WO2014124813A1

WO2014124813A1 - Network subsystem, wireless communication system and methods therefor

Info

Publication number: WO2014124813A1
Application number: PCT/EP2014/051838
Authority: WO
Inventors: David Brock; James Edward Brereton Harrow
Original assignee: Ip.Access Limited
Priority date: 2013-02-12
Filing date: 2014-01-30
Publication date: 2014-08-21
Also published as: GB2510637B; GB201302433D0; GB2510637A

Abstract

An apparatus and method for enabling communication between a "non-supporting" User Equipment (UE) (109) and one of several core networks (101, 102, 103) sharing a radio access network which includes a Home Node B (105) comprises configuring a look-up table (108) which links the PLMN code included in the IMSI of a UE with identities of one or more of the core networks to which a wireless communication unit is allowed access and inspecting the look-up table (108) to identify a core network to which a UE requesting a connection is allowed access, and forwarding the request for connection to the identified core network. The look-up table (108) may be pre-provisioned with lists of UE identities versus core networks to which each UE is allowed access or it may be compiled by a round-robin routing of a connection request to each core network in turn until one accepts the UEs request for connection, whereupon the look-up table is populated with a list linking wireless communication unit identities with those core networks that allow access..

Description

NETWORK SUBSYSTEM, WIRELESS COMMUNICATION SYSTEM AND METHODS THEREFOR

Field of the invention

The field of this invention relates to network subsystem, a wireless communication system and methods therefor and particularly to methods for facilitating communications between wireless communications units and a core network in systems comprising several core networks sharing a common radio access network.

Background of the Invention

Wireless communication systems, such as the 3^rd Generation (3G) of mobile telephone standards and technology, are well known. An example of such 3G standards and technology is the Universal Mobile Telecommunications System (UMTS™), developed by the 3^rd Generation Partnership Project (3GPP™) (www.3qpp.org). The 3^rd generation of wireless communications has generally been developed to support macro-cell mobile phone communications. Such macro cells utilise high power base stations (NodeBs in 3GPP parlance) to communicate with wireless communication units within a relatively large geographical coverage area. Typically, wireless communication units, or User Equipment (UEs) as they are often referred to in 3G parlance, communicate with a Core Network (CN) of the 3G wireless communication system via a Radio Network Subsystem (RNS). A wireless communication system typically comprises a plurality of radio network subsystems, each radio network subsystem comprising one or more cells to which UEs may attach, and thereby connect to the network. Each macro-cellular RNS further comprises a controller, in a form of a Radio Network Controller (RNC), operably coupled to the one or more Node Bs, via a so-called lub interface.

The second generation wireless communication system (2G), also known as GSM, is a well- established cellular, wireless communications technology whereby "base transceiver stations" (equivalent to the Node B's of the 3G system) and "mobile units" (user equipment) can transmit and receive voice and packet data. Several base transceiver stations are controlled by a Base Station Controller (BSC), equivalent to the RNC of 3G systems.

Communications systems and networks are developing towards a broadband and mobile system. The 3rd Generation Partnership Project has proposed a Long Term Evolution (LTE) solution, namely, an Evolved Universal Mobile Telecommunication System Territorial Radio Access Network, (E-UTRAN), for a mobile access network, and a System Architecture Evolution (SAE) solution, namely, an Evolved Packet Core ( EPC), for a mobile core network. An evolved packet system (EPS) network provides only packet switching (PS) domain data access so a voice service is provided by a 2G or 3G Radio Access Network (RAN) and circuit switched (CS) domain network. User Equipment UE) can access a CS domain core network through a 2G/3GRAN such as the (Enhanced Data Rate for GSM Evolution, EDGE) Radio Access Network (Radio Access Network, GERAN) or a Universal Mobile Telecommunication System Terrestrial Radio Access Network (Universal Mobile Telecommunication System Terrestrial Radio Access Network, UTRAN), and access the EPC through the E-UTRAN. Generally, the Core Network is responsible for switching and routing voice calls and data to and from wired telephone networks or the Internet. A RAN is located between the Core Network and the UE.

Lower power (and therefore smaller coverage area) cells are a recent development within the field of wireless cellular communication systems. Such small cells are effectively communication coverage areas supported by low power base stations. The terms "picocell" and "femtocell" are often used to mean a cell with a small coverage area, with the term femtocell being more commonly used with reference to residential small cells. Herein, the term" small cell" means any cell having a small coverage area and includes "picocells" and femtocells. The low power base stations which support small cells are referred to as Access points (AP's) with the term Home Node B (HNB's) or Evolved Home Node B (eHNB) identifying femtocell access points. These small cells are intended to augment the wide area macro network and support communications to User Equipments in a restricted, for example, indoor environment. An additional benefit of small cells is that they can offload traffic from the macro network, thereby freeing up valuable macro network resources.

