draft-ietf-fecframe-raptor-03.txt   draft-ietf-fecframe-raptor-04.txt 
FEC Framework M. Watson FEC Framework M. Watson
Internet-Draft Netflix Internet-Draft Netflix
Intended status: Standards Track T. Stockhammer Intended status: Standards Track T. Stockhammer
Expires: May 27, 2011 Nomor Research Expires: June 12, 2011 Nomor Research
November 23, 2010 M. Luby
Qualcomm Incorporated
December 9, 2010
Raptor FEC Schemes for FECFRAME Raptor FEC Schemes for FECFRAME
draft-ietf-fecframe-raptor-03 draft-ietf-fecframe-raptor-04
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 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
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This Internet-Draft will expire on May 27, 2011. This Internet-Draft will expire on June 12, 2011.
Copyright Notice Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Document Outline . . . . . . . . . . . . . . . . . . . . . . . 5 2. Document Outline . . . . . . . . . . . . . . . . . . . . . . . 5
3. Requirements Notation . . . . . . . . . . . . . . . . . . . . 5 3. Requirements Notation . . . . . . . . . . . . . . . . . . . . 5
4. Definitions and Abbreviations . . . . . . . . . . . . . . . . 5 4. Definitions and Abbreviations . . . . . . . . . . . . . . . . 5
4.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6 4.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 6 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 . . . . . . . . 8 6. Raptor FEC Schemes for arbitrary packet flows . . . . . . . . 8
6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 8 6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 8
6.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 8 6.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 8
6.2.1. FEC Framework Configuration Information . . . . . . . 8 6.2.1. FEC Framework Configuration Information . . . . . . . 8
6.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 9 6.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 9
6.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 10 6.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 10
6.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 12 6.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 11
6.3.1. Source symbol construction . . . . . . . . . . . . . . 12 6.3.1. Source symbol construction . . . . . . . . . . . . . . 11
6.3.2. Repair packet construction . . . . . . . . . . . . . . 12 6.3.2. Repair packet construction . . . . . . . . . . . . . . 11
6.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 12 6.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 12
7. Optimised Raptor FEC Scheme for arbitrary packet flows . . . . 13 7. Optimised Raptor FEC Scheme for arbitrary packet flows . . . . 12
7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 12
7.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 13 7.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 13
7.2.1. FEC Framework Configuration Information . . . . . . . 13 7.2.1. FEC Framework Configuration Information . . . . . . . 13
7.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 14 7.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 13
7.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 14 7.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 13
7.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 14 7.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 13
7.3.1. Source symbol construction . . . . . . . . . . . . . . 14 7.3.1. Source symbol construction . . . . . . . . . . . . . . 13
7.3.2. Repair packet construction . . . . . . . . . . . . . . 14 7.3.2. Repair packet construction . . . . . . . . . . . . . . 13
7.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 14 7.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 13
8. Raptor FEC Scheme for a single sequenced flow . . . . . . . . 15 8. Raptor FEC Scheme for a single sequenced flow . . . . . . . . 14
8.1. Formats and codes . . . . . . . . . . . . . . . . . . . . 15 8.1. Formats and codes . . . . . . . . . . . . . . . . . . . . 14
8.1.1. FEC Framework Configuration Information . . . . . . . 15 8.1.1. FEC Framework Configuration Information . . . . . . . 14
8.1.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 15 8.1.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 14
8.1.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 15 8.1.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 15
8.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 17
8.2.1. Source symbol construction . . . . . . . . . . . . . . 17 8.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 16
8.2.1. Source symbol construction . . . . . . . . . . . . . . 16
8.2.2. Derivation of Source FEC Packet Identification 8.2.2. Derivation of Source FEC Packet Identification
Information . . . . . . . . . . . . . . . . . . . . . 17 Information . . . . . . . . . . . . . . . . . . . . . 16
8.2.3. Repair packet construction . . . . . . . . . . . . . . 18 8.2.3. Repair packet construction . . . . . . . . . . . . . . 17
8.2.4. Procedures for RTP source flows . . . . . . . . . . . 18 8.2.4. Procedures for RTP source flows . . . . . . . . . . . 17
8.3. FEC Code Specification . . . . . . . . . . . . . . . . . . 18 8.3. FEC Code Specification . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19 9. Security Considerations . . . . . . . . . . . . . . . . . . . 18
10. Session Description Protocol (SDP) Signaling . . . . . . . . . 19 10. Session Description Protocol (SDP) Signaling . . . . . . . . . 18
