In case of a communication between the host 1406 and the PPP peer 1402, the host 1406 executes communication through a model 1405 while the PPP peer 1402 executes communication through a model 1403. [0165] In the present embodiment, there will be explained a configuration employing a modem and a PSTN as an example, but, the situation is basically same in other forms of communication such as a PHS