WO1999059371A1

WO1999059371A1 - Mobile switching center that completes a call to a roaming mobile station as if the mobile station were a local mobile station

Info

Publication number: WO1999059371A1
Application number: PCT/US1999/007985
Authority: WO
Inventors: Dipankar Ray; Vladimir Alperovich
Original assignee: Ericsson Inc.
Priority date: 1998-05-14
Filing date: 1999-04-12
Publication date: 1999-11-18
Also published as: AU3555499A

Abstract

A system and method for delivering a call to a roaming mobile station (64) as a local call, even though the local service region is not the primary service region of the mobile station. A unique routing code is associated with a gateway mobile switching center (GMSC) (14). When the telecommunications network delivers a call to the GMSC (14), the GMSC (14) obtains the directory number of the mobile station, and then determines the location of the roaming mobile station within a pre-specified local service region. The call is then routed to the MSC (34) on which the roaming mobile station is currently registered.

Description

-1-

MOBI E SWITCHING CENTER THAT COMPLETES A CALL

TO A ROAMING MOBILE STATION AS IF THE MOBILE

STATION WERE A LOCAL MOBILE STATION

TECHNICAL FIELD OF THE INVENTION This invention relates to completing a call to mobile station in a wireless network, and more specifically, to a system and method for completing a local call to a roaming mobile station without the call being routed to the mobile station's home network.

BACKGROUND OF THE INVENTION Wireless telecommunication services are available in most of the populated areas of the world. As a result, a subscriber can use his/her mobile station at home or away from home, as long as the visited wireless network uses the same basic technology as the subscriber's home system (i.e., Global System for Mobile Communications, Code Division Multiple Access, etc.). Using a mobile station away from its home network is known as roaming. Most wireless networks are structured to support both local and roaming mobile stations.

Whether a mobile station is in its home wireless network or is roaming, it must register with a local mobile switching center (MSC). "Registration" of a mobile station is similar to connecting a wire line telephone. The wire line telephone must have an identity in the local switching office (a directory number and line identification) before it can make and receive calls. Similarly, a mobile station must have an identity in the local MSC before it can make and receive calls.

A mobile station registers when it is switched on within a wireless network. The mobile station sends identification data (including its directory number) to the local MSC, which stores this data in a visitor location register (VLR). The local MSC notifies the home location register (HLR) of the wireless station that the mobile station is currently located in the MSC's service area. The HLR sends back data that the local MSC requires to provide service to the mobile station (e.g., equipment identification number and other authentication information). This data -2- is also stored in the local MSC's VLR. When this exchange of information and authentication are complete, the mobile station is ready to originate and receive calls. Originating a mobile call is basically the same whether the mobile station is in its home wireless network or is roaming, except that roaming charges may apply. Delivering a call to a mobile station, however, depends on whether the mobile station is in its home network or is roaming.

A call to a mobile station operating in its local wireless network originates from any wire line telephone or mobile station. The switching network receives the dialed directory number, recognizes that the call is to a mobile station, and routes the call to an MSC. The MSC queries its VLR, or, if the mobile station is not found there, the local HLR to determine the current location of the mobile station. The MSC then creates a connection through the facilities of the wireless network to the mobile station. Normal local charges accrue to the calling party and to the mobile station. In contrast, routing a call to a roaming mobile station is more complex. A call may originate from a wire line telephone or a mobile station near to the roaming mobile station. The dialed directory number is recognized as a directory number of the home wireless network of the roaming mobile station. Therefore, the call is routed through the public switched telephone network (which may include long distance networks) to the MSC of the roaming mobile station's home wireless. This MSC queries the local HLR to determine the current location of the roaming mobile station. The home MSC then routes the call to the MSC in the visited wireless network. The MSC of the visited wireless network uses its VLR to locate the mobile station and deliver the call. A problem in calling a roaming mobile station is that the mobile station may be in the same town, or even next door to the calling party. However, the calling party may be charged for a long distance call to the home wireless network, and either the calling or called party is charged for extending the call to the visited service region. This can be expensive both for the calling party and the called party.

