Abstract:
A system to enable communication between a base station controller ( 24 ) within a cellular network ( 12 ), and a wired telephone system ( 38, 39 ) in a wired subscriber loop ( 113 ), wherein the base station controller ( 24 ) is responsive to, and generates, cellular network signaling, and the wired telephone system is responsive to, and generates, wired signals. The system includes: a protocol processor ( 121 ) receptive to the wired signals, for generating processed signals; and a terminal adapter controller ( 34 ) conductively coupled both to the base station controller ( 24 ) and to the protocol processor ( 121 ), receptive to the processed signals, for generating cellular network signaling. In another feature of the invention, the cellular network signaling is GSM signaling. In another feature of the invention, the system also includes a voice service module ( 123 ) conductively coupled to the protocol processor, for compressing voice data to standard cellular compression. In another feature of the invention, the system also includes means ( 150 ) for converting mobility events in the wired telephone system to cellular network signaling.

Description:
This application is a continuation of Ser. No. 08/851,517, filed May 5, 1997, now U.S. Pat. No. 6,167,271. 
    
    
     TECHNICAL FIELD 
     The invention relates generally to cellular communication networks and, more particularly, to wired access to a cellular network. 
     BACKGROUND OF THE INVENTION 
     As cellular telephone service has increased, a need has arisen for a single telephony system that can service a subscriber both at his home, that is, fixed-base, or stationary, and when he is away from home, or mobile. 
     U.S. Pat. Nos. 5,412,760 and 5,528,665, issued to Peitz, describe a telephone system for both mobile and stationary subscribers, in which the stationary subscribers are not assigned permanent channel pairs, but rather ate treated as the mobile subscribers, and are assigned channel pairs at the time a telephone connection is made. All connection channel pairs are within the frequency spectrum of the broad band cable connecting the stationary subscribers. 
     However, the Peitz patents do not contemplate using unshielded copper pair telephone lines normally used for ISDN basic rate service. Rather, they teach installing new digital, preferably fiber optic, cables to subscribers&#39; homes. 
     Analog cellular telephone service originally developed independently in various countries, each country&#39;s equipment and service incompatible with the others&#39;. The Europeans eventually agreed on standards for digital cellular telephone service, called “GSM” (“Global System For Mobile Communications”). The European Telecommunication Standards Institute (ETSI) published phase I of the GSM specifications in 1990. ETSI published some GSM Technical Specifications, version 5.1.0, in March, 1996. 
     A need exists for a single telephone system for both mobile and stationary subscribers, which uses unshielded copper pair telephone lines normally used for ISDN basic rate service, and which is compatible with the GSM standards. 
     SUMMARY OF THE INVENTION 
     The present invention, accordingly, provides a system and method to enable communication between a base station controller within a cellular network, and a wired telephone system in a wired subscriber loop, wherein the base station controller is responsive to, and generates, cellular network signaling, and the wired telephone system is responsive to, and generates, wired signals. The system comprises a protocol processor receptive to the wired signals, for generating processed signals; and a terminal adapter controller conductively coupled both to the base station controller and to the protocol processor, receptive to the processed signals, for generating cellular network signaling. 
     In another feature of the invention, the cellular network signaling is GSM signaling. In another feature of the invention, the system also includes a voice service module conductively coupled to the protocol processor, for compressing voice data to standard cellular compression. In another feature of the invention, the system also includes means for converting mobility events in the wired telephone system to cellular network signaling. 
     The invention achieves a technical advantage in that it provides the same services to wireline subscribers as it provides to mobile subscribers. 
     The invention achieves another technical advantage in that it uses existing local loop with services provided by an existing MSC, so that an operator has to add neither wireline switching capabilities, nor use cellular radio frequency transmission spectrum for local loop service. 
     The invention achieves another technical advantage in that it provides standard interfaces for analog and ISDN BRI telephone sets, so that subscribers may use their existing telephone sets. 
     The invention achieves another technical advantage in that it complies with the A-bis interface from a base transceiver station to a base station controller, so that there is no change required in the construction or operation of 1) the base station controller, and 2) a mobile services switching center. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of the GSM wired access system of the present invention. 
     FIG. 2 is a schematic, in block diagram form, of the TA  36  of FIG.  1 . 
     FIG. 3 is a schematic, in block diagram form, of the TAC  34  of FIG.  1 . 
     FIG. 4 is a table listing the combination of ISDN protocols and GSM protocols used to carry signaling information. 
     FIG. 5 is a flow chart of the algorithms used by the TA  36  when it is powered on. 
     FIG. 6 is a flow chart of the algorithms used by the TA  36  when it is powered off. 
     FIG. 7 is a flow chart of the algorithms used by the protocol processor  121  when a subscriber places a call. 
     FIG. 8 is a flow chart of the algorithms used by the protocol processor  121  when a subscriber is called. 
     FIG. 9 is a flow chart of the algorithms used by the protocol processor  121  when the activate SIM switch  150  is deactivated. 
     FIG. 10 is a flow chart of the algorithm used by the TAC  34  when processing incoming messages. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     This description uses the following abbreviations: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 2B + D 
                 see BRI 
               
               
                 BRI 
                 ISDN Basic Rate Interface; 144,000 bits per second, two 
               
               
                   
                 bearer channels, and one D channel 
               
               
                 BSC 
                 Base Station Controller 
               
               
                 BTS 
                 Base Transceiver Station 
               
               
                 EFR 
                 Enhanced Full Rate 
               
               
                 ETSI 
                 European Telecommunication Standards Institute 
               
               
                 GSM 
                 Global System For Mobile Communications 
               
               
                 GSM _. —   
                 ETSI GSM Technical Specification _. —   
               
               
                 HLR 
                 Home Location Register 
               
               
                 HSCSD 
                 High Speed Circuit Switched Data 
               
               
                 IMSI 
                 International Mobile Subscriber Identity. 
               
