Dispersion unit, central unit, and method

Abstract

A communication system is disclosed in which multicast and broadcast services (MBS) can be provided via multicast to inactive user equipment (UE). A distributed unit of a base station device receives, from a central unit of the base station device, information identifying at least one MBS session and information identifying that the at least one MBS session is provided in a cell via multicast to inactive UEs.

Description

Technical Field

[0001] The present disclosure relates to wireless communication systems and devices.

Background Art

[0002] The present disclosure relates to wireless communication systems and devices operating according to 3rd Generation Partnership Project (3GPP (registered trademark)) standards or their equivalents or derivatives. The present disclosure has a particular, but not exclusive, relevance to improvements related to multimedia broadcast sessions in so-called "5G" (or "next generation") systems.

[0003] The latest evolution of 3GPP standards is referred to as "5G" or "New Radio" (NR). These terms refer to evolving communication technologies that support various applications and services. 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 from https: / / www.ngmn.org / 5g-white-paper.html. 3GPP intends to support 5G with so-called 3GPP Next Generation (NextGen) Radio Access Network (RAN), and 3GPP NextGen core network (NGC).

[0004] Under 3GPP standards, a base station (e.g., "eNB" for 4G or "gNB" for 5G) is a node for a communication device (user equipment or "UE") to connect to a core network and communicate with other communication devices or remote servers. For simplicity, the present disclosure uses the term base station to refer to any such base station.

[0005] In a 5G architecture, the internal structure of a gNB may be divided into two parts known as a Central Unit (CU) and a Distributed Unit (DU). In this "split" architecture, generally the "upper" CU layer (e.g., but not necessarily or exclusively, PDCP), and generally the "lower" DU layer (e.g., but not necessarily or exclusively, RLC / MAC / PHY) may be implemented separately. Thus, for example, in each of the gNBs, the CU functions of the upper layers of several gNBs may be implemented centrally (e.g., by a single processing unit, or in a cloud-based or virtualized system), while the DU functions of the lower layers may be held locally.

[0006] For simplicity, the present disclosure shall refer to any communication device capable of connecting to a core network via one or more base stations including distributed base stations and their units using the terms mobile device, user device, or UE.

[0007] The communication device may be, for example, a mobile communication device such as a mobile phone, smartphone, user equipment, personal digital assistant, laptop / tablet computer, web browser, e-book reader, etc. Such mobile (or generally fixed) devices are usually operated by a user. However, the 3GPP standard also enables connecting so-called "Internet of Things" (IoT) devices (e.g., Narrow-Band IoT (NB-IoT) devices) to the network, which typically includes various measurement devices, telemetry devices, monitoring systems, tracking and tracing devices, in-vehicle safety systems, vehicle maintenance systems, road sensors, digital billboards, point of sale (POS) terminals, remote control systems, and other automated devices. In fact, the Internet of Things is a network of devices (or "things") equipped with appropriate electronic devices, software, sensors, network connectivity, and / or others, enabling these devices to collect and exchange data with each other and with other communication devices via the network. It will be understood that IoT devices may also be referred to as Machine-Type Communication (MTC) communication devices or Machine-to-Machine (M2M) communication devices.

[0008] For simplicity, the present disclosure often refers to mobile devices in the description, but it will be understood that the technology described can be implemented on any (mobile and / or generally fixed) communication device that can be connected to a communication network to send / receive data, regardless of whether such a communication device is controlled by human input or by software instructions stored in memory.

[0009] The so-called Radio Resource Control (RRC) protocol is a control plane protocol between a UE and a radio access network (base station). RRC has three different states in (5G), namely RRC_IDLE, RRC_CONNECTED, and RRC_INACTIVE. The functions and state transitions in each state are defined in the 3GPP TS38.331 V16.7.0 standard (the Release 17 version is not publicly available). Briefly, in the RRC connected state, radio resources are allocated to the UE, and usually, active (user plane or control plane) communication is taking place between the UE and the network. When radio resources are no longer needed, the network can decide to release the RRC connection and transition the UE to the RRC idle state. In the RRC idle state, no active communication is taking place between the UE and the network. The third RRC inactive state was introduced in 5G to provide an "always-on" type of connection. Specifically, when the network decides to put the UE into the inactive state (instead of the idle state), the RRC connection can be resumed as needed without excessive signaling. This is achieved by maintaining the applicable radio and security configurations in the UE and the radio access network (base station). In the RRC connected state, UE mobility is controlled by the network via handovers between cells. In the RRC idle and inactive states, the UE performs measurements on neighboring cells and, if necessary, performs cell reselection based on the measurement results.

[0010] One of the recent features developed on the existing 5G framework is called Multicast and Broadcast Services (MBS). This feature aims to enhance the performance of 5G New Radio and 5G Core Network in order to deploy various multicast and broadcast services in a reliable, low-latency, resource-efficient, and large-scale manner. 3GPP is currently specifying the details of MBS for media delivery via mobile broadband networks. MBS (or "NR MBS" in 5G) aims to reuse cellular infrastructure such as so-called Low Power Low Tower (LPLT) infrastructure. One of the main use cases is the delivery of linear / live media content to smartphones, tablets, vehicles, and other mobile (or fixed) devices. MBS is designed to use the existing (or default) 3GPP infrastructure, but MBS can provide more efficient multicast / broadcast traffic delivery than unicast communication using the same infrastructure. Details of the architectural enhancements of MBS are described in 3GPP Technical Specification (TS) 23.247 V17.1.0, the content of which is incorporated herein by reference.

[0011] MBS uses a shared tunnel to deliver user plane data (e.g., F1 / NG user plane) to multiple UEs that have subscribed to a particular service in order to benefit from more efficient delivery of multicast / broadcast traffic. Thus, if a shared tunnel is established during the session initiation of MBS or there is already a shared tunnel established for a given MBS, the tunnel is shared for the MBS session. When a UE subscribes to an MBS service, an MBS session is established for that service on the user plane that is transmitted via an appropriate shared tunnel (using multicast). More specifically, the traffic of the MBS service is transmitted using multicast via the shared user plane tunnel of that MBS service, via the serving base station or its distributed unit. Note that this is quite different from unicast, which uses a dedicated user plane tunnel for each UE.

[0012] In the current (Release 17) version of the 3GPP specifications, MBS via multicast is supported for UEs in the Radio Resource Control (RRC) connected state. However, there is also interest in extending multicast MBS support to UEs in the RRC inactive state. This, however, may affect RRC inactive state mobility and state transitions as the current specifications do not specify how to provide the multicast configuration required for receiving multicast MBS data in the RRC inactive state to the UE.

Prior Art Documents

Non-Patent Documents

[0013]

Non-Patent Document 1

Non-Patent Document 2

Non-Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0014] The inventors recognized that when using a distributed base station unit, it can be particularly difficult to provide MBS to UEs in the RRC inactive state via multicast. Specifically, in Release 17, after a shared tunnel is established between the central unit and the distributed unit for the MBS service, the central unit distributes the relevant data (PDCP PDU) to the distributed unit. However, it is up to the distributed unit to determine whether to use unicast or multicast on the radio interface. In Release 17, only RRC-connected UEs are supported for receiving MBS (both unicast and multicast), so the distributed unit always has sufficient information (e.g., the number of UEs receiving a specific MBS session via that distributed unit, or the number of UEs interested in receiving) to determine whether to use unicast or multicast in the cell of the distributed unit. However, the distributed unit does not have accurate information (or any information) regarding the number of RRC inactive UEs camping on the cell of the distributed unit, or the number of RRC inactive UEs interested in a specific MBS session, even if such information is available at the central unit or the core network node. For example, a UE can enter the RRC connected state and participate in an MBS session within the cell of the distributed unit. Thus, at this stage, the distributed unit recognizes the presence of the UE and the MBS session received by the UEs in the cell. However, when the UE transitions to RRC inactive, the distributed unit no longer has this information (regardless of whether the UE performed cell reselection). In another example, the distributed unit may not have the correct MBS-related information due to mobility (cell reselection). Specifically, when a UE performs cell reselection to the cell of another base station (or distributed unit), neither the old base station nor the new base station can determine that the number of UEs camping on their respective cells has changed. Therefore, they also cannot determine whether it is appropriate to use unicast or multicast in their cells.Furthermore, a UE that has performed cell reselection may want to continue receiving MBS multicast in the new cell without having to transition to the connected RRC.

