draft-ietf-rmt-pi-norm-revised-11.txt   draft-ietf-rmt-pi-norm-revised-12.txt 
Network Working Group B. Adamson Network Working Group B. Adamson
Internet-Draft Naval Research Laboratory Internet-Draft Naval Research Laboratory
Obsoletes: 3940 (if approved) C. Bormann Obsoletes: 3940 (if approved) C. Bormann
Intended status: Standards Track Universitaet Bremen TZI Intended status: Standards Track Universitaet Bremen TZI
Expires: October 26, 2009 M. Handley Expires: November 29, 2009 M. Handley
University College London University College London
J. Macker J. Macker
Naval Research Laboratory Naval Research Laboratory
April 24, 2009 May 28, 2009
NACK-Oriented Reliable Multicast Protocol NACK-Oriented Reliable Multicast Protocol
draft-ietf-rmt-pi-norm-revised-11 draft-ietf-rmt-pi-norm-revised-12
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
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Trust the right to allow modifications of such material outside the Trust the right to allow modifications of such material outside the
IETF Standards Process. Without obtaining an adequate license from IETF Standards Process. Without obtaining an adequate license from
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and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
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This Internet-Draft will expire on October 26, 2009. This Internet-Draft will expire on November 29, 2009.
Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2009 IETF Trust and the persons identified as the
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This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
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2.1. Protocol Operation Overview . . . . . . . . . . . . . . . 11 2.1. Protocol Operation Overview . . . . . . . . . . . . . . . 11
2.2. Protocol Building Blocks . . . . . . . . . . . . . . . . . 13 2.2. Protocol Building Blocks . . . . . . . . . . . . . . . . . 13
2.3. Design Tradeoffs . . . . . . . . . . . . . . . . . . . . . 13 2.3. Design Tradeoffs . . . . . . . . . . . . . . . . . . . . . 13
3. Conformance Statement . . . . . . . . . . . . . . . . . . . . 14 3. Conformance Statement . . . . . . . . . . . . . . . . . . . . 14
4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 16 4. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 16
4.1. NORM Common Message Header and Extensions . . . . . . . . 16 4.1. NORM Common Message Header and Extensions . . . . . . . . 16
4.2. Sender Messages . . . . . . . . . . . . . . . . . . . . . 19 4.2. Sender Messages . . . . . . . . . . . . . . . . . . . . . 19
4.2.1. NORM_DATA Message . . . . . . . . . . . . . . . . . . 19 4.2.1. NORM_DATA Message . . . . . . . . . . . . . . . . . . 19
4.2.2. NORM_INFO Message . . . . . . . . . . . . . . . . . . 29 4.2.2. NORM_INFO Message . . . . . . . . . . . . . . . . . . 29
4.2.3. NORM_CMD Messages . . . . . . . . . . . . . . . . . . 30 4.2.3. NORM_CMD Messages . . . . . . . . . . . . . . . . . . 30
4.3. Receiver Messages . . . . . . . . . . . . . . . . . . . . 48 4.3. Receiver Messages . . . . . . . . . . . . . . . . . . . . 47
4.3.1. NORM_NACK Message . . . . . . . . . . . . . . . . . . 48 4.3.1. NORM_NACK Message . . . . . . . . . . . . . . . . . . 47
4.3.2. NORM_ACK Message . . . . . . . . . . . . . . . . . . . 54 4.3.2. NORM_ACK Message . . . . . . . . . . . . . . . . . . . 53
4.4. General Purpose Messages . . . . . . . . . . . . . . . . . 56 4.4. General Purpose Messages . . . . . . . . . . . . . . . . . 55
4.4.1. NORM_REPORT Message . . . . . . . . . . . . . . . . . 56 4.4.1. NORM_REPORT Message . . . . . . . . . . . . . . . . . 55
5. Detailed Protocol Operation . . . . . . . . . . . . . . . . . 56 5. Detailed Protocol Operation . . . . . . . . . . . . . . . . . 55
5.1. Sender Initialization and Transmission . . . . . . . . . . 58 5.1. Sender Initialization and Transmission . . . . . . . . . . 57
5.1.1. Object Segmentation Algorithm . . . . . . . . . . . . 59 5.1.1. Object Segmentation Algorithm . . . . . . . . . . . . 58
5.2. Receiver Initialization and Reception . . . . . . . . . . 60 5.2. Receiver Initialization and Reception . . . . . . . . . . 59
5.3. Receiver NACK Procedure . . . . . . . . . . . . . . . . . 60 5.3. Receiver NACK Procedure . . . . . . . . . . . . . . . . . 59
5.4. Sender NACK Processing and Response . . . . . . . . . . . 62 5.4. Sender NACK Processing and Response . . . . . . . . . . . 61
5.4.1. Sender Repair State Aggregation . . . . . . . . . . . 63 5.4.1. Sender Repair State Aggregation . . . . . . . . . . . 62
5.4.2. Sender FEC Repair Transmission Strategy . . . . . . . 64 5.4.2. Sender FEC Repair Transmission Strategy . . . . . . . 63
5.4.3. Sender NORM_CMD(SQUELCH) Generation . . . . . . . . . 65 5.4.3. Sender NORM_CMD(SQUELCH) Generation . . . . . . . . . 64
5.4.4. Sender NORM_CMD(REPAIR_ADV) Generation . . . . . . . . 65 5.4.4. Sender NORM_CMD(REPAIR_ADV) Generation . . . . . . . . 64
5.5. Additional Protocol Mechanisms . . . . . . . . . . . . . . 66 5.5. Additional Protocol Mechanisms . . . . . . . . . . . . . . 65
5.5.1. Greatest Round-trip Time Collection . . . . . . . . . 66 5.5.1. Greatest Round-trip Time Collection . . . . . . . . . 65
5.5.2. NORM Congestion Control Operation . . . . . . . . . . 67 5.5.2. NORM Congestion Control Operation . . . . . . . . . . 66
5.5.3. NORM Positive Acknowledgment Procedure . . . . . . . . 75 5.5.3. NORM Positive Acknowledgment Procedure . . . . . . . . 74
5.5.4. Group Size Estimate . . . . . . . . . . . . . . . . . 77 5.5.4. Group Size Estimate . . . . . . . . . . . . . . . . . 76
6. Security Considerations . . . . . . . . . . . . . . . . . . . 77 6. Security Considerations . . . . . . . . . . . . . . . . . . . 76
6.1. Baseline Secure NORM Operation . . . . . . . . . . . . . . 79 6.1. Baseline Secure NORM Operation . . . . . . . . . . . . . . 78
6.1.1. IPsec Approach . . . . . . . . . . . . . . . . . . . . 79 6.1.1. IPsec Approach . . . . . . . . . . . . . . . . . . . . 78
6.1.2. IPsec Requirements . . . . . . . . . . . . . . . . . . 82 6.1.2. IPsec Requirements . . . . . . . . . . . . . . . . . . 81
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 83 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 82
7.1. Explicit IANA Assignment Guidelines . . . . . . . . . . . 83 7.1. Explicit IANA Assignment Guidelines . . . . . . . . . . . 82
7.1.1. NORM Header Extension Types . . . . . . . . . . . . . 83 7.1.1. NORM Header Extension Types . . . . . . . . . . . . . 82
7.1.2. NORM Stream Control Codes . . . . . . . . . . . . . . 84 7.1.2. NORM Stream Control Codes . . . . . . . . . . . . . . 83
7.1.3. NORM_CMD Message Sub-types . . . . . . . . . . . . . . 85 7.1.3. NORM_CMD Message Sub-types . . . . . . . . . . . . . . 84
8. Suggested Use . . . . . . . . . . . . . . . . . . . . . . . . 86 8. Suggested Use . . . . . . . . . . . . . . . . . . . . . . . . 84
9. Changes from RFC3940 . . . . . . . . . . . . . . . . . . . . . 86 9. Changes from RFC3940 . . . . . . . . . . . . . . . . . . . . . 85
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 87 10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 86
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 87 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 86
11.1. Normative References . . . . . . . . . . . . . . . . . . . 87 11.1. Normative References . . . . . . . . . . . . . . . . . . . 86
11.2. Informative References . . . . . . . . . . . . . . . . . . 88 11.2. Informative References . . . . . . . . . . . . . . . . . . 87
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 90 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 89
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
distributed multicast session participation with minimal coordination distributed multicast session participation with minimal coordination
among senders and receivers. NORM allows senders and receivers to among senders and receivers. NORM allows senders and receivers to
dynamically join and leave multicast sessions at will with minimal dynamically join and leave multicast sessions at will with minimal
overhead for control information and timing synchronization among overhead for control information and timing synchronization among
participants. To accommodate this capability, NORM protocol message participants. To accommodate this capability, NORM protocol message
headers contain some common information allowing receivers to easily headers contain some common information allowing receivers to easily
synchronize to senders throughout the lifetime of a reliable synchronize to senders throughout the lifetime of a reliable
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 can 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. This document obsoletes the Experimental RFC 3940 delays. This document obsoletes the Experimental RFC 3940
specification. specification.
This document is a product of the IETF RMT working group and follows This document is a product of the IETF RMT working group and follows
the guidelines provided in the Author Guidelines for Reliable the guidelines provided in the Author Guidelines for Reliable
Multicast Transport (RMT) Building Blocks and Protocol Instantiation Multicast Transport (RMT) Building Blocks and Protocol Instantiation
documents [RFC3269]. documents [RFC3269].
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"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
1.2. NORM Data Delivery Service Model 1.2. 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 necessary a priori information for a specific NormSession (e.g.,
Session Description Protocol (SDP) [RFC4566], Session Announcement Session Description Protocol (SDP) [RFC4566], Session Announcement
Protocol (SAP) [RFC2974], 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. In future versions of NORM, it is
is possible that some aspects of protocol operation (e.g., round-trip possible that some aspects of protocol operation (e.g., round-trip
time collection) may provide for alternate modes allowing more time collection) will 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 to allocate for
allocated for received content (i.e., memory or file storage). Other received content (i.e., memory or file storage). Other than that
than that distinction, the two are identical, providing for reliable distinction, the two are identical, providing for reliable transport
transport of finite (but potentially very large) units of content. 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" transport object types, too. The use of the "NORM_OBJECT_STREAM"
type is at the application's discretion and could be used to carry type is at the application's discretion and could be used to carry
static data or file content also. The NORM reliable stream service static data or file content also. The NORM reliable stream service
opens up additional possibilities such as serialized reliable opens up additional possibilities such as serialized reliable
messaging or other unbounded, perhaps dynamically produced content. messaging or other unbounded, perhaps dynamically produced content.
The "NORM_OBJECT_STREAM" provides for reliable transport analogous to The "NORM_OBJECT_STREAM" provides for reliable transport analogous to
that of the Transmission Control Protocol (TCP), although NORM that of the Transmission Control Protocol (TCP), although NORM
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of data content within in its message headers. Note the "NORM_INFO" of data content within in its message headers. Note the "NORM_INFO"
out-of-band data mechanism could be leveraged by the application for out-of-band data mechanism could be leveraged by the application for
this purpose if desired, or identification could alternatively be this purpose if desired, or identification could alternatively be
embedded within the data content. NORM does identify transmitted embedded within the data content. NORM does identify transmitted
content (NormObjects) with transport identifiers that are applicable content (NormObjects) with transport identifiers that are applicable
only while the sender is transmitting and/or repairing the given only while the sender is transmitting and/or repairing the given
object. These transport data content identifiers (NormTransportIds) object. These transport data content identifiers (NormTransportIds)
are assigned in a monotonically increasing fashion by each NORM are assigned in a monotonically increasing fashion by each NORM
sender during the course of a NormSession. Each sender maintains its sender during the course of a NormSession. Each sender maintains its
NormTransportId assignments independently so that individual NormTransportId assignments independently so that individual
NormObjects may be uniquely identified during transport with the NormObjects can be uniquely identified during transport with the
concatenation of the sender session-unique identifier (NormNodeId) concatenation of the sender session-unique identifier (NormNodeId)
and the assigned NormTransportId. The NormTransportIds are assigned and the assigned NormTransportId. The NormTransportIds are assigned
from a large, but fixed, numeric space in increasing order and may be from a large, but fixed, numeric space in increasing order and will
reassigned during long-lived sessions. The NORM protocol provides be reassigned during long-lived sessions. The NORM protocol provides
mechanisms so that the sender application may terminate transmission mechanisms so that the sender application can terminate transmission
of data content and inform the group of this in an efficient manner. of data content and inform the group of this in an efficient manner.
Other similar protocol control mechanisms (e.g., session termination, Other similar protocol control mechanisms (e.g., session termination,
receiver synchronization, etc.) are specified so that reliable receiver synchronization, etc.) are specified so that reliable
multicast application variants may construct different, complete bulk multicast application variants can realize different, complete bulk
transfer communication models to meet their goals. transfer communication models to 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.
1.3. NORM Scalability 1.3. 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 [RmComparison]. NORM is a protocol for reliability is needed [RmComparison]. NORM is a protocol
centered around the use of selective NACKs to request repairs of centered around the use of selective NACKs to request repairs of
missing data. NORM provides for the use of packet-level forward missing data. NORM provides for the use of packet-level forward
error correction (FEC) techniques for efficient multicast repair and error correction (FEC) techniques for efficient multicast repair and
optional proactive transmission robustness [RFC3453]. FEC-based OPTIONAL proactive transmission robustness [RFC3453]. FEC-based
repair can be used to greatly reduce the quantity of reliable repair can be used to greatly reduce the quantity of reliable
multicast repair requests and repair transmissions [MdpToolkit] in a multicast repair requests and repair transmissions [MdpToolkit] in a
NACK-oriented protocol. The principal factor in NORM scalability is NACK-oriented protocol. The principal factor in NORM scalability is
the volume of feedback traffic generated by the receiver set to the volume of feedback traffic generated by the receiver set to
facilitate reliability and congestion control. NORM uses facilitate reliability and congestion control. NORM uses
probabilistic suppression of redundant feedback based on probabilistic suppression of redundant feedback based on
exponentially distributed random backoff timers. The performance of exponentially distributed random backoff timers. The performance of
this type of suppression relative to other techniques is described in this type of suppression relative to other techniques is described in
[McastFeedback]. NORM dynamically measures the group's round-trip [McastFeedback]. NORM dynamically measures the group's round-trip
timing status to set its suppression and other protocol timers. This timing status to set its suppression and other protocol timers. This
allows NORM to scale well while maintaining reliable data delivery allows NORM to scale well while maintaining reliable data delivery
transport with low latency relative to the network topology over transport with low latency relative to the network topology over
which it is operating. 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 relays 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 the NORM protocol will readily scale to group sizes on the order of
sizes on the order of tens of thousands of receivers. A study of the tens of thousands of receivers. A study of the quantity of feedback
quantity of feedback for this type of protocol is described in for this type of protocol is described in [NormFeedback]. NORM is
[NormFeedback]. NORM is able to operate with a smaller amount of able to operate with a smaller amount of feedback than a single TCP
feedback than a single TCP connection, even with relatively large connection, even with relatively large numbers of receivers. Thus,
numbers of receivers. Thus, depending upon the network topology, it depending upon the network topology, it is possible for NORM to scale
is possible that NORM may scale to larger group sizes. With respect to larger group sizes. With respect to computer resource usage, the
to computer resource usage, the NORM protocol does NOT require that NORM protocol does not need state to be kept on all receivers in the
state be kept on all receivers in the group. NORM senders maintain group. NORM senders maintain state only for receivers providing
state only for receivers providing explicit congestion control explicit congestion control feedback. However, NORM receivers need
feedback. However, NORM receivers must maintain state for each to maintain state for each active sender. This can constrain the
active sender. This may constrain the number of simultaneous senders number of simultaneous senders in some uses of NORM.
in some uses of NORM.
1.4. Environmental Requirements and Considerations 1.4. Environmental Requirements and Considerations
All of the environmental requirements and considerations that apply All of the environmental requirements and considerations that apply
to the Multicast NACK Building Block [RFC5401], FEC Building Block to the Multicast NACK Building Block [RFC5401], FEC Building Block
[RFC5052], and TCP-Friendly Multicast Congestion Control (TFMCC) [RFC5052], and TCP-Friendly Multicast Congestion Control (TFMCC)
Building Block [RFC4654] also apply to the NORM protocol. 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 Host Extensions for IP Multicasting [RFC1112], (ASM) model defined in Host Extensions for IP Multicasting [RFC1112],
but SHALL also be capable of scalable operation in asymmetric but SHALL also be capable of scalable operation in asymmetric
topologies such as Source-Specific Multicast (SSM) [RFC4607] where topologies such as Source-Specific Multicast (SSM) [RFC4607] where
there may only be unicast routing service from the receivers to the only unicast routing service is available from the receivers to the
sender(s). sender(s).
NORM is compatible with IPv4 and IPv6. Additionally, NORM may be NORM is compatible with IPv4 and IPv6. Additionally, NORM can 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
skipping to change at page 10, line 7 skipping to change at page 10, line 6
(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 "wild card" NormNodeId. While the protocol does "0xffffffff" is a "wild card" NormNodeId. While the protocol does
not preclude multiple sender nodes concurrently transmitting within not preclude multiple sender nodes concurrently transmitting within
the context of a single NORM session (i.e., many- to-many operation), the context of a single NORM session (i.e., many- to-many operation),
any type of interactive coordination among NORM senders is assumed to any type of interactive coordination among NORM senders is assumed to
be 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 "NORM_OBJECT_DATA", which is used for static, persistent blocks of
data content maintained in the sender's application memory storage. data content maintained in the sender's application memory storage.
The second type is "NORM_OBJECT_FILE", which corresponds to data The second type is "NORM_OBJECT_FILE", which corresponds to data
stored in the sender's non-volatile file system. The stored in the sender's non-volatile file system. The
"NORM_OBJECT_DATA" and "NORM_OBJECT_FILE" types both represent "NORM_OBJECT_DATA" and "NORM_OBJECT_FILE" types both represent
NormObjects of finite but potentially very large size. The third NormObjects of finite but potentially very large size. The third
type of data content is "NORM_OBJECT_STREAM", which corresponds to an type of data content is "NORM_OBJECT_STREAM", which corresponds to an
ongoing transmission of undefined length. This is analogous to the ongoing transmission of undefined length. This is analogous to the
reliable stream service provide by TCP for unicast data transport. reliable stream service provide by TCP for unicast data transport.
The format of the stream content is application-defined and may be The format of the stream content is application-defined and can be
byte or message oriented. The NORM protocol provides for "flushing" "byte" or "message" oriented. The NORM protocol provides for
of the stream to expedite delivery or possibly enforce application "flushing" of the stream to expedite delivery or possibly enforce
message boundaries. NORM protocol implementations may offer either application message boundaries. NORM protocol implementations MAY
(or both) in-order delivery of the stream data to the receive offer either (or both) in-order delivery of the stream data to the
application or out-of-order (more immediate) delivery of received receive application or out-of-order (more immediate) delivery of
segments of the stream to the receiver application. In either case, received segments of the stream to the receiver application. In
NORM sender and receiver implementations provide buffering to either case, NORM sender and receiver implementations provide
facilitate repair of the stream as it is transported. buffering to 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 needs to receive a sufficient number of symbols to
(via FEC decoding) the original user data for the given block. reconstruct (via FEC decoding) the original user data for the given
block.
