draft-ietf-fecframe-raptor-11.txt   rfc6681.txt 
FEC Framework M. Watson Internet Engineering Task Force (IETF) M. Watson
Internet-Draft Netflix Request for Comments: 6681 Netflix
Intended status: Standards Track T. Stockhammer Category: Standards Track T. Stockhammer
Expires: November 11, 2012 Nomor Research ISSN: 2070-1721 Nomor Research
M. Luby M. Luby
Qualcomm Incorporated Qualcomm Incorporated
May 10, 2012 August 2012
Raptor FEC Schemes for FECFRAME Raptor Forward Error Correction (FEC) Schemes for FECFRAME
draft-ietf-fecframe-raptor-11
Abstract Abstract
This document describes Fully-Specified Forward Error Correction This document describes Fully-Specified Forward Error Correction
(FEC) Schemes for the Raptor and RaptorQ codes and their application (FEC) Schemes for the Raptor and RaptorQ codes and their application
to reliable delivery of media streams in the context of FEC to reliable delivery of media streams in the context of the FEC
Framework. The Raptor and RaptorQ codes are systematic codes, where Framework. The Raptor and RaptorQ codes are systematic codes, where
a number of repair symbols are generated from a set of source symbols a number of repair symbols are generated from a set of source symbols
and sent in one or more repair flows in addition to the source and sent in one or more repair flows in addition to the source
symbols that are sent to the receiver(s) within a source flow. The symbols that are sent to the receiver(s) within a source flow. The
Raptor and RaptorQ codes offer close to optimal protection against Raptor and RaptorQ codes offer close to optimal protection against
arbitrary packet losses at a low computational complexity. Six FEC arbitrary packet losses at a low computational complexity. Six FEC
Schemes are defined, two for protection of arbitrary packet flows, Schemes are defined: two for the protection of arbitrary packet
two that are optimised for small source blocks and another two for flows, two that are optimized for small source blocks, and two for
protection of a single flow that already contains a sequence number. the protection of a single flow that already contains a sequence
Repair data may be sent over arbitrary datagram transport (e.g. UDP) number. Repair data may be sent over arbitrary datagram transport
or using RTP. (e.g., UDP) or using RTP.
Status of this Memo
This Internet-Draft is submitted in full conformance with the Status of This Memo
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering This is an Internet Standards Track document.
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by
material or to cite them other than as "work in progress." the Internet Engineering Steering Group (IESG). Further
information on Internet Standards is available in Section 2 of
RFC 5741.
This Internet-Draft will expire on November 11, 2012. Information about the current status of this document, any
errata, and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6681.
Copyright Notice Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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modifications of such material outside the IETF Standards Process. modifications of such material outside the IETF Standards Process.
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than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction ....................................................4
2. Document Outline . . . . . . . . . . . . . . . . . . . . . . . 6 2. Document Outline ................................................5
3. Requirements Notation . . . . . . . . . . . . . . . . . . . . 6 3. Requirements Notation ...........................................5
4. Definitions and Abbreviations . . . . . . . . . . . . . . . . 6 4. Definitions and Abbreviations ...................................5
4.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 7 4.1. Definitions ................................................6
4.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Abbreviations ..............................................6
5. General procedures for Raptor FEC Schemes . . . . . . . . . . 7 5. General Procedures for Raptor FEC Schemes .......................6
6. Raptor FEC Schemes for arbitrary packet flows . . . . . . . . 9 6. Raptor FEC Schemes for Arbitrary Packet Flows ...................8
6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 9 6.1. Introduction ...............................................8
6.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 9 6.2. Formats and Codes ..........................................8
6.2.1. FEC Framework Configuration Information . . . . . . . 9 6.2.1. FEC Framework Configuration Information .............8
6.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 10 6.2.2. Source FEC Payload ID ...............................9
6.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 11 6.2.3. Repair FEC Payload ID ..............................10
6.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 13 6.3. Procedures ................................................11
6.3.1. Source symbol construction . . . . . . . . . . . . . . 13 6.3.1. Source Symbol Construction .........................11
6.3.2. Repair packet construction . . . . . . . . . . . . . . 13 6.3.2. Repair Packet Construction .........................12
6.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 13 6.4. FEC Code Specification ....................................12
7. Optimised Raptor FEC Scheme for arbitrary packet flows . . . . 13 7. Optimized Raptor FEC Scheme for Arbitrary Packet Flows .........12
7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 14 7.1. Introduction ..............................................12
7.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 14 7.2. Formats and Codes .........................................13
7.2.1. FEC Framework Configuration Information . . . . . . . 14 7.2.1. FEC Framework Configuration Information ............13
7.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 15 7.2.2. Source FEC Payload ID ..............................13
7.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 15 7.2.3. Repair FEC Payload ID ..............................13
7.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 15 7.3. Procedures ................................................13
7.3.1. Source symbol construction . . . . . . . . . . . . . . 15 7.3.1. Source Symbol Construction .........................13
7.3.2. Repair packet construction . . . . . . . . . . . . . . 15 7.3.2. Repair Packet Construction .........................14
7.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 15 7.4. FEC Code Specification ....................................14
8. Raptor FEC Scheme for a single sequenced flow . . . . . . . . 16 8. Raptor FEC Scheme for a Single Sequenced Flow ..................15
8.1. Formats and codes . . . . . . . . . . . . . . . . . . . . 16 8.1. Formats and Codes .........................................15
8.1.1. FEC Framework Configuration Information . . . . . . . 16 8.1.1. FEC Framework Configuration Information ............15
8.1.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 16 8.1.2. Source FEC Payload ID ..............................15
8.1.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 16 8.1.3. Repair FEC Payload ID ..............................15
8.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 18 8.2. Procedures ................................................16
8.2.1. Source symbol construction . . . . . . . . . . . . . . 18 8.2.1. Source Symbol Construction .........................16
8.2.2. Derivation of Source FEC Packet Identification 8.2.2. Derivation of Source FEC Packet
Information . . . . . . . . . . . . . . . . . . . . . 18 Identification Information .........................17
8.2.3. Repair packet construction . . . . . . . . . . . . . . 19 8.2.3. Repair Packet Construction .........................18
8.2.4. Procedures for RTP source flows . . . . . . . . . . . 19 8.2.4. Procedures for RTP Source Flows ....................18
8.3. FEC Code Specification . . . . . . . . . . . . . . . . . . 20 8.3. FEC Code Specification ....................................18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 20 9. Security Considerations ........................................18
10. Session Description Protocol (SDP) Signaling . . . . . . . . . 20 10. Session Description Protocol (SDP) Signaling ..................19
11. Congestion Control Considerations . . . . . . . . . . . . . . 21 11. Congestion Control Considerations .............................19
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21 12. IANA Considerations ...........................................19
12.1. Registration of FEC Scheme IDs . . . . . . . . . . . . . . 21 12.1. Registration of FEC Scheme IDs ...........................19
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22 13. Acknowledgements ..............................................20
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 14. References ....................................................21
14.1. Normative References . . . . . . . . . . . . . . . . . . . 22
14.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
1. Introduction 1. Introduction
The Forward Error Correction (FEC) Framework [RFC6363] describes a The "Forward Error Correction (FEC) Framework" [RFC6363] describes a
general framework for the use of Forward Error Correction in general framework for the use of Forward Error Correction in
association with arbitrary packet flows. Modeled after the FEC association with arbitrary packet flows. Modeled after the FEC
Building Block developed by the IETF Reliable Multicast Transport Building Block developed by the IETF Reliable Multicast Transport
working group [RFC5052], the FEC Framework defines the concept of FEC working group [RFC5052], the FEC Framework defines the concept of FEC
Schemes which provide specific Forward Error Correction schemes. Schemes that provide specific Forward Error Correction Schemes. This
This document describes six FEC Schemes which make use of the Raptor document describes six FEC Schemes that make use of the Raptor and
and RaptorQ FEC codes as defined in [RFC5053] and [RFC6330]. RaptorQ FEC codes as defined in [RFC5053] and [RFC6330].
