WO2016096018A1

WO2016096018A1 - Early discovery of csg mismatch at tau

Info

Publication number: WO2016096018A1
Application number: PCT/EP2014/078508
Authority: WO
Inventors: Anna Hansen; Patrik EGERDAL; Daniel Karlsson
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2014-12-18
Filing date: 2014-12-18
Publication date: 2016-06-23
Anticipated expiration: 2017-06-18

Abstract

The invention relates to mobility management nodes and methods at the mobility management nodes of managing a request for a Tracking Area Update (TAU) in a wireless communications network. The method at a first mobility management node (15) in a wireless communications network (11) configured to manage a context request for a mobile terminal (11) served by the first mobility management node comprises receiving(S204)from a second mobility management node (16) a context request for the mobile terminal, which request indicates a CSG, determining (S205a) whether the mobile terminal is allowed to access the CSG based on the CSG indicated in the context request; and providing (S205) the first mobility management node with a response to the context request indicating whether the mobile terminal is allowed to access the indicated CSG.

Description

EARLY DISCOVERY OF CSG MISMATCH AT TAU

TECHNICAL FIELD

The invention relates to mobility management nodes and methods at the mobility management nodes of managing a request for a Tracking Area Update (TAU) in a wireless communications network. The invention further relates to a computer program performing the method according to the present invention, and a computer program product comprising computer readable medium having the computer program embodied therein.

BACKGROUND

A Closed Subscriber Group (CSG) is a 3GPP feature used for cells in Long Term Evolution (LTE) communications system. With CSG, a limited number of subscribers are permitted to access one or more CSG cells of a Public Land Mobile Network (PLMN) as a member of the CSG for a Home eNodeB, and exclusively use the CSG cell resources. The cell can thus be configured in closed mode, or an open access mode where any user is allowed access to the cell. There is a also a third mode, referred to as hybrid mode, being a combination of the closed and open mode, where the cell provides open access to all users but still can prioritize members of the CSG. Subscribed users can be prioritized compared to unsubscribed users and can be charged differently.

For closed mode, CSG access control functionality in a Mobility Management Entity (MME) ensures that a mobile terminal, such as a User Equipment (UE), has valid subscription at a CSG where it attempts an access. In closed mode, the CSG access control functionality in the MME will send a reject with a so called Non-Access Stratum (NAS) cause value 25 (i.e. "not authorized for this CSG") to the UE if the access control fails. For instance, UEs belonging to a particular household are authorized to access the CSG, while other UEs are not.

A Tracking Area (TA) is an area where a user can move around without updating the MME accordingly. The core network allocates a list with one or more TAs to the user. When the user moves outside her allocated TA, the UE must perform a Tracking Area Update (TAU) with the MME of the new TA. Assume that the UE performs an Inter MME TAU into a CSG cell where it is not allowed. The new MME will fetch UE context from the old MME; the UE context is a block of information in the MME associated with an active UE, and contains the necessary information required to maintain services towards the active UE, for instance UE state information, security

information, UE capability information and the UE identity, etc. There are different UE contexts stored in different nodes of the network; the UE-related context stored at an MME is referred to as "Mobility Management (MM) context", while e.g. the UE-related context stored at an eNodeB is referred to as "eNB UE context", and so on.

The new MME will then retrieve subscription data from a Home Subscription Server (HSS) and discover that the UE is not allowed in this CSG. The new MME will reject the TAU with cause code 25 (UE is not authorized for this CSG). However, as will be illustrated in the following with reference to Figure 1, at this point many rounds of signalling has been undertaken under the incorrect assumption that the UE was authorized for this CSG thus creating a lot of overhead signalling. Figure 1 shows a signalling diagram describing a TAU process in detail as set out in specification 3GPP TS 23.401. In step S101, a TAU is triggered at the UE, for instance being triggered by the user of the UE moving outside her allocated old TA and into a new TA, wherein the UE must perform a TAU with the MME of the new TA. Accordingly, the UE sends a TAU request to the eNodeB in step S102, which in its turn forwards the TAU request in step S103 to the new MME.

In LTE networks, a Globally Unique Temporary ID (GUTI) is used for 1) identifying the MME which allocated the GUTI, and 2) identifying the UE within the MME that allocated the GUTI. An Initial UE Message comprises a CSG ID and the TAU request carrying the old GUTI. The new MME identifies the old MME (or old Serving General Packet Radio Service (GPRS) Support Node (SGSN)) from the received GUTI and sends in step S104 a context request to the old MME to retrieve user information. The old MME responds in step S105 with a context response comprising the MM context for this particular UE. If the integrity check of TAU Request message sent in step S102 failed, then authentication with the HSS is mandatory in step S106. The new MME takes over the responsibility of the UE and indicates that to the old MME with a context acknowledgement in step S107. The old MME will as a result consider the old MM context to be invalid. In case the new MME selected a new Serving Gateway (SGW) it sends a create session request message to the selected new SGW in step S108.

