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SDPng Update

SDPng Update. draft-ietf-mmusic-sdpng-04.txt. Dirk Kutscher dku@tzi.org Jörg Ott jo@tzi.org Carsten Bormann cabo@tzi.org. Overview. Changes in -04 Open Issues Next steps. Changes in -04. Generic syntax mechanisms for re-using definitions sdpng:use for referencing named definitions

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SDPng Update

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  1. SDPng Update draft-ietf-mmusic-sdpng-04.txt Dirk Kutscher dku@tzi.org Jörg Ott jo@tzi.org Carsten Bormann cabo@tzi.org IETF 53, Minneapolis Kutscher/Ott/Bormann

  2. Overview • Changes in -04 • Open Issues • Next steps IETF 53, Minneapolis Kutscher/Ott/Bormann

  3. Changes in -04 • Generic syntax mechanisms for re-using definitions • sdpng:use for referencing named definitions • sdpng:group to name a group of definitions for later referencing • sdpng:prop to add properties to definitions • Capability negotiation IETF 53, Minneapolis Kutscher/Ott/Bormann

  4. Capability Negotiation • Offer/Answer: • Select one (or more) configuration alternatives from the set of offered configurations • Typically, the answerer matches offer against list of supported configurations • Problem: • Some applications (e.g., video) can require many configuration parameters • Representing each variant as an individual alternative not practical IETF 53, Minneapolis Kutscher/Ott/Bormann

  5. Capability Negotiation in SDPng • Language mechanisms to describe supported value ranges for configuration parameters • “For codec X, I can support frame rates 6,12,24 and codec options foo and bar” • Algorithms to compare and collapse two descriptions • Result: A commonly supported configuration (if it exists) IETF 53, Minneapolis Kutscher/Ott/Bormann

  6. Some Assumptions • This should be simple • Limited set of data types and collapsing rules • Usable for SIP, RTSP, SAP, MEGACO • Message size, implementation complexity • SIP: SDPng exchange in one offer/answer cycle • Extensible • No fixed identifiers • Collapsing is possible without knowing semantics of configuration descriptions • Can collapse without having to know schema definition etc. IETF 53, Minneapolis Kutscher/Ott/Bormann

  7. CAP(A) Conceptual Overview A determines potential configurationsand generates CAP(A) A B CAP(A) IETF 53, Minneapolis Kutscher/Ott/Bormann

  8. CAP(A) CAP(B) B generates CAP(B), according to the set of components from A’s description that B wants to support. A B CAP(A) CAP(B) IETF 53, Minneapolis Kutscher/Ott/Bormann

  9. CAP(A) CAP(B) Both A and B can compute CAP(AB), the list of commonly supported potential configurations. A B CAP(A) CAP(B) CAP(AB) CAP(AB) IETF 53, Minneapolis Kutscher/Ott/Bormann

  10. CAP(A) CAP(B) A selects the actual configuration CFG(AB). A B CAP(A) CAP(B) CAP(AB) CAP(AB) CFG(AB) IETF 53, Minneapolis Kutscher/Ott/Bormann

  11. CFG_T(A) CAP(A) CAP(B) A augments CFG(AB) with A’s non-negotiable transport parameters and generates CFG_T(A). A B CAP(A) CAP(B) CAP(AB) CAP(AB) CFG(AB) CFG_T(A) IETF 53, Minneapolis Kutscher/Ott/Bormann

  12. CFG_T(A) CAP(A) CFG_T(AB) CAP(B) B receives CFG_T(A) and adds its own transport parameters, resulting in CFG_T(AB). A B CAP(A) CAP(B) CAP(AB) CAP(AB) CFG(AB) CFG_T(A) CFG_T(AB) CFG_T(AB) IETF 53, Minneapolis Kutscher/Ott/Bormann

  13. CAP(A) + CFG_T(A) Optimization A sends capabilities and transport parameters. A B CAP(A) CFG_T(A) CAP(B) CFG_T(A) IETF 53, Minneapolis Kutscher/Ott/Bormann

