Mobile device, access network node, method for mobile device and method for access network node

Abstract

A method is disclosed for a User Equipment (UE) (3), the method including receiving, from an access network node (5), a message for moving the UE (3) to a Radio Resource Control (RRC) inactive state, the message including information indicating that the UE (3) may maintain a configuration for point to multipoint (PTM) transmissions while the UE (3) is in the RRC inactive state, and maintaining the configuration for PTM transmissions while the UE (3) is in the RRC inactive state based on the information.

Description

[Technical Field]

[0001] This disclosure relates to wireless communication systems and devices thereof that operate in accordance with the 3rd Generation Partnership Project (3GPP) standard or an equivalent or derivative thereof. This disclosure is particularly, but not exclusively, related to improvements relating to multicast and broadcast (MBS) services. [Background technology]

[0002] Under 3GPP standards, a NodeB (or "eNB" in LTE and "gNB" in 5G) is a base station through which communication devices (user equipment, or "UE") connect to the core network and communicate with other communication devices or remote servers. End-user communication devices are commonly referred to as User Equipment (UE) and may comprise human-operated or automated devices. Such communication devices may be mobile communication devices such as mobile phones, smartphones, smart watches, personal digital assistants, laptop / tablet computers, web browsers, e-book readers, connected vehicles, etc. Such mobile (or generally fixed) devices are typically operated by users (and thus are often collectively referred to as User Equipment "UE"), although Internet of Things (IoT) devices and similar Machine Type Communication (MTC) devices may also connect to the network. For simplicity, this application will use the term base station when referring to such a base station and the term mobile device or UE when referring to such a communication device.

[0003] A recent development in the 3GPP standards is the so-called “5G” or “New Radio (NR)” standard, which refers to an evolving communications technology that is expected to support a variety of applications and services, such as MTC, IoT / Industrial IoT (IIoT) communications, vehicle-to-vehicle communications and autonomous vehicles, high-definition video streaming, and smart city services. 3GPP intends to support 5G through the so-called 3GPP Next Generation (NextGen) radio access network (RAN) / radio access technology (RAT) and 3GPP NextGen core (NGC) network. Various details of 5G networks are described, for example, in the “NGMN 5G White Paper” V1.0 by the Next Generation Mobile Networks (NGMN) Alliance, which is available at https: / / www.ngmn.org / 5g-white-paper.html.

[0004] Multicast and broadcast services (MBS) enable resource-efficient distribution of transmissions for a group of user equipment (UE). For example, multicast communications to a group of UEs typically require less overall bandwidth than a corresponding set of individual unicast (one-to-one) communications. Multicast transmissions to UEs in a Radio Resource Control (RRC) connected state can provide higher quality of service (QoS) levels, improved reliability, and improved continuity than can be provided using broadcast. MBS can be used, for example, for public safety and mission-critical applications, vehicle-to-everything (V2X) applications, or video distribution to a group of UEs. However, improved MBS methods and procedures are needed to achieve improved resource efficiency, increased capacity, and reduced network congestion. Some multicast services may require UEs to be in an RRC connected state. However, maintaining the UE in the RRC connected state can be power inefficient and increase congestion within the cell, for example, due to uplink transmissions of Hybrid Automatic Repeat Request (HARQ) and reports performed in the RRC connected state. Therefore, there is a need for improved MBS services (e.g., multicast, including point-to-multipoint (PTM) and point-to-point (PTP) transmissions) that can be supported even when the UE is in the RRC inactive state.

[0005] More generally, improvements to MBS mechanisms and procedures are needed, including but not limited to procedures for configuring and / or maintaining PTM legs for MBS when the UE is in an RRC inactive state. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] "NGMN 5G White Paper" V1.0 Summary of the Invention [Problem to be solved by the invention]

[0007] The present disclosure seeks to provide a method and associated apparatus that addresses or at least ameliorate (at least some of) the problems discussed above. [Means for solving the problem]

[0008] In a first aspect, the present disclosure provides a method for a User Equipment (UE), the method including: receiving, from an access network node, a message for moving the UE to a Radio Resource Control (RRC) inactive state, the message including information indicating that the UE may retain a configuration for multicast point to multipoint (PTM) transmissions while the UE is in the RRC inactive state; and based on the information, retaining the configuration for PTM transmissions while the UE is in the RRC inactive state.

[0009] The information may include identification information of a bearer for the PTM transmission, and the retaining may be performed by retaining a configuration for the PTM transmission corresponding to a bearer for the PTM transmission.

[0010] The configuration for the PTM transmission may include a Radio Link Control (RLC) configuration including an indication that an RLC bearer for the PTM transmission can be used when the UE is in the RRC inactive state.

[0011] The method may further include determining to maintain a Radio Link Control (RLC) entity of the PTM of a radio bearer among one or more radio bearers for the PTM transmission.

[0012] The message may include an RRC release message.

[0013] The method may further include receiving the PTM transmission from the access network node when the UE is in an RRC connected state, transitioning to the RRC inactive state in response to receiving the message, and receiving a PTM transmission from the access network node in the RRC inactive state using the configuration.

[0014] The method may further include connecting to a multicast session for receiving the PTM transmission; transitioning to the RRC inactive state; receiving a further message from the access network node when the multicast session is inactive, indicating that the UE should transition to an RRC connected state, the further message including an indication of at least one service for which the PTM transmission is supported by the access network node; in response to receiving the further message, sending an indication of the PTM transmission of multicast to be received to the access network node; transitioning to the RRC connected state; receiving a bearer configuration for the PTM transmission from the access network node; transitioning to the RRC inactive state in response to receiving the message; and receiving the PTM transmission while the UE is in the RRC inactive state.

[0015] The further message may be a paging message.

[0016] Sending an indication of the PTM transmission of the multicast to be received may be done via an RRC resumption message, and receiving a bearer configuration for the PTM transmission may be done via an RRC reconfiguration message.

[0017] In a second aspect, the present disclosure provides a method for a User Equipment (UE), the method including: receiving, from an access network node, a message to cause the UE to enter a Radio Resource Control (RRC) connected state when the UE is in an RRC inactive state; and determining not to transition to the RRC connected state based on whether the UE has stored multicast configuration information for receiving multicast transmissions from the access network node.

[0018] The message may include a paging message including a Temporary Mobile Group Identity (TMGI), and the determining may be performed based on whether the UE has stored multicast configuration information corresponding to the TMGI.

[0019] The multicast configuration information may include an indication of the configuration of at least one radio bearer for receiving the multicast transmission from the access network node.

[0020] In a third aspect, the present disclosure provides a method for an access network node, the method including: transmitting, to a User Equipment (UE), a message to move a deferred UE to a Radio Resource Control (RRC) inactive state, the message including information indicating that the UE may retain a configuration for multicast point to multipoint (PTM) transmissions while the UE is in the RRC inactive state, and the configuration for PTM transmissions may be retained by the UE while the UE is in the RRC inactive state based on the information.

[0021] In a fourth aspect, the present disclosure provides a method for an access network node, the method including: sending a message to a User Equipment (UE) to transition the UE to a Radio Resource Control (RRC) connected state when the UE is in an RRC inactive state, wherein a decision not to transition to an RRC connected state is made based on whether the UE has stored multicast configuration information for receiving the multicast transmission from the access network node.

[0022] In a fifth aspect, the present disclosure provides a user equipment (UE), comprising: means for receiving a message from an access network node to move the UE to a Radio Resource Control (RRC) inactive state, the message including information indicating that the UE may retain a configuration for multicast point to multipoint (PTM) transmission while the UE is in the RRC inactive state, and means for retaining the configuration for PTM transmission while the UE is in the RRC inactive state based on the information.

[0023] In a sixth aspect, the present disclosure provides a User Equipment (UE), comprising: means for receiving a message from an access network node when the UE is in a Radio Resource Control (RRC) inactive state, to cause the UE to enter an RRC connected state; and means for determining not to transition to an RRC connected state based on whether the UE has stored multicast configuration information for receiving multicast transmissions from the access network node.

[0024] In a seventh aspect, the present disclosure provides an access network node, comprising: means for transmitting to a User Equipment (UE) a message to move the UE to a Radio Resource Control (RRC) inactive state, the message including information indicating that the UE may retain a configuration for multicast point to multipoint (PTM) transmission while the UE is in the RRC inactive state, and the configuration for PTM transmission may be retained by the UE while the UE is in the RRC inactive state based on the information.

