WO1997046043A2

WO1997046043A2 - System and method of delivering roamer port calls in multiple radio telecommunication switches

Info

Publication number: WO1997046043A2
Application number: PCT/SE1997/000811
Authority: WO
Inventors: George Foti
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 1996-05-30
Filing date: 1997-05-16
Publication date: 1997-12-04
Also published as: AU3051897A; BR9709480A; WO1997046043A3; CA2255847A1; CA2255847C

Abstract

A system and method are disclosed for extending roamer port coverage from a single mobile switching center (MSC) to a plurality of associated MSCs within a visited radio telecommunications network (70) in which a mobile subscriber (19) is roaming. In a first MSC (73), a roamer port number is defined to cover the associated plurality of MSCs (74, 75) within the visited radio telecommunications network (70). When a call is received through the roamer port number for the roaming mobile subscriber (19), the first MSC (73) simultaneously places calls by seizing trunks (76) to each of the associated plurality of MSCs (74, 75), and instructs each of the associated plurality of MSCs to simultaneously page for the roaming mobile subscriber (19). Alternatively, the first MSC may utilize network signaling messages to notify each of the associated plurality of MSCs (74, 75) that the call is a roamer port call and to instruct each of the MSCs to page for the roaming mobile subscriber (19). Upon receipt of a successful page response in one of the paging MSCs, the call is routed to the MSC with the successful page response.

Description

SYSTEM AND METHOD OF

DELIVERING ROAMER PORT CALLS IN MULTIPLE RADIO

TELECOMMUNICATION SWITCHES

BACKGROUND OF THE INVENTION

Technical Field of the Invention

This invention relates to radio telecommunication systems and, more particularly, to a system and method of utilizing a single roamer port number in a plurality of radio telecommunication switches. Description of Related Art

In radio telecommunications networks, mobile subscribers may roam from a home network to a visited network which may be located outside the local calling area of the home network. When a call is then made to the roaming mobile subscriber, long distance charges may be incurred by the mobile subscriber, the calling party, or both. This is true even if the calling party and the mobile subscriber are both located within the local calling area of the visited network.

Without the benefit of a roamer port number in the visited network, existing radio telecommunications networks utilize the following process of placing a call from a local subscriber in a visited network to a roaming mobile subscriber who is roaming in the visited network. The local subscriber dials the long distance number of the roaming subscriber since the local subscriber does not know that the roaming mobile subscriber has roamed into the visited network. The call from the local subscriber goes first to the Mobile Switching Center (MSC) in the visited network serving the local subscriber. The MSC routes the call long distance to the home MSC of the roaming mobile subscriber because the Subscriber Number

(SNB) of the called mobile station (MS) is identified as being from the mobile subscriber's home network. The home MSC interrogates the mobile subscriber's Home Location Register (HLR) in the mobile subscriber's home network to obtain subscriber profile information and location information for the roaming mobile subscriber. The mobile subscriber's HLR provides location information indicating that the mobile subscriber is roaming in the visited network. The call is then routed from the home MSC back to the visited network. Long distance charges are thus incurred by both the calling subscriber and the called subscriber.

If a call is made from the PSTN in the local calling area of the visited network, to a mobile subscriber who is roaming in the visited network, the call is first routed by the PSTN to a gateway MSC (G-MSC) in the mobile subscriber's home network, thereby incurring long distance charges for the calling party. The G-MSC interrogates the mobile subscriber's HLR and determines that the mobile subscriber is in the visited network. Then the call is routed from the G-MSC to the visited network MSC, thereby incurring long distance charges for the called mobile subscriber. Thus, two long distance trunks are established and both subscribers pay long distance charges.

