TELECOMMUNICATIONS SYSTEM AND METHOD RELATING TO TELECOMMUNICATIONS SERVICES WITH NUMBER TRANSLATION

Abstract: The present invention relates to a telecommunications system comprising a plurality of local and transit exchanges (TE) in which signalling and traffic data are routed between remote exchanges via a network service having routing code recalculation. Said telecommunications system is adapted to provide an ISDN End-to-End Supplementary Service involving an interaction between two subscribers in which a subscriber access code is generated by modification of a called subscriber routing code, used by said calling subscriber local exchange (LE). Said local exchanges (LE) which have an applications service element for providing said ISDN Supplementary Service, include a mechanism to trigger a query, which is sent to said translation means, whenever said Supplementary Service is requested and a subscriber routing code is detected. The subscriber access code thus returned from the translation means is forwarded to the applications service element, which, based on the received subscriber access code, will establish an end-to-end dialogue with it's counterpart at the called subcriber local exchange (LE) and provide said ISDN Supplementary Service. The invention enables the establishment of an unchained dialogue between the service elements in the local exchanges (LE) by introducing said trigger mechanism in the local exchange (LE) of the calling subscriber, thus accelerating and facilitating provision of said End-to-End Supplementary Service.

Description: Telecommunications System and Method Relating to Telecommunications Services with Number Translation The present invention relates to the implementation of certain telecommunications services, more particular to a telecommunications system in which such services can be implemented, a method of implementing such services and a local node (exchange) interacting with a transit node (exchange) of the ISDN or a Service Control Point SCP of the Intelligent Network IN for use in the implementation of such services . A CCBS (Completion of Calls to Busy Subscriber) Supplementary Service is one example of a subscriber service which uses end-to-end signalling, and in which the service is implemented by operations performed in both a calling subscriber local exchange and a called subscriber local exchange. Implementation of a CCBS service requires that the calling subscriber local exchange has knowledge of the called subscriber access code, as used in the called subscriber local exchange. Completion of Calls to Busy Subscriber is defined in ITU-T RECOMMENDATION 1.253.3 as follows: The completion of Calls to Busy Subscribers (CCBSs) Supplementary Service enables a calling user A, upon encountering a busy destination B, to be notified when the busy destination B becomes free and to have the service provider reinitiate the call to the specified destination B if user A desires. The CCBS Supplementary Service is applicable to users who are connected to the network via a basic access or a primary rate access. The CCBS Supplementary Service enables user A, upon encountering a busy destination B, to have the call completed without having to make a new call attempt when destination B becomes free. When user A requests the CCBS Supplementary Service, the network will monitor for destination B becoming free. When destination B becomes free, then the network will wait a short time as defined in the destination B idle guard timer in order to allow the resources to be reused for originating a call. If the resources are not reused by destination B within this time, then the network will automatically recall user A. When user A accepts the CCBS recall, then the network will automatically generate a CCBS call to destination B. GVNS (Global Virtual Network Service) is one example of a network service that modifies the routing code (dialled number) , with the result that there is no transparency through the network for the called subscriber access code, as used in the called subscriber local exchange. Global Virtual Network Service is defined in ITU-T RECOMMENDATION F.16 as follows: The Global Virtual Network Service (GVNS) is a multi-network international service which provides private network functions to users at geographically dispersed international locations while minimising the need for dedicated network resources. It may be offered to customers over the PSTN and/or ISDN. The Global Virtual Network Service is a feature-rich communications service. It provides the functions typically associated with the private networks, but utilising the public switched network(s). The GVNS Customer's network configuration is defined per the customer's direction using customer-specific service information resident in multiple networks. The network configurations may be administered by the GVNS Customer directly, the GVNS Participating Service Provider (s) and/or the GVNS Co-ordinator (s) . The GVNS provides the customers with global services as a result of internetworking among the GVNS Participating Service Providers in various countries. GVNS may accommodate this interconnection both via ISDN and non-ISDN facilities. Document [1] describes a solution to provide CCBS over GVNS for a telecommunications system comprising