. Architecture Definition . . . . . . . . . . . . . . . . . . . . . 9
2.1. Protocol Operation Overview. . . . . . . . . . . . . . . . . . 11
2.2. Protocol Building Blocks . . . . . . . . . . . . . . . . . . . 13
2.3. Design Tradeoffs . . . . . . . . . . . . . . . . . . . . . . . 13
3. Conformance Statement . . . . . . . . . . . . . . . . . . . . . . 14
4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . . . 16
4.1. NORM Common Message Header and Extensions. . . . . . . . . . . 17
4.2. Sender Messages. . . . . . . . . . . . . . . . . . . . . . . . 19
4.2.1. NORM_DATA Message . . . . . . . . . . . . . . . . . . . . . 20
4.2.2. NORM_INFO Message . . . . . . . . . . . . . . . . . . . . . 30
4.2.3. NORM_CMD Messages . . . . . . . . . . . . . . . . . . . . . 32
4.3. Receiver Messages. . . . . . . . . . . . . . . . . . . . . . . 50
4.3.1. NORM_NACK Message . . . . . . . . . . . . . . . . . . . . . 50
4.3.2. NORM_ACK Message. . . . . . . . . . . . . . . . . . . . . . 57
4.4. General Purpose Messages . . . . . . . . . . . . . . . . . . . 59
4.4.1. NORM_REPORT Message . . . . . . . . . . . . . . . . . . . . 59
5. Detailed Protocol Operation . . . . . . . . . . . . . . . . . . . 59
5.1. Sender Initialization and Transmission . . . . . . . . . . . . 61
5.1.1. Object Segmentation Algorithm . . . . . . . . . . . . . . . 62
5.2. Receiver Initialization and Reception. . . . . . . . . . . . . 63
5.3. Receiver NACK Procedure. . . . . . . . . . . . . . . . . . . . 63
5.4. Sender NACK Processing and Response. . . . . . . . . . . . . . 66
5.4.1. Sender Repair State Aggregation . . . . . . . . . . . . . . 66
5.4.2. Sender FEC Repair Transmission Strategy . . . . . . . . . . 67
5.4.3. Sender NORM_CMD(SQUELCH) Generation . . . . . . . . . . . . 68
5.4.4. Sender NORM_CMD(REPAIR_ADV) Generation. . . . . . . . . . . 69
5.5. Additional Protocol Mechanisms . . . . . . . . . . . . . . . . 69
5.5.1. Greatest Round-trip Time Collection . . . . . . . . . . . . 70
5.5.2. NORM Congestion Control Operation . . . . . . . . . . . . . 71
5.5.3. NORM Positive Acknowledgment Procedure. . . . . . . . . . . 80
5.5.4. Group Size Estimate . . . . . . . . . . . . . . . . . . . . 82
6. Security Considerations . . . . . . . . . . . . . . . . . . . . . 82
6.1. Baseline Secure NORM Operation . . . . . . . . . . . . . . . . 83
6.1.1. IPSec Approach. . . . . . . . . . . . . . . . . . . . . . . 84
6.1.2. IPSec Requirements. . . . . . . . . . . . . . . . . . . . . 86
6.1.2.1. Selectors. . . . . . . . . . . . . . . . . . . . . . . . 86
6.1.2.2. Mode . . . . . . . . . . . . . . . . . . . . . . . . . . 87
6.1.2.3. Key Management . . . . . . . . . . . . . . . . . . . . . 87
6.1.2.4. Security Policy. . . . . . . . . . . . . . . . . . . . . 87
6.1.2.5. Authentication and Encryption. . . . . . . . . . . . . . 87
6.1.2.6. Availability . . . . . . . . . . . . . . . . . . . . . . 87
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . . 88 Table of Contents
8. Suggested Use . . . . . . . . . . . . . . . . . . . . . . . . . . 89
9. Changes from RFC3940. . . . . . . . . . . . . . . . . . . . . . . 89 1. Introduction and Applicability . . . . . . . . . . . . . . . . 5
10. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . . 90 1.1. NORM Data Delivery Service Model . . . . . . . . . . . . . 6
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 1.2. NORM Scalability . . . . . . . . . . . . . . . . . . . . . 8
11.1. Normative References. . . . . . . . . . . . . . . . . . . . . 90 1.3. Environmental Requirements and Considerations . . . . . . 9
11.2. Informative References. . . . . . . . . . . . . . . . . . . . 91 2. Architecture Definition . . . . . . . . . . . . . . . . . . . 9
12. Authors’ Addresses . . . . . . . . . . . . . . . . . . . . . . . 93 2.1. Protocol Operation Overview . . . . . . . . . . . . . . . 11
13. Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 94 2.2. Protocol Building Blocks . . . . . . . . . . . . . . . . . 13
2.3. Design Tradeoffs . . . . . . . . . . . . . . . . . . . . . 13
3. Conformance Statement . . . . . . . . . . . . . . . . . . . . 14
4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 16
4.1. NORM Common Message Header and Extensions . . . . . . . . 16
4.2. Sender Messages . . . . . . . . . . . . . . . . . . . . . 19
4.2.1. NORM_DATA Message . . . . . . . . . . . . . . . . . . 19
4.2.2. NORM_INFO Message . . . . . . . . . . . . . . . . . . 29
4.2.3. NORM_CMD Messages . . . . . . . . . . . . . . . . . . 30
4.3. Receiver Messages . . . . . . . . . . . . . . . . . . . . 48
4.3.1. NORM_NACK Message . . . . . . . . . . . . . . . . . . 48
4.3.2. NORM_ACK Message . . . . . . . . . . . . . . . . . . . 54
4.4. General Purpose Messages . . . . . . . . . . . . . . . . . 56
4.4.1. NORM_REPORT Message . . . . . . . . . . . . . . . . . 56
5. Detailed Protocol Operation . . . . . . . . . . . . . . . . . 56
5.1. Sender Initialization and Transmission . . . . . . . . . . 58
5.1.1. Object Segmentation Algorithm . . . . . . . . . . . . 59
5.2. Receiver Initialization and Reception . . . . . . . . . . 60
5.3. Receiver NACK Procedure . . . . . . . . . . . . . . . . . 60
5.4. Sender NACK Processing and Response . . . . . . . . . . . 62
5.4.1. Sender Repair State Aggregation . . . . . . . . . . . 63
5.4.2. Sender FEC Repair Transmission Strategy . . . . . . . 64
5.4.3. Sender NORM_CMD(SQUELCH) Generation . . . . . . . . . 65
5.4.4. Sender NORM_CMD(REPAIR_ADV) Generation . . . . . . . . 65
5.5. Additional Protocol Mechanisms . . . . . . . . . . . . . . 66
5.5.1. Greatest Round-trip Time Collection . . . . . . . . . 66
5.5.2. NORM Congestion Control Operation . . . . . . . . . . 67
5.5.3. NORM Positive Acknowledgment Procedure . . . . . . . . 75
5.5.4. Group Size Estimate . . . . . . . . . . . . . . . . . 77
6. Security Considerations . . . . . . . . . . . . . . . . . . . 78
6.1. Baseline Secure NORM Operation . . . . . . . . . . . . . . 79
6.1.1. IPsec Approach . . . . . . . . . . . . . . . . . . . . 80
6.1.2. IPsec Requirements . . . . . . . . . . . . . . . . . . 82
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 83
7.1. Explicit IANA Assignment Guidelines . . . . . . . . . . . 83
8. Suggested Use . . . . . . . . . . . . . . . . . . . . . . . . 84
9. Changes from RFC3940 . . . . . . . . . . . . . . . . . . . . . 85
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 85
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 86
11.1. Normative References . . . . . . . . . . . . . . . . . . . 86
11.2. Informative References . . . . . . . . . . . . . . . . . . 86
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 88
Intellectual Property and Copyright Statements . . . . . . . . . . 90
1. Introduction and Applicability 1. Introduction and Applicability
The Negative-acknowledgment (NACK) Oriented Reliable Multicast (NORM) The Negative-acknowledgment (NACK) Oriented Reliable Multicast (NORM)
protocol is designed to provide reliable transport of data from one protocol is designed to provide reliable transport of data from one
or more sender(s) to a group of receivers over an IP multicast or more sender(s) to a group of receivers over an IP multicast
network. The primary design goals of NORM are to provide efficient, network. The primary design goals of NORM are to provide efficient,
scalable, and robust bulk data (e.g., computer files, transmission of scalable, and robust bulk data (e.g., computer files, transmission of
persistent data) transfer across possibly heterogeneous IP networks persistent data) transfer across possibly heterogeneous IP networks
and topologies. The NORM protocol design provides support for and topologies. The NORM protocol design provides support for
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multicast session. NORM is designed to be self-adapting to a wide multicast session. NORM is designed to be self-adapting to a wide
range of dynamic network conditions with little or no pre- range of dynamic network conditions with little or no pre-
configuration. The protocol is purposely designed to be tolerant of configuration. The protocol is purposely designed to be tolerant of
inaccurate timing estimations or lossy conditions that may occur in inaccurate timing estimations or lossy conditions that may occur in
many networks including mobile and wireless. The protocol is also many networks including mobile and wireless. The protocol is also
designed to exhibit convergence and efficient operation even in designed to exhibit convergence and efficient operation even in
situations of heavy packet loss and large queuing or transmission situations of heavy packet loss and large queuing or transmission
delays. delays.
This document is a product of the IETF RMT WG and follows the This document is a product of the IETF RMT WG and follows the
guidelines provided in RFC 3269 [9]. The key words "MUST", "MUST guidelines provided in [RFC3269].
NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT",
"RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be
interpreted as described in BCP 14, RFC 2119 [1].
Statement of Intent Statement of Intent
This memo contains the definitions necessary to fully specify a This memo contains the definitions necessary to fully specify a
Reliable Multicast Transport protocol in accordance with RFC 2357. Reliable Multicast Transport protocol in accordance with the criteria
RFC3940 [10] contained a previous description of the NORM Protocol of [RFC2357]. A prior document, [RFC3940], contained a previous
specification described in this document. RF3940 was published in description of the NORM Protocol specification described in this
the "Experimental" category. It was the stated intent of the RMT document. RFC3940 was published in the "Experimental" category. It
working group to re-submit this specifications as an IETF Proposed was the stated intent of the RMT working group to re-submit this
Standard in due course. specifications as an IETF Proposed Standard in due course.
This Proposed Standard specification is thus based on RFC3940 [10] This Proposed Standard specification is thus based on [RFC3940] and
and has been updated according to accumulated experience and growing has been updated according to accumulated experience and growing
protocol maturity since the publication of RFC3940. Said experience protocol maturity since the publication of RFC3940. Said experience
applies both to this specification itself and to congestion control applies both to this specification itself and to congestion control
strategies related to the use of this specification. strategies related to the use of this specification.
The differences between RFC3940 [10] and this document are listed in The differences between [RFC3940] and this document are listed in
Section 9. Section 9.
1.1. NORM Delivery Service Model 1.1. NORM Data Delivery Service Model
A NORM protocol instance (NormSession) is defined within the context A NORM protocol instance (NormSession) is defined within the context
of participants communicating connectionless (e.g., Internet Protocol of participants communicating connectionless (e.g., Internet Protocol
(IP) or User Datagram Protocol (UDP)) packets over a network using (IP) or User Datagram Protocol (UDP)) packets over a network using
pre-determined addresses and host port numbers. Generally, the pre-determined addresses and host port numbers. Generally, the
participants exchange packets using an IP multicast group address, participants exchange packets using an IP multicast group address,
but unicast transport may also be established or applied as an but unicast transport may also be established or applied as an
adjunct to multicast delivery. In the case of multicast, the adjunct to multicast delivery. In the case of multicast, the
participating NormNodes will communicate using a common IP multicast participating NormNodes will communicate using a common IP multicast
group address and port number that has been chosen via means outside group address and port number that has been chosen via means outside
the context of the given NormSession. Other IETF data format and the context of the given NormSession. Other IETF data format and
protocol standards exist that may be applied to describe and convey protocol standards exist that may be applied to describe and convey
the required "a priori" information for a specific NormSession (e.g., the required a priori information for a specific NormSession (e.g.,
Session Description Protocol (SDP) [11], Session Announcement Session Description Protocol (SDP) [RFC4566], Session Announcement
Protocol (SAP) [12], etc.). Protocol (SAP) [RFC2974], etc.).
The NORM protocol design is principally driven by the assumption of a The NORM protocol design is principally driven by the assumption of a
single sender transmitting bulk data content to a group of receivers. single sender transmitting bulk data content to a group of receivers.
However, the protocol MAY operate with multiple senders within the However, the protocol MAY operate with multiple senders within the
context of a single NormSession. In initial implementations of this context of a single NormSession. In initial implementations of this
protocol, it is anticipated that multiple senders will transmit protocol, it is anticipated that multiple senders will transmit
independent of one another and receivers will maintain state as independent of one another and receivers will maintain state as
necessary for each sender. However, in future versions of NORM, it necessary for each sender. However, in future versions of NORM, it
is possible that some aspects of protocol operation (e.g., round-trip is possible that some aspects of protocol operation (e.g., round-trip
time collection) may provide for alternate modes allowing more time collection) may provide for alternate modes allowing more
efficient performance for applications requiring multiple senders. efficient performance for applications requiring multiple senders.
NORM provides for three types of bulk data content objects NORM provides for three types of bulk data content objects
(NormObjects) to be reliably transported. These types include: (NormObjects) to be reliably transported. These types include:
1) static computer memory data content (NORM_OBJECT_DATA type), 1. static computer memory data content ("NORM_OBJECT_DATA" type),
2) computer storage files (NORM_OBJECT_FILE type), and 2. computer storage files ("NORM_OBJECT_FILE" type), and
3) non-finite streams of continuous data content 3. non-finite streams of continuous data content
(NORM_OBJECT_STREAM type). ("NORM_OBJECT_STREAM" type).
The distinction between NORM_OBJECT_DATA and NORM_OBJECT_FILE is The distinction between "NORM_OBJECT_DATA" and "NORM_OBJECT_FILE" is
simply to provide a "hint" to receivers in NormSessions serving simply to provide a hint to receivers in NormSessions serving
multiple types of content as to what type of storage should be multiple types of content as to what type of storage should be
allocated for received content (i.e., memory or file storage). Other allocated for received content (i.e., memory or file storage). Other
than that distinction, the two are identical, providing for reliable than that distinction, the two are identical, providing for reliable
transport of finite (but potentially very large) units of content. transport of finite (but potentially very large) units of content.
These static data and file services are anticipated to be useful for These static data and file services are anticipated to be useful for
multicast-based cache applications with the ability to reliably multicast-based cache applications with the ability to reliably
provide transmission of large quantities of static data. Other types provide transmission of large quantities of static data. Other types
of static data/file delivery services might make use of these of static data/file delivery services might make use of these
transport object types, too. The use of the NORM_OBJECT_STREAM type transport object types, too. The use of the "NORM_OBJECT_STREAM"
is at the application’s discretion and could be used to carry static type is at the application's discretion and could be used to carry
data or file content also. The NORM reliable stream service opens up static data or file content also. The NORM reliable stream service
additional possibilities such as serialized reliable messaging or opens up additional possibilities such as serialized reliable
other unbounded, perhaps dynamically produced content. The messaging or other unbounded, perhaps dynamically produced content.
NORM_OBJECT_STREAM provides for reliable transport analogous to that The "NORM_OBJECT_STREAM" provides for reliable transport analogous to
of the Transmission Control Protocol (TCP), although NORM receivers that of the Transmission Control Protocol (TCP), although NORM
will be able to begin receiving stream content at any point in time. receivers will be able to begin receiving stream content at any point
The applicability of this feature will depend upon the application. in time. The applicability of this feature will depend upon the
application.
The NORM protocol also allows for a small amount of "out-of-band" The NORM protocol also allows for a small amount of out-of-band data
data (sent as NORM_INFO messages) to be attached to the data content (sent as "NORM_INFO" messages) to be attached to the data content
objects transmitted by the sender. This readily-available "out-of- objects transmitted by the sender. This readily-available out-of-
band" data allows multicast receivers to quickly and efficiently band data allows multicast receivers to quickly and efficiently
determine the nature of the corresponding data, file, or stream bulk determine the nature of the corresponding data, file, or stream bulk
content being transmitted. This allows application-level control of content being transmitted. This allows application-level control of
the receiver nodes participation in the current transport activity. the receiver node's participation in the current transport activity.
This also allows the protocol to be flexible with minimal pre- This also allows the protocol to be flexible with minimal pre-
coordination among senders and receivers. The NORM_INFO content is coordination among senders and receivers. The "NORM_INFO" content is
designed to be atomic in that its size MUST fit into the payload designed to be atomic in that its size MUST fit into the payload
portion of a single NORM message. portion of a single NORM message.
NORM does _not_ provide for global or application-level NORM does NOT provide for global or application-level identification
identification of data content within in its message headers. Note of data content within in its message headers. Note the "NORM_INFO"
the NORM_INFO out-of-band data mechanism could be leveraged by the out-of-band data mechanism could be leveraged by the application for
application for this purpose if desired, or identification could this purpose if desired, or identification could alternatively be
alternatively be embedded within the data content. NORM does embedded within the data content. NORM does identify transmitted
identify transmitted content (NormObjects) with transport identifiers content (NormObjects) with transport identifiers that are applicable
that are applicable only while the sender is transmitting and/or only while the sender is transmitting and/or repairing the given
repairing the given object. These transport data content identifiers object. These transport data content identifiers (NormTransportIds)
(NormTransportIds) are assigned in a monotonically increasing fashion are assigned in a monotonically increasing fashion by each NORM
by each NORM sender during the course of a NormSession. Each sender sender during the course of a NormSession. Each sender maintains its
maintains its NormTransportId assignments independently so that NormTransportId assignments independently so that individual
individual NormObjects may be uniquely identified during transport NormObjects may be uniquely identified during transport with the
with the concatenation of the sender session-unique identifier concatenation of the sender session-unique identifier (NormNodeId)
(NormNodeId) and the assigned NormTransportId. The NormTransportIds and the assigned NormTransportId. The NormTransportIds are assigned
are assigned from a large, but fixed, numeric space in increasing from a large, but fixed, numeric space in increasing order and may be
order and may be reassigned during long-lived sessions. The NORM reassigned during long-lived sessions. The NORM protocol provides
protocol provides mechanisms so that the sender application may mechanisms so that the sender application may terminate transmission
terminate transmission of data content and inform the group of this of data content and inform the group of this in an efficient manner.
in an efficient manner. Other similar protocol control mechanisms Other similar protocol control mechanisms (e.g., session termination,
(e.g., session termination, receiver synchronization, etc.) are receiver synchronization, etc.) are specified so that reliable
specified so that reliable multicast application variants may multicast application variants may construct different, complete bulk
construct different, complete bulk transfer communication models to transfer communication models to meet their goals.
meet their goals.
To summarize, the NORM protocol provides reliable transport of To summarize, the NORM protocol provides reliable transport of
different types of data content (including potentially mixed types). different types of data content (including potentially mixed types).
The senders enqueue and transmit bulk content in the form of static The senders enqueue and transmit bulk content in the form of static
data or files and/or non-finite, ongoing stream types. NORM senders data or files and/or non-finite, ongoing stream types. NORM senders
provide for repair transmission of data and/or FEC content in provide for repair transmission of data and/or FEC content in
response to NACK messages received from the receiver group. response to NACK messages received from the receiver group.
Mechanisms for "out-of-band" information and other transport control Mechanisms for out-of-band information and other transport control
mechanisms are specified for use by applications to form complete mechanisms are specified for use by applications to form complete
reliable multicast solutions for different purposes. reliable multicast solutions for different purposes.
1.2. NORM Scalability 1.2. NORM Scalability
Group communication scalability requirements lead to adaptation of Group communication scalability requirements lead to adaptation of
negative acknowledgment (NACK) based protocol schemes when feedback negative acknowledgment (NACK) based protocol schemes when feedback
for reliability is required [13]. NORM is a protocol centered around for reliability is required [RmComparison]. NORM is a protocol
the use of selective NACKs to request repairs of missing data. NORM centered around the use of selective NACKs to request repairs of
provides for the use of packet-level forward error correction (FEC) missing data. NORM provides for the use of packet-level forward
techniques for efficient multicast repair and optional proactive error correction (FEC) techniques for efficient multicast repair and
transmission robustness [14]. FEC-based repair can be used to optional proactive transmission robustness [RFC3453]. FEC-based
greatly reduce the quantity of reliable multicast repair requests and repair can be used to greatly reduce the quantity of reliable
repair transmissions [15] in a NACK-oriented protocol. The principal multicast repair requests and repair transmissions [MdpToolkit] in a
factor in NORM scalability is the volume of feedback traffic NACK-oriented protocol. The principal factor in NORM scalability is
generated by the receiver set to facilitate reliability and the volume of feedback traffic generated by the receiver set to
congestion control. NORM uses probabilistic suppression of redundant facilitate reliability and congestion control. NORM uses
feedback based on exponentially distributed random backoff timers. probabilistic suppression of redundant feedback based on
The performance of this type of suppression relative to other exponentially distributed random backoff timers. The performance of
techniques is described in [16]. NORM dynamically measures the this type of suppression relative to other techniques is described in
group’s roundtrip timing status to set its suppression and other [McastFeedback]. NORM dynamically measures the group's round-trip
protocol timers. This allows NORM to scale well while maintaining timing status to set its suppression and other protocol timers. This
reliable data delivery transport with low latency relative to the allows NORM to scale well while maintaining reliable data delivery
network topology over which it is operating. transport with low latency relative to the network topology over
which it is operating.
Feedback messages can be either multicast to the group at large or Feedback messages can be either multicast to the group at large or
sent via unicast routing to the sender. In the case of unicast sent via unicast routing to the sender. In the case of unicast
feedback, the sender "advertises" the feedback state to the group to feedback, the sender relays the feedback state to the group to
facilitate feedback suppression. In typical Internet environments, facilitate feedback suppression. In typical Internet environments,
it is expected that the NORM protocol will readily scale to group it is expected that the NORM protocol will readily scale to group
sizes on the order of tens of thousands of receivers. A study of the sizes on the order of tens of thousands of receivers. A study of the
quantity of feedback for this type of protocol is described in [17]. quantity of feedback for this type of protocol is described in
NORM is able to operate with a smaller amount of feedback than a [NormFeedback]. NORM is able to operate with a smaller amount of
single TCP connection, even with relatively large numbers of feedback than a single TCP connection, even with relatively large
receivers. Thus, depending upon the network topology, it is possible numbers of receivers. Thus, depending upon the network topology, it
that NORM may scale to larger group sizes. With respect to computer is possible that NORM may scale to larger group sizes. With respect
resource usage, the NORM protocol does _not_ require that state be to computer resource usage, the NORM protocol does NOT require that
kept on all receivers in the group. NORM senders maintain state only state be kept on all receivers in the group. NORM senders maintain
for receivers providing explicit congestion control feedback. NORM state only for receivers providing explicit congestion control
receivers must maintain state for each active sender. This may feedback. However, NORM receivers must maintain state for each
constrain the number of simultaneous senders in some uses of NORM. active sender. This may constrain the number of simultaneous senders
in some uses of NORM.
1.3. Environmental Requirements and Considerations 1.3. Environmental Requirements and Considerations
All of the environmental requirements and considerations that apply All of the environmental requirements and considerations that apply
to the RMT NORM Building Block [3], the RMT FEC Building Block [4], to the RMT Multicast NACK Building Block
and the RMT TCP-Friendly Multicast Congestion Control (TFMCC) [I-D.ietf-rmt-bb-norm-revised], FEC Building Block [RFC5052], and
Building Block [5], also apply to the NORM protocol. TCP-Friendly Multicast Congestion Control (TFMCC) Building Block
[RFC4654], also apply to the NORM protocol.
The NORM protocol SHALL be capable of operating in an end-to-end The NORM protocol SHALL be capable of operating in an end-to-end
fashion with no assistance from intermediate systems beyond basic IP fashion with no assistance from intermediate systems beyond basic IP
multicast group management, routing, and forwarding services. While multicast group management, routing, and forwarding services. While
the techniques utilized in NORM are principally applicable to "flat" the techniques utilized in NORM are principally applicable to flat,
end-to-end IP multicast topologies, they could also be applied in the end-to-end IP multicast topologies, they could also be applied in the
sub-levels of hierarchical (e.g., tree-based) multicast distribution sub-levels of hierarchical (e.g., tree-based) multicast distribution
if so desired. NORM can make use of reciprocal (among senders and if so desired. NORM can make use of reciprocal (among senders and
receivers) multicast communication under the Any-Source Multicast receivers) multicast communication under the Any-Source Multicast
(ASM) model defined in RFC 1112 [2], but SHALL also be capable of (ASM) model defined in [RFC1112], but SHALL also be capable of
scalable operation in asymmetric topologies such as Source Specific scalable operation in asymmetric topologies such as Source-Specific
Multicast (SSM) [18] where there may only be unicast routing service Multicast (SSM) [RFC4607] where there may only be unicast routing
from the receivers to the sender(s). service from the receivers to the sender(s).
NORM is compatible with IPv4 and IPv6. Additionally, NORM may be NORM is compatible with IPv4 and IPv6. Additionally, NORM may be
used with networks employing Network Address Translation (NAT) used with networks employing Network Address Translation (NAT)
providing the NAT device supports IP multicast and/or can cache UDP providing the NAT device supports IP multicast and/or can cache UDP
traffic source port numbers for remapping feedback traffic from traffic source port numbers for remapping feedback traffic from
receivers to the sender(s). receivers to the sender(s).
2. Architecture Definition 2. Architecture Definition
A NormSession is comprised of participants (NormNodes) acting as A NormSession is comprised of participants (NormNodes) acting as
senders and/or receivers. NORM senders transmit data content in the senders and/or receivers. NORM senders transmit data content in the
form of NormObjects to the session destination address and the NORM form of NormObjects to the session destination address and the NORM
receivers attempt to reliably receive the transmitted content using receivers attempt to reliably receive the transmitted content using
negative acknowledgments to request repair. Each NormNode within a negative acknowledgments to request repair. Each NormNode within a
NormSession is assumed to have a preselected unique 32-bit identifier NormSession is assumed to have a preselected unique 32-bit identifier
(NormNodeId). NormNodes MUST have uniquely assigned identifiers (NormNodeId). NormNodes MUST have uniquely assigned identifiers
within a single NormSession to distinguish between possible multiple within a single NormSession to distinguish between possible multiple
senders and to distinguish feedback information from different senders and to distinguish feedback information from different
receivers. There are two reserved NormNodeId values. A value of receivers. There are two reserved NormNodeId values. A value of
0x00000000 is considered an invalid NormNodeId value and a value of "0x00000000" is considered an invalid NormNodeId value and a value of
0xffffffff is a "wildcard" NormNodeId. While the protocol does not "0xffffffff" is a "wild card" NormNodeId. While the protocol does
preclude multiple sender nodes concurrently transmitting within the not preclude multiple sender nodes concurrently transmitting within
context of a single NORM session (i.e., many- to-many operation), any the context of a single NORM session (i.e., many- to-many operation),
type of interactive coordination among NORM senders is assumed to be any type of interactive coordination among NORM senders is assumed to
controlled by the application or higher protocol layer. There are be controlled by the application or higher protocol layer. There are
some optional mechanisms specified in this document that can be some optional mechanisms specified in this document that can be
leveraged for such application layer coordination. leveraged for such application layer coordination.
As previously noted, NORM allows for reliable transmission of three As previously noted, NORM allows for reliable transmission of three
different basic types of data content. The first type is different basic types of data content. The first type is
NORM_OBJECT_DATA, which is used for static, persistent blocks of data "NORM_OBJECT_DATA", which is used for static, persistent blocks of
content maintained in the sender’s application memory storage. The data content maintained in the sender's application memory storage.
second type is NORM_OBJECT_FILE, which corresponds to data stored in The second type is "NORM_OBJECT_FILE", which corresponds to data
the sender’s non-volatile file system. The NORM_OBJECT_DATA and stored in the sender's non-volatile file system. The
NORM_OBJECT_FILE types both represent "NormObjects" of finite but "NORM_OBJECT_DATA" and "NORM_OBJECT_FILE" types both represent
potentially very large size. The third type of data content is NormObjects of finite but potentially very large size. The third
NORM_OBJECT_STREAM, which corresponds to an ongoing transmission of type of data content is "NORM_OBJECT_STREAM", which corresponds to an
undefined length. This is analogous to the reliable stream service ongoing transmission of undefined length. This is analogous to the
provide by TCP for unicast data transport. The format of the stream reliable stream service provide by TCP for unicast data transport.
content is application-defined and may be byte or message oriented. The format of the stream content is application-defined and may be
The NORM protocol provides for "flushing" of the stream to expedite byte or message oriented. The NORM protocol provides for "flushing"
delivery or possibly enforce application message boundaries. NORM of the stream to expedite delivery or possibly enforce application
protocol implementations may offer either (or both) in-order delivery message boundaries. NORM protocol implementations may offer either
of the stream data to the receive application or out-of-order (more (or both) in-order delivery of the stream data to the receive
immediate) delivery of received segments of the stream to the application or out-of-order (more immediate) delivery of received
receiver application. In either case, NORM sender and receiver segments of the stream to the receiver application. In either case,
implementations provide buffering to facilitate repair of the stream NORM sender and receiver implementations provide buffering to
as it is transported. facilitate repair of the stream as it is transported.
All NormObjects are logically segmented into FEC coding blocks and All NormObjects are logically segmented into FEC coding blocks and
symbols for transmission by the sender. In NORM, an FEC encoding symbols for transmission by the sender. In NORM, an FEC encoding
symbol directly corresponds to the payload of NORM_DATA messages or symbol directly corresponds to the payload of "NORM_DATA" messages or
"segment". Note that when systematic FEC codes are used, the payload "segment". Note that when systematic FEC codes are used, the payload
of NORM_DATA messages sent for the first portion of a FEC encoding of "NORM_DATA" messages sent for the first portion of a FEC encoding
block are source symbols (actual segments of original user data), block are source symbols (actual segments of original user data),
while the remaining symbols for the block consist of parity symbols while the remaining symbols for the block consist of parity symbols
generated by FEC encoding. These parity symbols are generally sent generated by FEC encoding. These parity symbols are generally sent
in response to repair requests, but some number may be sent in response to repair requests, but some number may be sent
proactively at the end each encoding block to increase the robustness proactively at the end each encoding block to increase the robustness
of transmission. When non-systematic FEC codes are used, all symbols of transmission. When non-systematic FEC codes are used, all symbols
sent consist of FEC encoding parity content. In this case, the sent consist of FEC encoding parity content. In this case, the
receiver must receive a sufficient number of symbols to reconstruct receiver must receive a sufficient number of symbols to reconstruct
(via FEC decoding) the original user data for the given block. In (via FEC decoding) the original user data for the given block.
this document, the terms "symbol" and "segment" are used
interchangeably.
Transmitted NormObjects are temporarily yet uniquely identified Transmitted NormObjects are temporarily yet uniquely identified
within the NormSession context using the given senders NormNodeId, within the NormSession context using the given sender's NormNodeId,
NormInstanceId, and a temporary NormObjectTransportId. Depending NormInstanceId, and a temporary NormObjectTransportId. Depending
upon the implementation, individual NORM senders may manage their upon the implementation, individual NORM senders may manage their
NormInstanceIds independently, or a common NormInstanceId may be NormInstanceIds independently, or a common NormInstanceId may be
agreed upon for all participating nodes within a session if needed as agreed upon for all participating nodes within a session if needed as
a session identifier. NORM NormObjectTransportId data content a session identifier. NORM NormObjectTransportId data content
identifiers are sender-assigned and applicable and valid only during identifiers are sender-assigned and applicable and valid only during
a NormObject’s actual _transport_ (i.e., for as long as the sender is a NormObject's actual transport (i.e., for as long as the sender is
transmitting and providing repair of the indicated NormObject). For transmitting and providing repair of the indicated NormObject). For
a long-lived session, the NormObjectTransportId field can wrap and a long-lived session, the NormObjectTransportId field can wrap and
previously-used identifiers may be re-used. Note that globally previously-used identifiers may be re-used. Note that globally
unique identification of transported data content is not provided by unique identification of transported data content is not provided by
NORM and, if required, must be managed by the NORM application. The NORM and, if required, must be managed by the NORM application. The
individual segments or symbols of the NormObject are further individual segments or symbols of the NormObject are further
identified with FEC payload identifiers which include coding block identified with FEC payload identifiers which include coding block
and symbol identifiers. These are discussed in detail later in this and symbol identifiers. These are discussed in detail later in this
document. document.
2.1. Protocol Operation Overview 2.1. Protocol Operation Overview
A NORM sender primarily generates messages of type NORM_DATA. These A NORM sender primarily generates messages of type "NORM_DATA".
messages carry original data segments or FEC symbols and repair These messages carry original data segments or FEC symbols and repair
segments/symbols for the bulk data/file or stream NormObjects being segments/symbols for the bulk data/file or stream NormObjects being
transferred. By default, redundant FEC symbols are sent only in transferred. By default, redundant FEC symbols are sent only in
response to receiver repair requests (NACKs) and thus normally little response to receiver repair requests (NACKs) and thus normally little
or no additional transmission overhead is imposed due to FEC or no additional transmission overhead is imposed due to FEC
encoding. However, the NORM implementation MAY be optionally encoding. However, the NORM implementation MAY be optionally
configured to proactively transmit some amount of redundant FEC configured to proactively transmit some amount of redundant FEC
symbols along with the original content to potentially enhance symbols along with the original content to potentially enhance
performance (e.g., improved delay) at the cost of additional performance (e.g., improved delay) at the cost of additional
transmission overhead. This option may be sensible for certain transmission overhead. This option may be sensible for certain
network conditions and can allow for robust, asymmetric multicast network conditions and can allow for robust, asymmetric multicast
(e.g., unidirectional routing, satellite, cable) [19] with reduced (e.g., unidirectional routing, satellite, cable) [FecHybrid] with
receiver feedback, or, in some cases, no feedback. reduced receiver feedback, or, in some cases, no feedback.
A sender message of type NORM_INFO is also defined and is used to A sender message of type "NORM_INFO" is also defined and is used to
carry OPTIONAL "out-of-band" context information for a given carry OPTIONAL out-of-band context information for a given transport
transport object. A single NORM_INFO message can be associated with object. A single "NORM_INFO" message can be associated with a
a NormObject. Because of its atomic nature, missing NORM_INFO NormObject. Because of its atomic nature, missing "NORM_INFO"
messages can be NACKed and repaired with a slightly lower delay messages can be NACKed and repaired with a slightly lower delay
process than NORM’s general FEC-encoded data content. NORM_INFO may process than NORM's general FEC-encoded data content. "NORM_INFO"
serve special purposes for some bulk transfer, reliable multicast may serve special purposes for some bulk transfer, reliable multicast
applications where receivers join the group mid-stream and need to applications where receivers join the group mid-stream and need to
ascertain contextual information on the current content being ascertain contextual information on the current content being
transmitted. The NACK process for NORM_INFO will be described later. transmitted. The NACK process for "NORM_INFO" will be described
When the NORM_INFO message type is used, its transmission should later. When the "NORM_INFO" message type is used, its transmission
precede transmission of any NORM_DATA message for the associated should precede transmission of any "NORM_DATA" message for the
NormObject. associated NormObject.