[0025] In an eighth aspect, the present disclosure provides an access network node, means for transmitting to a User Equipment (UE) a message to transition the UE to a Radio Resource Control (RRC) connected state when the UE is in an RRC inactive state, wherein a decision not to transition to an RRC connected state may be made based on whether the UE has stored multicast configuration information for receiving multicast transmissions from the access network node. [Brief explanation of the drawings]

[0026] Exemplary embodiments of the present disclosure will now be described, by way of example, with reference to the accompanying drawings, in which: [Figure 1] 1 illustrates schematically a mobile (cellular or wireless) telecommunications system in which embodiments of the present disclosure may be applied. [Figure 2] FIG. 1 is a schematic block diagram of a mobile device. [Figure 3] 1 is a schematic block diagram of an access network node (eg, a base station). [Figure 4] FIG. 2 is a schematic block diagram of a distributed unit of RAN equipment for the telecommunications system shown in FIG. 1. [Figure 5] FIG. 2 is a schematic block diagram of a central unit of RAN equipment for the telecommunications system shown in FIG. 1. [Figure 6] FIG. 1 illustrates point-to-point (PTM) communication and point to multipoint (PTM) communication. [Figure 7] 10 is a flow diagram illustrating a method by which a UE continues to receive multicast transmissions in an RRC inactive state. [Figure 8] A figure showing an example of information for maintaining a PTM leg in a UE. [Figure 9] 1 illustrates how an MBS radio bearer (MRB) list is transmitted to a UE. [Figure 10] FIG. 1 is a diagram illustrating a first example of an RLC configuration. [Figure 11] FIG. 10 is a diagram illustrating a second example of an RLC configuration. [Figure 12] A diagram showing how a UE enters an RRC connected state and receives an MRB configuration. [Figure 13] A diagram showing a further method for a UE to transition to an RRC connected state. [Figure 14] FIG. 2 illustrates a first part of a method for establishing and connecting a multicast session. [Figure 15]FIG. 10 illustrates a second part of a method for establishing and connecting a multicast session. [Figure 16] FIG. 10 illustrates a third part of a method for establishing and connecting a multicast session. [Figure 17] FIG. 1 illustrates a first part of a method for MBS session activation and deactivation. [Figure 18] FIG. 10 illustrates a second part of the MBS session activation and deactivation method. [Figure 19] A diagram showing how the UE does not transition to an RRC connected state when a PTM configuration is available in UE3. DETAILED DESCRIPTION OF THE INVENTION

[0027] FIG. 1 illustrates schematically a mobile (cellular or wireless) telecommunications system 1 in which embodiments of the present disclosure may be applied.

[0028] In this system 1, users of mobile devices 3 (UEs) can communicate with each other and other users via base stations 5 (and other access network nodes) and a core network 7 using an appropriate 3GPP radio access technology (RAT), such as Evolved Universal Terrestrial Radio Access (E-UTRA), a 5G RAT, and / or later generation radio access technologies. It will be appreciated that multiple base stations 5 form a (radio) access network or (R)AN. As those skilled in the art will appreciate, while FIG. 1 shows four mobile devices 3A, 3B, 3C, and 3D and two base stations 5A and 5B for illustrative purposes, the system, when implemented, will typically include other base stations / (R)AN nodes 5 and mobile devices (UEs) 3.

[0029] Each base station 5 controls (directly or via other nodes such as home base stations, relays, remote radio heads, distributed units, etc.) one or more associated cells 6. Base stations 5 that support next generation / 5G protocols may be referred to as "gNBs." It will be understood that some base stations 5 may be configured to support both 4G and 5G protocols, and / or any other 3GPP or non-3GPP communication protocol. It will be understood that several base stations 5 form a (radio) access network or (R)AN.

[0030] User Equipment (UE) FIG. 2 is a block diagram illustrating the main components of the mobile device (UE) 3 shown in FIG. 1. As shown, the UE 3 includes transceiver circuitry 21 operable to transmit signals to and receive signals from one or more connected nodes via one or more antennas 22. While not necessarily shown in FIG. 2, the UE 3 naturally has all the usual functionality of a conventional mobile device (such as a user interface 24), which may be provided by any one or any combination of hardware, software, and firmware, as appropriate. A controller 23 controls the operation of the UE 3 according to software stored in memory 25. The software may be pre-installed in memory 25 or may be downloaded via the communication network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 26, a communication control module 27, an MBS module 28, and an RRC module 29.

[0031] The communications control module 27 processes (generates / sends / receives) signaling messages and uplink / downlink data packets between the UE 3 and other nodes, including the (R)AN node 5 and core network nodes. The signaling may include control signaling (such as RRC signaling) related to configuring and assisting cell reselection by the UE 3.

[0032] The MBS module 28 controls MBS communications (generation, sending, and receiving transmissions). For example, the MBS module 28 may be configured to exercise control for receiving multicast communications. It will be appreciated that the MBS module 28 may be configured to exercise control for MBS communications in any of the manners described below. The RRC module 29 controls the RRC state of the UE 3. For example, the RRC module 29 may control the UE to transition to an RRC connected state or an RRC inactive state in response to receiving a corresponding instruction from the base station 5. It will be appreciated that the RRC module 29 may be configured to perform the control of the RRC state of the UE 3 in any of the manners described below.

[0033] Base station / gateway (access network node) FIG. 3 is a block diagram illustrating the main components of the gateway / base station 5 (a base station (gNB) or similar access network node, although the base station need not necessarily be a gNB 6) shown in FIG. 1. As shown, the gateway / base station 5 includes transceiver circuitry 41 operable to transmit signals to and receive signals from one or more connected UEs 3 via one or more antennas 42, and to transmit signals to and receive signals from other network nodes (directly or indirectly) via a network interface 43. The network interface 43 typically includes an appropriate base station-to-base station interface (such as X2 / Xn) and an appropriate base station-to-core network interface (such as S1 / NG-C / NG-U). A controller 44 controls the operation of the base station 5 according to software stored in memory 45. The software may be pre-installed in memory 45 or may be downloaded, for example, via the communications network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 46, a communications control module 47, an MBS module 48, and an RRC module.

[0034] The communication control module 47 handles (generates / sends / receives) signaling between the base station 5 and other nodes, such as the UE 3 and core network nodes. The signaling may include control signaling (such as RRC signaling) related to configuring and assisting cell reselection by the UE 3. The MBS module 48 controls MBS procedures and methods, including MBS transmissions (generation, transmission, and reception of transmissions). For example, the MBS module 48 may control multicast transmissions, including PTM transmissions, to a set of UEs 3. It will be appreciated that the MBS module 48 may be configured to perform control in any of the methods for MBS described below.

[0035] The RRC module controls RRC communications. For example, the RRC module 29 may control communications to transition the UE 3 to an RRC connected state or an RRC inactive state by sending a corresponding instruction to the UE 3. It will be understood that the RRC module 29 may be configured to control communications for RRC in any of the ways described below.

[0036] The present disclosure also relates to a base station (referred to as a "distributed" base station or gNB) that is divided into one or more distributed units (DUs) 50 and a central unit (CU) 60, where the CUs 60 typically perform high-level functions and communication with the next-generation core, and the DUs 50 perform lower-level functions and communication with nearby UEs 3 (i.e., within a cell operated by the gNB 5) over the air interface. In this disclosure, the DUs 50 may also be referred to as a "first unit" of the access network node 5 for wireless communication with the UEs 3, and the CUs 60 may also be referred to as a "second unit" of the access network node 5. An example of a distributed base station 5 will now be described in more detail with reference to FIGS. 4 and 5. However, it will be understood that the (R)AN node 5 need not necessarily be a gNB.

[0037] The distributed gNB5 includes the following functional units: gNB Central Unit (gNB-CU): A logical node that hosts the Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP), and Packet Data Convergence Protocol (PDCP) layers of a gNB (or the RRC and PDCP layers of an en-gNB) and controls the operation of one or more gNB-DUs. The gNB-CU terminates the so-called F1 interface connected to the gNB-DUs. gNB Distributed Unit (gNB-DU): A logical node that hosts the Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers of a gNB or en-gNB, and its operation is partially controlled by the gNB-CU. One gNB-DU supports one or more cells. One cell is supported by one gNB-DU. The gNB-DU terminates the F1 interface connected to the gNB-CU. gNB-Central Unit Control Plane (gNB-CU-CP): A logical node that hosts the control plane part of the RRC and PDCP protocols of the gNB-CU for an en-gNB or gNB-CU. The gNB-CU-CP terminates the so-called E1 interface connected to the gNB-CU-UP and the F1-C (F1 control plane) interface connected to the gNB-DU. gNB-Central Unit User Plane (gNB-CU-User Plane: gNB-CU-UP): A logical node that hosts the user plane portion of the PDCP protocol of the gNB-CU for the en-gNB, as well as the user plane portions of the PDCP protocol and SDAP protocol of the gNB-CU for the gNB. The gNB-CU-UP terminates the E1 interface connected to the gNB-CU-CP and the F1-U (F1 user plane) interface connected to the gNB-DU.

[0038] It will be appreciated that when a distributed base station or similar control plane-user plane (CP-UP) split is used, the base station 5 may be split into separate control plane and user plane entities, each of which includes associated transceiver circuitry, antennas, network interfaces, controllers, memory, operating systems, and communications control modules. If the base station 5 comprises a distributed base station, the network interfaces include E1 and F1 interfaces (F1-C for the control plane and F1-U for the user plane) for communicating signals between functions of the distributed base station 5. In this case, the communications control module also communicates (generates, sends, and receives signaling messages) between the control plane and user plane portions of the base station 5.

[0039] RAN equipment (DU) Figure 4 is a schematic block diagram illustrating the main components of a DU 50 that may be used as part of the RAN equipment 5 for the communications system 1 shown in Figure 1. As shown, the DU 50 includes transceiver circuitry 451 for transmitting signals to and receiving signals from communication devices (such as UE 3) via a radio unit (RU) and associated DU-RU interface 453, and transceiver circuitry 451 for transmitting signals to and receiving signals from the CU 60 of the RAN equipment 5 via a CU interface 454 (e.g., including an F1 interface that may be divided into an F1-U interface and an F1-C interface for user plane and control plane signaling, respectively).

[0040] The DU 50 has a controller 457 for controlling the operation of the DU 50. The controller 457 is associated with a memory 459. Software may be pre-installed in the memory 459 or may be downloaded via the communication network 1 or from a removable data storage device (RMD) or the like. The controller 457 is configured, in this example, to control the overall operation of the DU 50 by program instructions or software instructions stored in the memory 459.