The FEC protection mechanism is independent of the type of the source The FEC protection mechanism is independent of the type of source
data, which can be an arbitrary sequence of packets, for example data that can be an arbitrary sequence of packets, for example audio
audio or video data. In general, the operation of the protection or video data. In general, the operation of the protection mechanism
mechanism is as follows: is as follows:
o The sender determines a set of source packets (a source block) to o The sender determines a set of source packets (a source block) to
be protected together based on the FEC Framework Configuration be protected together based on the FEC Framework Configuration
Information. Information.
o The sender arranges the source packets into a set of source o The sender arranges the source packets into a set of source
symbols, each of which is the same size. symbols, each of which is the same size.
o The sender applies the Raptor/RaptorQ protection operation on the o The sender applies the Raptor/RaptorQ protection operation on the
source symbols to generate the required number of repair symbols. source symbols to generate the required number of repair symbols.
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repair packets in different source and repair flows, or in the repair packets in different source and repair flows, or in the
case Real-time Transport Protocol (RTP) transport is used for case Real-time Transport Protocol (RTP) transport is used for
repair packets, in different RTP streams. repair packets, in different RTP streams.
o At the receiver side, if all of the source packets are o At the receiver side, if all of the source packets are
successfully received, there is no need for FEC recovery and the successfully received, there is no need for FEC recovery and the
repair packets are discarded. However, if there are missing repair packets are discarded. However, if there are missing
source packets, the repair packets can be used to recover the source packets, the repair packets can be used to recover the
missing information. missing information.
The operation of the FEC mechanism requires that the receiver can The operation of the FEC mechanism requires that the receiver is able
identify the relationships between received source packets and repair to identify the relationships between received source packets and
packets and in particular which source packets are missing. In many repair packets, in particular, which source packets are missing. In
cases, data already exists in the source packets which can be used to many cases, data already exists in the source packets that can be
refer to source packets and to identify which packets are missing. used to refer to source packets and to identify which packets are
In this case we assume it is possible to derive a "sequence number" missing. In this case, we assume it is possible to derive a
directly or indirectly from the source packets and this sequence "sequence number" directly or indirectly from the source packets, and
number can be used within the FEC Scheme. This case is referred to this sequence number can be used within the FEC Scheme. This case is
as a "single sequenced flow". In this case the FEC Source Payload ID referred to as a "single sequenced flow". In this case, the FEC
defined in [RFC6363] is empty and the source packets are not modified Source Payload ID defined in [RFC6363] is empty and the source
by the application of FEC, with obvious backwards compatibility packets are not modified by the application of FEC, with obvious
advantages. backwards compatibility advantages.
Otherwise, it is necessary to add data to the source packets for FEC Otherwise, it is necessary to add data to the source packets for FEC
purposes in the form of a non-empty FEC Source Payload ID. This case purposes in the form of a non-empty FEC Source Payload ID. This is
is referred to as the "arbitrary packet flow" case. Accordingly, referred to as the "arbitrary packet flow" case. This document
this document defines six FEC Schemes, two for the case of a single defines six FEC Schemes, two for the case of a single sequenced flow
sequenced flow and four for the case of arbitrary packet flows. and four for the case of arbitrary packet flows.
2. Document Outline 2. Document Outline
This document is organised as follows: This document is organized as follows:
o Section 5 defines general procedures applicable to the use of the o Section 5 defines general procedures applicable to the use of the
Raptor and RaptorQ codes in the context of the FEC Framework. Raptor and RaptorQ codes in the context of the FEC Framework.
o Section 6 defines an FEC Scheme for the case of arbitrary source o Section 6 defines a FEC Scheme for the case of arbitrary source
flows and follows the format defined for FEC Schemes in [RFC6363]. flows and follows the format defined for FEC Schemes in [RFC6363].
When used with Raptor codes, this scheme is equivalent to that When used with Raptor codes, this scheme is equivalent to that
defined in "3GPP TS 26.346: Multimedia Broadcast/Multicast defined in 3GPP TS 26.346, "Multimedia Broadcast/Multicast Service
Service (MBMS); Protocols and codecs" [MBMSTS]. (MBMS); Protocols and codecs" [MBMSTS].
o Section 7 defines an FEC Scheme similar to that defined in o Section 7 defines a FEC Scheme similar to that defined in Section
Section 6 but with optimisations for the case where only limited 6 but with optimizations for the case where only limited source
source block sizes are required. When used with Raptor codes, block sizes are required. When used with Raptor codes, this
this scheme is equivalent to that defined in "ETSI TS 102.034: scheme is equivalent to that defined in ETSI TS 102.034, "Digital
Digital Video Broadcasting (DVB); Transport of MPEG-2 Based DVB Video Broadcasting (DVB); Transport of MPEG-2 Based DVB Services
Services over IP Based Networks" [dvbts] for arbitrary packet over IP Based Networks" [DVBTS] for arbitrary packet flows.
flows.
o Section 8 defines an FEC Scheme for the case of a single flow o Section 8 defines a FEC Scheme for the case of a single flow,
which is already provided with a source packet sequence number. which is already provided with a source packet sequence number.
When used with Raptor codes, this scheme is equivalent to that When used with Raptor codes, this scheme is equivalent to that
defined in [dvbts] for the case of a single sequenced flow. defined in [DVBTS] for the case of a single sequenced flow.
3. Requirements Notation 3. Requirements Notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"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 [RFC2119]. document are to be interpreted as described in [RFC2119].
4. Definitions and Abbreviations 4. Definitions and Abbreviations
The definitions, notations and abbreviations commonly used in this The definitions, notations, and abbreviations commonly used in this
document are summarized in this section. document are summarized in this section.
4.1. Definitions 4.1. Definitions
The FEC-specific terminology used in this document is defined in The FEC-specific terminology used in this document is defined in
[RFC6363]. In this document, as in [RFC6363], the first letter of [RFC6363]. In this document, as in [RFC6363], the first letter of
each FEC-specific is capitalized along with the new terms defined each FEC-specific term is capitalized along with the new terms
here: defined here:
Symbol: A unit of data. Its size, in octets, is referred to as the Symbol: A unit of data. Its size, in octets, is referred to as the
symbol size. symbol size.
FEC Framework Configuration Information: Information that controls FEC Framework Configuration Information: Information that controls
the operation of the FEC Framework. Each FEC Framework instance the operation of the FEC Framework. Each FEC Framework instance
has its own configuration information. has its own configuration information.
4.2. Abbreviations 4.2. Abbreviations
This document uses abbreviations that apply to FEC Framework in This document uses abbreviations that apply to the FEC Framework in
general as defined in [RFC6363]. In addition, this document uses the general as defined in [RFC6363]. In addition, this document uses the
following abbreviations following abbreviations
FSSI: FEC-Scheme-Specific Information. FSSI: FEC-Scheme-Specific Information.
SS-FSSI: Sender-Side FEC-Scheme-Specific Information.
RS-FSSI: Receiver-Side FEC-Scheme-Specific Information.
ADU: Application Data Unit ADU: Application Data Unit
ADUI: Application Data Unit Information. ADUI: Application Data Unit Information.
SPI: Source Packet Information. SPI: Source Packet Information.
