WO2025158043A1

WO2025158043A1 - Ue mobility among femtocells of different technologies

Info

Publication number: WO2025158043A1
Application number: PCT/EP2025/051868
Authority: WO
Inventors: Philippe Godin; Basavaraj KIRAGI; Ling Yu
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2024-01-25
Filing date: 2025-01-24
Publication date: 2025-07-31
Anticipated expiration: 2026-07-25

Abstract

There is provided a method, apparatus, and computer program for causing the following operations to be performed: receiving, a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network, wherein the first communication network and the second communication network are different communication networks; and transmitting the CSG identifier that is received to the second network node.

Description

UE MOBILITY AMONG FEMTOCELLS OF DIFFERENT TECHNOLOGIES

FIELD

[0001]The present application relates to apparatus, methods and computing programs for causing operations for receiving a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network to be performed.

BACKGROUND

[0002]A communication system can be seen as a facility that enables communication sessions between two or more entities such as user terminals, base stations and/or other nodes by providing carriers between the various entities involved in the communications session. A communication system can be provided for example by means of a communication network and one or more compatible communication devices. The communication sessions may comprise, for example, communication of data for carrying communications such as voice, video, electronic mail (email), text message, multimedia and/or content data and so on. Non-limiting examples of services provided comprise two-way or multi-way calls, data communication or multimedia services and access to a data network system, such as the Internet.

[0003]The communication system and associated devices typically operate in accordance with a given standard or specification which sets out what the various entities associated with the system are permitted to do and how that should be achieved. Communication protocols and/or parameters which shall be used for the connection are also typically defined. One example of a communications system is UTRAN (Universal Mobile Telecommunications Service terrestrial radio access network (e.g., 3G radio)). Other examples of communication systems are the longterm evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio-access technology and so-called 5G or New Radio (NR) networks. NR is being standardized by the 3rd Generation Partnership Project (3GPP).

[0004] 3GPP has described a flexible duplex slot (known as subband full duplex (SBFD) slot) which comprises resources for both uplink and downlink transmission opportunities within the same time slot. Stated differently, SBFD slots implement time duplex communication within a single carrier bandwidth in which transmissions in uplink and downlink simultaneously occur within different sub-bands of the carrier bandwidth

SUMMARY

[0005]According to a first aspect, there is provided a user equipment comprising means for performing operations, the operations comprising: receiving, a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network, wherein the first communication network and the second communication network are different communication networks; and transmitting the CSG identifier that is received to the second network node.

[0006]According to a second aspect, there is provided a user equipment comprising: at least one processor; and at least one memory comprising code that, when executed by the at least one processor, causes the user equipment to perform: receiving, a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network, wherein the first communication network and the second communication network are different communication networks; and transmitting the CSG identifier that is received to the second network node.

[0007]According to a third aspect, there is provided a method for a user equipment, the method comprising: receiving, a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network, wherein the first communication network and the second communication network are different communication networks; and transmitting the CSG identifier that is received to the second network node.

[0008]According to a fourth aspect, there is provided a user equipment comprising: receiving circuitry for receiving, a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network, wherein the first communication network and the second communication network are different communication networks; and transmitting circuitry for transmitting the CSG identifier that is received to the second network node. [0009]The following may apply in respect of each (e.g., any and/or all) of the above mentioned first to fourth aspects.

[0010]The transmitting may comprise transmitting a measurement report comprising the CSG identifier.

[0011]The receiving may comprise receiving an SIB1 message comprising the CSG identifier.

[0012] According to a fifth aspect, there is provided a second apparatus for a second network node of a second communication network, the second apparatus comprising means for performing operations, the operations comprising: receiving, from a user equipment, a closed subscriber group, CSG, identifier; encoding the CSG identifier that is received to generate an encoded closed access group, CAG, identifier; and using the encoded CAG identifier to determine whether to perform a mobility procedure for the terminal towards a first network node of a first communication network, wherein the first communication network and the second communication network are different communication networks.

[0013] According to a sixth aspect, there is provided a second apparatus for a second network node of a second communication network, the second apparatus comprising: at least one processor; and at least one memory comprising code that, when executed by the at least one processor, causes the second apparatus to perform: receiving, from a user equipment, a closed subscriber group, CSG, identifier; encoding the CSG identifier that is received to generate an encoded closed access group, CAG, identifier; and using the encoded CAG identifier to determine whether to perform a mobility procedure for the terminal towards a first network node of a first communication network, wherein the first communication network and the second communication network are different communication networks.

[0014]According to a seventh aspect, there is provided a method for a second apparatus for a second network node of a second communication network, the method comprising: receiving, from a user equipment, a closed subscriber group, CSG, identifier; encoding the CSG identifier that is received to generate an encoded closed access group, CAG, identifier; and using the encoded CAG identifier to determine whether to perform a mobility procedure for the terminal towards a first network node of a first communication network, wherein the first communication network and the second communication network are different communication networks. [0015] According to an eighth aspect, there is provided a second apparatus for a second network node of a second communication network, the second apparatus comprising: receiving circuitry for receiving, from a user equipment, a closed subscriber group, CSG, identifier; encoding circuitry for encoding the CSG identifier that is received to generate an encoded closed access group, CAG, identifier; and using circuitry for using the encoded CAG identifier to determine whether to perform a mobility procedure for the terminal towards a first network node of a first communication network, wherein the first communication network and the second communication network are different communication networks.

[0016]The following may apply in respect of each (e.g., any and/or all) of the above- mentioned fifth to eighth aspects.

[0017] The second apparatus operations may further comprise configuring the second apparatus with a set of encoded closed access group, CAG, identifiers, wherein the set of encoded CAG identifiers are reserved for first network nodes of the first communication network.

[0018]The configuring may comprise receiving an indication of one or more encoded CAG identifiers of the set of encoded CAG identifiers and respective access rights for the one or more encoded CAG identifiers of the set of encoded CAG identifiers from an operations and management function.

[0019] The receiving the CSG identifier may comprise receiving a measurement report comprising the CSG identifier.

[0020]The encoding may comprise: adding five dummy bits to the CSG identifier that is received.

[0021]The encoding may comprise: adding five leading zero bits to the CSG identifier that is received.

[0022] The encoded CAG identifier may have a same length as a CAG identifier.

[0023] The CSG identifier that is received may comprise 27 bits, and the encoded CAG identifier may comprise 32 bits.

[0024]The following may apply in respect of each (e.g., any and/or all) of the above first to eighth aspects.

[0025]The first communication network may comprise a 4G network.

[0026]The second communication network may comprise a 5G network or 6G network. [0027]According to an aspect, there is provided a non-transitory computer readable medium comprising program instructions that, when executed by an apparatus, cause the apparatus to perform at least the method according to any of the preceding aspects.

[0028] In the above, many different embodiments have been described. It should be appreciated that further embodiments may be provided by the combination of any two or more of the embodiments described above.

DESCRIPTION OF FIGURES

[0029] Embodiments will now be described, by way of example only, with reference to the accompanying Figures in which:

[0030] Figures 1A to 1 B show representations of a network system according to some example embodiments;

[0031] Figure 2 shows a representation of a control apparatus according to some example embodiments;

[0032] Figure 3 shows a representation of an apparatus according to some example embodiments;

[0033] Figures 4 to 7 illustrate operations that may be performed between apparatus in examples; and

[0034] Figures 8 to 17 illustrate operations that may be performed by apparatus described herein.

DETAILED DESCRIPTION

[0035] The following describes operations that may be performed in relation to interoperability between 4G and 5G (and beyond) communication systems.

[0036] In particular, the following considers issues that may arise when the 4G communication system has an access network node (e.g., a femto) that is configured to provide connectivity services (e.g., access via the 4G communication network) to a limited number of subscribers. This access network node configuration may be, for example, as in the case of femto cells that are operating in a closed subscriber group (CSG) mode, as described further below. This 4G access network node configuration may be problematic for network nodes of the other communication system (e.g., of 5G and/or 6G communication systems) when those network nodes are performing mobility operations that include 4G access network nodes, as not all terminals will be allowed to receive connectivity services from those 4G radio access network nodes.

[0037] In the following certain embodiments are explained with reference to mobile communication devices capable of communication via a wireless cellular system and mobile communication systems serving such mobile communication devices. Before explaining in detail the exemplifying embodiments, certain general principles of a wireless communication system, access systems thereof, and mobile communication devices are briefly explained with reference to Figures 1A, 1 B, 2 and 3 to assist in understanding the technology underlying the described examples.

[0038] Figure 1A shows a schematic representation of a 5G system (5GS) configured to communicate with a terminal (e.g., a user equipment (UE)). The 5GS may be a 5G radio access network (5GRAN) or next generation radio access network (NG-RAN), a 5G core network (5GC), one or more application function (AF) and one or more data networks (DN).

