Communication system and method

Abstract

A communication system is disclosed in which one or more procedures / techniques are implemented to support optimisation of procedures for mobility and / or connectivity in the context of small (femto) cells.

Description

COMMUNICATION SYSTEM AND METHOD

[0001] The present disclosure relates to a communication system and to parts thereof. The disclosure has particular but not exclusive relevance to wireless communication systems and devices thereof operating according to the 3rd Generation Partnership Project (3GPP) standards or equivalents or derivatives thereof (including Long-Term Evolution (LTE)-Advanced, Next Generation or 5G networks, future generations, and beyond). The disclosure has particular, although not necessarily exclusive relevance to, the optimisation of procedures for mobility and / or connectivity in the context of small (femto) cells.

[0002] Earlier developments of the 3GPP standards were referred to as the Long-Term Evolution (LTE) of Evolved Packet Core (EPC) network and Evolved Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access Network (E-UTRAN), also commonly referred as '4G'. More recently, the term '5G' and 'new radio' (NR) is used to refer to an evolving communication technology that supports a variety of applications and services. Various details of 5G networks are described in, for example, the 'NGMN 5G White Paper' V1.0 (NPL1). 3GPP intends to support 5G by way of the so-called 3GPP Next Generation (NextGen) radio access network (RAN) and the 3GPP NextGen core network.

[0003] Under the 3GPP standards, a NodeB (or an eNB in LTE, and gNB in 5G) is the radio access network (RAN) node (or simply 'access node', 'access network node' or 'base station') via which communication devices (user equipments or 'UEs') connect to a core network and communicate with other communication devices or remote servers. For simplicity, the present application may use the term access network node, RAN node (or simply RAN) or base station to refer to any such access nodes.

[0004] For simplicity, the present application will use the term mobile device, user device, or UE, to refer to any communication device that is able to connect to the core network via one or more RAN nodes. Although the present application may refer to mobile devices in the description, it will be appreciated that the technology described can be implemented on any communication devices (mobile and / or generally stationary) that can connect to a communication system for sending / receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory. For example, such a communication device may be operable by a human or may be a partially or fully automated (e.g., machine-type-communication (MTC) / Internet of Things (IoT)) device.

[0005] In the current 5G architecture, the RAN architecture may be distributed with the RAN node structure split into two or more parts. In some RAN implementations there are two parts, known as the Central Unit (CU or gNB-CU) - sometimes referred to as a 'control unit' - and the Distributed Unit (DU or gNB-DU), connected by an F1 interface. This enables the use of a 'split' architecture in which the typically 'higher' CU layers (for example, but not necessarily or exclusively, Packet Data Convergence Protocol (PDCP) and Radio Resource Control (RRC) layers) and the, 'lower' DU layers (for example, but not necessarily or exclusively, Radio Link Control (RLC), Media (sometimes referred to as 'Medium') Access Control (MAC), and Physical (PHY) layers) are separated between a particular CU, and one or more DUs that are connected to and controlled by that CU via the F1 interface. Thus, for example, the higher layer CU functionality for a number of RAN nodes may be implemented centrally (for example, by a single processing unit, or in a cloud-based or virtualised system), whilst retaining the lower layer DU functionality locally separately for each RAN node.

[0006] In more recently proposed RAN distributed architectures, in addition to the CU and DU, the concept of a Radio Unit (RU) - sometimes referred to as a 'remote unit' - has been introduced. In this architecture the RU is responsible for handling the digital front end (DFE), digital beamforming functionality and, typically, the functionality of the lower parts of the PHY layer, whilst the DU typically handles the higher parts of the PHY layer and the RLC and MAC layers. The CU in this architecture continues to be responsible for controlling one or more DUs (each DU corresponding to a different respective gNB) and to handle higher layer signalling (typically RRC and PDCP layers).

[0007] The actual functional split between the CU and DUs (and potentially RUs where applicable) of these distributed architectures is flexible allowing the functionality to be optimised for different use cases. Effectively, the split architecture enables a 5G network to use a different distribution of protocol stacks between CU and DUs (and potentially RUs) depending on, for example, midhaul availability and network design.

[0008] The choice of how to split functions in the architecture depends on, among other things, factors related to radio network deployment scenarios, constraints and intended supported use cases. Key considerations include: the need to support a specific quality of service for each service offered and for real / non-real time applications; support of specific user density and load demand in a given geographical area; and available transport networks with different performance levels.

[0009] In 5G, core network entities comprise logical nodes (or 'functions') including control plane functions (CPFs) and one or more user plane functions (UPFs). The CPFs include, amongst other things, one or more Access and Mobility Management Functions (AMFs), a session management function (SMF), an Authentication Server Function (AUSF), a Unified Data Management (UDM) entity for managing user specific data, a Policy Control Function (PCF), an Application Function (AF), a Security Anchor Function (SEAF), an Authentication credential Repository and Processing Function (ARPF), and / or the like. The AMF generally corresponds to the mobility management entity (MME) in 4G and performs many of the functions performed by the MME. Each UPF combines functionality of both the S-GW and P-GW - specifically user plane functionality of the S-GW (SGW-U) and user plane functionality of the P-GW (PGW-U). The SMF provides session management functionality (that formed part of MME functionality in 4G). The SMF also combines the some of the functionality provided by the S-GW and P-GW - specifically control plane functionality of the S-GW (SGW-C) and control plane functionality of the P-GW (PGW-C). The SMF also allocates IP addresses to each UE.

[0010] In earlier releases of communication technology, the concept of 'home' base stations (sometimes referred to as a 'home NodeB' (HNB), or 'home eNB (HeNB)') was introduced and developed. Home base stations were configured to provide a relatively small 'local' coverage area or cell compared to the much larger more conventional 'macro' base stations that were in use at the time. The term 'macro' is generally used to refer to RAN nodes / base stations that provide and control one or more 'macro' cells that cover a relatively large geographical area, whilst the term 'femto' (or sometimes 'pico') refers to a cell that covers a relatively small geographical area often, but not necessarily, overlapping with a macro cell.

[0011] Home base stations provide the same voice and data communication functionality offered by macro base stations but are designed to be deployed in a much more localised scenario, for example in the home of a user, or at enterprise premises (e.g., in a shop, restaurant, office, or the like). The introduction of home base stations offered a number of benefits both to operators and to end users. For example, from the perspective of operators, a home base station can take communication traffic that would otherwise have to be routed via an operator's macro base station, thus reducing the load on that base station. From the perspective of an end-user, a home base station can provide improved coverage in the form of enhanced signal strengths, and / or the filling of holes, or areas of weak signal, in the coverage provided by macro base stations. Since their introduction, home base stations have been deployed successfully for many different scenarios and use cases.

[0012] Historically, in earlier releases, the radio coverage provided by a home base station could be supported via an optional gateway node (e.g., a 'home NodeB gateway' (HNB-GW) or 'home eNB gateway' (HeNB-GW)). This gateway node would typically aggregate traffic from several home base stations and handle communication between each home base station and an appropriate core network entity (e.g., an MME for 4G systems). The gateway node is, in effect, transparent to the core network entity and to the home base station, with the gateway node appearing to be the core network entity the perspective of the home base station, and to be a base station from the perspective of the core network entity.

[0013] Historically, a home base station would typically provide one or more cells of a public land mobile network (PLMN). Each cell provided by the home base station could be associated with a closed subscriber group (CSG), to which a given UE could be subscribed, to allow (optional) restricted access to UEs that are members of (subscribed to) that CSG. In the context of CSG cells each home base station could generally be configured according to any of the following access modes: 　　a 'closed' access mode in which the home base station operates a closed subscriber group (CSG) cell to which only members of the CSG may be provided access; 　　a 'hybrid' access mode in which the home base station operates a CSG cell to which members of the CSG may be provided preferential access whilst non-members are allowed non-preferential (non-CSG) access (for example with a different charging structure, with a different level of service, and / or subject to CSG members being able to successfully access the cell during high load scenarios); and 　　an 'open' access mode in which the home base station operates as a normal (non-CSG) cell to which access is provided openly.

[0014] While a UE is in a connected state (e.g., RRC connected), the UE will perform conventional measurement and mobility procedures based on a configuration provided by the network (e.g., via a serving macro RAN node). However, in the context of home base stations providing CSG cells, there is a potential for a very large number of small (CSG) cells to be provided. In such a scenario, it would be inefficient for the UE to continuously preform measurements, and to continuously read the system information provided, for a large number of small (CSG) cells. To address this, the concept of a proximity indication was introduced for the purposes of indicating when a UE is entering (or leaving) the proximity of one or more CSG cells which the UE is allowed to access.

[0015] Specifically, in a case where the UE is able to determine, using an autonomous search procedure, that it is near a CSG cell that the UE is allowed to access, the UE may provide the serving (source) base station with an indication of proximity. Such a proximity indication may be used as follows: 　　- where a measurement configuration is not present for a frequency and / or radio access technology (RAT) associated with the small (CSG) cell, the serving (source) base station may configure the UE to perform measurements and reporting for that frequency / RAT; and 　　- the serving (source) base station may determine whether to perform other actions related to handover to a home base station based on having received the proximity indication (for example, the serving (source) base station may avoid configuring the UE to acquire system information from a home base station unless the serving (source) base station has received a proximity indication indicating that the UE is close to that home base station).

[0016] NPL 1:'NGMN 5G White Paper' V1.0, the Next Generation Mobile Networks (NGMN) Alliance, February 2015, https: / / ngmn.org / wp-content / uploads / NGMN_5G_White_Paper_V1_0.pdf

[0017] More recently, work has begun to enable home base stations to use more advanced communication technologies (e.g., but not limited to, those referred to as 5G or NR), in order to provide the benefits of those more advanced communication technologies for communication access via smaller cells (e.g., within homes or enterprise premises). In the context of these more advanced communication technologies, a RAN node providing functionality similar to that of a home base station, is typically known as a 'femto' node, 'femto' RAN node, 'femto' base station, or simply a 'femto'. Nevertheless, it will be appreciated that the term 'home base station' may also be used.

[0018] It is envisaged that the architecture for supporting femto nodes that provide access to more advanced communication technologies will be similar to that for more conventional home base stations that use earlier communication technologies. For example, the functionality supported by the femto node may be the same as those supported by a conventional (e.g., 'macro') RAN node, and the procedures between the femto node and the core network may be the same as those between the conventional (e.g., 'macro') RAN node and the core network.

[0019] Moreover, a femto node may be able to communicate with the core network either directly, or indirectly (e.g., via an optional gateway entity referred to as a femto gateway (femto GW)). More specifically, a femto node may be able to communicate, in the control plane, with an appropriate control plane core network entity (e.g., a CPF such as an AMF). This control plane communication may, optionally, be routed indirectly via a femto GW or may be transmitted directly to the core network. Similarly, a femto node will be able to communicate, in the user plane, with an appropriate user plane core network entity (e.g., a UPF). This user plane communication may, optionally, be communicated transparently via a femto GW, or may be transmitted directly to the core network. It will be appreciated that control plane communication for a given femto node may be routed via a femto GW whereas user plane communication for that same femto node may be routed directly to the core network.

[0020] Femto nodes may, however, be able to provide one or more cells of a non-public network (NPN) such as a public network integrated NPN (PNI-NPN), which is an NPN that is deployed with the help of a PLMN.

[0021] Each cell of a PNI-NPN provided by a femto node may be associated with at least a closed access group (CAG) to which a given UE could be subscribed. A CAG is thus similar to a CSG of a PLMN cell, in that it allows (optional) restricted access to UEs that are members of (subscribed to) that CAG. However, a CAG represents a group of subscribers that have access (or preferential access) to an NPN rather than a PLMN.

[0022] In the context of CAG cells, each femto node may generally be configured according to the same access modes that a home base station historically might provide in respect of CSG cells - namely an open access mode, a closed access mode, or a hybrid access mode.

[0023] As mentioned above, a femto node may provide one or more cells as part of a PNI-NPN in order to restrict access to UEs according to the respective subscription. However, each cell of the PNI-NPN may be operated as a cell that shared by both a PLMN and an NPN. Specifically, the cell may be operated as an NPN cell (e.g., that potentially requires access control based on an associated CAG) for one group of UEs (e.g., those with appropriate capabilities), and as a PLMN cell (that does not require access control based on an associated CAG) for another group of UEs - for example those that do not have CAG related capabilities (e.g., legacy UEs).

[0024] To support this capability, the femto node may broadcast, in a cell of a PNI-NPN, both a PLMN identity information list (e.g., in a plmn-IdentityInfoList information element ('IE') or the like) and an NPN identity information list (e.g., in a npn-IdentityInfoList IE, or the like) in system information (e.g., system information block type 1 (SIB1)) that contains the information required for a UE to access that cell. To activate the PNI-NPN cell as an NPN only cell, the femto node may include, in the system information (e.g., SIB1), an indication that the cell is reserved for other use (e.g., a cellReservedForOtherUse IE / indication set to 'TRUE', '1', or the like). To activate the cell as a cell that is shared by both a PLMN and an NPN, on the other hand, the femto node may omit the indication that the cell is reserved for other use (e.g., by setting a cellReservedForOtherUse IE / indication set to 'FALSE', '0', or the like - or by omitting it altogether).

[0025] Hence, a cell in which the indication that the cell is reserved for other use is not provided, may be accessible as an NPN cell by CAG capable UEs (e.g., which have an allowed CAG list that includes a CAG identifier (CAG ID) that is broadcast in that cell). For UEs that do not support CAGs (e.g., legacy UEs) that cell may, nevertheless, be accessible as a normal PLMN cell. Contrastingly, a cell in which the indication that the cell is reserved for other use is provided may only be accessible as an NPN cell, and only may only be accessible by CAG capable UEs (e.g., UEs which have an allowed CAG list that includes a CAG ID broadcast in that cell).

[0026] As with home base stations that provide CSG cells, in order to allow a UE to perform measurements efficiently and to handover to a femto (CAG) cell of a femto node in time, it would be beneficial to introduce a mechanism for letting a serving (source) base station know when the UE is entering or leaving the proximity of one or more CAG cells that the UE is allowed to access.

[0027] In the context of UE connection setup, or a handover procedure, or dual connectivity procedure, to a femto (CAG) cell, the core network entity for mobility management (e.g., the AMF in 5G), or the target femto node, preforms access control to establish whether the UE is allowed to access the network via a given CAG cell. In current communication technology, if the check is not successful, the core network entity for mobility management (e.g., the AMF in 5G), or the target femto node, will reject a UE-associated connection setup request, or handover request, and inform the serving (source) base station.

[0028] However, as the femto node is able to activate a femto cell that is shared by both a PLMN and an NPN, this can lead to unnecessary connection or handover failures because a connection / handover attempt by a CAG capable UE might be rejected (e.g., as a non-member that is not allowed to access the CAG) even though that UE might otherwise be able to access that femto cell - e.g., by accessing that femto cell as a PLMN cell in the manner of a non-CAG capable (legacy) UE.

[0029] There is, therefore, a need to provide one or more enhanced procedures or mechanisms that help to provide optimised connection and / or handover in which connection and / or handover success rates are increased, and / or UE experience is improved.

[0030] The disclosure aims to describe one or more apparatus and / or one or more associated methods that at least partially contributes to addressing one or more of the above needs and / or issues.

[0031] In one aspect, the present disclosure provides a method performed by a user equipment, UE, the method comprising: determining, in a case where the UE is connected via a first radio access network, RAN, node, whether the UE is in or near a closed access group, CAG, member cell of a second RAN node; acquiring from the second RAN node, in a case where the UE is in or near a given CAG member cell, a first cell identifier for the given CAG member cell; sending the first cell identifier to the first RAN node; and receiving from the first RAN node a message for triggering the UE to handover to the second RAN node.

[0032] In one aspect, the present disclosure provides a method performed by a first radio access network, RAN, node, the method comprising: sending, to a second RAN node or another communication node, a message for indicating that handover is requested or required, for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested or required including information indicating a first cell identifier and information indicating a list of at least one allowed CAG identifier; receiving, from the second RAN node or the another communication node, a first message for triggering the UE to handover to the second RAN node; and sending, to the UE, a second message for triggering the UE to handover to the second RAN node.

[0033] In one aspect, the present disclosure provides a method performed by a second radio access network, RAN, node, the method comprising: receiving, from a first RAN node or another communication node, a message for indicating that handover is requested for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested including information indicating a first cell identifier of the given CAG member cell; and sending, to the first RAN node or another communication node, a message for triggering the UE to handover to the second RAN node.

[0034] In one aspect, the present disclosure provides a method performed by a communication node, the method comprising: receiving, from a first RAN node, a message for indicating that handover is required for handover of a user equipment, UE, to a given closed access group, CAG, member cell of a second RAN node, the message for indicating that handover is required including information indicating a first cell identifier of the given CAG member cell and information indicating a list of at least one allowed CAG identifier; performing access control to determine whether the UE is allowed to access the given CAG member cell as a CAG member cell; and sending, to the first RAN node, a message for triggering the UE to handover to the second RAN node.

[0035] In one aspect, the present disclosure provides a method performed by a first radio access network, RAN, node, the method comprising: sending, to a second RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and receiving, from the second RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

[0036] In one aspect, the present disclosure provides a method performed by a second radio access network, RAN, node, the method comprising: receiving, from a first RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and sending, to the first RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

[0037] In one aspect, the present disclosure provides a method performed by a user equipment, UE, the method comprising: sending, to a radio access network, RAN, node, a message for requesting registration of the UE with a closed access group, CAG, member cell; and receiving from the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0038] In one aspect, the present disclosure provides a method performed by a radio access network, RAN, node, the method comprising: receiving, from a user equipment, UE, a first message for requesting registration of the UE with a closed access group, CAG, member cell; sending, to a core network node, the message for requesting registration of the UE with a CAG member cell; receiving from the core network node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell; and sending to the UE, in a case where the UE is not a member of a CAG associated with the CAG member cell, the information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0039] In one aspect, the present disclosure provides a method performed by a core network node, the method comprising: receiving, from a radio access network, RAN, node, a message for requesting registration of a user equipment, UE, with a CAG, member cell; and sending, to the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0040] In one aspect, the present disclosure provides a user equipment, UE, comprising: means for determining, in a case where the UE is connected via a first radio access network, RAN, node, whether the UE is in or near a closed access group, CAG, member cell of a second RAN node; means for acquiring from the second RAN node, in a case where the UE is in or near a given CAG member cell, a first cell identifier for the given CAG member cell; means for sending the first cell identifier to the first RAN node; and means for receiving from the first RAN node a message for triggering the UE to handover to the second RAN node.

[0041] In one aspect, the present disclosure provides a first radio access network, RAN, node comprising: means for sending, to a second RAN node or another communication node, a message for indicating that handover is requested or required, for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested or required including information indicating a first cell identifier and information indicating a list of at least one allowed CAG identifier; means for receiving, from the second RAN node or the another communication node, a first message for triggering the UE to handover to the second RAN node; and means for sending, to the UE, a second message for triggering the UE to handover to the second RAN node.

[0042] In one aspect, the present disclosure provides a second radio access network, RAN, node comprising: means for receiving, from a first RAN node or another communication node, a message for indicating that handover is requested for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested including information indicating a first cell identifier of the given CAG member cell; and means for sending, to the first RAN node or the another communication node, a message for triggering the UE to handover to the second RAN node.

[0043] In one aspect, the present disclosure provides a communication node comprising: means for receiving, from a first RAN node, a message for indicating that handover is required for handover of a user equipment, UE, to a given closed access group, CAG, member cell of a second RAN node, the message for indicating that handover is required including information indicating a first cell identifier of the given CAG member cell and information indicating a list of at least one allowed CAG identifier; means for performing access control to determine whether the UE is allowed to access the given CAG member cell as a CAG member cell; and means for sending, to the first RAN node, a message for triggering the UE to handover to the second RAN node.