SUMMARY OF THE INVENTION

This problem is solved and a technical advance is achieved in the art by a -3- system and method for delivering a call to a roaming mobile station as a local call, even though the local service region is not the mobile station's home service region. A unique routing code is associated with a local gateway mobile switching center (GMSC). When the local public switched telephone network (PSTN) receives a call with the unique routing code, it delivers the call to the local GMSC. The GMSC receives the directory number of the mobile station. The GMSC then locates the called roaming mobile station and routes the call to the MSC where the roaming mobile station is currently registered. Thus, the long distance routing to the roaming mobile station's home wireless network and back again, and the associated charges, are avoided.

In one embodiment of this invention, the PSTN delivers a directory number of the mobile station to a GMSC responsive to a code and the directory number of the roaming mobile station. In response, the GMSC sends a paging message to a predefined set of MSC's that comprise the local service region. Each MSC (including the GMSC) checks its respective visitor location register to determine if a roaming mobile station associated with the directory number is registered. If an MSC finds the roaming mobile station, it reports back to the GMSC, which then extends the call to the responding MSC. The responding MSC sets up delivery of the call to the roaming mobile station. In a further embodiment, the PSTN delivers a call for a roaming mobile station to a GMSC in response to a local directory number or a special code. The GMSC connects the received call to a system for prompting the caller to enter the roaming mobile station's directory number. Advantageously, an intelligent peripheral may be connected to the caller to prompt the caller and recognize and interpret digits as they are received. The intelligent peripheral then passes the directory number of the roaming mobile station back to the GMSC. The GMSC sends a message including the directory number of the roaming mobile station to the home location register (HRL) of the roaming mobile station. The HLR returns a message indicating the location of the roaming mobile station and routing information for delivering the call to the MSC associated with the location. The GMSC extends the call to the destination MSC, which sets up a call with the roaming mobile station. -4-

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of this invention may be obtained from consideration of the following description taken in conjunction with the drawings in which: Fig. 1 is a block diagram of a wireless network illustrating our methods for completing a call to a roaming mobile station;

Fig. 2 is a block diagram of a gateway mobile switching center of Fig.1 ;

Fig. 3 is a call flow diagram according to one exemplary embodiment of our method; and Fig. 4 is a call flow diagram according to a further embodiment of our method.

DETAILED DESCRIPTION OF THE INVENTION

Fig. 1 illustrates a typical wireless network, shown generally at 10, that supports both local and roaming mobile stations. Wireless network 10 is connected to the public switched telephone network (PSTN) 12, which comprises a plurality of other wireless and landline networks, by a plurality of lines and/or trunks 22. PSTN 12 is connected to wireless network 10 at a mobile switching center (MSC) 14, which is a "gateway" MSC (GMSC), because it connects wireless network 10 to a portion of PSTN 12. GMSC 14, as will be described in conjunction with Fig.2, below, controls the connection of calls between PSTN 12 and mobile stations in wireless network 10 and controls the connections of calls between mobile stations. GMSC 14 is connected to a visitor's location register (VLR) 32 via communications path 33.

GMSC 14 is further connected to a plurality of other MSC's, represented by MSC 34 and MSC 36. MSC's 34 and 36 connect calls between GMSC and base transceiver stations (including any intermediate units), and provides pathways to connect wireless calls to other MSC's or to connect wireless-to-wireless calls between mobile stations. MSC's 34 and 36 monitor the mobile stations in the portion of the wireless network under its control and manage wireless resources (such as base transceiver stations) to provide wireless communications for the mobile stations. MSC's 34 and 36 could also be gateways from different portions -5- of PSTN 12.

To provide service to mobile stations in wireless network 10, GMSC 14 is connected to a plurality of base transceiver stations (BTS's), represented by BTS 46 and 48, and manages mobility of mobile stations operating in the area. Each of BTS 46 and 48 provides radio communications and radio communications management for all mobile stations in its respective coverage area (cell). Thus, BTS's 46 and 48 provide coverage in cells 50 and 52, respectively. In this figure, all cells are shown as hexagons. In an operating wireless network, cells are irregularly shaped, overlapping areas, which are determined based upon the features of the terrain. Further, there are many more BTS's and may be intermediate units between the BTS's and the MSC.

MSC 34 supervises connection of calls within a geographical area of wireless network 10. MSC 34 controls and coordinates the actions of BTS's 54, 56 and 58 within cells 60, 62 and 64, respectively. MSC 36 supervises service for another region within wireless network 10. MSC 36 is connected to a plurality of BTS's, represented by BTS's 66 and 68, that provide radio communications and radio communications controls within cells 70 and 72 respectively.