[0039]The 5G-RAN may comprise one or more gNodeB (GNB) or one or more gNodeB (GNB) distributed unit functions connected to one or more gNodeB (GNB) centralized unit functions. This is illustrated in more detail below, with reference to Figure 1 B.

[0040] The 5GC may comprise the following entities: Network Slice Selection Function (NSSF); Network Exposure Function; Network Repository Function (NRF); Policy Control Function (PCF); Unified Data Management (UDM); Application Function (AF); Authentication Server Function (AUSF); an Access and Mobility Management Function (AMF); and Session Management Function (SMF). Figure 1 also shows the various interfaces (N1 , N2 etc.) that may be implemented between the various elements of the system.

[0041] Figure 1 B illustrates an example communication environment in which example embodiments of the present disclosure can be implemented.

[0042] Figure 1 B shows an example communication environment 100 in which example embodiments of the present disclosure can be implemented.

[0043] In the communication environment 100, a plurality of communication devices, comprising user devices 110 and 115 (also referred to herein as a “terminal” or “terminal device”) and a network device 120 (also referred to herein as a “network access node”), can communicate with each other. The network device 120 may serve a coverage area, called a cell 125. The user device 110 may have access to a communication network via the cell 125. In some example embodiments, both the user device 110 and the network device 120 may be configured to implement a beamforming technique and communicate with each other via a plurality of beams.

[0044] Communications in the communication environment 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1 G), the second generation (2G), the third generation (3G), the fourth generation (4G), the fifth generation (5G), the sixth generation (6G), and the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and/or any other technologies currently known or to be developed in the future.

[0045]The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a mobile device, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), a machine-type communications (MTC) device, an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and/or industrial wireless networks, and the like. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user device”, “user equipment” and “UE” may be used interchangeably.

[0046]As used herein, the term “network device” is used interchangeably with “network access node”, and refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0047]As a femto cell is mentioned further below with reference to examples, further information is herein provided. A femto cell refers to a cell (e.g., a region of coverage) provided by a femto. A femto may be considered as being a small form factor, low- power cellular base station that provides a femtocell with a region of coverage corresponding to low-power. A femto is typically designed for use in a home or small business. The use of femtocells allows network coverage in places where the signal to larger cells (e.g., cells having a greater coverage area than femtocells, cell’s having greater power than a femto) might be too weak. Furthermore, the provision of femtocells lower contention on those larger cells by forming a connection from the end user, through an internet connection, to the operator's private network infrastructure located elsewhere. WCDMA, CDMA2000, LTE (4G) and WiMAX have all previously utilized some form of femtos and femtocells, which terms are utilized interchangeably herein. [0048] In some example embodiments, a link from the network device 120 to the user device 110 or 115 is referred to as a DL, while a link from the user device 110 or 115 to the network device 120 is referred to as a UL. Links are also referred to herein as “channels”. In DL, the network device 120 is a Tx device (or a transmitter), and the user device 110 or 1 15 is a Rx device (or a receiver). In UL, the user device 110 or 115 is a Tx device (or a transmitter), and the network device 120 is a Rx device (or a receiver). A link between the user device 110 and another user device (not shown) is referred to as a sidelink (SL). In SL, one of the user devices is a Tx device (or a transmitter), and the other of the user devices is a Rx device (or a receiver).

[0049] Of the above mentioned communication protocols, at least some of these define cells that are configured to only provide services to a limited number of and/or type of terminal.

[0050] For example, 4G defines closed subscriber group (CSG) method for femtos.

[0051]A closed subscriber group (CSG) is a set of users with connectivity access to a femtocell provided by a femto. Each CSG is identified by a corresponding CSG identifier (CSG-ID). A CSG identifier is a unique identifier within the scope of PLMN, which identifies a CSG in the PLMN associated with a CSG cell or group of CSG cells. The CSG thus identifies a set of (e.g., group of subscribers) that are permitted, or otherwise authorised, to access one or more femtocells of a public land mobile network (PLMN) that corresponds to the CSG identifier(s) of the set of user(s). In other words, a set of users and a femtocell of a PLMN that the set of users are permitted, or otherwise authorised, to access are associated with a same CSG identifier. . A CSG identifier is a 27 bitstring. A base station hosting CSG cells is called a HeNB or 4G/LTE femto base station or 4G femto.

[0052] The femtocell maintains a list of CSG identifiers that are allowed to access specific services via the femtocell. This list is labelled as an access control list in 4G. Stated differently, the access control list is a list of CSG identifiers that are authorized to access the network service. A network operator creates and manages the access control list. The access control list is stored in the network's database and is updated by the network operator as needed. The access control list can be configured to allow or deny access to specific network services for each CSG identifier.

[0053] In order to access services via a CSG femtocell, a terminal having a subscription to a specific CSG is configured with the CSG identifier corresponding to that CSG. CSG membership of UE is configured in the user subscription data and on the terminal. Subsequently, when a femtocell is configured in CSG mode, the femtocell transmits those CSG identifiers corresponding to CSGs served by the femtocell (e.g., the femtocell’s access control list). The terminal receives the CSG identifiers that are transmitted (e.g., a list of CSF identifiers that is transmitted), and compares the CSG identifiers that are received to the CSG identifier(s) configured at the terminal. Only those terminals configured with at least one CSG identifier that is included in the femtocell’s access control list are allowed to use the femtocell resources. When a terminal tries to connect to a CSG cell (e.g., when the terminal believes itself to be configured with a CSG identifier corresponding to a CSG identifiers transmitted by the femtocell), the network (e.g., a mobility management entity (MME)) checks whether the terminal is allowed to do so, based on the subscription data for that terminal. Concept of CSG cells and handover between CSG cells in E-UTRAN and between UTRAN and E-UTRAN is described in TS 23.401 clause 5.5, and TS 36.300 clause 10.5.

[0054] As another example, 5G defines closed access group (CAG) method for access nodes of non-public networks (NPNs).

[0055]A Closed Access Group (CAG) is a set of users with connectivity access to a femtocell. Each CAG is identified by a corresponding CAG identifier (CAG-ID). The CAG identifier thus identifies a group of subscribers that are permitted, or otherwise authorised, to access one or more access nodes of a NPN that corresponds to the CAG identifier(s) configured at the NPN. In other words, a set of users and a access node of a NPN that the set of users are permitted, or otherwise authorised, to access are associated with a same CAG identifier. A CAG identifier is a 32 bitstring.

[0056] A cell (e.g., region of coverage) is provided by an NPN (also referred to as an NPN cell herein) maintains a list of CAG identifiers that are allowed to access specific services via the NPN cell. The list of CAG identifiers comprises one or more identifiers of CAGs that are authorized to access the network service. The network operator creates and manages this access control list of CAG identifiers. The access control list of CAG identifiers is stored in the network's database and is updated by the network operator as needed. The access control list of CAG identifiers can be configured to allow or deny access to specific network services for each CAG identifier on the access control list of CAG identifiers.

[0057] In order to access services via an NPN cell of a CAG, a terminal having a subscription to a specific CAG is configured with the CAG identifier corresponding to that CAG. CAG membership of UE (e.g., that the UE has a subscription to a specific CAG) is configured in the user subscription data and on the terminal. Subsequently, when an NPN cell is configured in CAG mode (e.g., a mode in which access to connectivity services provided by the NPN cell is controlled according to membership in a CAG), the NPN cell transmits those CAG identifiers corresponding to CAGs served by the NPN cell configured in CAG mode. The terminal receives the CAG identifiers ((e.g., a list of CAG identifiers), and compares the CAG identifiers that are transmitted by the NPN cell and received by the terminal to the CAG identifier(s) configured at the terminal. Only those terminals configured with at least one CAG identifier that is included in the NPN cell's list of CAG identifiers are allowed to use the NPN cell’s resources. When a terminal tries to connect to a NPN cell of a CAG (e.g., when the terminal believes itself to be configured with a CAG identifier corresponding to a transmitted CAG identifier), the network (e.g., an access and mobility function) checks whether the terminal is allowed to do so, based on the subscription data for that terminal.

[0058] CAG methods were originally introduced in the context of public network integrated non-public networks (PNI-NPNs) for preventing UE(s) that are not allowed to access an NPN via the associated cell(s) from automatically selecting and accessing the associated cell(s) configured in CAG mode. CAG-based access control was introduced in 3GPP Release-16. The existing 5G concept of PNI-NPN and of CAG cells is described in TS 23.501 clause 5.30.3.1 , and TS 38.300 clause 16.7.

