Abstract:
A communication interface and a method for establishing the communication interface for communications between a mobile station and a serving network node over a Gb interface in a GSM network are described herein. The communication interface comprises control logic, a network layer having a plurality of NSAPIs, and a link layer having a plurality of user-data SAPIs. The number of NSAPIs equals the number of user-data SAPIs. In one embodiment, the number of NSAPIs is limited to equal the number of user-data SAPIs. In another embodiment, the number of SPAIs is expanded to equal the number of NSAPIs. In both cases, the control logic performs one-to-one mapping between the NSAPIs and the user-data SAPIs.

Description:
[0001]     This patent claims priority from U.S. Provisional Application No. 60/795,791, filed 28 Apr. 2006, U.S. Provisional Application No. 60/816,380, filed 28 Jun. 2006, and U.S. Provisional Application No. 60/822,975, filed 21 Aug. 2006, all of which are incorporated herein by reference. 
     
    
     BACKGROUND  
       [0002]     Conventional Global System for Mobile communications (GSM) networks rely on activated Packet Data Protocol (PDP) contexts to provide packet data services to mobile stations. A PDP context is a data structure present in the mobile station and at the network that contains the session information associated with a subscriber&#39;s active packet data session. Each PDP context is associated with one or more packet data services, where each service associated with a single PDP context has similar operating characteristics. Further, each PDP context is associated with a unique network service access point in the network layer and identified by a Network Service Access Point Identifier (NSAPI). Conventional GSM networks provide up to eleven unique NSAPIs, which enables each mobile station to establish up to eleven PDP contexts.  
         [0003]     NSAPIs are used by the Sub Network Dependent Convergence Protocol (SNDCP), which interfaces the network layer with the data link layer. The SNDCP is situated between the Logical Link Control (LLC) protocol in the data link layer and a packet data protocol, e.g., Internet Protocol (IP), in the network layer. In addition to several other packet data and control functions, the SNDCP multiplexes network layer Packet Data Units (PDUs) from one or several network layer entities onto the appropriate LLC Service Access Point Identifiers (SAPIs). The LLC protocol in conventional GSM networks provides up to four unique user-data SAPIs.  
         [0004]     Because conventional GSM networks map eleven NSAPIs to four user-data SAPIs, the SNDCP may multiplex one or more NSAPIs onto a single user-data SAPI. In some cases, each NSAPI multiplexed onto a single user-data SAPI may be required to have one or more equivalent Quality of Service (QoS) attributes. Such QoS multiplexing limits the number of different QoS profiles for a particular mobile station, which in turn may overly limit the type of applications or services available to a subscriber. It will further be appreciated that the rules guiding the multiplexing operations are very open. Thus, different service providers often have different multiplexing implementations and/or infrastructures. The variations in multiplexing implementations and/or infrastructures make inter-operability in multi-vendor environments difficult.  
       SUMMARY  
       [0005]     The present invention comprises a communication interface and a method for establishing the communication interface for communications between a mobile station and a serving network node over a Gb interface in a GSM network. The communication interface comprises a network layer, a link layer, and control logic. The network layer has a plurality of network service access points, and the link layer has a plurality of user-data link service access points, where the number of network service access points equals the number of link service access points. In one embodiment, the number of network service access points is limited to equal the number of link service access points. In another embodiment, the number of link service access points is expanded to equal the number of network service access points. In both cases, the control logic performs one-to-one mapping between the network service access points and the link service access points. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  shows a block diagram of a GSM network.  
         [0007]      FIG. 2  shows the GSM protocol stack.  
         [0008]      FIG. 3  shows a conventional communication interface for an SGSN or mobile station in the GSM network.  
         [0009]      FIG. 4  shows the format for exemplary NSAPI and user-data SAPI information elements.  
         [0010]      FIG. 5  shows a communication interface according to one exemplary embodiment of the present invention.  
         [0011]      FIG. 6  shows a communication interface according to another exemplary embodiment of the present invention.  
