draft-ietf-fecframe-raptor-09.txt   draft-ietf-fecframe-raptor-10.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: September 2, 2012 Nomor Research Expires: September 2, 2012 Nomor Research
M. Luby M. Luby
Qualcomm Incorporated Qualcomm Incorporated
March 1, 2012 March 1, 2012
Raptor FEC Schemes for FECFRAME Raptor FEC Schemes for FECFRAME
draft-ietf-fecframe-raptor-09 draft-ietf-fecframe-raptor-10
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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6.3.2. Repair packet construction . . . . . . . . . . . . . . 13 6.3.2. Repair packet construction . . . . . . . . . . . . . . 13
6.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 13 6.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 13
7. Optimised Raptor FEC Scheme for arbitrary packet flows . . . . 13 7. Optimised Raptor FEC Scheme for arbitrary packet flows . . . . 13
7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 13 7.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 13
7.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 14 7.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 14
7.2.1. FEC Framework Configuration Information . . . . . . . 14 7.2.1. FEC Framework Configuration Information . . . . . . . 14
7.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 14 7.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 14
7.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 14 7.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 14
7.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 14 7.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 14
7.3.1. Source symbol construction . . . . . . . . . . . . . . 14 7.3.1. Source symbol construction . . . . . . . . . . . . . . 14
7.3.2. Repair packet construction . . . . . . . . . . . . . . 14 7.3.2. Repair packet construction . . . . . . . . . . . . . . 15
7.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 15 7.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 15
8. Raptor FEC Scheme for a single sequenced flow . . . . . . . . 15 8. Raptor FEC Scheme for a single sequenced flow . . . . . . . . 15
8.1. Formats and codes . . . . . . . . . . . . . . . . . . . . 15 8.1. Formats and codes . . . . . . . . . . . . . . . . . . . . 15
8.1.1. FEC Framework Configuration Information . . . . . . . 15 8.1.1. FEC Framework Configuration Information . . . . . . . 15
8.1.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 16 8.1.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 16
8.1.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 16 8.1.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 16
8.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 17 8.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 17
8.2.1. Source symbol construction . . . . . . . . . . . . . . 17 8.2.1. Source symbol construction . . . . . . . . . . . . . . 17
8.2.2. Derivation of Source FEC Packet Identification 8.2.2. Derivation of Source FEC Packet Identification
Information . . . . . . . . . . . . . . . . . . . . . 17 Information . . . . . . . . . . . . . . . . . . . . . 18
8.2.3. Repair packet construction . . . . . . . . . . . . . . 19 8.2.3. Repair packet construction . . . . . . . . . . . . . . 19
8.2.4. Procedures for RTP source flows . . . . . . . . . . . 19 8.2.4. Procedures for RTP source flows . . . . . . . . . . . 19
8.3. FEC Code Specification . . . . . . . . . . . . . . . . . . 19 8.3. FEC Code Specification . . . . . . . . . . . . . . . . . . 19
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19 9. Security Considerations . . . . . . . . . . . . . . . . . . . 19
10. Session Description Protocol (SDP) Signaling . . . . . . . . . 19 10. Session Description Protocol (SDP) Signaling . . . . . . . . . 19
11. Congestion Control Considerations . . . . . . . . . . . . . . 20 11. Congestion Control Considerations . . . . . . . . . . . . . . 20
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
12.1. Registration of FEC Scheme IDs . . . . . . . . . . . . . . 20 12.1. Registration of FEC Scheme IDs . . . . . . . . . . . . . . 20
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
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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 arbitrary 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 the Raptor codes specified in [RFC5053], this scheme
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 XXX1 when [RFC5053] is used and XXX2 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 NOTE: To the RFC Editor: please change these XXX notations once
assigned, and remove this NOTE. 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: A decimal non-negative integer less than 8192 MSBL Value range: A decimal non-negative integer less than 8192 for
(for Raptor) or 56403 (for RaptorQ), in units of symbols FEC Scheme XXX1 and less than 56403 for FEC Scheme XXX2, in units
of symbols
Encoding Symbol Size Name: "T", Value range: A decimal non- Encoding Symbol Size Name: "T", Value range: A decimal non-
negative integer less than 65536, in units of octets negative integer less than 65536, in units of octets
Payload ID Format Name: "P", Value range: "A" or "B" Payload ID Format Name: "P", Value range: "A" or "B"
An encoding format for The MSBL and Encoding Symbol Size is defined An encoding format for The MSBL and Encoding Symbol Size is defined
below. below.
1 2 3 1 2 3
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|P| Reserved | |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 may be omitted indicating that Payload ID Format Specific Information may be omitted indicating that Payload ID Format
A is in use. The Payload ID Format identifier defines which of the A is in use. The Payload ID Format identifier defines which of the
Source FEC Payload ID and Repair FEC Payload ID formats defined below Source FEC Payload ID and Repair FEC Payload ID formats defined below
shall be used. Payload ID Format B SHALL NOT be used when[RFC5053] shall be used. Payload ID Format B SHALL NOT be used for FEC Scheme
is used. The two formats enable different use cases. Format A is XXX1. The two formats enable different use cases. Format A is
appropriate in case the stream has many typically smaller source appropriate in case the stream has many typically smaller source
blocks and Format B is applicable if the stream has fewer large blocks and Format B is applicable if the stream has fewer 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 that
is used is signaled as part of the FEC Framework Configuration is used is signaled as part of the FEC Framework Configuration
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For format B, it is of size 8 bits. For format B, it is of size 8 bits.
