There are a variety of systems that can fail over a communication from a primary network to a secondary network. This works well when there is a single centralized system in the network that manages all aspects of the communication system. When the primary network fails, the centralized system is able to route a communication to the secondary network without any problems.
However, when the network has been decentralized, the problem becomes more acute. In distributed networks such as Session Initiation Protocol (SIP) networks, functionality has been distributed between devices such as proxy servers and other communication systems. For example, a proxy server may handle the initial call processing and another communication system will handle call features, such as call forwarding (e.g., by using a Back-to-Back User Agent (B2B UA)). In these distributed environments, the proxy server and the other communication system need to be included in the process of directing the communication to a secondary network so that the call features can still operate in a failover situation.