The Serving GW informs the Packet Data Network Gateway (PGW) about the change of for example Radio Access Technology (RAT) by sending a modify bearer request message in step S109. If dynamic Policy and Charging Control (PCC) is deployed, communication must be undertaken with a Policy and Charging Rules Function (PCRF) in step Si09a. The PGW updates its bearer contexts and returns, in step S110, a modify bearer response message to the new SGW, which in its turn updates its bearer context and returns a create session response message to the new MME in step S111. The new MME verifies whether it holds subscription data for the UE identified by the GUTI. If there are no subscription data in the new MME for this UE, the new MME sends an update location request message to the HSS in step S112.

The HSS sends in step S113 a cancel location message to the old MME in view of the update procedure. If a timer started in step S114 is not running, the old MME removes the MM context. Otherwise, the contexts are removed when the timer expires. This also ensures that the MM context is kept in the old MME for the case the UE initiates another TAU process before completing the ongoing TAU process to the new MME. In step S114, the old MME acknowledges with a cancel location ack message. In case the UE optionally is in Iu connected mode, steps S115 and S116 are undertaken.

Now, in step S117, the HSS acknowledges the update location request message by sending an update location ack message to the new MME. This may contain the contain the CSG subscription data for the registered PLMN and for the equivalent PLMN list requested by the new MME in step S112. If the update location is rejected by the HSS, the new MME rejects the TAU request from the UE with an appropriate cause. In such cases, the new MME releases any local MME EPS Bearer contexts for this particular UE, and additionally deletes the EPS bearer resources in the new SGW by sending a delete session request message to the new SGW.

If the UE initiates the TAU process at a CSG cell, the new MME shall check whether the CSG ID and associated PLMN is contained in the CSG

subscription and is not expired. If the CSG ID and associated PLMN is not present or is expired, the MME shall send a TAU reject message to the UE with an appropriate cause value. The UE shall remove the CSG ID from its allowed CSG list if present. If the UE has ongoing emergency bearer services no CSG access control shall be performed. If all checks are successful then the new MME constructs a context for the UE. The TAU process proceeds with steps S118, S119 and S120, where in case the UE is not allowed in the CSG, the MME rejects the TAU request with an appropriate cause to the UE.

A disadvantage of the current TAU process as illustrated in Figure 1 is that the new MME is not made aware of CSG membership of the UE until step S117, where the HSS informs the new MME accordingly with the update location ack message. However, the old MME already received a context acknowledge message in step S107 indicating that the new MME took over the responsibility of the UE from the old MME. In case of TAU rejection, the UE receives a TAU reject message in step S120 from the new MME, and the UE will not receive a new GUTI from the new MME, but will keep the GUTI from the old MME. Further, at this stage, the old MME considers the UE context - i.e. the MM context - to be invalid. The UE then tries to access another cell and sends a new TAU Request containing its old GUTI. The new MME will again try to retrieve MM context data from the old MME. This will not be successful since the old MME does not have a valid MM context for the UE anymore. The UE will thus receive a TAU rejection cause code 9 (i.e. "UE Identity cannot be derived by the network") from the new MME.

Consequently, the UE will have to re-register with the network by performing an International Mobile Subscriber Identity (IMSI) attach procedure, thereby connecting to the new MME. An IMSI attach procedure is unfavourable since it requires extensive signalling in the network.

SUMMARY

An object of the present invention is to solve, or at least mitigate, this problem in the art and thus to provide an improved method and mobility management node for managing TAU requests.

This object is attained in a first aspect of the present invention by a method at a second mobility management node in a wireless communications network of managing a request for a Tracking Area Update (TAU). The method comprises receiving from a requesting radio access network (RAN) node a request to perform a TAU for a mobile terminal served by the RAN node, requesting a Closed Subscriber Group (CSG) access control for the mobile terminal with respect to a CSG indicated in the request by providing, to a first mobility management node serving the mobile terminal, a context request for the mobile terminal, which request indicates the CSG, and receiving from the first mobility management node a context response to the context request indicating whether the mobile terminal is member of the indicated CSG. The method further comprises determining whether the mobile terminal is allowed to access the CSG based on a result of the requested CSG access control and if not providing the RAN node with a response to the TAU request indicating that the mobile terminal is not allowed to access the indicated CSG. This object is attained in a second aspect of the present invention by a method at a first mobility management node in a wireless communications network configured to manage a context request for a mobile terminal served by the first mobility management node. The method comprises receiving from a second mobility management node a context request for the mobile terminal, which request indicates a CSG, determining whether the mobile terminal is allowed to access the CSG based on the CSG indicated in the context request; and providing the first mobility management node with a response to the context request indicating whether the mobile terminal is allowed to access the indicated CSG.