[0059] 3GPP Release 19 envisions a use case that introduces 5G Home gNBs (HgNBs). These 5G femtos are expected to be operable in a mode of operation (called “closed access mode” herein) in which only certain subscribers will be allowed to access the HgNB cell provided by the 5G femto. This mode of operation is similar to closed subscriber mode for HeNBs in 4G, described above. HgNBs that provide closed access mode may be considered as a type of 5G femto.

[0060]To enable this closed access mode of operation for a HgNB cell, 5G systems will likely adopt and adapt the closed access group (CAG) concept mentioned above, which was introduced in 5G in 3GPP release 16 for non-public networks (NPN).

[0061]The introduction of such a closed access mode may have an impact on mobility operations, such as offloading and handover, as some terminals will not be allowed to access connectivity services through certain cells. [0062] It has been proposed to address this within the 5G system via the use of CAG identifiers for making mobility decisions.

[0063] Figure 2 illustrates an example of a control apparatus 200 for causing a network device 120 (such as the network device described in Figure 1A and/or Figure 1 B) to perform its operations. The control apparatus may comprise at least one random access memory (RAM) 211 a, at least on read only memory (ROM) 211 b, at least one processor 212, 213 and an input/output interface 214. The at least one processor 212, 213 may be coupled to the RAM 211 a and the ROM 211 b. The at least one processor 212, 213 may be configured to execute an appropriate software code 215. The software code 215 may for example allow to perform one or more steps to perform one or more of the present aspects. The software code 215 may be stored in the ROM 211 b. The control apparatus 200 may be interconnected with another control apparatus 200 controlling another function of the network device. In some embodiments, each function of the network device comprises a control apparatus 200. In some exemplary embodiments, the apparatus 200 may be implemented at the network device 120 or may be the network device 120.

[0064] Figure 3 illustrates an example of a terminal 300, such as the user device 110, 115 illustrated on Figure 1A and/or Figure 1 B. The terminal 300 may be provided by any device capable of sending and receiving radio signals, such as the user device described herein. The terminal 300 may provide, for example, communication of data for carrying communications. The communications may be one or more of voice, electronic mail (email), text message, multimedia, data, machine data and so on.

[0065] The terminal 300 may receive signals over an air or radio interface 307 via appropriate apparatus for receiving and may transmit signals via appropriate apparatus for transmitting radio signals. In Figure 3 transceiver apparatus is designated schematically by block 306. The transceiver apparatus 306 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

[0066] The terminal 300 may be provided with at least one processor 301 , at least one memory ROM 302a, at least one RAM 302b and other possible components 303 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with access systems (such as a network access system provided by the network device described above in relation to Figures 1 and 2) and other communication devices. The at least one processor 301 is coupled to the RAM 302b and the ROM 302a. The at least one processor 301 may be configured to execute an appropriate software code 308. The software code 308 may for example allow to perform one or more of the present aspects. The software code 308 may be stored in the ROM 302a.

[0067] The processor, storage and other relevant control apparatus can be provided on an appropriate circuit board and/or in chipsets. This feature is denoted by reference 304. The device may optionally have a user interface such as key pad 305, touch sensitive screen or pad, combinations thereof or the like. Optionally one or more of a display, a speaker and a microphone may be provided depending on the type of the device.

[0068] In some exemplary embodiments, the terminal 300 may be an apparatus comprising at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause a user device 110, 115 to perform examples or embodiments described in this document.

[0069] It is understood in the following that, where references are made to 5G alone, that this is not limited to only 5G. Instead, these references may comprise 5G and/or beyond 5G. For example, it is understood that references to 5G networks, and/or 5G network entities comprises references to 6G networks, and/or 6G network entities.

[0070] In communication systems that are or will be deployed, it is expected that the coverage area of 4G femtocells will overlap with cells provided by 5G (and/or beyond) access network nodes. This coexistence may lead to problems when considering the interoperability of 5G access network nodes (whether femtos or non-femtos) with 4G femtos. Stated differently, having a mixture of 4G and 5G (and/or beyond) cells in close proximity may impact mobility operations that are performed when a terminal moves from a 5G (and/or beyond) cell to a 4G femtocell.

[0071] For example, there may be deployed a mixture of 5G (and/or 6G) access network nodes and 4G femtos in close proximity to each other, each providing respective cells. The 5G (and/or 6G) access network node may determine that it would be advantageous to perform mobility operations such as offloading and/or handover from a 5G (and/or 6G) cell to a 4G femtocell, and so instruct the terminal to receive connectivity services from that 4G femtocell. The terminal that is part of such a mobility operation may not be a subscriber of the CSG(s) maintained by that 4G cell and so may be unable to receive connectivity services from the 4G cell. This means that an attempt to move connectivity services for the terminal from the 5G (and/or 6G) femtocell to the 4G femtocell is likely to fail, and the terminal will perform even more signalling to access a different cell following this feature. Stated differently, an attempted handover to a terminal that does not have subscriber access to the CSG(s) maintained at the 4G femtocell to which it is attempting to connect can result in wasted signalling and poor service metrics (e.g., a poor quality of service and/or quality of experience).

[0072] Some methods have been proposed for handling such mobility issues. These proposed methods have focused on the use of 5G core entities, such as access control in an access and mobility function (AMF), for assisting with mobility operations. For example, the current work task description agreed in 3GPP specifies both how to provide access control to the UE, and how a 5G Core can provide Access control to a terminal using a CSG identifier.

[0073] The following proposes at least one method for enabling terminal mobility from a 5G system (e.g. from macro 5G cell or from 5G femtocell) to a target 4G femtocell that is implemented by a source 5G network node. The source network node may be comprised in an access network node and/or a core network function. For example, the source network node may be comprised in an access network node (such as a 5G femto) and/or a core network function (such as an access and mobility function).

[0074] In more detail, the following proposes methods for mobility operations that utilise an encoded version of an existing CSG identifier as an identifier in the 5G network. In particular, an existing CSG identifier is modified to generate a dummy CAG identifier by using an encoding scheme that makes the CSG identifier into a suitable form (e.g., length) for use as a CAG identifier. In other words, a dummy CAG identifier (which may be alternatively termed herein as an encoded CAG identifier, a nonce CAG identifier, a CAG sub-identifier) comprises an encoded CSG identifier whose form (e.g., length) has been modified. The 5G network nodes performing access control may also be configured with the dummy CAG identifiers corresponding to the CSG identifiers served by neighbouring 4G femtos. This combination of information (e.g., CAG identifiers for the 5G network and the dummy CAG identifier corresponding to neighbouring 4G femtos) is subsequently used by the 5G system to perform access control based on CAG identifier.

[0075] Such a configuration may have minimal effect on the 4G system, and so be backwards compatible with such 4G systems. [0076]To help illustrate how this may be implemented, Figures 4 to 6 illustrate different example signalling. In these example signalling, the source 5G system node may comprise an access network node (e.g., a 5G base station and/or a 5G femto), and/or a 5G core network node (e.g., an access and mobility function). It is further understood that these references to 5G are not limiting, and that the presently described principles may be applied to 6G and/or beyond.

[0077] In these example signalling, the 5G system (which is acting as a source for a mobility procedure) is configured to reserve all dummy CAG identifiers for use in representing the 4G system. Although this reservation of dummy CAG identifiers means that the remaining number of CAG identifiers that may be used for the 5G intrasystem (e.g. NPN or HgNBs) is reduced from 2³² to (2³² - 2²⁷), this reservation only results in an approximately 3 percent reduction of CAG identifiers available for intrasystem operation, which is considered as minor and acceptable for the 5G intrasystem operation.

[0078] Figure 4 illustrates a first example method. In the example of Figure 4, a terminal (e.g., a UE) constructs a dummy CAG identifier, which is used for verification in a source 5G system node. The source 5G system node has previously been provisioned with the access rights associated with all CAG identifiers, which includes access rights associated with the dummy CAG identifiers related to 4G HeNB cells among others. The dummy CAG identifiers used for 4G femtocells may be identified using the encoding method used for converting CSG identifiers into dummy CAG identifiers. A simple way of performing such an encoding is to simply denote the address space of CAG identifiers comprising five zeroes at the front as being dummy CAG identifiers and to map CSG identifiers to CAG identifiers within this address space, although it is understood that other encoding methods may be used. The source 5G system node uses the received dummy CAG identifier to check access control for the terminal, based on a similar method as intra-system CAG identifier access control (e.g. for NPN or mobility to 5G femtos).

[0079] Figure 4 illustrates signalling and operations of a procedure involving a terminal 401 , a source 5G system node 402, a target 4G CSG cell 403, and an operations and management function (O&M) 404.

