Patent Publication Number: US-6912389-B2

Title: Interworking and interoperability of GPRS systems with systems of other technology families

Description:
CROSS REFERENCE TO RELATED APPLICATION 
   This application claims priority of Provisional Application Ser. No. 60/261,588, filed Jun. 12, 2001. 

   FIELD OF THE INVENTION 
   This invention relates to telecommunications systems, and more particularly to systems and methods for providing interworking and interoperability of certain services between telecommunications systems employing technology families that differ in air-interface, call model, or other protocols. 
   BACKGROUND OF THE INVENTION 
   Many wireless telecommunication subscribers desire to use their wireless terminals in conjunction with telecommunications systems other than their home systems. Subscribers also desire to obtain access to telecommunications services using their existing subscriptions, which access may be independent of their normal telecommunications terminals, through telecommunications systems other than their home systems. Frequently, the need for this occurs while the subscriber is travelling or otherwise outside the service area of their home system. Accordingly, telecommunications systems manufacturers and system operators have developed facilities to permit subscribers to receive services using their telecommunications terminals and subscriptions via a system which may not be the subscriber&#39;s home system, provided that the terminal and the serving system are compatible. This feature is often referred to as “roaming”. 
   Serving roaming subscribers is challenging even when the serving system and home system employ identical technologies. However, where the serving system is implemented using air interface and/or call model technology families that differ from those used in the home system, special challenges arise in providing interworking between such systems due to fundamental differences in message protocols, call models, and the basic structure and facilities of the underlying systems. Moreover, these differences are exacerbated over time as new technologies are introduced into networks containing a range of legacy technologies, and the old and new technologies are required to interwork. 
     FIG. 1  depicts a known arrangement  100  for the interconnection of selected components of two wireless systems: a “serving” system  110  using one of the conventional North American wireless technologies (such as Analog Cellular (AMPS), TDMA, CDMA, etc.); and a “home” GSM system  112 . The term “domestic wireless” (DW) is intended to refer to any of the wireless air interface and call model standards used in North America, including but not limited to those mentioned above. The components shown are selected to illustrate those needed for certain interworking between the systems in order to provide, within the service area of the “serving” domestic-wireless-type system  110 , service to a DW mobile station (MS)  114  having a home subscription on the GSM system  112 . It will be appreciated that both the serving DW system  110  and the home GSM system  112  have voice capabilities. Typically, the mobile station  114  would be a dual mode terminal which is compatible with one or more of the DW standards (other than GSM) and which is also compatible the GSM standard. The mobile station  114  would communicate with a DW MSC/VLR via a radio link  118 , radio base station equipment (not shown), and links connecting the base station equipment to the MSC/VLR  116 . The broken line  120  denotes the boundary between the two systems  110  and  112 . In order to provide interworking between the systems, the DW system  110  must communicate with the GSM system  112 . As is known in the art, the GSM system  112  may provide an Interworking and Interoperability Function (IIF)  122  comprising an HLR emulation function  124  compatible with the DW system  110 , connected to a GSM MSC/VLR emulation function  126 . The term “function” as applied to these elements is intended to be equivalent to “functional component.” The IIF  122  is connected to the DW MSC/VLR  116  via suitable signaling links, which may optionally include a Signal Transfer Point (STP)  128 . 
   The HLR emulation function  124  of IIF  122  appears to the DW MSC/VLR  116  as any other DW HLR, in that it appears to provide the functions of such an HLR more or less transparently to the DW MSC/VLR  116 . The GSM MSC/VLR component of  126  the IIF  122  similarly appears within the GSM network  112  as any other GSM MSC/VLR. The GSM MSC/VLR  126  is connected to a GSM HLR  130 . Thus, the IIF  122  provides signaling protocol, call model, and other necessary translations to permit the DW MSC/VLR  116  to perform normal registration, call processing and other transactions with the IIF  122 . To the extent the IIF  122  needs information or other resources from the GSM network  112  in order to perform the functions of a DW HLR, the GSM MSC/VLR component  126  may maintain those resources directly or may request them from other elements, such as the GSM HLR  130 . 
   As is known in the art, the MS  114  may register (message  132 ) with the DW MSC/VLR  116 , and the DW MSC/VLR  116  will propagate a suitable Register Notification message  134  (or messages  134   a  and  134   b  if a STP  128  is used) to the IIF  122 , which will perform any necessary translations, and further propagate resulting GSM protocol registration messages  136  to the GSM HLR  130 . Any acknowledgements (not shown) may be similarly be passed and translated in the opposite directions. 
     FIG. 2  depicts an arrangement  200  similar to that of  FIG. 1 , except that the serving system  210  and home-system  212  are reversed. That is, in  FIG. 2 , the serving system  210  is a GSM system and the home system is a DW  212  system. It will be appreciated that both the serving GSM system  210  and the home DW system  212  have voice capabilities. The MS  214 , which may be a dual-mode or multiple-mode mobile, or may be a GSM-only mobile containing a Subscriber Identity Module (SIM) corresponding to the subscriber&#39;s home DW subscription, may register (message  232 ) using normal GSM protocols. The GSM MSC/VLR  216  transmits, e.g., a Location Update message  234  to the Interworking and Interoperability Function (IIF)  222 . 
