draft-ietf-fecframe-raptor-07.txt   draft-ietf-fecframe-raptor-08.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, 2012 Nomor Research Expires: August 27, 2012 Nomor Research
M. Luby M. Luby
Qualcomm Incorporated Qualcomm Incorporated
November 24, 2011 February 24, 2012
Raptor FEC Schemes for FECFRAME Raptor FEC Schemes for FECFRAME
draft-ietf-fecframe-raptor-07 draft-ietf-fecframe-raptor-08
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
skipping to change at page 1, line 46 skipping to change at page 1, line 46
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
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Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 27, 2012. This Internet-Draft will expire on August 27, 2012.
Copyright Notice Copyright Notice
Copyright (c) 2011 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.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of (http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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4.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 7
5. General procedures for Raptor FEC Schemes . . . . . . . . . . 7 5. General procedures for Raptor FEC Schemes . . . . . . . . . . 7
6. Raptor FEC Schemes for arbitrary packet flows . . . . . . . . 9 6. Raptor FEC Schemes for arbitrary packet flows . . . . . . . . 9
6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 9 6.1. Introduction . . . . . . . . . . . . . . . . . . . . . . . 9
6.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 9 6.2. Formats and Codes . . . . . . . . . . . . . . . . . . . . 9
6.2.1. FEC Framework Configuration Information . . . . . . . 9 6.2.1. FEC Framework Configuration Information . . . . . . . 9
6.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 10 6.2.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 10
6.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 11 6.2.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 11
6.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 12 6.3. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 12
6.3.1. Source symbol construction . . . . . . . . . . . . . . 12 6.3.1. Source symbol construction . . . . . . . . . . . . . . 12
6.3.2. Repair packet construction . . . . . . . . . . . . . . 12 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 . . . . . . . . . . . . . . 14
7.4. FEC Code Specification . . . . . . . . . . . . . . . . . . 14 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 . . . . . . . . . . . . . . . . 15 8.1.2. Source FEC Payload ID . . . . . . . . . . . . . . . . 16
8.1.3. Repair FEC Payload ID . . . . . . . . . . . . . . . . 15 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 . . . . . . . . . . . . . . . . . . . . . 17
8.2.3. Repair packet construction . . . . . . . . . . . . . . 18 8.2.3. Repair packet construction . . . . . . . . . . . . . . 19
8.2.4. Procedures for RTP source flows . . . . . . . . . . . 18 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 . . . . . . . . . . . . . . 19 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 . . . . . . . . . . . . . . . . . . . . . . . 20 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 21
14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 21
14.1. Normative References . . . . . . . . . . . . . . . . . . . 20 14.1. Normative References . . . . . . . . . . . . . . . . . . . 21
14.2. Informative References . . . . . . . . . . . . . . . . . . 21 14.2. Informative References . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 22
1. Introduction 1. Introduction
The FEC Framework [RFC6363] describes a framework for the application The FEC Framework [RFC6363] describes a general framework for the use
of Forward Error Correction to arbitrary packet flows. Modeled after of Forward Error Correction in association with arbitrary packet
the FEC Building Block developed by the IETF Reliable Multicast flows. Modeled after the FEC Building Block developed by the IETF
Transport working group [RFC5052], the FEC Framework defines the Reliable Multicast Transport working group [RFC5052], the FEC
concept of FEC Schemes which provide specific Forward Error Framework defines the concept of FEC Schemes which provide specific
Correction schemes. This document describes six FEC Schemes which Forward Error Correction schemes. This document describes six FEC
make use of the Raptor and RaptorQ FEC codes as defined in [RFC5053] Schemes which make use of the Raptor and RaptorQ FEC codes as defined
and [RFC6330]. 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 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:
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.
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) and the source packets to the receiver(s). Per the FEC
Framework requirements, the sender MUST transmit the source and
repair packets in different source and repair flows, or in the
case RTP transport is used for repair packets, in different RTP
streams.
Per the FEC Framework requirements, the sender MUST transmit the o At the receiver side, if all of the source packets are
source and repair packets in different source and repair flows, or in successfully received, there is no need for FEC recovery and the
the case RTP transport is used for repair packets, in different RTP repair packets are discarded. However, if there are missing
streams. At the receiver side, if all of the source packets are source packets, the repair packets can be used to recover the
successfully received, there is no need for FEC recovery and the missing information.
repair packets are discarded. However, if there are missing source
packets, the repair packets can be used to recover the missing
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
refer to source packets and to identify which packets are missing. refer to source packets and to identify which packets are missing.
