Abstract:
Disclosed is an apparatus providing minimal systems alterations in non-GSM cellular systems wishing to incorporate GSM GPRS messaging capability. This is accomplished by giving a registering terminal or MS an IP address for use in receiving both signaling and traffic data messages rather than using the SGSN as the traffic receiving entity and forwarding traffic to the MS from the SGSN and requiring signaling messages to be transmitted from the MSC to the MS by other means. This approach simplifies the integration of GPRS capability into any non-GSM configuration cellular system by providing a generic way to exchange signaling information between any MSC, having a known IP address, and any MS with an assigned IP address.

Description:
TECHNICAL FIELD 
     The present invention relates in general to GPRS (General Packet Radio Service) and in particular to methods and systems for tunneling data packets whereby data packets could traverse either one of GSM (Global System for Mobile Communication) and a foreign network such as a TDMA (Time Division Multiple Access) network to reach a given MS (Mobile Station). 
     BACKGROUND 
     GPRS refers to a recently implemented high-speed packet data technology. GPRS is expected to profoundly alter and improve the end-user experience of mobile data computing, by making it possible and cost-effective to remain constantly connected, as well as to send and receive data at much higher speeds than in the past. Its main innovations are that it is packet based, that it can increase data transmission speeds from the previous 9.6 Kbps to over 480 Kbps, and that it may be used to extend the Internet connection all the way to the mobile PC. In other words, the user will no longer need to dial up a separate ISP. However, GPRS complements rather than replaces the prior art data services available through cellular networks, such as circuit-switched data and SMS (Short Message Service) that has been available in some cellular telephone networks such as GSM. 
     Because GPRS supports standard networking protocols, configuring computers to work with GPRS is very straightforward. In the case of IP communications, one is able to use existing TCP/IP protocol stacks, such as the stack that comes with widely available operating systems such as Windows 95. TCP/IP stacks are readily available for most other platforms as well. 
     Another feature of GPRS is that it supports a message transmission technology typically referred to as tunneling. Tunneling is the use of encapsulation to deliver messages through a network where that network has no knowledge of the message. One use of tunneling is to support private communications over a public network to provide what is known as a VPN (virtual private network). Software is used at each end of the communication to encapsulate sent and de-capsulate received messages. In accordance with the GPRS standard, traffic data packets are tunneled across any intervening networks from a SGSN (Serving GPRS Support Node) associated with a source of traffic data packets to a GGSN (Gateway GPRS Support Node) associated with the receipt of the traffic. To forward IP or X.25 packets between each other, the SGSN and GGSN encapsulate these packets using a specialized protocol called the GPRS tunnel protocol (GTP) which operates over the top of standard TCP/IP protocols. 
     The GPRS standard further defines three (3) classes of terminals or Mobile Stations. (MSs). A class A terminal may receive both switched circuit and packet data communications simultaneously. A class B terminal may be used in either a packet data mode or a switched circuit mode, but may not be used in both modes simultaneously. A class C terminal is only usable for packet data communications. 
     The GSM GPRS network, defined by ETSI standards beginning with 03.60, has been selected as the standard for use in the North American TDMA market for data packet service. Since GSM and TDMA use somewhat different approaches in providing signaling messages to and from a given MS there are some inconsistencies that need to be solved between the voice and data networks in the TDMA system. In other words, the standard TDMA method of delivering the signaling messages is not appropriate for an MS designed in accordance with the GSM GPRS packet data standard. 