This object is attained in a third aspect of the present invention by a second mobility management node in a wireless communications network configured to manage a request for a TAU, comprising a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby said node is operative to receive from a requesting RAN node a request to perform a TAU for a mobile terminal served by the RAN node, request a CSG access control for the mobile terminal with respect to a CSG indicated in the request by providing, to a first mobility

management node serving the mobile terminal, a context request for the mobile terminal, which request indicates the CSG, receive from the first mobility management node a context response to the context request indicating whether the mobile terminal is member of the indicated CSG, determine whether the mobile terminal is allowed to access the CSG based on the context response; and if not provide the RAN node with a response to the TAU request indicating that the mobile terminal is not allowed to access the indicated CSG.

This object is attained in a fourth aspect of the present invention by a first mobility management node in a wireless communications network configured to manage a context request for a mobile terminal served by the first mobility management node, comprising a processing unit and a memory, said memory containing instructions executable by said processing unit, whereby said node is operative to receive from a second mobility management node a context request for the mobile terminal, which request indicates a CSG, determine whether the mobile terminal is allowed to access the CSG based on the CSG indicated in the context request, and provide the second mobility management node with a response to the context request indicating whether the mobile terminal is allowed to access the indicated CSG.

When a user moves outside her allocated TA and into a new TA, the user's UE will via its eNodeB submit a TAU request to an MME of the new TA into which the user moves. The new MME, which also will be referred to as "the second MME" in the following, will in response to the TAU request of the UE received from the eNodeB turn to the MME of the TA currently allocated to the UE for determining whether the UE is authorized to access a CSG indicated in the Initial UE Message along with the TAU request. The MME which determines whether the UE is authorized to access the CSG will be referred to as the "old MME" or the "first MME". The CSG to which access is requested is typically indicated along with the TAU request by means of a CSG identifier (CSG ID). The new MME requests from the old MME a CSG access control for the UE with respect to a CSG indicated in the request sent from the new MME to the old MME. In reply to this context request comprising the CSG ID, the old MME determines whether the UE is authorized to access the CSG cell of the new TA, and provides the new MME with a context response accordingly. If the UE is allowed to access the CSG, a TAU can subsequently be successfully performed. However, if not, the old MME will provide the new MME with a context response indicating that the UE is not allowed to access the CSG, whereby the new MME provides the eNodeB with a TAU reject response advantageously indicating that the UE is not allowed to access the indicated CSG.

Hence, with the present invention, the new MME includes the CSG ID in the context request submitted to the old MME requesting CSG access control, and the old MME sends a context response to the new MME accordingly containing CSG membership information associated with the CSG ID for this particular UE in, which advantageously avoids further extensive signalling in the network regarding CSG access in case CSG access is denied. The old MME will undertake the CSG access control based on the CSG ID received with the context request, which was not possible in the art but required further extensive signaling before the new MME could be informed of CSG

membership by the HSS. The context response will thus inform the new MME that the TAU is to be rejected because of non-CSG membership. This may be implemented either by means of an Information Element (IE) or with a private extension to the context response. When the new MME receives this information with the context response, it may send the previously discussed cause code with value 25 to the UE via the eNodeB, thus informing the UE that it needs to move before requesting a new TAU, either via said new MME or another MME. Advantageously, the UE moves to another TA and the procedure is repeated. As can be concluded, extensive signaling is avoided by concluding at a relatively early stage that the UE fails the CSG access control in the context response from the old MME, and there is neither need to have the HSS provide the information later on, nor to re-register the UE with the network by performing an IMSI attach. In an embodiment of the present invention, a confirmation in the form of a context acknowledgement is received at the old MME from the new MME indicating whether the TAU is successful or not in order to explicitly indicate that the MM context should be maintained at the old MME.

In yet a further embodiment of the present invention, the response from the old MME to the context request comprises a General Packet Radio Service (GPRS) Tunnelling Protocol (GTPv2) cause code for indicating that the UE is not allowed to access the indicated CSG. Advantageously, the old MME may hence abort the TAU process already after sending the context response to the context request. Further provided is a computer program performing the method according to the present invention, and a computer program product comprising computer readable medium having the computer program embodied therein.