In this case we assume it is possible to derive a "sequence number" In this case we assume it is possible to derive a "sequence number"
directly or indirectly from the source packets and this sequence directly or indirectly from the source packets and this sequence
number can be used within the FEC Scheme. This case is referred to number can be used within the FEC Scheme. This case is referred to
as a "single sequenced flow". In this case the FEC Source Payload ID as a "single sequenced flow". In this case the FEC Source Payload ID
defined in [RFC6363] is empty and the source packets are not modified defined in [RFC6363] is empty and the source packets are not modified
by the application of FEC, with obvious backwards compatibility by the application of FEC, with obvious backwards compatibility
advantages. 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 case
if referred to as the "arbitrary packet flow" case. Accordingly, is referred to as the "arbitrary packet flow" case. Accordingly,
this document defines six FEC Schemes, two for the case of a single this document defines six FEC Schemes, two for the case of a single
sequenced flow and four for the case of arbitrary packet flows. sequenced flow and four for the case of arbitrary packet flows.
2. Document Outline 2. Document Outline
This document is organised as follows: This document is organised 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 6defines an FEC Scheme for the case of arbitrary source o Section 6defines an 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 [MBMSTS]. defined in "3GPP TS 26.346: Multimedia Broadcast/Multicast
Service (MBMS); Protocols and codecs" [MBMSTS].
o Section 7 defines an FEC Scheme similar to that defined in o Section 7 defines an FEC Scheme similar to that defined in
Section 6but with optimisations for the case where only limited Section 6but with optimisations for the case where only limited
source block sizes are required. When used with Raptor codes, source block sizes are required. When used with Raptor codes,
this scheme is equivalent to that defined in [dvbts] for arbitrary this scheme is equivalent to that defined in "ETSI TS 102.034:
packet flows. Digital Video Broadcasting (DVB); Transport of MPEG-2 Based DVB
Services over IP Based" Networks[dvbts] for arbitrary packet
flows.
o Section 8 defines an FEC Scheme for the case of a single flow o Section 8 defines an 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
This document uses the following definitions. For further This document uses definitions that apply to FEC Framework in general
definitions that apply to FEC Framework in general, see [RFC6363]. as defined in [RFC6363]. In addition, this document uses the
following definitions:
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 the following abbreviations. For further This document uses abbreviations that apply to FEC Framework in
abbreviations that apply to FEC Framework in general, see [RFC6363]. general as defined in [RFC6363]. In addition, this document uses the
following abbreviations
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.
ADUI: Application Data Unit Information. ADUI: Application Data Unit Information.
SPI: Source Packet Information.
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 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
[RFC6363] for each Application Data Unit (ADU) in a source block, the [RFC6363] for each Application Data Unit (ADU) in a source block, the
FEC Scheme is provided with: 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.
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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, 0
<= i < n. <= i < n.
o R[i] denote the number of octets in the (i+1)-th ADU. o f[i] denote the integer identifier associated with the source data
flow from which the i-th ADU was taken.
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 f[i] denote the integer identifier associated with the source data o R[i] denote the number of octets in the (i+1)-th ADU.
flow from which the i-th ADU was taken.
o F[i] denote a single octet representing the value of f[i].
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].
skipping to change at page 9, line 23 skipping to change at page 9, line 27
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
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 XXX when [RFC5053] is used and YYY when defined in this section is XXX(RFC5053-ARBITRARY) when [RFC5053] is
[RFC6330] is used, as assigned by IANA. used and XXX(RFC6330-ARBITRARY) when [RFC6330] is used, as assigned
by IANA.
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:
Maximum Source Block Length Name: "Kmax", Value range: A decimal MSBL Value range: A decimal non-negative integer less than 8192
non-negative integer less than 8192 (for Raptor) or 56403 (for (for Raptor) or 56403 (for RaptorQ), in units of symbols
RaptorQ), 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 Maximum Source Block Length and Encoding An encoding format for The MSBL and Encoding Symbol Size is defined
Symbol Size is defined below. below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Symbol Size (T) |Max. Source Block Length (Kmax)| | Symbol Size (T) | MSBL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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 Format A or to one to The P bit shall be set to zero to indicate Payload ID Format A or to
indicate Format B. The last octet of the above encoding may be one to indicate Payload ID Format B. The last octet of FEC Scheme
omitted, in which case Format A shall be assumed. Specific Information may be omitted indicating that Payload ID Format
A is in use. The Payload ID Format identifier defines which of the
The Payload ID Format identifier defines which of the Source FEC Source FEC Payload ID and Repair FEC Payload ID formats defined below
Payload ID and Repair FEC Payload ID formats defined below shall be shall be used. Payload ID Format B SHALL NOT be used when[RFC5053]
used. Payload ID Format B SHALL NOT be used when[RFC5053] is used. is used. The two formats enable different use cases. Format A is
appropriate in case the stream has many typically smaller source
blocks and Format B is applicable if the stream has fewer large
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
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.