Typical applications for such Access Points include, by way of example, residential and commercial locations, communication 'hotspots', etc., whereby Access Points can be connected to a core network via, for example, the Internet using a broadband connection or the like. In this manner, femto cells can be provided in a simple, scalable deployment in specific in-building locations where, for example, network congestion at the macro-cell level may be problematic.

Thus, an AP is a scalable, multi-channel, two-way communication device that may be provided within, say, residential and commercial (e.g. office) locations, 'hotspots' etc, to extend or improve upon network coverage within those locations. Although there are no standard criteria for the functional components of an AP (or HNB), an example of a typical AP/HNB for use within a 3GPP 3G system may comprise Node-B functionality and some aspects of Radio Network Controller (RNC) functionality as specified in 3GPP TS 25.467.

A HNB provides a radio access network connectivity to a user equipment (UE) using the so- called luh interface to a network Access Controller, also known as a Home Node B Gateway (HNB- GW). A HNB-GW is connected to the Core Network via the so-called lu interface.

In order to use network resources more efficiently, it has been proposed that multiple Core Network Operators share a RAN. In one such network sharing arrangement called Multi-Operator Core Network (MOCN), multiple Core Networks belonging to different Operators share a common RAN. A UE which supports network sharing (a "supporting UE") is configured to select a particular Core Network as its "serving Core Network" in the shared network and to signal this selection to the RAN (via a HNB-GW or RNC) to which the UE is attached. The RAN will then automatically route the registration for this UE to the selected Core Network. A supporting UE bases its CN selection on additionally broadcast MOCN system information. However, a UE not supporting network sharing (a "non-supporting UE") ignores such additional system information and leaves Core Network selection to the RAN. Conventionally, a RAN bases its Core Network selection on a Network Resource Indicator (NRI) initially received from the UE. A description of registration processes for supporting and non- supporting UE's can be found in 3GPP TS 23.251 In the case of non-supporting UE's the registration request is speculatively sent to an Operator and then redirected to further Operators until one is found that will accept the UE. This process increases load on the RAN and Core Networks and lengthens set-up time.

Thus, there exists a need for an improved method and apparatus which mitigates the aforementioned disadvantages.

Summary of the invention

Aspects of the invention provide a network subsystem, a cellular communication system and methods therefor as described in the appended claims.

According to a first aspect of invention there is provided a method for enabling communication between a wireless communication unit and one of a plurality of core networks through a shared radio access network, the method comprising; in a radio access network subsystem,

receiving from a wireless communication unit, a request for connection to a core network, receiving from the wireless communication unit an identity of the wireless communication unit requesting connection,

configuring a look-up table linking identities of wireless communication units with identities of one or more core networks of the plurality of core networks to which a wireless communication unit is allowed access,

inspecting the look-up table to identify a core network to which the wireless communicating unit requesting connection is allowed access, and

forwarding the request for connection to the identified core network.

The look-up table may be pre-provisioned with lists of wireless communication unit identities versus core networks to which each wireless communication unit is allowed access

Alternatively, the look-up table may be compiled by performing a round-robin routing of a connection request to each of the plurality of core networks in turn until one accepts the wireless communication unit's request for connection. Then, the look-up table is populated with a list linking wireless communication unit identities with those core networks that allow access. Once the look-up table is populated, there is no further need to carry out the the round-robin process as the radio access network subsystem can immediately forward the received request for connection to the correct core network.

Hence, the invention has the advantages of reducing load on the radio access network and core networks and reducing call set-up time.

In one embodiment, if a wireless communication unit requesting connection is allowed to access more than one core network (according to the look-up table) then the radio access network subsystem may decide to avoid forwarding the request for connection to a core network that is out of service or very heavily loaded and to forward the request for connection to that core network which is the least heavily loaded.

The identity of a wireless communication unit may comprise an IMSI (International Mobile Subscriber Identity) or a part of the IMSI such as a part which may comprise a mobile network code (MNC) identifier or may be an identifier which is derived from an IMSI.