The sender also generates messages of type NORM_CMD to assist in The sender also generates messages of type "NORM_CMD" to assist in
certain protocol operations such as congestion control, end-of- certain protocol operations such as congestion control, end-of-
transmission flushing, round trip time estimation, receiver transmission flushing, round trip time estimation, receiver
synchronization, and optional positive acknowledgment requests or synchronization, and optional positive acknowledgment requests or
application defined commands. The transmission of NORM_CMD messages application defined commands. The transmission of "NORM_CMD"
from the sender is accomplished by one of three different procedures. messages from the sender is accomplished by one of three different
These procedures are: single, best effort unreliable transmission of procedures. These procedures are: single, best effort unreliable
the command; repeated redundant transmissions of the command; and transmission of the command; repeated redundant transmissions of the
positively-acknowledged commands. The transmission technique used command; and positively-acknowledged commands. The transmission
for a given command depends upon the function of the command. technique used for a given command depends upon the function of the
Several core commands are defined for basic protocol operation. command. Several core commands are defined for basic protocol
Additionally, implementations MAY wish to consider providing the operation. Additionally, implementations MAY wish to consider
OPTIONAL application-defined commands that can take advantage of the providing the OPTIONAL application-defined commands that can take
transmission methodologies available for commands. This allows for advantage of the transmission methodologies available for commands.
application-level session management mechanisms that can make use of This allows for application-level session management mechanisms that
information available to the underlying NORM protocol engine (e.g., can make use of information available to the underlying NORM protocol
round-trip timing, transmission rate, etc.). A notable distinction engine (e.g., round-trip timing, transmission rate, etc.). A notable
between NORM_DATA message and some NORM_CMD message transmissions is distinction between "NORM_DATA" message and some "NORM_CMD" message
that typically a receiver will need to allocate resources to manage transmissions is that typically a receiver will need to allocate
reliable reception when NORM_DATA messages are received. However resources to manage reliable reception when "NORM_DATA" messages are
some NORM_CMD messages may be completely atomic and no specific state received. However some "NORM_CMD" messages may be completely atomic
may need to be kept. Thus, for session management or other purposes and no specific state may need to be kept. Thus, for session
it is possible that even participants acting principally as data management or other purposes it is possible that even participants
receivers MAY transmit NORM_CMD messages. However, it is RECOMMENDED acting principally as data receivers MAY transmit "NORM_CMD"
that this is not done within the context of the NORM multicast messages. However, it is RECOMMENDED that this is not done within
session unless congestion control is addressed. For example, many the context of the NORM multicast session unless congestion control
receiver nodes transmitting NORM_CMD messages simultaneously can is addressed. For example, many receiver nodes transmitting
cause congestion for the destination(s). "NORM_CMD" messages simultaneously can cause congestion for the
destination(s).
All sender transmissions are subject to rate control governed by a All sender transmissions are subject to rate control governed by a
peak transmission rate set for each participant by the application. peak transmission rate set for each participant by the application.
This can be used to limit the quantity of multicast data transmitted This can be used to limit the quantity of multicast data transmitted
by the group. When NORMs congestion control algorithm is enabled by the group. When NORM's congestion control algorithm is enabled
the rate for senders is automatically adjusted. In some networks, it the rate for senders is automatically adjusted. In some networks, it
may be desirable to establish minimum and maximum bounds for the rate may be desirable to establish minimum and maximum bounds for the rate
adjustment depending upon the application even when dynamic adjustment depending upon the application even when dynamic
congestion control is enabled. However, in the case of the general congestion control is enabled. However, in the case of the general
Internet, congestion control policy SHALL be observed that is Internet, congestion control policy SHALL be observed that is
compatible with coexistent TCP flows. compatible with coexistent TCP flows.
NORM receivers generate messages of type NORM_NACK or NORM_ACK in NORM receivers generate messages of type "NORM_NACK" or "NORM_ACK" in
response to transmissions of data and commands from a sender. The response to transmissions of data and commands from a sender. The
NORM_NACK messages are generated to request repair of detected data "NORM_NACK" messages are generated to request repair of detected data
transmission losses. Receivers generally detect losses by tracking transmission losses. Receivers generally detect losses by tracking
the sequence of transmission from a sender. Sequencing information the sequence of transmission from a sender. Sequencing information
is embedded in the transmitted data packets and end-of-transmission is embedded in the transmitted data packets and end-of-transmission
commands from the sender. NORM_ACK messages are generated in commands from the sender. "NORM_ACK" messages are generated in
response to certain commands transmitted by the sender. In the response to certain commands transmitted by the sender. In the
general (and most scalable) protocol mode, NORM_ACK messages are sent general (and most scalable) protocol mode, "NORM_ACK" messages are
only in response to congestion control commands from the sender. The sent only in response to congestion control commands from the sender.
feedback volume of these congestion control NORM_ACK messages is The feedback volume of these congestion control "NORM_ACK" messages
controlled using the same timer-based probabilistic suppression is controlled using the same timer-based probabilistic suppression
techniques as for NORM_NACK messages to avoid feedback implosion. In techniques as for "NORM_NACK" messages to avoid feedback implosion.
order to meet potential application requirements for positive In order to meet potential application requirements for positive
acknowledgment from receivers, other NORM_ACK messages are defined acknowledgment from receivers, other "NORM_ACK" messages are defined
and available for use. and available for use.
2.2. Protocol Building Blocks 2.2. Protocol Building Blocks
The operation of the NORM protocol is based primarily upon the The operation of the NORM protocol is based primarily upon the
concepts presented in the Nack-Oriented Reliable Multicast (NORM) concepts presented in the Multicast NACK Building Block document
Building Block document [3]. This includes the basic NORM [I-D.ietf-rmt-bb-norm-revised]. This includes the basic NORM
architecture and the data transmission, repair, and feedback architecture and the data transmission, repair, and feedback
strategies discussed in that document. Additional reliable multicast strategies discussed in that document. Additional reliable multicast
building blocks are applied in creating the full NORM protocol building blocks are applied in creating the full NORM protocol
instantiation [20]. NORM also makes use of Forward Error Correction instantiation as described in [RFC3048]. NORM also makes use of
encoding techniques for repair messaging and optional transmission Forward Error Correction encoding techniques for repair messaging and
robustness as described in [14]. NORM uses the FEC Payload ID as optional transmission robustness as described in [RFC3453]. NORM
specified by the FEC Building Block Document [4]. Additionally, for uses the FEC Payload ID as specified by the FEC Building Block
congestion control, this document includes a baseline congestion document [RFC5052]. Additionally, for congestion control, this
control mechanism (NORM-CC) based on the TCP-Friendly Multicast document fully specifies a baseline congestion control mechanism
Congestion Control (TFMCC) scheme described in [24] and [5]. (NORM-CC) based on the TCP-Friendly Multicast Congestion Control
(TFMCC) scheme of [TfmccPaper] and [RFC4654].
2.3. Design Tradeoffs 2.3. Design Tradeoffs
While the various features of NORM are designed to provide some While the various features of NORM are designed to provide some
measure of general purpose utility, it is important to emphasize the measure of general purpose utility, it is important to emphasize the
understanding that "no one size fits all" in the reliable multicast understanding that "no one size fits all" in the reliable multicast
transport arena. There are numerous engineering tradeoffs involved transport arena. There are numerous engineering trade-offs involved
in reliable multicast transport design and this requires an increased in reliable multicast transport design and this requires an increased
awareness of application and network architecture considerations. awareness of application and network architecture considerations.
Performance requirements affecting design can include: group size, Performance requirements affecting design can include: group size,
heterogeneity (e.g., capacity and/or delay), asymmetric delivery, heterogeneity (e.g., capacity and/or delay), asymmetric delivery,
data ordering, delivery delay, group dynamics, mobility, congestion data ordering, delivery delay, group dynamics, mobility, congestion
control, and transport across low capacity connections. NORM control, and transport across low capacity connections. NORM
contains various parameters to accommodate many of these differing contains various parameters to accommodate many of these differing
requirements. The NORM protocol and its mechanisms MAY be applied in requirements. The NORM protocol and its mechanisms MAY be applied in
multicast applications outside of bulk data transfer, but there is an multicast applications outside of bulk data transfer, but there is an
assumed model of bulk transfer transport service that drives the assumed model of bulk transfer transport service that drives the
skipping to change at page 13, line 50 skipping to change at page 13, line 51
The ability of NORM to provide reliable data delivery is also The ability of NORM to provide reliable data delivery is also
governed by any buffer constraints of the sender and receiver governed by any buffer constraints of the sender and receiver
applications. NORM protocol implementations SHOULD be designed to applications. NORM protocol implementations SHOULD be designed to
operate with the greatest efficiency and robustness possible within operate with the greatest efficiency and robustness possible within
application-defined buffer constraints. Buffer requirements for application-defined buffer constraints. Buffer requirements for
reliability, as always, are a function of the delay-bandwidth product reliability, as always, are a function of the delay-bandwidth product
of the network topology. NORM performs best when allowed more of the network topology. NORM performs best when allowed more
buffering resources than typical point-to-point transport protocols. buffering resources than typical point-to-point transport protocols.
This is because NORM feedback suppression is based upon randomly- This is because NORM feedback suppression is based upon randomly-
delayed transmissions from the receiver set, rather than immediately delayed transmissions from the receiver set, rather than immediately
transmitted feedback. There are definitive tradeoffs between buffer transmitted feedback. There are definitive trade-offs between buffer
utilization, group size scalability, and efficiency of performance. utilization, group size scalability, and efficiency of performance.
Large buffer sizes allow the NORM protocol to perform most Large buffer sizes allow the NORM protocol to perform most
efficiently in large delay-bandwidth topologies and allow for longer efficiently in large delay-bandwidth topologies and allow for longer
feedback suppression backoff timeouts. This yields improved group feedback suppression backoff timeouts. This yields improved group
size scalability. NORM can operate with reduced buffering but at a size scalability. NORM can operate with reduced buffering but at a
cost of decreased efficiency (lower relative goodput) and reduced cost of decreased efficiency (lower relative goodput) and reduced
group size scalability. group size scalability.
3. Conformance Statement 3. Conformance Statement
This Protocol Instantiation document, in conjunction with the RMT This Protocol Instantiation document, in conjunction with the RMT
skipping to change at page 14, line 13 skipping to change at page 14, line 15
Large buffer sizes allow the NORM protocol to perform most Large buffer sizes allow the NORM protocol to perform most
efficiently in large delay-bandwidth topologies and allow for longer efficiently in large delay-bandwidth topologies and allow for longer
feedback suppression backoff timeouts. This yields improved group feedback suppression backoff timeouts. This yields improved group
size scalability. NORM can operate with reduced buffering but at a size scalability. NORM can operate with reduced buffering but at a
cost of decreased efficiency (lower relative goodput) and reduced cost of decreased efficiency (lower relative goodput) and reduced
group size scalability. group size scalability.
3. Conformance Statement 3. Conformance Statement
This Protocol Instantiation document, in conjunction with the RMT This Protocol Instantiation document, in conjunction with the RMT
Building Block documents of [3] and [4], completely specifies a Building Block documents of [I-D.ietf-rmt-bb-norm-revised] and
working reliable multicast transport protocol that conforms to the [RFC5052], completely specifies a working reliable multicast
requirements described in RFC 2357 [21]. transport protocol that conforms to the requirements described in RFC
2357 [RFC2357].
This document specifies the following message types and mechanisms This document specifies the following message types and mechanisms
which are REQUIRED in complying NORM protocol implementations: which are REQUIRED in complying NORM protocol implementations:
+---------------------+----------------------------------------------+ +------------------------+------------------------------------------+
| Message Type | Purpose | | Message Type | Purpose |
+---------------------+----------------------------------------------+ +------------------------+------------------------------------------+
|NORM_DATA | Sender message for application data | | "NORM_DATA" | Sender message for application data |
| | transmission. Implementations must support | | | transmission. Implementations must |
| | at least one of the NORM_OBJECT_DATA, | | | support at least one of the |
| | NORM_OBJECT_FILE, or NORM_OBJECT_STREAM | | | "NORM_OBJECT_DATA", "NORM_OBJECT_FILE", |
| | delivery services. The use of the NORM FEC | | | or "NORM_OBJECT_STREAM" delivery |
| | services. The use of the NORM FEC |
| | Object Transmission Information header | | | Object Transmission Information header |
| | extension is OPTIONAL with NORM_DATA | | | extension is OPTIONAL with "NORM_DATA" |
| | messages. | | | messages. |
+---------------------+----------------------------------------------+ | "NORM_CMD(FLUSH)" | Sender command to excite receivers for |
|NORM_CMD(FLUSH) | Sender command to excite receivers for | | | repair requests in lieu of ongoing |
| | repair requests in lieu of ongoing NORM_DATA | | | "NORM_DATA" transmissions. Note the use |
| | transmissions. Note the use of the | | | of the "NORM_CMD(FLUSH)" for positive |
| | NORM_CMD(FLUSH) for positive acknowledgment | | | acknowledgment of data receipt is |
| | of data receipt is OPTIONAL. | | | OPTIONAL. |
+---------------------+----------------------------------------------+ | "NORM_CMD(SQUELCH)" | Sender command to advertise its current |
|NORM_CMD(SQUELCH) | Sender command to advertise its current | | | valid repair window in response to |
| | valid repair window in response to invalid | | | invalid requests for repair. |
| | requests for repair. | | "NORM_CMD(REPAIR_ADV)" | Sender command to advertise current |
+---------------------+----------------------------------------------+ | | repair (and congestion control state) to |
|NORM_CMD(REPAIR_ADV) | Sender command to advertise current repair | | | group when unicast feedback messages are |
| | (and congestion control state) to group when | | | detected. Used to control/suppress |
| | unicast feedback messages are detected. | | | excessive receiver feedback in |
| | Used to control/suppress excessive receiver | | | asymmetric multicast topologies. |
| | feedback in asymmetric multicast topologies. | | "NORM_CMD(CC)" | Sender command used in collection of |
+---------------------+----------------------------------------------+ | | round trip timing and congestion control |
|NORM_CMD(CC) | Sender command used in collection of round | | | status from group (this may be OPTIONAL |
| | trip timing and congestion control status | | | if alternative congestion control |
| | from group (this may be OPTIONAL if | | | mechanism and round trip timing |
| | alternative congestion control mechanism and | | | collection is used). |
| | round trip timing collection is used). | | "NORM_NACK" | Receiver message used to request repair |
+---------------------+----------------------------------------------+ | | of missing transmitted content. |
|NORM_NACK | Receiver message used to request repair of | | "NORM_ACK" | Receiver message used to proactively |
| | missing transmitted content. | | | provide feedback for congestion control |
+---------------------+----------------------------------------------+ | | purposes. Also used with the OPTIONAL |
|NORM_ACK | Receiver message used to proactively provide | | | NORM Positive Acknowledgment Process. |
| | feedback for congestion control purposes. | +------------------------+------------------------------------------+
| | Also used with the OPTIONAL NORM Positive |
| | Acknowledgment Process. |
+---------------------+----------------------------------------------+
This document also describes the following message types and This document also describes the following message types and
associated mechanisms which are OPTIONAL for complying NORM protocol associated mechanisms which are OPTIONAL for complying NORM protocol
implementations: implementations:
+-----------------------+----------------------------------------------+ +-------------------------+-----------------------------------------+
| Message Type | Purpose | | Message Type | Purpose |
+-----------------------+----------------------------------------------+ +-------------------------+-----------------------------------------+
|NORM_INFO | Sender message for providing ancillary | | "NORM_INFO" | Sender message for providing ancillary |
| | context information associated with NORM | | | context information associated with |
| | transport objects. The use of the NORM FEC | | | NORM transport objects. The use of the |
| | Object Transmission Information header | | | NORM FEC Object Transmission |
| | extension is OPTIONAL with NORM_INFO | | | Information header extension is |
| | messages. | | | OPTIONAL with "NORM_INFO" messages. |
+-----------------------+----------------------------------------------+ | "NORM_CMD(EOT)" | Sender command to indicate it has |
|NORM_CMD(EOT) | Sender command to indicate it has reached | | | reached end-of-transmission and will no |
| | end-of-transmission and will no longer | | | longer respond to repair requests. |
| | respond to repair requests. | | "NORM_CMD(ACK_REQ)" | Sender command to support |
+-----------------------+----------------------------------------------+ | | application-defined, positively |
|NORM_CMD(ACK_REQ) | Sender command to support application- | | | acknowledged commands sent outside of |
| | defined, positively acknowledged commands | | | the context of the bulk data content |
| | sent outside of the context of the bulk data | | | being transmitted. The NORM Positive |
| | content being transmitted. The NORM | | | Acknowledgment Procedure associated |
| | Positive Acknowledgment Procedure associated |
| | with this message type is OPTIONAL. | | | with this message type is OPTIONAL. |
+-----------------------+----------------------------------------------+ | "NORM_CMD(APPLICATION)" | Sender command containing |
|NORM_CMD(APPLICATION) | Sender command containing application- | | | application-defined commands sent |
| | defined commands sent outside of the context | | | outside of the context of the bulk data |
| | of the bulk data content being transmitted. | | | content being transmitted. |
+-----------------------+----------------------------------------------+ | "NORM_REPORT" | Optional message type reserved for |
|NORM_REPORT | Optional message type reserved for | | | experimental implementations of the |
| | experimental implementations of the NORM | | | NORM protocol. |
| | protocol. | +-------------------------+-----------------------------------------+
+-----------------------+----------------------------------------------+
4. Message Formats 4. Message Formats
As mentioned in Section 2.1, there are two primary classes of NORM As mentioned in Section 2.1, there are two primary classes of NORM
messages: sender messages and receiver messages. NORM_CMD, messages: sender messages and receiver messages. "NORM_CMD",
NORM_INFO, and NORM_DATA message types are generated by senders of "NORM_INFO", and "NORM_DATA" message types are generated by senders
data content, and NORM_NACK and NORM_ACK messages generated by of data content, and "NORM_NACK" and "NORM_ACK" messages generated by
receivers within a NormSession. Sender messages SHOULD be governed receivers within a NormSession. Sender messages SHOULD be governed
by congestion control for Internet use. For session management or by congestion control for Internet use. For session management or
other purposes, receivers may wish to employ NORM_CMD message other purposes, receivers may wish to employ "NORM_CMD" message
transmissions. The principal rationale for distiguishing sender and transmissions. The principal rationale for distinguishing sender and
receiver messages is that receivers will typically need to allocate receiver messages is that receivers will typically need to allocate
resources to support reliable reception from sender(s) and NORM resources to support reliable reception from sender(s) and NORM
sender messages are subject to congestion control. NORM receivers sender messages are subject to congestion control. NORM receivers
MAY employ the NORM_CMD message type for application-defined purposes MAY employ the "NORM_CMD" message type for application-defined
but it is RECOMMENDED that congestion control and feedback implosion purposes but it is RECOMMENDED that congestion control and feedback
issues be addressed. Additionally, an auxiliary message type of implosion issues be addressed. Additionally, an auxiliary message
NORM_REPORT is also provided for experimental purposes. This section type of "NORM_REPORT" is also provided for experimental purposes.
describes the message formats used by the NORM protocol. These This section describes the message formats used by the NORM protocol.
messages and their fields are referenced in the detailed functional These messages and their fields are referenced in the detailed
description of the NORM protocol given in Section 5. Individual NORM functional description of the NORM protocol given in Section 5.
messages are designed to be compatible with the MTU limitations of Individual NORM messages are designed to be compatible with the MTU
encapsulating Internet protocols including IPv4, IPv6, and UDP. The limitations of encapsulating Internet protocols including IPv4, IPv6,
current NORM protocol specification assumes UDP encapsulation and and UDP. The current NORM protocol specification assumes UDP
leverages the transport features of UDP. The NORM messages are encapsulation and leverages the transport features of UDP. The NORM
independent of network addresses and can be used in IPv4 and IPv6 messages are independent of network addresses and can be used in IPv4
networks. and IPv6 networks.
4.1. NORM Common Message Header and Extensions 4.1. NORM Common Message Header and Extensions
There are some common message fields contained in all NORM message There are some common message fields contained in all NORM message
types. Additionally, a header extension mechanism is defined to types. Additionally, a header extension mechanism is defined to
expand the functionality of the NORM protocol without revision to expand the functionality of the NORM protocol without revision to
this document. All NORM protocol messages begin with a common header this document. All NORM protocol messages begin with a common header
with information fields as follows: with information fields as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type | hdr_len | sequence | |version| type | hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM Common Message Header Format NORM Common Message Header Format
skipping to change at page 18, line 8 skipping to change at page 17, line 9
The "version" field is a 4-bit value indicating the protocol version The "version" field is a 4-bit value indicating the protocol version
number. NORM implementations SHOULD ignore received messages with number. NORM implementations SHOULD ignore received messages with
version numbers different from their own. This number is intended to version numbers different from their own. This number is intended to
indicate and distinguish upgrades of the protocol which may be non- indicate and distinguish upgrades of the protocol which may be non-
interoperable. The NORM version number for this specification is 1. interoperable. The NORM version number for this specification is 1.
The message "type" field is a 4-bit value indicating the NORM The message "type" field is a 4-bit value indicating the NORM
protocol message type. These types are defined as follows: protocol message type. These types are defined as follows:
Message Value +---------------+-------+
| Message | Value |
NORM_INFO 1 +---------------+-------+
NORM_DATA 2 | "NORM_INFO" | 1 |
NORM_CMD 3 | "NORM_DATA" | 2 |
NORM_NACK 4 | "NORM_CMD" | 3 |
NORM_ACK 5 | "NORM_NACK" | 4 |
NORM_REPORT 6 | "NORM_ACK" | 5 |
| "NORM_REPORT" | 6 |
+---------------+-------+
The 8-bit "hdr_len" field indicates the number of 32-bit words that The 8-bit "hdr_len" field indicates the number of 32-bit words that
comprise the given messages header portion. This is used to comprise the given message's header portion. This is used to
facilitate header extensions that may be applied. The presence of facilitate header extensions that may be applied. The presence of
header extensions are implied when the "hdr_len" value is greater header extensions are implied when the "hdr_len" value is greater
than the base value for the given message "type". than the base value for the given message "type".
The "sequence" field is a 16-bit value that is set by the message The "sequence" field is a 16-bit value that is set by the message
originator as a monotonically increasing number incremented with each originator as a monotonically increasing number incremented with each
NORM message transmitted. Note that two independent "sequence" NORM message transmitted. Note that two independent "sequence"
spaces MUST be maintained. One sequence space SHALL be kept for NORM spaces MUST be maintained. One sequence space SHALL be kept for NORM
sender messages (NORM_INFO, NORM_DATA, and NORM_CMD) generated, and a sender messages ("NORM_INFO", "NORM_DATA", and "NORM_CMD") generated,
separate, independent "sequence" space SHALL be kept for NORM and a separate, independent "sequence" space SHALL be kept for NORM
receiver messages (NORM_NACK and NORM_NACK). The sender message receiver messages ("NORM_NACK" and "NORM_NACK"). The sender message
"sequence" value can be monitored by receiving nodes to detect packet "sequence" value can be monitored by receiving nodes to detect packet
losses in the transmissions from a sender and used to estimate raw losses in the transmissions from a sender and used to estimate raw
packet loss for congestion control purposes. Note that this value is packet loss for congestion control purposes. Note that this value is
NOT used in the NORM protocol to detect missing reliable data content NOT used in the NORM protocol to detect missing reliable data content
and does NOT identify the application data or FEC payload that may be and does NOT identify the application data or FEC payload that may be
attached. The "sequence" field may also be leveraged for protection attached. The "sequence" field may also be leveraged for protection
from message "replay" attacks, particularly of NORM_NACK or other from message replay attacks, particularly of "NORM_NACK" or other
feedback messages. For this reason, NORM receiver messages are also feedback messages. For this reason, NORM receiver messages are also
sequence numbered. An independent sequence space MUST be used for sequence numbered. An independent sequence space MUST be used for
receiver messages because when receivers generate unicast NORM_NACK receiver messages because when receivers generate unicast "NORM_NACK"
or NORM_ACK messages, those messages will not be visible to the group or "NORM_ACK" messages, those messages will not be visible to the
at large that may be performing loss estimation. Also, NORM group at large that may be performing loss estimation. Also, NORM
congestion control is applied only to sender messages. The size of congestion control is applied only to sender messages. The size of
the "sequence" field is intended to be sufficient to allow detection the "sequence" field is intended to be sufficient to allow detection
of a reasonable range of packet loss within the delay-bandwidth of a reasonable range of packet loss within the delay-bandwidth
product of expected network connections. product of expected network connections.
The "source_id" field is a 32-bit value identifying the node that The "source_id" field is a 32-bit value identifying the node that
sent the message. A participants NORM node identifier (NormNodeId) sent the message. A participant's NORM node identifier (NormNodeId)
can be set according to application needs but unique identifiers must can be set according to application needs but unique identifiers must
be assigned within a single NormSession. In some cases, use of the be assigned within a single NormSession. In some cases, use of the
host IP address or a hash of it can suffice, but alternative host IP address or a hash of it can suffice, but alternative
methodologies for assignment and potential collision resolution of methodologies for assignment and potential collision resolution of
node identifiers within a multicast session need to be considered. node identifiers within a multicast session need to be considered.
For example, the "source identifier" mechanism defined in the Real- For example, the "source identifier" mechanism defined in the Real-
Time Protocol (RTP) specification [22] may be applicable to use for Time Protocol (RTP) specification [RFC3550] may be applicable to use
NORM node identifiers. At this point in time, the protocol makes no for NORM node identifiers. At this point in time, the protocol makes
assumptions about how these unique identifiers are actually assigned. no assumptions about how these unique identifiers are actually
assigned.
NORM Header Extensions NORM Header Extensions
When header extensions are applied, they follow the message types When header extensions are applied, they follow the message type's
base header and precede any payload portion. There are two formats base header and precede any payload portion. There are two formats
for header extensions, both of which begin with an 8-bit "het" for header extensions, both of which begin with an 8-bit "het"
(header extension type) field. One format is provided for variable- (header extension type) field. One format is provided for variable-
length extensions with "het" values in the range from 0 through 127. length extensions with "het" values in the range from 0 through 127.
The other format is for fixed length (one 32-bit word) extensions The other format is for fixed length (one 32-bit word) extensions
with "het" values in the range from 128 through 255. These formats with "het" values in the range from 128 through 255. These formats
are given here: are given here:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| het <=127 | hel | | | het <=127 | hel | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| Header Extension Content | | Header Extension Content |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM Variable Length Header Extension Format NORM Variable Length Header Extension Format
skipping to change at page 19, line 39 skipping to change at page 18, line 41
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM Variable Length Header Extension Format NORM Variable Length Header Extension Format
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| het >=128 | reserved | Header Extension Content | | het >=128 | reserved | Header Extension Content |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM Fixed Length (32-bit) Header Extension Format NORM Fixed Length (32-bit) Header Extension Format
The "Header Extension Content" portion of these header extension The "Header Extension Content" portion of the header extension is
format is defined for each header extension type defined for NORM defined for each extension type. Some header extensions are defined
messages. Some header extensions are defined within this document within this document for NORM baseline FEC and congestion control
for NORM baseline FEC and congestion control operations. operations.
4.2. Sender Messages 4.2. Sender Messages
NORM sender messages include the NORM_DATA type, the NORM_INFO type, NORM sender messages include the "NORM_DATA" type, the "NORM_INFO"
and the NORM_CMD type. NORM_DATA and NORM_INFO messages contain type, and the "NORM_CMD" type. "NORM_DATA" and "NORM_INFO" messages
application data content while NORM_CMD messages are used for various contain application data content while "NORM_CMD" messages are used
protocol control functions. for various protocol control functions.
4.2.1. NORM_DATA Message 4.2.1. NORM_DATA Message
The NORM_DATA message is expected to be the predominant type The "NORM_DATA" message is expected to be the predominant type
transmitted by NORM senders. These messages are used to encapsulate transmitted by NORM senders. These messages are used to encapsulate
segmented data content for objects of type NORM_OBJECT_DATA, segmented data content for objects of type "NORM_OBJECT_DATA",
NORM_OBJECT_FILE, and NORM_OBJECT_STREAM. NORM_DATA messages may "NORM_OBJECT_FILE", and "NORM_OBJECT_STREAM". "NORM_DATA" messages
contain original or FEC-encoded application data content. may contain original or FEC-encoded application data content.
The format of NORM_DATA messages is comprised of three logical The format of "NORM_DATA" messages is comprised of three logical
portions: 1) a fixed-format NORM_DATA header portion, 2) a FEC portions: 1) a fixed-format "NORM_DATA" header portion, 2) a FEC
Payload ID portion with a format dependent upon the FEC encoding Payload ID portion with a format dependent upon the FEC encoding
used, and 3) a payload portion containing source or encoded used, and 3) a payload portion containing source or encoded
application data content. Note for objects of type application data content. Note for objects of type
NORM_OBJECT_STREAM, the payload portion contains additional fields "NORM_OBJECT_STREAM", the payload portion contains additional fields
used to appropriately recover stream content. NORM implementations used to appropriately recover stream content. NORM implementations
MAY also extend the NORM_DATA header to include a FEC Object MAY also extend the "NORM_DATA" header to include a FEC Object
Transmission Information (EXT_FTI) header extension. This allows Transmission Information (EXT_FTI) header extension. This allows
NORM receivers to automatically allocate resources and properly NORM receivers to automatically allocate resources and properly
perform FEC decoding without the need for pre-configuration or out- perform FEC decoding without the need for pre-configuration or out-
of-band information. of-band information.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=2| hdr_len | sequence | |version| type=2| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 21, line 4 skipping to change at page 20, line 31
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| payload_len* | payload_msg_start* | | payload_len* | payload_msg_start* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| payload_offset* | | payload_offset* |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| payload_data* | | payload_data* |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_DATA Message Format NORM_DATA Message Format
*IMPORTANT NOTE: The "payload_len", "payload_msg_start" and
"payload_offset" fields are present only for objects of type
NORM_OBJECT_STREAM.
The "payload_len" and "payload_offset" fields allow senders to *IMPORTANT NOTE: The "payload_len", "payload_msg_start" and
arbitrarily vary the size of NORM_DATA payload segments for streams. "payload_offset" fields are present ONLY for objects of type
This allows applications to flush transmitted streams as needed to "NORM_OBJECT_STREAM". These fields, as with the entire payload, are
meet unique streaming requirements. For objects of types subject to any FEC encoding used. Thus, when systematic FEC codes
NORM_OBJECT_FILE and NORM_OBJECT_DATA, these fields are unnecessary are used, these values may be directly interpreted for packets
since the receiver can calculate the payload length and offset containing source symbols only while packets containing FEC parity
information from the "fec_payload_id" using the block partioning content require decoding before these fields can be interpreted.
algorithm described in the FEC Building Block document [4]. The
"payload_len" field indicates the length (in bytes) of the
"payload_data" content of the stream data segment. When
"payload_len" is equal to ZERO, this indicates that there is no
"payload_data" content and the "payload_msg_start" field is instead
to be interpreted as a stream control code.
The "payload_msg_start" field serves one of two exlusive purposes.
When "payload_len" is a non-zero value, the "payload_msg_start"
fields is used to mark the location (within the "payload_data") field
of the start byte of an application-defined message boundary. Note
that the "payload_msg_start" value is the byte offset of the message
boundary plus one. Thus, a value of "payload_msg_start" equal to
ZERO denotes that no message boundary is present, while a
"payload_msg_start" value of ONE indicates the message boundary is
aligned with the beginning of the "payload_data" field. This allows
NORM receiver applications to "synchronize" with NORM senders and to
be able to properly interpret application layer data when joining a
NORM session already in progress. The NORM sender implementation
SHOULD provide a mechanism for the application to mark such message
boundaries and set the "payload_msg_start" value accordingly. The
"payload_msg_start" value will always be less than or equal to the
"payload_len" value except for the special case of "payload_len = 0",
that indicates the "payload_msg_start" field should be interpreted as
a "stream control code" (See description below).
The "payload_len" and "payload_offset" fields allow senders to
arbitrarily vary the size of NORM_DATA payload segments for streams.
This allows applications to flush transmitted streams as needed to
meet unique streaming requirements. For objects of types
NORM_OBJECT_FILE and NORM_OBJECT_DATA, these fields are unnecessary
since the receiver can calculate the payload length and offset
information from the "fec_payload_id" using the block partioning
algorithm described in the FEC Building Block document [4]. When
systematic FEC codes (e.g., "fec_id" = 129) are used, the
"payload_len", "payload_msg_start", and "payload_offset" fields
contain actual payload_data length, start index (or stream control
code), and offset values for the associated application stream data
segment (the "payload_data" field content) for those NORM_DATA
messages containing source data symbols. In NORM_DATA messages that
contain parity information, these fields do not contain values that
can be directly interpreted, but instead are values computed from FEC
encoding the "payload_len", "payload_msg_start", and "payload_offset"
fields for the source data segments of the corresponding coding
block.
The "version", "type", "hdr_len", "sequence", and "source_id" fields The "version", "type", "hdr_len", "sequence", and "source_id" fields
form the NORM Common Message Header as described in Section 4.1. The form the NORM Common Message Header as described in Section 4.1. The
value of the NORM_DATA "type" field is 2. The NORM_DATA _base_ value of the "NORM_DATA" "type" field is 2. The "NORM_DATA" base
"hdr_len" value is 4 (32-bit words) plus the size of the "hdr_len" value is 4 (32-bit words) plus the size of the
"fec_payload_id" field. The "fec_payload_id" field size depends upon "fec_payload_id" field. The "fec_payload_id" field size depends upon
the FEC encoding used for the referenced NormObject. The "fec_id" the FEC encoding type referenced by the "fec_id" field. For example,
field is used to indicate the FEC coding type. For example, when when small block, systematic codes are used, a "fec_id" value of 129
small block, systematic codes are used, a "fec_id" value of 129 is is indicated and the size of the "fec_payload_id" is two 32-bit
indicated and the size of the "fec_payload_id" is two 32-bit words. words. In this case the . The "fec_id" field is used to indicate
In this case the NORM_DATA base "hdr_len" value is 6. The cumulative the FEC coding type. For example, when small block, systematic codes
size of any header extensions applied is added into the "hdr_len" are used, a "fec_id" value of 129 is indicated and the size of the
field. "fec_payload_id" is two 32-bit words. In this case the "NORM_DATA"
base "hdr_len" value is 6. The cumulative size of any header
extensions applied is added into the "hdr_len" field.
The "instance_id" field contains a value generated by the sender to The "instance_id" field contains a value generated by the sender to
uniquely identify its current instance of participation in the uniquely identify its current instance of participation in the
NormSession. This allows receivers to detect when senders have NormSession. This allows receivers to detect when senders have
perhaps left and rejoined a session in progress. When a sender perhaps left and rejoined a session in progress. When a sender
(identified by its "source_id") is detected to have a new (identified by its "source_id") is detected to have a new
"instance_id", the NORM receivers SHOULD drop their previous state on "instance_id", the NORM receivers SHOULD drop their previous state on
the sender and begin reception anew, or at least treat this the sender and begin reception anew, or at least treat this
"instance" as a new, separate sender. "instance" as a new, separate sender.