11. Congestion Control Considerations . . . . . . . . . . . . . . 19 11. Congestion Control Considerations . . . . . . . . . . . . . . 18
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
12.1. Registration of FEC Scheme IDs . . . . . . . . . . . . . . 19 12.1. Registration of FEC Scheme IDs . . . . . . . . . . . . . . 19
13. Normative References . . . . . . . . . . . . . . . . . . . . . 20 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
14.1. Normative References . . . . . . . . . . . . . . . . . . . 19
14.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction 1. Introduction
The FEC Framework [I-D.ietf-fecframe-framework] describes a framework The FEC Framework [I-D.ietf-fecframe-framework] describes a framework
for the application of Forward Error Correction to arbitrary packet for the application of Forward Error Correction to arbitrary packet
flows. Modelled after the FEC Building Block developed by the IETF flows. Modeled after the FEC Building Block developed by the IETF
Reliable Multicast Transport working group [RFC5052], the FEC Reliable Multicast Transport working group [RFC5052], the FEC
Framework defines the concept of FEC Schemes which provide specific Framework defines the concept of FEC Schemes which provide specific
Forward Error Correction schemes. This document describes six FEC Forward Error Correction schemes. This document describes six FEC
Schemes which make use of the Raptor and RaptorQ FEC codes as defined Schemes which make use of the Raptor and RaptorQ FEC codes as defined
in [RFC5053] and [I-D.ietf-rmt-bb-fec-raptorq]. in [RFC5053] and [I-D.ietf-rmt-bb-fec-raptorq].
The FEC protection mechanism is independent of the type of the source The FEC protection mechanism is independent of the type of the source
data, which can be an arbitrary sequence of packets, including for data, which can be an arbitrary sequence of packets, including for
example audio or video data. In general, the operation of the example audio or video data. In general, the operation of the
protection mechanism is as follows: protection mechanism is as follows:
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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.
o The sender packetizes the repair symbols and sends the repair o The sender packetizes the repair symbols and sends the repair
packet(s) along with the source packets to the receiver(s). packet(s) along with the source packets to the receiver(s).
Per the FEC Framework requirements, the sender MUST transmit the Per the FEC Framework requirements, the sender MUST transmit the
source and repair packets in different source and repair flows, or in source and repair packets in different source and repair flows, or in
the case RTP transport is used for Repair packets, in different RTP the case RTP transport is used for repair packets, in different RTP
streams. At the receiver side, if all of the source packets are streams. 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 source repair packets are discarded. However, if there are missing source
packets, the repair packets can be used to recover the missing packets, the repair packets can be used to recover the missing
information. information.
The operation of the FEC mechanism requires that the receiver can The operation of the FEC mechanism requires that the receiver can
identify the relationships between received source packets and repair identify the relationships between received source packets and repair
packets and in particular which source packets are missing. In many packets and in particular which source packets are missing. In many
cases, data already exists in the source packets which can be used to cases, data already exists in the source packets which can be used to
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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
This document uses the following definitions. For further This document uses the following definitions. For further
definitions that apply to FEC Framework in general, see definitions that apply to FEC Framework in general, see
[I-D.ietf-fecframe-framework]. [I-D.ietf-fecframe-framework].
Source Flow: The packet flow(s) or stream(s) carrying the source
data and to which FEC protection is to be applied.
Repair Flow: The packet flow(s) or stream(s) carrying the repair
data.
Symbol: A unit of data. Its size, in bytes, is referred to as the Symbol: A unit of data. Its size, in bytes, is referred to as the
symbol size. symbol size.
Source Symbol: The smallest unit of data used during the encoding
process.
Repair Symbol: Repair symbols are generated from the source symbols.
Source Packet: Data packets that contain only source symbols.
Repair Packet: Data packets that contain only repair symbols.
Source Block: A block of source symbols that are considered together
in the encoding process.
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.
FEC Payload ID: Information that identifies the contents of a packet
with respect to the FEC scheme.
Source FEC Payload ID: An FEC Payload ID specifically used with
source packets.
Repair FEC Payload ID: An FEC Payload ID specifically used with
repair packets.
4.2. Abbreviations 4.2. Abbreviations
This document uses the following abbreviations. For further
abbreviations that apply to FEC Framework in general, see
[I-D.ietf-fecframe-framework].