   The IIF  222  of  FIG. 2  contains a GSM HLR (or suitable emulator)  224 , and a DW MSC/VLR (or suitable emulator)  226 . The DW MSC/VLR  226  translates the message as necessary to employ DW protocols (e.g., it may prepare a suitable Register Notification message  236 ), and transmits it to the DW HLR  230 . In this case, because the GSM authentication function is complex and not supported by the DW HLR  230 , the GSM HLR  224  must also perform the authentication function. However, the DW HLR  230  may perform the other customary functions associated with registration of the mobile station. Any acknowledgements  238  produced by the DW HLR  230  may be transmitted and translated in the opposite direction. 
   As is known in the art, a call to the MS  214  while roaming in the GSM system  210  would be initially delivered to the home DW MSC/VLR (not shown), which would consult the DW HLR  230  to determine the location of the MS  210  and provide routing information needed to extend the call to the GSM MSC/VLR  216  for ultimate delivery. In this case, the DW HLR  230  will query the DW MSC/VLR emulating component  226  of the IIF  222  for a Temporary Local Directory Number (TLDN) and the IIF  222  will query the GSM MSC/VLR  216  for a Mobile Subscriber Roaming Number (MSRN). The IIF  222  will send the received MSRN as the TLDN back to the home DW MSC/VLR for it to extend the call to the GSM MSC/VLR  234 . 
   These processes assume that the mobile station  214  and GSM  210  network both have voice/circuit capabilities (although they may also have packet GPRS capabilities). In that case, the GSM HLR  224 , the GSM MSC/VLR  216 , and the DW HLR  230  are capable of providing traditional mobility management and other functions needed to provide telecommunications services to the mobile station  210 , including termination of calls. 
   However, there may be situations in which a subscriber would be unable to obtain utilize voice/circuit services from a GSM system  210 , but would desire to use GPRS services if they were available and roaming were possible. For example, a subscriber may be present in an area in which GPRS (i.e., packet data) service is available, but GSM service (i.e., circuit voice and data) is not available. Similarly, while travelling, there may be available to the subscriber a mobile station or terminal compatible with a GPRS system but not with a GSM system. For example, the mobile station may be a wireless Personal Digital Assistant lacking any voice capabilities. 
   Unfortunately, existing DW HLRs, such as DW HLR  230  of  FIG. 2 , are arranged to support circuit-switched voice or data devices only. Such DW HLRs are not equipped to accommodate registrations of terminals in GPRS- or packet-only mode or of terminals that have only GPRS or packet capabilities. Thus, existing DW HLRs are unaware of GPRS- or packet-only registrations. As a result, existing DW HLRs are unable to perform certain services in connection with GPRS- or packet-only mobile stations. 
   One service the existing DW HLR cannot perform is identification of a Serving GPRS Support Node (SGSN) in order to allow termination of an incoming Short Message Service message to the mobile station. Typically, such messages are initially directed to a Message Center element of the DW network, which element is connected to the DW HLR  230 . In DW networks, mobile stations do not attempt packet-only registrations, but rather these mobile stations register in a manner compatible with the DW HLR  230 . When a roaming GPRS- or packet-only terminal of a DW-native network registers in the GSM network  210 , the DW HLR  230  in the home network  212  has no facility for accepting information about such registration, and in particular, has no facility for storing the identity of the serving GPRS SGSN. Accordingly, when an SMS message arrives at the Message Center of the DW network  212 , the DW HLR  230  is unable to provide routing information to enable the SMS message to be forwarded to the serving SGSN for delivery to the mobile station. 
   OBJECT AND SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide an interworking and interoperability function that minimizes the aforementioned disadvantages of the prior art systems. 
   According to an aspect of the present invention, there are provided telecommunications system components and methods for use therewith which allow interworking and interoperability of a serving GSM and/or GPRS system with certain “domestic wireless” systems such that a mobile station homed on such a domestic wireless system, but registered with the serving system in a GPRS-only mode, may receive services from the serving system. The term “domestic wireless” (DW) is intended to refer to non-GSM systems compatible with ANSI or equivalent standards for TDMA, CDMA, and analog cellular systems, as generally used in North America, or compatible with other similar systems. The system includes a GPRS interworking and interoperability functional component (hereafter, IIF) that provides certain functions and services necessary for interworking and interoperability between the serving GPRS network and the home network. 
   The GPRS IIF includes a GPRS HLR component that provides the functions of a GPRS HLR, or emulates those functions, and interfaces with the serving GPRS system in a manner essentially indistinguishable from other GPRS HLRs. The GPRS IIF also includes a GPRS short message service-service center (SMS-SC) component which provides the functions of, or emulates, a regular SMS-SC. The GPRS IIF further includes an ANSI/DW mobile switching center/visitor location register (MSC/VLR) component that provides the functions of an ANSI/DW MSC/VLR, or emulates those functions, and interfaces with the home ANSI/DW system in a manner essentially indistinguishable from other ANSI/DW MSC/VLRs. The GPRS IIF further includes facilities for translating messages of the ANSI/DW system into functionally equivalent messages of the GSM/GPRS system, and vice versa, and for maintaining state information as needed to perform the translation between systems. The GPRS IIF may operate in cooperation with a GSM IIF, and in some embodiments, the functions of the GPRS IIF and the GSM IIF may be integrated or combined into a single IIF unit. 
