| 摘要 |
An interface (52) is provided between a satellite telephone system (4) and a cellular telephone system (5) for allowing calls to a user's cellular telephone to be diverted to a satellite telephone handset (25) when the user is unable to use his cellular telephone, for example when on board an aircraft (2) fitted with a satellite telephone system (20). The user inserts a card (which may be the SIM of his mobile phone, or a card compatible with existing satellite telephone equipment) into a suitable reader in the satellite telephone (20), which causes the satellite ground station's card verification system (42) to connect to a host cellular network (50). The host cellular network has an interface unit (520) which emulates the operation of a normal base station, so that the host cellular system (50) acts as if the mobile user's terminal is roaming on the host network, but is currently "busy". The interface (52) also resets the user's existing call diversion instructions so that when the host cellular system (5) receives a busy tone from the base station emulator (52), it routes calls to the directory number of the terminal (20). In order to allow the host network to retrieve the user's handset identity (IMSI), it makes use of a process by which data relating to a user having an identification code of a first type (the directory number) can be used to access a register in which identification codes of the first type are related to identification codes of the second type (the IMSI), and receiving from the register, in response to the signal, a code of the second type, so that location update information can then be transmitted to an associated switching system in respect of the identification code of the second type. |