The "grtt" field contains a non-linear quantized representation of The "grtt" field contains a non-linear quantized representation of
the sender’s current estimate of group round-trip time (GRTT) (this the sender's current estimate of group round-trip time (GRTT) (this
is also referred to as R_max in [24]). This value is used to control is also referred to as "R_max" in [TfmccPaper]). This value is used
timing of the NACK repair process and other aspects of protocol to control timing of the NACK repair process and other aspects of
operation as described in this document. Normally, the advertised protocol operation as described in this document. Normally, the
"grtt" value will correspond to what the sender has measured based on advertised "grtt" value will correspond to what the sender has
feedback from the group, but, at low transmission rates, the measured based on feedback from the group, but, at low transmission
advertised "grtt" SHALL be set to MAX(grttMeasured, rates, the advertised "grtt" SHALL be set to "MAX(grttMeasured,
NormSegmentSize/senderRate) where the "NormSegmentSize" is sender’s NormSegmentSize/senderRate)" where the "NormSegmentSize" is sender's
segment size in bytes and the "senderRate" is the sender’s current segment size in bytes and the "senderRate" is the sender's current
transmission rate in bytes per second. The algorithm for encoding transmission rate in bytes per second. The algorithm for encoding
and decoding this field is described in the RMT NORM Building Block and decoding this field is described in the RMT Multicast NACK
document [3]. Building Block document [I-D.ietf-rmt-bb-norm-revised].
The "backoff" field value is used by receivers to determine the The "backoff" field value is used by receivers to determine the
maximum backoff timer value used in the timer-based NORM NACK maximum backoff timer value used in the timer-based NORM NACK
feedback suppression. This 4-bit field supports values from 0-15 feedback suppression. This 4-bit field supports values from 0-15
which is multiplied by the sender GRTT to determine the maximum which is multiplied by the sender GRTT to determine the maximum
backoff timeout. The "backoff" field informs the receiver set of the backoff timeout. The "backoff" field informs the receivers of the
sender’s backoff factor parameter "Ksender". Recommended values and sender's backoff factor parameter "Ksender". Recommended values and
their use are described in the NORM receiver NACK procedure their use are described in the NORM receiver NACK procedure
description in Section 5.3. The "gsize" field contains a description in Section 5.3.
representation of the sender’s current estimate of group size. This
4-bit field can roughly represent values from ten to 500 million The "gsize" field contains a representation of the sender's current
where the most significant bit value of 0 or 1 represents a mantissa estimate of group size. This 4-bit field can roughly represent
of 1 or 5, respectively and the three least significant bits values from ten to 500 million where the most significant bit value
incremented by one represent a base 10 exponent (order of magnitude). of 0 or 1 represents a mantissa of 1 or 5, respectively and the three
For examples, a field value of "0x0" represents 1.0e+01 (10), a value least significant bits incremented by one represent a base 10
of "0x8" represents 5.0e+01 (50), a value of "0x1" represents 1.0e+02 exponent (order of magnitude). For examples, a field value of "0x0"
(100), and a value of "0xf" represents 5.0e+08. For NORM feedback represents 1.0e+01 (10), a value of "0x8" represents 5.0e+01 (50), a
suppression purposes, the group size does not need to be represented value of "0x1" represents 1.0e+02 (100), and a value of "0xf"
with a high degree of precision. The group size may even be represents 5.0e+08. For NORM feedback suppression purposes, the
estimated somewhat conservatively (i.e., overestimated) to maintain group size does not need to be represented with a high degree of
low levels of feedback traffic. A default group size estimate of precision. The group size may even be estimated somewhat
10,000 ("gsize" = 0x3) is recommended for general purpose reliable conservatively (i.e., overestimated) to maintain low levels of
multicast applications using the NORM protocol. feedback traffic. A default group size estimate of 10,000 ("gsize" =
0x3) is recommended for general purpose reliable multicast
applications using the NORM protocol.
The "flags" field contains a number of different binary flags The "flags" field contains a number of different binary flags
providing information and hints regarding how the receiver should providing information and hints regarding how the receiver should
handle the identified object. Defined flags in this field include: handle the identified object. Defined flags in this field include:
+---------------------+-------+----------------------------------------+ +------------------------+-------+----------------------------------+
| Flag | Value | Purpose | | Flag | Value | Purpose |
+---------------------+-------+----------------------------------------+ +------------------------+-------+----------------------------------+
|NORM_FLAG_REPAIR | 0x01 | Indicates message is a repair | | "NORM_FLAG_REPAIR" | 0x01 | Indicates message is a repair |
| | | transmission | | | | transmission |
+---------------------+-------+----------------------------------------+ | "NORM_FLAG_EXPLICIT" | 0x02 | Indicates a repair segment |
|NORM_FLAG_EXPLICIT | 0x02 | Indicates a repair segment intended to | | | | intended to meet a specific |
| | | meet a specific receiver erasure, as | | | | receiver erasure, as compared to |
| | | compared to parity segments provided | | | | parity segments provided by the |
| | | by the sender for general purpose | | | | sender for general purpose (with |
| | | (with respect to an FEC coding block) | | | | respect to an FEC coding block) |
| | | erasure filling. | | | | erasure filling. |
+---------------------+-------+----------------------------------------+ | "NORM_FLAG_INFO" | 0x04 | Indicates availability of |
|NORM_FLAG_INFO | 0x04 | Indicates availability of NORM_INFO | | | | "NORM_INFO" for object. |
| | | for object. | | "NORM_FLAG_UNRELIABLE" | 0x08 | Indicates that repair |
+---------------------+-------+----------------------------------------+ | | | transmissions for the specified |
|NORM_FLAG_UNRELIABLE | 0x08 | Indicates that repair transmissions | | | | object will be unavailable |
| | | for the specified object will be | | | | (One-shot, best effort |
| | | unavailable (One-shot, best effort |
| | | transmission). | | | | transmission). |
+---------------------+-------+----------------------------------------+ | "NORM_FLAG_FILE" | 0x10 | Indicates object is file-based |
|NORM_FLAG_FILE | 0x10 | Indicates object is "file-based" data | | | | data (hint to use disk storage |
| | | (hint to use disk storage for | | | | for reception). |
| | | reception). | | "NORM_FLAG_STREAM" | 0x20 | Indicates object is of type |
+---------------------+-------+----------------------------------------+ | | | "NORM_OBJECT_STREAM". |
|NORM_FLAG_STREAM | 0x20 | Indicates object is of type | +------------------------+-------+----------------------------------+
| | | NORM_OBJECT_STREAM. |
+---------------------+-------+----------------------------------------+
NORM_FLAG_REPAIR is set when the associated message is a repair "NORM_FLAG_REPAIR" is set when the associated message is a repair
transmission. This information can be used by receivers to help transmission. This information can be used by receivers to help
observe a join policy where it is desired that newly joining observe a join policy where it is desired that newly joining
receivers only begin participating in the NACK process upon receipt receivers only begin participating in the NACK process upon receipt
of new (non-repair) data content. NORM_FLAG_EXPLICIT is used to mark of new (non-repair) data content. "NORM_FLAG_EXPLICIT" is used to
repair messages sent when the data sender has exhausted its ability mark repair messages sent when the data sender has exhausted its
to provide "fresh" (previously untransmitted) parity segments as ability to provide "fresh" (not previously transmitted) parity
repair. This flag could possibly be used by intermediate systems segments as repair. This flag could possibly be used by intermediate
implementing functionality to control sub-casting of repair content systems implementing functionality to control sub-casting of repair
to different legs of a reliable multicast topology with disparate content to different legs of a reliable multicast topology with
repair needs. NORM_FLAG_INFO is set only when optional NORM_INFO disparate repair needs. "NORM_FLAG_INFO" is set only when optional
content is actually available for the associated object. Thus, "NORM_INFO" content is actually available for the associated object.
receivers will NACK for retransmission of NORM_INFO only when it is Thus, receivers will NACK for retransmission of "NORM_INFO" only when
available for a given object. NORM_FLAG_UNRELIABLE is set when the it is available for a given object. "NORM_FLAG_UNRELIABLE" is set
sender wishes to transmit an object with only "best effort" delivery when the sender wishes to transmit an object with only "best effort"
and will not supply repair transmissions for the object. NORM delivery and will not supply repair transmissions for the object.
receivers SHOULD NOT execute repair requests for objects marked with
the NORM_FLAG_UNRELIABLE flag. Note that receivers may inadvertently NORM receivers SHOULD NOT execute repair requests for objects marked
request repair of such objects when all segments (or info content) with the "NORM_FLAG_UNRELIABLE" flag. Note that receivers may
for those objects are not received (i.e., a gap in the inadvertently request repair of such objects when all segments (or
info content) for those objects are not received (i.e., a gap in the
"object_transport_id" sequence is noted). In this case, the sender "object_transport_id" sequence is noted). In this case, the sender
should invoke the NORM_CMD(SQUELCH) process as described in Section should invoke the "NORM_CMD(SQUELCH)" process as described in
4.2.3. NORM_FLAG_FILE can be set as a "hint" from the sender that Section 4.2.3.
the associated object should be stored in non-volatile storage.
NORM_FLAG_STREAM is set when the identified object is of type "NORM_FLAG_FILE" can be set as a hint from the sender that the
NORM_OBJECT_STREAM. The presence of NORM_FLAG_STREAM overrides that associated object should be stored in non-volatile storage.
of NORM_FLAG_FILE with respect to interpretation of object size and "NORM_FLAG_STREAM" is set when the identified object is of type
the format of NORM_DATA messages. "NORM_OBJECT_STREAM". The presence of "NORM_FLAG_STREAM" overrides
that of "NORM_FLAG_FILE" with respect to interpretation of object
size and the format of "NORM_DATA" messages.
The "fec_id" field corresponds to the FEC Encoding Identifier The "fec_id" field corresponds to the FEC Encoding Identifier
described in the FEC Building Block document [4]. The "fec_id" value described in the FEC Building Block document [RFC5052]. The "fec_id"
implies the format of the "fec_payload_id" field and, coupled with value implies the format of the "fec_payload_id" field and, coupled
FEC Object Transmission Information, the procedures to decode FEC with FEC Object Transmission Information, the procedures to decode
encoded content. Small block, systematic codes ("fec_id" = 129) are FEC encoded content. Small block, systematic codes ("fec_id" = 129)
expected to be used for most NORM purposes and the NORM_OBJECT_STREAM are expected to be used for most NORM purposes and the
requires systematic FEC codes for most efficient performance. "NORM_OBJECT_STREAM" requires systematic FEC codes for most efficient
performance.
The "object_transport_id" field is a monotonically and incrementally The "object_transport_id" field is a monotonically and incrementally
increasing value assigned by the sender to NormObjects being increasing value assigned by the sender to NormObjects being
transmitted. Transmissions and repair requests related to that transmitted. Transmissions and repair requests related to that
object use the same "object_transport_id" value. For sessions of object use the same "object_transport_id" value. For sessions of
very long or indefinite duration, the "object_transport_id" field may very long or indefinite duration, the "object_transport_id" field may
be repeated, but it is presumed that the 16-bit field size provides be repeated, but it is presumed that the 16-bit field size provides
an adequate enough sequence space to avoid object confusion amongst an adequate enough sequence space to avoid object confusion amongst
receivers and sources (i.e., receivers SHOULD re-synchronize with a receivers and sources (i.e., receivers SHOULD re-synchronize with a
server when receiving object sequence identifiers sufficiently out- server when receiving object sequence identifiers sufficiently out-
of-range with the current state kept for a given source). During the of-range with the current state kept for a given source). During the
course of its transmission within a NORM session, an object is course of its transmission within a NORM session, an object is
uniquely identified by the concatenation of the sender "source_id" uniquely identified by the concatenation of the sender "source_id"
and the given "object_transport_id". Note that NORM_INFO messages and the given "object_transport_id". Note that "NORM_INFO" messages
associated with the identified object carry the same associated with the identified object carry the same
"object_transport_id" value. "object_transport_id" value.
The "fec_payload_id" identifies the attached NORM_DATA "payload" The "fec_payload_id" identifies the attached "NORM_DATA" "payload"
content. The size and format of the "fec_payload_id" field depends content. The size and format of the "fec_payload_id" field depends
upon the FEC type indicated by the "fec_id" field. These formats are upon the FEC type indicated by the "fec_id" field. These formats are
given in the descriptions of specific FEC schemes as described in the given in the descriptions of specific FEC schemes as described in the
IETF FEC Basic Schemes document [25]. or additional FEC Scheme IETF FEC Basic Schemes document I-d
[I-D.ietf-rmt-bb-fec-basic-schemes-revised] or additional FEC Scheme
documents that may be defined. As an example, the format of the documents that may be defined. As an example, the format of the
"fec_payload_id" format for Small Block, Systematic codes ("fec_id" = "fec_payload_id" format for Small Block, Systematic codes ("fec_id" =
129) is given here: 129) is given here:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_number | | source_block_number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_len | encoding_symbol_id | | source_block_len | encoding_symbol_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example FEC Payload ID Field ("fec_payload_id") Format Example: FEC Payload Id Format for &quot;fec_id&quot; = 129
for Small Block, Systematic Codes ("fec_id" = 129)
In this example FEC payload identifier, the "source_block_number", In this example FEC payload identifier, the "source_block_number",
"source_block_len", and "encoding_symbol_id" fields correspond to the "source_block_len", and "encoding_symbol_id" fields correspond to the
"Source Block Number", "Source Block Length, and "Encoding Symbol ID" "Source Block Number", "Source Block Length, and "Encoding Symbol ID"
fields of the FEC Payload ID format given by the FEC Basic Schemes fields of the FEC Payload ID format given by the FEC Basic Schemes
document [25]. for the Small Block Systematic FEC Scheme identified document [I-D.ietf-rmt-bb-fec-basic-schemes-revised] for Small Block
by a "fec_id" value of 129. The "source_block_number" identifies the Systematic FEC Schemes identified by a "fec_id" value of 129. The
coding block’s relative position with a NormObject. Note that, for "source_block_number" identifies the coding block's relative position
NormObjects of type NORM_OBJECT_STREAM, the "source_block_number" may with a NormObject. Note that, for NormObjects of type
wrap for very long lived sessions. The "source_block_len" indicates "NORM_OBJECT_STREAM", the "source_block_number" may wrap for very
the number of user data segments in the identified coding block. long lived sessions. The "source_block_len" indicates the number of
Given the "source_block_len" information of how many symbols of user data segments in the identified coding block. Given the
application data are contained in the block, the receiver can "source_block_len" information of how many symbols of application
determine whether the attached segment is data or parity content and data are contained in the block, the receiver can determine whether
treat it appropriately. Some applications may dynamically "shorten" the attached segment is data or parity content and treat it
code blocks when the pending information content is not predictable appropriately. Some applications may dynamically "shorten" code
(e.g. real-time message streams). In that case, the blocks when the pending information content is not predictable (e.g.
"source_block_len" value given for an "encoding_symbol_id" that real-time message streams). In that case, the "source_block_len"
contains FEC parity content SHALL take precedence over the value given for an "encoding_symbol_id" that contains FEC parity
"source_block_len" value provided for any packets containing source content SHALL take precedence over the "source_block_len" value
symbols. Also, the "source_block_len" value given for an ordinally provided for any packets containing source symbols. Also, the
higher "encoding_symbol_id" SHALL take precedence over the "source_block_len" value given for an ordinally higher
"encoding_symbol_id" SHALL take precedence over the
"source_block_len" given for prior encoding symbols. The reason for "source_block_len" given for prior encoding symbols. The reason for
this is that the sender may only know the maximum source block length this is that the sender may only know the maximum source block length
at the time is transmitting source symbols, but then subsequently at the time is transmitting source symbols, but then subsequently
"shorten" the code and then provide that last source symbol and/or "shorten" the code and then provide that last source symbol and/or
encoding symbols with FEC parity content. The "encoding_symbol_id" encoding symbols with FEC parity content. The "encoding_symbol_id"
identifies which specific symbol (segment) within the coding block identifies which specific symbol (segment) within the coding block
the attached payload conveys. Depending upon the value of the the attached payload conveys. Depending upon the value of the
"encoding_symbol_id" and the associated "source_block_len" parameters "encoding_symbol_id" and the associated "source_block_len" parameters
for the block, the symbol (segment) referenced may be a user data or for the block, the symbol (segment) referenced may be a user data or
an FEC parity segment. For systematic codes, encoding symbols an FEC parity segment. For systematic codes, encoding symbols
numbered less than the source_block_len contain original application numbered less than the "source_block_len" contain original
data while segments greater than or equal to source_block_len contain application data while segments greater than or equal to
parity symbols calculated for the block. The concatenation of "source_block_len" contain parity symbols calculated for the block.
object_transport_id::fec_payload_id can be viewed as a unique The concatenation of "object_transport_id::fec_payload_id" can be
transport protocol data unit identifier for the attached segment with viewed as a unique transport protocol data unit identifier for the
respect to the NORM sender’s instance within a session. attached segment with respect to the NORM sender's instance within a
session.
Additional FEC Object Transmission Information (as described in the Additional FEC Object Transmission Information (FTI) (as described in
FEC Building Block document [4]) is required to properly receive and the FEC Building Block document [RFC5052]) is required to properly
decode NORM transport objects. This information MAY be provided as receive and decode NORM transport objects. This information MAY be
out-of-band session information. However, in some cases, it may be provided as out-of-band session information. However, in some cases,
useful for the sender to include this information "in-band" to it may be useful for the sender to include this information "in-band"
facilitate receiver operation with minimal preconfiguration. For to facilitate receiver operation with minimal pre-configuration. For
this purpose, the NORM FEC Object Transmission Information Header this purpose, the NORM FEC Object Transmission Information Header
Extension (EXT_FTI) is defined. This header extension MAY be applied Extension (EXT_FTI) is defined. This header extension MAY be applied
to NORM_DATA and NORM_INFO messages to provide this necessary to "NORM_DATA" and "NORM_INFO" messages to provide this necessary
information. The format of the EXT_FTI consists of two parts, a information. The format of the EXT_FTI consists of two parts, a
general part that contains the size of the associated transport general part that contains the size of the associated transport
object and a portion that depends upon the FEC scheme being used. object and a portion that depends upon the FEC scheme being used.
The "fec_id" field in NORM_DATA and NORM_INFO messages identifies the The "fec_id" field in "NORM_DATA" and "NORM_INFO" messages identifies
FEC scheme. The format of the EXT_FTI general part is given here. the FEC scheme. The format of the EXT_FTI general part is given
here.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| het = 64 | hel = 4 | object_size (msb) | | het = 64 | hel = 4 | object_size (msb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| object_size (lsb) | | object_size (lsb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC Scheme specific content ... | | FEC Scheme specific content ... |
FEC Object Transmission Information Header Extension (EXT_FTI) EXT_FTI Header Extension General Portion Format
The header extension type "het" field value for the EXT_FTI header The header extension type "het" field value for the EXT_FTI header
extension is 64. The header extension length "hel" value depends extension is 64. The header extension length "hel" value depends
upon the format of the FTI for FEC code type identified by the upon the format of the FTI for encoding type identified by the
"fec_id" field. "fec_id" field.
The 48-bit "object_size" field indicates the total length of the The 48-bit "object_size" field indicates the total length of the
object (in bytes) for the static object types of NORM_OBJECT_FILE and object (in bytes) for the static object types of "NORM_OBJECT_FILE"
NORM_OBJECT_DATA. This information is used by receivers to determine and "NORM_OBJECT_DATA". This information is used by receivers to
storage requirements and/or allocate storage for the received object. determine storage requirements and/or allocate storage for the
Receivers with insufficient storage capability may wish to forego received object. Receivers with insufficient storage capability may
reliable reception (i.e., not NACK for) of the indicated object. In wish to forego reliable reception (i.e., not NACK for) of the
the case of objects of type NORM_OBJECT_STREAM, the "object_size" indicated object. In the case of objects of type
field is used by the sender to advertise the size of its stream "NORM_OBJECT_STREAM", the "object_size" field is used by the sender
buffer to the receiver group. In turn, the receivers SHOULD use this to advertise the size of its stream buffer to the receiver group. In
information to allocate a stream buffer for reception of turn, the receivers SHOULD use this information to allocate a stream
corresponding size. buffer for reception of corresponding size.
As noted, the format of the extension depends upon the FEC code in As noted, the format of the extension depends upon the FEC code in
use, but in general it SHOULD contain any required details on the FEC use, but in general it SHOULD contain any required details on the FEC
code in use (e.g., FEC Instance ID, etc.). As an example, the format code in use (e.g., FEC Instance ID, etc.). As an example, the format
of the EXT_FTI for small block systematic codes ("fec_id" = 129) is of the EXT_FTI for small block systematic codes ("fec_id" = 129) is
given here: given here:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| het = 64 | hel = 4 | object_size (msb) | | het = 64 | hel = 4 | object_size (msb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| object_size (lsb) | | object_size (lsb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_instance_id | segment_size | | fec_instance_id | segment_size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_max_block_len | fec_num_parity | | fec_max_block_len | fec_num_parity |
skipping to change at page 28, line 17 skipping to change at page 26, line 20
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| het = 64 | hel = 4 | object_size (msb) | | het = 64 | hel = 4 | object_size (msb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| object_size (lsb) | | object_size (lsb) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_instance_id | segment_size | | fec_instance_id | segment_size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_max_block_len | fec_num_parity | | fec_max_block_len | fec_num_parity |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example FEC Object Transmission Information Header Extension Example: EXT_FTI Header Extension Format for &quot;fec_id&quot; = 129
(EXT_FTI) for Small Block, Systematic Codes ("fec_id" = 129)
In this example (for "fec_id" = 129), the "hel" field value is 4. In this example (for "fec_id" = 129), the "hel" field value is 4.
The size of the EXT_FTI header extension may be different for other The size of the EXT_FTI header extension may be different for other
FEC schemes. FEC schemes.
The 48-bit "object_size" serves the purpose described previously. The 48-bit "object_size" serves the purpose described previously.
The "fec_instance_id" corresponds to the "FEC Instance ID" described The "fec_instance_id" corresponds to the "FEC Instance ID" described
in the FEC Building Block document [4]. In this case, the in the FEC Building Block document [RFC5052]. In this case, the
"fec_instance_id" is a value corresponding to the particular type of "fec_instance_id" is a value corresponding to the particular type of
Small Block Systematic Code being used (e.g., Reed-Solomon GF(2^8), Small Block Systematic Code being used (e.g., Reed-Solomon GF(2^8),
Reed-Solomon GF(2^16), etc). The standardized assignment of FEC Reed-Solomon GF(2^16), etc). The standardized assignment of FEC
Instance ID values is described in [4]. The "segment_size" field Instance ID values is described in [RFC5052].
indicates the sender’s current setting for maximum message payload
content (in bytes). This allows receivers to allocate appropriate The "segment_size" field indicates the sender's current setting for
buffering resources and to determine other information in order to maximum message payload content (in bytes). This allows receivers to
properly process received data messaging. Typically, FEC parity allocate appropriate buffering resources and to determine other
symbol segments will be of this size. information in order to properly process received data messaging.
Typically, FEC parity symbol segments will be of this size.
The "fec_max_block_len" indicates the current maximum number of user The "fec_max_block_len" indicates the current maximum number of user
data segments per FEC coding block to be used by the sender during data segments per FEC coding block to be used by the sender during
the session. This allows receivers to allocate appropriate buffer the session. This allows receivers to allocate appropriate buffer
space for buffering blocks transmitted by the sender. space for buffering blocks transmitted by the sender.
The "fec_num_parity" corresponds to the "maximum number of encoding The "fec_num_parity" corresponds to the "maximum number of encoding
symbols that can be generated for any source block" as described in symbols that can be generated for any source block" as described in
for FEC Object Transmission Information for Small Block Systematic for FEC Object Transmission Information for Small Block Systematic
Codes in the FEC Building Block document [4]. For example, Reed- Codes in the FEC Building Block document [RFC5052]. For example,
Solomon codes may be arbitrarily shortened to create different code Reed-Solomon codes may be arbitrarily shortened to create different
variations for a given block length. In the case of Reed-Solomon code variations for a given block length. In the case of Reed-
(GF(2^8) and GF(2^16)) codes, this value indicates the maximum number Solomon (GF(2^8) and GF(2^16)) codes, this value indicates the
of parity segments available from the sender for the coding blocks. maximum number of parity segments available from the sender for the
This field MAY be interpreted differently for other systematic codes coding blocks. This field MAY be interpreted differently for other
as they are defined. systematic codes as they are defined.
The payload portion of NORM_DATA messages includes source data or FEC The payload portion of "NORM_DATA" messages includes source data or
encoded application content. Again, the content of this payload FEC encoded application content. The content of this payload depends
depends upon the FEC scheme being employed. Additionally, support upon the FEC scheme being employed, and support for streaming using
for streaming using the NORM_OBJECT_STREAM type, necessitates some the "NORM_OBJECT_STREAM" type, when applicable, necessitates some
additional content in the payload. additional content in the payload.
The "payload_len", "payload_msg_start", and "payload_offset" fields The "payload_len", "payload_msg_start", and "payload_offset" fields
are present ONLY for transport objects of type NORM_OBJECT_STREAM. are present ONLY for transport objects of type "NORM_OBJECT_STREAM".
For senders employing systematic FEC encoding, these fields contain These fields allow senders to arbitrarily vary the size of
values that can be interpreted directly for NORM_DATA messages "NORM_DATA" payload segments for streams. This allows applications
containing original application source data content. But, for to flush transmitted streams as needed to meet unique streaming
NORM_DATA messages containing calculated parity content, these fields requirements. For objects of types "NORM_OBJECT_FILE" and
will contain values computed by FEC encoding of the "NORM_OBJECT_DATA", these fields are unnecessary since the receiver
"payload_msg_start", "payload_len" and "payload_offset" values of the can calculate the payload length and offset information from the
NORM_DATA data segments for the corresponding FEC coding block and "fec_payload_id" using the REQUIRED block partitioning algorithm
cannot be interpreted directly. The actual "payload_msg_start", described in the FEC Building Block document [RFC5052]. When
"payload_len" and "payload_offset" values of missing data content can systematic FEC codes (e.g., "fec_id" = 129) are used, the
be determined upon decoding a FEC coding block. Note that these "payload_len", "payload_msg_start", and "payload_offset" fields
fields do NOT contribute to the value of the NORM_DATA "hdr_len" contain actual payload_data length, message start index (or stream
field. These fields are present only when the "flags" portion of the control code), and byte offset values for the associated application
NORM_DATA message indicate the transport object is of type stream data segment (the remainder of the "payload_data" field
NORM_OBJECT_STREAM. content) for those "NORM_DATA" messages containing source data
symbols. In "NORM_DATA" messages that contain FEC parity content,
these fields do not contain values that can be directly interpreted,
but instead are values computed from FEC encoding the "payload_len",
"payload_msg_start", and "payload_offset" fields for the source data
segments of the corresponding coding block. The actual
"payload_msg_start", "payload_len" and "payload_offset" values of
missing data content can be determined upon decoding a FEC coding
block. Note that these fields do NOT contribute to the value of the
"NORM_DATA" "hdr_len" field. These fields are present only when the
"flags" portion of the "NORM_DATA" message indicate the transport
object is of type "NORM_OBJECT_STREAM".
The "payload_len" value, when non-zero, indicates the size, in bytes, The "payload_len" value, when non-zero, indicates the length (in
of the source content contained in the "payload_data" field. If the bytes) of the source content contained in the associated
"payload_len" value is equal to ZERO, this indicates that the "payload_data" field. When the "payload_len" value is equal to ZERO,
"payload_msg_start" field should be alternatively interpreted as a this indicates that the "payload_msg_start" field should be
stream control code. The only stream control code currently defined alternatively interpreted as a "stream_control_code". The only
is NORM_STREAM_END = 0. This code indicates that the sender is "stream_control_code" value currently defined is "NORM_STREAM_END =
0". The "NORM_STREAM_END" code indicates that the sender is
terminating transmission of stream content at the corresponding terminating transmission of stream content at the corresponding
position in the stream and the receiver should not expect content (or position in the stream and the receiver should not expect content (or
NACK for any content) following that position in the stream. Future NACK for any content) following that position in the stream. Future
versions of this specification may define additional stream control versions of this specification may define additional stream control
codes if necessary. codes if necessary. Values of "stream_control_code" that are not
understood SHOULD be ignored.
The "payload_msg_start" field serves one of two exclusive purposes.
When the "payload_len" value is non-zero, the "payload_msg_start" When the "payload_len" value is non-zero, the "payload_msg_start"
field, when it is set to a non-zero value, indicates that the field, when also set to a non-zero value, indicates that the
associated "payload_data" content contains an application-defined associated "payload_data" content contains an application-defined
message boundary (start-of-message). When such a message boundary is message boundary (start-of-message). When such a message boundary is
indicated, the first byte of an application-defined message, with indicated, the first byte of an application-defined message, with
respect to the "payload_data" field, will be found at an offset of respect to the "payload_data" field, will be found at an offset of
"payload_msg_start - 1" bytes. Thus, if a NORM_OBJECT_STREAM "payload_msg_start - 1" bytes. Thus, if a "NORM_DATA" payload for a
NORM_DATA payload contains the start of an application message at the "NORM_OBJECT_STREAM" contains the start of an application message at
first byte of the "payload_data" field, the value of the the first byte of the "payload_data" field, the value of the
"payload_msg_start" field will be ’1’. Again, if the value of the "payload_msg_start" field will be '1'. NORM implementations SHOULD
"payload_msg_start" field is ZERO, no message boundary is indicated. provide sender stream applications with a capability to mark message
It is RECOMMENDED that NORM implementations provide sender stream boundaries in this manner. Similarly, the NORM receiver
applications with a capability to mark message boundaries in this implementation SHOULD enable the application to recover such message
manner. Similarly, the NORM receiver SHOULD enable the application boundary information. This enables NORM receivers to "synchronize"
to recover such message boundary information. This enables NORM reliable reception of transmitted message stream content in a
receivers to "synchronize" with transmitted message stream content in meaningful way (i.e., meaningful to the application) at any time,
a meaningful way (i.e., meaningful to the application) at any time, whether joining a session already in progress, or departing the
whether joining the session late, or departing the session and session and returning. Note that if the value of the
returning. "payload_msg_start" field is ZERO, no message boundary is present.
The "payload_msg_start" value will always be less than or equal to
the "payload_len" value except for the special case of "payload_len =
0", that indicates the "payload_msg_start" field should instead be
interpreted as a "stream_control_code"
and "payload_offset" fields indicate the size and relative position The "payload_offset" field indicates the relative byte position (from
(within the stream) of the source content contained in the the sender stream transmission start) of the source content contained
"payload_data" field. Note that for long-lived streams, the in the "payload_data" field. Note that for long-lived streams, the
"payload_offset" field may wrap. "payload_offset" field may wrap.
The "payload_data" field contains the original application source or The "payload_data" field contains the original application source or
parity content for the symbol identified by the "fec_payload_id". parity content for the symbol identified by the "fec_payload_id".
The length of this field SHALL be limited to a maximum of the The length of this field SHALL be limited to a maximum of the
senders NormSegmentSize bytes as given in the FTI for the object. sender's NormSegmentSize bytes as given in the FTI for the object.
Note the length of this field for messages containing parity content Note the length of this field for messages containing parity content
will always be of length NormSegmentSize. When encoding data will always be of length NormSegmentSize. When encoding data
segments of varying sizes, the FEC encoder SHALL assume ZERO value segments of varying sizes, the FEC encoder SHALL assume ZERO value
padding for data segments with length less than the NormSegmentSize. padding for data segments with length less than the NormSegmentSize.
It is RECOMMENDED that a sender’s NormSegmentSize generally be It is RECOMMENDED that a sender's NormSegmentSize generally be
constant for the duration of a given sender’s term of participation constant for the duration of a given sender's term of participation
in the session, but may possibly vary on a per-object basis. The in the session, but may possibly vary on a per-object basis. The
NormSegmentSize is expected to be configurable by the sender NormSegmentSize is expected to be configurable by the sender
application prior to session participation as needed for network application prior to session participation as needed for network
topology maximum transmission unit (MTU) considerations. For IPv6, topology maximum transmission unit (MTU) considerations. For IPv6,
MTU discovery may be possibly leveraged at session startup to perform MTU discovery may be possibly leveraged at session startup to perform
this configuration. The "payload_data" content may be delivered this configuration. The "payload_data" content may be delivered
directly to the application for source symbols (when systematic FEC directly to the application for source symbols (when systematic FEC
encoding is used) or upon decoding of the FEC block. For encoding is used) or upon decoding of the FEC block. For
NORM_OBJECT_FILE and NORM_OBJECT_STREAM objects, the data segment "NORM_OBJECT_FILE" and "NORM_OBJECT_STREAM" objects, the data segment
length and offset can be calculated using the block paritioning length and offset can be calculated using the block partitioning
algorithm described in the FEC Building Block document [4]. For algorithm described in the FEC Building Block document [RFC5052].
NORM_OBJECT_STREAM objects, the length and offset is obtained from For "NORM_OBJECT_STREAM" objects, the length and offset is obtained
the segment’s corresponding "payload_len" and "payload_offset" from the segment's corresponding embedded "payload_len" and
fields. "payload_offset" fields.
4.2.2. NORM_INFO Message 4.2.2. NORM_INFO Message
The NORM_INFO message is used to convey OPTIONAL, application- The "NORM_INFO" message is used to convey OPTIONAL, application-
defined, "out-of-band" context information for transmitted defined, out-of-band context information for transmitted NormObjects.
NormObjects. An example NORM_INFO use for bulk file transfer is to An example "NORM_INFO" use for bulk file transfer is to place MIME
place MIME type information for the associated file, data, or stream type information for the associated file, data, or stream object into
object into the NORM_INFO payload. Receivers may use the NORM_INFO the "NORM_INFO" payload. Receivers may use the "NORM_INFO" content
content to make a decision as whether to participate in reliable to make a decision as whether to participate in reliable reception of
reception of the associated object. Each NormObject can have an the associated object. Each NormObject can have an independent unit
independent unit of NORM_INFO associated with it. NORM_DATA messages of "NORM_INFO" associated with it. "NORM_DATA" messages contain a
contain a flag to indicate the availability of NORM_INFO for a given flag to indicate the availability of "NORM_INFO" for a given
NormObject. NORM receivers may NACK for retransmission of NORM_INFO NormObject. NORM receivers may NACK for retransmission of
when they have not received it for a given NormObject. The size of "NORM_INFO" when they have not received it for a given NormObject.
the NORM_INFO content is limited to that of a single NormSegmentSize The size of the "NORM_INFO" content is limited to that of a single
for the given sender. This atomic nature allows the NORM_INFO to be NormSegmentSize for the given sender. This atomic nature allows the
rapidly and efficiently repaired within the NORM reliable "NORM_INFO" to be rapidly and efficiently repaired within the NORM
transmission process. reliable transmission process.
When NORM_INFO content is available for a NormObject, the When "NORM_INFO" content is available for a NormObject, the
NORM_FLAG_INFO flag SHALL be set in NORM_DATA messages for the NORM_FLAG_INFO flag SHALL be set in "NORM_DATA" messages for the
corresponding "object_transport_id" and the NORM_INFO message shall corresponding "object_transport_id" and the "NORM_INFO" message shall
be transmitted as the first message for the NormObject. be transmitted as the first message for the NormObject.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=1| hdr_len | sequence | |version| type=1| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_INFO Message Format NORM_INFO Message Format
The "version", "type", "hdr_len", "sequence", and "source_id" fields The "version", "type", "hdr_len", "sequence", and "source_id" fields
form the NORM Common Message Header as described in Section 4.1. The form the NORM Common Message Header as described in Section 4.1. The
value of "hdr_len" field when no header extensions are present is 4. value of "hdr_len" field when no header extensions are present is 4.