[0041] As shown, these software instructions include, among other things, an operating system 461, a communication control module 463, an F1 module 465, a DU-RU module 468, a DU management module 472, a UE profile management module 473, an MBS module 475, and an RRC module 476. The functionality of the MBS module 475 and the RRC module 476 is the same as that described above with reference to Figure 3, depending on the division of functionality between the RU, the DU 50, and the CU 60.

[0042] The communication control module 463 is operable to control communications between the DU 50 and one or more RUs (and thus between the DU 50 and the UE 3), and between the DU 50 and the CU 60. The communication control module 463 is configured to generally control the reception of signals corresponding to uplink communications from the UE 3, and to handle the transmission of downlink communications destined for the UE 3.

[0043] The F1 module 465 performs appropriate processing of signals received from or transmitted to the CU 60 via one or more CU (e.g., F1) interfaces 454. These signals may be separated into user plane signals received from or transmitted to the CU-UP portion of the CU 60 via the F1-U interface and control plane signals received from or transmitted to the CU-CP portion of the CU 60 via the F1-C interface.

[0044] The DU-RU module 468 performs appropriate processing of signals received from or transmitted to one or more RUs (e.g., DU-RU) via interface 453 . The DU management module 472 manages the overall operation of the DU 50 and the overall performance of the tasks required by the DU 50. These tasks include generating and transmitting appropriate messages using the appropriate signaling application protocol depending on the division of functionality between the RU, DU 50, and CU 60, such as interpreting received MAC signaling and generating MAC signaling for transmission.

[0045] The UE profile management module 473 is responsible for performing functions related to UE profiles, including receiving and storing UE profiles or associated assistance / preference information from the UE 3 or elsewhere in the network (if applicable), determining appropriate mobility-specific configurations based on the UE profile / assistance / preference information (if applicable) for implementation in the UE 3 and / or RAN equipment, and / or providing configuration information to appropriately configure the UE using mobility-based configuration (if applicable). Note that, depending on the implementation, the gNB-DU may not implement at least some of these functions.

[0046] RAN equipment (CU) Figure 5 is a schematic block diagram showing the main components of a CU60 of the RAN equipment for the communication system 1 shown in Figure 1. As shown, the CU60 is provided with transceiver circuitry 551 for transmitting signals to and receiving signals from the DU50 via one or more DU interfaces 554 (including, for example, an F1 interface which may be divided into F1-U and F1-C interfaces for user plane signaling and control plane signaling, respectively), and transceiver circuitry 551 for transmitting signals to and receiving signals from core network 7 functions via one or more core network interfaces 555 (including, for example, an N2 interface and an N3 interface, etc.).

[0047] The CU 60 has a controller 557 for controlling the operation of the CU 60. The controller 557 is associated with a memory 559. Software may be pre-installed in the memory 559, downloaded via the communication network 1, or downloaded from a removable data storage device (RMD) or the like. The controller 557 is configured, in this example, to control the overall operation of the CU 60 by program or software instructions stored in the memory 559.

[0048] As shown, these software instructions include, among other things, an operating system 561, a communication control module 563, an F1 module 565, an E1 module 566, an N2 module 568, an N3 module 569, a CU-UP management module 571, a CU-CP management module 572, a UE profile management module 573, an MBS module 575, and an RRC module 576. The functionality of the MBS module 575 and the RRC module 576 is similar to that described with reference to FIG. 3, depending on the division of functionality between the RU, the DU 50, and the CU 60.

[0049] The communications control module 563 is operable to control communications between the CU 60 and one or more DUs 50 (and thus between the CU 60 and the UE 3), and between the CU 60 and the core network 7. The communications control module 563 is configured to generally control the reception of signals corresponding to uplink communications from the UE 3, and to handle the transmission of downlink communications destined for the UE 3.

[0050] The F1 module 565 performs appropriate processing of signals received from or transmitted to the DU 50 via one or more DU (e.g., F1) interfaces 554. These signals are divided into user plane signals received by or transmitted to the CU-UP portion of the CU 60 via the F1-U interface, and control plane signals received by or transmitted to the CU-CP portion of the CU 60 via the F1-C interface.

[0051] The E1 module 566 provides appropriate processing of signals transmitted between the CU-UP portion of the CU 60 and the CU-CP portion of the CU 60 via a corresponding internal CU interface (eg, E1).

[0052] The N2 module 568 performs appropriate processing of signals received from or sent to the AMF 8-1 via one or more corresponding core network interfaces (eg, N2) 555.

[0053] The N3 module 569 performs appropriate processing of signals received from or sent to one or more core network user plane functions 8-3 via one or more corresponding core network interfaces (e.g., N3) 555.

[0054] The CU-UP management module 571 manages the overall operation of the CU-UP portion of the CU 60 and the overall performance of tasks required for the CU-UP.

[0055] The CU-CP management module 572 manages the overall operation of the CU-CP portion of the CU 60 and the overall performance of the tasks required of the CU-CP, such as interpreting received RRC signaling and generating RRC signaling for transmission, and generating and transmitting appropriate messages using the appropriate signaling application protocol depending on the division of functionality between the RU, DU 50, and CU 60.

[0056] The UE profile management module 573 is responsible for performing functions related to UE (mobility) profiles, including receiving and storing UE profiles or associated assistance / preference information (if applicable) from the UE 3 or elsewhere in the network, determining appropriate mobility-specific configurations based on the UE profile / assistance / preference information for implementation in the UE 3 and / or RAN equipment 5, and / or providing configuration information to appropriately configure the UE with mobility-based configurations. Note that, depending on the implementation, the gNB-CU 60 may not implement at least some of these functions.

[0057] The mobile device 3 and its serving base station 5 are connected via an appropriate air interface (eg, the so-called "NR" air interface, the "Uu" interface, etc.).

[0058] The core network 7 (e.g., EPC in the case of LTE or NGC in the case of NR / 5G) typically includes logical nodes (or "functions") for subscriber management, mobility management, charging, security, and call / session management (among other things) to support communications in the telecommunications system 1. For example, the core network 7 in a "next generation" / 5G system includes user plane entities and control plane entities, such as one or more control plane functions (CPFs) and one or more user plane functions (UPFs) 8-3. The one or more control plane functions (CPFs) include a control plane function 8-1 that handles connectivity and mobility tasks for mobile devices 3, such as the so-called Access and Mobility Management Function (AMF) in 5G or a Mobility Management Entity (MME) in 4G. The one or more Control Plane Functions (CPFs) also include a control plane function 8-4 (such as a Session Management Function (SMF)) that handles communication sessions for the mobile device 3, such as session establishment, modification, and release, and may also include one or more additional control plane functions 8-2. Operations, Administration, and Maintenance (OAM) functions 8-5 may be implemented in software in one or more 5GCN nodes. As shown in Figure 1, the core network 7 connects to a data network 10, such as the Internet or a similar Internet Protocol (IP)-based network. When the UE 3 first establishes a Radio Resource Control (RRC) connection with the base station 5 via a cell, it registers with the appropriate core network node 8-1 (e.g., AMF, MME). The UE 3 is in the so-called RRC connected state, and an associated UE context is maintained by the network. When the UE 3 is in the so-called RRC inactive or RRC inactive state, the UE 3 can select a suitable cell to camp on, and the network can know the approximate location (though not necessarily at the cell level) of the UE 3.

[0059] Multicast and Broadcast Service (MBS) Next, a method for MBS will be described. This example relates to multicast transmission. In particular, a method for maintaining multicast transmission between a base station 5 and a UE 3, including point-to-multipoint (PTM) transmission, will be described.

[0060] A multicast service may include a PTP leg between a base station 5 and a single UE 3, and PTM legs between a base station 5 and multiple UEs 3. PTP and PTM transmissions are shown schematically in Figure 6. While the UEs 3 are shown separately in Figure 6, it will be understood that the UEs 3 may receive both the PTP and PTM portions of a multicast. A PTP may also be described as a PTP "leg" or "portion" of a multicast transmission. Similarly, a PTM may also be described as a PTM "leg" or "portion" of a multicast transmission.

[0061] The PTM leg has MBS radio bearers (MRBs) within the MBS session, which have corresponding MRB configurations. Each MRB has an associated identifier (e.g., an MRB identity) that can be used to identify the MRB. The MRB identity can be included in appropriate transmissions of the MRB configuration. The multicast service may be suspended (a process by which an MRB is released) or reactivated based on multicast data activity (or inactivity). The configuration of one or more MRBs can be provided to the UE 3 and / or base station 5, for example, in appropriate Radio Link Control (RLC) configuration signaling (e.g., RLC bearer configuration messages).

[0062] The multicast MRB may be suspended when UE 3 transitions from the RRC connected state to the RRC inactive state. The multicast PTP leg may not be suitable for use when the UE is in the RRC inactive state because the PTP leg is UE specific and the resources required to service the PTP leg may increase linearly with the number of UEs. However, in this example, there is an advantage in being able to maintain (or configure) the PTM portion of the multicast even when UE 3 is in the RRC inactive state.

[0063] It would be beneficial to be able to maintain reception of multicast transmissions when the UE 3 performs cell reselection to a neighboring cell in an RRC inactive state (without resuming the RRC connection). Methods for configuring, resuming, and maintaining multicast when the UE is in an RRC inactive state are described below.

[0064] We now describe an improved procedure for maintaining the PTM leg of a multicast when a UE 3 transitions from an RRC connected state to an RRC inactive state. It will be appreciated that in the manner described below, PTM transmissions from a base station can be received by UEs in an RRC inactive state and by UEs in an RRC connected state.