By regulation, every operator has at least one roamer port number in its network. Roamer port numbers utilize two-stage dialing to enable a local subscriber in the visited network to place a call to a mobile subscriber who is roaming in the visited network without incurring long distance charges. If a local subscriber in the visited network calls a mobile subscriber who is roaming in the visited network, the local subscriber dials the roamer port number for his MSC which is a local number. He then gets a second dial tone, and dials the mobile subscriber's number. The roamer port number is defined in the visited network subscriber's MSC and may be the entire service area of the visited MSC or some sub-area thereof. The roamer port number tells the visited MSC to page for the roaming mobile subscriber in the roamer port service area. That allows a local subscriber in the visited network to call the mobile subscriber who is roaming in the visited network without incurring long distance charges.

If there are multiple MSCs in the visited network, there may be a problem in locating the mobile subscriber and delivering the call because the mobile subscriber is only paged within the service area of the MSC in which the roamer port is defined. For example, if the visited network area is covered by MSC 3, MSC 4, and MSC 5, and the roamer port number is defined in MSC 3, then the mobile subscriber is only paged by MSC 3. Thus, there is only one chance in three of locating the mobile subscriber. If the mobile subscriber happens to be located in MSC 4 or MSC 5, then it is not located by the network, and the call is not delivered. As a result, paging resources are unsuccessfully utilized more often, since more attempts result in the mobile station not being found. Operators, therefore, lose revenue since there is a greater chance that the call will not be successfully completed. Some existing radio telecommunications networks may provide for sequential paging of all of the MSCs in a metropolitan area until a roaming mobile subscriber is found. The problem with this approach is that there may be an excessive delay before the mobile subscriber is located. As a result, the calling party often hangs up, or the trunks time out before the mobile subscriber is located. Since the number of MSCs continues to increase in major metropolitan areas, the sequential paging method is inadequate and unworkable. Existing radio telecommunications networks may also provide an enhanced roamer port feature. When a call comes into a roamer port in a visited MSC (V-MSC) , the V- MSC recognizes the MSNB of the MS as being associated with the mobile subscriber's home exchange. The V-MSC then interrogates the subscriber's HLR for location and profile information for the mobile subscriber. The mobile subscriber's HLR determines the location of the mobile subscriber and returns the location information to the V- MSC with a temporary routing number. If the routing number is a local number within the visited network, the V-MSC delivers the call. There are several problems with this solution, however. First, long distance interrogation of the mobile subscriber's HLR is not desirable to network operators due to the administrative overhead burden of having to update tables associating HLRs with every roaming mobile subscriber that enters the V-MSC. Second, network operators prefer that the roamer port process be an entirely local process within the visited network.

Although there are no known prior art teachings of a solution to the aforementioned deficiency and shortcoming such as that disclosed herein, U.S. Patent Number 5,153,902 to Buhl et al . (Buhl '902) and U.S. Patent Number 5,282,240 to Buhl et al . (Buhl '240) discuss subject matter that bears some relation to matters discussed herein. Buhl '902 discloses a mobile communication system in which a mobile subscriber may roam from one exchange to another. An interrogation exchange receives incoming calls to the mobile subscriber and requests information as to the location of the mobile subscriber from its home exchange. The home exchange initiates and coordinates the paging process to a plurality of possible exchanges in which the mobile subscriber may be located. Buhl '902, however, is not a local process. Buhl '902 requires long distance interrogation of the home exchange to obtain location information for the mobile subscriber. As noted above, this is not desirable to network operators due to the administrative overhead burden of having to update tables in the visited exchange associating HLRs with every roaming MS that enters the visited exchange. Additionally, calling subscribers as well as called mobile subscribers may incur long distance charges with the system of Buhl '902. Thus Buhl '902 does not teach or suggest the present invention.

Buhl '240 discloses a mobile communication system in which the home exchange of a mobile subscriber maintains location information for the mobile subscriber. Upon receipt of an incoming call for the mobile subscriber, the home exchange orders the exchange (s) where the mobile subscriber may be found to page the mobile subscriber and establish a voice channel to the mobile subscriber before routing the call through the network. Buhl '240, however, is not a local process. Buhl '240 requires long distance interrogation of the home exchange to obtain location information for the mobile subscriber. As noted above, this is not desirable to network operators due to the administrative overhead burden of having to update tables in the visited exchange associating HLRs with every roaming MS that enters the visited exchange. Additionally, calling subscribers as well as called mobile subscribers may incur long distance charges with the system of Buhl '240. Thus Buhl '240 does not teach or suggest the present invention.

