Abstract:
A call routing number for a mobile station operating in a wireless telecommunication system is obtained by first requesting a temporary routing number for use in routing a call to the mobile station. Provided in response to the request is a routing number that had already been assigned to the mobile station when the request was received.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to setup and routing of calls in a wireless telecommunications system and, more particularly, to management of temporary routing numbers used to route calls. 
     BACKGROUND OF THE INVENTION 
     FIG. 1 illustrates a known wireless telecommunications system wherein a public switched telephone network PSTN, a public land mobile network PLMN (e.g., AMPS, GSM, PDC) and a private wireless (e.g, cellular) network are interfaced with one another. A Gateway mobile switching center GMSC of the PLMN is coupled to the PSTN for communication therewith, and is also coupled to a home location register HLR of the PLMN. The PSTN is coupled for communication with the private network, as is the HLR of the PLMN. 
     The private network includes a so-called Wireless Office System WOS which is coupled to the HLR. The WOS provides a mobile extension of the wired communication systems used in office environments. Typical workspaces which can benefit from WOS technology include corporate campuses, health care facilities, manufacturing facilities, hotel chains, retail stores, etc. The WOS interfaces with HLR during call setup in the same manner as would a conventional mobile switching center (MSC). 
     A local exchange LE of the PSTN communicates with the WOS via a private branch exchange PBX in the private network. In some systems, the functionality of the private branch exchange PBX is included in the WOS, so the local exchange LE of the PSTN communicates directly with the WOS, as indicated diagrammatically by the broken line connection in FIG.  1 . FIG. 1 shows mobile stations (mobile subscriber units) MS 1  and MS 2  registered and operating in the WOS. The WOS provides basic wireless telephone services in addition to the PBX services offered by private networks. The WOS does not generally provide its services to PLMN subscribers roaming in the WOS coverage area. 
     The communications between the HLR and the GMSC at  12 , and between the HLR and the WOS at  14  can be carried out, for example, using the IS- 41  protocol of the D-AMPS standard, or the MAP protocol used in GSM systems. The communications links at  16 ,  17  and  18  in the PSTN can be, for example, R 2  or ISDN based. 
     Referring now also to FIG. 2, when a call to a mobile station registered in the WOS is received at  21  in the GMSC, a location request is sent at  23  from the GMSC to the HLR. The HLR then makes a routing request at  25  to the WOS to obtain therefrom a temporary routing number at  27 , which the HLR relays back to the GMSC at  29 . 
     In the setup request  21  received in the GMSC, a mobile directory number MDN (i.e., the published directory number) associated with the called mobile station is included, and the GMSC relays this mobile directory number MDN in the location request  23  to the HLR. The HLR translates the MDN to a mobile identification number MIN (each mobile station has a unique MIN conventionally coded therein), and then includes this mobile identification number MIN in the routing request  25  to the WOS. The WOS then responds just like a conventional visited MSC (VMSC), namely, it assigns a temporary local directory number TLDN to be used in routing the call. The WOS sends the TLDN to the HLR at  27  (just as a conventional VMSC would), and HLR relays the TLDN to the GMSC at  29 . This sequence is well known in the art. 
     Then, as shown in FIG. 3, the GMSC uses the TLDN to route the call through the PSTN and access the WOS from the nearest local exchange LE. The Transit block illustrated in FIG.  1  and also designated in FIG. 3 represents a conventional routing path from GMSC through PSTN to the local exchange LE nearest the WOS. The routing path represented by the Transit block can include, for example, a plurality of conventional exchanges or switches in the PSTN. 
     FIG. 4 illustrates a routing handler  41  in the WOS of FIG. 1 (or in a conventional VMSC). The routing handler receives the mobile identification number MIN from HLR, and provides to HLR the temporary local directory number TLDN from a pool of TLDNs allocated to the WOS by the PSTN operator. The TLDNs are part of the public number series issued by the PSTN operator. Thus, if the WOS requires additional TLDNs due, for example, to heavy traffic conditions, such new TLDNs must disadvantageously be issued by the local PSTN operator. Also, the TLDNs are typically allocated for only a short period of time (e.g., 30 seconds) so that, if the GMSC does not use the allocated TLDN to route a particular call, (e.g., caller hangs up), the TLDN will be freed for use in other calls. This feature minimizes the size of the TLDN pool that is required, but disadvantageously requires the routing handler  41  to implement a timer/time-out function. 
     According to the present invention, a private network such as (or including) a WOS provides to the PLMN direct in-dialing numbers in place of temporary routing numbers, and thus advantageously requires significantly less resources to manage temporary routing numbers than does the prior art arrangement. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates a known telecommunications system in which the present invention may be implemented. 
     FIG. 2 is a sequence diagram illustrating steps performed to obtain a temporary routing number in the system of FIG.  1 . 