Transmitted NormObjects are temporarily yet uniquely identified Transmitted NormObjects are temporarily yet uniquely identified
within the NormSession context using the given sender's 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 can manage their
NormInstanceIds independently, or a common NormInstanceId may be NormInstanceIds independently, or a common NormInstanceId could 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 will 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 necessary, is expected to be managed by the NORM
individual segments or symbols of the NormObject are further application. The individual segments or symbols of the NormObject
identified with FEC payload identifiers which include coding block are further identified with FEC payload identifiers which include
and symbol identifiers. These are discussed in detail later in this coding block and symbol identifiers. These are discussed in detail
document. later in this document.
2.1. Protocol Operation Overview 2.1. Protocol Operation Overview
A NORM sender primarily generates messages of type "NORM_DATA". A NORM sender primarily generates messages of type "NORM_DATA".
These 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 configured to
configured to proactively transmit some amount of redundant FEC proactively transmit some amount of redundant FEC symbols along with
symbols along with the original content to potentially enhance the original content to potentially enhance performance (e.g.,
performance (e.g., improved delay) at the cost of additional improved delay) at the cost of additional transmission overhead.
transmission overhead. This option may be sensible for certain This configuration is sensible for certain network conditions and can
network conditions and can allow for robust, asymmetric multicast allow for robust, asymmetric multicast (e.g., unidirectional routing,
(e.g., unidirectional routing, satellite, cable) [FecHybrid] with satellite, cable) [FecHybrid] with reduced receiver feedback, or, in
reduced receiver feedback, or, in some cases, no feedback. 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 transport carry OPTIONAL out-of-band context information for a given transport
object. A single "NORM_INFO" message can be associated with a object. A single "NORM_INFO" message can be associated with 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" process than NORM's general FEC-encoded data content. The
may serve special purposes for some bulk transfer, reliable multicast "NORM_INFO" message can serve special purposes for some bulk
applications where receivers join the group mid-stream and need to transfer, reliable multicast applications where receivers join the
ascertain contextual information on the current content being group mid-stream and need to ascertain contextual information on the
transmitted. The NACK process for "NORM_INFO" will be described current content being transmitted. The NACK process for "NORM_INFO"
later. When the "NORM_INFO" message type is used, its transmission will be described later. When the "NORM_INFO" message type is used,
should precede transmission of any "NORM_DATA" message for the its transmission SHOULD precede transmission of any "NORM_DATA"
associated NormObject. message for the 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" application defined commands. The transmission of "NORM_CMD"
messages from the sender is accomplished by one of three different messages from the sender is accomplished by one of three different
procedures. These procedures are: single, best effort unreliable procedures. These procedures are: single, best effort unreliable
transmission of the command; repeated redundant transmissions of the transmission of the command; repeated redundant transmissions of the
command; and positively-acknowledged commands. The transmission command; and positively-acknowledged commands. The transmission
technique used for a given command depends upon the function of the technique used for a given command depends upon the function of the
command. Several core commands are defined for basic protocol command. Several core commands are defined for basic protocol
operation. Additionally, implementations MAY wish to consider operation. Additionally, implementations MAY wish to consider
providing the OPTIONAL application-defined commands that can take providing the OPTIONAL application-defined commands that can take
advantage of the transmission methodologies available for commands. advantage of the transmission methodologies available for commands.
This allows for application-level session management mechanisms that This allows for application-level session management mechanisms that
can make use of information available to the underlying NORM protocol can make use of information available to the underlying NORM protocol
engine (e.g., round-trip timing, transmission rate, etc.). A notable engine (e.g., round-trip timing, transmission rate, etc.). A notable
distinction between "NORM_DATA" message and some "NORM_CMD" message distinction between "NORM_DATA" message and some "NORM_CMD" message
transmissions is that typically a receiver will need to allocate transmissions is that typically a receiver will need to allocate
resources to manage reliable reception when "NORM_DATA" messages are resources to manage reliable reception when "NORM_DATA" messages are
received. However some "NORM_CMD" messages may be completely atomic received. However some "NORM_CMD" messages are completely atomic and
and no specific state may need to be kept. Thus, for session no specific reliability (buffering) state needs to be kept. Thus,
management or other purposes it is possible that even participants for session management or other purposes it is possible that even
acting principally as data receivers MAY transmit "NORM_CMD" participants acting principally as data receivers MAY transmit
messages. However, it is RECOMMENDED that this is not done within "NORM_CMD" messages. However, it is RECOMMENDED that this is not
the context of the NORM multicast session unless congestion control done within the context of the NORM multicast session unless
is addressed. For example, many receiver nodes transmitting congestion control is addressed. For example, many receiver nodes
"NORM_CMD" messages simultaneously can cause congestion for the transmitting "NORM_CMD" messages simultaneously can cause congestion
destination(s). 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 NORM's 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 is 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
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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 Multicast NACK Building Block [RFC5401] concepts presented in the Multicast NACK Building Block [RFC5401]
document. This includes the basic NORM architecture and the data document. This includes the basic NORM architecture and the data
transmission, repair, and feedback strategies discussed in that transmission, repair, and feedback strategies discussed in that
document. The reliable multicast building block approach, as document. The reliable multicast building block approach, as
described in Reliable Multicast Transport Building Blocks for One-to- described in Reliable Multicast Transport Building Blocks for One-to-
Many Bulk-Data Transfer [RFC3048], is applied in creating the full Many Bulk-Data Transfer [RFC3048], is applied in creating the full
NORM protocol instantiation. NORM also makes use of the parity-based NORM protocol instantiation. NORM also makes use of the parity-based
encoding techniques for repair messaging and optional transmission encoding techniques for repair messaging and added transmission
robustness as described in The Use of Forward Error Correction (FEC) robustness as described in The Use of Forward Error Correction (FEC)
in Reliable Multicast [RFC3453]. NORM uses the FEC Payload ID as in Reliable Multicast [RFC3453]. NORM uses the FEC Payload ID as
specified by the FEC Building Block document [RFC5052]. specified by the FEC Building Block document [RFC5052].
Additionally, for congestion control, this document fully specifies a Additionally, for congestion control, this document fully specifies a
baseline congestion control mechanism (NORM-CC) based on the TCP- baseline congestion control mechanism (NORM-CC) based on the TCP-
Friendly Multicast Congestion Control (TFMCC) scheme[TfmccPaper], Friendly Multicast Congestion Control (TFMCC) scheme[TfmccPaper],
[RFC4654]. [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 trade-offs 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 necessitates an
awareness of application and network architecture considerations. increased awareness of application and network architecture
Performance requirements affecting design can include: group size, considerations. Performance requirements affecting design can
heterogeneity (e.g., capacity and/or delay), asymmetric delivery, include: group size, heterogeneity (e.g., capacity and/or delay),
data ordering, delivery delay, group dynamics, mobility, congestion asymmetric delivery, data ordering, delivery delay, group dynamics,
control, and transport across low capacity connections. NORM mobility, congestion control, and transport across low capacity
contains various parameters to accommodate many of these differing connections. NORM contains various parameters to accommodate many of
requirements. The NORM protocol and its mechanisms MAY be applied in these differing requirements. The NORM protocol and its mechanisms
multicast applications outside of bulk data transfer, but there is an MAY be applied in multicast applications outside of bulk data
assumed model of bulk transfer transport service that drives the transfer, but there is an assumed model of bulk transfer transport
trade-offs that determine the scalability and performance described service that drives the trade-offs that determine the scalability and
in this document. performance described in this document.
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-
skipping to change at page 14, line 34 skipping to change at page 14, line 34
working reliable multicast transport protocol that conforms to the working reliable multicast transport protocol that conforms to the
requirements described in RFC 2357. requirements described in RFC 2357.
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 | | | transmission. Implementations MUST |
| | support at least one of the | | | support at least one of the |
| | "NORM_OBJECT_DATA", "NORM_OBJECT_FILE", | | | "NORM_OBJECT_DATA", "NORM_OBJECT_FILE", |
| | or "NORM_OBJECT_STREAM" delivery | | | or "NORM_OBJECT_STREAM" delivery |
| | services. The use of the NORM FEC | | | 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" transmissions. Note the use | | | "NORM_DATA" transmissions. Note the use |
skipping to change at page 15, line 12 skipping to change at page 15, line 12
| | valid repair window in response to | | | valid repair window in response to |
| | invalid requests for repair. | | | invalid requests for repair. |
| "NORM_CMD(REPAIR_ADV)" | Sender command to advertise current | | "NORM_CMD(REPAIR_ADV)" | Sender command to advertise current |
| | repair (and congestion control state) to | | | repair (and congestion control state) to |
| | group when unicast feedback messages are | | | group when unicast feedback messages are |
| | detected. Used to control/suppress | | | detected. Used to control/suppress |
| | excessive receiver feedback in | | | excessive receiver feedback in |
| | asymmetric multicast topologies. | | | asymmetric multicast topologies. |
| "NORM_CMD(CC)" | Sender command used in collection of | | "NORM_CMD(CC)" | Sender command used in collection of |
| | round trip timing and congestion control | | | round trip timing and congestion control |
| | status from group (this may be OPTIONAL | | | status from group (this is OPTIONAL if |
| | if alternative congestion control | | | alternative congestion control mechanism |
| | mechanism and round trip timing | | | and round trip timing collection is |
| | collection is used). | | | used). |
| "NORM_NACK" | Receiver message used to request repair | | "NORM_NACK" | Receiver message used to request repair |
| | of missing transmitted content. | | | of missing transmitted content. |
| "NORM_ACK" | Receiver message used to proactively | | "NORM_ACK" | Receiver message used to proactively |
| | provide feedback for congestion control | | | provide feedback for congestion control |
| | purposes. Also used with the OPTIONAL | | | purposes. Also used with the OPTIONAL |
| | NORM Positive Acknowledgment Process. | | | 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
skipping to change at page 16, line 11 skipping to change at page 16, line 11
| | application-defined commands sent | | | application-defined commands sent |
| | outside of the context of the bulk data | | | outside of the context 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 protocol. | | | NORM protocol. |
+-------------------------+-----------------------------------------+ +-------------------------+-----------------------------------------+
4. Message Formats 4. Message Formats
As mentioned in Section 2.1, there are two primary classes of NORM There are two primary classes of NORM messages (see Section 2.1):
messages: sender messages and receiver messages. "NORM_CMD", sender messages and receiver messages. "NORM_CMD", "NORM_INFO", and
"NORM_INFO", and "NORM_DATA" message types are generated by senders "NORM_DATA" message types are generated by senders of data content,
of data content, and "NORM_NACK" and "NORM_ACK" messages generated by and "NORM_NACK" and "NORM_ACK" messages generated by receivers within
receivers within a NormSession. Sender messages SHOULD be governed a NormSession. Sender messages SHALL be governed by congestion
by congestion control for Internet use. For session management or control for Internet use. For session management or other purposes,
other purposes, receivers may wish to employ "NORM_CMD" message receivers can also employ "NORM_CMD" message transmissions. The
transmissions. The principal rationale for distinguishing sender and principal rationale for distinguishing sender and receiver messages
receiver messages is that receivers will typically need to allocate is that receivers will typically need to allocate resources to
resources to support reliable reception from sender(s) and NORM support reliable reception from sender(s) and NORM sender messages
sender messages are subject to congestion control. NORM receivers are subject to congestion control. NORM receivers MAY employ the
MAY employ the "NORM_CMD" message type for application-defined "NORM_CMD" message type for application-defined purposes but it is
purposes but it is RECOMMENDED that congestion control and feedback RECOMMENDED that congestion control and feedback implosion issues be
implosion issues be addressed. Additionally, an auxiliary message addressed. Additionally, an auxiliary message type of "NORM_REPORT"
type of "NORM_REPORT" is also provided for experimental purposes. is also provided for experimental purposes. This section describes
This section describes the message formats used by the NORM protocol. the message formats used by the NORM protocol. These messages and
These messages and their fields are referenced in the detailed their fields are referenced in the detailed functional description of
functional description of the NORM protocol given in Section 5. the NORM protocol given in Section 5. Individual NORM messages are
Individual NORM messages are designed to be compatible with the MTU designed to be compatible with the MTU limitations of encapsulating
limitations of encapsulating Internet protocols including IPv4, IPv6, Internet protocols including IPv4, IPv6, and UDP. The current NORM
and UDP. The current NORM protocol specification assumes UDP protocol specification assumes UDP encapsulation and leverages the
encapsulation and leverages the transport features of UDP. The NORM transport features of UDP. The NORM messages are independent of
messages are independent of network addresses and can be used in IPv4 network addresses and can be used in IPv4 and IPv6 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
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 are 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_INFO" | 1 |
| "NORM_DATA" | 2 | | "NORM_DATA" | 2 |
| "NORM_CMD" | 3 | | "NORM_CMD" | 3 |
| "NORM_NACK" | 4 | | "NORM_NACK" | 4 |
| "NORM_ACK" | 5 | | "NORM_ACK" | 5 |
| "NORM_REPORT" | 6 | | "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 message's 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 addition of header extensions. The presence of header
header extensions are implied when the "hdr_len" value is greater extensions are implied when the "hdr_len" value is greater than the
than the base value for the given message "type". 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. The "sequence" field serves two separate purposes, originator. The "sequence" field serves two separate purposes,
depending upon the message type: depending upon the message type:
1. NORM senders MUST set the "sequence" field of sender messages 1. NORM senders MUST set the "sequence" field of sender messages
("NORM_INFO", "NORM_DATA", and "NORM_CMD") so that receivers can ("NORM_INFO", "NORM_DATA", and "NORM_CMD") so that receivers can
monitor the "sequence" value to maintain an estimate of packet monitor the "sequence" value to maintain an estimate of packet
loss that can be used for congestion control purposes (See loss that can be used for congestion control purposes (See
Section 5.5.2 for a detailed description of NORM Congestion Section 5.5.2 for a detailed description of NORM Congestion
Control operation). A monotonically-increasing sequence number Control operation). A monotonically-increasing sequence number
space MUST be maintained to mark NORM sender messages in this space MUST be maintained to mark NORM sender messages in this
way. Note that this "sequence" number is explicitly NOT used in way. Note that this "sequence" number is explicitly NOT used in
NORM as part of its reliability procedures. The NORM object and NORM as part of its reliability procedures. The NORM object and
FEC payload identifiers are used to detect missing content for FEC payload identifiers are used to detect missing content for
reliable transfer purposes. reliable transfer purposes.
2. NORM receivers SHOULD set the "sequence" field to support 2. NORM receivers SHOULD set the "sequence" field to support
protection from message replay attacks of "NORM_NACK" or protection from message replay attacks of "NORM_NACK" or
"NORM_NACK" messages. Note that, depending upon configuration, "NORM_NACK" messages. Note that, depending upon configuration,
NORM feedback messages may be sent to the session multicast NORM feedback messages are sent to the session multicast address
address or unicast address[es] of the active NORM sender[s]. or the unicast address[es] of the active NORM sender[s]. Thus, a
Thus, a separate, monotonically-increasing sequence number space separate, monotonically-increasing sequence number space MUST be
MUST be maintained for each destination address to which the NORM maintained for each destination address to which the NORM
receiver is transmitting feedback messages. receiver is transmitting feedback messages.
Note that these two separate purposes necessitate the maintenance of Note that these two separate purposes necessitate the maintenance of
separate sequence spaces to support the functions described here. separate sequence spaces to support the functions described here.
And, in the case of NORM receivers, additional sequence spaces are And, in the case of NORM receivers, additional sequence spaces are
needed when feedback messages are sent to the sender unicast needed when feedback messages are sent to the sender unicast
address[es] instead of the session address. address[es] instead of the session address.
The "source_id" field is a 32-bit value that uniquely identifies the The "source_id" field is a 32-bit value that uniquely identifies the
node that sent the message within the context of a single node that sent the message within the context of a single
skipping to change at page 19, line 26 skipping to change at page 19, line 18
4.2. Sender Messages 4.2. Sender Messages
NORM sender messages include the "NORM_DATA" type, the "NORM_INFO" NORM sender messages include the "NORM_DATA" type, the "NORM_INFO"
type, and the "NORM_CMD" type. "NORM_DATA" and "NORM_INFO" messages type, and the "NORM_CMD" type. "NORM_DATA" and "NORM_INFO" messages
contain application data content while "NORM_CMD" messages are used contain application data content while "NORM_CMD" messages are used
for various 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 generally the predominant type transmitted
transmitted by NORM senders. These messages are used to encapsulate by NORM senders. These messages are used to encapsulate segmented
segmented data content for objects of type "NORM_OBJECT_DATA", data content for objects of type "NORM_OBJECT_DATA",
"NORM_OBJECT_FILE", and "NORM_OBJECT_STREAM". "NORM_DATA" messages "NORM_OBJECT_FILE", and "NORM_OBJECT_STREAM". "NORM_DATA" messages
may contain original or FEC-encoded application data content. 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
skipping to change at page 20, line 36 skipping to change at page 20, line 36
| payload_data* | | payload_data* |
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
NORM_DATA Message Format NORM_DATA Message Format
*IMPORTANT NOTE: The "payload_len", "payload_msg_start" and *IMPORTANT NOTE: The "payload_len", "payload_msg_start" and
"payload_offset" fields are present ONLY for objects of type "payload_offset" fields are present ONLY for objects of type
"NORM_OBJECT_STREAM". These fields, as with the entire payload, are "NORM_OBJECT_STREAM". These fields, as with the entire payload, are
subject to any FEC encoding used. Thus, when systematic FEC codes subject to any FEC encoding used. Thus, when systematic FEC codes
are used, these values may be directly interpreted for packets are used, these values can be directly interpreted for packets
containing source symbols only while packets containing FEC parity containing source symbols only while packets containing FEC parity
content require decoding before these fields can be interpreted. content need decoding before these fields can be interpreted.
