Access network node, further access network node, mobile device, and method

Abstract

A communications system (1) is disclosed in which a first access network node (base station) receives information indicative of whether a second access network node supports Multicast and Broadcast Services (MBS), and interactions, such as handovers, between the first and second access network nodes are controlled based on the information.

Description

[Technical Field]

[0001] The present disclosure relates to wireless communication systems and devices therein that operate in accordance with 3rd Generation Partnership Project (3GPP®) standards or equivalents or derivatives thereof. The present disclosure has particular, but not exclusive, relevance to improvements relating to the control plane for multimedia broadcast services in so-called "5G" (or "next generation") systems. [Background technology]

[0002] The latest evolution of the 3GPP® standards is referred to as “5G” or “New Radio” (NR). These terms refer to evolving communications 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 at https: / / www.ngmn.org / 5g-white-paper.html. 3GPP® intends to support 5G through the so-called 3GPP® NextGen Radio Access Network (RAN) and the 3GPP® NextGen core network (NGC).

[0003] Under 3GPP® standards, a base station (e.g., an "eNB" in 4G or a "gNB" in 5G) is a node through which communication devices (user equipment or "UE") connect to a core network and communicate with other communication devices or remote servers. For simplicity, this application uses the term base station to refer to any such base station.

[0004] For simplicity, this application uses the terms mobile device, user device, or UE to refer to any communication device that can connect to a core network via one or more base stations. A 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 more generally, fixed) devices are typically operated by a user. However, 3GPP® standards also enable so-called “Internet of Things” (IoT) devices (e.g., Narrow-Band IoT (NB-IoT) devices) to connect to the network, which typically includes various measurement equipment, telemetry equipment, 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 equipment. In effect, the Internet of Things is a network of devices (or “things”) equipped with appropriate electronics, software, sensors, network connectivity, etc., enabling these devices to collect and exchange data with each other and with other communication devices. It will be appreciated that IoT devices may also be referred to as Machine-Type Communication (MTC) communication devices or Machine-to-Machine (M2M) communication devices.

[0005] For simplicity, this application will often refer to mobile devices in the description, however, it will be understood that the described techniques can be implemented on any communication device (mobile and / or generally fixed) that can connect to a communication network to send / receive data, regardless of whether such communication device is controlled by human input or by software instructions stored in memory.

[0006] One of the recent features being developed for the existing 5G framework is called Multicast and Broadcast Services (MBS). This feature aims to enhance 5G New Radio and 5G Core network capabilities for the large-scale deployment of reliable, low-latency, resource-efficient, and diverse multicast and broadcast services. 3GPP is currently specifying the details of MBS for media distribution over mobile broadband networks. MBS (or "NR MBS" in 5G) aims to reuse cellular infrastructure, such as so-called Low Power Low Tower (PLT) infrastructure. One of the primary use cases is the distribution of linear / live media content to smartphones, tablets, vehicles, and other mobile (or fixed) devices. MBS is designed to use existing (or already specified) 3GPP infrastructure, but can provide more efficient delivery of multicast / broadcast traffic than unicast communication using the same infrastructure. Details of the MBS architectural enhancements can be found in 3GPP® Technical Specification (TS) 23.247 V17.0.0, the contents of which are incorporated herein by reference.

[0007] 3GPP discusses UE mobility between MBS support nodes and non-support nodes. In non-support MBS nodes, the base station (gNB) has a unicast context for the UE, rather than a multicast context within the MBS support node. More specifically, MBS aims to use multicast (via a shared user plane tunnel) whenever possible to deliver MBS traffic to multiple UEs in the same MBS session. This is because multicast is more efficient than unicast when the same data needs to be delivered to multiple users. The method for delivering MBS session data is sometimes called a "dedicated MBS traffic delivery method" in the case of unicast and a "shared MBS traffic delivery method" in the case of multicast.