     One possible solution for resolving the differences is to change the GPRS network to accept signaling information from the TDMA network. This approach is undesirable in that it would require a considerable amount of standards definition work. Further, if it came to pass that other networks wanted to be able to receive and transmit signaling messages to a MS designed in accordance with standards agreed upon in the in a GSM GPRS and North American TDMA (TDMA 136) GPRS, further standards definition work would be required. A more desirable approach is to find a method whereby a signaling path can be provided transparently through the GPRS network from any MSC (Mobile Switching Center) whether part of a GSM, TDMA-136, CDMA or other type cellular network, directly to any MS registered to that home MSC. If such a solution would allow a packet data MS to roam to and operate in foreign type networks, while still receiving signaling messages from its home network, the method would have great economic impact. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a method of permitting a home MSC and an MS, registered with that home MSC, located anywhere in the GPRS network to exchange signaling messages through the process of assigning IP addresses to both the MSC and to the MS, when the MS registers with the GPRS network, tunneling encapsulated signaling messages through the network between the MS and its associated home MSC and de-encapsulating the signaling messages at the signaling message destination. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a more complete understanding of the present invention, and its advantages, reference will now be made in the following Detailed Description to the accompanying drawings, in which: 
     FIG. 1 is a block diagram of the components involved when integrating GPRS with an existing GSM cellular network; 
     FIG. 2 is a block diagram of the components involved when integrating GPRS with an existing TIA/EIA-136 cellular network; 
     FIG. 3 illustrates the protocol stack interfaces needed, in practicing the present invention, to provide signaling between an MS and the home MSC when the MS is located in the home network; and 
     FIG. 4 illustrates the protocol stack interfaces needed, in practicing the present invention, to provide signaling between an MS and the home MSC when the MS is located in a network remote from the home network. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a drawing taken directly from the above referenced GSM 03.60 standard. In this drawing, a block  10  comprises SMS (Short Message Service) circuitry including the GMSC (Gateway Mobile Switching Center) and the IWMSC (InterWorking MSC). As illustrated in this drawing, the solid lines interconnecting blocks represent both data (traffic) and signaling interfaces while the dash lines represent signaling interfaces only. Block  10  is connected by a solid line to a block  12  further labeled with SM-SC (Short Message Service Centre). Block  10  is also connected to a SGSN (Serving GRPS Support Node) block  14  via a solid line  16 . Line  16  is further labeled G d  as a defined GSM interface. Block  10  is further connected to a MSC/VLR (MSC/Visitor Location Register) block  18  by a dash line E also labeled as  20  and is connected via a dash line C to an HLR (Home Location Register)  22 . Blocks  18  and  22  are interconnected by a dash line D. The SGSN block  14  is connected to a further SGSN block  24  via a solid line interface G n , and is connected via a similar interface to a GGSN (Gateway GPRS Support Mode) block  26 . The blocks  22  and  26  are interconnected by a dash line interface labeled G c . The GGSN  26  is connected via a solid line interface G i  to a PDN (Packet Data Network)  28  including at least one TE (Terminal Element) block  30 . A dash line interface G f  interconnects SGSN  14  with an EIR (Equipment Identity Register) block  32 . Another PLMN (Public Land Mobile Network) in shown interconnected to SGSN block  14  via a solid line interface labeled G p . This G p  connection would interface with one or more GGSN blocks within PLMN  34  such as GGSN block  36 . A solid line interface labeled G b  interconnects SGSN  14  with a BSS (Base Station System) block  38 . A dash line interface labeled A interconnects blocks  18  and  38 . BSS  38  is connected to a MT (Mobile Terminal) block  40  via a solid line interface U m . A TE block  42  communicates with MT  40  via a solid line interface R. The only blocks that had to be added to a GSM cellular network to enable concurrent use of GPRS are the SGSN and GGSN blocks. The interfaces labeled with a G and a subscript letter were either redefined from the original GSM cellular standards or added as new definitions to accommodate GPRS. 
     FIG. 2 is a drawing taken directly from a proposed industry standard defining the structure of a North American TDMA wireless service incorporating GPRS and having a document designation of SP-4027-932. A common reference for such a system is GPRS  136 . In this drawing, there are shown several blocks  50 ,  52 ,  54 ,  56  and  58  in the upper portion. Blocks  50 ,  52 ,  54  and  58  include the term ANSI- 41  to provide an indication that the function of component in that block needs to function differently from what it would if the cellular system did not have to accommodate GPRS signaling and traffic; in other words, a TDMA cellular system as defined in the TIA/EIA-136 standards. 
     Block  50  represents a circuit switched MSC/VLR. Block  52  represents a circuit switched HLR/AC where AC refers to the Authentication Center portion of the network. Blocks  50  and  52  communicate over a C-D interface. Block  54  represents the MC, where MC refers to the Message Center portion of the network, and block  54  communicates with block  52  over an N interface. The block comprises the SME (Security Management Entity) which communicates with block  54  over an M interface. The block  58  represents the GPRS Gateway MSC/VLR and communicates with blocks  50 ,  52  and  54  through interfaces labeled E, C-D and Q respectively. An SGSN block  60  communicates with block  58  over a signaling interface labeled G s ′, with a GPRS HLR block over a signaling interface labeled G r ′, with a GGSN block  64  over an interface labeled G n , with another PLMN  66  over an interface labeled G p  and with another SGSN  68  over an interface labeled G n . The GGSN  64  is shown communicating with a PDN  70  over an interface labeled Gi to a TE block  72 . A BS (Base Station) block communicates over a G b ′ interface and to an MT block  76  over a solid line interface U m . A TE block  78  is shown communicating with MT  76  over an interface R. 
     As set forth in the proposed standard for GPRS-136, blocks  52 ,  60 ,  74  and  76  in FIG. 2 operate differently from their corresponding counterparts in a GSM GPRS system as shown in FIG. 1 to accommodate the signaling message differences from TIA-136 systems. These differences require further signal translations, above those previously required, when the MS is located in the coverage area of a system of a type foreign to that of its home MSC. If other cellular network types wish to incorporate the GPRS data handling capability, the signal translation problems are compounded. 
