Clients can join a conference by sending a direct media INVITE. This method can only be used with conferencing servers that use SIP to establish sessions, such as the A/V Conferencing Server and the IM Conferencing Server. A media INVITE is an INVITE where the To:line contains the conferencing server URI.

A client can send the media session INVITE to the conferencing server URI directly, without any prior addUsercall. The INVITE is routed to the Focus. The Focus checks if the connection information is a routable SIP address and forwards the INVITE directly to the conferencing server. The Focus also sends the addUsercommand to the conferencing server on the client's behalf. The conferencing server authorizes the request and responds with the connection information.

The following figure shows the message flow between conferencing components when a client joins a conference by sending a direct media INVITE.

Client sending the media session INVITE to the conferencing server directly

* The BENOTIFY is sent to all clients subscribed to the conference state.

The following is a description of the message flow between conferencing components when a client joins a conference by sending the media session INVITE to the conferencing server URI directly:

Step 1.The client sends an INVITE to the focus/conference URI it received in the notification document. This INVITE is routed to the focus. The client might have included a session description for media negotiation. Since the focus recognizes that the INVITE was addressed to a particular conferencing server, it safely ignores any session description in the body of the INVITE.

Step 2.The Focus then sends an HTTP request to the conferencing server assigned by the Conferencing Server Factory to this conference asking it to expect a new participant ( addUser). Any bootstrapping requests that the Focus sends to initialize the conference on the conferencing server are not included in the call flow diagram.

Step 2.1.The conferencing server sends a successful response for the addUsercall. The response includes the actual URL that it wants the participant to use to communicate with the conferencing server. If the server sending the response is an A/V Conferencing Server, the URL indicates that the participant can communicate with the conferencing server using SIP.

Step 1.1.After the Focus receives the successful response for the addUserrequest, the Focus forwards the INVITE to the A/V Conferencing Server.

Step 1.2.The conferencing server sends a successful response to the client.

Step 1.3.The client sends an ACK to the conferencing server to complete the INVITE dialog. The same INVITE dialog is also used for media negotiation with the conferencing server.

Note:

Although the client establishes the INVITE dialog directly with the conferencing server, the SIP requests traverse the Focus.

Step 3.After the client successfully joins the conferencing server, it sends a participant joined event to the Focus.

Step 4.The Focus sends a participant joined conferencing server state change notification to all clients subscribed to the conference state.

Step 5.Direct media negotiation occurs between the client and the conferencing server. With an A/V Conferencing Server, the media are RTP/RTCP streams.