[0080] During 4001 , the terminal (e.g., UE) receives a broadcast of the CSG identifier from the target cell 403. This signalling may be comprised in a system information block 1 (SIB1 ) message. [0081] SIB1 is a type of message used in 4G that provides information to receiving terminal that enable the receiving terminal to determine whether the terminal can access the cell transmitting the SIB1 . Some fields that may be comprised in S I B 1 for this purpose may include, for example, a “cellAccessRelatedlnformation” field, a “cellSelectionlnfo” field, a “frequencyBandlndicator” field, etc. The “cellAccessRelatedlnformation” field may include additional fields such as, for example, a “PLMN-ldentity List” field, a Tracking Area Code (TAC) field (which is common for all PLMNs listed), a “Cellidentity” (Cell-ID) field, a “CSG Indication” field, a “CSG identifier” field, etc. Six different PLMN IDs (PLMN-ID 1 through PLMN-ID 6) may be provided through the “PLMN-ID List” field, and each PLMN-ID may include a field to convey three (3) decimal digits of Mobile Country Code (MCC) and 2 or 3 decimal digits of Mobile Network Code (MNC), wherein each decimal digit (from 0 through 9) may be represented by up to four binary bits.

[0082] During 4002, the O&M function 404 signals the source 5G system node 402. The O&M function may signal the source 5G system node by transmitting configuration information for configuring the source 5G system node with access rights corresponding to “dummy” CAG identifier values in the same database as access rights of normal CAG identifier values. Stated differently, the source 5G system node receives information for reserving those CAG identifier values corresponding to how the CSG identifiers are encoded into CAG identifiers in the system and stores the information. 4002 may be performed before or after 4001 .

[0083] During 4003, the terminal 401 constructs a dummy CAG identifier. This may be performed using any encoding method that transforms the received CSG identifier length into a CAG identifier length. For example, the dummy CAG identifier (i.e., encoded CSG identifier) may comprise five dummy bits (e.g., five zeros) followed by 27 bits of the CSG identifier bitstring that is received. Accordingly, the CSG identifier that is received may be encoded to generate an encoded CSG identifier. The encoding may add five dummy bits to the CSG identifier that is received. The encoding may add five leading zero bits to the CSG identifier that is received. The encoded CSG identifier has a same length as a CAG identifier.

[0084] During 4004, the terminal 401 signals the source 5G system node 402. This signalling may comprise a transmission of a 5G radio resource control (RRC) measurement report. This RRC measurement report may comprise values for cell- based measurements that were performed on the target cell 403. This signalling may comprise a dummy CAG identifier generated during 4003.

[0085] During 4005, the source 5G system node checks access rights for the dummy CAG identifier received during 4004 using CAG identifier-based access control (e.g., as if mobility towards 5G HgNBs was involved (using same algorithm and database). [0086] This check may be performed using the access rights configured during 4002. For example, the access rights configured during 4002 may provide an indication of which subscribers and/or terminal are allowed to access connectivity services through which CAG identifiers. The source 5G system node may, during 4005, use the encoded CSG to lookup any access rights corresponding to this previously configured access right information to determine whether the terminal 401 is allowed to access connectivity services through the target 4G cell 403.

[0087] When the source 5G system node determines that the terminal 401 is allowed to access connectivity services through the target 4G cell 403, the source 5G system may determine whether to perform a mobility operation for causing the terminal 401 to access connectivity services through the target 4G node. The determination of this mobility operation may consider additional information, such as, for example, metrics measuring current radio conditions corresponding the target 4G cell, network node capacity across a plurality of candidate target cells, etc.

[0088] When the source 5G system node determines that the terminal 401 is not allowed to access connectivity services through the target 4G cell 403, the source 5G system may not consider the target 4G cell 403 as being a candidate network node for performing a mobility operation for causing the terminal 401 to access connectivity services.

[0089] Stated differently, during 4005, the source 5G system node uses the received dummy CAG identifier and configured CAG access rights of 4002 as part of at least one criteria for identifying whether target 4G cell 403 may be a candidate target cell for a mobility operation. A mobility operation may be performed based on this identifying.

[0090] Considering the case when the encoding in this example of Figure 4 comprises adding 5 zero bits to the front of the CSG identifier to form a dummy CAG identifier, whenever a terminal measures the CSG identifier of the candidate target 4G HeNB cell, the terminal constructs a dummy CAG identifier out of it by including the 27 bits of the CSG identifier that is received from the target cell into the rightmost bits of a dummy CAG identifier 32 bitstring and adding leading dummy bits (e.g., zeros) into the five leftmost bits of the dummy CAG identifier 32 bitstring.

[0091]The terminal causes this dummy CAG identifier to be included in the 5G RRC measurement report message and sends the 5G RRC measurement report message to the source 5G system node. The source 5G system node uses this dummy CAG identifier similar to an intra-mobility procedure or NPN access rights checking logics, despite the fact that it relates to a 4G system entity.

[0092] Figure 5 illustrates another example. In this example of Figure 5, whenever a terminal measures the CSG identifier of the candidate target 4G HeNB cell, the terminal includes this CSG identifier into the 5G RRC Measurement report message sent to source NG-RAN node. The source 5G system node (e.g., source NG-RAN node or source AMF) takes the 27 bits of the received CSG identifier and constructs a dummy CAG identifier by including the 27 bits of the CSG identifier and five dummy bits. For example, the 27 bits of the CSG identifier may be placed to form the rightmost bits of the dummy CAG identifier 32 bitstring, and leading zeros may be placed into the five leftmost bits of the dummy CAG identifier 32 bitstring. In this example of Figure 5, the source 5G system node has been provisioned with the access rights associated with all CAG identifiers, which may include access rights associated with dummy CAG identifiers related to 4G HeNB cells. The source 5G system node subsequently uses the dummy CAG identifier that it constructs and handles the dummy CAG identifier to check access control in the same way as dealing with classical intra-system CAG identifier access control (e.g. for NPN or mobility to target 5G femtos).

[0093] Figure 5 illustrates signalling and operations of a procedure involving a terminal 501 , a source 5G system node 502, a target 4G CSG cell 503, and an operations and management function (O&M) 504.

[0094] During 5001 , the UE receives an SIB1 broadcast of the CSG identifier from the target cell 503.

[0095] During 5002, the O&M function 504 signals the source 5G system node 502. The O&M function may signal the source 5G system node by transmitting configuration information for configuring the source 5G system node with access rights corresponding to “dummy” CAG identifier values in the same database as access rights of normal CAG identifier values. Stated differently, the source 5G system node receives information for reserving those CAG identifier values corresponding to how the CSG identifiers are encoded into CAG identifiers in the system and stores the information. 5002 may be performed before or after 5001 . 5002 may be the same operation as 4002.

[0096] During 5003, the terminal 501 signals the source 5G system node 502. This signalling may comprise transmission of a 5G radio resource control (RRC) measurement report. This RRC measurement report may comprise values for cellbased measurements that were performed on the target cell 503. This signalling may comprise a CSG identifier (e.g., the CSG identifier received during 5001 ).

[0097] During 5004, the source 5G system node 502 constructs a dummy CAG identifier. This may be performed using any encoding method that transforms the received CSG identifier length into a CAG identifier length. For example, the dummy CAG identifier (i.e. , encoded CSG identifier) may comprise five dummy bits (e.g., five zeros) followed by 27 bits of the CSG identifier bitstring that is received. Accordingly, the CSG identifier that is received may be encoded to generate an encoded CSG identifier. The encoding may add five dummy bits to the CSG identifier that is received. The encoding may add five leading zero bits to the CSG identifier that is received. The encoded CSG identifier has a same length as a CAG identifier

[0098] During 5005, the source 5G system node checks access rights using the encoded CSG identifier and the CAG identifier-based access control (e.g., as if mobility towards 5G HgNBs was involved (using same algorithm and database).

[0099] This check may be performed using the access rights configured during 5002. For example, the access rights configured during 5002 may provide an indication of which subscribers and/or terminal are allowed to access connectivity services through which CAG identifiers. The source 5G system node may, during 5005, use the encoded CSG to lookup any access rights corresponding to this previously configured access right information to determine whether the terminal 501 is allowed to access connectivity services through the target 4G cell 503.

[0100] When the source 5G system node determines that the terminal 501 is allowed to access connectivity services through the target 4G cell 503, the source 5G system may determine whether to perform a mobility operation for causing the terminal 501 to access connectivity services through the target 4G node. The determination of this mobility operation may consider additional information, such as, for example, metrics measuring current radio conditions corresponding the target 4G cell, network node capacity across a plurality of candidate target cells, etc. [0101]When the source 5G system node determines that the terminal 501 is not allowed to access connectivity services through the target 4G cell 503, the source 5G system may not consider the target 4G cell 503 as being a candidate network node for performing a mobility operation for causing the terminal 501 to access connectivity. [0102] Stated differently, during 5005, the source 5G system node uses the encoded CSG identifier and configured CAG access rights of 5002 as part of at least one criteria for identifying whether target 4G cell 503 may be a candidate target cell for a mobility operation. A mobility operation may be performed based on this identifying.