FSSI: FEC-Scheme-Specific Information. FSSI: FEC-Scheme-Specific Information.
SS-FSSI: Sender-Side FEC-Scheme-Specific Information. SS-FSSI: Sender-Side FEC-Scheme-Specific Information.
RS-FSSI: Receiver-Side FEC-Scheme-Specific Information. RS-FSSI: Receiver-Side FEC-Scheme-Specific Information.
ADU Application Data Unit
ADUI Application Data Unit Information ADUI Application Data Unit Information
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 which 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. As described in symbols from a set of source transport payloads. As described in
[I-D.ietf-fecframe-framework] for each Application Data Unit (ADU) in [I-D.ietf-fecframe-framework] for each Application Data Unit (ADU) in
a source block, the FEC Scheme is provided with: a source block, the FEC Scheme is provided with:
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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 source blocks. The Source FEC Packet Identification Information
consists of the identity of the source block and the Encoding Symbol consists of the identity of the source block and the Encoding Symbol
ID associated with the packet. 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 an FEC Scheme for the application of the
Raptor and RaptorQ codes to arbitary packet flows. This scheme is Raptor 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 Raptor codes, this scheme is equivalent to that When used with Raptor codes, this scheme is equivalent to that
specified in [MBMSTS]. 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
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The Payload ID Format identifier defines which of the Source FEC The Payload ID Format identifier defines which of the Source FEC
Payload ID and Repair FEC Payload ID formats defined below shall be Payload ID and Repair FEC Payload ID formats defined below shall be
used. Payload ID Format B SHALL NOT be used when[RFC5053] is used. used. Payload ID Format B SHALL NOT be used when[RFC5053] is used.
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 that
is used is signalled as part of the FEC Framework Configuration 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) |
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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.
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
The number of repair symbols contained within a repair packet is The ESI value placed into a repair packet is calculated as specified
computed from the packet length. The ESI value placed into a repair in Section 5.3.2 of [RFC5053] when Raptor as defined in [RFC5053] is
packet is given by the following formula: used and as specified in Section 4.4.2 of
ESI_repair = I_repair + SBL,
where I_repair is the index of the repair symbol in the sequence of [I-D.ietf-rmt-bb-fec-raptorq] when RaptorQ as defined in
repair symbols generated according to Section 6.4, where the first [I-D.ietf-rmt-bb-fec-raptorq] is used, where K=SBL.
repair symbol has index 0, the second index 1 etc. and SBL is the
Source Block Length. The Source Block Length field of the Repair FEC
Payload ID field SHALL be set to the number of symbols included in
the Source Packet Information of packets associated with the source
block.
6.4. FEC Code Specification 6.4. FEC Code Specification
The Raptor FEC encoder defined in [RFC5053] or The Raptor FEC encoder defined in [RFC5053] or
[I-D.ietf-rmt-bb-fec-raptorq] SHALL be used. The source symbols [I-D.ietf-rmt-bb-fec-raptorq] SHALL be used. The source symbols
passed to the Raptor FEC encoder SHALL consist of the source symbols passed to the Raptor FEC encoder SHALL consist of the source symbols
constructed according to Section 6.3.1. Thus the value of the constructed according to Section 6.3.1. Thus the value of the
parameter K used by the FEC encoder (equal to the Source Block parameter K used by the FEC encoder (equal to the Source Block
Length) may vary amongst the blocks of the stream but SHALL NOT Length) may vary amongst the blocks of the stream but SHALL NOT
exceed the Maximum Source Block Length signalled in the FEC Scheme- exceed the Maximum Source Block Length signaled in the FEC Scheme-
specific information. The symbol size, T, to be used for source specific information. The symbol size, T, to be used for source
block construction and the repair symbol construction is equal to the block construction and the repair symbol construction is equal to the
Encoding Symbol Size signaled in the FEC Scheme Specific Information. Encoding Symbol Size signaled in the FEC Scheme Specific Information.
