WO2007103620A2

WO2007103620A2 - Method for routing calls in a mobile communication network

Info

Publication number: WO2007103620A2
Application number: PCT/US2007/062211
Authority: WO
Inventors: Jian-Hua Hou; Yun-Shan Ge; Chao Jiang; Hong Wang; Ying-Xin Zhou
Original assignee: Motorola, Inc.
Priority date: 2006-03-07
Filing date: 2007-02-15
Publication date: 2007-09-13
Also published as: CN101035361A; WO2007103620A3

Abstract

A method for routing calls in a mobile communication network is useful for decreasing a frequency of failed calls. The method includes processing at a Home Location Register (HLR) (315) a call setup message for a call to a Mobile Station (MS). In response to the call setup message, a first request for a roaming number associated with the MS is transmitted from the HLR (315) to a first Mobile. Switching Center (MSC) (325). After a roaming number associated with the MS is not received from the first MSC (325) in response to the first request, a second request for a roaming number associated with the MS is transmitted from the HLR (315) to a second MSC (330).

Description

CE15534CM METHOD FOR ROUTING CALLS

IN A MOBILE COMMUNICATION NETWORK

FIELD OF THE INVENTION

The present invention relates generally to routing telephone calls to mobile devices. In particular, although not exclusively, the invention relates to routing calls in a Global System for Mobile Communications (GSM) network through a Mobile Switching Center (MSC) using a Home Location Register (HLR).

BACKGROUND OF THE INVENTION

Telephone calls placed to mobile phones may not go through due to a variety of reasons. A called mobile phone may be busy, turned off, out of range of a wireless network, or may be otherwise non-reachable. Tn such situations, callers often place repetitive additional calls to the called mobile phone until a call goes through and the called mobile phone is answered. Placing such repetitive additional calls is inconvenient and problematic as it wastes the time of callers, who must continual re- key a phone dialing sequence, and because it wastes wireless network resources that must repetitively route and process the additional voice calls (which generally receive high network priority) until a called phone is answered.

In a Global System for Mobile Communications (GSM) network, calls arc routed to mobile phones operating in the network using Home Location Registers (HLRs). The HLRs store data about where in the network a particular mobile phone is operating. Thus when amobile phone roams to a new Radio Access Network CE15534CM (RAN) node in a GSM network, the phone connects to a Mobile Switching Center

(MSC) associated with that RAN node. The MSC identifies the phone and informs an HLR associated with the phone that the phone is now currently in wireless communication with the MSC. If an incoming call directed to the phone is then received in the network, the network first contacts the HLR associated with the phone to learn the identity of the MSC that is currently managing wireless communication with the phone. The incoming call is then routed through the MSC to the phone. However, technical problems sometimes arise with MSCs, which are then rendered temporarily out of service. When technical problems with an MSC arise suddenly, or are transient and reoccurring, calls to mobile phones associated with the out of service MSC will not go through. That is because an HLR generally designates only a single MSC with a particular mobile phone. Thus when an MSC is suddenly rendered out of service, all incoming calls that would normally be routed through the MSC to phones associated with the MSC do not go through.

SUMMARY OF THE INVENTION

According to one aspect, the present invention is a method for routing calls in a mobile communication network. The method includes processing at a Home Location Register (HLR) a call setup message for a call to a Mobile Station (MS). In response to the call setup message, a first request for a roaming number associated with the MS is transmitted from the HLR to a first Mobile Switching Center (MSC). After a roaming number associated with the MS is not received from the first MSC in response to the first request, a second request for a roaming number associated with the MS is transmitted from the HLR to a second MSC. CE15534CM Embodiments of the present invention therefore enable reducing a frequency of failed calls in a mobile communication network. Where multiple MSCs operate within a given pool area that covers a called mobile station, an HLR that manages the called mobile station is not limited to transmitting requests for roaming numbers for the mobile station to only a single MSC to which the mobile station was last registered. Rather, the HLR can iteratively contact each MSC from a plurality of MSCs operating in the pool area, until one of the MSCs is able to provide a roaming number for a particular called mobile station.