   In accord with an aspect of the present invention, the GPRS IIF accommodates the registration or attachment by an ANSI/DW-homed mobile station onto a GSM/GPRS or GPRS-only system in a GPRS-only mode. The GPRS IIF detects that the subscriber is attaching to the GPRS network in a GPRS- or packet-only mode. The GPRS IIF responsively transmits to the DW HLR an appropriate registration notification message according to the circuit-switched protocol of the DW network, simulating the registration of a voice- or circuit-services-capable mobile station. In doing so, the GPRS IIF provides to the DW HLR the identity of an associated serving GPRS support node (SGSN) through which the mobile station registered, in a field normally used to identify the GSM mobile switching center/visitor location register (MSC/VLR) through which the mobile station registered. As a result, the DW HLR maintains information about the GPRS- or packet-only-registered mobile station as through it were a conventional voice- or circuit-services-capable mobile station which registered in the ordinary fashion. However, the DW HLR treats the subscriber as being registered to the MSC/VLR emulating component of the IIF. Thereafter, when a call delivery or SMS delivery attempt for the mobile station causes a query to the DW HLR, the DW HLR provides as the MSC identifier the address of the GPRS IIF/MSC/VLR associated with the SGSN, as earlier received from the IIF during the registration procedure. 
   According to a further aspect of the present invention, there is provided telecommunications system components and methods for use therewith which allow termination of an SMS-type message to a subscriber through a serving GPRS network, where the subscriber is homed to a network of a different technology family or protocol, and the subscriber is registered in a GPRS- or packet-only mode. When a call delivery or SMS delivery attempt for the mobile station causes a query to the DW HLR, the DW HLR provides as the MSC identifier the address of the GPRS IIF/MSC/VLR associated with the SGSN, as earlier received from the IIF during the registration procedure. All future messages associated with the mobile station and destined for an MSC/VLR, related to call delivery, SMS delivery, or message waiting notification, are routed to the IIF emulating the DW MSC/VLR. Such messages, where appropriate (e.g., if an SMS message or message waiting notification), are transmitted to the SGSN serving the MS. The GPRS IIF may itself generate or translate some such messages. 
   According to a further aspect of the invention, the serving telecommunications system may generate messages, indications, or events, which may be propagated as SMS messages to the mobile station as described above. In some cases, the messages, indications, or events, must be translated, e.g., by the IIF/MSC/VLR from a format of the DW serving system, into appropriate SMS message for use by the mobile for special functions, or for display to the user. For example, if the network receives a voice or circuit call destined for a MS registered in GPRS- or packet-only mode, the call cannot be delivered to the mobile. Accordingly, the call receives appropriate treatment, such as forwarding to a voice-mail system located on the DW home network. If the caller chooses to leave a voice-mail message, the voice-mail system may use a proprietary interface to inform the serving DW system&#39;s HLR of the message waiting condition. The DW HLR preferably transmits a Qualification Directive (QualDir) message (in the DW protocol) containing a message waiting indication to the IIF/MSC/VLR of the GSM/GPRS system. The IIF translates the message to an appropriate SMS message containing a message-waiting indication for use by the mobile station. The IIF transmits the message to the serving SGSN, which propagates it to the GSM mobile station. A similar process could occur if the mobile station is capable and registered for voice or circuit-services but GPRS-not-reachable for some reason. However, in that case, the SMS message may optionally be delivered via the serving GSM MSC instead of via the serving SGSN. 
   According to a further aspect of the invention, if a call delivery is attempted to the mobile station but cannot be delivered, e.g., because the mobile station has registered in GPRS- or packet-only mode, or because the serving network is incapable of delivering a voice or circuit call or services, the IIF may generate a missed call indication to be delivered to the mobile station. The IIF prepares a Mobile-Terminating Forward Short Message (MT-FSM) message containing appropriate text. For example, the message may mention the missed call and the calling party number, the calling party name, or other similar information that may be useful to the called party. The message is delivered as other SMS messages may be. Note that it is conceivable that a GSM HLR could also generate such an SMS message to the subscriber when the subscriber misses a call due to a “subscriber not reachable” condition detected in or by the GSM HLR. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the invention will be best understood by reference to the following detailed description of one or more exemplary embodiments of the invention, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram of selected elements of interconnected networks, including a domestic wireless serving system and a GSM home system, showing a prior-art arrangement for interworking and interoperability between the systems; 
       FIG. 2  is a block diagram of selected elements of interconnected networks, including a GSM serving system and a domestic wireless home system, showing a prior art arrangement for interworking and interoperability between the systems; 
       FIG. 3  is a block diagram of selected elements of interconnected networks, including a GSM and GPRS serving system and a domestic wireless home system, showing a first exemplary embodiment  300  constructed according to an aspect of the present invention for interworking and interoperability between the systems; 
       FIG. 4  is a combined block diagram/message flow diagram depicting a second exemplary embodiment  400  constructed according to an aspect of the present invention for interworking and interoperability between the systems, and further depicting message generation and propagation steps for use in conjunction with the exemplary embodiment  400  for handling an attempted call delivery to a DW/ANSI-homed mobile station when the station is initially registered in GPRS-only mode; 
       FIG. 5  is a message flow diagram depicting message generation and propagation steps for use in conjunction with the exemplary embodiments  300  and  400  of  FIGS. 3 and 4 , respectively, for registering a DW/ANSI-homed mobile station in a GPRS-only mode; 
       FIG. 6  is a message flow diagram depicting message generation and propagation steps for use in conjunction with the exemplary embodiments  300  and  400  of  FIGS. 3 and 4 , respectively, for delivering a message received by a DW/ANSI message center to a DW/ANSI-homed mobile station when the mobile station has registered in a GPRS-only or GSM/GPRS mode; and 
       FIG. 7  is a message flow diagram depicting message generation and propagation steps for use in conjunction with the exemplary embodiments  300  and  400  of  FIGS. 3 and 4 , respectively, for generating and delivering to a DW/ANSI-homed mobile station registered in a GPRS-only mode an indication that a call destined for the mobile station has been missed. 
