Abstract:
A system for delivering a call to a mobile unit in a wireless network includes a mobile switching center that receives a call setup request message initiated in response to a request from an originating mobile switching center. The receiving mobile switching center initiates setting up the call between the receiving mobile switching center and the mobile unit before the call is setup between the receiving mobile switching center and the originating mobile switching center. Preferably, the receiving mobile switching center initiates setting up the call by issuing a page in response to receiving the call setup message.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of Provisional Application Serial No. 60/094,531, filed Jul. 29, 1998. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to the field of wireless telecommunications, and more particularly to a method of and system for delivering calls to a mobile unit in a wireless telecommunications system with improved call setup time. 
     DESCRIPTION OF THE PRIOR ART 
     Wireless telecommunications services are growing at a tremendous rate. Users have embraced the concept of having a telephone that is with them all the time. Mobile telecommunications systems provide users with the ability to receive telephone calls, faxes, pages, and short messages at virtually any location in the country. The development of general packet radio service (GPRS) system will enable users to receive high-speed data in wireless environment, and thereby access the Internet or other data networks from virtually any location. 
     One of the drawbacks associated with wireless telecommunications is the relative slowness of call delivery. In order to terminate a call to a mobile unit, a substantial amount of signaling is required. The termination time is increased when the mobile unit has roamed outside its home area. The mobile unit must be located and the call must be setup over multiple system links. Termination time is even slower in the case of GPRS terminations. In GPRS systems, the mobile unit is paged on a packet control channel (PCCH), which is the control channel associated with the data session side of the system. When the mobile unit is paged on the PCCH for a telephone call, the mobile unit must retune to the digital control channel (DCCH) in order to respond to page and proceed with call setup. In addition to the time spent retuning, there is a substantial amount of additional signaling associated with terminations of calls in a GPRS system. 
     Callers to mobile units may find the slow setup time annoying. Callers may even believe that an error has occurred and that the call will not be completed at all. Accordingly, it is an object of the present invention to provide a system and method for reducing the time required to complete calls to mobile units. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved method of and system for delivering a call to a mobile unit in a wireless network. The system includes a mobile switching center that receives a call setup request message initiated in response to a request from an originating mobile switching center. The receiving mobile switching center initiates setting up the call between the receiving mobile switching center and the mobile unit before completion of call setup between the receiving mobile switching center and the originating mobile switching center. Preferably, the receiving mobile switching center initiates setting up the call by issuing a page in response to receiving the call setup message. 
     The present invention is broadly applicable to all wireless telecommunications systems. For example, the receiving mobile switching center may be a serving mobile switching center that issues a page to a mobile unit. Alternatively, the receiving mobile switching center may be an anchor mobile switching center that issues an ISPAGE 2  to a boundary mobile switching center. In the general packet radio service (GPRS) environment, the receiving mobile switching center may be a gateway mobile switching center that issues an ISPAGE 2  to a serving mobile switching center and a hard page to a serving GPRS support node. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of a typical wireless telecommunications system. 
     FIG. 2 is a call flow diagram of a call delivery in a system of the type illustrated in FIG. 1 according to the prior art. 
     FIG. 3 is a call flow diagram of a call delivery in a system of the type illustrated in FIG. 1 according to the present invention. 
     FIG. 4 is a call flow diagram of an alternative call delivery in a system of the type illustrated in FIG. 1 according to the prior art. 
     FIG. 5 is a call flow diagram of an alternative call delivery in a system of the type illustrated in FIG. 1 according to the present invention. 
     FIG. 6 is a block diagram of a general packet radio service (GPRS) system. 
     FIG. 7 is a call flow diagram of a call delivery in a system of the type illustrated in FIG. 6 according to the prior art. 
     FIG. 8 is a call flow diagram of a call delivery in a system of the type illustrated in FIG. 6 according to the present invention. 
     FIG. 9 is a call flow diagram of an alternative call delivery in a system of the type illustrated in FIG. 6 according to the prior art. 
     FIG. 10 is a call flow diagram of an alternative call delivery in a system of the type illustrated in FIG. 6 according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, and first to FIG. 1, a wireless telecommunications system is designated generally by the numeral  11 . System  11  includes an originating mobile switching center (MSC-O)  13 . MSC-O  13  provides an interface between the public switched telephone network (PSTN)  15  and wireless system  11 . MSC-O  13  accesses a home location register (HLR)  17  for mobile subscriber information and the current location of a mobile unit  19 . 