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 (i.e. 4 32-bit words) plus the size of the "hdr_len" value is 4 (i.e. 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 type referenced by the "fec_id" field. For example, the FEC encoding type referenced by the "fec_id" field. For example,
when small block, systematic codes are used, a "fec_id" value of 129 when small block, systematic codes are used, a "fec_id" value of 129
is indicated and the size of the "fec_payload_id" is two 32-bit is indicated and the size of the "fec_payload_id" is two 32-bit
words. In this case the "NORM_DATA" base "hdr_len" value is 6. The words. In this case the "NORM_DATA" base "hdr_len" value is 6. The
skipping to change at page 21, line 45 skipping to change at page 21, line 45
The "gsize" field contains a representation of the sender's current The "gsize" field contains a representation of the sender's current
estimate of group size. This 4-bit field can roughly represent estimate of group size. This 4-bit field can roughly represent
values from ten to 500 million where the most significant bit value values from ten to 500 million where the most significant bit value
of 0 or 1 represents a mantissa of 1 or 5, respectively and the three of 0 or 1 represents a mantissa of 1 or 5, respectively and the three
least significant bits incremented by one represent a base 10 least significant bits incremented by one represent a base 10
exponent (order of magnitude). For examples, a field value of "0x0" exponent (order of magnitude). For examples, a field value of "0x0"
represents 1.0e+01 (10), a value of "0x8" represents 5.0e+01 (50), a represents 1.0e+01 (10), a value of "0x8" represents 5.0e+01 (50), a
value of "0x1" represents 1.0e+02 (100), and a value of "0xf" value of "0x1" represents 1.0e+02 (100), and a value of "0xf"
represents 5.0e+08. For NORM feedback suppression purposes, the represents 5.0e+08. For NORM feedback suppression purposes, the
group size does not need to be represented with a high degree of group size does not need to be represented with a high degree of
precision. The group size may even be estimated somewhat precision. The group size MAY even be estimated somewhat
conservatively (i.e., overestimated) to maintain low levels of conservatively (i.e., overestimated) to maintain low levels of
feedback traffic. A default group size estimate of 10,000 ("gsize" = feedback traffic. A default group size estimate of 10,000 ("gsize" =
0x3) is recommended for general purpose reliable multicast 0x3) is RECOMMENDED for general purpose reliable multicast
applications using the NORM protocol. 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 for the receiver to appropriately
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 meet a specific | | | | intended to meet a specific |
| | | receiver erasure, as compared to | | | | receiver erasure, as compared to |
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"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 of new (non-repair) data content. "NORM_FLAG_EXPLICIT" is used to
mark repair messages sent when the data sender has exhausted its mark repair messages sent when the data sender has exhausted its
ability to provide "fresh" (not previously transmitted) parity ability to provide "fresh" (not previously transmitted) parity
segments as repair. This flag could possibly be used by intermediate segments as repair. This flag could possibly be used by intermediate
systems implementing functionality to control sub-casting of repair systems implementing functionality to control sub-casting of repair
content to different legs of a reliable multicast topology with content to different legs of a reliable multicast topology with
disparate repair needs. "NORM_FLAG_INFO" is set only when optional disparate repair needs. "NORM_FLAG_INFO" is set only when OPTIONAL
"NORM_INFO" content is actually available for the associated object. "NORM_INFO" content is actually available for the associated object.
Thus, receivers will NACK for retransmission of "NORM_INFO" only when Thus, receivers will NACK for retransmission of "NORM_INFO" only when
it is available for a given object. "NORM_FLAG_UNRELIABLE" is set it is available for a given object. "NORM_FLAG_UNRELIABLE" is set
when the sender wishes to transmit an object with only "best effort" when the sender wishes to transmit an object with only "best effort"
delivery and will not supply repair transmissions for the object. delivery and will not supply repair transmissions for the object.
NORM receivers SHOULD NOT execute repair requests for objects marked NORM receivers SHOULD NOT execute repair requests for objects marked
with the "NORM_FLAG_UNRELIABLE" flag. Note that receivers may with the "NORM_FLAG_UNRELIABLE" flag. There are cases where
inadvertently request repair of such objects when all segments (or receivers can inadvertently request repair of such objects when all
info content) for those objects are not received (i.e., a gap in the segments (or info content) for those objects are not received (i.e.,
"object_transport_id" sequence is noted). In this case, the sender a gap in the "object_transport_id" sequence is noted). In this case,
should invoke the "NORM_CMD(SQUELCH)" process as described in the sender SHALL invoke the "NORM_CMD(SQUELCH)" process as described
Section 4.2.3. in Section 4.2.3.
"NORM_FLAG_FILE" can be set as a hint from the sender that the "NORM_FLAG_FILE" can be set as a hint from the sender that the
associated object should be stored in non-volatile storage. associated object SHOULD be stored in non-volatile storage.
"NORM_FLAG_STREAM" is set when the identified object is of type "NORM_FLAG_STREAM" is set when the identified object is of type
"NORM_OBJECT_STREAM". The presence of "NORM_FLAG_STREAM" overrides "NORM_OBJECT_STREAM". The presence of "NORM_FLAG_STREAM" overrides
that of "NORM_FLAG_FILE" with respect to interpretation of object that of "NORM_FLAG_FILE" with respect to interpretation of object
size and the format of "NORM_DATA" messages. 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 [RFC5052]. The "fec_id" described in the FEC Building Block document [RFC5052]. The "fec_id"
value implies the format of the "fec_payload_id" field and, coupled value implies the format of the "fec_payload_id" field and, coupled
with FEC Object Transmission Information, the procedures to decode with FEC Object Transmission Information, the procedures to decode
FEC encoded content. Small block, systematic codes ("fec_id" = 129) FEC encoded content. Small block, systematic codes ("fec_id" = 129)
are expected to be used for most NORM purposes and the are expected to be used for most NORM purposes and systematic FEC
"NORM_OBJECT_STREAM" requires systematic FEC codes for most efficient codes are RECOMMENDED for most efficient performance of
performance. "NORM_OBJECT_STREAM" transport.
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
be repeated, but it is presumed that the 16-bit field size provides will wrap and be repeated, but it is presumed that the 16-bit field
an adequate enough sequence space to avoid object confusion amongst size provides a sufficient sequence space to avoid object confusion
receivers and sources (i.e., receivers SHOULD re-synchronize with a amongst receivers and sources (i.e., receivers SHOULD re-synchronize
server when receiving object sequence identifiers sufficiently out- with a server when receiving object sequence identifiers sufficiently
of-range with the current state kept for a given source). During the out-of-range with the current state kept for a given source). During
course of its transmission within a NORM session, an object is the 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 such as those given in the descriptions of specific FEC schemes such as those
described in the FEC Basic Schemes [RFC5445] specification or in described in the FEC Basic Schemes [RFC5445] specification or in
skipping to change at page 24, line 23 skipping to change at page 24, line 23
Example: FEC Payload Id Format for 'fec_id' = 129 Example: FEC Payload Id Format for '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 for Small Block Systematic FEC fields of the FEC Payload ID format for Small Block Systematic FEC
Schemes identified by a "fec_id" value of 129 as specified by the FEC Schemes identified by a "fec_id" value of 129 as specified by the FEC
Basic Schemes [RFC5445] specification. The "source_block_number" Basic Schemes [RFC5445] specification. The "source_block_number"
identifies the coding block's relative position with a NormObject. identifies the coding block's relative position with a NormObject.
Note that, for NormObjects of type "NORM_OBJECT_STREAM", the Note that, for NormObjects of type "NORM_OBJECT_STREAM", the
"source_block_number" may wrap for very long lived sessions. The "source_block_number" will wrap for very long lived sessions. The
"source_block_len" indicates the number of user data segments in the "source_block_len" indicates the number of user data segments in the
identified coding block. Given the "source_block_len" information of identified coding block. Given the "source_block_len" information of
how many symbols of application data are contained in the block, the how many symbols of application data are contained in the block, the
receiver can determine whether the attached segment is data or parity receiver can determine whether the attached segment is data or parity
content and treat it appropriately. Some applications may content and treat it appropriately. Applications MAY dynamically
dynamically "shorten" code blocks when the pending information "shorten" code blocks when the pending information content is not
content is not predictable (e.g. real-time message streams). In that predictable (e.g. real-time message streams). In that case, the
case, the "source_block_len" value given for an "encoding_symbol_id" "source_block_len" value given for an "encoding_symbol_id" that
that contains FEC parity content SHALL take precedence over the contains FEC parity content SHALL take precedence over the
"source_block_len" value provided for any packets containing source "source_block_len" value provided for any packets containing source
symbols. Also, the "source_block_len" value given for an ordinally symbols. Also, the "source_block_len" value given for an ordinally
higher "encoding_symbol_id" SHALL take precedence over the 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 will only know the maximum source block
at the time is transmitting source symbols, but then subsequently length at the time is transmitting source symbols, but then
"shorten" the code and then provide that last source symbol and/or subsequently "shorten" the code and then provide that last source
encoding symbols with FEC parity content. The "encoding_symbol_id" symbol and/or encoding symbols with FEC parity content. The
identifies which specific symbol (segment) within the coding block "encoding_symbol_id" identifies which specific symbol (segment)
the attached payload conveys. Depending upon the value of the within the coding block the attached payload conveys. Depending upon
"encoding_symbol_id" and the associated "source_block_len" parameters the value of the "encoding_symbol_id" and the associated
for the block, the symbol (segment) referenced may be a user data or "source_block_len" parameters for the block, the symbol (segment)
an FEC parity segment. For systematic codes, encoding symbols referenced will be a user data or an FEC parity segment. For
numbered less than the "source_block_len" contain original systematic codes, encoding symbols numbered less than the
application data while segments greater than or equal to "source_block_len" contain original application data while segments
"source_block_len" contain parity symbols calculated for the block. greater than or equal to "source_block_len" contain parity symbols
The concatenation of "object_transport_id::fec_payload_id" can be calculated for the block. The concatenation of
viewed as a unique transport protocol data unit identifier for the "object_transport_id::fec_payload_id" can be viewed as a unique
attached segment with respect to the NORM sender's instance within a transport protocol data unit identifier for the attached segment with
session. respect to the NORM sender's instance within a session.
Additional FEC Object Transmission Information (FTI) (as described in Additional FEC Object Transmission Information (FTI) (as described in
the FEC Building Block [RFC5052]) is required to properly receive and the FEC Building Block [RFC5052]) is needed to properly receive and
decode NORM transport objects. This information MAY be provided as decode NORM transport objects. This information MAY be provided as
out-of-band session information. However, in some cases, it may be out-of-band session information. In some cases, it will be useful
useful for the sender to include this information "in-band" to for the sender to include this information "in-band" to facilitate
facilitate receiver operation with minimal pre-configuration. For receiver operation with minimal pre-configuration. For this purpose,
this purpose, the NORM FEC Object Transmission Information Header the NORM FEC Object Transmission Information Header Extension
Extension (EXT_FTI) is defined. This header extension MAY be applied (EXT_FTI) is defined. This header extension MAY be applied to
to "NORM_DATA" and "NORM_INFO" messages to provide this necessary "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 "fec_id" field in "NORM_DATA" and "NORM_INFO" messages identifies
the FEC scheme. The format of the EXT_FTI general part is given the FEC scheme. The format of the EXT_FTI general part is given
here. 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 25, line 41 skipping to change at page 25, line 41
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 encoding 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" object (in bytes) for the static object types of "NORM_OBJECT_FILE"
and "NORM_OBJECT_DATA". This information is used by receivers to and "NORM_OBJECT_DATA". This information is used by receivers to
determine storage requirements and/or allocate storage for the determine storage requirements and/or allocate storage for the
received object. Receivers with insufficient storage capability may received object. Receivers with insufficient storage capability
wish to forego reliable reception (i.e., not NACK for) of the might wish to forego reliable reception (i.e., not NACK for) of the
indicated object. In the case of objects of type indicated object. In the case of objects of type
"NORM_OBJECT_STREAM", the "object_size" field is used by the sender "NORM_OBJECT_STREAM", the "object_size" field is used by the sender
to advertise the size of its stream buffer to the receiver group. In to advertise the size of its stream buffer to the receiver group. In
turn, the receivers SHOULD use this information to allocate a stream turn, the receivers SHOULD use this information to allocate a stream
buffer for reception of 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 contains any necessary details on the code in
code in use (e.g., FEC Instance ID, etc.). As an example, the format use (e.g., FEC Instance ID, etc.). As an example, the format of the
of the EXT_FTI for small block systematic codes ("fec_id" = 129) is EXT_FTI for small block systematic codes ("fec_id" = 129) is given
given here: 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example: EXT_FTI Header Extension Format for 'fec_id' = 129 Example: EXT_FTI Header Extension Format for '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 will possibly be different
FEC schemes. for other 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 [RFC5052]. In this case, the in the FEC Building Block [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 RFC 5052. Instance ID values is described in RFC 5052.
skipping to change at page 26, line 47 skipping to change at page 26, line 47
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 [RFC5052]. For example, Reed-Solomon Codes in the FEC Building Block [RFC5052]. For example, Reed-Solomon
codes may be arbitrarily shortened to create different code codes can be arbitrarily shortened to create different code
variations for a given block length. In the case of Reed-Solomon variations for a given block length. In the case of Reed-Solomon
(GF(2^8) and GF(2^16)) codes, this value indicates the maximum number (GF(2^8) and GF(2^16)) codes, this value indicates the maximum number
of parity segments available from the sender for the coding blocks. of parity segments available from the sender for the coding blocks.
This field MAY be interpreted differently for other systematic codes This field MAY be interpreted differently for other systematic codes
as they are defined. as they are defined.
The payload portion of "NORM_DATA" messages includes source data or The payload portion of "NORM_DATA" messages includes source data or
FEC encoded application content. The content of this payload depends FEC encoded application content. The content of this payload depends
upon the FEC scheme being employed, and support for streaming using upon the FEC scheme being employed, and support for streaming using
the "NORM_OBJECT_STREAM" type, when applicable, necessitates some the "NORM_OBJECT_STREAM" type, when applicable, necessitates some
skipping to change at page 27, line 43 skipping to change at page 27, line 43
"payload_len" and "payload_offset" values of missing data content can "payload_len" and "payload_offset" values of missing data content can
be determined upon decoding a FEC coding block. Note that these be determined upon decoding a FEC coding block. Note that these
fields do NOT contribute to the value of the "NORM_DATA" "hdr_len" 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 field. These fields are present only when the "flags" portion of the
"NORM_DATA" message indicate the transport object is of type "NORM_DATA" message indicate the transport object is of type
"NORM_OBJECT_STREAM". "NORM_OBJECT_STREAM".
The "payload_len" value, when non-zero, indicates the length (in The "payload_len" value, when non-zero, indicates the length (in
bytes) of the source content contained in the associated bytes) of the source content contained in the associated
"payload_data" field. However, when the "payload_len" value is equal "payload_data" field. However, when the "payload_len" value is equal
to ZERO, this indicates that the "payload_msg_start" field should be to ZERO, this indicates that the "payload_msg_start" field be
alternatively interpreted as a "stream_control_code". The only alternatively interpreted as a "stream_control_code". The only
"stream_control_code" value defined is "NORM_STREAM_END = 0". The "stream_control_code" value defined is "NORM_STREAM_END = 0". The
"NORM_STREAM_END" code indicates that the sender is terminating "NORM_STREAM_END" code indicates that the sender is terminating
transmission of stream content at the corresponding position in the transmission of stream content at the corresponding position in the
stream and the receiver should not expect content (or NACK for any stream and the receiver MUST not expect content (or request repair
content) following that position in the stream. It is expected that for any content) following that position in the stream. Additional
additional specifications may extend the functionality of the NORM specifications MAY extend the functionality of the NORM stream
stream transport mode by defining additional stream control codes. transport mode by defining additional stream control codes. These
control codes are delivered to the recipient application reliably,
These control codes are delivered to the recipient application in-order with respect to the streamed application data content.
reliably, in-order with respect to the streamed application data
content.
The "payload_msg_start" field serves one of two exclusive purposes. 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 also 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_DATA" payload for a "payload_msg_start - 1" bytes. Thus, if a "NORM_DATA" payload for a
"NORM_OBJECT_STREAM" contains the start of an application message at "NORM_OBJECT_STREAM" contains the start of an application message at
skipping to change at page 28, line 31 skipping to change at page 28, line 29
boundaries in this manner. Similarly, the NORM receiver boundaries in this manner. Similarly, the NORM receiver
implementation SHOULD enable the application to recover such message implementation SHOULD enable the application to recover such message
boundary information. This enables NORM receivers to "synchronize" boundary information. This enables NORM receivers to "synchronize"
reliable reception of transmitted message stream content in a reliable reception of transmitted message stream content in a
meaningful way (i.e., meaningful to the application) at any time, meaningful way (i.e., meaningful to the application) at any time,
whether joining a session already in progress, or departing the whether joining a session already in progress, or departing the
session and returning. Note that if the value of the session and returning. Note that if the value of the
"payload_msg_start" field is ZERO, no message boundary is present. "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_msg_start" value will always be less than or equal to
the "payload_len" value except for the special case of "payload_len = the "payload_len" value except for the special case of "payload_len =
0", that indicates the "payload_msg_start" field should instead be 0", that indicates the "payload_msg_start" field be instead
interpreted as a "stream_control_code" interpreted as a "stream_control_code"
The "payload_offset" field indicates the relative byte position (from The "payload_offset" field indicates the relative byte position (from
the sender stream transmission start) of the source content contained the sender stream transmission start) of the source content contained
in the "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 will 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
sender's 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 can possibly vary on a per-object basis. The
NormSegmentSize is expected to be configurable by the sender NormSegmentSize SHOULD be configurable by the sender application
application prior to session participation as needed for network prior to session participation as needed for network topology maximum
topology maximum transmission unit (MTU) considerations. For IPv6, transmission unit (MTU) considerations. For IPv6, MTU discovery MAY
MTU discovery may be possibly leveraged at session startup to perform be possibly leveraged at session startup to perform this
this configuration. The "payload_data" content may be delivered configuration. The "payload_data" content MAY be delivered directly
directly to the application for source symbols (when systematic FEC to the application for source symbols (when systematic FEC encoding
encoding is used) or upon decoding of the FEC block. For is used) or upon decoding of the FEC block. For "NORM_OBJECT_FILE"
"NORM_OBJECT_FILE" and "NORM_OBJECT_STREAM" objects, the data segment and "NORM_OBJECT_STREAM" objects, the data segment length and offset
length and offset can be calculated using the block partitioning can be calculated using the block partitioning algorithm described in
algorithm described in the FEC Building Block [RFC5052]. For the FEC Building Block [RFC5052]. For "NORM_OBJECT_STREAM" objects,
"NORM_OBJECT_STREAM" objects, the length and offset is obtained from the length and offset is obtained from the segment's corresponding
the segment's corresponding embedded "payload_len" and embedded "payload_len" and "payload_offset" 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 NormObjects. defined, out-of-band context information for transmitted NormObjects.
An example "NORM_INFO" use for bulk file transfer is to place MIME An example "NORM_INFO" use for bulk file transfer is to place MIME
type information for the associated file, data, or stream object into type information for the associated file, data, or stream object into
the "NORM_INFO" payload. Receivers may use the "NORM_INFO" content the "NORM_INFO" payload. Receivers could then use the "NORM_INFO"
to make a decision as whether to participate in reliable reception of content to make a decision as whether to participate in reliable
the associated object. Each NormObject can have an independent unit reception of the associated object. Each NormObject can have an
of "NORM_INFO" associated with it. "NORM_DATA" messages contain a independent unit of "NORM_INFO" associated with it. "NORM_DATA"
flag to indicate the availability of "NORM_INFO" for a given messages contain a flag to indicate the availability of "NORM_INFO"
NormObject. NORM receivers may NACK for retransmission of for a given NormObject. NORM receivers will NACK for retransmission
"NORM_INFO" when they have not received it for a given NormObject. of "NORM_INFO" when they have not received it for a given NormObject.
The size of the "NORM_INFO" content is limited to that of a single The size of the "NORM_INFO" content is limited to that of a single
NormSegmentSize for the given sender. This atomic nature allows the NormSegmentSize for the given sender. This atomic nature allows the
"NORM_INFO" to be rapidly and efficiently repaired within the NORM "NORM_INFO" to be rapidly and efficiently repaired within the NORM
reliable 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.
