Mobile communications

Abstract: A flexible and equitable PCN/PSTN interconnection strategy between a communications network having mobile subscribers, such as a PCN network, and a PSTN whereby to form a communication system in which multiple tariffs can be applied, the tariff applied being determined by the actual location of the mobile subscriber involved in a call. The PSTN (2, 6, 9, 10) is not given total access to the PCN (1, 5, 8, 11) location registers, rather a PSTN to PCN call is via a PCN gateway (5) which does have access to the location registers. The gateway (5) accepts zonal calls with which are associated one tariff (zonal interconnect 4) but for, for example, local or interzonal calls, it provides drop back messages to the PSTN to arrange for appropriate rerouting to other gateways (1, 8) of the PCN which have different tariffs associated therewith (local interconnect 3, interzonal interconnect 7) (Fig 2).

Description: This invention relates to mobile communications and in particular to interconnect strategies between networks. In Europe there are currently a number of different mobile communications standards which are incompatible with one another so that a terminal designed for one system cannot be used with another. The Groupe Speciale Mobile (GSM) was set up in order to develop a single cellular standard for Europe. A GSM network basically comprises a base-station system (BSS), which includes a base-station controller (BSC) and one or more base-station transceiver stations (BTS), a mobile-services switching centre (MSC), a home location register (HLR) and a visitors location register (VLR). Every subscriber (mobile station MS) is allocated to a home network, and possibly an MSC within that network, this being achieved by making an entry in the HLR. Whenever a mobile is switched on, and at regular intervals thereafter it will register with the system and give its location area (group of cells). If the mobile is not in its home area, the subscriber's data will be added to the VLR of the then local MSC. In the GSM system the MSC attends to the routing of a call to its destination, each MSC being connected to other MSCs, having interfaces for connection to PSTNs (Public Switched Telephone Networks such as BT or Mercury) and other service providers, and network management etc. functions. A general description of a cellular communications network coupled to a fixed network is described in specification No GB-A-1,542,794. This document describes a system in which locally distributed radio exchanges are connected to a fixed network for the purpose of providing communication between mobile and fixed network subscribers. A discussion of automatic pursuit routing in a mobile network is given by Nakajima et al in Electronics and Communications in Japan, Vol 73, No. 3, March 1990, pages 81 to 90. Both these documents discuss the determination of call tariffing in a communications system comprising a mobile communications network connected to the PSTN. Personal Communication Networks (PCN) now being developed in the UK are based on GSM standards but will operate at 1.8GHz rather than the 900MHz of the basic GSM standards. PCN systems arose as a result of the UK Government's Department of Trade and Industry "Phone on the Move" document which was basically aimed at improvement to current mobile communications (cellular radiotelephones). The latter are analogue and restricted in capacity due to the limited band of wavelengths currently available. As a result of the UK Government freeing a higher wavelength band, nominally 2GHZ, and the use of digital techniques, improved communications can be obtained. PCNs will not however be restricted to such mobile communications but rather are intended to support communications to and from any standard radio or fixed telecommunication network and hence to provide a single communication network with a universal personal communicator, i.e. a truly personal portable telephone which permits communication at all times. Since the PCNs proposed are based on GSM standards they can include similar components to the GSM network referred to above, or may include variants which are compatible with both GSM and PCN networks. According to the present invention there is provided a communications system comprising a mobile communications network having a base station controller connected to a first mobile services switching centre for serving mobile subscribers, the mobile communications network being coupled to a PSTN fixed network having a local exchange connected to a first main switching unit and having a direct connection to the base station controller, the first mobile services switching centre being connected to the first main switching unit, the system being arranged to allow call set-up in either direction between the networks and having multiple tariffs, wherein, for call set-up in the PSTN to mobile communications network direction to a mobile subscriber, the system is arranged to send a mobile communications network message identifying the mobile subscriber to the first mobile switching centre so as to determine the location of that mobile subscriber in the mobile communications network, wherein the mobile switching centre has means for