Means for Solving the Problem

[0015] Therefore, the present disclosure seeks to provide a method and related apparatus for addressing or at least mitigating the above-described problem (at least in part).

[0016] In one aspect, the present disclosure provides a method executed by a distributed unit of a base station apparatus for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE). The method includes receiving, from a central unit of the base station apparatus, information for identifying at least one MBS session and identifying that at least one MBS session should be provided in the cell via multicast, in at least one of a UE context procedure and a multicast context procedure.

[0017] In one aspect, the present disclosure provides a method executed by a central unit of a base station apparatus for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE). The method includes transmitting, to a distributed unit of the base station apparatus, information for identifying at least one MBS session and identifying that at least one MBS session should be provided in the cell via multicast, in at least one of a UE context procedure and a multicast context procedure.

[0018] In one aspect, the present disclosure provides a method performed by a distributed unit of a base station device that provides a multicast and broadcast service (MBS) session to a user equipment (UE) in an inactive state, the method including receiving, from an associated central unit, information indicating that point-to-multipoint transmission associated with the MBS session is no longer required.

[0019] In one aspect, the present disclosure provides a method performed by a central unit of a base station device that provides a multicast and broadcast service (MBS) session to a user equipment (UE) in an inactive state, the method including transmitting, to a distributed unit of the base station device, information indicating that point-to-multipoint transmission associated with the MBS session is no longer required.

[0020] In one aspect, the present disclosure provides a method performed by a user equipment (UE), the method including receiving, in a cell served by a distributed unit of a base station device, a multicast and broadcast service (MBS) session in an inactive state using point-to-multipoint transmission; performing cell reselection to a new cell; and transmitting, to a network node associated with the new cell, information indicating that the UE has performed cell reselection.

[0021] In one aspect, the present disclosure provides a method performed by a network node, the method including receiving, from a user equipment (UE), information indicating that the UE has performed cell reselection to a cell associated with the network node when a multicast and broadcast service (MBS) session was provided to the UE in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of a base station device before the cell reselection.

[0022] In one aspect, the present disclosure provides a method performed by a user equipment (UE), the method including receiving information indicating whether at least one multicast session is provided in a cell, and performing cell reselection based on information for receiving the multicast session in an inactive state.

[0023] In one aspect, the present disclosure provides a method performed by a base station, the method including transmitting information indicating whether at least one multicast session is provided in a cell when a user equipment (UE) uses the information when performing cell reselection to receive the at least one multicast session in an inactive state.

[0024] In one aspect, the present disclosure provides a distributed unit of a base station apparatus for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE), the distributed unit including means (e.g., a memory, a controller, and a transceiver) for receiving from a central unit of the base station apparatus information identifying at least one MBS session and identifying that the at least one MBS session should be provided in the cell by multicast in at least one of a UE context procedure and a multicast context procedure.

[0025] In one aspect, the present disclosure provides a central unit of a base station apparatus for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE), the central unit including means (e.g., a memory, a controller, and a transceiver) for transmitting to a distributed unit of the base station apparatus information identifying at least one MBS session and identifying that the at least one MBS session should be provided in the cell by multicast in at least one of a UE context procedure and a multicast context procedure.

[0026] In one aspect, the present disclosure provides a distributed unit of a base station device that provides a multicast and broadcast service (MBS) session to a user equipment (UE) in an inactive state. The distributed unit includes means (e.g., a memory, a controller, and a transceiver) for receiving from an associated central unit information indicating that point-to-multipoint transmission associated with the MBS session is no longer essential.

[0027] In one aspect, the present disclosure provides a central unit of a base station device that provides a multicast and broadcast service (MBS) session to a user equipment (UE) in an inactive state. The central unit includes means (e.g., a memory, a controller, and a transceiver) for transmitting to a distributed unit of the base station device information indicating that point-to-multipoint transmission associated with the MBS session is no longer essential.

[0028] In one aspect, the present disclosure provides a user equipment (UE). The user equipment includes means (e.g., a memory, a controller, and a transceiver) for receiving a multicast and broadcast service (MBS) session in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of a base station device, means for performing cell reselection for a new cell, and means for transmitting to a network node associated with the new cell information indicating that the UE has performed cell reselection.

[0029] In one aspect, the present disclosure provides a network node. The network node includes means (e.g., a memory, a controller, and a transceiver) for receiving from a user equipment (UE) information indicating that the UE has performed cell reselection for a cell associated with the network node when a multicast and broadcast service (MBS) session is provided to the UE in an inactive state using point-to-multipoint transmission within a cell served by a distributed unit of a base station device before cell reselection.

[0030] In one aspect, the present disclosure provides a user equipment (UE), the user equipment comprising means (e.g., a memory, a controller, and a transceiver) for receiving information indicating whether at least one multicast session is provided in a cell, and means for performing cell reselection based on information for receiving a multicast session in an inactive state.

[0031] In one aspect, the present disclosure provides a base station, the base station comprising means (e.g., a memory, a controller, and a transceiver) for transmitting information indicating whether at least one multicast session is provided in a cell when a user equipment (UE) uses the information to perform cell reselection for receiving at least one multicast session in an inactive state.

[0032] Aspects of the present disclosure extend to computer program products, such as computer-readable storage media having corresponding systems, apparatuses, and instructions stored therein, the instructions being operable to program a programmable processor to perform the methods described in the aspects and possibilities presented above and / or to program a computer appropriately adapted to provide the apparatuses recited in any of the claims.

[0033] Each feature disclosed and / or illustrated in this specification (which term includes the claims) may be incorporated into the present disclosure independently of (or in combination with) any other disclosed and / or illustrated feature. In particular, without limitation, any feature of any dependent claim subordinate to a particular independent claim may be incorporated into that independent claim optionally in combination or individually.

[0034] Reference will now be made to the accompanying drawings to describe embodiments of the present disclosure by way of example.

Brief Description of the Drawings

[0035]

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Figure 16B

Mode for Carrying Out the Invention

[0036] Overview FIGS. 1 and 2 schematically show a mobile (cellular or wireless) remote communication system 1 to which embodiments of the present disclosure can be applied.

[0037] In this system 1, users of mobile devices 3 (UEs) can communicate with each other and with other users via a base station 5 (and other access network nodes) and a core network 7 using a suitable 3GPP radio access technology (RAT) such as, for example, Evolved Universal Terrestrial Radio Access (E-UTRA) and / or 5G RAT. It will be appreciated that a number of base stations 5 form a (wireless) access network or (R)AN. As will be understood by those skilled in the art, for illustrative purposes, one mobile device 3 and three base stations 5A - 5C are shown in FIG. 1, but the system will typically include other base stations / (R)AN nodes and mobile devices (UEs) when implemented.

[0038] Each base station 5 controls one or more associated cells (either directly or via other nodes such as home base stations, relays, remote radio heads, distributed units, and / or others). A base station 5 that supports the next generation / 5G protocol may be referred to as a "gNB". It will be appreciated 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.

[0039] (In this specification, it is called "distributed" gNB) The functions of gNB 5 may be split between one or more distributed units (DUs) and a central unit (CU). The CU typically performs higher-level functions and communication with the next-generation core, and the DU performs lower-level functions and communication via the air interface with UEs in the vicinity (i.e., of the cell operated by the gNB). It will be understood that the distributed gNB includes the following functional units. The gNB central unit (gNB-CU) is a logical node that hosts the radio resource control (RRC) layer, the Service Data Adaptation Protocol (SDAP) layer, and the Packet Data Convergence Protocol (PDCP) layer of the gNB (or the RRC and PDCP layers of the en-gNB) that controls the operation of one or more gNB-DUs. The gNB-CU terminates the so-called F1 interface connected to the gNB-DU. The gNB distributed unit (gNB-DU) 5D is a logical node that hosts the Radio Link Control (RLC), Medium Access Control (MAC), and Physical (PHY) layers of the gNB or en-gNB. The operation of the gNB-DU is partially controlled by the gNB-CU. One gNB-DU supports one or more cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected to the gNB-CU. The gNB-CU-control plane (gNB-CU-CP) 5C is a logical node that hosts the control plane portion of the RRC and PDCP protocols of the gNB-CU for the en-gNB or gNB. 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. The gNB-CU-User Plane (gNB-CU-UP) 5U is a logical node that hosts the user plane part of the PDCP protocol of the gNB-CU for the en-gNB, and the user plane parts of the PDCP protocol and the 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.

