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Alternate Offers / Capabilities in SIP/SDP

draft-bhatia-mmusic-sdp-altcap-01.txt Authors: Medhavi Bhatia John Oliver {mbhatia, joliver}@nextone.com. Alternate Offers / Capabilities in SIP/SDP. Problem: Three Categories. Caller allocates separate DSPs for separate codecs Caller cannot switch codecs at runtime

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Alternate Offers / Capabilities in SIP/SDP

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  1. draft-bhatia-mmusic-sdp-altcap-01.txt Authors: Medhavi Bhatia John Oliver {mbhatia, joliver}@nextone.com Alternate Offers / Capabilities in SIP/SDP

  2. Problem: Three Categories • Caller allocates separate DSPs for separate codecs • Caller cannot switch codecs at runtime • One of the offerred codecs needs to be transcoded on a separate IP host and must be sent directly to it. • Media clipping is undesirable • “FID” Semantics from RFC 3388 can be used with some extra SIP signaling. • Newer versions of the same offer using encryption or SDPng • Carrier architectures: SIP at Core. H.323/SIP/Megaco at access. H.323 messaging needs to be transparently passed through the core, especially when called party is H.323.

  3. Proposed Solution: Use of MIME multipart entities • Mandatory inclusion of Content-ID in each multipart entity • Definition of a new MIME header: Content-Reference • Allows answerer to indicate which MIME body in the offer is being responded to • Answerer must include one MIME body with Content-Reference header when offerer uses MIME multipart/alternative body

  4. How does it look like ? Offer Content-Type: multipart/alternative; boundary=’xxx’ --xxx Content-Type: application/sdp Content-ID: <o100@spock.nextone.com> v=0 o=- 25678 753849 IN IP4 128.96.41.1 s= c=IN IP4 128.96.41.1 t=0 0 m=audio 3456 RTP/AVP 0 m=video 3458 RTP/AVP 31 --xxx Content-Type: application/sdp Content-ID: <o101@spock.nextone.com> v=0 o=- 25678 753849 IN IP4 128.96.41.1 s= c=IN IP4 128.96.41.1 t=0 0 m=audio 3456 RTP/AVP 18 m=video 3458 RTP/AVP 34 --xxx-- Answer Content-Type: application/sdp Content-Reference: <o100@spock.nextone.com>;answer v=0 o=- 25678 753849 IN IP4 128.96.41.1 s= c=IN IP4 128.96.41.1 t=0 0 m=audio 49000 RTP/AVP 0 m=video 59000 RTP/AVP 31

  5. Proposed Solution: Use of MIME multipart entities • Other MIME multipart bodies allowed • Answer can include multiple bodies too (Negotiated bodies) • Subsequent exchanges must follow modification protocols for individual bodies (like RFC 3264) and must have the same number of negotiated bodies.

  6. Previous Version of draft -00.txt • Discussed multiple approaches: • “ALTS” semantics based on RFC 3388 • “ATLC” semantics based on RFC 3388 • Very complex and does not extend easily • SDP based. Works for non MIME based protocols too • MIME multipart/alternative w/o Content-Reference header • Answerer includes empty bodies to maintain positions of bodies. • Not elegant • Current approach (-01) address a much wider domain of problems and is simpler as well as elegant.

  7. Issues • Changes to title / organization of draft ? • Work Group ? • SIP Require header • Extension parameters in Content-Reference header reference := "Content-Reference" ":" msg-id 1*(";" reference-parm) reference-parm := “answer” | extension-token

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