This appINVITEmechanism can be used with new clients that support the app INVITE and the new C3P protocol. However, legacy clients can also be invited to conferences. To invite a legacy client to a conference, the client sends an addUserdial-out to another client.

The following figure shows the message flow between conferencing components when a client adds a participant to a conference using a C3P addUserdial-out command.

Client joining media with A/V Conferencing Server using addUser dial-out

The following is a description of the message flow between conferencing components when a client adds a participant to the conference using an addUserdial-out command:

Step 1.The client sends an INFO request addUserdial-out command to the Focus. The client uses the focus/conference URI it received in the notification document.

Step 2.The Focus determines if a conferencing server has been assigned to support this particular media type for this conference. If a conferencing server has not been assigned, the Focus sends an HTTP request to the Conferencing Server Factory asking it to allocate a conferencing server for this conference. In the diagram, it is assumed that the conferencing server has been assigned to the conference. The Focus then sends an HTTP request to the designated conferencing server asking it to dial out to the user. Any bootstrapping requests that the Focus sends to initialize the conference on the conferencing server are not included in the call flow diagram.

Step 3.The conferencing server dials out an INVITE to the client using an outbound SIP proxy, which is usually running on the same server as the Focus.

Step 4.The client directly establishes a RTP media channel with the conferencing server.

Step 5.After the client successfully joins the conferencing server, it sends a participant joined event to the Focus.

Step 6.The Focus sends a participant joined conferencing server state change notification to all clients subscribed to the conference state.