[0103] A third example is illustrated with respect to Figure 6. In this third example, the UE determines whether the signalling of Figure 4 or of Figure 5 is to be performed, based on an indication comprised in SIB1 from the 4G cell broadcast. The indication indicates whether the first network node is operating in a closed subscriber group, CSG, mode, or an open mode. The indication may be referred to as CSG bit.

[0104]The UE checks if the CSG bit is broadcast in the target HeNB cell. If the CSG bit is not set in the broadcast, it inhibits the signalling of Figure 4 and/or Figure 5 from being performed by the terminal (e.g., it inhibits the terminal from constructing and reporting dummy CAG identifier and/or it inhibits the terminal from reporting the target CSG identifier to source 5G system node).

[0105] Figure 6 illustrates signalling and operations of a procedure involving a terminal 601 , and a target 4G cell 602 (also referred to herein as a target cell).

[0106] During 6001 , the terminal receives an SIB1 broadcast of a CSG identifier from the target cell 602. This signalling broadcast also comprises the indication that indicates whether the first network node is operating in a closed subscriber group, CSG, mode, or an open mode. For example, a CSG bit may be comprised in the SIB1 . [0107]This signalling of 6001 may be comprised in the signalling of 4001 and/or 5001 when the target cell 602 comprises a CSG target cell. It is understood that the target cell 602 may be a CSG cell (e.g., a cell currently operating in a CSG mode) or a non- CSG cell (e.g., a cell currently operating in an open mode). A cell operating in open mode or a non-CSG cell does not limit access to CSG subscribers. A cell operating in CSG mode or a CSG cell does limit access to CSG subscribers.

[0108] During 6002, the terminal determines whether the operation and signalling of 4003 and 4004 or the signalling of 5003 is to be performed. For example, when the CSG bit in SIB1 is not set, the terminal performs mobility-related operations (such as cell measurement reporting) without causing the operation and signalling 4003 and 4004 or the signalling of 5003 to be performed. When the CSG bit in SIB1 is set, the terminal causes the operation and signalling of 4003 and 4004 or the signalling of 5003 to be performed. Which of the operation and signalling of 4003 and 4004 or the signalling of 5003 is performed when the CSG bit is set may have been previously configured at the terminal or may be indicated in the SIB 1 broadcast.

[0109]Stated differently, based on the signalling of 6001 , the terminal provides, to a source 5G system node, target cell-based measurement reporting that comprises a version of a CSG identifier for that target cell 602 (e.g., proceeds to 4003 and 4004 or proceeds to 5003 (based on the terminal’s configuration)), or the terminal provides, to the source 5G system, target cell-based measurement reporting that does not comprise a version of a CSG identifier for that target cell 602.

[0110] Although the above example methods have discussed mobility operations of a terminal from a 5G system to a 4G system, it is understood that the mobility operations may instead be performed in the opposite direction (e.g., from a 4G system to a 5G system). An example illustrating how this may be performed is described below in relation to Figure 7.

[0111] In this example procedure of Figure 7, the 4G system (which is acting as a source for a mobility procedure) is configured to reserve a set of CSG identifiers for use in representing CAG of the 5G system. The number of CSG identifiers in the reserved set may be preconfigured. The number of CSG identifiers in the reserved set may be updated (e.g., dynamically or semi-statically). The number of CSG identifiers in the reserved set may be preconfigured by an operations and management function. [0112] In an example, a predetermined set of CSG identifiers (less than all CSG identifiers) is reserved for neighbouring 5G femtocell. The number of the predetermined set of CSG identifiers may be a predetermined number (n) of CSG identifiers per neighbouring 5G femtocell (e.g., so when there are g femtocells neighbouring the 4G source node, the number of reserved addresses is gn. The predetermined number n may be based on a number defined in a communication standard and/or by a network operator and/or based on learned information of an average number of CAGs per femtocell. The reserved CSG identifiers may be updatable with the 5G CAG access rights (either dynamically and/or semi-statically) by the O&M function.

[0113] The terminal may be aware of which CSG identifiers are reserved in the 4G system. This awareness may have been configured in the terminal (e.g., via a 5G system node). The terminal may use this knowledge of which CSG identifiers have been reserved in order to encode a CAG identifier to a single one of the reserved set of CSG identifiers. The CAG identifier to CSG identifier encoding scheme may be known at a 5G system node and/or the O&M function, and/or the terminal may inform a 5G system node of which CAG identifier maps to which CSG identifier in order for the O&M to configure the access rights for that encoded CAG identifier (i.e. , dummy CSG value) at the 4G node.

[0114] In the example of Figure 7, a terminal (e.g., a UE) constructs a dummy CSG identifier by encoding a CAG identifier, which is used for verification in a source 4G system node. The source 4G system node has previously been provisioned with the access rights associated with CSG identifiers, which includes access rights associated with the such encoded CAG identifiers related to 5G HgNB cells, among others. The encoded CAG identifiers corresponding to 5G femtocells may be identified using the encoding method used for converting CAG identifiers into dummy CSG identifiers. A simple way of performing such an encoding is to simply identify a range of addresses (which may be referred to as an address space) of CSG identifiers, and to map CSG identifiers to CAG identifiers within this address space. It is understood that other encoding methods may be used. In another example, the encoded CAG identifier (i.e., the dummy CSG identifier) is formed by removing five bits of the 32 bitstring of the received CAG identifier. The removed five bits may correspond to the leftmost five bits of the 32 bitstring of the received CAG identifier.

[0115]The source 4G system node uses the received dummy CSG identifier (i.e., the encoded CAG identifier) to check access control for the terminal, based on a similar method as intra-system CSG identifier access control (e.g. for mobility to 4G femtos). [0116] Figure 7 illustrates signalling and operations of a procedure involving a terminal 701 , a source 4G system node 702, a target 5G CAG cell 703, and an operations and management function (O&M) 704. The target 5G CAG cell may comprise an access network node (e.g., a 5G femto). The source 4G system node may comprise an access network node (e.g., a 4G femto or 4G base station) or a core network node (such as a mobility management entity).

[0117] During 7001 , the terminal (e.g., UE) receives a broadcast of the CAG identifier from the target cell 703.

[0118] During 7002, the O&M function 704 signals the source 4G system node 702. The O&M function may signal the source 4G system node with access rights corresponding to encoded CAG identifier values in the same database as access rights of normal CSG identifier values. Stated differently, the source 4G system node receives information for reserving those CSG identifier values corresponding to how the CAG identifiers are encoded into CSG identifiers in the system and stores the information. 7002 may be performed before or after 7001 .

[0119] During 7003, the terminal 701 constructs a dummy CSG identifier. This may be performed using any encoding method that transforms the received CAG identifier length into a CSG identifier length. For example, the dummy CSG identifier (i.e., encoded CAG identifier) may be formed by mapping the received CAG identifier to a reserved CSG identifier of a set (e.g., one or more than one) of reserved CSG identifiers. In another example, the encoded CAG identifier (i.e., the dummy CSG identifier) is formed by removing five bits of the 32 bitstring of the received CAG identifier. The removed five bits may correspond to the leftmost five bits of the 32 bitstring of the received CAG identifier.

[0120] During 7004, the terminal 701 signals the dummy CSG identifier (i.e., the encoded CAG identifier) to the source 4G system node 702. This signalling may comprise a 4G radio resource control (RRC) measurement report. This RRC measurement report may comprise values for cell-based measurements that were performed on the target cell 703.

[0121] During 7005, the source 4G system node checks access rights using the received dummy CSG value and the CSG identifier-based access control (e.g., as if mobility towards 4G HeNBs was involved (using same algorithm and database).

[0122]This check may be performed using the access rights configured during 7002. For example, the access rights configured during 7002 may provide an indication of which subscribers and/or terminal are allowed to access connectivity services through which CSG identifiers. The source 4G system node may, during 7005, use the dummy CSG identifier (e.g., the encoded CAG identifier) to lookup any access rights corresponding to this previously configured access right information to determine whether the terminal 701 is allowed to access connectivity services through the target 5G cell 703.

[0123]When the source 4G system node determines that the terminal 701 is allowed to access connectivity services through the target 5G cell 703, the source 4G system may determine whether to perform a mobility operation for causing the terminal 701 to access connectivity services through the target 5G node. The determination of this mobility operation may consider additional information, such as, for example, metrics measuring current radio conditions corresponding the target 5G cell, network node capacity across a plurality of candidate target cells, etc.