A further wireless network is shown at 100. Wireless network 100 includes GMSC 102. GMSC 102 coordinates the actions BTS's 114 and 116. BTS's 114 and 116 deliver wireless services in cells 118 and 120, respectively.

One or more long distance networks 122 connect wireless network 100 to PSTN 12. Signaling links 125 connect signaling network 124 to GMSC's 102 and 14. Signaling network 124 may also be connected to MSC's 34 and 36 (not shown for clarity). Within signaling network 124, there is one or more home location registers (HLR) 126. HLR 126 stores the current location of mobile stations and information required to identify, authenticate, and verify a mobile station to provide service and prevent fraud.

All MSC's 102, 14, 34 and 36 are connected to a respective visitor location register (VLR) 128, 32, 130 and 132. Each VLR stores the identification and last location of mobile stations that are registered within their respective service regions. An intelligent peripheral (IP) 134 is connected to GMSC 14, by dedicated link 135. Alternatively, GMSC 14 may access IP 134 via signaling network 124. -6-

IP 134 provides services for GMSC 14 that GMSC 14 cannot do for itself. In this example, IP 130 includes digit recognition 136, speech recognition 138 and a voice prompting system 140.

Wire line telephone 142 is connected to PSTN 12. Wire line telephone 142 is within a local service region that includes portions of PSTN 12 and wireless network 10. There are, for purposes of this description, two wireless units operating within wireless network 10. Wireless mobile station 144 is a roaming mobile station whose home wireless network is wireless network 100. Mobile station 146 is operating in its home wireless network 10. Roaming mobile station 144, mobile station 146 and telephone 142 are all within the same local service region. If telephone 142 makes a call to mobile station 146 (whose home network is local network 10), both telephone 142 and mobile station 146 incur the usual local charges associated with such calls. According to the prior art, a call from telephone 142 to roaming mobile station 1 6 is routed to GMSC 102 and then back to wireless network 10. Telephone 142 is charged for a long distance call through long distance network 122, and either telephone 142 or roaming mobile station 144 is charged for routing the call back to wireless network 10. It is thus more expensive for telephone 142 to call a roaming mobile station 144, which is relatively close, than mobile station 146, which is on the other end of wireless network 10.

Fig. 2 illustrates GMSC 14 that supports our method. GMSC 14 generally comprises a wireline side 202 and a wireless side 204, which are controlled and coordinated by switch control 206. Calls for mobile stations arrive on lines or trunks 22 from PSTN 12 at telephone user part (TUP) 210, which is the terminal interface for analog calls. Although not shown in Fig. 2, ISDN calls from PSTN 12 arrive at ISDN user part (ISUP) 208, which interfaces ISDN lines, trunks and communication links to GMSC 14.

When a call is received at TUP 210 (or ISUP 208), transactional capabilities application part (TCAP) 214 begins a transaction to locate and connect the call to the destination mobile station. To this end, TCAP 214 informs mobile application protocol (MAP) 212 of the new call and the destination mobile station's directory number. MAP 212 sends a message through ISUP 208 and signaling network 124 -7- to HLR 126 (Fig. 1) to request the last registered location of the mobile station. When a response is received, MAP 212 informs TCAP 214 of the last registered location of the destination mobile station. If the mobile station is currently served by another MSC (such as MSC 34), TCAP 214 routes the call through ISUP 208 to MSC 34. If the mobile station is currently served by GMSC 14, the call is routed through the message protocol layers signaling collection control part (SCCP) 216 and message transport part (MAP) 218 to the wireless side 204.

Switch control 206 informs communication manager (CM) 226 to set up communication with the destination mobile station. The currently serving BTS is obtained from mobility manager (MM) 228, which tracks mobile stations as they move through wireless network 10. Radio resources (RR) 230 checks that there are radios available for the call. Base station system application part (BSSAP) 224 is then instructed to route the call to the appropriate BTS. The call is the received at MTP 230, routed through SCCP 228 and to BSSAP 224 to the serving BTS.

