WO2006127417A1

WO2006127417A1 - System to provide dual registration with an ip telephony network and a circuit-switched telephony network

Info

Publication number: WO2006127417A1
Application number: PCT/US2006/019331
Authority: WO
Inventors: Nagaraja Rao
Original assignee: Nokia Siemens Networks Gmbh & Co. Kg
Priority date: 2005-05-24
Filing date: 2006-05-18
Publication date: 2006-11-30

Abstract

Disclosed herein are systems and methods to provide simultaneous registration of a client telephony device (10) with a circuit-switched telephony network (20) and with an Internet Protocol (IP) telephony network (20). Such systems and methods may provide emulation of a Global System for Mobile Telecommunication (GSM) Home Location Register (312) to a Mobile Switching (314) and of a GSM Visitor Location Register (316) to a Home Location Register (312). In this regard, an application server (400) of the IP telephony network may be associated with an International Mobile Subscriber Identity of the client telephony device.

Description

SYSTEM TO PROVIDE DUAL REGISTRATION WITH AN IP

TELEPHONY NETWORK AND A CIRCUIT-SWITCHED

TELEPHONY NETWORK

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority to U.S. Provisional Patent Application Serial No. 60/683,974, filed on May 24, 2005 and entitled "New Roaming Concept", the contents of which are incorporated herein by reference for all purposes.

BACKGROUND Field

Embodiments may generally relate to mobile telephony. More particularly, some embodiments are concerned with interoperation of a mobile client telephony device with both a circuit-switched telephony network and an Internet Protocol (IP) telephony network.

Description

Conventional wireless telephony networks (e.g., Global System for Mobile Telecommunications (GSM) networks) provide user mobility and uninterrupted service across many geographical areas. Using a single wireless handset and a single telephone number, a user may roam between networks of different providers with seamless handover of calls therebetween.

IP telephony networks (e.g., IP Multimedia Subsystem (IMS) networks) are used increasingly to place and receive telephone calls. An IP telephony network client device may communicate wirelessly (e.g., via WiFi) with such a network. Accordingly, an IP telephony network client device may provide user mobility among wireless Local Area Networks (WLANs) as long as the device remains in communication with at least one WLAN. "Dual mode" handsets have been contemplated to provide mobile communication with a conventional circuit-switched network (e.g., GSM, Public Switch Telephone Network (PSTN), etc.) or with an IP telephony network. Such handsets generally consist of two separate subsystems, one each for supporting IP telephony and circuit-switched telephony. Of course, the two subsystems may share certain hardware elements such as a speaker, a microphone, a display and a keypad.

When operating in an IP telephony mode, the IP telephony subsystem of a dual mode handset may place and receive telephone calls using an IP telephony network with which the handset is in communication. Similarly, the circuit-switched telephony subsystem of a dual mode handset may be used to place and receive telephone calls in conjunction with a circuit-switched telephony network. The foregoing capabilities currently require the handset to be registered with the IP telephony network (i.e., to provide the former capabilities) or with the circuit-switched telephony network (i.e., to provide the latter). Moreover, the dual mode handset may be associated with one telephone number of the IP network and a different telephone number for the circuit-switched network. Simultaneous registration with both the circuit- switched telephony network and the IP telephony network is not supported by current systems.

Systems are desired that provide simultaneous registration of a client telephony device with a circuit-switched telephony network and an IP telephony network. Such systems may provide selectable termination of calls to the client telephony device via either telephony network.

SUMMARY

Some embodiments provide a system, method, program code and/or means to provide simultaneous registration of a client telephony device with a circuit-switched telephony network and with an Internet Protocol (IP) telephony network. According to some aspects, an International Mobile Subscriber Identity associated with the client telephony device is associated with an application server of the IP telephony network.

In some aspects, a first message is received at the IP telephony network from a Mobile Switching Center of the circuit-switched telephony network, and a second message based on the first message is transmitted from the IP telephony network to a Home Location Register of the circuit- switched telephony network. Receiving the first message may comprise emulating the Home Location Register of the circuit-switched telephony network, and transmitting the second message may comprise emulating a Visitor Location Register of the circuit-switched telephony network.

Some aspects may include receiving, at the IP telephony network, a first message to update a location of the client device within the circuit- switched telephony network, the first message including an identifier of the client device within the circuit-switched telephony network, and determining a server based on the identifier. The determined server may be associated with the IP telephony network if the identifier is associated with the IP telephony network. If the identifier is associated with the circuit-switched telephony network, a second message may be transmitted to the server to associate the client device with a server of the IP telephony network within the circuit- switched telephony network.

According to some aspects, a first message is received from a Home Location Register of the circuit-switched telephony network, the first message to request a roaming number for routing a call to a telephone number associated with the client device in the circuit-switched telephony network, a second message is transmitted to a Mobile Switching Center of the circuit- switched telephony network, the second message to request the roaming number corresponding to the telephone number, the roaming number is received from the Mobile Switching Center, and the roaming number is transmitted to the Home Location Register. It may be determined to offer the call to the client device via the circuit-switched telephony network, and, moreover, the client device may be roaming in the IP telephony network.

In some aspects, a first message is received at the IP telephony network from the client device, the message to register a number of the circuit-switched telephony network, and a second message is transmitted to a Home Location Register of the circuit-switched telephony network to associate a server of the IP telephony network with the number.