[0124]When the source 4G system node determines that the terminal 701 is not allowed to access connectivity services through the target 5G cell 703, the source 4G system may not consider the target 5G cell 703 as being a candidate network node for performing a mobility operation for causing the terminal 701 to access connectivity services.

[0125] Stated differently, during 7005, the source 4G system node uses the received dummy CSG identifier and configured CSG access rights of 7002 as part of at least one criteria for identifying whether target 5G cell 703 may be a candidate target cell for a mobility operation. A mobility operation may be performed based on this identifying.

[0126] Further, analogous signalling to that performed for Figure 6 may be performed, where the signalling of 6001 instead comprises a CAG bit, the 4G target cell is instead a 5G target cell, and the terminal determines whether to perform 7003 onwards based on the value of the received CAG bit.

[0127]These 4G to 5G mobility methods may be useful for enabling backwards compatibility with existing 4G communication standards and networks, as the source 4G network may perform access control towards target 5G femto CAG cells with same algorithm and database than handover towards 4G femto CSG cell.

[0128] Features of the above examples are now illustrated with respect to Figures 8 to 17. It is therefore understood that the above description may provide further understanding of the following described features.

[0129] Figures 8 to 10 illustrate operations that may be performed in respect of the example of Figure 4 (although it is understood that the operations discussed in relation to 901 to 903, and the operations discussed in relation to Figure 10 may also be performed in respect of the example of Figure 5).

[0130] Figure 8 illustrates operations that may be performed by a user equipment (e.g., a terminal as described above).

[0131] During 801 , the user equipment receives a closed subscriber group, CSG, identifier from a first network node of a first communication network while the user equipment is being served by a second network node of a second communication network. Stated differently, the user equipment may receive a CSG identifier from a first network node of a first communication network while the user equipment is receiving connectivity services from a second network node of a second communication network.

[0132]The first communication network and the second communication network are different communication networks. As an example, the first communication network may comprise a 4G network. As an example, the second communication network may comprise a 5G network. As an example, the second communication network may comprise a 6G network.

[0133] As an example, the first network node may comprise a 4G femto. As an example, the second network node may comprise a 5G system node. For example, the second network node may comprise a 5G access network node (such as a 5G base station and/or 5G femto, and/or as any other type of access network node described above). The second network node may comprise a 5G core network node, such as an access and mobility function.

[0134]The receiving may comprise receiving a broadcast message comprising the CSG identifier. For example, the receiving may comprise receiving an S IB1 message comprising the CSG identifier.

[0 35] During 802, the user equipment encodes the CSG identifier that is received to generate an encoded CSG identifier. This encoded CSG identifier may correspond to the above-mentioned dummy CAG identifier and/or encoded CSG identifier.

[0136] The encoding may be performed in any of a plurality of different ways.

[0137] For example, the encoding may be performed by adding dummy bits to the CSG identifier that is received.

[0138] The encoding the encoded CSG identifier may comprise transforming the CSG identifier from a CSG format into a closed access group, CAG, format.

[0139] The number of dummy bits added may correspond to the difference in the number of bits between the length of the received CSG identifier and the length of a CAG identifier used by the second communication network. This difference in length is currently 5 bits. Therefore, in current examples, the encoding may be performed by adding five dummy bits to the CSG identifier that is received. The CSG identifier that is received may comprise 27 bits, and the encoded CSG identifier may comprise 32 bits.

[0140]Although the five dummy bits may take any pre-configured value and/or location, in an example, these five dummy bits are zero bits at the leftmost side of the encoded CSG identifier. Stated differently, the encoding may comprise adding five leading zero bits to the CSG identifier that is received.

[0141]The encoded CSG identifier may have a same length as a CAG identifier.

[0142] During 803, the user equipment transmits the encoded CSG identifier to the second network node.

[0143]The transmitting may comprise transmitting a measurement report comprising the encoded CSG identifier. The measurement report may comprise an RRC measurement report. The measurement report may comprise at least one metric that represents a current state of at least one network condition (e.g., a radio access network condition) of the first network node. For example, the measurement report may comprise at least one value representing a signal to interference and noise ratio corresponding to the first network node.

[0144] Figure 9 illustrates operations that may be performed by an apparatus for a second network node of a second communication network. The second network node may correspond to the second network node mentioned above in relation to Figure 8. The second communication network may correspond to the second communication network mentioned above in relation to Figure 8.

[0145] During 901 , the apparatus configures the apparatus with a reserved set of closed access group, CAG, identifiers, wherein the reserved set of CAG identifiers are reserved for identifying first network nodes of a first communication network.

[0146] The set may comprise a single CAG identifier. The set may comprise a plurality of CAG identifiers.

[0147]The first communication network and the second communication network are different communication networks. As an example, the first communication network may comprise a 4G network. As an example, the second communication network may comprise a 5G network. As an example, the second communication network may comprise a 6G network.

[0148]As an example, the first network node may comprise a 4G femto. As an example, the second network node may comprise a 5G system node. For example, the second network node may comprise a 5G access network node (such as a 5G base station and/or 5G femto, and/or as any other type of access network node described above). The second network node may comprise a 5G core network node, such as an access and mobility function. [0149] The apparatus may receive, from a user equipment, a CAG identifier, determine whether the CAG identifier that is received corresponds to a CAG identifier of the reserved set of CAG identifiers, and decide to perform a mobility procedure (e.g., a mobility operation such as handover and/or offloading) for the user terminal towards a first network node of the first network nodes of the first communication network based on the determination.

[0150] Stated differently, the apparatus may use the received CAG identifier to determine whether the user equipment is restricted from receiving connectivity access from the first cell and use that determination (with other criteria being evaluated) to cause the user equipment to receive connectivity services from another network node than the second network node. For example, when the received CAG identifier indicates that the user equipment is not allowed to received connectivity services from the first network node corresponding to the received CAG identifier, the user equipment is not instructed to perform a mobility operation in respect of the first network node. Conversely, when the received CAG identifier indicates that the user equipment is allowed to received connectivity services from the first network node corresponding to the received CAG identifier, the apparatus proceeds with evaluating other criteria (such as any metrics comprised in a measurement report received from the user equipment) to determine whether to instruct or request the user equipment to perform a mobility operation in respect of the first network node.

[0151]The receiving the CAG identifier may comprise receiving a measurement report comprising the CAG identifier.

[0152] The configuring may comprise receiving an indication of one or more CAG identifiers of the reserved set of CAG identifiers and respective access rights for the one or more CAG identifiers of the reserved set of CAG identifiers from an operations and management function.

[0153] Figure 10 illustrates operations that may be performed by an operations and management function. The operations and management function may correspond to the operations and management function described above in relation to Figure 9.

[0154] During 1001 , the apparatus provides, to a second network node of a second communication network, a configuration indicating a reserved set of closed access group, CAG, identifiers corresponding to access rights of a first network node of a first communication network. [0155]The first communication network and the second communication network are different communication networks. As an example, the first communication network may comprise a 4G network. As an example, the second communication network may comprise a 5G network. As an example, the second communication network may comprise a 6G network.

[0156] As an example, the first network node may comprise a 4G femto. As an example, the second network node may comprise a 5G system node. For example, the second network node may comprise a 5G access network node (such as a 5G base station and/or 5G femto, and/or as any other type of access network node described above). The second network node may comprise a 5G core network node, such as an access and mobility function.

[0157] Figures 11 and 12 illustrate operations that may be performed by at least some of the apparatus described above in relation to Figure 5.

[0158] Figure 11 illustrates operations that may be performed by a user equipment. The user equipment may comprise the terminal of Figure 5.

[0159] During 1101 , the apparatus receives, a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network.

[0160] The first communication network and the second communication network are different communication networks. As an example, the first communication network may comprise a 4G network. As an example, the second communication network may comprise a 5G network. As an example, the second communication network may comprise a 6G network.

[0161] As an example, the first network node may comprise a 4G femto. As an example, the second network node may comprise a 5G system node. For example, the second network node may comprise a 5G access network node (such as a 5G base station and/or 5G femto, and/or as any other type of access network node described above). The second network node may comprise a 5G core network node, such as an access and mobility function.

[0162]The receiving may comprise receiving a broadcast message comprising the CSG identifier. For example, the receiving may comprise receiving an SIB1 message comprising the CSG identifier.

[0163] During 1102, the user equipment transmits the CSG identifier that is received to the second network node. [0164]The transmitting may comprise transmitting a measurement report comprising the CSG identifier that is received during 1101. The measurement report may comprise an RRC measurement report. The measurement report may comprise at least one metric that represents a current state of at least one network condition (e.g., a radio access network condition) of the first network node. For example, the measurement report may comprise at least one value representing a signal to interference and noise ratio corresponding to the first network node.