[0044] In one aspect, the present disclosure provides a first radio access network, RAN, node comprising: means for sending, to a second RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and means for receiving, from the second RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

[0045] In one aspect, the present disclosure provides a second radio access network, RAN, node, the second RAN node comprising: means for receiving, from a first RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and means for sending, to the first RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

[0046] In one aspect, the present disclosure provides a user equipment, UE comprising: means for sending, to a radio access network, RAN, node, a message for requesting registration of the UE with a closed access group, CAG, member cell; and means for receiving from the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0047] In one aspect, the present disclosure provides a radio access network, RAN, node, the RAN node comprising: means for receiving, from a user equipment, UE, a first message for requesting registration of the UE with a closed access group, CAG, member cell; means for sending, to a core network node, the message for requesting registration of the UE with a CAG, member cell; means for receiving from the core network node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell; and means for sending to the UE, in a case where the UE is not a member of a CAG associated with the CAG member cell, the information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0048] In one aspect, the present disclosure provides a core network node comprising: means for receiving, from a radio access network, RAN, node, a message for requesting registration of a user equipment, UE, with a CAG, member cell; and means for sending, to the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0049] Various examples described below may be implemented by means of a computer program product comprising computer implementable instructions for causing a programmable computer to carry out any of the methods described below. The computer implementable instructions may be provided as a signal or on a tangible computer readable medium.

[0050] Various apparatus and methods will now be described, by way of example, with reference to the accompanying drawings in which:Fig. 1 schematically illustrates a mobile ('cellular' or 'wireless') communication system;Fig. 2 is a simplified sequence diagram illustrating a UE-based / UE-centric procedure for supporting RAN node-to-RAN node interface based mobility in the communication system of Fig. 1;Fig. 3 is a simplified sequence diagram illustrating other UE-based / UE-centric procedures for supporting RAN node-to-RAN node interface based mobility in the communication system of Fig. 1;Fig. 4 is a simplified sequence diagram illustrating a network-based / network-centric procedure for supporting RAN node-to-RAN node interface based mobility in the communication system of Fig. 1;Fig. 5 is a simplified sequence diagram illustrating other network-based / network-centric procedures for supporting RAN node-to-RAN node interface based mobility in the communication system of Fig. 1;Fig. 6 illustrates an abstract syntax notation one (ASN.1) representation of a possible implementation of an information element that may be used to provide PCIs and CAG IDs of CAG cells to a UE as part of a measurement configuration in the communication system of Fig. 1;Fig. 7 is a simplified sequence diagram illustrating procedures for supporting RAN node-to-core network interface based mobility in the communication system of Fig. 1;Fig. 8 is a simplified sequence diagram illustrating a procedure for secondary RAN node addition preparation in respect of a femto node that provides one or more PNI-NPN cells in the communication system of Fig. 1;Fig. 9 is a simplified sequence diagram illustrating a procedure for supporting intra-femto gateway mobility in the communication system of Fig. 1;Fig. 10 is a simplified sequence diagram illustrating other procedures for supporting intra-femto gateway mobility in the communication system of Fig. 1;Fig. 11 is a simplified sequence diagrams illustrating procedures for supporting UE registration with a shared PNI-NPN (CAG) cell of a femto node in the communication system of Fig. 1;Fig. 12 is a simplified schematic block diagram illustrating the main components of a UE for the communication system of Fig. 1;Fig. 13 is a simplified schematic block diagram illustrating the main components of a base station for the communication system of Fig. 1;Fig. 14 is a simplified schematic block diagram illustrating the main components of a femto-gateway for the communication system of Fig. 1; andFig. 15 is a simplified schematic block diagram illustrating the main components of a core network node for the communication system of Fig. 1.

[0051] Overview 　　An exemplary communication system will now be described in general terms, by way of example only, with reference to Fig. 1.

[0052] Fig. 1 schematically illustrates a communication system 1 to which the examples described herein are applicable.

[0053] In the communication system 1, user equipments (UEs) 3 (3-1, 3-2, 3-3) (e.g. mobile telephones and / or other mobile devices) can communicate with each other via a corresponding radio access network (RAN) node 5-1, 5-2 that operates according to one or more compatible radio access technologies (RATs). In the illustrated example, each RAN node 5 (5-1, 5-2) comprises a base station that respectively operates one or more associated cells.

[0054] Communication via each RAN node 5 is typically routed through a core network 7 (e.g. a 5G or later generation core network, evolved packet core network (EPC), or any other core network).

[0055] As those skilled in the art will appreciate, whilst three UEs 3 and two RAN nodes 5 are shown in Fig. 1 for illustration purposes, the system, when implemented, will typically include other RAN nodes and UEs.

[0056] Each RAN node 5 controls one or more associated cells either directly, or indirectly via one or more other nodes (such as home base stations, relays, remote radio heads, distributed units, and / or the like). It will be appreciated that the RAN nodes 5 may be configured to support more than one radio access technology and its associated communication protocols (e.g., 4G, 5G, 6G, and / or later generation, and / or any other 3GPP or non-3GPP communication protocols).

[0057] In the illustrated example a first of the RAN nodes 5-1 is a RAN node (for example a 'wide area' or 'macro' RAN node / base station) that provides one or more relatively large cells (which may be referred to as 'wide area' or 'macro' cells). A second of the RAN nodes 5-2 is a 'femto' RAN node (which may be referred to as a 'local area' or 'home' RAN node / base station - or sometimes simply as a 'femto') that provides one or more relatively small cells (which may be referred to as 'femto' or a 'pico' cells). It will be appreciated that whilst the RAN node 5-1 is described, for clarity, in terms of being a wide area or macro RAN node that provides one or more wide area or macro cells, the RAN node 5-1 could potentially be a 'medium area' RAN node that provides one or more 'medium area' or 'micro' cells.

[0058] The functionality supported by the femto node 5-2 for facilitating communication by the UEs 3 is essentially the same as the functionality provided by the RAN node 5-1 for facilitating communication by the UEs 3. Similarly, the femto node 5-2 and the core network 7 are mutually configured to support the same or similar communication procedures between the femto node 5-2 and the core network 7 as are supported between the RAN node 5-1 and the core network 7.

[0059] As seen in Fig. 1, the femto node 5-2 may be able to communicate with the core network 7 indirectly via a gateway entity (which will be referred to as a femto gateway 9 (femto GW 9)). For example, control plane communication may, optionally, be routed indirectly via a first interface (e.g., a first NG-C / N2 interface) between the femto node 5-2 and the femto GW 9 and via a second interface (e.g., a second NG-C / N2 interface) between the femto GW 9 and the core network 7 (e.g., a CPF 10 such as the AMF 10-1). Similarly, user plane communication may, optionally, be routed transparently to the core network 7 (e.g., a UPF 11) via the femto GW 9 and an appropriate interface (e.g., an NG-U / N3 interface).

[0060] Nevertheless, the femto node 5-2 may be able to communicate with the core network 7 directly without any femto GW 9. Moreover, the femto node 5-2 may be able to communicate with the core network 7 indirectly via a femto GW 9 for some (e.g., control plane) communication and directly for other (e.g., user plane) communication.

[0061] The femto node 5-2 is able to provide one or more cells of a non-public network (NPN) such as a public network integrated NPN (PNI-NPN). Each cell of the PNI-NPN provided by the femto node 5-2 may be associated with at least a closed access group (CAG), to which a given UE 3 may be subscribed, to allow (optional) restricted access to UEs 3 that are members of (subscribed to) that CAG.

[0062] Each UE 3 may have an allowed CAG list, associated with that UE 3, that includes a respective CAG identifier (CAG ID) of each CAG (e.g., within a current PLMN) that the UE 3 may be allowed to access (e.g., as a member of the CAG). The allowed CAG list for the UE 3 may, for example, be provisioned to and stored and maintained at the UE 3. The allowed CAG list for the UE 3 may, for example, be stored / maintained in the core network 7 (e.g., at an AMF 10-1 or the like) and may be provided to a RAN node 5 that serves the UE 3 when needed. A CAG cell that the UE 3 may be allowed to access (i.e., the CAG ID for that CAG cell is in the corresponding allowed CAG list for that UE 3) may be referred to as a CAG member cell for that UE 3.

[0063] Cells served by a femto node 5-2 may be deployed as part of a PNI-NPN in order to restrict access to UEs according to the respective subscription.

[0064] The femto node may use the CAG mechanism for PNI-NPN as follows: 　　The femto node may activate a PLMN cell, which can be accessed by legacy UE without access control of CAG. 　　The femto node may activate an NPN-only cell, then this cell can only be accessed by the UEs whose allowed CAG list includes a CAG-ID broadcasted by the cell. 　　The femto node may activate a cell shared by both PLMN and PNI-NPN. Then this cell is accessible to UEs which have the allowed CAG list including a CAG-ID broadcasted by the cell. For the legacy UE not supporting CAG, this cell is viewed as a normal PLMN cell.

[0065] To support this capability, the femto node 5-2 may broadcast, in a cell of a PNI-NPN, both a PLMN identity information list (e.g., in a plmn-IdentityInfoList information element ('IE') or the like) and an NPN identity information list (e.g., in a npn-IdentityInfoList IE, or the like) in system information (e.g., system information block type 1 (SIB1)) that contains the information required for a UE 3 to access that cell. To activate the PNI-NPN cell as an NPN only cell, the femto node 5-2 may include, in the system information (e.g., SIB1), an indication that the cell is reserved for other use (e.g., a cellReservedForOtherUse IE / indication set to 'TRUE', '1', or the like). To activate the cell as a cell that is shared by both a PLMN and an NPN, on the other hand, the femto node 5-2 may omit the indication that the cell is reserved for other use (e.g., by setting a cellReservedForOtherUse IE / indication set to 'FALSE', '0', or the like - or by omitting it altogether).

[0066] Hence, a cell in which the indication that the cell is reserved for other use is not provided, may be accessible as an NPN cell by CAG capable UEs (e.g., which have an allowed CAG list that includes a CAG ID broadcast in that cell). For UEs that do not support CAGs (e.g., legacy UEs) that cell may, nevertheless, be accessible as a normal PLMN cell. Contrastingly, a cell in which the indication that the cell is reserved for other use is provided may only be accessible as an NPN cell, and only by CAG capable UEs (e.g., which have an allowed CAG list that includes a CAG ID that is broadcast in that cell).

[0067] The UEs 3 and their serving RAN node 5 are connected via an appropriate air interface (for example the so-called 'Uu' interface and / or the like). Neighbouring RAN nodes 5 may be connected to each other via an appropriate RAN node-to-RAN node interface (such as the so-called 'X2' interface, 'Xn' interface and / or the like).

[0068] The core network 7 includes a number of logical nodes (or 'functions') for supporting communication in the communication system 1. In this example, the core network 7 comprises control plane functions (CPFs) 10 and network node entities for the communication of user data (e.g. user plane functions (UPFs) 11). The CPFs 10 include one or more network node entities for the communication of control signalling (e.g. Access and Mobility Management Functions (AMFs) 10-1), one or more network node entities for session management (e.g. Session Management Functions (SMFs) 10-2) and a number of other functions 10-n. Additional functions may include, for example: an Authentication Server Function (AUSF) which facilitates security processes; a Unified Data Management (UDM) entity for managing user specific data (e.g., for access authorization, user registration, and data network profiles); a Policy Control Function (PCF); an Application Function (AF); a Security Anchor Function (SEAF) which is in a serving network and acts as a "middleman" during an authentication process between a UE 3 and its home network; an Authentication credential Repository and Processing Function (ARPF) which maintains the authentication credentials; and / or the like. It will be appreciated that the nodes or functions may have different names in different systems.

[0069] Each RAN node 5 is respectively connected to the core network nodes via appropriate interfaces (or 'reference points') such as an N2 (or NG-C) reference point between the RAN node 5 and the AMF 10-1 for the communication of control signalling, and an N3 (or NG-U) reference point between the RAN node 5 and each UPF 11 for the communication of user data. The UEs 3 are each connected to the AMF 10-1 via a non-access stratum (NAS) connection over an appropriate reference point (e.g., N1 reference point (analogous to the S1 reference point in LTE)). It will be appreciated, that N1 communication is routed transparently via the RAN node 5.

[0070] In a case where the femto node 5-2 communicates, in the control plane, with the core network 7 indirectly via the femto GW 9, that control plane communication may be transmitted via an appropriate control plane interface / reference point (e.g., N2 or the like) with the femto GW 9, and via a similar interface / reference point (e.g., N2 or the like) between the femto GW 9 and the AMF 10-1. In a case where the femto node 5-2 communicates, in the user plane, with the core network 7 indirectly via the femto GW 9, that user plane communication may be communicated transparently via an appropriate user plane interface / reference point (e.g., N3 or the like) between the femto node 5-2 and an associated UPF 11.

[0071] Each UPF 11 is respectively connected to an external data network 20 (e.g. an IP network such as the internet) via an appropriate reference point (e.g., N6 reference point) for communication of the user data.

[0072] The AMF 10-1 performs mobility management related functions, maintains the NAS connection with each UE 3 and manages UE registration. The AMF 10-1 is also responsible for managing paging.

[0073] The SMF 10-2 is connected to the AMF 10-1 via an appropriate reference point (e.g., N11 reference point). The SMF 10-2 provides session management functionality (that formed part of MME functionality in LTE) and additionally combines some control plane functions (provided by the serving gateway and packet data network gateway in LTE). The SMF 10-2 also allocates IP addresses to each UE 3. The SMF 10-2 uses user information provided via the AMF 10-1 to determine what session manager would be best assigned to the user. The SMF 10-2 may be considered effectively to be a gateway from the user plane to the control plane of the network. The SMF 10-2 also allocates IP addresses to each UE 3.

[0074] Each RAN node 5 is also configured for transmission of, and the UEs 3 are configured for the reception of, control information and user data via a number of downlink (DL) physical channels and for transmission of a number of physical signals. The DL physical channels correspond to resource elements (REs) carrying information originated from a higher layer, and the DL physical signals are used in the physical layer and correspond to REs which do not carry information originated from a higher layer.

[0075] The physical channels may include, for example, a physical downlink shared channel (PDSCH), a physical broadcast channel (PBCH), and a physical downlink control channel (PDCCH). The PDSCH carries data sharing the PDSCH's capacity on a time and frequency basis. The PDSCH can carry a variety of items of data including, for example, user data, UE-specific higher layer control messages mapped down from higher channels, system information blocks (SIBs), and paging. The PDCCH carries downlink control information (DCI) for supporting a number of functions including, for example, scheduling the downlink transmissions on the PDSCH and also the uplink data transmissions on a physical uplink shared channel (PUSCH). The PBCH provides at least the UEs 3 with the Master Information Block (MIB). It also, in conjunction with the PDCCH, supports the synchronisation of time and frequency, which aids cell acquisition, selection and re-selection. Specifically, a UE 3 may receive a Synchronization Signal / Physical Broadcast Channel (PBCH) Block (SSB), and the UE 3 may assume that reception occasions of a PBCH, primary synchronization signal (PSS) and secondary synchronization signal (SSS) are in consecutive symbols and form a SS / PBCH block. The RAN node 5 may transmit a number of SSBs corresponding to different DL beams. The total number of SSBs may be confined, for example, within a 5ms duration as an SS burst.

[0076] The DL physical signals may include, for example, reference signals (RSs) and synchronization signals (SSs). A reference signal (sometimes known as a pilot signal) is a signal with a predefined special waveform known to both the UE 3 and the RAN node 5. The reference signals may include, for example, cell specific RSs, UE-specific RSs (UE-RSs), downlink demodulation RSs (DMRSs), and channel state information (CSI) RSs (CSI-RSs).

[0077] Similarly, the UEs 3 are configured for transmission of, and the RAN node 5 is configured for the reception of, control information and user data via a number of uplink (UL) physical channels corresponding to REs carrying information originated from a higher layer, and UL physical signals which are used in the physical layer and correspond to REs which do not carry information originated from a higher layer. The physical channels may include, for example, the PUSCH, a physical uplink control channel (PUCCH), and / or a physical random-access channel (which may be abbreviated as either 'PRACH' or 'RACH' - the term (P)RACH will be used herein). The UL physical signals may include, for example, demodulation reference signals (DMRS) for a UL control / data signal, and / or sounding reference signals (SRS) used for UL channel measurement.

[0078] Control Information 　　In the communication system 1, the RAN node 5 is configured to transmit control information to the UE 3 using one or more control resource sets (CORESETs). A CORESET is a set of time-frequency resources within which the UE 3 can search for DCI transmitted by a RAN node 5 on a PDCCH. A CORESET is analogous to the control region at the start of subframes in earlier generations of communication technology. Unlike earlier generations, however, in which the frequency domain of the control region typically corresponded to the total system bandwidth, the frequency domain location for CORESET is localised to a specific region in the frequency domain and has a variable width that can be set to any suitable value (typically in multiples of six resource blocks where each resource block comprises twelve subcarriers in the frequency domain).

[0079] A number of different DCI formats can be used by the RAN node 5, depending on requirements, for transmission on a PDCCH corresponding to one of the PDCCH candidates in one of the search spaces configured for a given UE 3. For example, the RAN node 5 may be able to transmit DCI using one or more of the currently standardised DCI formats as set out in Table 1.

[0080] Different DCI formats may or may not have the same DCI size. Moreover, DCI using a given DCI format may be configured for a specific purpose by addressing the DCI using a corresponding radio network temporary identifier (RNTIs) that a UE 3 may monitor for (e.g., by using the corresponding RNTI to scramble the cyclic redundancy check (CRC) bits of the DCI). Depending on the specific purpose to which the RNTI used relates, a given DCI format used may have different fields for carrying a different corresponding payload.

[0081] Random-Access Procedures 　　Each UE 3 and each RAN node 5 of the communication system 1 are mutually configured for performing their part of a (P)RACH procedure, for example when the UE 3 initially accesses the network or at other times when necessary.

[0082] For example, for initial access, on detection and selection of a beam the UE 3 is able to attempt access to the cell via that beam using an initial RRC connection setup procedure comprising a contention-based random-access (CBRA) procedure. Prior to attempting initial access, the UE 3 chooses random-access resources (including, for example, a preamble) to use to initiate the (P)RACH procedure. The UE 3 then sends the selected preamble (e.g., in 'Msg1') to the RAN node 5 over a (P)RACH for initiating the process to obtain synchronization in the uplink (UL).

[0083] In response to Msg1, the RAN nodes 5 responds with a random-access response (RAR) (or 'Msg2'). The RAR indicates reception of the preamble and typically includes, for example: a timing-alignment (TA) command for adjusting the transmission timing of the UE 3 based on the timing of the received preamble; an uplink grant field indicating the resources to be used in the uplink for a physical uplink shared channel (PUSCH); a frequency hopping flag to indicate whether the UE 3 is to transmit on the PUSCH with or without frequency; a modulation and coding scheme (MCS) field from which the UE 3 can determine the MCS for the PUSCH transmission; and a transmit power control (TPC) command value for setting the power of the PUSCH transmission.

[0084] A random-access RNTI (RA-RNTI) is associated, by the RAN node 5, with a RACH occasion (RO) in which the preamble is sent by the UE 3. The RA-RNTI is used to scramble the CRC bits of a DCI (e.g., using DCI format 1_0) used for scheduling transmission of a PDSCH that carries the RAR.

[0085] The RA-RNTI may be computed follows: 　　RA-RNTI= 1 + s_id + 14 × t_id + 14 × 80 × f_id + 14 × 80 × 8 × ul_carrier_id Where: 　　s_id is an index of the first OFDM symbol of the RO (0 <= s_id < 14); 　　t_id is an index of the first slot of the RO in a system frame (0 <= t_id < 80); 　　f_id is an index of the RO in the frequency domain (0 <= f_id < 8); and 　　ul_carrier_id is an identifier of the uplink carrier used for the random-access preamble transmission.