Review of each of the foregoing references reveals no disclosure or suggestion of a system or method such as that described and claimed herein. In order to overcome the disadvantage of existing solutions, it would be advantageous to have a system and method of extending the coverage area of a roamer port number from a single MSC to multiple MSCs within a visited network. Such a system would greatly increase the probability of successfully completing each call when compared to existing systems which page for the mobile subscriber only in a single MSC within the visited network where the roamer port number is defined. It would be additionally advantageous for such a system to be implemented locally in the visited network, without requiring long distance HLR interrogation. Such an implementation would reduce the administrative overhead burden of having to update tables associating every roaming mobile subscriber that enters the V-MSC with the mobile subscriber's HLR. In addition, in the event a roaming mobile subscriber's HLR becomes inopertive, the system would provide a means of contacting the roaming mobile subscriber through the roamer port number. The present invention provides such a system and method.

SUMMARY OF THE INVENTION In one aspect, the present invention is a system for extending roamer port coverage from a single mobile switching center (MSC) to a plurality of MSCs within a visited radio telecommunications network in which a mobile subscriber is roaming. The system comprises means for associating a roamer port number with a plurality of MSCs within the visited radio telecommunications network, means for simultaneously paging for the roaming mobile subscriber within each of the associated plurality of MSCs upon receipt of a call for the mobile subscriber through the roamer port number, and means for routing the call to one of the plurality of associated MSCs in which a successful page response is received. The means for simultaneously paging for the roaming mobile subscriber within each of the associated plurality of MSCs may include means within a first MSC for placing simultaneous calls by seizing trunks to each of the associated plurality of MSCs upon receipt of the call for the roaming mobile subscriber, and means within the first MSC for instructing each of the associated plurality of MSCs to simultaneously page for the roaming mobile subscriber. Alternatively, the means for simultaneously paging for the roaming mobile subscriber within each of the associated plurality of MSCs may include means within the first MSC for utilizing network signaling messages to notify each of the associated plurality of MSCs that the call is a roamer port call and to instruct each of the associated plurality of MSCs to page for the roaming mobile subscriber.

In another aspect, the present invention is a method of extending roamer port coverage from a single mobile switching center (MSC) to a plurality of MSCs within a visited radio telecommunications network in which a mobile subscriber is roaming. The method comprises the steps of associating a roamer port number with a plurality of MSCs within the visited radio telecommunications network, simultaneously paging for the roaming mobile subscriber within each of the associated plurality of MSCs upon receipt of a call for the mobile subscriber through the roamer port number, and routing the call to one of the plurality of associated MSCs in which a successful page response is received. The step of simultaneously paging for the roaming mobile subscriber within each of the associated plurality of MSCs may include the steps of simultaneously placing calls by seizing trunks to each of the associated plurality of MSCs upon receipt of the call for the roaming mobile subscriber, and instructing each of the associated plurality of MSCs to simultaneously page for the roaming mobile subscriber. Alternatively, the step of simultaneously paging for the roaming mobile subscriber within each of the associated plurality of MSCs may include utilizing, within the first MSC, network signaling messages to notify each of the associated plurality of MSCs that the call is a roamer port call and to instruct each of the associated plurality of MSCs to page for the roaming mobile subscriber.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood and its numerous objects and advantages will become more apparent to those skilled in the art by reference to the following drawing, in conjunction with the accompanying specification, in which: FIG. 1 (Prior Art) is a high level block diagram of two existing radio telecommunications networks between which mobile subscribers may roam;

FIG. 2 is a flow chart illustrating the steps involved in the process of extending the coverage area of a roamer port number from a single mobile switching center