         [0012]      FIG. 7  shows a call flow diagram for a parameter negotiation process between a mobile station and SGSN according to one exemplary embodiment.  
         [0013]      FIG. 8  shows a call flow diagram for an attach/routing area update process between a mobile station and SGSN according to one exemplary embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0014]     To better present the present invention, the following first briefly describes a GSM network.  FIG. 1  shows a mobile station  20  exchanging packet data with an IP network  30  via a GSM network  40 . The GSM network  40  includes a base station subsystem (BSS)  42  and a core network (CN)  44  comprising a serving GPRS support node (SGSN)  46 . For downlink packet data communications, the SGSN  46  communicates packet data from the IP network  30  to the BSS  42  over a Gb interface. The BSS  42  communicates the packet data to the appropriate mobile station  20  over a wireless interface. For uplink packet data communications, the SGSN  46  communicates packet data received from a mobile station  20  via BSS  42  to the IP network  30  over a Gi interface.  
         [0015]      FIG. 2  shows the layered GSM protocol structure for the mobile station  20  and SGSN  46 . The protocol stack comprises a physical layer (L 1 )  110 , a data link layer (L 2 )  120 , and a network layer (L 3 )  130 . In the mobile station  20 , the physical layer  110  comprises a GSM radio access specific protocol (GSM RF), the data link layer  120  comprises a Medium Access Control (MAC) protocol, a Radio Link Control (RLC) protocol, and a Logical Link Control (LLC) protocol, and the network layer  130  comprises the SNDCP and Internet protocol (IP). The GSM RF, MAC, and RLC protocols in the mobile station  20  interface with the corresponding GSM RF, MAC, and RLC protocols in the BSS  42  over the Um (air) interface, as well known in the art. The LLC and SNDCP in the mobile station  20  interface with the corresponding LLC and SNDCP in the SGSN  46  over a Um/Gb interface.  
         [0016]     The SNDCP interfaces the network layer  130  with the data link layer  120  by mapping NSAPIs associated with packet data services in the network layer  130  to user-data SAPIs in the link layer  120 .  FIG. 3  shows a conventional communication interface  100  between the data link layer  120  and the network layer  130  for a SGSN  46  and/or a mobile station  20 . The link layer  120  has four unique link service access points identified by four user-data SAPIs  122  ( 3 ,  5 ,  9 , and  11 ), while the network layer  130  has eleven unique network service access points identified by eleven unique NSAPIs  132  ( 5 - 16 ). Each NSAPI  132  uniquely identifies a PDP context  134  associated with one or more packet data services  136 .  
         [0017]     To send and receive packet data for a packet data service  136  the mobile station  20  and the SGSN  46  activate a PDP context  134 . The activated PDP context is uniquely identified by an NSAPI  132 . To establish a PDP context  134 , the mobile station  20  sends an Activate PDP Context Request message including a requested NSAPI  132  and user-data SAPI  122  to the SGSN  46 . In response, the SGSN  46  may accept or reject the request. If the SGSN  46  accepts the request, it allocates a user-data SAPI  122  for the requested NSAPI  132  to the packet data service  136  and sends an Activate PDP Context Accept message to the mobile station  20 . The Activate PDP Context Request message identifies the requested NSAPI  132  and user data SAPI  122  to the SGSN  46  using an NSAPI Information Element (IE) and a SAPI IE, respectively. The Activate PDP Context Accept message identifies the allocated user-data SAPI  122  for the particular requested NSAPI  132  to the mobile station  20  using a SAPI IE.  FIG. 4  shows the format of one exemplary NSAPI IE and SAPI IE. The last four bits of each information element identify the selected and allocated NSAPI and user-data SAPI for the packet data session according to the requirements shown in Tables 1 and 2.  
                                                         TABLE 1                                       NSAPI bits                        4   3   2   1   Name/service                       0   0   0   0   reserved           0   0   0   1   reserved           0   0   1   0   reserved           0   0   1   1   reserved           0   1   0   0   reserved           0   1   0   1   NSAPI 5           0   1   1   0   NSAPI 6           0   1   1   1   NSAPI 7           1   0   0   0   NSAPI 8           1   0   0   1   NSAPI 9           1   0   1   0   NSAPI 10           1   0   1   1   NSAPI 11           1   1   0   0   NSAPI 12           1   1   0   1   NSAPI 13           1   1   1   0   NSAPI 14           1   1   1   1   NSAPI 15                      
 
         [0018]    
       
         
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                   
                 TABLE 2 
               
             
             
               
                   