               
                 ISDN 
                 Integrated Services Digital Network 
               
               
                 ISDN Q.921 
                 ITU-telecommunications recommendation for 
               
               
                   
                 Layer 2 Basic Access User-to-Network Interface. 
               
               
                   
                 Q.921 is commonly used as a reference to the 
               
               
                   
                 interface specified by ANSI T1.602-1989. 
               
               
                 ISDN Q.931 
                 ITU-telecommunications recommendation for 
               
               
                   
                 Layer 3 basic call control. Q.931 is commonly 
               
               
                   
                 used as a reference to the interface specified by 
               
               
                   
                 ANSI T1.607-1990. 
               
               
                 LAC 
                 Location Area Code 
               
               
                 LAPDm 
                 Link Access Protocol For The Mobile D Channel 
               
               
                 LEC 
                 Local Exchange Carrier 
               
               
                 MSC 
                 Mobile Services Switching Center 
               
               
                 MS 
                 Mobile Subscriber 
               
               
                 MSISDN 
                 Mobile Subscriber ISDN Number 
               
               
                 OAM 
                 Operations, Administration, and Maintenance - network 
               
               
                   
                 management functions 
               
               
                 OMC-R 
                 Radio Operations and Maintenance Center 
               
               
                 OMT 
                 Operations and Maintenance Terminal 
               
               
                 PLMN 
                 Public Land Mobile Network 
               
               
                 POT 
                 Plain Old Telephone, one example of a “Set” 
               
               
                 SIM 
                 Subscriber Identity Module, a “smart” card inserted into 
               
               
                   
                 a mobile telephone. The SIM contains subscriber-related 
               
               
                   
                 data. 
               
               
                 SOHO 
                 Small Office/Home Office 
               
               
                 TCU 
                 Transcoder Unit 
               
               
                 TA 
                 Terminal Adapter 
               
               
                 TAC 
                 Terminal Adapter Controller 
               
               
                 TCH 
                 Traffic Channel 
               
               
                 VLR 
                 Visitor&#39;s Location Register, a local database to an MSC 
               
               
                   
                 for registering visiting mobile station users. 
               
               
                   
               
             
          
         
       
     