skipping to change at page 12, line 17 skipping to change at page 12, line 17
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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) An integer identifier for the Source Block Number (SBN), (8 bits) An integer identifier for the
source block that the repair symbols within the packet relate to. source block that the repair symbols within the packet relate to.
For format A, it is of size 16 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. Specification in [RFC5053] and [RFC6330].
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 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
(Format A) or 255 (Format B). (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.
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 ESI value placed into a repair packet is calculated as specified When using Raptor [RFC5053], the ESI value placed into a repair
in Section 5.3.2 of [RFC5053] when Raptor as defined in [RFC5053] is packet is calculated as specified in Section 5.3.2 of [RFC5053].
used and as specified in Section 4.4.2 of [RFC6330] when RaptorQ as
defined in [RFC6330] is used, where K=SBL. When using Raptor! [RFC6330], the ESI value placed into a repair
packet is calculated as specified in Section 4.4.2 of [RFC6330].
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 Raptor FEC encoder defined in [RFC5053] or [RFC6330] SHALL be
used. The source symbols passed to the Raptor FEC encoder SHALL used. The source symbols passed to the Raptor 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.
Thus the value of the parameter K used by the FEC encoder (equal to Thus the value of the parameter K used by the FEC encoder (equal to
the Source Block Length) may vary amongst the blocks of the stream the Source Block Length) may vary amongst the blocks of the stream
but SHALL NOT exceed the Maximum Source Block Length signaled in the but SHALL NOT exceed the Maximum Source Block Length signaled in the
FEC Scheme-specific information. The symbol size, T, to be used for FEC Scheme-specific information. The symbol size, T, to be used for
skipping to change at page 13, line 37 skipping to change at page 13, line 46
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
Size field of the scheme-specific information. This allows for Length (MSBL) field of the scheme-specific information. This
efficient parallel encoding of multiple streams. Note that the allows for efficient parallel encoding of multiple streams. Note
padding operation is equivalent to the padding operation in that the padding operation is equivalent to the padding operation
[RFC6330] with K' the specified single source block size and K the in [RFC6330] with K' the specified MSBL and K the actual source
actual source block size K. block length K.
o The possible choices of the source block size for a stream is o The possible choices of the MSBL for a stream is restricted to a
restricted to a small specified set of sizes. This allows small specified set. This allows explicit operation sequences for
explicit operation sequences for encoding and decoding the encoding and decoding the restricted set of source block lengths
restricted set of source block sizes to be pre-calculated and to be pre-calculated and embedded in software or hardware.
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
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 XXX when [RFC5053] is used and YYY when defined in this section is XXX(RFC5053-OPTIMISED) when [RFC5053] is
[RFC6330] is used, as assigned by IANA. used and XXX(RFC6330-OPTIMISED) when [RFC6330] is used, as assigned
by IANA.
7.2.1.2. FEC Scheme specific information 7.2.1.2. FEC Scheme specific information
See . (Section 6.2.1.2) See . (Section 6.2.1.2). The MSBL value is one of the values as
defined in section . (Section 7.4).
7.2.2. Source FEC Payload ID 7.2.2. Source FEC Payload ID
See . (Section 6.2.2) See Section 6.2.2.
