SIP Conferencing

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					                SIP Conferencing

                  Henning Schulzrinne




5 August 2011          SIP conferencing   1
                    Outline
 Conference models
 Conference functions needed:
     – create conferences
     – add and delete members
     – floor control
     – media control (freeze frame, update,
       camera control, ...)



5 August 2011         SIP conferencing        2
                  Conference Control
 Focus on media-independent control
 Conference models:
    – centrally-signaled = single conference URI
          • "focus" of conference
          • media mixer associated with conference server
          • central signaling + distributed mixing
                – third-party call control for multicast or multi-unicast
          • dial-in or dial-out
    – distributed signaling
          • anybody can invite new members
          • multicast data or
          • full mesh
 Core property: single media “choke point”
5 August 2011                      SIP conferencing                         3
                      End system mixing
                   INVITE B           B

                         A+C
        A 
       RTP mixer
                     A+B              C

       classical three-way calling
       transparent to B, C
       RTCP indicates parties (SDES)
       departure of participant  partition
       users can join  GUI issue
5 August 2011                  SIP conferencing   4
                Multicast conference
                                                 C
                A
                               multicast group



                                               




 INVITE contains multicast group
 pair-wise signaling relationships
 no BYE is needed
5 August 2011          SIP conferencing              5
                      Dial-in conference
                B+C              RTP mixer

 A
                 INVITE conf42
                                    
                                                          B


                      A      conf42@example.com


                             REFER D                  C
                           D Refer-To: conf42

 Conferences identified by SIP URI
 ad-hoc (new URI) and pre-arranged

5 August 2011                      SIP conferencing           6
                  Dial-out conference
                B+C                 RTP mixer

 A                                     
                 INVITE A                                       B
                 From: conf42
                                                             REFER conf42
                                conf42@example.com           Refer-To: D
                      A



                                                         C
                          D



 Similar to dial-in conference


5 August 2011                         SIP conferencing                      7
                Centralized signaling,
                 distributed media
                                                  conf42
A                          A
                                                                       D
                                                                   
                    D

                A                                              D

                               B
                                     D                 
                                                           C
                                                                   D


 uses third-party call control
 can use multicast for media

5 August 2011                       SIP conferencing                   8
                Centralized signaling,
       A
                 distributed media
                    B                  C               D INV D           E
                                                         200 hold
                                                         INV 3held
                                                         200 3recv
                                             INV +D1
                                             200 +C3
                      INV +D2
                      200 +B3
            INV +D3

            200 +A3

                                                          INV A3,B3,C3
                                                          200


5 August 2011             SIP conferencing                           9
                                Full mesh
                                   B                            A




                A                                           
                                                                 C




                    E                                  D

 No central server
 Need SIP extensions to convey membership
  view
 Can work even if some members leave
5 August 2011                     SIP conferencing                   10
                             Scaling
                end      multicast    dial-     CS-DM   full mesh
                system                in/out
                                      UA/

    inbound     A        A            1/A       A       A
    bandwidth


    outbound    N-1      1            1/N       N-1     N-1
    bandwidth


    encodings   N-1      1            1/N       1       1




5 August 2011                SIP conferencing                       11
                           Properties
                  end      multicast       dial in/out   CS-DM    full mesh
                  system
 conference       UA       UA              conference conference UA + ?
 ID

 membership       RTCP     RTCP            RTCP          RTCP     INVITE list
 notification                              NOTIFY        NOTIFY

 invite to join   INVITE   INVITE          REFER         REFER    INVITE



 join             INVITE   SAP             INVITE        INVITE   INVITE




5 August 2011                    SIP conferencing                          12
                Non-SIP open issues
 device control for remote devices
  (cameras)
 freeze frame  SDP (like hold)
 intraframe request  RTCP?
 SDPng for description
     – channel description
     – better capabilities


5 August 2011          SIP conferencing   13
          Taxonomy of conference
             control functions
 Needed throughout conference life cycle
 Create new conference
     – properties: duration, media, user limit, ...
     – mass-invitation
     – but: is this needed beyond the current ad-hoc conference
       creation?
 Invite users  REFER
 Admit users
     – similar to presence subscriber problem?
           • proactive policy (“don’t admit *.fbi.gov”)  CPL?
           • individual decisions: “Alice wants to join”
 Eject users (less important?)
5 August 2011                    SIP conferencing                 14
                More requirements
 Anonymity?
     – request that presence not be announced
     – requires trust in conference server
 Get participant list
 Notification of members joining and
  leaving
 sidebars – listen to main conference in
  background

5 August 2011         SIP conferencing          15
                     Functions
 Not every conference needs all functions
 Web interface can be done, but hard to script
 Don’t assume single person has multiple roles
     – bouncer (sergeant-at-arms) vs. moderator
 Need to deal with moderator failure
     – distributed leader election problem is hard
     – may want to punt
 Provide mechanisms, avoid guessing at policy
     – “only admit Joe if fewer than 4 participants and if
       65% of participants agree”