     For definitions of other abbreviations, and definitions of other terms, see Newton&#39;s Telecom Dictionary, 11th edition, 1996. 
     Referring to FIG. 1, the GSM wired access system  10  of the present invention includes a PLMN  12 , a wire center  14 , and a SOHO or residence  16 . The PLMN  12  has an HLR  18 , which connects to an MSC  20 . The MSC  20  connects via an A-i/f interface  21  to a TCU  22 . The TCU  22  connects via an A-ter interface  23  to a GSM network&#39;s base station controller (“BSC”)  24 . An Operations and Maintenance Center for the Radio (“OMC-R”)  26  also connects to the BSC  24 . The BSC  24  connects to a BTS  28 . The BTS  28  connects via an air interface  29  (“wireless signals”) to a wireless set, “GSM MS”  30 . 
     The wire center  14  has LEC switching equipment  32  and a GSM wired terminal adapter controller (“TAC 34”). The TAC  34  connects to both the BSC  24  and an operation and maintenance terminal (“OMT”)  27 . Although the OMT  27  is shown as located in the PLMN  12 , it could be located anywhere. The TAC  34  connects via an A-bis interface  35  to the BSC  24 . The SOHO  16  has one or more GSM wired terminal adapters (“TA 36”), which connects to the TAC  34  via an ISDN BRI compatible subscriber loop  37 . The TA  36  also connects to an ISDN set  38 , and an analog set-with-an-ISDN-adapter  39 . In a oversimplified sense, the TAC  34  is a BTS with wired connections to the TA  36 , which functions like an MS. Together, the TAC  34  and the TA  36  are means for converting wired signals to cellular network signaling. 
     GSM Wired Terminal Adapter Controller (TAC  34 ) 
     Referring now to FIG. 2, the TAC  34  connects several TA&#39;s  36  (although only one TA  36  is shown in FIG. 1) to the BSC  24 . The TAC  34  contains several line modules  211  which terminate the wired subscriber loops  37  connecting the TA&#39;s  36  to the TAC  34 . The TAC  34  also contains an A-bis interface module  213  which presents the standard GSM A-bis interface to the BSC  24  as described in ETSI GSM Technical Specifications for GSM A-bis Interface: 
     GSM 8.51, Version 4.1.0, March 1995; 
     GSM 8.52, Version 4.2.0, August 1995; 
     GSM 8.54, Version 5.0.0, December 1995; 
     GSM 8.56, Version 4.0.2, September 1994; and 
     contains a switching module  212 , an operations and maintenance terminal interface  220 , and a terminal adapter controller application  214  (shown in FIG.  10 ). 
     At each line module  211 , the D-channel and the two B-channels from a TA  36  are separated into as many as nine separate connections (1 signaling channel and 8 traffic channels—4 traffic channels from each B-channel) to the switching module  212 . The switching module  212  dynamically switches a traffic channel from a line module  211  to the proper circuit of the A-bis interface module  213 . The switching module  212  performs this connection switching each time the BSC  24  assigns a channel to the TA  36  in response to a channel request from the TA  36 . The terminal adapter controller application  214  determines how to make the connection by looking at the contents of the GSM RIL3-RR channel request and GSM RIL3-RR channel assignment messages to see which circuit the BSC  24  has assigned to the TA  36  for a particular call. The terminal adapter controller application  214  looks at the GSM RIL3-RR channel release message to see when the circuit is released so that it can instruct the switching module  212  break the connection. The TAC  34  does not alter the contents of any of these messages. During each call, the TA controller application  214  stores information from these messages m order to properly instruct the switching module  212  to switch the traffic channel for that call. The TA controller application  214  instructs the switching module  212  via the control link  222  as to when a traffic channel from a line module  211  should be connected to a circuit on the A-bis interface  213 , and when the connection should be broken. 
     In addition to traffic channel switching, the TAC  34  transfers signaling messages, which are transmitted on the D-channel between the TA  36  and the line modules  211 , to the proper circuit on the A-bis interface module  213 . The switching module  212  connects a D-channel from a line module  211  to the TA controller application  214  through a signaling link  224 . The TA controller application  214  multiplexes the messages received on all the signaling links  224  to the A-bis interface module  213 . The TA controller application  214  transmits the multiplexed messages to the A-bis interface module  213  via the signaling link  223 . 
     Signaling messages from the BSC  24  are transmitted to the TA controller application  214  by the A-bis interface module  213  across the signaling link  223 . The TA controller application  214  transmits each of these messages on the signaling link  224  that is connected to the proper line module  211 . The switching module  212  connects each signaling link  224  to a line module  211  as instructed by the TA controller application  214 . The TA controller application  214  maps each signaling message received on the signaling link  223  to a line module  211 , and the signaling link  224  connected to that line module  211 , by examining the the LAPD terminal endpoint identifier in the message. 
     The TA controller application  214  also monitors the status of each line module  211  through a control link  221 . 
     The TAC  34  transmits unaltered all messages it receives from the TA  36  to the BSC  24 . Conversely, the TAC  34  transmits unaltered all messages it receives from the BSC  24  to the appropriate TA  36 , with one exception. When the TAC  34  receives a GSM RIL3-RR cipher mode message, it immediately replies with the GSM RIL3-RR cipher mode complete message to the BSC  24 . Thus, it is transparent to the BSC  24  and the MSC  20  that no ciphering is performed between the TA  36  and the TAC  34 . Ciphering is unnecessary on the wired subscriber loop because the transmission on this loop cannot be intercepted over the air. Ciphering is normally done between a GSM mobile station and a GSM BTS such that the over-the-air transmission is not understandable by anyone intercepting the transmission. 
     The A-bis interface module  213  is a telephony trunk circuit interface that manages several circuit groups that connect the TAC  34  to the BSC  24 . The TA Controller Application  214  monitors and controls the A-bis interface module  213  through the signaling link  223 . 
     The terminal adapter controller application  214  also performs maintenance and administrative operations as directed by the operation and maintenance terminal  27 . This includes loading software, changing configuration parameters, and reporting the status of line modules  211  and A-bis interface module  213 . 
