IMPROVEMENTS IN, OR RELATING TO, COMMUNICATION SYSTEM

Abstract: A communication system for the transmission of a call from a first mobile communication network to a second mobile communication network including mobile customers with mobile stations (MS). Said system including means adapted to transmit calls, between these both mobile communication network while a conversation is in progress and that said network are operated by different telecommunication operators with its own Public Land Mobile Network (PLMN) and that said transmission is adapted to not losing ongoing calls when a customer with a MS passes into another operators Public Land Mobile Network (PLMN).

Description: Title. Improvements in, or relating to, communication system. Technical area. The invention relates to a communication system, including two mobile communications network which are adapted for the transmission of a call from a first mobile communication network to a second mobile communication network including mobile customers with mobile stations (MS) . Technical background. Roaming is the cellular communication function, which allows customers to use their telephones in networks other than their own. When a customer switch on his mobile station (MS) it begins to search for the strongest frequency it find and lock on it and begins to read the broadcasting information. It depends, however, on the network and the telephone using the same technology (e.g. a GSM telephone in a GSM network, a NMT telephone in a NMT network) . For roaming to be possible there has to be an agreement between the two operators involved. The agreement clarifies the conditions under which visiting customers may use the network, lays down the costs for using each others networks, and the service and functions in the network which the customer can take advantage of. The operator being visited sends information daily to the home operator to enable the customer's account to be debited for the services utilised in the host network. Technical problem. Customers that have the possibility to utilise several GSM P MNs (international or national roaming) will today lose ongoing calls when moving from one PLMN to another. One problem with this type of communication is that when a subscriber to the first network moves in to a second networks coveragearea it happens that the call will be cut because the subscriber moves a to long distance from the sending/transmitting equipment which take care of the transmission of the call to the subscriber. For the moment it exist no means that is able to switch an ongoing call from a first network to a second network when a subscriber is moving into another network which operates by a different telecommunicationoperator . It is an object of the present invention to provide a mobile communication system adapted to co-operate with one or several other network with means for continuous transmission of digital signals from one network to another network when a subscribers are, continuously talking, and the mobile station (MS) moves from a first network operated by first telecommunicationoperator into a second network operated by a second telecommunicationoperator. It is another object of the present invention to provide the means with functionality to co-operate with the Mobile stations so when a call is switched from one network to another network the subscriber shall be notified. The means for transfer of the call shall disturb the call which is a completely different problem according to transfer of calls in an operator owned network. It is an another object of the invention to create billing possibilities which gives the billing arrangement in one or both the co-operating network information that and when a transfer have been performed. Technical solution. In accordance with the invention the solution is what is stated in the claims. Advantages . For the customer to a operator it exist many advantages. For the first we mention that a call will not be closed down when the customer for example move in to another operators network. The customer will be notified when he comes in to the other network with a perhaps other taxes for the call so he can decide if he want to quit the call or proceed to talk. The foregoing and other features of the present invention will be better understood from the following description with reference to the accompanying drawings, in which: Figure 1 diagrammatically illustrates, in form of a block diagram a communication system according to the invention. In order to facilitate an understanding of the present invention a glossary of terms used in this patent specification is provided below: PLMN - Public Land Mobile Network (GSM Network) MSC Mobile services Switching Centre MS Mobile station SIM Subscriber Identity Module BTS Base Transceiver Station BSC Base Station Controller HLR Home Location Register VLR Visitor Location Register As is diagra matically illustrated in fig.l is a communication system and a first mobile communication network which is a GSM network and a second communication network which also is a GSM network. In the system we have a mobile subscriber, which have a mobile telephone MS. The different GSM-networks are operated by different telecommunication operators in the same or in different countries. All operators in one land have its own network, a "Public Land Mobile Network" (PLMN) . Both networks illustrated in the figure is composed of several equal functional entities but can be built by different manufactures. The GSM network can be divided into three broad parts. The Mobile Station