BRIEF DESCRIPTION OF THE DRAWINGS

Tn order that the invention may be readily understood and put into practical effect, reference now will be made to exemplary embodiments as illustrated with reference to the accompanying figures, wherein like reference numbers refer to identical or functionally similar elements throughout the separate views. The figures together with a detailed description below, arc incorporated in and form part of the specification, and serve to further illustrate the embodiments and explain various principles and advantages, in accordance with the present invention, where:

FIG. 1 is a schematic diagram illustrating components of a typical Global System for Mobile Communications (GSM) voice data communications network that connects a calling station to a mobile station (MS); FIG. 2 is a schematic diagram illustrating components of a conventional GSM system that includes a pool area; CE15534CM FIG. 3 is a message sequence chart illustrating a method for routing calls in a mobile communication network, according to an embodiment of the present invention; and

FIG. 4 is a general flow diagram illustrating a method for routing calls in a mobile communication network, according to an embodiment of the present invention.

Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.

DETAILED DESCRIPTION

Before describing in detail embodiments that arc in accordance with the present invention, it should be observed that the embodiments reside primarily in combinations of method steps and apparatus components related to routing calls in a mobile communication network. Accordingly, the apparatus components and method steps have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention, so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein. CE15534CM In this document, relational terms such as left and right, first and second, front and rear, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element preceded by "comprises a . . ." does not, without more constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

Referring to FlG. 1, a schematic diagram illustrates components of a typical Global System for Mobile Communications (GSM) voice data communications network 100 that connects a calling station 105 to a mobile station (MS) 110. The calling station 105 can be any type of station, such as a mobile phone or a wireline terminal, capable of connecting to a Public Land Mobile Network (PLMN) 115 in which the MS 110 operates.

To initiate a call from the calling station 105 to the mobile station 110, the calling station 105 first sends an incoming call setup signal, such as an Initial Address Message (IAM), to a Gateway Mobile Switching Center (GMSC) 120 associated with the PLMN 115. If the calling station 105 is another mobile device, the IAM is routed to the GMSC 120 through another PLMN. If the calling station 105 is a wireline terminal, then the IAM is routed to the GMSC 120 through a local exchange. CE15534CM After receiving the incoming call setup signal, the GMSC 120 transmits a

Mobile Application Part (MAP) call setup message to a Home Location Register (HLR) 125 that is associated with the mobile station 110. The HLR 125 maintains subscriber data, such as a Mobile Subscriber Integrated Service Digital Network (MSISDN) number, associated with the called mobile station 110. The HLR 125 also maintains an identity of a Mobile Switching Center (MSC) 130 and corresponding Visitor Location Register (MSC/VLR) that provides current service to the mobile station 110. The MAP call setup message sent to the HLR 125 comprises for example a MAP_SEND_ROUTING_INFORMATION message that requests current routing information concerning the mobile station 110. In response to the received call setup message, the HLR 125 thus uses the

MSISDN of the called mobile station 110 to access information about the current location of the mobile station 110, and to identify the MSC 130 that is currently serving the mobile station 110. The HLR 125 then transmits a message to the MSC 130, such as a MAPJPRO VIDE RO AMING JSfUMBER message, requesting a roaming number associated with the mobile station 110. The MSC 130 responds by sending a MAP message back to the HLR 125, including a roaming number of the MSC 130, and the HLR 125 then forwards the roaming number to the GMSC 120. Using the roaming number, the GMSC 120 is then able to establish a call connection from the calling station 105, to the GMSC 120, and then directly to the MSC 130. Finally, the MSC 130 pages the mobile station 110 and assigns radio channels so that the call can go through between the calling station 105 and the mobile station 110.

Referring to FIG. 2, a schematic diagram illustrates components of a conventional GSM system 200 that includes a pool area 205. According to the Third CE15534CM Generation Partnership Project (3 GPP) standard 23.236, a pool area is an area within which a mobile station can roam without needing to change its serving Core Network (CN) node, such as an MSC. Pool areas can therefore reduce the frequency of inter- CN node updates, handovers and relocations, and reduce the volume of HLR update traffic.

The pool area 205 is served by one or more CN nodes, such as the first MSC

130, a second MSC 210, and a third MSC 215, all operating in parallel. All mobile stations, such as the mobile station 1 10, operating in the pool area 205 are controlled by a Radio Access Network (RAN) node 220. A RAN node 220 can comprise for example a Radio Network Controller (RNC) or a Base Station Controller (BSC).

