Abstract:
A telecommunication network includes a local switch for receiving and switching a telecommunication signal to remote switches in the network. A local control arrangement is provided which includes a memory for storing instructions and data and which uses the stored instructions and data to control the switching operation of the local switch. A remote control arrangement is provided which also includes a memory for storing equivalent instructions and data. The remote control arrangement is also adapted to control the switching operation of the local switch and the local switch can be controlled by either the local or the remote control arrangements. A manager is provided for modifying the instructions and data in the memories of the local and remote control means and modify the instructions and data in either the local or remote control arrangements immediately. A marker is then sent to the other of the local or remote control means to mark the instructions and data as being out of date. The manager can then modify the marked instructions and data at a later date. The switch is arranged to initially request control from the local control arrangement and the marker is checked to determine if the instructions and data in the local control arrangement are up to date. If not, control is passed to the remote control arrangement.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to a telecommunication network and a method of controlling the switching of a telecommunication signal in a telecommunication network. More particularly, the present invention relates to the control arrangement for controlling the switching of a telecommunication signal in a telecommunication network. 
     2. Related Art 
     In a modern telecommunication network there is a need to provide flexible call control architectures of the switched networks to facilitate the implementation of new features and services. Networks which provide such flexibility have been termed ‘intelligent networks’ and are discussed in detail in “Intelligent Networks” by Jan Thörner (Artech House. Boston. London). 
     A typical intelligent network is illustrated in FIG.  1 . In such a network when a local exchange  1  receives a telecommunication signal from a telephone  2 , the signal is interpreted by the call control function (CCF). Limited processing of the telecommunication signal can take place within the service switching function (SSF). However, if more advanced processing is required the SSF has the ability to generate a query i.e. a request for control from a centralised transaction processor termed the service control function (SCF). The query from the SSF is passed initially to a signalling transfer function which routes the query to the required SCF. The SCF is a centralised transaction processor which hosts advanced services controlled software termed service logic programs (SLPs) or applications. When an SCF receives a query, an application will be initiated which requires data. The application running in the SCF refers to a service data function (SDF) for the requisite data. The SCF can then return instructions to the SSF in the local exchange  1  via the STF. 
     The advantage of this arrangement is that the advanced services are provided at a centralised location. This enables both the applications in the SCF and the data in the SDF to be updated as desired when advanced services are to be updated. A customer is able to modify the applications for data in the SCF and SDF respectively by changing the application or data in a service management function (SMF). The SMF is able to update the applications and data in the SCFs and SDFs respectively easily in view of their centralisation location. The SMF is also able to manage the STF and SSF if required. 
     In order to standardise communication over intelligent networks, various standard signalling protocols have been agreed. For instance, communication between the SSFs, the STFs, the SCFs and the SDFs can be achieved using the CCITT (Consultative Council of International Telephone and Telegraph)  7  common channelling signalling network. The CCITT  7  protocol comprises a signalling connection control part (SCCP) and transaction capabilities (TCs). In addition an intelligent network application part (INAP) can be stacked on this C 7  transport. 
     The communication of the management functions from the service management function can be carried out using an asynchronous transfer mode (ATM) X25 link which uses a file transfer protocol (FTP) for the transfer of management data e.g. for the updating of the applications and data in the SCFs and SDFs respectively. 
     A centralised architecture has the advantage that it provides for flexibility compared with a distributed network. It also provides savings on management network infra structure since the centralised applications and data only have to be updated for one location. In a distributed network the applications and data would need to be updated throughout the network. 
     The centralised network however suffers from the disadvantage that the SSF must transmit a query to a centralised SCF thus causing switching delays for the signal over the speech path. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the present invention to reduce the switching delay in a telecommunication network without requiring a significant increase in the signalling network infra structure compared to the prior art centralised structure. 
     In accordance with one aspect, the present invention provides a telecommunication network comprising: 
     local switch means for receiving and switching a telecommunication signal to remote switch means in the network; 
     local control means including storage means for storing instructions and/or data, said local control means being adapted to use said stored instructions and/or data to control the switching operation of said local switch means; 
     remote control means including storage means for storing instructions and/or data equivalent to the instructions and/or data stored in said storage means of said local control means, said remote control means being adapted to control the switching operation of said local switch means, said local switch means being controlled by either said local control means or said remote control means; 
     management means for modifying said instructions and/or data of said storage means of said local and remote control means, said management means being adapted to modify said instructions and/or data of said storage means of one of said local and remote control means immediately, to associate a marker with said instructions and/or data in said storage means of said local control means to indicate whether said storage means of said local control means contains the most recently modified instructions and/or data, and to similarly modify said instructions and/or data of said storage means of the others of said local and remote control means subsequently; 
     said switching means being adapted to request control from said local control means; 
     marker checking means for checking said marker to determine if said instructions and/or data in said storage means of said local control means are the most recently modified instructions and/or data; and 
     passing means responsive to said marker means for passing the control request from said local switch means to said remote control means if said marker checking means determines that said instructions and/or data are not the most recently modified instructions and/or data. 
