Patent ID: 7639676

Claim:
A SIP (Session Initiation Protocol) server for connecting a call between terminals by relaying transfer of call control signals between the terminals, comprising: a call processing memory for storing call control data indicating a call state for each activated call, said call control data including a call duration time of each activated call; an external storage device including a save area for storing the call control data, said external storage device being configured to perform a mutual reference with the call processing memory; saving means for selecting one of busy calls whose call control data is stored in the call processing memory, and saving the call control data for the selected busy call from the call processing memory to the external storage device; and restoring means for restoring the saved call control data to the call processing memory when a call disconnect event is received for the call whose call control data is saved in the external storage device; wherein said saving means is configured to: (I) decide as to whether there is a need to save the call control data is order to accept a new call, (II) check if free space is available in the external storage device, (III) check if there is a call whose state is busy in the call processing memory, and (IV) save the call control data relating to the busy call in said save area.