| 摘要 |
Wireless calls to a private branch exchange (PBX) which does not support direct inward dialing-either due to limitations of the PBX itself or due to limitations of the PSTN to which the PBX is connected-are routed by means of an adjunct mobile switching center (MSC-A). An originating mobile switching center (MSC-O) serving the mobile unit which places the call by dialing the (typically) three- or four-digit PBX extension sends the dialed extension digits to the home location register (HLR) or service control point (SCP) via an ANSI-41 origination request (ORREQ) signaling message. The HLR or SCP transmits an ANSI-41 routing request (ROUTREQ) signaling message to the MSC-A requesting a temporary local directory number which will be used for connecting the call. The HLR relays the PBX extension number (which may be prefixed by "steering" digits that are used by the MSC-A to select the trunk group that connects the MSC-A to the PBX) that were received in the ORREQ message to the MSC-A via the ROUTREQ message. The MSC-A assigns a TLDN to the call and, when the call arrives, connects the call to the PBX and sends the extension to the PBX via trunk signaling. The PBX then routes the call in accordance with known methods. The invention thus allows a mobile unit to function as a PBX extension even if the PBX or the public telephone switch to which the PBX is connected to do not support direct inward dialing, providing virtual private network services.
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