Abstract:
A wireless communications system provides call transfer capability for an incoming call to a mobile subscriber unit. The mobile subscriber unit requests the call transfer to a serving MSC. The serving MSC relays the request to a home location register, and the home location register executes the request by initiating the call transfer in conjunction with an originating MSC. This arrangement obviates the need for supporting call transfer on the serving MSC and the need for inter-MSC facilities once the call transfer is completed. Moreover, the approach of the present invention enables call transfer to be ubiquitously supported within a wireless communications system.

Description:
FIELD OF THE INVENTION 
     This invention relates to a wireless communications system providing call transfer for an incoming call to a mobile subscriber unit. 
     BACKGROUND OF THE INVENTION 
     Wireless communications systems attempt to provide telephone services to mobile subscribers that are equivalent to traditional landline telephone networks. This objective is complicated by the fact that mobile subscribers may roam away from their home market. Different wireless markets may utilize different manufacturer&#39;s equipment. Consequently, mobile subscribers may not be able to use wireless features offered in their home markets if the serving markets do not support the features. 
     As an example, “call transfer” is a common landline telephone service in which a subscriber can transfer an incoming call to another designated telephone party. However, this service is not always available in a wireless communications system. Not all mobile switching centers (MSC), which provides the switching functionality of a wireless communications system, support call transfer. If an incoming call is delivered to the mobile subscriber&#39;s home market that supports call transfer and the mobile subscriber has roamed to another (serving) market, call transfer may not be available to the mobile subscriber. Moreover, even if call transfer is supported by the plurality of MSC&#39;s which an incoming call spans, the prior art requires that inter-MSC telephone facilities be configured between the MSC&#39;s. Having to support these facilities increases the cost to the wireless service provider, thus increasing the price of service to the wireless subscriber. Thus, there is an important need to provide ubiquitous call transfer to the wireless subscriber. 
     FIG. 1 illustrates an architecture supported by a wireless communications system that supports an incoming call to a mobile subscriber unit associated with a wireless subscriber in accordance with prior art. In FIG. 1, an incoming call originates from public switching telephone network (PSTN)  100  for mobile subscriber unit  105 . The incoming call is delivered to originating mobile switching center (“originating” MSC)  101  (in which mobile subscriber unit  105  may or may not be located) through telephone facility  106 . Typically, mobile subscriber unit  105  is provisioned (homed) at originating MSC  101 , and PSTN  100  delivers all incoming calls to originating MSC  101 . 
     If mobile subscriber unit  105  is not located within a region served by originating MSC  101 , the incoming call must be delivered to serving mobile switching center (serving MSC)  103  in which mobile subscriber unit  105  is located. Originating MSC  101  determines where mobile subscriber unit is located by querying home location register (HLR)  102  using data facility  107 . Whenever mobile subscriber unit  105  changes locations so that it is located in a region of a different serving MSC, HLR  102  is updated with the updated location through data facility  109 . HLR  102  may be physically separate entity or may be physically located at originated MSC  101 . The incoming call is delivered to serving MSC  103  through inter-mobile switching center (inter-MSC) facility  108 . Serving MSC  103  connects the incoming call through base station  104  (where mobile subscriber unit is currently located) over trunk  110 . Base station  104  establishes radio connection  111  to mobile subscriber unit  105 , thus completing the incoming call between PSTN  100  and mobile subscriber unit  105 . The telephone path of the incoming call consists of telephone facility  106 , inter-MSC facility  108 , trunk  110 , and radio connection  111 . Since the telephone path is completed at serving MSC  103 , if serving MSC  103  is situated in a billing zone that is associated with long-distance rates, the party initiating the incoming call may be charged at a long-distance rate even though the designated party to which the call was transferred is not in a billing zone that is charged at a long distance rate. 
