TELECOMMUNICATION NETWORK

Abstract: Method for use in a telecommunications network comprising local exchanges, LE, and transit exchanges, TE, with IN "Service Switching Points", SSPs, and "Signalling Control Points", SCPs. If in the LE to which a B subscriber is connected a first parameter is set which indicates that the B subscriber is subscribed to an IN service and therefore a query in the SCP has to be carried out, the call is interrupted by a Release message to the SSP and the SSP makes the SCP to carry out the requested service. The call is afterwards routed back to the LE accompanied by a second parameter, indicating that the said first parameter should not be read out and interpreted a second time. If for establishing connections between A and B subscribers use is made of ISUP IAM signalling messages, the "NatureOfAddress" field in the "CalledPartyNumber" parameter of the ISUP IAM message can be used for setting of the second parameter.

Description: Telecommunication network BACKGROUND OF THE INVENTION The invention relates to a telecommunications network comprising local exchanges and transit exchanges as well as IN functions. 'Intelligent Networks', IN, is a widespread method to implement different services in a PSTN or ISDN. The IN concept enables fast and flexible service creation to an operator without the necessity of large investments in the 'installed base' and a long implementation time. In most operational PSTN and ISDN networks the topology consists of a number of hierarchical levels , in particular the level of the local exchanges, LE, via which network users have access to the network, and all other exchanges, referred to as TE, transit exchanges. In order to offer IN possibilities in the public network, the existing switching equipment must be provided with a 'Service Switching Point' , SSP, through which calls are offered to the IN. In other words, the SSP can be considered as a gate to the IN service logic. Before the network operator can introduce IN in his network, he has to make a choice where that SSP has to be implemented. In the topology with more hierarchical layers , the network operator can choose whether he shall put the SSP in the LE layer, in the TE layer, or in both. In existing telecommunication networks it can be like this that the SSP can only be made available at the TE level because of the fact that some local exchanges (LEs) are not modern enough to be able to be provided with SSP or because the investments involved are too high. If the SSP can only be implemented at the TE level, some services cannot or not completely be offered with IN technology. An example of this is ' Incoming Call Barring Service ' , ICBS . There is thus a need for a generic mechanism for introducing IN at the central (TE) level without loss or decrease of functionalities . SUMMARY OF THE INVENTION The following acronyms are being used: IAM: Initial Address Message IN: Intelligent Network LE: Local Exchange TE: Transit Exchange ISUP: ISDN User Part REL: Release Message SCP: Signalling Control Point SSP: Service Switching Point In order to solve the problem of only being able to put the SSP at the TE level, the present invention uses a mechanism that is known per se (see references), the 'Query on Release' or 'Call Drop Back' mechanism, which can, among others, be used in the implementation of number portability. According to the invention however, that mechanism is combined with an additional parameter in the ISUP IAM following the REL operation. First a description will be given of the previously mentioned 'Query on Release' mechanism. A call is routed from the LE from the A subscriber via one or more TEs in the network to the LE of the B subscriber. The call is presented according to the regular ISUP IAM operation. In the LE the user profile of the B subscriber is read out. From this it is detected that the B subscriber is subscribed to a certain IN service. The LE of the B subscriber sends an ISUP RELease message with a CauseValue parameter with a value 'IN Service Requested' . The call is then stepwise broken down to the TE level where the SSF can intervene in the call. The TE that receives the REL message has an IN 'trigger' in the SSP at the event 'incoming REL message with CauseValue=' IN Service Requested 1 '. The TE then hands over the call control to the SCP, which carries out the service. This mechanism is known as 'Query on Release' or 'Call drop back'. For instance, a 'call forwarding unconditional' can be implemented in that way. The SCP instructs the SSP in the TE to connect the A subscriber to the number that is set by (or on behalf of) the B subscriber in the IN database. As said, there are however a few services that cannot be offered in that way, for instance 'Incoming Call Barring', ICB. ICB is the service that enables a B subscriber to establish a 'black list' of numbers, which are not allowed to be put through to B. With an IN implementation that list resides in the IN database. The reason that ICB cannot be implemented in that way, is that if the number of the A subscriber is not on the black list, the SCP would send a 'Continuous' signal, after which the TE would want to establish the call again on the basis of the B number to the LE of the B subscriber. This LE would then respond again with the REL message (it is namely the same LE of which the call in the first instance was disrupted) . For services like ICB the problem is in the fact that after carrying out the Query, the call is presented to the same physical line. That causes a repeated activation of the 'Query on Release' . To escape this problem the SCP has continually to consider whether the call should be presented to the same physical line (e.g. ICB and A subscriber not on black list) or another physical line (e.g. Call Forwarding). If the call has to be presented on the same physical line, the SCP has to instruct, according to the invention, the SSP to fill in a parameter field in the ISUP IAM message with a special new value, hereafter indicated as 'IN service executed'. From that parameter field the LE can deduce that the Query has already taken place and can the LE of the B subscriber as a result of this deny the parameter ' IN service subscribed' of the B subscriber. Preferably, the 'NatureOfAddress' field in the 'CalledPartyNumber' parameter of the ISUP IAM message is used for setting the presented 'IN service executed' parameter. EXEMPLARY EMBODIMENTS Figure 1 shows the course of the ISUP signals on establishing a connection between two subscribers that are connected to different local exchanges . Figure 2 shows the same , but for a connection between two subscribers at the same local exchange. In Figure 1 a subscriber A makes a call to a subscriber B. To this end, the former dials the number (1) of the B subscriber, which in the local exchange LE is converted into an ISUP Initial Address Message (2), which is passed on by the transit exchange TE (3) to the local exchange LE to which the subscriber B is connected. If there in said local exchange it appears from the profile database of subscriber B that the latter is subscribed to an IN service, the LE transmits a RELease signal (4) to the SSP of the TE. That REL signal triggers the SSP to carry out an IN Query (5) in the SCP database, resulting in an IN Response (6). Thereafter, a new IAM is sent to the LE of subscriber B, in which by the SSP a new parameter value has been entered in the NatureOfAddress field of the CalledPartyNumber, which is interpreted by the LE as denying the IN service parameter for that particular IN service. The rest of the user profile, in which can be referred to other IN services, is still read out. Then the call is put through to the B subscriber. Figure 2 shows the signalling course of a call between two subscribers that are connected to the same LE. In Figure 2 a subscriber A makes a call to a subscriber B. To this end, the latter chooses the number (1) of the B subscriber. If it appears from the profile database of subscriber B that the latter is subscribed to an IN service, the LE transmits an IAM signal (2) to the SSP of the TE, with a particular attribute that it concerns here an IN service . As an example for this a prefix can be used, which is inserted before the B number in the CalledPartyNumber parameter. This attribute triggers the SSP to carry out an IN Query (3) , after which the rest proceeds identically to the description in Figure 1. REFERENCES US5602909 US5610977

Claims: CLAIMS 1. Method for use in a telecommunications network comprising local exchanges, LE, and transit exchanges, TE, with IN 'Service Switching Points', SSPs, and 'Signalling Control Points', SCPs , wherein, if in the LE to which a B subscriber is connected, a first parameter is set, indicating that the B subscriber is subscribed to an IN service and therefore a query in the SCP has to be carried out, the call is interrupted by a RELease message to the SSP and the SSP makes the SCP to carry out the requested service, c h a r a c t e r i s e d in that the call, afterwards, is routed back to the LE, accompanied by a second parameter, indicating that said first parameter should not be read out and interpreted for a second time. 2. Method according to claim 1, in which, for establishing the connections between A and B subscribers , use is made of ISUP IAM signalling messages, c h a r a c t e r i s e d in that the 'NatureOfAdddress' field in the 'CalledPartyNumber' parameter of the ISUP IAM message is used for setting said second parameter. 3. Method according to claim 1, characterised in that per IN service an own pair of first and second parameter is used.

Inventors: BARNARD HERMAN JOHANNES, WIND BERNARDUS CORNELIS FREDER, BARNARD, HERMAN, JOHANNES, WIND, BERNARDUS, CORNELIS, FREDERIK
Applicants: BARNARD HERMAN JOHANNES, KONINKL KPN NV, WIND BERNARDUS CORNELIS FREDER, BARNARD, HERMAN, JOHANNES, KONINKLIJKE KPN N.V., WIND, BERNARDUS, CORNELIS, FREDERIK
Application year: 1999
Main classification: H04Q3
IPC codes: H04M3, H04Q3