According to the 3GPP standard 23.236, when an MSC such as the MSC 130 is unable to operate, such as if the MSC 130 suddenly falls out of service due to technical difficulties, calls to mobile stations managed by the out of service MSC 130 will not go through. Callers to such mobile stations are required to wait until a called mobile station performs a periodic location update, which can require a waiting time for example of more than six minutes, or wait until a called mobile station makes a mobile originated call. If the called mobile station makes a mobile originated call, the called mobile station will first execute a location update process and a new MSC will be assigned to the called mobile station. After the new MSC is assigned to the called mobile station, other mobile terminated calls will be able to again go through to the called mobile station.

Referring to FIG. 3, a message sequence chart 300 illustrates a method for routing calls in a mobile communication network, according to an embodiment of the present invention. At line 305, a call setup message such as a CE15534CM MAP_SEND_ROUTING_INFORMATION message is transmitted from a Gateway

Mobile Switching Center (GMSC) 310 to a Home Location Register (HLR) 315. The message identifies a called mobile station that is managed by the HLR 315. At line 320, the HLR 315 then transmits to a first Mobile Switching Center (MSC) 325, in response to the call setup message, a first request for a roaming number associated with the mobile station. For example, the first request for a roaming number can be a MAP_PROVIDE JR-OAMINGJS[UMBER message, and the first MSC 325 is generally the MSC to which the mobile station was last registered.

Where the first MSC 325 is out of service, or is otherwise unable to process the request from the HLR 315, no response to the first request for a roaming number will be received at the HLR 315. However, where the first MSC 325 operates in a pool area, other MSCs also will be within range of a RAN node that serves the mobile station to which the GMSC 310 is attempting to place a call.

According to an embodiment of the present invention, the HLR 315 maintains a listing that identifies alternative MSCs that are also operating within the same pool area as the first MSC 325. Therefore, when no response to the first request for a roaming number is received, the HLR 315 selects from its listing a second MSC 330 in the pool area covering the called mobile station. At line 335, the HLR 315 transmits to the second MSC 330 a second request for a roaming number associated with the called mobile station. If the second MSC 330 is not out of service, it will receive and process the second request for a roaming number. However, because the called mobile station is not registered with the second MSC 330, the second MSC 330 will not be able to immediately provide a roaming number associated with the called mobile station. At line 340 the second MSC 330 therefore transmits to the HLR 315 a CE15534CM request, such as a MAP_RESTORE_DATA message, for additional subscriber data concerning the called mobile station. The HLR 315 then transmits back to the second MSC 330 additional subscriber data, such as an International Mobile Subscriber Identity (IMSI) record, associated with the called mobile station. Finally, at line 345, the second MSC 330 transmits to the HLR 315 a roaming number associated with the called mobile station. The HLR 315 is then able to respond to the call setup message from the GMSC 310, and a call can be established through the GMSC 310 and the second MSC 330 to the called mobile station.

Those skilled in the art will appreciate that if the second MSC 330 shown in the message sequence chart 300 was also out of service when the HLR 315 transmitted the second request for a roaming number, the HLR 315 could simply select a third MSC (not shown) that is also in the pool area that covers the called mobile station. Thus according to an embodiment of the present invention the HLR 315 is able to itcrativcly step through a process of transmitting a plurality of requests for roaming numbers to a plurality of MSCs in a given pool area, until one of the MSCs provides an appropriate roaming number to the HLR 315.

Referring to FIG. 4, a general flow diagram illustrates a method 400 for routing calls in a mobile communication network, according to an embodiment of the present invention. At step 405, the HLR 315 processes a call setup message received from the GMSC 310 for a call to a mobile station (MS). At step 410, the HLR 315 transmits, to the first MSC 325, a first request for a roaming number associated with the called MS. At step 415, it is determined whether a response to the first request for a roaming number is received from the first MSC 325. If so, then at step 420 the roaming number is processed, the call to the mobile station is completed, and the CE15534CM method 400 ends. However, if at step 415 a roaming number is not received from the first MSC 325, then the method 400 continues at step 425 where a second request for a roaming number is transmitted from the HLR 315 to the second MSC 330. At step 430, the HLR 315 receives and processes a request for additional subscriber data from the second MSC 330. At step 435 additional subscriber data, such as an IMSI record associated with the called MS, is transmitted to the second MSC 330. At step 440, a roaming number, received from the second MSC 330, is processed at the HLR 315. The call to the MS therefore can be completed, and the method 400 then ends.

