Patent ID: 8127027

Claim:
A telephone system which comprises a plurality of terminal devices configured to process a signaling protocol, and a server which transmits and receives signals using a first transfer protocol or a second transfer protocol as a lower layer protocol to form a session of the signaling protocol, wherein each of the plurality of terminal devices comprises: a request processor configured to transmit a request signal to form the session using the first transfer protocol, and wherein the server comprises: a determination module configured to determine whether or not the first transfer protocol is available for transmitting signals; a session forming module configured to form a session with a request source by setting a transfer protocol to either (i) the first transfer protocol when the determination module determines that use of the first transfer protocol is available or (ii) the second transfer protocol; a switching module configured to switch, when a communication using the first transfer protocol becomes available turns, the lower layer protocol of the communication with the terminal device using the second transfer protocol from the second transfer protocol to the first transfer protocol while maintaining the session already formed in the signaling protocol; and a storage device comprises a management table which assigns a session formation priority using the first transfer protocol to each terminal device; wherein the determination module (i) confirms, by referring to the management table when the request signal from the terminal device arrives, the presence or absence of a terminal device having a lower session formation priority than the terminal device as the request source and using the first transfer protocol, (ii) instructs the switching module to change the lower layer protocol of a session already formed with the terminal device having the lower session formation priority than the terminal device as the request source from the first transfer protocol to the second transfer protocol, and (iii) grants permission to the request signal from the terminal device as the request source when a resource is assured after the lower layer protocol is changed.