7.2.3. Repair FEC Payload ID 7.2.3. Repair FEC Payload ID
SeeSection 6.2.3 See 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] when Raptor as defined in[RFC5053] is used
and as specified in Section 4.4.2 of [RFC6330] when RaptorQ as and as specified in Section 4.4.2 of [RFC6330] when RaptorQ as
defined in [RFC6330] is used, where K=SBL. The value of SBL SHALL be defined in [RFC6330] is used, where K=SBL. The 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 Raptor FEC encoder defined in [RFC5053] or [RFC6330] SHALL be
used. The source symbols passed to the Raptor FEC encoder SHALL used. The source symbols passed to the Raptor 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 Maximum Source Block of symbols in the source block is equal to the MSBL signaled in the
Length signaled in the FEC Scheme Specific Information. Thus the FEC Scheme Specific Information. Thus the value of the parameter K
value of the parameter K used by the FEC encoded is equal to the used by the FEC encoded is equal to the MSBL for all blocks of the
Maximum Source Block Length for all blocks of the stream. Padding stream. Padding symbols shall consist entirely of octets set to the
symbols shall consist entirely of octets set to the value zero. The value zero. The symbol size, T, to be used for source block
symbol size, T, to be used for source block construction and the 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.
When [RFC5053] is used, the parameter T SHALL be set such that the When [RFC5053] is used, 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
Maximum Source Block Length parameter - and hence the number of MSBL parameter - and hence the number of symbols used in the FEC
symbols used in the FEC Encoding and Decoding operations - SHALL be Encoding and Decoding operations - SHALL be set to one of the
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 When [RFC6330] is used, 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
Maximum Source Block Length parameter SHALL be set to one of the MSBL parameter SHALL be set to one of the supported values for K'
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 XXX when [RFC5053] is used and YYY when defined in this section is XXX(RFC5053-SINGLE) when [RFC5053] is used
[RFC6330] is used, as assigned by IANA. and XXX(RFC6330-SINGLE) when [RFC6330] is used, as assigned by IANA.
8.1.1.2. Scheme-specific elements 8.1.1.2. Scheme-specific elements
See Section 6.2.1.2 See 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 | Encoding Symbol ID | | Initial Sequence Number | Source Block Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Block Length | | 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. respectively.
Source Block Length (SBL) - 16 bits This field specifies the length
of the source block in symbols.
Encoding Symbol ID (ESI) - 16 bits This field indicates which repair Encoding Symbol ID (ESI) - 16 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.
Source Block Length (SBL) - 16 bits This field specifies the length
of the source block in symbols.
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
skipping to change at page 17, line 10 skipping to change at page 17, line 24
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 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.
sender MUST allocate Source Block Numbers to source blocks
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
Format B is used for FEC Payload IDs.
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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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. The Source Block Length
LB MUST be chosen such that it is at least as large as the largest
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
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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 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 [RFC6363]. No security considerations 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
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.
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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 three values in the FEC Framework (FECFRAME) This document registers six values in the FEC Framework (FECFRAME)
FEC Encoding IDs registry as follows: FEC Encoding IDs registry as follows:
o 1 for the Raptor FEC Scheme for Arbitrary Packet Flows (Section 6 o 1 for the Raptor FEC Scheme for Arbitrary Packet Flows (Section 6
using Raptor [RFC5053]. using Raptor [RFC5053].
o 2 for the Raptor FEC Scheme for Arbitrary Packet Flows (Section 6 o 2 for the RaptorQ FEC Scheme for Arbitrary Packet Flows (Section 6
using RaptorQ [RFC6330]. using RaptorQ [RFC6330].
o 3 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 4 for the Optimised Raptor FEC Scheme for Arbitrary Packet Flows o 4 for the Optimised RaptorQ FEC Scheme for Arbitrary Packet Flows
(Section 7) using RaptorQ [RFC6330]. (Section 7) using RaptorQ [RFC6330].
o 5 for the Raptor FEC Scheme for a single sequence flow (Section 8) o 5 for the Raptor FEC Scheme for a single sequence flow (Section 8)
using Raptor [RFC5053]. using Raptor [RFC5053].
o 6 for the Raptor FEC Scheme for a single sequence flow (Section 8) o 6 for the RaptorQ FEC Scheme for a single sequence flow
using RaptorQ [RFC6330]. (Section 8) using RaptorQ [RFC6330].
13. Acknowledgements 13. Acknowledgements
Thanks are due to Ali C. Begen for thorough review of earlier draft Thanks are due to Ali C. Begen and David Harrington for thorough
versions of this document. review of earlier draft versions of this document.
14. References 14. References
14.1. Normative References 14.1. Normative References
[RFC6363] Watson, M., Begen, A., and V. Roca, "Forward Error [RFC6363] Watson, M., Begen, A., and V. Roca, "Forward Error
Correction (FEC) Framework", RFC 6363, October 2011. Correction (FEC) Framework", RFC 6363, October 2011.
[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
 End of changes. 57 change blocks. 
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