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=1| hdr_len | sequence | |version| type=1| hdr_len | sequence |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| source_id | | source_id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| instance_id | grtt |backoff| gsize | | instance_id | grtt |backoff| gsize |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flags | fec_id | object_transport_id | | flags | fec_id | object_transport_id |
skipping to change at page 30, line 37 skipping to change at page 30, line 18
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, NORM implementations MAY apply the EXT_FTI when
EXT_FTI when used to "NORM_INFO" messages only and not to "NORM_DATA" 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
skipping to change at page 31, line 4 skipping to change at page 30, line 33
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 can 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 | |
skipping to change at page 32, line 23 skipping to change at page 32, line 17
| "NORM_CMD(REPAIR_ADV)" | 5 | Used to advertise sender's | | "NORM_CMD(REPAIR_ADV)" | 5 | Used to advertise sender's |
| | | aggregated repair/feedback | | | | aggregated repair/feedback |
| | | state for suppression of | | | | state for suppression of |
| | | unicast feedback from | | | | unicast feedback from |
| | | receivers. | | | | receivers. |
| "NORM_CMD(ACK_REQ)" | 6 | Used to request | | "NORM_CMD(ACK_REQ)" | 6 | Used to request |
| | | application-defined positive | | | | application-defined positive |
| | | acknowledgment from a list of | | | | acknowledgment from a list of |
| | | receivers (OPTIONAL). | | | | receivers (OPTIONAL). |
| "NORM_CMD(APPLICATION)" | 7 | Used for application-defined | | "NORM_CMD(APPLICATION)" | 7 | Used for application-defined |
| | | purposes which may need to | | | | purposes which need to |
| | | temporarily preempt data | | | | temporarily preempt or |
| | | transmission (OPTIONAL). | | | | supplement data 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 can indicate either a temporary or permanent end
transmission, but the sender is still willing to respond to repair of data transmission, but the sender is still willing to respond to
requests. This command is repeated once per "2*GRTT" to excite the repair requests. This command is repeated once per "2*GRTT" to
receiver set for any outstanding repair requests up to and including excite the receiver set for any outstanding repair requests up to and
the transmission point indicated within the "NORM_CMD(FLUSH)" including the transmission point indicated within the
message. The number of repeats is equal to "NORM_ROBUST_FACTOR" "NORM_CMD(FLUSH)" message. The number of repeats is equal to
unless a list of receivers from which explicit positive "NORM_ROBUST_FACTOR" unless a list of receivers from which explicit
acknowledgment is expected ("acking_node_list") is given. In that positive acknowledgment is expected ("acking_node_list") is given.
case, the "acking_node_list" is updated as acknowledgments are In that case, the "acking_node_list" is updated as acknowledgments
received and the "NORM_CMD(FLUSH)" is repeated according to the are received and the "NORM_CMD(FLUSH)" is repeated according to the
mechanism described in Section 5.5.3. The greater the mechanism described in Section 5.5.3. The greater the
"NORM_ROBUST_FACTOR", the greater the probability that all applicable "NORM_ROBUST_FACTOR", the greater the probability that all applicable
receivers will be excited for acknowledgment or repair requests receivers will be excited for acknowledgment or repair requests
(NACKs) AND that the corresponding NACKs are delivered to the sender. (NACKs) AND that the corresponding NACKs are delivered to the sender.
A default value of "NORM_ROBUST_FACTOR" equal to 20 is RECOMMENDED. A default value of "NORM_ROBUST_FACTOR" equal to 20 is RECOMMENDED.
If a "NORM_NACK" message interrupts the flush process, the sender If a "NORM_NACK" message interrupts the flush process, the sender
SHALL re-initiate the flush process after any resulting repair SHALL re-initiate the flush process after any resulting repair
transmissions are completed. 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
skipping to change at page 33, line 21 skipping to change at page 33, line 16
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 "NORM_OBJECT_FILE", the flush process (if there are no further
pending objects) occurs at the end of these objects. Thus, FEC pending objects) occurs at the end of these objects. Thus, FEC
repair information is always available for repairs in response to repair information is always available for repairs in response to
repair 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 "NORM_OBJECT_STREAM", the flush can occur at any time, including in
the middle of an FEC coding block if systematic FEC codes are the middle of an FEC coding block if systematic FEC codes are
employed. In this case, the sender will not yet be able to provide employed. In this case, the sender will not yet be able to provide
FEC parity content for the concurrent coding block and will be FEC parity content for the concurrent coding block and will be
limited to explicitly repairing the stream with source data content limited to explicitly repairing the stream with source data content
for that block. Applications that anticipate frequent flushing of for that block. Applications that anticipate frequent flushing of
stream content SHOULD be judicious in the selection of the FEC coding stream content SHOULD be judicious in the selection of the FEC coding
block size (i.e., do not use a very large coding block size if block size (i.e., do not use a very large coding block size if
frequent flushing occurs). For example, a reliable multicast frequent flushing occurs). For example, a reliable multicast
application transmitting an on-going series of intermittent, application transmitting an on-going series of intermittent,
relatively small messages will need to trade-off using the relatively small messages will need to trade-off using the
skipping to change at page 35, line 11 skipping to change at page 34, line 39
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. Note that a sender has the option of arbitrarily
of arbitrarily shortening a given code block when such an application shortening a given code block when such an application "flush"
"flush" occurs. In this case, the receiver will request explicit occurs. In this case, the receiver will request explicit repair, but
repair, but the sender MAY provide FEC-based repair (parity segments) the sender MAY provide FEC-based repair (parity segments) in
in response. These parity segments MUST contain the corrected 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 override 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. detail in Section 5.3.
The OPTIONAL "acking_node_list" field contains a list of NormNodeIds The OPTIONAL "acking_node_list" field contains a list of NormNodeIds
for receivers from which the sender is requesting explicit positive for receivers from which the sender is requesting explicit positive
acknowledgment of reception up through the transmission point acknowledgment of reception up through the transmission point
identified by the "object_transport_id" and "fec_payload_id" fields. identified by the "object_transport_id" and "fec_payload_id" fields.
The length of the list can be inferred from the length of the The length of the list can be inferred from the length of the
received "NORM_CMD(FLUSH)" message. When the "acking_node_list" is received "NORM_CMD(FLUSH)" message. When the "acking_node_list" is
skipping to change at page 36, line 47 skipping to change at page 36, line 17
The "NORM_CMD(SQUELCH)" command is sent once per "2*GRTT" at the The "NORM_CMD(SQUELCH)" command is sent once per "2*GRTT" at the
most. The "NORM_CMD(SQUELCH)" advertises the current "repair window" most. The "NORM_CMD(SQUELCH)" advertises the current "repair window"
of the sender by identifying the earliest (lowest) transmission point of the sender by identifying the earliest (lowest) transmission point
for which it will provide repair, along with an encoded list of for which it will provide repair, along with an encoded list of
objects from that point forward that are no longer valid for repair. objects from that point forward that are no longer valid for repair.
This 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 repair window that were sent with the "NORM_FLAG_UNRELIABLE" flag
set. In normal conditions, it is expected the "NORM_CMD(SQUELCH)" set. In normal conditions, the "NORM_CMD(SQUELCH)" will be needed
will be needed infrequently, and generally only to provide a infrequently, and generally only to provide a reference repair window
reference repair window for receivers who have fallen "out-of-sync" for receivers who have fallen "out-of-sync" with the sender due to
with the sender due to extremely poor network conditions. 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 sender's 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
skipping to change at page 37, line 47 skipping to change at page 37, line 18
value of the "hdr_len" field when no extensions are present is 4 plus value of the "hdr_len" field when no extensions are present is 4 plus
the size of the "fec_payload_id" field that is dependent upon the FEC the size of the "fec_payload_id" field that is dependent upon the FEC
scheme 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 sender's 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 sender's 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 sender's 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 packet's "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 a single "NORM_CMD(SQUELCH)" message cannot include the entire set of
the entire set of invalid objects in the repair window. In this invalid objects in the repair window. In this case, the sender SHALL
case, the sender SHALL ensure that the list begins with a ensure that the list begins with a NormObjectId that is greater than
NormObjectId that is greater than or equal to the lowest ordinal or equal to the lowest ordinal invalid NormObjectId from the NACK
invalid NormObjectId from the NACK message(s) that prompted the message(s) that prompted the "NORM_CMD(SQUELCH)" generation. The
"NORM_CMD(SQUELCH)" generation. The NormObjectIds in the NormObjectIds in the "invalid_object_list" MUST be ordinally greater
"invalid_object_list" MUST be ordinally greater than the than the "object_transport_id" marking the beginning of the sender's
"object_transport_id" marking the beginning of the sender's repair repair window. This insures convergence of the squelch process, even
window. This insures convergence of the squelch process, even if if multiple invalid NACK/ squelch iterations are required. This
multiple invalid NACK/ squelch iterations are required. This
explicit description of invalid content within the sender's current explicit description of invalid content within the sender's current
window allows the sender application (most notably for discrete window allows the sender application (most notably for discrete
object transport) to arbitrarily invalidate (i.e., dequeue) portions object transport) to arbitrarily invalidate (i.e., dequeue) portions
of enqueued content (e.g., certain objects) for which it no longer of enqueued content (e.g., certain objects) for which it no longer
wishes to provide reliable transport. 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 RFC 4654 is fully Multicast Congestion Control (TFMCC) scheme of RFC 4654 is fully
specified in Section 5.5.2 of this document. The "NORM_CMD(CC)" specified in Section 5.5.2 of this document. The "NORM_CMD(CC)"
message is usually transmitted as part of NORM-CC congestion control message is usually transmitted as part of NORM-CC congestion control
operation. A NORM header extension is defined below to be used with operation. A NORM header extension is defined below to be used with
the "NORM_CMD(CC)" message to support NORM-CC operation. Different the "NORM_CMD(CC)" message to support NORM-CC operation. Different
header extensions may be defined for the "NORM_CMD(CC)" (and/or other header extensions MAY be defined for the "NORM_CMD(CC)" (and/or other
NORM messages as needed) to support alternative congestion control NORM messages as needed) to support alternative congestion control
schemes in the future. If NORM is operated in a network where schemes in the future. If NORM is operated in a network where
resources are explicitly dedicated to the NORM session and therefore resources are explicitly dedicated to the NORM session and therefore
congestion control operation is disabled, the "NORM_CMD(CC)" message congestion control operation is disabled, the "NORM_CMD(CC)" message
is then used soley for GRTT measurement and may optionally be sent is then used soley for GRTT measurement and MAY be sent less
less frequently than 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| flavor = 4 | reserved | cc_sequence | | flavor = 4 | reserved | cc_sequence |
skipping to change at page 39, line 35 skipping to change at page 38, line 46
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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 is possible for alternative congestion
congestion control schemes may use the "NORM_CMD(CC)" message defined control schemes to use the "NORM_CMD(CC)" message defined here and
here and leverage the "reserved" field for scheme-specific purposes. 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 RFC 4654. The to the "feedback round number" ("fb_nr") described in RFC 4654. The
most recently received "cc_sequence" value is recorded by receivers most recently received "cc_sequence" value is recorded by receivers
and 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 receiver has received "NORM_CMD(CC)" probes from the sender. This
can be useful instrumentation for complex or experimental multicast can be useful instrumentation for complex or experimental multicast
skipping to change at page 41, line 5 skipping to change at page 40, line 17
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" might be attached as
the payload of the "NORM_CMD(CC)" message. The presence of this the payload of the "NORM_CMD(CC)" message. The presence of this
header extension also implies that NORM receivers should respond header extension also implies that NORM receivers MUST respond
according to the procedures described in Section 5.5.2. according to the procedures described in Section 5.5.2.
The "cc_node_list" consists of a list of NormNodeIds and their The "cc_node_list" consists of a list of NormNodeIds and their
associated congestion control status. This includes the current associated congestion control status. This includes the current
limiting receiver (CLR) node, any potential limiting receiver (PLR) limiting receiver (CLR) node, any potential limiting receiver (PLR)
nodes that have been identified, and some number of receivers for nodes that have been identified, and some number of receivers for
which congestion control status is being provided, most notably which congestion control status is being provided, most notably
including the receivers' current RTT measurement. The maximum length including the receivers' current RTT measurement. The maximum length
of the "cc_node_list" provides for at least the CLR and one other 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 receiver, but can be increased for more timely feedback to the group.
group. The list length can be inferred from the length of the The list length can be inferred from the length of the "NORM_CMD(CC)"
"NORM_CMD(CC)" message. message.
Each item in the "cc_node_list" is in the following format: 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 42, line 5 skipping to change at page 41, line 22
| "NORM_FLAG_CC_RTT" | 0x04 | Receiver has measured RTT with | | "NORM_FLAG_CC_RTT" | 0x04 | Receiver has measured RTT with |
| | | respect to sender. | | | | respect to sender. |
| "NORM_FLAG_CC_START" | 0x08 | Sender/receiver is in "slow start" | | "NORM_FLAG_CC_START" | 0x08 | Sender/receiver is in "slow start" |
| | | phase of congestion control | | | | phase of congestion control |
| | | operation (i.e., The receiver has | | | | operation (i.e., The receiver has |
| | | not yet detected any packet loss | | | | not yet detected any packet loss |
| | | and the "cc_rate" field is the | | | | and the "cc_rate" field is the |
| | | receiver's actual measured receive | | | | 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 considered in congestion | | | | not be considered in congestion |
| | | control operation. | | | | control 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 Multicast NACK of the RTT using the algorithm described in the Multicast NACK
Building Block [RFC5401]. Building Block [RFC5401].
skipping to change at page 43, line 16 skipping to change at page 42, line 35
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 SHALL 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
be applied to the "NORM_CMD(REPAIR_ADV)" representing the most SHOULD be applied to the "NORM_CMD(REPAIR_ADV)" representing the most
limiting (in terms of congestion control feedback suppression) limiting (in terms of congestion control feedback suppression)
congestion control response. This allows the "NORM_CMD(REPAIR_ADV)" congestion control response. This allows the "NORM_CMD(REPAIR_ADV)"
message to suppress receiver congestion control responses as well as message to suppress receiver congestion control responses as well as
NACK feedback messages. The field is defined as a header extension NACK feedback messages. The field is defined as a header extension
so that alternative congestion control schemes may be used with NORM so that alternative congestion control schemes can be used for 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) [PgmccPaper]) is used General Multicast Congestion Control (PGMCC) [PgmccPaper]) is used
within a NORM implementation, an additional header extension MAY need within a NORM implementation, an additional header extension MAY need
to be 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
skipping to change at page 44, line 5 skipping to change at page 43, line 23
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
receiver's 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 SHOULD choose to take
avoidance measures. For "NORM_CMD(REPAIR_ADV)" messages, the sender congestion avoidance measures. For "NORM_CMD(REPAIR_ADV)" messages,
SHALL set the "cc_sequence" field value to the value set in the last the sender SHALL set the "cc_sequence" field value to the value set
"NORM_CMD(CC)" message sent. in the last "NORM_CMD(CC)" message sent.
The "cc_flags" field contains bits representing the receiver's 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 feedback. For "NORM_CMD(REPAIR_ADV)" messages, the
"NORM_FLAG_CC_RTT" should be set only when all feedback messages "NORM_FLAG_CC_RTT" SHALL be set only when all feedback messages
received by the sender have the flag set. Similarly, the received by the sender have the flag set. Similarly, the
"NORM_FLAG_CC_CLR" or "NORM_FLAG_CC_PLR" should be set only when no "NORM_FLAG_CC_CLR" or "NORM_FLAG_CC_PLR" SHALL be set only when no
feedback has been received from non-CLR or non-PLR receivers. And feedback has been received from non-CLR or non-PLR receivers. And
the "NORM_FLAG_CC_LEAVE" should be set only when all feedback the "NORM_FLAG_CC_LEAVE" SHALL be set only when all feedback messages
messages the sender has received have this flag set. These the sender has received have this flag set. These heuristics for
heuristics for setting the flags in "NORM_CMD(REPAIR_ADV)" ensure the setting the flags in "NORM_CMD(REPAIR_ADV)" ensure the most effective
most effective suppression of receivers providing unicast feedback suppression of receivers providing unicast feedback messages.