[0086] Following receipt of the RAR, the UE 3 then sends a third message ('Msg3') to the network over a physical uplink shared channel (PUSCH) based on the information in the RAR. The specific message sent by the UE 3 in this step, and the content of the message, depends on the context in which the (P)RACH procedure is being used. In the example of initial radio RRC connection setup, however, Msg3 typically comprises an RRC setup request or similar message carrying a temporary randomly generated UE identifier. The network responds with a fourth message ('Msg4') which carries the randomly generated UE identifier received in Msg3 (for contention resolution purposes) to resolve any collisions between different UEs 3 using the same preamble sequence. When successful, Msg4 also transfers the UE 3 to a connected state.

[0087] While a four-step (P)RACH procedure is described it will be appreciated that, each UE 3 and RAN node 5 may be configured for performing a two-step (P)RACH procedure (e.g., as mentioned in the introduction). Effectively, the two-step (P)RACH procedure is achieved by combining the UE's (P)RACH preamble (Msg1) transmission and the scheduled PUSCH transmission (Msg3) into a single message (referred to as 'MsgA'). Similarly, the random-access response (RAR / Msg2) from the RAN node 5 to the UE 3 and the contention resolution message (Msg4) are combined in the two-step random-access procedure (and referred to as 'MsgB').

[0088] Moreover, it will be appreciated that, while a contention-based random-access (CBRA) procedure is described each UE 3 and each RAN node 5 may also be mutually configured for performing a non-contention based 'contention free' random-access (CFRA) procedure in which a dedicated preamble may be assigned by the RAN node 5 to the UE 3. For example, while the UE 3 can trigger initiation of a CBRA procedure itself (e.g., when the UE 3 needs to connect to the network), initiation of a CFRA procedure may be triggered by the network. For example, a (P)RACH procedure may be initiated via a message sent via DCI with an appropriate DCI format (e.g. 1_0) in a PDCCH - such a message is commonly known as a PDCCH order. A CFRA procedure may be also initiated by a RAN node 5 when handover is required (e.g., using a handover command message).

[0089] Carrier Aggregation (CA) 　　In the communication system 1, increases in bandwidth, and thereby bitrate can be achieved through carrier aggregation (CA), whereby multiple frequency blocks, i.e., component carriers (CCs), are assigned to the same UE 3 for use. Each CC in turn serves a cell which provides a particular bandwidth and set of services to the UE 3. For example, in CA each UE 3 has a first CC that provides a primary cell (PCell) that carries traffic and RRC signalling messages and may additionally any number of other CCs that each provide their own corresponding secondary cell (SCell) which carry traffic alone. The SCells are optional, and are added, removed, and / or reconfigured are required by the UE 3 and the network.

[0090] In CA, when initially scanning for a cell to camp on each UE 3 scans for a PCell. The PCell is serves as the main point of communication between the UE 3 and the RAN node 5 and is responsible for all control information signalling (e.g., RRC Configuration signalling), non-access stratum (NAS) signalling, and the like, between the UE 3 and the network, as well as initial data transmissions. The PCell typically offers a high bandwidth for low latency data transmission. It will be appreciated that when initially scanning for a PCell to camp on each UE 3 searches for SSB as described previously to enable efficient cell searching for, and initial access to the PCell.

[0091] As and when required, the UE 3 may be triggered to search for, and camp on one or more secondary cells (SCells) to provide additional capacity and adaptability in the network. For example, the UE 3 may be triggered to search for, and camp on one or more SCells to provide extra bandwidth when the network is experiencing high data traffic or congestion. Additionally, or alternatively, SCells may be camped on to provide specific specialist services, for example, the UE 3 may camp onto a SCell that caters for Internet-of-Things (IoT) devices, high-definition data streaming, or the like.

[0092] Dual Connectivity (DC) 　　The UEs 3 and RAN nodes 5 of the communication system are also mutually configured for dual connectivity in which the UE 3 can be configured to connect and communicate via (at least) two different RAN nodes 5 known as a master RAN node 5 and a secondary RAN node 5 that are themselves interconnected via an appropriate RAN node-to-RAN node interface (e.g., Xn or X2). It will be appreciated that, in dual connectivity, the master RAN node 5 and the secondary RAN node 5 may be configured to use the same, or a different, radio access technology (e.g., the RAN nodes 5 may each use a different one of a 4G, 5G, 6G (or other) radio access technology).

[0093] CA can also be used by a UE 3, in the context of dual connectivity. For example, a UE 3 may be configured to communicate via one, or multiple (carrier aggregated) cells of the master RAN node 5 and via one, or multiple (carrier aggregated) cells of the secondary RAN node 5.

[0094] A group of serving cells associated with the master RAN Node 5 may be referred to as a master cell group (MCG). The MCG typically comprises a so-called special cell (SpCell) which is the PCell (Primary Cell), and one or more SCells. A group of serving cells associated with the secondary RAN Node may be referred to as a secondary cell group (SCG). The SCG typically comprises an SpCell, which is known as a primary SCell (PSCell) in this case, and one or more SCells.

[0095] It will be appreciated that whilst CA and DC are conceptually similar, there are a number of differences. For example, in CA the user traffic is typically split between different carriers at the MAC layer, whereas in DC user traffic is typically split at the PDCP layer.

[0096] Mobility / Connectivity in the Context of Femto Cells 　　Beneficially, as described in more detail later, each RAN node 5, and UE 3, of the communication system 1 is mutually configured for implementing one or more procedures / mechanisms for supporting mobility and / or connectivity of the UE 3 to (and / or from) a CAG member cell, for the UE 3, provided by the femto node 5-2.

[0097] Beneficially, for example, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting RAN node-to-RAN node interface (e.g., 'Xn' interface) based mobility of the UE 3, to a CAG member cell provided by the femto node 5-2. Specifically, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more procedures / mechanisms for indicating, to a serving RAN node 5 (e.g., the RAN node 5-1), when the UE 3 might be in (or near to) a CAG member cell for the UE 3 - e.g., to allow the serving RAN node 5-1 to trigger a handover of the UE 3, to the femto node 5-2, that provides that CAG member cell.

[0098] The indication of when the UE 3 might be in (or near to) a CAG member cell, may be provided, in a UE-based or UE-centric manner, as an explicit 'proximity' indication from a connected (e.g., RRC connected) UE 3 when, following an autonomous search completed by the UE 3, the UE 3 determines that it may be in (or near) a CAG member cell (i.e., a CAG cell that the UE 3 may be allowed to access (CAG). This proximity indication may then trigger the serving RAN node 5-1 to configure the UE 3 to perform measurements and reporting for a corresponding frequency / RAT, and / or to configure the UE 3 to acquire system information from the femto node 5-2 for the CAG member cell (e.g., to obtain an associated cell global identity (CGI)) for subsequent reporting to the serving RAN node 5-1 for supporting a possible subsequent mobility procedure.

[0099] It will be appreciated that provision of the CGI, for the CAG member cell, to the serving RAN node 5-1, helps to mitigate the risk of PCI confusion that can arise because, due to the size of femto cells, there can be more than one femto cell within the coverage of the serving RAN node 5-1 that share the same PSC / PCI.

[0100] Nevertheless, the indication of when the UE 3 might be in (or near to) a CAG member cell, may be provided, in a network-based or network-centric manner, in which the serving RAN node 5 (e.g., the RAN node 5-1) provides, to a connected e.g., RRC connected) UE 3, a respective identifier (e.g., a physical cell identifier (PCI)) of each of one or more CAG cells having a corresponding CAG ID that is in the allowed CAG list for the UE 3 (e.g., with or in advance of a measurement configuration). When the UE 3 determines that it may be in (or near) a CAG member cell it can then acquire the required system information from the femto node 5-2 for the CAG member cell (e.g., to obtain an associated cell global identity (CGI)) for subsequent reporting to the serving RAN node 5-1 for supporting a possible subsequent mobility procedure in which access control may be performed at the femto node 5-2.

[0101] Beneficially, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting RAN node-to-core network interface (e.g., 'NG-C' or 'N2' interface) based mobility of the UE 3, to a CAG member cell provided by the femto node 5-2. For example, as with the procedures / mechanisms for supporting RAN node-to-RAN node interface based mobility mentioned above, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more procedures / mechanisms for indicating, to a serving RAN node 5-1, when the UE 3 might be in (or near to) a CAG member cell for the UE 3 - e.g., to allow the serving RAN node 5-1 to trigger a handover of the UE 3, to the femto node 5-2, that provides that CAG member cell. However, in this case, the handover may be managed over the interface (e.g., 'NG-C' or 'N2' interface) between the serving RAN node 5-1 and an appropriate core network entity (e.g., AMF 10-1) in the core network 7, and that core network entity (e.g., AMF 10-1) may perform access control.

[0102] Moreover, the indication of when the UE 3 might be in (or near to) a CAG member cell, may be provided, in a UE-based / UE-centric manner or a network-based / network-centric manner as described for the procedures / mechanisms for supporting RAN node-to-RAN node interface based mobility mentioned above.

[0103] Beneficially, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting dual connectivity involving both a PNI-NPN (CAG) cell and a normal PLMN (non-CAG) cell. Specifically, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more procedures / mechanisms for facilitating the addition of the femto node 5-2 as a secondary RAN node 5, and hence of a femto cell, provided by the femto node 5-2, as an SCell, to support dual connectivity.

[0104] Beneficially, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting intra-femto gateway handover in the context of PNI-NPN (CAG) cells.

[0105] Beneficially, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting UE attach to a shared PNI-NPN (CAG) cell.

[0106] It will be appreciated that whilst a number of different enhanced procedures / mechanisms are introduced above and described in more detail later, the procedures / mechanisms are neither mutually exclusive nor mutually dependent on one another. The communication system 1 may implement all, or a subset of one or more of the procedures / mechanisms described.

[0107] For example, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement both, or only one of, the procedures / mechanisms for supporting RAN node-to-RAN node interface (e.g., 'Xn' interface) based mobility involving the UE-based / UE-centric proximity mechanism and / or the procedures / mechanisms for supporting RAN node-to-RAN node interface (e.g., 'Xn' interface) based mobility involving the network-based / network-centric proximity mechanism. Similarly, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement both, or only one of, the procedures / mechanisms for supporting RAN node-to-core network based mobility involving the UE-based / UE-centric proximity mechanism and / or the procedures / mechanisms for supporting RAN node-to-core network based mobility involving the network-based / network-centric proximity mechanism.

[0108] RAN Node-to-RAN Node Interface (e.g., Xn) Based Handover 　　As mentioned above each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting RAN node-to-RAN node interface based mobility of the UE 3, to a CAG member cell provided by the femto node 5-2. A number of such procedures / mechanisms will now be described, by way of example only, with reference to Figs. 2 to 6.

[0109] UE-based Proximity Indication 　　Figs. 2 and 3 are simplified sequence diagrams illustrating UE-based / UE-centric procedures for supporting RAN node-to-RAN node interface based mobility in the communication system 1. The core procedures illustrated in Figs. 2 and 3 are essentially the same. However, Fig. 2 illustrates a case in which access control is successful, whereas Fig. 3 illustrates a case in which access control is not successful and different ways in which such a failure can be handled.

[0110] In the example of Fig. 2, the RAN node 5-1 is initially serving the UE 3 and acts as a source node for handover in the illustrated procedure. Similarly, the femto node 5-2 is operating as a target node for the handover in the illustrated procedure. Accordingly, the RAN node 5-1 will be referred to as the source RAN node 5-1, and the femto node 5-2 will be referred to as the target femto node 5-2, in the further description of this procedure.

[0111] Initially the UE 3 is in an RRC connected mode / state with respect to the source RAN node 5-1. It will be appreciated that, while in this RRC connected state, the UE 3 may perform normal measurement and mobility procedures, that will be familiar to those skilled in the art, based on appropriate measurement / measurement reporting configurations provided by the source RAN node 5-1.

[0112] As seen in Fig. 2, the source RAN node 5-1 configures the UE 3 with proximity indication control. For example, the source RAN node 5-1 may send an appropriate configuration message (e.g., an RRC reconfiguration message or the like) including an appropriate proximity reporting configuration (e.g., a reportProximityConfig IE or the like) which may indicate, for example, whether or not provision of a proximity indication is respectively enabled for CAG member cells of each RAT of interest.

[0113] When the UE 3 determines that it may be in (or near) one or more CAG member cells (e.g., of the target femto node 5-2) for that UE 3, the UE 3 sends, at S212, an appropriate proximity indication (e.g., using a proximityindication message or the like) to indicate that the UE 3 is entering the proximity of one or more (potential) CAG member cells. The determination of the proximity to a potential CAG member cell may, for example, be based on autonomous search procedures carried out at the UE 3. The proximity indication may, for example, include an indication that the proximity indication is an 'entering' type of proximity indication (e.g., as opposed to a 'leaving' type of proximity indication). The proximity indication may also include an indication of the RAT and / or frequency of the potential CAG member cell to which the proximity indication relates. For example, where the potential CAG member cell is an femto cell of a particular RAT (e.g., NR) the proximity indication may indicate a corresponding carrier frequency (e.g., NR carrier frequency) by including an appropriate absolute radio frequency channel number (ARFCN) value (e.g., ARFCN-valueNR) in an appropriate carrier frequency IE (e.g., a carrierFreq IE or the like).

[0114] If needed, following receipt of the proximity indication, the source RAN node 5-1 may then, at S214, configure the UE 3 to perform measurements and reporting for the frequency / RAT indicated in the proximity indication. The source RAN node 5-1 may, for example, configure the UE 3 with a relevant measurement configuration (including measurement gaps if needed) using an appropriate configuration message (e.g., an RRC reconfiguration message or the like).

[0115] The UE 3 may subsequently perform any measurements configured by the measurement configuration, on the corresponding RAT and frequency (as indicated by the proximity indication), and report the results of the measurements at S216.

[0116] The measurement report sent at S216 includes a PCI of the measured potential CAG member cell thus allowing the source RAN node 5-1 to configure the UE 3 to perform system information (SI) acquisition and reporting for that PCI. The source RAN node 5-1 may thus (e.g., based on the content of the measurement report) decide that handover of the UE 3 to the potential CAG member cell as a target cell is appropriate / needed.

[0117] At S218, the source RAN node 5-1 configures the UE 3 to perform SI acquisition (e.g., to acquire the CGI) of the potential CAG member cell (represented by a corresponding PCI). For example, the source RAN node 5-1 may configure the UE 3 to perform SI acquisition by including an appropriate indication (e.g. an si-Request IE) or the like in a corresponding measurement configuration which may be sent using an appropriate configuration message (e.g., an RRC reconfiguration message or the like).

[0118] The UE 3 then performs, at S220, SI acquisition by listening to a corresponding broadcast channel (BCCH), of the target femto node 5-2, using autonomous gaps. Specifically, the UE 3 may suspend reception and transmission with the source RAN node 5-1 to acquire the relevant system information (CGI) for the potential CAG member cell from the target femto node 5-2. When the system information (CGI) for the potential CAG member cell has been acquired, the UE 3 can send the CGI to the source RAN node 5-1 (e.g., in a measurement report or the like) as indicated at S222.

[0119] When the source RAN node 5-1 sends a handover request message to the target femto node 5-2 to initiate an attempted handover of the UE 3 to the potential CAG member cell as the target cell, at S224, the source RAN node 5-1 is thus able to include, in that handover request message, the CGI for the potential CAG member cell received from the UE 3. The source RAN node 5-1 also includes a list of the allowed CAG IDs for the UE 3 in the handover request message. The list of allowed CAG IDs may form part of information indicating allowed PNI-NPNs, allowed UE mobility, whether the UE 3 is allowed to access non-CAG cells for a given PLMN, and / or the like (e.g., part of an allowed PNI-NPN ID List IE or the like as seen in Fig. 2). It will be appreciated that the list of allowed CAG IDs may be provided to the RAN node 5-1 during a UE registration procedure or the like.

[0120] The target femto node 5-2 performs access control for the potential CAG member cell as the target cell) at S226 based on the allowed CAG ID List (and a selected target PLMN) to determine whether the UE 3 is allowed to access the potential CAG member cell. In the example, illustrated the access control procedure confirms that the UE 3 is allowed to access the potential CAG member cell (i.e., that the potential CAG member cell can be accessed as a CAG member cell for the UE 3). Accordingly, access control is successful and the target femto node 5-2 accepts the handover to the target cell, allocates appropriate resources, and sends, at S228 an appropriate message for acknowledging the handover request message (e.g., a handover request acknowledgement message or the like). The handover request acknowledgement message may, for example, include a handover command (e.g., an RRC reconfiguration message or the like), that contains information required to access the target cell, and that is to be sent by the source RAN node 5-1 to the UE 3 to perform the handover.

[0121] As indicated at S230, the handover command (e.g., the RRC reconfiguration message or the like) may thus be sent, by the source RAN node 5-1, to the UE 3, to complete the handover preparation phase and to initiate a handover execution phase.

[0122] Thus, the UE 3 and RAN nodes 5 can coordinate with one another to perform handover execution and handover completion (as indicated at S232), in a manner that will be familiar to those skilled in the art, to complete handover of the UE 3 to the target femto node 5-2.

[0123] As mentioned above, Fig. 3 illustrates a case in which access control is not successful and different ways in which such a failure can be handled. Specifically, in the example of Fig. 3 the initial part of the procedure is essentially the same as that shown and described with reference to steps S210 to S224 of Fig. 2. However, when access control is performed, the access control procedure determines that the UE 3 is not allowed to access the potential CAG member cell as a target cell (i.e., that the potential CAG member cell cannot be accessed as a CAG member cell for the UE 3). Accordingly, access control fails as indicated at S526.

[0124] The failure procedure may then proceed in either of two different ways.

[0125] First Option: 　　In a first option, illustrated at S330-1, the femto node 5-2 rejects the handover request by sending, at S332, an appropriate failure message (e.g., a handover preparation failure message or the like) including information indicating the cause of the failure (e.g., a value of a cause IE or the like) to be "Not a CAG member". Where the target cell of the femto node 5-2 is a shared cell (i.e. a cell that is shared as both a normal PLMN cell and as a CAG cell) (and the UE 3 is allowed to access non-CAG cells), then the source RAN node 5-1 may (optionally) decide whether or not to trigger a new attempt to handover the UE 3 to that target cell (as a normal PLMN cell) as if the UE 3 is a non-CAG (e.g., legacy) UE 3.

[0126] In the illustrated example the source RAN node 5-1 decides to trigger a new attempt to handover the UE 3 to the target cell (as a normal PLMN cell) as if the UE 3 is a non-CAG (e.g., legacy) UE 3 at S334. Accordingly, the source RAN node 5-1 sends, at S336, a new handover request message to the target femto node 5-2 to initiate another attempted handover of the UE 3 to the target cell (as a normal PLMN cell). However, in this case, the source RAN node 5-1 does not include the list of the allowed CAG IDs for the UE 3 (or allowed PNI-NPN ID List IE including the list of the allowed CAG IDs).

[0127] The target femto node 5-2 may then treat the UE 3 as a non-member (e.g., legacy) UE 3 attempting to handover to a normal PLMN cell. The target femto node 5-2 may (optionally), for example, perform appropriate admission control (not shown) - e.g., to determine if the required resources can be granted by the target femto node 5-2.

[0128] Assuming any admission control is successful, the target femto node 5-2 may accept the handover to the target cell (as a normal PLMN cell), allocate appropriate resources, and send, at S338 an appropriate message for acknowledging the handover request message (e.g., a handover request acknowledgement message or the like). The handover request acknowledgement message may, for example, include a handover command (e.g., an RRC reconfiguration message or the like), that contains information required to access the target cell (as a normal PLMN cell), and that is to be sent by the source RAN node 5-1 to the UE 3 to perform the handover.