determining whether the called mobile is local, zonal or interzonal within the mobile communications network, wherein the mobile switching centre has means for providing a first drop back message to the local exchange so as to set up the call via the direct connection employing a first tariff where the mobile subscriber is determined to be local, wherein the mobile switching centre has means for setting up the call via the first main switching unit employing a second tariff when the mobile subscriber is determined to be zonal, and wherein the mobile switching centre has means for providing a second drop back message to the local exchange for translation thereby for transmission to a second mobile switching centre of the mobile communications network and employing a third tariff where the mobile subscriber is determined to be interzonal, whereby the tariff applied to each call to a mobile subscriber is determined by the location of the mobile subscriber terminating the call. According to another aspect of the invention there is provided a method of determining call tariffing in a communications system comprising a mobile communications network having a base station controller connected to a first mobile services switching centre for serving mobile subscribers, the mobile communications network being coupled to a PSTN fixed network having a local exchange connected to a first main switching unit and having a direct connection to the base station controller, the first mobile services switching centre being connected to the first main switching unit, the system being arranged to allow call set-up in either direction between the networks and having multiple tariffs, the method including, for call set-up in the PSTN to mobile communications network direction to a mobile subscriber, sending a mobile communications network message identifying the mobile subscriber to the first mobile switching centre so as to determine the location of that mobile subscriber in the mobile communications network, determining whether the called mobile is local, zonal or interzonal within the mobile communications network, providing a first drop back message from the mobile switching centre to the local exchange so as to set up the call via the direct connection employing a first tariff where the mobile subscriber is determined to be local, setting up the call via the first main switching unit employing a second tariff when the mobile subscriber is determined to be zonal, and providing a second drop back message from the mobile switching centre to the local exchange for translation thereby for transmission to a second mobile switching centre of the mobile communications network and employing a third tariff where the mobile subscriber is determined to be interzonal, whereby the tariff applied to each call to a mobile suscriber is determined by the location of the mobile subcriber terminating the call. Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig 1 illustrates an equitable interconnect strategy Fig 2 illustrates another equitable interconnect strategy; Fig 3 illustrates a PSTN to PCN call signalling environment, and Fig 4 illustrates another PSTN to PCN call signalling environment. The interconnect strategy with the PSTN network will be a key factor in the success of PCN networks. PCN networks require: local connections at local call rates; a reciprocal strategy whereby Public Telephone Operators (PTOs) and the PCN operators equitably benefit from the growth of PCN; an interconnection mechanism that will operate with the PSTN as it actually exists. Taking the first two requirements: then a basic equitable interconnect structure would be as illustrated in Fig 1. Trunk calls originating in the PCN network (BTS, BSC, MSC) are carried by the PCN up to the nearest MSC interface with the PSTN network TE (LE (local exchange) TE (trunk exchange)), and vice versa although there may be local traffic paths between BSCS and LEs as indicated for low c-cost calls, Attention is directed to our Specification No GB-A-2,245,455 (published 2 January 1992) which describes an intelligent BSC for providing such low cost local calls i.e. routing local calls directly from the BSC to the PSTN LE without involving an MSC by virtue of having a local MSC function and its own location register. The basic structure of Fig 1 would require the PSTN network to be fully aware of the location of PCN subscribers and this is not currently envisaged. Whilst it is a possible long term objective, it is impractical in the short term. The interconnect strategy illustrated in Fig 2 is practical at this time and is termed a PCN flexible interconnect. Local traffic in both directions between the PCN BSCI, and a local PSTN exchange (LE) 2 is routed directly over what is termed a local interconnect 3 when the BSC-I is comprised by an intelligent BSC as described in said co-pending application, or such an intelligent BSC together with a local tandem for an increased capacity system as also described in said co-pending application. There is also a so-called zonal interconnect 4 between MSC 5 and principal local exchange PLE 6 for calls in both directions between the PCN (BTS, BSC, MSC) and the PSTN (LE, PLE), and an interzonal interconnect 7 for