7. Optimised 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 which is applicable to scenarios in which only
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substantial optimisations to both sender and receiver substantial optimisations 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 signalled in the Maximum Source Block to be used for a stream is signaled in the Maximum Source Block
Size field of the scheme-specific information. This allows for Size field of the scheme-specific information. This allows for
efficient parallel encoding of multiple streams. Note that th efficient parallel encoding of multiple streams. Note that the
epadding operation is equivalent to the padding operation in padding operation is equivalent to the padding operation in
[I-D.ietf-rmt-bb-fec-raptorq] with K' the specified single source [I-D.ietf-rmt-bb-fec-raptorq] with K' the specified single source
block size and K the actual source block size K. block size and K the actual source block size K.
o A restricted set of possible source block sizes is specified. o The possible choices of the source block size for a stream is
This allows explicit operation sequences for encoding the restricted to a small specified set of sizes. This allows
restricted set of block sizes to be pre-calculated and embedded in explicit operation sequences for encoding and decoding the
software or handware. restricted set of source block sizes to be pre-calculated and
embedded in software or hardware.
When the Raptor FEC encoder as defined in [RFC5053] is used, this When the Raptor FEC encoder as defined in [RFC5053] is used, this
scheme is equivalent to that specified in [dvbts] for arbitrary scheme is equivalent to that specified in [dvbts] for arbitrary
packet flows. packet 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
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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 given by the following formula: 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
ESI_repair = I_repair + MSBL Section 5.3.2 of [RFC5053] when Raptor as defined in[RFC5053] is used
and as specified in Section 4.4.2 of [I-D.ietf-rmt-bb-fec-raptorq]
Where I_repair is the index of the repair symbol in the sequence of when RaptorQ as defined in [I-D.ietf-rmt-bb-fec-raptorq] is used,
repair symbols generated according to Section 6.4, where the first where K=SBL. The value of SBL SHALL be at most the value of MSBL.
repair symbol has index 0, the second index 1 etc. and MSBL is the
Maximum Source Block Length signalled in the FEC Scheme Specific
Information. The Source Block Length field of the Repair FEC Payload
ID field SHALL be set to the number of symbols included in the Source
Packet Information of packets associated with the source block.
7.4. FEC Code Specification 7.4. FEC Code Specification
The Raptor FEC encoder defined in [RFC5053] or The Raptor FEC encoder defined in [RFC5053] or
[I-D.ietf-rmt-bb-fec-raptorq] SHALL be used. The source symbols [I-D.ietf-rmt-bb-fec-raptorq] SHALL be used. The source symbols
passed to the Raptor FEC encoder SHALL consist of the source symbols passed to the Raptor FEC encoder SHALL consist of the source symbols
constructed according to Section 6.3.1 extended with zero or more constructed according to Section 6.3.1 extended with zero or more
padding symbols such that the total number of symbols in the source padding symbols such that the total number of symbols in the source
block is equal to the Maximum Source Block Length signaled in the FEC block is equal to the Maximum Source Block Length signaled in the FEC
Scheme Specific Information. Thus the value of the parameter K used Scheme Specific Information. Thus the value of the parameter K used
skipping to change at page 16, line 46 skipping to change at page 16, line 5
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 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. respectively.
Encoding Symbol ID (ESI) - 16 bits This field indicates which repair
symbols are contained within this repair packet. The ESI provided
is the ESI of the first repair symbol in the packet.
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. of the source block in symbols.
Encoding Symbol ID (ESI) - 24 bits This field indicates which repair
symbols are contained within this repair packet. The ESI provided
is the ESI of the first repair symbol in the packet.
8.2. Procedures 8.2. Procedures
8.2.1. Source symbol construction 8.2.1. Source symbol construction
This FEC Scheme uses the procedures defined in Section 5 to construct This FEC Scheme uses the procedures defined in Section 5 to construct
a set of source symbols to which the FEC code can be applied. The a set of source symbols to which the FEC code can be applied. The
sender MUST allocate Source Block Numbers to source blocks sender MUST allocate Source Block Numbers to source blocks
sequentially, wrapping around to zero after Source Block Number 65535 sequentially, wrapping around to zero after Source Block Number 65535
in the case Format A is used for FEC Payload IDs and 255 in the case in the case Format A is used for FEC Payload IDs and 255 in the case
Format B is used for FEC Payload IDs. Format B is used for FEC Payload IDs.