Further aspects may include receiving, at the IP telephony network, a first message to initiate a call to a telephone number associated with the client device in the IP telephony network, determining to offer the call to the client device via the circuit-switched telephony network, and transmitting a second message to a Mobile Switching Center of the circuit-switched telephony network, the second message to request a roaming number corresponding to the client device in the circuit-switched telephony network. Also included may be receiving the roaming number from the Mobile Switching Center, and transmitting a third message to the Mobile Switching Center to initiate the call to the client device via the circuit-switched telephony network, the third message including the roaming number.

With these and other advantages and features that will become hereinafter apparent, further information may be obtained by reference to the following detailed description and appended claims, and to the figures attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments are illustrated in the accompanying figures, in which like reference numerals designate like parts, and wherein:

FIG. 1 is a block diagram of a system according to some embodiments;

FIG. 2 is a block diagram of IP and circuit-switched network components according to some embodiments;

FIG. 3 is a functional block diagram of a Mobility Management Application Server (MM-AS) according to some embodiments;

FIG. 4 is a tabular representation of telephone numbers of an IP telephony network and telephone numbers of a circuit-switched telephony network as associated with Mobile Switching Centers of the circuit-switched telephony network;

FIG. 5 is a block diagram of a hardware architecture of a client telephony device according to some embodiments;

FIG. 6 is a block diagram of a software architecture to support IP- based and circuit-switched-based telephony signaling according to some embodiments;

FIG. 7 is a block diagram of a software architecture to support telephony audio signals according to some embodiments;

FIG. 8 is a flow diagram of a process to support registration of a telephone number in a circuit-switched telephony network according to some embodiments;

FIG. 9 is a diagram to illustrate registration of a circuit-switched telephony network telephone number in a circuit-switched telephony network according to some embodiments;

FIG. 10 is a diagram to illustrate registration of an IP telephony network telephone number in a circuit-switched telephony network according to some embodiments;

FIG. 11 is a flow diagram of a process to support terminating a call to a circuit-switched telephony network telephone number at a circuit-switched telephony network according to some embodiments; FIG. 12 is a diagram to illustrate termination of a call to a circuit- switched telephony network telephone number at a circuit-switched telephony network according to some embodiments;

FIG. 13 is a flow diagram of a process to register a circuit-switched telephony network telephone number in an IP telephony network according to some embodiments;

FIG. 14 is a diagram to illustrate registration of a circuit-switched telephony network telephone number in an IP telephony network according to some embodiments;

FIG. 15 is a flow diagram of a process to support terminating a call to an IP telephony network telephone number at a circuit-switched telephony network according to some embodiments; and

FIG. 16 is a diagram to illustrate termination of a call to an IP telephony network telephone number at a circuit-switched telephony network according to some embodiments.

DETAILED DESCRIPTION

FIG. 1 is a block diagram of system 1 according to some embodiments. System 1 comprises client telephony device 10, IP telephony network 20 and circuit-switched (CS) telephony network 30. System 1 may provide simultaneous registration of device 10 with IP telephony network 20 and CS telephony network 30. Simultaneous registration of device 10 with each of networks 20 and 30 may provide selectable termination of calls to client telephony device 10 via either of networks 20 or 30. Several call termination scenarios will be described in detail below.

Device 10 may comprise a mobile telephony client device, and may also be configured to support a "fixed" connection to one or both of networks 20 and 30. Examples of device 10 according to some embodiments include cellular telephones, personal digital assistants (PDAs), digital media players, digital cameras, wireless email devices, and any other device for supporting wireless telephony that is or becomes known.

Device 10 includes processor 12 for executing program code to enable some or all of the functions attributed herein to device 10. Also included are hardware, software and/or firmware elements of IP network I/O 14 and CS network I/O 16. IP network I/O 14 and CS network I/O 16 support wireless communication with IP telephony network 20 and CS telephony network 30, respectively. Further details of hardware elements and software stacks of device 10 according to some embodiments are set forth below.

IP telephony network 20 may comprise any number of LANs, Wide Area Networks (WANs), and/or the Internet itself. IP telephony network 20 provides at least one wireless access point that may be accessed by device 10. IP telephony network 20 supports the IMS protocol according to some embodiments. In some embodiments, IP telephony network 20 includes an application server that is associated with an International Mobile Subscriber Identity corresponding to a user of client telephony device 10. As will be described below, such an association may cause a Mobile Switching Center of CS network 30 to identify the application server as a Home Location Register for client device 10.

CS telephony network 30 also provides at least one wireless access point to device 10. CS network 30 may comprise one or a combination of CS telephony networks, including but not limited to CDMA/IS-41 , WCDMA/UMTS, TDMA, GSM, PCS, and PSTN networks. As described above, such telephony networks may be owned by several separate providers.

FIG. 2 is a more detailed block diagram of system 1 according to some embodiments. With the exception of Mobility Management Application Server (MM-AS) 400, the core functionality of each illustrated element is known. Of course, some embodiments may require one or more illustrated elements to function differently than is currently known.

CS telephony network 30 includes PSTN 305, which is in communication through known interfaces with GSM network 310. GSM network 310 may comprise one or more GSM networks having different ownership. GSM network 310 comprises Home Location Registers (HLRs) 312, Mobile Switching Centers (MSCs) 314, and Visitor Location Registers (VLRs) 316. Current usage often combines the functions of an MSC and a VLR under the label MSC/VLR.

As mentioned above, embodiments may be used in conjunction with additional or alternative CS mobile telephony networks (e.g., CDMA/IS-41 , WCDMA/UMTS, TDMA, PCS). Such embodiments utilize known messages and protocols of the additional or alternative wireless networks. The messages and protocols may be roughly analogous to the messages described below with respect to GSM networks.

