Patent ID: 8001095

Claim:
A version update method for updating a version of a communication system application program installed in a plurality of terminals connected to a communication network and operating between at least two terminals, the version update method comprising: starting communications between a first terminal and a second terminal of the plurality of terminals; exchanging version information of the communication system application program between the first terminal and the second terminal and making a comparison between the version information held in the first terminal and the version information held in the second terminal; starting the communication system application program with a version common to the first terminal and the second terminal among the versions held in the first terminal and the second terminal and executing the communication system application program; making a request for a communication system application program file of a version not held in one of the first terminal and the second terminal, after the executing of the communication system application program; and transmitting the requested communication system application program file to the one of the first terminal and the second terminal making the request.