[0040] The mobile device 3 and the base station 5 are connected via an appropriate air interface (e.g., the so-called "NR" air interface, "Uu" interface, and / or the like). The nearby base stations 5 are connected to each other via an appropriate inter-base station interface (e.g., the so-called "Xn" interface, "X2" interface, etc.). The base station 5 is also connected to the core network node via an appropriate interface (e.g., the so-called "NG-U" interface for the user plane, the so-called "NG-C" interface for the control plane, etc.).

[0041] 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 supporting communications in the telecommunication system 1 and, in particular, for subscriber management, mobility management, charging, security, call / session management. For example, the core network 7 of a "next-generation" / 5G system includes user plane entities and control plane entities such as one or more Control Plane Functions (CPF) and one or more User Plane Functions (UPF). The so-called Access and Mobility Management Function (AMF) in 5G, or the Mobility Management Entity (MME) in 4G, is responsible for handling the connection and mobility management tasks of the mobile device 3. The so-called Session Management Function (SMF) is responsible for handling communication sessions for the mobile device 3 such as session establishment, modification, and release. In the example shown in FIG. 1, the core network 7 includes one or more AMFs 9, one or more UPFs 10, and one or more SMFs 11. It will be understood that nodes or functions may have different names in different systems.

[0042] Further details of the core network 7 are shown in FIG. 2, which also shows the interfaces between the respective network nodes or functions. As can be seen from the figure, the core network 7 can typically include, among other things, an Authentication Server Function (AUSF), a Unified Data Management (UDM) entity, a Policy Control Function (PCF), and an Application Function (AF). The core network 7 is coupled to a Data Network (DN), such as the Internet or a similar Internet Protocol (IP)-based network, via the UPF 10. The core network 7 may also be coupled to an Operation and Management (OAM) function (not shown). In this system 1, a Multicast Broadcast Service (MBS) function is provided to the UE 3 via the serving base station 5 of the UE 3 and related core network nodes such as the UPF 10 and the SMF 11. The UPF 10 may be a UPF specific to the MBS, in which case the UPF 10 may be referred to as the MB-UPF10M (for example, dedicated to the provision of the MBS function). Similarly, the SMF 11 may be an SMF specific to the MBS, in which case the SMF 11 may be referred to as the MB-SMF11M. However, it will be understood that any suitable UPF 10 / SMF 11 can be used for the MBS.

[0043] MBS traffic is distributed via a shared user plane tunnel as required. Specifically, the MBS user plane data (e.g., F1-U / NG-U data) of a given MBS session is delivered to the UEs participating in that particular service via the relevant shared tunnel using multicast transmission.

[0044] When the first UE participates in the MBS service, an MBS session is established for that service on the user plane between the core network 7 and the serving base station 5 of the UE (and, where applicable, between the units of the distributed gNB that processes the user plane). For UEs (at least one UE) interested in the MBS service, MBS traffic may be transmitted via multicast through a shared user plane tunnel via a given serving base station or its distributed unit.

[0045] To handle various scenarios that may occur when a UE3 in an inactive state receives or is interested in receiving an MBS session via multicast (point-to-multipoint: PTM) transmission, the following approach may be taken.

[0046] For example, in a first scenario, when UE3 participates in an MBS session within the cell of the distributed unit 5D (or when UE3 performs a handover to the cell while receiving the MBS session), UE3 may initially be in the RRC connected state. When UE3 transitions to the RRC inactive state, the distributed unit 5D no longer has information regarding the MBS session received by UE3 in the cell of the distributed unit 5D. The distributed unit 5D also does not recognize the current UE state (idle or inactive) or the cell selected by UE3 while in the RRC inactive state.

[0047] Advantageously, the distributed unit 5D may be notified regarding the current RRC state of the UE and whether UE3 has performed cell reselection to determine whether (and continue to provide) the PTM service to the RRC inactive UE3 within the cell served by the distributed unit 5D. For example, the central unit 5C may notify the distributed unit 5D in a message for releasing the UE context associated with UE3 that the RRC inactive UE3 is interested in (continuing to receive) the MBS service.

[0048] The central unit 5C can assist the distributed unit 5D in determining to switch to PTM (unicast) transmission for inactive UEs within the cell of the distributed unit 5D. For example, the central unit 5C can notify the distributed unit 5D, in a message for setting up or modifying a multicast context related to at least one MBS session, that the RRC inactive UE 3 is interested in the MBS service (or interested in continuing to receive the MBS service). Effectively, the message may be used to configure the distributed unit 5D such that the MBS session needs to turn on ("always on") or turn off PTM transmission for the inactive UE 3 within the cell of the distributed unit 5D.

[0049] In a second scenario, the UE 3 may be receiving an MBS session in the RRC inactive state in the first cell. When the UE 3 performs cell reselection for a second cell (which can be served by a neighboring base station 5), the distributed unit 5D may be notified that the RRC inactive UE has performed cell reselection. This information may be used by the distributed unit 5D to determine whether to provide PTM transmission in the cell of the distributed unit 5D for a particular MBS session. For example, the UE 3 may be configured to perform a RAN notification area update procedure, a registration procedure, or a small data transmission (SDT) to notify the new base station 5 about the cell reselection. The new base station 5 can contact the access and mobility functions of the UE, which can notify the old distributed unit 5D (via the central unit 5C) that the inactive UE 3 (previously served by the distributed unit 5D) has left the cell. The central unit 5C can instruct the distributed unit 5D to stop / deactivate multicast / PTM transmission in the cell of the distributed unit 5D.

[0050] In a third scenario that can be combined with the first and / or second scenarios, UE3 is configured to obtain information related to the provision of MBS sessions in neighboring cells to assist in cell reselection of the UE. For example, the serving base station 5 / distributed unit 5D can identify the frequencies used by neighboring cells, and UE3 can obtain system information from neighboring cells, such as an appropriate indication to identify whether PTM is always on in a particular neighboring cell, and information to identify any MBS services provided via multicast / PTM in that cell. Alternatively, this information may be provided by the serving base station 5 / distributed unit 5D (along with information identifying the frequencies used by the neighboring cell and / or related cell identifiers). Based on the indication that multicast / PTM is being used in a cell and based on the MBS services provided within that cell, UE3 can prioritize the cells that provide multicast for the MBS services that UE3 is interested in.

[0051] User Equipment (UE) FIG. 3 is a block diagram showing the main components of the mobile device (UE) 3 shown in FIG. 1. As shown, UE3 includes a transceiver circuit 31 operable to transmit signals to and receive signals from nodes connected via one or more antennas 33. Although not necessarily shown in FIG. 3, UE3 of course has all the normal functions of a conventional mobile device (such as user interface 35), which may be provided by any one or any combination of hardware, software, and firmware as needed. The control unit 37 controls the operation of UE3 according to software stored in the memory 39. The software may be pre-installed in the memory 39 and / or may be downloaded, for example, via the telecommunications network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 41, a communication control module 43, and an MBS module 45.

[0052] The communication control module 43 is responsible for processing (generating / sending / receiving) signaling messages and uplink / downlink data packets between the UE 3 and other nodes including the (R)AN node 5 and the core network node. The signaling may include RRC signaling to / from the (R)AN node 5 and / or NG-C / NG-U signaling to / from the core network 7.

[0053] The MBS module 45 is responsible for processing signaling related to the multimedia broadcast service (control signaling and / or MBS traffic), including signaling related to the provision of the multimedia broadcast service via multicast for the UE 3 in the inactive state.