is carried by the subscriber. The Base Station Subsystem controls the radio link with the Mobile Station. The Network Subsystem, the main part of which is the Mobile services Switching Center (MSC) , performs the switching of calls between the mobile users, and between mobile and fixed network users . The MSC also handles the mobility management operations. The mobile station (MS) consists of the mobile equipment (the terminal) and a smart card called the Subscriber Identity Module (SIM) . The SIM provides personal mobility, so that the user can have access to subscribed services irrespective of a specific terminal. The Base Station Subsystem is composed of two parts, the Base Transceiver Station (BTS) and the Base Station Controller (BSC) .. These communicate across the standardised Abis interface, allowing (as in the rest of the system) operation between components made by different suppliers. The Base Transceiver Station houses the radio transceivers that define a cell and handles the radio-link protocols with the Mobile Station. The Base Station Controller manages the radio resources for one or more BTSs. It handles radio-channel setup, frequency hopping, and handovers. The BSC is the connection between the mobile station and the Mobile service Switching Center (MSC) . The central component of the Network Subsystem is the Mobile services Switching Center (MSC) . It acts like a normal switching node of the PSTN or ISDN, and additionally provides all the functionality needed to handle a mobile subscriber, such as registration, authentication, location updating, handovers within the PLMN, and call routing to a roaming subscriber. These services are provided in conjuction with several functional entities, which together form the Network Subsystem. The MSC provides the connection to the fixed networks (such as the PSTN or ISDN) . Signalling between functional entities in the Network Subsystem uses Signalling System Number 7 (SS7) , used for trunk signalling in ISDN and widely used in. current public networks. The Home Location Register (HLR) and Visitor Location Register (VLR) , together with the MSC, provide the call- routing and roaming capabilities of GSM. The HLR contains all the administrative information of each subscriber registered in the corresponding GSM network, along with the current location of the mobile. The location of the mobile is typically in the form of the signalling address of the VLR associated with the mobile station. There is logically one HLR per GSM network, although it may be implemented as a distributed database. The Visitor Location Register (VLR) contains selected administrative information from the HLR, necessary for call control and provision of the subscribed services, for each mobile currently located in the geographical area controlled by the VLR. Although each functional entity can be implemented as an independent unit, all manufacturers of switching equipment to date implement the VLR together with - the MSC, so that the geographical area controlled by the MSC corresponds to that controlled by the VLR, thus simplifying the signalling required. MSC contains no information about particular mobile stations this information is stored in the location registers. Two other registers are used for authentication and security purposes. The Equipment Identity Register (EIR) is a database that contains a list of all valid mobile equipment on the network, where each mobile station is identified by its International Mobile Equipment Identity (IMEI) . In a cellular network, the radio and fixed links required are not permanently allocated for the duration of a call. Handover, is the switching of an on-going call to a different channel or cell. There are four different types of handover in the GSM system, which involve transferring a call between: • Channels (time slots) in the same cell • Cells (Base Transceiver Stations) under the control of the same Base Station Controller (BSC) , • Cells under the control of different BSCs, but belonging to the same Mobile services Switching Center (MSC) , and • Cells under the control of different MSCs in a PLMN, When a subscriber moves as illustrated in the direction of the arrow to the networkline of the PLMN it is possibly that all types of handover will be performed. The first two types of handover, called internal handovers, involve only one Base Station Controller (BSC) . To save signalling bandwidth, they are managed by the BSC without involving the Mobile services Switching Center (MSC) , except to notify it at the completion of the handover. The last two types of handover, called external handovers, are handled by the MSCs involved. An important aspect of GSM is that the original MSC, the anchor MSC, remains responsible for most call-related functions, with the exception of subsequent inter-BSC handovers under the control of the new MSC, called the relay MSC. Handovers can be initiated by either the mobile or the MSC (as a means of traffic load balancing) . During its idle time slots, the mobile scans the Broadcast Control Channel of up to 16 neighbouring cells, and forms a list of the six best candidates for possible handover, based on the received signal strength. This information is passed to the BSC and MSC, at least once per second, and is used by the handover algorithm. The algorithm for when a handover decision should be taken is not specified in the GSM recommendations. There are two basic algorithms used, both closely tied in with power control. This is because the BSC usually does not know whether the poor signal quality is due to