(MSC) to multiple MSCs within a visited network in a first embodiment of the present invention;

FIG. 3 is a flow chart illustrating the steps involved in the process of extending the coverage area of a roamer port number from a single MSC to multiple MSCs within a visited network in a second embodiment of the present invention;

FIG. 4 is a simplified block diagram of a radio telecommunications network suitable for implementing the present invention;

FIG. 5 is a simplified block diagram of a MSC illustrating the additional functions added to an existing

MSC in order to define and implement an extended roamer port in accordance with the teachings of the present invention; and

FIG. 6 is a simplified block diagram of a MSC illustrating the additional functions added to an existing

MSC in order to interact with the MSC of FIG. 5 and thereby implement an extended roamer port in accordance with the teachings of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 is a high level block diagram of two existing radio telecommunications networks between which mobile subscribers may roam. Network-1 (10) may include, by way of example, a first home location register (HLR-1) 11 and a plurality of mobile switching centers (MSCs) such as MSC-1 (12) and MSC-2 (13) . Network-2 (14) may include a second home location register (HLR-2) 15 and a plurality of MSCs such as MSC-3 (16) , MSC-4 (17) and MSC-5 (18) . A Subscriber-A (Sub-A) 19, whose home network is Network-1 (10) may roam from Network-1 (10) to Network-2 (14) . Sub-A may then desire to receive telephone calls originating from within the geographic area serviced by Network-2, and may wish to receive such calls without long distance charges accruing to either Sub-A or local calling parties. In accordance with the teachings of the present invention, the MSCs within Network-2 are modified so that the area covered by a roamer port number may be defined by the network operator. The area definition is saved in one of the network MSCs. For example, Roamer Port Number X may be defined in MSC-3, and may cover the service areas of MSC-3, MSC-4, and MSC-5. Sub-A is paged in all three MSCs (MSC-3, MSC-4, and MSC-5) after Roamer Port Number X is dialed and Sub-A is dialed.

When a call comes in on the roamer port number, MSC-3 pages Sub-A 19 in the service area of MSC-3. At the same time, MSC-3 instructs MSC-4 and MSC-5 to page for Sub-A in their respective service areas since the service areas of MSC-4 and MSC-5 are also covered by the roamer port number. In a first embodiment, MSC-3 simultaneously places calls to MSC-4 and MSC-5 by seizing trunks 21 to MSC-4 and MSC-5. MSC-3 may add a prefix to Sub-A's Subscriber Number (SNB) (for example #26) and send the prefix and SNB to MSC-4 and MSC-5. The prefix identifies the call to the SNB as a roamer port call, and instructs MSC-4 and MSC-5 to page for Sub-A in their service areas. MSC-4 and MSC-5 then remove the prefix and page for Sub-A in their respective service areas. Thus, Sub-A is paged in all three Network-2 MSCs at the same time. If a successful page response is received from Sub-A in either

MSC-4 or MSC-5, the call is completed to the mobile station. The originating MSC (MSC-3) then clears the call

(trunk) to the unsuccessful MSC. In a second embodiment, MSC-3 instructs MSC-4 and

MSC-5 to page for Sub-A in their respective service areas through network signaling messages rather than seizing trunks. For example, in a network utilizing the IS-41 intersystem signaling protocol, MSC-3 may be modified to send Routing Request (RouteReq) Invoke messages to both MSC-4 and MSC-5. The RouteReq messages include an indicator that the call is a roamer port call. Upon receipt of the RouteReq Invoke messages, MSC-4 and MSC-5 page for Sub-A in their respective service areas. Thus, Sub-A is paged in all three Network-2 MSCs at the same time. If a successful page response is received from Sub- A by one of the MSCs, the successful MSC notifies the originating MSC where paging is halted. Thereafter, the call is routed locally to the successful MSC and Sub-A.

In either the first or second embodiments, if a successful page response is not received from Sub-A by any of the MSCs, the calling party is notified that Sub-A was not found.