[0054] Access network node (base station) FIGS. 4 and 5 are block diagrams showing the main components of the base station 5 (or a similar access network node) shown in FIG. 1. As shown in FIG. 4, the base station 5 has a transceiver circuit 51 for transmitting and receiving signals to / from user equipment (such as the mobile device 3) via one or more antennas 53, and a network interface 55 for transmitting and receiving signals to / from the core network 7 and neighboring base stations. The base station 5 has a control unit 57 that controls the operation of the base station 5 according to software stored in the memory 59. The software may be pre-installed in the memory 59 and / or downloaded, for example, via the telecommunication network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 61 and at least a communication control module 63. Although not shown in FIG. 4, the network interface 55 typically also includes a base station-base station interface section (such as Xn, etc.) and a core network interface section (such as NG-C / NG-U / N2 / N3).

[0055] The communication control module 63 is responsible for processing (generating / sending / receiving) signaling between the base station 5 and other nodes such as the UE 3 and core network nodes. Such signaling may include, for example, control data (e.g., non-access stratum, radio resource control, system information, paging, etc.) for managing the operation of the mobile device 3. The communication control module 63 is also responsible for processing signaling related to multimedia broadcast services (control signaling and / or MBS traffic), including signaling related to the provision of MBS by multicast for inactive UE 3.

[0056] It will be understood that the communication control module 63 may include several sub-modules (or "layers") to support specific functions. For example, the communication control module 63 may include a PHY sub-module, a MAC sub-module, an RLC sub-module, a PDCP sub-module, an SDAP sub-module, an IP sub-module, an RRC sub-module, etc.

[0057] As shown in FIG. 5, when the base station 5 includes a distributed gNB or en-gNB, the network interface 55 also includes an E1 interface and an F1 interface (F1-C for the control plane and F1-U for the user plane) for communicating signals between the respective functions of the distributed gNB or en-gNB. In this case, the software also includes at least one of the gNB-CU-CP module 5C, the gNB-CU-UP module 5U, and the gNB-DU module 5D. If present, the gNB-CU-CP module 5C hosts the control plane portion of the RRC layer and the PDCP layer of the distributed gNB or en-gNB. If present, the gNB-CU-UP module 5U hosts the user plane portion of the PDCP and the user plane portion of the SDAP layer of the distributed gNB or the PDCP layer of the distributed en-gNB. If present, the gNB-DU module 5D hosts the RLC, MAC, and PHY layers of the distributed gNB or en-gNB.

[0058] Those skilled in the art will understand that the central unit (e.g., 5C and / or 5U) may be implemented and physically located together with the base station, or may be implemented remotely, as a single physical element, or as a cloud-based or virtualized system. It will also be understood that a single central unit may provide services to multiple base stations 5.

[0059] Core network node FIG. 6 is a block diagram showing the main components (e.g., AMF 9, UPF 10, or SMF 11) of the core network node shown in FIG. 1. As shown, the core network node includes a transceiver circuit 71 operable to transmit signals to and receive signals from a connected UE 3 via one or more antennas 73, and to transmit signals to and receive signals from other network nodes (directly or indirectly) via a network interface 75. Signals may be transmitted to and received from the UE 3 directly and / or via the base station 5 or other (R)AN nodes as required. The network interface 75 typically includes an appropriate base station interface (such as S1 / NG-C / NG-U, etc.). The control unit 77 controls the operation of the core network node according to software stored in the memory 79. The software may be pre-installed in the memory 79 and / or downloaded, for example, via the telecommunication network 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 81, a communication control module 83, and (optionally) an MBS module 85.

[0060] The communication control module 83 is responsible for processing (generating / sending / receiving) signaling between the core network node and other nodes such as the UE 3, (R)AN nodes, and other core network nodes.

[0061] For example, when present in the MB-SMF or MB-UPF, the MBS module 85 is responsible for processing signaling related to multimedia broadcast services (control signaling and / or MBS traffic), including signaling related to the provision of MBS via multicast to an inactive UE3.

[0062] Detailed Description The following is an explanation of some exemplary procedures performed by the nodes of the system shown in FIGS. 1 and 2 to support an MBS session for an RRC inactive UE.

[0063] Before discussing these procedures in detail, a brief overview of the protocol data unit (PDU) session change procedure for a UE3 participating in a multicast session MBS reception is provided. The procedure is shown in FIGS. 7 and 8 and is based on FIG. 7.2.1.3-1 of 3GPP TS 23.247 V17.2.0. This procedure may be followed, for example, when UE3 desires to receive an MBS service for the first time before entering the RRC inactive state. Although not shown, it will be understood that before UE3 requests to participate in an MBS session, an MBS session has been created within the core network 7, UE3 knows the identifier (MBS session ID) of the MBS session of at least the multicast group in which the UE can participate (the identifier may be provided to UE3 via an appropriate service notification, for example), and UE3 may have established a PDU session that is registered with the network and can be associated with the multicast session.

[0064] When a first UE3 in the RRC connected state participates in an MBS session, the core network 7 (5GC) triggers an MBS session establishment procedure as specified in section 7.2.1 of 3GPP TS 23.247 (titled "MBS join and Session establishment procedure"). Using this procedure, UE3 notifies the core network 7 that the UE is interested in participating in the multicast MBS session. The first accepted UE participation request triggers the establishment of a multicast MBS session to the radio access network (serving base station 5) and UE3. As seen in steps 15 to 18 of Figure 8, the multicast data is delivered using an MBS-specific UPF called MB-UPF10M. Between the radio access network (serving base station 5) and UE3, the multicast data can be transmitted using either a point-to-point (PTP) bearer or a point-to-multipoint (PTM) bearer, generally as shown in step 18. If multicast delivery is not supported across the network, the multicast data is transmitted using the UE-specific PDU session via the associated UPF10, generally as shown in steps 19 to 21. However, this delivery method is inefficient when multiple UE3s are interested in the same MBS session, especially since the multicast data needs to be delivered to each UE3 individually using their associated PDU sessions and UPF10s, rather than using a shared tunnel and common (PTM) bearer (e.g., between MB-UPF10M and base station 5 / distributed unit 5D).

[0065] Scenario 1 In this case, when UE3 participates in an MBS session in the cell of distributed unit 5D (or when UE3 performs a handover to the cell while receiving an MBS session), UE3 may initially be in the RRC connected state. Therefore, at this stage, the distributed unit 5D recognizes the presence of UE3 and the presence of the MBS session received by UE3 in the cells managed by the distributed unit 5D. When UE3 transitions to the RRC inactive state, the distributed unit 5D no longer has this information.

[0066] RRC is controlled by the central unit 5C. Thus, when UE3 transitions between RRC states, the central unit 5C recognizes the current UE state. However, the distributed unit 5D does not recognize the current UE state nor the cell selected by UE3 while in the RRC inactive state.

[0067] The only thing the distributed unit 5D knows is that the UE context has been released by the central unit 5C, but the distributed unit 5D does not know whether UE3 has transitioned to the RRC idle state or (UE3 can still receive MBS using multicast) to the RRC inactive state.

[0068] The following is an explanation of several ways in which the distributed unit 5D can be notified regarding the current RRC state of the UE and whether UE3 has performed cell reselection in order to determine whether to provide PTM services to the RRC inactive UE3 within the cell served by the distributed unit 5D.

[0069] For example, when three UEs 3 are receiving the MBS service in the RRC connected state, the distributed unit 5D can determine to use respective PTP bearers for each UE 3. If one of the UEs 3 that is still interested in the MBS session enters the RRC inactive state, the distributed unit 5D needs to know about the UE 3 that has entered the RRC inactive state so that the distributed unit 5D can set up PTM transmission for the RRC inactive UE 3.

[0070] FIG. 9 is a signaling (timing) diagram schematically showing a procedure to assist the distributed unit 5D in determining to switch to PTM (unicast) transmission for an inactive UE within the cell of the distributed unit 5D. In this case, the central unit 5C notifies the distributed unit 5D in a message for releasing the UE context associated with UE 3 that the RRC inactive UE 3 is interested in the MBS service (continuing to receive).