One embodiment of our invention will now be explained using the block diagram of Fig. 1 taken in conjunction with the call flow diagram of Fig. 2. The caller at telephone 142 wants to call roaming mobile station 144. The caller also knows that the roaming mobile station is in the local calling region of telephone 142. Therefore, the caller at telephone 142 dials a special code or local directory number. The special code indicates to PSTN 12 that the caller is requesting a local roaming connection. In response to the special code, PSTN 12 delivers the call to GMSC 14. GMSC 14 answers the call and prompts the user for the directory number of the mobile station. Advantageously, GMSC 14 generates a tone as a prompt (as is currently done in the areas of pagers).

When GSMC 14 receives the directory number of roaming mobile station 144, it sends a paging message to all other MSC's 34 and 36 in its predefined local area, which includes the directory number of roaming mobile station 144. These messages are sent simultaneously to all MSC's in this group. A predefined local area may include just one MSC, or may include two or more depending upon the local service provider, the size of the local service region, etc.

Each MSC 14, 34 and 36 checks its respective VLR's 32, 130 and 132 to -8- determine if a roaming mobile station with the dial directory number is present in its local area. In this case, VLR 130 associated with MSC 34 includes the location of roaming mobile station 144, because roaming mobile station 144 registered with MSC 34 when it was turned on. MSC 34 returns this information to GMSC 14. MSC 34 then sends a radio link paging message to BTS 58 in cell 64. Normal call setup is performed and the call is completed from telephone 142 through PSTN 12, GMSC 14, MSC 38, BTS 58 to roaming mobile station 144.

In this manner, a roaming mobile station, such as 144, can be contacted on a local billing cost basis even though the directory number may indicate a long distance, or even out-of-country, destination. That is, dialing the directory number directly would normally cause the PSTN to deliver the call to a remote destination (such as GMSC 102); but, because of the special code, it is delivered to local GMSC 14. Thus, substantial savings may be realized both for the calling party at telephone 142 and the called party at roaming mobile station 144. A further embodiment will now be described in connection with Fig. 1 taken in conjunction with the call flow diagram of Fig. 3. In this exemplary embodiment, the caller at telephone 142 dials a special directory number. This directory number may be a local directory number, some form of "800" or "888" number or a prefix code (office code or the first three digits of a seven digit number). PSTN 12 recognizes the special number and routes the call to the nearest gateway MSC.

GMSC 14 receives the call and routes it to intelligent peripheral (IP) 134.

A connection is made between telephone 142 and IP 134. The voice prompt unit

140 in IP 134 prompts the user of telephone 142 to enter the directory number of the destination roaming mobile station 144. Digit recognition may be through digit recognition unit 136 that receives and translate touch-tone signals and dial pulse signals, or through speech recognition unit 140, that can recognize and translate spoken digits. The collected digits are then sent to GMSC 14. By setting up a call through IP 134, the initial step of routing the call to the home GMSC is bypassed. In this manner, the call enters the wireless network at a local gateway rather than at a gateway that could be a great distance away.

Returning to Figs. 1 and 3, GMSC 14 sends a message on signaling network 124 to HLR 126 to determine the current location of roaming mobile -9- station 144. HLR 126 returns this information to GMSC 14 to set up a call to roaming mobile station 144. At this point, it is advantageous that GMSC 14 determines whether the location of roaming mobile station 144 is within the limited boundary for local calling. This check prevents abuse of local calling in order to make a long distance call through the wireless network.

If the roaming mobile station 144 is located (according to the information returned by HLR 12) within the set of MSCs which control a local calling area, GMSC 14 extends the call to that MSC, in this case MSC 34. MSC 34 then sends a radio link paging message for roaming mobile station 144, which responds, and a mobile call is set up. The call is then completed between the caller of telephone 142 and roaming mobile station 144.

This invention has been described in terms of specific embodiments set forth in detail, but it is to be understood that these are illustrative and that the invention is not necessarily so limited. Modifications and variations will be apparent from this disclosure and thus do not depart from the scope of this invention. Such variations and modifications of the disclosed invention are considered to be within the scope of this invention and the following claims.

Claims

-10-

CLAIMS:

1. A mobile switching center that delivers calls to a roaming mobile station in a local wireless service region, for use in a telecommunications network, said mobile switching center comprising: means for receiving call requests for a roaming mobile station; means responsive to receipt of said roaming mobile station's directory number for causing said roaming mobile station to be located within said local wireless service region; and means responsive to said roaming mobile station being located for establishing a connection between said roaming mobile station and said means for receiving call requests.