[0129] As indicated at S342, the handover command (e.g., the RRC reconfiguration message or the like) may thus be sent, by the source RAN node 5-1, to the UE 3, to complete the handover preparation phase and to initiate a handover execution phase. In this case, however, the handover command may include (or be sent with) information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0130] On receipt of a handover command including (or sent with) information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3, the UE 3 may determine whether or not to handover to the target cell (as a normal PLMN cell) of the target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3.

[0131] If the UE 3 decides to handover to the target cell (as a normal PLMN cell) of target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3, then the UE 3 and RAN nodes 5 can coordinate with one another to perform handover execution and handover completion, in a manner that will be familiar to those skilled in the art, to complete handover of the UE 3 to the target femto node 5-2.

[0132] Second Option: 　　In a second option, illustrated at S330-2, where the target cell of the femto node 5-2 is a shared cell (and the UE 3 is allowed to access non-CAG cells), the femto node 5-2 does not reject the handover request but instead allocates appropriate resources and sends, at S340, an appropriate message for acknowledging the handover request message (e.g., a handover request acknowledgement message or the like). The handover request acknowledgement message may, for example, include a handover command (e.g., an RRC reconfiguration message or the like), that contains information required to access the target cell, and that is to be sent by the source RAN node 5-1 to the UE 3 to perform the handover. The femto node 5-2 includes, in the handover request acknowledgement message (e.g., in (or with) the handover command), information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0133] As indicated at S342, the handover command (e.g., the RRC reconfiguration message or the like) may thus be sent, by the source RAN node 5-1, to the UE 3, to complete the handover preparation phase and to initiate a handover execution phase. In this case, however, the handover command may include (or be sent with) the information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0134] On receipt of a handover command including (or sent with) information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3, the UE 3 may determine whether or not to handover to the target cell (as a normal PLMN cell) of target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3.

[0135] If the UE 3 decides to handover to the target cell (as a normal PLMN cell) of target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3, then the UE 3 and RAN nodes 5 can coordinate with one another to perform handover execution and handover completion, in a manner that will be familiar to those skilled in the art, to complete handover of the UE 3 to the target femto node 5-2.

[0136] It will be appreciated that in the procedures described with reference to Figs. 2 and 3, whilst a femto GW 9 is not shown, the target femto node 5-2 may communicate with the core network 7 (e.g., an AMF 10-1 in the core network 7) via a femto GW 9.

[0137] Network-based Proximity Indication 　　Figs. 4 and 5 are simplified sequence diagrams illustrating network-based / network-centric procedures for supporting RAN node-to-RAN node interface based mobility in the communication system 1. The core procedures illustrated in Figs. 4 and 5 are essentially the same. However, Fig. 4 illustrates a case in which access control is successful, whereas Fig. 5 illustrates a case in which access control is not successful and different ways in which such a failure can be handled.

[0138] In the example of Fig. 4, at some time prior to the handover procedure, the RAN node 5-1 and the femto node 5-2 engage in a RAN node-to-RAN node interface application protocol (e.g., Xn application protocol (XnAP)) based setup procedure (e.g., an Xn setup procedure) to exchange application level configuration data needed for the two RAN nodes 5 to interoperate correctly over the RAN node-to-RAN node interface (as indicated at S406).

[0139] During this setup procedure, the femto node 5-2 sends a list of one or more supported CAG IDs and one or more associated PCIs of one or more CAG cells provided by the femto node 5-2, to the (neighbour) RAN node 5-1 (as indicated at S408). The list of one or more supported CAG IDs and one or more associated PCIs may, for example: be sent in a RAN node-to-RAN node interface application protocol (e.g., XnAP) setup request message (e.g., an Xn setup request or the like); or be sent in a RAN node-to-RAN node interface application protocol (e.g., XnAP) setup response message (e.g., an Xn setup response or the like).

[0140] The (neighbour) RAN node 5-1 then records this information in a neighbour relation table (NRT) at S410.

[0141] Later, when the UE 3 has entered an RRC connected mode / state with respect to the RAN node 5-1 (at S412), and the RAN node 5-1 has begun serving the UE 3, the RAN node 5-1 acts as a source node for handover in the procedure illustrated in Fig. 4. Similarly, the femto node 5-2 is acts as a target node for the handover in the procedure illustrated in Fig. 4. Accordingly, the RAN node 5-1 will be referred to as the source RAN node 5-1, and the femto node 5-2 will be referred to as the target femto node 5-2, in the further description of this procedure.

[0142] After the UE 3 has connected to the source RAN node 5-1 at S412, the source RAN node 5-1 sends, to the UE 3, the respective PCI and CAG ID of one or more CAG cells represented in the allowed CAG ID list for the UE 3. The allowed CAG ID list for the UE 3 may, for example, be obtained from an AMF 10-1 or a neighbour RAN node 5.

[0143] The PCI and CAG ID of each CAG cell may be sent separately to (e.g., in advance of) the transmission of measurement configuration. Nevertheless, as indicated at S414, the PCI and CAG ID of each CAG cell may be sent together with a relevant measurement configuration (including measurement gaps if needed) using an appropriate configuration message (e.g., an RRC reconfiguration message or the like). The PCI and CAG ID of each CAG cell may, for example, be sent as a conditional reconfiguration. By way of example only, Fig. 6 illustrates an abstract syntax notation one (ASN.1) representation of a possible implementation of an information element (a conditional trigger configuration IE) that may be used to provide the PCI and CAG ID of each CAG cell, to the UE 3, as part of a measurement configuration in the communication system 1.

[0144] When UE determines it is near a CAG member cell, the UE 3 then performs, at S422, SI acquisition by listening to a corresponding broadcast channel (BCCH), of the target femto node 5-2, using autonomous gaps. Specifically, the UE 3 may suspend reception and transmission with the source RAN node 5-1 to acquire the relevant system information (CGI) for the potential CAG member cell from the target femto node 5-2. When the system information (CGI) for the potential CAG member cell has been acquired, the UE 3 can send the CGI to the source RAN node 5-1 (e.g., in a measurement report or the like) as indicated at S422.

[0145] When the source RAN node 5-1 sends a handover request message to the target femto node 5-2 to initiate an attempted handover of the UE 3 to the potential CAG member cell as the target cell, at S424, the source RAN node 5-1 is thus able to include, in that handover request message, the CGI for the potential CAG member cell received from the UE 3. The source RAN node 5-1 also includes a list of the allowed CAG IDs for the UE 3 in the handover request message. The list of allowed CAG IDs may form part of information indicating allowed PNI-NPNs, allowed UE mobility, whether the UE 3 is allowed to access non-CAG cells for a given PLMN, and / or the like (e.g., part of an allowed PNI-NPN ID List IE or the like as seen in Fig. 4). It will be appreciated that the list of allowed CAG IDs may be provided to the RAN node 5-1 during a UE registration procedure or the like.

[0146] The target femto node 5-2 performs access control for the potential CAG member cell as the target cell) at S426 based on the allowed CAG ID List (and a selected target PLMN) to determine whether the UE 3 is allowed to access the potential CAG member cell. In the example illustrated, the access control procedure confirms that the UE 3 is allowed to access the potential CAG member cell (i.e., that the potential CAG member cell can be accessed as a CAG member cell for the UE 3). Accordingly, access control is successful and the target femto node 5-2 accepts the handover to the target cell, allocates appropriate resources, and sends, at S428 an appropriate message for acknowledging the handover request message (e.g., a handover request acknowledgement message or the like). The handover request acknowledgement message may, for example, include a handover command (e.g., an RRC reconfiguration message or the like), that contains information required to access the target cell, and that is to be sent by the source RAN node 5-1 to the UE 3 to perform the handover.

[0147] As indicated at S430, the handover command (e.g., the RRC reconfiguration message or the like) may thus be sent, by the source RAN node 5-1, to the UE 3, to complete the handover preparation phase and to initiate a handover execution phase.

[0148] Thus, the UE 3 and RAN nodes 5 can coordinate with one another to perform handover execution and handover completion (as indicated at S432), in a manner that will be familiar to those skilled in the art, to complete handover of the UE 3 to the target femto node 5-2.

[0149] As mentioned above, Fig. 5 illustrates a case in which access control is not successful and different ways in which such a failure can be handled. Specifically, in the example of Fig. 5 the initial part of the procedure is essentially the same as that shown and described with reference to steps S406 to S424 of Fig. 4. However, when access control is performed, the access control procedure determines that the UE 3 is not allowed to access the potential CAG member cell as a target cell (i.e., that the potential CAG member cell cannot be accessed as a CAG member cell for the UE 3). Accordingly, access control fails as indicated at S326.

[0150] The failure procedure may then proceed in either of two different ways.

[0151] First Option: 　　In a first option, illustrated at S530-1, the femto node 5-2 rejects the handover request by sending, at S532, an appropriate failure message (e.g., a handover preparation failure message or the like) including information indicating the cause of the failure (e.g., a value of a cause IE or the like) to be "Not a CAG member". Where the target cell of the femto node 5-2 is a shared cell (i.e. a cell that is shared as both a normal PLMN cell and as a CAG cell) (and the UE 3 is allowed to access non-CAG cells), then the source RAN node 5-1 may (optionally) decide whether or not to trigger a new attempt to handover the UE 3 to that target cell (as a normal PLMN cell) as if the UE 3 is a non-CAG (e.g., legacy) UE 3.

[0152] In the illustrated example the source RAN node 5-1 decides to trigger a new attempt to handover the UE 3 to the target cell (as a normal PLMN cell) as if the UE 3 is a non-CAG (e.g., legacy) UE 3 at S534. Accordingly, the source RAN node 5-1 sends, at S536, a new handover request message to the target femto node 5-2 to initiate another attempted handover of the UE 3 to the target cell (as a normal PLMN cell). However, in this case, the source RAN node 5-1 does not include the list of the allowed CAG IDs for the UE 3 (or allowed PNI-NPN ID List IE including the list of the allowed CAG IDs).

[0153] The target femto node 5-2 may then treat the UE 3 as a non-member (e.g., legacy) UE 3 attempting to handover to a normal PLMN cell. The target femto node 5-2 may (optionally), for example, perform appropriate admission control (not shown) - e.g., to determine if the required resources can be granted by the target femto node 5-2.

[0154] Assuming any admission control is successful, the target femto node 5-2 may accept the handover to the target cell (as a normal PLMN cell), allocate appropriate resources, and send, at S538 an appropriate message for acknowledging the handover request message (e.g., a handover request acknowledgement message or the like). The handover request acknowledgement message may, for example, include a handover command (e.g., an RRC reconfiguration message or the like), that contains information required to access the target cell (as a normal PLMN cell), and that is to be sent by the source RAN node 5-1 to the UE 3 to perform the handover.

[0155] As indicated at S542, the handover command (e.g., the RRC reconfiguration message or the like) may thus be sent, by the source RAN node 5-1, to the UE 3, to complete the handover preparation phase and to initiate a handover execution phase. In this case, however, the handover command may include (or be sent with) information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0156] On receipt of a handover command including (or sent with) information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3, the UE 3 may determine whether or not to handover to the target cell (as a normal PLMN cell) of the target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3.

[0157] If the UE 3 decides to handover to the target cell (as a normal PLMN cell) of target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3, then the UE 3 and RAN nodes 5 can coordinate with one another to perform handover execution and handover completion, in a manner that will be familiar to those skilled in the art, to complete handover of the UE 3 to the target femto node 5-2.

[0158] Second Option: 　　In a second option, illustrated at S530-2, where the target cell of the femto node 5-2 is a shared cell and the UE 3 is allowed to access non-CAG cells, the femto node 5-2 does not reject the handover request but instead, allocates appropriate resources, and sends, at S540, an appropriate message for acknowledging the handover request message (e.g., a handover request acknowledgement message or the like). The handover request acknowledgement message may, for example, include a handover command (e.g., an RRC reconfiguration message or the like), that contains information required to access the target cell, and that is to be sent by the source RAN node 5-1 to the UE 3 to perform the handover. The femto node 5-2 includes, in the handover request acknowledgement message (e.g., in (or with) the handover command), information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0159] As indicated at S542, the handover command (e.g., the RRC reconfiguration message or the like) may thus be sent, by the source RAN node 5-1, to the UE 3, to complete the handover preparation phase and to initiate a handover execution phase. In this case, however, the handover command may include (or be sent with) the information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0160] On receipt of a handover command including (or sent with) information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3, the UE 3 may determine whether or not to handover to the target cell (as a normal PLMN cell) of target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3.

[0161] If the UE 3 decides to handover to the target cell (as a normal PLMN cell) of target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3, then the UE 3 and RAN nodes 5 can coordinate with one another to perform handover execution and handover completion, in a manner that will be familiar to those skilled in the art, to complete handover of the UE 3 to the target femto node 5-2.

[0162] It will be appreciated that in the procedures described with reference to Figs. 4 and 5, whilst a femto GW 9 is not shown, the target femto node 5-2 may communicate with the core network 7 (e.g., an AMF 10-1 in the core network 7) via a femto GW 9.

[0163] RAN Node-to-Core Network Interface (e.g., NG-C / N2) Based Handover 　　As mentioned above each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting RAN node-to-core network interface (e.g., 'NG-C' or 'N2' interface) based mobility of the UE 3, to a CAG member cell provided by the femto node 5-2. A number of such procedures / mechanisms will now be described, by way of example only, with reference to Fig. 7.

[0164] Fig. 7 is a simplified sequence diagram illustrating procedures for supporting RAN node-to-core network interface based mobility in the communication system 1.

[0165] In the examples of Fig. 7, the RAN node 5-1 is initially serving the UE 3 and acts as a source node for handover in the illustrated procedure. Similarly, the femto node 5-2 is operating as a target node for the handover in the illustrated procedure. Accordingly, the RAN node 5-1 will be referred to as the source RAN node 5-1, and the femto node 5-2 will be referred to as the target femto node 5-2, in the further description of this procedure.

[0166] The core proximity indication procedures illustrated in Figs. 2 and 4 also apply in respect of RAN node-to-core network interface based mobility. For example, as seen in Fig. 7, a RAN node-to-core network interface based mobility procedure may implement the core UE-based / UE-centric proximity indication procedure shown and described with reference to steps S210 to S222 of Fig. 2. Alternatively, as seen in Fig. 7, a RAN node-to-core network interface based mobility procedure may implement the core UE-based / UE-centric proximity indication procedure shown and described with reference to steps S406 to S422 of Fig. 4.

[0167] However, in the example of Fig. 7, when the source RAN node 5-1 decides to initiate handover of the UE 3, the source RAN node 5-1 sends, at S724, a message to indicate that a handover is required (e.g., a handover required message) to the AMF 10-1 to initiate an attempted handover of the UE 3 to the potential CAG member cell as the target cell. The source RAN node 5-1 includes, in that handover required message, the CGI for the potential CAG member cell received from the UE 3. The source RAN node 5-1 also includes a list of the allowed CAG IDs for the UE 3 in the handover request message. The list of allowed CAG IDs may form part of information indicating allowed PNI-NPNs, allowed UE mobility, whether the UE 3 is allowed to access non-CAG cells for a given PLMN, and / or the like (e.g., part of an allowed PNI-NPN ID List IE or the like as seen in Fig. 7). It will be appreciated that the list of allowed CAG IDs may be provided to the RAN node 5-1 during a UE registration procedure or the like.

[0168] In the example of Fig. 7, as indicated at S726, access control is performed at the AMF 10-1 (rather than at the target femto node 5-2). If access control is successful then handover of the UE 3 from the source RAN node 5-1 to the target cell of the target femto node 5-2, as a CAG member of that target cell, can proceed in a conventional manner that will be familiar to those skilled in the art. However if, as illustrated in Fig. 7, access control fails then the failure procedure may then proceed in either of two different ways.

[0169] First Option: 　　In a first option, illustrated at S730-1, the AMF 10-1 ends the handover procedure by replying to the handover required message, at S732, with an appropriate failure message (e.g., a handover preparation failure message or the like) including information indicating the cause of the failure (e.g., a value of a cause IE or the like) to be "Not a CAG member".

[0170] It will be appreciated that, where the target cell of the femto node 5-2 is a shared cell (i.e. a cell that is shared as both a normal PLMN cell and as a CAG cell) (and the UE 3 is allowed to access non-CAG cells), then the source RAN node 5-1 may (optionally) decide whether or not to trigger a new attempt to handover the UE 3 to that target cell (as a normal PLMN cell) as if the UE 3 is a non-CAG (e.g., legacy) UE 3 (e.g., in a manner analogous to that illustrated in Figs 3 and 4 but over the RAN node-to-core network interface (e.g., NG-C / N2 interface)). For example, if the source RAN node 5-1 decides to trigger a new attempt to handover the UE 3 to the target cell (as a normal PLMN cell) as if the UE 3 is a non-CAG (e.g., legacy) UE 3 (as indicated at S734), then the source RAN node 5-1 may send a new handover required message to the AMF 10-1 to initiate another attempted handover of the UE 3 to the target cell (as a normal PLMN cell) (as indicated at S735). However, in this case, the source RAN node 5-1 does not include the list of the allowed CAG IDs for the UE 3 (or allowed PNI-NPN ID List IE including the list of the allowed CAG IDs).

[0171] Second Option: 　　In a second option, illustrated at S730-2, where the target cell of the femto node 5-2 is a shared cell (and the UE 3 is allowed to access non-CAG cells) the AMF 10-1 does not reject the handover request but instead decides, at S736, to attempt handover of the UE 3 to the target cell, as a normal PLMN cell, as if the UE 3 were a non-CAG (e.g., 'legacy') UE 3.

[0172] In a case where a decision is made to attempt handover of the UE 3 to the target cell, as a normal PLMN cell, as if the UE 3 were a non-CAG (e.g., 'legacy') UE 3 (e.g., by the AMF 10-1 (second option), or by the source RAN node 5-1 (first option)), the AMF 10-1 can send, at S738, a handover request message to the target femto node 5-2 to continue handover of the UE 3 to the target cell (as a normal PLMN cell). The AMF 10-1 includes, in that handover request message, information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0173] The target femto node 5-2 allocates appropriate resources and sends, at S740, a message for acknowledging the handover request message (e.g., a handover request acknowledgement message or the like) to the AMF 10-1. The handover request acknowledgement message may, for example, include a handover command (e.g., an RRC reconfiguration message or the like), that contains information required to access the target cell, and that is to be sent by the source RAN node 5-1 to the UE 3 to perform the handover. The femto node 5-2 includes, in the handover request acknowledgement message (e.g., in (or with) the handover command), information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0174] At S741, the AMF 10-1 sends the handover command to the source RAN node 5-1, together with the information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0175] As indicated at S742, the handover command (e.g., the RRC reconfiguration message or the like) may thus be sent, by the source RAN node 5-1, to the UE 3, to complete the handover preparation phase and to initiate a handover execution phase. In this case, however, the handover command may include (or be sent with) the information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0176] On receipt of a handover command including (or sent with) information indicating that the UE 3 is allowed to handover to the target cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3, the UE 3 may determine whether or not to handover to the target cell (as a normal PLMN cell) of target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3.

[0177] If the UE 3 decides to handover to the target cell (as a normal PLMN cell) of target femto node 5-2 as if it were a non-CAG (e.g., legacy) UE 3, then the UE 3, RAN nodes 5, and AMF 10-1 can coordinate with one another to perform handover execution and handover completion, in a manner that will be familiar to those skilled in the art, to complete handover of the UE 3 to the target femto node 5-2.

[0178] It will be appreciated that in the procedures described with reference to Fig. 7, whilst a femto GW 9 is not shown, the target femto node 5-2 may communicate with the core network 7 (e.g., an AMF 10-1 in the core network 7) via a femto GW 9. For example, the handover request and handover acknowledge messages sent to and from the target femto node 5-2 at S738 and S740 respectively may be sent via a femto GW 9.