MSBL: Maximum Source Block Length MSBL: Maximum Source Block Length
5. General procedures for Raptor FEC Schemes 5. General Procedures for Raptor FEC Schemes
This section specifies general procedures which apply to all Raptor This section specifies general procedures that apply to all Raptor
and RaptorQ FEC Schemes, specifically the construction of source and RaptorQ FEC Schemes, specifically the construction of source
symbols from a set of source transport payloads. symbols from a set of source transport payloads.
For any field defined in this document, the octets are ordered in For any field defined in this document, the octets are ordered in
network byte order. network byte order.
As described in [RFC6363] for each Application Data Unit (ADU) in a As described in [RFC6363], for each Application Data Unit (ADU) in a
source block, the FEC Scheme is provided with: source block, the FEC Scheme is provided with:
o A description of the source data flow with which the ADU is o A description of the source data flow with which the ADU is
associated and an integer identifier associated with that flow. associated and an integer identifier associated with that flow.
o The ADU itself. o The ADU itself.
o The length of the ADU. o The length of the ADU.
For each ADU, we define the Application Data Unit Information (ADUI) For each ADU, we define the Application Data Unit Information (ADUI)
as follows: as follows:
Let Let
o n be the number of ADUs in the source block. o n be the number of ADUs in the source block.
o T be the source symbol size in octets. Note: this information is o T be the source symbol size in octets. Note: this information is
provided by the FEC Scheme as defined below. provided by the FEC Scheme as defined below.
o i the index to the (i+1)-th ADU to be added to the source block, 0 o i the index to the (i+1)-th ADU to be added to the source block,
<= i < n. 0 <= i < n.
o f[i] denote the integer identifier associated with the source data o f[i] denote the integer identifier associated with the source data
flow from which the i-th ADU was taken. flow from which the i-th ADU was taken.
o F[i] denote a single octet representing the value of f[i]. o F[i] denote a single octet representing the value of f[i].
o l[i] be a length indication associated with the i-th ADU - the o l[i] be a length indication associated with the i-th ADU -- the
nature of the length indication is defined by the FEC Scheme. nature of the length indication is defined by the FEC Scheme.
o L[i] denote two octets representing the value of l[i] in network o L[i] denote two octets representing the value of l[i] in network
byte order (high order octet first) of the i-th ADU. byte order (high order octet first) of the i-th ADU.
o R[i] denote the number of octets in the (i+1)-th ADU. o R[i] denote the number of octets in the (i+1)-th ADU.
o s[i] be the smallest integer such that s[i]*T >= (l[i]+3). Note o s[i] be the smallest integer such that s[i]*T >= (l[i]+3). Note:
s[i] is the length of SPI[i] in units of symbols of size T octets. s[i] is the length of SPI[i] in units of symbols of size T octets.
o P[i] denote s[i]*T-(l[i]+3) zero octets. Note: P[i] are padding o P[i] denote s[i]*T-(l[i]+3) zero octets. Note: P[i] are padding
octets to align the start of each UDP packet with the start of a octets to align the start of each UDP packet with the start of a
symbol. symbol.
o ADUI[i] be the concatenation of F[i] ,L[i], R[i] and P[i]. o ADUI[i] be the concatenation of F[i], L[i], R[i], and P[i].
Then, a source data block is constructed by concatenating ADUI[i] for Then, a source data block is constructed by concatenating ADUI[i] for
i = 0, 1, 2, ... n-1. The source data block size, S, is then given i = 0, 1, 2, ... n-1. The source data block size, S, is then given
by sum {s[i]*T, i=0, ..., n-1}. Symbols are allocated integer by sum {s[i]*T, i=0, ..., n-1}. Symbols are allocated integer
Encoding Symbol IDs consecutively starting from zero within the encoding symbol IDs (ESI) consecutively starting from zero within the
source block. Each ADU is associated with the Encoding Symbol ID of source block. Each ADU is associated with the ESI of the first
the first symbol containing SPI for that packet. Thus, the Encoding symbol containing SPI for that packet. Thus, the encoding symbol ID
Symbol ID value associated with the j-th source packet, ESI[j], is value associated with the j-th source packet, ESI[j], is given by
given by ESI[j] = 0, for j=0 and ESI[j] = sum{s[i], i=0,...,(j-1)}, ESI[j] = 0, for j=0 and ESI[j] = sum{s[i], i=0,...,(j-1)}, for
for 0 < j < n. 0 < j < n.
Source blocks are identified by integer Source Block Numbers. This Source blocks are identified by integer Source Block Numbers. This
specification does not specify how Source Block Numbers are allocated specification does not specify how Source Block Numbers are allocated
to source blocks. The Source FEC Packet Identification Information to the source blocks. The Source FEC Packet Identification
consists of the identity of the source block and the Encoding Symbol Information consists of the identity of the source block and the
ID associated with the packet. encoding symbol ID associated with the packet.
6. Raptor FEC Schemes for arbitrary packet flows 6. Raptor FEC Schemes for Arbitrary Packet Flows
6.1. Introduction 6.1. Introduction
This section specifies an FEC Scheme for the application of the This section specifies a FEC Scheme for the application of the Raptor
Raptor and RaptorQ codes to arbitrary packet flows. This scheme is and RaptorQ codes to arbitrary packet flows. This scheme is
recommended in scenarios where maximal generality is required. recommended in scenarios where maximal generality is required.
When used with the Raptor codes specified in [RFC5053], this scheme When used with the Raptor codes specified in [RFC5053], this scheme
is equivalent to that specified in [MBMSTS]. is equivalent to that specified in [MBMSTS].
6.2. Formats and Codes 6.2. Formats and Codes
6.2.1. FEC Framework Configuration Information 6.2.1. FEC Framework Configuration Information
6.2.1.1. FEC Scheme ID 6.2.1.1. FEC Scheme ID
The value of the FEC Scheme ID for the fully-specified FEC scheme The value of the FEC Scheme ID for the Fully-Specified FEC scheme
defined in this section is XXX1 when [RFC5053] is used and XXX2 when defined in this section is 1 when [RFC5053] is used and 2 when
[RFC6330] is used, as assigned by IANA. [RFC6330] is used, as assigned by IANA.
NOTE: To the RFC Editor: please change these XXX notations once
assigned, and remove this NOTE.
6.2.1.2. Scheme-Specific Elements 6.2.1.2. Scheme-Specific Elements
The scheme-specific elements of the FEC Framework Configuration The scheme-specific elements of the FEC Framework Configuration
information for this scheme are as follows: information for this scheme are as follows:
MSBL Value range: An non-negative integer less than 8192 for FEC MSBL: The maximum source block length. A non-negative integer less
Scheme XXX1 and less than 56403 for FEC Scheme XXX2, in units of than 8192 for FEC Scheme 1 and less than 56403 for FEC Scheme 2,
symbols. The field type is unsigned integer. in units of symbols. The field type is unsigned integer.
Encoding Symbol Size Name: "T", Value range: A non-negative
integer less than 65536, in units of octets. The field type is
unsigned integer.
Payload ID Format Name: "P", Value range: "A" or "B". The P bit T: The encoding symbol size. A non-negative integer less than 65536,
shall be set to zero to indicate Payload ID Format A or to one to in units of octets. The field type is unsigned integer.
indicate Payload ID Format B.
An encoding format for the MSBL and Encoding Symbol Size is defined P: The payload ID format indicator. The P bit shall be set to zero
below. to indicate payload ID format A or to one to indicate payload ID
format B. The field type is unsigned integer.
