draft-ietf-mmusic-fec-grouping-00.txt   draft-ietf-mmusic-fec-grouping-01.txt 
MMUSIC Working Group Adam Li MMUSIC Working Group Adam Li
INTERNET-DRAFT HyerVision INTERNET-DRAFT HyerVision
Expires: April 22, 2006 October 22, 2005 Expires: May 28, 2006 November 28, 2005
FEC Grouping Semantics in SDP FEC Grouping Semantics in SDP
<draft-ietf-mmusic-fec-grouping-00.txt> <draft-ietf-mmusic-fec-grouping-01.txt>
Status of this memo Status of this memo
By submitting this Internet-Draft, each author represents that any By submitting this Internet-Draft, each author represents that any
applicable patent or other IPR claims of which he or she is aware applicable patent or other IPR claims of which he or she is aware
have been or will be disclosed, and any of which he or she becomes have been or will be disclosed, and any of which he or she becomes
aware will be disclosed, in accordance with Section 6 of BCP 79. aware will be disclosed, in accordance with Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that other Task Force (IETF), its areas, and its working groups. Note that other
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Session Description Protocol (RFC 3388) to group together "m" lines Session Description Protocol (RFC 3388) to group together "m" lines
in the same session. in the same session.
Table of Contents Table of Contents
1. Introduction.....................................................2 1. Introduction.....................................................2
2. Terminology......................................................2 2. Terminology......................................................2
3. Forward Error Correction (FEC)...................................2 3. Forward Error Correction (FEC)...................................2
4. FEC Grouping.....................................................3 4. FEC Grouping.....................................................3
4.1. FEC Group...................................................3 4.1. FEC Group...................................................3
4.2. FEC Grouping Semantics......................................3 4.2. Offer / Answer Consideration................................3
4.3. Offer / Answer Consideration................................3 4.3. Example of FEC Grouping.....................................4
4.4. Example of FEC Grouping.....................................4 5. Security Consideration...........................................4
5. Security Consideration...........................................5
6. IANA Considerations..............................................5 6. IANA Considerations..............................................5
7. Acknowledgments..................................................5 7. Acknowledgments..................................................5
8. Author's Address.................................................5 8. Author's Address.................................................5
9. References.......................................................5 9. References.......................................................5
9.1. Normative References........................................5 9.1. Normative References........................................5
9.2. Informative References......................................6 9.2. Informative References......................................5
1. Introduction 1. Introduction
The media lines in an SDP [3] session are usually associated with The media lines in an SDP [3] session are usually associated with
each other. SDP itself does not provide methods to convey the each other. SDP itself does not provide methods to convey the
relationships between the media lines. Such relationships are relationships between the media lines. Such relationships are
indicated the extension to SDP as defined in Grouping of Media Lines indicated the extension to SDP as defined in Grouping of Media Lines
in the Session Description Protocol (RFC 3388) [2]. RFC 3388 defines in the Session Description Protocol (RFC 3388) [2]. RFC 3388 defines
two types of semantics: Lip Synchronization, and Flow Identification. two types of semantics: Lip Synchronization, and Flow Identification.
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Grouping streams in a FEC group only indicates the association Grouping streams in a FEC group only indicates the association
relationship between streams. The detailed FEC protection relationship between streams. The detailed FEC protection
scheme/parameters are conveyed through the mechanism of the scheme/parameters are conveyed through the mechanism of the
particular FEC algorithm used. For example, the FEC grouping is used particular FEC algorithm used. For example, the FEC grouping is used
for generic RTP payload for FEC (RFC YYYY) [5] to indicate the for generic RTP payload for FEC (RFC YYYY) [5] to indicate the
association relationship between the FEC stream and the payload association relationship between the FEC stream and the payload
stream. The detailed protection level and length information for the stream. The detailed protection level and length information for the
ULP algorithm is communicated in band within the FEC stream. ULP algorithm is communicated in band within the FEC stream.
4.2. FEC Grouping Semantics 4.2. Offer / Answer Consideration
The FEC semantics is defined by the following BNF:
Semantics = "FEC"
4.3. Offer / Answer Consideration
The backward compatibility in offer / answer is generally handled as The backward compatibility in offer / answer is generally handled as
specified in RFC 3388 [2]. specified in RFC 3388 [2].
Depending on the implementation, a node that does not understand FEC Depending on the implementation, a node that does not understand FEC
grouping (either does not understand line grouping at all, or just grouping (either does not understand line grouping at all, or just
does not understand the FEC semantics) might respond to an offer does not understand the FEC semantics) might respond to an offer
containing FEC grouping either (1) with an answer which ignores the containing FEC grouping either (1) with an answer which ignores the
grouping attribute, or (2) with a refusal to the request (e.g., 488 grouping attribute, or (2) with a refusal to the request (e.g., 488
Not acceptable here or 606 Not Acceptable). Not acceptable here or 606 Not Acceptable).
In the first case, the original sender of the offer MUST establish In the first case, the original sender of the offer MUST establish
the connection without FEC. In the second case, if the sender of the the connection without FEC. In the second case, if the sender of the
offer still wishes to establish the session, it SHOULD re-try the offer still wishes to establish the session, it SHOULD re-try the
request with an offer without FEC. request with an offer without FEC.
4.4. Example of FEC Grouping 4.3. Example of FEC Grouping
The following example shows a session description of a multicast The following example shows a session description of a multicast
conference. The first media stream (mid:1) contains the audio stream. conference. The first media stream (mid:1) contains the audio stream.
The second media stream (mid:2) contains the Generic FEC [5] The second media stream (mid:2) contains the Generic FEC [5]
protection for the audio stream. These two streams form an FEC Group. protection for the audio stream. These two streams form an FEC Group.
The relationship between the two streams is indicated by the The relationship between the two streams is indicated by the
"a=group:FEC 1 2" line. The FEC stream is sent to the same multicast "a=group:FEC 1 2" line. The FEC stream is sent to the same multicast
group and has the same TTL as the audio, but on a port number two group and has the same TTL as the audio, but on a port number two
higher. Likewise, the video stream (mid:3) and its Generic FEC higher. Likewise, the video stream (mid:3) and its Generic FEC
protection stream (mid:4) forms another FEC group. The relationship protection stream (mid:4) forms another FEC group. The relationship
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modifications upon the publication of this specification: modifications upon the publication of this specification:
- Replace all occurrences of RFC XXXX with the RFC number this - Replace all occurrences of RFC XXXX with the RFC number this
specification receives when being published. specification receives when being published.
- Replace reference [5] and all occurrences of RFC YYYY with the - Replace reference [5] and all occurrences of RFC YYYY with the
corresponding title and RFC number of that ID when it is published. corresponding title and RFC number of that ID when it is published.
- Remove this Section. - Remove this Section.
This Internet-Draft expires October 22, 2006. This Internet-Draft expires May 28, 2006.
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