In this manner, the coverage area of a roamer port number is extended from a single MSC to multiple MSCs within a visited network. The probability of successfully completing each call is greatly increased over existing systems which page for roaming mobile subscribers only in a single MSC where the roamer port number is defined. In addition, the system of the present invention is implemented locally in the visited network. There is no requirement for long distance HLR interrogation. This reduces the administrative overhead burden of having to update tables associating HLRs with every roaming mobile subscriber that enters the visited network.

FIG. 2 is a flow chart illustrating the steps involved in the process of extending the coverage area of a roamer port number from a single MSC to multiple MSCs within a visited network in a first embodiment of the present invention. At step 31, the Network-2 operator defines Roamer Port Number-X in MSC-3 to cover the service areas of MSC-3, MSC-4, and MSC-5. At step 32, Sub-A 19 roams from Network-1 to Network-2. At step 33, an incoming call for Sub-A 19 is received on Roamer Port Number-X in MSC-3 in Network-2. The process then moves to step 34 where MSC-3 begins to page for Sub-A in the MSC-3 service area and simultaneously places calls to MSC- 4 and MSC-5 by seizing trunks 21. At step 35, MSC-3 adds a prefix to Sub-A' s SNB and sends the modified SNB to both MSC-4 and MSC-5. The process then moves to step 36 where MSC-3, MSC-4, and MSC-5 all page for Sub-A 19 at the same time .

The process then moves to step 37 where it is determined whether or not a successful page response was received from any of the paging MSCs. If not, then the process moves to step 38 where MSC-4 and MSC-5 notify MSC-

3 that Sub-A was not found. The process then moves to step 39 where MSC-3 notifies the calling party that Sub-A was not found. If, however, a successful page response was received at step 37, then the process moves to step

40 where the MSC with the successful page response notifies the originating MSC (MSC-3) of the response, and the call is completed to Sub-A 19. The originating MSC (MSC-3) then clears the call (trunk) to the unsuccessful MSC at 41.

FIG. 3 is a flow chart illustrating the steps involved in the process of extending the coverage area of a roamer port number from a single MSC to multiple MSCs within a visited network in a second embodiment of the present invention. At step 51, the Network-2 operator defines Roamer Port Number-X in MSC-3 to cover the service areas of MSC-3, MSC-4, and MSC-5. At step 52, Sub-A 19 roams from Network-1 to Network-2. At step 53, an incoming call for Sub-A 19 is received on Roamer Port Number-X in MSC-3 in Network-2. The process then moves to step 54 where MSC-3 begins to page for Sub-A in the MSC-3 service area and simultaneously sends intersystem signaling messages to MSC-4 and MSC-5 instructing MSC-4 and MSC-5 to page for Sub-A in their respective service areas. As noted earlier, in networks utilizing the IS-41 intersystem signaling protocol, MSC-3 may be modified to send Routing Request (RouteReq) Invoke messages to both MSC-4 and MSC-5. The RouteReq messages include an indicator that the call is a roamer port call . Upon receipt of the RouteReq Invoke messages at step 55, MSC-4 and MSC-5 page for Sub-A in their respective service areas at step 56.

The process then moves to step 57 where it is determined whether or not a successful page response was received from any of the paging MSCs. If not, MSC-4 and MSC-5 notify MSC-3 that Sub-A was not found at step 58. MSC-4 and MSC-5 may send RouteReq Return Result messages to MSC-3 indicating that Sub-A was not found. The process then moves to step 59 where MSC-3 notifies the calling party that Sub-A was not found. If, however, a successful page response was received at step 57, then the process moves to step 60 where the MSC with the successful page response notifies the originating MSC (MSC-3) of the response, and paging is halted. Finally, the process moves to step 61 where the call is routed locally to the successful MSC and Sub-A 19.