[0065] Maintaining PTM for Multicast FIG. 7 illustrates an example where UE 3 transitions from an RRC connected state to an RRC inactive state, but advantageously maintains the PTM leg of the multicast transmission. In step S701, UE 3 is in an RRC connected state and receives a multicast transmission from a base station (access network node) 5. An MRB including a PTM leg is configured for UE 3, and the PTM leg may also be configured for UE 3.

[0066] In step S702, the UE 3 receives an RRC release message from the base station 5. The base station 5 may decide to send the RRC release message to the UE 3, for example, to reduce congestion in the cell of the base station 5 or due to a data inactivity period for multicast. The RRC release message may include an indication that the corresponding configuration should be suspended (e.g., an information element such as suspendConfig). Advantageously, in this example, the RRC release message includes information (e.g., in SuspendConfig) for maintaining at least one PTM leg in the UE 3 (e.g., information indicating that the UE 3 should store information corresponding to the PTM leg). The information for maintaining at least one PTM leg may also be referred to as a "multicast indication."

[0067] In step S703, UE3 transitions to the RRC inactive state in response to receiving the RRC release message, but has the advantage that UE3 can continue to receive the PTM leg of the multicast transmission because UE3 received information to maintain the PTM leg in the RRC release message of step S702.

[0068] An example of information for maintaining at least one PTM leg in UE 3, which may be included in the RRC release message, is shown in FIG. 8. However, it will be understood that the information for maintaining at least one PTM leg in UE 3 may take any other suitable form. In this example, the information includes an indication "RRCINACTIVEMBS" indicating whether UE 3 should maintain (keep) the PTM RLC entity of the multicast MRB when UE 3 is in an RRC inactive state. In other words, upon receiving the indication, UE 3 decides whether to maintain the PTM RLC entity of the MRB. This indication may be, for example, "TRUE" indicating that UE 3 should maintain the PTM RLC entity of the MRB, or "FALSE" indicating that UE 3 should not maintain the PTM RLC entity of the MRB (however, it will be understood that the indication does not necessarily have to be "TRUE" or "FALSE" and any other suitable indication, such as "0" or "1," may alternatively be used). As shown in FIG. 8, in this example, the information included in the RRC release message includes a list of MRBs, and the UE 3 may decide to maintain the PTM RLC entities for the MRBs listed in the list.

[0069] When an MBS session is terminated or deactivated, the indication of whether UE3 should maintain at least one PTM leg can be used to indicate that no PTM legs should be maintained at UE3.

[0070] The RRC release message received by the UE 3 from the network (e.g., from base station 5) may include an indication of the MBS configuration for neighboring cells. This information may include a neighboring cell configuration associated with an MBS session list. The neighboring cell MBS session configuration may be used to implicitly indicate which MBS sessions (MRBs) should be maintained when the UE 3 transitions to the RRC inactive state. However, to avoid ambiguity in the indication, an explicit indication as shown in FIG. 8 may be preferred.

[0071] DU and CU Figure 9 illustrates an example of transmitting an MRB list to UE 3 as part of an RRC release procedure involving DU 50 and CU 60. DU 50 may also be referred to as a "first unit" of access network node 5 for wireless communication with UE 3, and CU 60 may also be referred to as a "second unit" of access network node 5. At the start of the method illustrated in Figure 9, UE 3 is in an RRC connected state and is receiving multicast transmissions from DU 50, including PTM transmissions.

[0072] In step S801, the CU 60 sends a UE context release request message to the DU 50. The UE context release request includes an identifier of the UE (e.g., "UE ID"). In this example, the UE context release request also includes a list of MRBs to be maintained for the UE 3 when the UE 3 enters an RRC inactive state. Alternatively, the UE context release request message may include an indication that all of the MRBs for PTM transmission for the UE 3 should be maintained (e.g., using an indication such as "KeepPTMindication," which may be "TRUE" or "FALSE," or similarly, "1" or "0"). The indication of which MRBs the DU 50 should retain (e.g., continue to store or transmit configurations) may be in the form of any suitable information element or list, such as an "INACTIVE MRB_ID list." Upon receiving the indication included in the UE context release request, the DU 50 may decide to retain the UE 3 context and retain one or more multicast FU tunnels associated with the list of bearers of the CU-UP (e.g., "INACTIVE MRB_ID list"). The instruction included in the UE context release request corresponds to a specific UE 3, so this instruction is sometimes called a "UE-specific" instruction. Based on this instruction, the DU 50 can determine which MBS services the UE 3 will receive when the UE 3 is in an RRC inactive state.

[0073] In step S802, DU50 determines to maintain the MRB for PTM transmission based on the information included in the UE context release request. Based on the instruction in the UE context release request, DU50 may determine that DU50 should continue PTM transmission for UE3 (e.g., all PTM transmissions from DU50 or a set of PTM transmissions indicated in the UE context release request).

[0074] In step S803, the DU50 sends an RRC release message to the UE3. The RRC release message includes a set (e.g., a list) of MRBs for PTM transmission to be maintained in the UE3. The UE3 receives the MRB list and decides to maintain the MRBs indicated in the list (e.g., continue to remember the configuration). The set of MRBs may also be referred to as "multicast indications." The UE3 may maintain the PTM legs corresponding to the MRBs indicated in the MRB list. This has the advantage that the UE3 can continue to receive multicast transmissions from the DU50 even after the UE3 transitions to the RRC inactive state.

[0075] If UE3 is the only UE3 in the cell that is in an RRC connected state and uses an MBS session, when CU60 releases the RRC connection of UE3 using a UE context release request, CU60 can advantageously instruct DU50 to maintain PTM transmission for UE3 using the list of MRBs to be maintained for UE3 (or an indication that all MRBs for PTM transmission to UE3 are maintained). Thus, UE3 can continue to receive PTM transmission even after there are no more UE3s in the cell that are in an RRC connected state (otherwise DU50 may stop PTM transmission). Furthermore, since the RRC release message that UE3 receives from DU50 contains the list of MRBs to be maintained, UE3 can exercise control to receive the corresponding PTM transmission.

[0076] The MRB for PTM transmission is configured when UE 3 is in the RRC connected state. Because the PTM RLC entity for each UE 3 is configured individually, the PTM RLC entity for different UEs 3 may differ. The RLC configuration includes, among other information, the logical channel ID (e.g., "logicalChannelIdentity") and the multicast RLC bearer configuration. In this example, if UE 3's RRC connection is released to the inactive state and UE 3 maintains a PTM RLC entity (e.g., based on the MRB list received from DU 50), the network (e.g., base station 5) maintains the corresponding PTM RLC entity in the network. More generally, the configuration used for PTM for a particular UE 3 may differ from the configuration used for PTM for another UE 3, so if a particular UE 3 maintains a PTM configuration based on the method shown in FIG. 9, that configuration is also maintained in the network (e.g., DU 50).

[0077] RLC configuration Alternatively or additionally, an RLC configuration may be used to indicate the PTM to be maintained for UE 3. For example, the RLC bearer configuration may include an indication that the PTM configuration can be used when UE 3 is in an RRC inactive state. This indication may also be referred to as a "multicast indication." An example of such an RLC bearer configuration that may be sent to UE 3 is shown in FIG. 10. As shown in FIG. 10, the RLC configuration includes an indication that the PTM configuration can be used when UE 3 is in an RRC inactive state. In the example of FIG. 10, the indication is an "INACTIVEPTMIndicator," which may be, for example, "TRUE" or "FALSE," or similarly, "1" or "0," indicating whether UE 3 can use the PTM configuration when in an RRC inactive state.

[0078] 11 shows an alternative whereby the multicast RLC bearer configuration for UEs in inactive state is provided separately (in this example as "InactiveMulticastRLC-BearerConfig-r18") rather than including a separate indication with the list of MBS radio bearers. If InactiveMulticastRLC-BearerConfig-r18 is included in the RLC configuration, UE 3 can use the corresponding PTM configuration when UE 3 is in RRC inactive state.

[0079] Cell Reselection If UE3 is receiving a multicast service and then performs cell reselection in an RRC inactive state (cell reselection without resuming the RRC connection), it can continue receiving the multicast service in the new cell. In particular, if the configuration of the multicast service in the new cell is available to UE3 (e.g., UE3 receives the configuration of the multicast service in the new cell from the network), continuity of the multicast service can be supported. If the configuration of the multicast service in the new cell is not available to UE3, UE3 may resume the RRC connection (transition to the RRC connected state) to obtain the multicast MRB configuration from the network.

[0080] Configuration for multicast when UE is RRC inactive As described above, after UE 3 enters the multicast session, UE 3 can transition from the RRC connected state to the RRC inactive state (e.g., according to any of the methods described above). However, the MBS session may become inactive (e.g., due to the base station deciding to deactivate the MBS due to a period of data inactivity, or due to UE 3 no longer being in a cell that is in the RRC connected state). If the MBS session becomes inactive, UE 3 may decide (e.g., independently of base station 5) to transition to the RRC inactive state to reduce power consumption.

[0081] When UE3 enters a multicast session, it receives the MBS configuration from the core network, but the corresponding MRB configuration is not sent to UE3 until the multicast session is activated. However, UE3 may need to transition from an RRC inactive state to an RRC connected state to receive the configuration for the MRB.

[0082] We now describe how the UE enters the RRC connected state and receives the MRB configuration.

[0083] 12 shows an example in which UE 3 receives a paging transmission from an (R)AN node 5 (e.g., base station 5). In step S121, UE 3 is in a multicast session and in an RRC inactive state.

[0084] In step S122, the MBS session is activated by the base station 5.

[0085] In step S123, the base station 5 sends a paging transmission to the UE 3.

[0086] In step S124, in response to receiving the paging from the base station 5, the UE 5 transitions to an RRC connected state.

