draft-ietf-fecframe-interleaved-fec-scheme-09.txt   rfc6015.txt 
FEC Framework A. Begen Internet Engineering Task Force (IETF) A. Begen
Internet-Draft Cisco Request for Comments: 6015 Cisco
Intended status: Standards Track January 12, 2010 Category: Standards Track October 2010
Expires: July 16, 2010 ISSN: 2070-1721
RTP Payload Format for 1-D Interleaved Parity FEC RTP Payload Format for 1-D Interleaved Parity
draft-ietf-fecframe-interleaved-fec-scheme-09 Forward Error Correction (FEC)
Abstract Abstract
This document defines a new RTP payload format for the Forward Error This document defines a new RTP payload format for the Forward Error
Correction (FEC) that is generated by the 1-D interleaved parity code Correction (FEC) that is generated by the 1-D interleaved parity code
from a source media encapsulated in RTP. The 1-D interleaved parity from a source media encapsulated in RTP. The 1-D interleaved parity
code is a systematic code, where a number of repair symbols are code is a systematic code, where a number of repair symbols are
generated from a set of source symbols and sent in a repair flow generated from a set of source symbols and sent in a repair flow
separate from the source flow that carries the source symbols. The separate from the source flow that carries the source symbols. The
1-D interleaved parity code offers a good protection against bursty 1-D interleaved parity code offers a good protection against bursty
packet losses at a cost of reasonable complexity. The new payload packet losses at a cost of reasonable complexity. The new payload
format defined in this document should only be used (with some format defined in this document should only be used (with some
exceptions) as a part of the DVB-IPTV Application-layer FEC exceptions) as a part of the Digital Video Broadcasting-IPTV (DVB-
specification. IPTV) Application-layer FEC specification.
Status of this Memo
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Internet-Drafts are draft documents valid for a maximum of six months Status of This Memo
and may be updated, replaced, or obsoleted by other documents at any
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http://www.ietf.org/shadow.html. (IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
This Internet-Draft will expire on July 16, 2010. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
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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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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
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described in the BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction ....................................................4
1.1. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . 6 1.1. Use Cases ..................................................6
1.2. Overhead Computation . . . . . . . . . . . . . . . . . . 8 1.2. Overhead Computation .......................................8
1.3. Relation to Existing Specifications . . . . . . . . . . . 8 1.3. Relation to Existing Specifications ........................8
1.3.1. RFC 2733 and RFC 3009 . . . . . . . . . . . . . . . . 8 1.3.1. RFCs 2733 and 3009 ..................................8
1.3.2. SMPTE 2022-1 . . . . . . . . . . . . . . . . . . . . . 8 1.3.2. SMPTE 2022-1 ........................................8
1.3.3. ETSI TS 102 034 . . . . . . . . . . . . . . . . . . . 9 1.3.3. ETSI TS 102 034 .....................................9
1.4. Scope of the Payload Format . . . . . . . . . . . . . . . 10 1.4. Scope of the Payload Format ...............................10
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 10 2. Requirements Notation ..........................................10
3. Definitions, Notations and Abbreviations . . . . . . . . . . . 10 3. Definitions, Notations, and Abbreviations ......................10
3.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . 10 3.1. Definitions ...............................................10
3.2. Notations . . . . . . . . . . . . . . . . . . . . . . . . 11 3.2. Notations .................................................11
4. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . . 11 4. Packet Formats .................................................11
4.1. Source Packets . . . . . . . . . . . . . . . . . . . . . 11 4.1. Source Packets ............................................11
4.2. Repair Packets . . . . . . . . . . . . . . . . . . . . . 11 4.2. Repair Packets ............................................11
5. Payload Format Parameters . . . . . . . . . . . . . . . . . . 15 5. Payload Format Parameters ......................................15
5.1. Media Type Registration . . . . . . . . . . . . . . . . . 15 5.1. Media Type Registration ...................................15
5.1.1. Registration of audio/1d-interleaved-parityfec . . . . 15 5.1.1. Registration of audio/1d-interleaved-parityfec .....15
5.1.2. Registration of video/1d-interleaved-parityfec . . . . 16 5.1.2. Registration of video/1d-interleaved-parityfec .....16
5.1.3. Registration of text/1d-interleaved-parityfec . . . . 18 5.1.3. Registration of text/1d-interleaved-parityfec ......18
5.1.4. Registration of 5.1.4. Registration of
application/1d-interleaved-parityfec . . . . . . . . . 19 application/1d-interleaved-parityfec ...............19
5.2. Mapping to SDP Parameters . . . . . . . . . . . . . . . . 20 5.2. Mapping to SDP Parameters .................................20
5.2.1. Offer-Answer Model Considerations . . . . . . . . . . 21 5.2.1. Offer-Answer Model Considerations ..................21
5.2.2. Declarative Considerations . . . . . . . . . . . . . . 21 5.2.2. Declarative Considerations .........................22
6. Protection and Recovery Procedures . . . . . . . . . . . . . . 22 6. Protection and Recovery Procedures .............................22
6.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 22 6.1. Overview ..................................................22
6.2. Repair Packet Construction . . . . . . . . . . . . . . . 22 6.2. Repair Packet Construction ................................22
6.3. Source Packet Reconstruction . . . . . . . . . . . . . . 24 6.3. Source Packet Reconstruction ..............................24
6.3.1. Associating the Source and Repair Packets . . . . . . 24 6.3.1. Associating the Source and Repair Packets ..........25
6.3.2. Recovering the RTP Header and Payload . . . . . . . . 25 6.3.2. Recovering the RTP Header and Payload ..............25
7. Session Description Protocol (SDP) Signaling . . . . . . . . . 27 7. Session Description Protocol (SDP) Signaling ...................27
8. Congestion Control Considerations . . . . . . . . . . . . . . 27 8. Congestion Control Considerations ..............................27
9. Security Considerations . . . . . . . . . . . . . . . . . . . 28 9. Security Considerations ........................................28
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 29 10. IANA Considerations ...........................................29
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 29 11. Acknowledgments ...............................................29
12. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 29 12. References ....................................................29
12.1. draft-ietf-fecframe-interleaved-fec-scheme-09 . . . . . . 29 12.1. Normative References .....................................29
12.2. draft-ietf-fecframe-interleaved-fec-scheme-08 . . . . . . 29 12.2. Informative References ...................................30
12.3. draft-ietf-fecframe-interleaved-fec-scheme-07 . . . . . . 29
12.4. draft-ietf-fecframe-interleaved-fec-scheme-06 . . . . . . 29
12.5. draft-ietf-fecframe-interleaved-fec-scheme-05 . . . . . . 30
12.6. draft-ietf-fecframe-interleaved-fec-scheme-04 . . . . . . 30
12.7. draft-ietf-fecframe-interleaved-fec-scheme-03 . . . . . . 30
12.8. draft-ietf-fecframe-interleaved-fec-scheme-02 . . . . . . 30
12.9. draft-ietf-fecframe-interleaved-fec-scheme-01 . . . . . . 30
12.10. draft-ietf-fecframe-interleaved-fec-scheme-00 . . . . . . 30
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 31
13.1. Normative References . . . . . . . . . . . . . . . . . . 31
13.2. Informative References . . . . . . . . . . . . . . . . . 31
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 32
1. Introduction 1. Introduction
This document extends the Forward Error Correction (FEC) header This document extends the Forward Error Correction (FEC) header
defined in [RFC2733] and uses this new FEC header for the FEC that is defined in [RFC2733] and uses this new FEC header for the FEC that is
generated by the 1-D interleaved parity code from a source media generated by the 1-D interleaved parity code from a source media
encapsulated in RTP [RFC3550]. The resulting new RTP payload format encapsulated in RTP [RFC3550]. The resulting new RTP payload format
is registered by this document. is registered by this document.
The type of the source media protected by the 1-D interleaved parity The type of the source media protected by the 1-D interleaved parity
code can be audio, video, text or application. The FEC data are code can be audio, video, text, or application. The FEC data are
generated according to the media type parameters that are generated according to the media type parameters that are
communicated through out-of-band means. The associations/ communicated through out-of-band means. The associations/
relationships between the source and repair flows are also relationships between the source and repair flows are also
communicated through out-of-band means. communicated through out-of-band means.
The 1-D interleaved parity FEC uses the exclusive OR (XOR) operation The 1-D interleaved parity FEC uses the exclusive OR (XOR) operation
to generate the repair symbols. In a nutshell, the following steps to generate the repair symbols. In a nutshell, the following steps
take place: take place:
1. The sender determines a set of source packets to be protected 1. The sender determines a set of source packets to be protected
together based on the media type parameters. together based on the media type parameters.
2. The sender applies the XOR operation on the source symbols to 2. The sender applies the XOR operation on the source symbols to
generate the required number of repair symbols. generate the required number of repair symbols.
3. The sender packetizes the repair symbols and sends the repair 3. The sender packetizes the repair symbols and sends the repair
packet(s) along with the source packets to the receiver(s) (in packet(s) along with the source packets to the receiver(s) (in
different flows). The repair packets MAY be sent proactively or different flows). The repair packets may be sent proactively or
on-demand. on demand.
Note that the source and repair packets belong to different source Note that the source and repair packets belong to different source
and repair flows, and the sender needs to provide a way for the and repair flows, and the sender needs to provide a way for the
receivers to demultiplex them, even in the case they are sent in the receivers to demultiplex them, even in the case in which they are
same transport flow (i.e., same source/destination address/port with sent in the same transport flow (i.e., same source/destination
UDP). This is required to offer backward compatibility (See address/port with UDP). This is required to offer backward
Section 4). At the receiver side, if all of the source packets are compatibility (see Section 4). At the receiver side, if all of the
successfully received, there is no need for FEC recovery and the source packets are successfully received, there is no need for FEC
repair packets are discarded. However, if there are missing source recovery and the repair packets are discarded. However, if there are
packets, the repair packets can be used to recover the missing missing source packets, the repair packets can be used to recover the
information. Block diagrams for the systematic parity FEC encoder missing information. Block diagrams for the systematic parity FEC
and decoder are sketched in Figure 1 and Figure 2, respectively. encoder and decoder are sketched in Figures 1 and 2, respectively.