     The present invention requires only a small amount of additional software in the MS to encapsulate and de-capsulate signaling messages and a modification of the protocol stack interfaces in the SGSN and the MSC. 
     In FIG. 3, an MT  100  is shown connected through a BSS  102  to an SGSN  104 . SGSN  104  is shown connected through a GGSN  106  to an IP Network  108  and is also connected via a SS 7  interface to a local or home MSC  110  in a GPRS-136 environment. A message stack  112  illustrates the format of messages received by or generated by MT  100 . The acronyms within stack  112  are defined in the GSM GPRS standards except for 136+RF and IS  136  Sig which would be GPRS-136 specific. Thus SNDCP (SubNetwork Dependent Convergence Protocol), GMM (GPRS Mobility Management), GSM (GPRS Session Management), LLC (Logical Link Control) and MAC (Medium Access Control) are well defined and understood by those familiar with GSM GPRS. The BSS  102  must translate some signals, thus the stack  114  has two columns. The BSS merely relays the portion of the stack starting with LLC and above from SGSN  104  to MT  100 . On the other hand the BSSGP (Base Station Subsystem GPRS Protocol) and NS (Network Services) layers are terminated in the BSS and SGSN and are used to deliver information between the two entities. The MAC and 136+RF layers are used to deliver information between the BSS and the MS. The SGSN  104  completely changes the stack between the formats shown in stack  116  and  118  in communicating from BSS  102  to MSC  110  in order to pass over the local SS 7  interface to the home MSC. The portions SCCP, MTP 2  (Message Transfer Part layer  2 ) and MPT 3  (Message Transfer Part layer  3 ) are defined in the GSM and ANSI standards. 
     In FIG. 4, communications from a roaming MT  150  are passed consecutively through a BSS  152 , an SGSN  154 , an GGSN  156  and an IP network  158  to get to a home MSC  160  located in a network foreign to the location of MT  150 . Stack interfaces  162 ,  164 ,  166 ,  168  and  170  shown below the equipment block represent respectively the stacks for blocks  150 ,  152 ,  154 ,  156  and  160  since the IP network  158  merely sees what it considers to be a standard IP communication. All the portions of each of the stacks comprise previously defined stack layers for GSM GPRS systems and are readily identifiable to those skilled in the art. The only layer not previously mentioned is the UDP (User Datagram Prototcol). 
     From the above, it will be apparent that the present approach eliminates standards redefinitions and compromises as required by the proposed TIA/EIA-136 document SP-4027-932. The only changes required by the MS (terminal equipment or mobile station) are the addition of software to accept signaling messages as well as traffic in the form of IP communications and a slight alteration in philosophy of system design whereby all signaling to an MS originates from the home MSC once registration is completed. All the signaling would be encapsulated within an IP protocol message and the MS can readily detect whether an incoming message packet is signaling or traffic data. Further, system simplification is obtained in that VLR tracking is not required by the local network within which an MS is presently located as long as the MS is registered and able to receive GPRS messages. 
     Referring back to FIG. 4, blocks  150  to  160  may be considered a GPRS system where MSC  160  is part of a home GPRS compliant network. The MSC has an IP address known to the MSs of that Network. The blocks  152 - 156  may be considered a foreign GPRS compliant network including a roaming MS or MT  150  which has MSC  160  as its home MSC. The IP network provides interconnection capability between said home MSC  160  and the roaming MS  150  wherein control signals for controlling MS  150 , after registration, are supplied, encapsulated in IP format, from said home MSC  160  rather than the MSC and cellular network (not shown other than in prior art FIGS. 1 and 2) that controls base station  152 . 
     In operation, the MS or MT  150  when being used in the packet data or GPRS mode includes means for accepting an IP address from the SGSN  154  and the GGSN  156  of the foreign network in which the MT  150  is located. This assigned IP address is used for the duration of the receipt of a traffic message regardless of the message source. The assigned IP address is forwarded by the MS  150  to the home MST  160  where this information is stored in the MSC  160 . The MS  150  then receives all further messages sent through the GPRS network using the accepted IP address. These messages, which are tunneled through the GPRS network, may be traffic or signaling messages and a portion of the encapsulated message will tell which type of message is being received. The MS  150  further includes means for decapsulating received messages to retrieve signaling messages embedded therein. Finally, MS  150  includes means for altering states of a connection process within said MS in accordance with retrieved signaling messages. 
     With the design philosophy set forth above, it will be apparent that other cellular networks may be readily adapted to provide signaling messages to a MS registered with a GPRS network without new standards being required. 
     Although the invention has been described with reference to a specific embodiment, these descriptions are not meant to be construed in a limiting sense. Various modifications of the disclosed embodiments, as well as alternative embodiments of the invention, will become apparent to persons skilled in the art upon reference to the description of the invention. It is therefore, contemplated that the claims will cover any such modifications or embodiments that fall within the true scope and spirit of the invention.