With VoIP and cloud communications being fast developed and widely used, enterprises are able to deploy the telephone solution based on distributed PBX communications or cloud/hosted communications networks at a lower cost. To prevent the interruption of calling and call-related services when headquarters server or cloud/hosted server disconnects, Redstone EGW series survivability appliances are designed to be deployed at local offices or branches to handle the calls instead of the disconnected server. After connection recovers, the calling services will be switched to the headquarters server or cloud/hosted server again.