     FIG. 2 presents a message flow for transferring an incoming call (from PSTN  100 ) by mobile subscriber  105  to a designated party served by PSTN  100  in accordance with prior art. PSTN  100  uses telephone facility  206  to deliver the incoming call to originating MSC  101 . Originating MSC  101  queries HLR  102  by sending LOCREQ message  207  in order to determine the current location of mobile subscriber  105  to route the call to the appropriate serving MSC  103 . (Message  207  is specified in American National Standards Institute ANSI-41.) Message  207  includes a BILLID parameter equal to O-CALLID to identify the call identification as assigned by originating MSC  101 . Consequently, HLR  102  sends ROUTREQ message  208  (specified in ANSI-41) to serving MSC  103  to determine the preferred method of routing the incoming call to serving MSC  103 . Message  208  contains the BILLID parameter equal to O-CALLID. Serving MSC  103  returns this information using routreq message  209  (specified in ANSI-41). Message  209  contains the BILLID parameter equal to S-CALLID, which is the call identification assigned by serving MSC  103 . Consequently, HLR  102  is able to relate the call identification assigned by originating MSC  101  (O-CALLID) with the call identification assigned by serving MSC  103  (S-CALLID) of the incoming call. Serving MSC  103  establishes a trunk to base station  104 , in which the mobile is located, in preparation for supporting the incoming call. Base station  104  consequently establishes radio connection  212  to mobile subscriber unit  105 . 
     HLR  102  returns the location of mobile subscriber unit  105  to originating MSC  101  by sending locreq message  211  (specified in ANSI-41). Message  211  contains the BILLID parameter equal to S-CALLID. Originating MSC  101  then establishes a connection to serving MSC  103  through inter-MSC facility  213 . Inter-MSC facility  213  corresponds to inter-MSC facility  108  in FIG.  1 . At this point of time, the incoming call to mobile subscriber unit  105  has been completed. 
     If mobile subscriber unit  105  wishes to transfer the incoming call to a designated party (and consequently causing mobile subscriber unit  105  to be disconnected from the call), mobile subscriber unit sends call transfer request message  214  to base station  104 . Message  214  is dependent upon the air interface technology, e.g. Advanced Mobile Phone Service (AMPS), Time Division Multiple Access (TDMA), Code Division Multiple Access (CDMA), and Groupe Special Mobile (GSM), being supported by base station  104 . (The specific messages for each air interface technology are known to one skilled in the art.) Base station  104  relays this request to serving MSC  103  utilizing facility request message  215 . Messages  214  and  215  contain dialed digits generated by mobile subscriber unit  105 . The dialed digits are interpreted by serving MSC  103  to signify a request for call transfer to a designated party. Serving MSC  103  establishes outgoing facility  216  and connects the incoming call to the designated party. At this point of time, the telephone path consists of telephone facility  206 , inter-MSC facility  213 , and outgoing facility  216 . 
     Serving MSC  103  initiates the removal of radio connection  212  by sending disconnect message  217 , which in turn causes base station  104  to send disconnect message  218  to mobile subscriber unit  105 . Disconnect message  218  is dependent upon the air interface technology. 
     In the prior art, the mobile subscriber unit can be afforded call transfer service only if the serving MSC supports call transfer. In other words, even if the originating MSC supports call transfer, the mobile subscriber unit cannot initiate call transfer if the serving MSC does not support it. The present invention does not require the serving MSC to support call transfer in order for the mobile subscriber unit to obtain a call transfer of an incoming call. Moreover, the number of required telephone facilities is reduced. 
     SUMMARY OF THE INVENTION 
     The apparatus and method of the present invention enables a wireless communications system to transfer an incoming call by utilizing call processing at a serving mobile switching center, an originating mobile switching center, and a home location register. 
     The serving mobile switching center (where the mobile subscriber unit is located) executes program instructions to generate a query to the home location register in response to a request for a call transfer from the mobile subscriber unit. The home location register executes program instructions that interpret the query from the serving mobile switching center and instructs the originating switching center, to which the incoming call was delivered from the public switching center, to redirect the incoming call to a designated party. The originating mobile switching center executes program instructions to redirect the incoming call and to remove telephone facilities to the serving mobile switching center. 