     In accordance with a second aspect, the present invention provides a method of controlling the switching of a telecommunication signal in a telecommunication network comprising local switch means for switching the telecommunication signal, local control means containing instructions and/or data for controlling the switching operation of said switch means, and remote control means containing equivalent instructions and/or data for controlling the switching operation of said switch means, the method comprising: 
     control modification steps of 
     modifying said instructions and/or data in one of said local and remote control means; 
     associating a marker with said instructions and/or data contained in said local control means to indicate wherein said local control means contains the most recently modified instructions and/or data; 
     subsequently similarly modifying said instructions and/or data of the other of said local and remote control means; 
     and switching control steps of 
     said local switch means requesting control from said local control means; 
     checking said marker to determine if said instructions and/or data of said local control means is not the most recently modified instructions and/or data; and 
     if it is determined that said instructions and/or data are not the most recently modified instruction and/or data; 
     passing the control request from said local switch means to said remote control means and controlling said local switch means from said remote control means, or if it is determined that said instructions and/or data re the most recently modified instructions and/or data, controlling said local switch means from said local control means. 
     In accordance with the third aspect, the present invention provides a local switching arrangement for use in the method of any one of claims  29  to  38  comprising: 
     said local switching means for receiving and switching a telecommunication signal to remote switch means in the telecommunication network; 
     said local control means including storage means for storing instructions and/or data and a marker associated with said instructions and/or dat, said local control means being adapted to use said stored instructions and/or data to control the switching operation of said local switch means; 
     receiving means for receiving instructions to set said marker to mark said instructions and/or data as being out of date; 
     said switch means being adapted to request control from said local control means; 
     marker checking means for checking said marker to determine if said instructions and/or data are out of date; 
     passing means responsive to said marker means for passing the control request from said local control means to a similar remote control means if said marker checking means determines that said instructions and/or data are out of date; 
     said receiving means being adapted to receive instructions to update said instructions and/or data stored in said storage means and to reset said marker to mark said instructions and/or data as being updated. 
     By providing both local control means and remote control means which mirror the instructions (or applications) and data, and by providing a marker such as a flag to mark the local control means as being out of date if the remote control means has been updated, the present invention provides for a greatly reduced switching delay compared to a centralised network without requiring the simultaneous real time updating of all of the local control means required in a decentralised network. The local switch means will initially refer to the local control means for control. If however the instructions and/or data in the local control means has been marked as being out of date compared with the instructions and/or data which have been updated in the remote control means, the switch means will refer to the remote control means for control. 
     The management means operates by updating the remote control means as a priority whereupon the local control means are marked as being out of date. Subsequently, when the flow of traffic over the communication paths permits, the management means will update the local control means and reset the mark. 
     Thus, the switch means will have to refer to the remote control means for control for a period after there has been update until the local control means is updated. Normally the switch means will refer to the local control means for control. In this way the switching delays in the telecommunication network are greatly reduced compared to a centralised network and the need for fast updates of the local control means is removed compared with a decentralised network. 
     Although the present invention is applicable to a telecommunication network having local control means and central control means, the present invention can also be applied to a telecommunication network having a plurality of like local control means. 
     In embodiments of the present invention, the instructions and/or data in the local control means can be marked by for example setting and resetting a flag, assigning a version number to each set of instructions, or, the address of the data or the application can simply be deleted when out of date. 
     When a flag or version number is used to mark the instructions and/or data, the flag or version number can be stored at any location e.g. in the local STF, the local SCF, or the local SDF. 