The "instance_id", "grtt", "backoff", "gsize", "flags", "fec_id", and The "instance_id", "grtt", "backoff", "gsize", "flags", "fec_id", and
"object_transport_id" fields carry the same information and serve the "object_transport_id" fields carry the same information and serve the
same purpose as with NORM_DATA messages. These values allow the same purpose as with "NORM_DATA" messages. These values allow the
receiver to prepare appropriate buffering, etc, for further receiver to prepare appropriate buffering, etc, for further
transmissions from the sender when NORM_INFO is the first message transmissions from the sender when "NORM_INFO" is the first message
received. received.
As with NORM_DATA messages, the NORM FTI Header Extension (EXT_FTI) As with "NORM_DATA" messages, the NORM FTI Header Extension (EXT_FTI)
may be optionally applied to NORM_INFO messages. To conserve may be optionally applied to "NORM_INFO" messages. To conserve
protocol overhead, some NORM implementations may wish to apply the protocol overhead, some NORM implementations may wish to apply the
EXT_FTI when used to NORM_INFO messages only and not to NORM_DATA EXT_FTI when used to "NORM_INFO" messages only and not to "NORM_DATA"
messages. messages.
The NORM_INFO "payload_data" field contains sender application- The "NORM_INFO" "payload_data" field contains sender application-
defined content which can be used by receiver applications for defined content which can be used by receiver applications for
various purposes as described above. various purposes as described above.
4.2.3. NORM_CMD Messages 4.2.3. NORM_CMD Messages
NORM_CMD messages are transmitted by senders to perform a number of "NORM_CMD" messages are transmitted by senders to perform a number of
different protocol functions. This includes functions such as round- different protocol functions. This includes functions such as round-
trip timing collection, congestion control functions, synchronization trip timing collection, congestion control functions, synchronization
of sender/receiver repair "windows", and notification of sender of sender/receiver repair "windows", and notification of sender
status. A core set of NORM_CMD messages is enumerated. status. A core set of "NORM_CMD" messages is enumerated.
Additionally, a range of command types remain available for potential Additionally, a range of command types remain available for potential
application-specific use. Some NORM_CMD types may have dynamic application-specific use. Some "NORM_CMD" types may have dynamic
content attached. Any attached content will be limited to maximum content attached. Any attached content will be limited to maximum
length of the sender NormSegmentSize to retain the atomic nature of length of the sender NormSegmentSize to retain the atomic nature of
commands. All NORM_CMD messages begin with a common set of fields, commands. All "NORM_CMD" messages begin with a common set of fields,
after the usual NORM message common header. The standard NORM_CMD after the usual NORM message common header. The standard "NORM_CMD"
fields are: fields are:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=3| hdr_len | sequence | |version| type=3| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor | | | flavor | |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor | | | flavor | |
+-+-+-+-+-+-+-+-+ NORM_CMD Content + +-+-+-+-+-+-+-+-+ NORM_CMD Content +
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_CMD Standard Fields NORM_CMD Standard Fields
The "version", "type", "hdr_len", "sequence", and "source_id" fields The "version", "type", "hdr_len", "sequence", and "source_id" fields
form the NORM Common Message Header as described in Section 4.1. The form the NORM Common Message Header as described in Section 4.1. The
value of the "hdr_len" field for NORM_CMD messages without header value of the "hdr_len" field for "NORM_CMD" messages without header
extensions present depends upon the "flavor" field. extensions present depends upon the "flavor" field.
The "instance_id", "grtt", "backoff", and "gsize" fields provide the The "instance_id", "grtt", "backoff", and "gsize" fields provide the
same information and serve the same purpose as with NORM_DATA and same information and serve the same purpose as with "NORM_DATA" and
NORM_INFO messages. The "flavor" field indicates the type of command "NORM_INFO" messages. The "flavor" field indicates the type of
to follow. The remainder of the NORM_CMD message is dependent upon command to follow. The remainder of the "NORM_CMD" message is
the command type ("flavor"). NORM command flavors include: dependent upon the command type ("flavor"). NORM command flavors
include:
+----------------------+--------+----------------------------------+ +-------------------------+--------+--------------------------------+
| Command | Flavor | Purpose | | Command | Flavor | Purpose |
+----------------------+--------+----------------------------------+ +-------------------------+--------+--------------------------------+
|NORM_CMD(FLUSH) | 1 | Used to indicate sender | | "NORM_CMD(FLUSH)" | 1 | Used to indicate sender |
| | | temporary end-of-transmission. | | | | temporary end-of-transmission. |
| | | (Assists in robustly initiating | | | | (Assists in robustly |
| | | outstanding repair requests from | | | | initiating outstanding repair |
| | | receivers). May also be | | | | requests from receivers). May |
| | | optionally used to collect | | | | also be optionally used to |
| | | positive acknowledgment of | | | | collect positive |
| | | reliable reception from subset | | | | acknowledgment of reliable |
| | | of receivers. | | | | reception from subset of |
+----------------------+--------+----------------------------------+ | | | receivers. |
|NORM_CMD(EOT) | 2 | Used to indicate sender | | "NORM_CMD(EOT)" | 2 | Used to indicate sender |
| | | permanent end-of-transmission. | | | | permanent end-of-transmission. |
+----------------------+--------+----------------------------------+ | "NORM_CMD(SQUELCH)" | 3 | Used to advertise sender's |
|NORM_CMD(SQUELCH) | 3 | Used to advertise sender’s |
| | | current repair window in | | | | current repair window in |
| | | response to out-of-range NACKs | | | | response to out-of-range NACKs |
| | | from receivers. | | | | from receivers. |
+----------------------+--------+----------------------------------+ | "NORM_CMD(CC)" | 4 | Used for GRTT measurement and |
|NORM_CMD(CC) | 4 | Used for GRTT measurement and | | | | collection of congestion |
| | | collection of congestion control | | | | control feedback. |
| | | feedback. | | "NORM_CMD(REPAIR_ADV)" | 5 | Used to advertise sender's |
+----------------------+--------+----------------------------------+ | | | aggregated repair/feedback |
|NORM_CMD(REPAIR_ADV) | 5 | Used to advertise sender’s | | | | state for suppression of |
| | | aggregated repair/feedback state | | | | unicast feedback from |
| | | for suppression of unicast | | | | receivers. |
| | | feedback from receivers. | | "NORM_CMD(ACK_REQ)" | 6 | Used to request |
+----------------------+--------+----------------------------------+ | | | application-defined positive |
|NORM_CMD(ACK_REQ) | 6 | Used to request application- | | | | acknowledgment from a list of |
| | | defined positive acknowledgment | | | | receivers (OPTIONAL). |
| | | from a list of receivers | | "NORM_CMD(APPLICATION)" | 7 | Used for application-defined |
| | | (OPTIONAL). |
+----------------------+--------+----------------------------------+
|NORM_CMD(APPLICATION) | 7 | Used for application-defined |
| | | purposes which may need to | | | | purposes which may need to |
| | | temporarily preempt data | | | | temporarily preempt data |
| | | transmission (OPTIONAL). | | | | transmission (OPTIONAL). |
+----------------------+--------+----------------------------------+ +-------------------------+--------+--------------------------------+
4.2.3.1. NORM_CMD(FLUSH) Message 4.2.3.1. NORM_CMD(FLUSH) Message
The NORM_CMD(FLUSH) command is sent when the sender reaches the end The "NORM_CMD(FLUSH)" command is sent when the sender reaches the end
of all data content and pending repairs it has queued for of all data content and pending repairs it has queued for
transmission. This may indicate a temporary or permanent end of data transmission. This may indicate a temporary or permanent end of data
transmission, but the sender is still willing to respond to repair transmission, but the sender is still willing to respond to repair
requests. This command is repeated once per 2*GRTT to excite the requests. This command is repeated once per "2*GRTT" to excite the
receiver set for any outstanding repair requests up to and including receiver set for any outstanding repair requests up to and including
the transmission point indicated within the NORM_CMD(FLUSH) message. the transmission point indicated within the "NORM_CMD(FLUSH)"
The number of repeats is equal to NORM_ROBUST_FACTOR unless a list of message. The number of repeats is equal to "NORM_ROBUST_FACTOR"
receivers from which explicit positive acknowledgment is expected unless a list of receivers from which explicit positive
("acking_node_list") is given. In that case, the "acking_node_list" acknowledgment is expected ("acking_node_list") is given. In that
is updated as acknowledgments are received and the NORM_CMD(FLUSH) is case, the "acking_node_list" is updated as acknowledgments are
repeated according to the mechanism described in Section 5.5.3. The received and the "NORM_CMD(FLUSH)" is repeated according to the
greater the NORM_ROBUST_FACTOR, the greater the probability that all mechanism described in Section 5.5.3. The greater the
applicable receivers will be excited for acknowledgment or repair "NORM_ROBUST_FACTOR", the greater the probability that all applicable
requests (NACKs) _and_ that the corresponding NACKs are delivered to receivers will be excited for acknowledgment or repair requests
the sender. A default value of NORM_ROBUST_FACTOR equal to 20 is (NACKs) AND that the corresponding NACKs are delivered to the sender.
RECOMMENDED. If a NORM_NACK message interrupts the flush process, A default value of "NORM_ROBUST_FACTOR" equal to 20 is RECOMMENDED.
the sender SHALL re-initiate the flush process after any resulting If a "NORM_NACK" message interrupts the flush process, the sender
repair transmissions are completed. SHALL re-initiate the flush process after any resulting repair
transmissions are completed.
Note that receivers also employ a timeout mechanism to self-initiate Note that receivers also employ a timeout mechanism to self-initiate
NACKing (if there are outstanding repair needs) when no messages of NACKing (if there are outstanding repair needs) when no messages of
any type are received from a sender. This inactivity timeout is any type are received from a sender. This inactivity timeout is
related to the NORM_CMD(FLUSH) and NORM_ROBUST_FACTOR and is related to the "NORM_CMD(FLUSH)" and "NORM_ROBUST_FACTOR" and is
specified in Section 5.3. Receivers SHALL self-initiate the NACK specified in Section 5.3. Receivers SHALL self-initiate the NACK
repair process when the inactivity has expired for a specific sender repair process when the inactivity has expired for a specific sender
and the receiver has pending repairs needed from that sender. With a and the receiver has pending repairs needed from that sender. With a
sufficiently large NORM_ROBUST_FACTOR value, data content is sufficiently large "NORM_ROBUST_FACTOR" value, data content is
delivered with a high assurance of reliability. The penalty of a delivered with a high assurance of reliability. The penalty of a
large NORM_ROBUST_FACTOR value is the potential transmission of large "NORM_ROBUST_FACTOR" value is the potential transmission of
excess NORM_CMD(FLUSH) messages and a longer inactivity timeout for excess "NORM_CMD(FLUSH)" messages and a longer inactivity timeout for
receivers to self-initiate a terminal NACK process. receivers to self-initiate a terminal NACK process.
For finite-size transport objects such as NORM_OBJECT_DATA and For finite-size transport objects such as "NORM_OBJECT_DATA" and
NORM_OBJECT_FILE, the flush process (if there are no further pending "NORM_OBJECT_FILE", the flush process (if there are no further
objects) occurs at the end of these objects. Thus, FEC repair pending objects) occurs at the end of these objects. Thus, FEC
information is always available for repairs in response to repair repair information is always available for repairs in response to
requests elicited by the flush command. However, for repair requests elicited by the flush command. However, for
NORM_OBJECT_STREAM, the flush may occur at any time, including in the "NORM_OBJECT_STREAM", the flush may occur at any time, including in
middle of an FEC coding block if systematic FEC codes are employed. the middle of an FEC coding block if systematic FEC codes are
In this case, the sender will not yet be able to provide FEC parity employed. In this case, the sender will not yet be able to provide
content for the concurrent coding block and will be limited to FEC parity content for the concurrent coding block and will be
explicitly repairing the stream with source data content for that limited to explicitly repairing the stream with source data content
block. Applications that anticipate frequent flushing of stream for that block. Applications that anticipate frequent flushing of
content SHOULD be judicious in the selection of the FEC coding block stream content SHOULD be judicious in the selection of the FEC coding
size (i.e., do not use a very large coding block size if frequent block size (i.e., do not use a very large coding block size if
flushing occurs). For example, a reliable multicast application frequent flushing occurs). For example, a reliable multicast
transmitting an on-going series of intermittent, relatively small application transmitting an on-going series of intermittent,
messages will need to trade-off using the NORM_OBJECT_DATA paradigm relatively small messages will need to trade-off using the
versus the NORM_OBJECT_STREAM paradigm with an appropriate FEC coding "NORM_OBJECT_DATA" paradigm versus the "NORM_OBJECT_STREAM" paradigm
block size. This is analogous to application trade-offs for other with an appropriate FEC coding block size. This is analogous to
transport protocols such as the selection of different TCP modes of application trade-offs for other transport protocols such as the
operation such as "no delay", etc. selection of different TCP modes of operation such as "no delay",
etc.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=3| hdr_len | sequence | |version| type=3| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| acking_node_list (if applicable) | | acking_node_list (if applicable) |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_CMD(FLUSH) Message Format NORM_CMD(FLUSH) Message Format
The "version", "type", "hdr_len", "sequence", and "source_id" fields The "version", "type", "hdr_len", "sequence", and "source_id" fields
form the NORM Common Message Header as described in Section 4.1. In form the NORM Common Message Header as described in Section 4.1. In
addition to the NORM common message header and standard NORM_CMD addition to the NORM common message header and standard "NORM_CMD"
fields, the NORM_CMD(FLUSH) message contains fields to identify the fields, the "NORM_CMD(FLUSH)" message contains fields to identify the
current status and logical transmit position of the sender. current status and logical transmit position of the sender.
The "fec_id" field indicates the FEC type used for the flushing The "fec_id" field indicates the FEC type used for the flushing
"object_transport_id" and implies the size and format of the "object_transport_id" and implies the size and format of the
"fec_payload_id" field. Note the "hdr_len" value for the "fec_payload_id" field. Note the "hdr_len" value for the
NORM_CMD(FLUSH) message is 4 plus the size of the "fec_payload_id" "NORM_CMD(FLUSH)" message is 4 plus the size of the "fec_payload_id"
field when no header extensions are present. field when no header extensions are present.
The "object_transport_id" and "fec_payload_id" fields indicate the The "object_transport_id" and "fec_payload_id" fields indicate the
sender’s current logical "transmit position". These fields are sender's current logical "transmit position". These fields are
interpreted in the same manner as in the NORM_DATA message type. interpreted in the same manner as in the "NORM_DATA" message type.
Upon receipt of the NORM_CMD(FLUSH), receivers are expected to check Upon receipt of the "NORM_CMD(FLUSH)", receivers are expected to
their completion state _through_ (including) this transmission check their completion state THROUGH (including) this transmission
position. If receivers have outstanding repair needs in this range, position. If receivers have outstanding repair needs in this range,
they SHALL initiate the NORM NACK Repair Process as described in they SHALL initiate the NORM NACK Repair Process as described in
Section 5.3. If receivers have no outstanding repair needs, no Section 5.3. If receivers have no outstanding repair needs, no
response to the NORM_CMD(FLUSH) is generated. response to the "NORM_CMD(FLUSH)" is generated.
For NORM_OBJECT_STREAM objects using systematic FEC codes, receivers For "NORM_OBJECT_STREAM" objects using systematic FEC codes,
MUST request "explicit-only" repair of the identified receivers MUST request "explicit-only" repair of the identified
"source_block_number" if the given "encoding_symbol_id" is less than "source_block_number" if the given "encoding_symbol_id" is less than
the "source_block_len". This condition indicates the sender has not the "source_block_len". This condition indicates the sender has not
yet completed encoding the corresponding FEC block and parity content yet completed encoding the corresponding FEC block and parity content
is not yet available. An "explicit-only" repair request consists of is not yet available. An "explicit-only" repair request consists of
NACK content for the applicable "source_block_number" which does not NACK content for the applicable "source_block_number" which does not
include any requests for parity-based repair. This allows NORM include any requests for parity-based repair. This allows NORM
sender applications to "flush" an ongoing stream of transmission when sender applications to "flush" an ongoing stream of transmission when
needed, even if in the middle of an FEC block. Once the sender needed, even if in the middle of an FEC block. Once the sender
resumes stream transmission and passes the end of the pending coding resumes stream transmission and passes the end of the pending coding
block, subsequent NACKs from receivers SHALL request parity-based block, subsequent NACKs from receivers SHALL request parity-based
repair as usual. Note that the use of a systematic FEC code is repair as usual. Note that the use of a systematic FEC code is
assumed here. It should also be noted that a sender has the option assumed here. It should also be noted that a sender has the option
of arbitrarily shortening a given code block when such an application of arbitrarily shortening a given code block when such an application
"flush" occurs. In this case, the receiver will request explicit "flush" occurs. In this case, the receiver will request explicit
repair, but the sender MAY provide FEC-based repair (parity segments) repair, but the sender MAY provide FEC-based repair (parity segments)
in response. These parity segments MUST contain the corrected in response. These parity segments MUST contain the corrected
"source_block_len" for the shortened block and that "source_block_len" for the shortened block and that
"source_block_len" associated with segments containing parity content "source_block_len" associated with segments containing parity content
SHALL overrride the previously advertised "source_block_len". SHALL override the previously advertised "source_block_len".
Similarly, the "source_block_len" associated with the highest ordinal Similarly, the "source_block_len" associated with the highest ordinal
"encoding_symbol_id" shall take precedence over prior symbols when a "encoding_symbol_id" shall take precedence over prior symbols when a
difference (e.g., due to code shortening at the sender) occurs. difference (e.g., due to code shortening at the sender) occurs.
Normal receiver NACK initiation and construction is discussed in Normal receiver NACK initiation and construction is discussed in
detail in Section 5.3. The OPTIONAL "acking_node_list" field detail in Section 5.3.
contains a list of NormNodeIds for receivers from which the sender is
requesting explicit positive acknowledgment of reception up through The OPTIONAL "acking_node_list" field contains a list of NormNodeIds
the transmission point identified by the "object_transport_id" and for receivers from which the sender is requesting explicit positive
"fec_payload_id" fields. The length of the list can be inferred from acknowledgment of reception up through the transmission point
the length of the received NORM_CMD(FLUSH) message. When the identified by the "object_transport_id" and "fec_payload_id" fields.
"acking_node_list" is present, the lightweight positive The length of the list can be inferred from the length of the
acknowledgment process described in Section 5.5.3 SHALL be observed. received "NORM_CMD(FLUSH)" message. When the "acking_node_list" is
present, the lightweight positive acknowledgment process described in
Section 5.5.3 SHALL be observed.
4.2.3.2. NORM_CMD(EOT) Message 4.2.3.2. NORM_CMD(EOT) Message
The NORM_CMD(EOT) command is sent when the sender reaches permanent The "NORM_CMD(EOT)" command is sent when the sender reaches permanent
end-of-transmission with respect to the NormSession and will not end-of-transmission with respect to the NormSession and will not
respond to further repair requests. This allows receivers to respond to further repair requests. This allows receivers to
gracefully reach closure of operation with this sender (without gracefully reach closure of operation with this sender (without
requiring any timeout) and free any resources that are no longer requiring any timeout) and free any resources that are no longer
needed. The NORM_CMD(EOT) command SHOULD be sent with the same needed. The "NORM_CMD(EOT)" command SHOULD be sent with the same
robust mechanism as used for NORM_CMD(FLUSH) commands to provide a robust mechanism as used for "NORM_CMD(FLUSH)" commands to provide a
high assurance of reception by the receiver set. high assurance of reception by the receiver set.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=3| hdr_len | sequence | |version| type=3| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor = 2 | reserved | | flavor = 2 | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_CMD(EOT) Message Format NORM_CMD(EOT) Message Format
The value of the "hdr_len" field for NORM_CMD(EOT) messages without The value of the "hdr_len" field for "NORM_CMD(EOT)" messages without
header extensions present is 4. The "reserved" field is reserved for header extensions present is 4. The "reserved" field is reserved for
future use and MUST be set to an all ZERO value. Receivers MUST future use and MUST be set to an all ZERO value. Receivers MUST
ignore the "reserved" field. ignore the "reserved" field.
4.2.3.3. NORM_CMD(SQUELCH) Message 4.2.3.3. NORM_CMD(SQUELCH) Message
The NORM_CMD(SQUELCH) command is transmitted in response to outdated The "NORM_CMD(SQUELCH)" command is transmitted in response to
or invalid NORM_NACK content received by the sender. Invalid outdated or invalid "NORM_NACK" content received by the sender.
NORM_NACK content consists of repair requests for NormObjects for Invalid "NORM_NACK" content consists of repair requests for
which the sender is unable or unwilling to provide repair. This NormObjects for which the sender is unable or unwilling to provide
includes repair requests for outdated objects, aborted objects, or repair. This includes repair requests for outdated objects, aborted
those objects which the sender previously transmitted marked with the objects, or those objects which the sender previously transmitted
NORM_FLAG_UNRELIABLE flag. This command indicates to receivers what marked with the "NORM_FLAG_UNRELIABLE" flag. This command indicates
content is available for repair, thus serving as a description of the to receivers what content is available for repair, thus serving as a
sender’s current "repair window". Receivers SHALL not generate description of the sender's current "repair window". Receivers SHALL
repair requests for content identified as invalid by a not generate repair requests for content identified as invalid by a
NORM_CMD(SQUELCH). "NORM_CMD(SQUELCH)".
The NORM_CMD(SQUELCH) command is sent once per 2*GRTT at the most. The "NORM_CMD(SQUELCH)" command is sent once per "2*GRTT" at the
The NORM_CMD(SQUELCH) advertises the current "repair window" of the most. The "NORM_CMD(SQUELCH)" advertises the current "repair window"
sender by identifying the earliest (lowest) transmission point for of the sender by identifying the earliest (lowest) transmission point
which it will provide repair, along with an encoded list of objects for which it will provide repair, along with an encoded list of
from that point forward that are no longer valid for repair. This objects from that point forward that are no longer valid for repair.
mechanism allows the sender application to cancel or abort This mechanism allows the sender application to cancel or abort
transmission and/or repair of specific previously enqueued objects. transmission and/or repair of specific previously enqueued objects.
The list also contains the identifiers for any objects within the The list also contains the identifiers for any objects within the
repair window that were sent with the NORM_FLAG_UNRELIABLE flag set. repair window that were sent with the "NORM_FLAG_UNRELIABLE" flag
In normal conditions, it is expected the NORM_CMD(SQUELCH) will be set. In normal conditions, it is expected the "NORM_CMD(SQUELCH)"
needed infrequently, and generally only to provide a reference repair will be needed infrequently, and generally only to provide a
window for receivers who have fallen "out-of-sync" with the sender reference repair window for receivers who have fallen "out-of-sync"
due to extremely poor network conditions. with the sender due to extremely poor network conditions.
The starting point of the invalid NormObject list begins with the The starting point of the invalid NormObject list begins with the
lowest invalid NormTransportId greater than the current "repair lowest invalid NormTransportId greater than the current "repair
window" start from the invalid NACK(s) that prompted the generation window" start from the invalid NACK(s) that prompted the generation
of the squelch. The length of the list is limited by the senders of the squelch. The length of the list is limited by the sender's
NormSegmentSize. This allows the receivers to learn the status of NormSegmentSize. This allows the receivers to learn the status of
the sender’s applicable object repair window with minimal the sender's applicable object repair window with minimal
transmission of NORM_CMD(SQUELCH) commands. The format of the transmission of "NORM_CMD(SQUELCH)" commands. The format of the
NORM_CMD(SQUELCH) message is: "NORM_CMD(SQUELCH)" message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=3| hdr_len | sequence | |version| type=3| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor = 3 | fec_id | object_transport_id | | flavor = 3 | fec_id | object_transport_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_payload_id | | fec_payload_id |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| invalid_object_list | | invalid_object_list |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_CMD(SQUELCH) Message Format NORM_CMD(SQUELCH) Message Format
In addition to the NORM common message header and standard NORM_CMD In addition to the NORM common message header and standard "NORM_CMD"
fields, the NORM_CMD(SQUELCH) message contains fields to identify the fields, the "NORM_CMD(SQUELCH)" message contains fields to identify
earliest logical transmit position of the sender’s current repair the earliest logical transmit position of the sender's current repair
window and an "invalid object list" beginning with the index of the window and an "invalid_object_list" beginning with the index of the
logically earliest invalid repair request from the offending NACK logically earliest invalid repair request from the offending NACK
message which initiated the squelch transmission. The value of the message which initiated the "NORM_CMD(SQUELCH)" transmission. The
"hdr_len" field when no extensions are present is 4 plus the size of value of the "hdr_len" field when no extensions are present is 4 plus
the "fec_payload_id" field that is dependent upon the FEC scheme the size of the "fec_payload_id" field that is dependent upon the FEC
identified by the "fec_id" field. scheme identified by the "fec_id" field.
The "object_transport_id" and "fec_payload_id" fields are The "object_transport_id" and "fec_payload_id" fields are
concatenated to indicate the beginning of the senders current repair concatenated to indicate the beginning of the sender's current repair
window (i.e., the logically earliest point in its transmission window (i.e., the logically earliest point in its transmission
history for which the sender can provide repair). The "fec_id" field history for which the sender can provide repair). The "fec_id" field
implies the size and format of the "fec_payload_id" field. This implies the size and format of the "fec_payload_id" field. This
serves as an advertisement of a "synchronization point" for receivers serves as an advertisement of a "synchronization" point for receivers
to request repair. Note, that while an "encoding_symbol_id" may be to request repair. Note, that while an "encoding_symbol_id" may be
included in the "fec_payload_id" field, the senders repair window included in the "fec_payload_id" field, the sender's repair window
SHOULD be aligned on FEC coding block boundaries and thus the SHOULD be aligned on FEC coding block boundaries and thus the
"encoding_symbol_id" SHOULD be zero. "encoding_symbol_id" SHOULD be zero.
The "invalid_object_list" is a list of 16-bit NormTransportIds that, The "invalid_object_list" is a list of 16-bit NormTransportIds that,
although they are within the range of the senders current repair although they are within the range of the sender's current repair
window, are no longer available for repair from the sender. For window, are no longer available for repair from the sender. For
example, a sender application may dequeue an out-of-date object even example, a sender application may dequeue an out-of-date object even
though it is still within the repair window. The total size of the though it is still within the repair window. The total size of the
"invalid_object_list" content is can be determined from the packets "invalid_object_list" content is can be determined from the packet's
payload length and is limited to a maximum of the NormSegmentSize of payload length and is limited to a maximum of the NormSegmentSize of
the sender. Thus, for very large repair windows, it is possible that the sender. Thus, for very large repair windows, it is possible that
a single NORM_CMD(SQUELCH) message may not be capable of listing the a single "NORM_CMD(SQUELCH)" message may not be capable of listing
entire set of invalid objects in the repair window. In this case, the entire set of invalid objects in the repair window. In this
the sender SHALL ensure that the list begins with a NormObjectId that case, the sender SHALL ensure that the list begins with a
is greater than or equal to the lowest ordinal invalid NormObjectId NormObjectId that is greater than or equal to the lowest ordinal
from the NACK message(s) that prompted the NORM_CMD(SQUELCH) invalid NormObjectId from the NACK message(s) that prompted the
generation. The NormObjectIds in the "invalid_object_list" MUST be "NORM_CMD(SQUELCH)" generation. The NormObjectIds in the
greater than the "object_transport_id" marking the beginning of the "invalid_object_list" MUST be ordinally greater than the
sender’s repair window. This insures convergence of the squelch "object_transport_id" marking the beginning of the sender's repair
process, even if multiple invalid NACK/ squelch iterations are window. This insures convergence of the squelch process, even if
required. This explicit description of invalid content within the multiple invalid NACK/ squelch iterations are required. This
sender’s current window allows the sender application (most notably explicit description of invalid content within the sender's current
for discrete "object" based transport) to arbitrarily invalidate window allows the sender application (most notably for discrete
(i.e., dequeue) portions of enqueued content (e.g., certain objects) object transport) to arbitrarily invalidate (i.e., dequeue) portions
for which it no longer wishes to provide reliable transport. of enqueued content (e.g., certain objects) for which it no longer
wishes to provide reliable transport.
4.2.3.4. NORM_CMD(CC) Message 4.2.3.4. NORM_CMD(CC) Message
The NORM_CMD(CC) messages contains fields to enable sender-to- The "NORM_CMD(CC)" messages contains fields to enable sender-to-
receiver group greatest round-trip time (GRTT) measurement and to receiver group greatest round-trip time (GRTT) measurement and to
excite the group for congestion control feedback. A baseline NORM excite the group for congestion control feedback. A baseline NORM
congestion control scheme (NORM-CC), based on the TCP-Friendly congestion control scheme (NORM-CC), based on the TCP-Friendly
Multicast Congestion Control (TFMCC) scheme of [5] is described in Multicast Congestion Control (TFMCC) scheme of [RFC4654] is described
Section 5.5.2 of this document. The NORM_CMD(CC) message is usually in Section 5.5.2 of this document. The "NORM_CMD(CC)" message is
transmitted as part of NORM-CC congestion control operation. A NORM usually transmitted as part of NORM-CC congestion control operation.
header extension is defined below to be used with the NORM_CMD(CC) A NORM header extension is defined below to be used with the
message to support NORM-CC operation. Different header extensions "NORM_CMD(CC)" message to support NORM-CC operation. Different
may be defined for the NORM_CMD(CC) (and/or other NORM messages as header extensions may be defined for the "NORM_CMD(CC)" (and/or other
needed) to support alternative congestion control schemes in the NORM messages as needed) to support alternative congestion control
future. If NORM is operated in a private network with congestion schemes in the future. If NORM is operated in a private network with
control operation disabled, the NORM_CMD(CC) message is then used for congestion control operation disabled, the "NORM_CMD(CC)" message is
GRTT measurement only and may optionally be sent less frequently than then used for GRTT measurement only and may optionally be sent less
with congestion control operation. frequently than with congestion control operation.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=3| hdr_len | sequence | |version| type=3| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 40, line 29 skipping to change at page 39, line 29
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| header extensions (if applicable) | | header extensions (if applicable) |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| cc_node_list (if applicable) | | cc_node_list (if applicable) |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_CMD(CC) Message Format NORM_CMD(CC) Message Format
The NORM common message header and standard NORM_CMD fields serve The NORM common message header and standard "NORM_CMD" fields serve
their usual purposes. The value of the "hdr_len" field when no their usual purposes. The value of the "hdr_len" field when no
header extensions are present is 6. header extensions are present is 6.
The "reserved" field is for potential future use and MUST be set to The "reserved" field is for potential future use and MUST be set to
ZERO in this version of the NORM protocol and its baseline NORM-CC ZERO in this version of the NORM protocol and its baseline NORM-CC
congestion control scheme. It may be possible that alternative congestion control scheme. It may be possible that alternative
congestion control schemes may use the NORM_CMD(CC) message defined congestion control schemes may use the "NORM_CMD(CC)" message defined
here and leverage the "reserved" field for scheme-specific purposes. here and leverage the "reserved" field for scheme-specific purposes.
The "cc_sequence" field is a sequence number applied by the sender. The "cc_sequence" field is a sequence number applied by the sender.
For NORM-CC operation, it is used to provide functionality equivalent For NORM-CC operation, it is used to provide functionality equivalent
to the "feedback round number" (fb_nr)described in [5]. The most to the "feedback round number" ("fb_nr")described in [RFC4654]. The
recently received "cc_sequence" value is recorded by receivers and most recently received "cc_sequence" value is recorded by receivers
can be fed back to the sender in congestion control feedback and can be fed back to the sender in congestion control feedback
generated by the receivers for that sender. The "cc_sequence" number generated by the receivers for that sender. The "cc_sequence" number
can also be used in NORM implementations to assess how recently a can also be used in NORM implementations to assess how recently a
receiver has received NORM_CMD(CC) probes from the sender. This can receiver has received "NORM_CMD(CC)" probes from the sender. This
be useful instrumentation for complex or experimental multicast can be useful instrumentation for complex or experimental multicast
routing environments. routing environments.
The "send_time" field is a timestamp indicating the time that the The "send_time" field is a timestamp indicating the time that the
NORM_CMD(CC) message was transmitted. This consists of a 64-bit "NORM_CMD(CC)" message was transmitted. This consists of a 64-bit
field containing 32-bits with the time in seconds ("send_time_sec") field containing 32-bits with the time in seconds ("send_time_sec")
and 32-bits with the time in microseconds ("send_time_usec") since and 32-bits with the time in microseconds ("send_time_usec") since
some reference time the source maintains (usually 00:00:00, 1 January some reference time the source maintains (usually 00:00:00, 1 January
1970). The byte ordering of the fields is "Big Endian" network 1970). The byte ordering of the fields is "Big Endian" network
order. Receivers use this timestamp adjusted by the amount of delay order. Receivers use this timestamp adjusted by the amount of delay
from the time they received the NORM_CMD(CC) message to the time of from the time they received the "NORM_CMD(CC)" message to the time of
their response as the "grtt_response" portion of NORM_ACK and their response as the "grtt_response" portion of "NORM_ACK" and
NORM_NACK messages generated. This allows the sender to evaluate "NORM_NACK" messages generated. This allows the sender to evaluate
round-trip times to different receivers for congestion control and round-trip times to different receivers for congestion control and
other (e.g., GRTT determination) purposes. other (e.g., GRTT determination) purposes.