                   
               
               
                   
                   
               
               
                   
                 user-data SAPI bits 
                   
                   
               
             
          
           
               
                   
                 4 
                 3 
                 2 
                 1 
                 Name/service 
               
               
                   
                   
               
               
                   
                 0 
                 0 
                 0 
                 0 
                 reserved 
               
               
                   
                 0 
                 0 
                 0 
                 1 
                 LLGMM 
               
               
                   
                 0 
                 0 
                 1 
                 0 
                 TOM2 
               
               
                   
                 0 
                 0 
                 1 
                 1 
                 LL3 
               
               
                   
                 0 
                 1 
                 0 
                 0 
                 reserved 
               
               
                   
                 0 
                 1 
                 0 
                 1 
                 LL5 
               
               
                   
                 0 
                 1 
                 1 
                 0 
                 reserved 
               
               
                   
                 0 
                 1 
                 1 
                 1 
                 LLSMS 
               
               
                   
                 1 
                 0 
                 0 
                 0 
                 TOM8 
               
               
                   
                 1 
                 0 
                 0 
                 1 
                 LL9 
               
               
                   
                 1 
                 0 
                 1 
                 0 
                 reserved 
               
               
                   
                 1 
                 0 
                 1 
                 1 
                 LL11 
               
               
                   
                 1 
                 1 
                 0 
                 0 
                 reserved 
               
               
                   
                 1 
                 1 
                 0 
                 1 
                 reserved 
               
               
                   
                 1 
                 1 
                 1 
                 0 
                 reserved 
               
               
                   
                 1 
                 1 
                 1 
                 1 
                 reserved 
               
               
                   
                   
               
             
          
         
       