     When mobile unit  19  is outside its home area, it registers with, and is served by, a serving mobile switching center and visitor location register (MSC-S/VLR)  21 . When mobile unit  19  registers with MSC-S/VLR  21 , the VLR informs HLR  17  of the current location of mobile  19  and HLR  17  downloads subscriber information for mobile unit  19  to the VLR. When MSC-O  13  receives a call to mobile unit  19 , the call is delivered to MSC-S  21 , and a base station  23  pages mobile unit  19  over a digital control channel (DCCH). If mobile unit  19  is still in the area served by the paging base station, call completion proceeds. 
     Occasionally, mobile unit  19  will have moved into a border area without having changed its area of registration. In order to accommodate such instances, MSC-S  21  sends a special paging message (ISPAGE 2 ) to a border mobile switching center (MSC-B)  25  substantially simultaneously with sending the page to mobile unit  19 . MSC-B  25  sends a page to base stations  27 , which in turn attempt to page mobile unit  19  on their digital control channels. When mobile unit  19  responds to the page, call completion proceeds. 
     Referring now FIG. 2, there is shown a call flow diagram of a call completion according to the prior art in a system of the type illustrated in FIG. 1. A call  29  is received at MSC-O  13 . MSC-O  13  sends a location request (LOCREQ) message  31  to HLR  17 . HLR  17  determines that mobile unit  19  is registered with MSC-S  21 . Accordingly, HLR  17  sends a routing request (ROUTREQ) message  33  to MSC-S  21 . 
     According to the prior art, the receipt of the ROUTREQ message at MSC-S  21  triggers a routing request return result (routreq)  35  back to HLR  17 . Upon receipt of the routreq  35 , HLR  17  sends a location request return result (locreq)  37  back to MSC-O  13 . When MSC-O  13  receives locreq  37 , the call is connected between MSC-O  13  and MSC-S  21 . When MSC-S  21  receives the call, MSC-S  21  sends a PAGE  39  to mobile unit  19 . As will be discussed in connection with FIG. 4, MSC-S  21  also sends an ISPAGE 2  to an MSC-B  25 . When mobile unit  19  receives page  39 , mobile unit  19  responds with a page response  41  back to MSC-S  21 . Upon receipt of the page response  41 , the call is connected between MSC-S  21  and mobile unit  19 , thus connecting the calling party with mobile unit  19 . From the foregoing, it may be seen that in the prior art, the call is set up completely between MSC-O  13  and MSC-S  21 , before call setup is even initiated between MSC-S  21  and mobile unit  19  Referring to now FIG. 3, there is shown a call flow of one embodiment of a call completion according to be present invention. Again, call  29  is received at MSC-O  13 . MSC- 0   13  sends a LOCREQ message  31  to HLR  17 . Again, HLR  17  determines that mobile unit  19  is registered with MSC-S  21 . Accordingly, HLR  17  sends a ROUTREQ message  33  to an MSC-S  21   a  of the present invention. 
     According to the present invention, the receipt of the ROUTREQ message at MSC-S  21   a  triggers substantially simultaneously a PAGE  39  to mobile unit  19  and a routreq  35  back to HLR  17 . Then, the completion of call setup between MSC- 0   13  and MSC-S  21   a , and the call setup between MSC-S  21   a  and mobile unit  19  then proceed independently and concurrently along separate paths. Upon receipt of the routreq  35 , HLR  17  sends a locreq  37  back to MSC- 0   13 . When MSC- 0   13  receives locreq  37 , the call is connected between MSC- 0   13  and MSC-S  21 . 
     Concurrently, when mobile unit  19  receives PAGE  39 , mobile unit  19  responds with a page response  41  back to MSC-S  21 . Upon receipt of the page response  41 , the call is connected between MSC-S  21  and mobile unit  19 . According to the present invention, the call may finish being setup between MSC-S  21   a  and mobile unit  19  before the call setup is completed between MSC-O  13  and MSC-S  21   a . When both parts of the call are setup, the calling party is connected to mobile unit  19 . 