     GSM Wired Terminal Adapter (TA  36 ) 
     Referring now to FIG. 3, the TA  36  includes as functional components a GSM/ISDN protocol processor  121 , an ISDN S/T bus interface  120 , a voice service module  123 , a U′ Interface  124 , a GSM subscriber identity module interface  122 , and a switched SIM interface  125 . 
     The protocol processor  121  contains protocol processing logic which converts wired signals (ISDN Q.931 messages) from the S/T bus interface  120  into GSM radio interface layer 3—call control messages which are passed to the U′ Interface  124 . It also converts GSM radio interface layer 3—call control messages from the U′ interface  124  into wired signals (ISDN Q.931) messages which are passed to the S/T bus interface  120  over a control and signaling link  142 . 
     The protocol processor  121  generates (1) GSM radio interface layer 3—mobility management (RIL3-MM) messages in response to mobility events detected in the SOHO  16 , and (2) GSM radio interface layer 3—radio resource (RIL3-RR) messages. Both types of messages are sent to the TAC  34  via the U′ Interface  124 . 
     The protocol processor  121  also receives and processes GSM RIL3-MM and GSM RIL3-RR messages received from the GSM TAC  34  at the U′ Interface  124 . GSM 4.08, version 5.3.0, release date July, 1996, which is incorporated herein by reference, describes the processing of these messages. These messages are not passed on to the S/T bus interface  120  or to any terminal attached to the S/T bus interface  120 . 
     The GSM(ISDN protocol conversion and GSM RIL3-MM and RR protocol processing performed by the protocol processor  121  allows the TAC  34  to comply with the A-bis interface  35 . This A-bis interface compliance enables the TA/TAC wired access system to be added to an existing GSM wireless network with no hardware or software modifications to the BSC  24 , the MSC  20 , the HLR  18 , and the VLR  19 . 
     GSM RIL3 mobility management messaging allows the GSM network to locate a particular SIM inserted in any TA  36  using the existing GSM network logic for locating a SIM in a mobile station. This means that the directory number used to call a telephone set attached to a TA  36  can be changed simply by replacing the SIM in the TA  36 . Furthermore, a TA  36  can be moved from one physical location to another and, assuming that the subscriber loop at the new location is connected to a TAC  34 , the TA  36  can be connected and will operate in the new location with the same directory number as in the old location. This is accomplished automatically by the GSM network using existing GSM mobility management procedures with no human interaction by the network operator. 
     The GSM RIL3-RR messages are transmitted between the TA  36  and BSC  24  unaltered by the TAC  36 , but the TAC  36  looks at certain GSM RIL3-RR messages to see how to allocate the traffic channels on the subscriber loop  37 . 
     The protocol processor  121  uses the signaling connection  146  to control and monitor the U′ Interface  124 , as well as sending and receiving D-channel information (signaling messages) that is transmitted and received by the U′ Interface  124 . 
     The voice service module  123  provides several digital signal processing capabilities, but primarily it functions as a GSM enhanced full rate voice encoder/decoder complying with GSM 6.51, version 5.1.0, release date March, 1996. The voice service module  123  compresses the digitally encoded voice signal from the normal 64 kbps wireline rate to the GSM standard 16 kbps fill rate. The voice service module  123  functions as a means for compressing voice data to standard cellular compression. 
     Both the B-channels of the U′ Interface  124  operate at 64 kbps, while the voice service module  123  encodes each conversation at 16 kbps. This means that the U′ Interface  124  can support up to eight simultaneous conversations at 16 kbps each. In the preferred embodiment, however, the voice service module  123  just rate adapts each 16 kbps voice channel to a 64 kbps B-channel on the U′ Interface  124 . 
     In an alternate embodiment of the GSM Wired Terminal Adapter that enables more than two simultaneous conversations, the voice service module  123  is responsible for multiplexing the 16 kbps conversations onto the 64 kpbs B-channels to the U′ Interface  124 . In GSM terms, each conversation is referred to as a “traffic channel”. So, each B-channel can carry up to four traffic channels multiplexed on it, for a total of eight conversations per TA  36 . However, an ISDN S/T bus such as an ISDN S/T bus  113  can support only two B-channels (two simultaneous conversations/data calls). 
     In the alternate embodiment that uses more than two traffic channels per TA  36 , the TA  36  must be constructed with multiple S/T buses, up to four, and each S/T bus is assigned two of the eight traffic channels. 
     Standard ISDN sets  38  and standard analog-to-ISDN adapters  116  connect to the S/T bus interface  120 , which supports the standard ISDN S/T bus  113  defined in ANSI standard T1.605, which is incorporated herein by reference. (ANSI T1.605-1991, ISDN Basic Access Layer 1 Interface at S and T Reference Points, corresponds to ITU-T Recommendation I.430). The S/T bus interface  120  separates the B-channel information from the D-channel signaling information coming into the TA  36  on the S/T bus. The S/T bus interface  120  connects to the voice service module  123  via a connection  140 , over which B-channel information passes. B-channel transmission links  140  and  144  carry digitally encoded voice or bearer data (for data transfer use by data calls). The B-channel information passes through the voice service module  123 , via the link  144 , to the U′ Interface  124 . When a B-channel is carrying data, the protocol processor  121  instructs the voice service module  123  not to perform EFR voice compression, but to rate adapt the data transfer to 16 kbps. D-channel signaling is transmitted to the protocol processor  121  over the separate signaling and control connection  142 . 
     The U′ Interface  124 , under control of the protocol processor  121 , multiplexes the D-channel information and B-channel information onto the subscriber loop  37  connecting the TA  34  to the TAC  36  in the same manner as a standard ISDN U interface. As on the standard ISDN U interface, one D-channel and two B-channels are transmitted on the subscriber loop  37 . However, in the preferred embodiment, each B-channel can carry up to four traffic channels. 
     FIG. 4 shows the combination of ISDN basic access protocols (Layer 1 and Layer 2) and GSM 4.08 protocols (Layer 3) that are used to carry signaling information on the D-channel of the subscriber loop  37 . 
