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: The number of simultaneous connections to a SIP server is increased without degrading overall performance. If it is judged that, when a newly requested call is accepted, the number of calls whose call control data is stored in a call processing memory or the amount of the call control data stored in the call processing memory would exceed an upper limit, the call control data stored in the call processing memory for a busy call is saved in an external storage device. As the frequency of occurrence of an event is low in the case of a busy call, it becomes possible to accept the new call without degrading overall performance.

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.

Abstract: The number of simultaneous connections to a SIP server is increased without degrading overall performance. If it is judged that, when a newly requested call is accepted, the number of calls whose call control data is stored in a call processing memory or the amount of the call control data stored in the call processing memory would exceed an upper limit, the call control data stored in the call processing memory for a busy call is saved in an external storage device. As the frequency of occurrence of an event is low in the case of a busy call, it becomes possible to accept the new call without degrading overall performance.