     In a centralised system having local control means and central control means, the management means can communicate with local control means either directly or via the central control means. In a distributed network of a plurality of local control means, the management means can communicate with each of the local control means using a wide area network. This also enables each of the local control means to communicate with one another which is necessary to enable them to locate the most recently modified instructions and/or data. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Embodiments of the present invention will now be described with reference to the accompanying drawings in which: 
     FIG. 1 is a schematic drawing of a prior art centralised telecommunication network; 
     FIG. 2 is a schematic drawing of a centralised telecommunication network in accordance with one embodiment of the present invention; 
     FIGS. 3 a  and  3   b  provide a flow diagram of a first switching control method using the first embodiment of the present invention; 
     FIGS. 4 a  and  4   b  provide a flow diagram of a second switching control method using the first embodiment of the present invention; 
     FIGS. 5 a  and  5   b  provide a flow diagram of a third switching control method using the first embodiment of the present invention; 
     FIGS. 6 a  and  6   b  provide a flow diagram of a fourth switching control method using the first embodiment of the present invention; 
     FIGS. 7 a  and  7   b  provide a flow diagram of a fifth switching control method using the first embodiment of the present invention; 
     FIGS. 8 a  and  8   b  provide a flow diagram of a sixth switching control method using the first embodiment of the present invention; 
     FIGS. 9A and 9B are flow diagrams of methods of modifying or updating the applications and/or data in the local SCF/SDFs of the first embodiment of the present invention; 
     FIG. 10 is a schematic illustration of a distributed telecommunication network in accordance with a second embodiment of the present invention; 
     FIGS. 11 a  and  11   b  provide a flow diagram of a first switching control method using the second embodiment of the present invention; 
     FIGS. 12 a  and  12   b  provide a flow diagram of a second switching control method using the second embodiment of the present invention; 
     FIGS. 13 a  and  13   b  provide a flow diagram of a third switching control method using the second embodiment of the present invention; and 
     FIG. 14 is a flow diagram illustrating a method of modifying or updating the applications and/or data in the local SCF/SDFs of the second embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Referring now to the drawings, FIG. 2 schematically illustrates a centralised telecommunication network in accordance with one embodiment of the present invention. FIG. 2 differs from the prior art in that a local exchange  1  is provided with a local service control function (SCF)  3 , a local service data function (SDF)  4 , and a local service transfer function (STF)  5 . The STF  5  receives the query from the SSF in the local exchange  1  and can either route the query to the local SCF  3  or to the central SCF  6  with its associated central SDF  7 , in dependent upon whether the local SCF  3  and local SDF  4  have been marked as being out of date in view of a recent update. The service management function (SMF)  8  is able to update the applications and data in the central SCF  6  and central SDF  7  as well as the local SCF  3  and local SDF  4 . 
     In this embodiment the signalling protocols used by the SSF of the local exchange  1 , the local STF  5 , the local SCF  3 , the local SDF  4 , the central SCF  6  and the central SDF  7  can be the same as the prior art i.e. the C 7  transport protocol with for instance INAP stacked on top. The communication protocol between the SCFs  3  and  6 , the SDFs  4  and  7  and the SMF  8  can also be the same as the prior art i.e. the X25/ATM protocol with a modification to include the transmission of a marker such as a flag or version number to the local SCF  3  and/or local SDF  4 . 
     This telecommunication network is based on the CCITT standard termed Capability Set 1 (CS-1) specified in the CCITT Q. 1200 series of recommendations. 
     The various methods of operating this embodiment will now be described with reference to FIGS. 3 to  9 . 
     FIGS. 3 a  and  3   b  illustrates one method of operating the telecommunication network illustrated in FIG.  2 . In this method the local SCF  3  contains a flag for the application to be run and the local SDF contains a flag for the data required by the SCF application. When a telephone call is placed the line is seized and the digits are dialled in step S 1 . When the local exchange  1  receives the dialled digits, the SSF generates a query message and logical address for the local SCF  3  and passes it to the local STF  5  in step S 2 . The local STF identifies the logical address and passes the query message to the local SCF  3  in step S 3 . In step S 4  the local SCF identifies the application which is to be run and in step S 5  the flag or marker for the application is examined to determine if the flag is set or reset. If the flag is reset, the local SCF invokes the application in step S 6  which is the subject of the query from the SSF. The local SCF application queries the local SDF  4  for data in step S 7 . The flag or marker for the data is then examined in step S 8  and if this is reset a data valid message is returned to the local SCF application in step S 9 . The data is then returned to the local SCF application in step S 10  and in step S 11  the local SCF application returns instructions to the SSF in the local exchange  1 . The SSF then instructs the CCF in step S 12  and in step S 13  the CCF controls the switch to form the required switching path. 
     If in step S 5  it is determined that the flag for the application is set, i.e. the application is out of date, the call control is passed to an STF application in the local STF  5  in step S 14 . Similarly, if the flag for the data is determined to be set in step S 8  indicating that the data is out of date, a data invalid message is returned to the local SCF application in step S 15  and call control is passed to an STF application in step S 14 . The STF application then regenerates the query message with the logical address for the central SCF  6  and it is passed to the central SCF  6  in step S 16 . The central SCF  6  then identifies and invokes the required application in step S 17  and in step S 18  the central SCF application queries the central SDF  7  for data. The central SDF  7  then returns the data requested to the central SCF application in step S 19  and in step S 20  the central SCF application returns instructions to the SSF of the local exchange  1  via the local STF  5 . The SSF then instructs the CCF in step S 12  and the CCF controls the switch in step S 13 . 
     In this method, the flags for the application and the data are associated with the application and data respectively and if either one is set, indicating that either one is out of date, control is passed to the central SCF  6 . 