     FIG. 3 is a sequence diagram illustrating a call routing procedure executed in the system of FIG.  1 . 
     FIG. 4 illustrates a conventional routing handler of the conventional wireless office system of FIG.  1 . 
     FIG. 5 is a sequence diagram illustrating steps performed to obtain a routing number according to the present invention. 
     FIG. 6 is a sequence diagram illustrating call routing according to the present invention. 
     FIG. 7 illustrates a routing handler according to the present invention for use in a wireless office system. 
     FIG. 8 illustrates in more detail a portion of the converter of FIG.  7 . 
     FIG. 9 is a flow diagram illustrating exemplary operations of the routing handler of FIG.  7 . 
    
    
     DETAILED DESCRIPTION 
     The present invention utilizes the fact that mobile stations registered in private networks such as the WOS of FIG. 1 are each typically assigned a direct in-dialing (DID) number. The DID number can be assigned, for example, by the PSTN operator, and is used to dial the mobile station directly through PSTN without the need to contact an operator or answering service to direct the call to the correct number. As shown in the example of FIG. 5, according to the invention, when the WOS receives from HLR a routing request  51  including MIN, the WOS responds at  53  by sending back to HLR the DID of the mobile station identified by the MIN, rather than sending the HLR a TLDN. The HLR then relays the DID number to the GMSC at  55 . As shown in the example of FIG. 6, the GMSC then uses the DID number to route the call through the PSTN to the WOS. 
     FIG. 7 illustrates an exemplary routing handler  71  which can, according to the invention, be implemented in the WOS of FIG. 1 to provide the DID number to HLR in response to receiving the MIN in the routing request from HLR. The routing handler  71  includes a MIN-to-DID converter  73  coupled between the input  75  thereof and the output  77  thereof. FIG. 7 also indicates that the routing handler  71  may provide a TLDN to HLR in the event that a DID number does not exist for a particular mobile station registered in the WOS. In such cases, the call is set up and routed as shown in FIGS. 2 and 3. 
     FIG. 8 illustrates an example of how the MIN-to-DID converter  73  can map MINs into DID numbers, namely a lookup table  81  stored in a suitable memory apparatus  83  in the converter  73 . In the lookup table, the DID numbers DID 1 , DID 2 , etc. assigned to the mobile stations by the PSTN operator are indexed against the MINs that identify the respective mobile stations. As one example, if the MIN received from HLR is MIN 2 , then the lookup table of FIG. 8 indicates that the mobile station identified by the mobile identification number MIN 2  (e.g., mobile station MS 2  of FIG. 1) has a corresponding DID number of DID 2 . Thus, DID 2  would be returned to HLR in response to the MIN 2  routing request. The lookup table is easily updated as new DID numbers are assigned to new mobile stations in the WOS. 
     Because nearly all mobile stations registered in the WOS can be expected to have assigned thereto a DID number, the routing handler  71  of FIG. 7 will rarely need to access a TLDN pool and output a TLDN in response to a routing request from HLR. Therefore, requests for the PSTN operator to issue a new TLDN will be even more rare. Thus, issuance of new TLDNs by the PSTN operator will be significantly less frequent than in the prior art, and the PSTN operator&#39;s charges for the new TLDNs will be incurred much less frequently than in the prior art. 
     FIG. 9 illustrates exemplary operations of the routing handler  71  of FIG.  7 . When a routing request with MIN is received at  91 , it is thereafter determined at  93  whether the mobile station identified by the MIN has a DID number assigned thereto. If not, then at  95 , the routing handler  71  obtains in conventional fashion a TLDN to be used in routing the call. Thereafter at  99 , the routing handler  71  sends to the HLR a message including the TLDN. 
     If the mobile station identified by the MIN has a DID number already assigned thereto, then at  97  the routing handler  71  maps the MIN into a DID number (e.g., obtains the DID number from the memory table of FIG.  8 ), and thereafter at  99  sends a message to HLR including the DID number. After the message is sent at  99 , the next routing request/MIN is awaited at  91 . 
     It can be seen from the foregoing description that the present invention greatly simplifies the operation of the routing handling function in a Wireless Office System or other private network arrangement whose registered mobile stations already have DID numbers assigned thereto. The routing handling function of the present invention provides, in response to a request for a temporary routing number, a direct in-dialing number that has already been assigned previously to that mobile station by, for example, the PSTN operator. 
     It will be evident to workers in the art that the embodiments of FIGS. 4-9 can be readily implemented in software, hardware, or a combination of software and hardware, in a suitable data processing circuit portion of the routing handler of a prior art WOS or VMSC. 
     Although exemplary embodiments of the present invention have been described above in detail, this does not limit the scope of the invention, which can be practiced in a variety of embodiments.