[0008] During mobility procedures such as handover, the UE context is shared in handover signaling between a source base station (gNB) and a target base station (gNB). However, a base station that supports MBS maintains different data in the UE context than a base station that does not support MBS due to the different delivery methods used, which can lead to data loss and / or a poor user experience when performing handovers between different types of base stations. Such data loss can be caused, for example, by different types of bearers used for multicast and unicast.

[0009] When a UE joins an MBS session, a shared user plane tunnel is established for that session between the serving base station and the user plane function in the core network for delivery of MBS traffic. The base station can decide whether to use a point-to-point (PTP) tunnel / bearer or a point-to-multipoint (PTM) tunnel / bearer. A shared user plane tunnel (NG-U / F1-U tunnel) is used for PTM. A multicast radio bearer (MRB) is used for the MBS session. The MRB may be provided on the PTP leg, the PTM leg, or both. For the PTP leg, a shared user plane tunnel may be configured, but this has not yet been specified by 3GPP. [Prior art documents] [Non-patent literature]

[0010] [Non-Patent Document 1] "NGMN 5G White Paper" V1.0 [Non-patent document 2] 3GPP Technical Specification(TS)23.247 V17.0.0 Summary of the Invention [Problem to be solved by the invention]

[0011] The inventors have recognized that when a UE performs a handover from an MBS support node to a non-MBS support node, the MRB should be converted to a DRB (and vice versa). Although the target NG-RAN node can indicate to the core network whether it currently supports MBS (in the Path Switch Request message), it cannot signal this support capability to the source base station. Thus, the source base station does not know whether the target base station is an MBS support node, which can result in inefficiency and data loss.

[0012] Furthermore, legacy handover signaling does not support UE handover from an MBS support node to an MBS non-support node, which may result in handover failure (in which case the UE may need to establish a new connection with an appropriate base station).

[0013] Accordingly, the present invention seeks to provide a method and associated apparatus that addresses or at least alleviates (at least some of) the problems set forth above. [Means for solving the problem]

[0014] In one aspect, the present invention provides a method performed by a first access network node, the method comprising receiving information indicating whether a second access network node supports multicast and broadcast services (MBS) (“MBS support information”), and controlling interaction between the first access network node and the second access network node based on the information.

[0015] In one aspect, the present invention provides a method performed by a first access network node, the method comprising: transmitting information to a second access network node indicating whether the first access network node supports multicast and broadcast services (MBS), where if the first access network node supports MBS, the information comprises information identifying at least one service area, MBS service information, and information identifying a delivery mode; and controlling interaction between the first access network node and the second access network node based on the information.

[0016] In one aspect, the present invention provides a method performed by a user equipment (UE), the method including transmitting information indicating whether a cell supports a multicast broadcast service (MBS) to an access network node, and controlling communication between the UE and the cell based on the information.

[0017] In one aspect, the present invention provides a method performed by a first access network node acting as a source node for handover of a user equipment (UE) communicating using a multicast radio bearer (MRB) via the first access network node, the method comprising: if a second access network node acting as a target node for the handover does not support MBS via the MRB, reconfiguring the UE to use a first data radio bearer (DRB) at the first access network node for multicast broadcast service (MBS), and performing a procedure for handover of the UE to the second access network node, whereby MBS service is provided to the UE via the second DRB at the second access network node.

[0018] In one aspect, the present invention provides a method performed by a first access network node acting as a source node for handover of a user equipment (UE) communicating using a multicast radio bearer (MRB) via the first access network node, the method comprising: initiating a procedure for handover of the UE to a second access network node; and, if the second access network node acting as a target node for the handover does not support multicast broadcast service (MBS) via the MRB, reconfiguring the UE to use a first data radio bearer (DRB) at the second access network node, whereby MBS service is provided to the UE via the first DRB.

[0019] In one aspect, the present invention provides a method performed by a first access network node acting as a target node for handover of a user equipment (UE) communicating using a multicast radio bearer (MRB) via a second access network node, the method including: receiving, from the second access network node acting as a source node for the handover, a message including configuration information for a data radio bearer (DRB) to be used by the UE for multicast broadcast service (MBS) service at the first access network node; performing handover for the UE, including establishing the DRB at the first access network node based on the configuration information; and providing the MBS service to the UE via the DRB at the first access network node.