[0179] Addition of Femto node as Secondary RAN Node for Dual Connectivity 　　As mentioned above, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting dual connectivity involving both a PNI-NPN (CAG) cell and a normal PLMN (non-CAG) cell. A number of such procedures / mechanisms will now be described, by way of example only, with reference to Fig. 8.

[0180] Fig. 8 is a simplified sequence diagram illustrating a procedure for secondary RAN node addition preparation in respect of a femto node 5-2 that provides one or more PNI-NPN (CAG) cells in the communication system 1.

[0181] In the example illustrated in Fig. 8, the secondary RAN node addition preparation procedure illustrated in Fig. 8 is initiated by a RAN node 5-1 (operating as a master RAN node 5-1) for the purpose of requesting the femto node 5-2 (which is to be added as a secondary femto node 5-2), to allocate resources for dual connectivity operation for a specific UE 3. The procedure uses UE-associated signalling. Accordingly, the RAN node 5-1 will be referred to as the master RAN node 5-1, and the femto node 5-2 will be referred to as the secondary femto node 5-2, in the further description of this procedure.

[0182] The master RAN node 5-1 initiates the procedure by sending to the secondary femto node 5-2, at S810, a message to request secondary node addition (e.g., an s-node addition request message or the like). When the master RAN node 5-1 sends the message to request secondary node addition, the master RAN node 5-1 includes a list of the allowed CAG IDs for the UE 3. The list of allowed CAG IDs may form part of information indicating allowed PNI-NPNs, allowed UE mobility, whether the UE 3 is allowed to access non-CAG cells for a given PLMN, and / or the like (e.g., part of an allowed PNI-NPN ID List IE or the like as seen in Fig. 8).

[0183] At S812, the secondary femto node 5-2 performs UE access control based on the received list of allowed CAG IDs. In a case where access control is successful, the secondary femto node 5-2 can allocate the resources of a PNI-NPN (CAG) cell as an SCell for the purposes dual connectivity. In this case, the secondary femto node 5-2 responds to the master RAN node 5-1 with an appropriate acknowledgement message (e.g., an s-node addition request acknowledge message or the like) and addition of secondary femto node 5-2 for the purposes of dual connectivity can be completed in a manner that will be familiar to those skilled in the art.

[0184] However, in a case where, as illustrated in Fig. 8, access control fails the failure procedure may then proceed in either of two different ways.

[0185] First Option: 　　In a first option, illustrated at S820-1, in a case where the secondary femto node 5-2 operates a PNI-NPN (CAG) cell (for possible operation as an SCell for dual connectivity) that is a shared cell (i.e. a cell that is shared as both a normal PLMN cell and as a CAG cell), the secondary femto node 5-2 may still send an appropriate acknowledgement message (e.g., an s-node addition request acknowledge message or the like). However, in this case, the secondary femto node 5-2 may include, in the acknowledgement message, information indicating that addition of the PNI-NPN cell (as a normal PLMN cell) as an SCell is allowed for the UE 3 as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like).

[0186] Second Option: 　　In a second option, illustrated at S820-2, the secondary femto node 5-2 may simply reject the procedure using an appropriate reject message (e.g., an s-node addition request reject message or the like), including information indicating the cause of the failure (e.g., a value of a cause IE or the like) to be "Not a CAG member" (as indicated at S822).

[0187] It will be appreciated that in the procedures described with reference to Fig. 8, whilst a femto GW 9 is not shown, the target femto node 5-2 may communicate with the core network 7 (e.g., an AMF 10-1 in the core network 7) via a femto GW 9.

[0188] Intra-Femto Gateway Handover 　　As mentioned above, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting intra-femto gateway handover in the context of PNI-NPN (CAG) cells.

[0189] Specifically, it will be appreciated that, in a scenario where there is a plurality of femto nodes 5-2 in the communication system 1, it is possible that there may be no direct RAN node-to-RAN node interface between those femto nodes 5-2. In a case where a plurality of femto nodes 5-2 are connected to the core network 7 via the same femto GW 9, and no RAN node-to-RAN node interface is (or can be) set up between those femto nodes 5-2, it would be beneficial for the communication system 1 to support an intra-femto gateway handover procedure over the respective interface (e.g., over a respective NG-C / N2 interface) between the femto GW 9 and each femto node 5-2 connected to the femto GW 9.

[0190] Figs. 9 and 10 are simplified sequence diagrams illustrating procedures for supporting intra-femto gateway mobility in the communication system 1. The core procedures illustrated in Figs. 9 and 10 are essentially the same. However, Fig. 9 illustrates a case in which access control is successful, whereas Fig. 10 illustrates a case in which access control is not successful, and different ways in which such a failure can be handled.

[0191] In the example of Fig. 9, there are a plurality of different femto nodes 5-2-1, 5-2-2 (5-2) connected via the same femto GW 9. Specifically, the plurality of femto nodes 5-2 include: a first femto node 5-2-1 that will become a source RAN node in a subsequent intra-femto gateway handover procedure; and a second femto node 5-2-2 that will become a target RAN node in the subsequent intra-femto gateway handover procedure. Accordingly, the first femto node 5-2-1 will be referred to as the source femto node 5-2-1, and the second femto node 5-2-2 will be referred to as the target femto node 5-2-2, in the further description of this intra-femto gateway procedure.

[0192] At some time prior to the handover procedure, as indicated at S906, each femto node 5-2 may respectively engage in a procedure for exchanging application level configuration data needed for the femto nodes 5-2 to correctly interoperate on the RAN node-to-core network interface (e.g., NG-C interface) with the femto GW 9. It will be appreciated that, in this context, the femto GW 9 behaves like the core network 7 (e.g., like an AMF 10-1) from the perspective of the femto nodes 5-2 and like a femto node 5-2 from the perspective of the core network 7 (e.g., AMF 10-1). Specifically, as indicated at S906, each femto node 5-2 may respectively engage in a respective RAN node-to-core network interface application protocol (e.g., NGAP) based setup procedure (e.g., an NG setup procedure) with the femto GW 9.

[0193] During the setup procedure at S906, each femto node 5-2 respectively sends a list of one or more supported CAG IDs and one or more associated PCIs of one or more CAG cells provided by the femto node 5-2, to the femto GW 9 (as indicated at S908-1 and 908-2). The list of one or more supported CAG IDs and one or more associated PCIs may, for example be sent in a RAN node-to-core network interface setup request message (e.g., an NG setup request or the like). The femto GW 9 then records this information at S910. It will be appreciated that whilst, in Fig. 9, the different femto nodes 5-2 are engaging the setup procedures with the femto GW 9 at the same time, in reality each femto node 5-2 may engage in a corresponding setup procedure with the femto GW 9 at a different time.

[0194] The list of one or more supported CAG IDs and one or more associated PCIs may be provided in any suitable manner in the setup request message - for example in a specific information element for indicating the PNI-NPN ID information broadcast by the femto node 5-2 (e.g., a broadcast PNI-NPN ID IE or the like). By way of example only, the configuration of a possible broadcast PNI-NPN ID IE is summarised in Table 2.

[0195] Later, after the UE 3 has connected to the source femto node 5-2-1 at S912, and the source femto node 5-2-1 decides to attempt to handover the UE 3 to a potential CAG member cell (target cell) of the target femto node 5-2-2, the source femto node 5-2-1 sends, at S924, an appropriate message to the femto GW 9 to indicate that handover is required (e.g., a handover required message or the like). The source femto node 5-2-1 also includes an identifier of the target femto node 5-2-2, a CGI of the target cell, and a list of the allowed CAG IDs for the UE 3, in the handover request message. The list of allowed CAG IDs may form part of information indicating allowed PNI-NPNs, allowed UE mobility, whether the UE 3 is allowed to access non-CAG cells for a given PLMN, and / or the like (e.g., part of an allowed PNI-NPN ID List IE or the like as seen in Fig. 9).

[0196] On receiving the handover required message from the source femto node 5-2-1, the femto GW 9 checks if the target femto node 5-2-2, and hence the target cell for the handover, is under the control of the femto GW 9 (e.g., by checking a target RAN node identifier included in the handover required message or the like). If the target cell is under the control of the femto GW 9, the femto GW 9 performs access control based on the corresponding supported CAG ID list provided for the target femto node 5-2-2 and stored at the femto GW 9 (e.g., during the setup procedure at S906), and on the list of allowed CAG IDs for the UE 3 received from the source femto node 5-2-1.

[0197] In the example illustrated, the access control procedure confirms that the UE 3 is allowed to access the potential CAG member cell (i.e., that the potential CAG member cell can be accessed as a CAG member cell for the UE 3). Accordingly, access control is successful and the femto GW 9 continues the handover to the target cell. Specifically, the femto GW 9 sends, at S928, a handover request message to the target femto node 5-2-2 to continue handover of the UE 3 to the CAG cell as the target cell. The femto GW 9 includes (or retains), in that handover request message, the CGI for the target (CAG) cell, and the list of the allowed CAG IDs for the UE 3. The list of allowed CAG IDs may form part of information indicating allowed PNI-NPNs, allowed UE mobility, whether the UE 3 is allowed to access non-CAG cells for a given PLMN, and / or the like (e.g., part of an allowed PNI-NPN ID List IE or the like as seen in Fig. 9).

[0198] The target femto node 5-2-2, allocates appropriate resources and sends, to the femto GW 9 an appropriate message for acknowledging the handover request message (e.g., a handover request acknowledgement message or the like) as indicated at S930. The handover request acknowledgement message may, for example, include a handover command (e.g., an RRC reconfiguration message or the like), that contains information required to access the target cell, and that is to be sent by the source femto node 5-2-1, to the UE 3, to perform the handover.

[0199] At S932, the femto GW 9 sends the handover command to the source femto node 5-2-1. As indicated at S934, the handover command (e.g., the RRC reconfiguration message or the like) may thus be sent, by the source femto node 5-2-1, to the UE 3, to complete the handover preparation phase and to initiate a handover execution phase.

[0200] Thus, the UE 3, the femto nodes 5-2 and the femto GW 9 can coordinate with one another to perform handover execution and handover completion (as indicated at S936), in a manner that will be familiar to those skilled in the art, to complete handover of the UE 3 to the target femto node 5-2-2.

[0201] As mentioned above, Fig. 10 illustrates a case in which access control is not successful and different ways in which such a failure can be handled. Specifically, in the example of Fig. 10 the initial part of the procedure is essentially the same as that shown and described with reference to steps S906 to S924 of Fig. 9. However, when access control is performed at the femto GW 9, the access control procedure determines that the UE 3 is not allowed to access the potential CAG member cell as a target cell (i.e., that the potential CAG member cell cannot be accessed as a CAG member cell for the UE 3). Accordingly, access control fails as indicated at S1026.

[0202] The failure procedure may then proceed in either of two different ways.

[0203] First Option: 　　In a first option, illustrated at S1030-1, the femto GW 9 rejects the handover procedure by replying to the handover required message, at S1032, with an appropriate failure message (e.g., a handover preparation failure message or the like) including information indicating the cause of the failure (e.g., a value of a cause IE or the like) to be "Not a CAG member".

[0204] It will be appreciated that, where the target cell of the femto node 5-2-2 is a shared cell (i.e. a cell that is shared as both a normal PLMN cell and as a CAG cell) (and the UE 3 is allowed to access non-CAG cells), then the source femto node 5-2-1 may (optionally) decide whether or not to trigger a new attempt to handover the UE 3 to that target cell (as a normal PLMN cell) as if the UE 3 is a non-CAG (e.g., legacy) UE 3 (e.g., in a manner analogous to that illustrated in Figs 3 and 4 but over the interface (e.g., NG-C / N2 interface) with the femto GW 9). For example, if the source femto node 5-2-1 decides to trigger a new attempt to handover the UE 3 to the target cell (as a normal PLMN cell) as if the UE 3 is a non-CAG (e.g., legacy) UE 3 (as indicated at S1034), then the source femto node 5-2-1 may send a new handover required message to the AMF 10-1 to initiate another attempted handover of the UE 3 to the target cell (as a normal PLMN cell) (as indicated at S1035). However, in this case, the source femto node 5-2-1 does not include the list of the allowed CAG IDs for the UE 3 (or allowed PNI-NPN ID List IE including the list of the allowed CAG IDs).

[0205] Second Option: 　　In a second option, illustrated at S1030-2, where the target cell of the femto node 5-2-2 is a shared cell (and the UE 3 is allowed to access non-CAG cells), the femto GW 9 does not reject the handover request but instead decides, at S1036, to attempt handover of the UE 3 to the target cell, as a normal PLMN cell, as if the UE 3 were a non-CAG (e.g., 'legacy') UE 3.

[0206] In a case where a decision is made to attempt handover of the UE 3 to the target cell, as a normal PLMN cell, as if the UE 3 were a non-CAG (e.g., 'legacy') UE 3 (e.g., by the femto GW 9 (second option), or by the source femto node 5-2-1 (first option)), the femto GW 9 can send, at S1038, a handover request message to the target femto node 5-2-2 to continue handover of the UE 3 to the target cell (as a normal PLMN cell). However, the femto GW 9 may omit (e.g., remove) from that handover request message, the list of the allowed CAG IDs for the UE 3.

[0207] The target femto node 5-2-2, allocates appropriate resources and sends, to the femto GW 9 an appropriate message for acknowledging the handover request message (e.g., a handover request acknowledgement message or the like) as indicated at S1040. The handover request acknowledgement message may, for example, include a handover command (e.g., an RRC reconfiguration message or the like), that contains information required to access the target cell (as a normal PLMN cell), and that is to be sent by the source femto node 5-2-1, to the UE 3, to perform the handover.

[0208] At S1041, the femto GW 9 sends the handover command to the source femto node 5-2-1. As indicated at S1042, the handover command (e.g., the RRC reconfiguration message or the like) may thus be sent, by the source femto node 5-2-1, to the UE 3, to complete the handover preparation phase and to initiate a handover execution phase.

[0209] Thus, the UE 3, the femto nodes 5-2, and the femto GW 9 can coordinate with one another to perform handover execution and handover completion (as indicated at S1044), in a manner that will be familiar to those skilled in the art, to complete handover of the UE 3 to the target femto node 5-2-2.

[0210] UE Registration with Shared PNI-NPN (CAG) Cell of a Femto node 　　Beneficially, each RAN node 5, and UE 3, of the communication system 1 may be mutually configured to implement one or more enhanced procedures / mechanisms for supporting UE attach to a shared PNI-NPN (CAG) cell of the femto node 5-2.

[0211] Fig. 11 is a simplified sequence diagrams illustrating procedures for supporting UE registration with a shared PNI-NPN (CAG) cell of the femto node 5-2 in the communication system 1.

[0212] In the example of Fig. 11, the UE 3 is performing an initial registration procedure with the femto node 5-2, and AMF 10-1, to connect (attach / register) the UE 3 with the core network 7 by establishing a UE-associated logical connection between the femto node 5-2 and the AMF 10-1 over the associated interface (e.g., NG-C / N2).

[0213] The procedure begins when the UE 3 and femto node 5-2 engage in an RRC connection setup procedure at S1110. By way of example only, when the UE 3 needs to connect to the network it may initiate a random-access channel (RACH) procedure to access the network (e.g., as described above) by sending a selected preamble (e.g., in 'Msg1') to the femto node 5-2. In response, the femto node 5-2 may respond with a RAR (or 'Msg2'). The UE 3 may then send a third message ('Msg3') to the network over the PUSCH based on the information in the RAR. The specific message sent by the UE 3 in this step, and the content of the message, depends on the context in which the random-access procedure is being used. In the example of initial RRC connection setup at S1110, however, Msg3 may typically comprise an RRC connection request or similar message carrying a temporary randomly generated UE identifier (e.g., a serving temporary mobile subscriber identity (S-TMSI)). The femto node 5-2 may then respond with a fourth message ('Msg4') carrying the randomly generated UE identifier received in Msg3 (e.g., for contention purposes to resolve any collisions between different UEs 3 using the same preamble sequence). When successful, Msg4 also transfers the UE 3 to a connected state.

[0214] At the end of the RRC connection setup procedure at S1110, the UE 3 can then attempt to achieve packet data network (PDN) connectivity by sending to the femto node 5-2, at S1112, a message indicating that RRC setup has been completed. This message includes as a NAS payload, a registration request to initiate the attach procedure. The femto node 5-2 then sends, at S1114, its first message to the core network 7 (e.g., AMF 10-1) - an initial UE message containing the registration request. This message is sent to the AMF 10-1. This message is sent via the RAN node-to-core network interface (e.g., NG-C / N2).

[0215] At S1116, the AMF 10-1 performs access control during which it checks whether the UE 3 is allowed to access the CAG cell of the femto node 5-2 in which the UE 3 is attempting to connect.

[0216] If the check is successful, the AMF 10-1 sets up the UE-associated logical connection between the femto node 5-2 and the AMF 10-1 over the associated interface (e.g., NG-C / N2) in a conventional manner that will be familiar to those skilled in the art. During this stage the AMF 10-1 provides the list of allowed CAG IDs for the UE 3 to the femto node 5-2, and may also provide an indication of whether or not the UE 3 is allowed to access non-CAG cells (e.g., in / with a registration accept message provided in an initial context setup request message or the like). However if, as illustrated in Fig. 11, access control fails then the failure procedure may then proceed in either of two different ways.

[0217] First Option: 　　In a first option, illustrated at S1120-1, assuming the UE 3 is allowed to access non-CAG cells, the AMF 10-1 does not reject the registration request but instead still sets up the UE-associated logical connection between the femto node 5-2 and the AMF 10-1 over the associated interface (e.g., NG-C / N2). Accordingly, the AMF 10-1 sends, at S1122-1, a registration accept message to the femto node 5-2 (e.g., in an initial context setup request message or the like). However, the AMF 10-1 includes, in / with a registration accept message, information indicating that the UE 3 is allowed to access the CAG cell (as a normal PLMN cell) as if it were a legacy UE 3, but not as a CAG member UE 3 (e.g., a "Not a CAG member" indication or the like). It will be appreciated that, to allow the AMF 10-1 to determine whether the UE 3 is allowed to access a non-CAG cell, a CAG-capable UE 3 may be configured with a CAG-only indication, which indicates if the UE 3 is only allowed to access the network via CAG cells or not. This CAG-only indication may be stored in UE subscription information that is available to the AMF 10-1.

[0218] The registration accept message (together with the "Not a CAG member" indication) may then be sent by the femto node 5-2 to the UE 3 at S1122-2 (e.g., in an RRC reconfiguration message or the like.

[0219] Second Option: 　　In a second option, illustrated at S1120-2, the AMF 10-1 rejects the registration request by sending a registration reject message to the femto node 5-2 at S1124-1. The AMF 10-1 includes, in / with a registration reject message, information indicating the cause of the rejection / failure (e.g., a value of a cause IE or the like) to be "Not a CAG member", and may also include an indication of whether or not the UE 3 is allowed to access non-CAG cells.

[0220] The registration reject message may then be sent by the femto node 5-2 to the UE 3 at S1124-2. The registration reject message sent by the femto node 5-2 to the UE 3 at S1124-2 may also include the information indicating the cause of the rejection / failure (e.g., a value of a cause IE or the like) to be "Not a CAG member" and / or the indication of whether or not the UE 3 is allowed to access non-CAG cells.

[0221] Accordingly, the UE 3 / femto node 5-2 may potentially make a follow-up attempt to connect (attach / register) the UE 3 with the core network 7 by establishing a UE-associated logical connection between the femto node 5-2 and the AMF 10-1 over the associated interface (e.g., NG-C / N2) in the CAG cell (as a normal PLMN cell), as if the UE 3 were a legacy UE 3, but not as a CAG member UE 3.

[0222] Devices of the Communication System User Equipment 　　Fig. 12 is a schematic block diagram illustrating the main components of a UE 3 as shown in Fig. 1.