[0165] Figure 12 illustrates operations that may be performed by a second apparatus for a second network node of a second communication network. This second network node may correspond to the second network node of Figure 11 .

[0166] During 1201 , the second apparatus receives, from a user equipment, a closed subscriber group, CSG, identifier. The user equipment may correspond to the user equipment of Figure 11 .

[0167] The receiving the CSG identifier may comprise receiving a measurement report comprising the CSG identifier. The measurement report may comprise an RRC measurement report. The measurement report may comprise at least one metric that represents a current state of at least one network condition (e.g., a radio access network condition) of the first network node. For example, the measurement report may comprise at least one value representing a signal to interference and noise ratio corresponding to the first network node.

[0168] During 1202, the second apparatus encodes the CSG identifier that is received to generate an encoded closed access group, CAG, identifier.

[0169]This encoded CAG identifier may correspond to the above-mentioned dummy CAG identifier and/or encoded CSG identifier.

[0170] The encoding may be performed in any of a plurality of different ways.

[0171] For example, the encoding may be performed by adding dummy bits to the CSG identifier that is received.

[0172] The encoding the encoded CSG identifier may comprise transforming the CSG identifier from a CSG format into a closed access group, CAG, format.

[0173] The number of dummy bits added may correspond to the difference in the number of bits between the length of the received CSG identifier and the length of a CAG identifier used by the second communication network. This difference in length is currently 5 bits. Therefore, in current examples, the encoding may be performed by adding five dummy bits to the CSG identifier that is received. The CSG identifier that is received may comprise 27 bits, and the encoded CAG identifier may comprise 32 bits.

[0174] Although the five dummy bits may take any pre-configured value and/or location, in an example, these five dummy bits are zero bits at the leftmost side of the encoded (e.g., dummy) CAG identifier. Stated differently, the encoding may comprise adding five leading zero bits to the CSG identifier that is received.

[0175] The encoded CAG identifier may have a same length as a CAG identifier.

[0176] During 1203, the second apparatus uses the encoded CAG identifier to determine whether to perform a mobility procedure for the terminal towards a first network node of a first communication network.

[0177]The first communication network and the second communication network are different communication networks. As an example, the first communication network may comprise a 4G network. As an example, the second communication network may comprise a 5G network. As an example, the second communication network may comprise a 6G network.

[0178] As an example, the first network node may comprise a 4G femto. As an example, the second network node may comprise a 5G system node. For example, the second network node may comprise a 5G access network node (such as a 5G base station and/or 5G femto, and/or as any other type of access network node described above). The second network node may comprise a 5G core network node, such as an access and mobility function.

[0179] The second apparatus may configure itself with a set of encoded closed access group, CAG, identifiers, wherein the set of encoded CAG identifiers are reserved for first network nodes of the first communication network.

[0180]The configuring may comprise receiving an indication of one or more encoded CAG identifiers of the set of encoded CAG identifiers and respective access rights for the one or more encoded CAG identifiers of the set of encoded CAG identifiers from an operations and management function. This may be as described in relation to 901 . [0181] Figure 13 illustrates operations that may be performed in relation to the apparatus of Figure 6. It is understood that these operations may be performed by the correspondingly named apparatus of Figures 8 to 12.

[0182] Figure 13 illustrates operations that may be performed by a user equipment. The user equipment of Figure 13 may correspond to the user equipment of Figure 8 and/or Figure 11 . [0183] During 1301 , the user equipment receives, from a first network node of a first communication network while being served by a second network node of a second communication network, an indication indicating whether the first network node is operating in a closed subscriber group, CSG, mode, or an open mode.

[0184]The first communication network and the second communication network are different communication networks. As an example, the first communication network may comprise a 4G network. As an example, the second communication network may comprise a 5G network. As an example, the second communication network may comprise a 6G network.

[0185] As an example, the first network node may comprise a 4G femto. As an example, the second network node may comprise a 5G system node. For example, the second network node may comprise a 5G access network node (such as a 5G base station and/or 5G femto, and/or as any other type of access network node described above). The second network node may comprise a 5G core network node, such as an access and mobility function.

[0186] During 1302, the user equipment determines whether to transmit a version of a CSG identifier that is received to the second network node when the indication indicates that the first network node is operating in a CSG mode.

[0187] The version may comprise the CSG identifier that is received when the user equipment of Figure 13 corresponds to the user equipment of Figure 11 .

[0188] The version may comprise a modified version of the CSG identifier that is received when the user equipment of Figure 13 corresponds to the user equipment of Figure 8.

[0189] In this latter case, the user equipment may encode the CSG identifier that is received to generate an encoded CSG identifier. This encoded CSG identifier may correspond to the above-mentioned dummy CAG identifier and/or encoded CSG identifier.

[0190] The encoding may be performed in any of a plurality of different ways.

[0191] For example, the encoding may be performed by adding dummy bits to the CSG identifier that is received.

[0192] The encoding the encoded CSG identifier may comprise transforming the CSG identifier from a CSG format into a closed access group, CAG, format.

[0193] The number of dummy bits added may correspond to the difference in the number of bits between the length of the received CSG identifier and the length of a CAG identifier used by the second communication network. This difference in length is currently 5 bits. Therefore, in current examples, the encoding may be performed by adding five dummy bits to the CSG identifier that is received. The CSG identifier that is received may comprise 27 bits, and the encoded CSG identifier may comprise 32 bits.

[0194] Although the five dummy bits may take any pre-configured value and/or location, in an example, these five dummy bits are zero bits at the leftmost side of the encoded CSG identifier. Stated differently, the encoding may comprise adding five leading zero bits to the CSG identifier that is received.

[0195] The encoded CSG identifier may have a same length as a CAG identifier.

[0196]The user equipment of Figure 13 may transmit a measurement report comprising the version. The measurement report may comprise an RRC measurement report. The measurement report may comprise at least one metric that represents a current state of at least one network condition (e.g., a radio access network condition) of the first network node. For example, the measurement report may comprise at least one value representing a signal to interference and noise ratio corresponding to the first network node.

[0197]The user equipment of Figure 13 may further receive an SIB1 message comprising the indication.

[0198] Figures 14 to 17 illustrate operations that may be performed by apparatus described above in relation to Figure 7.

[0199] Figure 14 illustrates operations that may be performed by a user equipment (e.g., the terminal of Figure 7).

[0200] During 1401 , the user equipment receives, a closed access group, CAG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network.

[0201]The first communication network and the second communication network are different communication networks. As an example, the second communication network may comprise a 4G network. As an example, the first communication network may comprise a 5G network. As an example, the first communication network may comprise a 6G network.

[0202]As an example, the first network node may comprise a 5G femto. As an example, the second network node may comprise a 4G system node. For example, the second network node may comprise a 4G access network node (such as a 4G base station and/or 4G femto, and/or as any other type of access network node described above). The second network node may comprise a 4G core network node, such as mobility management entity.

[0203]The receiving may comprise receiving an SIB1 message comprising the CAG identifier.

[0204] During 1402, the user equipment encodes the CAG identifier that is received to generate an encoded CAG identifier.

[0205] The encoding the CAG identifier may comprise transforming the CAG identifier from a CAG format into a closed subscriber group, CSG, format. The encoded CAG identifier may have a same length as a closed subscriber group, CSG, identifier.

[0206] The CAG identifier that is received may comprise 32 bits, and the encoded CAG identifier may comprise 27 bits.

[0207]The encoding may comprise removing five dummy bits from the CAG identifier that is received. The encoding may comprise removing five leading zero bits from the CAG identifier that is received.

[0208] During 1403, the user equipment transmits the encoded CAG identifier to the second network node.

[0209] The transmitting the encoded CAG identifier may comprise transmitting a measurement report comprising the encoded CAG identifier. The measurement report may comprise an RRC measurement report. The measurement report may comprise at least one metric that represents a current state of at least one network condition (e.g., a radio access network condition) of the first network node. For example, the measurement report may comprise at least one value representing a signal to interference and noise ratio corresponding to the first network node.

[0210]The user equipment may transmit the encoded CAG identifier to the second network node.

[0211] Figure 15 illustrates operations that may be performed by an apparatus for a second network node of a second communication network. The second network node may comprise the second network node of Figure 14.

[0212] During 1501 , the apparatus configures the second apparatus with a reserved set of closed subscriber group, CSG, identifiers, wherein the reserved set of CSG identifiers are reserved for identifying first network nodes of a first communication network. [0213]The first communication network and the second communication network are different communication networks. As an example, the second communication network may comprise a 4G network. As an example, the first communication network may comprise a 5G network. As an example, the first communication network may comprise a 6G network.