[0071] In step 1, the central unit 5C sends a message for releasing the UE context associated with UE 3 to the distributed unit 5D. The message (such as a UE context request, etc.) includes information for identifying UE 3 (UE ID), information for identifying at least one MBS session that UE 3 is interested in (MBS session ID / TMGI), and an appropriate PTM multicast radio bearer (MRB) configuration for the MBS session. For example, the PTM MRB configuration may be included in a message for releasing the UE context associated with UE 3 (such as a UE context release message, and / or others). The RRC release message may be included in the message for releasing the UE context (shown in FIG. 9) or may be sent separately. Based on the MBS session information received from the central unit 5C, the distributed unit 5D knows which MBS services UE 3 will (continue to) receive after UE 3 migrates to the RRC inactive mode.

[0072] In step 2, an RRC release (including an appropriate PTM MRB configuration from the central unit 5C for the MBS session) is sent from the distributed unit 5D to the UE3. The UE3 obtains the PTM MRB configuration from the RRC release message. As a note, the PTM MRB configuration for establishing the PTM MRB usually includes appropriate PDCP, RLC, MAC, multicast / MBS control channel (MCCH), and multicast / MBS traffic channel (MTCH) configurations.

[0073] In step 3, (when the distributed unit 5D determines that there is at least one inactive UE in the cell of the distributed unit 5D based on the information included in the UE context release message), the distributed unit 5D decides to keep the PTM transmission to at least one inactive UE3 in the cell of the distributed unit 5D always on. This decision may be based on, for example, the number of UE3s reaching or exceeding an associated threshold (where the inactive UE can be "one"). It will be recognized that different (higher) thresholds can be used when determining whether to use PTM for the connected UE3s in the cell.

[0074] FIG. 10 is a signaling (timing) diagram schematically showing another procedure that helps the distributed unit 5D decide to switch to PTM (unicast) transmission for the inactive UEs in the cell of the distributed unit 5D.

[0075] In this case, the central unit 5C notifies the distributed unit 5D in a message for setting up or changing a multicast context associated with at least one MBS session that the RRC inactive UE3 is interested in the MBS service (or is interested in continuing to receive the MBS service). Such a message is shown in step 1 of FIG. 10. Substantially, the central unit 5C configures the distributed unit 5D in which the PTM transmission of the MBS session needs to be turned on for the inactive UE3 within the cell of the distributed unit 5D. This is achieved by including appropriate information in the message transmitted in step 1. The information may be an instruction related to PTM, such as an instruction on whether the PTM should be turned on (always on) or an instruction that the PTM in the cell may be turned off. In the specific example illustrated in FIG. 10, the multicast context setup request is adapted to include an instruction for identifying whether the PTM should be on or off. It will be understood that the multicast context change request message may be adapted in a similar manner (if an existing multicast context exists).

[0076] The instruction may be in the form of a "PTM always on" instruction (or similar), in which case the distributed unit 5D knows that there is at least one RRC inactive mode UE3 interested in the MBS session. In other words, this type of instruction may need to be transmitted to at least the first inactive UE3 within the cell of the distributed unit 5D (however, this type of instruction may also be transmitted to any subsequent UE).

[0077] The instruction may be in the form of an instruction that "PTM can be off", in which case the central unit 5C knows that there is no inactive UE3 still interested in receiving the MBS session within the cell of the distributed unit 5D. Therefore, in this case, the distributed unit 5D does not need to provide (or continue to provide) PTM transmission in the cell of the distributed unit 5D for that specific MBS service.

[0078] In this case, it will be understood that the base station 5 can provide the UE3 with an appropriate PTM MRB configuration for the MBS session in the RRC release message as described above with reference to FIG. 9. Alternatively, the PTM MRB configuration may be provided using a system information block. For example, the system information may include the PTM MRB configuration itself or information for receiving the MCCH, and for each MBS session, the relevant PTM MRB configuration (e.g., PDCP, RLC, MAC, MTCH configuration) may be notified via the MCCH.

[0079] In summary, the distributed unit (which provides MBS in the cells of the distributed unit) receives from the central unit information identifying at least one MBS session and information identifying that at least one MBS session is provided in the cell via multicast (using point-to-multipoint transmission) to user equipment (UE) in an inactive state. The information may be included in an appropriately formatted UE context release message, which may also include a further message for releasing the UE to the inactive state. The further message may include information for configuring each multicast radio bearer for at least one MBS session. Alternatively, the information for configuring the multicast radio bearer may be included in a message for setting up or modifying a multicast context associated with at least one MBS session. The distributed unit can transmit the configuration information for configuring each multicast radio bearer for receiving at least one MBS session in the inactive state to the UE (e.g., in a message for releasing the UE's connection, in a system information block, or via a multicast control channel). The configuration information enables a UE in the RRC inactive state to use multicast to receive at least one MBS session.

[0080] Scenario 2 The following is an explanation of another MBS-related scenario, specifically several ways for the distributed unit 5D to be notified that an RRC-inactive UE has performed cell reselection. This information may be used by the distributed unit 5D to determine whether to provide PTM transmission within the cell of the distributed unit 5D for a specific MBS session.

[0081] First, UE3 may be receiving an MBS session in an RRC-inactive state in the first cell. UE3 may have obtained the relevant PTM MRB configuration as described above. At some point, UE3 may perform cell reselection to a second cell (which may be served by a neighboring base station 5). Usually, if the tracking area of the second cell is within the UE's tracking area list, UE3 does not perform a registration update procedure. In other words, UE3 camps on the second cell and remains in the RRC-inactive state.

[0082] In this scenario, if this UE3 is the last RRC-inactive UE within the first (source) cell, the source distributed unit 5D is unaware that there are no longer any RRC-inactive UEs interested in the MBS service. Since the source distributed unit 5D has to keep the PTM transmission operating (always on) within the cell of the distributed unit 5D, it may result in waste of resources. If only RRC-connected UE3s interested in that specific MBS session exist, it may be more appropriate for the source distributed unit 5D to use PTP transmission for those UE3s (especially depending on the number and / or capabilities of the UEs).

[0083] Therefore, for MBS multicast within the cell of the distributed unit 5D, the following procedure, which will be described with reference to FIGS. 11 to 16, can be used to assist the distributed unit 5D in making an appropriate decision.

[0084] FIG. 11 is a signaling (timing) diagram schematically showing a procedure for notifying a distributed unit 5D that a non-active UE (previously served by the distributed unit 5D) has left the cell of the distributed unit 5D.

[0085] More specifically, while receiving an MBS session via the cell of the distributed unit 5D (denoted as the "old DU" in FIG. 11), the UE3 performs cell reselection for a cell served by another base station 5 (denoted as the "new gNB" in FIG. 11). Next, in step 1, the UE3 notifies the new base station 5 that the UE3 has performed cell reselection. For example, the information indicating that the UE3 has performed cell reselection may be included in at least one of a registration request message, a resume request message, a radio access network (RAN) notification area update message, and a small data transmission message. In step 2, the new base station 5 notifies the old base station (its central unit 5C) via the base station - base station interface that the UE3 has performed cell reselection for the cell of the new base station 5. The central unit 5C transfers this instruction to the distributed unit 5D in step 3, whereby the distributed unit 5D can make an appropriate decision regarding whether to maintain multicast transmission for the related MBS session or release the related MRB.

[0086] FIG. 12 is a signaling (timing) diagram schematically showing an example of a procedure for notifying a distributed unit 5D that a non-active UE3 has left the cell of the distributed unit 5D. In this case, the new base station 5 determines that the UE3 has performed cell reselection in the registration procedure initiated by the UE3 and notifies the distributed unit 5D. The UE3 is initially in the RRC non-active state and receives the MBS session using the related MRB configuration within the cell of the distributed unit 5D (denoted as the "old DU" in FIG. 12). Thereby, multicast MBS transmission is performed within the cell of the distributed unit 5D.

[0087] UE3 performs cell reselection and then, in step 1, generates and transmits a message appropriately formatted to register the new cell of UE3 with the mobility and access management function (in this case, the new AMF9’) associated with the new cell. The new AMF9’ and the AMF9 associated with the old cell of the UE execute an appropriate UE context transfer procedure as generally shown in steps 2 and 3. The new AMF9’ may be the same as the AMF9 associated with the old cell of the UE, in which case it will be understood that there is no need to execute UE context transfer (i.e., steps 2 and 3 are optional). At this point, the old distributed unit 5D of the UE is unaware of the cell reselection.