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 receiver's 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:
skipping to change at page 46, line 40 skipping to change at page 46, line 9
congestion control operation. Similarly, the "NORM_ACK_FLUSH" is congestion control operation. Similarly, the "NORM_ACK_FLUSH" is
provided for use only in "NORM_ACKs" generated in response to provided for use only in "NORM_ACKs" generated in response to
applicable "NORM_CMD(FLUSH)" messages. "NORM_CMD"(ACK_REQ) messages applicable "NORM_CMD(FLUSH)" messages. "NORM_CMD"(ACK_REQ) messages
with "ack_type" of "NORM_ACK_CC" or "NORM_ACK_FLUSH" SHALL NOT be with "ack_type" of "NORM_ACK_CC" or "NORM_ACK_FLUSH" SHALL NOT be
generated by the sender. 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 can 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 can 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
skipping to change at page 47, line 22 skipping to change at page 46, line 39
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 can 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 can 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 needs 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 50, line 4 skipping to change at page 49, line 7
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 adjusts the source's "NORM_CMD(CC)" "send_time" timestamp by adding
the time delta from when the receiver received the "NORM_CMD(CC)" to the time delta from when the receiver received the "NORM_CMD(CC)" to
when the "NORM_NACK" is transmitted in response to calculate the when the "NORM_NACK" is transmitted in response to calculate the
value in the "grtt_response" field. This is the value in the "grtt_response" field. This is the
"receive_to_response_delta" 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 indicate that it has not yet received a "NORM_CMD(CC)" message from
the indicated sender and that the sender should ignore the the indicated sender and that the sender MUST 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_payload" 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 needs from the
sender in order to complete reliable reception up to the sender's sender to complete reliable reception up to the sender's transmission
transmission position at the moment the receiver initiates the NACK position at the moment the receiver initiates the NACK Procedure as
Procedure as described in Section 5.3. A single NORM Repair Request described in Section 5.3. A single NORM Repair Request consists of a
consists of a list of items, ranges, and/or FEC coding block erasure list of items, ranges, and/or FEC coding block erasure counts for
counts for needed "NORM_DATA" and/or "NORM_INFO" content. Multiple needed "NORM_DATA" and/or "NORM_INFO" content. Multiple repair
repair requests may be concatenated within the "nack_payload" field requests can be concatenated within the "nack_payload" field of a
of a "NORM_NACK" message. Note that a single NORM Repair Request can "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 |
| ... | | ... |
skipping to change at page 51, line 33 skipping to change at page 50, line 33
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 | | "NORM_NACK_SEGMENT" | 0x01 | Indicates the listed segment(s) or |
| | | range of segments are required as | | | | range of segments needed as repair. |
| | | repair. |
| "NORM_NACK_BLOCK" | 0x02 | Indicates the listed block(s) or | | "NORM_NACK_BLOCK" | 0x02 | Indicates the listed block(s) or |
| | | range of blocks in entirety are | | | | range of blocks in entirety are |
| | | required as repair. | | | | needed as repair. |
| "NORM_NACK_INFO" | 0x04 | Indicates that "NORM_INFO" is | | "NORM_NACK_INFO" | 0x04 | Indicates that "NORM_INFO" is |
| | | required as repair for the listed | | | | needed as repair for the listed |
| | | object(s). | | | | object(s). |
| "NORM_NACK_OBJECT" | 0x08 | Indicates the listed object(s) or | | "NORM_NACK_OBJECT" | 0x08 | Indicates the listed object(s) or |
| | | range of objects in entirety are | | | | range of objects in entirety are |
| | | required as repair. | | | | needed as repair. |
+---------------------+-------+-------------------------------------+ +---------------------+-------+-------------------------------------+
When the "NORM_NACK_SEGMENT" flag is set, the "object_transport_id" When the "NORM_NACK_SEGMENT" flag is set, the "object_transport_id"
and "fec_payload_id" fields are used to determine which sets or and "fec_payload_id" fields are used to determine which sets or
ranges of individual "NORM_DATA" segments are needed to repair ranges of individual "NORM_DATA" segments are needed to repair
content at the receiver. When the "NORM_NACK_BLOCK" flag is set, content at the receiver. When the "NORM_NACK_BLOCK" flag is set,
this indicates the receiver is completely missing the indicated this indicates the receiver is completely missing the indicated
coding block(s) and requires transmissions sufficient to repair the coding block(s) and transmissions sufficient to repair the indicated
indicated block(s) in their entirety. When the "NORM_NACK_INFO" flag block(s) in their entirety are needed. When the "NORM_NACK_INFO"
is set, this indicates the receiver is missing the "NORM_INFO" flag is set, this indicates the receiver is missing the "NORM_INFO"
segment for the indicated "object_transport_id". Note the segment for the indicated "object_transport_id". Note the
"NORM_NACK_INFO" may be set in combination with the "NORM_NACK_BLOCK" "NORM_NACK_INFO" can be set in combination with the "NORM_NACK_BLOCK"
or "NORM_NACK_SEGMENT" flags, or may be set alone. When the or "NORM_NACK_SEGMENT" flags, or can be set alone. When the
"NORM_NACK_OBJECT" flag is set, this indicates the receiver is "NORM_NACK_OBJECT" flag is set, this indicates the receiver is
missing the entire NormTransportObject referenced by the missing the entire NormTransportObject referenced by the
"object_transport_id". This also implicitly requests any available "object_transport_id". This also implicitly requests any available
"NORM_INFO" for the NormObject, if applicable. The "fec_payload_id" "NORM_INFO" for the NormObject, if applicable. The "fec_payload_id"
field is ignored when the flag "NORM_NACK_OBJECT" 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
skipping to change at page 52, line 49 skipping to change at page 51, line 48
"NORM_NACK_OBJECT" flag is set, the value of the "fec_payload_id" "NORM_NACK_OBJECT" flag is set, the value of the "fec_payload_id"
field is ignored. When the "NORM_NACK_BLOCK" flag is set, only the field is ignored. When the "NORM_NACK_BLOCK" flag is set, only the
FEC code 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 receiver's 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 needed to complete reliable
reliable transmission, multiple NORM Repair Requests with different transmission, multiple NORM Repair Requests with different "form" and
"form" and or "flags" values can be concatenated within a single or "flags" values can be concatenated within a single "NORM_NACK"
"NORM_NACK" message. Additionally, NORM receivers SHALL construct message. Additionally, NORM receivers SHALL construct "NORM_NACK"
"NORM_NACK" messages with their repair requests in ordinal order with messages with their repair requests in ordinal order with respect to
respect to "object_transport_id" and "fec_payload_id" values. The "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 possible content of a "NORM_NACK" message. Note that FEC coding
block erasure counts could also be provided in each case. However, block erasure counts could also be provided in each case. However,
the erasure counts are not really necessary since the sender can the erasure counts are not really necessary since the sender can
easily 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 can 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,and 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 |
skipping to change at page 54, line 37 skipping to change at page 53, line 37
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 The "NORM_ACK" message is intended to be used primarily as part of
NORM congestion control operation and round-trip timing measurement. NORM congestion control operation and round-trip timing measurement.
As mentioned in the "NORM_CMD(ACK_REQ)" message description, the The acknowledgment type "NORM_ACK_CC" is provided for this purpose as
acknowledgment type "NORM_ACK_CC" is provided for this purpose. The described in the "NORM_CMD(ACK_REQ)" message description. The
generation of "NORM_ACK(CC)" messages for round-trip timing generation of "NORM_ACK(CC)" messages for round-trip timing
estimation and congestion-control operation is described in estimation and congestion-control operation is described in
Section 5.5.1 and Section 5.5.2, respectively. However, some Section 5.5.1 and Section 5.5.2, respectively. However, some
multicast applications may benefit from some limited form of positive multicast applications can benefit from some limited form of positive
acknowledgment for certain functions. A simple, scalable positive acknowledgment for certain functions. A simple, scalable positive
acknowledgment scheme is defined in Section 5.5.3 that can be acknowledgment scheme is defined in Section 5.5.3 that can be
leveraged by protocol implementations when appropriate. The leveraged by protocol implementations when appropriate. The
"NORM_CMD(FLUSH)" may be used for OPTIONAL collection of positive "NORM_CMD(FLUSH)" can also be used for OPTIONAL collection of
acknowledgment of reliable reception to a certain "watermark" positive acknowledgment of reliable reception to a certain
transmission point from specific receivers using this mechanism. The "watermark" transmission point from specific receivers using this
"NORM_ACK" type "NORM_ACK_FLUSH" is provided for this purpose and the mechanism. The "NORM_ACK" type "NORM_ACK_FLUSH" is provided for this
format of the "nack_payload" for this acknowledgment type is given purpose and the format of the "nack_payload" for this acknowledgment
below. Beyond that, a range of application-defined "ack_type" values type is given below. Beyond that, a range of application-defined
is provided for use at the NORM application's discretion. "ack_type" values is provided for use at the NORM application's
Implementations making use of application-defined positive discretion. Implementations making use of application-defined
acknowledgments may also make use the "nack_payload" as needed, positive acknowledgments MAY also make use the "nack_payload" as
observing the constraint that the "nack_payload" field size be needed, observing the constraint that the "nack_payload" field size
limited to a maximum of the NormSegmentSize for the sender to which be limited to a maximum of the NormSegmentSize for the sender to
the "NORM_ACK" is destined. 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 55, line 40 skipping to change at page 54, line 40
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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. same purpose as the corresponding fields in "NORM_NACK" messages.
And header extensions may be applied to support congestion control And header extensions can 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 verify that a "NORM_ACK" message received actually applies to a
current acknowledgment request. The "ack_id" field is not used in current acknowledgment request. The "ack_id" field is not used in
the case of the "NORM_ACK_CC" and "NORM_ACK_FLUSH" acknowledgment the case of the "NORM_ACK_CC" and "NORM_ACK_FLUSH" acknowledgment
skipping to change at page 56, line 36 skipping to change at page 55, line 36
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 may be used for periodic performance reports from receivers message can 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 compliant NORM implementations. different compliant 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 round-trip timing and congestion needed to initialize and collect round-trip timing and congestion
control feedback from the receiver set. control feedback from the receiver set.
2. The sender transmits an ordinal set of NormObjects segmented in 2. The sender transmits an ordinal set of NormObjects segmented in
the form of "NORM_DATA" messages labeled with NormTransportIds the form of "NORM_DATA" messages labeled with NormTransportIds
and logically identified with FEC encoding block numbers and and logically identified with FEC encoding block numbers and
symbol identifiers. "NORM_INFO" messages may optionally precede symbol identifiers. "When applicable, NORM_INFO" messages MAY
the transmission of data content for NORM transport objects. optionally precede the transmission of data content for 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 objectId::fecPayloadId receivers track the sender's most recent objectId::fecPayloadId
transmit position and NACK ONLY for content ordinally prior to transmit position and NACK ONLY for content ordinally prior to
that transmit position. The receivers schedule random backoff that transmit position. The receivers schedule random backoff
timeouts before generating "NORM_NACK" messages and wait an timeouts before generating "NORM_NACK" messages and wait an
appropriate amount of time before repeating the "NORM_NACK" if appropriate amount of time before repeating the "NORM_NACK" if
their repair request is not satisfied. their repair request is 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 appropriate logically "rewinds" its transmit position to send appropriate
repair messages. The sender sends repairs for the earliest repair messages. The sender sends repairs for the earliest
ordinal transmit position first and maintains this ordinal repair ordinal transmit position first and maintains this ordinal repair
transmission sequence. FEC parity content not previously transmission sequence. FEC parity content not previously
transmitted for the applicable FEC coding block is used for transmitted for the applicable FEC coding block is used for
repair transmissions to the greatest extent possible. If the repair transmissions to the greatest extent possible. If the
sender exhausts its available FEC parity content on multiple sender exhausts its available FEC parity content on multiple
repair cycles for the same coding block, it resorts to an repair cycles for the same coding block, it resorts to an
explicit repair strategy (possibly using parity content) to explicit repair strategy (possibly using parity content) to
complete repairs. (The use of explicit repair is expected to be complete repairs. (The use of explicit repair is an exception in
an exception in general protocol operation, but the possibility general protocol operation, but the possibility does exist for
does exist for extreme conditions). The sender immediately extreme conditions). The sender immediately assumes transmission
assumes transmission of new content once it has sent pending of new content once it has sent pending repairs.
repairs.
5. The sender transmits "NORM_CMD(FLUSH)" messages when it reaches 5. The sender transmits "NORM_CMD(FLUSH)" messages when it reaches
the end of enqueued transmit content and pending repairs. the end of enqueued transmit content and pending repairs.
Receivers respond to the "NORM_CMD(FLUSH)" messages with Receivers respond to the "NORM_CMD(FLUSH)" messages with
"NORM_NACK" transmissions (following the same suppression backoff "NORM_NACK" transmissions (following the same suppression backoff
timeout strategy as for data) if they require further repair. timeout strategy as for data) if they need 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 baseline determined by congestion control mechanisms. In the baseline
NORM-CC operation, each sender in a NormSession maintains its own NORM-CC operation, each sender in a NormSession maintains its own
independent congestion control state. Receivers provide independent congestion control state. Receivers provide
congestion control feedback in "NORM_NACK" and "NORM_ACK" congestion control feedback in "NORM_NACK" and "NORM_ACK"
messages. "NORM_ACK" feedback for congestion control purposes is messages. "NORM_ACK" feedback for congestion control purposes is
governed using a suppression mechanism similar to that for governed using a suppression mechanism 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
skipping to change at page 58, line 14 skipping to change at page 57, line 14
5.1. Sender Initialization and Transmission 5.1. Sender Initialization and Transmission
Upon startup, the NORM sender immediately begins sending Upon startup, the NORM sender immediately begins sending
"NORM_CMD(CC)" messages to collect round trip timing and other "NORM_CMD(CC)" messages to collect round trip timing and other
information from the potential group. If NORM-CC congestion control information from the potential group. If NORM-CC congestion control
operation is enabled, the NORM-CC Rate header extension MUST be operation is enabled, the NORM-CC Rate header extension MUST be
included in these messages. Congestion control operation SHALL be included in these messages. Congestion control operation SHALL be
observed at all times when not operating using dedicated resources, observed at all times when not operating using dedicated resources,
like in the general Internet. Even if congestion control operation like in the general Internet. Even if congestion control operation
is disabled at the sender, it may be desirable to use the is disabled at the sender, it can be desirable to use the
"NORM_CMD(CC)" messaging to collect feedback from the group using the "NORM_CMD(CC)" messaging to collect feedback from the group using the
baseline NORM-CC feedback mechanisms. This proactive feedback baseline NORM-CC feedback mechanisms. This proactive feedback
collection can be used to establish a GRTT estimate prior to data collection can be used to establish a GRTT estimate prior to data
transmission and potential NACK operation. transmission and potential NACK operation.
In some cases, applications may wish for the sender to also proceed In some cases, applications might need the sender to also proceed
with data transmission immediately. In other cases, the sender may with data transmission immediately. In other cases, the sender might
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 via other means. As noted, the periodic transmission of
"NORM_CMD(CC)" messages may precede actual data transmission in order "NORM_CMD(CC)" messages MAY precede actual data transmission in order
to have an 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 means. Additionally, applications MAY leverage the use of
"NORM_INFO" messages associated with the session data objects in the "NORM_INFO" messages associated with the session data objects in the
session to provide application-specific context information for the session to provide application-specific context information for the
session and data being transmitted. These mechanisms allow for session and data being transmitted. These mechanisms allow for
operation with minimal pre-coordination among the senders and operation with minimal pre-coordination among the senders and
receivers. 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 "NORM_DATA" segments and transmitting it to the group. For objects
of 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 [RFC5052] is RECOMMENDED. algorithm described in FEC Building Block [RFC5052] is RECOMMENDED.
For objects of type "NORM_OBJECT_STREAM", segmentation will typically For objects of type "NORM_OBJECT_STREAM", segmentation will typically
be into uniform FEC coding block sizes, with individual segment sizes be into uniform FEC coding block sizes, with individual segment sizes
controlled by the application. In most cases, the application and controlled by the application. In most cases, the application and
NORM implementation SHOULD strive to produce full-sized NORM implementation SHOULD strive to produce full-sized
("NormSegmentSize") segments when possible. The rate of transmission ("NormSegmentSize") segments when possible. The rate of transmission
is controlled via congestion control mechanisms or is a fixed rate if is controlled via congestion control mechanisms or is a fixed rate if
desired for closed network operations. The receivers participating desired for closed network operations. The receivers participating
in the multicast group provide feedback to the sender as needed. in the multicast group provide feedback to the sender as needed.
When the sender reaches the end of data it has enqueued for When the sender reaches the end of data it has enqueued for
transmission or any pending repairs, it transmits a series of transmission or any pending repairs, it transmits a series of
"NORM_CMD(FLUSH)" messages at a rate of one per "2*GRTT". Receivers "NORM_CMD(FLUSH)" messages at a rate of one per "2*GRTT". Similar to
may respond to these "NORM_CMD(FLUSH)" messages with additional end of each transmitted FEC coding block during transmission,
repair requests. A protocol parameter ""NORM_ROBUST_FACTOR"" receivers SHALL respond to these "NORM_CMD(FLUSH)" messages with
determines the number of flush messages sent. If receivers request additional repair requests as needed. A protocol parameter
repair, the repair is provided and flushing occurs again at the end ""NORM_ROBUST_FACTOR"" determines the number of flush messages sent.
of repair transmission. The sender may attach an OPTIONAL If receivers request repair, the repair is provided and flushing
"acking_node_list" to "NORM_CMD(FLUSH)" containing the NormNodeIds occurs again at the end of repair transmission. The sender MAY
for receivers from which it expects explicit positive acknowledgment attach an OPTIONAL "acking_node_list" to "NORM_CMD(FLUSH)" containing
of reception. The "NORM_CMD(FLUSH)" message may be also used for the NormNodeIds for receivers from which it expects explicit positive
this optional function any time prior to the end of data enqueued for acknowledgment of reception. The "NORM_CMD(FLUSH)" message MAY be
transmission with the "NORM_CMD(FLUSH)" messages multiplexed with also used for this OPTIONAL purpose any time prior to the end of data
ongoing data transmissions. The OPTIONAL NORM positive enqueued for transmission with the "NORM_CMD(FLUSH)" messages
acknowledgment procedure is described in Section 5.5.3. multiplexed with ongoing data transmissions. The OPTIONAL NORM
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 messages. Each "NORM_DATA" message will contain one or more source
or encoding symbol(s) identified by the "fec_payload_id" field and or encoding symbol(s) identified by the "fec_payload_id" field and
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FEC blocks. Note this algorithm applies only to the statically-sized FEC blocks. Note this algorithm applies only to the statically-sized
"NORM_OBJECT_DATA" and "NORM_OBJECT_FILE" transport object types "NORM_OBJECT_DATA" and "NORM_OBJECT_FILE" transport object types
where the object size is fixed and predetermined. For where the object size is fixed and predetermined. For
"NORM_OBJECT_STREAM" objects, the object is segmented according to "NORM_OBJECT_STREAM" objects, the object is segmented according to
the maximum source block length given in the FEC Transmission the maximum source block length given in the FEC Transmission
Information, unless the FEC Payload ID indicates an alternative size Information, unless the FEC Payload ID indicates an alternative size
for a given block. 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 can join and leave
the group at will. However, some applications may be constrained the group at will. However, some applications might 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 impose additional constraints to limit the ability
ability of receivers to disrupt reliable multicast performance by of receivers to disrupt reliable multicast performance by joining,
joining, leaving, and rejoining the group often. Different receiver leaving, and rejoining the group often. Different receiver "join
"join policies" may be appropriate for different applications and/or policies" might 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, NORM receivers will join a specified multicast
specified multicast group and/or listen on an specific port number group and/or listen on an specific port number for sender
for sender transmissions. As the NORM receiver receives "NORM_DATA" transmissions. As the NORM receiver receives "NORM_DATA" messages it
messages it will provide content to its application as appropriate. 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 sender's 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, NormObject boundaries, upon receipt of a "NORM_CMD(FLUSH)" message,
or 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:
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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 Multicast NACK Building Block [RFC5401] algorithm described in the Multicast NACK Building Block [RFC5401]
using ("Ksender*GRTTsender") for the "maxTime" parameter and the using ("Ksender*GRTTsender") for the "maxTime" parameter and the
sender advertised group size ("GSIZEsender") as the "groupSize" sender advertised group size ("GSIZEsender") as the "groupSize"
parameter. NORM senders provide values for "GRTTsender", "Ksender" parameter. NORM senders provide values for "GRTTsender", "Ksender"
and "GSIZEsender" via the "grtt", "backoff", and "gsize" fields of and "GSIZEsender" via the "grtt", "backoff", and "gsize" fields of
transmitted messages. The "GRTTsender" value is determined by the transmitted messages. The "GRTTsender" value is determined by the
sender based on feedback it has received from the group while the sender based on feedback it has received from the group while the
"Ksender" and "GSIZEsender" values may determined by application "Ksender" and "GSIZEsender" values can be determined by application
requirements and expectations or ancillary information. The backoff requirements and expectations or ancillary information. The backoff
factor ""Ksender"" MUST be greater than "one" to provide for factor ""Ksender"" MUST be greater than "one" to provide for
effective feedback suppression. A value of "K = 4" is RECOMMENDED effective feedback suppression. A value of "K = 4" is RECOMMENDED
for the Any Source Multicast (ASM) model while a value of "K = 6" is for the Any Source Multicast (ASM) model while a value of "K = 6" is
RECOMMENDED for Single Source Multicast (SSM) operation. 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
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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 might have transmitted 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 receiver's 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 needed to satisfy its total erasure needs for the block. The goal of
of this strategy is for the overall receiver set to request a lowest 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 does not demand synchronization among the receiver set in their
requests for the sender. repair 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 will need to occasionally "rewind" its logical transmission
satisfy the repair needs of receivers who have NACKed. Aggregation point to satisfy the repair needs of receivers who have NACKed.
of multiple NACKs is used to determine an optimal repair strategy Aggregation of multiple NACKs is used to determine an optimal repair
when a NACK event occurs. Since receivers initiate the NACK process strategy when a NACK event occurs. Since receivers initiate the NACK
on coding block or object boundaries, there is some loose degree of process on coding block or object boundaries, there is some loose
synchronization of the repair process even when receivers experience degree of synchronization of the repair process even when receivers
uncorrelated data loss. experience 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 state from "NORM_NACK" messages before beginning repair
transmissions. Note that this period of aggregating repair state transmissions. Note that this period of aggregating repair state
does NOT interfere with its ongoing transmission of new data. does NOT interfere with its ongoing transmission of new data.