a plurality of local exchanges in which signalling and traffic data are routed between remote exchanges via a network service having routing code recalculation. Said network service includes a plurality of transit nodes, a method to provide a supplementary subscriber service involving an interaction between two subscribers in which: knowledge of a subscriber access code, used in a called subscriber local exchange, is required in a calling subscriber local exchange; said subscriber access code is generated by modification of a called subscriber routing code, used by said calling subscriber local exchange; and said modification occurs in a transit node of said network service. According to [1], said telecommunications system is characterised in that at least some GVNS transit nodes include a relay applications service element (see [1], Fig. 3, new CCBS- ASE) which is adapted to relay signalling data between local exchanges and which includes translation means for converting a subscriber access code used at a called subscriber local exchange into a called subscriber routing code used by a calling subscriber exchange, and in that signalling data is transmitted between said calling and said called local exchanges via said relay application service element CCBS-ASE in said GVNS transit node. For the backward direction (local exchange of the called subscriber to local exchange of the calling subscriber) the subscriber access code has to be translated into the called subscriber routing code and signalling data has to be transmitted between said called and said calling local exchanges via said relay application service element CCBS-ASE in said GVNS transit node. In addition to the requirement of said relay application service element CCBS-ASE in said GVNS transit node this solution requires resources such as Transaction IDs (Transaction Identifiers, see list 1, positions 24, 25 below). In the GVNS transit node, where two sections of an the end-to-end dialog are connected, all messages being part of this dialog have to pass through the complete protocol stack (up and down) which increases the propagation delay of those messages. The present invention solves the problem of providing CCBS over GVNS while avoiding above mentioned drawbacks. In order to overcome said problems an additional type of a CCBS-ASE as used in [1], Fig. 3, which provides indirect end- to-end chained dialogue between CCBS-ASEs in the local exchanges LE of the calling and the called subscriber, is avoided. Instead the invention provides a direct, unchained dialogue between the (CCBS-) ASEs (see [1], Fig. 1) by introducing a trigger mechanism in the Call Control Function CCF of the local exchange LE of the calling subscriber. In a further step said trigger mechanism is equipped with a memory unit, which at least temporarily retains the translated number. The invention has also application to interacting between any network service with routing code (dialled number) recalculation, referred to as number translation and any ISDN End-to-End Supplementary Service. With GVNS, as initially defined, there is nothing to prevent a terminating local exchange LE sending a CCBS possible indicator in the backward release message, since that exchange cannot distinguish between a normal call and a GVNS call. Thus, the CCBS possible indicator is repeated all the way back to the originating exchange. If no solution is found to this problem, all GVNS calls, for which CCBS is requested, will lead to unnecessary signalling procedures. The problem created by interaction between CCBS and GVNS will not be solved by simply omitting CCBS for GVNS calls. The CCBS request must either be prevented, or some means provided for handling it. The present invention is based on a telecommunications system comprising a plurality of local exchanges LE in which signalling and traffic data are routed between remote exchanges via a network service having routing code (dialled number) recalculation, referred to as number translation, which network includes a plurality of transit nodes and/or nodes of the intelligent network, said telecommunications system being adapted to provide an ISDN End-to-End Supplementary Service involving an interaction between two subscribers in which: knowledge of a subscriber access code, used in a called subscriber local exchange LE, is required in a calling subscriber local exchange LE; said subscriber access code is generated by modification (number translation) of a called subscriber routing code (dialled number) , used by said calling subscriber local exchange LE; and said modification (number translation) occurs in a transit node or in a Service Control Point SCP of said network service. According to a first aspect of the present invention said telecommunications system is characterised in: that the Call Control Function CCF in each local exchange LE comprises a trigger mechanism for providing access to the number translation function to allow for said Supplementary Service, that at least some transit nodes or Service Control Points SCP include an application for converting a subscriber routing code (dialled number) used by a calling subscriber local exchange LE into a called subscriber access code used at a called subscriber local exchange LE, - that converted number is sent