  14. CAP(A) + CFG_T(A) CFG_T(AB) B computes CAP(AB) and generates CFG_T(AB). A B CAP(A) CFG_T(A) CAP(B) CFG_T(A) CFG_T(AB) CFG_T(AB) IETF 53, Minneapolis Kutscher/Ott/Bormann

  15. Properties of the Negotiation Procedure • Integration of transport parameters in “offer” • Concept of non-negotiable parameters • “Context-free” processing • Process capability descriptions without knowing schema definition and semantics • Encode type info into parameters, infer collapsing rule IETF 53, Minneapolis Kutscher/Ott/Bormann

  16. Collapsing Example <x a="[BAR, 3, 5, 8]" b="(2,8)" c="foo"> <y b="[UVW, XYZ]"/> </x> A <x a="[3, 6, 8]" b="(5,10)" c="bar"> <y b="[RST, XYZ]"/> </x> B <x a="[3, 8]" b="(5,8)"> <y b="[XYZ]"/> </x> Result IETF 53, Minneapolis Kutscher/Ott/Bormann

  17. Data Types • Set of symbols • [FOO,4,5]  [BAR,3,4]  [4] • Collapsing rule: intersection • Numerical ranges • (3,10)  (5,12)  (5,10) • Collapsing rule: determine common range • Optional string parameters • “FOO”  “BAR”  “” • Collapsing rule: test for equality IETF 53, Minneapolis Kutscher/Ott/Bormann

  18. Open Issue #1: Global View • With SIP/SDP, we send participant-specific descriptions • Can lead to ambiguity (e.g., asymmetric configurations) • Global view: • Disambiguate all descriptions • Relate to participant • Participant-identifier? • Useful for multi-party scenarios • Adds some complexity IETF 53, Minneapolis Kutscher/Ott/Bormann

  19. Open Issue #2:External Definitions • External libraries • How useful are they in real life? • Resolving references to librariesat call-setup time… • Always include all definitions? IETF 53, Minneapolis Kutscher/Ott/Bormann

  20. Open Issue #3:Capability Negotiation • What functionality is really needed? • Current draft provides a simple, limited solution • Limited set of data types • Optimized, application specific processing rules • Other, more generic work exists • CC/PP, CONNEG etc. • How much re-use is useful? • Technical discussion required! IETF 53, Minneapolis Kutscher/Ott/Bormann

  21. Open Issue #4:Capability Negotiation • Semantics of descriptions and negotiation results • Multiple alternatives for a component • Select one? Support any? • Ranges for parameters in final descriptions • Are senders free to select values? • Do changes require signaling? • Non-negotiable parameters • Currently under-specified… IETF 53, Minneapolis Kutscher/Ott/Bormann

  22. Open Issue #5:Internal References • SPDng provides mechanisms to name definitions and re-use them • Compact definitions, grouping etc. • For capability negotiation, all references MUST be resolved • Collapsing process yields a new description instance • How to generate a compact description instance again? IETF 53, Minneapolis Kutscher/Ott/Bormann

  23. Open Issue #6: Profiles • Designing profiles • Current draft provides merely examples • Audio, RTP, UDP, IPv4 • Complete set of basic profiles for RTP/AVP required • Payload type assignment • Security: MIKEY in SDPng • QoS • Different types of QoS parameters IETF 53, Minneapolis Kutscher/Ott/Bormann

  24. Next Steps • Restructuring specification • Split document: • Framework document • General model, scenarios •  Informational? • SPDng spec. • Syntax, processing algorithms •  Standards track • Profiles • Some basic profiles covering RTP/AVP •  Standards track • Editorial changes required • Make examples consistent, fix bugs IETF 53, Minneapolis Kutscher/Ott/Bormann

  25. Next Steps • Complete list of open issues • Discuss (and resolve) on the mailing list • Work on profiles • Fix remaining issues IETF 53, Minneapolis Kutscher/Ott/Bormann

  26. SDPng implementation • C++ library • Works with expat (XML parser) • Any other event-based parser should be fine • Covers sdpng-03 • Newer stuff currently being implemented IETF 53, Minneapolis Kutscher/Ott/Bormann

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