RTP Payload Format for Generic Forward Error Correction
RFC 5109
| Document | Type |
RFC - Proposed Standard
(December 2007; Errata)
Was draft-ietf-avt-ulp (avt WG)
|
|
|---|---|---|---|
| Last updated | 2015-10-14 | ||
| Replaces | draft-li-ulp | ||
| Stream | IETF | ||
| Formats | plain text pdf html bibtex | ||
| Reviews | |||
| Stream | WG state | (None) | |
| Document shepherd | No shepherd assigned | ||
| IESG | IESG state | RFC 5109 (Proposed Standard) | |
| Consensus Boilerplate | Unknown | ||
| Telechat date | |||
| Responsible AD | Cullen Jennings | ||
| Send notices to | magnus.westerlund@ericsson.com, csp@csperkins.org | ||
Network Working Group A. Li, Ed.
Request for Comments: 5109 December 2007
Obsoletes: 2733, 3009
Category: Standards Track
RTP Payload Format for Generic Forward Error Correction
Status of This Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Abstract
This document specifies a payload format for generic Forward Error
Correction (FEC) for media data encapsulated in RTP. It is based on
the exclusive-or (parity) operation. The payload format described in
this document allows end systems to apply protection using various
protection lengths and levels, in addition to using various
protection group sizes to adapt to different media and channel
characteristics. It enables complete recovery of the protected
packets or partial recovery of the critical parts of the payload
depending on the packet loss situation. This scheme is completely
compatible with non-FEC-capable hosts, so the receivers in a
multicast group that do not implement FEC can still work by simply
ignoring the protection data. This specification obsoletes RFC 2733
and RFC 3009. The FEC specified in this document is not backward
compatible with RFC 2733 and RFC 3009.
Li Standards Track [Page 1]
RFC 5109 RTP Payload Format for Generic FEC December 2007
Table of Contents
1. Introduction ....................................................2
2. Terminology .....................................................5
3. Basic Operation .................................................6
4. Parity Codes ....................................................7
5. Uneven Level Protection (ULP) ...................................7
6. RTP Media Packet Structure ......................................9
7. FEC Packet Structure ............................................9
7.1. Packet Structure ...........................................9
7.2. RTP Header for FEC Packets ................................10
7.3. FEC Header for FEC Packets ................................11
7.4. FEC Level Header for FEC Packets ..........................12
8. Protection Operation ...........................................15
8.1. Generation of the FEC Header ..............................15
8.2. Generation of the FEC Payload .............................16
9. Recovery Procedures ............................................16
9.1. Reconstruction of the RTP Header ..........................16
9.2. Reconstruction of the RTP Payload .........................18
10. Examples ......................................................19
10.1. An Example Offers Similar Protection as RFC 2733 .........19
10.2. An Example with Two Protection Levels ....................21
10.3. An Example with FEC as Redundant Coding ..................26
11. Security Considerations .......................................29
12. Congestion Considerations .....................................30
13. IANA Considerations ...........................................31
13.1. Registration of audio/ulpfec .............................31
13.2. Registration of video/ulpfec .............................32
13.3. Registration of text/ulpfec ..............................34
13.4. Registration of application/ulpfec .......................35
14. Multiplexing of FEC ...........................................36
14.1. FEC as a Separate Stream .................................36
14.2. FEC as Redundant Encoding ................................38
14.3. Offer / Answer Consideration .............................39
15. Application Statement .........................................40
16. Acknowledgments ...............................................42
17. References ....................................................42
17.1. Normative References .....................................42
17.2. Informative References ...................................43
1. Introduction
The nature of real-time applications implies that they usually have
more stringent delay requirements than normal data transmissions. As
a result, retransmission of the lost packets is generally not a valid
option for such applications. In these cases, a better method to
attempt recovery of information from packet loss is through Forward
Error Correction (FEC). FEC is one of the main methods used to
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