calls involving a remote MSC 8 or a remote PLE 9. This enables three different tariffs to be employed i.e. a PCN local tariff associated with a BSC junction, a PCN zonal network tariff associated with an MSC junction (local) and a PCN interzonal tariff associated with a remote MSC junction. An example of a numbering and translation scheme which permits the different tariffs to be employed as appropriate will now be described with reference to Fig 3. It is assumed that the PCN number is in the form shown in Fig 3 but this is not the only possibility. The number has four basic components, a-PCN designation, a PCN operator discriminator digit, a BSC discrimination code and a subscriber number within the BSC. Hence as illustrated a PCN number is in the form 01 XYYYY ZZZZ The choice of 01 for the PCN designation is only one possibility although it is particularly attractive now that it is no longer employed for the London numbers. In addition to the PCN number there is a PCN routing code, shown in Fig 3, for routing through this fixed network. This includes a national number group code allocated to the PCN (1 nn) added to the PCN designation (01), two digits of the BSC discrimination code (YY) and the subscriber number within the BSC. The PCN routing code is thus in the form 011 nn YYZZZZ When the PSTN LE 20 receives a call for mobile subscriber OIX YYYY ZZZZ from a PSTN subscriber, it initially translates OIX as being a PCN zonal call with a zonal network tariff and identifies an MSC junction. A number 7 signalling message is (IAM OIX YYYY ZZZZ) is then sent to the nearest MSC 21 via the PSTN main switching unit (MSU) 22. The MSC 21 determines from the location registers whether the called mobile is local, zonal or interzonal. If the call is a zonal call MSC 21 will be that identified and the call proceeds using the zonal tariff i.e. is terminated. However if the call is a local call, then the MSC 21 translates the message to give a DDI code comprising part of the PCN number (DDI Code YYZZZZ), identifying a PCN local tariff and a respective BSC junction (23), and that is sent back (drop back) to the local exchange LE 20, which routes it as a CCITT Q 931 or national variant e.g. DASS 2, or a CCITT No 7 NUP, message to the identified BSC 23 and the call proceeds using the PCN local tariff. Alternatively, if the call is an interzonal call then the MSC 21 translates the message to give a national number group PCN routing code, 011 nnYYZZZZ with a PCN interzonal tariff and a remote MSC junction (24) and this is dropped back to the LE 20 and thence sent to the identified remote MSC 24 via MSU 22 and remote MSU 25 as a IAM (011nnYYZZZZ) message and thence to the appropriate mobile. Fig 4 illustrates another possible numbering scheme with translations which enables the tariffs to be employed (local and zonal), as opposed to the three tariffs of Fig 3 (local, zonal and interzonal). In this example the PCN number is in the form 01 X YYY ZZZZZ but this is not the only possibility. The PCN number is comprised, as before, of a PCN designation, an operator discriminator, a BSC discrimination code and a subscriber number within the BSC. When the PSTN LE 30 receives a call for mobile 01XYYYZZZZZ it translates 01X as being a PCN zonal tariff and gives the nearest MSC junction, MSC 31 in this example. A number 7 signalling message (IAM(01XYYYZZZZZ)) is then sent to MSC 31 via PSTN MSU 32 as illustrated. If the call is a zonal call, as determined by the MSC from the location register, the call will proceed using the zonal tariff i.e. the call is terminated. If the call is not a zonal call, i.e. it is a local call, then the MSC 31 translates the message to give a DDI code comprising part of the message (PCN number) as DDI code YZZZZZ identifying a PCN tariff and a BSC junction (33 in the example) and that is sent back (drop back) to PSTN LE 30, via MSU 32. The PSTN LE 30 routes the message e.g. as a DASS 2 or No 7 signalling message to BSC 33 and the call proceeds using the local tariff. The interconnect structure of Fig 2 is such that for all local calls between the PCN (BSC 1) and the PSTN (LE 2), for example, signalling is e.g. DASS 2 or CCITT No 7 (in either direction) and at a local tariff. For PCN to PSTN local calls this is as a result of the intelligent BSC noting that they are local calls and the local MSC function thereof routing them directly to LE 2. For PSTN to PCN local calls this is as a result of the MSC 5 noting that they are local calls and the subsequent drop back. All zonal calls between the PSTN and the PCN, in either direction, are via the MSC 5 in the conventional manner and involve the zonal tariff. All interzonal calls between the PSTN and the PCN, in either direction, are via the appropriate MSC, after drop back if necessary, and at the interzonal tariff. A PCN to PSTN interzonal call, e.g. BSC1 to LE 10, is via the nearest MSC to (8) to LE 10 and the relevant PLE (9) in the usual way. A PSTN to PCN interzonal call e.g. LE 2 to BSC 11, is via the nearest MSC 5 to LE 2, to determine the actual MSC required from the location registers, with drop back and translation to the appropriate PCN routing code to reach MSC 8 and thence BSC 11 via the PLE 6 and PLE 9. The schemes of both