An IMSI is a unique identifier which is stored in a subscriber identity module or other memory inside the wireless communication unit. It is usually presented as a 15 digit-long number. Typically the first three digits are the mobile country code (MCC) followed by two or three digits representing the mobile network code (MNC). The remaining digits are a mobile subscriber identity number within the network's customer database. The MCC and MNC identify the public land mobile network (PLMN) to which the subscriber has subscribed. Other identifiers used in messaging include the TMSI (temporary mobile subscriber identity) and the IDNNS (intra-domain network access server node selector). The IDNNS comprises bit string information which may be generated using the TIMSI when available. The IDNNS acts as a routing parameter.

According to a second aspect of the invention, there is provided a radio access network subsystem for supporting communications between at least one of a plurality of core networks and wireless communication units, each wireless communication unit having an identity associated therewith, the radio access network subsystem including a signal processor and a lookup table, said lookup table linking each said wireless communication unit identity with one or more core networks to which a wireless communication unit is allowed access, and wherein the signal processor is arranged to receive the identity of a wireless communication unit requesting connection to a core network, to determine from inspection of the lookup table the identity of a core network to which the wireless communication unit requesting connection is allowed access, and to forward the request for connection to the identified core network.

The signal processor and look-up table may be implemented in one or more integrated circuits. The signal processor and look-table may be co-located in the same network element forming a part of the radio access network subsystem. Such a network element may comprise a Home Node B Gateway (HNB-GW) or a Radio Network Controller (RNC) for example. The network element may then receive a wireless communication unit identity via an access point which serves the wireless communication unit via a wireless link. The access point may receive a request for connection to a core network from a wireless communication unit and forward such a request to the network element along with the wireless communication unit's identity.

In one embodiment, the access point is a Home Node B (HNB) which uses its Identity Request function to obtain an IMSI (International Mobile Subscriber Identity) from a wireless communication unit requesting connection. The IMSI or a part thereof or an identifier derived from the IMSI may then be used by the signal processor in a Home Node B Gateway (HNB-GW) to feed a MOCN operator selection algorithm for "non-supporting UE's.' ln alternative embodiments, the signal processor and look-up table are located in an access point which may be a Home Node B

The invention has particular applicability when a UE is roaming abroad, away from home and needs to register with a foreign network Operator. There may be several core networks sharing a radio access network and operating in the particular country that the UE finds itself in but not necessarily all of them will have roaming agreements with the UE's home Operator,. The invention minimises the time it takes to find an appropriate foreign core network which will allow access to the roaming UE.

According to a third aspect of the invention there is provided a wireless communication system arranged to support the method and the radio access network subsystem of the above aspects.

According to a fourth aspect of the invention, there is provided a tangible computer program product having executable program code stored thereon for execution by a processor to perform a method in accordance with the first aspect.

The tangible computer program product may comprise at least one from a group consisting of: a hard disk, a CD-ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory

These and other aspects, features and advantages of the invention will be apparent from, and elucidated with reference to, the embodiments described hereinafter.

Brief Description of the Drawings

Further details, aspects and embodiments of the invention will be described, by way of example only, with reference to the drawings. Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. Like reference numerals have been included in the respective drawings to ease understanding.

FIG. 1 illustrates a part of a wireless communication system comprising multi-operator core networks sharing a common radio access network and operating in accordance with an example embodiment.

FIG. 2 is a message sequence chart of an example embodiment of a method of establishing communication between a user equipment and a core network; and

FIG.3 is a simplified flowchart of an example embodiment of a method of establishing communication between a user equipment and a core network;

Detailed Description

The inventive concept finds particular applicability in a wireless communication system comprising multiple operators sharing a common radio access network.

Those skilled in the art will recognise and appreciate that the specifics of the specific examples described are merely illustrative of some embodiments and that the teachings set forth herein are applicable in a variety of alternative settings. For example, implementations within cellular communication systems conforming to different standards are contemplated and are within the scope of the various teachings described.

Referring now to FIG. 1 , an example of a 3G wireless communication system operating in accordance with some embodiments of the invention is illustrated and indicated generally at 100.

