draft-ietf-mmusic-rfc4756bis-00.txt   draft-ietf-mmusic-rfc4756bis-01.txt 
MMUSIC A. Begen MMUSIC A. Begen
Internet-Draft Cisco Systems Internet-Draft Cisco Systems
Updates: 4756 (if approved) January 21, 2009 Updates: 4756 (if approved) March 8, 2009
Intended status: Standards Track Intended status: Standards Track
Expires: July 25, 2009 Expires: September 9, 2009
Forward Error Correction Grouping Semantics in Session Description Forward Error Correction Grouping Semantics in Session Description
Protocol Protocol
draft-ietf-mmusic-rfc4756bis-00 draft-ietf-mmusic-rfc4756bis-01
Status of this Memo Status of this Memo
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to this document.
Abstract Abstract
The Session Description Protocol (SDP) supports grouping media lines. The Session Description Protocol (SDP) supports grouping media lines.
SDP also has semantics defined for grouping the associated source and SDP also has semantics defined for grouping the associated source and
Forward Error Correction (FEC)-based repair flows. However, the Forward Error Correction (FEC)-based repair flows. However, the
semantics that were defined in RFC 4756 generally fail to provide the semantics that were defined in RFC 4756 generally fail to provide the
specific grouping relationships between the source and repair flows specific grouping relationships between the source and repair flows
when there are more than one source and/or repair flows in the same when there are more than one source and/or repair flows in the same
group. Furthermore, the existing semantics also do not support group. Furthermore, the existing semantics also do not support
additive repair flows. This document addresses these issues by additive repair flows. This document addresses these issues by
introducing new FEC grouping semantics. introducing new FEC grouping semantics.
Table of Contents Table of Contents
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 5 2. Requirements Notation . . . . . . . . . . . . . . . . . . . . 5
3. Requirements and Issues with RFC 4756 . . . . . . . . . . . . 5 3. Requirements and Issues with RFC 4756 . . . . . . . . . . . . 5
3.1. Source and Repair Flow Association . . . . . . . . . . . . 5 3.1. Source and Repair Flow Association . . . . . . . . . . . . 5
3.2. Support for Additivity . . . . . . . . . . . . . . . . . . 6 3.2. Support for Additivity . . . . . . . . . . . . . . . . . . 6
4. FEC Grouping . . . . . . . . . . . . . . . . . . . . . . . . . 6 4. FEC Grouping . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. New Grouping Semantics . . . . . . . . . . . . . . . . . . 6 4.1. New Grouping Semantics . . . . . . . . . . . . . . . . . . 6
4.2. Offer / Answer Consideration . . . . . . . . . . . . . . . 7 4.2. Offer-Answer Model Considerations . . . . . . . . . . . . 7
4.3. Example of FEC Grouping . . . . . . . . . . . . . . . . . 7 4.3. Example of FEC Grouping . . . . . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative References . . . . . . . . . . . . . . . . . . . 9 8.1. Normative References . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
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between the source and repair flows. The flows included in one between the source and repair flows. The flows included in one
"a=group" line are called an "FEC Group." If there are more than one "a=group" line are called an "FEC Group." If there are more than one
repair flows included in an FEC group, they are considered to be repair flows included in an FEC group, they are considered to be
additive. Repair flows that are in different FEC groups are non- additive. Repair flows that are in different FEC groups are non-
additive. additive.
By extending [I-D.ietf-mmusic-rfc3388bis] we define "FEC-XR" as the By extending [I-D.ietf-mmusic-rfc3388bis] we define "FEC-XR" as the
new grouping semantics that can support the features of the FEC new grouping semantics that can support the features of the FEC
Framework. Framework.
4.2. Offer / Answer Consideration 4.2. Offer-Answer Model Considerations
The backward compatibility in offer / answer is generally handled as The backward compatibility in offer / answer is generally handled as
specified in [RFC3388]. specified in [RFC3388].
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) SHOULD respond to an offer does not understand the FEC grouping semantics) SHOULD respond to an
containing FEC grouping either (1) with an answer that ignores the offer containing FEC grouping either (1) with an answer that ignores
grouping attribute or (2) with a refusal to the request (e.g., 488 the grouping attribute or (2) with a refusal to the request (e.g.,
Not acceptable here or 606 Not acceptable in SIP). 488 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.
Editor's note: This section may need to be updated according to
[I-D.ietf-mmusic-rfc3388bis].