+------------+ +------------+
+--+ +--+ +--+ +--+ --> | Systematic | --> +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ --> | Systematic | --> +--+ +--+ +--+ +--+
+--+ +--+ +--+ +--+ | Parity FEC | +--+ +--+ +--+ +--+ +--+ +--+ +--+ +--+ | Parity FEC | +--+ +--+ +--+ +--+
| Encoder | | Encoder |
| (Sender) | --> +==+ +==+ | (Sender) | --> +==+ +==+
+------------+ +==+ +==+ +------------+ +==+ +==+
Source Packet: +--+ Repair Packet: +==+ Source Packet: +--+ Repair Packet: +==+
+--+ +==+ +--+ +==+
skipping to change at page 5, line 30 skipping to change at page 5, line 30
| Decoder | | Decoder |
+==+ +==+ --> | (Receiver) | +==+ +==+ --> | (Receiver) |
+==+ +==+ +------------+ +==+ +==+ +------------+
Source Packet: +--+ Repair Packet: +==+ Lost Packet: X Source Packet: +--+ Repair Packet: +==+ Lost Packet: X
+--+ +==+ +--+ +==+
Figure 2: Block diagram for systematic parity FEC decoder Figure 2: Block diagram for systematic parity FEC decoder
Suppose that we have a group of D x L source packets that have Suppose that we have a group of D x L source packets that have
sequence numbers starting from 1 running to D x L. If we apply the sequence numbers starting from 1 running to D x L. If we apply the
XOR operation to the group of the source packets whose sequence XOR operation to the group of the source packets whose sequence
numbers are L apart from each other as sketched in Figure 3, we numbers are L apart from each other as sketched in Figure 3, we
generate L repair packets. This process is referred to as 1-D generate L repair packets. This process is referred to as 1-D
interleaved FEC protection, and the resulting L repair packets are interleaved FEC protection, and the resulting L repair packets are
referred to as interleaved (or column) FEC packets. referred to as interleaved (or column) FEC packets.
+-------------+ +-------------+ +-------------+ +-------+ +-------------+ +-------------+ +-------------+ +-------+
| S_1 | | S_2 | | S3 | ... | S_L | | S_1 | | S_2 | | S3 | ... | S_L |
| S_L+1 | | S_L+2 | | S_L+3 | ... | S_2xL | | S_L+1 | | S_L+2 | | S_L+3 | ... | S_2xL |
| . | | . | | | | | | . | | . | | | | |
skipping to change at page 6, line 34 skipping to change at page 6, line 34
In Figure 3, S_n and C_m denote the source packet with a sequence In Figure 3, S_n and C_m denote the source packet with a sequence
number n and the interleaved (column) FEC packet with a sequence number n and the interleaved (column) FEC packet with a sequence
number m, respectively. number m, respectively.
1.1. Use Cases 1.1. Use Cases
We generate one interleaved FEC packet out of D non-consecutive We generate one interleaved FEC packet out of D non-consecutive
source packets. This repair packet can provide a full recovery of source packets. This repair packet can provide a full recovery of
the missing information if there is only one packet missing among the the missing information if there is only one packet missing among the
corresponding source packets. This implies that 1-D interleaved FEC corresponding source packets. This implies that 1-D interleaved FEC
protection performs well under bursty loss conditions provided that L protection performs well under bursty loss conditions provided that a
is chosen large enough, i.e., L-packet duration should not be shorter large enough value is chosen for L, i.e., L packet duration should
than the duration of the burst that is intended to be repaired. not be shorter than the duration of the burst that is intended to be
repaired.
For example, consider the scenario depicted in Figure 4 where the For example, consider the scenario depicted in Figure 4 in which the
sender generates interleaved FEC packets and a bursty loss hits the sender generates interleaved FEC packets and a bursty loss hits the
source packets. Since the number of columns is larger than the source packets. Since the number of columns is larger than the
number of packets lost due to the bursty loss, the repair operation number of packets lost due to the bursty loss, the repair operation
succeeds. succeeds.
+---+ +---+
| 1 | X X X | 1 | X X X
+---+ +---+
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
skipping to change at page 7, line 24 skipping to change at page 7, line 24
| 9 | | 10| | 11| | 12| | 9 | | 10| | 11| | 12|
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
+===+ +===+ +===+ +===+ +===+ +===+ +===+ +===+
|C_1| |C_2| |C_3| |C_4| |C_1| |C_2| |C_3| |C_4|
+===+ +===+ +===+ +===+ +===+ +===+ +===+ +===+
Figure 4: Example scenario where 1-D interleaved FEC protection Figure 4: Example scenario where 1-D interleaved FEC protection
succeeds error recovery succeeds error recovery
The sender may generate interleaved FEC packets to combat with the The sender may generate interleaved FEC packets to combat the bursty
bursty packet losses. However, two or more random packet losses may packet losses. However, two or more random packet losses may hit the
hit the source and repair packets in the same column. In that case, source and repair packets in the same column. In that case, the
the repair operation fails. This is illustrated in Figure 5. Note repair operation fails. This is illustrated in Figure 5. Note that
that it is possible that two or more bursty losses may occur in the it is possible that two or more bursty losses may occur in the same
same source block, in which case interleaved FEC packets may still source block, in which case interleaved FEC packets may still fail to
fail to recover the lost data. recover the lost data.
+---+ +---+ +---+ +---+ +---+ +---+
| 1 | X | 3 | | 4 | | 1 | X | 3 | | 4 |
+---+ +---+ +---+ +---+ +---+ +---+
+---+ +---+ +---+ +---+ +---+ +---+
| 5 | X | 7 | | 8 | | 5 | X | 7 | | 8 |
+---+ +---+ +---+ +---+ +---+ +---+
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
skipping to change at page 8, line 7 skipping to change at page 8, line 7
+===+ +===+ +===+ +===+ +===+ +===+ +===+ +===+
|C_1| |C_2| |C_3| |C_4| |C_1| |C_2| |C_3| |C_4|
+===+ +===+ +===+ +===+ +===+ +===+ +===+ +===+
Figure 5: Example scenario where 1-D interleaved FEC protection fails Figure 5: Example scenario where 1-D interleaved FEC protection fails
error recovery error recovery
1.2. Overhead Computation 1.2. Overhead Computation
The overhead is defined as the ratio of the number of bytes belonging The overhead is defined as the ratio of the number of bytes that
to the repair packets to the number of bytes belonging to the belong to the repair packets to the number of bytes that belong to
protected source packets. the protected source packets.
Assuming that each repair packet carries an equal number of bytes Assuming that each repair packet carries an equal number of bytes
carried by a source packet, we can compute the overhead as follows: carried by a source packet and ignoring the size of the FEC header,
we can compute the overhead as follows:
Overhead = 1/D Overhead = 1/D
where D is the number of rows in the source block. where D is the number of rows in the source block.
1.3. Relation to Existing Specifications 1.3. Relation to Existing Specifications
This section discusses the relation of the current specification to This section discusses the relation of the current specification to
other existing specifications. other existing specifications.
1.3.1. RFC 2733 and RFC 3009 1.3.1. RFCs 2733 and 3009
The current specification extends the FEC header defined in [RFC2733] The current specification extends the FEC header defined in [RFC2733]
and registers a new RTP payload format. This new payload format is and registers a new RTP payload format. This new payload format is
not backward compatible with the payload format that was registered not backward compatible with the payload format that was registered
by [RFC3009]. by [RFC3009].
1.3.2. SMPTE 2022-1 1.3.2. SMPTE 2022-1
In 2007, the Society of Motion Picture and Television Engineers In 2007, the Society of Motion Picture and Television Engineers
(SMPTE) - Technology Committee N26 on File Management and Networking (SMPTE) - Technology Committee N26 on File Management and Networking
Technology - decided to revise the Pro-MPEG Code of Practice (CoP) #3 Technology - decided to revise the Pro-MPEG Code of Practice (CoP) #3
Release 2 specification, which (was initially produced by the Pro- Release 2 specification (initially produced by the Pro-MPEG Forum in
MPEG Forum in 2004) discussed the several aspects of the transmission 2004), which discussed several aspects of the transmission of MPEG-2
of MPEG-2 transport streams over IP networks. The new SMPTE transport streams over IP networks. The new SMPTE specification is
specification is referred to as [SMPTE2022-1]. referred to as [SMPTE2022-1].
The Pro-MPEG CoP #3 r2 document was originally based on [RFC2733]. The Pro-MPEG CoP #3 Release 2 document was originally based on
SMPTE revised the document by extending the FEC header (by setting [RFC2733]. SMPTE revised the document by extending the FEC header
the E bit) proposed in [RFC2733]. This extended header offers some proposed in [RFC2733] (by setting the E bit). This extended header
improvements. offers some improvements.
For example, instead of utilizing the bitmap field used in [RFC2733], For example, instead of utilizing the bitmap field used in [RFC2733],
[SMPTE2022-1] introduces separate fields to convey the number of rows [SMPTE2022-1] introduces separate fields to convey the number of rows
(D) and columns (L) of the source block as well as the type of the (D) and columns (L) of the source block as well as the type of the
repair packet (i.e., whether the repair packet is an interleaved FEC repair packet (i.e., whether the repair packet is an interleaved FEC
packet computed over a column or a non-interleaved FEC packet packet computed over a column or a non-interleaved FEC packet
computed over a row). These fields plus the base sequence number computed over a row). These fields, plus the base sequence number,
allow the receiver side to establish the associations between the allow the receiver side to establish associations between the source
source and repair packets. Note that although the bitmap field is and repair packets. Note that although the bitmap field is not
not utilized, the FEC header of [SMPTE2022-1] inherently carries over utilized, the FEC header of [SMPTE2022-1] inherently carries over the
the bitmap field from [RFC2733]. bitmap field from [RFC2733].
