Conference Recovery
Microsoft Unified Communications Managed API (UCMA) 3.0 provides three levels of support for conference recovery to applications.
Focus Front-End failover
When UCMA 3.0 detects that the Focus has failed over to another Front End server, the ConferenceSession state changes to Reconnecting. The state of any active McuSession subclass instance changes to the Retrying state. Note that any calls connected to the MCUs are not disconnected.
After failover is detected, pending conference operations fail immediately with an OperationFailureException with FailureReason set to SessionRetrying. Any BeginXxx method invoked on the ConferenceSession or an McuSession subclass fails with a RealTimeInvalidOperationException with FailureReason set to RetryableOperation.
The ConferenceSession attempts to reconnect to the conference only once. If that attempt fails, the ConferenceSession is terminated, otherwise the state of the ConferenceSession is again changed to the Connected state. A fresh roster notification is sent and events are raised for any changes that occur during the reconnection process. The state of the McuSession subclass changes again to active when the MCUs are reported to be activated on the server.
MCU failover
During conference activation, an MCU can failover to another Front End server. The corresponding McuSession state is changed to Retrying and the call with the MCU is terminated. The application can reestablish the call after the MCU becomes active again.
Intermediate Hop failover
If an intermediate hop fails when a conference command is sent, UCMA 3.0 attempts to repair the route automatically. If the initial recovery attempt fails, the ConferenceSession instance enters the Reconnecting state. In this state, conferencing or MCU control commands and instant messages might fail. Other media such as audio, which do not travel over the signaling path, might still continue to work. The session will actively try to heal the route by periodically sending UPDATE messages. If healing succeeds, the ConferenceSession state will transition to the Connected or InLobby state. Because the ConferenceSession does not leave the Reconnecting state unless route healing succeeds, the application should implement timers or use other criteria such as media termination to determine when to terminate the ConferenceSession if recovery takes too long.