Three core networks represented by three Mobile Switching Centres MSC A 101 , MSC B 102 and MSC C 103 are operated by three different Operators. Each MSC 101 , 102, 103 has a link to a Radio Access Network subsystem 104 over the so-called lu interface. A core network may typically comprise many network elements but for clarity purposes only the MSC's are shown in FIG.1. Similarly, a typical Radio Access Network (RAN) can comprise many subsystems but for clarity, just one comprising two elements is shown in the example of FIG. 1. Specifically, the RAN subsystem 104 comprises an Access Point comprising a Home Node B (HNB) 105 and a Home Node B Gateway (HNB-GW) 106. The HNB 105 and HNB-GW 106 are linked via the so-called luh interface. The HNB- GW is provided with a signal processor 107 and a database in the form of a look-up table 108. The HNB 105 provides a wireless link to one or more User Equipments (UE) 109 over the so-called Uu interface. The HNB 105 provides wireless coverage over a relatively small area, eg. a femtocell.

In this example, the UE 109 is a "non-supporting UE" and is subscribed to its home network Operator. The UE 109 is roaming abroad and currently located in the coverage area of the HNB 105 and requires connection to a core network. None of the MSC's 101 , 102, 103, which are connected with the RAN 104, is the home network operator but one (or more) of them may have a roaming agreement with the home Operator which permits the UE to use its core network. The signal processor 107 and look-up table 108 serve to assist the RAN subsystem 104 in determining which MSC(s) permit access to the roaming UE 109.

The user equipment (UE) 109 may send its temporary mobile subscriber identity (TMSI) to the HNB 105 at initial access. In this case, the HNB may exploit its identity request capability in order to recover an IMSI from the UE. The HNB 105 sends the UE's IMSI as part of a UE register message to the HNB-GW 106 and is received by the signal processor 107 in the HNB-GW 106. Subsequently the HNB forwards a location update request from the UE to the HNB-GW along with a IDNNS derived from the TIMSI. In this case the IDNNS does not identify a specific core network node. From the IMSI provided in the UE Register Request, the signal processor 107 can extract the initial HPLMN (Home Public Land Mobile Network) identity from the first 5-6 digits. The signal processor then examines the look-up table 108 to determine which core network allows access to a user equipment subscribing to that particular HPLMN and therefore which is the appropriate MSC to forward a location update request to. The HNB-GW106 sends the TIMSI to the core network as part of a location update request. If an MSC accepts a location update successfully, then the signal processor 107 in the HNB- GW tags this against a user equipment's context (in the look-up table 108) so that all future messages and calls are routed to the correct core network. Any new requests from other UE's belonging to the same Home PLMN will also be directed towards the same Core network.

With reference to the message flow chart of FIG.2; At 201 a Radio Resource Control (RRC) connection request which includes the TMSI of the UE 109 is sent from the user equipment 109 to the HNB 105.

At 202 the HNB 105 responds with a RRC connection setup message.

At 203 the UE 109 responds with an RRC connection setup complete message sent to the HNB 105.

At 204 the UE 109 sends an RRC initial direct transfer message as a location update request to the HNB 105.

At 205 the HNB 105 sends to the UE 109 a RRC downlink direct transfer (MM-identity request) message.

At 206 the UE 109 responds with a RRC downlink direct transfer (MM-identity response) including its IMSI.

At 207 the HNB 105 sends the HNB-GW 106 a HNBAP (Home Node B Application Part) UE register request message (including the IMSI).

At 208 the HNB-GW 106 sends a HNBAP UE register accept message to the HNB 105.

At 209 the HNB 105 sends the HNB-GW 106 a RUA (RANAP User Adaptation) connect

(RANAP (Radio Access Network Application Part) initial UE message (location update request), IDNNS)). The IDNNS is constructed using the normal procedures but does not allow the HNB-GW to associate directly the UE 109 with any core network node. The HNB-GW therefore uses the IMSI received at UE Registration (step 207) to determine the most likely core network (mobile switching centre C in this example).

At 210 a RANAP initial UE message location update request, redirect-attempt-flag and the TMSI is sent from the HNB-GW to the Mobile Switching Centre C 103.

At 21 1 Mobile Switching Centre C 103 sends to the HNB-GW 106 a reroute complete (location update accept) message.

At 212 the HNB-GW 106 sends a RUA direct transfer (RRC initial direct transfer (location update request)) to the HNB 105.

At 213 the HNB 105 sends to the UE 109 a RRC downlink direct transfer (location update accept).

A communications link is now established between the UE 109 and the MSC C 103.

Referring now to FIG.3 which is a simplified flowchart of an example embodiment of a method of establishing communication between a user equipment and one of several a core network sharing the same RAN: at 301 , the HNB-GW 106 receives the UE's 109 registration request along with its IMSI and initial direct transfer message, the IDNNS of which does not identify a core network node. The IMSI is passed to the signal processor 107 in the HNB-GW 106 which, at 302, checks the first five digits (which comprise the PLMN code) against PLMN's listed in the look up table (LUT) 108.

