draft-ietf-mmusic-fec-grouping-04.txt   draft-ietf-mmusic-fec-grouping-05.txt 
MMUSIC Working Group Adam Li MMUSIC Working Group Adam Li
INTERNET-DRAFT HyerVision INTERNET-DRAFT HyerVision
Expires: October 4, 2006 April 4, 2006 Expires: December 25, 2006 June 25, 2006
Forward Error Correction Grouping Semantics Forward Error Correction Grouping Semantics
in Session Description Protocol in Session Description Protocol
<draft-ietf-mmusic-fec-grouping-04.txt> <draft-ietf-mmusic-fec-grouping-05.txt>
Status of this memo Status of this memo
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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.
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This document is an individual submission to the IETF. Comments This document is an individual submission to the IETF. Comments
should be directed to the authors. should be directed to the authors.
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When FEC data are sent as a separate stream from the payload data, When FEC data are sent as a separate stream from the payload data,
the association relationship can be indicated in various ways. This the association relationship can be indicated in various ways. This
document on the FEC media line grouping specifies a mechanism for document on the FEC media line grouping specifies a mechanism for
indicating such relationships. indicating such relationships.
4. FEC Grouping 4. FEC Grouping
4.1. FEC Group 4.1. FEC Group
Each "a=group" line are used to indicate the association relationship Each "a=group" line is used to indicate an association relationship
between the FEC streams and the payload stream. The streams included between the FEC streams and the payload stream. The streams included
in one "a=group" line are called a "FEC Group". in one "a=group" line are called a "FEC Group".
Each FEC group MAY have one or more than one FEC streams, and one or Each FEC group MAY have one or more than one FEC streams, and one or
more than one payload streams. For example, it is possible to have more than one payload streams. For example, it is possible to have
one payload streams protected by more than one FEC streams, or one payload streams protected by more than one FEC streams, or
multiple payload streams sharing one FEC stream. multiple payload streams sharing one FEC stream.
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
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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. Offer / Answer Consideration 4.2. 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) SHOULD 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 in SIP). Not acceptable here or 606 Not Acceptable in SIP).
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.
4.3. Example of FEC Grouping 4.3. Example of FEC Grouping
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c=IN IP4 224.2.17.13/127 c=IN IP4 224.2.17.13/127
a=rtpmap:101 ulpfec/8000 a=rtpmap:101 ulpfec/8000
a=mid:4 a=mid:4
5. Security Consideration 5. Security Consideration
There is a weak threat for the receiver that the FEC grouping can be There is a weak threat for the receiver that the FEC grouping can be
modified to indicate FEC relationships that do not exist. Such modified to indicate FEC relationships that do not exist. Such
attacks may result in failure of FEC protect, and/or mishandling of attacks may result in failure of FEC protect, and/or mishandling of
other media payload streams. It is recommended that the receiver other media payload streams. It is recommended that the receiver
implementation SHOULD do integrity check to thwart such threats. SHOULD do integrity check on SDP and follow the security
considerations of SDP to only trust SDP from trusted sources.
6. IANA Considerations 6. IANA Considerations
This document defines the semantics to be used with grouping of media This document defines the semantics to be used with grouping of media
lines in SDP as defined in RFC 3388. The semantics defined in this lines in SDP as defined in RFC 3388. The semantics defined in this
document are to be registered by the IANA when they are published in document are to be registered by the IANA when they are published in
standard track RFCs. standard track RFCs.
The following semantics need to be registered with IANA. The following semantics need to be registered with IANA in Semantic
for the "group" SDP Attribute under SDP Parameters.
Semantics Token Reference Semantics Token Reference
------------------------ ----- --------- ------------------------ ----- ----------
Forward Error Correction FEC RFC XXXX Forward Error Correction FEC [RFC XXXX]
7. Acknowledgments 7. Acknowledgments
The author would like to thank Magnus Westerlund, Colin Perkins, and The author would like to thank Magnus Westerlund, Colin Perkins,
Joerg Ott for their feedback on this document. Joerg Ott, and Cullen Jennings for their feedback on this document.
8. Author's Address 8. Author's Address
Adam Li Adam Li
HyerVision HyerVision
10194 Wateridge Circle #152 10194 Wateridge Circle #152
San Diego, CA 92121 San Diego, CA 92121
U.S.A. U.S.A.
Tel: +1 858 622 9038 Tel: +1 858 622 9038
Email: adamli@hyervision.com Email: adamli@hyervision.com
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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 4, 2006. This Internet-Draft expires December 25, 2006.
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