[0020] In one aspect, the present invention provides a method performed by a user equipment (UE) receiving a multicast broadcast service (MBS) service using a multicast radio bearer (MRB) via a first access network node, the method including: if a second access network node acting as a target node for handover does not support MBS via the MRB, receiving a message from the first access network node acting as a source node for handover to reconfigure the UE to use a first data radio bearer (DRB) at the first access network node for the MBS service; performing handover by reconfiguring from the first DRB to a second DRB at the second access network node; and receiving the MBS service via the second DRB.

[0021] In one aspect, the present invention provides a method performed by a user equipment (UE) receiving a multicast broadcast service (MBS) service using a multicast radio bearer (MRB) via a first access network node, the method including: receiving, if a second access network does not support MBS via the MRB, a message from the first access network node acting as a source node for handover to reconfigure the UE to use a data radio bearer (DRB) in a second access network node acting as a target node for handover; performing a handover from the MRB to the DRB; and receiving the MBS service via the DRB.

[0022] In one aspect, the present invention provides a method performed by a network node for handling connectivity and mobility management for a user equipment (UE), the method comprising: receiving, from a first access network node acting as a target node for handover of the UE, a request to switch a path from a second access network node acting as a source node to the first access network node, the request including information identifying at least one Multicast Broadcast Service (MBS) service supported by the first access network node and information identifying at least one associated MBS service area; and transmitting a message acknowledging the path switch request to the first access network node, the message being adapted to include information for providing the first MBS service to the UE via the first access network node using a shared MBS traffic distribution method (e.g., multicast / broadcast) when it is determined that the first MBS service is supported by the first access network node within the associated MBS service area if the first MBS service is provided to the UE via the second access network node using an individual MBS traffic distribution method (e.g., unicast).

[0023] In one aspect, the present invention provides a method performed by a first access network node acting as a target node for handover of a user equipment (UE), the method comprising: sending a request to a network node for handling connectivity and mobility management for the UE to switch a path from a second access network node acting as a source node to a first access network node, the request including information identifying at least one Multicast Broadcast Service (MBS) service supported by the first access network node and information identifying at least one associated MBS service area; and receiving a message from the network node acknowledging the path switch request, the message being adapted to include information for providing the first MBS service to the UE via the first access network node using a shared MBS traffic distribution method (e.g., multicast / broadcast) when the first MBS service is supported by the first access network node within an associated MBS service area if the first MBS service is provided to the UE via the second access network node using an individual MBS traffic distribution method (e.g., unicast).

[0024] In one aspect, the present invention provides a first access network node comprising: means (e.g., a memory, a transceiver, and a processor) for receiving information indicating whether a second access network node supports a multicast broadcast service (MBS); and means for controlling interaction between the first access network node and the second access network node based on the information.

[0025] In one aspect, the present invention provides a first access network node comprising: means (e.g., a memory, a transceiver, and a processor) for transmitting information to a second access network node indicating whether the first access network node supports Multicast Broadcast Service (MBS), where if the first access network node supports MBS, the information includes information identifying at least one service area, MBS service information, and information identifying a delivery mode; and means for controlling interaction between the first access network node and the second access network node based on the information.

[0026] In one aspect, the present invention provides a user equipment (UE) comprising means (e.g., a memory, a transceiver, and a processor) for transmitting information indicating whether a cell supports a multicast broadcast service (MBS) to an access network node, and means for controlling communication between the UE and the cell based on the information.

[0027] In one aspect, the present invention provides a first access network node acting as a source node for handover of a user equipment (UE) communicating using a multicast radio bearer (MRB) via the first access network node, the first access network node comprising: means (e.g., a memory, a transceiver, and a processor) for reconfiguring the UE to use a first data radio bearer (DRB) at the first access network node for multicast broadcast service (MBS) if a second access network acting as a target node for the handover does not support MBS via the MRB; and means for performing a procedure for handover of the UE to the second access network node, whereby MBS service is provided to the UE via the second DRB at the second access network node.