As described in [RFC5401], the period of time during which the sender As described in [RFC5401], the period of time during which the sender
aggregates "NORM_NACK" messages is equal to: 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 [RFC5401], the even if "NORM_NACK" messages arrive. As described in [RFC5401], the
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position exceeds the lowest ordinal position of their repair needs. position exceeds the lowest ordinal position of their repair needs.
With the new NACK aggregation period, the sender repeats the same With the new NACK aggregation period, the sender repeats the same
process of incorporating accumulated repair state into its process of incorporating accumulated repair state into its
transmission plan and subsequently "rewinding" to transmit the lowest transmission plan and subsequently "rewinding" to transmit the lowest
ordinal repair data when the aggregation period expires. Again, this ordinal repair data when the aggregation period expires. Again, this
is conducted in concert with ongoing new data and/or pending repair is conducted in concert with ongoing new data and/or pending repair
transmissions. 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. The sender SHOULD NOT resort
supply of "fresh" (unsent) parity segments for a given coding block to explicit transmission of the receiver set's repair needs until
should the sender resort to explicit transmission of the receiver after exhausting its supply of "fresh" (unsent) parity segments for a
set's repair needs. In general, if a sufficiently powerful FEC code given coding block. 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 continue to operate under even very extreme
circumstances. circumstances.
"NORM_DATA" messages sent as repair transmissions SHALL be flagged "NORM_DATA" messages sent as repair transmissions SHALL be flagged
with 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-tree's 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 need to
required to conduct repair state accumulation for sub-routes in a conduct repair state accumulation for sub-routes in a manner similar
manner similar to the sender's repair state accumulation in order to to the sender's repair state accumulation in order to have sufficient
have sufficient information to perform the sub-casting. information to perform the sub-casting. Additionally, the
Additionally, the intermediate systems could perform additional intermediate systems could perform additional "NORM_NACK"
"NORM_NACK" suppression/aggregation as it conducts this repair state suppression/aggregation as it conducts this repair state accumulation
accumulation for NORM repair cycles. The detail of this type of for NORM repair cycles. The detail of this type of operation are
operation are beyond the scope of this document, but this information beyond the scope of this document, but this information is provided
is provided for possible future consideration. 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 invalid "NORM_NACK" messages received since the last
"NORM_CMD(SQUELCH)" transmission. Lower ordinal invalid "NORM_CMD(SQUELCH)" transmission. The list includes as many lower
"object_transport_ids" should be included only while the ordinal invalid "object_transport_ids" that can fit for the
"NORM_CMD(SQUELCH)" payload is less than the sender's NormSegmentSize "NORM_CMD(SQUELCH)" payload size to less than or equal to the
parameter. 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
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feedback suppression in the same manner as with "NORM_NACK" messages feedback suppression in the same manner as with "NORM_NACK" messages
directly received from other receivers. Note the sender does not directly received from other receivers. Note the sender does not
merely retransmit NACK content it receives, but instead transmits a merely retransmit NACK content it receives, but instead transmits a
representation of its aggregated repair state. The transmission of representation of its aggregated repair state. The transmission of
"NORM_CMD(REPAIR_ADV)" messages are subject to the sender transmit "NORM_CMD(REPAIR_ADV)" messages are subject to the sender transmit
rate limit and NormSegmentSize limitation. When the rate limit and NormSegmentSize limitation. When the
"NORM_CMD(REPAIR_ADV)" message is of maximum size, receivers SHALL "NORM_CMD(REPAIR_ADV)" message is of maximum size, receivers SHALL
consider the maximum ordinal transmission position value embedded in consider the maximum ordinal transmission position value embedded in
the message as the senders current transmission position and the message as the senders current transmission position and
implicitly suppress requests for ordinally higher repair. For implicitly suppress requests for ordinally higher repair. For
congestion control operation, the sender may also need to provide congestion control operation, the sender will also need to provide
information so that dynamic congestion control feedback can be any information needed so that dynamic congestion control feedback
suppressed as needed among receivers. This document specifies the can be suppressed among receivers. This document specifies the
NORM-CC Feedback Header Extension that is applied for baseline NORM-CC Feedback Header Extension that is applied for baseline
NORM-CC operation. If other congestion control mechanisms are used NORM-CC operation. If other congestion control mechanisms are used
within a NORM implementation, other header extensions may be defined. within a NORM implementation, other header extensions MAY be defined.
Whatever content format is used for this purpose should ensure that Whatever content format is used for this purpose SHOULD ensure that
maximum possible suppression state is conveyed to the 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 need
agree on a common timeout basis. Each NORM sender monitors the to use a common timeout basis. Each NORM sender monitors the round-
round-trip time of active receivers and determines the group greatest 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 message ("NORM_NACK" or "NORM_ACK"). The adjustment adds the amount
of time the receiver held the timestamp before generating its of time the receiver held the timestamp before generating its
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or configuration. 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 messages, the receivers respond to "NORM_CMD(CC)" messages as
described 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 generated. In this case, the "NORM_CMD(CC)" messages MAY be sent
less frequently, perhaps as little as once per minute, to conserve less frequently, perhaps as little as once per minute, to conserve
network capacity. Note that the NORM-CC Rate header extension may network capacity. Note that the NORM-CC Rate header extension MAY
also be used to proactively solicit RTT feedback from the receiver also be used to proactively solicit RTT feedback from the receiver
group per congestion control operation even though the sender may not group per congestion control operation even when the sender is not
be conducting congestion control rate adjustment. NORM operation 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[RFC4654]. Friendly Multicast Congestion Control (TFMCC) approach[RFC4654].
This congestion control scheme is REQUIRED for operation within the This congestion control scheme is REQUIRED for operation within the
general Internet unless the NORM implementation is adapted to use general Internet unless the NORM implementation is adapted to use
another IETF-sanctioned reliable multicast congestion control another IETF-sanctioned reliable multicast congestion control
mechanism. With this TFMCC-based approach, the transmissions of NORM mechanism. With this TFMCC-based approach, the transmissions of NORM
senders are controlled in a rate-based manner as opposed to window- senders are controlled in a rate-based manner as opposed to window-
based congestion control algorithms as in TCP. However, it is based congestion control algorithms as in TCP. However, it is
possible that the NORM protocol message set may alternatively be used possible that the NORM protocol message set MAY alternatively be used
to support a window-based multicast congestion control scheme such as to support a window-based multicast congestion control scheme such as
PGMCC. The details of that alternative may be described separately PGMCC. The details of that alternative MAY be described separately
or in a future revision of this document. In either case (rate-based or in a future revision of this document. In either case (rate-based
TFMCC or window-based PGMCC), successful control of sender TFMCC or window-based PGMCC), successful control of sender
transmission depends upon collection of sender-to-receiver packet transmission depends upon collection of sender-to-receiver packet
loss estimates and RTTs to identify the congestion control bottleneck loss estimates and RTTs to identify the congestion control bottleneck
path(s) within the multicast topology and adjust the sender rate path(s) within the multicast topology and adjust the sender rate
accordingly. The receiver with loss and RTT estimates that accordingly. The receiver with loss and RTT estimates that
correspond to the lowest resulting calculated transmission rate is correspond to the lowest resulting calculated transmission rate is
identified as the "current limiting receiver" (CLR). In the case of identified as the "current limiting receiver" (CLR). In the case of
a tie (where candidate CLRs are within 10% of the same calculated a tie (where candidate CLRs are within 10% of the same calculated
rate), the receiver with the largest RTT value SHOULD be designated rate), the receiver with the largest RTT value SHOULD be designated
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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 current closely track the dynamics of congestion control for that current
worst path in the group multicast topology. worst path in the group multicast topology.
The format of the "NORM_CMD(CC)" message is described in The format of the "NORM_CMD(CC)" message is described in
Section 4.2.3 of this document. The "NORM_CMD(CC)" message contains Section 4.2.3 of this document. The "NORM_CMD(CC)" message contains
information to allow measurement of RTTs, to inform the group of the information to allow measurement of RTTs, to inform the group of the
congestion control CLR, and to provide feedback of individual RTT congestion control CLR, and to provide feedback of individual RTT
measurements to the receivers in the group. The "NORM_CMD(CC)" also measurements to the receivers in the group. The "NORM_CMD(CC)" also
provides for exciting feedback from OPTIONAL "potential limiting provides for exciting feedback from OPTIONAL "potential limiting
receiver" (PLR) nodes that may be determined administratively or receiver" (PLR) nodes that might be determined administratively or
possibly algorithmically based on congestion control feedback. PLR possibly algorithmically based upon congestion control feedback. PLR
nodes are receivers that have been identified to have potential for nodes are receivers that have been identified to have potential for
(perhaps soon) becoming the CLR and thus immediate, up-to-date (perhaps soon) becoming the CLR and thus immediate, up-to-date
feedback is beneficial for congestion control performance. The PLR feedback is beneficial for congestion control performance. The PLR
list may be populated with a small number of receivers the sender list MAY be populated with a small number of receivers the sender
identifies as approaching the CLR loss and delay conditions based on identifies as approaching the CLR loss and delay conditions based on
feedback from the group. feedback from the group.
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 can 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 A "NORM_CMD(CC)" message is immediately transmitted at sender
startup. The interval of subsequent "NORM_CMD(CC)" message startup. The interval of subsequent "NORM_CMD(CC)" message
transmission is determined as follows: transmission is determined as follows:
1. By default, the interval is set according to the current sender 1. By default, the interval is set according to the current sender
GRTT estimate. A startup GRTT of 0.5 seconds is recommended when GRTT estimate. A startup GRTT of 0.5 seconds is RECOMMENDED when
no feedback has yet been received from the group. no feedback has yet been received from the 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 interval "NORM_CMD(CC)" interval is doubled up from its current interval
to a maximum of once per 30 seconds. This results in a low duty to a maximum of once per 30 seconds. This results in a low duty
cycle for "NORM_CMD(CC)" probing when no CLR is identified or cycle for "NORM_CMD(CC)" probing when no CLR is identified or
there is no pending data to transmit. there is no pending data to transmit.
3. When a CLR has been identified (based on receiver feedback) and 3. When a CLR has been identified (based on receiver feedback) and
data transmission is pending, the probing interval is set to the data transmission is pending, the probing interval is set to the
RTT between the sender and the CLR ("RTT_clr"). RTT between the sender and the CLR ("RTT_clr").
4. Additionally, when the data transmission rate is low with respect 4. Additionally, when the data transmission rate is low with respect
to the "RTT_clr" interval used for probing, the implementation to the "RTT_clr" interval used for probing, the implementation
should ensure that no more than one "NORM_CMD(CC)" message is SHOULD ensure that no more than one "NORM_CMD(CC)" message is
sent per "NORM_DATA" message when there is data pending sent per "NORM_DATA" message when there is data pending
transmission. This ensures that the transmission of this control transmission. This ensures that the transmission of this control
message is not done to the exclusion of user data transmission. message is not done to the exclusion of user data transmission.
The "NORM_CMD(CC)" "cc_sequence" field is incremented with each The "NORM_CMD(CC)" "cc_sequence" field is incremented with each
transmission of a "NORM_CMD(CC)" command. The greatest "cc_sequence" 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 will 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 will 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 can 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 "NORM_CMD(CC)" messages. The maximum length of the list corresponds
to 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 get 1. Receivers that have not yet been provided a RTT measurement get
first priority. Of these, those with the greatest loss fraction first priority. Of these, those with the greatest loss 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 can 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 might not have
have been collected and thus the "cc_rtt" field does not contain a yet 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 MUST be treated as an invalid value and
and be ignored for the purposes of feedback suppression, etc. 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 Receivers explicitly respond to "NORM_CMD(CC)" messages in the form
of a "NORM_ACK(RTT)" message. The goal of the congestion control of a "NORM_ACK(RTT)" message. The goal of the congestion control
feedback is to determine the receivers with the lowest congestion feedback is to determine the receivers with the lowest congestion
control 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 "NORM_CMD(CC)" "cc_node_list" immediately provide feedback in the
form of a "NORM_ACK" to this message. When a "NORM_CMD(CC)" is form of a "NORM_ACK" to this message. When a "NORM_CMD(CC)" is
received, non-CLR or non-PLR nodes initiate random feedback backoff received, non-CLR or non-PLR nodes initiate random feedback backoff
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follows: 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 Multicast NACK distributed random number and is described in the Multicast NACK
Building Block [RFC5401]. The same backoff factor "K = Ksender" MAY Building Block [RFC5401]. The same backoff factor "K = Ksender" MAY
be used as with "NORM_NACK" suppression. However, in cases where the be used as with "NORM_NACK" suppression. However, in cases where the
application purposefully specifies a very small "Ksender" backoff application purposefully specifies a very small "Ksender" backoff
factor to minimize the NACK repair process latency (trading off group factor to minimize the NACK repair process latency (trading off group
size scalability), it is RECOMMENDED that a larger backoff factor for size scalability), it is RECOMMENDED that a larger backoff factor for
congestion control feedback is maintained, since there may often be a congestion control feedback is maintained, since there can often be a
larger volume of congestion control feedback than NACKs in many cases larger volume of congestion control feedback than NACKs in many cases
and some congestion control feedback latency may be tolerable where and some congestion control feedback latency might be tolerable where
reliable delivery latency is not. As previously noted, a backoff reliable delivery latency is not. As previously noted, a backoff
factor value of "K = 4" is generally recommended for ASM operation factor value of "K = 4" is generally RECOMMENDED for ASM operation
and "K = 6" for SSM operation. A receiver SHALL cancel the backoff and "K = 6" for SSM operation. A receiver SHALL cancel the backoff
timeout and thus its pending transmission of a "NORM_ACK(RTT)" timeout and thus its pending transmission of a "NORM_ACK(RTT)"
message under the following conditions: message under the following conditions:
1. The receiver generates another feedback message ("NORM_NACK" or 1. The receiver generates another feedback message ("NORM_NACK" or
other "NORM_ACK") before the congestion control feedback timeout other "NORM_ACK") before the congestion control feedback timeout
expires (these messages will convey the current congestion expires (these messages will convey the current 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
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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 competing receiver's feedback is "suppressed" if the rate of the competing
feedback ("Rfb") is sufficiently close to or less than the local feedback ("Rfb") is sufficiently close to or less than the local
receiver's calculated rate ("Rcalc"). The local receiver's receiver's calculated rate ("Rcalc"). The local receiver's
feedback is canceled when "Rcalc > (0.9 * Rfb)". Also note feedback is canceled when "Rcalc > (0.9 * Rfb)". Also note
receivers that have not yet received an RTT measurement from the receivers that have not yet received an RTT measurement from the
sender are suppressed only by other receivers that have not yet sender are suppressed only by other receivers that have not yet
measured RTT. Additionally, receivers whose RTT estimate has measured RTT. Additionally, receivers whose RTT estimate has
aged considerably (i.e., they haven't been included in the 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 "NORM_CMD(CC)" "cc_node_list" in a long time) might wish to
as a receiver with no prior RTT measurement after some long term compete as a receiver with no prior RTT measurement after some
expiration period. long term 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 the "cc_sequence" value from that command in the applicable
"NORM_ACK" or "NORM_NACK" message fields. For NORM-CC operation, any "NORM_ACK" or "NORM_NACK" message fields. For NORM-CC operation, any
generated feedback message SHALL also contain the NORM-CC Feedback generated feedback message SHALL also contain the NORM-CC Feedback
header extension. The receiver provides its current "cc_rate" header extension. The receiver provides its current "cc_rate"
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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 the "NORM_FLAG_CC_LEAVE" in its congestion control feedback message
as an indication that the sender should not select it as the CLR. as an indication that the sender SHOULD NOT select it as the CLR.
When 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 received The sender SHOULD also track the age of the feedback it has 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 transmission rate. After "NORM_ROBUST_FACTOR" consecutive
"NORM_CMD(CC)" rounds without any feedback from the CLR, the sender "NORM_CMD(CC)" rounds without any feedback from the CLR, the sender
SHOULD assume the CLR has left the group and pick the receiver with SHOULD assume the CLR has left the group and pick the receiver with
the next lowest rate as the new CLR. Note this assumes that the the next lowest rate as the new CLR. Note this assumes that the
sender does not have explicit knowledge that the CLR intentionally sender does not have explicit knowledge that the CLR intentionally
left the group. If no receiver feedback is received, the sender MAY left the group. If no receiver feedback is received, the sender MAY
wish to withhold further transmissions of "NORM_DATA" segments and wish to withhold further transmissions of "NORM_DATA" segments and
maintain "NORM_CMD(CC)" transmissions only until feedback is maintain "NORM_CMD(CC)" transmissions only until feedback is
detected. After such a CLR timeout, the sender will be transmitting detected. After such a CLR timeout, the sender will be transmitting
with a minimal rate and should return to slow start as described here with a minimal rate and SHOULD return to slow start as described here
for a break in data 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 "NORM_FLAG_START" flag in its "NORM_CMD(CC)" messages upon restart
and the group should observer slow start congestion control and the group SHOULD observe slow start congestion control procedures
procedures until any receiver experiences a new loss event. 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
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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 of the receivers expected to 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 or source application with a priori knowledge of participating nodes 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 of watermark transmission point is echoed in the corresponding fields 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 can 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 spread "NORM_ACK" messages uniformly in time over a window of
(1*GRTT). These "NORM_ACK" messages are typically unicast to the (1*GRTT). These "NORM_ACK" messages are typically unicast to the
sender. (Note that "NORM_ACK(CC)" messages SHALL be multicast or sender. (Note that "NORM_ACK(CC)" messages SHALL be multicast or
unicast in the same 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 sender acknowledgment is requested is limited to a maximum of the sender
NormSegmentSize setting per round of the positive acknowledgment NormSegmentSize setting per round of the positive acknowledgment
process. process.