     Referring now to FIGS. 4 a  and  4   b,  this flow diagram illustrates a second method of operating the telecommunication network illustrated in FIG.  2 . In this method the local SDF  4  contains a flag for the data to be used by the SCF application. No flag for the application in the local SCF  3  is used in this method. When a telephone call is placed, the line is seized and the digits are dialled in step S 21 . When the local exchange  1  receives the dialled digits, the SSF generates a query message and the logical address for the local SCF  3  and passes it to the local STF  5  in step S 22 . The local STF  5  identifies the logical address and passes the query message to the local SCF  3  in step S 23 . In step S 24  the local SCF  3  identifies and invokes the application to be run. Then the local SCF application queries the local SDF  4  for the data required by the application in step S 25 . The flag or marker for the data is then examined in step S 26  and if this is reset a data valid message is returned to the local SCF application in step S 27 . The data is then returned to the local SCF application in step S 28  and in step S 29  the local SCF application returns instructions to the SSF in the local exchange  1 . The SSF then instructs the CCF in step S 30  and in step S 31  the CCF controls the switch to form the required switching path. 
     If in step S 26  it is determined that the flag for the data is determined to be set, indicating that the data is out of date, a data invalid message is returned to the local SCF application in step S 32  and call control is passed to an STF application in step S 33 . The STF application then regenerates the query message with a logical address for the central SCF  6  and it is passed to the central SCF  6  in step S 34 . The central SCF  6  then identifies and invokes the required application in step S 35  and in step S 36  the central SCF application queries the central SDF  7  for data. The central SDF  7  then returns the data requested by the central SCF application in step S 37  and in step S 38  the central SCF application returns instructions to the SSF of the local exchange  1  via the local STF  5 . The SSF then instructs the CCF in step S 30  and the CCF controls the switching in step S 31 . 
     Referring now to FIGS. 5 a  and  5   b,  this flow diagram illustrates a third method of operating the telecommunication network illustrated in FIG.  2 . In this method the local SCF  3  holds flags for both the SCF applications and the data held in the local 
     SDF  4  which is required by the SCF applications. This method is applicable where the SCF application only uses one set of data i.e. the SCF application has dedicated data. 
     When a telephone call is placed, the line is seized and the digits are dialled in step S 40 . When the local exchange  1  receives the dialled digits, the SSF generates a query message and logical address for the local SCF  3  and passes it to the local STF  5  in step S 41 . The local STF identifies the logical address and passes the query message to the local SCF  3  in step S 42 . In step S 43  the local SCF identifies and invokes the application which is to be run. In step S 44  the flag or marker for the application and the data is examined to determine if the flag for the application or the data is set or reset. If either of the flags is reset, the local SCF application queries the local SDF  4  for data in step S 45 . The data is then returned to the local SCF application in step S 46  and in step S 47  the local SCF application returns instructions to the SSF in the local exchange  1 . The SSF then instructs the CCF in step S 48  and in step S 49  the CCF controls the switch to form the required switching path. 
     If in step S 44  it is determined that the flag for the application or the data is set, i.e. the application and/or data is out of date, the call control is passed to an STF application in the local STF  5  in step S 50 . The STF application then regenerates the query message with a logical address for the central SCF  6  and it is passed to the central SCF  6  in step S 51 . The central STF  6  then identifies and invokes the required application in step S 52  and in step S 53  the central SCF application queries the central SDF  7  for data. The central SDF  7  then returns the data requested to the central SCF application in step S 54  and in step S 55  the central SCF application returns instructions to the SSF of the local exchange  1  via the local STF  5 . The SSF then instructs the CCF in step S 48  and the CCF controls the switch in step S 49 . 
     Referring now to FIGS. 6 a  and  6   b,  this flow diagram illustrates a fourth method of operating the telecommunication network illustrated in FIG.  2 . In this method the local SDF  4  stores the flags for the applications run in the local SCF  3 . In this method the flag for the applications can be stored in a look-up table. No flag for the data is used in this method. 
     When a telephone call is placed, the line is seized and the digits are dialled in step S 60 . When the local exchange  1  receives the dialled digits, the SSF generates a query message and a logical address for the local SCF  3  and passes it to the local SCF  3  via the STF  5 . The SCF then invokes a look-up application in step S 62  and in step S 63  the local SCF look-up application queries the flag table in the local SDF to determine the status of the flag for the application to be run in the local SCF  3  to control the switch in the local exchange  1 . In step S 64  it is determined whether the flag in the flag table in the local SDF  4  is set or reset. If the flag is reset the local SCF  3  invokes the application which is the subject of the query from the SSF in step S 66 . The local SCF application queries the local SDF  4  for data in step S 67 . The data is then returned to the local SCF application in step S 68  and in step S 69  the local SCF application returns instructions to the SSF in the local exchange  1 . The SSF then instructs the CCF in step S 70  and in step S 71  the CCF controls the switch to form the required switching path. 