On the other hand, some parts of [SMPTE2022-1] are not in compliant On the other hand, some parts of [SMPTE2022-1] are not in compliance
with RTP [RFC3550]. For example, [SMPTE2022-1] sets the SSRC field with RTP [RFC3550]. For example, [SMPTE2022-1] sets the
to zero and does not use the timestamp field in the RTP headers of Synchronization Source (SSRC) field to zero and does not use the
the repair packets (Receivers ignore the timestamps of the repair timestamp field in the RTP headers of the repair packets (receivers
packets). Furthermore, [SMPTE2022-1] also sets the CC field in the ignore the timestamps of the repair packets). Furthermore,
RTP header to zero and does not allow any Contributing Source (CSRC) [SMPTE2022-1] also sets the CSRC Count (CC) field in the RTP header
entry in the RTP header. to zero and does not allow any Contributing Source (CSRC) entry in
the RTP header.
The current document adopts the extended FEC header of [SMPTE2022-1] The current document adopts the extended FEC header of [SMPTE2022-1]
and registers a new RTP payload format. At the same time, this and registers a new RTP payload format. At the same time, this
document fixes the parts of [SMPTE2022-1] that are not compliant with document fixes the parts of [SMPTE2022-1] that are not compliant with
RTP [RFC3550], except the one discussed below. RTP [RFC3550], except the one discussed below.
The baseline header format first proposed in [RFC2733] does not have The baseline header format first proposed in [RFC2733] does not have
fields to protect the P and X bits and the CC fields of the source fields to protect the P and X bits and the CC fields of the source
packets associated with a repair packet. Rather, the P bit, X bit packets associated with a repair packet. Rather, the P bit, X bit,
and CC field in the RTP header of the repair packet are used to and CC field in the RTP header of the repair packet are used to
protect those bits and fields. This, however, may sometimes result protect those bits and fields. This, however, may sometimes result
in failures when doing the RTP header validity checks as specified in in failures when doing the RTP header validity checks as specified in
[RFC3550]. While this behavior has been fixed in [RFC5109] that [RFC3550]. While this behavior has been fixed in [RFC5109], which
obsoleted [RFC2733], the RTP payload format defined in this document obsoleted [RFC2733], the RTP payload format defined in this document
still allows for this behavior for legacy purposes. Implementations still allows this behavior for legacy purposes. Implementations
following this specification must be aware of this potential issue following this specification must be aware of this potential issue
when RTP header validity checks are applied. when RTP header validity checks are applied.
1.3.3. ETSI TS 102 034 1.3.3. ETSI TS 102 034
In 2009, the Digital Video Broadcasting (DVB) consortium published a In 2009, the Digital Video Broadcasting (DVB) consortium published a
technical specification [ETSI-TS-102-034] through European technical specification [ETSI-TS-102-034] through the European
Telecommunications Standards Institute (ETSI). This specification Telecommunications Standards Institute (ETSI). This specification
covers several areas related to the transmission of MPEG-2 transport covers several areas related to the transmission of MPEG-2 transport
stream-based services over IP networks. stream-based services over IP networks.
The Annex E of [ETSI-TS-102-034] defines an optional protocol for Annex E of [ETSI-TS-102-034] defines an optional protocol for
Application-layer FEC (AL-FEC) protection of streaming media for Application-layer FEC (AL-FEC) protection of streaming media for
DVB-IP services carried over RTP [RFC3550] transport. The DVB-IPTV DVB-IP services carried over RTP [RFC3550] transport. The DVB-IPTV
AL-FEC protocol uses two layers for protection: a base layer that is AL-FEC protocol uses two layers for protection: a base layer that is
produced by a packet-based interleaved parity code, and an produced by a packet-based interleaved parity code, and an
enhancement layer that is produced by a Raptor code enhancement layer that is produced by a Raptor code [DVB-AL-FEC].
[I-D.ietf-fecframe-dvb-al-fec]. While the use of the enhancement While the use of the enhancement layer is optional, the use of the
layer is optional, the use of the base layer is mandatory wherever base layer is mandatory wherever AL-FEC is used. The DVB-IPTV AL-FEC
AL-FEC is used. The DVB-IPTV AL-FEC protocol is also described in protocol is also described in [DVB-AL-FEC].
[I-D.ietf-fecframe-dvb-al-fec].
The interleaved parity code that is used in the base layer is a The interleaved parity code that is used in the base layer is a
subset of [SMPTE2022-1]. In particular, AL-FEC base layer uses only subset of [SMPTE2022-1]. In particular, the AL-FEC base layer uses
the 1-D interleaved FEC protection from [SMPTE2022-1]. The new RTP only the 1-D interleaved FEC protection from [SMPTE2022-1]. The new
payload format that is defined and registered in this document (with RTP payload format that is defined and registered in this document
some exceptions listed in [I-D.ietf-fecframe-dvb-al-fec]) is used as (with some exceptions listed in [DVB-AL-FEC]) is used as the AL-FEC
the AL-FEC base layer. base layer.
1.4. Scope of the Payload Format 1.4. Scope of the Payload Format
The payload format specified in this document must only be used in The payload format specified in this document must only be used in
legacy applications where the limitations explained in Section 1.3.2 legacy applications where the limitations explained in Section 1.3.2
are known not to impact any system components or other RTP elements. are known not to impact any system components or other RTP elements.
Whenever possible a payload format that is fully compliant with Whenever possible, a payload format that is fully compliant with
[RFC3550], such as [RFC5109] or other newer payload formats, must be [RFC3550], such as [RFC5109] or other newer payload formats, must be
used. used.
2. Requirements Notation 2. 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].
3. Definitions, Notations and Abbreviations 3. Definitions, Notations, and Abbreviations
The definitions and notations commonly used in this document are The definitions and notations commonly used in this document are
summarized in this section. summarized in this section.
3.1. Definitions 3.1. Definitions
This document uses the following definitions: This document uses the following definitions:
Source Flow: The packet flow(s) carrying the source data and to Source Flow: The packet flow(s) carrying the source data to which FEC
which FEC protection is to be applied. protection is to be applied.
Repair Flow: The packet flow(s) carrying the repair data. Repair Flow: The packet flow(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 Source Symbol: The smallest unit of data used during the encoding
process. process.
Repair Symbol: Repair symbols are generated from the source symbols. Repair Symbol: Repair symbols are generated from the source symbols.
Source Packet: Data packets that contain only source symbols. Source Packet: Data packets that contain only source symbols.
Repair Packet: Data packets that contain only repair symbols. Repair Packet: Data packets that contain only repair symbols.
Source Block: A block of source symbols that are considered together Source Block: A block of source symbols that are considered together
in the encoding process. in the encoding process.
3.2. Notations 3.2. Notations
o L: Number of columns of the source block. o L: Number of columns of the source block.
o D: Number of rows of the source block. o D: Number of rows of the source block.
4. Packet Formats 4. Packet Formats
This section defines the formats of the source and repair packets. This section defines the formats of the source and repair packets.
4.1. Source Packets 4.1. Source Packets
The source packets need to contain information that identifies the The source packets need to contain information that identifies the
source block and the position within the source block occupied by the source block and the position within the source block occupied by the
packet. Since the source packets that are carried within an RTP packet. Since the source packets that are carried within an RTP
stream already contain unique sequence numbers in their RTP headers stream already contain unique sequence numbers in their RTP headers
[RFC3550], we can identify the source packets in a straightforward [RFC3550], we can identify the source packets in a straightforward
manner and there is no need to append additional field(s). The manner, and there is no need to append additional field(s). The
primary advantage of not modifying the source packets in any way is primary advantage of not modifying the source packets in any way is
that it provides backward compatibility for the receivers that do not that it provides backward compatibility for the receivers that do not
support FEC at all. In multicast scenarios, this backward support FEC at all. In multicast scenarios, this backward
compatibility becomes quite useful as it allows the non-FEC-capable compatibility becomes quite useful as it allows the non-FEC-capable
and FEC-capable receivers to receive and interpret the same source and FEC-capable receivers to receive and interpret the same source
packets sent in the same multicast session. packets sent in the same multicast session.
4.2. Repair Packets 4.2. Repair Packets
The repair packets MUST contain information that identifies the The repair packets MUST contain information that identifies the
source block they pertain to and the relationship between the source block to which they pertain and the relationship between the
contained repair symbols and the original source block. For this contained repair symbols and the original source block. For this
purpose, we use the RTP header of the repair packets as well as purpose, we use the RTP header of the repair packets as well as
another header within the RTP payload, which we refer to as the FEC another header within the RTP payload, which we refer to as the FEC
header, as shown in Figure 6. header, as shown in Figure 6.