     Referring now FIG. 4, there is shown a call flow diagram of an alternative call completion according to the prior art in a system of the type illustrated FIG.  1 . Again, call  29  is received at MSC-O  13 . MSC-O  13  sends a LOCREQ  31  to HLR  17 . HLR  17  determines that mobile unit  19  is registered with MSC-S  21 , which in the embodiment of FIG. 4 becomes an anchor mobile switching center (MSC-A). Accordingly, HLR  17  sends a ROUTREQ  33  to MSC-A  21 . Again, according to the prior art, the receipt of the ROUTREQ at MSC-A  21  triggers a routreq  35  back to HLR  17 . Upon receipt of the routreq  35 , HLR  17  sends a locreq  37  back to MSC-O  13 . When MSC- 0   13  receives locreq  37 , the call is connected between MSC-O  13  and MSC-A  21 . When MSC-A  21  receives the call, MSC-A  21  sends an ISPAGE 2   43  to MSC-B  25  (as well as a PAGE to mobile unit  19 , as discussed with respect to FIG.  2 ). MSC-B  25  sends a PAGE  45  to base station ACCH  47 , which in turn sends a PAGE  49  to mobile unit  19 . When mobile unit  19  receives PAGE  49 , mobile unit  19  responds with a page response  51  back to ACCH  47 , which in turn sends a page response  53  back to MSC-B  25 . Upon receipt of page response  53 , MSC-B  25  sends an ispage 2  return result  55  back to MSC-A  21 . MSC-A then sends an ISSETUP message  57  to MSC-B  25 . When MSC-B  25  responds with an issetup return result  59  the call is connected between MSC-A  21  and mobile unit  19 , thus connecting the calling party with mobile unit  19 . From the foregoing, it may again be seen that in the prior art, the call is set up completely between MSC-O  13  and MSC-A  21 , before call setup is even initiated between MSC-A  21  and mobile unit  19 . 
     Referring to now FIG. 5, there is shown a call flow of an alternative embodiment of a call completion according to be present invention. Again, a call  29  is received at MSC-O  13 . MSC-O  13  sends a LOCREQ message  31  to HLR  17 . Again, HLR  17  determines that mobile unit  19  is registered with MSC-A  21 . Accordingly, HLR  17  sends a ROUTREQ message  33  to an MSC-A  21   a  of the present invention. 
     According to the present invention, the receipt of the ROUTREQ message at MSC-S  21   a  triggers substantially simultaneously an ISPAGE 2   43  to MSC-B  25  (as well as a PAGE described with respect to FIG.  4 ), and a routreq  35  back to HLR  17 . Then, the completion of call setup between MSC-O  13  and MSC-A  21   a , and the call setup between MSC-A  21   a  and mobile unit  19  proceed independently and concurrently along separate paths. Upon receipt of the routreq  35 , HLR  17  sends a locreq  37  back to MSC-O  13 . When MSC-O  13  receives locreq  37 , the call is connected between MSC-O  13  and MSC-A  21 . 
     Concurrently, When MSC-B  25  receives ISPAGE 2   43 , MSC-B  25  sends a PAGE  45  to base station ACCH  47 , which in turn sends a PAGE  49  to mobile unit  19 . When mobile unit  19  receives PAGE  49 , mobile unit  19  responds with a page response  51  back to ACCH  47 , which in turn sends a page response  53  back to MSC-B  25 . Upon receipt of page response  53 , MSC-B sends an ispage 2  return result  55  back to MSC-A  21 . MSC-A then sends an ISSETUP message  57  to MSC-B  25 . When MSC-B  25  responds with an issetup return result  59  the call is connected between MSC-A  21  and mobile unit  19 . When both parts of the call are setup, the calling party is connected to mobile unit  19 . 
     Referring now to FIG. 6, a general packet radio service (GPRS) system is designated generally by the numeral  61 . GPRS system  61  enables a mobile unit  63  to access both a data network, such as the Internet  65 , and the public switched telephone network (PSTN)  67 . An originating mobile switching center (MSC-O)  69  provides an interface between GPRS system  61  and PSTN  67 . An HLR  71  provides MSC-O  69  with subscriber and location information for the mobile units in its home area. A gateway mobile switching center (G-MSC)  73  is connected to MSC-O  69  and a visitor location register (VLR)  75  provides HLR  71  with location information for mobile unit  63 . A serving mobile switching center (MSC-S)  77  is connected to G-MSC  73  and a VLR  75  provides location information to HLR  71 . MSC-S  77  is connected to a plurality of base stations  81 , which use digital control channels (DCCHs) for paging and registration of mobile units in their respective areas. 
     A gateway GPRS support node (GGSN)  83  provides the interface between Internet  65  and GPRS system  61 . A GPRS HLR  85  provides GGSN  83  with location and subscriber information. GGSN  83  and GPRS HLR  85  are in communication with a serving GPRS support node (SGSN)  87 , which communicates with mobile units in its area through a plurality of base stations  89 . Base stations  89  use packet control channels (PCCHs) for paging and registration of mobile units in their respective areas. 