Conventionally, an HLR provides a central subscriber database that maintains a location of a client device within a GSM network. A GSM network may include many HLRs. A location of a client device is maintained in a single HLR, and a single HLR may maintain locations of many client devices within several geographic areas. An MSC/VLR is assigned to each geographic area, which may include several cellular communication towers. Also conventionally, a client device is registered with an MSC/VLR if the client device is located in a geographic area to which the MSC/VLR is assigned. This registration is stored in an HLR associated with the MSC/VLR.

IP telephony network 20 is illustrated as comprising three sub-units, although actual implementations might not reflect such distinctions. Session control unit 210 includes Home Subscriber Server (HSS) 212, Call Session Control Function (CSCF) 214, and MM-AS 400. Core functions of HSS and CSCF are known and are roughly equivalent, within the IP domain, to the core functions of an HLR and an MSC/VLR, respectively.

Some embodiments leverage the existing infrastructure and protocols by having MSCs 314 identify MM-AS 400 as the HLR which maintains the location of client device 10, and by having HLRs 312 identify MM-AS 400 as the MSC/VLR with which client device 10 is registered. Simultaneously, client device 10 may be registered with HSS 212 and CSCF 214 in the IP telephony domain.

As mentioned above, MM-AS 400 may provide simultaneous registration of device 10 with IP telephony network 20 and CS telephony network 30, and may emulate an HLR to MSCs 314 and a VLR to HLRs 312. MM-AS 400 may also and/or alternatively provide much of the functionality described herein.

MM-AS 400 may implement IP-based interfaces for communicating with HSS 212, CSCF 214 and Media Gateway Control Function (MGCF) 222, and may implement Mobile Application Part (MAP) interfaces for communicating with GSM elements such as HLRs 312, MSCs 314 and VLRs 316. In this regard, MGCF 222 is an element of legacy internetworking unit 220 and may allow interoperability between IP telephony network 20 and CS network 30 signaling protocols over a legacy interface, such as a Signaling System No. 7 (SS7) interface. Media Gateway 224 of unit 220 enables the transfer of audio data (e.g. representing the voices of the calling and called parties) between IP telephony network 20 and CS network 30.

Applications unit 230 provides telephony applications to IP network 20. For example, instant messaging server 232 may provide instant messaging services, and Rich Voice-over-IP (VoIP) Application Server 234 may provide other telephony applications such as call forwarding, call transfer, call waiting, etc. within IP telephony network 20.

Accordingly, IP telephony network 20 may support conventional IP telephony client devices using conventional means. Such conventional devices may include fixed IP client devices 50 (e.g., coupled to network 20 via a Digital Subscriber Line connection) and mobile IP client devices 40 (e.g., coupled to network 20 via a General Packed Radio System connection). Fixed IP client devices may comprise desktop computers, fixed IP telephones, conventional PSTN telephones coupled to an IP-PSTN telephone router, or the like. Mobile IP client devices 40 may include, but are not limited to, cellular telephones, PDAs, digital media players, digital cameras, and wireless email devices.

FIG. 3 is a functional block diagram of MM-AS 400 according to some embodiments. The illustrated functional blocks may be implemented by any combination of hardware and/or software, some of which may be located remote from one another. According to some embodiments, the functional blocks are implemented in program code for execution by a processor.

As shown, MM-AS 400 includes subscriber and call data module 410, mobility management module 420 and protocol stacks 430. Subscriber and call data module 410 includes information for tracking client devices within IP telephony network 20 and CS telephony network 30 and for associating CS- based telephone numbers with client devices during certain scenarios. Accordingly, module 410 provides an ENUM interface to MGCF 222 for receiving a CS-based telephone number from MGCF 222 and transmitting an identifier of an associated client device to MGCF 222 in response. MGCF 222 may use the identifier to connect a call from network 30 to the client device.

Mobility management module 420 includes mobility management state event handling block 422, MAP state event handling block 424, and Session Initiation Protocol (SIP) state event handling block 426 for executing the processes described herein in response to received SIP and MAP messages. The MAP messages are received from GSM network 310 via MAP protocol stack 432 and the SIP messages are received from CSCF 214 via the SIP protocol stack 434. FIG. 4 is a tabular representation that may be used by MM-AS 400 in some embodiments. The illustrated data may be stored in any location, media, and form that are accessible to MM-AS 400. Table 440 associates each of several International Mobile Subscriber Identities (IMSIs) with several data fields. For example, table 440 indicates whether a telephone number associated with the IMSI is owned by network 20 or network 30. Table 440 also associates each IMSI with an MSC with which a corresponding client device is registered and, if the associated telephone number is owned by CS telephony network 30, with an HLR that stores VLR registration and other information associated with the IMSI. Processes for using the data of table 440 are described below.

FIG. 5 is a block diagram of an internal hardware architecture of device 10 according to some embodiments. Device 10 may be referred to as a dual mode handset due to its capability to operate as an IP telephony network client and a wireless CS telephony network client. Device 10 may include primarily conventional components, and may include program code to perform certain functions described herein. Embodiments may operate in conjunction with devices that differ in part or in whole from device 10 of FIG. 5.

Device 10 includes microphone 52 to receive audio signals that may represent speech of a user. In some embodiments, the audio signals may comprise commands for operating device 10, such as a command to dial a particular telephone number. Speaker 55 emits audio signals from device 10. The audio signals may comprise speech or other audio signals received from telephony networks and/or ring tones, beeps and other tones used during operation of device 10.