Encoding Symbol ID (ESI), (24 bits) Integer identifier for the Encoding Symbol ID (ESI), (24 bits) Integer identifier for the
encoding symbols within the packet. encoding symbols within the packet.
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 source block.
The interpretation of the Source Block Number, Encoding Symbol The interpretation of the Source Block Number, Encoding Symbol
Identifier and Source Block Length is defined by the FEC Code Identifier and Source Block Length is defined by the FEC Code
Specification in [RFC5053] and [RFC6330]. Specification in [RFC5053] for FEC Scheme XXX1 and [RFC6330] for FEC
Scheme XXX2.
6.3. Procedures 6.3. Procedures
6.3.1. Source symbol construction 6.3.1. Source symbol construction
This FEC Scheme uses the procedures defined in Section 5 to construct FEC Scheme XXX1 and FEC Scheme XXX2 use the procedures defined in
a set of source symbols to which the FEC code can be applied. The Section 5 to construct a set of source symbols to which the FEC code
sender MUST allocate Source Block Numbers to source blocks can be applied. The sender MUST allocate Source Block Numbers to
sequentially, wrapping around to zero after Source Block Number 65535 source blocks sequentially, wrapping around to zero after Source
(Format A) or 255 (Format B). Block 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
When using Raptor [RFC5053], the ESI value placed into a repair For FEC Scheme XXX1, the ESI value placed into a repair packet is
packet is calculated as specified in Section 5.3.2 of [RFC5053]. calculated as specified in Section 5.3.2 of [RFC5053].
When using Raptor! [RFC6330], the ESI value placed into a repair For FEC Scheme XXX2 [RFC6330], the ESI value placed into a repair
packet is calculated as specified in Section 4.4.2 of [RFC6330]. packet 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 Raptor FEC encoder defined in [RFC5053] or [RFC6330] SHALL be The FEC encoder defined in [RFC5053] SHALL be used FEC Scheme XXX1
used. The source symbols passed to the Raptor FEC encoder SHALL and the FEC encoder defined in [RFC6330] SHALL be used for FEC Scheme
consist of the source symbols constructed according to Section 6.3.1. XXX2. For both FEC Scheme XXX1 and FEC Scheme XXX2, the source
Thus the value of the parameter K used by the FEC encoder (equal to symbols passed to the FEC encoder SHALL consist of the source symbols
the Source Block Length) may vary amongst the blocks of the stream constructed according to Section 6.3.1. Thus the value of the
but SHALL NOT exceed the Maximum Source Block Length signaled in the parameter K used by the FEC encoder (equal to the Source Block
FEC Scheme-specific information. The symbol size, T, to be used for Length) may vary amongst the blocks of the stream but SHALL NOT
source block construction and the repair symbol construction is equal exceed the Maximum Source Block Length signaled in the FEC Scheme-
to the Encoding Symbol Size signaled in the FEC Scheme Specific specific information. The symbol size, T, to be used for source
Information. block construction and the repair symbol construction is equal to the
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
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 optimisations to both sender and receiver
implementations. implementations.
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allows for efficient parallel encoding of multiple streams. Note allows for efficient parallel encoding of multiple streams. Note
that the padding operation is equivalent to the padding operation that the padding operation is equivalent to the padding operation
in [RFC6330] with K' the specified MSBL and K the actual source in [RFC6330] with K' the specified MSBL and K the actual source
block length K. block length 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 the Raptor FEC encoder as defined in [RFC5053] is used, this When used with the Raptor codes specified in [RFC5053], this scheme
scheme is equivalent to that specified in [dvbts] for arbitrary is equivalent to that specified in [dvbts] for arbitrary packet
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 XXX3 when [RFC5053] is used and XXX4 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 NOTE: To the RFC Editor: please change these XXX notations once
assigned, and remove this NOTE. assigned, and remove this NOTE.
7.2.1.2. FEC Scheme specific information 7.2.1.2. FEC Scheme specific information
See . (Section 6.2.1.2). The MSBL value is one of the values as The same as specified for FEC Scheme XXX1 for FEC Scheme XXX3, and
defined in section . (Section 7.4). the same as specified for FEC Scheme XXX2 for FEC Scheme XXX4, as
specified in Section 6.2.2, except that the MSBL value is as defined
in Section 7.4.
7.2.2. Source FEC Payload ID 7.2.2. Source FEC Payload ID
See Section 6.2.2. The same as specified for FEC Scheme XXX1 for FEC Scheme XXX3, and
the same as specified for FEC Scheme XXX2 for FEC Scheme XXX4, as
specified in Section 6.2.2.