To facilitate the baseline NORM-CC scheme described in Section 5.5.2, To facilitate the baseline NORM-CC scheme described in Section 5.5.2,
a NORM-CC Rate header extension (EXT_RATE) is defined to inform the a NORM-CC Rate header extension (EXT_RATE) is defined to inform the
group of the senders current transmission rate. This is used along group of the sender's current transmission rate. This is used along
with the loss detection "sequence" field of all NORM sender messages with the loss detection "sequence" field of all NORM sender messages
and the NORM_CMD(CC) GRTT collection process to support NORM-CC and the "NORM_CMD(CC)" GRTT collection process to support NORM-CC
congestion control operation. The format of this header extension is congestion control operation. The format of this header extension is
as follows: as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| het = 128 | reserved | send_rate | | het = 128 | reserved | send_rate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM-CC Rate Header Extension Format (EXT_RATE) The "send_rate" field indicates the sender's current transmission
The "send_rate" field indicates the sender’s current transmission
rate in bytes per second. The 16-bit "send_rate" field consists of rate in bytes per second. The 16-bit "send_rate" field consists of
12 bits of mantissa in the most significant portion and 4 bits of 12 bits of mantissa in the most significant portion and 4 bits of
base 10 integer exponent (E) information in the least significant base 10 integer exponent (E) information in the least significant
portion. The 12-bit mantissa portion of the field is scaled such portion. The 12-bit mantissa portion of the field is scaled such
that a base 10 mantissa (M) floating point value of 0.0 corresponds that a base 10 mantissa (M) floating point value of 0.0 corresponds
to 0 and a value of 10.0 corresponds to 4096 in the upper 12 bits of to 0 and a value of 10.0 corresponds to 4096 in the upper 12 bits of
the 16-bit "send_rate" field . Thus: the 16-bit "send_rate" field . Thus:
send_rate = (((int)(M * 4096.0 / 10.0 + 0.5)) << 4) | E; send_rate = (((int)(M * 4096.0 / 10.0 + 0.5)) << 4) | E;
skipping to change at page 41, line 46 skipping to change at page 40, line 43
to 0 and a value of 10.0 corresponds to 4096 in the upper 12 bits of to 0 and a value of 10.0 corresponds to 4096 in the upper 12 bits of
the 16-bit "send_rate" field . Thus: the 16-bit "send_rate" field . Thus:
send_rate = (((int)(M * 4096.0 / 10.0 + 0.5)) << 4) | E; send_rate = (((int)(M * 4096.0 / 10.0 + 0.5)) << 4) | E;
For example, to represent a transmission rate of 256kbps (3.2e+04 For example, to represent a transmission rate of 256kbps (3.2e+04
bytes per second), the lower 4 bits of the 16-bit field contain a bytes per second), the lower 4 bits of the 16-bit field contain a
value of 0x04 to represent the exponent (E) while the upper 12 bits value of 0x04 to represent the exponent (E) while the upper 12 bits
contain a value of 0x51f (M) as determined from the equation given contain a value of 0x51f (M) as determined from the equation given
above: above:
send_rate = (((int)((3.2 * 4096.0 / 10.0) + 0.5)) << 4) | 4; send_rate = (((int)((3.2 * 4096.0 / 10.0) + 0.5)) << 4) | 4;
= (0x51f << 4) | 0x4 = (0x51f << 4) | 0x4
= 0x51f4 = 0x51f4
To decode the "send_rate" field, the following equation can be used:
To decode the "send_rate" field, the following equation can be used:
value = (send_rate >> 4) * (10/4096) * power(10, (send_rate & x000f)) value = (send_rate >> 4) * (10/4096) * power(10, (send_rate & x000f))
Note the maximum transmission rate that can be represented by this Note the maximum transmission rate that can be represented by this
scheme is approximately 9.99e+15 bytes per second. scheme is approximately 9.99e+15 bytes per second.
When this extension is present, a "cc_node_list" may be attached as When this extension is present, a "cc_node_list" may be attached as
the payload of the NORM_CMD(CC) message. The presence of this header the payload of the "NORM_CMD(CC)" message. The presence of this
extension also implies that NORM receivers should respond according header extension also implies that NORM receivers should respond
to the procedures described in Section 5.5.2. The "cc_node_list" according to the procedures described in Section 5.5.2.
consists of a list of NormNodeIds and their associated congestion
control status. This includes the current limiting receiver (CLR)
node, any potential limiting receiver (PLR) nodes that have been
identified, and some number of receivers for which congestion control
status is being provided, most notably including the receivers’
current RTT measurement. The maximum length of the "cc_node_list"
provides for at least the CLR and one other receiver, but may be
configurable for more timely feedback to the group. The list length
can be inferred from the length of the NORM_CMD(CC) message.
Each item in the "cc_node_list" is in the following format: The "cc_node_list" consists of a list of NormNodeIds and their
associated congestion control status. This includes the current
limiting receiver (CLR) node, any potential limiting receiver (PLR)
nodes that have been identified, and some number of receivers for
which congestion control status is being provided, most notably
including the receivers' current RTT measurement. The maximum length
of the "cc_node_list" provides for at least the CLR and one other
receiver, but may be configurable for more timely feedback to the
group. The list length can be inferred from the length of the
"NORM_CMD(CC)" message.
Each item in the "cc_node_list" is in the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| cc_node_id | | cc_node_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| cc_flags | cc_rtt | cc_rate | | cc_flags | cc_rtt | cc_rate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Congestion Control Node List Item Format
The "cc_node_id" is the NormNodeId of the receiver which the item The "cc_node_id" is the NormNodeId of the receiver which the item
represents. represents.
The "cc_flags" field contains flags indicating the congestion control The "cc_flags" field contains flags indicating the congestion control
status of the indicated receiver. The following flags are defined: status of the indicated receiver. The following flags are defined:
+-------------------+-------+------------------------------------------+ +----------------------+-------+------------------------------------+
| Flag | Value | Purpose | | Flag | Value | Purpose |
+-------------------+-------+------------------------------------------+ +----------------------+-------+------------------------------------+
|NORM_FLAG_CC_CLR | 0x01 | Receiver is the current limiting | | "NORM_FLAG_CC_CLR" | 0x01 | Receiver is the current limiting |
| | | receiver (CLR). | | | | receiver (CLR). |
+-------------------+-------+------------------------------------------+ | "NORM_FLAG_CC_PLR" | 0x02 | Receiver is a potential limiting |
|NORM_FLAG_CC_PLR | 0x02 | Receiver is a potential limiting |
| | | receiver (PLR). | | | | receiver (PLR). |
+-------------------+-------+------------------------------------------+ | "NORM_FLAG_CC_RTT" | 0x04 | Receiver has measured RTT with |
|NORM_FLAG_CC_RTT | 0x04 | Receiver has measured RTT with respect | | | | respect to sender. |
| | | to sender. | | "NORM_FLAG_CC_START" | 0x08 | Sender/receiver is in "slow start" |
+-------------------+-------+------------------------------------------+ | | | phase of congestion control |
|NORM_FLAG_CC_START | 0x08 | Sender/receiver is in "slow start" phase | | | | operation (i.e., The receiver has |
| | | of congestion control operation (i.e., | | | | not yet detected any packet loss |
| | | The receiver has not yet detected any | | | | and the "cc_rate" field is the |
| | | packet loss and the "cc_rate" field is | | | | receiver's actual measured receive |
| | | the receiver’s actual measured receive |
| | | rate). | | | | rate). |
+-------------------+-------+------------------------------------------+ | "NORM_FLAG_CC_LEAVE" | 0x10 | Receiver is imminently leaving the |
|NORM_FLAG_CC_LEAVE | 0x10 | Receiver is imminently leaving the | | | | session and its feedback should |
| | | session and its feedback should not be | | | | not be considered in congestion |
| | | considered in congestion control | | | | control operation. |
| | | operation. | +----------------------+-------+------------------------------------+
+-------------------+-------+------------------------------------------+
The "cc_rtt" contains a quantized representation of the RTT as The "cc_rtt" contains a quantized representation of the RTT as
measured by the sender with respect to the indicated receiver. This measured by the sender with respect to the indicated receiver. This
field is valid only if the NORM_FLAG_CC_RTT flag is set in the field is valid only if the "NORM_FLAG_CC_RTT" flag is set in the
"cc_flags" field. This one byte field is a quantized representation "cc_flags" field. This one byte field is a quantized representation
of the RTT using the algorithm described in the NORM Building Block of the RTT using the algorithm described in the Multicast NACK
document [3]. The "cc_rate" field contains a representation of the Building Block document [I-D.ietf-rmt-bb-norm-revised].
receiver’s current calculated (during steady-state congestion control
operation) or twice its measured (during the "slow start" phase)
congestion control rate. This field is encoded and decoded using the
same technique as described for the NORM_CMD(CC) "send_rate" field.
4.2.3.5. NORM_CMD(REPAIR_ADV) Message The "cc_rate" field contains a representation of the receiver's
current calculated (during steady-state congestion control operation)
or twice its measured (during the slow start phase) congestion
control rate. This field is encoded and decoded using the same
technique as described for the "NORM_CMD(CC)" "send_rate" field.
The NORM_CMD(REPAIR_ADV) message is used by the sender to "advertise" 4.2.3.5. NORM_CMD(REPAIR_ADV) Message
its aggregated repair state from NORM_NACK messages accumulated
during a repair cycle and/or congestion control feedback received.
This message is sent only when the sender has received NORM_NACK
and/or NORM_ACK(CC) (when congestion control is enabled) messages via
unicast transmission instead of multicast. By "echoing" this
information to the receiver set, suppression of feedback can be
achieved even when receivers are unicasting that feedback instead of
multicasting it among the group [17].
The "NORM_CMD(REPAIR_ADV)" message is used by the sender to
"advertise" its aggregated repair state from "NORM_NACK" messages
accumulated during a repair cycle and/or congestion control feedback
received. This message is sent only when the sender has received
"NORM_NACK" and/or "NORM_ACK(CC)" (when congestion control is
enabled) messages via unicast transmission instead of multicast. By
relaying this information to the receiver set, suppression of
feedback can be achieved even when receivers are unicasting that
feedback instead of multicasting it among the group [NormFeedback].
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=3| hdr_len | sequence | |version| type=3| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor = 5 | flags | reserved | | flavor = 5 | flags | reserved |
skipping to change at page 44, line 22 skipping to change at page 43, line 4
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor = 5 | flags | reserved | | flavor = 5 | flags | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| header extensions (if applicable) | | header extensions (if applicable) |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| repair_adv_payload | | repair_adv_payload |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_CMD(REPAIR_ADV) Message Format NORM_CMD(REPAIR_ADV) Message Format
The "instance_id", "grtt", "backoff", "gsize", and "flavor" fields The "instance_id", "grtt", "backoff", "gsize", and "flavor" fields
serve the same purpose as in other NORM_CMD messages. The value of serve the same purpose as in other "NORM_CMD" messages. The value of
the "hdr_len" field when no extensions are present is 4. the "hdr_len" field when no extensions are present is 4.
The "flags" field provide information on the NORM_CMD(REPAIR_ADV) The "flags" field provide information on the "NORM_CMD(REPAIR_ADV)"
content. There is currently one NORM_CMD(REPAIR_ADV) flag defined: content. There is currently one "NORM_CMD(REPAIR_ADV)" flag defined:
NORM_REPAIR_ADV_FLAG_LIMIT = 0x01 NORM_REPAIR_ADV_FLAG_LIMIT = 0x01
This flag is set by the sender when it is unable to fit its full This flag is set by the sender when it is unable to fit its full
current repair state into a single NormSegmentSize. If this flag is current repair state into a single NormSegmentSize. If this flag is
set, receivers should limit their NACK response to generating NACK set, receivers should limit their NACK response to generating NACK
content only up through the maximum ordinal transmission position content only up through the maximum ordinal transmission position
(objectId::fecPayloadId) included in the "repair_adv_content". (objectId::fecPayloadId) included in the "repair_adv_content".
When congestion control operation is enabled, a header extension may When congestion control operation is enabled, a header extension may
be applied to the NORM_CMD(REPAIR_ADV) representing the most limiting be applied to the "NORM_CMD(REPAIR_ADV)" representing the most
(in terms of congestion control feedback suppression) congestion limiting (in terms of congestion control feedback suppression)
control response. This allows the NORM_CMD(REPAIR_ADV) message to congestion control response. This allows the "NORM_CMD(REPAIR_ADV)"
suppress receiver congestion control responses as well as NACK message to suppress receiver congestion control responses as well as
feedback messages. The field is defined as a header extension so NACK feedback messages. The field is defined as a header extension
that alternative congestion control schemes may be used with NORM so that alternative congestion control schemes may be used with NORM
without revision to this document. A NORM-CC Feedback Header without revision to this document. A NORM-CC Feedback Header
Extension (EXT_CC) is defined to encapsulate congestion control Extension (EXT_CC) is defined to encapsulate congestion control
feedback within NORM_NACK, NORM_ACK, and NORM_CMD(REPAIR_ADV) feedback within "NORM_NACK", "NORM_ACK", and "NORM_CMD(REPAIR_ADV)"
messages. If another congestion control technique (e.g., Pragmatic messages. If another congestion control technique (e.g., Pragmatic
General Multicast Congestion Control (PGMCC) [26]) is used within a General Multicast Congestion Control (PGMCC) [PgmccPaper]) is used
NORM implementation, an additional header extension MAY need to be within a NORM implementation, an additional header extension MAY need
defined encapsulate any required feedback content. The NORM-CC to be defined encapsulate any required feedback content. The NORM-CC
Feedback Header Extension format is: Feedback Header Extension format is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| het = 3 | hel = 3 | cc_sequence | | het = 3 | hel = 3 | cc_sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| cc_flags | cc_rtt | cc_loss | | cc_flags | cc_rtt | cc_loss |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| cc_rate | cc_reserved | | cc_rate | cc_reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 45, line 17 skipping to change at page 43, line 45
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| het = 3 | hel = 3 | cc_sequence | | het = 3 | hel = 3 | cc_sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| cc_flags | cc_rtt | cc_loss | | cc_flags | cc_rtt | cc_loss |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| cc_rate | cc_reserved | | cc_rate | cc_reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM-CC Feedback Header Extension (EXT_CC) Format
The "cc_sequence" field contains the current greatest "cc_sequence" The "cc_sequence" field contains the current greatest "cc_sequence"
value receivers have received in NORM_CMD(CC) messages from the value receivers have received in "NORM_CMD(CC)" messages from the
sender. This information assists the sender in congestion control sender. This information assists the sender in congestion control
operation by providing an indicator of how current ("fresh") the operation by providing an indicator of how current ("fresh") the
receivers round-trip measurement reference time is and whether the receiver's round-trip measurement reference time is and whether the
receiver has been successfully receiving recent congestion control receiver has been successfully receiving recent congestion control
probes. For example, if it is apparent the receiver has not been probes. For example, if it is apparent the receiver has not been
receiving recent congestion control probes (and thus possibly other receiving recent congestion control probes (and thus possibly other
messages from the sender), the sender may choose to take congestion messages from the sender), the sender may choose to take congestion
avoidance measures. For NORM_CMD(REPAIR_ADV) messages, the sender avoidance measures. For "NORM_CMD(REPAIR_ADV)" messages, the sender
SHALL set the "cc_sequence" field value to the value set in the last SHALL set the "cc_sequence" field value to the value set in the last
NORM_CMD(CC) message sent. "NORM_CMD(CC)" message sent.
The "cc_flags" field contains bits representing the receivers state The "cc_flags" field contains bits representing the receiver's state
with respect to congestion control operation. The possible values with respect to congestion control operation. The possible values
for the "cc_flags" field are those specified for the NORM_CMD(CC) for the "cc_flags" field are those specified for the "NORM_CMD(CC)"
message node list item flags. These fields are used by receivers in message node list item flags. These fields are used by receivers in
controlling (suppressing as necessary) their congestion control controlling (suppressing as necessary) their congestion control
feedback. For NORM_CMD(REPAIR_ADV) messages, the NORM_FLAG_CC_RTT feedback. For "NORM_CMD(REPAIR_ADV)" messages, the
should be set only when all feedback messages received by the sender "NORM_FLAG_CC_RTT" should be set only when all feedback messages
have the flag set. Similarly, the NORM_FLAG_CC_CLR or received by the sender have the flag set. Similarly, the
NORM_FLAG_CC_PLR should be set only when no feedback has been "NORM_FLAG_CC_CLR" or "NORM_FLAG_CC_PLR" should be set only when no
received from non-CLR or non-PLR receivers. And the feedback has been received from non-CLR or non-PLR receivers. And
NORM_FLAG_CC_LEAVE should be set only when all feedback messages the the "NORM_FLAG_CC_LEAVE" should be set only when all feedback
sender has received have this flag set. These heuristics for setting messages the sender has received have this flag set. These
the flags in NORM_CMD(REPAIR_ADV) ensure the most effective heuristics for setting the flags in "NORM_CMD(REPAIR_ADV)" ensure the
suppression of receivers providing unicast feedback messages. most effective suppression of receivers providing unicast feedback
messages.
The "cc_rtt" field SHALL be set to a default maximum value and the The "cc_rtt" field SHALL be set to a default maximum value and the
NORM_FLAG_CC_RTT flag SHALL be cleared when no receiver has yet "NORM_FLAG_CC_RTT" flag SHALL be cleared when no receiver has yet
received RTT measurement information. When a receiver has received received RTT measurement information. When a receiver has received
RTT measurement information, it shall set the "cc_rtt" value RTT measurement information, it shall set the "cc_rtt" value
accordingly and set the NORM_FLAG_CC_RTT flag in the "cc_flags" accordingly and set the "NORM_FLAG_CC_RTT" flag in the "cc_flags"
field. For NORM_CMD(REPAIR_ADV) messages, the sender SHALL set the field. For "NORM_CMD(REPAIR_ADV)" messages, the sender SHALL set the
"cc_rtt" field value to the largest non-CLR/non-PLR RTT it has "cc_rtt" field value to the largest non-CLR/non-PLR RTT it has
measured from receivers for the current feedback round. measured from receivers for the current feedback round.
The "cc_loss" field represents the receivers current packet loss The "cc_loss" field represents the receiver's current packet loss
fraction estimate for the indicated source. The loss fraction is a fraction estimate for the indicated source. The loss fraction is a
value from 0.0 to 1.0 corresponding to a range of zero to 100 percent value from 0.0 to 1.0 corresponding to a range of zero to 100 percent
packet loss. The 16-bit "cc_loss" value is calculated by the packet loss. The 16-bit "cc_loss" value is calculated by the
following formula: following formula:
"cc_loss" = decimal_loss_fraction * 65535.0 "cc_loss" = decimal_loss_fraction * 65535.0
For NORM_CMD(REPAIR_ADV) messages, the sender SHALL set the "cc_loss" For "NORM_CMD(REPAIR_ADV)" messages, the sender SHALL set the
field value to the largest non-CLR/non-PLR loss estimate it has "cc_loss" field value to the largest non-CLR/non-PLR loss estimate it
received from receivers for the current feedback round. has received from receivers for the current feedback round.
The "cc_rate" field represents the receivers current local congestion The "cc_rate" field represents the receivers current local congestion
control rate. During "slow start", when the receiver has detected no control rate. During "slow start", when the receiver has detected no
loss, this value is set to twice the actual rate it has measured from loss, this value is set to twice the actual rate it has measured from
the corresponding sender and the NORM_FLAG_CC_START is set in the the corresponding sender and the "NORM_FLAG_CC_START" is set in the
"cc_flags’ field. Otherwise, the receiver calculates a congestion "cc_flags' field. Otherwise, the receiver calculates a congestion
control rate based on its loss measurement and RTT measurement control rate based on its loss measurement and RTT measurement
information (even if default) for the "cc_rate" field. For information (even if default) for the "cc_rate" field. For
NORM_CMD(REPAIR_ADV) messages, the sender SHALL set the "cc_loss" "NORM_CMD(REPAIR_ADV)" messages, the sender SHALL set the "cc_loss"
field value to the lowest non-CLR/non-PLR "cc_rate" report it has field value to the lowest non-CLR/non-PLR "cc_rate" report it has
received from receivers for the current feedback round. received from receivers for the current feedback round.
The "cc_reserved" field is reserved for future NORM protocol use. The "cc_reserved" field is reserved for future NORM protocol use.
Currently, senders SHALL set this field to ZERO, and receivers SHALL Currently, senders SHALL set this field to ZERO, and receivers SHALL
ignore the content of this field. ignore the content of this field.
The "repair_adv_payload" is in exactly the same form as the The "repair_adv_payload" is in exactly the same form as the
"nack_content" of NORM_NACK messages and can be processed by "nack_content" of "NORM_NACK" messages and can be processed by
receivers for suppression purposes in the same manner, with the receivers for suppression purposes in the same manner, with the
exception of the condition when the NORM_REPAIR_ADV_FLAG_LIMIT is exception of the condition when the "NORM_REPAIR_ADV_FLAG_LIMIT" is
set. set.
4.2.3.6. NORM_CMD(ACK_REQ) Message 4.2.3.6. NORM_CMD(ACK_REQ) Message
The NORM_CMD(ACK_REQ) message is used by the sender to request The "NORM_CMD(ACK_REQ)" message is used by the sender to request
acknowledgment from a specified list of receivers. This message is acknowledgment from a specified list of receivers. This message is
used in providing a lightweight positive acknowledgment mechanism used in providing a lightweight positive acknowledgment mechanism
that is OPTIONAL for use by the reliable multicast application. A that is OPTIONAL for use by the reliable multicast application. A
range of acknowledgment request types is provided for use at the range of acknowledgment request types is provided for use at the
applications discretion. Provision for application-defined, application's discretion. Provision for application-defined,
positively-acknowledged commands allows the application to positively-acknowledged commands allows the application to
automatically take advantage of transmission and round-trip timing automatically take advantage of transmission and round-trip timing
information available to the NORM protocol. The details of the NORM information available to the NORM protocol. The details of the NORM
positive acknowledgment process including transmission of the positive acknowledgment process including transmission of the
NORM_CMD(ACK_REQ) messages and the receiver response (NORM_ACK) are "NORM_CMD(ACK_REQ)" messages and the receiver response ("NORM_ACK")
described in Section 5.5.3. The format of the NORM_CMD(ACK_REQ) are described in Section 5.5.3. The format of the
message is: "NORM_CMD(ACK_REQ)" message is:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=3| hdr_len | sequence | |version| type=3| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor = 6 | reserved | ack_type | ack_id | | flavor = 6 | reserved | ack_type | ack_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| acking_node_list | | acking_node_list |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_CMD(ACK_REQ) Message Format NORM_CMD(ACK_REQ) Message Format
The NORM common message header and standard "NORM_CMD" fields serve
The NORM common message header and standard NORM_CMD fields serve
their usual purposes. The value of the "hdr_len" field for their usual purposes. The value of the "hdr_len" field for
NORM_CMD(ACK_REQ) messages with no header extension present is 4. "NORM_CMD(ACK_REQ)" messages with no header extension present is 4.
The "ack_type" field indicates the type of acknowledgment being The "ack_type" field indicates the type of acknowledgment being
requested and thus implies rules for how the receiver will treat this requested and thus implies rules for how the receiver will treat this
request. The following "ack_type" values are defined and are also request. The following "ack_type" values are defined and are also
used in NORM_ACK messages described later: used in "NORM_ACK" messages described later:
+---------------------+--------+----------------------------------+ +------------------------+--------+---------------------------------+
| ACK Type | Value | Purpose | | ACK Type | Value | Purpose |
+---------------------+--------+----------------------------------+ +------------------------+--------+---------------------------------+
|NORM_ACK_CC | 1 | Used to identify NORM_ACK | | "NORM_ACK_CC" | 1 | Used to identify "NORM_ACK" |
| | | messages sent in response to | | | | messages sent in response to |
| | | NORM_CMD(CC) messages. | | | | "NORM_CMD(CC)" messages. |
+---------------------+--------+----------------------------------+ | "NORM_ACK_FLUSH" | 2 | Used to identify "NORM_ACK" |
|NORM_ACK_FLUSH | 2 | Used to identify NORM_ACK |
| | | messages sent in response to | | | | messages sent in response to |
| | | NORM_CMD(FLUSH) messages. | | | | "NORM_CMD(FLUSH)" messages. |
+---------------------+--------+----------------------------------+ | "NORM_ACK_RESERVED" | 3-15 | Reserved for possible future |
|NORM_ACK_RESERVED | 3-15 | Reserved for possible future |
| | | NORM protocol use. | | | | NORM protocol use. |
+---------------------+--------+----------------------------------+ | "NORM_ACK_APPLICATION" | 16-255 | Used at application's |
|NORM_ACK_APPLICATION | 16-255 | Used at application’s |
| | | discretion. | | | | discretion. |
+---------------------+--------+----------------------------------+ +------------------------+--------+---------------------------------+
The NORM_ACK_CC value is provided for use only in NORM_ACKs generated The "NORM_ACK_CC" value is provided for use only in "NORM_ACKs"
in response to the NORM_CMD(CC) messages used in congestion control generated in response to the "NORM_CMD(CC)" messages used in
operation. Similarly, the NORM_ACK_FLUSH is provided for use only in congestion control operation. Similarly, the "NORM_ACK_FLUSH" is
NORM_ACKs generated in response to applicable NORM_CMD(FLUSH) provided for use only in "NORM_ACKs" generated in response to
messages. NORM_CMD(ACK_REQ) messages with "ack_type" of NORM_ACK_CC applicable "NORM_CMD(FLUSH)" messages. "NORM_CMD"(ACK_REQ) messages
or NORM_ACK_FLUSH SHALL NOT be generated by the sender. with "ack_type" of "NORM_ACK_CC" or "NORM_ACK_FLUSH" SHALL NOT be
generated by the sender.
The NORM_ACK_RESERVED range of "ack_type" values is provided for The "NORM_ACK_RESERVED" range of "ack_type" values is provided for
possible future NORM protocol use. possible future NORM protocol use.
The NORM_ACK_APPLICATION range of "ack_type" values is provided so The "NORM_ACK_APPLICATION" range of "ack_type" values is provided so
that NORM applications may implement application-defined, positively- that NORM applications may implement application-defined, positively-
acknowledged commands that are able to leverage internal transmission acknowledged commands that are able to leverage internal transmission
and round-trip timing information available to the NORM protocol and round-trip timing information available to the NORM protocol
implementation. implementation.
The "ack_id" provides a sequenced identifier for the given The "ack_id" provides a sequenced identifier for the given
NORM_CMD(ACK_REQ) message. This "ack_id" is returned in NORM_ACK "NORM_CMD(ACK_REQ)" message. This "ack_id" is returned in "NORM_ACK"
messages generated by the receivers so that the sender may associate messages generated by the receivers so that the sender may associate
the response with its corresponding request. the response with its corresponding request.
The "reserved" field is reserved for possible future protocol use and The "reserved" field is reserved for possible future protocol use and
SHALL be set to ZERO by senders and ignored by receivers. SHALL be set to ZERO by senders and ignored by receivers.
The "acking_node_list" field contains the NormNodeIds of the current The "acking_node_list" field contains the NormNodeIds of the current
NORM receivers that are desired to provide positive acknowledge NORM receivers that are desired to provide positive acknowledge
(NORM_ACK) to this request. The packet payload length implies the ("NORM_ACK") to this request. The packet payload length implies the
length of the "acking_node_list" and its length is limited to the length of the "acking_node_list" and its length is limited to the
sender NormSegmentSize. The individual NormNodeId items are listed sender NormSegmentSize. The individual NormNodeId items are listed
in network (Big Endian) byte order. If a receivers NormNodeId is in network (Big Endian) byte order. If a receiver's NormNodeId is
included in the "acking_node_list", it SHALL schedule transmission of included in the "acking_node_list", it SHALL schedule transmission of
a NORM_ACK message as described in Section 5.5.3. a "NORM_ACK" message as described in Section 5.5.3.
4.2.3.7. NORM_CMD(APPLICATION) Message 4.2.3.7. NORM_CMD(APPLICATION) Message
This command allows the NORM application to robustly transmit This command allows the NORM application to robustly transmit
application-defined commands. The command message preempts any application-defined commands. The command message preempts any
ongoing data transmission and is repeated up to NORM_ROBUST_FACTOR ongoing data transmission and is repeated up to "NORM_ROBUST_FACTOR"
times at a rate of once per 2*GRTT. This rate of repetition allows times at a rate of once per "2*GRTT". This rate of repetition allows
the application to observe any response (if that is the application’s the application to observe any response (if that is the application's
purpose for the command) before it is repeated. Possible responses purpose for the command) before it is repeated. Possible responses
may include initiation of data transmission, other may include initiation of data transmission, other
NORM_CMD(APPLICATION) messages, or even application-defined, "NORM_CMD(APPLICATION)" messages, or even application-defined,
positively-acknowledge commands from other NormSession participants. positively-acknowledge commands from other NormSession participants.
The transmission of these commands will preempt data transmission The transmission of these commands will preempt data transmission
when they are scheduled and may be multiplexed with ongoing data when they are scheduled and may be multiplexed with ongoing data
transmission. This type of robustly transmitted command allows NORM transmission. This type of robustly transmitted command allows NORM
applications to define a complete set of session control mechanisms applications to define a complete set of session control mechanisms
with less state than the transfer of FEC encoded reliable content with less state than the transfer of FEC encoded reliable content
requires while taking advantage of NORM transmission and round-trip requires while taking advantage of NORM transmission and round-trip
timing information. timing information.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=3| hdr_len | sequence | |version| type=3| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor = 7 | reserved | | flavor = 7 | reserved |
skipping to change at page 49, line 50 skipping to change at page 47, line 49
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor = 7 | reserved | | flavor = 7 | reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Application-Defined Content | | Application-Defined Content |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_CMD(APPLICATION) Message Format NORM_CMD(APPLICATION) Message Format
The NORM common message header and NORM_CMD fields are interpreted as The NORM common message header and "NORM_CMD" fields are interpreted
previously described. The value of the NORM_CMD(APPLICATION) as previously described. The value of the "NORM_CMD(APPLICATION)"
"hdr_len" field when no header extensions are present is 4. "hdr_len" field when no header extensions are present is 4.
The "Application-Defined Content" area contains information in a The "Application-Defined Content" area contains information in a
format at the discretion of the application. The size of this format at the discretion of the application. The size of this
payload SHALL be limited to a maximum of the sender’s NormSegmentSize payload SHALL be limited to a maximum of the sender's NormSegmentSize
setting. setting. Upon reception, the NORM protocol implementation SHALL
deliver the content to the receiver application. Note that any
detection of duplicate reception of a "NORM_CMD(APPLICATION)" message
is the responsibility of the application.
4.3. Receiver Messages 4.3. Receiver Messages
The NORM message types generated by participating receivers consist The NORM message types generated by participating receivers consist
of NORM_NACK and NORM_ACK message types. NORM_NACK messages are sent of the "NORM_NACK" and "NORM_ACK" message types. "NORM_NACK"
to request repair of missing data content from sender transmission messages are sent to request repair of missing data content from
and NORM_ACK messages are generated in response to certain sender sender transmission and "NORM_ACK" messages are generated in response
commands including NORM_CMD(CC) and NORM_CMD(ACK_REQ). to certain sender commands including "NORM_CMD(CC)" and
"NORM_CMD(ACK_REQ)".
4.3.1. NORM_NACK Message 4.3.1. NORM_NACK Message
The principal purpose of NORM_NACK messages is for receivers to The principal purpose of "NORM_NACK" messages is for receivers to
request repair of sender content via selective, negative request repair of sender content via selective, negative
acknowledgment upon detection of incomplete data. NORM_NACK messages acknowledgment upon detection of incomplete data. "NORM_NACK"
will be transmitted according to the rules of NORM_NACK generation messages will be transmitted according to the rules of "NORM_NACK"
and suppression described in Section 5.3. NORM_NACK messages also generation and suppression described in Section 5.3. "NORM_NACK"
contain additional fields to provide feedback to the sender(s) for messages also contain additional fields to provide feedback to the
purposes of round-trip timing collection and congestion control. sender(s) for purposes of round-trip timing collection and congestion
control.
The payload of NORM_NACK messages contains one or more repair The payload of "NORM_NACK" messages contains one or more repair
requests for different objects or portions of those objects. The requests for different objects or portions of those objects. The
NORM_NACK message format is as follows: "NORM_NACK" message format is as follows:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=4| hdr_len | sequence | |version| type=4| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| server_id | | server_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 51, line 30 skipping to change at page 49, line 30
| header extensions (if applicable) | | header extensions (if applicable) |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| nack_payload | | nack_payload |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_NACK Message Format NORM_NACK Message Format
The NORM common message header fields serve their usual purposes. The NORM common message header fields serve their usual purposes.
The value of the "hdr_len" field for NORM_NACK messages without The value of the "hdr_len" field for "NORM_NACK" messages without
header extensions present is 6. header extensions present is 6.
The "server_id" field identifies the NORM sender to which the The "server_id" field identifies the NORM sender to which the
NORM_NACK message is destined. "NORM_NACK" message is destined.
The "instance_id" field contains the current session identifier given The "instance_id" field contains the current session identifier given
by the sender identified by the "server_id" field in its sender by the sender identified by the "server_id" field in its sender
messages. The sender SHOULD ignore feedback messages which contain messages. The sender SHOULD ignore feedback messages which contain
an invalid "instance_id" value. an invalid "instance_id" value.
The "grtt_response" fields contain an adjusted version of the The "grtt_response" fields contain an adjusted version of the
timestamp from the most recently received NORM_CMD(CC) message for timestamp from the most recently received "NORM_CMD(CC)" message for
the indicated NORM sender. The format of the "grtt_response" is the the indicated NORM sender. The format of the "grtt_response" is the
same as the "send_time" field of the NORM_CMD(CC). The same as the "send_time" field of the "NORM_CMD(CC)". The
"grtt_response" value is _relative_ to the "send_time" the source "grtt_response" value is relative to the "send_time" the source
provided with a corresponding NORM_CMD(CC) command. The receiver provided with a corresponding "NORM_CMD(CC)" command. The receiver
adjusts the source’s NORM_CMD(CC) "send_time" timestamp by adding the adjusts the source's "NORM_CMD(CC)" "send_time" timestamp by adding
time delta from when the receiver received the NORM_CMD(CC) to when the time delta from when the receiver received the "NORM_CMD(CC)" to
the NORM_NACK is transmitted in response to calculate the value in when the "NORM_NACK" is transmitted in response to calculate the
the "grtt_response" field. This is the "receive_to_response_delta" value in the "grtt_response" field. This is the
value used in the following formula: "receive_to_response_delta" value used in the following formula:
grtt_response = NORM_CMD(CC) send_time + receive_to_response_delta grtt_response = NORM_CMD(CC) send_time + receive_to_response_delta
The receiver SHALL set the "grtt_response" to a ZERO value, to The receiver SHALL set the "grtt_response" to a ZERO value, to
indicate that it has not yet received a NORM_CMD(CC) message from the indicate that it has not yet received a "NORM_CMD(CC)" message from
indicated sender and that the sender should ignore the the indicated sender and that the sender should ignore the
"grtt_response" in this message. "grtt_response" in this message.
For NORM-CC operation, the NORM-CC Feedback Header Extension, as For NORM-CC operation, the NORM-CC Feedback Header Extension, as
described in the NORM_CMD(REPAIR_ADV} message description, is added described in the "NORM_CMD(REPAIR_ADV}" message description, is added
to NORM_NACK messages to provide feedback on the receivers current to "NORM_NACK" messages to provide feedback on the receivers current
state with respect to congestion control operation. Note that state with respect to congestion control operation. Note that
alternative header extensions for congestion control feedback may be alternative header extensions for congestion control feedback may be
defined for alternative congestion control schemes for NORM use in defined for alternative congestion control schemes for NORM use in
the future. the future.
The "reserved" field is for potential future NORM use and SHALL be The "reserved" field is for potential future NORM use and SHALL be
set to ZERO for this version of the protocol. set to ZERO for this version of the protocol.
The "nack_content" of the NORM_NACK message specifies the repair The "nack_payload" of the "NORM_NACK" message specifies the repair
needs of the receiver with respect to the NORM sender indicated by needs of the receiver with respect to the NORM sender indicated by
the "server_id" field. The receiver constructs repair requests based the "server_id" field. The receiver constructs repair requests based
on the NORM_DATA and/or NORM_INFO segments it requires from the on the "NORM_DATA" and/or "NORM_INFO" segments it requires from the
sender in order to complete reliable reception up to the sender’s sender in order to complete reliable reception up to the sender's
transmission position at the moment the receiver initiates the NACK transmission position at the moment the receiver initiates the NACK
Procedure as described in Section 5.3. A single NORM Repair Request Procedure as described in Section 5.3. A single NORM Repair Request
consists of a list of items, ranges, and/or FEC coding block erasure consists of a list of items, ranges, and/or FEC coding block erasure
counts for needed NORM_DATA and/or NORM_INFO content. Multiple counts for needed "NORM_DATA" and/or "NORM_INFO" content. Multiple
repair requests may be concatenated within the "nack_payload" field repair requests may be concatenated within the "nack_payload" field
of a NORM_NACK message. Note that a single NORM Repair Request can of a "NORM_NACK" message. Note that a single NORM Repair Request can
possibly include multiple "items", "ranges", or "erasure_counts". In possibly include multiple "items", "ranges", or "erasure_counts". In
turn, the "nack_payload" field may contain multiple repair requests. turn, the "nack_payload" field MAY contain multiple repair requests.