skipping to change at page 17, line 34 skipping to change at page 16, line 38
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 bytes) for source The length of the Source Packet Information (in bytes) for source
packets within a source block is equal to length of the payload packets within a source block is equal to 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 including
the Repair FEC Payload ID) for that block, which MUST be the same for the Repair FEC Payload ID) for that block, which MUST be the same for
all repair packets. The Application Data Unit Information Length all repair packets. The Application Data Unit Information Length
(ADUIL) in symbols is equal to this length divided by the Encoding (ADUIL) in symbols is equal to this length divided by the Encoding
Symbol Size (which is signaled in the FEC Framework Configuration Symbol Size (which is signaled in the FEC Framework Configuration
Information). The set of source packets which are included in the Information). The set of source packets which are included in the
skipping to change at page 18, line 4 skipping to change at page 17, line 7
containing encoding symbols of the repair packets (i.e. not including containing encoding symbols of the repair packets (i.e. not including
the Repair FEC Payload ID) for that block, which MUST be the same for the Repair FEC Payload ID) for that block, which MUST be the same for
all repair packets. The Application Data Unit Information Length all repair packets. The Application Data Unit Information Length
(ADUIL) in symbols is equal to this length divided by the Encoding (ADUIL) in symbols is equal to this length divided by the Encoding
Symbol Size (which is signaled in the FEC Framework Configuration Symbol Size (which is signaled in the FEC Framework Configuration
Information). The set of source packets which are included in the Information). The set of source packets which are included in the
source block is determined from the Initial Sequence Number (ISN) and source block is determined from the Initial Sequence Number (ISN) and
Source Block Length (SBL) as follows: 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. inclusive are included in the source block.
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
skipping to change at page 19, line 13 skipping to change at page 18, line 17
See Section 7.4 See 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 [I-D.ietf-fecframe-framework]. No security considerations refer to [I-D.ietf-fecframe-framework]. No security considerations
specific to this document have been identified. specific to 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 following This section provides an SDP [RFC4566] example. The syntax follows
example uses the SDP elements for FEC Framework, which were the definition in [I-D.ietf-fecframe-sdp-elements] .Assume we have
introduced in [I-D.ietf-fecframe-sdp-elements], and the FEC grouping one source video stream (mid:S1) and one FEC repair stream (mid:R1).
semantics [I-D.ietf-mmusic-rfc4756bis]. We form one FEC group with the "a=group:FEC-FR S1 R1" line. The
source and repair streams are sent to the same port on different
In this example, we have one source video stream (mid:S1) and one FEC multicast groups. The repair window is set to 200 ms.
repair stream (mid:R1). We form one FEC group with the "a=group:FEC
S1 R1" line. The source and repair streams are sent to the same port
on different multicast groups. The repair 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 S1 R1 a=group:FEC-FR S1 R1
m=video 30000 RTP/AVP 100 m=video 30000 RTP/AVP 100
c=IN IP4 233.252.0.1/127 c=IN IP4 233.252.0.1/127
a=rtpmap:100 MP2T/90000 a=rtpmap:100 MP2T/90000
a=fec-source-flow: id=0; tag-len=4 a=fec-source-flow: id=0
a=mid:S1 a=mid:S1
m=application 30000 udp/fec m=application 30000 UDP/FEC
c=IN IP4 233.252.0.2/127 c=IN IP4 233.252.0.2/127
a=fec-repair-flow: encoding-id=0; fssi=Kmax:8192,T:128,P:A a=fec-repair-flow: encoding-id=6; fssi=Kmax:8192,T:128,P:A
a=repair-window:200 a=repair-window:200ms
a=mid:R1 a=mid:R1
11. Congestion Control Considerations 11. Congestion Control Considerations
For the general congestion control considerations related to the use For the general congestion control considerations related to the use
of FEC, refer to [I-D.ietf-fecframe-framework]. of FEC, refer to [I-D.ietf-fecframe-framework].
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 [I-D.ietf-fecframe-framework]. document, refer to [I-D.ietf-fecframe-framework].