     Referring back to FIG. 3, all transmission between the TA  34  and the TAC  36  passes through the U′ interface  124 . ANSI Standard T1.601-1992, ISDN Basic Access Layer 1 User-to-Network Interface, is the BRI physical interface implementation for the subscriber loop  37  made up of a single pair of wires, which is normal in North America. 
     The SIM Interface  122  accepts a normal GSM subscriber identity module card or plug-in module as described in GSM 11.11, Version 5.3.0, July 1996, which is incorporated herein by reference. The SIM interface  114  is a standard interface. GSM 11.11 describes the physical, electrical and functional specifications of the SIM interface  114 . 
     A SIM  111  is associated with the subscriber&#39;s directory number by the GSM network. The presence of a SIM in the TA  36  allows the GSM network to deliver calls to the subscriber whose SIM is associated with the dialed directory number. A SIM must be in place at the SIM interface  122  in order for the TA  36  to originate or terminate telephone calls. A signaling link  148   a  connects the protocol processor  121  and the SIM Interface  122 . A similar signaling link  148   b  connects the protocol processor  121  and the switched SIM interface  125 . 
     In the preferred embodiment, the TA  36  has a SIM  111   a  plugged into the SIM Interface  122 , and a SIM  111   b  plugged into the switched SIM interface  125 . Both SIM&#39;s are associated with each ISDN terminal on the S/T Bus  113 . This means that a call to the directory number associated with either SIM will cause all telephone sets connected to the S/T Bus  113  to ring. 
     In an alternate embodiment, multiple SIM&#39;s are installed at both the SIM Interface  122  and the switched SIM interface  125 . 
     The switched SIM interface  125  accepts a SIM card or a plug-in SIM, using the SIM interface  114 , which is described in. GSM 11.11, Version 5.3.0, July 1996. The switched SIM interface  125  connects to an activate SIM switch  150  via a switch circuit interface  152  which carries an on/off or activate/deactivate signal. When the activate SIM switch  150  is in an off/deactivate state, the switched SIM interface  125  will indicate to the protocol processor  121  that the SIM is not installed. The activate SIM switch  150  functions as a means for converting mobility events in the wired telephone system to cellular network signaling. In addition to the signalling link  148   b,  the switched SIM interface  125  also has a switch circuit connection  154  to relay the on/off state of the activate SIM switch  150  to the protocol processor  121 . When the activate SIM switch  150  is turned on, the protocol processor  121  will activate the SIM using the TA power up procedure described elsewhere in this document, as if the TA  36  had just powered on. When the activate SIM switch  150  is turned off, the protocol processor  121  will deactivate the SIM using the “Deactivate Switched SIM” procedure. The SIM does not have to be physically removed. The activate SIM switch  150  can be placed in many locations, including on the TA  36  or on an external device, such as an MS cradle or cordless telephone base station. This allows convenient switching between public and private mode operation. “Public mode” means that the normal GSM air interface is used to deliver a call to a subscriber. “Private mode” means that a call to a GSM subscriber is delivered over the wired subscriber loop  37  to a GSM Wired Terminal Adapter. 
     The ISDN set  112  originates and terminates circuit-switched data communications service using normal ISDN data call procedures. The TA  36  supports data transfer rates up to 9.6 kbps. The TA  36  also supports higher data rates by setting up a high-speed circuit-switched data call, using the high speed circuit switched data service specified in the 1996 release of the ETSI GSM technical specifications (referred to as GSM 96). 
     TA  36  Location Updates 
     A location area in a PLMN  12  consists of a group of BTS  28 , and each location area has a unique location area identifier. A location area in the wired environment consists of a group of TAC  34 , and each location area has a unique location area identifier. A location update message is sent from a device (MS  30  or TA  36 ) to a visitor location register (VLR  19 ) to identify the location area within which the device is currently operating. 
     When power is applied to the TA  36 , mobility logic in the TA  36  will send a location update message to the VLR  19  in the PLMN  12  for each SIM  111   a  installed in the TA  36 . The VLR  19  will pass the location update information to the HLR  18 , and both will record location information associated with the TA  36 . When the activate SIM switch  150  is toggled to “On”, mobility logic in the TA  36  will issue a location update message to the VLR  19  for that activated SIM  111   b.  The TA  36  will also issue location update messages for each active SIM  111   a  and SIM  111   b  in response to periodic location update requests from the VLR  19  which requests the VLR  19  issues to refresh its own knowledge of active SIM  111 . 
     Seamless Transition from Wireless Operation to Wired Operation 
     Location update messages are used to identify the location area of the MS  30  (which contains a SIM) and SIM  111   b  in the TA  36 . Seamless transition between PLMN  12  wireless and SOHO  16  wired operation is achieved by using duplicate copies of SIM  111   b  in the MS  30  and switched SIM interface  125 . To switch from wireless operation to wired operation, the MS  30  is powered off, and the activate SIM switch  150  is toggled to “On”. The activate SIM switch  150  may be physically located in various places, including on the TA  36 , in a battery recharging cradle for the MS  30 , or in a cordless telephone base station. As described previously, the TA  36  will send a location update message to the VLR  19  to indicate SIM  111   b  is active in the TA&#39;s  36  location area. After the location update, calls to the MS  30  MSISDN will cause page messages from the MSC  20  to be routed to the TA  36 . The TA  36  will respond to the page messages, and terminate the call to the ISDN set  38  or analog set  118  associated with the SIM  111   b.    
     Seamless transition between SOHO  16  wired and PLMN  12  wireless operation occurs when the activate SIM switch  150  is toggled to “Off”, and the MS  30  is powered on. This will cause the TA  36  to send a detach message to the PLMN  12  for SIM  111   b.  Subsequently, the MS  30  will send a location update message to the BTS  28  in the PLMN  12 . When the user carries the MS  30  away from home, calls to the MS  30  MSISDN are delivered to the MS  30  as normal mobile terminated calls. 
     The TA  36  has a semi-permanent SIM  111   a  installed. A unique MSISDN associated with the SIM  111   s  causes calls to the TA  36  MSISDN to be routed to the wired TA  36 . 
