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FEC Dependency Examples A Review of Existing Tools – January 29 th , 2008

FEC Dependency Examples A Review of Existing Tools – January 29 th , 2008. Ali C. Begen abegen@cisco.com. FEC Framework Flexibility. Requirement: One FEC Framework instance per FEC scheme We’d like to support flexible grouping A source flow MAY be protected by multiple instances

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FEC Dependency Examples A Review of Existing Tools – January 29 th , 2008

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  1. FEC Dependency ExamplesA Review of Existing Tools – January 29th, 2008 Ali C. Begen abegen@cisco.com

  2. FEC Framework Flexibility • Requirement: One FEC Framework instance per FEC scheme • We’d like to support flexible grouping • A source flow MAY be protected by multiple instances • Within an instance, multiple repair flows MAY exist • Source flows MAY be grouped prior to FEC protection • If multiple repair flows are associated with a source flow, we’d like to support • Additive repair flows so that they MAY be used together • Prioritization among the repair flows

  3. Can We Do This with Existing Tools? _____| FEC FRAMEWORK / | 4: Repair Flow / | 5: Repair Flow / SOURCE FLOWS / __| FEC FRAMEWORK 1: Source Flow |___/ |---' | 6: Repair Flow 2: Source Flow | |____ 3: Source Flow | \ | FEC FRAMEWORK \ | 7: Repair Flow \_| 8: Repair Flow | 9: Repair Flow

  4. Tools Available to US • RFC 3388 – Grouping of Media Lines in SDP • RFC 4756 – FEC Grouping Semantics in SDP • draft-ietf-mmusic-decoding-dependency

  5. draft-ietf-mmusic-decoding-dependency • Goal: Propose a generic solution for SDP grouping semantics for signaling decoding dependency • Two Decoding Dependencies (DDP) are defined: • LAY: Layered coding • Strict dependence • Directed graph • MDC: Multiple description coding • No dependence but there is a mutual benefit • Not a directed graph • The mechanism is transport protocol independent (while version-00 seems to be solely RTP-based)

  6. Requirements • All media streams in a DDP group MUST have the same decoding dependency  We cannot mix LAY and MDC in one DDP group • In offer/answer model, the media streams MUST have the same dependency structure

  7. Example: LAY a=group:DDP 1 2 m=video 40000 RTP/AVP 94 194 a=rtpmap:94 H264/90000 a=rtpmap:194 H264/90000 a=mid:1 m=video 40002 RTP/AVP 95 195 a=rtpmap:95 SVC/90000 a=rtpmap:195 SVC/90000 a=mid:2 a=depend:95 lay 1:94,195 lay 1:194 • In other words • PT 95 depends on PT 94 • PT 195 depends on PT 194

  8. Example: LAY a=group:DDP 1 2 3 4 m=video 40000 RTP/AVP 94 a=mid:1 m=video 40002 RTP/AVP 95 a=mid:2 a=depend:95 lay 1:94 m=video 40004 RTP/AVP 96 a=mid:3 a=depend:96 lay 1:94 m=video 40006 RTP/AVP 97 a=mid:4 a=depend:97 lay 1:94 3:96  Multiple dependencies • In other words • PT 95 depends on PT 94 • PT 96 depends on PT 94 • PT 97 depends on both PT 94 and 96

  9. Example: MDC a=group:DDP 1 2 3 m=video 40000 RTP/AVP 94 a=mid:1 a=depend:94 mdc 2:95 3:96 m=video 40002 RTP/AVP 95 a=mid:2 a=depend:95 mdc 1:94 3:96 m=video 40004 RTP/AVP 96 a=mid:3 a=depend:96 mdc 1:94 2:95 • In other words • PT 94, 95 and 96 don’t depend on each other • They help each other to improve quality (i.e., they are additive)

  10. RFC 4756 – FEC Grouping Semantics a=group:FEC 1 2 3 m=audio 30000 RTP/AVP 0 a=mid:1 m=audio 30002 RTP/AVP 100 a=mid:2 m=audio 30004 RTP/AVP 102 a=mid:3 • “a=group:FEC” line MAY have • One or more source flows sharing the FEC flow(s) – We want this • One or more repair flows – We want this