Because the size of the included list is limited to the sender's Because the size of the included list is limited to the sender's
NormSegmentSize setting, multiple "NORM_CMD(ACK_REQ)" rounds may be NormSegmentSize setting, multiple "NORM_CMD(ACK_REQ)" rounds will
required to achieve responses from all receivers specified. The sometimes be necessary to achieve responses from all receivers
content of the attached NormNodeId list will be dynamically updated specified. The content of the attached NormNodeId list will be
as this process progresses and "NORM_ACK" responses are received from dynamically updated as this process progresses and "NORM_ACK"
the specified receiver set. As the sender receives valid responses responses are received from the specified receiver set. As the
(i.e., matching watermark point or "ack_id") from receivers, it SHALL sender receives valid responses (i.e., matching watermark point or
eliminate those receivers from the subsequent "NORM_CMD(ACK_REQ)" "ack_id") from receivers, it SHALL eliminate those receivers from the
message "acking_node_list" and add in any pending receiver subsequent "NORM_CMD(ACK_REQ)" message "acking_node_list" and add in
NormNodeIds while keeping within the NormSegmentSize limitation of any pending receiver NormNodeIds while keeping within the
the list size. Each receiver is queried a maximum number of times NormSegmentSize limitation of the list size. Each receiver is
("NORM_ROBUST_FACTOR", by default). Receivers not responding within queried a maximum number of times ("NORM_ROBUST_FACTOR", by default).
this number of repeated requests are removed from the payload list to Receivers not responding within this number of repeated requests are
make room for other potential receivers pending acknowledgment. The removed from the payload list to make room for other potential
transmission of the "NORM_CMD(ACK_REQ)" is repeated until no further receivers pending acknowledgment. The transmission of the
responses are required or until the repeat threshold is exceeded for "NORM_CMD(ACK_REQ)" is repeated until no further responses are needed
all pending receivers. The transmission of "NORM_CMD(ACK_REQ)" or or until the repeat threshold is exceeded for all pending receivers.
"NORM_CMD(FLUSH)" messages to conduct the positive acknowledgment The transmission of "NORM_CMD(ACK_REQ)" or "NORM_CMD(FLUSH)" messages
process is multiplexed with ongoing sender data transmissions. to conduct the positive acknowledgment process is multiplexed with
However, the "NORM_CMD(FLUSH)" positive acknowledgment process may be ongoing sender data transmissions. However, the "NORM_CMD(FLUSH)"
interrupted in response to negative acknowledgment repair requests positive acknowledgment process MAY be interrupted in response to
(NACKs) received from receivers during the acknowledgment period. negative acknowledgment repair requests (NACKs) received from
The "NORM_CMD(FLUSH)" positive acknowledgment process is restarted receivers during the acknowledgment period. The "NORM_CMD(FLUSH)"
for receivers pending acknowledgment once any the repairs have been positive acknowledgment process is restarted for receivers pending
transmitted. acknowledgment once any the repairs have been transmitted.
In the case of "NORM_CMD(FLUSH)" commands with an attached In the case of "NORM_CMD(FLUSH)" commands with an attached
"acking_node_list", receivers will not ACK until they have received "acking_node_list", receivers will not ACK until they have received
complete transmission of all data up to and including the given complete transmission of all data up to and including the given
watermark transmission point. All receivers SHALL interpret the watermark transmission point. All receivers SHALL interpret the
watermark point provided in the request NACK for repairs if needed as watermark point provided in the request NACK for repairs if needed as
for "NORM_CMD(FLUSH)" commands with no attached "acking_node_list". for "NORM_CMD(FLUSH)" commands with no attached "acking_node_list".
5.5.4. Group Size Estimate 5.5.4. Group Size Estimate
NORM sender messages contain a "gsize" field that is a representation NORM sender messages contain a "gsize" field that is a representation
of the group size and is used in scaling random backoff timer ranges. of the group size and is used in scaling random backoff timer ranges.
The use of the group size estimate within the NORM protocol does not The use of the group size estimate within the NORM protocol does not
require a precise estimation and works reasonably well if the demand a precise estimation and works reasonably well if the estimate
estimate is within an order of magnitude of the actual group size. is within an order of magnitude of the actual group size. By
By default, the NORM sender group size estimate may be default, the NORM sender group size estimate MAY be administratively
administratively configured. Also, given the expected scalability of configured. Also, given the expected scalability of the NORM
the NORM protocol for general use, a default value of 10,000 is protocol for general use, a default value of 10,000 is RECOMMENDED
RECOMMENDED for use as the group size estimate. for use as the group size estimate. It is also possible that group
size MAY be algorithmically approximated from the volume of
It is possible that group size may be algorithmically approximated congestion control feedback messages which follow the exponentially
from the volume of congestion control feedback messages which follow weighted random backoff. However, the specification of such an
the exponentially weighted random backoff. However, the algorithm is currently beyond the scope of this document.
specification of such an algorithm is currently beyond the scope of
this document.
6. Security Considerations 6. Security Considerations
The same security considerations that apply to the Multicast NACK The same security considerations that apply to the Multicast NACK
[RFC5401], TFMCC [RFC4654], and FEC [RFC5052] Building Blocks also [RFC5401], TFMCC [RFC4654], and FEC [RFC5052] Building Blocks also
apply to the NORM protocol. In addition to the vulnerabilities that apply to the NORM protocol. In addition to the vulnerabilities to
any IP and IP multicast protocol implementation may be generally which any IP and IP multicast protocol implementation are subject,
subject to, the NACK-based feedback of NORM may be exploited by the NACK-based feedback of NORM can be exploited by replay attacks
replay attacks which force the NORM sender to unnecessarily transmit which force the NORM sender to unnecessarily transmit repair
repair information. This MAY be addressed by network layer IP information. This MAY be addressed by network layer IP security
security implementations that guard against this potential security implementations that guard against this potential security
exploitation or alternatively with a security mechanism that uses the exploitation or alternatively with a security mechanism that uses the
"EXT_AUTH" header extension for similar purposes. Such security "EXT_AUTH" header extension for similar purposes. Such security
mechanisms SHOULD be deployed and used when available. mechanisms SHOULD be deployed and used when available.
The NORM protocol is compatible with the use of IP security (IPsec) The NORM protocol is compatible with the use of IP security (IPsec)
[RFC4301] and the IPsec Encapsulating Security Payload (ESP) protocol [RFC4301] and the IPsec Encapsulating Security Payload (ESP) protocol
or Authentication Header (AF) extension can be used to secure IP or Authentication Header (AF) extension can be used to secure IP
packets transmitted by NORM participants. A baseline approach to packets transmitted by NORM participants. A baseline approach to
secure NORM operation using IPsec is described below. Compliant secure NORM operation using IPsec is described below. Compliant
implementations of this specification are REQUIRED to be compatible implementations of this specification are REQUIRED to be compatible
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for use by security mechanisms to provide an alternative form of for use by security mechanisms to provide an alternative form of
authentication and/or encryption of NORM messages. The format of authentication and/or encryption of NORM messages. The format of
this header extension and its processing is outside the scope of this this header extension and its processing is outside the scope of this
document and is to be communicated out-of-band as part of the session document and is to be communicated out-of-band as part of the session
description. It is possible that an EXT_AUTH implementation of MAY description. It is possible that an EXT_AUTH implementation of MAY
also provide for encryption of NORM message payloads as well as also provide for encryption of NORM message payloads as well as
authentication. The use of this approach as compared to IPsec can authentication. The use of this approach as compared to IPsec can
allow for header compression techniques to be applied jointly to IP allow for header compression techniques to be applied jointly to IP
and NORM protocol headers. In cases where security analysis deems and NORM protocol headers. In cases where security analysis deems
that encryption of NORM protocol header content is beneficial or that encryption of NORM protocol header content is beneficial or
necessary, the aforementioned use of IPsec ESP may be more necessary, the aforementioned use of IPsec ESP might be more
appropriate. If EXT_AUTH is present, whatever packet authentication appropriate. If EXT_AUTH is present, whatever packet authentication
checks that can be performed immediately upon reception of the packet checks that can be performed immediately upon reception of the packet
MUST be performed before accepting the packet and performing any MUST be performed before accepting the packet and performing any
congestion control-related action on it. Some packet authentication congestion control-related action on it. Some packet authentication
schemes impose a delay of several seconds between when a packet is schemes impose a delay of several seconds between when a packet is
received and when the packet can be fully authenticated. Any received and when the packet can be fully authenticated. Any
congestion control related action that is appropriate MUST NOT be congestion control related action that is appropriate MUST NOT be
postponed by any such full packet authentication. postponed by any such full packet authentication.
Consideration MUST also be given to the potential for replay-attacks Consideration MUST also be given to the potential for replay-attacks
that would transplant authenticated packets from one NORM session to that would transplant authenticated packets from one NORM session to
another to disrupt service. To avoid this potential, unique keys another to disrupt service. To avoid this potential, unique keys
SHOULD be assigned on a per-session basis or NORM sender nodes SHOULD SHOULD be assigned on a per-session basis or NORM sender nodes SHOULD
be configured to use unique "instance_id" identifiers that are be configured to use unique "instance_id" identifiers that are
managed as part of the security association for the sessions. managed as part of the security association for the sessions.
It should be noted that NORM implementations can use the "sequence" Note that NORM implementations can use the "sequence" field from the
field from the NORM Common Message Header to detect replay attacks. NORM Common Message Header to detect replay attacks. This can be
This can be accomplished if the NORM sender maintains state on accomplished if the NORM sender maintains state on receivers which
receivers which are NACKing. A cache of such receiver state can be are NACKing. A cache of such receiver state can be used to provide
used to provide protection against NACK replay attacks. NORM protection against NACK replay attacks. NORM receivers MUST also
receivers MUST also maintain similar state for protection against maintain similar state for protection against possible replay of
possible replay of other receiver messages in ASM operation as well. other receiver messages in ASM operation as well. For example, a
For example, a receiver could be suppressed from providing NACK or receiver could be suppressed from providing NACK or congestion
congestion control feedback by replay of certain receiver messages. control feedback by replay of certain receiver messages. For these
For these reasons, authentication of NORM messages (e.g., via IPsec) reasons, authentication of NORM messages (e.g., via IPsec) SHOULD be
SHOULD be applied for protection against similar attacks that use applied for protection against similar attacks that use fabricated
fabricated messages. Also, encryption of messages to provide messages. Also, encryption of messages to provide confidentiality of
confidentiality of application data and protect privacy of users MAY application data and protect privacy of users MAY also be applied
also be applied using IPsec or similar mechanisms. using IPsec or similar mechanisms.
When applicable security measures are used, automated key management When applicable security measures are used, automated key management
mechanisms such as those described in the Group Domain of mechanisms such as those described in the Group Domain of
Interpretation (GDOI) [RFC3547], Multimedia Internet KEYing (MIKEY) Interpretation (GDOI) [RFC3547], Multimedia Internet KEYing (MIKEY)
[RFC3830] or Group Secure Association Key Management Protocol [RFC3830] or Group Secure Association Key Management Protocol
(GSAKMP) [RFC4535] specifications SHOULD be applied. (GSAKMP) [RFC4535] specifications SHOULD be applied.
It is also important to note that while NORM does leverage FEC-based While NORM does leverage FEC-based repair for scalability, this alone
repair for scalability, this alone does not guarantee integrity of does not guarantee integrity of received data. Application-level
received data. Application-level integrity-checking of received data integrity-checking of received data content is highly RECOMMENDED.
content is highly RECOMMENDED.
6.1. Baseline Secure NORM Operation 6.1. Baseline Secure NORM Operation
This section describes a baseline mode of secure NORM protocol This section describes a baseline mode of secure NORM protocol
operation based on application of the IPsec security protocol. This operation based on application of the IPsec security protocol. This
approach is documented here to provide a reference, interoperable approach is documented here to provide a reference, interoperable
secure mode of operation. However, additional approaches to NORM secure mode of operation. Additional approaches to NORM security,
security, including other forms of IPsec application, MAY be including other forms of IPsec application, MAY be specified in the
specified in the future. For example, the use of the EXT_AUTH header future. For example, the use of the EXT_AUTH header extension could
extension could enable NORM-specific authentication or security enable NORM-specific authentication or security encapsulation headers
encapsulation headers similar to those of IPsec to be specified and similar to those of IPsec to be specified and inserted into the NORM
inserted into the NORM protocol message headers. This would allow protocol message headers. This would allow header compression
header compression techniques to be applied to IP and NORM protocol techniques to be applied to IP and NORM protocol headers when needed
headers when needed in a similar fashion to that of RTP [RFC3550] and in a similar fashion to that of RTP [RFC3550] and as preserved in the
as preserved in the specification for Secure Real Time Protocol specification for Secure Real Time Protocol (SRTP) [RFC3711].
(SRTP) [RFC3711].
The baseline approach described is applicable to NORM operation The baseline approach described is applicable to NORM operation
configured for SSM (or SSM-like) operation where there is a single configured for SSM (or SSM-like) operation where there is a single
sender and the receivers are providing unicast feedback. This form sender and the receivers are providing unicast feedback. This form
of NORM operation allows for IPsec to be used with a manageable of NORM operation allows for IPsec to be used with a manageable
number of security associations (SA). number of security associations (SA).
6.1.1. IPsec Approach 6.1.1. IPsec Approach
For NORM one-to-many SSM operation with unicast feedback from For NORM one-to-many SSM operation with unicast feedback from
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messaging from the receiver(s) to the sender. messaging from the receiver(s) to the sender.
The NORM sender SHALL use an IPsec SA configured for ESP protocol The NORM sender SHALL use an IPsec SA configured for ESP protocol
[RFC4303] operation with the option for data origination [RFC4303] operation with the option for data origination
authentication enabled. It is also RECOMMENDED that this IPsec ESP authentication enabled. It is also RECOMMENDED that this IPsec ESP
SA be also configured to provide confidentiality protection for IP SA be also configured to provide confidentiality protection for IP
packets containing NORM protocol messages. This is suggested to make packets containing NORM protocol messages. This is suggested to make
the realization of complex replay attacks much more difficult. The the realization of complex replay attacks much more difficult. The
encryption key for this SA SHALL be preplaced at the sender and encryption key for this SA SHALL be preplaced at the sender and
receiver(s) prior to NORM protocol operation. Use of automated key receiver(s) prior to NORM protocol operation. Use of automated key
management is RECOMMENDED as a rekey SHALL be required prior to management is RECOMMENDED as a rekey SHALL be REQUIRED prior to
expiration of the sequence space for the SA. This is necessary so expiration of the sequence space for the SA. This is necessary so
that receivers may use the built-in IPsec replay attack protection that receivers can use the built-in IPsec replay attack protection
possible for an IPsec SA with a single source (the NORM sender). possible for an IPsec SA with a single source (the NORM sender).
Thus the receivers SHALL enable replay attack protection for this SA Thus the receivers SHALL enable replay attack protection for this SA
used to secure NORM sender traffic. An IPsec SPD entry MUST be used to secure NORM sender traffic. An IPsec SPD entry MUST be
configured to process outbound packets to the session (destination) configured to process outbound packets to the session (destination)
address and UDP port number of the applicable (NormSession). address and UDP port number of the applicable (NormSession).
The NORM receiver(s) MUST be configured with the SA and SPD entry to The NORM receiver(s) MUST be configured with the SA and SPD entry to
properly process the IPsec-secured packets from the sender. The NORM properly process the IPsec-secured packets from the sender. The NORM
receiver(s) SHALL also use a common, second IPsec SA (common Security receiver(s) SHALL also use a common, second IPsec SA (common Security
Parameter Index (SPI) and encryption key) configured for ESP Parameter Index (SPI) and encryption key) configured for ESP
operation with the option for data origination authentication operation with the option for data origination authentication
enabled. Similar to the NORM sender, is RECOMMENDED this IPsec ESP enabled. Similar to the NORM sender, is RECOMMENDED this IPsec ESP
SA be also configured to provide confidentiality protection for IP SA be also configured to provide confidentiality protection for IP
packets containing NORM protocol messages. The receivers MUST have packets containing NORM protocol messages. The receivers MUST have
an IPsec SPD entry configured to process outbound NORM/UDP packets an IPsec SPD entry configured to process outbound NORM/UDP packets
directed to the NORM sender source address and port number using this directed to the NORM sender source address and port number using this
second SA. As noted for NORM unicast feedback, the sender's second SA. To support NORM unicast feedback, the sender's
transmission port number SHOULD be selected to be distinct from the transmission port number SHOULD be selected to be distinct from the
multicast session port number to allow discrimination between unicast multicast session port number to allow discrimination between unicast
and multicast feedback messages when access to the IP destination and multicast feedback messages when access to the IP destination
address is not possible (e.g., a user-space NORM implementation). address is not possible (e.g., a user-space NORM implementation).
For processing of packets from receivers, the NORM sender SHALL be For processing of packets from receivers, the NORM sender SHALL be
configured with this common, second SA (and the corresponding SPD configured with this common, second SA (and the corresponding SPD
entry needed) in order to properly process messages from the entry needed) in order to properly process messages from the
receiver. receiver.
Multiple receivers using a common IPsec SA for traffic directed to Multiple receivers using a common IPsec SA for traffic directed to
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the NORM sender (i.e., many-to-one) typically prevents the use of the NORM sender (i.e., many-to-one) typically prevents the use of
built-in IPsec replay attack protection by the NORM sender with built-in IPsec replay attack protection by the NORM sender with
current IPsec implementations. Thus the built-in IPsec replay attack current IPsec implementations. Thus the built-in IPsec replay attack
protection for this second SA at the sender MUST be disabled unless protection for this second SA at the sender MUST be disabled unless
the particular IPsec implementation manages its replay protection on the particular IPsec implementation manages its replay protection on
a per-source basis. So, to support a fully secure mode of operation, a per-source basis. So, to support a fully secure mode of operation,
the NORM sender implementation MUST provide replay attack protection the NORM sender implementation MUST provide replay attack protection
based upon the "sequence" field of NORM protocol messages from based upon the "sequence" field of NORM protocol messages from
receivers. This can be accomplished with high assurance of security, receivers. This can be accomplished with high assurance of security,
even with the limited size (16-bits) of this field, because even with the limited size (16-bits) of this field, because
1. NORM receiver NACK and non-CLR ACK feedback messages are sparse. 1. NORM receiver NACK and non-CLR ACK feedback messages are sparse.
2. The more frequent "NORM_ACK" feedback from CLR or PLR nodes are 2. The more frequent "NORM_ACK" feedback from CLR or PLR nodes are
only a small set of receivers for which the sender must keep more only a small set of receivers for which the sender needs to keep
persistent replay attack state. more persistent replay attack state.
3. "NORM_NACK" feedback messages that precede the sender's current 3. "NORM_NACK" feedback messages that precede the sender's current
repair window do not significantly impact protocol operation repair window do not significantly impact protocol operation
(generation of "NORM_CMD(SQUELCH)" is limited) and could be in (generation of "NORM_CMD(SQUELCH)" is limited) and could be in
fact ignored. This means the sender can prune any replay attack fact ignored. This means the sender can prune any replay attack
state for receivers that precede the current repair window. state that precedes the current repair window.
4. "NORM_ACK" messages correspond to either a specific sender 4. "NORM_ACK" messages correspond to either a specific sender
"ack_id", the sender "cc_sequence" for ACKs sent in response to "ack_id", the sender "cc_sequence" for ACKs sent in response to
"NORM_CMD(CC)", or the sender's current repair window in the case "NORM_CMD(CC)", or the sender's current repair window in the case
of ACKs sent in response to "NORM_CMD(FLUSH)". Thus, the sender of ACKs sent in response to "NORM_CMD(FLUSH)". Thus, the sender
can prune any replay attack state for receivers that precede the can prune any replay attack state for receivers that precede the
current applicable sequence or repair window space. current applicable sequence or repair window space.