     Home, Office, and Public Mobility 
     The MS  30  is not limited to using only one wired TA  36 . For example, a subscriber can place TA&#39;s in his residence and office. This subscriber moving from home to office would be able to receive calls via the wired TA  36  at home, then via the public PLMN  12  in transit, and then, upon updating location with the wired TA  36  at his office, receive calls at his office via a wired subscriber loop  37 . 
     Alternate Embodiments 
     The invention is not limited to the GSM standards for digital cellular telephone service. The invention applies equally well to the following systems: 
     1) Advanced Mobile Phone System (AMPS) analog cellular systems; 
     2) Time Division Multiple Access (TDMA) (Telecommunications Industry Association (TIA)—TIA IS-54 is the standard for TDMA digital cellular systems); and 
     3) Code Division Multiple Access (CDMA) (TIA IS-95 is the standard for Code Division Multiple Access digital cellular systems.) 
     Operation of the Preferred Embodiment 
     In operation, the TA  36  provides standard telephony interfaces to analog and ISDN BRI terminals. The TA  36  interworks the standard terminal signals to GSM Radio interface layer 3 messages and procedures. That is, the signals to the BSC  24  from the BTS  28  and from the TAC  34  appear identical, as to their format and protocol. 
     Terminal Adapter (TA  36 ) Flow Charts (FIGS. 5-9) 
     The following flow charts describe the logic of the Protocol Processor  121  of the GSM Wired Terminal Adapter  36 . Protocol errors are handled as described by the appropriate ISDN and GSM specifications. 
     Terminal Adapter Power On (FIG. 5) 
     The algorithm shown in FIG. 5 is executed when, in step  301 , a power switch (not shown) on the terminal adapter  36  is moved to the “On” position. In step  302 , the protocol processor  121  first checks if the Subscriber Identity Module (SIM)  111   a  is installed at the SIM Interface  122 , and if the SIM  111   b  is installed at the Switched SIM Interface  125 . For each SIM that is installed, the TA  36  follows the normal GSM Radio Interface Layer 3 (RIL3 ) procedures for performing a location update with the GSM Network Switching System&#39;s Home Location Register, as described in GSM 4.08, sending the GSM Radio Interface Layer 3 messages for Radio Resource (RR) and Mobility Management (MM) on the D-channel of the wired subscriber loop  131 , connecting the U′ Interface  124  of the TA  36  to the GSM wired terminal adapter controller  34 . The GSM location update procedure enables the GSM network to deliver a call to the directory number associated with a SIM to the TA  36  where that SIM is installed. 
     If the protocol processor  121  does not detect the SIM  111   a  installed at the SIM interface  122 , or the SIM  111   b  installed at the switched SIM interface  125 , then the protocol processor  121  at step  303  enters a state in which it performs no further processing, until, in step  304 , it does detect the SIM  111   b  inserted in the switched SIM interface  125 . 
     The protocol processor  121  then proceeds at step  305  executing the GSM location updating procedure. At step  305 , the protocol processor  121  sends a GSM RIL3-RR channel request message to the TAC  34 . In response, in step  306  the protocol processor  121  receives a GSM RIL3-RR channel assignment message from the TAC  34 . Next, in step  307 , the protocol processor  121  sends a GSM RIL3-MM location update message to the TAC  34 . In step  308 , the protocol processor  121  immediately receives a GSM RIL3-RR LAPD unnumbered acknowledgment (UA) message from the TAC  34 . 
     In step  309 , the protocol processor  121  receives a GSM RIL3-MM authentication request from the TAC  34 . In step  310 , the protocol processor  121  calculates the value for the authentication response, according to normal GSM authentication procedures. In step  311  the protocol processor  121  sends the GSM RIL3-MM authentication response message to the TAC  34 . In step  312 , the protocol processor  121  receives a GSM RIL3-MM location update accepted message from the TAC  34 . Following this, in step  313 , the protocol processor  121  receives a GSM RIL3-RR channel release message from the TAC  34 . In step  314 , the protocol processor  121  checks if there is a SIM installed for which no GSM location update has been sent. If so, the protocol processor  121  proceeds to step  305 . In step  315 , the protocol processor  121  enters a state where it is waiting for a call origination from the ISDN set  38  or the ISDN adapter  116 , a call termination from the TAC  34 , deactivation of the activate SIM switch  150 , or the TA  36  power switched off. 
     Terminal Adapter Power Switched Off (FIG. 6) 
     The protocol processor  121  executes the algorithm in FIG. 6 when, in step  401 , the power switch (not shown) of the TA  36  is moved to the off position. The protocol processor  121  performs the GSM detach procedure for both SIMs  111   a  and  111   b,  which informs the HLR  18  that the directory number associated with each SIM can no longer be reached through the network. The TA  36  remains powered until it has completed the GSM detach procedure. In step  402 , the protocol processor  121  sends a GSM RIL3-RR channel request message to the TAC  34 . In response, in step  403  the protocol processor  121  receives a GSM RIL3-RR channel assignment message. In step  404  the protocol processor  121  then sends a GSM RIL3-MM detach message for the SIM  111   a  to the TAC  34 . In step  405 , the response to the GSM RIL3-MM detach message is a LAPDm unnumbered acknowledgment (UA) message from the TAC  34 , followed, in step  406 , by the GSM RIL3-MM authentication request received. On receipt of the authentication request, the protocol processor  121  in step  407  calculates the authentication response using the GSM authentication algorithm, and in step  408  sends it to the TAC  34  in a GSM RIL3-MM authentication response message. In step  409 , the response from the TAC  34  is a GSM-RIL3-MM detach acknowledgment received by the protocol processor  121 . In step  410 , the protocol processor  121  receives a GSM RIL3-RR channel release from the TAC  34 . In step  411 , the protocol processor  121  checks if the SIM  111   b  is installed at the switched SIM interface  125 . If it is, the GSM detach procedure is repeated starting at step  402 , but this time specifying the SIM  111   b  in the GSM RIL3-MM detach message in step  404 . In step  412 , only after the GSM detach procedure has been completed for each installed SIM is the power turned off to the TA  36 . The TA  36  must be powered off prior to removing the SIM  111   a  from the SIM Interface  122 . The activate SIM switch  150  must be in the “deactivated” position prior to removing the SIM  111   b  from the switched SIM interface  125 . 