If the PLMN is listed, then at 303, a location update request is forwarded to the MSC which is linked with that particular PLMN. If the MSC does not accept the location update request (perhaps because it is out of service or heavily loaded), then the request is re-routed to another MSC. Reverting to 302, if the signal processor 107 does not find the PLMN listed in the look-up table 108, then the process enters a round-robin mode to find an MSC that will accept the UE. Hence, at 304, the initial direct transfer message is sent to a first MSC. If the first MSC will not accept the UE, then alternative MSC's are tried, at 305, one by one in sequence. If all MSC's have been tried and none will accept the UE then the UE is ignored (306) by the RAN subsystem 105, 106.

On the other hand, if an MSC does accept the location update, then at 307, the signal processor 107 updates the look-up table 108 by storing the PLMN of the UE and linking it with an identity of the MSC which accepted its location update request.

Hence, when the same PLMN is received again (either from the same UE or another UE with the same prefix in its IMSI), the location update request will be sent straight to the linked MSC rather than entering the round-robin process.

The signal processing functionality of the embodiments of the invention, particularly the function of the signal processor 107, may be achieved using computing systems or architectures known to those who are skilled in the relevant art. Computing systems such as, a desktop, laptop or notebook computer, hand-held computing device (PDA, cell phone, palmtop, etc.), mainframe, server, client, or any other type of special or general purpose computing device as may be desirable or appropriate for a given application or environment can be used. The computing system can include one or more processors which can be implemented using a general or special-purpose processing engine such as, for example, a microprocessor, microcontroller or other control module.

The computing system can also include a main memory, such as random access memory

(RAM) or other dynamic memory, for storing information and instructions to be executed by a processor. Such a main memory also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by the processor. The computing system may likewise include a read only memory (ROM) or other static storage device for storing static information and instructions for a processor.

The computing system may also include an information storage system which may include, for example, a media drive and a removable storage interface. The media drive may include a drive or other mechanism to support fixed or removable storage media, such as a hard disk drive, a floppy disk drive, a magnetic tape drive, an optical disk drive, a compact disc (CD) or digital video drive (DVD) read or write drive (R or RW), or other removable or fixed media drive. Storage media may include, for example, a hard disk, floppy disk, magnetic tape, optical disk, CD or DVD, or other fixed or removable medium that is read by and written to by media drive. The storage media may include a computer-readable storage medium having particular computer software or data stored therein.

In alternative embodiments, an information storage system may include other similar components for allowing computer programs or other instructions or data to be loaded into the computing system. Such components may include, for example, a removable storage unit and an interface , such as a program cartridge and cartridge interface, a removable memory (for example, a flash memory or other removable memory module) and memory slot, and other removable storage units and interfaces that allow software and data to be transferred from the removable storage unit to computing system.

The computing system can also include a communications interface. Such a communications interface can be used to allow software and data to be transferred between a computing system and external devices. Examples of communications interfaces can include a modem, a network interface (such as an Ethernet or other NIC card), a communications port (such as for example, a universal serial bus (USB) port), a PCMCIA slot and card, etc. Software and data transferred via a communications interface are in the form of signals which can be electronic, electromagnetic, and optical or other signals capable of being received by a communications interface medium.

In this document, the terms 'computer program product', 'computer-readable medium' and the like may be used generally to refer to tangible media such as, for example, a memory, storage device, or storage unit. These and other forms of computer-readable media may store one or more instructions for use by the processor comprising the computer system to cause the processor to perform specified operations. Such instructions, generally referred to as 'computer program code' (which may be grouped in the form of computer programs or other groupings), when executed, enable the computing system to perform functions of embodiments of the present invention. Note that the code may directly cause a processor to perform specified operations, be compiled to do so, and/or be combined with other software, hardware, and/or firmware elements (e.g., libraries for performing standard functions) to do so.

In an embodiment where the elements are implemented using software, the software may be stored in a computer-readable medium and loaded into computing system using, for example, removable storage drive. A control module (in this example, software instructions or executable computer program code), when executed by the processor in the computer system, causes a processor to perform the functions of the invention as described herein.

Furthermore, the inventive concept can be applied to any circuit for performing signal processing functionality within a network element. It is further envisaged that, for example, a semiconductor manufacturer may employ the inventive concept in a design of a stand-alone device, such as a microcontroller of a digital signal processor (DSP), or application-specific integrated circuit (ASIC) and/or any other sub-system element.