[0223] As shown, the UE 3 has a transceiver circuit 31 that is operable to transmit signals to and to receive signals from a RAN node 5 via one or more antennas 33 (e.g., comprising one or more antenna elements). The UE 3 has a controller 37 to control the operation of the UE 3. The controller 37 is associated with a memory 39 and is coupled to the transceiver circuit 31. Although not necessarily required for its operation, the UE 3 might, of course, have all the usual functionality of a conventional UE 3 (e.g., a user interface 35, such as a touch screen / keypad / microphone / speaker and / or the like for, allowing direct control by and interaction with a user) and this may be provided by any one or any combination of hardware, software, and firmware, as appropriate. Software may be pre-installed in the memory 39 and / or may be downloaded via the communication system 1 or from a removable data storage device (RMD), for example.

[0224] The controller 37 is configured to control overall operation of the UE 3 by, in this example, program instructions or software instructions stored within memory 39. As shown, these software instructions include, among other things, an operating system 41, and a communication control module 43.

[0225] The communication control module 43 is operable to control the communication between the UE 3 and its serving RAN node 5 (and other communication devices connected to the RAN node 5, such as further UEs and / or core network nodes). The communication control module 43 is configured for the overall handling of uplink communication via associated uplink channels (e.g., via a physical uplink control channel (PUCCH), random access channel (RACH), and / or a physical uplink shared channel (PUSCH)) including both dynamic and semi-static signalling (e.g., SRS). The communication control module 43 is also configured for the overall handling of receipt of downlink communication via associated downlink channels (e.g., of DCI via a physical downlink control channel (PDCCH) and / or a physical downlink shared channel (PDSCH)) including both dynamic and semi-persistent scheduling (e.g., SPS). The communication control module 43 is responsible, for example: for determining where to monitor for downlink control information; for determining the resources to be used by the UE 3 for transmission / reception of UL / DL communication (including interleaved resources and resources subject to frequency hopping); for managing frequency hopping at the UE side; for determining how slots / symbols are configured (e.g., for UL, DL or full duplex communication, or the like); for determining which bandwidth parts are configured for the UE 3; for determining how uplink transmissions should be encoded and the like.

[0226] It will be appreciated that the communication control module 43 may include a number of sub-modules ('layers' or 'entities') to support specific functionalities. For example, the communication control module 43 may include a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an RRC sub-module, etc.

[0227] The communication control module 43 is configured, in particular, to control the UE's communication, where applicable, in accordance with any of the methods described herein.

[0228] RAN node 　　Fig. 13 is a schematic block diagram illustrating the main components of the RAN node 5 for the communication system 1 shown in Fig. 1. As shown, the RAN node 5 has a transceiver circuit 51 for transmitting signals to and for receiving signals from the communication devices (such as UEs 3) via one or more antennas 53 (e.g. a single or multi-panel antenna array / massive antenna), and a core network interface 55 (e.g. comprising the N2, N3 and other reference points / interfaces) for transmitting signals to and for receiving signals from network nodes in the core network 7. Although not shown, the RAN node 5 may also be coupled to other RAN nodes 5 via an appropriate interface (e.g. the so-called 'Xn' interface in NR). The RAN node 5 has a controller 57 to control the operation of the RAN node 5. The controller 57 is associated with a memory 59. Software may be pre-installed in the memory 59 and / or may be downloaded via the communication system 1 or from a removable data storage device (RMD), for example. The controller 57 is configured to control the overall operation of the RAN node 5 by, in this example, program instructions or software instructions stored within memory 59.

[0229] As shown, these software instructions include, among other things, an operating system 61, and a communication control module 63.

[0230] The communication control module 63 is operable to control the communication between the RAN node 5 and UEs 3 and other network entities that are connected to the RAN node 5. The communication control module 63 is configured for the overall control of the reception and decoding of uplink communication, via associated uplink channels (e.g. via a physical uplink control channel (PUCCH), a random-access channel (RACH), and / or a physical uplink shared channel (PUSCH)) including both dynamic and semi-static signalling (e.g., SRS). The communication control module 63 is also configured for the overall handling the transmission of downlink communication via associated downlink channels (e.g. via a physical downlink control channel (PDCCH) and / or a physical downlink shared channel (PDSCH)) including both dynamic and semi-static signalling (e.g., CSI-RS, SSBs etc.). The communication control module 63 is also responsible, for example, for determining and scheduling the resources to be used by the UE 3 for receiving in DL / transmitting in UL, for configuring slots / symbols appropriately (e.g., for UL, DL, flexible, full duplex communication, or the like), for configuring one or more bandwidth parts for the UE 3, and for providing related configuration signalling to the UE 3.

[0231] It will be appreciated that the communication control module 63 may include a number of sub-modules (or 'layers') to support specific functionalities. For example, the communication control module 63 may include a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an RRC sub-module, etc.

[0232] The communication control module 63 is configured, in particular, to control the RAN node's communication, where applicable, in accordance with any of the methods described herein.

[0233] Small Cell 'Femto' Gateway 　　Fig. 14 is a schematic block diagram illustrating the main components of the femto GW 9 for the communication system 1 shown in Fig. 1.

[0234] As shown, the femto GW 9 has a transceiver circuit 611 for transmitting signals to and for receiving signals from nodes of the communication system 1 (such as nodes / functions of the core network 7 (e.g., an AMF 10-1), and / or RAN nodes 5) via one or more network interfaces 612.

[0235] The femto GW 9 has a controller 613 to control the operation of the femto GW 9 in accordance with the specific functions that that femto GW 9 is required to provide. The controller 613 is configured to control the overall operation of the femto GW 9 by, in this example, program instructions or software instructions stored within memory 614. Software may, for example, be pre-installed in the memory 614 and / or may be downloaded via the communication system 1 or from a removable data storage device (RMD). As shown, these software instructions include, among other things, an operating system 615, and a communication control module 616.

[0236] The communication control module 616 is operable to control the communication between the femto GW 9 and other network entities. The communication control module 616 is configured, in particular, to control the communication of femto GW 9, where applicable, in accordance with any of the methods described herein.

[0237] Core Network Function 　　Fig. 15 is a schematic block diagram illustrating the main components of a core network function 10 / 11 that may be used in the communication system 1.

[0238] As shown, the core network function 10 / 11 has a transceiver circuit 711 for transmitting signals to and for receiving signals from nodes of the communication system 1 (such as other nodes / functions of the core network 7, and / or RAN nodes 5) via one or more network interfaces 712.

[0239] The core network function 10 / 11 has a controller 713 to control the operation of the core network function 10 / 11 in accordance with the specific functions that that core network function 10 / 11 is required to provide (e.g., when operating as an AMF 10-1, SMF 10-2, UDM, AUSF, PCF, AF, SEAF, ARPF, UPF 11 and / or the like). The controller 713 is configured to control the overall operation of the core network function 10 / 11 by, in this example, program instructions or software instructions stored within memory 714. Software may, for example, be pre-installed in the memory 714 and / or may be downloaded via the communication system 1 or from a removable data storage device (RMD). As shown, these software instructions include, among other things, an operating system 715, and a communication control module 716.

[0240] The communication control module 716 is operable to control the communication between the core network function 10 / 11 and other network entities. The communication control module 716 is configured, in particular, to control the communication of core network function 10 / 11, where applicable, in accordance with any of the methods described herein.

[0241] Modifications and Alternatives 　　Detailed examples have been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above examples whilst still benefiting from the innovations embodied therein.

[0242] It will be appreciated, for example, that whilst cellular communication generation (2G, 3G, 4G, 5G, 6G etc.) specific terminology may be used, in the interests of clarity, to refer to specific communication entities, the technical features described for a given entity are not limited to devices of that specific communication generation. The technical features may be implemented in any functionally equivalent communication entity regardless of any differences in the terminology used to refer to them.

[0243] In the above description, the UEs and the RAN node are described for ease of understanding as having a number of discrete functional components or modules. Whilst these modules may be provided in this way for certain applications, for example where an existing system has been modified to implement the innovative features described above, in other applications, for example in systems designed with the innovative features in mind from the outset, these modules may be built into the overall operating system or code and so these modules may not be discernible as discrete entities.

[0244] In the above examples, a number of software modules were described. As those skilled in the art will appreciate, the software modules may be provided in compiled or un-compiled form and may be supplied to the RAN node, to the mobility management entity, or to the UE as a signal over a computer network, or on a recording medium. Further, the functionality performed by part, or all of, this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates the updating of the RAN node or the UE in order to update their functionalities.

[0245] The software module or the program includes instructions (or software codes) that, when loaded into a computer, cause the computer to perform one or more of the functions described in the above examples. The program may be stored in a non-transitory computer readable medium or a tangible storage medium. By way of example, and not a limitation, non-transitory computer readable media or tangible storage media can include a random-access memory (RAM), a read-only memory (ROM), a flash memory, a solid-state drive (SSD) or other types of memory technologies, a CD-ROM, a digital versatile disc (DVD), a Blu-ray disc or other types of optical disc storage, and magnetic cassettes, magnetic tape, magnetic disk storage or other types of magnetic storage devices. The program may be transmitted on a transitory computer readable medium or a communication medium. By way of example, and not a limitation, transitory computer readable media or communication media can include electrical, optical, acoustical, or other forms of propagated signals.

[0246] Each controller may comprise any suitable form of processing circuitry including (but not limited to), for example: one or more hardware implemented computer processors; microprocessors; central processing units (CPUs); arithmetic logic units (ALUs); input / output (IO) circuits; internal memories / caches (program and / or data); processing registers; communication buses (e.g. control, data and / or address buses); direct memory access (DMA) functions; hardware or software implemented counters, pointers and / or timers; and / or the like. Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0247] The base station may comprise a 'distributed' base station having a central unit 'CU' and one or more separate distributed units (DUs).

[0248] The User Equipment (or "UE", "mobile station", "mobile device" or "wireless device") in the present disclosure is an entity connected to a network via a wireless interface.

[0249] It should be noted that the present disclosure is not limited to a dedicated communication device and can be applied to any device having a communication function as explained in the following paragraphs.

[0250] The terms "User Equipment" or "UE" (as the term is used by 3GPP), "mobile station", "mobile device", and "wireless device" are generally intended to be synonymous with one another, and include standalone mobile stations, such as terminals, cell phones, smart phones, tablets, cellular IoT devices, IoT devices, and machinery. It will be appreciated that the terms "mobile station" and "mobile device" also encompass devices that remain stationary for a long period of time.

[0251] A UE may, for example, be an item of equipment for production or manufacture and / or an item of energy related machinery (for example equipment or machinery such as: boilers; engines; turbines; solar panels; wind turbines; hydroelectric generators; thermal power generators; nuclear electricity generators; batteries; nuclear systems and / or associated equipment; heavy electrical machinery; pumps including vacuum pumps; compressors; fans; blowers; oil hydraulic equipment; pneumatic equipment; metal working machinery; manipulators; robots and / or their application systems; tools; molds or dies; rolls; conveying equipment; elevating equipment; materials handling equipment; textile machinery; sewing machines; printing and / or related machinery; paper converting machinery; chemical machinery; mining and / or construction machinery and / or related equipment; machinery and / or implements for agriculture, forestry and / or fisheries; safety and / or environment preservation equipment; tractors; precision bearings; chains; gears; power transmission equipment; lubricating equipment; valves; pipe fittings; and / or application systems for any of the previously mentioned equipment or machinery etc.).

[0252] A UE may, for example, be an item of transport equipment (for example transport equipment such as: rolling stocks; motor vehicles; motorcycles; bicycles; trains; buses; carts; rickshaws; ships and other watercraft; aircraft; rockets; satellites; drones; balloons etc.). A UE may, for example, be an item of information and communication equipment (for example information and communication equipment such as: electronic computer and related equipment; communication and related equipment; electronic components etc.).

[0253] A UE may, for example, be a refrigerating machine, a refrigerating machine applied product, an item of trade and / or service industry equipment, a vending machine, an automatic service machine, an office machine or equipment, a consumer electronic and electronic appliance (for example a consumer electronic appliance such as: audio equipment; video equipment; a loud speaker; a radio; a television; a microwave oven; a rice cooker; a coffee machine; a dishwasher; a washing machine; a dryer; an electronic fan or related appliance; a cleaner etc.).

[0254] A UE may, for example, be an electrical application system or equipment (for example an electrical application system or equipment such as: an x-ray system; a particle accelerator; radio isotope equipment; sonic equipment; electromagnetic application equipment; electronic power application equipment etc.).

[0255] A UE may, for example, be an electronic lamp, a luminaire, a measuring instrument, an analyser, a tester, or a surveying or sensing instrument (for example a surveying or sensing instrument such as: a smoke alarm; a human alarm sensor; a motion sensor; a wireless tag etc.), a watch or clock, a laboratory instrument, optical apparatus, medical equipment and / or system, a weapon, an item of cutlery, a hand tool, or the like.

[0256] A UE may, for example, be a wireless-equipped personal digital assistant or related equipment (such as a wireless card or module designed for attachment to or for insertion into another electronic device (for example a personal computer, electrical measuring machine)).

[0257] A UE may be a device or a part of a system that provides applications, services, and solutions described below, as to "internet of things (IoT)", using a variety of wired and / or wireless communication technologies.

[0258] Internet of Things devices (or "things") may be equipped with appropriate electronics, software, sensors, network connectivity, and / or the like, which enable these devices to collect and exchange data with each other and with other communication devices. IoT devices may comprise automated equipment that follow software instructions stored in an internal memory. IoT devices may operate without requiring human supervision or interaction. IoT devices might also remain stationary and / or inactive for a long period of time. IoT devices may be implemented as a part of a (generally) stationary apparatus. IoT devices may also be embedded in non-stationary apparatus (e.g., vehicles) or attached to animals or persons to be monitored / tracked.

[0259] It will be appreciated that IoT technology can be implemented on any communication devices that can connect to a communication network for sending / receiving data, regardless of whether such communication devices are controlled by human input or software instructions stored in memory.

[0260] It will be appreciated that IoT devices are sometimes also referred to as Machine-Type Communication (MTC) devices or Machine-to-Machine (M2M) communication devices. It will be appreciated that a UE may support one or more IoT or MTC applications. Some examples of MTC applications are listed in the following table. This list is not exhaustive and is intended to be indicative of some examples of machine-type communication applications.

[0261] Applications, services, and solutions may be an MVNO (Mobile Virtual Network Operator) service, an emergency radio communication system, a PBX (Private Branch eXchange) system, a PHS / Digital Cordless Telecommunication system, a POS (Point of sale) system, an advertise calling system, an MBMS (Multimedia Broadcast and Multicast Service), a V2X (Vehicle to Everything) system, a train radio system, a location related service, a Disaster / Emergency Wireless Communication Service, a community service, a video streaming service, a femto cell application service, a VoLTE (Voice over LTE) service, a charging service, a radio on demand service, a roaming service, an activity monitoring service, a telecom carrier / communication NW selection service, a functional restriction service, a PoC (Proof of Concept) service, a personal information management service, an ad-hoc network / DTN (Delay Tolerant Networking) service, etc.

[0262] Further, the above-described UE categories are merely examples of applications of the technical ideas and examples described in the present document. Needless to say, these technical ideas and examples are not limited to the above-described UE and various modifications can be made thereto.

[0263] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0264] While the present disclosure has been particularly shown and described with reference to example embodiments thereof, the present disclosure is not limited to these example embodiments. It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present disclosure as defined by the claims. And each embodiment can be appropriately combined with at least one of embodiments.

[0265] Each of the drawings or figures is merely an example to illustrate one or more example embodiments. Each figure may not be associated with only one particular example embodiment, but may be associated with one or more other example embodiments. As those of ordinary skill in the art will understand, various features or steps described with reference to any one of the figures can be combined with features or steps illustrated in one or more other figures, for example, to produce example embodiments that are not explicitly illustrated or described. Not all of the features or steps illustrated in any one of the figures to describe an example embodiment are necessarily essential, and some features or steps may be omitted. The order of the steps described in any of the figures may be changed as appropriate.

[0266] This application is based upon and claims the benefit of priority from United Kingdom patent application No. 2501772.4, filed on February 6, 2025, the disclosure of which is incorporated herein in its entirety by reference.

[0267] The whole or part of the examples disclosed above can be described as, but not limited to, the following supplementary notes.

[0268] (Supplementary note 1) 　　A method performed by a user equipment, UE, the method comprising: 　　determining, in a case where the UE is connected via a first radio access network, RAN, node, whether the UE is in or near a closed access group, CAG, member cell of a second RAN node; 　　acquiring from the second RAN node, in a case where the UE is in or near a given CAG member cell, a first cell identifier for the given CAG member cell; 　　sending the first cell identifier to the first RAN node; and 　　receiving from the first RAN node a message for triggering the UE to handover to the second RAN node.

[0269] (Supplementary note 2) 　　The method according to Supplementary note 1, wherein the first cell identifier is a cell global identifier, CGI.

[0270] (Supplementary note 3) 　　The method according to Supplementary note 1, wherein the determining whether the UE is in or near a CAG member cell is carried out by the UE using an autonomous search procedure.

[0271] (Supplementary note 4) 　　The method according to any one of Supplementary notes 1-3, wherein the method further comprises sending, to the first RAN node, when the UE determines that the UE is in or near the given CAG member cell of the second RAN node, information indicating that the UE is in or near the given CAG member cell of the second RAN node.

[0272] (Supplementary note 5) 　　The method according to Supplementary note 4, wherein the information indicating that the UE is in or near the given CAG member cell of the second RAN node comprises information indicating at least one of a radio access technology, and / or a carrier frequency associated with the given CAG member cell.

[0273] (Supplementary note 6) 　　The method according to Supplementary note 4 or 5, wherein the method further comprises receiving, from the first RAN node, a configuration for proximity reporting, wherein the configuration for proximity reporting configures the UE to send the information indicating that the UE is in or near the given CAG member cell of the second RAN node in the case where the UE is in or near a given CAG member cell.

[0274] (Supplementary note 7) 　　The method according to any one of Supplementary notes 1-6, wherein the method further comprises performing measurements in respect of the given CAG member cell and sending, to the first RAN node, a first measurement report comprising results of the measurements and a physical cell identifier, PCI, for the given CAG member cell.

[0275] (Supplementary note 8) 　　The method according to Supplementary note 7, wherein the method further comprises receiving a message for configuring the UE to measure the radio access technology, and / or a carrier frequency associated.

[0276] (Supplementary note 9) 　　The method according to Supplementary note 7, wherein the method further comprises receiving a message comprises information for triggering the UE to acquire the first cell identifier sent by the first RAN node based on the first measurement report.

[0277] (Supplementary note 10) 　　The method according to Supplementary note 9, wherein the information comprises the physical cell identifier, PCI, of the given CAG member cell.

[0278] (Supplementary note 11) 　　The method according to Supplementary note 1, wherein the method further comprises receiving, from the first RAN node, a message for configuring the UE to perform measurements in respect of at least one CAG member cell to be measured, the message for configuring the UE to perform measurements in respect of at least one CAG member cell including a respective physical cell identifier, PCI, and / or CAG identifier for each CAG member cell to be measured.

[0279] (Supplementary note 12) 　　The method according to Supplementary note 9, wherein the determining of whether the UE is in or near a CAG member cell is performed in respect of each CAG member cell identified by a respective PCI and / or CAG identifier included in the message for configuring the UE to perform measurements in respect of at least one CAG member cell.

[0280] (Supplementary note 13) 　　The method according to any one of Supplementary notes 1-12, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member, the message for triggering the UE to handover to the given CAG member cell includes information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0281] (Supplementary note 14) 　　The method according to Supplementary note 12, wherein the method further comprises determining whether to handover to the given CAG member cell as a non-CAG cell and, in a case where the UE determines to handover to the given CAG member cell as a non-CAG cell, coordinating with the second RAN node to complete handover to the given CAG member cell as a non-CAG cell.