back to the said calling subscriber local exchange LE and that in the calling subscriber local exchange LE the subscriber routing code (dialled number) is linked to the called subscriber access code. Preferably said ISDN End-to-End Supplementary Service is a CCBS service. Preferably said network service having routing code (dialled number) recalculation (number translation) is a GVNS service. Preferably said telecommunications system is a single unitary ISDN system. A CCBS-ASE may be located in each local exchange LE within said telecommunications system providing CCBS to subscribers connected thereto. Each of said plurality of transit nodes or Service Control Points SCP may be adapted, in use, to receive a request for number translation from a local exchange LE, providing CCBS to subscribers connected thereto, has an application for number translation located therein. Preferably said application is restricted to the number translation function. According to a second aspect of the present invention, there is provided a network service transit node or Service Control Point SCP, for use with the method specified above, characterised by: - said transit node or Service Control Point SCP includes receiving means for receiving signalling data transmitted from a calling subscriber local exchange LE, said data including the subscriber routing code (dialled number) ; converting means for converting said subscriber routing code (dialled number) to a subscriber access code; signal generating means for generating modified signalling data, from signalling data received by said receiving means, by substitution of said subscriber access code for said subscriber routing code (dialled number) ; and - transmitting means for transmitting said modified signalling data to said calling subscriber local exchange LE. Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 illustrates the network and protocol architecture for CCBS, Fig. 2 illustrates the network architecture for GVNS, realized as an IN-service (Figure 2a) and realized in a transit exchange TE supplemented by a GVNS-routing function (Figure 2b) , Fig. 3 illustrates the protocol architecture according to the present invention, for provision of CCBS over GVNS, Fig. 4 illustrates the functional entities involved, for provision of CCBS over GVNS and Fig. 5 illustrates the adaption in the CCF part of the existing protocol machine for the access signalling The present invention is described below with reference to the provision of CCBS over GVNS, but as explained above the invention has application to the interaction between other telecommunications services. In this specification a number of abbreviations and terms of the art are used. Their meanings are briefly explained in the list below. In column 2 reference is given to document [2] in which the used terms are shown and described in detail (C. : chapter) : List 1 In order to fully understand the present invention, it is necessary to consider the way in which CCBS is provided on the Public Switched Telephone Network/ ISDN and the way in which GVNS operates. CCBS is an ISDN End-to-End Supplementary Service in which, when the called subscriber is busy, a new call is established between the called subscriber and the calling subscriber as soon as the called subscriber's terminal equipment goes from the off-hook condition (busy) , to the on-hook (idle) condition. Operation of such a service requires a signalling relation between the local exchanges LE, which allows for an "end-to-end" TC based dialogue. Figure 1 shows the network and protocol architecture for the provision of CCBS as shown in [1], Fig. 1. CCBS operates by establishing a dialogue between CCBS-ASEs (CCBS-Application Service Elements) located in the local exchanges LE of the called and calling parties. The transit exchanges TE which may be, for example, trunk Telephone exchanges, are completely transparent to the signalling dialogue established between the two CCBS-ASEs. In other words, the transit exchanges TE do not change the information contained in the signalling data transmitted between CCBS-ASEs. The signalling system used to establish a call between the two local exchanges LE is in accordance with ISUP. The signalling system used at the access is e.g. DSS1. For the signalling data transmitted end-to-end a virtual path exists between the two CCBS-ASEs, as shown by the dotted line. It should be noted that the SCCPs (see list 1, pos. 23: signalling connection control part) in the transit exchanges TE do not effect the signalling data originating from the CCBS-ASEs. The signalling for the CCBS service is "end-to-end" between the CCBS-ASE containing a CCBS register and the CCBS-ASE containing a CCBS queue. This "end-to-end" signalling is a user of TC (list 1, pos. 25: Transaction Capability), the messages are routed through the network via SCCPs with normal public E.164 numbers, indicating a subscriber access at the local exchange LE. Interworking with Q.931 accesses, e.g. PBX, are possible but, in this case, the "end-to-end" information flow will not use TCs all the way. This does not, however, effect the information flow itself, only the medium and coding of the information. CCBS-ASEs do not exist in intermediate exchanges. The CCBS call indicator and the CCBS possible indicator