Figs 3 and 4 assume that the BSC is intelligent. However, a multiple tariff arrangement (zonal/interzonal) can also be envisaged if the BSC has a standard GSM structure i.e. it is not intelligent. In this case the local interconnect (cheap local calls) is not provided. Zonal calls will be processed via the MSC 21 and MSU 22 in the conventional manner and use the zonal tariff but interzonal calls (PSTN to PCN) will be identified at the MSC 21 as described above with resultant drop back and retranslation to the PCN routing code and use of the interzonal tariff. The interconnect structure proposed in Fig 2 is both flexible and equitable and allows application of multiple tariffs (local and zonal, or local, zonal and interzonal, or zonal and interzonal in the above examples) depending on the actual location of the mobile subscriber. By equitable it is to be understood that the structure supports calls set up in either direction PCN to PSTN or PSTN to PCN, with the same tariffs being applied in both direction. The PSTN does not need to know where the mobile is, rather this is determined from or via the "nearest" MSC and to which the IAM message is first directed, i.e. a gateway having access to the GSM location registers, and sent back to the PSTN as a drop back message (as defined in BTNR 167 Issue 3, July 1987, SS No 7 NUP). Thus the whole of the PSTN fixed network does not have to be given access to the location registers of the PCN and major changes to the fixed network to acquire the location knowledge are not required. The gateway to the PCN (MSC 21 or 31 in the above examples) accepts zonal calls and translates digits received into a DDI code if the call is local, i.e. the mobile is local, or into a PCN national number code if the call is interzonal. The information message received at (dropped back to) the local exchange is used to restart translation giving a new tariff and a new destination. The fixed network does not require massive change, rather a simple information message is implemented in order to determine mobile location information. Overall, therefore, the PCN is allowed to have different tariffs e.g. for local, zonal or interzonal calls, rather than the present cellular systems which have one tariff for all interconnect purposes. Basically this is achieved by translating a PCN number called by a PSTN subscriber into DDI code for local calls and national network code for distant ones, the basic PCN number resulting in a zonal call and the zonal tariff. It should be noted that a basic starting assumption of GSM is that the fixed network has access to the location registers but the GSM standard does not disclose how this should be achieved. Attention is also directed to our specification No GB-A-2249693 which relates to a PCN cordless PABX, the contents of which is also incorporated herein by reference. Whilst the invention has been described in terms of GSM and PCN communications networks having mobile subscribers, this is not the only application and it is also applicable to other communications standards/systems/networks having mobile subscribers and employing elements equivalent to the BTS, BSC and MSC of the PCN/GSM system.

Claims: A communications system comprising a mobile communications network having a base station controller (1, 23) connected to a first mobile services switching centre (5, 21) for serving mobile subscribers, the mobile communications network being coupled to a PSTN fixed network having a local exchange (2, 20) connected to a first main switching unit (6, 22) and having a direct connection (3) to the base station controller, the first mobile services switching centre (5,21) being connected to the first main switching unit (6,22), the system being arranged to allow call set-up in either direction between the networks and having multiple tariffs, wherein, for call set-up in the PSTN to mobile communications network direction to a mobile subscriber, the system is arranged to send a mobile communications network message identifying the mobile subscriber to the first mobile switching centre (5,21) so as to determine the location of that mobile subscriber in the mobile communications network, wherein the mobile switching centre has means for determining whether the called mobile is local, zonal or interzonal within the mobile communications network, wherein the mobile switching centre (5,21) has means for providing a first drop back message to the local exchange (2,20) so as to set up the call via the direct connection (3) employing a first tariff where the mobile subscriber is determined to be local, wherein the mobile switching centre (5,21) has means for setting up the call via the first main switching unit (6,22) employing a second tariff when the mobile subscriber is determined to be zonal, and wherein the mobile switching centre has means for providing a second drop back message to the local exchange (2,20) for translation thereby for transmission to a second mobile switching centre (8, 24) of the mobile communications network and employing a third tariff where the mobile subscriber is determined to be interzonal, whereby the tariff applied to each call to a mobile suscriber is determined by the location of the mobile subcriber terminating