[0214]As an example, the first network node may comprise a 5G femto. As an example, the second network node may comprise a 4G system node. For example, the second network node may comprise a 4G access network node (such as a 4G base station and/or 4G femto, and/or as any other type of access network node described above). The second network node may comprise a 4G core network node, such as mobility management entity.

[0215] The apparatus of Figure 15 may receive, from a user equipment, a CSG identifier, determining whether the CSG identifier that is received corresponds to a CSG identifier of the reserved set of CSG identifiers, and decide to perform a mobility procedure for the user terminal towards a first network node of the first network nodes of the first communication network based on the determination. The receiving the CSG identifier may comprise receiving a measurement report comprising the CSG identifier. The measurement report may comprise an RRC measurement report. The measurement report may comprise at least one metric that represents a current state of at least one network condition (e.g., a radio access network condition) of the first network node. For example, the measurement report may comprise at least one value representing a signal to interference and noise ratio corresponding to the first network node.

[0216] The configuring may comprise receiving an indication of one or more CSG identifiers of the reserved set of CSG identifiers and respective access rights for the one or more CSG identifiers of the reserved set of CSG identifiers from an operations and management function.

[0217] Figure 16 illustrates operations that may be performed by an apparatus for an operations and management function.

[0218] During 1601 , the apparatus provides, to a second network node of a second communication network, a configuration indicating a set of closed subscriber group, CSG, identifiers corresponding to access rights of a first network node of a first communication network. The second network node may be as described above in relation to Figure 15. [0219]The first communication network and the second communication network are different communication networks. As an example, the second communication network may comprise a 4G network. As an example, the first communication network may comprise a 5G network. As an example, the first communication network may comprise a 6G network.

[0220]As an example, the first network node may comprise a 5G femto. As an example, the second network node may comprise a 4G system node. For example, the second network node may comprise a 4G access network node (such as a 4G base station and/or 4G femto, and/or as any other type of access network node described above). The second network node may comprise a 4G core network node, such as mobility management entity.

[0221]The apparatus may receive, from the first network node, an indication of correspondences between CSG identifiers comprised in the set of CSG identifiers and respective closed access group identifiers.

[0222] Figure 17 illustrates operations that may be performed by apparatus for a first network node of a first communication network. The first network node may be as described above in relation to Figures 14 to 16.

[0223] During 1701 , the apparatus provides, to an operations and management function, an indication of correspondences between closed subscriber group, CSG, identifiers of a second network comprised in a set of CSG identifiers and respective closed access group, CAG, identifiers, wherein the first communication network and second communication network are different communication networks.

[0224]The first communication network and the second communication network are different communication networks. As an example, the second communication network may comprise a 4G network. As an example, the first communication network may comprise a 5G network. As an example, the first communication network may comprise a 6G network.

[0225]As an example, the first network node may comprise a 5G femto. As an example, the second network node may comprise a 4G system node. For example, the second network node may comprise a 4G access network node (such as a 4G base station and/or 4G femto, and/or as any other type of access network node described above). The second network node may comprise a 4G core network node, such as mobility management entity. [0226]The apparatus of Figure 17 may receive an indication of at least one of said correspondences between a CSG identifier in the set of CSG identifiers and a respective CAG identifier from a user equipment, such as the user equipment of Figure 14.

[0227]The apparatus of Figure 17 may determine at least one of said correspondences between a CSG identifier in the set of CSG identifiers and a respective CAG identifier from a user equipment by performing an encoding operation that maps said CSG identifier to said respective CAG identifier. This may be as described above in connection with Figure 7.

[0228] The above-described systems may be considered advantageous as they help to support mobility operations (such as offloading and/or handover) from a 5G (or 6G) network node to a 4G network node with minimal additional signalling.

[0229] It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

[0230] It is noted that whilst some embodiments have been described in relation to 5G networks, similar principles can be applied in relation to other networks and communication systems. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein. [0231] It is also noted herein that while the above describes example embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the present invention.

[0232] As used herein, “at least one of the following: <a list of two or more elements:*” and “at least one of <a list of two or more elements:*” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0233] In general, the various embodiments may be implemented in hardware or special purpose circuitry, software, logic or any combination thereof. Some aspects of the disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0234]As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analog and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable):

(c) a combination of analog and/or digital hardware circuit(s) with software/firmware and

(d) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(e) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0235]This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0236] The embodiments of this disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer-executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it. [0237] Further in this regard it should be noted that any blocks of the logic flow as in the Figures may represent program steps, or interconnected logic circuits, blocks and functions, or a combination of program steps and logic circuits, blocks and functions. The software may be stored on such physical media as memory chips, or memory blocks implemented within the processor, magnetic media such as hard disk or floppy disks, and optical media such as for example DVD and the data variants thereof, CD. The physical media is a non-transitory media.

[0238] The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal ) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

[0239] The memory may be of any type suitable to the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. The data processors may be of any type suitable to the local technical environment, and may comprise one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs), application specific integrated circuits (ASIC), FPGA, gate level circuits and processors based on multi core processor architecture, as non-limiting examples.

[0240] Embodiments of the disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

[0241]The scope of protection sought for various embodiments of the disclosure is set out by the independent claims. The embodiments and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the disclosure. [0242]The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of this disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this disclosure will still fall within the scope of this invention as defined in the appended claims. Indeed, there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

1 ) A user equipment comprising means for performing operations, the operations comprising: receiving, a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network, wherein the first communication network and the second communication network are different communication networks; and transmitting the CSG identifier that is received to the second network node.

2) A user equipment as claimed in claim 1 , wherein the transmitting comprises transmitting a measurement report comprising the CSG identifier.

3) A user equipment as claimed in any preceding claim, wherein the receiving comprises receiving an SIB1 message comprising the CSG identifier.

4) A second apparatus for a second network node of a second communication network, the second apparatus comprising means for performing operations, the operations comprising: receiving, from a user equipment, a closed subscriber group, CSG, identifier; encoding the CSG identifier that is received to generate an encoded closed access group, CAG, identifier; and using the encoded CAG identifier to determine whether to perform a mobility procedure for the terminal towards a first network node of a first communication network, wherein the first communication network and the second communication network are different communication networks.

5) A second apparatus as claimed in claim 4, the operations further comprising configuring the second apparatus with a set of encoded closed access group, CAG, identifiers, wherein the set of encoded CAG identifiers are reserved for first network nodes of the first communication network. 6) A second apparatus as claimed in claim 5, wherein the configuring comprises receiving an indication of one or more encoded CAG identifiers of the set of encoded CAG identifiers and respective access rights for the one or more encoded CAG identifiers of the set of encoded CAG identifiers from an operations and management function.

7) A second apparatus as claimed in any of claims 4 to 6, wherein the receiving the CSG identifier comprises receiving a measurement report comprising the CSG identifier.

8) A second apparatus as claimed in any of claims 4 to 7, wherein the encoding comprises: adding five dummy bits to the CSG identifier that is received.

9) A second apparatus as claimed in any of claims 4-8, wherein the encoding comprises: adding five leading zero bits to the CSG identifier that is received.

10)A second apparatus as claimed in any of claims 4-8, wherein the encoded CAG identifier has a same length as a CAG identifier.

11 )A second apparatus as claimed in any of claims 4 to 10, wherein the CSG identifier that is received comprises 27 bits, and wherein the encoded CAG identifier comprises 32 bits.

12)An apparatus as claimed in any preceding claims, wherein the first communication network comprises a 4G network.

13)An apparatus as claimed in any preceding claim, wherein the second communication network comprises a 5G network or 6G network. )A method for a user equipment, the method comprising: receiving, a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network, wherein the first communication network and the second communication network are different communication networks; and transmitting the CSG identifier that is received to the second network node. )A method for a second apparatus for a second network node of a second communication network, the method comprising: receiving, from a user equipment, a closed subscriber group, CSG, identifier; encoding the CSG identifier that is received to generate an encoded closed access group, CAG, identifier; and using the encoded CAG identifier to determine whether to perform a mobility procedure for the terminal towards a first network node of a first communication network, wherein the first communication network and the second communication network are different communication networks. )A computer program comprising instructions which, when the program is executed by a computer of a user equipment, cause the computer to carry out: receiving, a closed subscriber group, CSG, identifier from a first network node of a first communication network while being served by a second network node of a second communication network, wherein the first communication network and the second communication network are different communication networks; and transmitting the CSG identifier that is received to the second network node. )A computer program comprising instructions which, when the program is executed by a computer of a second network node of a second communication network, cause the computer to carry out: receiving, from a user equipment, a closed subscriber group, CSG, identifier; encoding the CSG identifier that is received to generate an encoded closed access group, CAG, identifier; and using the encoded CAG identifier to determine whether to perform a mobility procedure for the terminal towards a first network node of a first communication network, wherein the first communication network and the second communication network are different communication networks.