2. A mobile switching center in accordance with claim 1 wherein said means for receiving call requests is identified in said telecommunications network by a local directory number.

3. A mobile switching center in accordance with claim 1 wherein said means for receiving call requests is identified in said telecommunications network by an area code.

4. A mobile switching center in accordance with claim 1 wherein said means for receiving call requests is identified in said telecommunications network by a prefix code.

5. A mobile switching center in accordance with claim 1 further comprising means connected to said means for receiving call requests for prompting a calling party for said directory number of said mobile station.

6. A mobile switching center in accordance with claim 5 wherein said means for prompting comprises an intelligent peripheral device. -11-

7. A mobile switching center in accordance with claim 1 wherein said means for locating said roaming mobile station comprises means for querying a home location register for information relating to the location of said roaming mobile station.

8. A mobile switching center in accordance with claim 7 wherein said means for connecting uses said information relating to the location of said roaming mobile station to complete said call.

9. A mobile switching center in accordance with claim 1 wherein said means for locating said roaming mobile station comprises means for sending a paging message including said directory number of said roaming mobile station to a set of mobile switching centers to determine whether said roaming mobile station is in one of said mobile switching centers' visitor location register.

10. A mobile switching center in accordance with claim 9 wherein said mobile switching center further includes means for receiving a response from one of said mobile switching centers and for connecting said means for receiving said call to said responding mobile switching center.

11. A mobile switching center for connecting a call from a telecommunications network to a roaming mobile station having a directory number in a local wireless service region, said wireless service region comprising a plurality of mobile switching centers, comprising: means for receiving a call from said telecommunications network, said call including said directory number of said roaming mobile station; means responsive to receipt of said directory number for sending a paging message to each of said plurality of mobile switching centers, each of said paging messages including said directory number; and means responsive to a response from one of said plurality of mobile switching systems for connecting the call to said responding mobile switching center in order to complete said call. -12-

13. A mobile switching center for connecting a call from a caller to a roaming mobile station having a directory number in a local wireless service region, for use in a telecommunications network, said telecommunications network including a home location register, said mobile switching center comprising: means for receiving a call for said roaming mobile station from said telecommunications network; means responsive to receipt of said call for connecting said call to a voice prompt, said voice prompt prompting said caller to enter said directory number; means responsive to receipt of said directory number for sending a query message to a home location register, said query message including said directory number; and means responsive to a response from said home location register including an identification of the location of said roaming mobile station for routing said call to said location and connecting said call through between said caller and said roaming mobile station.

14. A mobile switching center in accordance with claim 13 wherein said voice prompt comprises an intelligent peripheral.

15. A mobile switching center in accordance with claim 13 wherein said telecommunications network includes a signaling network and said home location register is in communication with said signaling network, said means for sending a query message comprising a connection to said signaling network and means for sending and receiving messages on said signaling network.

16. A mobile switching center in accordance with claim 13 wherein said telecommunication network includes a signaling network, said signaling network connected to an intelligent peripheral, further comprising means for connecting said call to said voice prompt includes means for connecting said mobile switching center to said intelligent peripheral through said signaling network. -13-

17. A method for delivering a call to a roaming mobile station in a local wireless service area, said mobile station switching center connected to a telecommunications network, said method comprising the steps of: receiving a call from said telecommunications network responsive to a dialed number other than a directory number of said mobile station; receiving said directory number from said telecommunications network; determining the location of said roaming wireless mobile in said local service area using said directory number; and connecting said call to said roaming mobile station.

18. A method in accordance with claim 17 wherein said step of determining a location of said roaming wireless station includes sending messages including said directory7 number to a plurality of mobile switching centers and receiving location information from one of said mobile switching centers.

19. A method in accordance with claim 18 wherein said step of receiving said directory number from said telecommunications network includes connecting said call to a voice prompt, said voice prompt prompting for said directory number; said voice prompt receiving said directory number and returning said directory number to said mobile switching center.

20. A method in accordance with claim 19 wherein said mobile switching office is connected to an intelligent peripheral; and wherein said step of connecting said call to a prompting device comprises connecting said call to said intelligent peripheral.