are transmitted via ISUP. A CCBS request is a direct communication between a CCBS register in the originating CCBS-ASE, normally located in the calling subscriber local exchange LE and the CCBS queue in the destination CCBS-ASE, normally located in the called subscriber local exchange LE. The called party's E.164 number must not be manipulated when signalling data is transmitted between the two CCBS-ASEs, because the signalling is identified by this E.164 number and the CCBS register must know the called party number identifying the called party in the CCBS queue location. It should be noted that the following CCBS functions, among others, are also handled by the "end-to-end" signalling established between the CCBS register in the calling party's CCBS-ASE and the CCBS queue in the called party's CCBS-ASE: CCBS Cancel; CCBS Suspend; CCBS Resume; and Retain option None of these functions are dependant on signalling transparency between the two CCBS-ASEs. Figure 2a shows the network architecture for GVNS. One, or more of the transit exchanges TE may include a GVNS routing function, Figure 2b. The GVNS function may alternatively be provided in a Service Control Point SCP, Figure 2a. The GVNS routing function operates with database support and modifies the called subscriber routing code (dialled number) to make the call possible. The CCBS service uses the called party's E.164 number. This number is used in the CCBS register for later CCBS call setup, and in the CCBS queue for monitoring of the called subscriber and identification of the received CCBS call. If this were not done, the called subscriber in the original call, the CCBS request and the CCBS call cannot be tied to each other. Other signalling information used by the CCBS-ASE has no relevance to routing the CCBS messages through the network and is not affected by GVNS. The GVNS routing function manipulates the called party number. The GVNS routing function creates, by use of data received from a data base, the terminating network routing number instead of the terminating participating service provider identification. I.e. the originating local exchange LE and the destination local exchange LE are not aware of the same called party number. The basic problem for CCBS is that, for a GVNS call, the functional entities, where the CCBS register and the CCBS queue are located, do not identify the called subscriber with the same E.164 called party number. They are not aware of the number used at the remote location. Since the CCBS service is based on usage of the same number in the CCBS register and the CCBS queue, the service will not work over GVNS without additional procedures in either CCBS, GVNS, or both. The called party number used at the destination is known only by the terminating local exchange LE and by the GVNS routing function. Since the terminating local exchange LE does not know that the call is a GVNS call, (and, therefore, that special procedures should be applied) , the node with the GVNS routing function must send that number back to the originating local exchange LE, (or where appropriate the originating private network, PBX) , when the called user is busy, (or where there is congestion at the interworking point with private networks) . The only message sent in this call state is "REL" (list 1, pos. 19: REL, Release message). A new parameter, or the backward GVNS parameter with the addition of TNRN (which amounts to a new parameter) has to be added to the release message REL to carry this number. If the connected number is used, the originating local exchange LE will not know that special CCBS procedures will apply. In any case the connected number is not included in the REL message. If the called party number used at the destination local exchange LE can be received by the originating local exchange LE, this number could be used in the CCBS request, instead of the stored called party number, (i.e. the dialled number). The recall would work in these circumstances. When a CCBS call is set up, the originating local exchange LE may use the stored called party number (i.e. the dialled number) and not the received number (i.e. the number used at the destination and in the CCBS request operation) , since the number in the CCBS call set-up should be manipulated, in the same way as for the original call, in the GVNS routing function and the resulting called party number, received by the destination local exchange LE, will be the same as the number stored in the CCBS queue. If the converted number is used for the CCBS call from the originating local exchange LE, no request for number translation will be sent to the GVNS routing function, since the conversion in the GVNS routing function will not work, since it would be the wrong number used as input to the conversion. The solution to this problem, proposed by the present invention, is illustrated in Figure 3. A special trigger mechanism is provided in the Call Control Function CCF of the access signalling protocol entity. This mechanism will then initiate a request for a number translation. This will be done using the existing interface to IN, which can also be used, when the GVNS routing function or a Service Control Function SCF is not provided in a Service Control Point SCP but in a supplement to a transit exchange