[0282] (Supplementary note 15) 　　The method according to Supplementary note 12, wherein the given CAG member cell is a shared cell that is shared with a public land mobile network, PLMN, cell.

[0283] (Supplementary note 16) 　　The method according to any one of Supplementary notes 1-15, wherein, in a case where the UE is allowed to access the given CAG member cell as a CAG member, the method further comprises coordinating with the second RAN node to complete handover to the Given CAG member cell as a CAG member.

[0284] (Supplementary note 17) 　　A method performed by a first radio access network, RAN, node, the method comprising: 　　sending, to a second RAN node or another communication node, a message for indicating that handover is requested or required, for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested or required including information indicating a first cell identifier and information indicating a list of at least one allowed CAG identifier; 　　receiving, from the second RAN node or the another communication node, a first message for triggering the UE to handover to the second RAN node; and 　　sending, to the UE, a second message for triggering the UE to handover to the second RAN node.

[0285] (Supplementary note 18) 　　The method according to Supplementary note 17, wherein the method further comprises sending, to the UE, a configuration for proximity reporting.

[0286] (Supplementary note 19) 　　The method according to Supplementary note 18, wherein the method further comprises receiving, from the UE, based on the configuration for proximity reporting, information indicating that the UE is in or near the given CAG member cell of the second RAN node.

[0287] (Supplementary note 20) 　　The method according to any of Supplementary notes 17-19, wherein the method further comprises receiving, from the UE, a first measurement report comprising results of the measurements and a physical cell identifier, PCI, for the given CAG member cell.

[0288] (Supplementary note 21) 　　The method according to Supplementary note 20, wherein the method further comprises sending, based on the first measurement report, a message for triggering the UE to acquire the first cell identifier.

[0289] (Supplementary note 22) 　　The method according to any of Supplementary notes 20-21, wherein the first cell identifier is a cell global identifier, CGI, and the method further comprises receiving the CGI, of the given CAG member cell in a second measurement report sent by the UE based on the message for triggering the UE to acquire the first cell identifier.

[0290] (Supplementary note 23) 　　The method according to Supplementary note 17, wherein the method further comprises receiving, from the second RAN node, information identifying, for at least one CAG member cell of the second RAN node, a respective physical cell identifier, PCI, and / or CAG identifier for each CAG member cell.

[0291] (Supplementary note 24) 　　The method according to Supplementary note 23, wherein the method further comprises storing the respective PCI, and / or CAG identifier for each CAG member cell in a neighbour relation table, NRT.

[0292] (Supplementary note 25) 　　The method according to Supplementary note 17, 23, or 24, wherein the method further comprises sending, to the UE, a message for configuring the UE to perform measurements in respect of at least one CAG member cell to be measured, the message for configuring the UE to perform measurements in respect of at least one CAG member cell including a respective PCI, and / or CAG identifier for each CAG member cell to be measured.

[0293] (Supplementary note 26) 　　The method according to Supplementary note 25, wherein the first cell identifier is a cell global identifier, CGI, and the method further comprises receiving the CGI in a measurement report sent by the UE based on the message for configuring the UE to perform measurements in respect of at least one CAG member cell.

[0294] (Supplementary note 27) 　　The method according to any of Supplementary notes 17-26, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member, the second message for triggering the UE to handover to the given CAG member cell is sent with information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0295] (Supplementary note 28) 　　The method according to any of Supplementary notes 17-27, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member, the method further comprises receiving, from the second RAN node or the another communication node, a failure message including information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0296] (Supplementary note 29) 　　The method according to Supplementary note 28, wherein the method further comprises determining whether to attempt handover of the UE to a cell of a public land mobile network, PLMN, that is a shared cell with the given CAG member cell.

[0297] (Supplementary note 30) 　　The method according to Supplementary note 29, wherein, in a case where the first RAN node determines to attempt handover of the UE to the given CAG member cell as a cell of a PLMN, the method further comprises sending, to the second RAN node or the another communication node, a further message for indicating that handover is requested or required, the further message for indicating that handover is requested or required including information indicating the first cell identifier.

[0298] (Supplementary note 31) 　　The method according to Supplementary note 28, wherein the method further comprises determining whether to attempt handover of the UE to the given CAG member cell as a non-CAG cell.

[0299] (Supplementary note 32) 　　The method according to Supplementary note 31, wherein, in a case where the first RAN node determines to attempt handover of the UE to the given CAG member cell as a non-CAG cell, the method further comprises sending, to the second RAN node or the another communication node, a further message for indicating that handover is requested or required, the further message for indicating that handover is requested or required including information indicating the first cell identifier.

[0300] (Supplementary note 33) 　　The method according to Supplementary note 30 or 32, wherein the first message for triggering the UE to handover to the given CAG member cell is received from the second RAN node or the another communication node after the further message for indicating that handover is requested or required.

[0301] (Supplementary note 34) 　　The method according to any of Supplementary notes 17-27, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the first message for triggering the UE to handover to the given CAG member cell is received with information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0302] (Supplementary note 35) 　　The method according to Supplementary note 34, wherein the first message for triggering the UE to handover to the given CAG member cell and information indicating that the UE is not a member of the CAG associated with the given CAG member cell is received from the second RAN node or the another communication node after the message for indicating that handover is requested or required.

[0303] (Supplementary note 36) 　　The method according to any of Supplementary notes 17-35, wherein the first message for triggering the UE to handover to the given CAG member cell is received in a message for acknowledging that handover is requested or required.

[0304] (Supplementary note 37) 　　The method according to any of Supplementary notes 17-36, wherein the message for indicating that handover is requested or required is sent to, and the first message for triggering the UE to handover to the second RAN node is received from, the second RAN node.

[0305] (Supplementary note 38) 　　The method according to any of Supplementary notes 17-37, wherein the message for indicating that handover is requested or required is sent to, and the first message for triggering the UE to handover to the second RAN node is received from, the another communication node, and the another communication node is a core network node.

[0306] (Supplementary note 39) 　　The method according to any of Supplementary notes 17-38, wherein the message for indicating that handover is requested or required is sent to, and the first message for triggering the UE to handover to the second RAN node is received from, the another communication node, and the another communication node is a gateway node.

[0307] (Supplementary note 40) 　　The method as claimed in Supplementary note 39, wherein the method further comprises sending, to the gateway node, before the message for indicating that handover is required is sent, information indicating at least one supported CAG, the information indicating at least one supported CAG including, for each supported CAG, a respective physical cell identifier, PCI, and / or CAG identifier.

[0308] (Supplementary note 41) 　　A method performed by a second radio access network, RAN, node, the method comprising: 　　receiving, from a first RAN node or another communication node, a message for indicating that handover is requested for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested including information indicating a first cell identifier of the given CAG member cell; and 　　sending, to the first RAN node or another communication node, a message for triggering the UE to handover to the second RAN node.

[0309] (Supplementary note 42) 　　The method according to Supplementary note 41, wherein the message for triggering the UE to handover to the second RAN node is sent in an acknowledgement message for acknowledging the message for indicating that handover is requested.

[0310] (Supplementary note 43) 　　The method according to Supplementary note 41 or 42, wherein the message for indicating that handover is requested is received from the first RAN node, and the message for triggering the UE to handover to the second RAN node is sent to the first RAN node.

[0311] (Supplementary note 44) 　　The method according to Supplementary note 43, wherein the method further comprises performing access control to determine whether the UE is allowed to access the given CAG member cell as a CAG member cell.

[0312] (Supplementary note 45) 　　The method according to Supplementary note 44, wherein the message for indicating that handover is requested includes information indicating a list of at least one allowed CAG identifier.

[0313] (Supplementary note 46) 　　The method according to Supplementary note 43 or 44, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the method further comprises sending, to the first RAN node, a failure message including information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0314] (Supplementary note 47) 　　The method according to Supplementary note 46, wherein the method further comprises receiving, from the first RAN node, a further message for indicating that handover is requested, the further message for indicating that handover is requested including information indicating the first cell identifier of the given CAG member cell, and the message for triggering the UE to handover to the given CAG member cell is sent based on the further message for indicating that handover is requested.

[0315] (Supplementary note 48) 　　The method according to Supplementary note 45, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the message for triggering the UE to handover to the given CAG member cell is sent with information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0316] (Supplementary note 49) 　　The method according to Supplementary note 41 or 42, wherein the message for indicating that handover is requested is received from the another communication node, the message for triggering the UE to handover to the second RAN node is sent to the another communication node, and the another communication node is a core network node.

[0317] (Supplementary note 50) 　　The method according to Supplementary note 49, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the information indicating that the UE is not a member of a CAG associated with the given CAG member cell is included with the message for triggering the UE to handover to the second RAN node.

[0318] (Supplementary note 51) 　　The method according to Supplementary note 49 or 50, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the message for indicating that handover is requested includes information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0319] (Supplementary note 52) 　　The method according to Supplementary note 41 or 42, wherein the message for indicating that handover is requested is received from the another communication node, the message for triggering the UE to handover to the second RAN node is sent to the another communication node, and the another communication node is a gateway node.

[0320] (Supplementary note 53) 　　The method according to Supplementary note 52, wherein, in a case where the UE is allowed to access the given CAG member cell as a CAG member cell, the message for indicating that handover is requested includes information indicating a list of at least one allowed CAG identifier.

[0321] (Supplementary note 54) 　　The method as claimed in Supplementary note 52 or 53, wherein the method further comprises sending, to the communication node, before the message for indicating that handover is requested is received, information indicating at least one supported CAG, the information indicating at least one supported CAG including, for each supported CAG, a respective physical cell identifier, PCI, and / or CAG identifier.

[0322] (Supplementary note 55) 　　A method performed by a communication node, the method comprising: 　　receiving, from a first RAN node, a message for indicating that handover is required for handover of a user equipment, UE, to a given closed access group, CAG, member cell of a second RAN node, the message for indicating that handover is required including information indicating a first cell identifier of the given CAG member cell and information indicating a list of at least one allowed CAG identifier; 　　performing access control to determine whether the UE is allowed to access the given CAG member cell as a CAG member cell; and 　　sending, to the first RAN node, a message for triggering the UE to handover to the second RAN node.

[0323] (Supplementary note 56) 　　The method according to Supplementary note 55, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the method further comprises sending, to the first RAN node, a failure message including information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0324] (Supplementary note 57) 　　The method according to Supplementary note 56, wherein the method further comprises receiving, from the first RAN node, a further message for indicating that handover is required, the further message for indicating that handover is required including information indicating the first cell identifier of the given CAG member cell.

[0325] (Supplementary note 58) 　　The method according to Supplementary note 55, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the method further comprises determining whether to attempt handover of the UE to the given CAG member cell as a cell of a public land mobile network, PLMN.

[0326] (Supplementary note 59) 　　The method according to Supplementary note 55, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the method further comprises determining whether to attempt handover of the UE to the given CAG member cell as a non-CAG cell.

[0327] (Supplementary note 60) 　　The method according to any of Supplementary notes 55 to 59, wherein the method further comprises sending, to the second RAN node, a message for indicating that handover is requested, the message for indicating that handover is requested including the first cell identifier of the given CAG member cell.

[0328] (Supplementary note 61) 　　The method according to Supplementary note 60, wherein the method further comprises receiving, from the second RAN node, an acknowledgement message for acknowledging the message for indicating that handover is requested, the acknowledgement message including the message for triggering the UE to handover to the second RAN node.

[0329] (Supplementary note 62) 　　The method according to Supplementary note 61, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the acknowledgement message includes information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0330] (Supplementary note 63) 　　The method according to any of Supplementary notes 60 to 62, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the message for indicating that handover is requested includes information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

[0331] (Supplementary note 64) 　　The method as claimed in any of Supplementary notes 55 to 63, wherein the communication node is a core network node.

[0332] (Supplementary note 65) 　　The method according to Supplementary note 60 or 61, wherein, in a case where the UE is allowed to access the given CAG member cell as a CAG member cell, the message for indicating that handover is requested includes the information indicating a list of at least one allowed CAG identifier.

[0333] (Supplementary note 66) 　　The method as claimed in any of Supplementary notes 55 to 61, or 65 wherein the method further comprises receiving, from the first RAN node and / or the second RAN node, before the message for indicating that handover is required is received, information indicating at least one supported CAG, the information indicating at least one supported CAG including, for each supported CAG, a respective physical cell identifier, PCI, and / or CAG identifier.

[0334] (Supplementary note 67) 　　The method as claimed in any of Supplementary notes 55 to 61, 65 or 66, wherein the communication node is a gateway node.

[0335] (Supplementary note 68) 　　A method performed by a first radio access network, RAN, node, the method comprising: 　　sending, to a second RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and 　　receiving, from the second RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

[0336] (Supplementary note 69) 　　A method performed by a second radio access network, RAN, node, the method comprising: 　　receiving, from a first RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and 　　sending, to the first RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

[0337] (Supplementary note 70) 　　The method according to Supplementary note 68 or 69, wherein, in the case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, the information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node is sent in a message for acknowledging the message for requesting addition of a secondary node.

[0338] (Supplementary note 71) 　　The method according to Supplementary note 68 or 69, wherein, in the case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, the information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node is sent in a message for rejecting the message for requesting addition of a secondary node.

[0339] (Supplementary note 72) 　　A method performed by a user equipment, UE, the method comprising: 　　sending, to a radio access network, RAN, node, a message for requesting registration of the UE with a closed access group, CAG, member cell; and 　　receiving from the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0340] (Supplementary note 73) 　　The method as claimed in Supplementary note 72, wherein the information indicating that the UE is not a member of the CAG is received from the RAN node with information indicating that registration is accepted.

[0341] (Supplementary note 74) 　　The method as claimed in Supplementary note 72, wherein the information indicating that the UE is not a member of the CAG is received from the RAN node in a message indicating that registration is rejected.

[0342] (Supplementary note 75) 　　A method performed by a radio access network, RAN, node, the method comprising: 　　receiving, from a user equipment, UE, a first message for requesting registration of the UE with a closed access group, CAG, member cell; 　　sending, to a core network node, the message for requesting registration of the UE with a CAG member cell; 　　receiving from the core network node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell; and 　　sending to the UE, in a case where the UE is not a member of a CAG associated with the CAG member cell, the information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0343] (Supplementary note 76) 　　The method as claimed in Supplementary note 75, wherein the information indicating that the UE is not a member of the CAG is received from the core network node with information indicating that registration is accepted.

[0344] (Supplementary note 77) 　　The method as claimed in Supplementary note 75 or 76, wherein the information indicating that the UE is not a member of the CAG is sent to the UE with information indicating that registration is accepted.

[0345] (Supplementary note 78) 　　The method as claimed in Supplementary note 75, wherein the information indicating that the UE is not a member of the CAG is received from the core network node in a message indicating that registration is rejected.

[0346] (Supplementary note 79) 　　The method as claimed in Supplementary note 75 or 76, wherein the information indicating that the UE is not a member of the CAG is sent to the UE in a message indicating that registration is rejected.

[0347] (Supplementary note 80) 　　A method performed by a core network node, the method comprising: 　　receiving, from a radio access network, RAN, node, a message for requesting registration of a user equipment, UE, with a CAG, member cell; and 　　sending, to the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0348] (Supplementary note 81) 　　The method as claimed in Supplementary note 80, wherein the information indicating that the UE is not a member of the CAG is sent to the RAN node with information indicating that registration is accepted.

[0349] (Supplementary note 82) 　　The method as claimed in Supplementary note 80, wherein the information indicating that the UE is not a member of the CAG is sent to the RAN node in a message indicating that registration is rejected.

[0350] (Supplementary note 83) 　　A user equipment, UE, comprising: 　　means for determining, in a case where the UE is connected via a first radio access network, RAN, node, whether the UE is in or near a closed access group, CAG, member cell of a second RAN node; 　　means for acquiring from the second RAN node, in a case where the UE is in or near a given CAG member cell, a first cell identifier for the given CAG member cell; 　　means for sending the first cell identifier to the first RAN node; and 　　means for receiving from the first RAN node a message for triggering the UE to handover to the second RAN node.

[0351] (Supplementary note 84) 　　A first radio access network, RAN, node comprising: 　　means for sending, to a second RAN node or another communication node, a message for indicating that handover is requested or required, for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested or required including information indicating a first cell identifier and information indicating a list of at least one allowed CAG identifier; 　　means for receiving, from the second RAN node or the another communication node, a first message for triggering the UE to handover to the second RAN node; and 　　means for sending, to the UE, a second message for triggering the UE to handover to the second RAN node.

[0352] (Supplementary note 85) 　　A second radio access network, RAN, node comprising: 　　means for receiving, from a first RAN node or another communication node, a message for indicating that handover is requested for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested including information indicating a first cell identifier of the given CAG member cell; and 　　means for sending, to the first RAN node or the another communication node, a message for triggering the UE to handover to the second RAN node.

[0353] (Supplementary note 86) 　　A communication node comprising: 　　means for receiving, from a first RAN node, a message for indicating that handover is required for handover of a user equipment, UE, to a given closed access group, CAG, member cell of a second RAN node, the message for indicating that handover is required including information indicating a first cell identifier of the given CAG member cell and information indicating a list of at least one allowed CAG identifier; 　　means for performing access control to determine whether the UE is allowed to access the given CAG member cell as a CAG member cell; and 　　means for sending, to the first RAN node, a message for triggering the UE to handover to the second RAN node.

[0354] (Supplementary note 87) 　　A first radio access network, RAN, node comprising: 　　means for sending, to a second RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and 　　means for receiving, from the second RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

[0355] (Supplementary note 88) 　　A second radio access network, RAN, node, the second RAN node comprising: 　　means for receiving, from a first RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and 　　means for sending, to the first RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

[0356] (Supplementary note 89) 　　A user equipment, UE comprising: 　　means for sending, to a radio access network, RAN, node, a message for requesting registration of the UE with a closed access group, CAG, member cell; and 　　means for receiving from the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0357] (Supplementary note 90) 　　A radio access network, RAN, node, the RAN node comprising: 　　means for receiving, from a user equipment, UE, a first message for requesting registration of the UE with a closed access group, CAG, member cell; 　　means for sending, to a core network node, the message for requesting registration of the UE with a CAG, member cell; 　　means for receiving from the core network node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell; and 　　means for sending to the UE, in a case where the UE is not a member of a CAG associated with the CAG member cell, the information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0358] (Supplementary note 91) 　　A core network node comprising: 　　means for receiving, from a radio access network, RAN, node, a message for requesting registration of a user equipment, UE, with a CAG, member cell; and 　　means for sending, to the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

[0359] Some or all of elements (e.g., structures and functions) specified in Supplementary Notes 2 to 16 dependent on Supplementary Note 1 may also be dependent on Supplementary Note 17, 41, 55, 68, 69, 72, 75, 80, 83-91 in dependency similar to that of Supplementary Notes 2 to 16 on Supplementary Note 1. Some or all of elements specified in any of Supplementary Notes may be applied to various types of hardware, software, and recording means for recording software, systems, and methods.