     If in step S 64  it is determined that the flag for the application is set, i.e. the application is out of date, an application invalid message is returned to the local SCF look-up application in step S 72 . The local SCF look-up application then passes the call control to an STF application in step S 73 . The STF application then regenerates the queried message from the logical address SCF  6  and it is passed to the central SCF  6  in step S 74 . The central SCF  6  then identifies and invokes the required application in step S 75  and in S 76  the central SCF application queries the central SDF  7  for data. The central SDF  7  then returns the data requested to the central SCF application in step S 77  and in step S 78  the central SCF application returns instructions to the SSF of the local exchange  1  via the local STF  5 . The SSF then instructs the CCF in step S 70  and the CCF controls the switch in step S 71 . 
     Referring now to FIGS. 7 a  and  7   b,  this flow diagram illustrates a fifth method of operating the telecommunication network illustrated in FIG.  2 . In this method the local SDF  4  contains a table of flags for the local SCF applications and a table of flags for the data stored in the local SDF  4 . 
     When a telephone call is placed, the line is seized and the digits are dialled in step S 80 . When the local exchange  1  receives the dialled digits, the SSF generates a query message and the logical address for the local SCF  3  and passes it to the local SCF via the STF in step S 81 . The local SCF  3  invokes a look-up application in step S 82  and in step S 83  the local SCF look-up application queries the flag table in the local SDF  4  for the addressed application which is the subject of the query from the SSF of the local exchange  1 . In step S 84  it is determined whether the flag for the application is set or reset. If the flag is reset, an application valid message is returned to the local SCF look-up application in step S 85 . In step S 86  the local SCF  3  invokes the addressed application which is the subject of the query from the SSF. The local SCF application then queries the flag table in the local SDF  4  for the data required by the application in step S 87 . In step S 88  it is determined whether the flag is set or reset. If the flag is reset, a data valid message is returned to the local SCF application and in step S 90  the local SCF application queries the local SDF for data. The data is then returned to the local SCF application in step S 91  and in step S 92  the local SCF application returns instructions to the SSF in the local exchange  1 . The SSF then instructs the CCF in step S 93  and in step S 94  the CCF controls the switch to form the required switching path. If in step S 84  it is determined that the flag for the application is set, i.e. the application is out of date, an application invalid message is returned to the local SCF look-up application in step S 96 . The local SCF look-up application then passes the call control to an STF application in step S 97 . Similarly, if the flag for the data is determined to be set in step S 88 , indicating that the data is out of date, a data invalid message is returned to the local SCF application in step S 95  and the local SCF application passes the call control to an STF application in step S 97 . The STF application then regenerates the query message with the logical address for the central SCF  6  and is passes to the central SCF  6  in step S 98 . The central SCF  6  then identifies and invokes the required application in step S 99  and in step S 100  the central SCF application queries the central SDF  7  for data. The central SDF  7  then returns the data requested to the central SCF application in step S 101  and in step S 102  the central SCF application returns instructions to the SSF of the local exchange  1  via the local STF  5 . The SSF then instructs the CCF in step S 93  and the CCF controls the switch in step S 94 . 
     Referring now to FIGS. 8 a  and  8   b,  this flow diagram illustrates a sixth method of operating the telecommunication network illustrated in FIG.  2 . In this method the STF  5  contains a table of flags for the applications to be run in the local SCF  3 . The local SOF contains a table of flags for the data to be used by the applications run in the local SCF  3 . 
     When a telephone call is placed, the line is seized and the digits are dialled in step S 110 . When the local exchange  1  receives the dialled digits, the SSF generates a query message and logical address from the local SCF  3  and passes it to the local STF  5  in step S 111 . The local STF identifies the logical address and queries the flag table contained in local STF  5  for the local SCF applications. In step S 113  it is determined whether the flag for the application is set or reset. If the flag is reset, the local STF  5  passes the query message to the local SCF  3  in step S 114 . The local SCF  3  then identifies and invokes the application in step S 115  and in step S 116  the local SCF application queries the local SDF  4  for data. The flag or marker for the data in the table in the local SDF  4  is then examined in step S 117  and if this is reset a data valid message is returned to the local SCF application in step S 118 . The data is then returned to the local SCF application and the local SCF application queries the local SDF  4  for the data in step S 119 . The data is then returned to the local SDF application in step S 120  and in step S 121  the local SCF application returns instructions to the SSF. The SSF then instructs the CCF in step S 122  and in step S 123  the CCF controls the switch to form the required switching path. 