This document registers three values in the FEC Framework (FECFRAME) This document registers three values in the FEC Framework (FECFRAME)
FEC Encoding IDs registry as follows: FEC Encoding IDs registry as follows:
o XXX for the Raptor FEC Scheme for Arbitrary Packet Flows o 1 for the Raptor FEC Scheme for Arbitrary Packet Flows (Section 6
(Section 6 using Raptor [RFC5053]. using Raptor [RFC5053].
o XXX for the Raptor FEC Scheme for Arbitrary Packet Flows o 2 for the Raptor FEC Scheme for Arbitrary Packet Flows (Section 6
(Section 6 using RaptorQ [I-D.ietf-rmt-bb-fec-raptorq]. using RaptorQ [I-D.ietf-rmt-bb-fec-raptorq].
o XXX for the Optimised Raptor FEC Scheme for Arbitrary Packet Flows o 3 for the Optimised Raptor FEC Scheme for Arbitrary Packet Flows
(Section 7) using Raptor [RFC5053]. (Section 7) using Raptor [RFC5053].
o XXX for the Optimised Raptor FEC Scheme for Arbitrary Packet Flows o 4 for the Optimised Raptor FEC Scheme for Arbitrary Packet Flows
(Section 7) using RaptorQ [I-D.ietf-rmt-bb-fec-raptorq]. (Section 7) using RaptorQ [I-D.ietf-rmt-bb-fec-raptorq].
o XXX for the Raptor FEC Scheme for a single sequence flow o 5 for the Raptor FEC Scheme for a single sequence flow (Section 8)
(Section 8) using Raptor [RFC5053]. using Raptor [RFC5053].
o XXX for the Raptor FEC Scheme for a single sequence flow o 6 for the Raptor FEC Scheme for a single sequence flow (Section 8)
(Section 8) using RaptorQ [I-D.ietf-rmt-bb-fec-raptorq]. using RaptorQ [I-D.ietf-rmt-bb-fec-raptorq].
13. Normative References 13. Acknowledgements
Thanks are due to Ali C. Begen for thorough review of earlier draft
versions of this document.
14. References
14.1. Normative References
[I-D.ietf-fecframe-framework] [I-D.ietf-fecframe-framework]
Watson, M., "Forward Error Correction (FEC) Framework", Watson, M., "Forward Error Correction (FEC) Framework",
draft-ietf-fecframe-framework-10 (work in progress), draft-ietf-fecframe-framework-10 (work in progress),
September 2010. September 2010.
[I-D.ietf-fecframe-sdp-elements]
Begen, A., "Session Description Protocol Elements for FEC
Framework", draft-ietf-fecframe-sdp-elements-11 (work in
progress), October 2010.
[RFC5052] Watson, M., Luby, M., and L. Vicisano, "Forward Error
Correction (FEC) Building Block", RFC 5052, August 2007.
[RFC5053] Luby, M., Shokrollahi, A., Watson, M., and T. Stockhammer, [RFC5053] Luby, M., Shokrollahi, A., Watson, M., and T. Stockhammer,
"Raptor Forward Error Correction Scheme for Object "Raptor Forward Error Correction Scheme for Object
Delivery", RFC 5053, October 2007. Delivery", RFC 5053, October 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[I-D.ietf-mmusic-rfc4756bis]
Begen, A., "Forward Error Correction Grouping Semantics in
Session Description Protocol",
draft-ietf-mmusic-rfc4756bis-10 (work in progress),
June 2010.
[I-D.ietf-rmt-bb-fec-raptorq] [I-D.ietf-rmt-bb-fec-raptorq]
Luby, M., Shokrollahi, A., Watson, M., Stockhammer, T., Luby, M., Shokrollahi, A., Watson, M., Stockhammer, T.,
and L. Minder, "RaptorQ Forward Error Correction Scheme and L. Minder, "RaptorQ Forward Error Correction Scheme
for Object Delivery", draft-ietf-rmt-bb-fec-raptorq-04 for Object Delivery", draft-ietf-rmt-bb-fec-raptorq-04
(work in progress), August 2010. (work in progress), August 2010.
14.2. Informative References
[RFC5052] Watson, M., Luby, M., and L. Vicisano, "Forward Error
Correction (FEC) Building Block", RFC 5052, August 2007.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
[I-D.ietf-fecframe-sdp-elements]
Begen, A., "Session Description Protocol Elements for FEC
Framework", October 2010.
[dvbts] "ETSI TS 102 034 - Digital Video Broadcasting (DVB); [dvbts] "ETSI TS 102 034 - Digital Video Broadcasting (DVB);
Transport of MPEG-2 Based DVB Services over IP Based Transport of MPEG-2 Based DVB Services over IP Based
Networks", March 2005. Networks", March 2005.
[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
skipping to change at line 920 skipping to change at page 21, line 4
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
Qualcomm Incorporated
3165 Kifer Road
Santa Clara, CA 95051
U.S.A.
Email: luby@qualcomm.com
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