FIG. 4 is a simplified block diagram of a radio telecommunications network 70 suitable for implementing the present invention. A HLR 71 is connected by signaling links 72 to MSC-3 (73), MSC-4 (74), and MSC-5 (75) . MSC-3 may establish multiple voice trunks 76 to MSC-4 and MSC-5. MSC-3 is modified to define a roamer port number to cover the service areas of MSC-3, MSC-4, and MSC-5. MSC-3 is also modified to add a prefix to any SNB which is called through the roamer port . FIG. 5 is a simplified block diagram of a MSC (for example MSC-3) illustrating the additional functions added to an existing MSC in order to define and implement an extended roamer port in accordance with the teachings of the present invention. In the exemplary network of FIG. 4, the roamer port number is defined in MSC-3 to cover the service areas of MSC-3, MSC-4, and MSC-5 in instruction block 81. Instruction block 82 identifies roamer port calls by adding a prefix (for example #26) to any SNB which is called through the roamer port. Instruction block 83 enables MSC-3 to simultaneously place calls to other MSCs by seizing multiple voice trunks to other MSCs covered in the roamer port definition in block 81. Instruction block 84 enables MSC-3 to direct the paging of a mobile station within the service area of MSC-3 while MSC-4 and MSC-5 also page for the mobile station. Finally, instruction block 85 enables MSC-3 to order MSC-4 and MSC-5 to stop paging if MSC-3 is the first MSC to receive a page response from the mobile station. The call is then delivered to MSC-3 and the mobile station.

FIG. 6 is a simplified block diagram of a MSC (for example MSC-4) illustrating the additional functions add with the MSC of FIG. 5 and thereby implement an extended roamer port in accordance with the teachings of the present invention. When MSC-4 receives a SNB from MSC-3 with a prefix added to the SNB, instruction block 91 enables MSC-4 to recognize the call as a roamer port call, and instructs MSC-4 to page for the associated mobile station within the service area of MSC-4 utilizing paging mechanism 92. If MSC-4 is the first paging MSC to receive a page response from the mobile station, instruction block 93 enables MSC-4 to notify the originating MSC (for example MSC-3) . The call is then delivered to MSC-4 and the mobile station.

It is thus believed that the operation and construction of the present invention will be apparent from the foregoing description. While the method, apparatus and system shown and described has been characterized as being preferred, it will be readily apparent that various changes and modifications could be made therein without departing from the spirit and scope of the invention as defined in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A system for extending roamer port coverage from a single mobile switching center (MSC) to a plurality of MSCs within a visited radio telecommunications network in which a mobile subscriber is roaming, said system comprising: means for associating a roamer port number with a plurality of MSCs within said visited radio telecommunications network; means for simultaneously paging for said roaming mobile subscriber within each of said associated plurality of MSCs upon receipt of a call for said mobile subscriber through said roamer port number; and means for routing said call to one of said plurality of associated MSCs in which a successful page response is received.

2. The system for extending roamer port coverage of claim 1 wherein said means for associating a roamer port number with a plurality of MSCs includes a first MSC in which the roamer port number is defined to cover said associated plurality of MSCs within said visited telecommunications network.

3. The system for extending roamer port coverage of claim 2 wherein said means for simultaneously paging for said roaming mobile subscriber within each of said associated plurality of MSCs includes: means within said first MSC for simultaneously placing calls by seizing trunks to each of said associated plurality of MSCs upon receipt of said call for said roaming mobile subscriber; and means within said first MSC for instructing each of said associated plurality of MSCs to simultaneously page for said roaming mobile subscriber.

4. The system for extending roamer port coverage of claim 3 wherein said means for instructing each of said associated plurality of MSCs to simultaneously page for said roaming mobile subscriber includes means within said first MSC for adding a prefix to said mobile subscriber's subscriber number (SNB) , said prefix identifying said call as a roamer port call .

5. The system for extending roamer port coverage of claim 4 further comprising: means within each of said associated plurality of MSCs for determining whether a page response from said roaming mobile subscriber has been successfully received; means within each of said associated plurality of MSCs for notifying said first MSC of said successful page response; and means within said first MSC for clearing calls to each of said associated plurality of MSCs where page responses were not received.