A single NORM Repair Request has the following format: A single NORM Repair Request has the following format:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| form | flags | length | | form | flags | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| repair_request_items | | repair_request_items |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM Repair Request Format NORM Repair Request Format
skipping to change at page 53, line 4 skipping to change at page 50, line 44
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| form | flags | length | | form | flags | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| repair_request_items | | repair_request_items |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM Repair Request Format NORM Repair Request Format
The "form" field indicates the type of repair request items given in The "form" field indicates the type of repair request items given in
the "repair_request_items" list. Possible values for the "form" the "repair_request_items" list. Possible values for the "form"
field include: field include:
Form Value +----------------------+-------+
NORM_NACK_ITEMS 1 | Form | Value |
NORM_NACK_RANGES 2 +----------------------+-------+
NORM_NACK_ERASURES 3 | "NORM_NACK_ITEMS" | 1 |
| "NORM_NACK_RANGES" | 2 |
| "NORM_NACK_ERASURES" | 3 |
+----------------------+-------+
A "form" value of NORM_NACK_ITEMS indicates each repair request item A "form" value of "NORM_NACK_ITEMS" indicates each repair request
in the "repair_request_items" list is to be treated as an individual item in the "repair_request_items" list is to be treated as an
request. A value of NORM_NACK_RANGES indicates that the individual request. A value of "NORM_NACK_RANGES" indicates that the
"repair_request_items" list consists of pairs of repair request items "repair_request_items" list consists of pairs of repair request items
that correspond to inclusive ranges of repair needs. And the that correspond to inclusive ranges of repair needs. And the
NORM_NACK_ERASURES "form" indicates that the repair request items are "NORM_NACK_ERASURES" "form" indicates that the repair request items
to be treated individually and that the "encoding_symbol_id" portion are to be treated individually and that the "encoding_symbol_id"
of the "fec_payload_id" field of the repair request item (see below) portion of the "fec_payload_id" field of the repair request item (see
is to be interpreted as an "erasure count" for the FEC coding block below) is to be interpreted as an erasure count for the FEC coding
identified by the repair request item’s "source_block_number". block identified by the repair request item's "source_block_number".
The "flags" field is currently used to indicate the level of data The "flags" field is currently used to indicate the level of data
content for which the repair request items apply (i.e., an individual content for which the repair request items apply (i.e., an individual
segment, entire FEC coding block, or entire transport object). segment, entire FEC coding block, or entire transport object).
Possible flag values include: Possible flag values include:
+------------------+-------+------------------------------------------+ +---------------------+-------+-------------------------------------+
| Flag | Value | Purpose | | Flag | Value | Purpose |
+------------------+-------+------------------------------------------+ +---------------------+-------+-------------------------------------+
|NORM_NACK_SEGMENT | 0x01 | Indicates the listed segment(s) or range | | "NORM_NACK_SEGMENT" | 0x01 | Indicates the listed segment(s) or |
| | | of segments are required as repair. | | | | range of segments are required as |
+------------------+-------+------------------------------------------+
|NORM_NACK_BLOCK | 0x02 | Indicates the listed block(s) or range |
| | | of blocks in entirety are required as |
| | | repair. |
+------------------+-------+------------------------------------------+
|NORM_NACK_INFO | 0x04 | Indicates that NORM_INFO is required as |
| | | repair for the listed object(s). |
+------------------+-------+------------------------------------------+
|NORM_NACK_OBJECT | 0x08 | Indicates the listed object(s) or range |
| | | of objects in entirety are required as |
| | | repair. | | | | repair. |
+------------------+-------+------------------------------------------+ | "NORM_NACK_BLOCK" | 0x02 | Indicates the listed block(s) or |
| | | range of blocks in entirety are |
| | | required as repair. |
| "NORM_NACK_INFO" | 0x04 | Indicates that "NORM_INFO" is |
| | | required as repair for the listed |
| | | object(s). |
| "NORM_NACK_OBJECT" | 0x08 | Indicates the listed object(s) or |
| | | range of objects in entirety are |
| | | required as repair. |
+---------------------+-------+-------------------------------------+
When the NORM_NACK_SEGMENT flag is set, the "object_transport_id" and When the "NORM_NACK_SEGMENT" flag is set, the "object_transport_id"
"fec_payload_id" fields are used to determine which sets or ranges of and "fec_payload_id" fields are used to determine which sets or
individual NORM_DATA segments are needed to repair content at the ranges of individual "NORM_DATA" segments are needed to repair
receiver. When the NORM_NACK_BLOCK flag is set, this indicates the content at the receiver. When the "NORM_NACK_BLOCK" flag is set,
receiver is completely missing the indicated coding block(s) and this indicates the receiver is completely missing the indicated
requires transmissions sufficient to repair the indicated block(s) in coding block(s) and requires transmissions sufficient to repair the
their entirety. When the NORM_NACK_INFO flag is set, this indicates indicated block(s) in their entirety. When the "NORM_NACK_INFO" flag
the receiver is missing the NORM_INFO segment for the indicated is set, this indicates the receiver is missing the "NORM_INFO"
"object_transport_id". Note the NORM_NACK_INFO may be set in segment for the indicated "object_transport_id". Note the
combination with the NORM_NACK_BLOCK or NORM_NACK_SEGMENT flags, or "NORM_NACK_INFO" may be set in combination with the "NORM_NACK_BLOCK"
may be set alone. When the NORM_NACK_OBJECT flag is set, this or "NORM_NACK_SEGMENT" flags, or may be set alone. When the
indicates the receiver is missing the entire NormTransportObject "NORM_NACK_OBJECT" flag is set, this indicates the receiver is
referenced by the "object_transport_id". This also implicitly missing the entire NormTransportObject referenced by the
requests any available NORM_INFO for the NormObject, if applicable. "object_transport_id". This also implicitly requests any available
The "fec_payload_id" field is ignored when the flag NORM_NACK_OBJECT "NORM_INFO" for the NormObject, if applicable. The "fec_payload_id"
is set. field is ignored when the flag "NORM_NACK_OBJECT" is set.
The "length" field value is the length in bytes of the The "length" field value is the length in bytes of the
"repair_request_items" field. "repair_request_items" field.
The "repair_request_items" field consists of a list of individual or The "repair_request_items" field consists of a list of individual or
range pairs of transport data unit identifiers in the following range pairs of transport data unit identifiers in the following
format. format.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_id | reserved | object_transport_id | | fec_id | reserved | object_transport_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_payload_id | | fec_payload_id |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM Repair Request Item Format NORM Repair Request Item Format
skipping to change at page 54, line 45 skipping to change at page 52, line 39
NORM Repair Request Item Format NORM Repair Request Item Format
The "fec_id" indicates the FEC type and can be used to determine the The "fec_id" indicates the FEC type and can be used to determine the
format of the "fec_payload_id" field. The "reserved" field is kept format of the "fec_payload_id" field. The "reserved" field is kept
for possible future use and SHALL be set to a ZERO value and ignored for possible future use and SHALL be set to a ZERO value and ignored
by NORM nodes processing NACK content. by NORM nodes processing NACK content.
The "object_transport_id" corresponds to the NormObject for which The "object_transport_id" corresponds to the NormObject for which
repair is being requested and the "fec_payload_id" identifies the repair is being requested and the "fec_payload_id" identifies the
specific FEC coding block and/or segment being requested. When the specific FEC coding block and/or segment being requested. When the
NORM_NACK_OBJECT flag is set, the value of the "fec_payload_id" field "NORM_NACK_OBJECT" flag is set, the value of the "fec_payload_id"
is ignored. When the NORM_NACK_BLOCK flag is set, only the FEC code field is ignored. When the "NORM_NACK_BLOCK" flag is set, only the
block identifier portion of the "fec_payload_id" is to be FEC code block identifier portion of the "fec_payload_id" is to be
interpreted. interpreted.
The format of the "fec_payload_id" field depends upon the "fec_id" The format of the "fec_payload_id" field depends upon the "fec_id"
field value. field value.
When the receivers repair needs dictate that different forms (mixed When the receiver's repair needs dictate that different forms (mixed
ranges and/or individual items) or types (mixed specific segments ranges and/or individual items) or types (mixed specific segments
and/or blocks or objects in entirety) are required to complete and/or blocks or objects in entirety) are required to complete
reliable transmission, multiple NORM Repair Requests with different reliable transmission, multiple NORM Repair Requests with different
"form" and or "flags" values can be concatenated within a single "form" and or "flags" values can be concatenated within a single
NORM_NACK message. Additionally, NORM receivers SHALL construct "NORM_NACK" message. Additionally, NORM receivers SHALL construct
NORM_NACK messages with their repair requests in ordinal order with "NORM_NACK" messages with their repair requests in ordinal order with
respect to "object_transport_id" and "fec_payload_id" values. The respect to "object_transport_id" and "fec_payload_id" values. The
"nack_payload" size SHALL NOT exceed the NormSegmentSize for the "nack_payload" size SHALL NOT exceed the NormSegmentSize for the
sender to which the NORM_NACK is destined. sender to which the "NORM_NACK" is destined.
NORM_NACK Content Examples: NORM_NACK Content Examples:
In these examples, a small block, systematic FEC code ("fec_id" = In these examples, a small block, systematic FEC code ("fec_id" =
129) is assumed with a user data block length of 32 segments. In 129) is assumed with a user data block length of 32 segments. In
Example 1, a list of individual NORM_NACK_ITEMS repair requests is Example 1, a list of individual "NORM_NACK_ITEMS" repair requests is
given. In Example 2, a list of NORM_NACK_RANGES requests _and_ a given. In Example 2, a list of "NORM_NACK_RANGES" requests AND a
single NORM_NACK_ITEMS request are concatenated to illustrate the single "NORM_NACK_ITEMS" request are concatenated to illustrate the
possible content of a NORM_NACK message. Note that FEC coding block possible content of a "NORM_NACK" message. Note that FEC coding
erasure counts could also be provided in each case. However, the block erasure counts could also be provided in each case. However,
erasure counts are not really necessary since the sender can easily the erasure counts are not really necessary since the sender can
determine the erasure count while processing the NACK content. easily determine the erasure count while processing the NACK content.
However, the erasure count option may be useful for operation with However, the erasure count option may be useful for operation with
other FEC codes or for intermediate system purposes. other FEC codes or for intermediate system purposes.
Example 1: NORM_NACK "nack_payload" for: Object 12, Coding Block 3, Example 1: "NORM_NACK" "nack_payload" for: Object 12, Coding Block 3,
Segments 2,5,8 Segments 2,5,and 8
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| form = 1 | flags = 0x01 | length = 36 | | form = 1 | flags = 0x01 | length = 36 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_id = 129 | reserved | object_transport_id = 12 | | fec_id = 129 | reserved | object_transport_id = 12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_number = 3 | | source_block_number = 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_length = 32 | encoding_symbol_id = 2 | | source_block_length = 32 | encoding_symbol_id = 2 |
skipping to change at page 57, line 4 skipping to change at page 54, line 4
| source_block_number = 3 | | source_block_number = 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_length = 32 | encoding_symbol_id = 5 | | source_block_length = 32 | encoding_symbol_id = 5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_id = 129 | reserved | object_transport_id = 12 | | fec_id = 129 | reserved | object_transport_id = 12 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_number = 3 | | source_block_number = 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_length = 32 | encoding_symbol_id = 8 | | source_block_length = 32 | encoding_symbol_id = 8 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example 2: NORM_NACK "nack_payload" for: Object 18 Coding Block 6, Example 2: "NORM_NACK" "nack_payload" for: Object 18, Coding Block 6,
Segments 5, 6, 7, 8, 9, 10; and Object 19 NORM_INFO and Coding Block Segments 5, 6, 7, 8, 9, 10; and Object 19 "NORM_INFO" and Coding
1, segment 3 Block 1, segment 3
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| form = 2 | flags = 0x01 | length = 24 | | form = 2 | flags = 0x01 | length = 24 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_id = 129 | reserved | object_transport_id = 18 | | fec_id = 129 | reserved | object_transport_id = 18 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_number = 6 | | source_block_number = 6 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_length = 32 | encoding_symbol_id = 5 | | source_block_length = 32 | encoding_symbol_id = 5 |
skipping to change at page 57, line 35 skipping to change at page 54, line 35
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_id = 129 | reserved | object_transport_id = 19 | | fec_id = 129 | reserved | object_transport_id = 19 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_number = 1 | | source_block_number = 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_block_length = 32 | encoding_symbol_id = 3 | | source_block_length = 32 | encoding_symbol_id = 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.3.2. NORM_ACK Message 4.3.2. NORM_ACK Message
The NORM_ACK message is intended to be used primarily as part of NORM The "NORM_ACK" message is intended to be used primarily as part of
congestion control operation and round-trip timing measurement. As NORM congestion control operation and round-trip timing measurement.
mentioned in the NORM_CMD(ACK_REQ) message description, the As mentioned in the "NORM_CMD(ACK_REQ)" message description, the
acknowledgment type NORM_ACK_CC is provided for this purpose. The acknowledgment type "NORM_ACK_CC" is provided for this purpose. The
generation of NORM_ACK(CC) messages for round-trip timing estimation generation of "NORM_ACK(CC)" messages for round-trip timing
and congestion-control operation is described in Sections 5.5.1 and estimation and congestion-control operation is described in
5.5.2, respectively. However, some multicast applications may Section 5.5.1 and Section 5.5.2, respectively. However, some
benefit from some limited form of positive acknowledgment for certain multicast applications may benefit from some limited form of positive
functions. A simple, scalable positive acknowledgment scheme is acknowledgment for certain functions. A simple, scalable positive
defined in Section 5.5.3 that can be leveraged by protocol acknowledgment scheme is defined in Section 5.5.3 that can be
implementations when appropriate. The NORM_CMD(FLUSH) may be used leveraged by protocol implementations when appropriate. The
for OPTIONAL collection of positive acknowledgment of reliable "NORM_CMD(FLUSH)" may be used for OPTIONAL collection of positive
reception to a certain "watermark" transmission point from specific acknowledgment of reliable reception to a certain "watermark"
receivers using this mechanism. The NORM_ACK type NORM_ACK_FLUSH is transmission point from specific receivers using this mechanism. The
provided for this purpose and the format of the "nack_payload" for "NORM_ACK" type "NORM_ACK_FLUSH" is provided for this purpose and the
this acknowledgment type is given below. Beyond that, a range of format of the "nack_payload" for this acknowledgment type is given
application-defined "ack_type" values is provided for use at the NORM below. Beyond that, a range of application-defined "ack_type" values
application’s discretion. Implementations making use of application- is provided for use at the NORM application's discretion.
defined positive acknowledgments may also make use the "nack_payload" Implementations making use of application-defined positive
as needed, observing the constraint that the "nack_payload" field acknowledgments may also make use the "nack_payload" as needed,
size be limited to a maximum of the NormSegmentSize for the sender to observing the constraint that the "nack_payload" field size be
which the NORM_ACK is destined. limited to a maximum of the NormSegmentSize for the sender to which
the "NORM_ACK" is destined.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|version| type=5| hdr_len | sequence | |version| type=5| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| server_id | | server_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | ack_type | ack_id | | instance_id | ack_type | ack_id |
skipping to change at page 58, line 39 skipping to change at page 55, line 39
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_ACK Message Format NORM_ACK Message Format
The NORM common message header fields serve their usual purposes. The NORM common message header fields serve their usual purposes.
The value of the "hdr_len" field when no header extensions are The value of the "hdr_len" field when no header extensions are
present is 6. present is 6.
The "server_id", "instance_id", and "grtt_response" fields serve the The "server_id", "instance_id", and "grtt_response" fields serve the
same purpose as the corresponding fields in NORM_NACK messages. And same purpose as the corresponding fields in "NORM_NACK" messages.
header extensions may be applied to support congestion control And header extensions may be applied to support congestion control
feedback or other functions in the same manner. feedback or other functions in the same manner.
The "ack_type" field indicates the nature of the NORM_ACK message. The "ack_type" field indicates the nature of the "NORM_ACK" message.
This directly corresponds to the "ack_type" field of the This directly corresponds to the "ack_type" field of the
NORM_CMD(ACK_REQ) message to which this acknowledgment applies. "NORM_CMD(ACK_REQ)" message to which this acknowledgment applies.
The "ack_id" field serves as a sequence number so that the sender can The "ack_id" field serves as a sequence number so that the sender can
verify that a NORM_ACK message received actually applies to a current verify that a "NORM_ACK" message received actually applies to a
acknowledgment request. The "ack_id" field is not used in the case current acknowledgment request. The "ack_id" field is not used in
of the NORM_ACK_CC and NORM_ACK_FLUSH acknowledgment types. the case of the "NORM_ACK_CC" and "NORM_ACK_FLUSH" acknowledgment
types.
The "ack_payload" format is a function of the "ack_type". The The "ack_payload" format is a function of the "ack_type". The
NORM_ACK_CC message has no attached content. Only the NORM_ACK "NORM_ACK_CC" message has no attached content. Only the "NORM_ACK"
header applies. In the case of NORM_ACK_FLUSH, a specific header applies. In the case of "NORM_ACK_FLUSH", a specific
"ack_payload" format is defined: "ack_payload" format is defined:
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_id | reserved | object_transport_id | | fec_id | reserved | object_transport_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| fec_payload_id | | fec_payload_id |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_ACK_FLUSH "ack_payload" Format
The "object_transport_id" and "fec_payload_id" are used by the The "object_transport_id" and "fec_payload_id" are used by the
receiver to acknowledge applicable NORM_CMD(FLUSH) messages receiver to acknowledge applicable "NORM_CMD(FLUSH)" messages
transmitted by the sender identified by the "server_id" field. transmitted by the sender identified by the "server_id" field.
The "ack_payload" of NORM_ACK messages for application-defined The "ack_payload" of "NORM_ACK" messages for application-defined
"ack_type" values is specific to the application but is limited in "ack_type" values is specific to the application but is limited in
size to a maximum the NormSegmentSize of the sender referenced by the size to a maximum the NormSegmentSize of the sender referenced by the
"server_id". "server_id".
4.4. General Purpose Messages 4.4. General Purpose Messages
Some additional message formats are defined for general purpose in Some additional message formats are defined for general purpose in
NORM multicast sessions whether the participant is acting as a sender NORM multicast sessions whether the participant is acting as a sender
and/or receiver within the group. and/or receiver within the group.
4.4.1. NORM_REPORT Message 4.4.1. NORM_REPORT Message
This is an optional message generated by NORM participants. This This is an optional message generated by NORM participants. This
message could be used for periodic performance reports from receivers message could be used for periodic performance reports from receivers
in experimental NORM implementations. The format of this message is in experimental NORM implementations. The format of this message is
currently undefined. Experimental NORM implementations may define currently undefined. Experimental NORM implementations may define
NORM_REPORT formats as needed for test purposes. These report "NORM_REPORT" formats as needed for test purposes. These report
messages SHOULD be disabled for interoperability testing between messages SHOULD be disabled for interoperability testing between
different NORM implementations. different NORM implementations.
5. Detailed Protocol Operation 5. Detailed Protocol Operation
This section describes the detailed interactions of senders and This section describes the detailed interactions of senders and
receivers participating in a NORM session. A simple synopsis of receivers participating in a NORM session. A simple synopsis of
protocol operation is given here: protocol operation is given here:
1) The sender periodically transmits NORM_CMD(CC) messages as 1. The sender periodically transmits "NORM_CMD(CC)" messages as
needed to initialize and collect roundtrip timing and needed to initialize and collect round-trip timing and congestion
congestion control feedback from the receiver set. control feedback from the receiver set.
2) The sender transmits an ordinal set of NormObjects segmented 2. The sender transmits an ordinal set of NormObjects segmented in
in the form of NORM_DATA messages labeled with the form of "NORM_DATA" messages labeled with NormTransportIds
NormTransportIds and logically identified with FEC encoding and logically identified with FEC encoding block numbers and
block numbers and symbol identifiers. NORM_INFO messages symbol identifiers. "NORM_INFO" messages may optionally precede
may optionally precede the transmission of data content for the transmission of data content for NORM transport objects.
NORM transport objects.
3) As receivers detect missing content from the sender, they 3. As receivers detect missing content from the sender, they
initiate repair requests with NORM_NACK messages. Note the initiate repair requests with "NORM_NACK" messages. Note the
receivers track the sender’s most recent receivers track the sender's most recent objectId::fecPayloadId
objectId::fecPayloadId transmit position and NACK _only_ for transmit position and NACK ONLY for content ordinally prior to
content ordinally prior to that transmit position. The that transmit position. The receivers schedule random backoff
receivers schedule random backoff timeouts before generating timeouts before generating "NORM_NACK" messages and wait an
NORM_NACK messages and wait an appropriate amount of time appropriate amount of time before repeating the "NORM_NACK" if
before repeating the NORM_NACK if their repair request is their repair request is not satisfied.
not satisfied.
4) The sender aggregates repair requests from the receivers and 4. The sender aggregates repair requests from the receivers and
logically "rewinds" its transmit position to send logically "rewinds" its transmit position to send appropriate
appropriate repair messages. The sender sends repairs for repair messages. The sender sends repairs for the earliest
the earliest ordinal transmit position first and maintains ordinal transmit position first and maintains this ordinal repair
this ordinal repair transmission sequence. Previously transmission sequence. FEC parity content not previously
untransmitted FEC parity content for the applicable FEC transmitted for the applicable FEC coding block is used for
coding block is used for repair transmissions to the repair transmissions to the greatest extent possible. If the
greatest extent possible. If the sender exhausts its sender exhausts its available FEC parity content on multiple
available FEC parity content on multiple repair cycles for repair cycles for the same coding block, it resorts to an
the same coding block, it resorts to an explicit repair explicit repair strategy (possibly using parity content) to
strategy (possibly using parity content) to complete complete repairs. (The use of explicit repair is expected to be
repairs. (The use of explicit repair is expected to be an an exception in general protocol operation, but the possibility
exception in general protocol operation, but the possibility
does exist for extreme conditions). The sender immediately does exist for extreme conditions). The sender immediately
assumes transmission of new content once it has sent pending assumes transmission of new content once it has sent pending
repairs. repairs.
5) The sender transmits NORM_CMD(FLUSH) messages when it 5. The sender transmits "NORM_CMD(FLUSH)" messages when it reaches
reaches the end of enqueued transmit content and pending the end of enqueued transmit content and pending repairs.
repairs. Receivers respond to the NORM_CMD(FLUSH) messages Receivers respond to the "NORM_CMD(FLUSH)" messages with
with NORM_NACK transmissions (following the same suppression "NORM_NACK" transmissions (following the same suppression backoff
backoff timeout strategy as for data) if they require timeout strategy as for data) if they require further repair.
further repair.
6) The sender transmissions are subject to rate control limits 6. The sender transmissions are subject to rate control limits
determined by congestion control mechanisms. In the determined by congestion control mechanisms. In the baseline
baseline NORM-CC operation, each sender in a NormSession NORM-CC operation, each sender in a NormSession maintains its own
maintains its own independent congestion control state. independent congestion control state. Receivers provide
Receivers provide congestion control feedback in NORM_NACK congestion control feedback in "NORM_NACK" and "NORM_ACK"
and NORM_ACK messages. NORM_ACK feedback for congestion messages. "NORM_ACK" feedback for congestion control purposes is
control purposes is governed using a suppression mechanism governed using a suppression mechanism similar to that for
similar to that for NORM_NACK messages. "NORM_NACK" messages.
While this overall concept is relatively simple, there are details to While this overall concept is relatively simple, there are details to
each of these aspects that need to be addressed for successful, each of these aspects that need to be addressed for successful,
efficient, robust, and scalable NORM protocol operation. efficient, robust, and scalable NORM protocol operation.
5.1. Sender Initialization and Transmission 5.1. Sender Initialization and Transmission
Upon startup, the NORM sender immediately begins sending NORM_CMD(CC) Upon startup, the NORM sender immediately begins sending
messages to collect round trip timing and other information from the "NORM_CMD(CC)" messages to collect round trip timing and other
potential group. If NORM-CC congestion control operation is enabled, information from the potential group. If NORM-CC congestion control
the NORM-CC Rate header extension MUST be included in these messages. operation is enabled, the NORM-CC Rate header extension MUST be
Congestion control operation SHALL be observed at all times when included in these messages. Congestion control operation SHALL be
operating in the general Internet. Even if congestion control observed at all times when operating in the general Internet. Even
operation is disabled at the sender, it may be desirable to use the if congestion control operation is disabled at the sender, it may be
NORM_CMD(CC) messaging to collect feedback from the group using the desirable to use the "NORM_CMD(CC)" messaging to collect feedback
baseline NORM-CC feedback mechanisms. This proactive feedback from the group using the baseline NORM-CC feedback mechanisms. This
collection can be used to establish a GRTT estimate prior to data proactive feedback collection can be used to establish a GRTT
transmission and potential NACK operation. estimate prior to data transmission and potential NACK operation.
In some cases, applications may wish for the sender to also proceed In some cases, applications may wish for the sender to also proceed
with data transmission immediately. In other cases, the sender may with data transmission immediately. In other cases, the sender may
wish to defer data transmission until it has received some feedback wish to defer data transmission until it has received some feedback
or request from the receiver set indicating that receivers are indeed or request from the receiver set indicating that receivers are indeed
present. Note, in some applications (e.g., web push), this present. Note, in some applications (e.g., web push), this
indication may come out-of-band with respect to the multicast session indication may come out-of-band with respect to the multicast session
via other means. As noted, the periodic transmission of NORM_CMD(CC) via other means. As noted, the periodic transmission of
messages may precede actual data transmission in order to have an "NORM_CMD(CC)" messages may precede actual data transmission in order
initial GRTT estimate. to have an initial GRTT estimate.
With inclusion of the OPTIONAL NORM FEC Object Transmission With inclusion of the OPTIONAL NORM FEC Object Transmission
Information Header Extension (EXT_FTI), the NORM protocol sender Information Header Extension (EXT_FTI), the NORM protocol sender
message headers can contain all information necessary to prepare message headers can contain all information necessary to prepare
receivers for subsequent reliable reception. This includes FEC receivers for subsequent reliable reception. This includes FEC
coding parameters, the sender NormSegmentSize, and other information. coding parameters, the sender NormSegmentSize, and other information.
If this header extension is not used, it is presumed that receivers If this header extension is not used, it is presumed that receivers
have received the FEC Object Transmission Information via other have received the FEC Object Transmission Information via other
means. Additionally, applications may leverage the use of NORM_INFO means. Additionally, applications may leverage the use of
messages associated with the session data objects in the session to "NORM_INFO" messages associated with the session data objects in the
provide application-specific context information for the session and session to provide application-specific context information for the
data being transmitted. These mechanisms allow for operation with session and data being transmitted. These mechanisms allow for
minimal pre-coordination among the senders and receivers. operation with minimal pre-coordination among the senders and
receivers.
The NORM sender begins segmenting application-enqueued data into The NORM sender begins segmenting application-enqueued data into
NORM_DATA segments and transmitting it to the group. For objects of "NORM_DATA" segments and transmitting it to the group. For objects
type NORM_OBJECT_DATA and NORM_OBJECT_FILE, the segmentation of type "NORM_OBJECT_DATA" and "NORM_OBJECT_FILE", the segmentation
algorithm described in FEC Building Block document. [4]. is algorithm described in FEC Building Block document [RFC5052] is
RECOMMENDED. For objects of type NORM_OBJECT_STREAM, segmentation RECOMMENDED. For objects of type "NORM_OBJECT_STREAM", segmentation
will typically be done into uniform FEC coding block sizes, with will typically be into uniform FEC coding block sizes, with
individual segment sizes controlled by the application, although in individual segment sizes controlled by the application. In most
many cases, the application and NORM implementation should strive to cases, the application and NORM implementation SHOULD strive to
produce full-sized (NormSegmentSize) segments when possible. The produce full-sized ("NormSegmentSize") segments when possible. The
rate of transmission is controlled via congestion control mechanisms rate of transmission is controlled via congestion control mechanisms
or is a fixed rate if desired for closed network operations. The or is a fixed rate if desired for closed network operations. The
receivers participating in the multicast group provide feedback to receivers participating in the multicast group provide feedback to
the sender as needed. When the sender reaches the end of data it has the sender as needed. When the sender reaches the end of data it has
enqueued for transmission or any pending repairs, it transmits a enqueued for transmission or any pending repairs, it transmits a
series of NORM_CMD(FLUSH) messages at a rate of one per 2*GRTT. series of "NORM_CMD(FLUSH)" messages at a rate of one per "2*GRTT".
Receivers may respond to these NORM_CMD(FLUSH) messages with Receivers may respond to these "NORM_CMD(FLUSH)" messages with
additional repair requests. A protocol parameter additional repair requests. A protocol parameter
"NORM_ROBUST_FACTOR" determines the number of flush messages sent. ""NORM_ROBUST_FACTOR"" determines the number of flush messages sent.
If receivers request repair, the repair is provided and flushing If receivers request repair, the repair is provided and flushing
occurs again at the end of repair transmission. The sender may occurs again at the end of repair transmission. The sender may
attach an OPTIONAL "acking_node_list" to NORM_CMD(FLUSH) containing attach an OPTIONAL "acking_node_list" to "NORM_CMD(FLUSH)" containing
the NormNodeIds for receivers from which it expects explicit positive the NormNodeIds for receivers from which it expects explicit positive
acknowledgment of reception. The NORM_CMD(FLUSH) message may be also acknowledgment of reception. The "NORM_CMD(FLUSH)" message may be
used for this optional function any time prior to the end of data also used for this optional function any time prior to the end of
enqueued for transmission with the NORM_CMD(FLUSH) messages data enqueued for transmission with the "NORM_CMD(FLUSH)" messages
multiplexed with ongoing data transmissions. The OPTIONAL NORM multiplexed with ongoing data transmissions. The OPTIONAL NORM
positive acknowledgment procedure is described in Section 5.5.3. positive acknowledgment procedure is described in Section 5.5.3.
5.1.1. Object Segmentation Algorithm 5.1.1. Object Segmentation Algorithm
NORM senders and receivers MUST use a common algorithm for logically NORM senders and receivers MUST use a common algorithm for logically
segmenting transport data into FEC encoding blocks and symbols so segmenting transport data into FEC encoding blocks and symbols so
that appropriate NACKs can be constructed to request repair of that appropriate NACKs can be constructed to request repair of
missing data. NORM FEC coding blocks are comprised of multi-byte missing data. NORM FEC coding blocks are comprised of multi-byte
symbols (segments) that are transmitted in the payload of NORM_DATA symbols (segments) that are transmitted in the payload of "NORM_DATA"
messages. Each NORM_DATA message will contain one or more source or messages. Each "NORM_DATA" message will contain one or more source
encoding symbol(s) identified by the "fec_payload_id" field and the or encoding symbol(s) identified by the "fec_payload_id" field and
NormSegmentSize sender parameter defines the maximum size (in bytes) the NormSegmentSize sender parameter defines the maximum size (in
of the "payload_data" field containing the content (a "segment"). bytes) of the "payload_data" field containing the content (a
The FEC encoding type and associated parameters govern the source "segment"). The FEC encoding type and associated parameters govern
block size (number of source symbols per coding block, etc.). NORM the source block size (number of source symbols per coding block,
senders and receivers use these FEC parameters, along with the etc.). NORM senders and receivers use these FEC parameters, along
NormSegmentSize and transport object size to compute the source block with the NormSegmentSize and transport object size to compute the
structure for transport objects. These parameters are provided in source block structure for transport objects. These parameters are
the FEC Object Transmission Information for each object. The block provided in the FEC Object Transmission Information for each object.
partioning algorithm described in the FEC Building Block document [4] The block partitioning algorithm described in the FEC Building Block
is RECOMMENDED for use to compute a source block structure such that document [RFC5052] is RECOMMENDED for use to compute a source block
all source blocks are as close to being equal length as possible. structure such that all source blocks are as close to being equal
This helps avoid the performance disadvantages of "short" FEC blocks. length as possible. This helps avoid the performance disadvantages
Note this algorithm applies only to the statically-sized of "short" FEC blocks. Note this algorithm applies only to the
NORM_OBJECT_DATA and NORM_OBJECT_FILE transport object types where statically-sized "NORM_OBJECT_DATA" and "NORM_OBJECT_FILE" transport
the object size is fixed and predetermined. For NORM_OBJECT_STREAM object types where the object size is fixed and predetermined. For
objects, the object is segmented according to the maximum source "NORM_OBJECT_STREAM" objects, the object is segmented according to
block length given in the FEC Transmission Information, unless the the maximum source block length given in the FEC Transmission
FEC Payload ID indicates an alternative size for a given block. Information, unless the FEC Payload ID indicates an alternative size
for a given block.
5.2. Receiver Initialization and Reception 5.2. Receiver Initialization and Reception
The NORM protocol is designed such that receivers may join and leave The NORM protocol is designed such that receivers may join and leave
the group at will. However, some applications may be constrained the group at will. However, some applications may be constrained
such that receivers need to be members of the group prior to start of such that receivers need to be members of the group prior to start of
data transmission. NORM applications may use different policies to data transmission. NORM applications may use different policies to
constrain the impact of new receivers joining the group in the middle constrain the impact of new receivers joining the group in the middle
of a session. For example, a useful implementation policy is for new of a session. For example, a useful implementation policy is for new
receivers joining the group to limit or avoid repair requests for receivers joining the group to limit or avoid repair requests for
transport objects already in progress. The NORM sender transport objects already in progress. The NORM sender
implementation may wish to impose additional constraints to limit the implementation may wish to impose additional constraints to limit the
ability of receivers to disrupt reliable multicast performance by ability of receivers to disrupt reliable multicast performance by
joining, leaving, and rejoining the group often. Different receiver joining, leaving, and rejoining the group often. Different receiver
"join policies" may be appropriate for different applications and/or "join policies" may be appropriate for different applications and/or
scenarios. For general purpose operation, a default policy where scenarios. For general purpose operation, a default policy where
receivers are allowed to request repair only for coding blocks with a receivers are allowed to request repair only for coding blocks with a
NormTransportId and FEC coding block number greater than or equal to NormTransportId and FEC coding block number greater than or equal to
the first non-repair NORM_DATA or NORM_INFO message received upon the first non-repair "NORM_DATA" or "NORM_INFO" message received upon
joining the group is RECOMMENDED. For objects of type joining the group is RECOMMENDED. For objects of type
NORM_OBJECT_STREAM it is RECOMMENDED that the join policy constrain "NORM_OBJECT_STREAM" it is RECOMMENDED that the join policy constrain
receivers to start reliable reception at the current FEC coding block receivers to start reliable reception at the current FEC coding block
for which non-repair content is received. for which non-repair content is received.
For typical operation, it is expected that NORM receivers will join a For typical operation, it is expected that NORM receivers will join a
specified multicast group and/or listen on an specific port number specified multicast group and/or listen on an specific port number
for sender transmissions. As the NORM receiver receives NORM_DATA for sender transmissions. As the NORM receiver receives "NORM_DATA"
messages it will provide content to its application as appropriate. messages it will provide content to its application as appropriate.
