RADIO SYSTEM FORMING A WIRELESS SUBSCRIBER INTERFACE

Abstract: A radio system providing a wireless subscriber interface comprising subscriber stations (1, 2, MS) and a network element (4) comprising means for transmitting telecommunication signals between the subscriber stations and a fixed telephone network exchange (3), whereby the system comprises a subscriber station (1, 2) consisting of a radio unit (6) and a fixed telephone network telecommunication terminal (5) connected to the radio unit. In order to route a local call correctly even when the subscriber does not dial an area code, the network element (4) comprises a register (10) including the fixed telephone network area code corresponding to the location (A, B) of the subscriber station (1, 2). In addition, the network element (4) comprises means for retrieving an area code from the register (10) and for adding it as a prefix to the number dial transmitted from the subscriber station (1, 2) in connection with call set-up if the number dial transmitted from the subscriber station (1, 2) does not include an area code.

Description: RADIO SYSTEM FORMING A WIRELESS SUBSCRIBER INTERFACE The invention relates to a method of transmitting a number dial from a subscriber station of a radio system providing a wireless subscriber interface to an exchange in a fixed telephone network, in which method a number dial transmitted from a subscriber station is received. The invention also relates to a radio system providing a wireless subscriber interface and comprising subscriber stations and a network element comprising means for transmitting telecommunication signals between subscriber stations and an exchange in a fixed telephone network, the system comprising at least one subscriber station consisting of a radio unit and a telecommunication terminal connected to a fixed telephone network radio unit. The invention further relates to a network element of a radio system providing a wireless subscriber interface, the element comprising means for transmitting telecommunication signals between subscriber stations and an exchange in a fixed telephone network. The present invention relates to a radio system providing a wireless subscriber interface, i.e. a WLL system (Wireless Local Loop), wherein telephone sets are connected by a radio connection through base stations and a WLL network element to the exchange of a public switched telephone network (PSTN). Any kind a conventional telecommunication terminal of a fixed tele- phone network can be connected to the WLL system through a special terminal, the radio path being transparent to the user. A problem with known WLL systems is that in systems where the network element is connected to the fixed public switched telephone network (PSTN) via a trunk network, an upper layer trunk exchange cannot route a lo- cal call correctly if the number dial transmitted from a subscriber station does not include an area code. This means that if an attempt is made to make a local call (to e.g. the next building) from a WLL subscriber station located physically within the area code area of a fixed network, the call is incorrectly connected if the number dial does not include the area code of that specific area. The object of the present invention is to solve the above problem and provide a method wherein a local call made from a WLL subscriber station is connected correctly also when the user does not key in an area code in connection with the number dial. This goal is achieved with the method of the invention, characterized in that the received number dial is tested for an area code; if an area code is not included, a predetermined area code is prefixed to the number dial, and the number dial is forwarded to the exchange of the fixed network. The invention also relates to a system to which the method of the invention can be applied. The system of the invention is characterized in that the network element comprises a register including a fixed telephone network area code corresponding to the location of the subscriber station comprising said fixed network telecommunication terminal, and that the network element comprises means for retrieving said area code from the register, and for prefixing it to the number dial transmitted from the subscriber station in connec- tion with the set-up of a call originating from the subscriber station if the number dial transmitted from the subscriber station does not include an area code. The invention further relates to a network element for implementing the method of the invention, and which can be utilized in the system of the invention. The network element according to the invention is characterized in that it comprises a register including a fixed telephone network area code corresponding to the location of predetermined subscribers stations, and that the network element comprises means for retrieving said area code from the register, and for prefixing it to the number dial transmitted from a predetermined subscriber station in connection with the set-up of a call originating from the subscriber station if the number dial transmitted from the subscriber station does not include an area code. The invention is based on the idea that when a WLL system connected to a fixed telephone network via a PSTN exchange uses a subscriber station register in which the parameters of each WLL subscriber include, be- sides other parameters, information on the PSTN area code corresponding to the physical location of a subscribe station, the network element can retrieve the necessary area code from said data base and add it as a prefix to the local number dialled. Information on the local area code of a WLL subscriber may be input into the register from the system network management centre. The most significant advantage of the solution according to the invention is that a local call is routed correctly without the subscriber having to add an area code to the number dial, the WLL system even in this aspect functionally corresponding better to the operation of a conventional fixed telephone network, and the radio path is more effectively made transparent to the user. In a preferred embodiment of the invention, the radio system consists of a mobile telephone system, such as a GSM system, connected to the trunk exchange of a fixed telephone network, and the network element consists of a mobile telephone exchange. In this case both the mobile stations of the mobile telephone