Analog/digital coder/decoder (A/D codec) 60 may receive analog signals from microphone 52, convert the analog signals to digital signals, and pass the digital signals to processor 12. Conversely, processor 12 may transmit digital signals to A/D codec 60, which converts the digital signals to analog signals and passes the analog signals to speaker 55. Speaker 55 then emits sound based on the analog signals. Processor 12 may be a conventional microprocessor, microcontroller and/or digital signal processor (DSP) or other control circuit conventionally provided in a mobile telephony client device.

Processor 12 is also in communication with input 65 and display 70. Input 65 may comprise any system to receive input from a user, including but not limited to an alphanumeric keypad, dedicated function keys, a touchscreen, etc. Display 70 may comprise any system to display a user interface for presenting information to a user.

Antennae 75 and 85 may receive and transmit radio frequency signals from and to a CS telephony network and an IP telephony network, respectively. Antennae 75 and 85 may be configured to transmit and receive any types of signals that comply with the communication protocol of a CS telephony network or IP telephony network in which device 10 is employed.

GSM transceiver 80 is operatively coupled to antenna 75 and WiFi transceiver 90 is operatively coupled to antenna 85. GSM transceiver 80 and WiFi transceiver 90 may be configured to operate at different frequencies. Transceivers 80 and 90 may, in accordance with conventional practices, each comprise a combination of two or more different receive/transmit modules (not separately shown) that operate in accordance with mutually different radio communication protocols to provide various services for device 10.

Device 10 also includes internal memory 95 and removable memory 100. Internal memory 95 may include one or more of ROM (read only memory), RAM (random access memory, e.g., static RAM), and flash memory. Removable memory 100 may comprise a flash memory, a Subscriber Identity Module (SIM) card or any other removable memory that is or becomes known. Such a SIM card may store an IMSI to identify a subscriber within a GSM network. The IMSI may be used by an MSC to determine a HLR associated with the subscriber. As described above, in some embodiments, the IMSI is associated with MM-AS 400.

Memories 95 and 100 may store program code that is executable by processor 12 to control device 10 in accordance with the processes described herein. The program code may include but is not limited to operating system program code, application program code, device driver program code, and database connector program code. Memories 95 and 100 may also store data used in the operation of device 10. Such data may include contacts, phone numbers, addresses, voice mailbox access numbers, voice mailbox access codes, and other data. Some or all of the data may be read-only, while other of the data may be rewritable.

Those in the art will understand that the block diagram of FIG. 5 is simplified in a number of ways. For example, all power and power management components of device 10 are omitted from the diagram. Also, some embodiments may employ an internal architecture somewhat different or completely different from that shown in FIG. 5. Each illustrated element of device 10 may comprise any combination of hardware and/or software components suitable for providing the functions attributed thereto herein.

FIG. 6 is a block diagram of a software architecture for device 10 to signal speech in accordance with some embodiments. Accordingly, each block of FIG. 6 may be implemented in software. The architecture of FIG. 6 supports operation in conjunction with GSM and IMS networks, but other CS or IP networks may be supported.

User interface 110 may provide a common user experience regardless of whether device 10 is registered with a GSM network or an IMS network. User interface 110 may provide an indication of a current mode of operation, a menu for changing the mode of operation, and a common dialing application for GSM and IMS-based modes.

Mode manager 115 may support simultaneous registration within GSM and IMS networks. For example, mode manager 115 may monitor signal strengths of GSM and WiFi signals, determine a mode to use based on the determined signal strengths, manage a handover algorithm during a call, and route a user request and indication to GSM services 120 or IMS services 125 depending on the mode of operation. Mode manager 115 or any other software block of FIGS. 6 and 7 may comprise a plug-in application written in Java or C and may also or alternatively be embodied in native program code of device 10.

The above-mentioned requests and indications are processed by GSM signaling stack 130 and IMS signaling stack 135. As will be described below, seamless handover may require a change to the known function of Radio Resource layer 132 of GSM signaling stack 130. Also, according to some embodiments, SIP/RTP layer 137 complies with the 3^rd Generation Partnership Project (3GPP) SIP call control specification.

FIG. 7 is a block diagram of a software architecture for device 10 to support speech in accordance with some embodiments. Again, each block of FIG. 7 may be implemented in software, and the architecture of FIG. 7 is intended for use with GSM and IMS networks. The FIG. 7 architecture includes audio driver 140 for execution by processor 12, mode manager 115, GSM audio stack 145 and WiFi IMS audio stack 150.

FIG. 8 is a flow diagram of process 500 to support registration of a client telephony device in a CS telephony network. Process 500 addresses scenarios in which the telephone number of the client device is owned by a CS network operator and in which the telephone number is owned by an IP network operator. Although process 500 and the other flow diagrams herein are described below in reference to a GSM telephony network, an IMS telephony network and associated signaling protocols, the teachings thereof may be applied to implementations associated with other CS telephony networks and IP telephony networks. Process 500, as well as the other processes described herein, may be executed by MM-AS 400 using any suitable hardware and/or software arrangement, and may be executed by any suitable device or devices that are or become known. For example, process 500 may be embodied in program code executed by a processor.

Prior to process 500, it is assumed that a client telephony device has moved into the geographic area of a particular MSC. FIG. 9 illustrates one scenario in which client device 10 has moved into the area of MSC 314. As a result, device 10 transmits a Location Update message to MSC 314. The Location Update message includes an IMSI associated with client device 10.

