A Survivable Core Server (SCS), formerly known as Enterprise Survivable Processor, provides geo-redundant Communication Manager Feature Server redundancy. It supports multiple Data Centers for a failed or unreachable main Communication Manager. Session Manager works with the SCS as follows:

• After the main Communication Manager goes down, Session Manager starts sending SIP messages to the SCS.

• When the main Communication Manager recovers, Session Manager again starts sending SIP messages to the main Communication Manager instead of the SCS.