Abstract:
A method and apparatus for generating a billing identifier for a subscriber from a first network roaming within a second network is disclosed. A node interconnecting the first and second networks receives a call message that does not include a billing identifier from the first network. A billing functionality within the node responsive to the call message generates a billing identifier enabling billing records within the second network to be associated with the subscriber from the first network. Messages containing the billing identifier are then transmitted to the second network from the interconnecting node.

Description:
RELATED APPLICATIONS 
     This application claims priority from and incorporates herein by reference the entire disclosure of U.S. patent application Ser. No. 60/124,918, filed Mar. 17, 1999. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field of the Invention 
     The present invention relates to billing ID correlation, and more particularly, to a system and method for correlating billing ID information for subscribers roaming between wireless communication systems utilizing differing technologies. 
     2. Description of Related Art 
     Within cellular networks, a mobile subscriber may roam between service areas of different networks. Various techniques have been developed to enable a mobile subscriber to continue being provided with mobile telephone services once they have left their home service area. In a first alternative, once a mobile subscriber travels into a new mobile switching center (MSC) coverage area and turns on their mobile station for the first time, the mobile station attempts to register with the servicing MSC for the area by transmitting an associated identification number known as the international mobile subscriber identity (IMSI) number or mobile identification number (MIN). The serving MSC communicates with the home location register associated with the mobile station using the received IMSI/MIN. This communication is to inform the HLR of the mobile station&#39;s new location and to receive requisite subscriber information from the HLR necessary to provide mobile services to the newly registering mobile station. 
     However, when mobile subscribers move between networks utilizing different technologies, for example, a GSM system utilizing a GSM MAP protocol and a TDMA system using a ANSI- 41  protocol, the various information required to be transmitted between the networks creates problems in converting information between the protocols useable by each system. 
     One of the problems arising with subscribers roaming from a GSM system to a TDMA system involves the inability to track billing information for a GSM subscriber within a TDMA system. This arises because of the differences in the way billing ID information is transmitted within the separate systems. The billing information is necessary in order to correlate a billing record generated in the gateway mobile switching center (GMSC) with a billing record generated in a visited mobile switching center (MSC). Since the billing information formats are different between GSM and TDMA networks (and also GSM networks where TAP is the utilized standard), there exists a need for a system capable of providing billing information when a GSM subscriber roams outside of its home technology network into a system utilizing a differing technology. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the foregoing and other problems with a system and method for generating a billing identifier for a call to a subscriber from-a GSM network which is presently located within a TDMA or other technology network. A mobility gateway interconnecting the GSM network with the TDMA network receives a call message from the GSM network which does not include a billing identifier. A functionality within the mobility gateway generates a billing identifier enabling billing records within the TDMA network to be associated with the subscriber from the GSM network. 
     The billing identifier includes a mobility gateway switch ID, a mobility gateway switch number and an additional part which identifies the mobile country code and a mobile network code for the subscriber. The mobility gateway transmits the billing identifier to the TDMA network. Later, the mobile country code and mobile network code for the subscriber from the GSM system may be determined from the billing identifier, and the billing record within the TDMA network associated with the subscriber using this information. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawings wherein: 
     FIG. 1 is a functional block diagram illustrating a mobility gateway including the functionality of the present invention between a GSM network and a TDMA network; 
     FIG. 2 is a signaling diagram illustrating a call connection within a TDMA network; 
     FIG. 3 is signal diagram illustrating a call connection within a GSM network; 
     FIG. 4 illustrates a call connection to a GSM subscriber which has roamed into a TDMA network using the billing identifier according to the present invention; and 
     FIG. 5 illustrates the billing identifier produced by a mobility gateway according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the Drawings, and more particularly to FIG. 1, there is illustrated a block diagram of a GSM network  10  utilizing a GSM MAP protocol interconnected with a TDMA network  15  using a ANSI- 41  protocol through a mobility gateway  20 . The mobility gateway  20  comprises an inter-system location register (ILR) or inter-working inter-operability function (IIF). The GSM network  10  enables subscribers to access telecommunications functionalities utilizing GSM technologies. The TDMA network enables mobile subscribers to access telecommunications functionalities using TDMA technologies. 
     The mobility gateway  20  enables mobile subscribers from the GSM network  20  to roam within the TDMA network  15  and mobile subscribers from the TDMA network to roam within the GSM network  10  while maintaining access to substantially all of the services and functionalities provided to them within their home network. While-the present system is described with respect to interconnections between a TDMA system using the ANSI- 41  protocol and a GSM system utilizing a GSM MAP protocol, it should be realized that the mobility gateway  20  and discussions with respect thereto may be extended to include other mobile protocols and networks such that the described system is not limited to use between GSM and TDMA networks. 
     As mentioned previously, a major problem with a GSM subscriber roaming within a TDMA network is the difference in the protocols utilized in each type of network with respect to the transmission of billing ID information. The present invention uses a billing functionality  25  to create a billing identifier for a call passing from a GSM to a TDMA network. A discussion of the manner in which calls are set up and billing information transmitted within TDMA and GSM networks will more clearly point out these differences. 
     Referring now to FIG. 2, there is illustrated a signaling diagram describing a call connection within a TDMA system. It should be noted that the billing information within a TDMA call set-up is transmitted from the GMSC and expected by both the HLR  55  and MSC/VLR  65  during call set-up. An incoming call message  30  is received at a public switch telephone network (PSTN)  35 . The PSTN  35  forwards a call message  40  to the TDMA GMSC  45 . The TDMA GMSC  45  generates a location request message  50  which is transmitted to a TDMA HLR  55 . The TDMA GMSC  45  includes billing information within the location request  50 . If the call originated from a mobile phone, the serving MSC would serve as the GMSC and the PSTN would not be involved. The TDMA HLR  55  generates a routing request message  60  to the TDMA MSC/VLR  65 . The HLR  55  also includes the billing information received from the GMSC  45  in the routing request message  60 . 
