MCU Call Establishment and Handling

The audio-video MCU does not support multiple points of conference, but does permit a given endpoint to join the audio-video MCU under more than one identity. To overcome the lack of support for multiple points of conference, the platform creates each new call under a fictitious identity. This topic discusses how the platform establishes these calls.

Fictitious Identity

The UseGeneratedIdentityForTrustedConference property on an AudioVideoCallEstablishOptions instance can be used to specify whether a fictitious identity is used when the call is established.

Temporary Focus Dialog

To dial into an MCU, an application sends a C3P addUser request (for more information, see [MS-CONFBAS]: Centralized Conference Control Protocol: Basic Architecture and Signaling Specification) to the MCU (by way of the Focus) declaring that a specific identity will be dialing into the MCU. After this action, the application sends a media-INVITE request. The Focus intercepts any media-INVITE request that is sent to confirm that the caller already has an active Focus dialog under the same identity.

For the media-INVITE request to succeed, the platform creates a temporary signaling dialog with the Focus under the fictitious identity. The temporary dialog is established for a trusted user, which means that the Focus and audio-video MCU endpoints for this fictitious identity do not appear in the user roster, as would normally be the case. The temporary dialog includes establishing a signaling session, but does not include a subscription.