[0087] In step S125, when the UE 3 is in an RRC connected state, the UE 3 and the base station 5 communicate to provide the UE 3 with an MRB configuration for multicast.

[0088] In step S126, an RRC release procedure is performed to return UE 3 to an inactive state (e.g., to reduce power consumption in UE 3). The RRC release procedure may be, for example, any of the RRC release procedures described above with reference to Figures 7 to 11, which allows UE 3 to continue receiving multicast transmissions after UE 3 returns to the RRC inactive state.

[0089] Advantageously, in the method shown in Figure 12, UE3 is able to obtain the configuration for multicast despite initially being in RRC inactive mode, return to RRC inactive mode (which may beneficially reduce power consumption and also reduce cell congestion), and continue to receive multicast transmissions at the end of the procedure.

[0090] FIG. 13 shows a further example of a UE transitioning to an RRC connected state to receive information for receiving multicast transmissions. The network may activate multiple MBS sessions, and the network may not know which MBS session to use for the UE 3 unless the UE 3 provides a corresponding indication to the network. In this example, a Temporary Mobile Group Identity (TMGI) is used to indicate a specific MBS session. The TMGI may be used to identify an MBS bearer service. If the TMGI is not reported by the UE 3 after paging from the base station 5, the UE 3 may need to report the TMGI via additional signaling (e.g., using an "MBSinterestedIndication" message). This causes additional delay, which is particularly disadvantageous for delay-sensitive services. Therefore, it is advantageous to include an indication of the MBS session after paging from the base station 5 (e.g., in direct response to the paging).

[0091] In step S131, when the MBS session is activated, the (R)AN node 5 (eg, base station 5) sends a paging message to the UE 3 including the TMGI (or TMGIs) of the MBS session.

[0092] In step S132, after receiving the paging from the base station 5, the UE 3 sends an RRC Resume message to the base station 5. The RRC Resume message includes the TMGI of the MBS service that the UE 3 should receive. By providing the TMGI in the RRC Resume message, the network can advantageously identify the MBS service that the UE 3 should receive. If the UE 3 does not notify the base station 5 of the TMGI in step S132, the UE 3 may alternatively perform part of the multicast session connection and session establishment procedure (steps 1a to 8), for example, as described in TS23.247 and described below with reference to Figures 14 to 16.

[0093] In step S133, an RRC resumption procedure is performed in which the UE 3 moves to an RRC connected state.

[0094] In step S134, after receiving the TMGI from the UE 3, the network configures a PTM leg for the UE 3. Then, an RRC configuration message including a corresponding MRB configuration instruction is sent from the base station 5 to the UE 3. Since the UE 3 is MRB configured, the UE 3 can receive multicast from the base station 5.

[0095] In step S135, an RRC release procedure is performed to return UE 3 to an inactive state (e.g., to reduce power consumption in UE 3). The RRC release procedure may be, for example, any of the RRC release procedures described above with reference to Figures 7 to 11, which allows UE 3 to continue receiving multicast transmissions (a procedure to maintain the PTM leg) even after UE 3 returns to the RRC inactive state.

[0096] Advantageously, at the end of the procedure, the UE 3 has an MRB configuration for receiving the multicast and returns to an RRC inactive state, reducing power consumption in the UE 3 during subsequent reception of the multicast.

[0097] 14 to 16 illustrate the multicast session connection and session establishment procedures, which are described in more detail in, for example, TS23.247 V17.4.0.

[0098] In step 1a, the UE 3 sends an uplink (UL) non-access stratum (NAS) message to the AMF 8-1.

[0099] In step 1b, the AMF 8-1 sends an Nsmf_PDU Session_Update SM Context Request to the SMF 8-4.

[0100] In step 2, Nnrf_NF discovery requests / responses are sent between the SMF 8-4 and the Network Repository Function (NRF).

[0101] In step 3, a Nmbsmf_MBSSession_ContextStatusSubscribeRequest / Response is sent between the SMF 8-4 and the NRF.

[0102] In step 4, an authorization check procedure is performed in the SMF 8-4 and UPF 8-3.

[0103] In step 5, an Nsmf_PDU Session_Update SM Context Response is sent from the SMF 8-4 to the AMF 8-1.

[0104] In step 6, an N2 message request is sent from AMF 8-1 to (R)AN node 5.

[0105] In step 7, the procedure for establishing shared distribution to RAN nodes is performed if the NG-RAN supports 5G MBS.

[0106] In step 8, RRC messages (PDU Session Modification Commands) are exchanged between the UE 3 and the (R)AN node 5.

[0107] In step 9, an N2 message response is sent from the (R)AN node 5 to the AMF 8-1.

[0108] In step 10, an Nsmf_PDU Session_Update SM Context Request is sent from the AMF 8-1 to the SMF 8-4.

[0109] Referring now to Figure 16, there is shown the establishment of 5GC Individual MBS traffic delivery when the NG-RAN does not support 5G MBS.

[0110] In step 11a, N4 session modification messages are exchanged between the SMF 8-4 and the UPF 8-3. Then, the procedure for setting up unicast transport or requesting multicast DL tunnel information for multicast transport is performed.

[0111] In step 11b, an Nmbsmf_MBSSession_ContextUpdate request is sent from SMF 8-4 to MB-SMF.

[0112] In step 11c, N4mb SessionModify / Create messages are exchanged between the MB-SMF and the MB-UPF.

[0113] In step 11d, an Nmbsmf_MBSSession_ContextUpdate response is sent from the MB-SMF to the SMF 8-4. In step 11e, an N4 session modification message is exchanged between the SMF 8-4 and the UPF 8-3.

[0114] In step 12, an Nsmf_PDU Session_Update SM Context Response message is sent from the SMF 8-4 to the AMF 8-1.

[0115] In step 13, the multicast data is sent from the AF to the MB-UPF.

[0116] 16 shows that transmission via 5GC shared MBS traffic distribution is then performed. In step 14, multicast data is transmitted from the MB-UPF to the (R)AN node 5.

[0117] In step 15, bearer selection is performed in the (R)AN node 5.

[0118] In step 16, the multicast data is transmitted from the (R)AN node 5 to the UE 3 via PTP or PTM.

[0119] 16 also shows the transmission via 5GC individual MBS traffic distribution. In step 17, multicast data is transmitted from MB-UPF to UPF 8-3.

[0120] In step 18, the multicast data via the PDU session is transmitted from the UPF 8-3 to the (R)AN node 5.

[0121] In step 19, multicast data via a PDU session is transmitted from the (R)AN node 5 to the UE 3.

[0122] Reduced occurrence of RRC connected mode While in some of the above methods it is advantageous for the UE 3 to return to the RRC connected mode to receive information for receiving multicast (e.g., MRB configuration), it is also advantageous to reduce the number of times the UE 3 transitions to the RRC connected state. For example, it is advantageous to avoid a situation where the multicast configuration is changed and many UEs are simultaneously transitioned to the RRC connected state to acquire the new configuration, as this may cause congestion on the random access channel (RACH). Advantageously, in this example, the UE 3 does not transition to the RRC connected state when it already has a configuration for PTM transmission of multicast.

[0123] Figures 17 and 18 show the MBS session activation and deactivation procedures described in more detail in TS23.247 V17.4.0.

[0124] In step 1, the MB-SMF triggers session activation.

[0125] In step 2, a NMBsmf_MBSSession_Context Status notification is sent from MB-SMF to SMF8-4.

[0126] In step 3, a request to validate reachability of the Namf_MT_group is sent from the SMF 8-4 to the AMF 8-1.

[0127] In step 4a, a response validating the reachability of the Namf_MT_group is sent from the AMF 8-1 to the SMF 8-4.

[0128] In step 4b, a Namf_Communication N1N2 message transmission is sent from the SMF 8-4 to the AMF 8-1.

[0129] In step 5, the AMF pages the UE in idle mode.

[0130] In step 6, a service request is sent from the UE 3 to the AMF 8-1.

[0131] In step 7a, an NSmf_PDU Session_Update SM Context Request is sent from the AMF 8-1 to the SMF 8-4.

[0132] In step 7b, an NSmf_PDU Session_Update SM Context Response is sent from the SMF 8-4 to the AMF 8-1.

[0133] Now referring to Figure 18, in step 8a, Namf_MT_UE reachability information_notification is sent from AMF 8-1 to SMF 8-4.

[0134] In step 8b, a Namf_Communication N1N2 message transmission is sent from SMF 8-4 to AMF 8-1.

[0135] In step 9, an N2 request is sent from AMF 8-1 to (R)AN node 5.

[0136] In step 10a, establishment of 5GC shared MBS traffic distribution is performed.

[0137] In step 10b, steps 8 to 12 described in clause 7.2.1.3 of TS23.247 V17.4.0 are performed.

[0138] In step 11, a Namf_MBS communication_N2 message transmission request (TMGI) is sent from the MB-SMF to the AMF 8-1.

[0139] In step 12, an NGAP activation request (TMGI) is sent from the AMF 8-1 to the (R)AN node 5.

[0140] In step 13, an NGAP activation response is sent from the (R)AN node 5 to the AMF 8-1.

[0141] In step 14, a Namf_MBS communication_N2 message transmission response is sent from AMF 8-1 to MB-SMF.

[0142] In step 15, N4mb Session Modification messages are exchanged between the MB-UPF and MB-SMF.