1 2 3 An encoding format for the encoding symbol size, MSBL and payload ID
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 format indicator is defined below.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 1 2 3
| Symbol Size (T) | MSBL | 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P| Reserved | | Symbol Size (T) | MSBL |
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|P| Reserved |
+-+-+-+-+-+-+-+-+
Figure 1: FEC Scheme Specific Information Figure 1: FEC-Scheme-Specific Information
The P bit shall be set to zero to indicate Payload ID Format A or to The P bit shall be set to zero to indicate Payload ID format A or to
one to indicate Payload ID Format B. The last octet of FEC Scheme one to indicate Payload ID format B. The last octet of FEC-Scheme-
Specific Information SHOULD be omitted indicating that Payload ID Specific Information SHOULD be omitted, indicating that Payload ID
Format A is in use. The Payload ID Format identifier defines which format A is in use. The payload ID format indicator defines which of
of the Source FEC Payload ID and Repair FEC Payload ID formats the Source FEC Payload ID and Repair FEC Payload ID formats defined
defined below shall be used. Payload ID Format B SHALL NOT be used below shall be used. Payload ID format B SHALL NOT be used for FEC
for FEC Scheme XXX1. The two formats enable different use cases. Scheme 1. The two formats enable different use cases. Format A is
Format A is appropriate in case the stream has many typically smaller appropriate in case the stream has many typically smaller source
source blocks and Format B is applicable if the stream has fewer blocks, and format B is applicable if the stream has fewer large
large source blocks each with many encoding symbols. source blocks, each with many encoding symbols.
6.2.2. Source FEC Payload ID 6.2.2. Source FEC Payload ID
This scheme makes use of an Explicit Source FEC Payload ID, which is This scheme makes use of an Explicit Source FEC Payload ID, which is
appended to the end of the source packets. Two formats are defined appended to the end of the source packets. Two formats are defined
for the Source FEC Payload ID, format A and format B. The format that for the Source FEC Payload ID, format A and format B. The format
is used is signaled as part of the FEC Framework Configuration that is used is signaled as part of the FEC Framework Configuration
Information. Information.
The Source FEC Payload ID for format A is provided in Figure 2. The Source FEC Payload ID for format A is provided in Figure 2.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Block Number (SBN) | Encoding Symbol ID (ESI) | | Source Block Number (SBN) | Encoding Symbol ID (ESI) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Source FEC Payload ID - Format A Figure 2: Source FEC Payload ID - Format A
Source Block Number (SBN), (16 bits): Identifier for the source Source Block Number (SBN), (16 bits): Identifier for the source block
block that the source data within the packet relates. The field that the source data within the packet relates. The field type is
type is unsigned integer. unsigned integer.
Encoding Symbol ID (ESI), (16 bits): The starting symbol index of Encoding Symbol ID (ESI), (16 bits): The starting symbol index of the
the source packet in the source block. The field type is unsigned source packet in the source block. The field type is unsigned
integer. integer.
The Source FEC Payload ID for format B is provided in Figure 3. The Source FEC Payload ID for format B is provided in Figure 3.
1 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SBN | Encoding Symbol ID (ESI) | | SBN | Encoding Symbol ID (ESI) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Source FEC Payload ID - Format B Figure 3: Source FEC Payload ID - Format B
Source Block Number (SBN), (8 bits): Identifier for the source block Source Block Number (SBN), (8 bits): Identifier for the source block
that the source data within the packet relates. The field type is that the source data within the packet relates. The field type is
unsigned integer. unsigned integer.
Encoding Symbol ID (ESI), (24 bits): The starting symbol index of Encoding Symbol ID (ESI), (24 bits): The starting symbol index of the
the source packet in the source block. The field type is unsigned source packet in the source block. The field type is unsigned
integer. integer.
6.2.3. Repair FEC Payload ID 6.2.3. Repair FEC Payload ID
Two formats for the Repair FEC Payload ID, Format A and Format B are Two formats for the Repair FEC Payload ID, format A and format B, are
defined below. defined below.
The Repair FEC Payload ID for format A is provided in Figure 4. The Repair FEC Payload ID for format A is provided in Figure 4.
1 2 3 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Block Number (SBN) | Encoding Symbol ID (ESI) | | Source Block Number (SBN) | Encoding Symbol ID (ESI) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Block Length (SBL) | | Source Block Length (SBL) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Repair FEC Payload ID - Format A Figure 4: Repair FEC Payload ID - Format A
Source Block Number (SBN), (16 bits) Identifier for the source block Source Block Number (SBN), (16 bits): Identifier for the source block
that the repair symbols within the packet relate. For format A, that the repair symbols within the packet relate. For format A,
it is of size 16 bits. The field type is unsigned integer. it is of size 16 bits. The field type is unsigned integer.
Encoding Symbol ID (ESI), (16 bits) Identifier for the encoding Encoding Symbol ID (ESI), (16 bits): Identifier for the encoding
symbols within the packet. The field type is unsigned integer. symbols within the packet. The field type is unsigned integer.
Source Block Length (SBL), (16 bits) The number of source symbols in Source Block Length (SBL), (16 bits): The number of source symbols in
the source block. The field type is unsigned integer. the source block. The field type is unsigned integer.
The Repair FEC Payload ID for format B is provided in Figure 5. The Repair FEC Payload ID for format B is provided in Figure 5.
1 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SBN | Encoding Symbol ID (ESI) | | SBN | Encoding Symbol ID (ESI) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Block Length (SBL) | | Source Block Length (SBL) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Repair FEC Payload ID - Format B Figure 5: Repair FEC Payload ID - Format B
Source Block Number (SBN), (8 bits) Identifier for the source block Source Block Number (SBN), (8 bits): Identifier for the source block
that the repair symbols within the packet relate. For format B, that the repair symbols within the packet relate. For format B,
it is of size 8 bits. The field type is unsigned integer. it is of size 8 bits. The field type is unsigned integer.
Encoding Symbol ID (ESI), (24 bits) Identifier for the encoding Encoding Symbol ID (ESI), (24 bits): Identifier for the encoding
symbols within the packet. The field type is unsigned integer. symbols within the packet. The field type is unsigned integer.
Source Block Length (SBL), (16 bits) The number of source symbols in Source Block Length (SBL), (16 bits): The number of source symbols in
the source block. The field type is unsigned integer. the source block. The field type is unsigned integer.
The interpretation of the Source Block Number, Encoding Symbol The interpretation of the Source Block Number, encoding symbol ID,
Identifier and Source Block Length is defined by the FEC Code and Source Block Length is defined by the FEC Code Specification in
Specification in [RFC5053] for FEC Scheme XXX1 and [RFC6330] for FEC [RFC5053] for FEC Scheme 1 and [RFC6330] for FEC Scheme 2.
Scheme XXX2.
6.3. Procedures 6.3. Procedures
6.3.1. Source symbol construction 6.3.1. Source Symbol Construction
FEC Scheme XXX1 and FEC Scheme XXX2 use the procedures defined in FEC Scheme 1 and FEC Scheme 2 use the procedures defined in Section 5
Section 5 to construct a set of source symbols to which the FEC code to construct a set of source symbols to which the FEC Code can be
can be applied. The sender MUST allocate Source Block Numbers to applied. The sender MUST allocate Source Block Numbers to source
source blocks sequentially, wrapping around to zero after Source blocks sequentially, wrapping around to zero after Source Block
Block Number 65535 (Format A) or 255 (Format B). Number 65535 (format A) or 255 (format B).
During the construction of the source block: During the construction of the source block:
o the length indication, l[i], included in the Source Packet o the length indication, l[i], included in the Source Packet
Information for each packet shall be the transport payload length, Information for each packet shall be the transport payload length,
i.e. the length of the ADU. i.e., the length of the ADU.
o the value of s[i] in the construction of the Source Packet o the value of s[i] in the construction of the Source Packet
Information for each packet shall be the smallest integer such Information for each packet shall be the smallest integer such
that s[i]*T >= (l[i]+3). that s[i]*T >= (l[i]+3).