If the message successfully reaches MSC 314, MSC 314 attempts to determine a server (e.g., an HLR) of CS telephony network 30 based on the IMSI. According to conventional protocols, MSC 314 may perform Global Title Translation on the IMSI to determine that MM-AS 400 is the "HLR" associated with the IMSI. MSC 314 therefore transmits a MAP Location Update message to MM-AS 400 because MSC 314 believes that MM-AS 400 is a "conventional" HLR 312.

The message is received by MM-AS 400 at step S510. The message is intended to update a location of client device 10 within CS network 30. The received message also includes the IMSI as an identifier of client device 10. Next, at step S520, MM-AS 400 determines a server based on the IMSI.

According to the present example, it will be assumed that MM-AS 400 consults table 440 to determine that the received IMSI is associated with a telephone number owned by CS network 30 and with HLR 312 of FIG. 9. MM-AS 400 may also update the MSC field that is associated with the received IMSI to identify MSC 314 from which the MAP Location Update message was received. As a result, MM-AS 400 remains apprised of the MSC with which each client device is currently registered. Flow proceeds from step S530 to S540 because the received IMSI is associated with a telephone number owned by CS network 30. At step S540, a second message is transmitted to the determined server to associate client device 10 with a server of IP telephony network 20. In particular, MM-AS 400 may transmit a MAP Location Update message to HLR 312 at step S540 to indicate a registration of client device 10 with MM-AS 400.

As a result, HLR 312 stores information indicating that MM-AS 400 is a VLR 316 (i.e., as shown in FIG. 2) associated with client device 10. Since either no other VLR is associated with client device 10 in HLR 312 (if client device 10 is initially registering with network 30), or MM-AS 400 is currently associated with client device 10 in HLR 312, HLR 312 would not transmit a MAP Cancel Location message in response to the MAP Location Update message received from MM-AS 400.

As shown in FIG. 9, HLR 312 may return profile data associated with client device 10 to MM-AS 400 via a MAP Insert Subscriber Data message. MM-AS 400 may use the profile data to update a record of VLR database 450 associated with client device 10, and may also transmit a MAP Insert Subscriber Data message including some profile data to MSC 314. Lastly, MSC 314 may acknowledge the Location Update message received from client device 10.

FIG. 10 illustrates an alternative scenario of process 500 in which the telephone number of client device 10 is owned by IP telephony network 20. Accordingly, at step S510, MM-AS 400 receives the MAP Location Update message from MSC 314, which includes an IMSI associated with an IP network-owned telephone number. Next, at step S520, MM-AS 400 determines that no HLR is associated with the received IMSI based on table 440. MM-AS 400 also determines that the IMSI is not associated with the CS network at step S530. Process 500 thereafter terminates. As shown in FIG. 10, MM-AS 400 may respond to MSC 314 with a MAP Insert Subscriber Data message including profile data from HSS 212. Since the telephone number of client device 10 is owned by IP network 20, associated profile data is maintained in HSS 212 and need not be retrieved from an HLR of CS network 30. Again, MSC 314 may then acknowledge the original Location Update message received from client device 10.

Process 500 may therefore allow MM-AS 400 to emulate an HLR from the point of view of an MSC, and to emulate a VLR, if necessary, from the point of view of an HLR. Process 500 may also allow profile data of IP network subscribers to be primarily maintained in IP network 20 and profile data of CS network subscribers to be primarily maintained in an HLR of network 30 as dictated by conventional protocols.

FIG. 11 is a flow diagram of process 600 to provide termination of a call to a CS network-owned telephone number according to some embodiments. The call may be terminated by a client device roaming in an IP telephony network and/or in a CS telephony network. Process 600 may be executed by MM-AS 400 in some embodiments.

Prior to process 600, a call is placed from a CS telephony network to a telephone number owned by the CS telephony network. Since the telephone number is owned by the CS telephony network, the call may be routed from PSTN 305 to Gateway MSC (GMSC) 314 as illustrated in FIG. 12. Moreover, the call may be routed via an Integrated Service Digital Network User Part (ISUP) Initial Address Message (IAM) that includes the telephone number.

In response to the ISUP IAM message, and according to conventional GSM protocols, GMSC 314 may query HLR 312 for an MSC/VLR with which client device 10 is currently registered. This query may comprise an MAP Send Routing Info message that includes the telephone number received from PSTN 305. As described with respect to FIGS. 8 and 9, the subscriber database of HLR 312 indicates that MM-AS 400 is the MSC/VLR currently serving device 10. Therefore, and again according to conventional GSM protocols, HLR 312 transmits a message requesting MM-AS 400 to generate a roaming number associated with client device 10.

The message is received at step S610 of process 600. As shown in FIG. 12, the message may comprise a MAP Provide Roaming Number message including the IMSI of client device 10, which HLR 312 has determined from the received telephone number. Next, at step S620, MM-AS 400 transmits a second message to MSC 314 to request a roaming number that corresponds to the telephone number. MM-AS 400 may determine the particular MSC 314 to which the message is transmitted based on table 440 and the IMSI received at step S610. As described with respect to process 500, table 440 maintains an updated indication of a particular MSC with which each client device is registered.

MSC 314 then generates a roaming number associated with client device 10. The generated roaming number is a number that terminates to MSC 314, and is received by MM-AS 400 from MSC 314 at step S630. MM- AS 400 then transmits the roaming number to HLR 312 at step S630 via a response to the MAP Provide Roaming Number message received in step S610.