Further preferred embodiments of the invention will be described in the following.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is now described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 shows a prior art TAU process;

Figure 2 shows a schematic overview of an exemplifying wireless

communication system in which the present application can be implemented;

Figure 3a illustrates a new MME according to one embodiment of the present invention, and an old MME according to another embodiment of the present invention;

Figure 3b shows a signaling diagram describing a TAU process according to an embodiment of the present invention;

Figure 4 illustrates a TAU process according to a further embodiment of the present invention;

Figure 5 shows a signaling diagram describing a new TAU process being initiated after the UE has received the TAU reject in Figure 3b and Figure 4; Figure 6 illustrates a flowchart of a method of managing a TAU request at the new MME according to an embodiment of the present invention;

Figure 7 illustrates a flowchart of a method of managing a TAU request at the old MME according to an embodiment of the present invention; Figure 8 shows a second management mobility node according to an embodiment of the present invention; and

Figure 9 shows a first management mobility node according to an

embodiment of the present invention.

DETAILED DESCRIPTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout the description.

Figure 1 shows a prior art TAU process as previously has been discussed in detail. Figure 2 shows a schematic overview of an exemplifying wireless

communication system in which the present invention can be implemented. The wireless communication system is an LTE based system. It should be pointed out that the terms "LTE" and "LTE based" system is here used to comprise both present and future LTE based systems, such as, for example, advanced LTE systems. It should be appreciated that although Figure 2 shows a wireless communication system in the form of an LTE based system, the example embodiments herein may also be utilized in connection with other wireless communication systems, such as e.g. Global System for Communication (GSM) or Universal Mobile Telecommunications System (UMTS), comprising nodes and functions that correspond to the nodes and functions of the system in Figure 2.

The wireless communication system comprises one or more base stations in the form of an eNodeB, operatively connected to a Mobility Management Entity (MME) and to a Serving Gateway (SGW), in turn operatively connected to the MME and a Packet Data Network Gateway (PGW), which in turn is operatively connected to a Policy and Charging Rules Function

(PCRF). The eNodeB is a radio access node that interfaces with a mobile radio terminal, e.g. a UE or an Access Point. The eNodeB of the system forms the E-UTRAN for LTE communicating with the UE over an air interface such as LTE-Uu. The core network in LTE is known as Evolved Packet Core (EPC), and the EPC together with the E-UTRAN is referred to as Evolved Packet System (EPS). The SGW routes and forwards user data packets over the Si-U interface, whilst also acting as the mobility anchor for the user plane during inter-eNodeB handovers and as the anchor for mobility between LTE and other 3rd Generation Partnership Project (3GPP) technologies (terminating S4 interface and relaying the traffic between 2G/3G systems and PGW). For idle state UEs, the SGW terminates the downlink data path and triggers paging when downlink data arrives for the UE, and further manages and stores UE contexts, e.g. parameters of the IP bearer service, network internal routing information. It also performs replication of the user traffic in case of lawful interception. The SGW communicates with the MME via interface S11 and with the PGW via the S5 interface. Further, the SGW may communicate with the UMTS radio access network UTRAN and with the GSM EDGE ("Enhanced Data rates for GSM Evolution") Radio Access Network (GERAN) via the S12 interface via radio base stations referred to as NodeBs in UTRAN and Base Station Transceivers (BTSs). The UTRAN is shown to comprise a home NodeB.

The MME is responsible for idle mode UE tracking and paging procedure including retransmissions. It is involved in the bearer activation/deactivation process and is also responsible for choosing the SGW for a UE at the initial attach and at time of handover. It is responsible for authenticating the user by interacting with the Home Subscriber Server (HSS). The Non-Access Stratum (NAS) signaling terminates at the MME and it is also responsible for generation and allocation of temporary identities to UEs via the Si-MME interface. It checks the authorization of the UE to camp on the service provider's Public Land Mobile Network (PLMN) and enforces UE roaming restrictions. The MME is the termination point in the network for

ciphering/integrity protection for NAS signaling and handles the security key management. Lawful interception of signaling is also supported by the MME. The MME also provides the control plane function for mobility between LTE and 2G/3G access networks with the S3 interface terminating at the MME from the Serving General Packet Radio Service (GPRS) Support Node

(SGSN). The MME also terminates the S6a interface towards the home HSS for roaming UEs. Further, there is an interface S10 configured for

communication between MMEs for MME relocation and MME-to-MME information transfer.