7.2.3. Repair FEC Payload ID 7.2.3. Repair FEC Payload ID
See Section 6.2.3. The same as specified for FEC Scheme XXX1 for FEC Scheme XXX3, and
the same as specified for FEC Scheme XXX2 for FEC Scheme XXX4, 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] when Raptor as defined in[RFC5053] is used Section 5.3.2 of [RFC5053] for FEC Scheme XXX3 and as specified in
and as specified in Section 4.4.2 of [RFC6330] when RaptorQ as Section 4.4.2 of [RFC6330] for FEC Scheme XXX4, where K=SBL. The
defined in [RFC6330] is used, where K=SBL. The value of SBL SHALL be value of SBL SHALL be at most the value of MSBL.
at most the value of MSBL.
7.4. FEC Code Specification 7.4. FEC Code Specification
The Raptor FEC encoder defined in [RFC5053] or [RFC6330] SHALL be The FEC encoder defined in [RFC5053] SHALL be used for FEC Scheme
used. The source symbols passed to the Raptor FEC encoder SHALL XXX3 and the FEC encoder defined in [RFC6330] SHALL be used for FEC
Scheme XXX4. The source symbols passed to the FEC encoder SHALL
consist of the source symbols constructed according to Section 6.3.1 consist of the source symbols constructed according to Section 6.3.1
extended with zero or more padding symbols such that the total number extended with zero or more padding symbols such that the total number
of symbols in the source block is equal to the MSBL signaled in the of symbols in the source block is equal to the MSBL signaled in the
FEC Scheme Specific Information. Thus the value of the parameter K FEC Scheme Specific Information. Thus the value of the parameter K
used by the FEC encoded is equal to the MSBL for all blocks of the used by the FEC encoded is equal to the MSBL for all blocks of the
stream. Padding symbols shall consist entirely of octets set to the stream. Padding symbols shall consist entirely of octets set to the
value zero. The symbol size, T, to be used for source block value zero. The symbol size, T, to be used for source block
construction and the repair symbol construction is equal to the 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.
When [RFC5053] is used, the parameter T SHALL be set such that the For FEC Scheme XXX3, the parameter T SHALL be set such that the
number of source symbols in any source block is at most 8192. The number of source symbols in any source block is at most 8192. The
MSBL parameter - and hence the number of symbols used in the FEC MSBL parameter - and hence the number of symbols used in the FEC
Encoding and Decoding operations - SHALL be set to one of the Encoding 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
When [RFC6330] is used, the parameter T SHALL be set such that the For FEC Scheme XXX4, the parameter T SHALL be set such that the
number of source symbols in any source block is less than 56403. The number of source symbols in any source block is less than 56403. The
MSBL parameter SHALL be set to one of the supported values for K' MSBL parameter SHALL be set to one of the supported values for K'
defined in Section 5.6 of [RFC6330]. defined 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 XXX5 when [RFC5053] is used and XXX6 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 NOTE: To the RFC Editor: please change these XXX notations once
assigned, and remove this NOTE. assigned, and remove this NOTE.
8.1.1.2. Scheme-specific elements 8.1.1.2. Scheme-specific elements
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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 XXX5 when [RFC5053] is used and XXX6 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 NOTE: To the RFC Editor: please change these XXX notations once
assigned, and remove this NOTE. assigned, and remove this NOTE.
8.1.1.2. Scheme-specific elements 8.1.1.2. Scheme-specific elements
See Section 6.2.1.2 The same as specified for FEC Scheme XXX1 for FEC Scheme XXX5, and
the same as specified for FEC Scheme XXX2 for FEC Scheme XXX6, 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.
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of the source block in symbols. of the source block in symbols.
Encoding Symbol ID (ESI) - 24 bits This field indicates which repair Encoding Symbol ID (ESI) - 24 bits This field indicates which repair
symbols are contained within this repair packet. The ESI provided symbols are contained within this repair packet. The ESI provided
is the ESI of the first repair symbol in the packet. 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 FEC Scheme XXX5 and FEC Scheme XXX6 use the procedures defined in
a set of source symbols to which the FEC code can be applied. Section 5 to construct a set of source symbols to which the FEC code
can be 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
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In the specific case of RTP source packet flows, then the RTP In the specific case of RTP source packet flows, then the RTP
Sequence Number field SHALL be used as the sequence number in the Sequence Number field SHALL be used as the sequence number in the
procedures described above. The length indication included in the procedures described above. The length indication included in the
Application Data Unit Information SHALL be the RTP payload length Application Data Unit Information SHALL be the RTP payload length
plus the length of the CSRCs, if any, the RTP Header Extension, if plus the length of the CSRCs, if any, the RTP Header Extension, if
present, and the RTP padding octets, if any. Note that this length present, and the RTP padding octets, if any. Note that this length
is always equal to the UDP payload length of the packet minus 12. is always equal to the UDP payload length of the packet minus 12.
8.3. FEC Code Specification 8.3. FEC Code Specification
See Section 7.4 The same as specified for FEC Scheme XXX3 for FEC Scheme XXX5, and
the same as specified for FEC Scheme XXX4 for FEC Scheme XXX6, 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]. No security vulnerabilities specific to this refer to [RFC6363]. No security vulnerabilities specific to this
document have been identified. 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
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