Patent ID: 7940780

Claim:
A data communication system, comprising: a first communications device; a second communications device; a session management server that manages a session whereby the first and second communications devices conduct data communication; and one or more function-providing servers that provide functions required for establishing the session, wherein: when a request message requesting the establishment of a session with the second communications device is received from the first communications device, the session management server executes, in parallel: (a) a process of forwarding the request message to the second communications device and then waiting for a response, and (b) a process of issuing a request that the one or more function-providing servers execute a process required for establishing the session and then waiting for a response, the session management server selects subsequent processes depending on the contents of responses or difference in the timing for receiving the responses, and if a message denying provision of a service from the second communications device to the first communications device is received from the one or more function-providing servers before a response message with respect to the request message is received from the second communications device, then the session management server transmits a cancel message canceling the session establishment request that was transmitted to the second communications device, and a cancel message canceling the request, whose result has not yet been received, that the one or more function-providing servers execute the process required for establishing the session to the one or more function-providing servers.