     
         [0019]     The network layer  130  in the conventional communication interface  100  also includes control logic  140  that maps the allocated NSAPI  132  to the allocated user-data SAPI  122 . When the number of active PDP contexts  134  associated with the network layer  130  exceeds the number of user-data SAPIs  122  in the link layer  120 , control logic  140  multiplexes two or more allocated NSAPIs  132  to one user-data SAPI  122  using any known multiplexing technique. In the example shown in  FIG. 3 , NSAPI  8  and  11  are multiplexed to SAPI  5 . As discussed above, this multiplexing operation limits the number and/or type of packet data services  136  available to a mobile station  20 . In addition, the open rules guiding the multiplexing operations are very broad and allow for very different implementations, which may cause inter-operability problems in multi- or vendor environments.  
         [0020]     The present invention provides one-to-one mapping between NSAPIs  132  in the network layer  130  and user-data SAPIs  122  in the link layer  120 . In general, a communication interface for an SGSN  46  and/or a mobile station  20  according to the present invention provides an equal number of NSAPIs  132  and user-data SAPIs  122  for GSM packet data services. In one embodiment, the communication interface limits the number of NSAPIs  132  to equal the number of user-data SAPIs  122 , e.g., four. In another embodiment, the communication interface expands the number of user-data SAPIs  122  to equal the number of NSAPIs  132 , e.g., eleven. For simplicity, mobile station  20  may represent a legacy mobile station having a conventional communication interface  100  or a mobile station having a communication interface  200 ,  300  according to either the limited or expanded embodiments.  
         [0021]      FIG. 5  shows one exemplary communication interface  200  for the limited embodiment. Communication interface  200  limits the number of NSAPIs  132  associated with SNDCP in the network layer  130  to equal the number of user-data SAPIs  122  in link layer  120 . In the example shown in  FIG. 5 , only four NSAPIs  132  ( 5 - 8 ) are available. Each NSAPI  132  uniquely identifies a PDP context  134  associated with one or more packet data services  136 . The control logic  240  maps each NSAPI  132  to one user-data SAPI  122 . The control logic  240  may associate multiple packet data services  136  having similar performance characteristics with a single PDP context  134 , and therefore, a single NSAPI  132 , as shown in  FIG. 5 . It will be appreciated that while  FIG. 5  shows NSAPIs 5-8, any four of the original eleven NSAPIs  132  may be used, e.g., {10, 11, 12, 13}, {5, 7, 9, 11}, etc., at any given time. Further, it will be appreciated that any one NSAPI  132  may be mapped to any one user-data SAPI  122 .  
         [0022]     To ensure backwards compatibility with legacy mobile stations  20  and/or legacy SGSNs, which have more than four NSAPIs  122 , a communication interface  200  for an SGSN  46  according to the limited embodiment also limits the number of NSAPIs allocated to a mobile station  20  having a conventional control interface  100 . If a mobile station  20  requests more than four packet data services  136 , the control logic  240  in the SGSN  46  may associate multiple packet data services  136  having similar service performance characteristics with a single PDP context  134 , and therefore, a single NSAPI  132 , as shown in  FIG. 5 . When the control logic  140  of a mobile station  20  attempts to activate more than four PDP contexts  134 , the control logic  240  in the limited SGSN communication interface  200  sends a reject message to the mobile station  20 , e.g., an Activate PDP Context Reject message. In one embodiment, the reject message may identify the number of allowed PDP contexts  134 . It will be appreciated that because a mobile station  20  having a limited communication interface  200  will only attempt to activate up to four PDP contexts  134 , such mobile stations  20  are fully compatible with SGSNs  44  having a conventional communication interface  100 , which allows up to eleven PDP contexts  134 .  
         [0023]     The present invention also addresses handover of a mobile station  20  between an SGSN  46  having a conventional communication interface  100  and an SGSN having a limited communication interface  200 . Handover from an SGSN  46  with a limited communication interface  200  to an SGSN  46  with a conventional communication interface  100  does not require any modification. This is because the existing number of allocated NSAPIs  132  in this type of handover will always be less than the number of available NSAPIs  132  in the SGSN  46  receiving control of the mobile station  20 . However, handover of a mobile station  20  from an SGSN  46  with a conventional communication interface  100  to an SGSN  46  with a limited communication interface  200  may require some modifications to the NSAPI allocation when the number of allocated NSAPIs  132  exceeds the number of NSAPIs  132  in the SGSN  46  receiving control of the mobile station  20 . In one embodiment, the control logic  240  in the receiving SGSN  46  may deactivate one or more PDP contexts  134  to ensure that there are no more than four active PDP contexts  134 , which require no more than four NSAPIs  132 . It will be appreciated that the control logic  240  may deactivate the PDP contexts  134  according to any predetermined criteria. For example, control logic  240  may deactivate one or more PDP contexts  134  based on a performance criteria, frequency of use criteria, etc.  
         [0024]      FIG. 6  shows one exemplary communication interface  300  for the expanded embodiment, which expands the number user-data SAPIs  122  in the link layer  120  to equal the number of NSAPIs  132  in the network layer  130 . As shown in  FIG. 6  and Table 3, eleven user-data SAPIs  122  ( 3 - 6 ,  9 - 15 ) are available for one-to-one mapping with the eleven NSAPIs  132  ( 5 - 15 ). The control logic  340  maps each NSAPI  132  to one user-data SAPI  122 , where each NSAPI  132  uniquely identifies a PDP context  134  associated with one or more packet data service  136 . The control logic  340  may associate multiple packet data services  136  having similar performance characteristics with single PDP context  134 , and therefore, a single NSAPI  132 , as shown in  FIG. 6 .  