Advantages of the present invention thus include reducing failed calls in a mobile communication network. Where multiple mobile switching centers (MSCs) operate within a given pool area that covers a called mobile station, a Home Location Register (HLR) that manages the called mobile station is not limited to transmitting requests for roaming numbers for the called mobile station to only a single MSC to which the mobile station was last registered. Rather, the HLR can itcrativcly contact each MSC from a plurality of MSCs operating in the pool area, until one of the MSCs is able to provide a roaming number for a particular called mobile station. By reducing a frequency of failed calls, embodiments of the present invention thus enable improved Quality of Service (QoS) for network subscribers and a more efficient use of network resources.

The above detailed description provides an exemplary embodiment only, and is not intended to limit the scope, applicability, or configuration of the present invention. Rather, the detailed description of the exemplary embodiment provides those skilled in the art with an enabling description for implementing the exemplary embodiment of the invention. It should be understood that various changes can be CE15534CM made in the function and arrangement of elements and steps without departing from the spirit and scope of the invention as set forth in the appended claims. It will be appreciated that embodiments of the invention described herein may be comprised of one or more conventional processors and unique stored program instructions that control the one or more processors to implement, in conjunction with certain non- processor circuits, some, most, or all of the functions of routing calls in a mobile communication network as described herein. The non-processor circuits may include, but are not limited to, a radio receiver, a radio transmitter, signal drivers, clock circuits, power source circuits, and user input devices. As such, these functions may be interpreted as steps of a method for routing calls in a mobile communication network. Alternatively, some or all functions could be implemented by a state machine that has no stored program instructions, or in one or more application specific integrated circuits (ASICs), in which each function or some combinations of certain of the functions are implemented as custom logic. Of course, a combination of the two approaches could be used. Thus, methods and means for these functions have been described herein. Further, it is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation.

In the foregoing specification, specific embodiments of the present invention have been described. However, one of ordinary skill in the art appreciates that various modifications and changes can be made without departing from the scope of CE15534CM the present invention as set forth in the claims below. Accordingly, the specification and figures are to be regarded in an illustrative rather than a restrictive sense, and all such modifications are intended to be included within the scope of the present invention. The benefits, advantages, solutions to problems, and any elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of any or all of the claims. The invention is defined solely by the appended claims including any amendments made during the pendency of this application and all equivalents of those claims.

Claims

CE15534CMClaimsWc Claim:

1. A method for routing calls in a mobile communication network, the method comprising:

. processing at a Home Location Register (HLR) a call setup message for a call to a Mobile Station (MS); transmitting from the HLR to a first Mobile Switching Center (MSC), in response to the call setup message, a first request for a roaming number associated with the MS; and transmitting from the HLR to a second MSC, after a roaming number associated with the MS is not received from the first MSC in response to the first request, a second request for a roaming number associated with the MS.

2. The method of claim 1 , further comprising: processing at the HLR a request, received from the second MSC, for additional subscriber data; transmitting from the HLR to the second MSC, in response to the request for additional subscriber data, additional subscriber data associated with the MS; and processing at the HLR, a roaming number associated with the MS₅ where the roaming number is received at the HLR from the second MSC in response to the additional subscriber data. CE15534CM

3. The method of claim 1 , further comprising receiving at the HLR from the second MSC, a roaming number associated with the MS.

4. The method of claim 1 , wherein the first MSC and the second MSC comprise elements of a single pool area.

5. The method of claim 1, wherein the call setup message comprises a mobile application part MAP_SEND_ROUTrNG_INFORMATION message transmitted from a Gateway Mobile Switching Center (GMSC).

6. The method of claim 1 , wherein the first request for a roaming number associated with the MS comprises a mobile application part MAP_PROVIDE_ROAMING_NUMBER message.

7. The method of claim 2, wherein the request for additional subscriber data comprises a mobile application part MAP_RESTORE_DATA message.

8. The method of claim 2, wherein the additional subscriber data associated with the MS comprises an International Mobile Subscriber Identity (IMSI) record associated with the MS.

9. The method of claim 1 , wherein a roaming number associated with the MS is not received from the first MSC in response to the first request because the first MSC is out of service. CE15534CM

10. The method of claim 1 , wherein the first MSC and the second MSC are identified from a listing, stored at the HLR, comprising identifiers of a plurality of MSCs associated with a pool area serving the MS.

11. The method of claim 10, wherein the listing stored at the HLR conforms to a Third Generation Partnership Project (3GPP) standard.