4.3. Example of FEC Grouping 4.3. Example of FEC Grouping
For the scenario sketched in Figure 1, we can write the following For the scenario sketched in Figure 1, we can write the following
SDP: SDP:
v=0 v=0
o=ali 1122334455 1122334466 IN IP4 fec.example.com o=ali 1122334455 1122334466 IN IP4 fec.example.com
s=New FEC Grouping Semantics s=New FEC Grouping Semantics
t=0 0 t=0 0
a=group:FEC-XR S1 R1 a=group:FEC-XR S1 R1
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a=rtpmap:101 MP2T/90000 a=rtpmap:101 MP2T/90000
a=mid:S2 a=mid:S2
m=application 30000 RTP/AVP 110 m=application 30000 RTP/AVP 110
c=IN IP4 224.1.2.1/127 c=IN IP4 224.1.2.1/127
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
m=application 30000 RTP/AVP 111 m=application 30000 RTP/AVP 111
c=IN IP4 224.1.2.2/127 c=IN IP4 224.1.2.2/127
a=rtpmap:111 1d-interleaved-parityfec/90000 a=rtpmap:111 1d-interleaved-parityfec/90000
a=fmtp:111 L:10; D:10; repair-window: 200000 a=fmtp:111 L:10; D:10; repair-window: 400000
a=mid:R2 a=mid:R2
For the additivity issues, let us consider the scenario sketched in For the additivity issues, let us consider the scenario sketched in
Figure 3. Suppose that repair flows R5 and R6 are additive but Figure 3. Suppose that repair flows R5 and R6 are additive but
repair flow R7 is not additive with any of the other repair flows. repair flow R7 is not additive with any of the other repair flows.
In this case, we must write In this case, we must write
a=group:FEC-XR S4 R5 R6 a=group:FEC-XR S4 R5 R6
a=group:FEC-XR S4 R7 a=group:FEC-XR S4 R7
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a=group:FEC-XR S4 R5 a=group:FEC-XR S4 R5
a=group:FEC-XR S4 R6 a=group:FEC-XR S4 R6
a=group:FEC-XR S4 R7 a=group:FEC-XR S4 R7
5. Security Considerations 5. Security Considerations
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 to protect, and/or mishandling attacks may result in failure of FEC to protect, and/or mishandling
of other media payload streams. It is recommended that the receiver of other media payload streams. It is RECOMMENDED that the receiver
SHOULD do integrity check on SDP and follow the security SHOULD do integrity check on SDP and follow the security
considerations of SDP [RFC4566] to only trust SDP from trusted considerations of SDP [RFC4566] to only trust SDP from trusted
sources. sources.
6. IANA Considerations 6. IANA Considerations
This document registers the following semantics with IANA in This document registers the following semantics with IANA in
Semantics for the "group" SDP Attribute under SDP Parameters. Semantics for the "group" SDP Attribute under SDP Parameters.
Semantics Token Reference Semantics Token Reference
--------------------------- ------ ------------- --------------------------- ------ -------------
Forward Error Correction XR FEC-XR This document Forward Error Correction XR FEC-XR This document
7. Acknowledgments 7. Acknowledgments
Some parts of this document is based on [RFC4756]. Thus, the author Some parts of this document are based on [RFC4756]. Thus, the author
would like to thank those who contributed to [RFC4756]. would like to thank those who contributed to [RFC4756].
8. References 8. References
8.1. Normative References 8.1. Normative References
[I-D.ietf-fecframe-framework]
Watson, M., "Forward Error Correction (FEC) Framework",
draft-ietf-fecframe-framework-03 (work in progress),
October 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session [RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006. Description Protocol", RFC 4566, July 2006.
[I-D.ietf-mmusic-rfc3388bis] [I-D.ietf-mmusic-rfc3388bis]
Camarillo, G., "The SDP (Session Description Protocol) Camarillo, G., "The SDP (Session Description Protocol)
Grouping Framework", draft-ietf-mmusic-rfc3388bis-02 (work Grouping Framework", draft-ietf-mmusic-rfc3388bis-02 (work
in progress), January 2009. in progress), January 2009.
8.2. Informative References 8.2. Informative References
[I-D.ietf-fecframe-framework]
Watson, M., "Forward Error Correction (FEC) Framework",
draft-ietf-fecframe-framework-03 (work in progress),
October 2008.
[RFC4756] Li, A., "Forward Error Correction Grouping Semantics in [RFC4756] Li, A., "Forward Error Correction Grouping Semantics in
Session Description Protocol", RFC 4756, November 2006. Session Description Protocol", RFC 4756, November 2006.
[RFC3388] Camarillo, G., Eriksson, G., Holler, J., and H. [RFC3388] Camarillo, G., Eriksson, G., Holler, J., and H.
Schulzrinne, "Grouping of Media Lines in the Session Schulzrinne, "Grouping of Media Lines in the Session
Description Protocol (SDP)", RFC 3388, December 2002. Description Protocol (SDP)", RFC 3388, December 2002.
Author's Address Author's Address
Ali Begen Ali Begen
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