| 摘要 |
A mobile communications handset (12) is capable of connection through two different networks (2, 27). When it is out of contact with its preferred local wireless access system (27), the handset will seek a hand-over to the cellular network (2), and will become registered as a "roaming" handset currently connected to the cellular network (2). The cellular network (2) reports this location information to the call server (28), as it would to the HLR of any normal visiting handset, so that incoming calls to the PSTN (6) destined for the user (12) can be routed by way of the cellular network. Outgoing calls are handled as conventional cellular telephony calls. When contact with a local wireless access system (27) is re-established, the contact information is passed to the call server 28, which reports to the cellular network (2) that a handover has occurred. An interface between the call server (28) and cellular network (2) is configured such that the call server (28) emulates a base site controller of the cellular network (2). The cellular network therefore operates conventionally, with the handset (12) logged as operating through this quasi-base site controller. However, the cellular system would continue to register the presence of the handset as co-operating with the quasi-base station (28), even though it would have no visibility of most calls being made to and from the handset (12). This avoids the cellular system (2) attempting to seize control of the handset through a normal cellular base station (21).
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