+------------------------------+ +------------------------------+
| IP Header | | IP Header |
+------------------------------+ +------------------------------+
| Transport Header | | Transport Header |
+------------------------------+ +------------------------------+
skipping to change at page 12, line 22 skipping to change at page 12, line 22
| FEC Header | \ | FEC Header | \
+------------------------------+ > RTP Payload +------------------------------+ > RTP Payload
| Repair Symbols | / | Repair Symbols | /
+------------------------------+ __| +------------------------------+ __|
Figure 6: Format of repair packets Figure 6: Format of repair packets
The RTP header is formatted according to [RFC3550] with some further The RTP header is formatted according to [RFC3550] with some further
clarifications listed below: clarifications listed below:
o Version: The version field is set to 2. o Version: The version field is set to 2.
o Padding (P) Bit: This bit is equal to the XOR sum of the o Padding (P) Bit: This bit is equal to the XOR sum of the
corresponding P bits from the RTP headers of the source packets corresponding P bits from the RTP headers of the source packets
protected by this repair packet. However, padding octets are protected by this repair packet. However, padding octets are
never present in a repair packet, independent of the value of the never present in a repair packet, independent of the value of the
P bit. P bit.
o Extension (X) Bit: This bit is equal to the XOR sum of the o Extension (X) Bit: This bit is equal to the XOR sum of the
corresponding X bits from the RTP headers of the source packets corresponding X bits from the RTP headers of the source packets
protected by this repair packet. However, an RTP header extension protected by this repair packet. However, an RTP header extension
is never present in a repair packet, independent of the value of is never present in a repair packet, independent of the value of
the X bit. the X bit.
o CSRC Count (CC): This field is equal to the XOR sum of the o CSRC Count (CC): This field is equal to the XOR sum of the
corresponding CC values from the RTP headers of the source packets corresponding CC values from the RTP headers of the source packets
protected by this repair packet. However, a CSRC list is never protected by this repair packet. However, a CSRC list is never
present in a repair packet, independent of the value of the CC present in a repair packet, independent of the value of the CC
field. field.
o Marker (M) Bit: This bit is equal to the XOR sum of the o Marker (M) Bit: This bit is equal to the XOR sum of the
corresponding M bits from the RTP headers of the source packets corresponding M bits from the RTP headers of the source packets
protected by this repair packet. protected by this repair packet.
o Payload Type: The (dynamic) payload type for the repair packets o Payload Type: The (dynamic) payload type for the repair packets is
is determined through out-of-band means. Note that this document determined through out-of-band means. Note that this document
registers a new payload format for the repair packets (Refer to registers a new payload format for the repair packets (refer to
Section 5 for details). According to [RFC3550], an RTP receiver Section 5 for details). According to [RFC3550], an RTP receiver
that cannot recognize a payload type must discard it. This action that cannot recognize a payload type must discard it. This action
provides backward compatibility. The FEC mechanisms can then be provides backward compatibility. The FEC mechanisms can then be
used in a multicast group with mixed FEC-capable and non-FEC- used in a multicast group with mixed FEC-capable and non-FEC-
capable receivers. If a non-FEC-capable receiver receives a capable receivers. If a non-FEC-capable receiver receives a
repair packet, it will not recognize the payload type, and hence, repair packet, it will not recognize the payload type, and hence,
discards the repair packet. discards the repair packet.
o Sequence Number (SN): The sequence number has the standard o Sequence Number (SN): The sequence number has the standard
definition. It MUST be one higher than the sequence number in the definition. It MUST be one higher than the sequence number in the
previously transmitted repair packet. The initial value of the previously transmitted repair packet. The initial value of the
sequence number SHOULD be random (unpredictable) [RFC3550]. sequence number SHOULD be random (unpredictable) [RFC3550].
o Timestamp (TS): The timestamp SHALL be set to a time o Timestamp (TS): The timestamp SHALL be set to a time corresponding
corresponding to the repair packet's transmission time. Note that to the repair packet's transmission time. Note that the timestamp
the timestamp value has no use in the actual FEC protection value has no use in the actual FEC protection process and is
process and is usually useful for jitter calculations. usually useful for jitter calculations.
o Synchronization Source (SSRC): The SSRC value SHALL be randomly o Synchronization Source (SSRC): The SSRC value SHALL be randomly
assigned as suggested by [RFC3550]. This allows the sender to assigned as suggested by [RFC3550]. This allows the sender to
multiplex the source and repair flows on the same port, or multiplex the source and repair flows on the same port or
multiplex multiple repair flows on a single port. The repair multiplex multiple repair flows on a single port. The repair
flows SHOULD use the RTCP CNAME field to associate themselves with flows SHOULD use the RTP Control Protocol (RTCP) CNAME field to
the source flow. associate themselves with the source flow.
In some networks, the RTP Source, which produces the source In some networks, the RTP Source (which produces the source
packets and the FEC Source, which generates the repair packets packets) and the FEC Source (which generates the repair packets
from the source packets may not be the same host. In such from the source packets) may not be the same host. In such
scenarios, using the same CNAME for the source and repair flows scenarios, using the same CNAME for the source and repair flows
means that the RTP Source and the FEC Source MUST share the same means that the RTP Source and the FEC Source MUST share the same
CNAME (for this specific source-repair flow association). A CNAME (for this specific source-repair flow association). A
common CNAME may be produced based on an algorithm that is known common CNAME may be produced based on an algorithm that is known
both to the RTP and FEC Source. This usage is compliant with both to the RTP and FEC Source. This usage is compliant with
[RFC3550]. [RFC3550].
Note that due to the randomness of the SSRC assignments, there is Note that due to the randomness of the SSRC assignments, there is
a possibility of SSRC collision. In such cases, the collisions a possibility of SSRC collision. In such cases, the collisions
MUST be resolved as described in [RFC3550]. MUST be resolved as described in [RFC3550].
Note that the P bit, X bit, CC field and M bit of the source packets Note that the P bit, X bit, CC field, and M bit of the source packets
are protected by the corresponding bits/fields in the RTP header of are protected by the corresponding bits/fields in the RTP header of
the repair packet. On the other hand, the payload of a repair packet the repair packet. On the other hand, the payload of a repair packet
protects the concatenation of (if present) the CSRC list, RTP protects the concatenation of (if present) the CSRC list, RTP
extension, payload and padding of the source RTP packets associated extension, payload, and padding of the source RTP packets associated
with this repair packet. with this repair packet.
The FEC header is 16 octets. The format of the FEC header is shown The FEC header is 16 octets. The format of the FEC header is shown
in Figure 7. in Figure 7.
0 1 2 3 0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SN base low | Length recovery | | SN base low | Length recovery |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 14, line 22 skipping to change at page 14, line 22
| TS recovery | | TS recovery |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|N|D|Type |Index| Offset | NA | SN base ext | |N|D|Type |Index| Offset | NA | SN base ext |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Format of the FEC header Figure 7: Format of the FEC header
The FEC header consists of the following fields: The FEC header consists of the following fields:
o The SN base low field is used to indicate the lowest sequence o The SN base low field is used to indicate the lowest sequence
number, taking wrap around into account, of those source packets number, taking wraparound into account, of those source packets
protected by this repair packet. protected by this repair packet.
o The Length recovery field is used to determine the length of any o The Length recovery field is used to determine the length of any
recovered packets. recovered packets.
o The E bit is the extension flag introduced in [RFC2733] and used o The E bit is the extension flag introduced in [RFC2733] and used
to extend the [RFC2733] FEC header. to extend the [RFC2733] FEC header.
o The PT recovery field is used to determine the payload type of the o The PT recovery field is used to determine the payload type of the
recovered packets. recovered packets.
o The Mask field is not used. o The Mask field is not used.
o The TS recovery field is used to determine the timestamp of the o The TS recovery field is used to determine the timestamp of the
recovered packets. recovered packets.
o The N bit is the extension flag that is reserved for future uses. o The N bit is the extension flag that is reserved for future use.
o The D bit is not used. o The D bit is not used.
o The Type field indicates the type of the error-correcting code o The Type field indicates the type of the error-correcting code
used. This document defines only one error-correcting code. used. This document defines only one error-correcting code.
o The Index field is not used. o The Index field is not used.
o The Offset and NA fields are used to indicate the number of o The Offset and NA fields are used to indicate the number of
columns (L) and rows (D) of the source block, respectively. columns (L) and rows (D) of the source block, respectively.
o The SN base ext field is not used. o The SN base ext field is not used.
The details on setting the fields in the FEC header are provided in The details on setting the fields in the FEC header are provided in
Section 6.2. Section 6.2.
It should be noted that a mask-based approach (similar to the one It should be noted that a Mask-based approach (similar to the one
specified in [RFC2733]) may not be very efficient to indicate which specified in [RFC2733]) may not be very efficient to indicate which
source packets in the current source block are associated with a source packets in the current source block are associated with a
given repair packet. In particular, for the applications that would given repair packet. In particular, for the applications that would
like to use large source block sizes, the size of the mask that is like to use large source block sizes, the size of the Mask that is
required to describe the source-repair packet associations may be required to describe the source-repair packet associations may be
prohibitively large. Instead, a systematized approach is inherently prohibitively large. Instead, a systematized approach is inherently
more efficient. more efficient.
5. Payload Format Parameters 5. Payload Format Parameters
This section provides the media subtype registration for the 1-D This section provides the media subtype registration for the 1-D
interleaved parity FEC. The parameters that are required to interleaved parity FEC. The parameters that are required to
configure the FEC encoding and decoding operations are also defined configure the FEC encoding and decoding operations are also defined
in this section. in this section.
5.1. Media Type Registration 5.1. Media Type Registration
This registration is done using the template defined in [RFC4288] and This registration is done using the template defined in [RFC4288] and
following the guidance provided in [RFC3555]. following the guidance provided in [RFC4855].
Note to the RFC Editor: In the following sections, please replace
"XXXX" with the number of this document prior to publication as an
RFC.