[0028] In one aspect, the present invention provides a first access network node acting as a source node for handover of a user equipment (UE) communicating using a multicast radio bearer (MRB) via the first access network node, the first access network node comprising: means (e.g., a memory, a transceiver, and a processor) for initiating a procedure for handover of the UE to a second access network node; and means for reconfiguring the UE to use a first data radio bearer (DRB) at the second access network node if the second access network node acting as a target node for the handover does not support multicast broadcast service (MBS) via the MRB, whereby MBS service is provided to the UE via the first DRB.

[0029] In one aspect, the present invention provides a first access network node acting as a target node for handover of a user equipment (UE) communicating using a multicast radio bearer (MRB) via a second access network node, the first access network node comprising: means (e.g., a memory, a transceiver, and a processor) for receiving, from the second access network node acting as a source node for the handover, a message including configuration information for a data radio bearer (DRB) to be used by the UE for multicast broadcast service (MBS) service at the first access network node; means for performing handover for the UE, including establishing a DRB at the first access network node based on the configuration information; and means for providing the MBS service to the UE via the DRB at the first access network node.

[0030] In one aspect, the present invention provides a user equipment (UE) that receives a multicast broadcast service (MBS) service using a multicast radio bearer (MRB) via a first access network node, the UE comprising: means (e.g., a memory, a transceiver, and a processor) for receiving a message from the first access network node that functions as a source node for handover to reconfigure the UE to use a first data radio bearer (DRB) at the first access network node for the MBS service if a second access network node that functions as a target node for handover does not support MBS via the MRB; means for performing the handover by reconfiguring from the first DRB to a second DRB at the second access network node; and means for receiving the MBS service via the second DRB.

[0031] In one aspect, the present invention provides a user equipment (UE) that receives a multicast broadcast service (MBS) service using a multicast radio bearer (MRB) via a first access network node, the UE comprising: means (e.g., a memory, a transceiver, and a processor) for receiving a message from the first access network node acting as a source node for handover to reconfigure the UE to use a data radio bearer (DRB) in the second access network node acting as a target node for handover if the second access network does not support MBS via the MRB; means for performing a handover from the MRB to the DRB; and means for receiving the MBS service via the DRB.

[0032] In one aspect, the present invention provides a network node for handling connectivity and mobility management for a user equipment (UE), the network node comprising means (e.g., a memory, a transceiver, and a processor) for receiving a request from a first access network node acting as a target node for handover of the UE to switch a path from a second access network node acting as a source node to the first access network node, the request including information identifying at least one Multicast Broadcast Service (MBS) service supported by the first access network node and information identifying at least one associated MBS service area. and means for transmitting a message to the first access network node acknowledging the path switch request, wherein if the first MBS service is provided to the UE via the second access network node using an individual MBS traffic distribution method (e.g., unicast), the message is adapted to include information for providing the first MBS service to the UE via the first access network node using a shared MBS traffic distribution method (e.g., multicast / broadcast) when it is determined that the first MBS service is supported by the first access network node within an associated MBS service area.

[0033] In one aspect, the present invention provides a first access network node acting as a target node for handover of a user equipment (UE), the first access network node comprising means (e.g., a memory, a transceiver, and a processor) for transmitting a request to a network node for handling connectivity and mobility management for the UE to switch a path from a second access network node acting as a source node to the first access network node, the request comprising information identifying at least one Multicast Broadcast Service (MBS) service supported by the first access network node and identifying at least one associated MBS service area. and means for receiving from the network node a message acknowledging the path switch request, the message being adapted to include information for providing the first MBS service to the UE via the first access network node using a shared MBS traffic delivery method (e.g., multicast / broadcast) when the first MBS service is supported by the first access network node in an associated MBS service area, if the first MBS service is provided to the UE via the second access network node using an individual MBS traffic delivery method (e.g., unicast).