     Numerous other advantages and features of the present invention will become readily apparent from the detailed description of the invention and the embodiments thereof, from the claims, and from the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates an architecture of a wireless communications system supporting an incoming call in accordance with prior art; 
     FIG. 2 presents a message flow for transferring an incoming call from a mobile subscriber unit to a designated party in accordance with prior art; 
     FIG. 3 illustrates a message flow for transferring an incoming call from a mobile subscriber unit to a designated party in accordance with the present invention; 
     FIG. 4 illustrates a message flow utilizing call waiting in which a designated incoming call, selected from one of two incoming calls, is transferred to a designated party in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 3 illustrates a message flow for transferring an incoming call from a mobile subscriber unit to a designated party in accordance with the present invention. The message flow in FIG. 3 is analogous as the message flow in FIG. 2 up to the instance in which mobile subscriber unit  105  requests a call transfer. 
     As shown in FIG. 3, the incoming call originates from PSTN  100 . However, the incoming call may originate from a second mobile subscriber unit. If the second mobile subscriber unit is served by the same wireless communications system as mobile subscriber unit  105 , the incoming call may be delivered to originating MSC  101  without being routed through PSTN  100 . 
     An exemplary embodiment shown in FIG. 3 does not require that call transfer functionality be supported at serving MSC  103  itself in order for mobile subscriber  105  to be able to utilize a call transfer. In FIG. 3, mobile subscriber unit  105  sends call transfer request message  314  to base station  104 , requesting a call transfer. Message  104  identifies the designated party to which the incoming call shall be transferred as contained in a DGTSDIAL field. The actual format is dependent upon the air interface technology and is known to one skilled in the art. Base station  104  passes the feature request from mobile subscriber  105  to serving MSC  103  without attempting to execute the feature request by sending initiation message  315 . Also, whenever possible, standardized messages specified in ANSI-41 are utilized to provide compatibility between MSC&#39;s manufactured by different vendors. Message  315  contains the dialed digits, as specified in a DGTSDIAL parameter, from mobile subscriber unit  105 . Serving MSC  103  does not process the request; rather serving MSC  103  sends the dialed digits in FEATREQ message  316  (specified in ANSI-41) to HLR  102 . HLR  102  processes the dialed digits and determines that the incoming call shall be transferred to a designated party as specified by the DGTSDIAL parameter. Serving MSC  103  is notified of subsequent call processing in the FEATRESULT parameter of featreq message  317  (specified in ANSI-41). 
     HLR  102  requests that originating MSC  101  transfer the incoming call to the designated party by sending REDDIR message  318  (specified in ANSI-41) to originating MSC  101 . HLR  102  identifies the call identification of the incoming call by setting the value of the BILLID parameter to O-CALLID. (As previously discussed in FIG. 2, HLR  102  is able to relate the call identification assigned by originating MSC  101  with the call identification assigned by serving MSC  103  for the corresponding incoming call.) Message  318  also contains the DGTSDEST parameter, which specifies the designated party. HLR  102  determines the DGTSDEST parameter from a DGTSDIAL parameter contained in message  316 . Originating MSC establishes outgoing facility  319  to complete a telephone path between the incoming call and the designated party. The telephone path consists of telephone facility  206  and outgoing facility  319 . Originating MSC  101  notifies HLR  102  by sending reddir message  320  (specified in ANSI-41). Also, originating MSC  101  removes inter-MSC facility  213  from the call configuration by sending remove facility message  321  to serving MSC  103 . Serving MSC  103  initiates the removal of radio connection  212  by sending disconnect request message  217  to base station  104 . Consequently, base station removes radio connection  212  by sending disconnect message  218 . 
     In another exemplary embodiment, FIG. 4 illustrates a message flow with call waiting in which a designated incoming call, selected from one of two incoming calls, is transferred to a designated party in accordance with the present invention. The message flow in FIG. 4 is analogous to the message flow in FIG. 3 up to the instance in which inter-MSC facility  414  is established. Thus, first originating MSC  401  corresponds to originating MSC  101 ; telephone facility  407  corresponds to telephone facility  206 ; LOCREQ message  408  corresponds to LOCREQ message  207 ; ROUTREQ message  409  corresponds to ROUTREQ message  208 ; routreq message  410  corresponds to routreq  209 ; locreq message  412  corresponds to locreq message  211 ; and inter-MSC facility  414  corresponds to inter-MSC facility  213 . 