5.1.1. Registration of audio/1d-interleaved-parityfec 5.1.1. Registration of audio/1d-interleaved-parityfec
Type name: audio Type name: audio
Subtype name: 1d-interleaved-parityfec Subtype name: 1d-interleaved-parityfec
Required parameters: Required parameters:
o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate
SHALL be larger than 1000 to provide sufficient resolution to RTCP SHALL be larger than 1000 to provide sufficient resolution to RTCP
operations. However, it is RECOMMENDED to select the rate that operations. However, it is RECOMMENDED to select the rate that
matches the rate of the protected source RTP stream. matches the rate of the protected source RTP stream.
o L: Number of columns of the source block. L is a positive o L: Number of columns of the source block. L is a positive integer
integer that is less than or equal to 255. that is less than or equal to 255.
o D: Number of rows of the source block. D is a positive integer o D: Number of rows of the source block. D is a positive integer
that is less than or equal to 255. that is less than or equal to 255.
o repair-window: The time that spans the source packets and the o repair-window: The time that spans the FEC block (i.e., source
corresponding repair packets. An FEC encoder processes a block of packets and the corresponding repair packets). An FEC encoder
source packets and generates a number of repair packets, which are processes a block of source packets and generates a number of
then transmitted within a certain duration. At the receiver, the repair packets, which are then transmitted within a certain
FEC decoder tries to decode all the packets received within the duration not larger than the value of the repair window. At the
repair window to recover the missing packets. Assuming that there receiver side, the FEC decoder should wait at least for the
is no issue of delay variation, the FEC decoder SHOULD NOT wait duration of the repair window after getting the first packet in an
longer than the repair window since additional waiting would not FEC block to allow all the repair packets to arrive (the waiting
help the recovery process. The size of the repair window is time can be adjusted if there are missing packets at the beginning
specified in microseconds. of the FEC block). The FEC decoder can start decoding the already
received packets sooner; however, it SHOULD NOT register an FEC
decoding failure until it waits at least for the repair-window
duration. The size of the repair window is specified in
microseconds.
Optional parameters: None. Optional parameters: None.
Encoding considerations: This media type is framed (See Section 4.8 Encoding considerations: This media type is framed (see Section 4.8
in the template document [RFC4288]) and contains binary data. in the template document [RFC4288]) and contains binary data.
Security considerations: See Section 9 of [RFCXXXX]. Security considerations: See Section 9 of [RFC6015].
Interoperability considerations: None. Interoperability considerations: None.
Published specification: [RFCXXXX]. Published specification: [RFC6015].
Applications that use this media type: Multimedia applications that Applications that use this media type: Multimedia applications that
want to improve resiliency against packet loss by sending redundant want to improve resiliency against packet loss by sending redundant
data in addition to the source media. data in addition to the source media.
Additional information: None. Additional information: None.
Person & email address to contact for further information: Ali Begen Person & email address to contact for further information: Ali Begen
<abegen@cisco.com> and IETF Audio/Video Transport Working Group. <abegen@cisco.com> and the IETF Audio/Video Transport Working Group.
Intended usage: COMMON. Intended usage: COMMON.
Restriction on usage: This media type depends on RTP framing, and Restriction on usage: This media type depends on RTP framing, and
hence, is only defined for transport via RTP [RFC3550]. hence, is only defined for transport via RTP [RFC3550].
Author: Ali Begen <abegen@cisco.com>. Author: Ali Begen <abegen@cisco.com>.
Change controller: IETF Audio/Video Transport Working Group Change controller: IETF Audio/Video Transport Working Group delegated
delegated from the IESG. from the IESG.
5.1.2. Registration of video/1d-interleaved-parityfec 5.1.2. Registration of video/1d-interleaved-parityfec
Type name: video Type name: video
Subtype name: 1d-interleaved-parityfec Subtype name: 1d-interleaved-parityfec
Required parameters: Required parameters:
o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate
SHALL be larger than 1000 to provide sufficient resolution to RTCP SHALL be larger than 1000 to provide sufficient resolution to RTCP
operations. However, it is RECOMMENDED to select the rate that operations. However, it is RECOMMENDED to select the rate that
matches the rate of the protected source RTP stream. matches the rate of the protected source RTP stream.
o L: Number of columns of the source block. L is a positive o L: Number of columns of the source block. L is a positive integer
integer that is less than or equal to 255. that is less than or equal to 255.
o D: Number of rows of the source block. D is a positive integer o D: Number of rows of the source block. D is a positive integer
that is less than or equal to 255. that is less than or equal to 255.
o repair-window: The time that spans the source packets and the o repair-window: The time that spans the FEC block (i.e., source
corresponding repair packets. An FEC encoder processes a block of packets and the corresponding repair packets). An FEC encoder
source packets and generates a number of repair packets, which are processes a block of source packets and generates a number of
then transmitted within a certain duration. At the receiver, the repair packets, which are then transmitted within a certain
FEC decoder tries to decode all the packets received within the duration not larger than the value of the repair window. At the
repair window to recover the missing packets. Assuming that there receiver side, the FEC decoder should wait at least for the
is no issue of delay variation, the FEC decoder SHOULD NOT wait duration of the repair window after getting the first packet in an
longer than the repair window since additional waiting would not FEC block to allow all the repair packets to arrive (the waiting
help the recovery process. The size of the repair window is time can be adjusted if there are missing packets at the beginning
specified in microseconds. of the FEC block). The FEC decoder can start decoding the already
received packets sooner; however, it SHOULD NOT register an FEC
decoding failure until it waits at least for the repair-window
duration. The size of the repair window is specified in
microseconds.
Optional parameters: None. Optional parameters: None.
Encoding considerations: This media type is framed (See Section 4.8 Encoding considerations: This media type is framed (see Section 4.8
in the template document [RFC4288]) and contains binary data. in the template document [RFC4288]) and contains binary data.
Security considerations: See Section 9 of [RFCXXXX]. Security considerations: See Section 9 of [RFC6015].
Interoperability considerations: None. Interoperability considerations: None.
Published specification: [RFCXXXX]. Published specification: [RFC6015].
Applications that use this media type: Multimedia applications that Applications that use this media type: Multimedia applications that
want to improve resiliency against packet loss by sending redundant want to improve resiliency against packet loss by sending redundant
data in addition to the source media. data in addition to the source media.
Additional information: None. Additional information: None.
Person & email address to contact for further information: Ali Begen Person & email address to contact for further information: Ali Begen
<abegen@cisco.com> and IETF Audio/Video Transport Working Group. <abegen@cisco.com> and the IETF Audio/Video Transport Working Group.
Intended usage: COMMON. Intended usage: COMMON.
Restriction on usage: This media type depends on RTP framing, and Restriction on usage: This media type depends on RTP framing, and
hence, is only defined for transport via RTP [RFC3550]. hence, is only defined for transport via RTP [RFC3550].
Author: Ali Begen <abegen@cisco.com>. Author: Ali Begen <abegen@cisco.com>.
Change controller: IETF Audio/Video Transport Working Group Change controller: IETF Audio/Video Transport Working Group delegated
delegated from the IESG. from the IESG.
5.1.3. Registration of text/1d-interleaved-parityfec 5.1.3. Registration of text/1d-interleaved-parityfec
Type name: text Type name: text
Subtype name: 1d-interleaved-parityfec Subtype name: 1d-interleaved-parityfec
Required parameters: Required parameters:
o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate
SHALL be larger than 1000 to provide sufficient resolution to RTCP SHALL be larger than 1000 to provide sufficient resolution to RTCP
operations. However, it is RECOMMENDED to select the rate that operations. However, it is RECOMMENDED to select the rate that
matches the rate of the protected source RTP stream. matches the rate of the protected source RTP stream.
o L: Number of columns of the source block. L is a positive o L: Number of columns of the source block. L is a positive integer
integer that is less than or equal to 255. that is less than or equal to 255.
o D: Number of rows of the source block. D is a positive integer o D: Number of rows of the source block. D is a positive integer
that is less than or equal to 255. that is less than or equal to 255.
o repair-window: The time that spans the source packets and the o repair-window: The time that spans the FEC block (i.e., source
corresponding repair packets. An FEC encoder processes a block of packets and the corresponding repair packets). An FEC encoder
source packets and generates a number of repair packets, which are processes a block of source packets and generates a number of
then transmitted within a certain duration. At the receiver, the repair packets, which are then transmitted within a certain
FEC decoder tries to decode all the packets received within the duration not larger than the value of the repair window. At the
repair window to recover the missing packets. Assuming that there receiver side, the FEC decoder should wait at least for the
is no issue of delay variation, the FEC decoder SHOULD NOT wait duration of the repair window after getting the first packet in an
longer than the repair window since additional waiting would not FEC block to allow all the repair packets to arrive (the waiting
help the recovery process. The size of the repair window is time can be adjusted if there are missing packets at the beginning
specified in microseconds. of the FEC block). The FEC decoder can start decoding the already
received packets sooner; however, it SHOULD NOT register an FEC
decoding failure until it waits at least for the repair-window
duration. The size of the repair window is specified in
microseconds.
Optional parameters: None. Optional parameters: None.
Encoding considerations: This media type is framed (See Section 4.8 Encoding considerations: This media type is framed (see Section 4.8
in the template document [RFC4288]) and contains binary data. in the template document [RFC4288]) and contains binary data.
Security considerations: See Section 9 of [RFCXXXX]. Security considerations: See Section 9 of [RFC6015].
Interoperability considerations: None. Interoperability considerations: None.
Published specification: [RFCXXXX]. Published specification: [RFC6015].
Applications that use this media type: Multimedia applications that Applications that use this media type: Multimedia applications that
want to improve resiliency against packet loss by sending redundant want to improve resiliency against packet loss by sending redundant
data in addition to the source media. data in addition to the source media.
Additional information: None. Additional information: None.
Person & email address to contact for further information: Ali Begen Person & email address to contact for further information: Ali Begen
<abegen@cisco.com> and IETF Audio/Video Transport Working Group. <abegen@cisco.com> and the IETF Audio/Video Transport Working Group.
Intended usage: COMMON. Intended usage: COMMON.
Restriction on usage: This media type depends on RTP framing, and Restriction on usage: This media type depends on RTP framing, and
hence, is only defined for transport via RTP [RFC3550]. hence, is only defined for transport via RTP [RFC3550].
Author: Ali Begen <abegen@cisco.com>. Author: Ali Begen <abegen@cisco.com>.
Change controller: IETF Audio/Video Transport Working Group Change controller: IETF Audio/Video Transport Working Group delegated
delegated from the IESG. from the IESG.