[0034] Aspects of the present invention extend to corresponding systems, apparatus, and computer program products, such as computer readable storage media having instructions stored thereon, operable to program a programmable processor to perform the methods described above or in the claimed aspects and possibilities, and / or to program a computer suitably adapted to provide an apparatus as described in any of the claims.

[0035] Each feature disclosed in this specification (which term includes claims) and / or shown in the drawings may be incorporated into the present invention independently (or in combination) with any other disclosed and / or shown feature. In particular, but not limited to, any feature of a claim depending from a particular independent claim may be introduced into that independent claim in any combination or individually. [Brief explanation of the drawings]

[0036] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Figure 1] 1 is a schematic diagram of a mobile (cellular or wireless) telecommunications system in which embodiments of the present invention may be applied; [Figure 2] 1 is a schematic diagram of a mobile (cellular or wireless) telecommunications system in which embodiments of the present invention may be applied; [Figure 3] 2 is a schematic block diagram of a mobile device forming part of the system shown in FIG. 1; [Figure 4] 2 is a schematic block diagram of an access network node (eg, a base station) forming part of the system shown in FIG. 1; [Figure 5] FIG. 2 is a schematic block diagram of a core network node (e.g., AMF) forming part of the system shown in FIG. 1; [Figure 6] 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present invention. [Figure 7] 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present invention. [Figure 8] 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present invention. [Figure 9] 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present invention. [Figure 10] 1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present invention. [Figure 11]1 is a schematic signaling (timing) diagram illustrating some exemplary embodiments of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0037] overview 1 and 2 illustrate schematically a mobile (cellular or wireless) telecommunications system 1 in which embodiments of the present invention may be applied.

[0038] In this system 1, users of mobile devices 3 (UE) may 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) and / or 5G RAT. It will be understood that several base stations 5 form a (Radio) Access Network or (R)AN. As will be understood by those skilled in the art, while one mobile device 3 and three base stations 5A-5C are shown in FIG. 1 for illustrative purposes, when implemented the system will typically include other base stations / (R)AN nodes and mobile devices (UE).

[0039] 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. Base stations 5 that support next generation / 5G protocols may be referred to as "gNBs." It will be appreciated that some base stations 5 may be configured to support both 4G and 5G, and / or any other 3GPP or non-3GPP communication protocol.

[0040] A mobile device 3 and its serving base station 5 are connected via an appropriate air interface (e.g., the so-called "NR" air interface, the "Uu" interface, etc.). Neighboring base stations 5 are connected to each other via appropriate inter-base station interfaces (e.g., the so-called "Xn" interface, the "X2" interface, etc.). The base stations 5 are also connected to core network nodes via appropriate interfaces (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 telecommunications system 1, as well as for (among other things) subscriber management, mobility management, charging, security, and call / session management. For example, the core network 7 in a "next generation" / 5G system includes user plane and control plane entities, such as one or more Control Plane Functions (CPFs) and one or more User Plane Functions (UPFs). The so-called Access and Mobility Management Function (AMF) in 5G, or Mobility Management Entity (MME) in 4G, is responsible for handling attachment and mobility management tasks for mobile devices 3. The so-called Session Management Function (SMF) is responsible for handling communication sessions for mobile devices 3, such as session establishment, modification, and release. 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 appreciated that nodes or functions may have different names in different systems.

[0042] Further details of the core network 7 are shown in Figure 2, which also shows the interfaces between each network node. As can be seen, the core network 7 may typically include, among other things, an Authenticate 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 (via the UPF 10) to a Data Network (DN), such as the Internet or a similar Internet Protocol (IP)-based network. The core network 7 may also be coupled to an Operation and Management (OAM) function (not shown).

[0043] In this system 1, multicast broadcast service (MBS) functionality is provided to UE 3 via its serving base station 5 and associated core network nodes such as UPF 10 and SMF 11. UPF 10 may be an MBS-specific UPF, in which case it may be referred to as MB-UPF 10M (e.g., dedicated to providing MBS functionality). Similarly, SMF 11 may be an MBS-specific SMF, in which case it may be referred to as MB-SMF 11M. However, it will be appreciated that any suitable UPF 10 / SMF 11 may be used for MBS.

