Abstract: A call connection number management unit acquires the number of call connections. A server suspension control unit transfers a calling process allocated to a call control server selected based on the number of call connections for each of call control servers to the call control server, and suspends the call control server when the calling process allocated to the call control server ceases. An assignment control unit assigns a request to the call control server to which the calling process responding to the request has been transferred, when the call control server that has performed the calling process responding to the request is suspended. A prediction activation control unit calculates a change rate of an increase rate of the number of calls, obtains a prediction value of the number of calls based on the change rate, and when the prediction value exceeds a value, activates the suspended call control server.

Abstract: An IP version storage section included in the server stores an IP version implemented in the destination terminal under the control of the server. A message receiving section receives a message from the source terminal. An IP version acquisition section acquires the IP version implemented in the destination terminal corresponding to the message from the IP version storage section. An IP version comparison section compares an IP version which is implemented in the source terminal and which is included in the message with the IP version which is implemented in the destination terminal and which is acquired by the IP version acquisition section. A comparison result sending section sends a result of the comparison by the IP version comparison section to an address converter which makes an address conversion so that IP versions of data frames exchanged between the source terminal and the destination terminal will match.

Abstract: A server by which time taken to establish a session can be shortened by reducing the number of messages exchanged between a destination terminal and the server and by which the manufacturing costs of terminals can be reduced. An IP version storage section included in the server stores an IP version implemented in the destination terminal under the control of the server. A message receiving section receives a message for establishing a session between a source terminal and the destination terminal from the source terminal. An IP version acquisition section acquires the IP version implemented in the destination terminal corresponding to the message from the IP version storage section. An IP version comparison section compares an IP version which is implemented in the source terminal and which is included in the message with the IP version which is implemented in the destination terminal and which is acquired by the IP version acquisition section.