5.3. Receiver NACK Procedure 5.3. Receiver NACK Procedure
When the receiver detects it is missing data from a senders NORM When the receiver detects it is missing data from a sender's NORM
transmissions, it initiates its NACKing procedure. The NACKing transmissions, it initiates its NACKing procedure. The NACKing
procedure SHALL be initiated _only_ at FEC coding block boundaries, procedure SHALL be initiated ONLY at FEC coding block boundaries,
NormObject boundaries, upon receipt of a NORM_CMD(FLUSH) message, or NormObject boundaries, upon receipt of a "NORM_CMD(FLUSH)" message,
upon an "inactivity" timeout when NORM_DATA or NORM_INFO or upon an "inactivity" timeout when "NORM_DATA" or "NORM_INFO"
transmissions are no longer received from a previously active sender. transmissions are no longer received from a previously active sender.
The RECOMMENDED value of such an inactivity timeout is: The RECOMMENDED value of such an inactivity timeout is:
T_inactivity = NORM_ROBUST_FACTOR * 2 * GRTTSender T_inactivity = NORM_ROBUST_FACTOR * 2 * GRTTSender
where the "GRTTsender" value corresponds to the GRTT estimate where the ""GRTTsender"" value corresponds to the GRTT estimate
advertised in the "grtt" field of NORM sender messages. A minimum advertised in the "grtt" field of NORM sender messages. A minimum
"T_inactivity" value of 1 second is RECOMMENDED. The NORM receiver ""T_inactivity"" value of 1 second is RECOMMENDED. The NORM receiver
SHOULD reset this inactivity timer and repeat NACK initiation upon SHOULD reset this inactivity timer and repeat NACK initiation upon
timeout for up to NORM_ROBUST_FACTOR times or more depending upon the timeout for up to "NORM_ROBUST_FACTOR" times or more depending upon
application’s need for persistence by its receivers. It is also the application's need for persistence by its receivers. It is also
important that receivers rescale the "T_inactivity" timeout as the important that receivers rescale the ""T_inactivity"" timeout as the
sender’s advertised GRTT changes. sender's advertised GRTT changes.
The NACKing procedure begins with a random backoff timeout. The The NACKing procedure begins with a random backoff timeout. The
duration of the backoff timeout is chosen using the "RandomBackoff" duration of the backoff timeout is chosen using the "RandomBackoff"
algorithm described in the NORM Building Block document [3] using algorithm described in the Multicast NACK Building Block document
(Ksender*GRTTsender) for the "maxTime" parameter and the sender [I-D.ietf-rmt-bb-norm-revised] using ("Ksender*GRTTsender") for the
advertised group size (GSIZEsender) as the "groupSize" parameter. "maxTime" parameter and the sender advertised group size
NORM senders provide values for GRTTsender, Ksender and GSIZEsender ("GSIZEsender") as the "groupSize" parameter. NORM senders provide
via the "grtt", "backoff", and "gsize" fields of transmitted values for "GRTTsender", "Ksender" and "GSIZEsender" via the "grtt",
messages. The GRTTsender value is determined by the sender based on "backoff", and "gsize" fields of transmitted messages. The
feedback it has received from the group while the Ksender and "GRTTsender" value is determined by the sender based on feedback it
GSIZEsender values may determined by application requirements and has received from the group while the "Ksender" and "GSIZEsender"
expectations or ancillary information. The backoff factor "Ksender" values may determined by application requirements and expectations or
MUST be greater than one to provide for effective feedback ancillary information. The backoff factor ""Ksender"" MUST be
suppression. A value of K = 4 is RECOMMENDED for the Any Source greater than "one" to provide for effective feedback suppression. A
Multicast (ASM) model while a value of K = 6 is RECOMMENDED for value of "K = 4" is RECOMMENDED for the Any Source Multicast (ASM)
Single Source Multicast (SSM) operation. model while a value of "K = 6" is RECOMMENDED for Single Source
Multicast (SSM) operation.
Thus: Thus:
T_backoff = RandomBackoff(Ksender*GRTTsender, GSIZEsender) T_backoff = RandomBackoff(Ksender*GRTTsender, GSIZEsender)
To avoid the possibility of NACK implosion in the case of sender or To avoid the possibility of NACK implosion in the case of sender or
network failure during SSM operation, the receiver SHALL network failure during SSM operation, the receiver SHALL
automatically suppress its NACK and immediately enter the "holdoff" automatically suppress its NACK and immediately enter the "holdoff"
period described below when T_backoff is greater than period described below when "T_backoff" is greater than
(Ksender-1)*GRTTsender. Otherwise, the backoff period is entered and "(Ksender-1)*GRTTsender". Otherwise, the backoff period is entered
the receiver MUST accumulate external pending repair state from and the receiver MUST accumulate external pending repair state from
NORM_NACK messages and NORM_CMD(REPAIR_ADV) messages received. At "NORM_NACK" messages and "NORM_CMD(REPAIR_ADV)" messages received.
the end of the backoff time, the receiver SHALL generate a NORM_NACK At the end of the backoff time, the receiver SHALL generate a
message only if the following conditions are met: "NORM_NACK" message only if the following conditions are met:
1) The sender’s current transmit position (in terms of 1. The sender's current transmit position (in terms of objectId::
objectId::fecPayloadId) exceeds the earliest repair position fecPayloadId) exceeds the earliest repair position of the
of the receiver. receiver.
2) The repair state accumulated from NORM_NACK and 2. The repair state accumulated from "NORM_NACK" and
NORM_CMD(REPAIR_ADV) messages do not equal or supersede the "NORM_CMD(REPAIR_ADV)" messages do not equal or supersede the
receiver’s repair needs up to the sender transmission receiver's repair needs up to the sender transmission position at
position at the time the NACK procedure (backoff timeout) the time the NACK procedure (backoff timeout) was initiated.
was initiated.
If these conditions are met, the receiver immediately generates a If these conditions are met, the receiver immediately generates a
NORM_NACK message when the backoff timeout expires. Otherwise, the "NORM_NACK" message when the backoff timeout expires. Otherwise, the
receiver’s NACK is considered to be "suppressed" and the message is receiver's NACK is considered to be "suppressed" and the message is
not sent. At this time, the receiver begins a "holdoff" period not sent. At this time, the receiver begins a "holdoff" period
during which it constrains itself to not reinitiate the NACKing during which it constrains itself to not re-initiate the NACKing
process. The purpose of this timeout is to allow the sender worst- process. The purpose of this timeout is to allow the sender worst-
case time to respond to the repair needs before the receiver requests case time to respond to the repair needs before the receiver requests
repair again. The value of this "holdoff" timeout (T_rcvrHoldoff) repair again. The value of this "holdoff" timeout ("T_rcvrHoldoff")
as described in [3] is: as described in [I-D.ietf-rmt-bb-norm-revised] is:
T_rcvrHoldoff =(Ksender+2)*GRTTsender T_rcvrHoldoff =(Ksender+2)*GRTTsender
The NORM_NACK message contains repair request content beginning with The "NORM_NACK" message contains repair request content beginning
lowest ordinal repair position of the receiver up through the coding with lowest ordinal repair position of the receiver up through the
block prior to the most recently heard ordinal transmission position coding block prior to the most recently heard ordinal transmission
for the sender. If the size of the NORM_NACK content exceeds the position for the sender. If the size of the "NORM_NACK" content
sender’s NormSegmentSize, the NACK content is truncated so that the exceeds the sender's NormSegmentSize, the NACK content is truncated
receiver only generates a single NORM_NACK message per NACK cycle for so that the receiver only generates a single "NORM_NACK" message per
a given sender. In summary, a single NACK message is generated NACK cycle for a given sender. In summary, a single NACK message is
containing the receiver’s lowest ordinal repair needs. generated containing the receiver's lowest ordinal repair needs.
For each partially-received FEC coding block requiring repair, the For each partially-received FEC coding block requiring repair, the
receiver SHALL, on its _first_ repair attempt for the block, request receiver SHALL, on its FIRST repair attempt for the block, request
the parity portion of the FEC coding block beginning with the lowest the parity portion of the FEC coding block beginning with the lowest
ordinal _parity_ "encoding_symbol_id" (i.e., "encoding_symbol_id" = ordinal parity "encoding_symbol_id" (i.e., "encoding_symbol_id" =
"source_block_len") and request the number of FEC symbols "source_block_len") and request the number of FEC symbols
corresponding to its data segment erasure count for the block. On corresponding to its data segment erasure count for the block. On
_subsequent_ repair cycles for the same coding block, the receiver subsequent repair cycles for the same coding block, the receiver
SHALL request only those repair symbols from the first set it has not SHALL request only those repair symbols from the first set it has not
yet received up to the remaining erasure count for that applicable yet received up to the remaining erasure count for that applicable
coding block. Note that the sender may have provided other coding block. Note that the sender may have provided other
different, additional parity segments for other receivers that could different, additional parity segments for other receivers that could
also be used to satisfy the local receivers erasure-filling needs. also be used to satisfy the local receiver's erasure-filling needs.
In the case where the erasure count for a partially-received FEC In the case where the erasure count for a partially-received FEC
coding block exceeds the maximum number of parity symbols available coding block exceeds the maximum number of parity symbols available
from the sender for the block (as indicated by the NORM_DATA from the sender for the block (as indicated by the "NORM_DATA"
"fec_num_parity" field), the receiver SHALL request all available "fec_num_parity" field), the receiver SHALL request all available
parity segments plus the ordinally highest missing data segments parity segments plus the ordinally highest missing data segments
required to satisfy its total erasure needs for the block. The goal required to satisfy its total erasure needs for the block. The goal
of this strategy is for the overall receiver set to request a lowest of this strategy is for the overall receiver set to request a lowest
common denominator set of repair symbols for a given FEC coding common denominator set of repair symbols for a given FEC coding
block. This allows the sender to construct the most efficient repair block. This allows the sender to construct the most efficient repair
transmission segment set and enables effective NACK suppression among transmission segment set and enables effective NACK suppression among
the receivers even with uncorrelated packet loss. This approach also the receivers even with uncorrelated packet loss. This approach also
requires no synchronization among the receiver set in their repair requires no synchronization among the receiver set in their repair
requests for the sender. requests for the sender.
For FEC coding blocks or NormObjects missed in their entirety, the For FEC coding blocks or NormObjects missed in their entirety, the
NORM receiver constructs repair requests with NORM_NACK_BLOCK or NORM receiver constructs repair requests with "NORM_NACK_BLOCK" or
NORM_NACK_OBJECT flags set as appropriate. The request for "NORM_NACK_OBJECT" flags set as appropriate. The request for
retransmission of NORM_INFO is accomplished by setting the retransmission of "NORM_INFO" is accomplished by setting the
NORM_NACK_INFO flag in a corresponding repair request. "NORM_NACK_INFO" flag in a corresponding repair request.
5.4. Sender NACK Processing and Response 5.4. Sender NACK Processing and Response
The principle goal of the sender is to make forward progress in the The principle goal of the sender is to make forward progress in the
transmission of data its application has enqueued. However, the transmission of data its application has enqueued. However, the
sender must occasionally "rewind" its logical transmission point to sender must occasionally "rewind" its logical transmission point to
satisfy the repair needs of receivers who have NACKed. Aggregation satisfy the repair needs of receivers who have NACKed. Aggregation
of multiple NACKs is used to determine an optimal repair strategy of multiple NACKs is used to determine an optimal repair strategy
when a NACK event occurs. Since receivers initiate the NACK process when a NACK event occurs. Since receivers initiate the NACK process
on coding block or object boundaries, there is some loose degree of on coding block or object boundaries, there is some loose degree of
synchronization of the repair process even when receivers experience synchronization of the repair process even when receivers experience
uncorrelated data loss. uncorrelated data loss.
5.4.1. Sender Repair State Aggregation 5.4.1. Sender Repair State Aggregation
When a sender is in its normal state of transmitting new data and When a sender is in its normal state of transmitting new data and
receives a NACK, it begins a procedure to accumulate NACK repair receives a NACK, it begins a procedure to accumulate NACK repair
state from NORM_NACK messages before beginning repair transmissions. state from "NORM_NACK" messages before beginning repair
Note that this period of aggregating repair state does _not_ transmissions. Note that this period of aggregating repair state
interfere with its ongoing transmission of new data. does NOT interfere with its ongoing transmission of new data.
As described in [3], the period of time during which the sender
aggregates NORM_NACK messages is equal to:
As described in [I-D.ietf-rmt-bb-norm-revised], the period of time
during which the sender aggregates "NORM_NACK" messages is equal to:
T_sndrAggregate = (Ksender+1)*GRTT T_sndrAggregate = (Ksender+1)*GRTT
where "Ksender" is the same backoff scaling value used by the where ""Ksender"" is the same backoff scaling value used by the
receivers, and "GRTT" is the sender’s current estimate of the group’s receivers, and "GRTT" is the sender's current estimate of the group's
greatest round-trip time. Note that for NORM unicast sessions the greatest round-trip time. Note that for NORM unicast sessions the
"T_sndrAggregate" time can be set to ZERO since there is only one ""T_sndrAggregate"" time can be set to ZERO since there is only one
receiver. Similarly, the "Ksender" value should be set to ZERO for receiver. Similarly, the ""Ksender"" value should be set to ZERO for
NORM unicast sessions to minimize repair latency. NORM unicast sessions to minimize repair latency.
When this period ends, the sender "rewinds" by incorporating the When this period ends, the sender "rewinds" by incorporating the
accumulated repair state into its pending transmission state and accumulated repair state into its pending transmission state and
begins transmitting repair messages. After pending repair begins transmitting repair messages. After pending repair
transmissions are completed, the sender continues with new transmissions are completed, the sender continues with new
transmissions of any enqueued data. Also, at this point in time, the transmissions of any enqueued data. Also, at this point in time, the
sender begins a "holdoff" timeout during which time the sender sender begins a "holdoff" timeout during which time the sender
constrains itself from initiating a new repair aggregation cycle, constrains itself from initiating a new repair aggregation cycle,
even if NORM_NACK messages arrive. As described in [3], the value of even if "NORM_NACK" messages arrive. As described in
this sender "holdoff" period is: [I-D.ietf-rmt-bb-norm-revised], the value of this sender "holdoff"
period is:
T_sndrHoldoff = (1*GRTT) T_sndrHoldoff = (1*GRTT)
If additional NORM_NACK messages are received during this sender If additional "NORM_NACK" messages are received during this sender
"holdoff" period, the sender will immediately incorporate these "late "holdoff" period, the sender will immediately incorporate these late-
messages" into its pending transmission state ONLY if the NACK arriving messages into its pending transmission state ONLY if the
content is ordinally greater than the sender’s current transmission NACK content is ordinally greater than the sender's current
position. This "holdoff" time allows worst case time for the sender transmission position. This "holdoff" time allows worst case time
to propagate its current transmission sequence position to the group, for the sender to propagate its current transmission sequence
thus avoiding redundant repair transmissions. After the holdoff position to the group, thus avoiding redundant repair transmissions.
timeout expires, a new NACK accumulation period can be begun (upon After the holdoff timeout expires, a new NACK accumulation period can
arrival of a NACK) in concert with the pending repair and new data be begun (upon arrival of a NACK) in concert with the pending repair
transmission. Recall that receivers are not to initiate the NACK and new data transmission. Recall that receivers are not to initiate
repair process until the sender’s logical transmission position the NACK repair process until the sender's logical transmission
exceeds the lowest ordinal position of their repair needs. With the position exceeds the lowest ordinal position of their repair needs.
new NACK aggregation period, the sender repeats the same process of With the new NACK aggregation period, the sender repeats the same
incorporating accumulated repair state into its transmission plan and process of incorporating accumulated repair state into its
subsequently "rewinding" to transmit the lowest ordinal repair data transmission plan and subsequently "rewinding" to transmit the lowest
when the aggregation period expires. Again, this is conducted in ordinal repair data when the aggregation period expires. Again, this
concert with ongoing new data and/or pending repair transmissions. is conducted in concert with ongoing new data and/or pending repair
transmissions.
5.4.2. Sender FEC Repair Transmission Strategy 5.4.2. Sender FEC Repair Transmission Strategy
The NORM sender should leverage transmission of FEC parity content The NORM sender should leverage transmission of FEC parity content
for repair to the greatest extent possible. Recall that the for repair to the greatest extent possible. Recall that the
receivers use a strategy to request a lowest common denominator of receivers use a strategy to request a lowest common denominator of
explicit repair (including parity content) in the formation of their explicit repair (including parity content) in the formation of their
NORM_NACK messages. Before falling back to explicitly satisfying "NORM_NACK" messages. Before falling back to explicitly satisfying
different receivers’ repair needs, the sender can make use of the different receivers' repair needs, the sender can make use of the
general erasure-filling capability of FEC-generated parity segments. general erasure-filling capability of FEC-generated parity segments.
The sender can determine the maximum erasure filling needs for The sender can determine the maximum erasure filling needs for
individual FEC coding blocks from the NORM_NACK messages received individual FEC coding blocks from the "NORM_NACK" messages received
during the repair aggregation period. Then, if the sender has a during the repair aggregation period. Then, if the sender has a
sufficient number (less than or equal to the maximum erasure count) sufficient number (less than or equal to the maximum erasure count)
of previously unsent parity segments available for the applicable of previously unsent parity segments available for the applicable
coding blocks, the sender can transmit these in lieu of the specific coding blocks, the sender can transmit these in lieu of the specific
packets the receiver set has requested. Only after exhausting its packets the receiver set has requested. Only after exhausting its
supply of "fresh" (unsent) parity segments for a given coding block supply of "fresh" (unsent) parity segments for a given coding block
should the sender resort to explicit transmission of the receiver should the sender resort to explicit transmission of the receiver
sets repair needs. In general, if a sufficiently powerful FEC code set's repair needs. In general, if a sufficiently powerful FEC code
is used, the need for explicit repair will be an exception, and the is used, the need for explicit repair will be an exception, and the
fulfillment of reliable multicast can be accomplished quite fulfillment of reliable multicast can be accomplished quite
efficiently. However, the ability to resort to explicit repair efficiently. However, the ability to resort to explicit repair
allows the protocol to be reliable under even very extreme allows the protocol to be reliable under even very extreme
circumstances. circumstances.
NORM_DATA messages sent as repair transmissions SHALL be flagged with "NORM_DATA" messages sent as repair transmissions SHALL be flagged
the NORM_FLAG_REPAIR flag. This allows receivers to obey any with the "NORM_FLAG_REPAIR" flag. This allows receivers to obey any
policies that limit new receivers from joining the reliable policies that limit new receivers from joining the reliable
transmission when only repair transmissions have been received. transmission when only repair transmissions have been received.
Additionally, the sender SHOULD additionally flag NORM_DATA Additionally, the sender SHOULD additionally flag "NORM_DATA"
transmissions sent as explicit repair with the NORM_FLAG_EXPLICIT transmissions sent as explicit repair with the "NORM_FLAG_EXPLICIT"
flag. flag.
Although NORM end system receivers do not make use of the Although NORM end system receivers do not make use of the
NORM_FLAG_EXPLICIT flag, this message transmission status could be "NORM_FLAG_EXPLICIT" flag, this message transmission status could be
leveraged by intermediate systems wishing to "assist" NORM protocol leveraged by intermediate systems wishing to "assist" NORM protocol
performance. If such systems are properly positioned with respect to performance. If such systems are properly positioned with respect to
reciprocal reverse-path multicast routing, they need to sub-cast only reciprocal reverse-path multicast routing, they need to sub-cast only
a sufficient count of non-explicit parity repairs to satisfy a a sufficient count of non-explicit parity repairs to satisfy a
multicast routing sub-trees erasure filling needs for a given FEC multicast routing sub-tree's erasure filling needs for a given FEC
coding block. When the sender has resorted to explicit repair, then coding block. When the sender has resorted to explicit repair, then
the intermediate systems should sub-cast all of the explicit repair the intermediate systems should sub-cast all of the explicit repair
packets to those portions of the routing tree still requiring repair packets to those portions of the routing tree still requiring repair
for a given coding block. Note the intermediate systems will be for a given coding block. Note the intermediate systems will be
required to conduct repair state accumulation for sub-routes in a required to conduct repair state accumulation for sub-routes in a
manner similar to the senders repair state accumulation in order to manner similar to the sender's repair state accumulation in order to
have sufficient information to perform the sub-casting. have sufficient information to perform the sub-casting.
Additionally, the intermediate systems could perform additional Additionally, the intermediate systems could perform additional
NORM_NACK suppression/aggregation as it conducts this repair state "NORM_NACK" suppression/aggregation as it conducts this repair state
accumulation for NORM repair cycles. The detail of this type of accumulation for NORM repair cycles. The detail of this type of
operation are beyond the scope of this document, but this information operation are beyond the scope of this document, but this information
is provided for possible future consideration. is provided for possible future consideration.
5.4.3. Sender NORM_CMD(SQUELCH) Generation 5.4.3. Sender NORM_CMD(SQUELCH) Generation
If the sender receives a NORM_NACK message for repair of data it is If the sender receives a "NORM_NACK" message for repair of data it is
no longer supporting, the sender generates a NORM_CMD(SQUELCH) no longer supporting, the sender generates a "NORM_CMD(SQUELCH)"
message to advertise its repair window and squelch any receivers from message to advertise its repair window and squelch any receivers from
additional NACKing of invalid data. The transmission rate of additional NACKing of invalid data. The transmission rate of
NORM_CMD(SQUELCH) messages is limited to once per 2*GRTT. The "NORM_CMD(SQUELCH)" messages is limited to once per "2*GRTT". The
"invalid_object_list" (if applicable) of the NORM_CMD(SQUELCH) "invalid_object_list" (if applicable) of the "NORM_CMD(SQUELCH)"
message SHALL begin with the lowest "object_transport_id" from the message SHALL begin with the lowest "object_transport_id" from the
invalid NORM_NACK messages received since the last NORM_CMD(SQUELCH) invalid "NORM_NACK" messages received since the last
transmission. Lower ordinal invalid "object_transport_ids" should be "NORM_CMD(SQUELCH)" transmission. Lower ordinal invalid
included only while the NORM_CMD(SQUELCH) payload is less than the "object_transport_ids" should be included only while the
sender’s NormSegmentSize parameter. "NORM_CMD(SQUELCH)" payload is less than the sender's NormSegmentSize
parameter.
5.4.4. Sender NORM_CMD(REPAIR_ADV) Generation 5.4.4. Sender NORM_CMD(REPAIR_ADV) Generation
When a NORM sender receives NORM_NACK messages from receivers via When a NORM sender receives "NORM_NACK" messages from receivers via
unicast transmission, it uses NORM_CMD(REPAIR_ADV) messages to unicast transmission, it uses "NORM_CMD(REPAIR_ADV)" messages to
advertise its accumulated repair state to the receiver set since the advertise its accumulated repair state to the receiver set since the
receiver set is not directly sharing their repair needs via multicast receiver set is not directly sharing their repair needs via multicast
communication. A NORM sender implementation MAY use a separate port communication. A NORM sender implementation MAY use a separate port
number from the NormSession port number as the source port for its number from the NormSession port number as the source port for its
transmissions. Thus NORM receivers can direct any _unicast_ feedback transmissions. Thus NORM receivers can direct any unicast feedback
messages to this sender port number that is distinct from the messages to this sender port number that is distinct from the NORM
"session" port number. Then, the NORM sender implementation can session (or destination) port number. Then, the NORM sender
discriminate unicast feedback messages from multicast feedback implementation can discriminate unicast feedback messages from
messages when there is a mix of multicast and unicast feedback multicast feedback messages when there is a mix of multicast and
receivers. The NORM_CMD(REPAIR_ADV) message is multicast to the unicast feedback receivers. The "NORM_CMD(REPAIR_ADV)" message is
receiver set by the sender. The payload portion of this message has multicast to the receiver set by the sender. The payload portion of
content in the same format as the NORM_NACK receiver message payload. this message has content in the same format as the "NORM_NACK"
Receivers are then able to perform feedback suppression in the same receiver message payload. Receivers are then able to perform
manner as with NORM_NACK messages directly received from other feedback suppression in the same manner as with "NORM_NACK" messages
receivers. Note the sender does not merely retransmit NACK content directly received from other receivers. Note the sender does not
it receives, but instead transmits a representation of its aggregated merely retransmit NACK content it receives, but instead transmits a
repair state. The transmission of NORM_CMD(REPAIR_ADV) messages are representation of its aggregated repair state. The transmission of
subject to the sender transmit rate limit and NormSegmentSize "NORM_CMD(REPAIR_ADV)" messages are subject to the sender transmit
limitation. When the NORM_CMD(REPAIR_ADV) message is of maximum rate limit and NormSegmentSize limitation. When the
size, receivers SHALL consider the maximum ordinal transmission "NORM_CMD(REPAIR_ADV)" message is of maximum size, receivers SHALL
position value embedded in the message as the senders "current" consider the maximum ordinal transmission position value embedded in
transmission position and implicitly suppress requests for ordinally the message as the senders current transmission position and
higher repair. For congestion control operation, the sender may also implicitly suppress requests for ordinally higher repair. For
need to provide information so that dynamic congestion control congestion control operation, the sender may also need to provide
feedback can be suppressed as needed among receivers. This document information so that dynamic congestion control feedback can be
specifies the NORM-CC Feedback Header Extension that is applied for suppressed as needed among receivers. This document specifies the
baseline NORM-CC operation. If other congestion control mechanisms NORM-CC Feedback Header Extension that is applied for baseline
are used within a NORM implementation, other header extensions may be NORM-CC operation. If other congestion control mechanisms are used
defined. Whatever content format is used for this purpose should within a NORM implementation, other header extensions may be defined.
ensure that maximum possible suppression state is conveyed to the Whatever content format is used for this purpose should ensure that
receiver set. maximum possible suppression state is conveyed to the receiver set.
5.5. Additional Protocol Mechanisms 5.5. Additional Protocol Mechanisms
In addition to the principal function of data content transmission In addition to the principal function of data content transmission
and repair, there are some other protocol mechanisms that help NORM and repair, there are some other protocol mechanisms that help NORM
to adapt to network conditions and play fairly with other coexistent to adapt to network conditions and play fairly with other coexistent
protocols. protocols.
5.5.1. Greatest Round-trip Time Collection 5.5.1. Greatest Round-trip Time Collection
For NORM receivers to appropriately scale backoff timeouts and the For NORM receivers to appropriately scale backoff timeouts and the
senders to use proper corresponding timeouts, the participants must senders to use proper corresponding timeouts, the participants must
agree on a common timeout basis. Each NORM sender monitors the agree on a common timeout basis. Each NORM sender monitors the
round-trip time of active receivers and determines the group greatest round-trip time of active receivers and determines the group greatest
round-trip time (GRTT). The sender advertises this GRTT estimate in round-trip time (GRTT). The sender advertises this GRTT estimate in
every message it transmits so that receivers have this value every message it transmits so that receivers have this value
available for scaling their timers. To measure the current GRTT, the available for scaling their timers. To measure the current GRTT, the
sender periodically sends NORM_CMD(CC) messages that contain a sender periodically sends "NORM_CMD(CC)" messages that contain a
locally generated timestamp. Receivers are expected to record this locally generated timestamp. Receivers are expected to record this
timestamp along with the time the NORM_CMD(CC) message is received. timestamp along with the time the "NORM_CMD(CC)" message is received.
Then, when the receivers generate feedback messages to the sender, an Then, when the receivers generate feedback messages to the sender, an
adjusted version of the sender timestamp is embedded in the feedback adjusted version of the sender timestamp is embedded in the feedback
message (NORM_NACK or NORM_ACK). The adjustment adds the amount of message ("NORM_NACK" or "NORM_ACK"). The adjustment adds the amount
time the receiver held the timestamp before generating its response. of time the receiver held the timestamp before generating its
Upon receipt of this adjusted timestamp, the sender is able to response. Upon receipt of this adjusted timestamp, the sender is
calculate the round-trip time to that receiver. able to calculate the round-trip time to that receiver.
The round-trip time for each receiver is fed into an algorithm that The round-trip time for each receiver is fed into an algorithm that
weights and smoothes the values for a conservative estimate of the weights and smoothes the values for a conservative estimate of the
GRTT. The algorithm and methodology are described in the NORM GRTT. The algorithm and methodology are described in the Multicast
Building Block document [3] in the section entitled "One-to-Many NACK Building Block document [I-D.ietf-rmt-bb-norm-revised] in the
Sender GRTT Measurement". A conservative estimate helps feedback section entitled "One-to-Many Sender GRTT Measurement". A
suppression at a small cost in overall protocol repair delay. The conservative estimate helps guarantee feedback suppression at a small
sender’s current estimate of GRTT is advertised in the "grtt" field cost in overall protocol repair delay. The sender's current estimate
found in all NORM sender messages. The advertised GRTT is also of GRTT is advertised in the "grtt" field found in all NORM sender
limited to a minimum of the nominal inter-packet transmission time messages. The advertised GRTT is also limited to a minimum of the
given the sender’s current transmission rate and system clock nominal inter-packet transmission time given the sender's current
granularity. The reason for this additional limit is to keep the transmission rate and system clock granularity. The reason for this
receiver somewhat "event driven" by making sure the sender has had additional limit is to keep the receiver somewhat event-driven by
adequate time to generate any response to repair requests from making sure the sender has had adequate time to generate any response
receivers given transmit rate limitations due to congestion control to repair requests from receivers given transmit rate limitations due
or configuration. to congestion control or configuration.
When the NORM-CC Rate header extension is present in NORM_CMD(CC) When the NORM-CC Rate header extension is present in "NORM_CMD(CC)"
messages, the receivers respond to NORM_CMD(CC) messages as described messages, the receivers respond to "NORM_CMD(CC)" messages as
in Section 5.5.2, "NORM Congestion Control Operation". The described in Section 5.5.2, "NORM Congestion Control Operation". The
NORM_CMD(CC) messages are periodically generated by the sender as "NORM_CMD(CC)" messages are periodically generated by the sender as
described for congestion control operation. This provides for described for congestion control operation. This provides for
proactive, but controlled, feedback from the group in the form of proactive, but controlled, feedback from the group in the form of
NORM_ACK messages. This provides for GRTT feedback even if no "NORM_ACK" messages. This provides for GRTT feedback even if no
NORM_NACK messages are being sent. If operating without congestion "NORM_NACK" messages are being sent. If operating without congestion
control in a closed network, the NORM_CMD(CC) messages may be sent control in a closed network, the "NORM_CMD(CC)" messages may be sent
periodically without the NORM-CC Rate header extension. In this periodically without the NORM-CC Rate header extension. In this
case, receivers will only provide GRTT measurement feedback when case, receivers will only provide GRTT measurement feedback when
NORM_NACK messages are generated since no NORM_ACK messages are "NORM_NACK" messages are generated since no "NORM_ACK" messages are
generated. In this case, the NORM_CMD(CC) messages may be sent less generated. In this case, the "NORM_CMD(CC)" messages may be sent
frequently, perhaps as little as once per minute, to conserve network less frequently, perhaps as little as once per minute, to conserve
capacity. Note that the NORM-CC Rate header extension may also be network capacity. Note that the NORM-CC Rate header extension may
used proactively solicit RTT feedback from the receiver group per also be used to proactively solicit RTT feedback from the receiver
congestion control operation even though the sender may not be group per congestion control operation even though the sender may not
conducting congestion control rate adjustment. NORM operation be conducting congestion control rate adjustment. NORM operation
without congestion control should be considered only in closed without congestion control should be considered only in closed
networks. networks.
5.5.2. NORM Congestion Control Operation 5.5.2. NORM Congestion Control Operation
This section describes baseline congestion control operation for the This section describes baseline congestion control operation for the
NORM protocol (NORM-CC). The supporting NORM message formats and NORM protocol (NORM-CC). The supporting NORM message formats and
approach described here are an adaptation of the equation-based TCP- approach described here are an adaptation of the equation-based TCP-
Friendly Multicast Congestion Control (TFMCC) approach described in Friendly Multicast Congestion Control (TFMCC) approach described in
[5]. This congestion control scheme is REQUIRED for operation within [RFC4654]. This congestion control scheme is REQUIRED for operation
the general Internet unless the NORM implementation is adapted to use within the general Internet unless the NORM implementation is adapted
another IETF-sanctioned reliable multicast congestion control to use another IETF-sanctioned reliable multicast congestion control
mechanism (e.g., PGMCC [26]). With this TFMCC-based approach, the mechanism (e.g., PGMCC [PgmccPaper]). With this TFMCC-based
transmissions of NORM senders are controlled in a rate-based manner approach, the transmissions of NORM senders are controlled in a rate-
as opposed to window-based congestion control algorithms as in TCP. based manner as opposed to window-based congestion control algorithms
However, it is possible that the NORM protocol message set may as in TCP. However, it is possible that the NORM protocol message
alternatively be used to support a window-based multicast congestion set may alternatively be used to support a window-based multicast
control scheme such as PGMCC. The details of that alternative may be congestion control scheme such as PGMCC. The details of that
described separately or in a future revision of this document. In alternative may be described separately or in a future revision of
either case (rate-based TFMCC or window-based PGMCC), successful this document. In either case (rate-based TFMCC or window-based
control of sender transmission depends upon collection of sender-to- PGMCC), successful control of sender transmission depends upon
receiver packet loss estimates and RTTs to identify the congestion collection of sender-to-receiver packet loss estimates and RTTs to
control bottleneck path(s) within the multicast topology and adjust identify the congestion control bottleneck path(s) within the
the sender rate accordingly. The receiver with loss and RTT multicast topology and adjust the sender rate accordingly. The
estimates that correspond to the lowest resulting calculated receiver with loss and RTT estimates that correspond to the lowest
transmission rate is identified as the "current limiting receiver" resulting calculated transmission rate is identified as the "current
(CLR). In the case of a "tie" (where candidate CLRs are within 10% limiting receiver" (CLR). In the case of a tie (where candidate CLRs
of the same calculated rate), the receiver with the largest RTT value are within 10% of the same calculated rate), the receiver with the
SHOULD be designated as the CLR. largest RTT value SHOULD be designated as the CLR.
As described in [27], a steady-state sender transmission rate, to be
"friendly" with competing TCP flows can be calculated as:
As described in [TcpModel], a steady-state sender transmission rate,
to be "friendly" with competing TCP flows can be calculated as:
S S
Rsender = -------------------------------------------------------------- Rsender = --------------------------------------------------------------
tRTT*(sqrt((2/3)*p) + 12 * sqrt((3/8)*p) * p * (1 + 32*(p^2))) tRTT*(sqrt((2/3)*p) + 12 * sqrt((3/8)*p) * p * (1 + 32*(p^2)))
where where
S = Nominal transmitted packet size. (In NORM, the "nominal" "S" = nominal transmitted packet size. (In NORM, the "nominal"
packet size can be determined by the sender as an packet size can be determined by the sender as an exponentially
exponentially weighted moving average (EWMA) of transmitted weighted moving average (EWMA) of transmitted packet sizes to account
packet sizes to account for variable message sizes). for variable message sizes).
tRTT = The RTT estimate of the current "current limiting receiver" "tRTT" = RTT estimate of the current "current limiting receiver"
(CLR). (CLR).
p = The loss event fraction of the CLR. "p" = loss event fraction of the CLR.
To support congestion control feedback collection and operation, the To support congestion control feedback collection and operation, the
NORM sender periodically transmits NORM_CMD(CC) command messages. NORM sender periodically transmits "NORM_CMD(CC)" command messages.