GMSC 314 receives the roaming number from HLR 312 and places a call thereto using an ISUP IAM message that includes the roaming number. The message is received by MSC 314 because the roaming number terminates at MSC 314. MSC 314 then sets up the call with client device 10 using conventional GSM protocols.

According to some embodiments, client device 10 is roaming in IP telephony network 20 during process 600. Some embodiments of process 600 include determining, after step S610, to offer the call to the client device via the CS telephony network or the IP telephony network. Such a determination may be based on one or more of an operator policy (e.g., offer via IP network if client device is connected to a WLAN), a type of the call (e.g., some types of calls are offered via CS network, others via IP network), or a preference associated with the client device (e.g., only offer via CS network). The latter preference may be stored in VLR database 450 and/or in a HLR 312 associated with the client device.

Process 700 of FIG. 13 may provide registration of a telephone number owned by a CS telephony network while a client device is roaming in an IP telephony network. Prior to process 700, and following standard IMS registration procedures, WLAN-connected device 10 of FIG. 14 transmits a message to register the telephone number to IP network 20. The transmitted message includes an SIP Uniform Resource Identifier (URI) associated with device 10, and the SIP URI is an identifier of device 10 within IP network 20. Any suitable message (e.g., SIP Register, SIP Publish) may be transmitted by device 10 in some embodiments.

The message from client device 10 is received at IP network 20 in step S710. In some embodiments, the message is received by CSCF 214 of network 20 and is transmitted to MM-AS 400. HSS 212 of network 20 may include a table mapping an SIP URI of each supported client device to an IMSI of the client device. MM-AS 400 therefore accesses the table to determine an IMSI that is associated with the SIP URI received at step S710. The determined IMSI is an identifier of client device 10 within GSM network 30.

MM-AS 400 may then use table 440 to identify an HLR 312 associated with the IMSI. Since the corresponding telephone number is owned by CS network 30, table 440 should include an identifier of an HLR 312 that is associated with the IMSI.

Next, at step S720, a second message is transmitted to the identified HLR 312 to associate a server of IP telephony network 20 with the telephone number. In particular, MM-AS 400 may transmit a MAP Location Update message to HLR 312 at step S720 to indicate a registration of client device 10 with MM-AS 400. HLR 312 therefore stores information indicating that MM- AS 400 is a VLR 316 associated with client device 10.

HLR 312 may also return profile data associated with client device 10 to MM-AS 400 via a MAP Insert Subscriber Data message, as shown in FIG. 14. MM-AS 400 may use the profile data to update a record of VLR database 450 associated with client device 10.

Process 800 of FIG. 15 may provide termination of a call to an IP network-owned telephone number according to some embodiments. The call may be offered via a CS network and terminated by a client telephony device roaming in an IP telephony network.

The call may be initially placed from a CS telephony network to a telephone number owned by an IP telephony network. According to conventional CS-to-IP protocols, the CS network routes the call to a gateway between the CS network and the IP network, since the telephone number is owned by IP network 20. FIG. 16 illustrates PSTN 305 routing such a call to a first MGCF/Media Gateway (MG) 222/224 of IP network 20. PSTN 305 of FIG. 16 routes the call via an Integrated Service Digital Network User Part (ISUP) Initial Address Message (IAM) that includes the telephone number.

The first MGCF/MG 222/224 transmits an SIP Invite message to CSCF 214, which may determine a corresponding SIP URI from the telephone number based on data stored in HSS 212. HSS 212 may also store a user profile in association with the SIP URI indicating that the CSCF 214 is to forward all SIP calls to MM-AS 400. Accordingly, at step S810, MM-AS 400 receives a message from CSCF 214 to initiate a call to the telephone number.

Next, at step S820, MM-AS 400 determines to offer the call to client device 10 via the CS telephony network. As mentioned above, the determination at step S820 may be based on one or more of an operator policy, a type of the call, or a preference associated with the client device.

MM-AS 400 transmits a second message at step S830 to an MSC 314 of CS network 30. The second message requests a roaming number that corresponds to client device 10. MM-AS 400 may determine the particular MSC 314 to which the message is transmitted based on table 440 and on the SIP URI determined by CSCF 214. In response, MSC 314 generates a roaming number associated with client device 10. The generated roaming number is a number that terminates to MSC 314, and is received by MM-AS 400 from MSC 314 at step S840.

MM-AS 400 then transmits the roaming number to CSCF 214 via another SIP Invite message. CSCF 214 then transmits a second SIP Invite message to a second MGCF/MG 222/224 that is associated with the roaming number (e.g., geographically). In this regard, the second MGCF/MG 222/224 may be located physically closer than the first MGCF/MG 222/224 to the determined MSC 314.

At step S850, the second MGCF/MG 222/224 transmits a third message to MSC 314 to initiate the call to client device 10 via CS network 30. As shown in FIG. 16, the message may comprise an ISUP IAM message including the roaming number. MSC 314 receives the message, identifies client device 10 as being associated with the roaming number, and sets up the call with client device 10 using conventional CS network protocols.

The above-mentioned signals and messages may pass through any number of networks, devices and protocols before reaching their intended recipient. Such networks include but are not limited to local area networks, wide area networks, telephone networks, cellular networks, fiber-optic networks, satellite networks, infra-red networks, radio frequency networks, and any other type of networks which may be used to transmit information between devices. Additionally, data may be transmitted using one or more currently- or hereafter-known network protocols, including but not limited to Asynchronous Transfer Mode (ATM), Internet Protocol (IP), Hypertext Transfer Protocol (HTTP) and Wireless Application Protocol (WAP).