[0143] In step 12 of the procedure shown in Figure 18, the AMF 8-1 sends an NGAP activation request message to the (R)AN node 5, and then the UE 3 receives a paging from the (R)AN node 5, which allows the UE 3 to receive the corresponding configuration for PTM. In a situation where the UE 3 is in an MBS session but is currently in an RRC inactive state, if the UE 3 is configured with a PTM configuration before transitioning to the RRC inactive state, the UE 3 does not need to transition to an RRC connected state to obtain the PTM configuration. However, the UE 3 may enter the RRC connected state in response to receiving a paging from the (R)AN node 5. Here, an improved method is described to prevent the UE 3 from transitioning to the RRC connected state if a PTM configuration is available to the UE 3.

[0144] 19 shows an example in which UE 3 does not transition to an RRC connected state after receiving a paging from (R)AN node 5 if a PTM configuration is available at UE 3. It will be understood that the paging in FIG. 19 does not necessarily have to be a paging corresponding to the methods illustrated in FIGS. 17 and 18, and the paging may be any other suitable paging from (R)AN node 5. More generally, (R)AN node 5 may decide to send a transmission to UE 3 to cause UE 3 to transition to an RRC connected state, thereby receiving a configuration for PTM, but in this example, it is advantageous for UE 3 to remain in an RRC inactive state if UE 3 already has (e.g., stored) a configuration for PTM available at UE 3.

[0145] In step 191, a paging is sent from the (R)AN node 5 to the UE 3. The paging is to transition the UE 3 to an RRC connected state so that a configuration for PTM can be sent from the (R)AN node 5 to the UE 3.

[0146] In step 192, the UE 3 decides not to transition to the RRC connected state despite receiving a paging from the (R)AN node 5. The UE 3 may decide not to transition to the RRC connected state based on information for multicast stored in the UE 3 (e.g., an MRB configuration for PTM stored in the UE 3). Thus, advantageously, the UE 3 does not transition to the RRC connected state unnecessarily, reducing power consumption and the UE 3 and reducing the risk of network congestion.

[0147] Alternatively, the (R)AN node 5 may determine that the UE 3 already has a PTM configuration available to the UE 3 and decide not to send a paging to the UE 3. The (R)AN node 5 may determine that the UE 3 already has a PTM configuration, for example, based on a PTM configuration previously sent from the (R)AN node 5 to the UE 3. If the (R)AN node 5 is not the same (R)AN node 5 that previously sent the PTM configuration to the UE 3, the (R)AN node 5 may receive an indication from the network that the UE 3 already has a PTM configuration and decide not to send a corresponding paging to the UE 3.

[0148] Modifications and Alternatives Detailed embodiments have been described above. As those skilled in the art will appreciate, multiple modifications and alternatives can be made to the above embodiments while still benefiting from the disclosure embodied therein. By way of example only, some of these alternatives and modifications are described herein.

[0149] Base stations for 5G / NR communication systems are commonly referred to as New Radio Base Stations ("NR-BS" or "gNB"), although it will be understood that they may also be referred to using the term "eNB" (or 5G / NR eNB), which is more typically associated with Long Term Evolution (LTE) base stations (also commonly referred to as "4G" base stations). 3GPP Technical Specification (TS) 38.300 V16.7.0 and TS 37.340 V16.7.0 define, among other things, the following nodes: gNB: A node that provides NR user plane and control plane protocol termination towards the UE and is connected to the 5G core network (5GC) via the NG interface. ng-eNB: A node that provides E-UTRA user plane and control plane protocol termination towards the UE and is connected to the 5GC via the NG interface. En-gNB: A node that provides protocol termination for the NR user plane and control plane towards the UE and functions as a secondary node in E-UTRA-NR Dual Connectivity (EN-DC). NG-RAN node: Either gNB or ng-eNB.

[0150] It will be understood that the above embodiments may be applied to both 5G new radio systems and LTE systems (E-UTRAN). A base station (gateway) supporting E-UTRA / 4G protocols may be referred to as an "eNB," and a base station supporting next-generation / 5G protocols may be referred to as a "gNB." It will be understood that some base stations may be configured to support both 4G and 5G protocols, or any other 3GPP or non-3GPP communication protocols.

[0151] Each cell may have an associated NR Cell Global Identifier (NCGI) to globally identify the cell. The NCGI is constructed from the Public Land Mobile Network (PLMN) identity (PLMN ID) to which the cell belongs and the NR Cell Identity (NCI) of the cell. The PLMN ID included in the NCGI is the first PLMN ID in the PLMN ID set associated with the NR Cell Identity in System Information Block Type 1 (SIB1). The gNB Identifier (gNB ID) is used to identify a specific gNB within a PLMN. The gNB ID is included in the NCI of that cell. The global gNB ID is used to globally identify a gNB and is constructed from the PLMN identity and gNB ID to which the gNB belongs. The Mobile Country Code (MCC) and Mobile Network Code (MNC) are the same as those included in the NCGI.

[0152] In the above description, for ease of understanding, the UE 3 and the Access R(AN) node 5 are described as having several separate modules (such as a communications control module). These modules may be provided in this manner for a particular application, for example, where an existing system is modified to implement the present disclosure; however, in other applications, for example, in a system designed from the beginning with the features of the present invention in mind, these modules may be incorporated into the overall operating system or code, and they may not be identifiable as separate entities. These modules may be implemented in software, hardware, firmware, or a combination thereof.

[0153] Each controller may include any suitable form of processing circuitry including, for example (but not limited to), one or more hardware-implemented computer processors, microprocessors, central processing units (CPUs), arithmetic logic units (ALUs), input / output (IO) circuitry, internal memory / cache (program and / or data), processing registers, communication buses (e.g., control buses, data buses and / or address buses), direct memory access (DMA) functions, hardware or software-implemented counters, pointers and / or timers, etc.

[0154] In the above embodiment, several software modules have been described. As will be understood by those skilled in the art, the software modules may be provided in compiled or uncompiled form, and may be supplied as a signal via a computer network or on a recording medium. Furthermore, the functionality performed by some or all of this software may be implemented using one or more dedicated hardware circuits. However, the use of software modules is preferred because it facilitates functionality updates.

[0155] The above embodiments are also applicable to "non-mobile" or generally fixed user equipment. The mobile devices (UE) mentioned above may comprise MTC / IoT devices, power-saving UEs, etc.

[0156] User equipment 3 (or "UE", "mobile station", "mobile device", or "wireless device") in this disclosure is an entity connected to a network via a radio interface.

[0157] It should be noted that the present disclosure is not limited to dedicated communication devices, but may be applied to any device having communication capabilities as described in the following paragraphs.

[0158] The terms "user equipment" or "UE" (as this term is used by 3GPP), "mobile station," "mobile device," and "wireless device" are generally intended to be synonymous with each other and include standalone mobile stations such as terminals, cell phones, smartphones, tablets, cellular IoT devices, IoT devices, and machines. It will be understood that the terms "mobile station" and "mobile device" also encompass devices that remain stationary for extended periods of time.

[0159] The UE may be, for example, an item of production or manufacturing equipment and / or an item of energy-related machinery (e.g., equipment or machinery such as boilers, engines, turbines, solar panels, wind turbines, hydroelectric generators, thermal generators, nuclear generators, batteries, nuclear systems and / or related equipment, heavy electrical machinery, pumps including vacuum pumps, compressors, fans, blowers, hydraulic equipment, pneumatic equipment, metalworking machinery, manipulators, robots and / or application systems thereof, tools, dies or molds, rolls, conveying equipment, elevators, material handling equipment, textile machinery, sewing machinery, printing and / or related machinery, paper converting machinery, chemical machinery, mining machinery and / or construction machinery and / or related equipment, machinery and / or implements for agriculture, forestry and / or fisheries, safety and / or environmental protection equipment, tractors, precision bearings, chains, gears, power transmission equipment, lubrication equipment, valves, fittings, and / or application systems for any of the foregoing equipment or machinery, etc.).

[0160] A UE may be, for example, an item of transportation equipment (e.g., rail cars, vehicles (automobiles), motorcycles, bicycles, trains, buses, carts, rickshaws, ships and other watercraft, aircraft, rockets, satellites, drones, balloons, and other transportation equipment).

[0161] A UE may be, for example, an item of information and communications equipment (eg, information and communications equipment such as electronic computers and related equipment, communications and related equipment, electronic components, etc.).

[0162] The UE may be, for example, a refrigerator, a refrigerator application product, an item of trade and / or service industry equipment, a vending machine, an automated service machine, an office machine or equipment, a home appliance or electronic device (e.g., a home appliance such as audio equipment, video equipment, loudspeakers, radios, televisions, microwave ovens, rice cookers, coffee machines, dishwashers, washing machines, dryers, electronic fans or related equipment, vacuum cleaners, etc.).

[0163] The UE may be, for example, an electrical application system or device (eg, an electrical application system or device such as an x-ray system, a particle accelerator, a radioisotope device, a sonic device, an electromagnetic application device, a power application device, etc.).

[0164] The UE may be, for example, an electronic lamp, a lighting fixture, a measuring instrument, an analyzer, a tester, or a surveying or detecting device (e.g., a smoke alarm, a human alarm sensor, a motion sensor, a radio tag, or other surveying or detecting device), a watch or clock, laboratory equipment, an optical device, a medical device and / or system, a weapon, a blade, a hand tool, etc.

[0165] A UE may be, for example, a wireless-equipped personal digital assistant or related equipment, such as a wireless card or module designed to be attached to or inserted into another electronic device (e.g., a personal computer, an electrical measuring instrument), etc.

[0166] The UE may be a device or part of a system that uses various wired and or wireless communication technologies to provide the applications, services, and solutions described below in relation to the "Internet of things" (IoT).