5.1.4. Registration of application/1d-interleaved-parityfec 5.1.4. Registration of application/1d-interleaved-parityfec
Type name: application Type name: application
Subtype name: 1d-interleaved-parityfec Subtype name: 1d-interleaved-parityfec
Required parameters: Required parameters:
o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate o rate: The RTP timestamp (clock) rate in Hz. The (integer) rate
SHALL be larger than 1000 to provide sufficient resolution to RTCP SHALL be larger than 1000 to provide sufficient resolution to RTCP
operations. However, it is RECOMMENDED to select the rate that operations. However, it is RECOMMENDED to select the rate that
matches the rate of the protected source RTP stream. matches the rate of the protected source RTP stream.
o L: Number of columns of the source block. L is a positive o L: Number of columns of the source block. L is a positive integer
integer that is less than or equal to 255. that is less than or equal to 255.
o D: Number of rows of the source block. D is a positive integer o D: Number of rows of the source block. D is a positive integer
that is less than or equal to 255. that is less than or equal to 255.
o repair-window: The time that spans the source packets and the o repair-window: The time that spans the FEC block (i.e., source
corresponding repair packets. An FEC encoder processes a block of packets and the corresponding repair packets). An FEC encoder
source packets and generates a number of repair packets, which are processes a block of source packets and generates a number of
then transmitted within a certain duration. At the receiver, the repair packets, which are then transmitted within a certain
FEC decoder tries to decode all the packets received within the duration not larger than the value of the repair window. At the
repair window to recover the missing packets. Assuming that there receiver side, the FEC decoder should wait at least for the
is no issue of delay variation, the FEC decoder SHOULD NOT wait duration of the repair window after getting the first packet in an
longer than the repair window since additional waiting would not FEC block to allow all the repair packets to arrive (the waiting
help the recovery process. The size of the repair window is time can be adjusted if there are missing packets at the beginning
specified in microseconds. of the FEC block). The FEC decoder can start decoding the already
received packets sooner; however, it SHOULD NOT register an FEC
decoding failure until it waits at least for the repair-window
duration. The size of the repair window is specified in
microseconds.
Optional parameters: None. Optional parameters: None.
Encoding considerations: This media type is framed (See Section 4.8 Encoding considerations: This media type is framed (see Section 4.8
in the template document [RFC4288]) and contains binary data. in the template document [RFC4288]) and contains binary data.
Security considerations: See Section 9 of [RFCXXXX]. Security considerations: See Section 9 of [RFC6015].
Interoperability considerations: None. Interoperability considerations: None.
Published specification: [RFCXXXX]. Published specification: [RFC6015].
Applications that use this media type: Multimedia applications that Applications that use this media type: Multimedia applications that
want to improve resiliency against packet loss by sending redundant want to improve resiliency against packet loss by sending redundant
data in addition to the source media. data in addition to the source media.
Additional information: None. Additional information: None.
Person & email address to contact for further information: Ali Begen Person & email address to contact for further information: Ali Begen
<abegen@cisco.com> and IETF Audio/Video Transport Working Group. <abegen@cisco.com> and the IETF Audio/Video Transport Working Group.
Intended usage: COMMON. Intended usage: COMMON.
Restriction on usage: This media type depends on RTP framing, and Restriction on usage: This media type depends on RTP framing, and
hence, is only defined for transport via RTP [RFC3550]. hence, is only defined for transport via RTP [RFC3550].
Author: Ali Begen <abegen@cisco.com>. Author: Ali Begen <abegen@cisco.com>.
Change controller: IETF Audio/Video Transport Working Group Change controller: IETF Audio/Video Transport Working Group delegated
delegated from the IESG. from the IESG.
5.2. Mapping to SDP Parameters 5.2. Mapping to SDP Parameters
Applications that are using RTP transport commonly use Session Applications that use RTP transport commonly use Session Description
Description Protocol (SDP) [RFC4566] to describe their RTP sessions. Protocol (SDP) [RFC4566] to describe their RTP sessions. The
The information that is used to specify the media types in an RTP information that is used to specify the media types in an RTP session
session has specific mappings to the fields in an SDP description. has specific mappings to the fields in an SDP description. In this
In this section, we provide these mappings for the media subtype section, we provide these mappings for the media subtype registered
registered by this document ("1d-interleaved-parityfec"). Note that by this document ("1d-interleaved-parityfec"). Note that if an
if an application does not use SDP to describe the RTP sessions, an application does not use SDP to describe the RTP sessions, an
appropriate mapping must be defined and used to specify the media appropriate mapping must be defined and used to specify the media
types and their parameters for the control/description protocol types and their parameters for the control/description protocol
employed by the application. employed by the application.
The mapping of the media type specification for "1d-interleaved- The mapping of the media type specification for "1d-interleaved-
parityfec" and its parameters in SDP is as follows: parityfec" and its parameters in SDP is as follows:
o The media type (e.g., "application") goes into the "m=" line as o The media type (e.g., "application") goes into the "m=" line as
the media name. the media name.
skipping to change at page 21, line 40 skipping to change at page 22, line 6
D values determine the lower limit for the repair-window size. D values determine the lower limit for the repair-window size.
The upper limit of the repair-window size does not depend on the L The upper limit of the repair-window size does not depend on the L
and D values. and D values.
o Although combinations with the same L and D values but with o Although combinations with the same L and D values but with
different repair-window sizes produce the same FEC data, such different repair-window sizes produce the same FEC data, such
combinations are still considered different offers. The size of combinations are still considered different offers. The size of
the repair-window is related to the maximum delay between the the repair-window is related to the maximum delay between the
transmission of a source packet and the associated repair packet. transmission of a source packet and the associated repair packet.
This directly impacts the buffering requirement on the receiver This directly impacts the buffering requirement on the receiver
side and the receiver must consider this when choosing an offer. side, and the receiver must consider this when choosing an offer.
o There are no optional format parameters defined for this payload. o There are no optional format parameters defined for this payload.
Any unknown option in the offer MUST be ignored and deleted from Any unknown option in the offer MUST be ignored and deleted from
the answer. If FEC is not desired by the receiver, it can be the answer. If FEC is not desired by the receiver, it can be
deleted from the answer. deleted from the answer.
5.2.2. Declarative Considerations 5.2.2. Declarative Considerations
In declarative usage, like SDP in the Real-time Streaming Protocol In declarative usage, like SDP in the Real-time Streaming Protocol
(RTSP) [RFC2326] or the Session Announcement Protocol (SAP) (RTSP) [RFC2326] or the Session Announcement Protocol (SAP)
skipping to change at page 22, line 39 skipping to change at page 23, line 6
The FEC header includes 16 octets. It is constructed by applying the The FEC header includes 16 octets. It is constructed by applying the
XOR operation on the bit strings that are generated from the XOR operation on the bit strings that are generated from the
individual source packets protected by this particular repair packet. individual source packets protected by this particular repair packet.
The set of the source packets that are associated with a given repair The set of the source packets that are associated with a given repair
packet can be computed by the formula given in Section 6.3.1. packet can be computed by the formula given in Section 6.3.1.
The bit string is formed for each source packet by concatenating the The bit string is formed for each source packet by concatenating the
following fields together in the order specified: following fields together in the order specified:
o Padding bit (1 bit) (This is the most significant bit of the bit o Padding bit (1 bit) (This is the most significant bit of the bit
string) string.)
o Extension bit (1 bit) o Extension bit (1 bit)
o CC field (4 bits) o CC field (4 bits)
o Marker bit (1 bit) o Marker bit (1 bit)
o PT field (7 bits) o PT field (7 bits)
o Timestamp (32 bits) o Timestamp (32 bits)
skipping to change at page 23, line 4 skipping to change at page 23, line 17
o Extension bit (1 bit) o Extension bit (1 bit)
o CC field (4 bits) o CC field (4 bits)
o Marker bit (1 bit) o Marker bit (1 bit)
o PT field (7 bits) o PT field (7 bits)
o Timestamp (32 bits) o Timestamp (32 bits)
o Unsigned network-ordered 16-bit representation of the source o Unsigned network-ordered 16-bit representation of the source
packet length in bytes minus 12 (for the fixed RTP header), i.e., packet length in bytes minus 12 (for the fixed RTP header), i.e.,
the sum of the lengths of all the following if present: the CSRC the sum of the lengths of all the following if present: the CSRC
list, header extension, RTP payload and RTP padding (16 bits) list, header extension, RTP payload, and RTP padding (16 bits).
o If CC is nonzero, the CSRC list (variable length) o If CC is nonzero, the CSRC list (variable length)
o If X is 1, the header extension (variable length) o If X is 1, the header extension (variable length)
o Payload (variable length) o Payload (variable length)
o Padding, if present (variable length) o Padding, if present (variable length)
Note that if the lengths of the source packets are not equal, each Note that if the lengths of the source packets are not equal, each
shorter packet MUST be padded to the length of the longest packet by shorter packet MUST be padded to the length of the longest packet by
adding octet 0's at the end. Due to this possible padding and adding octet(s) of 0 at the end. Due to this possible padding and
mandatory FEC header, a repair packet has a larger size than the mandatory FEC header, a repair packet has a larger size than the
source packets it protects. This may cause problems if the resulting source packets it protects. This may cause problems if the resulting
repair packet size exceeds the Maximum Transmission Unit (MTU) size repair packet size exceeds the Maximum Transmission Unit (MTU) size
of the path over which the repair flow is sent. of the path over which the repair flow is sent.
By applying the parity operation on the bit strings produced from the By applying the parity operation on the bit strings produced from the
source packets, we generate the FEC bit string. Some parts of the source packets, we generate the FEC bit string. Some parts of the
RTP header and the FEC header of the repair packet are generated from RTP header and the FEC header of the repair packet are generated from
the FEC bit string as follows: the FEC bit string as follows:
skipping to change at page 24, line 10 skipping to change at page 24, line 23
o The next 16 bits are written into the Length recovery field in the o The next 16 bits are written into the Length recovery field in the
FEC header. This allows the FEC procedure to be applied even when FEC header. This allows the FEC procedure to be applied even when
the lengths of the protected source packets are not identical. the lengths of the protected source packets are not identical.
o The remaining bits are set to be the payload of the repair packet. o The remaining bits are set to be the payload of the repair packet.
