Ims Conference Call

IMS Conference (IMS Conference Call)Calling UE IMS Network Called UECaller UserEquipment

IMS 1 IMS 1 MRF IMS 2 Called UserEquipment

ConferenceInitiator

InitiatingP-CSCF

InitiatingS-CSCF

MRFC-AS MRFP ParticipatingI-CSCF

ParticipatingS-CSCF

ParticipatingP-CSCF

ConferenceParticipant

EventStudio System Designer 4.0

18-May-08 10:40 (Page 1)

This sequence diagram was generated with EventStudio System Designer 4.0 (http://www.EventHelix.com/EventStudio). Copyright © 2008 EventHelix.com Inc. All Rights Reserved. TheEventStudio source files for this document can be downloaded from http://www.eventhelix.com/call-flow/ims-conference.zip.

This sequence diagram shows an IMS user creating a conference by using a conference-factory URI. The conference is created at a MRFC-AS of the users home network. The stepsinvolved in the conference scenario covered here are:

(1) The conference initiator UE uses the conference factory URI to initiate a conference with the MRFC-AS (Multimedia Resource Function Control/Application Server).

(2) The MRFC-AS assigns a conference URI to the conference and configures the MRFP (Multimeda Resource Function Processor).

(3) The conference call is setup and the RTP data begins flowing between the conference initiating UE and the MRFP.

(4) The conference initiator then uses the refer procedure to add more users to the conference. The new users establish a call to the conference URI passed in the refer message.

(5) When the conference is in progress, RTP media streams are being mixed and propagated to all the participants.

(6) The conference user drops out of the conference. All users are notified for this exit from the conference.

Initiating an IMS conference using the Conference Factory URI

Prepare a list of supportedvoice and video codecs

The Conference Caller includes allsupported codecs. This information isincluded as the first SDP offer in theinitial invite. The Conference Callersupports audio and video codecs.

INVITEINVITE Request URI:[email protected] SIP/2.0,To: [email protected]/2.0,From: <sip:[email protected]>,P-Preferred-Identity: <[email protected]>,Via: <Calling UE IP> :Port,Route: <P-CSCF address>, <S-CSCFaddress>,Contact: <Calling UE IP> :Port,SDP: <Caller Supported Codec List>

Conference Initiator UE is aware of aconference-factory URI due topre-configuration. When creating aconference, the Conference Callergenerates an initial INVITE requestwith its request URI set to conferencefactory URI.

100 Trying The P-CSCF responds to INVITE with100 Trying.

INVITE...,Via: <Calling UE IP> :Port, <Orig P-CSCF>,Route: <S-CSCF address>,Record-Route: <P-CSCF address>,...

The P-CSCF forwards the INVITErequest to the S-CSCF.

100 Trying The S-CSCF responds to INVITE with100 Trying.

INVITE...,Via: <Calling UE IP> :Port, <Orig P-CSCF>,<Orig S-CSCF>,Record-Route: <P-CSCF address>,<S-CSCF address>,...

The S-CSCF forwards the INVITErequest to the MRFC-AS that isindicated in the host part of theRequest URI.



ConferenceInitiator

InitiatingP-CSCF

InitiatingS-CSCF


ParticipatingS-CSCF

ParticipatingP-CSCF



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100 Trying The MRF responds to INVITE with100 Trying.

allocateConference URI

The MRFC-AS allocates a conferenceURI, based on local information andinformation gained from theconference-factory URI in the RequestURI field of INVITE message.

H.248 interaction to create IMS connection point forConference Initiator UE in MRFP and to determine media

capabilities of the MRFP.

Select MRFP

H.248 interactions to create conference connectionresources for Conference Initiator UE

183 Session Prog183 Session Prog183 Session Prog The media stream capabilities of theMRFP are returned along thesignalling path, in a 183 (SessionProgress) provisional response.

PRACK PRACK PRACK The Conference Initiator UEdetermines which media flows shouldbe used for this session, and whichcodecs should be used for each ofthose media flows. If there is anychange, Conference Caller sends anew codec request in PRACK.

H.248 interaction to modify connection MRFC-AS initiates H.248 interactionto modify the connection. It instructsthe MRFP to reserve multimediaresources for the negotiated codecs.

beginResource reservation for

conference session

200 OK (PRACK)200 OK (PRACK)200 OK (PRACK) The MRFC-AS acknowledges thePRACK request with a 200 (OK)response.

endResource reservation for

conference session

UPDATE UPDATE UPDATE When the resource reservation iscompleted, the Conference InitiatorUE sends the UPDATE requesttowards the MRFC-AS

200 OK (UPDATE)200 OK (UPDATE)200 OK (UPDATE) The MRFC-AS acknowledges theUPDATE with a 200 (OK) response.

H.248 interaction to through connect conferenceconnection resources for Conference Caller

MRFC initiates a H.248 interaction toconnect through the multimediaprocessing resources for Conference



ConferenceInitiator

InitiatingP-CSCF

InitiatingS-CSCF


ParticipatingS-CSCF

ParticipatingP-CSCF



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Caller in MRFP.200 OK (INVITE)

Contact: <sip:conf1 @mrfc1.home1. net>; isfocus

200 OK (INVITE)200 OK (INVITE) The MRFC-AS sends "200 OK" as afinal response to INVITE request.MRFC creates a focus for the newlycreated conference, assigns itconference URI and returns it inContact header. On receiving 200(OK) with isfocus parameter, theConference initiator stores theContact header content as theconference URI.

RTP Stream The Conference Initiator starts themedia flow for this session. The RTPdata stream is started towards theMRFP.

ACK ACK ACK The conference initiator responds tothe "200 OK" with an ACK towardsMRFC-AS.