5 August 2011            SIP conferencing                    16
                 Conference events
•   SUBSCRIBE to conference, get NOTIFY'd
•   incremental or full state
•   user state: active, departed, booted, failed (dial-out)
•   dialog state
•   for each user, media status: media stream
     • sending: received-by-all, muted
     • receiving: receiving-all, anchor-only

<conference-info version="0" state="full" entity="conf233@example.com">
<user uri="sip:jdrosen@dynamicsoft.com" display-name="Jonathan Rosenberg">
  <status>active</status>
  <media-status>
  <media-stream media-type="audio"/>
  </media-status> </user>
  <user uri="sip:hgs@cs.columbia.edu" display-name="Henning Schulzrinne">
<status>active</status>
</user>
</conference-info>




5 August 2011                     SIP conferencing                           17
                 Floor control
 General: management of shared
  resources
     – audio channel (right to talk; typically, one)
     – video (limited by bandwidth, screen)
     – pointer and input focus for whiteboard and
       shared applications (one, but also multiple
       pointers)
 = safe and mutually exclusive input
  access to shared resource
5 August 2011          SIP conferencing            18
                       Floor control
 Managed by
     – automated queuing
           • policy can be messy (“priority to speakers that have
             talked for less than 5 minutes”)
           • suggestion: punt on policy
     – one or more moderators
 control at signaling level
     – mute participants
     – cooperative users
 may also control media resources (mixer)

5 August 2011                  SIP conferencing                     19
       Floor control requirements
   Determine floor controlled sessions
   floor may encompass more than one media session
   restrict creation of floor
   create and destroy floors dynamically
   moderator-controlled policy
     – also automated policies (FCFS, random, least time held, ...)
 multiple moderators
 participants can claim and release floor
 parameters such as time limits



5 August 2011                SIP conferencing                         20
           Floor control proposal
 SDP for indication
   a=type:moderated
   a=group:FL 1 2 4
   a=group:FL 3 5
   m=audio 10000 RTP/AVP 0
   a=mid:1
   m=video 20000 RTP/AVP 31
   a=mid:2
   m=application 30000 udp wb
   a=mid:3
   m=control 80 HTTP SOAP
   a=mid:4
   m=control 5060 SIP SOAP
   a=mid:5

 SOAP for requests
 SIP events for notification
   – floorCreated, floorRemoved, configChanged, floorChanged,
     queueChanged
 Uploaded policy document for policy decisions and
    configuration
5 August 2011         SIP conferencing                          21
              Floor control operations
CreateFloor        create a floor for some resource      moderator
RemoveFloor        remove the floor for some resource    moderator
ChangeConfig       Change the configuration of a floor   moderator
ClaimFloor         Request a floor                       user
ReleaseFloor       Give up the floor                     user
GrantFloor         Grant floor to some users             moderator
RevokeFloor        Force release floor from some users   moderator
RemoveClaims       Remove existing floor claims          moderator
ReorderClaims      Reorder the claims in the queue       moderator




   5 August 2011                     SIP conferencing            22
       Floor control requirements
 Create a managed resource
     – zero, one or multiple media
 Remove managed resource
 Change resource configuration
     – moderator, users, concurrency
 Request resource
 Grant resource
 Revoke resource
     – including pending requests
 Release resource
 Reorder resource claims
5 August 2011               SIP conferencing   23
                Commonalities across
                   functionalities
 Functions are largely orthogonal
 But share communication needs:
     – asynchronous events
           • “Bob joined conference” (sip-call-package)
           • “Carol has released floor”
           • “David has requested floor”
     – commands to conference
           • avoid commands directly to participants



5 August 2011              SIP conferencing               24
       Suggested implementations
 Floor and conference control commands
   SOAP
 Events (floor control, join)  SIP
  events
 Merging and splitting conferences 
  REFER



5 August 2011    SIP conferencing     25
                         Questions
 How hostile is the conference?
     – If participants basically trust each other,
       moderator failure is much easier to deal with
     – Define trusted subgroup?
           • Panel discussion model: panel vs. mob audience
 Scaling requirements?
     – Primarily notifications are issue
     – Centralized conference model imposes some
       limitations, but can still be hundreds
 REFER can provide some functionality (invite,
  eject)

5 August 2011                 SIP conferencing                26
 Current Conferencing Internet
            Drafts
 Conference models
     – draft-ietf-sipping-conferencing-models-01
 Event package
     – draft-ietf-sipping-conference-package-00
 Floor control
     – draft-wu-sipping-floor-control-01
 Requirements
     – draft-khartabil-sip-conferencing-00
     – draft-koskelainen-sipping-conf-requirements-00
     – draft-levin-sipping-conferencing-requirements-01

5 August 2011            SIP conferencing                 27
                   Summary
 Conference control probably misnomer
 Keep media stream control separate –
  may be needed for unicast just as much
 Divide into components, possibly
  prioritize:
     – conference creation and deletion
     – user admission
     – resource management

5 August 2011         SIP conferencing    28

				
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