[0088] Advantageously, AMF9 is configured to notify the central unit 5C that UE3 has performed cell reselection and has detached from the cell of the distributed unit 5D associated with this central unit 5C. This notification may be sent when receiving a message in step 2 or (when there is no AMF change) when receiving a registration request in step 1.

[0089] In step 5, the central unit 5C notifies the distributed unit 5D that it can stop PTM transmission. It will be understood that step 5 can only be executed after the central unit 5C determines that the non-active UE3 interested in a given MBS session no longer exists within the cell.

[0090] If appropriate, based on the notification received in step 5, the source distributed unit 5D may, in step 6, confirm that the UE3 in question was the last non-active UE interested in the MBS service, and the source distributed unit 5D may decide to turn off PTM transmission within the cell.

[0091] FIG. 13 is a signaling (timing) diagram schematically showing an example of a procedure for notifying a distributed unit 5D that an inactive UE3 has left the cell of the distributed unit 5D. In this case, the new base station 5 determines that the UE3 has performed cell reselection in the RAN notification area update procedure started by the UE3 and notifies the distributed unit 5D.

[0092] As shown in the figure, while the UE3 is receiving an MBS session via PTM in the cell of the distributed unit 5D (denoted as "last serving gNB-DU" in FIG. 13), it is initially in the RRC inactive state and the connection management (CM) connected state.

[0093] In this case, following cell reselection to a new cell served by the new base station 5', the UE3 executes an appropriate RAN notification area update procedure to notify the new base station 5' of the cell reselection. Thus, in step 1, the UE3 generates and transmits an appropriately formatted RRC resume request (which requests to resume an inactive RRC connection at the new base station 5'). The request also includes a RAN notification area update. In step 2, the new base station 5' contacts the central unit 5C of the UE's old base station (denoted as "last serving gNB-CU" in FIG. 13) to obtain the UE context associated with the UE3. Upon receiving this message, the central unit 5C generates and transmits, in step 4, an appropriately formatted multicast context setup request, or multicast context change request message (as described above with reference to FIG. 10 for example), which includes an indication identifying whether PTM should be on or off in the cell of the distributed unit 5D.

[0094] FIG. 14 is a signaling (timing) diagram schematically showing an example of a procedure for notifying a distributed unit 5D that an inactive UE3 has left the cell of the distributed unit 5D. In this case, UE3 does not need to execute a RAN notification area update procedure or a registration procedure (for example, when a tracking area of a new cell is within the tracking area list of UE3).

[0095] In this case, UE3 is configured to perform a small data transmission (SDT) to notify a new base station (the new central unit 5C' in FIG. 14) of cell reselection.

[0096] More specifically, before this procedure, UE3 is in the RRC inactive state and receives an MBS session via PTM in the cell of the distributed unit 5D (denoted as "old DU" in FIG. 14). When UE3 performs cell reselection, in step 1, UE3 sends information for identifying the MBS session (by their associated MBS session ID and / or TMGI) to the new base station / central unit 5C' using an SDT message. Upon receiving this message, in step 2, the new central unit 5C' contacts the central unit 5C of the old base station of the UE (denoted as "old CU" in FIG. 14) to obtain the UE context associated with UE3.

[0097] In step 3, the old central unit 5C determines, based on the message from the new central unit 5C', that the UE3 in question has performed cell reselection to another cell.

[0098] In step 4, if the old central unit 5C determines that this specific UE3 was the last inactive UE that received an MBS session in the cell of the old distributed unit 5D via multicast / PTM, the old central unit 5C instructs the old distributed unit 5D to deactivate the relevant PTM transmission, if appropriate. However, it should be understood that there may be UEs with RRC connections receiving the same session, in which case the distributed unit 5D may decide to continue using PTM transmission for those UEs.

[0099] If the old distributed unit 5D confirms that UE3 was the last UE interested in the MBS service, the old distributed unit 5D may decide to turn off PTM in the cell in step 5.

[0100] Scenario 3 Referring again to Figure 8, as shown in step 16, the central unit 5C sends PDCP PDUs to the distributed unit 5D. As shown in step 18, it is up to the distributed unit 5D to decide whether to map the received PDCP PDUs to a PTM leg or a PTP leg (between the distributed unit 5D and UE3). This is a dynamic decision of the distributed unit 5D, and the distributed unit 5D does not need to notify the central unit 5C of the decision. The decision changes over time, by the UE, and by the MBS session. Thus, UE3 having a control plane connection with the central unit 5C will also not be able to know whether the cell, for example a neighboring cell, uses PTM or PTP as the last leg for the MBS session that UE3 is interested in.

[0101] The following is an explanation of some exemplary ways to provide this information to UE3.

[0102] In the first option shown in FIGS. 15 and 16(a), the serving base station 5 (serving cell 500) indicates the frequency of the neighboring cell 501 to the UE3. Specifically, as shown in step 1 of FIG. 15, the serving cell 500 transmits information for identifying neighboring frequencies via the MCCH.

[0103] In step 2, the UE3 monitors the identified frequency and acquires system information from the neighboring cell 501, or acquires at least a part of the system information block related to the MCCH in the neighboring cell 501, or the system information block. The system information / MCCH of the neighboring cell 501 includes an appropriate indication for identifying whether PTM is always on within the cell 501 and information for identifying any MBS service provided via multicast / PTM. This information is shown in detail in FIG. 16A.

[0104] Based on this indication and the identified MBS service, the UE3 can prioritize the cell 501 that provides multicast for the MBS service of interest to the UE3.

[0105] If there are RRC inactive UEs receiving the MBS service in the neighboring cell 501, it will be understood that the neighboring cell 501 continues to transmit multicast data to those UEs by PTM and continues to broadcast the PTM always-on indication associated with the MBS session ID or TMGI.

[0106] In another option shown in FIG. 16B, the serving cell 500 may be configured to transmit PTM-related information associated with the neighboring cell 501. For example, for each neighboring cell 501, the serving cell 500 can broadcast the associated PTM always-on indication, the associated cell ID, information for identifying the used frequency, and at least one MBS session ID or TMGI. This information may be transmitted in the MCCH within the cell 500 or in one or more system information blocks.

[0107] Changes and Alternatives As described above in detail, those skilled in the art will understand that, while benefiting from the disclosure embodied in the above embodiments, some changes and alternatives can be made to those embodiments. By way of example, only some of these alternatives and changes are described here.

[0108] It will be understood that cell reselection may trigger either a RAN notification area update or a registration update depending on the selected cell. Therefore, the UE can start either the procedure illustrated in FIG. 12 or the procedure illustrated in FIG. 13 depending on the selected cell.

[0109] Base stations in a 5G / NR communication system are typically called new radio base stations (“NR-BS”) or “gNBs”, but it will be understood that these may more typically be referred to using the term “eNB” (or 5G / NReNB) associated with long term evolution (LTE) base stations (which are also commonly called “4G” base stations). 3GPP TS 38.300 V16.7.0 and 3GPP TS 37.340 V16.7.0 define, inter alia, the following nodes. gNB: A node that provides NR user plane and control plane protocol terminations to the UE and is connected to the 5G core network (5GC) via the NG interface. ng-eNB is a node that provides E-UTRA user plane and control plane protocol terminations to the UE and is connected to the 5GC via the NG interface. En-gNB is a node that provides NR user plane and control plane protocol terminations to the UE and functions as a secondary node in E-UTRA-NR dual connectivity (EN-DC). NG-RAN nodes are either gNBs or ng-eNBs.

[0110] It will be understood that the above-described embodiments are applicable to 5G New Radio and LTE systems (E-UTRAN), and any future generation systems. A base station that supports the E-UTRA / 4G protocol may be referred to as an "eNB", and a base station that supports the NextGeneration / 5G protocol 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, and / or any other 3GPP or non-3GPP communication protocols.

[0111] In the above description, for ease of understanding, the UE, access network node, and data network node are described as having several individual modules (such as a communication control module). These modules can be provided in this way, for example, in certain applications where existing systems have been modified to implement the present disclosure, but in other applications, such as a system designed from the beginning with the features of the present invention in mind, these modules can be incorporated into the overall operating system or code, so these modules may not be distinguishable as separate entities. These modules may be implemented in software, hardware, firmware, or a combination thereof.