   

   DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS 
   A telecommunications system constructed according to an aspect of the present invention may, in various embodiments, provide communications bearing voice signals, data, video, and any other content. Hereinafter, the term “call” is used herein to refer a session of information transfer between a set of subscriber terminals (or other endpoints) via a telecommunications system or network. The term “call” is intended to refer broadly to any type of call, service, connection, session, packet, or datagram, or any related group or stream thereof, regardless of media or content, and regardless of whether or not the communication is circuit, connection, or session oriented. Thus, the term “call” is intended to include, but not be limited to traditional circuit voice calls, packet voice calls, circuit data calls, connectionless calls, or packet data calls, and multimedia variants thereof. 
   The present application relates to telecommunications systems, including multimedia telecommunications systems, which may be implemented using a variety of electronic and optical technologies, including but not limited to: analog electronic systems; digital electronic systems; microprocessors and other processing elements; and software and other embodied collections of steps, instructions, and the like, for implementing methods, processes, or policies in conjunction with such systems and processing elements. The embodiments described herein are exemplary. Thus it will be appreciated that although the embodiments are described in terms of specific technologies, other equivalent technologies could be used to implement systems in keeping with the spirit of the present invention. 
   It will be appreciated that in the telecommunications arts, various signal leads, busses, data paths, data structures, channels, buffers, and other communications paths may be used to implement a facility, structure, or method for conveying information or signals, and are often functionally equivalent. Accordingly, unless otherwise noted, references to apparatus or data structures for conveying a signal or information are intended to refer generally to all functionally equivalent apparatus and data structures. 
   According to an aspect of the present invention, there are provided telecommunications system components and methods for use therewith which allow interworking and interoperability of a serving GSM and/or GPRS system with certain “domestic wireless” systems such that a mobile station homed on such a domestic wireless system, but registered with the serving system in a GPRS-only mode, may receive services from the serving system. The term “domestic wireless” (DW) is intended to refer to non-GSM systems compatible with ANSI or equivalent standards for TDMA, CDMA, and analog cellular systems, as generally used in North America, or compatible with other similar systems. The system includes a GPRS interworking and interoperability functional component (hereafter, IIF) that provides certain functions and services necessary for interworking and interoperability between the serving GPRS network and the home network. 
     FIG. 3  is a block diagram showing a first exemplary embodiment  300  including selected network elements arranged in accord with the present invention. A GSM and GPRS serving system  350  is connected to a domestic wireless (DW) home system  352 . The broken line  354  represents the boundary between the two systems  350  and  352 . A mobile station (MS)  356  compatible with serving system  350 , but homed to the DW home system  352 , is present in the coverage area of the serving system  350 . The MS  356  communicates with radio equipment  360  of the serving system  350  via a radio link  358 . The radio equipment is connected to a GSM mobile switching center  362  via a link  310  and to a GPRS serving GPRS support node (SGSN)  364  via a link  312 . MSC  362  and SGSN  364  each may be connected to one or more counterpart elements (not shown), which elements may be part of serving system  350  or part of other systems of the same technology family. MSC  362  and SGSN  364  may be implemented using any suitable components conforming to GSM and GPRS standards. 
   As best seen in  FIG. 3 , the DW home system  352  comprises a GPRS interworking and interoperability function (GPRS IIF)  380 , a GSM interworking and interoperability function (GSM IIF)  370 , an ANSI/DW home location register (HLR)  378 , and a DW message center  388 . The ANSI/DW HLR  378  is connected to the GSM IIF  370  via a link  394  and to the GPRS IIF  380  via a link  302 . The DW message center  388  is connected to the GSM IIF  370  via a link  396  and to the GPRS IIF  380  via a link  308 . The ANSI/DW HLR  378  and the DW message center  388  are interconnected via a link  398 . The ANSI/DW HLR  378  and the DW message center  388  may be implemented using any suitable components conforming to the standard of the DW home system  352 . The ANSI DW HLR  378  is preferably connected to one or more other MSC/VLRs (not shown) via a link  390  in order that it may exchange traffic with the other MSC/VLRs. The DW message center  388  is preferably connected to one or more other message centers (not shown) via a link  392  in order that it may exchange traffic with the other message centers. 
   The GPRS IIF  380  includes a GPRS HLR component  382  that provides the functions of a GPRS HLR, or emulates those functions, and interfaces with the serving GPRS/GSM system  350  in a manner essentially indistinguishable from other GPRS HLRs. The GPRS IIF  380  also includes a GPRS short message service-service center (SMS-SC) component  384  which provides the functions of, or emulates, a regular SMS-SC. Accordingly, the GPRS HLR component  382  is connected to SGSN  364  via a link  306 , and the GPRS SMS-SC  384  is connected to SGSN  364  via a continuation of link  308 . The GPRS IIF  380  may also have a standard Gc interface (not shown) to a Gateway GPRS Support Node (GGSN) (not shown). 
   The GPRS IIF  380  further includes an ANSI/DW mobile switching center/visitor location register (MSC/VLR) component  386  that provides the functions of an ANSI/DW MSC/VLR, or emulates those functions, and interfaces with the home ANSI/DW system  352  in a manner essentially indistinguishable from other ANSI/DW MSC/VLRs. The aforementioned components of GPRS IIF  380  further include facilities for translating messages of the ANSI/DW system into functionally equivalent messages of the GSM/GPRS system, and vice versa, and for maintaining state information as needed to perform the translation between systems. 