[0360] 1　　COMMUNICATION SYSTEM 3　　USER EQUIPMENT (UE) 5　　RADIO ACCESS NETWORK (RAN) NODE 5-1　　RAN NODE 5-2　　FEMTO NODE 7　　CORE NETWORK 9　　FEMTO GATEWAY (GW) 10　　CONTROL PLANE FUNCTION (CPF) 10-1　　ACCESS AND MOBILITY MANAGEMENT FUNCTION (AMF) 10-2　　SESSION MANAGEMENT FUNCTION (SMF) 10-n　　OTHER FUNCTION 11　　USER PLANE FUNCTION (UPF) 20　　EXTERNAL DATA NETWORK 31　　TRANSCEIVER CIRCUIT 33　　ANTENNA 35　　USER INTERFACE 37　　CONTROLLER 39　　MEMORY 41　　OPERATING SYSTEM 43　　COMMUNICATION CONTROL MODULE 51　　TRANSCEIVER CIRCUIT 53　　ANTENNA 55　　CORE NETWORK INTERFACE 57　　CONTROLLER 59　　MEMORY 61　　OPERATING SYSTEM 63　　COMMUNICATION CONTROL MODULE 611　　TRANSCEIVER CIRCUIT 612　　NETWORK INTERFACE 613　　CONTROLLER 614　　MEMORY 615　　OPERATING SYSTEM 616　　COMMUNICATION CONTROL MODULE 711　　TRANSCEIVER CIRCUIT 712　　NETWORK INTERFACE 713　　CONTROLLER 714　　MEMORY 715　　OPERATING SYSTEM 716　　COMMUNICATION CONTROL MODULE

Claims

1. A method performed by a user equipment, UE, the method comprising: 　　determining, in a case where the UE is connected via a first radio access network, RAN, node, whether the UE is in or near a closed access group, CAG, member cell of a second RAN node; 　　acquiring from the second RAN node, in a case where the UE is in or near a given CAG member cell, a first cell identifier for the given CAG member cell; 　　sending the first cell identifier to the first RAN node; and 　　receiving from the first RAN node a message for triggering the UE to handover to the second RAN node.

2. The method according to claim 1, wherein the first cell identifier is a cell global identifier, CGI.

3. The method according to claim 1, wherein the determining whether the UE is in or near a CAG member cell is carried out by the UE using an autonomous search procedure.

4. The method according to any one of claims 1-3, wherein the method further comprises sending, to the first RAN node, when the UE determines that the UE is in or near the given CAG member cell of the second RAN node, information indicating that the UE is in or near the given CAG member cell of the second RAN node.

5. The method according to claim 4, wherein the information indicating that the UE is in or near the given CAG member cell of the second RAN node comprises information indicating at least one of a radio access technology, and / or a carrier frequency associated with the given CAG member cell.

6. The method according to claim 4 or 5, wherein the method further comprises receiving, from the first RAN node, a configuration for proximity reporting, wherein the configuration for proximity reporting configures the UE to send the information indicating that the UE is in or near the given CAG member cell of the second RAN node in the case where the UE is in or near a given CAG member cell.

7. The method according to any one of claims 1-6, wherein the method further comprises performing measurements in respect of the given CAG member cell and sending, to the first RAN node, a first measurement report comprising results of the measurements and a physical cell identifier, PCI, for the given CAG member cell.

8. The method according to claim 7, wherein the method further comprises receiving a message for configuring the UE to measure the radio access technology, and / or a carrier frequency associated.

9. The method according to claim 7, wherein the method further comprises receiving a message comprises information for triggering the UE to acquire the first cell identifier sent by the first RAN node based on the first measurement report.

10. The method according to claim 9, wherein the information comprises the physical cell identifier, PCI, of the given CAG member cell.

11. The method according to claim 1, wherein the method further comprises receiving, from the first RAN node, a message for configuring the UE to perform measurements in respect of at least one CAG member cell to be measured, the message for configuring the UE to perform measurements in respect of at least one CAG member cell including a respective physical cell identifier, PCI, and / or CAG identifier for each CAG member cell to be measured.

12. The method according to claim 9, wherein the determining of whether the UE is in or near a CAG member cell is performed in respect of each CAG member cell identified by a respective PCI and / or CAG identifier included in the message for configuring the UE to perform measurements in respect of at least one CAG member cell.

13. The method according to any one of claims 1-12, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member, the message for triggering the UE to handover to the given CAG member cell includes information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

14. The method according to claim 12, wherein the method further comprises determining whether to handover to the given CAG member cell as a non-CAG cell and, in a case where the UE determines to handover to the given CAG member cell as a non-CAG cell, coordinating with the second RAN node to complete handover to the given CAG member cell as a non-CAG cell.

15. The method according to claim 12, wherein the given CAG member cell is a shared cell that is shared with a public land mobile network, PLMN, cell.

16. The method according to any one of claims 1-15, wherein, in a case where the UE is allowed to access the given CAG member cell as a CAG member, the method further comprises coordinating with the second RAN node to complete handover to the Given CAG member cell as a CAG member.

17. A method performed by a first radio access network, RAN, node, the method comprising: 　　sending, to a second RAN node or another communication node, a message for indicating that handover is requested or required, for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested or required including information indicating a first cell identifier and information indicating a list of at least one allowed CAG identifier; 　　receiving, from the second RAN node or the another communication node, a first message for triggering the UE to handover to the second RAN node; and 　　sending, to the UE, a second message for triggering the UE to handover to the second RAN node.

18. The method according to claim 17, wherein the method further comprises sending, to the UE, a configuration for proximity reporting.

19. The method according to claim 18, wherein the method further comprises receiving, from the UE, based on the configuration for proximity reporting, information indicating that the UE is in or near the given CAG member cell of the second RAN node.

20. The method according to any of claims 17-19, wherein the method further comprises receiving, from the UE, a first measurement report comprising results of the measurements and a physical cell identifier, PCI, for the given CAG member cell.

21. The method according to claim 20, wherein the method further comprises sending, based on the first measurement report, a message for triggering the UE to acquire the first cell identifier.

22. The method according to any of claims 20-21, wherein the first cell identifier is a cell global identifier, CGI, and the method further comprises receiving the CGI, of the given CAG member cell in a second measurement report sent by the UE based on the message for triggering the UE to acquire the first cell identifier.

23. The method according to claim 17, wherein the method further comprises receiving, from the second RAN node, information identifying, for at least one CAG member cell of the second RAN node, a respective physical cell identifier, PCI, and / or CAG identifier for each CAG member cell.

24. The method according to claim 23, wherein the method further comprises storing the respective PCI, and / or CAG identifier for each CAG member cell in a neighbour relation table, NRT.

25. The method according to claim 17, 23, or 24, wherein the method further comprises sending, to the UE, a message for configuring the UE to perform measurements in respect of at least one CAG member cell to be measured, the message for configuring the UE to perform measurements in respect of at least one CAG member cell including a respective PCI, and / or CAG identifier for each CAG member cell to be measured.

26. The method according to claim 25, wherein the first cell identifier is a cell global identifier, CGI, and the method further comprises receiving the CGI in a measurement report sent by the UE based on the message for configuring the UE to perform measurements in respect of at least one CAG member cell.

27. The method according to any of claims 17-26, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member, the second message for triggering the UE to handover to the given CAG member cell is sent with information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

28. The method according to any of claims 17-27, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member, the method further comprises receiving, from the second RAN node or the another communication node, a failure message including information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

29. The method according to claim 28, wherein the method further comprises determining whether to attempt handover of the UE to a cell of a public land mobile network, PLMN, that is a shared cell with the given CAG member cell.

30. The method according to claim 29, wherein, in a case where the first RAN node determines to attempt handover of the UE to the given CAG member cell as a cell of a PLMN, the method further comprises sending, to the second RAN node or the another communication node, a further message for indicating that handover is requested or required, the further message for indicating that handover is requested or required including information indicating the first cell identifier.

31. The method according to claim 28, wherein the method further comprises determining whether to attempt handover of the UE to the given CAG member cell as a non-CAG cell.

32. The method according to claim 31, wherein, in a case where the first RAN node determines to attempt handover of the UE to the given CAG member cell as a non-CAG cell, the method further comprises sending, to the second RAN node or the another communication node, a further message for indicating that handover is requested or required, the further message for indicating that handover is requested or required including information indicating the first cell identifier.

33. The method according to claim 30 or 32, wherein the first message for triggering the UE to handover to the given CAG member cell is received from the second RAN node or the another communication node after the further message for indicating that handover is requested or required.

34. The method according to any of claims 17-27, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the first message for triggering the UE to handover to the given CAG member cell is received with information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

35. The method according to claim 34, wherein the first message for triggering the UE to handover to the given CAG member cell and information indicating that the UE is not a member of the CAG associated with the given CAG member cell is received from the second RAN node or the another communication node after the message for indicating that handover is requested or required.

36. The method according to any of claims 17-35, wherein the first message for triggering the UE to handover to the given CAG member cell is received in a message for acknowledging that handover is requested or required.

37. The method according to any of claims 17-36, wherein the message for indicating that handover is requested or required is sent to, and the first message for triggering the UE to handover to the second RAN node is received from, the second RAN node.

38. The method according to any of claims 17-37, wherein the message for indicating that handover is requested or required is sent to, and the first message for triggering the UE to handover to the second RAN node is received from, the another communication node, and the another communication node is a core network node.

39. The method according to any of claims 17-38, wherein the message for indicating that handover is requested or required is sent to, and the first message for triggering the UE to handover to the second RAN node is received from, the another communication node, and the another communication node is a gateway node.

40. The method as claimed in claim 39, wherein the method further comprises sending, to the gateway node, before the message for indicating that handover is required is sent, information indicating at least one supported CAG, the information indicating at least one supported CAG including, for each supported CAG, a respective physical cell identifier, PCI, and / or CAG identifier.

41. A method performed by a second radio access network, RAN, node, the method comprising: 　　receiving, from a first RAN node or another communication node, a message for indicating that handover is requested for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested including information indicating a first cell identifier of the given CAG member cell; and 　　sending, to the first RAN node or another communication node, a message for triggering the UE to handover to the second RAN node.

42. The method according to claim 41, wherein the message for triggering the UE to handover to the second RAN node is sent in an acknowledgement message for acknowledging the message for indicating that handover is requested.

43. The method according to claim 41 or 42, wherein the message for indicating that handover is requested is received from the first RAN node, and the message for triggering the UE to handover to the second RAN node is sent to the first RAN node.

44. The method according to claim 43, wherein the method further comprises performing access control to determine whether the UE is allowed to access the given CAG member cell as a CAG member cell.

45. The method according to claim 44, wherein the message for indicating that handover is requested includes information indicating a list of at least one allowed CAG identifier.

46. The method according to claim 43 or 44, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the method further comprises sending, to the first RAN node, a failure message including information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

47. The method according to claim 46, wherein the method further comprises receiving, from the first RAN node, a further message for indicating that handover is requested, the further message for indicating that handover is requested including information indicating the first cell identifier of the given CAG member cell, and the message for triggering the UE to handover to the given CAG member cell is sent based on the further message for indicating that handover is requested.

48. The method according to claim 45, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the message for triggering the UE to handover to the given CAG member cell is sent with information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

49. The method according to claim 41 or 42, wherein the message for indicating that handover is requested is received from the another communication node, the message for triggering the UE to handover to the second RAN node is sent to the another communication node, and the another communication node is a core network node.

50. The method according to claim 49, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the information indicating that the UE is not a member of a CAG associated with the given CAG member cell is included with the message for triggering the UE to handover to the second RAN node.

51. The method according to claim 49 or 50, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the message for indicating that handover is requested includes information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

52. The method according to claim 41 or 42, wherein the message for indicating that handover is requested is received from the another communication node, the message for triggering the UE to handover to the second RAN node is sent to the another communication node, and the another communication node is a gateway node.

53. The method according to claim 52, wherein, in a case where the UE is allowed to access the given CAG member cell as a CAG member cell, the message for indicating that handover is requested includes information indicating a list of at least one allowed CAG identifier.

54. The method as claimed in claim 52 or 53, wherein the method further comprises sending, to the communication node, before the message for indicating that handover is requested is received, information indicating at least one supported CAG, the information indicating at least one supported CAG including, for each supported CAG, a respective physical cell identifier, PCI, and / or CAG identifier.

55. A method performed by a communication node, the method comprising: 　　receiving, from a first RAN node, a message for indicating that handover is required for handover of a user equipment, UE, to a given closed access group, CAG, member cell of a second RAN node, the message for indicating that handover is required including information indicating a first cell identifier of the given CAG member cell and information indicating a list of at least one allowed CAG identifier; 　　performing access control to determine whether the UE is allowed to access the given CAG member cell as a CAG member cell; and 　　sending, to the first RAN node, a message for triggering the UE to handover to the second RAN node.

56. The method according to claim 55, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the method further comprises sending, to the first RAN node, a failure message including information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

57. The method according to claim 56, wherein the method further comprises receiving, from the first RAN node, a further message for indicating that handover is required, the further message for indicating that handover is required including information indicating the first cell identifier of the given CAG member cell.

58. The method according to claim 55, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the method further comprises determining whether to attempt handover of the UE to the given CAG member cell as a cell of a public land mobile network, PLMN.

59. The method according to claim 55, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the method further comprises determining whether to attempt handover of the UE to the given CAG member cell as a non-CAG cell.

60. The method according to any of claims 55 to 59, wherein the method further comprises sending, to the second RAN node, a message for indicating that handover is requested, the message for indicating that handover is requested including the first cell identifier of the given CAG member cell.

61. The method according to claim 60, wherein the method further comprises receiving, from the second RAN node, an acknowledgement message for acknowledging the message for indicating that handover is requested, the acknowledgement message including the message for triggering the UE to handover to the second RAN node.

62. The method according to claim 61, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the acknowledgement message includes information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

63. The method according to any of claims 60 to 62, wherein, in a case where the UE is not allowed to access the given CAG member cell as a CAG member cell, the message for indicating that handover is requested includes information indicating that the UE is not a member of a CAG associated with the given CAG member cell.

64. The method as claimed in any of claims 55 to 63, wherein the communication node is a core network node.

65. The method according to claim 60 or 61, wherein, in a case where the UE is allowed to access the given CAG member cell as a CAG member cell, the message for indicating that handover is requested includes the information indicating a list of at least one allowed CAG identifier.

66. The method as claimed in any of claims 55 to 61, or 65 wherein the method further comprises receiving, from the first RAN node and / or the second RAN node, before the message for indicating that handover is required is received, information indicating at least one supported CAG, the information indicating at least one supported CAG including, for each supported CAG, a respective physical cell identifier, PCI, and / or CAG identifier.

67. The method as claimed in any of claims 55 to 61, 65 or 66, wherein the communication node is a gateway node.

68. A method performed by a first radio access network, RAN, node, the method comprising: 　　sending, to a second RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and 　　receiving, from the second RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

69. A method performed by a second radio access network, RAN, node, the method comprising: 　　receiving, from a first RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and 　　sending, to the first RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

70. The method according to claim 68 or 69, wherein, in the case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, the information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node is sent in a message for acknowledging the message for requesting addition of a secondary node.

71. The method according to claim 68 or 69, wherein, in the case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, the information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node is sent in a message for rejecting the message for requesting addition of a secondary node.

72. A method performed by a user equipment, UE, the method comprising: 　　sending, to a radio access network, RAN, node, a message for requesting registration of the UE with a closed access group, CAG, member cell; and 　　receiving from the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

73. The method as claimed in claim 72, wherein the information indicating that the UE is not a member of the CAG is received from the RAN node with information indicating that registration is accepted.

74. The method as claimed in claim 72, wherein the information indicating that the UE is not a member of the CAG is received from the RAN node in a message indicating that registration is rejected.

75. A method performed by a radio access network, RAN, node, the method comprising: 　　receiving, from a user equipment, UE, a first message for requesting registration of the UE with a closed access group, CAG, member cell; 　　sending, to a core network node, the message for requesting registration of the UE with a CAG member cell; 　　receiving from the core network node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell; and 　　sending to the UE, in a case where the UE is not a member of a CAG associated with the CAG member cell, the information indicating that the UE is not a member of the CAG associated with the CAG member cell.

76. The method as claimed in claim 75, wherein the information indicating that the UE is not a member of the CAG is received from the core network node with information indicating that registration is accepted.

77. The method as claimed in claim 75 or 76, wherein the information indicating that the UE is not a member of the CAG is sent to the UE with information indicating that registration is accepted.

78. The method as claimed in claim 75, wherein the information indicating that the UE is not a member of the CAG is received from the core network node in a message indicating that registration is rejected.

79. The method as claimed in claim 75 or 76, wherein the information indicating that the UE is not a member of the CAG is sent to the UE in a message indicating that registration is rejected.

80. A method performed by a core network node, the method comprising: 　　receiving, from a radio access network, RAN, node, a message for requesting registration of a user equipment, UE, with a CAG, member cell; and 　　sending, to the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

81. The method as claimed in claim 80, wherein the information indicating that the UE is not a member of the CAG is sent to the RAN node with information indicating that registration is accepted.

82. The method as claimed in claim 80, wherein the information indicating that the UE is not a member of the CAG is sent to the RAN node in a message indicating that registration is rejected.

83. A user equipment, UE, comprising: 　　means for determining, in a case where the UE is connected via a first radio access network, RAN, node, whether the UE is in or near a closed access group, CAG, member cell of a second RAN node; 　　means for acquiring from the second RAN node, in a case where the UE is in or near a given CAG member cell, a first cell identifier for the given CAG member cell; 　　means for sending the first cell identifier to the first RAN node; and 　　means for receiving from the first RAN node a message for triggering the UE to handover to the second RAN node.

84. A first radio access network, RAN, node comprising: 　　means for sending, to a second RAN node or another communication node, a message for indicating that handover is requested or required, for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested or required including information indicating a first cell identifier and information indicating a list of at least one allowed CAG identifier; 　　means for receiving, from the second RAN node or the another communication node, a first message for triggering the UE to handover to the second RAN node; and 　　means for sending, to the UE, a second message for triggering the UE to handover to the second RAN node.

85. A second radio access network, RAN, node comprising: 　　means for receiving, from a first RAN node or another communication node, a message for indicating that handover is requested for handover of a user equipment, UE, to a given closed access group, CAG, member cell of the second RAN node, the message for indicating that handover is requested including information indicating a first cell identifier of the given CAG member cell; and 　　means for sending, to the first RAN node or the another communication node, a message for triggering the UE to handover to the second RAN node.

86. A communication node comprising: 　　means for receiving, from a first RAN node, a message for indicating that handover is required for handover of a user equipment, UE, to a given closed access group, CAG, member cell of a second RAN node, the message for indicating that handover is required including information indicating a first cell identifier of the given CAG member cell and information indicating a list of at least one allowed CAG identifier; 　　means for performing access control to determine whether the UE is allowed to access the given CAG member cell as a CAG member cell; and 　　means for sending, to the first RAN node, a message for triggering the UE to handover to the second RAN node.

87. A first radio access network, RAN, node comprising: 　　means for sending, to a second RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and 　　means for receiving, from the second RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

88. A second radio access network, RAN, node, the second RAN node comprising: 　　means for receiving, from a first RAN node, a message for requesting addition of a secondary node, for a user equipment, UE, the message for requesting addition of a secondary node including information indicating a list of at least one allowed CAG identifier; and 　　means for sending, to the first RAN node, in a case where the UE is not allowed to access at least one CAG member cell of the second RAN node as a CAG member cell, information indicating that the UE is not a member of a CAG associated with at least one CAG member cell of the second RAN node.

89. A user equipment, UE comprising: 　　means for sending, to a radio access network, RAN, node, a message for requesting registration of the UE with a closed access group, CAG, member cell; and 　　means for receiving from the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

90. A radio access network, RAN, node, the RAN node comprising: 　　means for receiving, from a user equipment, UE, a first message for requesting registration of the UE with a closed access group, CAG, member cell; 　　means for sending, to a core network node, the message for requesting registration of the UE with a CAG, member cell; 　　means for receiving from the core network node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell; and 　　means for sending to the UE, in a case where the UE is not a member of a CAG associated with the CAG member cell, the information indicating that the UE is not a member of the CAG associated with the CAG member cell.

91. A core network node comprising: 　　means for receiving, from a radio access network, RAN, node, a message for requesting registration of a user equipment, UE, with a CAG, member cell; and 　　means for sending, to the RAN node, in a case where the UE is not a member of a CAG associated with the CAG member cell, information indicating that the UE is not a member of the CAG associated with the CAG member cell.

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