[0167] Internet of Things devices (or "Things") may be equipped with appropriate electronics, software, sensors, network connections, etc. that enable these devices to collect and exchange data with each other and other communicating devices. IoT devices may include automated equipment that follows software instructions stored in internal memory. IoT devices may operate without the need for human supervision or interaction. IoT devices may also remain stationary and / or inactive for long periods of time. IoT devices may be implemented as part of a (typically) stationary device. IoT devices may also be embedded in non-stationary equipment (e.g., a vehicle) or attached to an animal or person being monitored / tracked.

[0168] It will be understood that IoT technology may be implemented on any communication device that can connect to a communication network to send / receive data, whether such communication device is controlled by human input or software instructions stored in memory.

[0169] It will be understood that IoT devices may also be referred to as Machine-Type Communication (MTC) devices or Machine-to-Machine (M2M) communication devices. It will be understood that a UE may support one or more IoT or MTC applications. Some examples of MTC applications are listed in the table below (Source: 3GPP TS 22.368 V13.1.0, Annex B, the contents of which are incorporated herein by reference). This list is not exhaustive and is intended to illustrate some examples of machine-type communication applications.

[0170] [Table 1]

[0171] The applications, services, and solutions may be Mobile Virtual Network Operator (MVNO) services, emergency wireless communication systems, Private Branch eXchange (PBX) systems, PHS / digital cordless telecommunications systems, Point of sale (POS) systems, advertising call systems, Multimedia Broadcast and Multicast Service (MBMS), Vehicle to Everything (V2X) systems, train radio systems, location-related services, disaster / emergency wireless communication services, community services, video streaming services, femtocell application services, Voice over LTE (VoLTE) services, billing services, wireless on-demand services, roaming services, activity monitoring services, telecommunications carrier / communication NW selection services, function restriction services, Proof of Concept (PoC) services, personal information management services, ad hoc networks / delay tolerant networking (DTN) services, and the like.

[0172] Furthermore, the above-mentioned UE categories are merely examples of applications of the technical concepts and embodiments described in this document, and it goes without saying that these technical concepts and embodiments are not limited to the above-mentioned UEs and can be modified in various ways.

[0173] This application claims the benefit of priority to UK Patent Application No. 2215057.7 filed on October 12, 2022, the disclosure of which is incorporated herein by reference in its entirety.

[0174] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here. (Appendix 1) 1. A method for a User Equipment (UE), the method comprising: receiving a multicast point to multipoint (PTM) transmission when the UE is in a Radio Resource Control (RRC) connected state; receiving a multicast indication from an access network node indicating a configuration for receiving the PTM transmission of the multicast; determining, based on the multicast indication, that the PTM transmission of the multicast is supported for reception at the UE when the UE is in an RRC inactive state; Transitioning to an RRC inactive state; receiving, in the RRC inactive state, from an access network node, the PTM transmission of the multicast using a configuration; Including, the multicast indication includes an indication of one or more radio bearers for the PTM transmission of the multicast to be used by the UE to receive the PTM transmission of the multicast when the UE is in the RRC inactive state. method. (Appendix 2) 2. The method of claim 1, wherein the multicast indication is included in an RRC release message received at the UE from the access network node. (Appendix 3) 2. The method of claim 1, comprising receiving Radio Link Control (RLC) configuration information from the access network node indicating that an RLC bearer for multicast can be used when the UE is in an RRC inactive state. (Appendix 4) 4. The method of any one of Supplementary Notes 1 to 3, wherein the multicast indication includes an indication that all bearers for receiving the PTM transmission should be maintained at the UE when the UE is in an RRC inactive state. (Appendix 5) 5. The method of any one of Supplementary Notes 1 to 4, wherein the multicast indication includes an indication of a set of radio bearers for the PTM transmission to be used by the UE to receive the PTM transmission of the multicast when the UE is in the RRC inactive state. (Appendix 6) 6. The method of claim 5, wherein the set of radio bearers is used by the UE to receive multicast PTM transmissions when the UE is in an RRC inactive state and is a subset of radio bearers for PTM transmissions associated with the access network node. (Appendix 7) 7. The method of any one of Supplementary Notes 1 to 6, further comprising: determining, based on the multicast indication, to maintain a PTM Radio Link Control (RLC) entity of a radio bearer among one or more radio bearers for the multicast. (Appendix 8) 1. A method for a User Equipment (UE), the method comprising: connecting to a multicast session for receiving multicast point to multipoint (PTM) transmissions from an access network node; Transitioning to a Radio Resource Control (RRC) inactive state; receiving a transmission from the access network node indicating that the UE should transition to an RRC connected state when a multicast session is inactive; the transmission includes an indication of at least one multicast service supported by the access network node; transmitting to the access network node an indication of a multicast PTM transmission to be received at the UE in response to receiving a transmission indicating that the UE should transition to an RRC connected state; Transitioning to an RRC connected state; receiving a bearer configuration for the PTM transmission from the access network node; transitioning to an RRC inactive state in response to signaling received from the access network node indicating that the UE should enter an RRC inactive state and receive the PTM transmission; receiving the PTM transmission when the UE is in the RRC inactive state. (Appendix 9) 9. The method of claim 8, wherein the indication of the PTM transmission of the multicast to be received at the UE includes a Temporary Mobile Group Identity (TMGI). (Appendix 10) 10. The method of claim 8 or 9, wherein the transmission indicating that the UE will transition to an RRC connected state is a paging transmission. (Appendix 11) 11. The method of any one of Supplementary Notes 8 to 10, wherein the UE sends an indication of the PTM transmission of the multicast to be received at the UE to the access network node in an RRC resumption message, and a bearer configuration for the PTM transmission is received from the access network node in an RRC reconfiguration message. (Appendix 12) 1. A method for a User Equipment (UE), the method comprising: receiving a transmission from an access network node to transition the UE to a Radio Resource Control (RRC) connected state when the UE is in an RRC inactive state; determining, based on multicast configuration information stored in the UE for receiving multicast transmissions from the access network node, not to transition to an RRC connected state in response to receiving a transmission from the access network node; A method comprising: (Appendix 13) 13. The method of claim 12, wherein the transmission for transitioning the UE to an RRC connected state is a paging transmission including a Temporary Mobile Group Identity (TMGI). (Appendix 14) 14. The method of claim 12 or 13, wherein the multicast configuration information comprises an indication of the configuration of at least one radio bearer for receiving the multicast transmission from the access network node. (Appendix 15) 1. A method for an access network node, the method comprising: transmitting a multicast point to multipoint (PTM) transmission to a Radio Resource Control (RRC) connected User Equipment (UE); sending a multicast indication to the UE indicating a configuration for receiving the PTM transmission of the multicast when the UE is in an RRC inactive state; Including, the multicast indication includes an indication that the PTM transmission of the multicast should be received at the UE when the UE is in an RRC inactive state; The multicast indication includes an indication of one or more radio bearers for the PTM transmission of the multicast to be used by the UE to receive the PTM transmission of the multicast in the RRC inactive state. method. (Appendix 16) 16. The method of claim 15, wherein the multicast indication is sent to the UE in an RRC release message. (Appendix 17) 16. The method of claim 15, wherein the multicast indication is sent to the UE as part of Radio Link Control (RLC) configuration information. (Appendix 18) 18. The method of any one of Supplementary Notes 15 to 17, wherein the multicast indication includes an indication that all bearers for receiving the PTM transmission should be maintained at the UE when the UE is in the RRC inactive state. (Appendix 19) 19. The method of any one of Supplementary Notes 15 to 18, wherein the multicast indication includes an indication of a set of radio bearers for the PTM transmission to be used by the UE to receive the PTM transmission of the multicast when the UE is in the RRC inactive state. (Appendix 20) 19. The method of claim 18, wherein the set of radio bearers is a subset of the radio bearers for the PTM transmission associated with the access network node used by the UE to receive the PTM transmission of the multicast when the UE is in the RRC inactive state. (Appendix 21) The method comprises: 21. The method of claim 19 or 20, further comprising receiving, at a first portion of the access network node for wireless communication with the UE, from a second portion of the access network node, an indication of the set of bearers for the PTM transmission of the multicast. (Appendix 22) 22. The method of claim 21, wherein the indication of the set of bearers is received at the first part of the access network node from the second part of the access network node in an RRC context release request. (Appendix 23) The method comprises: 23. The method of claim 21 or 22, further comprising: determining, based on an indication of the set of bearers received at the first part of the access network nodes from the second part of the access network nodes, to continue transmitting the PTM transmission of the multicast using at least one bearer of the set of bearers. (Appendix 24) 24. The method of any one of Supplementary Notes 21 to 23, wherein the first part of the access network node is a distributed unit of the access network node and the second part of the access network node is a central unit of the access network node. (Appendix 25) 25. The method of any one of Supplementary Notes 21 to 24, further comprising: determining, in the second part of the access network nodes, if the UE associated with the PTM transmission is not present in a cell of the access network node in the RRC connected state, to send from the second part of the access network nodes to the first part of the access network nodes an indication that the PTM transmission of the multicast will continue to be transmitted by the first part of the access network nodes. (Appendix 26) 26. The method of any one of Supplementary Notes 15 to 25, further comprising determining to maintain a PTM radio link control (RLC) entity associated with the UE when the UE is in the RRC inactive mode. (Appendix 27) 1. A method for an access network node, the method comprising: sending a transmission to a User Equipment (UE) indicating that the UE should transition to an RRC connected state when in a Radio Resource Control (RRC) inactive state and a multicast session provided by the access network node is inactive, the transmission including an indication of at least one of the multicast services supported by the access network node; receiving, from the UE, an indication of a PTM transmission to be received at the UE; sending a bearer configuration for the PTM transmission to the UE when the UE is in an RRC connected state; sending a transmission to the UE indicating that the UE should enter an RRC inactive state and receive the PTM transmission; transmitting the PTM transmission to a UE; A method comprising: (Appendix 28) 28. The method of claim 27, wherein the indication of the PTM transmission of the multicast to be received at the UE includes a Temporary Mobile Group Identity (TMGI). (Appendix 29) 29. The method of claim 27 or 28, wherein the transmission indicating that the UE should transition to an RRC connected state is a paging transmission. (Appendix 30) 30. The method of any one of Supplementary Notes 27 to 29, wherein an indication of the PTM transmission of the multicast to be received at the UE is received from the UE in an RRC resumption message, and a bearer configuration for the PTM transmission is sent to the UE in an RRC reconfiguration message. (Appendix 31) A user equipment (UE), means for receiving a multicast point to multipoint (PTM) transmission when the UE is in a Radio Resource Control (RRC) connected state; means for receiving, from an access network node, a multicast indication indicating a configuration for receiving the PTM transmission of the multicast; means for determining, based on the multicast indication, that the PTM transmission of the multicast is supported for reception at the UE when the UE is in an RRC inactive state; means for transitioning to an RRC inactive state; means for receiving, in the RRC inactive state, from the access network node using the configuration, the PTM transmission for multicast; Equipped with The multicast indication includes an indication of one or more radio bearers for the PTM transmission of the multicast to be used by the UE to receive the PTM transmission of the multicast when the UE is in an RRC inactive state. User equipment. (Appendix 32) A user equipment (UE), means for connecting to a multicast session for receiving a multicast PTM transmission from an access network node; means for transitioning to a Radio Resource Control (RRC) inactive state; means for receiving a transmission from the access network node indicating that the UE should transition to an RRC connected state when the multicast session is inactive; the transmission includes an indication of at least one multicast service supported by the access network node; means for transmitting to the access network node, in response to receiving a transmission indicating that the UE should transition to an RRC connected state, an indication of the PTM transmission of the multicast to be received at the UE; means for transitioning to an RRC connected state; means for receiving a bearer configuration for the PTM transmission from the access network node; means for transitioning to an RRC inactive state in response to signaling received from the access network node indicating that the UE should enter the RRC inactive state and receive the PTM transmission; means for receiving the PTM transmission when the UE is in the RRC inactive state; A user device comprising: (Appendix 33) A user equipment (UE), means for receiving a transmission from an access network node to transition the UE to a Radio Resource Control (RRC) connected state when the UE is in an RRC inactive state; means for determining, based on multicast configuration information stored in the UE for receiving multicast transmissions from the access network node, not to transition to an RRC connected state in response to receiving a transmission from the access network node; A user device comprising: (Appendix 34) an access network node, means for transmitting a multicast point to multipoint (PTM) transmission to a Radio Resource Control (RRC) connected User Equipment (UE); means for transmitting a multicast indication to the UE indicating a configuration for receiving the PTM transmission of the multicast when the UE is in an RRC inactive state; Equipped with the multicast indication includes an indication that the PTM transmission of the multicast should be received at the UE when the UE is in the RRC inactive state; The multicast indication includes an indication of one or more radio bearers for the PTM transmission of the multicast to be used by the UE to receive the PTM transmission of the multicast in the RRC inactive state. Access network node. (Appendix 35) an access network node, means for sending a transmission to a User Equipment (UE) indicating that the UE should transition to a Radio Resource Control (RRC) connected state when in an RRC inactive state and a multicast session provided by the access network node is inactive; the transmission includes an indication of at least one multicast service supported by the access network node; means for receiving, from the UE, an indication of a PTM transmission received at the UE; means for transmitting a bearer configuration for the PTM transmission to the UE when the UE is in the RRC connected state; means for transmitting a transmission to the UE indicating that the UE has entered the RRC inactive state and will receive the PTM transmission; means for transmitting the PTM transmission to the UE; An access network node comprising: [Explanation of symbols]