                                                         TABLE 3                                       user-data SAPI bits                        4   3   2   1   Name/service                       0   0   0   0   reserved           0   0   0   1   LLGMM           0   0   1   0   TOM2           0   0   1   1   LL3           0   1   0   0   LL4           0   1   0   1   LL5           0   1   1   0   LL6           0   1   1   1   LLSMS           1   0   0   0   TOM8           1   0   0   1   LL9           1   0   1   0   LL10           1   0   1   1   LL11           1   1   0   0   LL12           1   1   0   1   LL13           1   1   1   0   LL14           1   1   1   1   LL15                        
         [0025]     To ensure backwards compatibility with legacy devices, which only have four user-data SAPIs  122  in the link layer  120 , the control logic  340  in the expanded communication interface  300  for an SGSN  46  and/or a mobile station  20  may include an indication of said support in exchanged control messages. For example, the indicator may be included in an information element of a control message communicated between SGSN  46  and mobile station  20 . The mobile stations  20  and/or SGSNs  44  having the expanded communication interface  300  includes the indicator in the transmitted control messages and properly interprets the indicator in the received control messages. In one embodiment, the indicator may comprise one or more bits that identify the version number of the controlling protocol, the number of available user-data SAPIs  122 , etc. It will be appreciated that the mobile stations  20  and/or SGSNs  44  having the conventional communication interface  100  do not include an indicator with transmitted control message and ignore any indicators included in received control messages.  
         [0026]     In one embodiment, the mobile station  20  and/or the SGSN  46  may include the indicator with a control message communicated during a parameter negotiation process, such as an exchange identifier (XID) negotiation procedure.  FIG. 7  shows a call flow diagram for one exemplary negotiation process. To communicate with the SGSN  46 , a mobile station  20  includes an indicator in a transmitted control message, such as a parameter negotiation command (step  400 ). One exemplary parameter negotiation command includes an XID command. In response, the SGSN  46  sends a parameter negotiation response, i.e., an XID response, to the mobile station  20  that includes the indicator (step  410 ). It will be appreciated the call flow diagram shown in  FIG. 7  may be reversed, such that the SGSN  46  sends a parameter negotiation command to the mobile station  20 , and the mobile station  20  answers with a parameter negotiation response.  
         [0027]     In another embodiment, mobile station  20  and/or SGSN  46  may include the indicator with an attach message or a routing area update message.  FIG. 8  shows a call flow diagram for one exemplary attach/routing area update procedures. The mobile station  20  sends an Attach Request or Routing Area Update Request message to the SGSN  46  (step  430 ). In response, the SGSN  46  may include the indicator with an Attach Accept or Routing Area Update Accept message (step  440 ). For example, the mobile station  20  may modify the MS Network Capabilities IE associated with the Attach/Routing Area Update Request messages to include the indicator, while the SGSN  46  may modify the Network Feature Support IE associated with the Attach/Routing Area Update Accept messages to include the indicator. Alternatively, the mobile station  20  and/or the SGSN  46  may put the indicator in a new information element and include the new information element with the control message.  
         [0028]     The present invention also addresses handover of a mobile station  20  having NSAPIs  132  mapped to more than four user-data SAPIs  122  from an SGSN  46  with the expanded communication interface  300  to an SGSN  46  having a conventional communication interface  100  or a limited communication interface  200 . Handover from an SGSN  46  with a conventional communication interface  100  or a limited communication interface  200  to an SGSN  46  with an expanded communication interface  300  does not require any modification. This is because the existing number of allocated NSAPIs  132  in this type of handover will always be less than or equal to the number user-data SAPIs  132  at the SGSN  46  receiving control of the mobile station  20 . However, handover of a mobile station  20  from an SGSN  46  with an expanded communication interface  300  to an SGSN  46  with a conventional communication interface  100  or limited communication interface  200  may require some modifications to the existing NSAPI allocation when the number of allocated NSAPIs  132  exceeds the number of user-data SAPIs  122  in the SGSN  46  receiving control of the mobile station  20 . In one embodiment, the control logic  140 ,  240  in the SGSN  46  receiving control of the mobile station  20  may deactivate one or more PDP contexts  134  to ensure that there are no more than four active PDP contexts  134 , and therefore, no more than four allocated NSAPIs  132 . It will be appreciated that the control logic  140 ,  240  may deactivate the PDP contexts  134  according to any predetermined criteria. For example, control logic  140 ,  240  may deactivate one or more PDP contexts  134  based on a performance criteria, frequency of use criteria, etc. Alternatively or in addition, the SGSN  46  receiving control of the mobile station  20  may determine whether two or more services  136  having similar performance parameters may be combined with a single PDP context  134 , and therefore, multiplexed onto a single NSAPI  132  to reduce the number of allocated NSAPIs  132 .  
         [0029]     The present invention describes a method and apparatus for implementing one-to-one mapping between NSAPIs  132  in a network layer  130  and user-data SAPIs  122  in a link layer  120 . Such one-to-one mapping removes the need for multiplexing multiple NSAPIs  132  onto a single user-data SAPI  122 . By removing the multiplexing requirements, the present invention removes the multiplexing problems and constraints present in a conventional GSM network.  
         [0030]     The present invention may, of course, be carried out in other ways than those specifically set forth herein without departing from essential characteristics of the invention. The present embodiments are to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.