6.3.2. Repair packet construction 6.3.2. Repair Packet Construction
For FEC Scheme XXX1, the ESI value placed into a repair packet is For FEC Scheme 1 [RFC5053], the ESI value placed into a repair packet
calculated as specified in Section 5.3.2 of [RFC5053]. is calculated as specified in Section 5.3.2 of [RFC5053].
For FEC Scheme XXX2 [RFC6330], the ESI value placed into a repair For FEC Scheme 2 [RFC6330], the ESI value placed into a repair packet
packet is calculated as specified in Section 4.4.2 of [RFC6330]. is calculated as specified in Section 4.4.2 of [RFC6330].
In both cases K is identical to SBL. In both cases, K is identical to SBL.
6.4. FEC Code Specification 6.4. FEC Code Specification
The FEC encoder defined in [RFC5053] SHALL be used FEC Scheme XXX1 The FEC encoder defined in [RFC5053] SHALL be used for FEC Scheme 1
and the FEC encoder defined in [RFC6330] SHALL be used for FEC Scheme and the FEC encoder defined in [RFC6330] SHALL be used for FEC Scheme
XXX2. For both FEC Scheme XXX1 and FEC Scheme XXX2, the source 2. For both FEC Scheme 1 and FEC Scheme 2, the source symbols passed
symbols passed to the FEC encoder SHALL consist of the source symbols to the FEC encoder SHALL consist of the source symbols constructed
constructed according to Section 6.3.1. Thus the value of the according to Section 6.3.1. Thus, the value of the parameter K used
parameter K used by the FEC encoder (equal to the Source Block by the FEC encoder (equal to the Source Block Length) may vary
Length) may vary amongst the blocks of the stream but SHALL NOT amongst the blocks of the stream but SHALL NOT exceed the Maximum
exceed the Maximum Source Block Length signaled in the FEC Scheme- Source Block Length signaled in the FEC-Scheme-Specific Information.
specific information. The symbol size, T, to be used for source The symbol size, T, to be used for source block construction and the
block construction and the repair symbol construction is equal to the repair symbol construction is equal to the encoding symbol size
Encoding Symbol Size signaled in the FEC Scheme Specific Information. signaled in the FEC-Scheme-Specific Information.
7. Optimized Raptor FEC Scheme for Arbitrary Packet Flows
7. Optimised Raptor FEC Scheme for arbitrary packet flows
7.1. Introduction 7.1. Introduction
This section specifies a slightly modified version of the FEC Scheme This section specifies a slightly modified version of the FEC Scheme
specified in Section 6 which is applicable to scenarios in which only specified in Section 6 that is applicable to scenarios in which only
relatively small block sizes will be used. These modifications admit relatively small block sizes will be used. These modifications admit
substantial optimisations to both sender and receiver substantial optimizations to both sender and receiver
implementations. implementations.
In outline, the modifications are: In outline, the modifications are:
o All source blocks within a stream are encoded using the same o All source blocks within a stream are encoded using the same
source block size. Code shortening is used to encode blocks of source block size. Code shortening is used to encode blocks of
different sizes. This is achieved by padding every block to the different sizes. This is achieved by padding every block to the
required size using zero symbols before encoding. The zero required size using zero symbols before encoding. The zero
symbols are then discarded after decoding. The source block size symbols are then discarded after decoding. The source block size
to be used for a stream is signaled in the Maximum Source Block to be used for a stream is signaled in the Maximum Source Block
skipping to change at page 14, line 34 skipping to change at page 13, line 13
consists of T octets where the value of each octet is zero. MSBL consists of T octets where the value of each octet is zero. MSBL
MUST be selected as the smallest value of the possible values in MUST be selected as the smallest value of the possible values in
Section 7.4 that is greater than or equal to K. Section 7.4 that is greater than or equal to K.
o The possible choices of the MSBL for a stream is restricted to a o The possible choices of the MSBL for a stream is restricted to a
small specified set. This allows explicit operation sequences for small specified set. This allows explicit operation sequences for
encoding and decoding the restricted set of source block lengths encoding and decoding the restricted set of source block lengths
to be pre-calculated and embedded in software or hardware. to be pre-calculated and embedded in software or hardware.
When used with the Raptor codes specified in [RFC5053], this scheme When used with the Raptor codes specified in [RFC5053], this scheme
is equivalent to that specified in [dvbts] for arbitrary packet is equivalent to that specified in [DVBTS] for arbitrary packet
flows. flows.
7.2. Formats and Codes 7.2. Formats and Codes
7.2.1. FEC Framework Configuration Information 7.2.1. FEC Framework Configuration Information
7.2.1.1. FEC Scheme ID 7.2.1.1. FEC Scheme ID
The value of the FEC Scheme ID for the fully-specified FEC scheme The value of the FEC Scheme ID for the Fully-Specified FEC scheme
defined in this section is XXX3 when [RFC5053] is used and XXX4 when defined in this section is 3 when [RFC5053] is used and 4 when
[RFC6330] is used, as assigned by IANA. [RFC6330] is used, as assigned by IANA.
NOTE: To the RFC Editor: please change these XXX notations once 7.2.1.2. FEC-Scheme-Specific Information
assigned, and remove this NOTE.
7.2.1.2. FEC Scheme specific information
The same as specified for FEC Scheme XXX1 for FEC Scheme XXX3, and The elements for FEC Scheme 3 are the same as specified for FEC
the same as specified for FEC Scheme XXX2 for FEC Scheme XXX4, as Scheme 1, and the elements specified for FEC Scheme 4 are the same as
specified in Section 6.2.1.2, except that the MSBL value is as specified for FEC 2, as specified in Section 6.2.1.2, except that the
defined in Section 7.4. MSBL value is as defined in Section 7.4.
7.2.2. Source FEC Payload ID 7.2.2. Source FEC Payload ID
The same as specified for FEC Scheme XXX1 for FEC Scheme XXX3, and The elements for FEC Scheme 3 are the same as specified for FEC
the same as specified for FEC Scheme XXX2 for FEC Scheme XXX4, as Scheme 1, and the elements specified for FEC Scheme 4 are the same as
specified in Section 6.2.2. specified for FEC 2, as specified in Section 6.2.2.
7.2.3. Repair FEC Payload ID 7.2.3. Repair FEC Payload ID
The same as specified for FEC Scheme XXX1 for FEC Scheme XXX3, and The elements for FEC Scheme 3 are the same as specified for FEC
the same as specified for FEC Scheme XXX2 for FEC Scheme XXX4, as Scheme 1, and the elements specified for FEC Scheme 4 are the same as
specified in Section 6.2.3. specified for FEC 2, as specified in Section 6.2.3.
7.3. Procedures 7.3. Procedures
7.3.1. Source symbol construction 7.3.1. Source Symbol Construction
See Section 6.3.1. See Section 6.3.1.
7.3.2. Repair packet construction 7.3.2. Repair Packet Construction
The number of repair symbols contained within a repair packet is The number of repair symbols contained within a repair packet is
computed from the packet length. The ESI value placed into a repair computed from the packet length. The ESI value placed into a repair
packet is calculated as X + MSBL - SBL, where X would be the ESI packet is calculated as X + MSBL - SBL, where X would be the ESI
value of the repair packet if the ESI were calculated as specified in value of the repair packet if the ESI were calculated as specified in
Section 5.3.2 of [RFC5053] for FEC Scheme XXX3 and as specified in Section 5.3.2 of [RFC5053] for FEC Scheme 3 and as specified in
Section 4.4.2 of [RFC6330] for FEC Scheme XXX4, where K=SBL. The Section 4.4.2 of [RFC6330] for FEC Scheme 4, where K=SBL. The value
value of SBL SHALL be at most the value of MSBL. of SBL SHALL be, at most, the value of MSBL.