     If in step S 113  it is determined that the flag for the application is set, i.e. the application is out of date, the local STF  5  regenerates the query message with the logical address for the central SCF  6  and it is passed to the central SCF  6  in step S 126 . The central SCF  6  then identifies and invokes the application in step S 127  and in step S 128  the central SCF application queries the central SDF  7  for data. In step S 129  the central SDF  7  returns the data to the central SCF application and in step S 130  the central SCF application returns instructions to the SSF via the STF  5 . The SSF then instructs the CCF in step S 122  and the CCF controls the switch in step S 123 . 
     If in step S 117  it is determined that the flag for the data is reset, a data invalid message is returned to the local SCF application in step S 124 . The local SCF  3  then passes the call control to the STF  5  in step S 125 . The STF  5  then regenerates the query message with logical address for the central SCF  6  and it is passed to the central SCF  6  in step S 126 . The central SCF  6  then identifies and invokes the application in step S 127  and in step S 128  the central SCF application queries the central SDF  7  for data. In step S 129  the central SDF  7  then returns the data to the central SCF application and in step S 130  the central SCF application returns instructions to the local SSF  3  via the STF  5 . The SSF then instructs the CCF in step S 122  and the CCF controls the switch in step S 123 . 
     Referring now to FIGS. 9A and 9B, these flow diagrams illustrate methods of modifying or updating the applications and/or data in the local SCFs and SDFs in the centralised telecommunication network illustrated in FIG.  2 . 
     In FIG. 9A, the customer changes the application and/or data in the SMF  8  in step S 200 . The SMF  8  then updates the application and/or the data in the central SCF  6  and/or the central SDF  7  respectively. At the same time (or very shortly after the SMF  8  updates the central SCF  6  and/or the central SDF  7 ), the SMF  8  sends a set flag command to the local SCFs  3  and/or local SDFs  4  in step S 202 . In step S 203  the local SCFs  3  and/or local SDFs  4  respond to the set flag command by identifying and setting the application and/or data flag respectively. Once the local SCFs  3  and/or local SDFs  4  have set the appropriate flag, they return a verification message to the SMF  8  in step S 204 . Thus, in this method the SMF  8  is able to update the central SCF  6  and/or the central SDF  7  with a new application or data as appropriate. The SMF is also then able to ensure that the updated application and/or data will be used to control the switch in the local exchange  2  by associating a mark with the application and/or data used in the local SCF  3  and/or local SDF  4  respectively to mark the application and/or data as out of date, then ensuring that the query from the SSF in the local exchange  2  is routed to the central SCF  6  which uses the central SDF  7 . 
     FIG. 9B illustrates an alternative method of modifying the application in the local SCF  3  and the data in the local SDF  4  by transmitting signals via the central SCF  6 . In step S 210  the customer changes the application and/or data in the SMF  8 . The SMF  8  then updates the central SCF  6  and/or the central SDF  7 . The SMF  8  then generates a set flag command in step S 211  which is sent in step S 213  initially to the central SCF  6 . In step S 214  the central SCF  6  runs a management application which responds to the set flag command to generate an SCF to SCF message. This is then transmitted from the central SCF  6  to the local SCF  3 . The local SCF  3  receives the SCF to SCF message in step S 215  and sets the flag for the application and/or data in the local SCF  3  and/or local SDF  4  as appropriate. The local SCF  3  then returns a verification message in step S 216  which is received by the central SCF  6  causing the central SCF management application to send a verification message to the SMF  8  in step S 217 . 
     Thus, FIG. 9B provides a method of setting flags in the local STF  5 , the local SCF  3  or the local SDF  4  utilising the command network which is already in place between the central SCF  6  and the local exchange  1 . Unlike the method of FIG. 9B, no direct command control lines are necessary between the local SCF  3 , the local SDF  4  and the SMF  8 . 
     When the control lines between the SMF  8  and the local SCFs  3  and the local SDFs  4  are not busy, the SMF  8  is able to update the applications in the local SCF  3  and the data in the local SDF  4  and reset the appropriate flags. This process can take place non-real time. While the applications in the local SCF  3  and the data in the local SDF  4  are out of date, the SSF of the local exchange  1  will refer to the central SCF  6  and the central SDF  7  for instructions. Thus, in a large network wherein a central SCF  6  controls many local exchanges  1 , whilst the SMF  8  is updating all of the applications and data in the local SCFs  3  and local SDFs  4  respectively, some local exchanges will be using the central SCF  6  and central SDF  7  whilst others will be using their respective local SCF  3  and local SDF  4  depending upon the state of updating. 
     FIG. 10 illustrates a second embodiment of the present invention which represents a distributed local processing environment. This arrangement differs to the first embodiment in that there are no central SCFs or SDFs provided. Instead a plurality of local SCFs and local SDFs are provided each associated with a local exchange. This system operates on the principle that if the local exchange cannot locate up to date applications or data in the local SCF or SDF respectively, instead of referring to a central SCF or central SDF, another local SCF and SDF is referred to. 