     Referring now to FIG. 7, there is shown a call flow diagram of a call completion according to the prior art in a GPRS system of the type illustrated FIG. 6. A call  91  to mobile unit  63  is received-at MSC-O  69 . MSC-O  69  sends a LOCREQ  93  to HLR  71 . HLR  71  determines that mobile unit  63  is registered with VLR  75 . Accordingly, HLR  71  sends a ROUTREQ  95  to VLR  75 , which in turn sends a ROUTREQ  97  to G-MSC  73 . According to the prior art, the receipt of ROUTREQ  97  at G-MSC  73  triggers a routreq  99  back to VLR  75 , which in turn sends a routreq  101  back to HLR  71 . Upon receipt of the routreq  101 , HLR  71  sends a locreq  103  back to MSC-O  69 . When MSC-O  69  receives locreq  103 , the call is connected between MSC-O  69  and G-MSC  73 . 
     In the GPRS system, a mobile unit is normally tuned to a packet control channel (PCCH). Accordingly, when a call is to be terminated to mobile unit  63 , mobile unit  63  must be instructed to retune to a digital control channel (DCCH). When G-MSC  73  receives the call, G-MSC  73  substantially simultaneously sends an ISPAGE 2   105  to MSC-S  77  and a hard page  107  to SGSN  87 . The ISPAGE 2  alerts MSC-S  77  that it will receive a call for mobile unit  63 . Upon receipt of hard page  107 , SGSN  87  sends a paging request  109  to PCCH  89 , which forwards a paging request  111  to mobile unit  63 . Mobile unit  63  responds to SGSN  87  with suspend response  113 , which indicates to SGSN  87  that mobile unit  63  is changing from data session mode to circuit mode, and retunes to the DCCH frequency. Then, mobile unit  63  sends a page response  115  on DCCH  81  to MSC-S  77 . Upon receipt of page response  115 , MSC-S  77  sends an ispage 2  return result  117  back to G-MSC  73 . G-MSC  73  then sends an ISSETUP message  119  to MSC-S  77 . When MSC-S  77  responds with an issetup return result  121 , the call is connected between G-MSC  73  and mobile unit  63 , thus connecting the calling party with mobile unit  63 . From the foregoing, it may again be seen that in the prior art, the call is set up completely between MSC-O  69  and G-MSC  73 , before call setup is even initiated between G-MSC  73  and mobile unit  63 . 
     Referring now to FIG. 8, there is shown a call flow diagram of a call completion according to the present invention in a GPRS system of the type illustrated FIG.  6 . Again, call  91  to mobile unit  63  is received at MSC-O  69 . MSC-O  69  sends a LOCREQ  93  to HLR  71 . HLR  71  determines that mobile unit  63  is registered with VLR  75  and sends a ROUTREQ  95  to VLR  75 , which in turn sends a ROUTREQ  97  to G-MSC  73   a.    
     According to the present invention, the receipt of ROUTREQ  97  at G-MSC  73   a  substantially simultaneously triggers both an ISPAGE 2  message to MSC-S  77  and a hard page  107  to SGSN  87 , as well as a routreq  99  back to VLR  75 . Then, according to the present invention and generally in the manner described with respect to FIGS. 3 and 5, the completion of call setup between MSC-O  69  and G-MSC  73   a , and the call setup between G-MSC  73   a  and mobile unit  63  proceed independently and concurrently along separate paths. VLR  75  sends a routreq  101  back to HLR  71 . Upon receipt of the routreq  101 , HLR  71  sends a locreq  103  back to MSC-O  69 . When MSC-O  69  receives locreq  103 , the call is connected between MSC-O  69  and G-MSC  73   a.    
     Concurrently, the receipt of ISPAGE 2   105  alerts MSC-S  77  that it will receive a call for mobile unit  63 . Upon receipt of hard page  107 , SGSN  87  sends a paging request  109  on PCCH  89  to mobile unit  63 . Mobile unit  63  responds to SGSN  87  with a suspend return result  113 , and retunes to the DCCH frequency. Then, mobile unit  63  sends a page response  115  on DCCH  81  to MSC-S  77 . Upon receipt of page response  115 , MSC-S  77  sends an ispage 2  return result  117  back to G-MSC  73   a . G-MSC  73   a  then sends an ISSETUP message  119  to MSC-S  77 . When MSC-S  77  responds with an issetup return result  121  the call is connected between G-MSC  73   a  and mobile unit  63 , thus connecting the calling party with mobile unit  63 . 