It will be appreciated that, for clarity purposes, the above description has described embodiments of the invention with reference to a single processing logic. However, the inventive concept may equally be implemented by way of a plurality of different functional units and processors to provide the signal processing functionality. Thus, references to specific functional units are only to be seen as references to suitable means for providing the described functionality, rather than indicative of a strict logical or physical structure or organisation.

Aspects of the invention may be implemented in any suitable form including hardware, software, firmware or any combination of these. The invention may optionally be implemented, at least partly, as computer software running on one or more data processors and/or digital signal processors or configurable module components such as FPGA devices. Thus, the elements and components of an embodiment of the invention may be physically, functionally and logically implemented in any suitable way. Indeed, the functionality may be implemented in a single unit, in a plurality of units or as part of other functional units.

Although the present invention has been described in connection with some embodiments, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. Additionally, although a feature may appear to be described in connection with particular embodiments, one skilled in the art would recognize that various features of the described embodiments may be combined in accordance with the invention. In the claims, the term 'comprising' does not exclude the presence of other elements or steps.

Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. Also, the inclusion of a feature in one category of claims does not imply a limitation to this category, but rather indicates that the feature is equally applicable to other claim categories, as appropriate.

Furthermore, the order of features in the claims does not imply any specific order in which the features must be performed and in particular the order of individual steps in a method claim does not imply that the steps must be performed in this order. Rather, the steps may be performed in any suitable order. In addition, singular references do not exclude a plurality. Thus, references to 'a', 'an', 'first', 'second', etc. do not preclude a plurality.

Claims

A method, for enabling communication between a wireless communication unit (109) and one of a plurality of core networks (101 , 102, 103) through a shared radio access network, the method comprising; in a radio access network subsystem (104), receiving (301 ) from a wireless communication unit, (109) a request for connection to a core network (101 , 102, 103), receiving (301 ) from the wireless communication unit an identity of the wireless communication unit requesting connection, configuring (307) a look-up table (108) linking identities of wireless communication units with identities of one or more core networks of the plurality of core networks to which a wireless communication unit is allowed access, inspecting (302) the look-up table (108) to identify a core network to which the wireless communicating unit requesting connection is allowed access, and forwarding (303) the request for connection to the identified core network.

The method of claim 1 wherein the look-up table (108) is pre-provisioned with lists of wireless communication unit identities versus core networks to which each wireless communication unit is allowed access.

The method of claim 1 wherein the look-up table (108) is compiled by a round-robin routing (304, 305) of a connection request to each of the plurality of core networks in turn until one accepts the wireless communication unit's request for connection, whereupon the look-up table is populated (307) with a list linking wireless

communication unit identities with those core networks that allow access..

The method of any preceding claim wherein if it is determined that a wireless communication unit (109) requesting connection is allowed access to more than one core network (101 , 102, 102), then the radio access network subsystem (104) forwards the request for connection to that core network which is the least heavily loaded.

The method of any preceding claim wherein the identity of a wireless communication unit comprises an IMSI (International Mobile Subscriber Identity) or a part of the IMSI or an identifier which is derived from an IMSI.

A radio access network subsystem (104) for supporting communications between at least one of a plurality of core networks (101 , 102, 103) and wireless communication units (109), each wireless communication unit having an identity associated therewith, the radio access network subsystem (104) including a signal processor (107) and a lookup table (108), said lookup table linking each said wireless communication unit identity with one or more core networks to which a wireless communication unit is allowed access, and wherein the signal processor is arranged to receive the identity of a wireless communication unit requesting connection to a core network, to determine from inspection of the lookup table the identity of a core network to which the wireless communication unit requesting connection is allowed access, and to forward the request for connection to the identified core network.

A radio access network subsystem (104) according to claim 6 wherein the signal processor (107) and look-up table (109) are implemented in at least one integrated circuit.

A wireless communication system (100) arranged to support the methods according to claims 1-5 and the radio access network subsystem of claims 6 and 7.

A tangible computer program product (107) having executable program code stored thereon for execution by a processor to perform a method in accordance with claim 1 .

The tangible computer program product of claim 9 wherein the tangible computer program product comprises at least one from a group consisting of: a hard disk, a CD- ROM, an optical storage device, a magnetic storage device, a Read Only Memory, a Programmable Read Only Memory, an Erasable Programmable Read Only Memory, EPROM, an Electrically Erasable Programmable Read Only Memory and a Flash memory