Abstract: A data communication system in which a data communication address for a communication terminal can arbitrarily be changed whenever the communication terminal is used. This data communication system includes a database 60 for storing a corresponding relation between an identifier 41 of a communication terminal 40 and a plurality of data communication addresses used for the communication. The database 60 stores a corresponding relation between the identifier 41 of the communication terminal and the data communication addresses during a period of use thereof in accordance with instructions from the communication terminal 40. When incoming data is received that is directed to certain data communication address, a network switching device 50 obtains an identifier corresponding to the certain data communication address and transmits the data to the communication terminal with the identifier.

Abstract: In order to provide a packet transfer scheme in which various data can easily be used commonly with other communication methods and a packet can be transferred at a high speed, a mobile communication system comprises a database (20) for storing an identification number of a mobile terminal (40) and location information indicating a zone in which the mobile terminal is currently located, a packet switch (10), and another packet switch (30) capable of communication when the mobile terminal (40) is located in a zone under the packet switch (30). The packet switch (10) inquires of the database (20) about the location information of the mobile terminal (40) when the packet switch (10) receives a packet addressed to the mobile terminal (40). When the mobile terminal (40) is located in the zone under the packet switch (30), the packet is transferred to the mobile terminal (40) through the packet switch (30).

Abstract: In a mobile communication system, a data communication fixed station 3 and a voice communication fixed station 4 control a common service area, the connection between a mobile station 5 and the data communication fixed station 3 can be quickened. The data communication fixed station 3 notifies, sequentially, the voice communication fixed station 4 of channel informations (e.g., usable channels, traffic quantity). The voice communication fixed station 4 receives the channel information via a broadcast channel for voice communication, and broadcasts the channel information to the mobile stations. When the mobile station 5 is to execute packet communication with an ISDN 1 via the data communication fixed station 3, the mobile station 5 selects an appropriate channel among the channels broadcasted thereto, and notifies the data communication fixed station 3 of the selected channel.