     In response to the routing request  60 , the TDMA MSC/VLR  65  generates a routing request return message  70  back to the TDMA HLR  55  which in turn generates a location request return message  75  to the TDMA GMSC  45 . Using the information received in the location request return message  75 , the TDMA GMSC  45  provides a call connection  80  with the MSC/VLR  65  over a voice trunk circuit. The TDMA MSC/VLR  65  may then establish a call connection  82  with the TDMA subscriber  85 . 
     A different call set-up procedure, with respect to the treatment of billing information, is illustrated in FIG. 3 for a GSM network. An incoming call message  90  is received at the PSTN  95  which generates an incoming call message  100  to the GSM GMSC  105 . In response to the incoming call message  100 , the GMSC  105  generates a send routing information request message  110  to a GSM HLR  115 . Next, a provide roaming number message  120  is transmitted to the GSM MSC/VLR  125  from the HLR  115 . The MSC/VLR  125  responds with a provide roaming number result message  130  to the HLR  115 . The HLR  115  transmits a send routing information result message  135  to the GMSC  105 . Using this information, a call connection  140  is established between the GMSC  105  and the MSC/VLR  125 . In a GSM network, the billing information is generated within the GMSC and transmitted to the MSC/VLR with the call connection  140  on the voice trunk over the ISUP. The “network call reference” parameter within the ISUP IAM message (initial address message) contains the billing information. A call connection  145  may then be established between the MSC/VLR  125  and the GSM subscriber  150 . 
     As can be concluded from the foregoing descriptions of FIGS. 2 and 3, if a GSM subscriber is roaming within a TDMA network, the TDMA MSC/VLR  65  will expect billing information to be provided in response to a call set-up command. This, of course, creates a problem since GSM systems do not transmit billing information until the call delivery is performed. Thus, a system for providing call billing information for GSM subscribers within a TDMA network is needed. 
     Referring now to FIG. 4, there is illustrated a method of the present invention for providing billing information for a GSM subscriber in a TDMA network. In response to an incoming call  155 , the PSTN  160  transmits an incoming call message  165  to the GSM GMSC  170 . The GMSC  170  transmits a send routing information message  175  to the GSM HLR  180 . The HLR  180  transmits a provide roaming number message  185  to the mobility gateway  190 . Within the mobility gateway  190 , a billing functionality  25  (FIG. 1) generates a billing identification  232  to be included within the routing request message  195  from the mobility gateway  190  to the TDMA MSC/VLR  200 . This is necessary because the GSM system has not yet generated any billing information, and the TDMA MSC/VLR  200  expects billing information within the routing request message  195 . 
     The billing functionality  25  generates the billing identification  232  as illustrated in FIG.  5 . The billing identification  232  includes three separate portions; namely, the system identifier  235 , the switch number  240 , the billing ID number  245 , and the segment number  250 . The system identifier  235  is two bytes long and includes the mobility gateway switch ID (SID). The switch number  240  is one byte long and includes the mobility gateway switch number. The billing ID number  245  is three bytes long and is based upon the GSM subscriber IMSI number. The billing functionality  25  uses the mobile country code (MCC) and the mobile network code (MNC) of the GSM subscriber to generate a 5 digit billing ID number  245 . The remaining digits within the three byte portion are filled with a filler data (e.g., F), if necessary. The segment number  250  is not used and is only 1 byte long. The segment number  250  may be filled with a value such as H′FF. The system identifier and switch number provide information on the mobility gateway switch from which the call information came. The mobile country code and mobile network code within the billing ID number  245  are used to correlate the billing records of the GSM GMSC and the TDMA MSC to know which subscriber the call should be billed to. 
     Referring now back to FIG. 4, once the billing identification  232  has been generated by the billing functionality  25  within the mobility gateway  190 , a routing request message  195  including the billing identification is transmitted to the TDMA MSC/VLR  200 . The routing request message  195  from the mobility gateway  190  appears to come from a TDMA HLR from the point of view of the TDMA MSC/VLR  200 . In response thereto, the MSC/VLR  200  transmits a routing request result message  205  to the mobility gateway  190  which transmits a provide roaming number result message  210  to the GSM HLR  180 . Messages to the GSM HLR  180  from the mobility gateway  190  appear to come from a GSM MSC/VLR from the point of view of the GSM HLR. The GSM HLR  180  notifies the GSM GMSC  170  of the roaming number with a send routing information result message  215 . A call connection  220  is provided between the GSM GMSC  170  and the TDMA MSC/VLR  200  over a voice trunk. The call connection  220  will necessarily include the billing information over the ISUP, but this information is neither expected nor interpreted by the TDMA MSC/VLR  200 . A call connection  225  may then be established between the MSC/VLR  200  and the GSM subscriber  230 . 
     Using the above described system and method, billing records associated with the GSM subscriber that has roamed into a TDMA network may be properly tracked and accounted for using the billing ID number such that the proper GSM subscriber  230  is billed for calls occurring while the subscriber is within the TDMA network. The derived billing ID number is used to direct charging information to the country and operator associated with the subscriber. 
     Although a preferred embodiment of the method and apparatus of the present invention has been illustrated in the accompanying Drawings and described in the foregoing Detailed Description, it is understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications, and substitutions without departing from the spirit of the invention as set forth and defined by the following claims.