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Offer/Answer & Multipart Alternative

Offer/Answer & Multipart Alternative. Cullen Jennings <fluffy@cisco.com> & Medhavi Bhatia John Oliver {mbhatia, joliver}@nextone.com. Documents. draft-jennings-sipping-certs-04 Cullen Jennings Jon Peterson draft-bhatia-mmusic-sdp-altcap-01.txt Medhavi Bhatia John Oliver

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Offer/Answer & Multipart Alternative

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  1. Offer/Answer & Multipart Alternative Cullen Jennings <fluffy@cisco.com> & Medhavi Bhatia John Oliver {mbhatia, joliver}@nextone.com

  2. Documents • draft-jennings-sipping-certs-04 • Cullen Jennings • Jon Peterson • draft-bhatia-mmusic-sdp-altcap-01.txt • Medhavi Bhatia • John Oliver • {mbhatia, joliver}@nextone.com

  3. Problem • Example that started it: • Alice offers two SDP bodies, one for RTP, one for SRTP. How does Bob indicate which offer was selected? • Side note: Can not try SRTP then try RTP. If voicemail does SRTP, will never get a RTP UA. • General problem: • If Alice sends a multipart/alternative, how does Bob indicate which alternative was used.

  4. Solution • 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.

  5. Example Offer Content-Type: multipart/alternative; boundary=’xxx’ --xxx Content-Type: application/sdp Content-ID: <o100@spock.example.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.example.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.example.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 49000 RTP/AVP 0 m=video 59000 RTP/AVP 31

  6. Require Header • SIP Require header needed? • Can implicitly deal with this by saying if a UAS supports multipart/alternative, then it needs to add the header. • Recommendation: Make it explicit and add an option tag.

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