   The GSM IIF  370  includes a GSM HLR component  372  that provides the functions of a GSM HLR, or emulates those functions, and interfaces with the serving GSM/GPRS system  350  in a manner essentially indistinguishable from other GSM HLRs. The GSM IIF  370  also includes a GSM short message service-service center (SMS-SC) component  374  which provides the functions of, or emulates, a regular SMS-SC. Accordingly, the GSM HLR component  372  is connected to MSC  362  via a link  304 , and the GSM SMS-SC  374  is connected to MSC  362  via a continuation of link  396 . The GSM IIF  370  further includes an ANSI/DW mobile switching center/visitor location register (MSC/VLR) component  376  that provides the functions of an ANSI/DW MSC/VLR, or emulates those functions, and interfaces with the home ANSI/DW system  352  in a manner essentially indistinguishable from other ANSI/DW MSC/VLRs. The aforementioned components of GPRS IIF  370  further include facilities for translating messages of the ANSI/DW system into functionally equivalent messages of the GSM/GPRS system, and vice versa, and for maintaining state information as needed to perform the translation between systems. 
   The GPRS IIF  380  preferably operates in cooperation with a GSM IIF  370 , and in some embodiments, the functions of the GPRS IIF  380  and the GSM IIF  370  may be integrated or combined into a single IIF unit, illustrated as combined IIF  368 . 
   In conjunction with exemplary embodiments  300  (discussed above) and  400  (discussed below), the mobile station  356  may occupy various states of registration in the serving system  350  and/or the home system  352 . The mobile station&#39;s initial registration state, and any changes the mobile station  356  makes to its registration state, may affect the way further registration, call delivery, and message delivery are carried out. The following discussion considers the message flow and related steps required to accomplish registration, call delivery, and message delivery for each of four particular initial registration state scenarios. 
   In a first scenario, the DW-native MS  356  is idle and not registered on any network. When that MS registers on a GPRS network  350  (or more properly, the SGSN  364  thereof), a GPRS location update must performed and sent to the IIF component  382  emulating the GPRS HLR. The GPRS IIF  380  then pretends as if the MS  356  had just registered on a GSM MSC/VLR, and it sends a DW/ANSI-41 REGNOT to the DW/ANSI-41 HLR  378  (which records the IIF address as the MSC/VLR and VLR address). 
   Thereafter, call delivery attempts will result in the DW/ANSI-41 HLR  378  querying the GPRS IIF  380  (acting like a MSC/VLR in an ANSI-41 network). The GPRS IIF  380  will detect that the MS is GPRS-only attached, and thus reply with a “not reachable” type indication, and secondary treatment will occur (e.g. an announcement may be played, or the call may be forwarded). At that point in time, the IIF may generate an SMS message to the GPRS-only MS, indicating that the subscriber missed a call and indicating the calling party number of that call&#39;s originator. 
   All incoming SMS messages destined for the subscriber will be sent by the ANSI-41 MC  388  to the GPRS IIF  380  for conversion to GSM format if the subscriber is GPRS-attached. The Message Center  388  will query the DW/ANSI-41 HLR  378  which will inform the MC  388  to send a “Short Message Delivery Point-to-Point” (SMDPP) message to the GPRS IIF  380  (since the DWI/ANSI-41 HLR  378  operates as though the MS is registered on a MSC/VLR). The GPRS IIF  380  will then send the GSM-formatted SMS message (FSM) to the SGSN  364  (because the MS is packet-only registered. If the MS subsequently registers on a TDMA MSC/VLR, then that MSC/VLR will send a REGNOT to the DW/ANSI-41 HLR  378 . The DW/ANSI-41 HLR  378  will then send a REGCANC to the GPRS IIF  380 , which in turn will send a Cancel Location to the SGSN  364  (if GPRS attached). 
   In a second scenario, the DW-native MS  356  is currently registered on a GSM MSC/VLR, such as MSC/VLR  362 . When the MS  356  registers on a GPRS network  350  (SGSN  364 ), a GPRS location update will be performed and sent to the IIF component  382  emulating the GPRS HLR. The IIF  368  does not need to pretend that the MS has just registered on a GSM MSC/VLR because the DW/ANSI-41 HLR  378  already has the IIF address as the MSC/VLR and VLR address. 
   Thereafter, call delivery attempts will result in the DW/ANSI-41 HLR  378  querying the IIF  368 , which acts like a MSC/VLR in an DW/ANSI-41 network. The IIF  368  will detect that the customer is both GSM circuit-switched attached and GPRS attached, and query the GSM MSC/VLR  362  as normal in the GAIT standard specifications. If the MS  356  missed the call due to a not reachable indication (which may occur either if so identified in the IIF  368 , or if the GSM MSC/VLR  362  responds with a PRN error{absent subscriber} message), the IIF  368  may generate an SMS message to the MS  362 , indicating that the subscriber missed a call and indicating the calling party number of that call&#39;s originator. The IIF  368  will determine whether to send the SMS message via the SGSN  364  or the MSC/VLR  362  for delivery. 