Embodiments described above are not intended to be limited to the specific form set forth herein, but are intended to cover such alternatives, modifications and equivalents as can reasonably be included within the spirit and scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method comprising: providing simultaneous registration of a client telephony device with a circuit-switched telephony network and with an Internet Protocol (IP) telephony network.

2. A method according to Claim 1 , wherein an International Mobile Subscriber Identity associated with the client telephony device is associated with an application server of the IP telephony network.

3. A method according to Claim 1 , further comprising: receiving, at the IP telephony network, a first message from a Mobile Switching Center of the circuit-switched telephony network; and transmitting, from the IP telephony network, a second message based on the first message to a Home Location Register of the circuit-switched telephony network.

4. A method according to Claim 3, wherein receiving the first message comprises emulating the Home Location Register of the circuit-switched telephony network, and wherein transmitting the second message comprises emulating a Visitor Location Register of the circuit-switched telephony network.

5. A method according to Claim 1 , further comprising: receiving, at the IP telephony network, a first message to update a location of the client device within the circuit-switched telephony network, the first message including an identifier of the client device within the circuit- switched telephony network; and determining a server based on the identifier.

6. A method according to Claim 5, wherein the identifier is associated with the IP telephony network, and wherein the determined server is associated with the IP telephony network.

7. A method according to Claim 5, wherein the identifier is associated with the circuit-switched telephony network, and further comprising: transmitting a second message to the server to associate the client device with a server of the IP telephony network within the circuit-switched telephony network.

8. A method according to Claim 7, wherein the first message comprises a Mobile Application Part Location Update message, wherein the first identifier comprises an International Mobile Subscriber Identity, wherein the second message comprises a Mobile Application Part Location Update message, and wherein the server of the circuit-switched telephony network comprises a Home Location Register.

9. A method according to Claim 1 , further comprising: receiving a first message from a Home Location Register of the circuit- switched telephony network, the first message to request a roaming number for routing a call to a telephone number associated with the client device in the circuit-switched telephony network; transmitting a second message to a Mobile Switching Center of the circuit-switched telephony network, the second message to request the roaming number corresponding to the telephone number; receiving the roaming number from the Mobile Switching Center; and transmitting the roaming number to the Home Location Register.

10. A method according to Claim 9, further comprising: determining to offer the call to the client device via the circuit-switched telephony network, wherein the client device is roaming in the IP telephony network.

11. A method according to Claim 1 , further comprising: receiving, at the IP telephony network, a first message from the client device, the message to register a number of the circuit-switched telephony network; and transmitting a second message to a Home Location Register of the circuit-switched telephony network to associate a server of the IP telephony network with the number.

12. A method according to Claim 11 , wherein the first message comprises a Session Initiation Protocol message, and wherein the second message comprises a Mobile Access Part Location Update message.

13. A method according to Claim 1 , further comprising: receiving, at the IP telephony network, a first message to initiate a call to a telephone number associated with the client device in the IP telephony network; determining to offer the call to the client device via the circuit-switched telephony network; transmitting a second message to a Mobile Switching Center of the circuit-switched telephony network, the second message to request a roaming number corresponding to the client device in the circuit-switched telephony network; receiving the roaming number from the Mobile Switching Center; and transmitting a third message to the Mobile Switching Center to initiate the call to the client device via the circuit-switched telephony network, the third message including the roaming number.

14. A method according to Claim 13, wherein the first message comprises an Integrated Service Digital Network User Part Initial Address Message; wherein the second message comprises a Mobile Access Part Provide Roaming Number message, and wherein the third message comprises an Integrated Service Digital Network User Part Initial Address Message.

15. A method according to Claim 1 , further comprising: determining to offer a call to the client device via the circuit-switched telephony network or the IP telephony network.

16. A method according to Claim 15, wherein determining to offer the call comprises: determining to offer the call based on one or more of: an operator policy; a type of the call; or a preference associated with the client device.

17. A medium storing program code, the program code comprising: code to provide simultaneous registration of a client telephony device with a circuit-switched telephony network and with an Internet Protocol (IP) telephony network.

18. A medium according to Claim 17, wherein an International Mobile Subscriber Identity associated with the client telephony device is associated with an application server of the IP telephony network.

19. A medium according to Claim 17, the program code further comprising: code to receive, at the IP telephony network, a first message from a Mobile Switching Center of the circuit-switched telephony network; and code to transmit, from the IP telephony network, a second message based on the first message to a Home Location Register of the circuit- switched telephony network.

20. A medium according to Claim 19, wherein the code to receive the first message comprises code to emulate the Home Location Register of the circuit-switched telephony network, and wherein the code to transmit the second message comprises code to emulate a Visitor Location Register of the circuit-switched telephony network.

21. A medium according to Claim 17, the program code further comprising: code to receive, at the IP telephony network, a first message to update a location of the client device within the circuit-switched telephony network, the first message including an identifier of the client device within the circuit- switched telephony network; and code to determine a server based on the identifier.

22. A medium according to Claim 21 , wherein the identifier is associated with the IP telephony network, and wherein the determined server is associated with the IP telephony network.

23. A medium according to Claim 21 , wherein the identifier is associated with the circuit-switched telephony network, the program code further comprising: code to transmit a second message to the server to associate the client device with a server of the IP telephony network within the circuit-switched telephony network.

24. A medium according to Claim 23, wherein the first message comprises a Mobile Application Part Location Update message, wherein the first identifier comprises an International Mobile Subscriber Identity, wherein the second message comprises a Mobile Application Part Location Update message, and wherein the server of the circuit-switched telephony network comprises a Home Location Register.