NORM_CMD(CC) messages are multiplexed with NORM data and repair "NORM_CMD(CC)" messages are multiplexed with NORM data and repair
transmissions and serve several purposes: transmissions and serve several purposes:
1) Stimulate explicit feedback from the general receiver set to 1. Stimulate explicit feedback from the general receiver set to
collect congestion control information. collect congestion control information.
2) Communicate state to the receiver set on the sender’s 2. Communicate state to the receiver set on the sender's current
current congestion control status including details of the congestion control status including details of the CLR.
CLR.
3) Initiate rapid (immediate) feedback from the CLR in order to 3. Initiate rapid (immediate) feedback from the CLR in order to
closely track the dynamics of congestion control for that closely track the dynamics of congestion control for that current
current "worst path" in the group multicast topology. worst path in the group multicast topology.
The format of the NORM_CMD(CC) message is describe in Section 4.2.3 The format of the "NORM_CMD(CC)" message is describe in Section 4.2.3
of this document. The NORM_CMD(CC) message contains information to of this document. The "NORM_CMD(CC)" message contains information to
allow measurement of RTTs, to inform the group of the congestion allow measurement of RTTs, to inform the group of the congestion
control CLR, and to provide feedback of individual RTT measurements control CLR, and to provide feedback of individual RTT measurements
to the receivers in the group. The NORM_CMD(CC) also provides for to the receivers in the group. The "NORM_CMD(CC)" also provides for
exciting feedback from OPTIONAL "potential limiting receiver" (PLR) exciting feedback from OPTIONAL "potential limiting receiver" (PLR)
nodes that may be determined administratively or possibly nodes that may be determined administratively or possibly
algorithmically based on congestion control feedback. PLR nodes are algorithmically based on congestion control feedback. PLR nodes are
receivers that have been identified to have potential for (perhaps receivers that have been identified to have potential for (perhaps
soon) becoming the CLR and thus immediate, up-to-date feedback is soon) becoming the CLR and thus immediate, up-to-date feedback is
beneficial for congestion control performance. The details of PLR beneficial for congestion control performance. The details of PLR
selection are not discussed in this document. selection are not discussed in this document.
5.5.2.1. NORM_CMD(CC) Transmission 5.5.2.1. NORM_CMD(CC) Transmission
The NORM_CMD(CC) message is transmitted periodically by the sender The "NORM_CMD(CC)" message is transmitted periodically by the sender
along with its normal data transmission. Note that the repeated along with its normal data transmission. Note that the repeated
transmission of NORM_CMD(CC) messages may be initiated some time transmission of "NORM_CMD(CC)" messages may be initiated some time
before transmission of user data content at session startup. This before transmission of user data content at session startup. This
may be done to collect some estimation of the current state of the may be done to collect some estimation of the current state of the
multicast topology with respect to group and individual RTT and multicast topology with respect to group and individual RTT and
congestion control state. congestion control state.
A NORM_CMD(CC) message is immediately transmitted at sender startup. A "NORM_CMD(CC)" message is immediately transmitted at sender
The interval of subsequent NORM_CMD(CC) message transmission is startup. The interval of subsequent "NORM_CMD(CC)" message
determined as follows: transmission is determined as follows:
1) By default, the interval is set according to the current 1. By default, the interval is set according to the current sender
sender GRTT estimate. A startup GRTT of 0.5 seconds is GRTT estimate. A startup GRTT of 0.5 seconds is recommended when
recommended when no feedback has yet been received from the no feedback has yet been received from the group.
group.
2) Until a CLR has been identified (based on previous receiver 2. Until a CLR has been identified (based on previous receiver
feedback) or when no data transmission is pending, the feedback) or when no data transmission is pending, the
NORM_CMD(CC) interval is doubled up from its current "NORM_CMD(CC)" interval is doubled up from its current interval
interval to a maximum of once per 30 seconds. This results to a maximum of once per 30 seconds. This results in a low duty
in a low duty cycle for NORM_CMD(CC) probing when no CLR is cycle for "NORM_CMD(CC)" probing when no CLR is identified or
identified or there is no pending data to transmit. T}.sp there is no pending data to transmit.
3) T{ When a CLR has been identified (based on receiver
feedback) and data transmission is pending, the probing
interval is set to the RTT between the sender and the CLR
(RTT_clr).
4) Additionally, when the data transmission rate is low with 3. When a CLR has been identified (based on receiver feedback) and
respect to the RTT_clr interval used for probing, the data transmission is pending, the probing interval is set to the
implementation should ensure that no more than one RTT between the sender and the CLR ("RTT_clr").
NORM_CMD(CC) message is sent per NORM_DATA message when
there is data pending transmission. This ensures that the
transmission of this control message is not done to the
exclusion of user data transmission.
The NORM_CMD(CC) "cc_sequence" field is incremented with each 4. Additionally, when the data transmission rate is low with respect
transmission of a NORM_CMD(CC) command. The greatest "cc_sequence" to the "RTT_clr" interval used for probing, the implementation
should ensure that no more than one "NORM_CMD(CC)" message is
sent per "NORM_DATA" message when there is data pending
transmission. This ensures that the transmission of this control
message is not done to the exclusion of user data transmission.
The "NORM_CMD(CC)" "cc_sequence" field is incremented with each
transmission of a "NORM_CMD(CC)" command. The greatest "cc_sequence"
recently received by receivers is included in their feedback to the recently received by receivers is included in their feedback to the
sender. This allows the sender to determine the "age" of feedback to sender. This allows the sender to determine the age of feedback to
assist in congestion avoidance. assist in congestion avoidance.
The NORM-CC Rate Header Extension is applied to the NORM_CMD(CC) The NORM-CC Rate Header Extension is applied to the "NORM_CMD(CC)"
message and the sender advertises its current transmission rate in message and the sender advertises its current transmission rate in
the "send_rate" field. The rate information is used by receivers to the "send_rate" field. The rate information is used by receivers to
initialize loss estimation during congestion control startup or initialize loss estimation during congestion control startup or
restart. restart.
The "cc_node_list" contains a list of entries identifying receivers The "cc_node_list" contains a list of entries identifying receivers
and their current congestion control state (status "flags", "rtt" and and their current congestion control state (status "flags", "rtt" and
"loss" estimates). The list may be empty if the sender has not yet "loss" estimates). The list may be empty if the sender has not yet
received any feedback from the group. If the sender has received received any feedback from the group. If the sender has received
feedback, the list will minimally contain an entry identifying the feedback, the list will minimally contain an entry identifying the
CLR. A NORM_FLAG_CC_CLR flag value is provided for the "cc_flags" CLR. A "NORM_FLAG_CC_CLR" flag value is provided for the "cc_flags"
field to identify the CLR entry. It is RECOMMENDED that the CLR field to identify the CLR entry. It is RECOMMENDED that the CLR
entry be the first in the list for implementation efficiency. entry be the first in the list for implementation efficiency.
Additional entries in the list are used to provide sender-measured Additional entries in the list are used to provide sender-measured
individual RTT estimates to receivers in the group. The number of individual RTT estimates to receivers in the group. The number of
additional entries in this list is dependent upon the percentage of additional entries in this list is dependent upon the percentage of
control traffic the sender application is willing to send with control traffic the sender application is willing to send with
respect to user data message transmissions. More entries in the list respect to user data message transmissions. More entries in the list
may allow the sender to be more responsive to congestion control may allow the sender to be more responsive to congestion control
dynamics. The length of the list may be dynamically determined dynamics. The length of the list may be dynamically determined
according to the current transmission rate and scheduling of according to the current transmission rate and scheduling of
NORM_CMD(CC) messages. The maximum length of the list corresponds to "NORM_CMD(CC)" messages. The maximum length of the list corresponds
the sender’s NormSegmentSize parameter for the session. The to the sender's NormSegmentSize parameter for the session. The
inclusion of additional entries in the list based on receiver inclusion of additional entries in the list based on receiver
feedback are prioritized with following rules: feedback are prioritized with following rules:
1) Receivers that have not yet been provided a RTT measurement 1. Receivers that have not yet been provided a RTT measurement get
get first priority. Of these, those with the greatest loss first priority. Of these, those with the greatest loss fraction
fraction receive precedence for list inclusion. receive precedence for list inclusion.
2) Secondly, receivers that have previously been provided a RTT 2. Secondly, receivers that have previously been provided a RTT
measurement are included with receivers yielding the lowest measurement are included with receivers yielding the lowest
calculated congestion rate getting precedence. calculated congestion rate getting precedence.
There are "cc_flag" values in addition to NORM_FLAG_CC_CLR that are There are "cc_flag" values in addition to "NORM_FLAG_CC_CLR" that are
used for other congestion control functions. The NORM_FLAG_CC_PLR used for other congestion control functions. The "NORM_FLAG_CC_PLR"
flag value is used to mark additional receivers from that the sender flag value is used to mark additional receivers from that the sender
would like to have immediate, non-suppressed feedback. These may be would like to have immediate, non-suppressed feedback. These may be
receivers that the sender algorithmically identified as potential receivers that the sender algorithmically identified as potential
future CLRs or that have been pre-configured as potential congestion future CLRs or that have been pre-configured as potential congestion
control points in the network. The NORM_FLAG_CC_RTT indicates the control points in the network. The "NORM_FLAG_CC_RTT" indicates the
validity of the "cc_rtt" field for the associated receiver node. validity of the "cc_rtt" field for the associated receiver node.
Normally, this flag will be set since the receivers in the list will Normally, this flag will be set since the receivers in the list will
typically be receivers from which the sender has received feedback. typically be receivers from which the sender has received feedback.
However, in the case that the NORM sender has been pre-configured However, in the case that the NORM sender has been pre-configured
with a set of PLR nodes, feedback from those receivers may not yet with a set of PLR nodes, feedback from those receivers may not yet
have been collected and thus the "cc_rtt" field does not contain a have been collected and thus the "cc_rtt" field does not contain a
valid value when this flag is not set. Similarly, a value of ZERO valid value when this flag is not set. Similarly, a value of ZERO
for the "cc_rate" field here should be treated as an invalid value for the "cc_rate" field here should be treated as an invalid value
and be ignored for the purposes of feedback suppression, etc. and be ignored for the purposes of feedback suppression, etc.
5.5.2.2. NORM_CMD(CC) Feedback Response 5.5.2.2. NORM_CMD(CC) Feedback Response
Receivers explicitly respond to NORM_CMD(CC) messages in the form of Receivers explicitly respond to "NORM_CMD(CC)" messages in the form
a NORM_ACK(RTT) message. The goal of the congestion control feedback of a "NORM_ACK(RTT)" message. The goal of the congestion control
is to determine the receivers with the lowest congestion control feedback is to determine the receivers with the lowest congestion
rates. Receivers that are marked as CLR or PLR nodes in the control rates. Receivers that are marked as CLR or PLR nodes in the
NORM_CMD(CC) "cc_node_list" immediately provide feedback in the form "NORM_CMD(CC)" "cc_node_list" immediately provide feedback in the
of a NORM_ACK to this message. When a NORM_CMD(CC) is received, non- form of a "NORM_ACK" to this message. When a "NORM_CMD(CC)" is
CLR or non-PLR nodes initiate random feedback backoff timeouts received, non-CLR or non-PLR nodes initiate random feedback backoff
similar to that used when the receiver initiates a repair cycle (see timeouts similar to that used when the receiver initiates a repair
Section 5.3) in response to detection of data loss. The backoff cycle (see Section 5.3) in response to detection of data loss. The
timeout for the congestion control response is generated as follows: backoff timeout for the congestion control response is generated as
follows:
T_backoff = RandomBackoff(K*GRTTsender, GSIZEsender) T_backoff = RandomBackoff(K*GRTTsender, GSIZEsender)
The "RandomBackoff()" algorithm provides a truncated exponentially The ""RandomBackoff()"" algorithm provides a truncated exponentially
distributed random number and is described in the NORM Building Block distributed random number and is described in the Multicast NACK
document [3]. The same backoff factor K = Ksender MAY be used as Building Block document [I-D.ietf-rmt-bb-norm-revised]. The same
with NORM_NACK suppression. However, in cases where the application backoff factor "K = Ksender" MAY be used as with "NORM_NACK"
purposefully specifies a very small Ksender backoff factor to suppression. However, in cases where the application purposefully
minimize the NACK repair process latency (trading off group size specifies a very small "Ksender" backoff factor to minimize the NACK
scalability), it is RECOMMENDED that a larger backoff factor for repair process latency (trading off group size scalability), it is
congestion control feedback is maintained, since there may often be a RECOMMENDED that a larger backoff factor for congestion control
larger volume of congestion control feedback than NACKs in many cases feedback is maintained, since there may often be a larger volume of
and some congestion control feedback latency may be tolerable where congestion control feedback than NACKs in many cases and some
reliable delivery latency is not. As previously noted, a backoff congestion control feedback latency may be tolerable where reliable
factor value of K = 4 is generally recommended for ASM operation and delivery latency is not. As previously noted, a backoff factor value
K = 6 for SSM operation. A receiver SHALL cancel the backoff timeout of "K = 4" is generally recommended for ASM operation and "K = 6" for
and thus its pending transmission of a NORM_ACK(RTT) message under SSM operation. A receiver SHALL cancel the backoff timeout and thus
the following conditions: its pending transmission of a "NORM_ACK(RTT)" message under the
following conditions:
1) The receiver generates another feedback message (NORM_NACK 1. The receiver generates another feedback message ("NORM_NACK" or
or other NORM_ACK) before the congestion control feedback other "NORM_ACK") before the congestion control feedback timeout
timeout expires (these messages will convey the current expires (these messages will convey the current congestion
congestion control feedback information), control feedback information),
2) A NORM_CMD(CC) or other receiver feedback with an ordinally 2. A "NORM_CMD(CC)" or other receiver feedback with an ordinally
greater "cc_sequence" field value is received before the greater "cc_sequence" field value is received before the
congestion control feedback timeout expires (this is similar congestion control feedback timeout expires (this is similar to
to the TFMCC feedback round number), the TFMCC feedback round number),
3) When the T_backoff is greater than 1*GRTTsender. This 3. When the "T_backoff" is greater than "1*GRTTsender". This
prevents NACK implosion in the event of sender or network prevents NACK implosion in the event of sender or network
failure, failure,
4) "Suppressing" congestion control feedback is heard from 4. "Suppressing" congestion control feedback is heard from another
another receiver (in a NORM_ACK or NORM_NACK) or via a receiver (in a "NORM_ACK" or "NORM_NACK") or via a
NORM_CMD(REPAIR_ADV) message from the sender. The local "NORM_CMD(REPAIR_ADV)" message from the sender. The local
receiver’s feedback is "suppressed" if the rate of the receiver's feedback is "suppressed" if the rate of the competing
competing feedback (Rfb) is sufficiently close to or less feedback ("Rfb") is sufficiently close to or less than the local
than the local receiver’s calculated rate (Rcalc). The receiver's calculated rate ("Rcalc"). The local receiver's
local receiver’s feedback is canceled when: feedback is canceled when "Rcalc > (0.9 * Rfb)". Also note
receivers that have not yet received an RTT measurement from the
Rcalc > (0.9 * Rfb) sender are suppressed only by other receivers that have not yet
measured RTT. Additionally, receivers whose RTT estimate has
Also note receivers that have not yet received an RTT aged considerably (i.e., they haven't been included in the
measurement from the sender are suppressed only by other "NORM_CMD(CC)" "cc_node_list" in a long time) may wish to compete
receivers that have not yet measured RTT. Additionally, as a receiver with no prior RTT measurement after some long term
receivers whose RTT estimate has "aged" considerably (i.e.,
they haven’t been included in the NORM_CMD(CC)
"cc_node_list" in a long time) may wish to compete as a
receiver with no prior RTT measurement after some long term
expiration period. expiration period.
When the backoff timer expires, the receiver SHALL generate a When the backoff timer expires, the receiver SHALL generate a
NORM_ACK(RTT) message to provide feedback to the sender and group. "NORM_ACK(RTT)" message to provide feedback to the sender and group.
This message may be multicast to the group for most effective This message may be multicast to the group for most effective
suppression in ASM topologies or unicast to the sender depending upon suppression in ASM topologies or unicast to the sender depending upon
how the NORM protocol is deployed and configured. how the NORM protocol is deployed and configured.
Whenever any feedback is generated (including this NORM_ACK(RTT) Whenever any feedback is generated (including this "NORM_ACK(RTT)"
message), receivers include an adjusted version of the sender message), receivers include an adjusted version of the sender
timestamp from the most recently received NORM_CMD(CC) message and timestamp from the most recently received "NORM_CMD(CC)" message and
the "cc_sequence" value from that command in the applicable NORM_ACK the "cc_sequence" value from that command in the applicable
or NORM_NACK message fields. For NORM-CC operation, any generated "NORM_ACK" or "NORM_NACK" message fields. For NORM-CC operation, any
feedback message SHALL also contain the NORM-CC Feedback header generated feedback message SHALL also contain the NORM-CC Feedback
extension. The receiver provides its current "cc_rate" estimate, header extension. The receiver provides its current "cc_rate"
"cc_loss" estimate, "cc_rtt" if known, and any applicable "cc_flags" estimate, "cc_loss" estimate, "cc_rtt" if known, and any applicable
via this header extension. "cc_flags" via this header extension.
During slow start (when the receiver has not yet detected loss from During slow start (when the receiver has not yet detected loss from
the sender), the receiver uses a value equal to two times its the sender), the receiver uses a value equal to two times its
measured rate from the sender in the "cc_rate" field. For steady- measured rate from the sender in the "cc_rate" field. For steady-
state congestion control operation, the receiver "cc_rate" value is state congestion control operation, the receiver "cc_rate" value is
from the equation-based value using its current loss event estimate from the equation-based value using its current loss event estimate
and sender<->receiver RTT information. (The GRTT is used when the and sender<->receiver RTT information. (The GRTT is used when the
receiver has not yet measured its individual RTT). receiver has not yet measured its individual RTT).
The "cc_loss" field value reflects the receivers current loss event The "cc_loss" field value reflects the receiver's current loss event
estimate with respect to the sender in question. estimate with respect to the sender in question.
When the receiver has a valid individual RTT measurement, it SHALL When the receiver has a valid individual RTT measurement, it SHALL
include this value in the "cc_rtt" field. The NORM_FLAG_CC_RTT MUST include this value in the "cc_rtt" field. The "NORM_FLAG_CC_RTT"
be set when the "cc_rtt" field is valid. MUST be set when the "cc_rtt" field is valid.
After a congestion control feedback message is generated or when the After a congestion control feedback message is generated or when the
feedback is suppressed, a non-CLR receiver begins a "holdoff" timeout feedback is suppressed, a non-CLR receiver begins a "holdoff" timeout
period during which it will restrain itself from providing congestion period during which it will restrain itself from providing congestion
control feedback, even if NORM_CMD(CC) messages are received from the control feedback, even if "NORM_CMD(CC)" messages are received from
sender (unless the receive becomes marked as a CLR or PLR node). The the sender (unless the receive becomes marked as a CLR or PLR node).
value of this holdoff timeout (T_ccHoldoff) period is: The value of this holdoff timeout ("T_ccHoldoff") period is:
T_ccHoldoff = (K*GRTT) T_ccHoldoff = (K*GRTT)
Thus, non-CLR receivers are constrained to providing explicit Thus, non-CLR receivers are constrained to providing explicit
congestion control feedback once per K*GRTT intervals. Note, congestion control feedback once per "K*GRTT" intervals. Note,
however, that as the session progresses, different receivers will be however, that as the session progresses, different receivers will be
responding to different NORM_CMD(CC) messages and there will be responding to different "NORM_CMD(CC)" messages and there will be
relatively continuous feedback of congestion control information relatively continuous feedback of congestion control information
while the sender is active. while the sender is active.
5.5.2.3. Congestion Control Rate Adjustment 5.5.2.3. Congestion Control Rate Adjustment
During steady-state operation, the sender will directly adjust its During steady-state operation, the sender will directly adjust its
transmission rate to the rate indicated by the feedback from its transmission rate to the rate indicated by the feedback from its
currently selected CLR. As noted in [24], the estimation of currently selected CLR. As noted in [TfmccPaper], the estimation of
parameters (loss and RTT) for the CLR will generally constrain the parameters (loss and RTT) for the CLR will generally constrain the
rate changes possible within acceptable bounds. For rate increases, rate changes possible within acceptable bounds. For rate increases,
the sender SHALL observe a maximum rate of increase of one packet per the sender SHALL observe a maximum rate of increase of one packet per
RTT at all times during steady-state operation. RTT at all times during steady-state operation.
The sender processes congestion control feedback from the receivers The sender processes congestion control feedback from the receivers
and selects the CLR based on the lowest rate receiver. Receiver and selects the CLR based on the lowest rate receiver. Receiver
rates are either determined directly from the slow start "cc_rate" rates are either determined directly from the slow start "cc_rate"
provided by the receiver in the NORM-CC Feedback header extension or provided by the receiver in the NORM-CC Feedback header extension or
by performing the equation-based calculation using individual RTT and by performing the equation-based calculation using individual RTT and
loss estimates ("cc_loss") as feedback is received. loss estimates ("cc_loss") as feedback is received.
The sender can calculate a current RTT for a receiver (RTT_rcvrNew) The sender can calculate a current RTT for a receiver ("RTT_rcvrNew")
using the "grtt_response" timestamp included in feedback messages. using the "grtt_response" timestamp included in feedback messages.
When the "cc_rtt" value in a response is not valid, the sender simply When the "cc_rtt" value in a response is not valid, the sender simply
uses this RTT_rcvrNew value as the receiver’s current RTT (RTT_rcvr). uses this "RTT_rcvrNew" value as the receiver's current RTT
For non-CLR and non-PLR receivers, the sender can use the "cc_rtt" ("RTT_rcvr"). For non-CLR and non-PLR receivers, the sender can use
value provided in the NORM-CC Feedback header extension as the the "cc_rtt" value provided in the NORM-CC Feedback header extension
receiver’s previous RTT measurement (RTT_rcvrPrev) to smooth as the receiver's previous RTT measurement ("RTT_rcvrPrev") to smooth
according to: according to:
RTT_rcvr = 0.5 * RTT_rcvrPrev + 0.5 * RTT_rcvrNew RTT_rcvr = 0.5 * RTT_rcvrPrev + 0.5 * RTT_rcvrNew
For CLR receivers where feedback is received more regularly, the For CLR receivers where feedback is received more regularly, the
sender SHOULD maintain a more smoothed RTT estimate upon new feedback sender SHOULD maintain a more smoothed RTT estimate upon new feedback
from the CLR where: from the CLR where:
RTT_clr = 0.9 * RTT_clr + 0.1 * RTT_clrNew RTT_clr = 0.9 * RTT_clr + 0.1 * RTT_clrNew
""RTT_clrNew"" is the new RTT calculated from the timestamp in the
"RTT_clrNew" is the new RTT calculated from the timestamp in the feedback message received from the CLR. The "RTT_clr" is initialized
feedback message received from the CLR. The RTT_clr is initialized to "RTT_clrNew" on the first feedback message received. Note that
to RTT_clrNew on the first feedback message received. Note that the the same procedure is observed by the sender for PLR receivers and
same procedure is observed by the sender for PLR receivers and that that if a PLR is "promoted" to CLR status, the smoothed estimate can
if a PLR is "promoted" to CLR status, the smoothed estimate can be be continued.
continued.
There are some additional periods besides steady-state operation that There are some additional periods besides steady-state operation that
need to be considered in NORM-CC operation. These periods are: need to be considered in NORM-CC operation. These periods are:
1) during session startup, 1. during session startup,
2) when no feedback is received from the CLR, and 2. when no feedback is received from the CLR, and
3) when the sender has a break in data transmission. 3. when the sender has a break in data transmission.
During session startup, the congestion control operation SHALL During session startup, the congestion control operation SHALL
observe a "slow start" procedure to quickly approach its fair observe a "slow start" procedure to quickly approach its fair
bandwidth share. An initial sender startup rate is assumed where: bandwidth share. An initial sender startup rate is assumed where:
Rinitial = MIN(NormSegmentSize / GRTT, NormSegmentSize) bytes/second. Rinitial = MIN(NormSegmentSize / GRTT, NormSegmentSize) bytes/second.
The rate is increased only when feedback is received from the The rate is increased only when feedback is received from the
receiver set. The "slow start" phase proceeds until any receiver receiver set. The "slow start" phase proceeds until any receiver
provides feedback indicating that loss has occurred. Rate increase provides feedback indicating that loss has occurred. Rate increase
during slow start is applied as: during slow start is applied as:
Rnew = Rrecv_min Rnew = Rrecv_min
where "Rrecv_min" is the minimum reported receiver rate in the where "Rrecv_min" is the minimum reported receiver rate in the
"cc_rate" field of congestion control feedback messages received from "cc_rate" field of congestion control feedback messages received from
the group. Note that during "slow start", receivers use two times the group. Note that during slow start, receivers use two times
their measured rate from the sender in the "cc_rate" field of their their measured rate from the sender in the "cc_rate" field of their
feedback. Rate increase adjustment is limited to once per GRTT feedback. Rate increase adjustment is limited to once per GRTT
during slow start. during slow start.
If the CLR or any receiver intends to leave the group, it will set If the CLR or any receiver intends to leave the group, it will set
the NORM_FLAG_CC_LEAVE in its congestion control feedback message as the "NORM_FLAG_CC_LEAVE" in its congestion control feedback message
an indication that the sender should not select it as the CLR. When as an indication that the sender should not select it as the CLR.
the CLR changes to a lower rate receiver, the sender should When the CLR changes to a lower rate receiver, the sender should
immediately adjust to the new lower rate. The sender is limited to immediately adjust to the new lower rate. The sender is limited to
increasing its rate at one additional packet per RTT towards any new, increasing its rate at one additional packet per RTT towards any new,
higher CLR rate. higher CLR rate.
The sender should also track the "age" of the feedback it has The sender should also track the age of the feedback it has received
received from the CLR by comparing its current "cc_sequence" value from the CLR by comparing its current "cc_sequence" value
(Seq_sender) to the last "cc_sequence" value received from the CLR ("Seq_sender") to the last "cc_sequence" value received from the CLR
(Seq_clr). As the "age" of the CLR feedback increases with no new ("Seq_clr"). As the age of the CLR feedback increases with no new
feedback, the sender SHALL begin reducing its rate once per RTT_clr feedback, the sender SHALL begin reducing its rate once per "RTT_clr"
as a congestion avoidance measure. The following algorithm is used as a congestion avoidance measure. The following algorithm is used
to determine the decrease in sender rate (Rsender bytes/sec) as the to determine the decrease in sender rate (Rsender bytes/sec) as the
CLR feedback, unexpectedly, excessively ages: CLR feedback, unexpectedly, excessively ages:
Age = Seq_sender - Seq_clr; Age = Seq_sender - Seq_clr;
if (Age > 4) Rsender = Rsender * 0.5; if (Age > 4) Rsender = Rsender * 0.5;
This rate reduction is limited to the lower bound on NORM This rate reduction is limited to the lower bound on NORM
transmission rate. After NORM_ROBUST_FACTOR consecutive NORM_CMD(CC) transmission rate. After "NORM_ROBUST_FACTOR" consecutive
rounds without any feedback from the CLR, the sender SHOULD assume "NORM_CMD(CC)" rounds without any feedback from the CLR, the sender
the CLR has left the group and pick the receiver with the next lowest SHOULD assume the CLR has left the group and pick the receiver with
rate as the new CLR. Note this assumes that the sender does not have the next lowest rate as the new CLR. Note this assumes that the
explicit knowledge that the CLR intentionally left the group. If no sender does not have explicit knowledge that the CLR intentionally
receiver feedback is received, the sender MAY wish to withhold left the group. If no receiver feedback is received, the sender MAY
further transmissions of NORM_DATA segments and maintain NORM_CMD(CC) wish to withhold further transmissions of "NORM_DATA" segments and
transmissions only until feedback is detected. After such a CLR maintain "NORM_CMD(CC)" transmissions only until feedback is
timeout, the sender will be transmitting with a minimal rate and detected. After such a CLR timeout, the sender will be transmitting
should return to slow start as described here for a break in data with a minimal rate and should return to slow start as described here
transmission. for a break in data transmission.
When the sender has a break in its data transmission, it can continue When the sender has a break in its data transmission, it can continue
to probe the group with NORM_CMD(CC) messages to maintain RTT to probe the group with "NORM_CMD(CC)" messages to maintain RTT
collection from the group. This will enable the sender to quickly collection from the group. This will enable the sender to quickly
determine an appropriate CLR upon data transmission restart. determine an appropriate CLR upon data transmission restart.
However, the sender should exponentially reduce its target rate to be However, the sender should exponentially reduce its target rate to be
used for transmission restart as time since the break elapses. The used for transmission restart as time since the break elapses. The
target rate SHOULD be recalculated once per RTT_clr as: target rate SHOULD be recalculated once per "RTT_clr" as:
Rsender = Rsender * 0.5; Rsender = Rsender * 0.5;
If the minimum NORM rate is reached, the sender should set the If the minimum NORM rate is reached, the sender should set the
NORM_FLAG_START flag in its NORM_CMD(CC) messages upon restart and "NORM_FLAG_START" flag in its "NORM_CMD(CC)" messages upon restart
the group should observer "slow start" congestion control procedures and the group should observer slow start congestion control
until any receiver experiences a new loss event. procedures until any receiver experiences a new loss event.
5.5.3. NORM Positive Acknowledgment Procedure 5.5.3. NORM Positive Acknowledgment Procedure
NORM provides options for the source application to request positive NORM provides options for the source application to request positive
acknowledgment (ACK) of NORM_CMD(FLUSH) and NORM_CMD(ACK_REQ) acknowledgment (ACK) of "NORM_CMD(FLUSH)" and "NORM_CMD(ACK_REQ)"
messages from members of the group. There are some specific messages from members of the group. There are some specific
acknowledgment requests defined for the NORM protocol and a range of acknowledgment requests defined for the NORM protocol and a range of
acknowledgment request types that are left to be defined by the acknowledgment request types that are left to be defined by the
application. One predefined acknowledgment type is the application. One predefined acknowledgment type is the
NORM_ACK_FLUSH type. This acknowledgment is used to determine if "NORM_ACK_FLUSH" type. This acknowledgment is used to determine if
receivers have achieved completion of reliable reception up through a receivers have achieved completion of reliable reception up through a
specific logical transmission point with respect to the sender’s specific logical transmission point with respect to the sender's
sequence of transmission. The NORM_ACK_FLUSH acknowledgment may be sequence of transmission. The "NORM_ACK_FLUSH" acknowledgment may be
used to assist in application flow control when the sender has used to assist in application flow control when the sender has
information on a portion of the receiver set. Another predefined information on a portion of the receiver set. Another predefined
acknowledgment type is NORM_ACK(CC), which is used to explicitly acknowledgment type is "NORM_ACK(CC)", which is used to explicitly
provide congestion control feedback in response to NORM_CMD(CC) provide congestion control feedback in response to "NORM_CMD(CC)"
messages transmitted by the sender for NORM-CC operation. Note the messages transmitted by the sender for NORM-CC operation. Note the
NORM_ACK(CC) response does NOT follow the positive acknowledgment "NORM_ACK(CC)" response does NOT follow the positive acknowledgment
procedure described here. The NORM_CMD(ACK_REQ) and NORM_ACK procedure described here. The "NORM_CMD(ACK_REQ)" and "NORM_ACK"
messages contain an "ack_type" field to identify the type of messages contain an "ack_type" field to identify the type of
acknowledgment requested and provided. A range of "ack_type" values acknowledgment requested and provided. A range of "ack_type" values
is provided for application-defined use. While the application is is provided for application-defined use. While the application is
responsible for initiating the acknowledgment request and interprets responsible for initiating the acknowledgment request and interprets
application-defined "ack_type" values, the acknowledgment procedure application-defined "ack_type" values, the acknowledgment procedure
SHOULD be conducted within the protocol implementation to take SHOULD be conducted within the protocol implementation to take
advantage of timing and transmission scheduling information available advantage of timing and transmission scheduling information available
to the NORM transport. to the NORM transport.
The NORM positive acknowledgment procedure uses polling by the sender The NORM positive acknowledgment procedure uses polling by the sender
to query the receiver group for response. Note this polling to query the receiver group for response. Note this polling
procedure is not intended to scale to very large receiver groups, but procedure is not intended to scale to very large receiver groups, but
could be used in large group setting to query a critical subset of could be used in large group setting to query a critical subset of
the group. Either the NORM_CMD(ACK_REQ), or when applicable, the the group. Either the "NORM_CMD(ACK_REQ)", or when applicable, the
NORM_CMD(FLUSH) message is used for polling and contains a list of "NORM_CMD(FLUSH)" message is used for polling and contains a list of
NormNodeIds for receivers that should respond to the command. The NormNodeIds for receivers that should respond to the command. The
list of receivers providing acknowledgment is determined by the list of receivers providing acknowledgment is determined by the
source application with "a priori" knowledge of participating nodes source application with a priori knowledge of participating nodes or
or via some other application-level mechanism. via some other application-level mechanism.
The ACK process is initiated by the sender that generates The ACK process is initiated by the sender that generates
NORM_CMD(FLUSH) or NORM_CMD(ACK_REQ) messages in periodic "rounds". "NORM_CMD(FLUSH)" or "NORM_CMD(ACK_REQ)" messages in periodic rounds.
For NORM_ACK_FLUSH requests, the NORM_CMD(FLUSH) contain a For "NORM_ACK_FLUSH" requests, the "NORM_CMD(FLUSH)" contain a
"object_transport_id" and "fec_payload_id" denoting the watermark "object_transport_id" and "fec_payload_id" denoting the watermark
transmission point for which acknowledgment is requested. This transmission point for which acknowledgment is requested. This
watermark transmission point is "echoed" in the corresponding fields watermark transmission point is echoed in the corresponding fields of
of the NORM_ACK(FLUSH) message sent by the receiver in response. the "NORM_ACK(FLUSH)" message sent by the receiver in response.
NORM_CMD(ACK_REQ) messages contain an "ack_id" field which is "NORM_CMD(ACK_REQ)" messages contain an "ack_id" field which is
similarly "echoed" in response so that the sender may match the similarly echoed in response so that the sender may match the
response to the appropriate request. response to the appropriate request.
In response to the NORM_CMD(ACK_REQ), the listed receivers randomly In response to the "NORM_CMD(ACK_REQ)", the listed receivers randomly
spread NORM_ACK messages uniformly in time over a window of (1*GRTT). spread "NORM_ACK" messages uniformly in time over a window of
These NORM_ACK messages are typically unicast to the sender. (Note (1*GRTT). These "NORM_ACK" messages are typically unicast to the
that NORM_ACK(CC) messages SHALL be multicast or unicast in the same sender. (Note that "NORM_ACK(CC)" messages SHALL be multicast or
manner as NORM_NACK messages). unicast in the same manner as "NORM_NACK" messages).
The ACK process is self-limiting and avoids ACK implosion in that: The ACK process is self-limiting and avoids ACK implosion in that:
1) Only a single NORM_CMD(ACK_REQ) message is generated once per 1. Only a single "NORM_CMD(ACK_REQ)" message is generated once per
(2*GRTT), and, (2*GRTT), and,
2) The size of the "acking_node_list" of NormNodeIds from which 2. The size of the "acking_node_list" of NormNodeIds from which
acknowledgment is requested is limited to a maximum of the