     Additionally, in FIG. 4 a second incoming call is delivered to second originating MSC  402  over telephone facility  415 . (The exemplary embodiment shown in FIG. 4 does allow first originating MSC  401  and second originating MSC  402  to be the same originating MSC.) Second originating MSC  402  delivers the second incoming call to serving MSC  103  in an analogous way as first originating MSC  401  delivered the first incoming call to serving MSC  103 . Thus, LOCREQ message  416  corresponds to LOCREQ message  408 ; ROUTREQ message  417  corresponds to ROUTREQ message  409 ; routreq message  418  corresponds to routreq message  410 ; locreq message  419  corresponds to locreq message  412 ; and inter-MSC facility  420  corresponds to inter-MSC facility  414 . In messages  408 ,  409 ,  410 , and  412 , the BILLID parameter contains the call identification associated with the first incoming call (corresponding to O-CALLID 1 , O-CALLID 1 , S-CALLID 1 , and S-CALLID 1 , respectively). However, the value of the BILLID parameter in messages  416 ,  417 ,  418 , and  419  is set to the call identification of the second incoming call (corresponding to O-CALLID 2 , O-CALLID 2 , S-CALLID 2 , and S-CALLID 2 , respectively). 
     At this point of time, the second incoming call is delivered to serving MSC  103 . However, radio connection  212  supports one incoming call at a particular instance of time. Thus, mobile subscriber unit  105  may talk and listen only to one incoming call (either the first incoming call or the second incoming call). Mobile subscriber unit  105  and toggle from one incoming call to another by sending flash message  421 . The capability of toggling from one incoming call to another is supported by call waiting. Call waiting is a commonly supported feature of telephony systems, including wireless communications systems. Base station  104  relays this toggle request by sending flash request message to serving MSC  103 . At this point in the message flow, mobile subscriber unit  105  is talking and listening to the second incoming call, i.e. the second incoming call is active. 
     Mobile subscriber unit  105  initiates call transfer by sending call transfer request message  423  (analogous to message  314  in FIG.  3 ). The dialed digits as entered at mobile subscriber unit  105  may explicitly specify the incoming call to be transferred (either the first or second incoming call). Alternatively, if the identification of the incoming call is not specified in the dialed digits, the incoming call is understood to be the active incoming call. In FIG. 4, the active incoming call is the second incoming call. Base station  104  relays the transfer request by sending initiation message  424  to serving MSC  103  (analogous to message  315  in FIG.  315 ). Serving MSC  103  relays this request to HLR  102  by sending FEATREQ  425  (analogous to message  316  in FIG.  3 ). 
     HLR  102  processes the dialed digits contained in the DGTSDIAL parameter of message  425  and instructs serving MSC  103  about subsequent call processing of the feature request by returning featreq message  426  to serving MSC  103  (analogous to message  317  in FIG.  3 ). HLR  102  determines that the second incoming call shall be transferred to the designated party; thus, HLR  102  sends REDDIR message  427  to second originating MSC  402 . Message  427  contains the BILLID parameter equal to O-CALLID 2 , which is the call identification of the second incoming call. Consequently, originating MSC  402  performs a call transfer of ,the second incoming call. Second originating MSC  402  establishes outgoing facility  428  to complete the call transfer between the second incoming call and the designated party. At this point of time, the telephone path at second originating MSC  402  consists of telephone facility  415  and outgoing facility  428 . Second originating MSC  402  notifies HLR  102  about the completion of the call transfer by sending reddir message  429  to HLR  102 . Inter-MSC facility  420  is removed by second originating MSC  402  sending remove facility message  430  to serving MSC  103 . 
     At this point of time, the message flow in FIG. 4 differs from the message flow of FIG. 3 in that the radio connection is not removed in FIG.  4 . The reason is that mobile subscriber unit is still connected to the first incoming call. However, this exemplary embodiment allows mobile subscriber unit  105  to initiate a subsequent call transfer request. Subsequent call processing would follow the message flow as illustrated in FIG. 3 in such a case. 
     It is to be understood that the above-described embodiment is merely an illustrative principle of the invention and that many variations may be devised by those skilled in the art without departing from the scope of the invention. It is, therefore, intended that such variations be included with the scope of the claims.