     Subscriber Places a Call (FIGS. 7 a  and  7   b ) 
     The algorithm shown in FIG. 7 is executed by the protocol processor  121  when the ISDN set  38  or the analog set with ISDN adapter  39  is used by the subscriber to place a call. From the perspective of the protocol processor  121 , the analog set with ISDN adapter  39  presents the same call control signaling interface as the ISDN set  38 . Either of these devices, when used by the subscriber to place a call, will, in step  450  of FIG. 7 a,  send an ISDN Q.931 setup message via the S/T Bus interface  120  to the protocol processor  121 , which initiates the call setup procedure. References to “ISDN set” in FIG. 7 refer to both the ISDN set  38  and/or the analog set with ISDN adapter  39 . 
     In step  451 , the protocol processor  121  checks if the SIM  111   a  is installed at the SIM interface  122 , or if the SIM  111   b  is installed at the switched SIM interface  125 . If neither the SIM  111   a  nor the SIM  111   b  is installed, then in step  452  the protocol processor  121  instructs the voice service module  123  to provide an audible treatment to the subscriber. This treatment can be a pre-recorded voice announcement stating that there is no SIM installed, or a standard telephony “reorder” tone. If either the SIM  111   a  or the SIM  111   b  is installed, then the protocol processor  121  proceeds to step  453 . 
     When placing a call, the subscriber must press the octothorpe key (#) after dialing the called number. In step  453 , the protocol processor  121  examines the contents of the ISDN Q.931 setup message. If the ISDN Q.931 setup message contains no dialed digits, or if the called party address in the ISDN Q.931 setup message contains a string of dialed digits that does not end with an octothorpe (#), then in step  454  the protocol processor  121  starts an interdigit timer, and collects digits until an octothorpe (#) is encountered. In step  455 , the protocol processor  121  determines if the ISDN Q.931 setup message contains dialed digits. 
     If there are no dialed digits, then in step  457  the protocol processor  121  also instructs the voice service module  123  to play dialtone to the ISDN set  38  or ISDN adapter  116 . In step  459 , when the protocol processor  121  receives the first digit, then in step  460  it instructs the voice service module  123  to stop the dial tone. When the protocol processor  121  receives a digit in step  458  or in step  459 , then in step  461  it stops the interdigit timer. 
     The interdigit timer is normally five seconds, but can be configured to other values. If the interdigit timer expires (step  466 ) between the reception of individual digits at any time prior to the protocol processor  121  receiving an octothorpe, then in step  467  the voice service module  123  provides an audible treatment to the ISDN set  38  or ISDN adapter  116 . This treatment can be a pre-recorded voice announcement instructing the subscriber to redial the called number, or a standard telephony “reorder” tone. 
     Each time the protocol processor  121  receives a digit at step  458  and step  459 , it first stops the interdigit timer at step  461 , and then in step  462  checks if the received digit is an octothorpe. If it is not, the protocol processor  121  starts the interdigit timer, and in step  463  waits for the next digit. 
     If the digit is an octothorpe, then, referring to FIG. 7 b,  the protocol processor  121  proceeds with the normal GSM call setup procedure in step  468 , beginning by sending a GSM RIL3-radio resource channel request message to the TAC  34 . If, in step  453  of FIG. 7 a,  the called party address in the ISDN Q.931 setup message contains a string of dialed digits ending with an octothorpe (#), then beginning at step  468  in FIG. 7 b,  the protocol processor  121  performs the normal GSM call setup procedure. In response to the GSM RIL3-RR channel request message, in step  469  the TA  36  receives a GSM RIL3-RR channel assignment. In step  470  the protocol processor  121  sends a GSM RIL3-MM CM service request. 
     The response to the GSM RIL3-MM CM service request is a GSM RIL3-RR LAPDm unnumbered acknowledgment (UA) message received in step  471 , followed by the GSM RIL3-MM authentication request received in step  472 . On receipt of the authentication request, the protocol processor  121  calculates the authentication response in step  473  using the GSM authentication algorithm, and sends it to the TAC in a GSM RIL3-MM authentication response message in step  474 . At this point, the protocol processor  121  in step  475  converts the ISDN Q.931 setup message that was received in step  450  into a GSM RIL3-CC setup message, and sends it to the TAC  34 . 
     Following this, in step  476  the TA  36  receives a GSM RIL3-CC call proceeding message, which the protocol processor  121  converts into an ISDN Q.931 call proceeding message. In step  477 , the protocol processor  121  sends it to the ISDN set  38  or ISDN adapter  116  via the S/T Bus Interface  120 . In a similar fashion, in step  478  the protocol processor  121  converts the incoming GSM RIL3-CC alerting message into an ISDN Q.931 alerting message, which, in step  479  is sent to the ISDN set  38  or ISDN adapter  116 . When the called party answers, in step  480  the protocol processor  121  converts the resultant incoming GSM RIL3-CC connect message from the TAC  34  into an ISDNQ.931 connect message, which in step  481  is passed to the ISDN set  38  or ISDN adapter  116 . 
     In step  482 , an ISDN Q.931 connect acknowledgment message is received from the ISDN set  38  or ISDN adapter  116 . In step  483 , the protocol processor  121  sends a GSM RIL3-CC connect acknowledgment to the TAC  34 . In step  484  the protocol processor  121  enters an active call state, waiting for either an ISDN Q.931 disconnect message from the ISDN set  38  or ISDN adapter  116 , or a GSM RIL3-CC disconnect message from the TAC  34 . 
     Subscriber is Called (FIGS. 8 a  and  8   b ) 
     In step  501  the protocol processor  121  waits for a paging request. The algorithm shown in FIG. 8 is executed when, in step  502 , the TA  36  receives a GSM RIL3-RR paging request message from the TAC  34 . In step  503 , the protocol processor  121  checks if the SIM specified in the paging request is installed at the SIM interface  122  or the switched SIM interface  125 . If the specified SIM is not installed, then the protocol processor  121  does not respond to the paging request, but returns to step  501 , where it waits for a paging request. 