The remaining parts of the FEC header are set as follows: The remaining parts of the FEC header are set as follows:
o The SN base low field MUST be set to the lowest sequence number, o The SN base low field MUST be set to the lowest sequence number,
taking wrap around into account, of those source packets protected taking wraparound into account, of those source packets protected
by this repair packet. by this repair packet.
o The E bit MUST be set to 1 to extend the [RFC2733] FEC header. o The E bit MUST be set to 1 to extend the [RFC2733] FEC header.
o The Mask field SHALL be set to 0 and ignored by the receiver. o The Mask field SHALL be set to 0 and ignored by the receiver.
o The N bit SHALL be set to 0 and ignored by the receiver. o The N bit SHALL be set to 0 and ignored by the receiver.
o The D bit SHALL be set to 0 and ignored by the receiver. o The D bit SHALL be set to 0 and ignored by the receiver.
o The Type field MUST be set to 0. o The Type field MUST be set to 0 and ignored by the receiver.
o The Index field SHALL be set to 0 and ignored by the receiver. o The Index field SHALL be set to 0 and ignored by the receiver.
o The Offset field MUST be set to the number of columns of the o The Offset field MUST be set to the number of columns of the
source block (L). source block (L).
o The NA field MUST be set to the number of rows of the source block o The NA field MUST be set to the number of rows of the source block
(D). (D).
o The SN base ext field SHALL be set to 0 and ignored by the o The SN base ext field SHALL be set to 0 and ignored by the
skipping to change at page 25, line 15 skipping to change at page 25, line 29
and row is available from the media type parameters specified in the and row is available from the media type parameters specified in the
SDP description. This set of information uniquely identifies all of SDP description. This set of information uniquely identifies all of
the source packets associated with a given repair packet. the source packets associated with a given repair packet.
Mathematically, for any received repair packet, p*, we can determine Mathematically, for any received repair packet, p*, we can determine
the sequence numbers of the source packets that are protected by this the sequence numbers of the source packets that are protected by this
repair packet as follows: repair packet as follows:
p*_snb + i * L (modulo 65536) p*_snb + i * L (modulo 65536)
where p*_snb denotes the value in the SN base low field of p*'s FEC where p*_snb denotes the value in the SN base low field of the FEC
header, L is the number of columns of the source block and header of the p*, L is the number of columns of the source block and
0 <= i < D 0 <= i < D
where D is the number of rows of the source block. where D is the number of rows of the source block.
We denote the set of the source packets associated with repair packet We denote the set of the source packets associated with repair packet
p* by set T(p*). Note that in a source block whose size is L columns p* by set T(p*). Note that in a source block whose size is L columns
by D rows, set T includes D source packets. Recall that 1-D by D rows, set T includes D source packets. Recall that 1-D
interleaved FEC protection can fully recover the missing information interleaved FEC protection can fully recover the missing information
if there is only one source packet missing in set T. If the repair if there is only one source packet missing in set T. If the repair
packet that protects the source packets in set T is missing, or the packet that protects the source packets in set T is missing, or the
repair packet is available but two or more source packets are repair packet is available but two or more source packets are
missing, then missing source packets in set T cannot be recovered by missing, then missing source packets in set T cannot be recovered by
1-D interleaved FEC protection. 1-D interleaved FEC protection.
6.3.2. Recovering the RTP Header and Payload 6.3.2. Recovering the RTP Header and Payload
For a given set T, the procedure for the recovery of the RTP header For a given set T, the procedure for the recovery of the RTP header
of the missing packet, whose sequence number is denoted by SEQNUM, is of the missing packet, whose sequence number is denoted by SEQNUM, is
as follows: as follows:
1. For each of the source packets that are successfully received in 1. For each of the source packets that are successfully received in
set T, compute the bit string as described in Section 6.2. set T, compute the bit string as described in Section 6.2.
2. For the repair packet associated with set T, compute the bit 2. For the repair packet associated with set T, compute the bit
string in the same fashion except use the PT recovery field string in the same fashion except use the PT recovery field
instead of the PT field and TS recovery field instead of the instead of the PT field and TS recovery field instead of the
Timestamp field, and set the CSRC list, header extension and Timestamp field, and set the CSRC list, header extension and
padding to null regardless of the values of the CC field, X bit padding to null regardless of the values of the CC field, X bit,
and P bit. and P bit.
3. If any of the bit strings generated from the source packets are 3. If any of the bit strings generated from the source packets are
shorter than the bit string generated from the repair packet, shorter than the bit string generated from the repair packet,
pad them to be the same length as the bit string generated from pad them to be the same length as the bit string generated from
the repair packet. For padding, the padding of octet 0 MUST be the repair packet. For padding, the padding of octet 0 MUST be
added at the end of the bit string. added at the end of the bit string.
4. Calculate the recovered bit string as the XOR of the bit strings 4. Calculate the recovered bit string as the XOR of the bit strings
generated from all source packets in set T and the FEC bit generated from all source packets in set T and the FEC bit
skipping to change at page 26, line 40 skipping to change at page 27, line 6
13. Set the TS field in the new packet to the next 32 bits in the 13. Set the TS field in the new packet to the next 32 bits in the
recovered bit string. recovered bit string.
14. Take the next 16 bits of the recovered bit string and set the 14. Take the next 16 bits of the recovered bit string and set the
new variable Y to whatever unsigned integer this represents new variable Y to whatever unsigned integer this represents
(assuming network order). Convert Y to host order and then take (assuming network order). Convert Y to host order and then take
Y bytes from the recovered bit string and append them to the new Y bytes from the recovered bit string and append them to the new
packet. Y represents the length of the new packet in bytes packet. Y represents the length of the new packet in bytes
minus 12 (for the fixed RTP header), i.e., the sum of the minus 12 (for the fixed RTP header), i.e., the sum of the
lengths of all the following if present: the CSRC list, header lengths of all the following if present: the CSRC list, header
extension, RTP payload and RTP padding. extension, RTP payload, and RTP padding.
15. Set the SSRC of the new packet to the SSRC of the source RTP 15. Set the SSRC of the new packet to the SSRC of the source RTP
stream. stream.
This procedure completely recovers both the header and payload of an This procedure completely recovers both the header and payload of an
RTP packet. RTP packet.
7. Session Description Protocol (SDP) Signaling 7. Session Description Protocol (SDP) Signaling
This section provides an SDP [RFC4566] example. The following This section provides an SDP [RFC4566] example. The following
example uses the FEC grouping semantics [I-D.ietf-mmusic-rfc4756bis]. example uses the FEC grouping semantics [RFC5956].
In this example, we have one source video stream (mid:S1) and one FEC In this example, we have one source video stream (mid:S1) and one FEC
repair stream (mid:R1). We form one FEC group with the "a=group:FEC repair stream (mid:R1). We form one FEC group with the "a=group:
S1 R1" line. The source and repair streams are sent to the same port FEC-FR S1 R1" line. The source and repair streams are sent to the
on different multicast groups. The repair window is set to 200 ms. 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=Interleaved Parity FEC Example s=Interleaved Parity 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=mid:S1 a=mid:S1
m=application 30000 RTP/AVP 110 m=application 30000 RTP/AVP 110
c=IN IP4 233.252.0.2/127 c=IN IP4 233.252.0.2/127
a=rtpmap:110 1d-interleaved-parityfec/90000 a=rtpmap:110 1d-interleaved-parityfec/90000
a=fmtp:110 L:5; D:10; repair-window:200000 a=fmtp:110 L=5; D=10; repair-window=200000
a=mid:R1 a=mid:R1
8. Congestion Control Considerations 8. Congestion Control Considerations
FEC is an effective approach to provide applications resiliency FEC is an effective approach to provide applications with resiliency
against packet losses. However, in networks where the congestion is against packet losses. However, in networks where the congestion is
a major contributor to the packet loss, the potential impacts of a major contributor to the packet loss, the potential impacts of
using FEC SHOULD be considered carefully before injecting the repair using FEC SHOULD be considered carefully before injecting the repair
flows into the network. In particular, in bandwidth-limited flows into the network. In particular, in bandwidth-limited
networks, FEC repair flows may consume most or all of the available networks, FEC repair flows may consume most or all of the available
bandwidth and may consequently congest the network. In such cases, bandwidth and may consequently congest the network. In such cases,
the applications MUST NOT arbitrarily increase the amount of FEC the applications MUST NOT arbitrarily increase the amount of FEC
protection since doing so may lead to a congestion collapse. If protection since doing so may lead to a congestion collapse. If
desired, stronger FEC protection MAY be applied only after the source desired, stronger FEC protection MAY be applied only after the source
rate has been reduced. rate has been reduced.
skipping to change at page 28, line 19 skipping to change at page 28, line 31
is best for them. is best for them.
9. Security Considerations 9. Security Considerations
RTP packets using the payload format defined in this specification RTP packets using the payload format defined in this specification
are subject to the security considerations discussed in the RTP are subject to the security considerations discussed in the RTP
specification [RFC3550] and in any applicable RTP profile. specification [RFC3550] and in any applicable RTP profile.
The main security considerations for the RTP packet carrying the RTP The main security considerations for the RTP packet carrying the RTP
payload format defined within this memo are confidentiality, payload format defined within this memo are confidentiality,
integrity and source authenticity. Confidentiality is achieved by integrity, and source authenticity. Confidentiality is achieved by
encrypting the RTP payload. Altering the FEC packets can have a big encrypting the RTP payload. Altering the FEC packets can have a big
impact on the reconstruction operation. An attack by changing some impact on the reconstruction operation. An attack that changes some
bits in the FEC packets can have a significant effect on the bits in the FEC packets can have a significant effect on the
calculation and the recovery of the source packets. For example, calculation and the recovery of the source packets. For example,
changing the length recovery field can result in the recovery of a changing the length recovery field can result in the recovery of a
packet that is too long. Depending on the application, it may be packet that is too long. Depending on the application, it may be
helpful to perform a sanity check on the received source and FEC helpful to perform a sanity check on the received source and FEC
packets before performing the recovery operation and to determine the packets before performing the recovery operation and to determine the
validity of the recovered packets before using them. validity of the recovered packets before using them.