7.4. FEC Code Specification 7.4. FEC Code Specification
The FEC encoder defined in [RFC5053] SHALL be used for FEC Scheme The FEC encoder defined in [RFC5053] SHALL be used for FEC Scheme 3
XXX3 and the FEC encoder defined in [RFC6330] SHALL be used for FEC and the FEC encoder defined in [RFC6330] SHALL be used for FEC Scheme
Scheme XXX4. The source symbols passed to the FEC encoder SHALL 4. The source symbols passed to the FEC encoder SHALL consist of the
consist of the source symbols constructed according to Section 6.3.1 source symbols constructed according to Section 6.3.1 extended with
extended with zero or more padding symbols. The extension SHALL be zero or more padding symbols. The extension SHALL be such that the
such that the total number of symbols in the source block is equal to total number of symbols in the source block is equal to the MSBL
the MSBL signaled in the FEC Scheme Specific Information. Thus the signaled in the FEC-Scheme-Specific Information. Thus, the value of
value of the parameter K used by the FEC encoded is equal to the MSBL the parameter K used by the FEC encoder is equal to the MSBL for all
for all blocks of the stream. Padding symbols shall consist entirely blocks of the stream. Padding symbols shall consist entirely of
of octets set to the value zero. The symbol size, T, to be used for octets set to the value zero. The symbol size, T, to be used for the
source block construction and the repair symbol construction is equal source block construction and the repair symbol construction, is
to the Encoding Symbol Size signaled in the FEC Scheme Specific equal to the encoding symbol size signaled in the FEC-Scheme-Specific
Information. Information.
For FEC Scheme XXX3, the parameter T SHALL be set such that the For FEC Scheme 3, the parameter T SHALL be set such that the number
number of source symbols in any source block is at most 8192. The of source symbols in any source block is, at most, 8192. The MSBL
MSBL parameter, and hence the number of symbols used in the FEC parameter, and hence the number of symbols used in the FEC Encoding
Encoding and Decoding operations, SHALL be set to one of the and Decoding operations, SHALL be set to one of the following values:
following values:
101, 120, 148, 164, 212, 237, 297, 371, 450, 560, 680, 842, 1031, 101, 120, 148, 164, 212, 237, 297, 371, 450, 560, 680, 842, 1031,
1139, 1281 1139, 1281
For FEC Scheme XXX4, the parameter T SHALL be set such that the For FEC Scheme 4, the parameter T SHALL be set such that the number
number of source symbols in any source block is less than 56403. The of source symbols in any source block is less than 56403. The MSBL
MSBL parameter SHALL be set to one of the supported values for K' parameter SHALL be set to one of the supported values for K' defined
defined in Section 5.6 of [RFC6330]. in Section 5.6 of [RFC6330].
8. Raptor FEC Scheme for a single sequenced flow 8. Raptor FEC Scheme for a Single Sequenced Flow
8.1. Formats and codes 8.1. Formats and Codes
8.1.1. FEC Framework Configuration Information 8.1.1. FEC Framework Configuration Information
8.1.1.1. FEC Scheme ID 8.1.1.1. FEC Scheme ID
The value of the FEC Scheme ID for the fully-specified FEC scheme The value of the FEC Scheme ID for the Fully-Specified FEC scheme
defined in this section is XXX5 when [RFC5053] is used and XXX6 when defined in this section is 5 when [RFC5053] is used and 6 when
[RFC6330] is used, as assigned by IANA. [RFC6330] is used, as assigned by IANA.
NOTE: To the RFC Editor: please change these XXX notations once 8.1.1.2. Scheme-Specific Elements
assigned, and remove this NOTE.
8.1.1.2. Scheme-specific elements
The same as specified for FEC Scheme XXX1 for FEC Scheme XXX5, and The elements for FEC Scheme 5 are the same as specified for FEC
the same as specified for FEC Scheme XXX2 for FEC Scheme XXX6, as Scheme 1, and the elements specified for FEC Scheme 6 are the same as
specified in Section 6.2.1.2. specified for FEC 2, as specified in Section 6.2.1.2.
8.1.2. Source FEC Payload ID 8.1.2. Source FEC Payload ID
The Source FEC Payload ID field is not used by this FEC Scheme. The Source FEC Payload ID field is not used by this FEC Scheme.
Source packets are not modified by this FEC Scheme. Source packets are not modified by this FEC Scheme.
8.1.3. Repair FEC Payload ID 8.1.3. Repair FEC Payload ID
Two formats for the Repair FEC Payload ID are defined, Format A and Two formats for the Repair FEC Payload ID are defined, format A and
Format B. format B.
1 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial Sequence Number | Source Block Length | | Initial Sequence Number | Source Block Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoding Symbol ID | | Encoding Symbol ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Repair FEC Payload ID - Format A Figure 6: Repair FEC Payload ID - Format A
Initial Sequence Number (Flow i ISN) - 16 bits This field specifies Initial Sequence Number (Flow i ISN), (16 bits): This field specifies
the lowest 16 bits of the sequence number of the first packet to the lowest 16 bits of the sequence number of the first packet to
be included in this sub-block. If the sequence numbers are be included in this sub-block. If the sequence numbers are
shorter than 16 bits then the received Sequence Number SHALL be shorter than 16 bits, then the received Sequence Number SHALL be
logically padded with zero bits to become 16 bits in length logically padded with zero bits to become 16 bits in length,
respectively. The field type is unsigned integer. respectively. The field type is unsigned integer.
Source Block Length (SBL) - 16 bits This field specifies the length Source Block Length (SBL), (16 bits): This field specifies the length
of the source block in symbols. The field type is unsigned of the source block in symbols. The field type is unsigned
integer. integer.
Encoding Symbol ID (ESI) - 16 bits This field indicates which repair Encoding Symbol ID (ESI), (16 bits): This field indicates which
symbols are contained within this repair packet. The ESI provided repair symbols are contained within this repair packet. The ESI
is the ESI of the first repair symbol in the packet. The field provided is the ESI of the first repair symbol in the packet. The
type is unsigned integer. field type is unsigned integer.
1 2 3 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial Sequence Number | Source Block Length | | Initial Sequence Number | Source Block Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Encoding Symbol ID | | Encoding Symbol ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Repair FEC Payload ID - Format B Figure 7: Repair FEC Payload ID - Format B
Initial Sequence Number (Flow i ISN) - 16 bits This field specifies Initial Sequence Number (Flow i ISN), (16 bits): This field specifies
the lowest 16 bits of the sequence number of the first packet to the lowest 16 bits of the sequence number in the first packet to
be included in this sub-block. If the sequence numbers are be included in this sub-block. If the sequence numbers are
shorter than 16 bits then the received Sequence Number SHALL be shorter than 16 bits, then the received Sequence Number SHALL be
logically padded with zero bits to become 16 bits in length logically padded with zero bits to become 16 bits in length,
respectively. The field type is unsigned integer. respectively. The field type is unsigned integer.
Source Block Length (SBL) - 16 bits This field specifies the length Source Block Length (SBL), (16 bits): This field specifies the length
of the source block in symbols. The field type is unsigned of the source block in symbols. The field type is unsigned
integer. integer.