The PGW provides connectivity to the UE to external packet data networks (PDNs) by being the point of exit and entry of traffic for the UE. A UE may have simultaneous connectivity with more than one PGW for accessing multiple PDNs. The PGW performs policy enforcement, packet filtering for each user, charging support, lawful Interception and packet screening.

Another key role of the PGW is to act as the anchor for mobility between 3 GPP and non-3GPP technologies such as WiMAX and 3GPP2 (CDMA lX and EvDO). The interface between the PGW and the packet data network, being for instance the Internet, is referred to as the SGi. The packet data network may be an operator external public or private packet data network or an intra operator packet data network, e.g. for provision of IP Multimedia Subsystem (IMS) services.

The PCRF determines policy rules in real-time with respect to the radio terminals of the system. This may e.g. include aggregating information in real-time to and from the core network and operational support systems, etc. of the system so as to support the creation of rules and/or automatically making policy decisions for user radio terminals currently active in the system based on such rules or similar. The PCRF provides the PGW with such rules and/or policies or similar to be used by the acting PGW as a Policy and Charging Enforcement Function (PCEF) via interface Gx. The PCRF further communicates with the packet data network via the Rx interface. Figure 3a illustrates how a UE 11 moves from an old TA 12 served by an old eNodeB 10 and an old MME 15 of an embodiment of the present invention into a new TA 13 served by a new eNodeB 14 and a new MME 16 of an embodiment of the present invention. As will be discussed in the following, the new MME 16 and the old MME 15 will according to embodiments of the present invention manage a request for a TAU from the UE 11. Still a further TA 23 and a further eNodeB 24 are also shown. In practice, the method at the respective MME 15, 16 of managing TAU requests is performed by a processing unit 17, 20 embodied in the form of one or more microprocessors arranged to execute a computer program 18, 21 downloaded to a suitable storage medium 19, 22 associated with the microprocessor, such as a

Random Access Memory (RAM), a Flash memory or a hard disk drive. The respective processing unit 17, 20 is arranged to carry out the method according to embodiments of the present invention when the appropriate computer program 18, 21 comprising computer-executable instructions is downloaded to the storage medium 19, 22 and executed by the processing unit 17, 20. The storage medium 19, 22 may also be a computer program product comprising the computer program 18, 21. Alternatively, the computer program 18, 21 may be transferred to the storage medium 19, 22 by means of a suitable computer program product, such as a Digital Versatile Disc (DVD) or a memory stick. As a further alternative, the computer program 18, 21 may be downloaded to the storage medium 19, 22 over a network. The processing unit 17, 20 may alternatively be embodied in the form of a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), a complex programmable logic device (CPLD), etc.

Figure 3b shows a signaling diagram describing a TAU process according to an embodiment of the present invention. Reference will further be made to Figure 3a for structural elements. Like numbers of the steps performed in Figure 3b refer to corresponding steps of the TAU process described with reference to Figure 1. Hence, when a user moves outside her allocated TA 12 and into a new TA 13, the user's UE 11 will trigger the TAU process in step S201 and submit a TAU request in step 202 to its home eNodeB 14, which in its turn will submit the TAU request in step S203 to the MME 16 of the new TA 13 into which the user moves. The TAU request comprises the old GUTI and further submitted along with the TAU request is a CSG ID. The new MME 16 will turn to the MME 15 (the "old" MME) of the TA 12 currently allocated to the UE 11 for determining whether the UE 11 is authorized to access the CSG indicated along with the TAU request. The new MME 16 thus submits a context request message comprising the old GUTI to the old MME 15 in step S204 and advantageously includes an indication of the CSG, i.e. the CSG ID, in the context request, thereby requesting from the old MME 15 a CSG access control for the UE 11 with respect to the CSG indicated in the request by means of the CSG ID. The CSG ID may be transferred from the new MME 16 to the old MME 15 in the context request in step S204 using private extension of new Information Element (IE).