system and the WLL subscriber stations may utilize the mobile telephone system. In this case, information stating which subscriber stations are WLL subscriber stations and information on the area codes of the PSTN local directory area may be stored in the VLR register (Visitor Location Register) of the mobile telephone exchange. This embodiment of the invention allows efficient utilization of the mobile telephone system, because in this case there is no need to construct a separate WLL system in the geographic area covered by the mobile telephone system, but instead the calls of WLL subscriber stations, too, may be switched through the mobile telephone system. In addition, one can be certain that local calls made by WLL subscribers are correctly connected even if the number dial does not include an area code. The preferred embodiments of the method, system, and network element according to the invention are disclosed in the attached dependent claims 2, 4 to 6, and 8 to 9. The invention will be described in more detail below by means of a preferred embodiment with reference to the attached Figure 1 showing a block diagram of a first preferred embodiment of the system according to the inven- tion. In the case of Figure 1 , the WLL system has been implemented as a part of a GSM mobile telephone system (Groupe Speciale Mobile), whereby the same radio system can be used to switch both mobile station MS calls and WLL subscriber station 1 and 2 calls. In addition to the case in Figure 1 , the solution according to the invention may naturally be applied to some other mobile telephone system, e.g. an NMT or DCS system (Nordisk Mobil Telefon, Digital Cellular System), or alternatively in a WLL system exclusively designed for switching WLL subscriber station calls. In the case of Figure 1 , a mobile telephone exchange 4 of a mobile telephone system serves as the network element of the WLL system, the exchange being connected to a PSTN network trunk exchange 3. The mobile telephone exchange is in connection with the subscriber stations MS, 1 , and 2 of the radio system via base station controllers BSC and base stations BTS. The mobile telephone exchange 4 comprises a VLR register for maintaining information on mobile stations "temporarily" roaming the geographical area covered by the system in accordance with GSM specifications. In accordance with the invention, the VLR register also serves as the subscriber station register 10 of the WLL system, i.e. information on the WLL subscriber stations 1 and 2 utilizing the mobile telephone system of Figure 1 is stored in said register. In the case of Figure 1 , the WLL subscriber stations are physically located in the areas A and B of the different directory areas of the fixed telephone network. Both of the WLL subscriber stations 1 and 2 consist of a conventional telecommunication terminal 5 of a type used in fixed telephone networks, such as a telephone, a telefax terminal or a computer/modem combi- nation linked to a WLL terminal 6 by means of a two-wire line. The terminal 6 comprises signal processing means for adapting the speech path to the radio channel. Such signal processing means include e.g. a radio part comprising an antenna, a radio transmitter and a radio receiver, and a teleadapter for adapting the radio part to a conventional telecommunication terminal 5 of a fixed telephone network. In the case of Figure 1 , the subscriber station 1 uses radio signals to communicate with a base station 7 via which calls are switched through the base station controller BSC to the mobile telephone exchange and further to the trunk exchange 3 of the PSTN network (Public Switched Telephone Net- work), i.e. a fixed telephone network. In accordance with the invention the parameters of the WLL subscriber stations are stored in the VLR register 10 of the mobile telephone exchange 4. Said parameters also include information on the area code of the fixed PSTN local directory area corresponding to the location of a subscriber. The locations of the WLL subscriber stations are known because the WLL subscriber stations are installed permanently at specific locations, similarly as is a telephone 8 of the PSTN network. When a call is made from a WLL subscriber station 2 located in the area of the local directory area A to the telephone 8 of the PSTN network, the mobile telephone exchange 4 identifies it as a WLL subscriber station on the basis of the information in the VLR register. The mobile telephone exchange 4 then tests the number dial received from the subscriber station 2 for an area code. If the dialled number does not include an area code, i.e. in Finland, for example, this may be concluded by the first number of the dialled number series being between 2 and 8, the mobile telephone exchange retrieves from the VLR register 10 the area code stored therein for subscriber station 2; the area code corresponding to the area code of area A in the case of Figure 1. The mobile telephone exchange then adds the area code retrieved as a prefix to the number dial transmitted from the subscriber station before routing the call further. Thus, the call is switched from the trunk exchange 3 of the fixed telephone network via the PSTN network to the telephone 8. The mobile telephone exchange may retrieve the local number from the VLR register immediately having received a SETUP message from subscriber A, i.e. the subscriber station 2, this being the time when the mobile telephone exchange retrieves the other parameters of subscriber A from the VLR register. Call set-up from the GSM system to a fixed telephone network has been described in more detail in e.g. GSM specification part 09.09 (GSM 09.09 - Version 3.0.0. - point 3.2.2.1.1) and is hence not described in any more detail here. It is possible for the operator to key in manually the local area code of a WLL subscriber to the VLR register from an operation and maintenance centre 9 (O & M, Operations & Maintenance). Simultaneously a restriction should be made in the VLR register to the effect that the WLL subscriber station 2 must not register in the network in other parts than the area of said directory area. It is obvious that the above description and the related figures are only intended to illustrate the present invention. A variety of modifications and variations will be apparent to those skilled in the art without deviating from the scope and spirit of the invention disclosed in the appended claims.

