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SIP Conferencing

SIP Conferencing. Henning Schulzrinne Columbia University IETF SIP Interim Meeting, Feb. 2001. Overview. Conference models Issues: Membership awareness Transitioning between models Conference identification Full-mesh conferences. SIP Conference Modes. Central mixer End system mixing

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SIP Conferencing

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  1. SIP Conferencing Henning Schulzrinne Columbia University IETF SIP Interim Meeting, Feb. 2001

  2. Overview • Conference models • Issues: • Membership awareness • Transitioning between models • Conference identification • Full-mesh conferences

  3. SIP Conference Modes • Central mixer • End system mixing • Similar to central, but participant is mixer • IP multicast for media • Full mesh signaling • Full-mesh media distribution • Multicast media?

  4. Membership Notification • RTCP SDES • works well for multicast • Can be suppressed by participant in “stealth mode” • SIP SUBSCRIBE/NOTIFY • Works well for central server • Not needed for mesh

  5. Transition between Conference Models • Need to be able to move participants from central/UA mixer to multicast or from mesh to mixer or multicast • Similar to (supervised?) call transfer

  6. Conference Identification • We have two identifiers: SIP call-ID and (SDP) conference ID • Doesn’t matter for (UA) mixer or multicast, as only mixer needs to know that call-legs are related • Can use conference URL as identifier for notifications

  7. Conference Identification • Call-out: only current participants can add new ones • For call-out, all conference participants can have same IDs • If call-in allowed, neither Call-ID nor SDP session id can identify conference • Does call-in make sense for mesh?

  8. Full-Mesh Conferencing • Establish via • INVITE with membership list, or • REFER with Refer-To list of members • Rule: Both UAC and UAS send membership list in request and 200 • Send INVITE to all new, recurse • Allow joining of separated clouds(?)

  9. Full-Mesh Conferencing Cases • Simultaneous out-calls to two parties • Departures and re-joins • Departures while other party joins • Liveness detection of mesh? • Single user participating in multiple simultaneous conferences

  10. Simultaneous Joins A B C D B A B B,C A,B A,B INVITE or INVITE + REFER

  11. Deleting Members • Member leaving group send BYE to everyone • May still be contacted by a new arrival that just joins before the BYE arrives – just refuse invitation • Propagate member only once INVITE succeeded

  12. REFER vs. INVITE • REFER is in line with general architecture, but more messages • Use Refer-To with multiple addresses? • However, here Refer-To entries need to be skipped if already contacted – contradicts normal behavior needed for re-INVITE request • Could use SDP session ID, but meaning unclear for call-in (check unicast definition for both sides)

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