multipath fading or to the mobile having moved to another cell. This is especially true in small urban cells . The handover in a PLMN is the necessary overhead in order to switch the call to a new cell site without either interrupts the call or alerting the user. The handoverprocedure between two PLMN and their co-operation with the involved networks describes in the following. Because of the fact that two different operators network are involved, the handover between them will always be between the exchanges (MSCs) of the two networks. The connection between the exchanges (MSCs) is a normal telephony network connection. In the network subsystem preferably in the MSC are situated a means adapted to transmit calls between these both network and this means include an arrangement for collecting specific parameters (such as frequencies) corresponding to the cells which are situated near the networksline in the communication system. Said means can be a telecommunicationcomputor which automatically read the information at specific time intervals or it can be manually given. Said arrangement can also be a database on each side of the networksline and connected to each other and respective MSC . The information received from this arrangement and corresponding information from the first network serves as input for the handoverprocedure, which is basically the same as the handoverprocedure between two MSC which are situated in one PLMN. In the network are also situated an arrangement for notifying in real time the subscriber, when he is still talking in the MS, that the transmission of the call to another PLMN is effected. The arrangement is adapted to receive information from the handoverprocedure so that it can give the subscriber an audible signal such as a special tone or a message that the transmission to the other network is performed. If there are different tariffs in the PLMNs , the subscriber is then informed that the tariff has changed. After the handover the reley station (MSC) takes care of the radio resources and when required performs handovers internal to the exchange . One of the basic characteristics of the interexchange handover is that the control of the connection (e.g. services, charging) stays in the exchange, where the initial call set-up was performed arid is not moved to another exchange with the handover. The arrangement for notifying the customer that a transmission is performed also give information to the existing billingarrangement in each network that a handover have been performed. The billingarrangement then produce bills according to the operator's implementation of the new service, which can have the name "Seamless roaming".

Claims: CLAIMS 1. A communication system, including two mobile communications network which are adapted for the transmission of a call from a first mobile communication network to a second mobile communication network including mobile customers with mobile stations (MS) characterised in that said system including means adapted to transmit calls, between these both mobile communication network while a conversation is in progress and that said network are operated by different telecommunication operators with its own Public Land Mobile Network (PLMN) and that said transmission is adapted to not losing ongoing calls when a customer with a MS passes into another operators Public Land Mobile Network (PLMN) . 2. A communication system, as claimed in claim 1 characterised in that said means for transmitting calls have - a arrangement for collecting specific parameters from the said second mobile communication network and - a arrangement for use of the said parameter from the second mobile communication network and parameters from the first mobile communication network in a procedure corresponding to the handoverprocedure between two Mobile services Switching Centre (MSC) in a GSM network. 3. A communication system, as claimed in claim 1 or 2 characterised in that the means adapted to transmit calls includes an arrangement for notifying, in real time, a customer that a transmission to another PLMN is effected. 4. A communication system, as claimed in claim 3 characterised in that the notifying is performed by an audible signal such as a special tone, or a message that the transmission to the other network have been performed. 5. A communication system, as claimed in claim 4 characterised in that the message is viewed on the display of a mobiletelephone. 6. A communication system, as claimed in claim 3 characterised in that the arrangement for notifying gives the existing billingarrangement in both co-operating network information that a transmission of a call have been performed. 7. A communication system, as claimed in claim 2 to 6 characterised in that said arrangement for collecting specific parameters is automatically transferred to said means for transmitting calls. 8. A communication system, as claimed in claim 7 characterised in that the parameters are cellinformation from the second network. 9. A communication system, as claimed in claim 8 characterised in that the parameters are from cells near the networksline. 10. A communication system, as claimed in claim 1-9 characterised in that it is possible to use the functionality as a service both in national and international roaming.

Inventors: ALSAE JOHAN, ARNAUTOVIC ASIM, WINBERG OLE, ALSAE, JOHAN, ARNAUTOVIC, ASIM, WINBERG, OLE
Applicants: ALSAE JOHAN, ARNAUTOVIC ASIM, TELIA AB, WINBERG OLE, ALSAE, JOHAN, ARNAUTOVIC, ASIM, TELIA AB (PUBL), WINBERG, OLE
Application year: 1999
Main classification: H04Q7
IPC codes: H04W36