   All incoming SMS messages destined for the subscriber will be sent by the DW/ANSI-41 MC  388  to the IIF  368  for conversion to GSM format. The Message Center  388  will query the DW/ANSI-41 HLR  378 , which will inform the MC  388  to send an SMDPP message to the IIF  368 . (The DW/ANSI-41 HLR operates as though the MS  356  is registered on a MSC/VLR.) The IIF will then determine whether to send the GSM-formatted SMS message (FSM) to the SGSN or MSC/VLR. Because the MS  356  is registered both on GSM MSC/VLR  362  and GPRS SGSN  364 , the IIF will determine an appropriate priority controlling the entity to which it will send the SMS message. For example, the GPRS SGSN  364  may have the highest priority, and the GSM MSC/VLR  362  may have the next priority. This priority may be overridden depending on whether the IIF detects that the MS is unreachable on one of the nodes. If the MS  356  subsequently registers on a TDMA MSC/VLR, then that MSC/VLR will send a REGNOT message to the DW/ANSI-41 HLR  378 . The DW/ANSI-41 HLR  378  will then send a REGCANC message to the IIF  368 , which in turn will send a Cancel Location message to the SGSN  380  (if GPRS attached). 
   In a third scenario, the DW-native MS  356  is currently registered on both a GSM MSC/VLR, such as MSC/VLR  362 , and a GPRS SGSN such as SGSN  364 . If the mobile station  356  performs a GSM-only detach, the IIF  368 , which is emulating a GSM HLR, will not be notified. Accordingly, the IIF  368  and DW/ANSI-41 HLR  378  continue operating as though the MS  356  is registered on the DW/ANSI MSC/VLR-emulating component  376  of IIF  368 . If however, the GSM MSC/VLR  362  sends a MS-Purged to the GSM HLR-emulating component  372  of IIF  368 , the IIF  368  will remove the circuit-switched profile data stored. In addition, the IIF  68  will not send a ANSI-41 MS-inactive message to the DW/ANSI-41 HLR  378  because the HLR  378  must continue to operate as though that the MS is currently registered on a GSM MSC/VLR. If the MS  356  subsequently registers on the same or different GSM MSC/VLR, then the IIF  368  would need to send the HLR a REGNOT message in order to obtain the profile information. If the MS subsequently registers on a TDMA MSC/VLR, then that MSC/VLR will send a REGNOT message to the DW/ANSI-41 HLR  378 , and the DW/ANSI-41 HLR  378  will send a REGCANC message to the IIF  368 . The IIF  368  in turn will send a Cancel Location message to the GSM MSC/VLR  362  (if CS attached) and/or the SGSN  364  (if GPRS attached). 
   In a fourth scenario, the DW/ANSI-41-native MS  356  is idle and currently registered on a DW/TDMA MSC/VLR. The message exchange need to perform the registration portion of this scenario are discussed in greater detail below in connection with FIG.  5 . Then the MS  356  registers on a GPRS network  350  (SGSN  364 ), a GPRS location update is be performed and sent to the GPRS HLR-emulating component  382  of GPRS IIF  380 . The GPRS IIF  380  then pretends that the MS  356  has just registered on a GSM MSC/VLR. The GPRS IIF  380  sends an DW/ANSI-41 REGNOT message to the DW/ANSI-41 HLR  378 . The DW/ANSI-41 HLR  378  records the address of GPRS IIF  380  as the MSC/VLR and VLR address. 
   Subsequent call delivery attempts will result in the DW/ANSI-41 HLR  378  querying the DW/ANSI-41 MSC/VLR-emulating component  386  of GPRS IIF  380 . The GPRS IIF  380  detects that the MS is GPRS-only attached, and thus replies with a “not reachable” type indication. As a result, secondary call treatment will be applied (e.g. an announcement may be played, or the call may be forwarded). At that point in time, the GPRS IIF  380  generates an SMS message to the GPRS-only MS, indicating that the subscriber missed a call and indicating the calling party number of that call&#39;s originator. 
   All incoming SMS messages destined for the subscriber will be sent by the DW/ANSI-41 MC  388  to the GPRS IIF  380  for conversion to GSM format if the subscriber is GPRS-attached. The Message Center  388  will query the DW/ANSI-41 HLR  378  which will inform the MC  388  to send the SMDPP message to the GPRS IIF  380 . (The DW/ANSI-41 HLR  380  continues to operate as though the MS  356  is registered on a MSC/VLR.) Because the MS  356  is packet-only registered, the GPRS IIF  380  will then transmit a GSM-formatted SMS message (FSM) to the SGSN  364 . If the MS subsequently registers on a TDMA MSC/VLR, then that MSC/VLR will send a REGNOT message to the DW/ANSI-41 HLR  378 . The DW/ANSI-41 HLR will send a REGCANC message to the GPRS IIF  380 , which in turn will send a Cancel Location message to the SGSN  364  (if GPRS attached). 
     FIG. 5  depicts message flow when a mobile station, which has previously registered in a DW/ANSI-41 network, subsequently requests GPRS only service. When an ANSI- 136  or other DW-native MS requests GPRS only service after having previously registered in a DW/ANSI-41 network, the MS performs a GPRS location update using its IMSI. In this case, the IIF emulates both a GPRS and GSM HLR/Authorization Center and a DW/ANSI-41 VLR. From the point of view of the subscriber&#39;s DW/ANSI-41 HLR, this situation is indistinguishable from one in which the subscriber has become registered on another ANSI- 136  MSC/VLR. 
   In step  510 , the MS  356  powers up and performs a GPRS Attach  560  in a GSM network. In step  512 , if the Serving GPRS Support Node (SGSN)  364  does not have authentication information (authentication triplets) in order to perform authentication, it requests authentication information from the GPRS IIF  380  (message  562 ). The IIF emulates a GSM HLR/AuC in this case. In step  514 , the GPRS IIF  380  returns the necessary authentication information (message  564 ). In step  566 , the SGSN  364  initiates authentication (message  566 ) towards the MS  356 . 