In reply to this context request, the old MME 15 determines in step 8205a whether the UE 11 is authorized to access the CSG cell of the new TA 13, and provides the new MME 16 with a context response accordingly in step S205. The old MME 15 identifies the UE 11 by means of the old GUTI and the CSG by means of the CSG ID. From previous update location procedures, the old MME 15 holds the CSG subscription data as received from the HSS. The old MME 15 is thus capable of performing a CSG access control. If the UE 11 is allowed to access the CSG, the old MME 15 will indicate (e.g. in a private extension of the context response) that the UE is member of the CSG group to the new MME 16 in the context response, and a TAU can subsequently be successfully performed, and the TAU process may continue as described with reference to Figure 1. However, if not, the old MME 15 will provide the new MME 16 with a context response in step S205 indicating in a private extension that the UE 11 is not a member of the CSG. The new MME 16 thus determines in step 8207a that the 11 is not allowed to access the CSG based on the result of the requested CSG access control, whereby the new MME 16 provides the new eNodeB 14 with a TAU reject response with cause code 25 in step S207b indicating that the UE 11 is not allowed to access the indicated CSG. The new eNodeB 14 will in its turn forward the TAU reject to the UE 11 in step S207C. Advantageously, with this embodiment of the present invention, the new MME is made aware of whether the UE 11 is allowed to access the CSG at a much earlier stage as compared to the prior art TAU process described with reference to Figure 1 and the extensive signalling of Figure 1 is avoided. In addition, the IMSI attach procedure is advantageously avoided. It should be noted that the authentication performed in step S106 with the HSS in Figure 1 has been omitted for illustration purposes.

In an embodiment of the present invention, the context response from the old MME 15 sent in step S205 to the new MME 16 in reply to the context request comprises a GTPv2 cause code for indicating whether the UE 11 is a member of the indicated CSG. Advantageously, in case the UE 11 is not a member of the CSG, the old MME 15 may hence abort the TAU process already after sending the context response to the new MME 16 in step S205. In such a case, there is no need to send a context acknowledgement (as will be described in the following) from the new MME 16, since it is the old MME 15 that takes the decision to reject to TAU request.

Figure 4 illustrates a TAU process according to a further embodiment of the present invention, wherein after the new MME 16 has determined in step S207a whether CSG access is allowed for the UE 11, the new MME 16 sends a context acknowledge message accordingly in step S207 to the old MME 15. In case of non-allowance, the old MME maintains the MM context of the UE 11. This is advantageous, since if no context acknowledge is received at the old MME 15, it will perform a configurable number of retransmissions of the context response, thus trying to obtain an acknowledgement. Eventually, the old MME 15 will stop the retransmissions and consider the procedure rejected, but this embodiment will advantageously thus have the old MME 15 avoid such retransmissions. Figure 5 shows a signaling diagram describing a new TAU process being initiated after the UE 11 has received the TAU reject in step 207c of Figure 3b and Figure 4. After having received the TAU reject, the UE 11 needs to move before requesting a new TAU, either via the new MME or another MME. In this particular example, the UE requests access to a further TA 23 served by yet a new eNodeB 24. Hence, the UE 11 triggers the TAU process in step S201 and submits a TAU request in step 202 to the new eNodeB 24, which in its turn will submit the TAU request in step S203 to the new MME 16 also handling the further TA 23 into which the user moves. The TAU request comprises the old GUTI, and further a CSG ID is submitted in case the further TA 23 is assumed to be a CSG cell. In this particular example, the UE 11 is assumed to be a member of the CSG. The new MME 16 thus submits a context request message including the new CSG ID to the old MME 15 in step S204, and the old MME 15 performs the CSG access control and provides the new MME 16 with a context response accordingly including CSG membership information in step S205, thereby transferring the MM context to the new MME 16. The new MME 16 responds with a context acknowledgement in step S207, and a TAU can subsequently be successfully performed by submitting from the new MME 16 a TAU accept in step S207d to the new eNodeB 24, which in its turn forwards the TAU accept to the UE 11 in step

S207e. Advantageously, since in an embodiment of the present invention, the MM context of this particular UE 11 is maintained at the old MME 15, an IMSI attach is advantageously avoided.

Figure 6 illustrates a flowchart of a method of managing a TAU request at the new MME 16 according to an embodiment of the present invention. In a first step S203, an inter MME TAU process is initiated at the new MME 16. Thus, the new MME 16 receives a TAU request from the home eNodeB 14 indicating the old GUTI, i.e. addressing the old MME 15. The new MME 16 determines in step S204a whether a CSG ID is submitted along with the TAU request, and that cell access mode is not set to "hybrid". If so, the new MME 16 includes in step 8204b the received CSG ID in the context request and sends the context request in step S204 to the old MME 15. If not, the CSG ID is not included in the context request sent to the old MME 15 in step S204.

If the CSG ID was included in the context request, the new MME 16 receives in step S205 a context response with the result of the CSG access control. If in step S207a the CSG access control indicates that the UE 11 is not allowed in the CSG, the new MME 16 sends a context acknowledgement message to the old MME 15 in step S207 with a suitable reject cause, e.g. "User

Authentication Failed". Thereafter, the new MME 16 sends a TAU reject to the home eNodeB 14 in step 8207b with reject cause 25: "Not Authorized for this CSG". If it is determined in step 8207a that the UE 11 indeed is a CSG member, a TAU accept is sent in step S207d.