     If the requested SIM is installed-at either the SIM interface  122  or at the Switched SIM Interface  125 , then in step  504  the protocol processor  121  sends a GSM RIL3-RR channel request to the TAC  34 . In step  505 , the protocol processor  121  receives a GSM RIL3-RR channel assignment message from the TAC  34 . In step  506 , the protocol processor  121  sends a GSM RIL3-RR paging response message to the TAC 34 , indicating that the paged SIM is available at the TA  36 . The TAC  34  immediately responds with a GSM RIL3-RR LAPD unnumbered acknowledgment (UA) message which, in step  507 , the Protocol processor  121  receives. 
     Following this, in step  508  the protocol processor  121  receives a GSM RIL3-MM authentication request from the TAC  34 . In step  509  the protocol processor  121  calculates the value for the authentication response according to normal GSM authentication procedures. In step  510  the protocol processor  121  sends the GSM RIL3-MM authentication response message to the TAC  34 . In step  511 , the protocol processor  121  receives a GSM RIL3-call control (CC) setup message from the TAC  34 . In step  512 , the protocol processor  121  responds to the TAC  34  with a GSM RIL3-CC call confirmed message, then converts the GSM RIL3-CC Setup message into an ISDN Q.931 Setup message and at step  513  sends that to the ISDN set  38  and to the ISDN adapter  116 . In step  514 , the protocol processor  121  receives an ISDN Q.931 call proceeding message from the ISDN set  38  and the ISDN adapter  116 . 
     Referring now to FIG. 8b, in step  515 , the protocol processor  121  receives an ISDN Q.931 alerting message. In step  516 , the protocol processor  121  sends a GSM RIL3-CC alerting message to the TAC  34 . In step  517 , when the protocol processor  121  receives an ISDN Q.931 connect message from either the ISDN set  38  or the ISDN adapter  116 , in step  518  it is converted toa GSM RIL3-CC connect message, which is sent to the TAC  34 . In step  519 , in response to this message, the TAC  34  sends a GSM RIL3-CC connect acknowledgment message. In step  520 , the protocol processor  121  converts this to a ISDNQ.931 connect acknowledgment message, and sends it to the ISDN set  38  or the ISDN adapter  116 . In step  521 , the protocol processor  121  then enters an active call state, waiting for either an ISDN Q.931 disconnect message from the ISDN set  38  or ISDNadapter  116 , or a GSM RIL3-CC disconnect message from the TAC  34 . 
     Switched SIM Deactivation (FIG. 9) 
     The algorithm shown in FIG. 9 is executed when the activate SIM switch  150  is set to the “deactivate” position. In step  550  the protocol processor  121  detects this change through the switch circuit connection  154 . In step  551  the protocol processor  121  sends a GSM RIL3-RR channel request message to the TAC  34 . In response, the protocol processor  121  receives a GSM RIL3-RR channel assignment message in step  552 . The protocol processor  121  then sends a GSM RIL3-MM detach message for the SIM  111   b  to the TAC  34  in step  553 . In step  554 , the response to the GSM RIL3-MM detach message is a LAPDm unnumbered acknowledgment (UA) message from the TAC  34 , followed by the GSM RIL3-MM authentication request received, in step  555 . On receipt of the authentication request, the protocol processor  121  calculates the authentication response in step  656  using the GSM authentication algorithm, and sends it to the TAC  34  in a GSM RIL3-MM authentication responsemessage in step  557 . In step  558 , the protocol processor  121  receives a GSMRIL3-MM detach acknowledgment from the TAC  34 . Following this, the protocol processor  121  receives a GSM RIL3-RR channel release message from the TAC  34  in step  559 . In step  560 , the protocol processor  121  enters a state in which it waits for the activate SIM switch  125  to be switched back to the “activate” position. 
     Terminal Adapter Controller (TAC  34 ) Flow Chart (FIG. 10) 
     The algorithms of the TAC  34  are shown in FIG.  10 . When the TAC  34  receives a message from the BSC  24  in step  602 , the TA controller application  214  checks in step  603  whether the message is from the TA  36  or from the BSC  24 . If from the TA  36 , in step  604  the TA controller application  214  checks if it is a GSM RIL3-RR channel request message. If not, the TA controller application  214  relays the message unaltered to the BSC  24  in step  605 , and proceeds to step  601 , where it waits for the next incoming message. 
     If the message in step  604  is a GSM RIL3-RR channel request message, then in step  609  the TA controller application  214  stores information from the message that it needs to properly switch the traffic channel connection. The TA controller application  214  then sends the message unaltered to the BSC  24  in step  610 , and proceeds to step  601 , where it waits for the next incoming message. 
     At step  603 , if the message is from the BSC  24 , then the TA controller application  214  checks in step  606  if it is a GSM RIL3-RR channel assignment message, a GSM RIL3-channel release message, a GSM RIL3-RR cipher mode message, or a GSM RIL3-RR paging request. If it is not one of these, the TA controller application  214  relays the message unaltered to the TA  36  in step  607 , and proceeds to step  601  where it waits for the next incoming message. If the TA Controller Application  214  is processing a GSM RIL3-RR channel assignment message, it stores information from the message in step  613  that it needs to properly switch the traffic channel connection. It then relays the message unaltered to the TA  36  in step  614 , and proceeds to step  601  where it waits for the next incoming message. 
     In step  606 , if the message is a GSM RIL3-RR channel release message, the TA controller application  214  clears the information for switching the traffic channel connection associated with that message in step  616 . It then relays the message unaltered to the TA  36  in step  617 , and proceeds to step  601  where it waits for the next incoming message. In step  606 , if the message is a GSM RIL3-RR paging request message, then in step  619  the TA Controller application  214  broadcasts the message to all TA&#39;s  36  which are connected to the TAC  34 . The TA Controller application  214  then proceeds to step  601  where it waits for the next incoming message. 
     In step  606 , if the message is a GSM RIL3-RR cipher mode, then the TA controller application  214  sends a GSM RIL3-RR cipher mode complete message to the BSC  24  in step  621 . The GSM RIL3-RR cipher mode message is not relayed to the TA  36 . The TA controller application  214  then proceeds to step  601  where it waits for the next incoming message. 
     Although an illustrative embodiment of the invention has been shown and described, other modifications, changes, and substitutions are intended in the foregoing disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.