25. A medium according to Claim 17, the program code further comprising: code to receive a first message from a Home Location Register of the circuit-switched telephony network, the first message to request a roaming number for routing a call to a telephone number associated with the client device in the circuit-switched telephony network; code to transmit a second message to a Mobile Switching Center of the circuit-switched telephony network, the second message to request the roaming number corresponding to the telephone number; code to receive the roaming number from the Mobile Switching Center; and code to transmit the roaming number to the Home Location Register.

26. A medium according to Claim 25, the program code further comprising: code to determine to offer the call to the client device via the circuit- switched telephony network, wherein the client device is roaming in the IP telephony network.

27. A medium according to Claim 17, the program code further comprising: code to receive, at the IP telephony network, a first message from the client device, the message to register a number of the circuit-switched telephony network; and code to transmit a second message to a Home Location Register of the circuit-switched telephony network to associate a server of the IP telephony network with the number.

28. A medium according to Claim 27, wherein the first message comprises a Session Initiation Protocol message, and wherein the second message comprises a Mobile Access Part Location Update message.

29. A medium according to Claim 17, the program code further comprising: code to receive, at the IP telephony network, a first message to initiate a call to a telephone number associated with the client device in the IP telephony network; code to determine to offer the call to the client device via the circuit- switched telephony network; code to transmit a second message to a Mobile Switching Center of the circuit-switched telephony network, the second message to request a roaming number corresponding to the client device in the circuit-switched telephony network; code to receive the roaming number from the Mobile Switching Center; and code to transmit a third message to the Mobile Switching Center to initiate the call to the client device via the circuit-switched telephony network, the third message including the roaming number.

30. A medium according to Claim 29, wherein the first message comprises an Integrated Service Digital Network User Part Initial Address Message; wherein the second message comprises a Mobile Access Part Provide Roaming Number message, and wherein the third message comprises an Integrated Service Digital Network User Part Initial Address Message.

31. A medium according to Claim 17, the program code further comprising: code to determine to offer a call to the client device via the circuit- switched telephony network or the IP telephony network.

32. A medium according to Claim 31 , wherein the code to determine to offer the call comprises: code to determine to offer the call based on one or more of: an operator policy; a type of the call; or a preference associated with the client device.

33. An Internet Protocol (IP) telephony network comprising: an IP Multimedia Subsystem (IMS) Home Subscriber Server; an IMS Call Session Control Function; and an application server in communication with the IMS Call Session Control Function to provide simultaneous registration of a client telephony device with a circuit-switched telephony network and with an Internet Protocol (IP) telephony network.

34. A system according to Claim 33, wherein the application server is to emulate a Global System for Mobile Telecommunication (GSM) Home Location Register to a Mobile Switching Center and to emulate a GSM Visitor Location Register to a Home Location Register.

35. A system according to Claim 33, wherein the application server is associated with an International Mobile Subscriber Identity of the client telephony device.

36. A system according to Claim 33, the application server to receive a Mobile Access Part Location Update message from a Mobile Switching Center to update a location of the client device within the circuit-switched telephony network, the Mobile Access Part Location Update message including an identifier of the client device within the circuit-switched telephony network, and to determine a server based on the identifier.

37. A system according to Claim 36, wherein the identifier is associated with the IP telephony network, and wherein the determined server is the application server.

38. A system according to Claim 36, wherein the identifier is associated with the circuit-switched telephony network, and the determined server is a Home Location Register, and wherein the application server is further to transmit a Mobile Access Part Location Update message to the Home Location Register to associate the client device with the application server within the circuit-switched telephony network.

39. A system according to Claim 33, the application server further to: receive a first message from a Home Location Register of the circuit- switched telephony network, the first message to request a roaming number for routing a call to a telephone number associated with the client device in the circuit-switched telephony network; transmit a second message to a Mobile Switching Center of the circuit- switched telephony network, the second message to request the roaming number corresponding to the telephone number; receive the roaming number from the Mobile Switching Center; and transmit the roaming number to the Home Location Register.

40. A system according to Claim 39, the application server further to: determine to offer the call to the client device via the circuit-switched telephony network, wherein the client device is roaming in the IP telephony network.

41. A system according to Claim 33, the application server further to: receive a Session Initiation Protocol message from the client device, the message to register a number of the circuit-switched telephony network; and transmit a Mobile Access Part Location Update message to a Home Location Register of the circuit-switched telephony network to associate the application server with the number.

42. A system according to Claim 33, the application server further to: receive an Integrated Service Digital Network User Part Initial Address

Message to initiate a call to a telephone number associated with the client device in the IP telephony network; determine to offer the call to the client device via the circuit-switched telephony network; transmit a Mobile Access Part Provide Roaming Number message to a Mobile Switching Center of the circuit-switched telephony network, the Mobile Access Part Provide Roaming Number message to request a roaming number corresponding to the client device in the circuit-switched telephony network; receive the roaming number from the Mobile Switching Center; and transmit an Integrated Service Digital Network User Part Initial Address Message to the Mobile Switching Center to initiate the call to the client device via the circuit-switched telephony network, the third message including the roaming number.

43. A system according to Claim 33, the application server further to: determine to offer a call to the client device via the circuit-switched telephony network or the IP telephony network.

44. A system according to Claim 43, wherein the determination to offer the call comprises: a determination to offer the call based on one or more of: an operator policy; a type of the call; or a preference associated with the client device.