Figure 7 illustrates a flowchart of a method of managing a TAU request at the old MME 15 according to an embodiment of the present invention. In a first step S204, an inter MME TAU process is initiated at the old MME 15. Thus, the old MME 15 receives a context request from the new MME 16. The old MME 15 determines in step S204C whether a CSG ID is included in context request. If so, the old MME 15 performs a CSG access control in step 8205a, and responds in the context response sent to the new MME 16 in step S205 whether the UE 11 is allowed in the CSG (via the "true" branch) or not (via the "false" branch), possibly by adding an IE to the context response indicating CSG membership information.

If it is determined in step S204C that no CSG ID is included in the context request, the old MME 15 sends a regular context response in step S205.

Figure 8 shows a second management mobility node 16 according to an embodiment of the present invention. The second management mobility node 16 comprises receiving means 31 adapted to receive from a requesting radio access network RAN node a request to perform a TAU for a mobile terminal served by the RAN node, requesting means 32 adapted to request a CSG access control for the mobile terminal with respect to a CSG indicated in the request by providing, to a first mobility management node serving the l8 mobile terminal, a context request for the mobile terminal, which request indicates the CSG. Further, the second management mobility node 16 comprises receiving means 33 adapted to receive from the first mobility management node a context response to the context request indicating whether the mobile terminal is member of the indicated CSG, determining means 34 adapted to determine whether the mobile terminal is allowed to access the CSG based on the context response, and providing means 35 adapted to provide the RAN node with a response to the TAU request indicating that the mobile terminal is not allowed to access the indicated CSG. The means 31-35 may comprise a communications interface for receiving and providing information, and further a local storage for storing data. The means 31-35 may (in analogy with the description given in connection to Figure 3a) be implemented by a processor embodied in the form of one or more microprocessors arranged to execute a computer program downloaded to a suitable storage medium associated with the microprocessor, such as a RAM, a Flash memory or a hard disk drive. The means 31-35 may comprise one or more transmitters and/or receivers and/or transceivers, comprising analogue and digital components and a suitable number of antennae for radio communication. Figure 9 shows a first management mobility node 15 according to an embodiment of the present invention. The first management mobility node 15 comprises receiving means 41 adapted to receive from a second mobility management node a context request for the mobile terminal , which request indicates a CSG, determining means 42 adapted to determine whether the mobile terminal is allowed to access the CSG based on the CSG indicated in the context request, and providing means 43 adapted to provide the second mobility management node with a response to the context request indicating whether the mobile terminal is allowed to access the indicated CSG. The means 41-43 may comprise a communications interface for receiving and providing information, and further a local storage for storing data. The means 41-43 may (in analogy with the description given in connection to Figure 3a) be implemented by a processor embodied in the form of one or more microprocessors arranged to execute a computer program downloaded to a suitable storage medium associated with the microprocessor, such as a RAM, a Flash memory or a hard disk drive. The means 41-43 may comprise one or more transmitters and/or receivers and/or transceivers, comprising analogue and digital components and a suitable number of antennae for radio communication.

The invention has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.

Claims

1. Method at a second mobility management node (16) in a wireless communications network of managing a request for a Tracking Area Update, TAU, comprising:

receiving (S203) from a requesting radio access network, RAN, node

(14) a request to perform a TAU for a mobile terminal (11) served by the RAN node;

requesting (S204) a Closed Subscriber Group, CSG, access control for the mobile terminal (11) with respect to a CSG indicated in the request by providing, to a first mobility management node (15) serving the mobile terminal (11), a context request for the mobile terminal (11), which request indicates the CSG;

receiving (S205) from the first mobility management node (15) a context response to the context request indicating whether the mobile terminal (11) is member of the indicated CSG;

determining (8207a) whether the mobile terminal (11) is allowed to access the CSG based on the context response; and if not

providing (8207b) the RAN node (14) with a response to the TAU request indicating that the mobile terminal (11) is not allowed to access the indicated CSG.

2. The method of claim 1, further comprising:

providing (S207) the second mobility management node (15) with a context acknowledgement that the request for TAU is rejected.

3. The method of claim 1, wherein the received (S205) context response comprises a General Packet Radio Service, GPRS, Tunnelling Protocol,

GTPv2, cause code for indicating that the mobile terminal (11) is not allowed to access the indicated CSG, and the RAN node (14) being provided (8207a) with a response to the TAU request comprising a TAU reject with cause code 25·

4. The method of any one of claims 1-3, wherein the context request is configured with a private extension or Information Element, IE, indicating the CSG.