[0044] MBS traffic is distributed to UEs that have joined a particular MBS service / session using multicast (via a shared user plane tunnel) where appropriate. However, not all base stations 5 (all cells) support MBS via multicast. Therefore, in some cells it may be necessary to provide MBS via unicast.

[0045] In the example shown in Figure 1, the UE's current serving base station 5A provides an MBS session to the UE 3 via unicast, while another base station (or another cell), e.g., base station 5B, may support the same MBS session via multicast.

[0046] To facilitate efficient and lossless delivery of MBS to UE 3, base station 5 is configured to obtain information about neighboring MBS capabilities. For example, such MBS capabilities may include whether the base station (or its cell) supports MBS, the MBS delivery methods supported by the base station (or its cell), and a list of MBS services supported by the base station (or its cell).

[0047] In one option, the base stations 5 are configured to obtain such MBS-related information during connection setup (or modification) between neighboring base stations 5. Connection setup between base stations 5 typically involves an Xn setup procedure (for 5G base stations) or an X2 setup procedure (for 4G base stations). Connection modification typically involves an Xn or X2 modification procedure.

[0048] In another option, the base station 5 is configured to obtain MBS-related information about the other base stations during handover of the UE 3 from one base station 5A (source) to another base station 5B (target). In this case, the source base station 5A may receive information in the handover request acknowledgement from the target base station 5B indicating whether the target base station 5B supports MBS (and which service / delivery mode). It will be appreciated that the source base station 5A may be configured to indicate its MBS support to the target base station 5B in the handover request sent to the target base station 5B (if not already indicated during Xn / X2 setup or modification). This information may be useful if the UE 3 (or another UE) needs to be returned to the cell of the base station 5A.

[0049] In yet another option, the serving base station 5A may be configured to obtain MBS-related information about neighboring base stations 5B from the UE 3 during an Automatic Neighbor Relation (ANR) procedure. For example, the UE 3 may obtain MBS information from a neighboring cell (cell B) and provide this information to its current serving cell (cell A). The obtained information may indicate whether the neighboring base station 5B (or a neighboring cell) supports MBS (and, if so, which MBS services and which delivery modes are supported). The information may be included in a "CGI-InfoNR" information element, etc.

[0050] In this system 1, data loss during handover can be avoided (or at least reduced) by performing the following actions: The (source) base station 5A provides the MBS session via an associated multicast radio bearer (MRB). In one alternative, when performing handover for the UE 3, the (source) base station 5A converts the MRB configuration (used to deliver traffic for the MBS session) into an appropriate DRB configuration and provides the UE with information to use the DRB instead of the MRB. In this case, the information can be provided in the form of a mapping table or the like that the UE 3 can use to derive and apply the required DRB configuration before handover to the target base station 5B. The information can be included in RRC signaling (e.g., RRCReconfiguration). Once the UE 3 confirms that it is using a DRB for the MBS session, the source base station 5A initiates handover to the target base station 5B using the converted DRB, which can be handed over to the corresponding DRB in the target base station 5B without data loss. In another alternative, the source base station 5A converts the MRB configuration into a DRB based on the mapping table (without reconfiguring the UE 3 at this stage). In this case, the source base station 5A sends the converted DRB configuration to the target base station 5B in a handover request message and receives from the target base station 5B (in a handover request acknowledgement message) an RRC configuration applicable to the target DRB. The source base station 5A then sends an appropriately formatted RRC Reconfiguration message (based on the DRB configuration received from the target) to the UE 3. The RRC Reconfiguration message includes information identifying a mapping between the UE's MRB configuration (currently in use at the source) and the associated new DRB configuration to be used at the target base station 5B. This allows the UE 3 to perform a handover from the MRB at the source to the DRB at the target without data loss.It will be appreciated that in some cases it may be necessary to first convert the MRB to a DRB at the source (as in the first alternative) before handing over the UE 3 to a DRB at the target base station 5B.