Encoding Symbol ID (ESI) - 24 bits This field indicates which repair Encoding Symbol ID (ESI); (24 bits): This field indicates which
symbols are contained within this repair packet. The ESI provided repair symbols are contained within this repair packet. The ESI
is the ESI of the first repair symbol in the packet. The field provided is the ESI of the first repair symbol in the packet. The
type is unsigned integer. field type is unsigned integer.
8.2. Procedures 8.2. Procedures
8.2.1. Source symbol construction 8.2.1. Source Symbol Construction
FEC Scheme XXX5 and FEC Scheme XXX6 use the procedures defined in FEC Scheme 5 and FEC Scheme 6 use the procedures defined in Section 5
Section 5 to construct a set of source symbols to which the FEC code to construct a set of source symbols to which the FEC code can be
can be applied. applied.
During the construction of the source block: During the construction of the source block:
o the length indication, l[i], included in the Source Packet o the length indication, l[i], included in the Source Packet
Information for each packet shall be dependent on the protocol Information for each packet shall be dependent on the protocol
carried within the transport payload. Rules for RTP are specified carried within the transport payload. Rules for RTP are specified
below. below.
o the value of s[i] in the construction of the Source Packet o the value of s[i] in the construction of the Source Packet
Information for each packet shall be the smallest integer such Information for each packet shall be the smallest integer such
that s[i]*T >= (l[i]+3) that s[i]*T >= (l[i]+3)
8.2.2. Derivation of Source FEC Packet Identification Information 8.2.2. Derivation of Source FEC Packet Identification Information
The Source FEC Packet Identification Information for a source packet The Source FEC Packet Identification Information for a source packet
is derived from the sequence number of the packet and information is derived from the sequence number of the packet and information
received in any repair FEC packet belonging to this Source Block. received in any repair FEC packet belonging to this source block.
Source blocks are identified by the sequence number of the first Source blocks are identified by the sequence number of the first
source packet in the block. This information is signaled in all source packet in the block. This information is signaled in all
repair FEC packets associated with the source block in the Initial repair FEC packets associated with the source block in the Initial
Sequence Number field. Sequence Number field.
The length of the Source Packet Information (in octets) for source The length of the Source Packet Information (in octets) for source
packets within a source block is equal to length of the payload packets within a source block is equal to the length of the payload
containing encoding symbols of the repair packets (i.e. not including containing encoding symbols of the repair packets (i.e., not
the Repair FEC Payload ID) for that block, which MUST be the same for including the Repair FEC Payload ID) for that block, which MUST be
all repair packets. The Application Data Unit Information Length the same for all repair packets. The Application Data Unit
(ADUIL) in symbols is equal to this length divided by the Encoding Information Length (ADUIL) in symbols is equal to this length divided
Symbol Size (which is signaled in the FEC Framework Configuration by the encoding symbol size (which is signaled in the FEC Framework
Information). The set of source packets which are included in the Configuration Information). The set of source packets included in
source block is determined from the Initial Sequence Number (ISN) and the source block is determined by the Initial Sequence Number (ISN)
Source Block Length (SBL) as follows: and Source Block Length (SBL) as follows:
Let, Let,
o I be the Initial Sequence Number of the source block o I be the Initial Sequence Number of the source block
o LP be the Source Packet Information Length in symbols o LP be the Source Packet Information Length in symbols
o LB be the Source Block Length in symbols o LB be the Source Block Length in symbols
Then, source packets with sequence numbers from I to I +(LB/LP)-1 Then, source packets with sequence numbers from I to I +(LB/LP)-1
inclusive are included in the source block. The Source Block Length inclusive are included in the source block. The Source Block Length,
LB MUST be chosen such that it is at least as large as the largest LB, MUST be chosen such that it is at least as large as the largest
Source Packet Information Length LP. Source Packet Information Length LP.
Note that if no FEC repair packets are received then no FEC decoding Note that if no FEC repair packets are received, then no FEC decoding
is possible and it is unnecessary for the receiver to identify the is possible, and it is unnecessary for the receiver to identify the
Source FEC Packet Identification Information for the source packets. Source FEC Packet Identification Information for the source packets.
The Encoding Symbol ID for a packet is derived from the following The encoding symbol ID for a packet is derived from the following
information: information:
o The sequence number, Ns, of the packet o The sequence number, Ns, of the packet
o The Source Packet Information Length for the source block, LP o The Source Packet Information Length for the source block, LP
o The Initial Sequence Number of the source block, I o The Initial Sequence Number of the source block, I
Then the Encoding Symbol ID for packet with sequence number Ns is Then, the encoding symbol ID for the packet with sequence number Ns
determined by the following formula: is determined by the following formula:
ESI = ( Ns - I ) * LP ESI = ( Ns - I ) * LP
Note that all repair packet associated to a given Source Block MUST Note that all repair packets associated to a given source block MUST
contain the same Source Block Length and Initial Sequence Number. contain the same Source Block Length and Initial Sequence Number.
Note also that the source packet flow processed by the FEC encoder Note also that the source packet flow processed by the FEC encoder
MUST have consecutive sequence numbers. In case the incoming source MUST have consecutive sequence numbers. In case the incoming source
packet flow has a gap in the sequence numbers then implementors packet flow has a gap in the sequence numbers, then implementors
SHOULD insert an ADU in the source block that complies to the format SHOULD insert an ADU in the source block that complies to the format
of the source packet flow, but is ignored at the application with of the source packet flow, but is ignored at the application with
high probability. For additional guidelines refer to [RFC6363], high probability. For additional guidelines, refer to [RFC6363],
Section 10.2, paragraph 5. Section 10.2, paragraph 5.
8.2.3. Repair packet construction 8.2.3. Repair Packet Construction
See Section 7.3.2 See Section 7.3.2
8.2.4. Procedures for RTP source flows 8.2.4. Procedures for RTP Source Flows
In the specific case of RTP source packet flows, then the RTP In the specific case of RTP source packet flows, the RTP Sequence
Sequence Number field SHALL be used as the sequence number in the Number field SHALL be used as the sequence number in the procedures
procedures described above. The length indication included in the described above. The length indication included in the Application
Application Data Unit Information SHALL be the RTP payload length Data Unit Information SHALL be the RTP payload length plus the length
plus the length of the CSRCs, if any, the RTP Header Extension, if of the contributing sources (CSRCs), if any, the RTP Header
present, and the RTP padding octets, if any. Note that this length Extension, if present, and the RTP padding octets, if any. Note that
is always equal to the UDP payload length of the packet minus 12. this length is always equal to the UDP payload length of the packet
minus 12.
8.3. FEC Code Specification 8.3. FEC Code Specification
The same as specified for FEC Scheme XXX3 for FEC Scheme XXX5, and The elements for FEC Scheme 5 are the same as specified for FEC
the same as specified for FEC Scheme XXX4 for FEC Scheme XXX6, as Scheme 3, and the elements specified for FEC Scheme 6 are the same as
specified in Section 7.4. specified for FEC 4, as specified in Section 7.4.
9. Security Considerations 9. Security Considerations
For the general security considerations related to the use of FEC, For the general security considerations related to the use of FEC,
refer to [RFC6363]. Also consider relevant security considerations refer to [RFC6363]. Also consider relevant security considerations
in [RFC5053] and [RFC6330]. No security vulnerabilities specific to in [RFC5053] and [RFC6330]. No security vulnerabilities specific to
this document have been identified. this document have been identified.