5. Method at a first mobility management node (15) in a wireless communications network of managing a context request for a mobile terminal (11) served by the first mobility management node (15), comprising: receiving (S204) from a second mobility management node (16) a context request for the mobile terminal (11), which request indicates a Closed

Subscriber Group, CSG;

determining (8205a) whether the mobile terminal (11) is allowed to access the CSG based on the CSG indicated in the context request; and

providing (S205) the second mobility management node (16) with a response to the context request indicating whether the mobile terminal (11) is allowed to access the indicated CSG.

6. The method of claim 5, further comprising:

receiving (S207) a context acknowledgment from the second mobility management node (16) indicating that the request for TAU is rejected.

7. The method of claims 5, wherein the response to the context request comprises a General Packet Radio Service, GPRS, Tunnelling Protocol, GTPv2, cause code for indicating that the mobile terminal (11) is not allowed to access the indicated CSG.

8. The method of any one of claims 5-7, wherein the context response is configured with a private extension or Information Element, IE, indicating whether the mobile terminal (11) is allowed to access the indicated CSG.

9. A second mobility management node (16) in a wireless communications network configured to manage a request for a Tracking Area Update, TAU, comprising a processing unit (20) and a memory (22), said memory containing instructions executable by said processing unit, whereby said node is operative to:

receive from a requesting radio access network, RAN, node (14) a request to perform a TAU for a mobile terminal (11) served by the RAN node; request a Closed Subscriber Group, CSG, access control for the mobile terminal (11) with respect to a CSG indicated in the request by providing, to a first mobility management node (15) serving the mobile terminal (11), a context request for the mobile terminal (11), which request indicates the CSG; receive from the first mobility management node (15) a context response to the context request indicating whether the mobile terminal (11) is member of the indicated CSG;

determine whether the mobile terminal (11) is allowed to access the CSG based on the context response; and if not

provide the RAN node (14) with a response to the TAU request indicating that the mobile terminal (11) is not allowed to access the indicated CSG.

10. The second mobility management node (16) of claim 9, further being operative to:

provide the second mobility management node (15) with a context acknowledgement that the request for TAU is rejected.

11. The second mobility management node (16) of claims 9 or 10, wherein the context request is configured with a private extension or Information Element, IE, indicating the CSG.

12. The second mobility management node (16) of claims 9-11, wherein the received (S205) context response comprises a General Packet Radio Service, GPRS, Tunnelling Protocol, GTPv2, cause code for indicating that the mobile terminal (11) is not allowed to access the indicated CSG, and the RAN node (14) being provided (8207a) with a response to the TAU request comprising a TAU reject with cause code 25.

13. A first mobility management node (15) in a wireless communications network configured to manage a context request for a mobile terminal (11) served by the first mobility management node (15), comprising a processing unit (17) and a memory (19), said memory containing instructions executable by said processing unit, whereby said node is operative to:

receive from a second mobility management node (16) a context request for the mobile terminal (11), which request indicates a Closed Subscriber Group, CSG;

determine whether the mobile terminal (11) is allowed to access the CSG based on the CSG indicated in the context request; and

provide the second mobility management node (16) with a response to the context request indicating whether the mobile terminal (11) is allowed to access the indicated CSG.

14. The first mobility management node (15) of claim 13, further being operative to:

receive a context acknowledgment from the second mobility

management node (16) indicating that the request for TAU is rejected.

15. The first mobility management node (15) of claims 13 or 14, wherein the response to the context request comprises a General Packet Radio Service,

GPRS, Tunnelling Protocol, GTPv2, cause code for indicating that the mobile terminal (11) is not allowed to access the indicated CSG.

16. The first mobility management node (15) of any one of claims 13-15, wherein the context response is configured with a private extension or Information Element, IE, indicating whether the mobile terminal (11) is allowed to access the indicated CSG.

17. A computer program (21) comprising computer-executable instructions for causing a device (16) to perform steps recited in any one of claims 1-4 when the computer-executable instructions are executed on a processing unit (20) included in the device.

18. A computer program product comprising a computer readable medium (22), the computer readable medium having the computer program (21) according to claim 17 embodied therein.

19. A computer program (18) comprising computer-executable instructions for causing a device (15) to perform steps recited in any one of claims 5-8 when the computer-executable instructions are executed on a processing unit (17) included in the device.

20. A computer program product comprising a computer readable medium (19), the computer readable medium having the computer program (18) according to claim 19 embodied therein.