Claims: CLAIMS 1. A method of transmitting a number dial from a subscriber station of a radio system providing a wireless subscriber interface to an exchange in a fixed telephone network, in which method a number dial is received from a subscriber station, characterized in that said method comprises testing the received number dial for an area code, adding a predetermined area code as a prefix to the number dial if an area code is not included, and forwarding the number dial to the exchange of the fixed network. 2. A method as claimed in claim 1, characterized in that a fixed telephone network area code corresponding to the location of the subscriber station which transmitted the dial is added as a prefix to the received number dial if the received number dial does not include an area code. 3. A radio system providing a wireless subscriber interface and comprising subscriber stations (1, 2, MS) and a network element (4) comprising means for transmitting telecommunication signals between subscriber stations (1, 2) and an exchange (3) in a fixed telephone network, the system comprising at least one subscriber station (1, 2) consisting of a radio unit (6) and a telecommunication terminal (5) of a type used in fixed telephone net- works connected to said radio unit, characterized in that the network element (4) comprises a register (10) including a fixed telephone network area code for said subscriber station (1, 2) with a fixed network telecommunication terminal (5), said area code corresponding to the location (A, B) of the subscriber station (1, 2), and that the network element (4) comprises means for retrieving said area code from the register (10), and for adding it as a prefix to a number dial received from the subscriber station (1, 2) in connection with the set-up of a call originating from the subscriber station if the number dial received from the subscriber station (1, 2) does not include an area code. 4. A system as claimed in claim 3, characterized in that said fixed network telephone exchange is a trunk exchange (3) of the PSTN network. 5. A system as claimed in claim 3 or 4, characterized in that said radio system consists of a mobile telephone system, and that said net- work element (4) consists of a mobile telephone exchange, at least one of the system subscriber stations consists of a mobile station (MS). 6. A system as claimed in claim 5, characterized in that said mobile communication system is a GSM or DCS system, whereby said register (10) consists of the VLR register of the mobile telephone exchange (4), the register comprising the fixed telephone area code corresponding to the location of the station (1, 2) for each subscriber station (1, 2) comprising a telecommunication terminal (5) of a type used in fixed telephone networks. 7. A network element (4) of a radio system providing a wireless subscriber interface, the element comprising means for transmitting telecom- munication signals between subscriber stations (1, 2) and an exchange (3) in a fixed telephone network, characterized in that the network element comprises a register (10) including fixed telephone network area codes corresponding to the location (A, B) of predetermined subscribers stations (1, 2), and that the network element (4) comprises means for retrieving said area code from the register (10), and for adding it as a prefix to a number dial received from a predetermined subscriber station (1, 2) in connection with the set-up of a call originating from the subscriber station if the number dial received from the subscriber station (1, 2) does not include an area code. 8. A network element as claimed in claim 7, characterized in that said radio system consists of a mobile telephone system connected to a trunk exchange (3) of a fixed telephone network, the network element consisting of a mobile telephone exchange (4) of the mobile telephone system. 9. A network element as claimed in claim 8, characterized in that said mobile telephone system is a GSM or DCS system, and that said register (10) consists of the VLR register of the mobile telephone exchange.

Inventors: VIRTANEN ANU, VIRTANEN, ANU
Applicants: NOKIA TELECOMMUNICATIONS OY, VIRTANEN ANU, VIRTANEN, ANU
Application year: 1997
Main classification: H04Q7
IPC codes: H04M1, H04M3, H04W84