     Referring now to FIG. 9, there is shown a call flow diagram of an alternative call completion according to the prior art in a GPRS system of the type illustrated FIG. 6. A call  91  to mobile unit  63  is received at MSC-O  69 . MSC-O  69  sends a LOCREQ  93  to HLR  71 . HLR  71  determines that mobile unit  77  is registered with VLR  75 . Accordingly, HLR  71  sends a ROUTREQ  95  to VLR  75 , which in turn sends a ROUTREQ  97  to G-MSC  73 . According to the prior art, the receipt of ROUTREQ  97  at G-MSC  73  triggers a routreq  99  back to VLR  75 , which in turn sends a routreq  101  back to HLR  71 . Upon receipt of the routreq  101 , HLR  71  sends a locreq  103  back to MSC-O  69 . When MSC-O  69  receives locreq  103 , the call is connected between MSC-O  69  and G-MSC  73 . 
     When G-MSC  73  receives the call, G-MSC  73  sends a hard page  107  to SGSN  87 . Upon receipt of hard page  107 , SGSN  87  sends a paging request  109  to PCCH  89 , which forwards a paging request  111  to mobile unit  63 . Mobile unit  63  responds to SGSN  87  with a suspend  113 , and retunes to the DCCH frequency. Then, mobile unit  63  sends a page response  115  on DCCH  81  to MSC-S  77 . Upon receipt of page response  115 , MSC-S  77  sends an unsolicited response (UNSOLRES)  118  to G-MSC  73 . An UNSOLRES is the invoke message that IS- 41  instructs an MSC-S to use when a page response is received that the MSC-S did not request. G-MSC  73  responds with an unsolres return result  120 , and sends an ISSETUP message  119  to MSC-S  77 . When MSC-S  77  responds with an issetup return result  121 , the call is connected between G-MSC  73  and mobile unit  63 , thus connecting the calling party with mobile unit  63 . From the foregoing, it may again be seen that in the prior art, the call is set up completely between MSC-O  69  and G-MSC  73 , before call setup is even initiated between G-MSC  73  and mobile unit  63 . 
     Referring now to FIG. 10, there is shown a call flow diagram of an alternative call completion according to the present invention in a GPRS system of the type illustrated FIG.  6 . Again, call  91  to mobile unit  63  is received at MSC-O  69 . MSC-O  69  sends a LOCREQ  93  to HLR  71 . HLR  71  determines that mobile unit  63  is registered with VLR  75  and sends a ROUTREQ  95  to VLR  75 , which in turn sends a ROUTREQ  97  to G-MSC  73   a.    
     According to the present invention, the receipt of ROUTREQ  97  at G-MSC  73   a  substantially simultaneously triggers a hard page  107  to SGSN  87  and a routreq  99  back to VLR  75 . Then, according to the present invention and generally in the manner described with respect to FIGS. 3,  5 , and  8 , the completion of call setup between MSC-O  69  and G-MSC  73   a , and the call setup between G-MSC  73   a  and mobile unit  63  proceed independently and concurrently along separate paths. VLR  75  sends a routreq  101  back to HLR  71 . Upon receipt of the routreq  101 , HLR  71  sends a locreq  103  back to MSC-O  69 . When MSC-O  69  receives locreq  103 , the call is connected between MSC-O  69  and G-MSC  73   a.    
     Concurrently, the receipt of hard page  107 , SGSN  87  sends a paging request  109  on PCCH  89  to mobile unit  63 . Mobile unit  63  responds to SGSN  87  with a suspend  113 , and retunes to the DCCH frequency. Then, mobile unit  63  sends a page response  115  on DCCH  81  to MSC-S  77 . Upon receipt of page response  115 , MSC-S  77  sends an UNSOLRES  118  to G-MSC  73   a . G-MSC  73   a  responds with an unsolres return result  120 , and sends an ISSETUP message  119  to MSC-S  77 . When MSC-S  77  responds with an issetup return result  121 , the call is connected between G-MSC  73  and mobile unit  63 , thus connecting the calling party with mobile unit  63 . 
     From the foregoing, it may be seen that the present invention reduces call setup time by initiating setup of the call between the serving or gateway MSC and the mobile unit before completion of call setup between the originating MSC and the serving or gateway MSC. In the present invention, the two phases of call setup proceed at least partially in parallel, rather than serially as in the prior art. The present invention results in substantially decreased call setup time for calls to mobile units that have roam outside their home area or to GPRS mobile units. 
     While the invention has been described with respect to presently preferred embodiments, those skilled in the art will recognize alternative embodiments and implementations. Accordingly, the foregoing is intended for purposes of illustration and not of limitation.