the call. A system as claimed in claim 1, characterised in that the PSTN network includes a second main switching unit (9, 25) connected to the first main switching unit (6, 22), that the second mobile switching centre (8, 24) is connected to the second main switching unit via a respective interconnect, that for a call set-up from a PSTN network subscriber of interconnect, that for a call set-up from a PSTN network subscriber of the local exchange (2, 20) to an interzonal mobile subscriber associated with the second mobile switching centre, a message identifying the mobile subscriber is sent from the first mobile switching centre to the second mobile switching centre whereby to determine the location of that mobile subscriber. A system as claimed in claim 2, characterised in that the PSTN fixed network includes a first principal local exchange (6) comprising said first main switching unit and a second principal local exchange (9) comprising said second main switching unit connected in series, that the first mobile switching centre is connected to the first principal local exchange via a zonal interconnect (4) between the base station controller and the local exchange, that the second mobile switching centre is connected to the second principal local exchange via a further interconnect providing an interzonal interconnect, and that said first, second and third tariffs are associated respectively with said direct connection, said zonal interconnect and said interzonal interconnect. A system as claimed in claim 1, 2 or 3, characterised in that, for calls set up from a PSTN fixed network subscriber to a mobile network subscriber, the location of the mobile subscriber is determined, at a gateway to the mobile network which accepts zonal calls, from location registers of the mobile network, which zonal calls involve said second tariff, and that the system is so arranged that, if the calls are not zonal, the gateway translates the message received identifying the mobile subscriber involved in the call into a direct dialling in (DDI) code if the call is local or into a national number if the call is interzonal, which translated messages are dropped back to the PSTN which, in response thereto, restarts the translation setting the first or third tariff respectively and setting an appropriate destination for the call. A method of determining call tariffing in a communications system comprising a mobile communications network having a base station controller (1, 23) connected to a first mobile services switching centre (5, 21) for serving mobile subscribers, the mobile communications network being coupled to a PSTN fixed network having a local exchange (2, 20) connected to a first main switching unit (6, 22) and having a direct connection (3) to the base station controller, the first mobile services switching centre (5,21) being connected to the first main switching unit (6,22), the system being arranged to allow call set-up in either direction between the networks and having multiple tariffs, the method including, for call set-up in the PSTN to mobile communications network direction to a mobile subscriber, sending a mobile communications network message identifying the mobile subscriber to the first mobile switching centre (5,21) as to determine the location of that mobile subscriber in the mobile communications network, determining whether the called mobile is local, zonal or interzonal within the mobile communications network, providing a first drop back message from the mobile switching centre (5,21) to the local exchange (2,20) so as to set up the call via the direct connection (3) employing a first tariff where the mobile subscriber is determined to be local, setting up the call via the first main switching unit (6,22), employing a second tariff when the mobile subscriber is determined to be zonal, and providing a second drop back message from the mobile switching centre (5,21) the local exchange (2,20) or translation thereby for transmission to a second mobile switching centre (8, 24) of the mobile communications network and employing a third tariff where the mobile subscriber is determined to be interzonal, whereby the tariff applied to each call to a mobile suscriber is determined by the location of the mobile subcriber terminating the call. A method as claimed in claim 5, characterised in that, for calls set up from a PSTN fixed network subscriber to a mobile network subscriber, the location of the mobile subscriber is determined, at a gateway to the mobile network which accepts zonal calls, from location registers of the mobile network, which zonal calls involve said second tariff, and that, where the calls are not zonal, the message received identifying the mobile subscriber involved in the call is translated by the gateway into a direct dialling in (DDI) code if the call is local or into a national number if the call is interzonal, the translated message is dropped back to the PSTN so as to restart the translation setting the first or third tariff respectively and setting an appropriate destination for the call.

Inventors: MAUGER RAY, MAUGER, RAY
Applicants: NORTHERN TELECOM LTD, NORTHERN TELECOM LIMITED
Application year: 1991
Main classification: H04Q7
IPC codes: H04W4