datatracker.ietf.org
Sign in
Version 5.3.0, 2014-04-12
Report a bug

Forward Error Correction Grouping Semantics in Session Description Protocol
RFC 4756

Document type: RFC - Proposed Standard (November 2006)
Obsoleted by RFC 5956
Document stream: IETF
Last updated: 2013-03-02
Other versions: plain text, pdf, html

IETF State: (None)
Consensus: Unknown
Document shepherd: No shepherd assigned

IESG State: RFC 4756 (Proposed Standard)
Responsible AD: Cullen Jennings
Send notices to: csp@csperkins.org, magnus.westerlund@ericsson.com, adamli@hyervision.com

Network Working Group                                              A. Li
Request for Comments: 4756                                    Hyervision
Category: Standards Track                                  November 2006

              Forward Error Correction Grouping Semantics
                    in Session Description Protocol

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.

Copyright Notice

   Copyright (C) The IETF Trust (2006).

Abstract

   This document defines the semantics that allow for grouping of
   Forward Error Correction (FEC) streams with the protected payload
   streams in Session Description Protocol (SDP).  The semantics defined
   in this document are to be used with "Grouping of Media Lines in the
   Session Description Protocol" (RFC 3388) to group together "m" lines
   in the same session.

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................2
   3. Forward Error Correction (FEC) ..................................2
   4. FEC Grouping ....................................................3
      4.1. FEC Group ..................................................3
      4.2. Offer / Answer Consideration ...............................3
      4.3. Example of FEC Grouping ....................................3
   5. Security Considerations .........................................4
   6. IANA Considerations .............................................4
   7. Acknowledgments .................................................5
   8. References ......................................................5
      8.1. Normative References .......................................5
      8.2. Informative References .....................................5

Li                          Standards Track                     [Page 1]
RFC 4756             FEC Grouping Semantics in SDP         November 2006

1.  Introduction

   The media lines in an SDP [3] session may be associated with each
   other in various ways.  SDP itself does not provide methods to convey
   the relationships between the media lines.  Such relationships are
   indicated by the extension to SDP as defined in "Grouping of Media
   Lines in the Session Description Protocol" (RFC 3388) [2].  RFC 3388
   defines two types of semantics: Lip Synchronization and Flow
   Identification.

   Forward Error Correction (FEC) is a common technique to achieve
   robust communication in error-prone environments.  In this document,
   we define the semantics that allows for grouping of FEC streams with
   the protected payload streams in SDP by further extending RFC 3388.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD, "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [1].

3.  Forward Error Correction (FEC)

   Forward Error Correction (FEC) is a common technique to achieve
   robust communication in error-prone environments.  In FEC,
   communication uses a bandwidth that is more than payload to send
   redundantly coded payload information.  The receivers can readily
   recover the original payload even when some communication is lost in
   the transmission.  Compared to other error correction techniques
   (such as retransmission), FEC can achieve much lower transmission
   delay, and it does not have the problem of implosion from
   retransmission requests in various multicast scenarios.

   In general, the FEC data can be sent in two different ways: (1)
   multiplexed together with the original payload stream or (2) as a
   separate stream.  It is thus necessary to define mechanisms to
   indicate the association relationship between the FEC data and the
   payload data they protect.

   When FEC data are multiplexed with the original payload stream, the
   association relationship may, for example, be indicated as specified
   in "An RTP Payload for Redundant Audio Data" (RFC 2198) [4].  The
   generic RTP payload format for FEC [5] uses that method.

   When FEC data are sent as a separate stream from the payload data,
   the association relationship can be indicated in various ways.  This
   document on the FEC media line grouping specifies a mechanism for

[include full document text]