     In FIG. 10, a telecommunication signal from telephone  2  is received in a local exchange  1  for switching onto a network of switches  9 . In the local exchange  1 , the switch is controlled by a CCF which is instructed by a SSF. The SSF is connected over a local area network (LAN) to a local SCF  11  and a local SDF  12 . A further local exchange  1   a  connected to a further telephone  2  is connected over a LAN to a further local SCF  14  and a further local SDF  15 . The LAN&#39;s of the two local exchanges  1  and  1   a  are connected together by a wide area network (WAN). Also connected to the WAN is an SMF  16  for performing management functions in the distributed network. 
     In this arrangement the SMF  16  is able to communicate with the local SCFs  11  and  14 , and the local SDFs  12  and  15 . Each of the local SCFs  11  and  14  is able to reroute a query from a local exchange  1  or  1   a  to another local SCF  10  and  13  over the LAN and WAN in order to ensure that the local exchange is controlled by the up to date application and/or data. The SMF  16  is able to transmit updates to the applications and/or data using file transfer protocol (FTP) using ATM (asynchronous transfer mode) over the WAN, and TCP/IP (transmission control protocol/internet protocol) (an ethernet protocol) over the LAN. Over the LAN the ethernet messaging protocol can be used to provide a transmission speed of 10 MBits per second or alternatively the FDDI (fibre distribution data interface) messaging protocol can be used to provide a transmission speed of 100 MBits per second. 
     The various methods of operating this embodiment will now be described with reference to FIGS. 11 to  14 . 
     FIGS. 11 a  and  11   b  illustrate a first method of operating the distributed telecommunication network illustrated in FIG.  10 . When a telephone call is placed, the line is seized and the digits are dialled in step S 140 . When the local exchange  1  receives the dialled digits, the SSF generates a query message and logical address for the local SCF  11  and passes it to the local SCF  11  in step S 141 . The local SCF  10  identifies the application in step S 142  and in step S 143  it is determined whether the flag for the application for the application is set or reset. If it is reset, in step S 144  the local SCF  11  invokes the application and in step S 145  the local SCF application queries the local SDF  12  for the requisite data. The local SDF  12  returns the data to the local SCF application in step S 146  and in step S 147  the local SCF application returns instructions to the SSF. The SSF then instructs the CCF in step S 148  and the CCF control the switch in step S 149 . 
     If in step S 143  it is determined that the flag for the application is reset, the call control is passed to an service transfer application in the local SCF  11  in step S 150 . The service transfer application then regenerates the query message and hunts in the remote local SCFs for a reset flag in step S 151 . When a reset flag is found in step S 152  the local SCF  11  service transfer application passes the query message to the remote local SCF  14  having the reset flag. The remote local SCF  14  then identifies and invokes the application in step S 153  and the remote local SCF application queries the remote local SDF  15  for the requisite data in step S 154 . The remote local SDF  15  then returns the requisite data to the remote local SCF application in step S 155 . The remote local SCF application then returns instructions to the SSF over the WAN in step S 156 . The SSF then instructs the CCF in step S 148  and the CCF controls the switch in step S 149 . 
     In this first method of controlling the network of FIG. 10, the flag for the applications are held in the local SCFs  11  and  14 . No flags are held for the data. 
     Referring now to FIGS. 12 a  and  12   b,  this flow diagram illustrates a second method of operating the telecommunication network illustrated in FIG.  10 . In this method the local SCFs  11  and  14  hold the flags for the applications and the local SDFs  12  and hold the flags for the data. 
     Referring now to FIG. 12, when a telephone call is placed, the line is seized and the digits are dialled in step S 160 . When the local exchange  1  receives the dialled digits, the SSF generates a query message and logical address for the local SCF  11  and passes it to the local SCF  11  in step S 161 . The local SCF  11  then identifies the application which is to be run in step S 162  and in step S 163  the flag or marker for the application is examined to determine if the flag or marker is set or reset. If the flag is reset, the local SCF  11  invokes the application which is the subject of the query from the SSF in step S 164 . The local SCF application queries the local SDF  12  for data in step S 165 . The flag or marker for the data is then examined in step S 166  and if this is reset a data valid message is returned to the local SCF application in step S 167 . The data is then returned to the local SCF application in step S 168  and in step S 169  the local SCF application returns instructions to the SSF in the local exchange  1 . The SSF then instructs the CCF in step S 170  and in step S 171  the CCF controls the switch to form the required switching paths. 