TE. For the communication between the local exchange LE and the GVNS routing function or the Service Control Function SCF the INAP protocol can therefore be used. Upon receiving the converted number from the GVNS routing function or the Service Control Function SCF the access signalling protocol entity will then inform the CCBS-ASE. From hereon normal CCBS procedures apply. Since the converted number is now available in the CCBS-ASE of the local exchange LE a "direct" end-to-end dialogue between the CCBS-ASEs involved can be established and maintained without modification of said ASEs. The use of the trigger mechanism solution means that no additions need to be made in the signalling protocols for GVNS and CCBS. The CCBS Supplementary Service realised in the local exchange LE is not affected at all. Thus, the interworking problem can be resolved, in accordance with the present invention, entirely within the access signalling protocol entity, without affecting the existing CCBS implementations. Until completion of a requested service (e.g. CCBS) the converted number will preferably be kept available by the Call Control Function CCF. In case of a calling subscriber connected to said local exchange LE a further number translation during the CCBS call could be avoided: as soon as the called subscriber has terminated his call (and is therefore no longer busy) the calling procedure can be resumed (execution of the CCBS call: the local exchange LE of the calling subscriber processes the circuit related call) while using the converted number which has been kept available in the Memory M of the Call Control Function CCF. In case of a calling subscriber connected to an PBX the CCBS call may enter the PSTN/ISDN via a local exchange LE different from the one that was involved in the CCBS dialog: since the converted number is not available in the CCF of this local exchange LE the normal procedure for circuit related call establishment applies. Figure 4 illustrates the functional entities involved, for provision of CCBS over GVNS. Process communication is taking place between the Call Control Function CCF and the Service Switching Function SSF contained in the local exchange LE of the calling subscriber, acting temporary as a Service Switching Point SSP on the one hand and between the Call Control Function CCF and the Application Service Element (e.g. for CCBS) on the other hand. The Application Service Element for CCBS, is the service handler for CCBS which, among other things, creates the signalling contents of the dialogue between two CCBS-ASEs, one in the local exchange LE of the A-Subscriber and one in the local exchange LE of the B-Subscriber. The Call Control Function CCF comprises a memory M in which the translated number is stored for future use. Figure 5 shows the changes in the protocol entity of the access signalling (described as a finite state machine) . Upon a CCBS request (CCBS req) from a subscriber, whose call reached a busy subscriber • the called number is analysed in a first step (nr- check) . • In a second step (tr-req) it is decided whether a number translation is required (e.g. : the called number is XX XX which must be converted to 031 - 322 XX XX) . • In case that number translation is not required a CCBS- ASE is invoked and the (called) number which is the actual number of the called subscriber, is forwarded to the CCBS-ASE. • In case that number translation is required a query is sent to the GVNS routing function. • Upon receipt of the new number (see Figure 5) the dialled number is replaced with the new number, stored in memory M and a CCBS-ASE is invoked and the converted number is forwarded to the CCBS-ASE. The inventive concept resides in introducing a mechanism that allows the reuse of existing means to query a database and a memory location for the converted number. The invention has application in all connection set-ups in which the following service combinations exist: completion of calls - GVNS; completion of calls - VPN; - completion of calls - free number group; completion of calls - personal number service; and - completion of calls - Intelligent Network Services having number recalculation in SCP The invention is not limited to completion of calls, but can be used for any ISDN End-to-End Supplementary Service using service logic distributed between two local exchanges LE, communicating with TC based dialogues in those cases where the services interact with other services performing B-number recalculation (number translation) . Literature [1] WO 97/17794 [2] P. Bocker, ISDN Das diensteintegrierende digitale Nachrichtennetz , Springer Verlag, Berlin 1990, Dritte Auflage [3] P. Bocker, ISDN - Digitale Netze fur Sprach-, Text-, Daten-, Video- und Multimediakommunikation, Springer Verlag, Berlin 1997, vierte Auflage