6. The system for extending roamer port coverage of claim 2 wherein said means for simultaneously paging for said roaming mobile subscriber within each of said associated plurality of MSCs includes means within said first MSC for utilizing network signaling messages to notify each of said associated plurality of MSCs that said call is a roamer port call and to instruct each of said associated plurality of MSCs to page for said roaming mobile subscriber.

7. The system for extending roamer port coverage of claim 6 further comprising: means within each of said associated plurality of MSCs for determining whether a page response from said roaming mobile subscriber has been successfully received; and means within each of said associated plurality of MSCs for notifying said first MSC that a successful page response has been received.

8. A method of extending roamer port coverage from a single mobile switching center (MSC) to a plurality of

MSCs within a visited radio telecommunications network in which a mobile subscriber is roaming, said method comprising the steps of: associating a roamer port number with a plurality of

MSCs within said visited radio telecommunications network; simultaneously paging for said roaming mobile subscriber within each of said associated plurality of

MSCs upon receipt of a call for said mobile subscriber through said roamer port number; and routing said call to one of said plurality of associated MSCs in which a successful page response is received.

9. The method of extending roamer port coverage of claim 8 wherein said step of associating a roamer port number with a plurality of MSCs includes defining the roamer port number in a first MSC to cover said associated plurality of MSCs within said visited telecommunications network.

10. The method of extending roamer port coverage of claim 9 wherein said step of simultaneously paging for said roaming mobile subscriber within each of said associated plurality of MSCs includes the steps of: simultaneously placing calls by seizing trunks to each of said associated plurality of MSCs upon receipt of said call for said roaming mobile subscriber; and instructing each of said associated plurality of MSCs to simultaneously page for said roaming mobile subscriber.

11. The method of extending roamer port coverage of claim 10 wherein said step of instructing each of said associated plurality of MSCs to simultaneously page for said roaming mobile subscriber includes adding a prefix to said mobile subscriber's subscriber number (SNB) in said first MSC, said prefix identifying said call as a roamer port call .

12. The method of extending roamer port coverage of claim 11 wherein said step of simultaneously paging for said roaming mobile subscriber within each of said associated plurality of MSCs includes the steps of: determining within each of said associated plurality of MSCs whether a page response from said roaming mobile subscriber has been successfully received; notifying said first MSC of said successful page response; and clearing calls to each of said associated plurality of MSCs where page responses were not received.

13. The method of extending roamer port coverage of claim 9 wherein said step of simultaneously paging for said roaming mobile subscriber within each of said associated plurality of MSCs includes utilizing, within said first MSC, network signaling messages to notify each of said associated plurality of MSCs that said call is a roamer port call and to instruct each of said associated plurality of MSCs to page for said roaming mobile subscriber.

14. The method of extending roamer port coverage of claim 13 wherein said step of simultaneously paging for said roaming mobile subscriber within each of said associated plurality of MSCs includes the steps of: determining within each of said associated plurality of MSCs whether a page response from said roaming mobile subscriber has been successfully received; and notifying said first MSC that a successful page response has been received.

15. A method of placing a call to a mobile subscriber roaming within a visited radio telecommunications network, said roaming mobile subscriber having a home network in which location information regarding said roaming mobile subscriber cannot be retrieved from a malfunctioning home location register associated with said roaming mobile subscriber, said method comprising the steps of : placing said call through a roamer port number in an originating mobile switching center in said visited radio telecommunications network; associating said roamer port number with a plurality of MSCs within said visited radio telecommunications network; simultaneously paging for said roaming mobile subscriber within each of said associated plurality of MSCs upon receipt of a call for said mobile subscriber through said roamer port number; determining within each of said associated plurality of MSCs whether a page response from said roaming mobile subscriber has been successfully received; notifying said originating mobile switching center of said successful page response; and routing said call to one of said plurality of associated MSCs in which said successful page response is received.