   In step  518 , the MS  356  responds (message  568 ) to the authentication request. In step  520 , the SGSN  364  initiates a GPRS location update towards the GPRS IIF  380 . The Update Location Request message  570  contains the IMSI. In step  522 , the GPRS IIF  380  validates whether the GPRS service request is authorized. The DW/ANSI-41 HLR can also authorize service. The GPRS IIF  380  emulates an DW/ANSI-41 VLR and issues an REGNOT INVOKE message  572  to the DW/ANSI-41 HLR  378  in order to remove the subscriber&#39;s associated circuit switch service registration from the TDMA MSC/VLR  502 . If necessary, the subscriber IMSI in the Update Location Request is mapped to the associated MIN. 
   In step  524 , the HLR  378  updates its location information and deletes the previous VLR record by sending a REGCANC message  574  to the previous VLR  502 . In step  526 , the VLR acknowledges the REGCANC in a message  576 . In step  528 , the HLR  378  returns the regnot acknowledgement message  578 . Ordinarily, the GPRS IIF  380  does not need to store the profile data received in the regnot acknowledgement message  578 , because the MS is only GPRS-attached (and the profile is circuit switching specific). However if some SMS-specific provisioned data from the ANSI-41 HLR is to be used for GPRS SMS, or if data is desired to be stored for subsequent GSM IIF usage (e.g., if the subscriber registers on an MSC), the IIF  368  may store the profile data. 
   In step  530 , the GPRS IIF  380  (emulating a GPRS HLR) sends the GSM MAP Insert Subscriber Data message  580  towards the SGSN  364 . This procedure is used to download subscriber data to the SGSN  364 . Multiple Insert Subscriber Data transactions may be necessary to complete the transfer of subscriber data to the SGSN. In step  532 , the SGSN  364  acknowledges the ISD Operation(s) using a message  582 . In step  534 , once the GPRS IIF  380  has received an acknowledgement to the Insert Subscriber Data operation, the GPRS IIF  380  returns an acknowledgement message  584  for the Update GPRS Location Request. In step  536 , the SGSN  364  acknowledges the GPRS Attach request using a message  586 . 
   According to a further aspect of the present invention, there is provided telecommunications system components and methods for use therewith which allow termination of an SMS-type message to a mobile station through a serving GPRS network, where the mobile station is homed to a network of a different technology family or protocol, and the mobile station is registered in a GPRS- or packet-only mode. When a call delivery or SMS delivery attempt for the mobile station causes a query to the DW HLR, the DW HLR provides as the MSC identifier the address of the GPRS IIF/MSC/VLR associated with the SGSN, as earlier received from the IIF during the registration procedure. All future messages associated with the mobile station and destined for an MSC/VLR, related to call delivery, SMS delivery, or message waiting notification, are routed to the IIF emulating the DW MSC/VLR. Such messages, where appropriate (e.g., if an SMS message or message waiting notification), are transmitted to the SGSN serving the MS. The GPRS IIF may itself generate or translate some such messages. 
     FIG. 6  is a message flow diagram depicting message generation and propagation steps for use in conjunction with the exemplary embodiments  300  and  400  of  FIGS. 3 and 4 , respectively, for delivering a message received by a DW/ANSI message center to a DW/ANSI-homed mobile station when the mobile station has registered in a GPRS-only mode. In step  610 , the BW/ANSI-41 message center (MC)  388  transmits an SMSRequest Invoke message  660  to the HLR  378 , including as arguments the MIN (MSISDN) of the mobile station and SMS Notification Indicator. In step  612 , the HLR  378  determines whether the message should be forwarded to the MS and transmits a response to the MC  388  in a SMSRequest Return Result message  662 , with the SMS_Address set to the IIF address (which may be a point code or E. 164 address). 
   In step  614 , the MC  388  formats a Short-Message Delivery Point-to-Point (SMDPP) message  664  and transmits it to the GPRS IIF  380 . Optionally, the message may take the form of a GSM-Hosted SMS Teleservice (GHOST) message encapsulated in the SMDPP message. In step  616 , the GPRS IIF  380  builds a Forward Short Message (FSM)  666 . If the message was in the GHOST format, the GPRS IIF  380  strips off the GHOST encapsulation. The IIF routes the FSM  666  to the SGSN  364  as a first choice. 
   Alternatively, the GPRS IIF  380  could send the FSM  666  to the GSM MSC. In some systems, the HLR may maintain a “mobile not reachable” flag which corresponds to a mobile station or subscription, and which may be activated under control of the subscriber. If that flag is set, then transmission of the FSM  666  to the GSM MSC would be inhibited. 
   In a further step (not shown), the SGSN  364  packages the information received in the FSM message  666  (referred to as GSM SMS RP-Data) into a CP-DATA message and delivers it across the GSM air interface to the mobile station. The mobile station acknowledges receipt of the CP-DATA and RP-DATA messages via CP-ACK and CP-ACK[RP-ACK], respectively. In step  618 , upon successful receipt of the RP-ACK message from the mobile station, the SGSN  364  sends a positive acknowledgement Forward Short Message  668  back to the GPRS IIF  380 . In step  620 , the GPRS IIF  380  maps the received acknowledgement Forward Short Message  668  into a SMDPP Return Result message  670  and sends it to the MC  388 . 