Claims: CLAIMS 1. A telecommunications system comprising a plurality of local exchanges (LE) in which signalling and traffic data are routed between remote exchanges via a network service having routing code recalculation (translation of a dialled number) , which network service includes a plurality of transit exchanges (TE) (nodes) or an access to a Service Control Point (SCP) of an Intelligent Network, said telecommunications system being adapted to provide an ISDN End-to-End Supplementary Service involving an interaction between two subscribers in which - knowledge of a subscriber access code, used in a called subscriber local exchange (LE) , is required in a calling subscriber local exchange (LE) ; - said subscriber access code is generated by modification of a called subscriber routing code (dialled number) , used by said calling subscriber local exchange (LE) ; and said modification occurs in a transit exchange (TE) (node) or in a Service Control Point (SCP) of the Intelligent Network of said network service, where translation means for converting a called subscriber routing code into a subscriber access code are available, each local exchange (LE) having an applications service element for providing said ISDN End-to-End Supplementary Service, said telecommunications system being characterised in that local exchanges (LE) which support the Supplementary Service include a mechanism to trigger a query, which is sent to said translation means, whenever said Supplementary Service is requested and a subscriber routing code is detected and that the subscriber access code thus returned from the translation means is forwarded to the applications service element, which, based on the received subscriber access code, will establish an end-to-end dialogue with it's counterpart at the called subscriber local exchange (LE) and provide said ISDN End-to-End Supplementary Service. 2. A telecommunications system as claimed in claim 1 characterised in that said trigger mechanism includes a memory location for the called subscriber routing code as well as for the called subscriber access code. 3. A telecommunications system as claimed in claim 2 characterised in that detection of subscriber routing code is done for every called number processed in the local exchange (LE) , that said query is triggered when a subscriber routing code is detected and that the subscriber access code returned from the translation means is also used for the establishment of circuit related traffic. 4. A telecommunications system as claimed in any of claims 1 to 3 , characterised in that said ISDN Supplementary Service is a CCBS service. 5. A telecommunications system as claimed in any of claims 1 to 4 , characterised in that said network service having routing code recalculation is a GVNS service. 6. A telecommunications system as claimed in any of claims 1 to 5 , characterised in that said telecommunications system is a single unitary ISDN system. 7. A telecommunications system as claimed in any of claims 1 to 6, characterised in that a CCBS-ASE is located in each local exchange (LE) within said telecommunications system providing CCBS to subscribers connected thereto and to subscribers connected to a private network, PBX. 8. A method for a telecommunications system comprising a plurality of local exchanges (LE) in which signalling and traffic data are routed between remote exchanges via a network service having routing code recalculation (translation of a dialled number) , which network service includes a plurality of transit exchanges (TE) (nodes) or an access to a Service Control Point (SCP) of an Intelligent Network, said telecommunications system being adapted to provide an ISDN End-to-End Supplementary Service involving an interaction between two subscribers in which knowledge of a subscriber access code, used in a called subscriber local exchange (LE) , is required in a calling subscriber local exchange (LE) ; - said subscriber access code is generated by modification of a called subscriber routing code (dialled number) , used by said calling subscriber local exchange (LE) ; and - said modification occurs in a transit exchange (TE) (node) or in a Service Control Point (SCP) of the Intelligent Network of said network service, where translation means for converting a called subscriber routing code into a subscriber access code are available, each local exchange (LE) having an applications service element for providing said ISDN End-to-End Supplementary Service, said telecommunications system being characterised in that local exchanges (LE) which support the Supplementary Service include a mechanism which triggers and forwards a query to said translation means, whenever said Supplementary Service is requested and a subscriber routing code is detected and that the subscriber access code thus returned from the translation means is forwarded to the applications service element, which, based on the received subscriber access code, will establish an end-to-end dialogue with it's counterpart at the called subscriber local exchange (LE) and provide said ISDN End-to-End Supplementary Service. 9. A method as claimed in claim 8 characterised in that detection of subscriber routing code is done for every called number processed in the local exchange (LE) , that said query is triggered when a subscriber routing code is detected and that the subscriber access code returned from the translation means is also used for the establishment of circuit related traffic. 10. A method as claimed in claim 8 or 9, characterised in that said ISDN End-to-End Supplementary Service is a CCBS service.

Inventors: GOLDSTEIN PETER, GOLDSTEIN, PETER
Applicants: GOLDSTEIN PETER, SIEMENS SCHWEIZ AG, GOLDSTEIN, PETER
Application year: 2000
Main classification: H04Q3
IPC codes: H04M3, H04Q3