10. Session Description Protocol (SDP) Signaling 10. Session Description Protocol (SDP) Signaling
This section provides an SDP [RFC4566] example. The syntax follows This section provides an SDP [RFC4566] example. The syntax follows
the definition in [RFC6364] .Assume we have one source video stream the definition in [RFC6364]. Assume we have one source video stream
(mid:S1) and one FEC repair stream (mid:R1). We form one FEC group (mid:S1) and one FEC repair stream (mid:R1). We form one FEC group
with the "a=group:FEC-FR S1 R1" line. The source and repair streams with the "a=group:FEC-FR S1 R1" line. The source and repair streams
are sent to the same port on different multicast groups. The repair are sent to the same port on different multicast groups. The repair
window is set to 200 ms. window is set to 200 ms.
v=0 v=0
o=ali 1122334455 1122334466 IN IP4 fec.example.com o=ali 1122334455 1122334466 IN IP4 fec.example.com
s=Raptor FEC Example s=Raptor FEC Example
t=0 0 t=0 0
a=group:FEC-FR S1 R1 a=group:FEC-FR S1 R1
skipping to change at page 21, line 18 skipping to change at page 19, line 43
of FEC, refer to [RFC6363]. of FEC, refer to [RFC6363].
12. IANA Considerations 12. IANA Considerations
12.1. Registration of FEC Scheme IDs 12.1. Registration of FEC Scheme IDs
The value of FEC Scheme IDs is subject to IANA registration. For The value of FEC Scheme IDs is subject to IANA registration. For
general guidelines on IANA considerations as they apply to this general guidelines on IANA considerations as they apply to this
document, refer to [RFC6363]. document, refer to [RFC6363].
This document registers six values in the FEC Framework (FECFRAME) This document registers six values in the "FEC Framework (FECFRAME)
FEC Encoding IDs registry (http://www.iana.org/assignments/ FEC Encoding IDs" registry (http://www.iana.org/assignments/
rmt-fec-parameters/rmt-fec-parameters.xml#fecframe-fec-encoding-ids) rmt-fec-parameters/) as provided in Table 1. Each value refers to a
as provided in Table 1. Each value refers to a fully-specified FEC Fully-Specified FEC scheme.
scheme.
NOTE: To the RFC Editor: please change these XXX notations once
assigned, and remove this NOTE.
+----------+---------------------+----------------------------------+ +----------+---------------------+----------------------------------+
| FEC | FEC Scheme | Reference | | FEC | FEC Scheme | Reference |
| Encoding | Description | | | Encoding | Description | |
| ID | | | | ID | | |
+----------+---------------------+----------------------------------+ +----------+---------------------+----------------------------------+
| XXX1 | Raptor FEC Scheme | Section 6 in this document using | | 1 | Raptor FEC Scheme | Section 6 in this document using |
| | for Arbitrary | [RFC5053] | | | for Arbitrary | [RFC5053] |
| | Packet Flows | | | | Packet Flows | |
+----------+---------------------+----------------------------------+ +----------+---------------------+----------------------------------+
| XXX2 | RaptorQ FEC Scheme | Section 6 in this document using | | 2 | RaptorQ FEC Scheme | Section 6 in this document using |
| | for Arbitrary | [RFC6330]. | | | for Arbitrary | [RFC6330]. |
| | Packet Flows | | | | Packet Flows | |
+----------+---------------------+----------------------------------+ +----------+---------------------+----------------------------------+
| XXX3 | Raptor FEC Scheme | Section 7 in this document using | | 3 | Raptor FEC Scheme | Section 7 in this document using |
| | Optimised for | Raptor [RFC5053]. | | | Optimized for | Raptor [RFC5053]. |
| | Arbitrary Packet | | | | Arbitrary Packet | |
| | Flows | | | | Flows | |
+----------+---------------------+----------------------------------+ +----------+---------------------+----------------------------------+
| XXX4 | RaptorQ FEC Scheme | XXX4 for the Optimised RaptorQ | | 4 | RaptorQ FEC Scheme | Section 7 in this document |
| | Optimised for | FEC Scheme for Arbitrary Packet | | | Optimized for | using RaptorQ [RFC6330]. |
| | Arbitrary Packet | Flows (Section 7) using RaptorQ | | | Arbitrary Packet | |
| | Flows | [RFC6330]. | | | Flows | |
+----------+---------------------+----------------------------------+
+----------+---------------------+----------------------------------+ +----------+---------------------+----------------------------------+
| XXX5 | Raptor FEC Scheme | XXX5 for the Raptor FEC Scheme | | 5 | Raptor FEC Scheme | Section 8 in this document using |
| | for a single | for a single sequence flow | | | for a Single | Raptor [RFC5053]. |
| | sequence flow | (Section 8) using Raptor | | | Sequence Flow | |
| | | [RFC5053]. |
+----------+---------------------+----------------------------------+ +----------+---------------------+----------------------------------+
| XXX6 | RaptorQ FEC Scheme | XXX6 for the RaptorQ FEC Scheme | | 6 | RaptorQ FEC Scheme | Section 8 in this document using |
| | for a single | for a single sequence flow | | | for a Single | RaptorQ [RFC6330]. |
| | sequence flow | (Section 8) using RaptorQ | | | Sequence Flow | |
| | | [RFC6330]. |
+----------+---------------------+----------------------------------+ +----------+---------------------+----------------------------------+
Table 1: FEC Framework (FECFRAME) FEC Encoding IDs Table 1: FEC Framework (FECFRAME) FEC Encoding IDs
13. Acknowledgements 13. Acknowledgements
Thanks are due to Ali C. Begen and David Harrington for thorough Thanks are due to Ali C. Begen and David Harrington for thorough
review of earlier draft versions of this document. review of earlier draft versions of this document.
14. References 14. References
skipping to change at page 23, line 7 skipping to change at page 21, line 35
[RFC5052] Watson, M., Luby, M., and L. Vicisano, "Forward Error [RFC5052] Watson, M., Luby, M., and L. Vicisano, "Forward Error
Correction (FEC) Building Block", RFC 5052, August 2007. Correction (FEC) Building Block", RFC 5052, August 2007.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
[RFC6364] Begen, A., "Session Description Protocol Elements for the [RFC6364] Begen, A., "Session Description Protocol Elements for the
Forward Error Correction (FEC) Framework", RFC 6364, Forward Error Correction (FEC) Framework", RFC 6364,
October 2011. October 2011.
[dvbts] "ETSI TS 102 034 - Digital Video Broadcasting (DVB); [DVBTS] ETSI, "Digital Video Broadcasting (DVB); Transport of
Transport of MPEG-2 Based DVB Services over IP Based MPEG-2 Based DVB Services over IP Based Networks", ETSI TS
Networks", March 2005. 102 034, March 2009.
[MBMSTS] 3GPP, "Multimedia Broadcast/Multicast Service (MBMS); [MBMSTS] 3GPP, "Multimedia Broadcast/Multicast Service (MBMS);
Protocols and codecs", 3GPP TS 26.346, April 2005. Protocols and codecs", 3GPP TS 26.346, April 2005.
Authors' Addresses Authors' Addresses
Mark Watson Mark Watson
Netflix Netflix
100 Winchester Circle 100 Winchester Circle
Los Gatos, CA 95032 Los Gatos, CA 95032
U.S.A. United States
Email: watsonm@netflix.com EMail: watsonm@netflix.com
Thomas Stockhammer Thomas Stockhammer
Nomor Research Nomor Research
Brecherspitzstrasse 8 Brecherspitzstrasse 8
Munich 81541 Munich 81541
Germany Germany
Email: stockhammer@nomor.de EMail: stockhammer@nomor.de
Michael Luby Michael Luby
Qualcomm Incorporated Qualcomm Research Berkeley
3165 Kifer Road 2030 Addison Street
Santa Clara, CA 95051 Berkeley, CA 94704
U.S.A. United States
Email: luby@qualcomm.com EMail: luby@qualcomm.com
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