User inviting another user to a conference by sending a REFER request

REFERRequest URI = <sip:user2_public1 @home2.net>,From = <sip: user1_public1@home1 .net>,To = <sip: user2_public1@home2 .net>,Route: <sip: pcscf1.visited1. net>, <sip:orig@scscf1 .home1 .net>,Refer-To: <sip: conf1@mrfc1 .home1 .net;method=INVITE>,Referred-By: <sip:[email protected]>

REFER Conference Caller creates aconference and then sends REFERmessage with Refer-To containing theconference URI as learned during theconference establishment.Additionally the "method" uriparameter indicates that the otheruser is requested to send an INVITErequest to this conference URI.

REFERRequest URI = <sip:[email protected]>,From = <sip:[email protected]>,To = <sip:[email protected]>,Refer-To: <sip:[email protected];method=INVITE>,Referred-By: <sip:[email protected]>

The originating S-CSCF performs ananalysis of the destination address,determines the terminating I-CSCFand forwards the REFER message toit.

REFER REFER REFER The terminating I-CSCF performs alocation query to the HSS to find outthe terminating S-CSCF and forwardsthe REFER request to that S-CSCF.

202 Accepted202 Accepted202 Accepted202 Accepted202 Accepted202 Accepetd The Called Conference Participantaccepts the REFER request bysending a 202 (Accepted) response.

NOTIFYNOTIFYNOTIFYTo: <sip:[email protected]>,From: <sip:[email protected]>,Subscription-State: active;expires:7200,Event: refer

NOTIFYNOTIFY The NOTIFY message is sent toinform that the REFER message isbeing processed.



ConferenceInitiator

InitiatingP-CSCF

InitiatingS-CSCF


ParticipatingS-CSCF

ParticipatingP-CSCF



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200 OK (NOTIFY) 200 OK (NOTIFY) 200 OK (NOTIFY) 200 OK (NOTIFY) 200 OK (NOTIFY) The "200 OK" Acknowledges theNOTIFY message.

Called Conference Participant enters Conference

INVITETo: [email protected]/2.0,From: <sip:[email protected]>,SDP: <Caller Supported Codec List>

Called Conference UE is aware of aconference-factory URI from REFER.

100 Trying

INVITE

100 Trying

INVITE The S-CSCF forwards the INVITErequest to the MRFC-AS that isindicated in the message.

100 Trying

H.248 interaction to create conference connectionresources for called conference participant UE.

183 Session Prog 183 Session Prog 183 Session Prog 183 Session Prog

PRACKPRACKPRACK

Allocate resources for negotiated codec

beginResource reservation for

conference session

200 OK (PRACK) 200 OK (PRACK) 200 OK (PRACK)

H.248 interaction to modify conference connectionresources for Called Conference Participant UE

endResource reservation for

conference session

UPDATEUPDATEUPDATE

200 OK (UPDATE) 200 OK (UPDATE) 200 OK (UPDATE)

H.248 interaction to through connect conferenceconnection resources for Called Conference Participant

200 OK (INVITE) 200 OK (INVITE) 200 OK (INVITE)



ConferenceInitiator

InitiatingP-CSCF

InitiatingS-CSCF


ParticipatingS-CSCF

ParticipatingP-CSCF



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RTP Stream

ACKACKACK

Notify Conference Initiator that the user has successfully entered the conference

NOTIFYNOTIFYNOTIFYTo: <sip:[email protected]>,From: <sip:[email protected]>,Subscription-State: terminated,Event: refer

NOTIFYNOTIFY

200 OK (NOTIFY) 200 OK (NOTIFY) 200 OK (NOTIFY) 200 OK (NOTIFY) 200 OK (NOTIFY)

Conference in progress

RTP Stream RTP Stream The conference is now in progress.The MRFP is merging and distributingthe media stream for the conference.

Conference Caller leaving the Conference

BYERequest URI: sip:[email protected],From: <sip:[email protected]>,To: <sip:[email protected]>

The Called Conference Participantwants to leave the conference. Forthis purpose it sends a BYE messageto the P-CSCF with theConference-URI as the Request-URI.

Remove resource reservation forConference

Indicate GPRS to release IP Bearersfor the Conference Call

BYEBYERequest URI: sip:[email protected],From: <sip:[email protected]>,To: <sip:[email protected]>

H.248 interaction to release resources The MRFC-AS interacts with theMRFP to release the resourcesreserved for Conference Caller in thisconference.

200 OK (BYE) 200 OK (BYE) 200 OK (BYE)

NOTIFYTo: <sip: user3_public1 @home1.net>,From: <sip: conf1@mrfc1 .home1.net>,Subscription -State: terminated,Event: conference,Conference status information of all conference participants

NOTIFY NOTIFY The MRFC-AS generates a NOTIFYrequest to indicate that CalledConference Participant has left theconference and automaticallyunsubscribes it from its subscriptionto the conference event package.

Notify other Conference participantsthat Called Conference Participant has

left conference

MRFC-AS similarly notifies otherconference participants that havesubscribed to the conference eventpackage that Called Conference



ConferenceInitiator

InitiatingP-CSCF

InitiatingS-CSCF


ParticipatingS-CSCF

ParticipatingP-CSCF



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Participant has left the conference.200 OK (NOTIFY)200 OK (NOTIFY)200 OK (NOTIFY)

NOTIFYTo: <sip:[email protected]>,From: <sip:[email protected]>,Subscription -State:terminated,Event: conference,Conference statusinformation of all conferenceparticipants

NOTIFYNOTIFY The conference initiator is alsonotified about a user dropping out ofthe conference.

200 OK (NOTIFY) 200 OK (NOTIFY) 200 OK (NOTIFY)

Documents

Ims Conference Call