Telecommunications call preservation in the presence of control failure

In a telecommunications network, apparatus for providing reliable service for the control of the establishment of calls, comprising:

• means for receiving interoffice signaling messages related to a call, and for transmitting the received messages to a call processor;
• means for receiving interoffice signaling messages related to said call;
• a plurality of at least three call processors responsive to receipt of interoffice signaling messages for controlling establishment of calls, one of said call processors for controlling establishment of said call, and another of said call processors designated as a backup processor for said call;
• wherein said one call processor serves a plurality of calls and a plurality of processors serve as backup processors for different calls served by said one of said processors;
• means for detecting failure of the one call processor and for activating said backup processor for said call;
• means for transmitting only the stored interoffice signaling messages and not the call in process progress information to said backup processor;
• said backup processor, responsive to being activated, for processing the interoffice signaling messages stored prior to a detection of a failure of said one call processor in order to build up a call state for said call;
• said backup processor processing signaling messages received after the detection of said failure in order to continue the control of the establishment of said call;
• wherein said backup processor processes interoffice signaling messages received prior to detection of said failure only if a failure is detected.