  11. RFC 3388 – Grouping Requirements • RFC 3388 states that An “m” line identified by its “mid” attribute MUST NOT appear in more than one “a=group” line using the same semantics • So, what about the example given in slide 3? a=group:FEC 1 2 4 5 a=group:FEC 1 6 a=group:FEC 2 3 7 8 9  This is not allowed by RFC 3388  But we can write a=group:FEC 1 2 3 4 5 6 7 8 9  “group:FEC” line does not indicate any particular association

  12. Pro-MPEG CoP3 2-D (Parity) Codes R #1 (PT:90, mid:5) • Column and Row FECs are additive and do not depend on each other • We could write a=group:FEC 1 5 6  Group source & repair flows a=group:DDP 5 6  Group repair flows a=mid:1 % Source flow a=mid:5 % Column FEC a=depend:90 mdc 6:91 a=mid:6 % Row FEC a=depend:91 mdc 5:90  This works FEC #1 S #1 (PT:80, mid:1) R #2 (PT:91, mid:6)

  13. DVB Hybrid FEC (CoP3 Column + Raptor) R #1 (PT:90, mid:5) • DVB uses a hybrid combination of CoP3 Column and Raptor codes • The Hybrid Decoding Procedure: • If there are missing source packet(s) • Decode CoP3 packets • Convert CoP3 packets to Raptor packets and try decoding again • While CoP3 packets are used for recovery before Raptor packets, there is no dependency between the repair flows  They can be considered “additive”  So, we can use an SDP similar to the one in the previous slide FEC #1 S #1 (PT:80, mid:1) R #2 (PT:91, mid:6)

  14. Protecting a Group of Source Flows R #1 (PT:90, mid:5) • We could write a=group:FEC 1 2 5 6  Group source & repair flows a=group:DDP 5 6  Group repair flows a=mid:1 % Source flow #1 a=mid:2 % Source flow #2 a=mid:5 % Repair flow #1 a=depend:90 mdc 6:91 a=mid:6 % Repair flow #2 a=depend:91 mdc 5:90 OR a=depend:91 lay 5:90  This works, too S #1 (PT:80, mid:1) FEC #1 R #2 (PT:91, mid:6) S #2 (PT:81, mid:2) R #1 (PT:90, mid:5) R #2 (PT:91, mid:6) R #1 (PT:90, mid:5) R #2 (PT:91, mid:6)

  15. Protecting a Group of Source Flows R #1 (PT:90, mid:5) R #2 (PT:91, mid:6) • The following IS NOT allowed (per decoding-dependency draft) a=group:FEC 1 2 5 6 7 a=group:DDP 5 6 7 a=depend:90 mdc 6:91 a=depend:91 mdc 5:90  We cannot mix lay and mdc in one DDP a=depend:92 lay 5:90 • The following IS NOT allowed, either (per RFC 3388) a=group:FEC 1 2 5 6 7 a=group:DDP 5 6 a=group:DDP 5 7  mid:5 MUST NOT appear twice in a DDP line a=depend:90 mdc 6:91 a=depend:91 mdc 5:90 a=depend:92 lay 5:90 S #1 (PT:80, mid:1) FEC #1 S #2 (PT:81, mid:2) R #3 (PT:92, mid:7)

  16. Protecting by Multiple FEC Schemes R #1 (PT:90, mid:5) • E.g.: FEC #1  CoP3 Column+Row FEC, FEC #2  Reed-Solomon a=group:FEC 1 5 6 7  Group source & repair flow a=group:DDP 5 6  Group repair flows a=mid:1 % Source flow #1 a=mid:5 % Repair flow #1 a=depend:90 mdc 6:91 a=mid:6 % Repair flow #2 a=depend:91 mdc 5:90 a=mid:7 % Repair flow #3  This works, too FEC #1 S #1 (PT:80, mid:1) R #2 (PT:91, mid:6) FEC #2 R #3 (PT:92, mid:7)

  17. Conclusion • decoding-dependency draft offers • A signaling mechanism for “lay” dependencies • A signaling mechanism for “mdc” dependencies (additivity) • But, it does not support • Using “lay” and “mdc” in the same DDP group  We won’t need “lay” dependency between the repair flows, we just need additivity • Prioritization of streams  We need prioritization among the repair flows

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