[0112] Each control unit can include any suitable form of processing circuit, 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) circuits, internal memory / cache (program and / or data), processing registers, communication buses (e.g., control bus, data bus, and / or address bus), direct memory access (DMA) functions, hardware or software-implemented counters, pointers, and / or timers, etc.

[0113] In the above embodiments, a number of software modules have been described. Those skilled in the art will understand that the software modules may be provided in a compiled form or in an uncompiled form, and may be supplied to the UE, the access network node, and the data network node as signals via a computer network or a recording medium. Further, the functions executed by some or all of this software may be executed using one or more dedicated hardware circuits. However, the use of software modules is preferred because it facilitates the update of the UE, the access network node, and the data network node to update their functions.

[0114] The above embodiments are also applicable to "non-mobile" or generally fixed user equipment.

[0115] The method executed by the distributed unit may further include transmitting to the UE information for configuring each multicast radio bearer for receiving at least one MBS session by the non-active UE. In this case, the transmission may include transmitting information for configuring each multicast radio bearer, which uses at least one of a message for releasing the UE's connection, a system information block, and a multicast control channel.

[0116] The information for configuring each multicast radio bearer may include at least one configuration among Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), Multicast Control Channel (MCCH), and Multicast Traffic Channel (MTCH) associated with the MBS session.

[0117] In the UE context procedure, the distributed unit can receive, from the central unit, a message for releasing the UE context associated with the UE. The message includes information that identifies at least one MBS session and identifies that at least one MBS session should be provided in the cell via multicast.

[0118] The method performed by the distributed unit may further include receiving, from the central unit, a further message for releasing the UE to an inactive state. The further message may include information for configuring each multicast radio bearer for at least one MBS session.

[0119] In the multicast context procedure, the distributed unit can receive, from the central unit, a message for setting up or modifying the multicast context associated with at least one MBS session. The message for setting up or modifying the multicast context may include information that identifies whether it is essential to turn on multicast for at least one MBS session in the cell.

[0120] The method performed by the distribution unit may further include transmitting data for at least one MBS session via multicast in a cell, based on information identifying at least one MBS session and identifying that it is essential that at least one MBS session is provided in the cell via multicast.

[0121] Multicast may include point-to-multipoint transmission between the distribution unit and a plurality of UEs.

[0122] The information received by the distribution unit from the associated central unit may include at least one of information indicating that the UE has reselected for another cell, information identifying at least one MBS session, and information identifying whether multicast should be turned on for at least one MBS session within the cell of the distribution unit.

[0123] The method performed by the distribution unit may further include deactivating point-to-multipoint transmission associated with the MBS session or switching from point-to-multipoint transmission associated with the MBS session to point-to-point transmission, based on the information.

[0124] The information received by the network node from the UE may be included in at least one of a registration request message, a resume request message, a radio access network (RAN) notification area update message, and a small data transmission message. The information may be used when controlling an MBS session in the cell served by the distribution unit.

[0125] The network node may be a base station or a core network node responsible for the access and mobility role of the UE.

[0126] Information indicating whether at least one multicast session is provided in a cell may be included in at least one of a message for releasing the UE's connection, a system information block associated with the cell, and a multicast control channel associated with the cell. This information includes at least one of information identifying that a multicast session must be available in the cell, information identifying at least one multicast and broadcast service (MBS) session provided in the cell, information identifying the cell, and information identifying the frequency associated with the cell.

[0127] Performing cell reselection based on this information may include preferring the cell if the information indicates that at least one multicast session is provided in the cell.

[0128] Information identifying at least one multicast session may include, for each multicast session, a respective multicast session identifier or a respective temporary mobile group identifier.

[0129] Various other modifications will be apparent to those skilled in the art and are not further elaborated here.

[0130] For example, all or part of the exemplary embodiments disclosed above can be described as follows in the appendices, but are not limited thereto. (Appendix 1) A method performed by a distributed unit of a base station apparatus to provide multicast and broadcast services (MBS) to a user equipment (UE) in a cell, receiving, in at least one of a UE context procedure and a multicast context procedure, information from a central unit of the base station apparatus, the information identifying at least one MBS session and identifying that at least one MBS session should be provided in the cell via multicast A method comprising (Appendix 2) Further comprising transmitting to the UE information for configuring each multicast radio bearer for reception of at least one MBS session by the UE in an inactive state The method according to Appendix 1 (Appendix 3) Transmitting comprises A message for releasing the connection of the UE, A system information block, and A multicast control channel, Including transmitting information for configuring each multicast radio bearer using at least one of The method according to Appendix 2 (Appendix 4) The information for configuring each multicast radio bearer is Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), Multicast Control Channel (MCCH), and Multicast Traffic Channel (MTCH) associated with the MBS session, Including a configuration for at least one of The method according to Appendix 2 or 3 (Appendix 5) Receiving includes receiving, in a UE context procedure, from a central unit, a message for releasing the UE context associated with the UE, the message identifying at least one MBS session and including information identifying that at least one MBS session should be provided in the cell via multicast The method according to any one of Appendices 1 to 4 (Appendix 6) Further comprising receiving from the central unit a further message for releasing the UE to an inactive state The method according to any one of Appendices 1 to 5. (Appendix 7) A further message includes information for configuring each multicast radio bearer for at least one MBS session. The method according to Appendix 6. (Appendix 8) Receiving includes receiving, from a central unit, a message for setting up or changing a multicast context associated with at least one MBS session in a multicast context procedure. The method according to any one of Appendices 1 to 7. (Appendix 9) A message for setting up or changing a multicast context includes information for identifying whether it is essential to turn on multicast for at least one MBS session in a cell. The method according to Appendix 8. (Appendix 10) Further including transmitting, via multicast, data for at least one MBS session into a cell, based on information for identifying at least one MBS session and for identifying that it is essential for at least one MBS session to be provided in the cell via multicast. The method according to any one of Appendices 1 to 9. (Appendix 11) Multicast includes point-to-multipoint transmission between a distributed unit and a plurality of UEs. The method according to any one of Appendices 1 to 10. (Appendix 12) A method performed by a central unit of a base station apparatus for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE), In at least one of a UE context procedure and a multicast context procedure, identifying at least one MBS session and transmitting information identifying that at least one MBS session should be provided in a cell via multicast to a distributed unit of a base station apparatus A method comprising the above (Appendix 13) A method executed by a distributed unit of a base station apparatus that provides a multicast and broadcast service (MBS) session to a user equipment (UE) in an inactive state, comprising: Receiving, from an associated central unit, information indicating that point-to-multipoint transmission associated with the MBS session is no longer required A method comprising the above (Appendix 14) The information is information indicating that the UE has reselected to another cell, information identifying at least one MBS session, and information identifying whether multicast for at least one MBS session should be turned on in the cell of the distributed unit, including at least one of the above, The method according to Appendix 13 (Appendix 15) Further comprising deactivating point-to-multipoint transmission associated with the MBS session or switching from point-to-multipoint transmission associated with the MBS session to point-to-point transmission based on the information The method according to Appendix 13 or 14 (Appendix 16) A method executed by a central unit of a base station apparatus that provides a multicast and broadcast service (MBS) session for a user equipment (UE) in an inactive state, comprising: Transmitting, to a distributed unit of the base station apparatus, information indicating that point-to-multipoint transmission associated with the MBS session is no longer required A method comprising: (Appendix 17) A method performed by a user equipment (UE), the method comprising: Receiving a multicast and broadcast service (MBS) session in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of a base station apparatus; Performing cell reselection for a new cell; Transmitting information indicating that the UE has performed cell reselection to a network node associated with the new cell. A method comprising: (Appendix 18) A method performed by a network node, the method comprising: Before cell reselection, when a multicast and broadcast service (MBS) session is provided to a UE in an inactive state using point-to-multipoint transmission within a cell served by a distributed unit of a base station apparatus, receiving from the user equipment (UE) information indicating that the UE has performed cell reselection for a cell associated with the network node A method comprising: (Appendix 19) The information includes: A registration request message, A resume request message, A radio access network (RAN) notification area update message, and A small data transmission message, wherein at least one of the above is included, The method according to Appendix 17 or 18. (Appendix 20) The information is used when controlling an MBS session in a cell served by a distributed unit. The method according to any one of Appendices 17 to 19. (Appendix 21) The network node is a base station or a core network node responsible for the access and mobility roles of the UE. The method according to any one of Supplementary Notes 17 to 20. (Supplementary Note 22) A method executed by a user equipment (UE), receiving information indicating whether at least one multicast session is provided in a cell; in an inactive state, performing cell reselection based on information for receiving a multicast session; A method including the above. (Supplementary Note 23) The information includes a message for releasing the connection of the UE, a system information block associated with the cell, and a multicast control channel associated with the cell, including at least one of the above. The method according to Supplementary Note 22. (Supplementary Note 24) The information is information identifying that it is essential that a multicast session is available in the cell, information identifying at least one multicast and broadcast service (MBS) session provided in the cell, information identifying the cell, and information identifying the frequency associated with the cell, including at least one of the above. The method according to Supplementary Note 22 or 23. (Supplementary Note 25) Performing cell reselection based on the information includes preferring the cell when the information indicates that at least one multicast session is provided in the cell. The method according to any one of Supplementary Notes 22 to 24. (Supplementary Note 26) Information for identifying at least one multicast session includes, for each multicast session, its respective multicast session identifier or its respective temporary mobile group identifier. The method according to any one of Supplementary Notes 1, 5, 12, 14, and 24. (Supplementary Note 27) A method performed by a base station, when performing cell reselection for receiving at least one multicast session in an inactive state, transmitting information indicating whether at least one multicast session used by a user equipment (UE) is provided in the cell A method including the above. (Supplementary Note 28) A distributed unit of a base station apparatus for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE), means for receiving, from a central unit of the base station apparatus, information for identifying at least one MBS session and for identifying that at least one MBS session should be provided in the cell via multicast in at least one of a UE context procedure and a multicast context procedure A distributed unit of a base station apparatus comprising the above. (Supplementary Note 29) A central unit of a base station apparatus for providing multicast and broadcast services (MBS) in a cell to a user equipment (UE), means for transmitting, to a distributed unit of the base station apparatus, information for identifying at least one MBS session and for identifying that at least one MBS session should be provided in the cell via multicast in at least one of a UE context procedure and a multicast context procedure A central unit of a base station apparatus including the above. (Supplementary Note 30) A distributed unit of a base station apparatus for providing a multicast and broadcast services (MBS) session to an inactive user equipment (UE), Means for receiving from an associated central unit information indicating that point-to-multipoint transmission associated with an MBS session is no longer mandatory A distributed unit of a base station apparatus, comprising: (Appendix 31) A central unit of a base station apparatus that provides a multicast and broadcast service (MBS) session for a user equipment (UE) in an inactive state, comprising: Means for transmitting to a distributed unit of the base station apparatus information indicating that point-to-multipoint transmission associated with the MBS session is no longer mandatory A central unit of a base station apparatus, comprising: (Appendix 32) A user equipment (UE), comprising: Means for receiving a multicast and broadcast service (MBS) session in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of a base station apparatus; Means for performing cell reselection for a new cell; Means for transmitting to a network node associated with the new cell information indicating that the UE has performed cell reselection A user equipment (UE), comprising: (Appendix 33) A network node, comprising: Means for receiving from a user equipment (UE) information indicating that the UE has performed cell reselection for a cell associated with the network node when a multicast and broadcast service (MBS) session was provided to the UE in an inactive state using point-to-multipoint transmission in a cell served by a distributed unit of a base station apparatus before cell reselection A network node, comprising: (Appendix 34) A user equipment (UE), comprising: Means for receiving information indicating whether at least one multicast session is provided in a cell Means for performing cell reselection based on information for receiving a multicast session in an inactive state; A user equipment (UE) comprising the same. (Appendix 35) A base station, Means for transmitting information indicating whether at least one multicast session provided in the cell is used by a user equipment (UE) when performing cell reselection for receiving at least one multicast session in an inactive state; A base station comprising the same.