Integrity of the RTP packets is achieved through a suitable The integrity of the RTP packets is achieved through a suitable
cryptographic integrity protection mechanism. Such a cryptographic cryptographic integrity protection mechanism. Such a cryptographic
system may also allow the authentication of the source of the system may also allow the authentication of the source of the
payload. A suitable security mechanism for this RTP payload format payload. A suitable security mechanism for this RTP payload format
should provide source authentication capable of determining if an RTP should provide source authentication capable of determining if an RTP
packet is from a member of the RTP session. packet is from a member of the RTP session.
Note that the appropriate mechanism to provide security to RTP and Note that the appropriate mechanism to provide security to RTP and
payloads following this memo may vary. It is dependent on the payloads following this memo may vary. It is dependent on the
application, transport and signaling protocol employed. Therefore, a application, transport and signaling protocol employed. Therefore, a
single mechanism is not sufficient, although if suitable, using the single mechanism is not sufficient, although if suitable, using the
Secure Real-time Transport Protocol (SRTP) [RFC3711] is RECOMMENDED. Secure Real-time Transport Protocol (SRTP) [RFC3711] is RECOMMENDED.
Other mechanisms that may be used are IPsec [RFC4301] and Transport Other mechanisms that may be used are IPsec [RFC4301] and Transport
Layer Security (TLS) [RFC5246]; other alternatives may exist. Layer Security (TLS) [RFC5246]; other alternatives may exist.
If FEC protection is applied on already encrypted source packets, If FEC protection is applied on already encrypted source packets,
there is no need for additional encryption. However, if the source there is no need for additional encryption. However, if the source
packets are encrypted after FEC protection is applied, the FEC packets are encrypted after FEC protection is applied, the FEC
packets should be cryptographically as secure as the source packets. packets should be cryptographically as secure as the source packets.
Failure to provide an equal level of confidentiality, integrity and Failure to provide an equal level of confidentiality, integrity, and
authentication to the FEC packets can compromise the source packets' authentication to the FEC packets can compromise the source packets'
confidentiality, integrity or authentication since the FEC packets confidentiality, integrity or authentication since the FEC packets
are generated by applying XOR operation across the source packets. are generated by applying XOR operation across the source packets.
10. IANA Considerations 10. IANA Considerations
New media subtypes are subject to IANA registration. For the New media subtypes are subject to IANA registration. For the
registration of the payload format and its parameters introduced in registration of the payload format and its parameters introduced in
this document, refer to Section 5. this document, refer to Section 5.
11. Acknowledgments 11. Acknowledgments
A major part of this document is borrowed from [RFC2733], [RFC5109] A major part of this document is borrowed from [RFC2733], [RFC5109],
and [SMPTE2022-1]. Thus, the author would like to thank the authors and [SMPTE2022-1]. Thus, the author would like to thank the authors
and editors of these earlier specifications. The author also thanks and editors of these earlier specifications. The author also thanks
Colin Perkins for his constructive suggestions for this document. Colin Perkins for his constructive suggestions for this document.
12. Change Log 12. References
12.1. draft-ietf-fecframe-interleaved-fec-scheme-09
The following are the major changes compared to version 08:
o The last sentence in the abstract has been changed per IESG
comment.
12.2. draft-ietf-fecframe-interleaved-fec-scheme-08
The following are the major changes compared to version 07:
o Comments from the gen-art, media-type and IESG reviews have been
addressed.
12.3. draft-ietf-fecframe-interleaved-fec-scheme-07
The following are the major changes compared to version 06:
o The definition of "rate" in the media type registration has been
clarified.
12.4. draft-ietf-fecframe-interleaved-fec-scheme-06
The following are the major changes compared to version 05:
o Comments from IETF LC have been addressed.
12.5. draft-ietf-fecframe-interleaved-fec-scheme-05
The following are the major changes compared to version 04:
o Comments from Vincent Roca have been addressed.
12.6. draft-ietf-fecframe-interleaved-fec-scheme-04
The following are the major changes compared to version 03:
o Further comments from AVT WG have been addressed.
12.7. draft-ietf-fecframe-interleaved-fec-scheme-03
The following are the major changes compared to version 02:
o Comments from WGLC have been addressed.
12.8. draft-ietf-fecframe-interleaved-fec-scheme-02
The following are the major changes compared to version 01:
o Some details were added regarding the use of CNAME field.
o Offer-Answer and Declarative Considerations sections have been
completed.
o Security Considerations section has been completed.
12.9. draft-ietf-fecframe-interleaved-fec-scheme-01
The following are the major changes compared to version 00:
o The timestamp field definition has changed.
12.10. draft-ietf-fecframe-interleaved-fec-scheme-00
This is the initial version, which is based on an earlier individual
submission. The following are the major changes compared to that
document:
o Per the discussion in the WG, references to the FEC Framework have
been removed and the document has been turned into a pure RTP
payload format specification.
o A new section is added for congestion control considerations.
o Editorial changes to clarify a few points.
13. References
13.1. Normative References 12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to
Requirement Levels", BCP 14, RFC 2119, March 1997. Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997.
[RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and V.
Jacobson, "RTP: A Transport Protocol for Real-Time Jacobson, "RTP: A Transport Protocol for Real-Time
Applications", STD 64, RFC 3550, July 2003. Applications", STD 64, RFC 3550, July 2003.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP:
Description Protocol", RFC 4566, July 2006. Session Description Protocol", RFC 4566,
July 2006.
[I-D.ietf-mmusic-rfc4756bis] [RFC5956] Begen, A., "Forward Error Correction Grouping
Begen, A., "Forward Error Correction Grouping Semantics in Semantics in Session Description Protocol",
Session Description Protocol", RFC 5956, September 2010.
draft-ietf-mmusic-rfc4756bis-05 (work in progress),
October 2009.
[RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and [RFC4288] Freed, N. and J. Klensin, "Media Type
Registration Procedures", BCP 13, RFC 4288, December 2005. Specifications and Registration Procedures",
BCP 13, RFC 4288, December 2005.
[RFC3555] Casner, S. and P. Hoschka, "MIME Type Registration of RTP [RFC4855] Casner, S., "Media Type Registration of RTP
Payload Formats", RFC 3555, July 2003. Payload Formats", RFC 4855, February 2007.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer
with Session Description Protocol (SDP)", RFC 3264, Model with Session Description Protocol (SDP)",
June 2002. RFC 3264, June 2002.
13.2. Informative References 12.2. Informative References
[I-D.ietf-fecframe-dvb-al-fec] [DVB-AL-FEC] Begen, A. and T. Stockhammer, "Guidelines for
Begen, A. and T. Stockhammer, "Guidelines for Implementing Implementing DVB-IPTV Application-Layer Hybrid FEC
DVB-IPTV Application-Layer Hybrid FEC Protection", Protection", Work in Progress, December 2009.
draft-ietf-fecframe-dvb-al-fec-04 (work in progress),
December 2009.
[RFC2733] Rosenberg, J. and H. Schulzrinne, "An RTP Payload Format [RFC2733] Rosenberg, J. and H. Schulzrinne, "An RTP Payload
for Generic Forward Error Correction", RFC 2733, Format for Generic Forward Error Correction",
December 1999. RFC 2733, December 1999.
[RFC3009] Rosenberg, J. and H. Schulzrinne, "Registration of [RFC3009] Rosenberg, J. and H. Schulzrinne, "Registration of
parityfec MIME types", RFC 3009, November 2000. parityfec MIME types", RFC 3009, November 2000.
[RFC5109] Li, A., "RTP Payload Format for Generic Forward Error [RFC5109] Li, A., "RTP Payload Format for Generic Forward
Correction", RFC 5109, December 2007. Error Correction", RFC 5109, December 2007.
[ETSI-TS-102-034] [ETSI-TS-102-034] ETSI TS 102 034 V1.4.1, "Transport of MPEG 2 TS
ETSI TS 102 034 V1.4.1, "Transport of MPEG 2 TS Based DVB Based DVB Services over IP Based Networks",
Services over IP Based Networks", August 2009. August 2009.
[RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real
Streaming Protocol (RTSP)", RFC 2326, April 1998. Time Streaming Protocol (RTSP)", RFC 2326,
April 1998.
[RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session
Announcement Protocol", RFC 2974, October 2000. Announcement Protocol", RFC 2974, October 2000.
[SMPTE2022-1] [SMPTE2022-1] SMPTE 2022-1-2007, "Forward Error Correction for
SMPTE 2022-1-2007, "Forward Error Correction for Real-Time Real-Time Video/Audio Transport over IP Networks",
Video/Audio Transport over IP Networks", 2007. 2007.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. [RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E.,
Norrman, "The Secure Real-time Transport Protocol (SRTP)", and K. Norrman, "The Secure Real-time Transport
RFC 3711, March 2004. Protocol (SRTP)", RFC 3711, March 2004.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the [RFC4301] Kent, S. and K. Seo, "Security Architecture for
Internet Protocol", RFC 4301, December 2005. the Internet Protocol", RFC 4301, December 2005.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer
(TLS) Protocol Version 1.2", RFC 5246, August 2008. Security (TLS) Protocol Version 1.2", RFC 5246,
August 2008.
Author's Address Author's Address
Ali Begen Ali Begen
Cisco Cisco
170 West Tasman Drive 181 Bay Street
San Jose, CA 95134 Toronto, ON M5J 2T3
USA Canada
Email: abegen@cisco.com EMail: abegen@cisco.com
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