   According to a further aspect of the invention, the serving telecommunications system may generate messages, indications, or events, which may be propagated as SMS messages to the mobile station as described above. For example, messages destined for the mobile station may be generated as a consequence of a failed attempt to deliver a call to the mobile station. A message may be sent to the mobile to indicate there is a voice-mail message waiting, or to indicate that an attempted call to the mobile station was missed. In some cases, the messages, indications, or events, must be translated, e.g., by the IIF/MSC/VLR from a format of the DW serving system, into appropriate SMS messages for use by the mobile for special functions, or for display to the user. 
     FIG. 4  is a combined block diagram/message flow diagram depicting a second exemplary embodiment  400  constructed according to an aspect of the present invention for interworking and interoperability between the systems, and further depicting message generation and propagation steps for use in conjunction with the exemplary embodiment  400  for handling an attempted call delivery to a DW/ANSI-homed mobile station when the station is initially registered in GPRS-only mode. The embodiment  400  of  FIG. 4  is highly similar to the embodiment  300  of  FIG. 3 , but in the embodiment  400 , a single combined interworking and interoperability function  468  for both GSM and GPRS is provided. 
   As best seen in  FIG. 4 , a voice or circuit call arriving at the DW/ANSI MSC/VLR  502  may indicate in an initial address message (IAM)  420  that the call is destined for the mobile station  356 . If the MS  356  is registered in GPRS- or packet-only mode, the call cannot be delivered to the mobile. Accordingly, the call receives appropriate treatment, such as forwarding to a voice-mail system  450  located on the DW home network. See forwarding IAM message  432 . Messages  422 - 430  are conventional ANSI-41 call delivery messages. 
   If the caller chooses to leave a voice-mail message, the voice-mail system  450  may use a proprietary interface (see message waiting notification  434 ) to inform the serving DW system&#39;s HLR  378  of the message waiting condition. The DW HLR  378  preferably transmits a Qualification Directive (QualDir) message  436  (in the DW protocol) containing a message waiting indication to the IIF/MSC/VLR  468 ,  386  and  376  of the GSM/GPRS system. The IIF  468  translates the message to an appropriate SMS message  442  containing a message-waiting indication for use by the mobile station  356 . The IIF  468  transmits the message  442  to the serving SGSN  364 , which propagates it to the GSM mobile station  356 . A similar process could occur if the mobile station  356  is capable and registered for voice or circuit-services but unreachable for some reason. However, in that case, an SMS message  438  may optionally be delivered via the serving GSM MSC  362  instead of via the serving SGSN  364 . 
   According to a further aspect of the invention, if a call delivery is attempted to the mobile station  356  but cannot be delivered, e.g., because the mobile station has registered in GPRS- or packet-only mode, or because the serving network is incapable of delivering a voice or circuit call or services, the IIF  468  may generate a missed call indication to be delivered to the mobile station  356 . The IIF  468  prepares a Mobile-Terminating Forward Short Message (MT-FSM) message  426  containing appropriate text. For example, the message may mention the missed call and the calling party number, the calling party name, or other similar information that may be useful to the called party. The message is delivered as other SMS messages may be, as generally depicted in  FIG. 4 , and shown more particularly in FIG.  7 . Note that it is conceivable that a GSM HLR could also generate such an SMS message to the subscriber when the subscriber misses a call due to a “subscriber not reachable” condition detected in or by the GSM HLR. 
     FIG. 7  is a message flow diagram depicting message flow and associate message generation and propagation steps for use in conjunction with the exemplary embodiments  300  and  400  of  FIGS. 3 and 4 , respectively, for generating and delivering to a DW/ANSI-homed mobile station attached for GPRS-only services an indication that a call destined for the mobile station has been missed. The IIF  468  has already registered itself (as an ANSI-41 MSC/VLR) with the ANSI-41 HLR  378 . Because the subscriber is attached for GPRS-only service, incoming calls are not deliverable to the subscriber. 
   In step  710 , the DW/ANSI MSC/VLR  502  receives an incoming call  760  for the MS  356 , which is roaming in the GSM network. In step  712 , the DW/ANSI MSC/VLR  502  sends a LOCREC message  762  to the DW/ANSI HLR  378 . In step  714 , the HLR  378  has the address of the GPRS IIF  380  (acting as an ANSI-41 MSC/VLR) and sends a ROUTEREQ message  764  to the GPRS IIF  380 . 
   In step  716 , the IIF  468  recognizes that the addressed station is a GAIT subscriber roaming in a GSM network. The IIF, from its dynamic data, sees that the MS is attached for GPRS-only services and hence, cannot have call delivery. The IIF  468  sends a routreq message  766  with the field “AccessDeniedReason” set to “No Page Response.” Other error or reason codes could also be used. In step  718 , the HLR  378  returns a locreq message  768  to the DW/ANSI MSC/VLR  502 . At this point, the calling party may receive secondary treatment. 
   The IIF  468  contains the functionality to act as a GSM SMS-SC. In this case, the IIF  468  has the calling party DN available (from the ROUTEREQ message  764 ). In step  720 , the IIF  468  proceeds to act as an SMS-SC and sends an FSM SMS message  770  to the SGSN  364  with the calling party number of the missed call. In step  772 , the SGSN  364  delivers an mobile-terminated FSM SMS message  772  containing the calling party&#39;s DN to the MS  356  and waits for an acknowledgement. In step  774 , the SGSN  364  sends the FSM acknowledgement message  774  back to the IIF  468 . 
   The above-described embodiment of the invention is merely one example of a way in which the invention may be carried out. Other ways may also be possible and are within the scope of the following claims defining the invention.