[0131] This application claims the benefit of priority based on UK Patent Application No. 2204294.9 filed on Mar. 25, 2022, the disclosure of which is incorporated herein by reference in its entirety.

Explanation of Reference Signs

[0132] 1 Telecommunication system 3 Mobile device 5 Base station 7 Core network 9 AMF 10 UPF 11 SMF 31 Transceiver circuit 33 Antenna 35 User interface 37 Control unit 39 Memory 41 Operating system 43 Communication control module 45 MBS module 51 Transceiver circuit 53 Antenna 55 Network interface 57 Control unit 59 Memory 61 Operating system 63 Communication control module 5C gNB-CU-CP module 5U gNB-CU-UP module 5D gNB-DU module 71 Transceiver circuit 75 Network interface 77 Control unit 79 Memory 81 Operating system 83 Communication control module 85 MBS module

Claims

1. A distributed unit of a base station for providing multicast and broadcast services (Multicast and Broadcast Services: MBS) in a cell to a user equipment (User Equipment: UE) in a Radio Resource Control (RRC) inactive state, means for receiving, from a central unit of the base station, MBS session information indicating whether a communication mode in multicast on at least one MBS session to the UE in the RRC inactive state should be activated or deactivated in the cell; means for determining, based on the MBS session information, to activate or deactivate the communication mode in multicast on at least one MBS session to the UE in the RRC inactive state; A distributed unit comprising the above.

2. Comprising means for transmitting to the UE configuration information for configuring respective multicast radio bearers for the at least one MBS session, The distributed unit according to Claim 1.

3. The configuration information is a message for releasing the connection of the UE, a message for releasing a UE context associated with the UE, a message for setting the UE to the RRC inactive state, a message for setting up or changing a multicast context associated with the at least one MBS session, a system information block, and a multicast control channel (Multicast Control Channel: MCCH), and is transmitted using at least any one of the above, The distributed unit according to Claim 2.

4. The configuration information is Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC), a multicast control channel (Multicast Control Channel: MCCH), and a Multicast Traffic Channel (MTCH) associated with the at least one MBS session comprising a configuration for at least one of the distributed unit according to claim 2

5. means for transmitting to the UE information indicating that the communication mode in multicast on at least one MBS session to the UE in the RRC inactive state is activated in the cell the distributed unit according to any one of claims 1 to 4

6. a central unit of a base station for providing multicast and broadcast services (MBS) to a user equipment (UE) in a Radio Resource Control (RRC) inactive state in a cell, means for transmitting MBS session information to the distributed unit of the base station, the MBS session information indicating whether the communication mode in multicast on at least one MBS session to the UE in the RRC inactive state should be activated or deactivated in the cell, wherein the MBS session information is used in the distributed unit to determine whether to activate or deactivate the communication mode in multicast on at least one MBS session to the UE in the RRC inactive state central unit

7. the MBS session information is included in a multicast context setup request message or a multicast context change request message the central unit according to claim 6

8. the MBS session information indicates the at least one MBS session the central unit according to claim 6 or 7

9. the MBS session information is a request for a UE context from another base station, and information indicating that the UE has reselected to another cell from a core network node for mobility management, transmitted when the central unit receives at least one of the central unit according to claim 6 or 7

10. A method in a distributed unit of a base station for providing multicast and broadcast services (MBS) to a user equipment (UE) in a radio resource control (RRC) inactive state in a cell, comprising: receiving, from a central unit of the base station, MBS session information indicating whether a multicast communication mode on at least one MBS session to the RRC inactive state UE should be activated or deactivated in the cell; determining, based on the MBS session information, to activate or deactivate the multicast communication mode on at least one MBS session to the RRC inactive state UE; A method comprising the above. **Claim 11** A method in a central unit of a base station for providing multicast and broadcast services (MBS) to a user equipment (UE) in a radio resource control (RRC) inactive state in a cell, comprising: transmitting, to a distributed unit of the base station, MBS session information indicating whether a multicast communication mode on at least one MBS session to the RRC inactive state UE should be activated or deactivated in the cell, wherein the MBS session information is used in the distributed unit to determine to activate or deactivate the multicast communication mode on at least one MBS session to the RRC inactive state UE. A method.

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