[0175] 1 Mobile (cellular or wireless) telecommunications systems 3. Mobile Devices 5 Base Station / (R)AN Node 6 Related Cells 7 Core Network 10. Data Network 21 Transceiver circuit 22 Antenna 23 Controller 24 User Interface 25 memory 26 Operating Systems 27 Communication Control Module 28 MBS modules 29 RRC Module 41 Transceiver Circuit 42 Antenna 43 Network Interfaces 44 Controller 45 memory 46 Operating Systems 47 Communication Control Module 48 MBS modules 49 RRC modules

Claims

1. 1. A method for a user equipment (UE), the method comprising: receiving a message from an access network node to transition the UE to a Radio Resource Control (RRC) inactive state; The message includes information indicating that the UE can maintain a configuration for multicast point-to-multipoint (PTM) transmission while the UE is in the RRC inactive state; and maintaining a configuration for PTM transmission while the UE is in the RRC inactive state based on the information; A method comprising:

2. the information includes an identification of a bearer for the PTM transmission; the maintaining is performed by maintaining the configuration for the PTM transmission corresponding to the bearer of the PTM transmission. The method of claim 1.

3. the information includes identification information of a session of the PTM transmission; the maintaining is performed by maintaining a configuration for the PTM transmission corresponding to the session of the PTM transmission. The method according to claim 1 or 2.

4. The configuration for the PTM transmission includes a Radio Link Control (RLC) configuration including an indication that an RLC bearer for the PTM transmission can be used when the UE is in the RRC inactive state.

4. The method according to any one of claims 1 to 3.

5. determining, based on the information, to maintain a Radio Link Control (RLC) entity for PTM of a radio bearer among the one or more radio bearers for the PTM transmission.

5. The method according to any one of claims 1 to 4.

6. The message includes an RRC release message.

6. The method according to any one of claims 1 to 5.

7. receiving the PTM transmission from the access network node when the UE is in an RRC connected state; transitioning to the RRC inactive state in response to the reception of the message; receiving, in the RRC inactive state, the PTM transmission from the access network node using the configuration; The method of any one of claims 1 to 6, further comprising:

8. joining a multicast session to receive the PTM transmission; transitioning to the RRC inactive state; receiving a further message from the access network node indicating that the UE should transition to the RRC connected state if the multicast session is inactive; The further message includes an indication of at least one service of the PTM transmission supported by the access network node. transmitting to the access network node, in response to receiving the further message, an indication of the PTM transmission of the multicast to be received; Transitioning to the RRC connected state; receiving a bearer configuration for the PTM transmission from the access network node; transitioning to the RRC inactive state in response to the reception of the message; receiving the PTM transmission while the UE is in the RRC inactive state; 7. The method of claim 1, further comprising:

9. the further message is a paging message. The method of claim 8.

10. transmitting an indication of the multicast PTM transmission to be received via an RRC resume message; receiving the bearer configuration for the PTM transmission via an RRC reconfiguration message; 10. The method according to claim 8 or 9.

11. 1. A method for a user equipment (UE), the method comprising: receiving, from an access network node, a message for transitioning the UE to a Radio Resource Control (RRC) connected state when the UE is in an RRC inactive state; determining not to transition to an RRC connected state based on whether the UE stores multicast configuration information for receiving multicast transmissions from the access network node; A method comprising:

12. the message comprises a paging message including a Temporary Mobile Group Identity (TMGI); The determining is performed based on whether the UE stores the multicast configuration information corresponding to the TMGI. The method of claim 11.

13. the multicast configuration information includes an indication of the configuration of at least one radio bearer for receiving the multicast transmission from the access network node.

13. The method of claim 11 or 12.

14. 1. A method for an access network node, the method comprising: sending a message to a User Equipment (UE) to move the UE to a Radio Resource Control (RRC) inactive state; The message includes information indicating that the UE can maintain a configuration for multicast point-to-multipoint (PTM) transmission while the UE is in the RRC inactive state; and The configuration for PTM transmission is maintained by the UE while the UE is in the RRC inactive state based on the information. method.

15. 1. A method of an access network node, the method comprising: transmitting a message to a user equipment (UE) to transition the UE to a radio resource control (RRC) connected state when the UE is in an RRC inactive state; determining not to transition to an RRC connected state based on whether the UE has stored multicast configuration information for receiving multicast transmissions from the access network node; method.

16. A user equipment (UE), means for receiving a message from an access network node to move the UE to a Radio Resource Control (RRC) inactive state; The message includes information indicating that the UE can maintain a configuration for multicast point-to-multipoint (PTM) transmission while the UE is in the RRC inactive state; and means for maintaining a configuration for PTM transmission while the UE is in the RRC inactive state based on the information; A user device comprising:

17. A user equipment (UE), means for receiving, from an access network node, a message for transitioning the UE to a Radio Resource Control (RRC) connected state when the UE is in an RRC inactive state; means for determining not to transition to an RRC connected state based on whether the UE has stored multicast information for receiving multicast transmissions from the access network node; A user device comprising:

18. an access network node, means for transmitting, to a User Equipment (UE), a message to move the UE to a Radio Resource Control (RRC) inactive state; The message includes information indicating that the UE can maintain a configuration for multicast point-to-multipoint (PTM) transmission while the UE is in the RRC inactive state; and The configuration for PTM transmission is maintained by the UE while the UE is in the RRC inactive state based on the information. Access network node.

19. an access network node, means for transmitting, to a user equipment (UE), a message for transitioning the UE to a radio resource control (RRC) connected state when the UE is in an RRC inactive state; determining not to transition to an RRC connected state based on whether the UE has stored multicast configuration information for receiving multicast transmissions from the access network node; Access network node.

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