With the Call Preservation feature, the dialog context of the SIP user agent can survive a Session Manager failure even when the Session Manager context is lost. The dialog continues with end-to-end signaling of the intact user agent through an alternate Session Manager. The Call Preservation feature is available for SIP Routing Element (SRE) flows.

For the Call Preservation, a Session Manager Failover Group comprising a pair of Session Manager servers is associated with peer entities. The peer entities, such as Avaya SBC, use enhanced SIP timing and recovery techniques to provide signaling path continuity during Session Manager failure. When Avaya SBC detects that a Session Manager is unreachable, it uses the Failover Group Domain Name (FGDN) in the Session Manager through and Record-route headers to route the SIP traffic through the alternate Session Manager. The FGDN is a fully qualified domain name (FQDN) that resolves to an ordered set of Session Manager servers within a Session Manager Failover Group that provides a high availability SRE service. When the preferred Session Manager becomes unresponsive, the peer SIP entity uses the Session Manager Failover Group Domain resolution to identify and communicate with the alternate Session Manager.

Avaya SBC supports the following features of Call Preservation: