WO2001022657A1

WO2001022657A1 - Triggering of intelligent network service

Info

Publication number: WO2001022657A1
Application number: PCT/FI2000/000814
Authority: WO
Inventors: Heikki Salovuori
Original assignee: Nokia Networks Oy
Priority date: 1999-09-23
Filing date: 2000-09-22
Publication date: 2001-03-29
Also published as: FI19992040A; AU7294000A; EP1131918A1; CN1327664A

Abstract

A connection (Y) between a first network node (DXT) not comprising an intelligent network service switching function and a second network node (SSP) comprising an intelligent network service switching function is divided into at least two parallel buses (V1, V2, V3) for pretriggering an intelligent network service from the first network node (DXT). An intelligent-network-specific meaning is defined for each bus (V1, V2, V3). In addition, service data is maintained to indicate whether an intelligent network service is needed and to indicate, directly or indirectly, the bus to be used. When processing a call set-up request the first network node (DXT) uses the service data to check whether an intelligent network service is needed in the call and, if it is, the node sets up the call from the first network node to the second network node using a first bus indicated in the service data, the intelligent-network-specific meaning of the first bus being that intelligent network service is needed.

Description

TRIGGERING OF INTELLIGENT NETWORK SERVICE

BACKGROUND OF THE INVENTION

The present invention relates to the triggering of an intelligent network service and particularly to the pretriggering of an intelligent network service from a network node which does not comprise a switching function for intelligent network services.

In telecommunications networks intelligence refers to the ability to access stored data, to process the data and to make decisions based on the data. Even present telecommunications networks, such as public switched telephone networks PSTN, are to some extent intelligent, since they are capable of processing stored data for routing a call, for example. A typical 'intelligent' facility in present telecommunications networks is conditional call forwarding in which the call situation must be analysed and the call forwarded according to a stored call forwarding service profile. Intelligent facilities of this kind have, however, been an inseparable part of the basic network, and therefore the changing and adding of facilities has required software updating, for example, in all network switching centres.

An intelligent network is a network architecture attached to a basic network (fixed or mobile network, for example), which enables faster, easier and more flexible implementation and control of services. This is achieved by moving service control away from the switching centre to a separate functional unit in the intelligent network. Hereinafter, this unit will be referred to as a Service Control Point SCP. This allows the services to be made independent of the operation of the basic network, and the structure and software of the basic network need not be altered when services are changed or added. Network nodes responsible for intelligent network interfaces are called service switching points SSP, and they contain at least a service switching function SSF and a call control function CCF. The call control function CCF is not a function related to the intelligent network, but a standard switching centre function comprising high-level call processing functions of the centre, such as the set-up and release of transmission links. The service switching function SSF provides the interface between the call control function CCF and the service control point SCP. A network node comprising the service switching function SSF detects for example call set-up events that may trigger an intelligent network service. An intelligent network service is triggered when certain pre-determined conditions are met. The SSP is a network node which is typically responsible for connection set-up, such as a switching centre in a basic network or in a mobile communications system. In this application the service switching point SSP is equal to the functional entity formed by the CCF and the SSF, so the term SSP will be used hereinafter.

A problem with the above described arrangement is that it is not reasonable to arrange an intelligent service switching function in all network nodes, such as switching centres, or exchanges (PABX, PBX) participating in call routing, even if the network nodes might need to influence an intelligent network service related to a call or to use one. A problem that arises from this is that the desired service is not obtained. The problem can be partly solved by routing all calls to a switching centre where the service switching function is available. However, this loads the SSP extremely. This routing causes an unnecessary load on the network, too, because calls are routed through the SSP even when it is not necessary. Moreover, the routing of every call through the SSP prolongs the call switching time unnecessarily. Additional problems may arise if the network node and the SSP are network elements of different systems and employ different codings. This may lead to unnecessary multiple coding, which impairs speech quality and causes longer delays.

BRIEF DESCRIPTION OF THE INVENTION

It is therefore an object of the invention to provide a method and an equipment implementing the method so as to allow the above problems to be solved. The objects of the invention are achieved with a method for pretriggering an intelligent network service from a first network node which does not comprise a switching function for intelligent network services and which has a connection to a second network node that comprises an intelligent network service switching function, the method being characterized in that the method comprises the steps of dividing the connection between the first network node and the second network node at least into two parallel buses; defining an intelligent-network-specific meaning to both the at least two parallel buses; maintaining service data available to the first network node, the data indicating the need for an intelligent network service and indicating, directly or indirectly, the bus to be used; receiving a call set-up request in the first network node; using the service data in the first network node to check whether an intelligent network service is needed in the call the call set-up request relates to; and, if an intelligent network service is needed, setting up the call from the first network node to the second network node using a first bus indicated in the service data, the intelligent-network-specific meaning of the first bus denoting that there is a need for an intelligent network service. In this application, call set-up comprises at least the relaying of the signalling data associated with call control.

The invention further relates to a telecommunications system comprising a first network node for switching calls to or from a subscriber in the telecommunications system, the first network node not comprising an intelligent network service switching function; and a connection from the first network node to a second network node comprising the intelligent network service switching function. The telecommunications system is characterized in that the connection is divided into at least two parallel buses, an intelligent- network-specific meaning being defined for the at least two parallel buses; the system is arranged to maintain service data that indicates a need for an intelligent network service and indicates, directly or indirectly, the bus to be used; and the first network node is arranged to use the service data to check, in response to a call set-up request, whether an intelligent network service is needed and to set up the call to the second network node, in response to a need for the intelligent network service, on the bus indicated in the service data.

The invention still further relates to a network node for switching calls to or from a subscriber in a telecommunications network, the network node not comprising an intelligent network service switching function and the network node being arranged to communicate with a second network node which comprises an intelligent network service switching function. The network node is characterized in that it is arranged to communicate with the second network node at least on two parallel buses, an intelligent-network-specific meaning being defined for the at least two parallel buses; to use service data maintained in the telecommunications system, the service data indicating a need for an intelligent network service and indicating, directly or indirectly, the bus to be used; to check, in response to the call set-up request, whether an intelligent network service is needed and to set up, in response to a need for the intelligent network service, the call to the second network node using the bus indicated in the service data. The invention also relates to a network node comprising an intelligent network service switching function. The network node is characterized in that it is arranged to communicate with a second network node at least on two parallel buses, an intelligent-network-specific meaning being defined for the at least two parallel buses; and to detect on the basis of a bus used by a call coming from the second network node whether an intelligent network service is needed in the call; and to initiate the triggering of the intelligent network service, in response to the call received on the bus indicating that an intelligent network service is needed. The invention is based on detecting a call where an intelligent network service is needed at a lower level switching centre and on pretriggering the service by routing the call on a specific bus towards a switching centre comprising an intelligent network service switching function and thereby capable of triggering the service needed. For this purpose, a plural number of parallel buses are arranged between the switching centre comprising the intelligent network service switching function and a lower level switching centre, or an exchange, each of the buses having its specific intelligent-network-service-related meaning. One of the buses preferably has a meaning indicating that intelligent network service is not needed. To detect that a call needs an intelligent network service, service data is arranged into the lower level switching centre, or the centre has access to the service data. The switching centre comprising intelligent network services detects whether an incoming call needs an intelligent network service on the basis of the bus used by the call. Depending on the embodiment, the centre may even identify the intelligent service required.

In this application, a lower level centre refers to a switching centre, or a similar network node, which does not comprise an intelligent network service switching function.

A call in which an intelligent network service is needed refers in this application also to a call in which the service is possibly needed, the actual need for the service being not established until the call reaches the SSP.

An advantage of the invention is that an intelligent network switching function does not need to be arranged in all network nodes and still the availability of intelligent network services can be ensured by applying selective routing, which saves the intelligent network capacity. In a preferred embodiment of the invention, service data is maintained in a subscriber data register, such as an HLR. This embodiment offers an additional advantage in that it allows the implementation of the invention, i.e. the pretriggering, to be easily carried out. Another advantage of this embodiment is that the service data is easy to manage, flexible to modify and it is available in an identical form to all lower level switching centres that may need it.

According to another preferred embodiment of the invention, the connection between a lower level switching centre and the SSP is divided into buses, at least some of which are virtual ones. A further advantage of this embodiment is that it allows a specific bus to be determined for each intelligent network service and/or combination of services, which allows a very specific and efficient pretriggering to be obtained.

According to yet another preferred embodiment of the invention a call in which an intelligent network service is needed is set up as a pseudo call between the lower level switching centre and the switching centre where the intelligent network service is available. An advantage of this is that the network is not unnecessarily loaded by routing the call through the switching centre providing the intelligent network service switching function during the entire duration of the call. If the pseudo call is set up as signalling messages, then the call itself does not need to be routed through the switching centre providing the intelligent network service switching function at all.

The preferred embodiments of the method, system and network node of the invention are disclosed in the accompanying dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in greater detail in connection with preferred embodiments and with reference to the accompanying drawings, in which

Figure 1 is a block diagram illustrating a schematic view of a telecommunications system of a first preferred embodiment of the invention;

Figure 2 is a flow diagram illustrating the operation of a network node in the first preferred embodiment of the invention;

Figure 3 is a flow diagram illustrating the operation of a network node in a second preferred embodiment of the invention; and Figure 4 illustrates signalling between the network node and the SSP in the first preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention and its background are described in the following with reference to the present structure of intelligent networks and the intelligent network terminology laid down in the ETS 300 374-1 CorelNAP standard, but the invention can be used equally well in intelligent network structures and similar application platforms implemented according to other intelligent network standards (such as ANSI, AIN or WIN). In this application, intelligent network refers generally to a solution where a node SSP containing an SSF functionality and transmitting a call, session or packet data contacts the service control function which provides the node with instructions associated with the transmission of the call, session or packet data. The node contacts the service control function on the basis of service trigger data available to the node. Characteristic features of the intelligent network comprise triggers, state models and control protocols or an API (Application Protocol Interface) between the control function and the SSP. The transmission of a call, session or packet data may be defined in the SSP using a state model visible to the control function, the state model comprising steps and detection points associated with the steps where the processing of the call can be halted so as to wait for instructions from the control function. The control and the operations may also consist of methods applied to call instances and event notifications associated with the methods. In this application the term 'call' refers not only to a conventional call but also to other, possibly virtual, connection states associated with transmission of user data, such as data sessions, packet data or speech items alone, if a call is processed as separate speech items in the telecommunications system. Examples of a call include a packet radio session (such as a GPRS session), VoIP session (Voice over IP), multimedia sessions according to H.323 and speech items of the TETRA system or another similar system.

In the following the invention will be described in greater detail assuming that the network node which does not comprise the service switching function is a digital radio network exchange DXT of the TETRA (TErrestrial Trunked Radio) standard defined by the ETSI (European Telecommunications Standards Institute), without, however, limiting the invention to this particular solution. The TETRA standard defines standards for example for interfaces to other networks, air interfaces and interfaces to other TETRA standard networks. The TETRA standard does not, however, define how intelligent network services can be utilized, which makes the TETRA network most suitable as an example. In addition, the TETRA standard defines diverse subscriber data because a network conforming to the TETRA standard is meant to be used by public authorities, for example.

Figure 1 shows those parts of the structure of a telecommunications system 1 of the TETRA standard and the structure of an intelligent network IN that are relevant to the understanding of the invention. Since the internal structure of the Switching and Management Infrastructure SwMI has not been defined in the TETRA standard, only one solution is described herein by way of example. The network infrastructure will be hereinafter also referred to as a transmission network. A mobile station MS communicates with a base station BS over a radio path. Each base station BS is coupled with a connecting wire to one of the TETRA exchanges DXT (Digital Exchange for TETRA) in the fixed transmission network, the exchange being shown in Figure 1. TETRA exchanges DXT are coupled with a fixed connection to other exchanges DXT (not shown in Figure 1) and to a Digital Central Exchange for TETRA DXTc (not shown in Figure 1) to which other exchanges DXT and/or other node exchanges DXTc are connected to provide alternative traffic routes. The TETRA standard defines various alternative interfaces, such as interfaces to the public switched telephone network PSTN, other public land mobile networks PLMN, the integrated services digital network ISDN, private automatic branch exchanges PABX and the packet data network PDN.

In the example shown in Figure 1 , a connection Y between the exchange DXT and the intelligent network IN service switching point SSP is divided into three buses V1, V2 and V3. An intelligent-network-specific meaning is defined for each bus; in other words, each bus corresponds to a desired functionality, which means, at its simplest, information about whether a call includes the option for triggering an intelligent network service. The buses allow the necessary information to be transmitted in accordance with standards defined for telephone technology, which enables unpleasant surprising consequences to be avoided. The number of buses available determines to what extent the intelligent-network-specific meaning of the bus is service-specific. For example, the buses can be given the following meanings: bus V1 is a bus used for routing a call not associated with an intelligent network service; bus V2 is a bus associated with a call forwarding service, calls including a call forwarding option being routed to this bus; and bus V3 is a bus used for calls associated with another intelligent network service option, i.e. bus V3 is a bus associated with all other intelligent network services. In this case bus V2 is a service-specific bus and on the basis of the bus the switching point detects that a call forwarding service is concerned and starts to trigger the service. Naturally the values provided by the user are not changed; for example, if a call forwarding request does not contain a number to which the calls are to be forwarded, such a number is not added there. Any number of buses needed may be defined. A minimum requirement, however, is two buses, one of which is used in connection with all intelligent network services and the other when the call is not associated with an intelligent network service, but it is to be routed via the SSP because it is addressed to a GSM mobile station, for example. It is also possible that some of the buses are physical buses and other virtual ones. A virtual bus may be formed either directly, by means of signalling, or via a packet protocol of a gateway between an IP telephony router and a PSTN exchange or a call processing server, for example. In the packet protocol, the virtual bus may be established for example by means of a connection identifier. Virtual paths allow a specific bus to be allocated to each intelligent network service and even to various service combinations, which in turn ensures precise and efficient pretriggering.

The intelligent network IN service switching point SSP is connected to the intelligent network service control point SCP which is responsible for providing the intelligent network service. In connection with an intelligent network service, a service logic program is initiated at the service control point SCP, the operation of the service logic program defining the instructions that the SCP sends to the SSP at each stage of the call. In the example of Figure 1 , the SSP is a mobile services switching centre located in the pan-European Global Mobile Communications System GSM to which an intelligent network service switching function has been added. The SSP could equally well be an exchange in another wireless or fixed network, such as the PSTN, or a server in an IP network, through which call-related signalling is routed. The lower level network node and the SSP may also be exchanges located in one and the same system or even in one and the same network. On the basis of the bus selected, the SSP separates the calls that the lower level exchange DXT considers will need an intelligent network service from the ones where the exchange considers intelligent network services are not needed. Depending on how the buses have been defined, the SSP may even preferably identify the service to be triggered on the basis of the bus in use. In other words, the buses provide a method conforming to the standard for indirectly transmitting information associated with intelligent network service trigger conditions between two exchanges. A minimum information element is that the call is routed to the SSP on a bus associated with an intelligent network service. Usually a bus not associated with an intelligent network service, such as bus V1 , does not exclude the possibility that one of the SSP's own trigger conditions is met and an intelligent network service triggered. In this case the service in question is one that is not needed in the lower level switching centre. It is also possible to define a bus such that an intelligent network service is never triggered for the calls routed on the bus. The system 1 also comprises subscriber registers, at least a home location register HLR and a visitor location register VLR not shown in Figure 1. Subscriber data are permanently or semi-permanently stored in the home location register HLR of the system. Most of the subscriber data in the home location register are loaded (copied) into the visitor location register of the switching centre in the area of which the mobile station MS is located. Both of the registers may be separate network nodes, registers decentralized into exchanges DXT or node exchanges DXTc, or a register centrally integrated into one of them. In a system 1 implemented in a very small scale the home location register HLR may be all that is needed, the register then functioning like a VLR. It is not essential how the registers have been implemented as long as the exchange DXT finds for example the subscriber data needed in routing.

The TETRA system 1 network nodes shown in Figure 1 are interconnected via a signalling network SS7. A standardized ISDN Primary Access ISDN PRA is used between the TETRA exchange DXT and the GSM mobile services switching centre acting as the SSP. The SSP and the SCP usually employ I NAP signalling in their reciprocal data transfer. However, the invention is not limited to networks and signalling methods of this type, but other networks and signalling alternatives, such as ATM and IP, may also be used. The telecommunications system providing the functionality of the present invention comprises, in addition to the means needed for implementing the prior art services, means for connecting the lower level network node with the intelligent network service switching function on two or more buses, and means for selecting a bus associated with an intelligent network service and to route a call from the lower level network node to the network node comprising an intelligent network switching function when the call requires an intelligent network service, and means for identifying such a call. Current network nodes comprise processors and memory that can be utilized in the functions of the invention. All modifications required in order to implement the invention can be carried out as added or updated software routines, by defining various parameters, as lists and/or using application specific integrated circuits (ASIC).

In the first preferred embodiment of the invention this functionality has been implemented by maintaining a list of the buses at each TETRA exchange. The first preferred embodiment of the invention assumes that if the subscriber has subscribed to an intelligent network service A, all the subscriber's calls are always routed on the bus reserved for service A to the SSP, where the routine checks whether the conditions for the triggering of service A are met. Usually the bus alone is sufficient for triggering the service. Each bus is given a specific index, and the indexes of the services available to the subscriber are stored in the home location register in the form of service data associated with the intelligent network service subscriber concerned. On the basis of the indexes the exchange is able to find out the bus/buses used in connection with the services of the subscriber in question. Instead of indexes, also other similar keys may be used. The subscriber data of subscribers to which the intelligent network service is not available or who have not subscribed to the service do not contain the index. If the index is missing, the exchange routes the subscriber's service towards the network node SSP which contains the intelligent network service switching function using a bus not associated with an intelligent network service only if the call is to be routed towards the SSP any way. The service data is preferably maintained in the subscriber data because it is then always copied into the visitor location register and its updating and modification is simple and flexible. Moreover, intelligent network services are usually subscriber-specific, which means that all services are not necessarily available to all subscribers. For example, subscribers in the TETRA system may be divided into classes which determine the actions the subscriber is allowed to take.

In a preferred embodiment of the invention the index can also be added to the subscriber data of a subscriber who does not have an intelligent network service at his/her disposal. Such an index can then be associated with conditional bus data, for example, i.e. if the call is to be routed towards the SSP, a bus not associated with an intelligent network service is to be used (bus 1 in the example of Figure 1).

According to a preferred embodiment of the invention the bus to be used is given as the service data in the subscriber data. If the bus is missing, the call is routed as in the prior art towards the destination address, and if it is to be routed towards the SSP, a bus not associated with intelligent network services is used.

In a preferred embodiment of the invention, the service data is formed of service data added to the call control and service data included in the subscriber data. The service data added to the call control comprises the criteria set for the subscriber and a condition which causes the call to be routed to the bus associated with the respective service when the condition is met. The service data added to the call control relates to those intelligent network services, such as call forwarding, that have a same condition (such as the entering of specific codes) for all subscribers that meet the defined criteria. The service data may appear in the subscriber data either in the form of an index or directly as a bus. The service data may be added to the call control for example by adding it to the program code and/or by maintaining lists of the subscriber's buses and the criteria and conditions set to the subscriber in the lower level network node.

In a preferred embodiment of the invention the service data is added only to the call control and it comprises all the criteria set to the subscriber. According to this embodiment for example all the phone numbers dialled by the caller that begin with 456 can be routed to the SSP using a bus associated with an intelligent network service.

In the above embodiments, the subscriber data need not appear in the home location register. It is sufficient that the subscriber data is available for use to the lower level exchange and that it can be easily complemented as required by the invention. Figure 2 illustrates the operation of the lower level network node in the first preferred embodiment of the invention where a pseudo call is established to the intelligent network service switching point when necessary. The pseudo call will be described in greater detail in connection with Figure 4. In the first preferred embodiment of the invention, the network node is one of the TETRA network exchanges DXT. For the sake of simplicity it is assumed that there is only one index in the subscriber's service data. Also for the sake of simplicity it is assumed that the lower level network node is connected to only one network node SSP comprising the intelligent network service switching function. It is further assumed that the intelligent network service needed in this case is one that is implemented by a single request-reply pair (transaction).

With reference to Figure 2, a call set-up request is received from the subscriber in step 201 , the identifier of the caller, i.e. subscriber A, being separated from the request in step 202. In the first preferred embodiment receipt from the subscriber means that the call set-up request arrives from a lower level in the network hierarchy and not from node on the same level or a higher level. This ensures that the call is handled only once (the principle of a single call handling process). There are other embodiments in which this can be ensured in a different way. The known identifier of subscriber A will be used in step 203 for searching the subscriber data for service data. The subscriber data is retrieved from the visitor location register serving the exchange, the data being loaded there from the home location register. In the TETRA system, a visitor location register is usually integrated into the exchange DXT, in which case the information retrieval is an internal operation of the network node. In step 204 is checked whether the service data comprises an index. If it does, then the routine proceeds to step 205 to find out the bus indicated by the index and in step 206 a call is set up to the SSP using the bus indicated by the index. The SSP thereby receives an indication of a call that requires an intelligent network service and it may start to trigger the intelligent network service. In step 207 is then checked whether the call would have had to be routed towards the SSP any way. If the call is not addressed in the direction of the SSP, then the routine waits in step 208 a reply from the SSP, the reply being received in step 209. After the reply has been received, the connection between the SSP and the DXT is released and the routine proceeds in step 211 by routing the call to the right direction, as if the call was one that is not associated with a need for an intelligent network service. If the service involved several transactions, then the connection SSP-DXT would not be released. Information indicating whether the call is to be released or not may be added to the bus data, for example. If the call is to be routed to the SSP in any case (step 207), then the routine proceeds to step 212 and allows the SSP to continue the call set-up. In other words, the call between the DXT and the SSP is not released after the reply has been received.

If it is detected in step 204 that the service data is not provided with an index, the routine checks in step 213 whether the call is to be routed towards the SSP. If it is, then the call is set up to the SSP in step 214 using a bus the intelligent-network-specific meaning of which is "no intelligent network service". The bus is used for informing the SSP that there is no need for intelligent network services in the TETRA network for the call. This allows unnecessary triggering of intelligent network services to be avoided in the SSP, but it continues to route the call towards (the called) subscriber B. It is naturally possible that the SSP's own trigger conditions are met and the intelligent network service is triggered, but in that case the service concerned is one for which the triggering does not need to be controlled in the TETRA network. If the routing does not take place towards the SSP (step 213), the call is routed forward normally in step 215, i.e. in accordance with the prior art.

If the exchange is connected to several SSPs, the routine could check after step 210 whether the call is forwarded to another SSP. If it is, then a bus not associated with an intelligent network service is used in that direction.

Call set-up requests arriving (transmitted) from a higher level or the same level of the network hierarchy are handled as calls not provided with indexes.

If the subscriber's subscriber data includes a plural number of indexes and thereby a plural number of buses, the service control logic will be responsible for selecting the right bus in the preferred embodiment. The service control logic may be one where each subscriber has a similar bus table, and when a plural number of indexes is concerned, the routine looks up point i in the table which shows the bus for the desired triggering. This bus is used in step 206. If there is no bus in point i, the processing of the call continues in a usual manner. In embodiments where a connection already set up is not released any more, but the call is routed, for example, always through the SSP (i.e. subscriber A - DXT - SSP - DXT - subscriber B) steps 207-212 are not carried out. In embodiments where the subscriber's service data indicates the bus directly, step 205 shown in Figure 2 is skipped.

In embodiments where all the calls are not routed through the SSP, but the service data of each subscriber contains either an index/indexes or a bus/buses, the check in step 204 is omitted. Instead, the routine checks after steps 205 and 203 whether the intelligent-network-specific meaning of the bus to be used is "no intelligent network service". It is, then the routine proceeds to step 213 and if not, then the process continues from step 206.

In embodiments where all the calls are routed through the SSP and the service data of each subscriber contains either an index/indexes or a bus/buses, the check in step 204 and the steps 213-215 are omitted, and the call is always set up on the indicated bus.

In embodiments where the need for the intelligent network service is examined in greater detail in the network node, i.e. the mere possibility that the need exists is not enough, as in the first preferred embodiment, the need for the service is checked for example in step 205 and if the need exists, the service is routed using the bus indicated by the index. The need may be analysed for example by adding a condition or conditions to the subscriber's service data, the condition being met when an intelligent network service is needed. The conditions may also be included in the definitions of each bus. Figure 3 shows the operation of the lower level network node in the second preferred embodiment of the invention. The second preferred embodiment of the invention assumes that the call control comprises service data which includes both the criterion set to the subscriber and the condition causing the call to be routed to the SSP on a bus triggering the intelligent network service. For the sake of clarity, the example in Figure 3 assumes that the subscribers have only one intelligent network service, i.e. call forwarding, at their disposal and therefore only two buses are used. One of the buses is associated with the call forwarding and the other is used for calls not associated with the intelligent network service. Also for the sake of clarity, it is assumed that the lower level network node is only connected to one network node SSP comprising the intelligent network service switching function. With reference to Figure 3, a call set-up request is received in step 301 from the subscriber, the telephone number of the caller, i.e. subscriber A, being separated from the request in step 302. The identifier of subscriber A being now known, the routine checks in step 303 whether the subscriber meets a predetermined criterion. In this example we assume that the telephone numbers of all the subscribers who have an intelligent network service at their disposal begins with 45. Consequently, the routine checks in step 303 whether the number of subscriber A begins with 45. If it does, then the subscriber meets the criterion and the routine proceeds to step 304 to check whether a condition is met. In the example of Figure 3 the condition is that instead of the telephone number of subscriber B (subscriber B being the called party), initial call forwarding codes must be entered. This example assumes that the initial code is #22#. If the call set-up request comprises an initial code, the condition is met and the call is routed in step 305 to the SSP on a service bus associated with an intelligent network service. On the basis of the bus the SSP identifies that intelligent network service is needed and starts to trigger the service.

If the number of subscriber A does not begin with 45 (step 303), or the call set-up request does not comprise the initial code #22# (step 304), the routine proceeds to step 306 where it is checked whether the call is to be routed towards the SSP. If it is, then the call is set up to the SSP in step 307 using a bus the intelligent-network-specific meaning of which is "no intelligent network service". On the basis of the bus, the SSP identifies the call as a call in which no need for intelligent network service has been detected in the TETRA network and continues to route the call towards subscriber B (the called party). It is naturally possible that the trigger conditions of the SSP are met and the intelligent network service is triggered, but in that case the triggering of the service concerned does not need to be controlled in the TETRA network. If the call is not to be routed towards the SSP, it is routed normally in step 308, i.e. in the prior art manner.

Also in the second preferred embodiment of the invention call setup requests arriving (transmitted) from a higher or the same level of hierarchy are handled as calls where intelligent network services are not needed, in accordance with the principle of the single call handling process. Figure 3 shows a highly schematic example of the use of the criteria and the conditions. However, a person skilled in the art will find it apparent to apply the embodiment of Figure 1 in connection with various services, more complicated criteria, conditions, deduction logics and/or a plural number of different buses.

In embodiments where a separate condition has not been defined, the check in step 304 is omitted.

In embodiments where service data is included in both call control and subscriber data, the steps shown in Figures 2 and 3 are combined. One way to combine the operations (steps) is not to proceed to step 307 shown in Figure 3 but to step 203 in Figure 2. There are also other ways of combining operations.

The order of the steps shown in Figures 2 and 3 may deviate from the above description, or the steps may be carried out as parallel operations. Between the steps can also be other steps not shown in the Figures. Furthermore, some of the steps shown in the Figures can be left out, for example step 205 where the bus indicated by the index is searched for, is skipped in embodiments in which the service data included in the subscriber data indicates the bus directly.

Figure 4 illustrates signalling in the first preferred embodiment of the invention. For the sake of clarity, the example in Figure 4 assumes that subscriber A, i.e. the calling party, is an intelligent network service subscriber, the subscriber data of which has already been loaded from the home location register HLR to the visitor location register VLR. It is also assumed that the conditions for triggering the service are met at the SSP/MSC and that the intelligent network service needed is one which is implemented by a single request-reply pair (transaction). An example of such a service is number conversion. It is further assumed that the call is addressed to another subscriber located in the TETRA network, i.e. there is no need to route the call through the SSP/MSC. In this example, the messages between the mobile station MS, the exchange DXT and the visitor location register VLR used by subscriber A are messages of the signalling system SS7 adopted into the TETRA, and the signalling messages between the DXT and the SSP/MSC are ISDN PRA messages. If the VLR is integrated into the exchange DXT, the data transfer takes place within the node, thereby allowing also other messages to be used. The invention is not, however, limited to these messages and protocols, but other protocols and messages may also be used for transmitting the same information. The information is most preferably transmitted in messages according to the standard.

With reference to Figure 4, subscriber A makes a phone call using his/her mobile station MS. The MS sends a signalling message 4-1 to the exchange DXT where it requests for call set-up. After having received the signalling message 4-1 , the exchange DXT separates the identifier of subscriber A from the message and requests for subscriber data from the visitor location register VLR in a message 4-2. The VLR sends the subscriber data in a message 4-3. In the first preferred embodiment of the invention, the message 4-3 contains a new parameter which is the service data index. The DXT uses the index to search (step 4-4) for a bus corresponding to the index and sends a message 4-5 to the SSP/MSC. The message 4-5 comprises parameters that may be needed for triggering an intelligent network service, the parameters being preferably given in connection with the bus data. The parameters are not obligatory, but if they are used, they are preferably parameters included in the protocol used (such as the PRA). It is also possible to use new, not standardized parameters, but then changes have to be made to both network nodes (DXT and SSP). On the other hand, non-standard parameters allow the operation to be optimized. The SSP/MSC receives the message 4-5 and detects (step 4-6) on the basis of the bus (IN bus) that the event concerned is associated with an intelligent network service. The SSP/MSC therefore starts (step 4-6) to check the trigger conditions and since they are met, the SSP/MSC triggers the intelligent network service and transmits the service. The service is activated in the SCP in a fully normal manner and the SCP does not know that it is serving a TETRA subscriber. When the service has been completed, the SSP/MSC sends the DXT a reply message 4-7 which in the case of a number conversion service, for example, contains the converted number. After having received the message 4-7, the DXT releases (step 4-8) the connection DXT- SSP/MSC and continues to route the call.

If the call is associated with a plural number of transactions, in the first preferred embodiment the call is routed through the SSP during the entire duration of the call.

The DXT uses the message 4-5 to set up a pseudo call to the SSP/MSC. The most simple way to carry this out is to actually connect the pseudo call to the SSP/MSC, but after the intelligent network service the call is dropped back to the DXT, whereby the speech links and codings between the DXT and the SSP/MSC are removed. Another way to set up a pseudo call is not to connect the call, but to only transmit the information in standard signalling messages. However, it is non-standard to leave the call unconnected, therefore in that case minor software changes are required in the SSP. The pseudo call is most advantageous in single transaction services such as the number conversion service.

The signalling messages described above in connection with Figure 4 are only examples and may contain even a plurality of separate messages for transmitting a single piece of information, in addition to which the messages may contain other information as well. Furthermore, the messages can be freely combined. Depending on the operators and the system, also other network elements containing different decentralized functions may participate in the data transmission and the signalling. In IP telephony, and in other similar traffic where signalling is transmitted in separate elements and even on separate routes than the actual speech or data, at least the signalling controlling the call is routed through the SSP either during the entire duration of the call or only during the intelligent network service, depending on the embodiment. Although the invention is described above with reference to subscriber A, the ways in which the invention can be applied to intelligent network services of subscriber B are apparent to a person skilled in the art. Further, the above embodiments and/or their characteristics may be combined to produce new embodiments conforming to the invention. Although the invention is described above using a mobile communications network as an example, the invention is not restricted to the switching centres of radio networks or other wireless networks, but a person skilled in the art will find it apparent to apply the invention using other telecommunications systems both in networks based on wireless data transmission and in fixed networks comprising lower level switching centres or similar network nodes, such as different exchanges. The invention is particularly advantageously applied together with VoIP technique where virtual buses are easy and simple to create.

It is to be understood that the above description and the related drawings are only intended to illustrate the present invention. It will be apparent to those skilled in the art that many variations and modifications can be made to the invention without departing from the scope and spirit of the invention disclosed in the attached claims.

Claims

1. A method for pretriggering an intelligent network service from a first network node which does not comprise a switching function for intelligent network services and which has a connection to a second network node that comprises an intelligent network service switching function c h a r a c t e r i z e d in that the method comprises the steps of dividing the connection between the first network node and the second network node at least into two parallel buses; defining an intelligent-network-specific meaning to both the at least two parallel buses; maintaining service data available to the first network node, the data indicating the need for an intelligent network service and indicating, directly or indirectly, the bus to be used; receiving (201 , 301) a call set-up request in the first network node; using the service data in the first network node to check (204, 303,

304) whether an intelligent network service is needed in the call the call set-up request relates to; and, if an intelligent network service is needed, setting up (206, 305) the call from the first network node to the second network node using the first bus indicated by the service data, the intelligent-network-specific meaning of the first bus denoting a need for an intelligent network service.

2. A method according to claim ^ c h a r a c t e r i z e d in that the method further comprises the step of setting up the call that requires the intelligent network service from the first network node to the second network node as a pseudo call.

3. A method according to claim 1 or 2, c h a r a c t e r i z e d in that the method further comprises the steps of determining that at least one of the at least two parallel buses is a second bus; determining that the intelligent-network-specific meaning of the second bus is that no intelligent network service is needed; and if intelligent network services are not needed in the call, checking (213, 306) whether the call is to be routed towards the second network node; and if so, setting up (214, 307) the call from the first network node to the second network node using the second bus.

4. A method according to claim 1, 2, or 3, characterized in that the method further comprises the steps of initiating the triggering of the intelligent network service in the second network node in response to a call set-up received from the first bus; and routing the call forward in the second network node in response to the call set-up received from the second bus.

5. A method according to any one of the preceding claims, characterized in that the method further comprises the steps of maintaining subscriber data which are available to the first network node; and maintaining at least part of the service data in the subscriber data.

6. A method according to any one of the preceding claims, characterized in that at least some of the service data is maintained in the first network node.

7. A method according to any one of the preceding claims, characterized by transferring the signalling associated with the call and the contents of the call in different elements; and setting up the call from the first network node to the second network node by forming at least a signalling connection between the first and the second network node.

8. A telecommunications system (1) comprising a first network node (DXT) for switching calls to or from a telecommunications system subscriber, the first network node (DXT) not comprising an intelligent network service switching function; and a connection (Y) from the first network node to a second network node (SSP) comprising the intelligent network service switching function, characterized in that the connection (Y) is divided into at least two parallel buses (V1,

V2, V3), an intelligent-network-specific meaning being defined for the at least two parallel buses; the system (1) is arranged to maintain service data that indicates a need for an intelligent network service and indicates, directly or indirectly, the bus to be used (V1 , V2, V3); and the first network node (DXT) is arranged to use the service data to check, in response to a call set-up request, whether an intelligent network service is needed, and to set up the call to the second network node, in response to a need for the intelligent network service, on the bus (V1, V2, V3) indicated in the service data.

9. A telecommunications system (1) according to claim 8, characterized in that the first network node (DXT) is further arranged to check, in response to the need for an intelligent network service, whether the call is to be routed towards the second network node; and if the call is not to be routed towards the second network node, to set up the call as a pseudo call.

10. A telecommunications system (1) according to claim 9, characterized in that the first network node (DXT) is further arranged to form the pseudo call by connecting the call from the first network node (DXT) to the second network node (SSP) and to release the pseudo call in response to the accomplishment of the intelligent network service performance.

11. A telecommunications system (1) according to claim 9, characterized in that the first network node (DXT) is further arranged to set up the pseudo call by transmitting information to the second network node (SSP) in signalling messages; and the second network node (SSP) is arranged to process the pseudo call.

12. A telecommunications system according to any one of the preceding claims 8 to 11, characterized in that the intelligent-network- specific meaning of at least one bus (V1, V2, V3) is that intelligent network services are not needed.

13. A telecommunications system according to any one of the preceding claims 8 to 12, characterized in that the second network node (SSP) is further arranged to check on the basis of the bus whether an intelligent network service is needed in the call and to initiate the triggering of the intelligent network service in response to a call received from a bus indicating that the service is needed.

14. A telecommunications system according to any one of the preceding claims 8 to 13, characterized in that at least some of the buses (V1 , V2, V3) are virtual buses.

15. A telecommunications system according to any one of the preceding claims 8 to 14, characterized in that the system (1) is further arranged to maintain at least some of the service data in the subscriber data (HLR) of the system.

16. A telecommunications system according to any one of the preceding claims 8 to 15, characterized in that the first network node (DXT) is a network node in the first telecommunications system (1); and the second network node (SSP) is a network node in a second telecommunications system.

17. A telecommunications system according to any of the preceding claims 8 to 16, cha racterized in that the system is further arranged to transfer call-related signalling and the contents of the call in separate elements; and the first network node is further arranged to set up the call to the second network node by establishing at least a signalling connection to the second network node.

18. A network node (DXT) in a telecommunications system network for switching calls to or from a subscriber in the telecommunications network, the network node (DXT) not comprising an intelligent network service switching function and the network node being arranged to communicate with a second network node which comprises an intelligent network service switching function, characterized in that the network node is arranged to communicate with the second network node at least on two parallel buses, an intelligent-network-specific meaning being defined for the at least two parallel buses; use service data maintained in the telecommunications system, the service data indicating a need for an intelligent network service and indicating, directly or indirectly, the bus to be used; to check, in response to a call set-up request, whether an intelligent network service is needed and to set up, in response to a need for the intelligent network service, a call to the second network node using the bus (V1 , V2, V3) indicated in the service data.

19. A network node (DXT) according to claim 18, characterized in that the network node (DXT) is further arranged to check, in response to the need for the intelligent network service, whether the call is to be routed towards the second network node; and, if the call is not to be routed towards the second network node, to set up the call as a pseudo call.

20. A network node (DXT) according to claim 19, characterized in that the network node (DXT) is arranged to set up the pseudo call by connecting the call from the network node to the second network node and to release the pseudo call in response to the completion of the intelligent network service performance.

21. A network node (DXT) according to claim 19, characterized in that the network node (DXT) is arranged to set up the pseudo call by transmitting information in signalling messages to the second network node.

22. A network node (DXT) according to any one of the preceding claims 18 to 21, characterized in that the network node (DXT) comprises at least some of the service data.

23. A network node according to any one of the preceding claims 18 to 22, characterized in that the network node (DXT) is an exchange according to the TETRA standard.

24. A network node (SSP) comprising an intelligent network service switching function, characterized in that the network node (SSP) is arranged to communicate with the second network node at least on two parallel buses, an intelligent-network- specific meaning being defined for the at least two parallel buses; and to identify on the basis of the bus used by the call coming from the second network node whether intelligent network services are needed in the call and to initiate the triggering of the intelligent network service in response to a call received from a bus indicating that an intelligent network service is needed.