     If in step S 163  it is determined that the flag of the application is set, i.e. the application is out of date, the call control is passed to a service transfer application in the local SCF  11  in step S 173 . Similarly, if the flag for the data is determined to be set in step S 166 , indicating that the data is out of date, a data invalid message is returned to the local SCF application in step S 172  and call control is passed to a service transfer application in the local SCF  11  in step S 173 . The service transfer application then regenerates the query message and hunts the remote local SCFs  14  for a reset flag for the application in step S 174 . In step S 175  when a reset flag for the application is found the service transfer application passes the query message to the remote local SCF  14  having the reset flag. The remote local SCF  14  then identifies and invokes the application in step S 176 . The remote local SCF  15  application then queries the remote local SDF  15  for the requisite data in step S 177  and the remote local SDF returns the data. to the remote local SCF application in step S 178 . In step S 179  the remote local SCF application then returns instructions to the SSF of the local exchange  1 . The SSF then instructs the CCF in step S 170  and the CCF control the switch in step S 171 . 
     Referring now to FIGS. 13 a  and  13   b,  this flow diagram illustrates a third method of operating the telecommunication network illustrated in FIG.  10 . In this method instead of using flags, the applications in the local SCFs  11  and  14  are marked with version numbers. When one of the local SCFs  11  or  14  is updated, the SMF  16 , in addition to sending the updated application to the local SCF  11  or  14  also sends a version number to the SSF in the local exchange  1 . 
     Thus referring to FIG. 13, when a telephone call is placed, the line is seized and the digits are dialled in step S 180 . When the local exchange  1  receives the dialled digits, the SSF generates a query message and logical address for the local SCF  11  and sends with this message and address the latest version number of the application to be invoked in step S 181 . In step S 182  the local SCF  11  identifies the application and in step S 183  the version number for the application is compared with the version number transmitted from the SSF. In step S 184  it is determined if the version number of the application in the local SCF  11  is the latest version. If it is the local SCF  11  then invokes the application in step S 185  and the local SCF application then queries the local SDF  12  for the requisite data in step S 186 . Data is then returned to the local SCF application in step S 187  and the local SCF application returns instructions to the SSF in step S 188 . The SSF then instructs the CCF in step S 189  and the CCF controls the switch in step S 190 . 
     If however in step S 184  it is determined that the version number of the application in the local SCF  11  is not the latest version number, call control is passed to an service transfer application in the local SCF  11  in step S 191 . The service transfer application then regenerates the query message and hunts the remote local SCFs for the latest version umber in step S 192 . When the latest version number is found in a remote local SCF  14 , the service transfer application passes the query message to the remote local SCF  14  which has the latest version number for the application which is the subject of the query from the SSF of the local exchange  1  in step S 193 . In step S 194  the remote local SCF  14  then identifies and invokes the application and the remote local SCF application queries the remote local SDF  15  for the requisite data in step S 195 . In step S 196  the remote local SDF  15  returns the data to the remote local SCF application and the remote local SCF application returns instructions to the SSF of the local exchange  2  in step S 197 . The SSF then instructs the CCF in step S 189  and the CCF controls the switch in step S 190 . 
     Referring now to FIG. 14, this flow diagram illustrates a method of updating the applications and data in the local SCFs  11  and  14  and local SDFs  12  and  15  respectively. In step S 220  the customer changes the application and/or data in the SMF  16 . The SMF  16  then updates a selected local SCF and/or SDF in step S 221 . The SMF  16  then sends a set flag command to the rest of the local SCFs and/or SDFs in step S 222 . The local SCFs and/or SDFs identify and set the flag for the application and/or data as appropriate in step S 223 . The local SCFs and/or SDFs then return a verification message to the SMF in step S 224 . 
     Thus in this method of updating the local SCFs and local SDFs in the distributed network, one local SCF and/or SDF is updated initially and the others are updated by the SMF at a later date when traffic over the WAN allows. An alternative method of performing the update would be to include a management application in each local SCF such that once it had received an update from the SMF  16 , the management application then proceeded to send updated information to one or more others of the local SCFs. This option reduces the central processing requirements but increases the local processing requirements. 
     Also, in this distributed network, an alternative method of marking the application and/or data would be to not only mark the application and/or data as being out of date but also provide a pointer as to where the updated application and/or data can be found in the distributed network i.e. the address of the updated SCF and/or SDF. This method removes the requirement to hunt through the network to locate the updated SCF and/or SDF. 
     In the distributed network, as for the centralised network embodiment, the markers for the applications and/or data can be stored in the local SCF, or the local SDF. Also, the markers can comprise simple flags, version numbers, or for applications or data the address of the applications or data which is out of date can be deleted from a local SCF or SDF respectively. Any combination of these markers can be used for the applications and data in both the centralised and distributed network embodiments. 
     Further, although the embodiments of the present invention have been described with reference to the CS- 1  standard, the present invention is not limited to this standard and is applicable to any intelligent telecommunication network. 
     Although specific embodiments have been described hereinabove with reference to the drawings, the present invention is not limited to these embodiments and modifications which fall within the scope of the present invention will be clear to a skilled person in the art.