3.11 Conference Control – addUser Dial-in Command Details


The addUser dial-in command is used to connect a participant to an MCU. This section specifies the basic addUser dial-in behavior to which all client, focus, and MCU implementations adhere.

The addUser dial-in protocol sequence is shown in the following figure.

addUser Dial-in call flow

Figure 11: addUser Dial-in call flow

In the preceding figure, the client sends an addUser dial-in request, over SIP INFO, to the focus. The focus authorizes it and then forwards it to the MCU. This is shown in steps 1a and 1b.

The MCU processes the addUser dial-in request and then responds with an addUser dial-in response to the focus, which is forwarded by the focus to the client, as shown in steps 1c and 1d.

Subsequent to processing the addUser dial-in response, the client establishes a session with the MCU. The figure titled "addUser Dial-in call flow" assumes a SIP-based MCU. Thus, in step 2a, the client sends an INVITE request to the MCU. This specification does not specify the actual contents of the SIP request body. Extensions to this specification can define the actual contents, such as the SDP format. The MCU accepts the INVITE request, processes the request, and then responds to it in step 2b.

At this point, the client and the MCU might negotiate media. Extensions to this specification can define how media negotiation is done.

At the end of media negotiation, the MCU notifies the focus that the user has connected, as shown in step 3a, which in turn is propagated to all conference watchers, as shown in step 3b.

The dial-in request can be sent by the client or by the focus itself to the MCU. It specifies the user who is attempting to join the MCU. The dial-in response indicates whether the MCU is prepared to accept the user's join request and also conveys extra information necessary to attempt the join. The dial-in request is followed by a client-to-MCU-specific signaling handshake such as an INVITE. This is a user level command.

The MCU MAY fail the addUser dial-in request if it has not indicated successful activation, for example by publishing its entity-view element in the conference document. MCU implementers can specify extensions to the addUser dial-in protocol.

Unless specified otherwise, the protocol details specified in section 3.5 SHOULD be used for command processing.

Detailed command call flows are given in section 4.