Note that use of ESP confidentiality for secure NORM protocol The use of ESP confidentiality for secure NORM protocol operation
operation makes it more difficult for adversaries to conduct any form makes it more difficult for adversaries to conduct any form of replay
of replay attacks. Additionally, it should be noted that a NORM attacks. Additionally, a NORM sender implementation with access to
sender implementation with access to the full ESP protocol header the full ESP protocol header could also use the ESP sequence
could also use the ESP sequence information to make replay attack information to make replay attack protection even more robust by
protection even more robust, by maintaining per-source sequence maintaining per-source sequence state. The design of this baseline
state. The design of this baseline security approach for NORM security approach for NORM intentionally places any more complex
intentionally places any more complex processing state or processing processing state or processing (e.g. replay attack protection given
(e.g. replay attack protection given multiple receivers) at the NORM multiple receivers) at the NORM sender since NORM receiver
sender since NORM receiver implementations may need to have a more implementations might often need to be less complex.
light-weight realization in many cases.
This baseline approach can be used for NORM protocol sessions with This baseline approach can be used for NORM protocol sessions with
multiple senders if the SA pairs described are established for each multiple senders if the SA pairs described are established for each
sender. For small-sized groups, it is even possible that many-to- sender. For small-sized groups, it is even possible that many-to-
many (ASM) IPsec configuration could be achieved where each many (ASM) IPsec configuration could be achieved where each
participant uses a unique SA (with a unique SPI). This does not participant uses a unique SA (with a unique SPI). This does not
scale to larger group sizes given the complex set of SA and SPD scale to larger group sizes given the complex set of SA and SPD
entries each participant would need to maintain. entries each participant would need to maintain.
It is anticipated in early deployments of this baseline approach to It is anticipated in early deployments of this baseline approach to
NORM security that key management will be conducted out-of-band with NORM security that key management will be conducted out-of-band with
respect to NORM protocol operation. In the case of one-to-many NORM respect to NORM protocol operation. In the case of one-to-many NORM
operation, it is possible that receivers may retrieve keying operation, it is possible that receivers will retrieve keying
information from a central server as needed or otherwise conduct information from a central server as needed or otherwise conduct
group key updates with a similar centralized approach. However, it group key updates with a similar centralized approach.
may be possible with some key management schemes for rekey messages Alternatively, it is possible with some key management schemes for
to be transmitted to the group as a message or transport object rekey messages to be transmitted to the group as a message or
within the NORM reliable transfer session. Similarly, for group-wise transport object within the NORM reliable transfer session.
communication sessions it is possible that potential group Similarly, for group-wise communication sessions it is possible that
participants may request keying and/or rekeying as part of NORM potential group participants request keying and/or rekeying as part
communications. Additional specification is necessary to define an of NORM communications. Additional specification is necessary to
in-band key management scheme for NORM sessions perhaps using the define an in-band key management scheme for NORM sessions perhaps
mechanisms of the automated group key management specifications cited using the mechanisms of the automated group key management
in this document. specifications cited in this document.
6.1.2. IPsec Requirements 6.1.2. IPsec Requirements
In order to implement this secure mode of NORM protocol operation, In order to implement this secure mode of NORM protocol operation,
the following IPsec capabilities are required. the following IPsec capabilities are REQUIRED.
6.1.2.1. Selectors 6.1.2.1. Selectors
The implementation MUST be able to use the source address, The implementation MUST be able to use the source address,
destination address, protocol (UDP), and UDP port numbers as destination address, protocol (UDP), and UDP port numbers as
selectors in the SPD. selectors in the SPD.
6.1.2.2. Mode 6.1.2.2. Mode
IPsec in transport mode MUST be supported. The use of IPsec IPsec in transport mode MUST be supported. The use of IPsec
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that unauthenticated packets are not received by the NORM protocol that unauthenticated packets are not received by the NORM protocol
implementation. implementation.
6.1.2.3. Key Management 6.1.2.3. Key Management
An automated key management scheme for group key distribution and An automated key management scheme for group key distribution and
rekeying such as GDOI [RFC3547], GSAKMP [RFC4535], or MIKEY [RFC3830] rekeying such as GDOI [RFC3547], GSAKMP [RFC4535], or MIKEY [RFC3830]
is RECOMMENDED for use. Relatively short-lived NORM sessions MAY be is RECOMMENDED for use. Relatively short-lived NORM sessions MAY be
able to use Manual Keying with a single, preplaced key, particularly able to use Manual Keying with a single, preplaced key, particularly
if Extended Sequence Numbering (ESN) [RFC4303] is available in the if Extended Sequence Numbering (ESN) [RFC4303] is available in the
IPsec implementation used. It should also be noted that it may be IPsec implementation used. Note it is possible for key update
possible for key update messages (e.g., the GDOI GROUPKEY-PUSH messages (e.g., the GDOI GROUPKEY-PUSH message) to be included as
message) to be included as part of the NORM application reliable data part of the NORM application reliable data transmission if
transmission if appropriate interfaces are available between the NORM appropriate interfaces are available between the NORM application and
application and the key management daemon. the key management daemon.
6.1.2.4. Security Policy 6.1.2.4. Security Policy
Receivers MUST accept protocol messages only from the designated, Receivers MUST accept protocol messages only from the designated,
authorized sender(s). It is expected that appropriate key management authorized sender(s). Appropriate key management will provide
will provide encryption keys only to receivers authorized to encryption keys only to receivers authorized to participate in a
participate in a designated session. The approach outlined here designated session. The approach outlined here allows receiver sets
allows receiver sets to be controlled on a per-sender basis. to be controlled on a per-sender basis.
6.1.2.5. Authentication and Encryption 6.1.2.5. Authentication and Encryption
Large NORM group sizes will necessitate some form of key management Large NORM group sizes will necessitate some form of key management
that does rely upon shared secrets. The GDOI and GSAKMP protocols that does rely upon shared secrets. The GDOI and GSAKMP protocols
mentioned here allow for certificate-based authentication. It is mentioned here allow for certificate-based authentication. It is
RECOMMENDED these certificates use IP addresses for authentication RECOMMENDED these certificates use IP addresses for authentication.
although it may alternatively possible to have authentication
associated with pre-assigned NormNodeId values. However, it is
likely that available group key management implementations will not
be NORM-specific.
6.1.2.6. Availability 6.1.2.6. Availability
The IPsec requirements profile outlined here is commonly available on The IPsec requirements profile outlined here is commonly available on
many potential NORM hosts. The principal issue is that configuration many potential NORM hosts. Configuration and operation of IPsec
and operation of IPsec typically requires privileged user typically requires privileged user authorization. Automated key
authorization. Automated key management implementations are management implementations are typically configured with the
typically configured with the privileges necessary to effect system privileges necessary to effect system IPsec configuration needed.
IPsec configuration needed.
7. IANA Considerations 7. IANA Considerations
Values of NORM Header Extension Types, Stream Control Codes, and Values of NORM Header Extension Types, Stream Control Codes, and
"NORM_CMD" message sub-types are subject to IANA registration. They "NORM_CMD" message sub-types are subject to IANA registration. They
are in the registry named "Reliable Multicast Transport (RMT) NORM are in the registry named "Reliable Multicast Transport (RMT) NORM
Protocol Parameters" located at time of publication at: Protocol Parameters" located at time of publication at:
http:///www.iana.org/assignments/norm-parameters http://www.iana.org/assignments/norm-parameters
It should be also noted that reliable multicast building block Note that reliable multicast building block components used by this
components used by this specification also have their respective IANA specification also have their respective IANA considerations and
considerations and those documents should be consulted accordingly. those documents SHOULD be consulted accordingly. In particular, the
In particular, the FEC Building Block used by NORM does require IANA FEC Building Block used by NORM does REQUIRE IANA registration of the
registration of the FEC codecs used. The registration instructions FEC codecs used. The registration instructions for FEC codecs are
for FEC codecs are provided in RFC 5052. provided in RFC 5052. It is possible that additional extensions of
the NORM protocol might be speciified in the future (e.g., additional
NORM message types) and additional registries be established at that
time with appropriate IETF standards action.
7.1. Explicit IANA Assignment Guidelines 7.1. Explicit IANA Assignment Guidelines
This document introduces three namespaces that are registered for the This document introduces three registries for the NORM Header
NORM Header Extension Types, Stream Control Codes and "NORM_CMD" Extension Types, Stream Control Codes and "NORM_CMD" Message sub-
Message Sub-types. This section describes explicit IANA assignment types. This section describes explicit IANA assignment guidelines
guidelines for each of these. for each of these.
7.1.1. NORM Header Extension Types 7.1.1. NORM Header Extension Types
This document defines a namespace for NORM Header Extension Types This document defines a registry for NORM Header Extensions named
named: "NORM Header Extension Types".
"ietf:rmt:norm:extension"
The NORM Header Extension Type field is an 8-bit value. The values The NORM Header Extension Type field is an 8-bit value. The values
of this field identify extended header content that allows the of this field identify extended header content that allows the
protocol functionality to be expanded to include additional features protocol functionality to be expanded to include additional features
and operating modes. The values that can be assigned within the and operating modes. The values that can be assigned within the
"ietf:rmt:norm:extension" namespace are numeric indexes in the range "NORM Header Extensions" registry are numeric indexes in the range
{0, 255}, boundaries included. Values in the range {0,127} indicate {0, 255}, boundaries included. Values in the range {0,127} indicate
variable length extended header fields while values in the range variable length extended header fields while values in the range
{128,255} indicate extensions of a fixed 4-byte length. This {128,255} indicate extensions of a fixed 4-byte length. This
specification registers the following NORM Header Extension Types: specification registers the following NORM Header Extension Types:
+-------+------------+--------------------+ +-------+------------+--------------------+
| Value | Name | Reference | | Value | Name | Reference |
+-------+------------+--------------------+ +-------+------------+--------------------+
| 1 | "EXT_AUTH" | This specification | | 1 | "EXT_AUTH" | This specification |
| 3 | "EXT_CC" | This specification | | 3 | "EXT_CC" | This specification |
| 64 | "EXT_FTI" | This specification | | 64 | "EXT_FTI" | This specification |
| 128 | "EXT_RATE" | This specification | | 128 | "EXT_RATE" | This specification |
+-------+------------+--------------------+ +-------+------------+--------------------+
Requests for assignment of additional NORM Header Extension Type Requests for assignment of additional NORM Header Extension Type
values are granted on a "Specification Required" basis as defined by values are granted on a "Specification Required" basis as defined by
IANA Guidelines [RFC5226]. Any such header extension specifications IANA Guidelines [RFC5226]. Any such header extension specifications
MUST include a description of protocol actions to be taken when the MUST include a description of protocol actions to be taken when the
extension type is encountered by a protocol implementation not extension type is encountered by a protocol implementation not
supporting that specific option. For example, it may be possible for supporting that specific option. For example, it is often possible
protocol implementations to ignore unknown header extensions in many for protocol implementations to ignore unknown header extensions.
cases.
7.1.2. NORM Stream Control Codes 7.1.2. NORM Stream Control Codes
This document defines a namespace for NORM Stream Control Codes This document defines a registry for NORM Stream Control Codes named
named: "NORM Stream Control Codes".
"ietf:rmt:norm:streamControlCode"
NORM Stream Control Codes are 16-bit values that may be inserted NORM Stream Control Codes are 16-bit values that can be inserted
within a "NORM_OBJECT_STREAM" delivery object to convey sequenced, within a "NORM_OBJECT_STREAM" delivery object to convey sequenced,
out-of-band (with respect to the stream data) control signaling out-of-band (with respect to the stream data) control signaling
applicable to the referenced stream object. These control codes are applicable to the referenced stream object. These control codes are
to be delivered to the application or protocol implementation with to be delivered to the application or protocol implementation with
reliable delivery, in-order with respect to the their inserted reliable delivery, in-order with respect to the their inserted
position within the stream. This specification registers the position within the stream. This specification registers the
following NORM Stream Control Code: following NORM Stream Control Code:
+-------+-------------------+--------------------+ +-------+-------------------+--------------------+
| Value | Name | Reference | | Value | Name | Reference |
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granted on a "Specification Required" basis as defined by IANA granted on a "Specification Required" basis as defined by IANA
Guidelines [RFC5226]. The full 16-bit space outside of the value Guidelines [RFC5226]. The full 16-bit space outside of the value
assigned in this specification are available for future assignment. assigned in this specification are available for future assignment.
Note that in addition to describing the control code's expected Note that in addition to describing the control code's expected
interpretation, such specifications MUST include a description of interpretation, such specifications MUST include a description of
protocol actions to be taken when the control code is encountered by protocol actions to be taken when the control code is encountered by
a protocol implementation not supporting that specific option. a protocol implementation not supporting that specific option.
7.1.3. NORM_CMD Message Sub-types 7.1.3. NORM_CMD Message Sub-types
This document defines a namespace for "NORM_CMD" Message Sub-types This document defines a registry for "NORM_CMD" message sub-types
named: named "NORM Command Message Sub-types".
"ietf:rmt:norm:command"
The "NORM_CMD" sub-type field is an 8-bit value with valid values in The "NORM_CMD" message sub-type (a.k.a. "flavor") field is an 8-bit
the range of 1-255. Note the value 0 is reserved to indicate an value with valid values in the range of 1-255. Note the value 0 is
invalid "NORM_CMD" message sub-type. The current specification reserved to indicate an invalid "NORM_CMD" message sub-type. The
defines a number of "NORM_CMD" message sub-types that senders can use current specification defines a number of "NORM_CMD" message sub-
to signal the receivers in various aspects of NORM protocol types that senders can use to signal the receivers in various aspects
operation. This specification registers the following "NORM_CMD" of NORM protocol operation. This specification registers the
Message Sub-types: following "NORM_CMD" Message Sub-types:
+-------+-------------------------+--------------------+ +-------+-------------------------+--------------------+
| Value | Name | Reference | | Value | Name | Reference |
+-------+-------------------------+--------------------+ +-------+-------------------------+--------------------+
| 0 | reserved | This specification | | 0 | reserved | This specification |
| 1 | "NORM_CMD(FLUSH)" | This specification | | 1 | "NORM_CMD(FLUSH)" | This specification |
| 2 | "NORM_CMD(EOT)" | This specification | | 2 | "NORM_CMD(EOT)" | This specification |
| 3 | "NORM_CMD(SQUELCH)" | This specification | | 3 | "NORM_CMD(SQUELCH)" | This specification |
| 4 | "NORM_CMD(CC)" | This specification | | 4 | "NORM_CMD(CC)" | This specification |
| 5 | "NORM_CMD(REPAIR_ADV)" | This specification | | 5 | "NORM_CMD(REPAIR_ADV)" | This specification |
| 6 | "NORM_CMD(ACK_REQ)" | This specification | | 6 | "NORM_CMD(ACK_REQ)" | This specification |
| 7 | "NORM_CMD(APPLICATION)" | This specification | | 7 | "NORM_CMD(APPLICATION)" | This specification |
+-------+-------------------------+--------------------+ +-------+-------------------------+--------------------+
Future specifications extending NORM may wish to define additional Future specifications extending NORM MAY define additional "NORM_CMD"
"NORM_CMD" messages to enhance protocol functionality. "NORM_CMD" messages to enhance protocol functionality. "NORM_CMD" message sub-
message sub-type value assignment requests are granted on a type value assignment requests are granted on a "Specification
"Specification Required" basis as defined by IANA Guidelines Required" basis as defined by IANA Guidelines [RFC5226]. Note that
[RFC5226]. Note that in addition to describing the command sub- in addition to describing the command sub-type's expected
type's expected interpretation, specifications MUST include a interpretation, specifications MUST include a description of protocol
description of protocol actions to be taken when the command is actions to be taken when the command is encountered by a protocol
encountered by a protocol implementation not supporting that specific implementation not supporting that specific option.
option.
Note that this specification already provides for an "application- Note that this specification already provides for an "application-
defined" "NORM_CMD" message sub-type that may be used at the defined" "NORM_CMD" message sub-type that can be used at the
discretion of individual applications using NORM for transport. discretion of individual applications using NORM for transport.
These "application-defined" commands may be suitable for many These "application-defined" commands are suitable for many
application-specific purposes and do not require standards action. application-specific purposes and do not involve standards action.
In any case, such additional messages SHALL be subject to the same In any case, such additional messages SHALL be subject to the same
congestion control constraints as the existing NORM sender message congestion control constraints as the existing NORM sender message
set. set.
8. Suggested Use 8. Suggested Use
The present NORM protocol is seen as useful tool for the reliable The present NORM protocol is seen as useful tool for the reliable
data transfer over generic IP multicast services. It is not the data transfer over generic IP multicast services. It is not the
intention of the authors to suggest it is suitable for supporting all intention of the authors to suggest it is suitable for supporting all
envisioned multicast reliability requirements. NORM provides a envisioned multicast reliability requirements. NORM provides a
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of receivers and a generic web content reliable "push" application. of receivers and a generic web content reliable "push" application.
In addition, this framework approach has some design features making In addition, this framework approach has some design features making
it attractive for bulk transfer in asymmetric and wireless it attractive for bulk transfer in asymmetric and wireless
internetwork applications. NORM is capable of successfully operating internetwork applications. NORM is capable of successfully operating
independent of network structure and in environments with high packet independent of network structure and in environments with high packet
loss, delay, and out-of-order delivery. Hybrid proactive/reactive loss, delay, and out-of-order delivery. Hybrid proactive/reactive
FEC-based repairing improve protocol performance in some multicast FEC-based repairing improve protocol performance in some multicast
scenarios. A sender-only repair approach often makes additional scenarios. A sender-only repair approach often makes additional
engineering sense in asymmetric networks. NORM's unicast feedback engineering sense in asymmetric networks. NORM's unicast feedback
capability may be suitable for use in asymmetric networks or in capability is suitable for use in asymmetric networks or in networks
networks where only unidirectional multicast routing/delivery service where only unidirectional multicast routing/delivery service exists.
exists. Asymmetric architectures supporting multicast delivery are Asymmetric architectures supporting multicast delivery are likely to
likely to make up an important portion of the future Internet make up an important portion of the future Internet structure (e.g.,
structure (e.g., DBS/cable/PSTN hybrids) and efficient, reliable bulk DBS/cable/PSTN hybrids) and efficient, reliable bulk data transfer
data transfer will be an important capability for servicing large will be an important capability for servicing large groups of
groups of subscribed receivers. subscribed receivers.
9. Changes from RFC3940 9. Changes from RFC3940
This section lists the changes between the Experimental version of This section lists the changes between the Experimental version of
this specification, RFC 3940, and this version: this specification, RFC 3940, and this version:
1. Removal of the "NORM_FLAG_MSG_START" for "NORM_OBJECT_STREAM", 1. Removal of the "NORM_FLAG_MSG_START" for "NORM_OBJECT_STREAM",
replacing it with the "payload_msg_start" field in the FEC- replacing it with the "payload_msg_start" field in the FEC-
encoded preamble of the "NORM_OBJECT_STREAM NORM_DATA" payload, encoded preamble of the "NORM_OBJECT_STREAM NORM_DATA" payload,
2. Definition of IANA namespace for header extension assignment, 2. Definition of IANA namespace for header extension assignment,
 End of changes. 215 change blocks. 
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