[0051] When performing a handover from an access network node (e.g., base station 5A) that does not support MBS (and therefore MBS traffic is delivered via unicast) to a node that supports MBS via multicast MRB, the UE 3 needs to be configured to use an appropriate MRB in the target (e.g., base station 5B). The core network node needs to recognize that the unicast bearer in the non-supporting node 5A is no longer in use and ensure that the UE 3 is handed over to an appropriate MRB in the target base station 5B. This is achieved by the target base station 5B sending a properly formatted message requesting a path switch to the AMF 9, including in the message information identifying at least one MBS service supported by the target base station 5B (e.g., an MBS session ID list) and at least one associated MBS service area (e.g., a service area list). The supported MBS services can be provided per service area. Using this information, the AMF 9 can decide whether to establish a shared MBS session (or reuse an existing shared MBS session) at the target node 5B. If a shared MBS session is not suitable, the AMF 9 can establish a dedicated MBS session at the target node 5B.

[0052] In effect, using information about each other's MBS capabilities and supported MBS services / service areas (if appropriate), the base station 5 can control interactions with other nodes, including handover-related procedures (e.g., performing lossless handover), selecting a unicast or multicast tunnel for the UE 3, and requesting the UE 3 to perform RRC reconfiguration to change between the MRB and DRB delivery methods for the MBS service to which the UE 3 has joined. The MBS information of neighboring base stations can also be useful for base stations that do not support MBS, since it can be used to optimize MBS delivery after a handover to a different base station (or cell) that supports MBS. For example, when the UE 3 is handed over to a new cell that supports MBS, the UE 3 can be configured to use a specific shared tunnel (already established) for the MBS session to which the UE 3 has joined. The information obtained by the base station may also be shared with a core network node (e.g., the AMF or SMF) to control path switching and session management.

[0053] User Equipment (UE) FIG. 3 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 31 operable to transmit signals to and receive signals from connected nodes via one or more antennas 33. While not necessarily shown in FIG. 3, the UE 3 naturally has all the usual functionality of a conventional mobile device (e.g., a user interface 35), which may be provided by any one or any combination of hardware, software, and firmware, as appropriate. A controller 37 controls the operation of the UE 3 in accordance with software stored in memory 39. The software may be pre-installed in memory 39 and / or 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 communications control module 43, and an MBS module 45.

[0054] The communication control module 43 is responsible for handling (generating / sending / receiving) 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 RRC signaling (to / from the (R)AN node 5) and / or NG-C / NG-U signaling (to / from the core network 7).

[0055] The MBS module 45 is responsible for handling signaling related to multimedia broadcast services.

[0056] Access network node (base station) FIG. 4 is a block diagram illustrating the main components of the base station 5 (or a similar access network node) shown in FIG. 1. As shown, the base station 5 includes a transceiver circuit 51 for transmitting signals to and receiving signals from user equipment (e.g., mobile device 3) via one or more antennas 53, and a network interface 55 for transmitting signals to and receiving signals from the core network 7 and neighboring base stations. The base station 5 also includes a controller 57 for controlling the operation of the base station 5 in accordance with software stored in memory 59. The software may be pre-installed in the memory 59 and / or 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 61 and at least a communication control module 63. Although not shown in FIG. 4, the network interface 55 also typically includes an inter-base station interface unit (e.g., Xn) and a core network interface unit (e.g., NG-C / NG-U / N2 / N3).

[0057] The communications control module 63 is responsible for handling (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. It will be understood that the communications control module 63 may include several sub-modules (or “layers”) for supporting specific functions. For example, the communications 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. The RRC submodule is operable to generate, send, and receive signaling messages formatted according to the RRC standard. Such messages are exchanged between base stations 5 and mobile devices 3 served by the base stations 5. RRC messages may include messages related to handover and / or MBS reconfiguration.

[0058] Core Network Node FIG. 5 is a block diagram illustrating the main components of the core network node (e.g., AMF 9, UPF 10, or SMF 11) shown in FIG. 1 . As shown, the core network node includes transceiver circuitry 71 operable to transmit signals to and receive signals from connected UEs 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 UEs 3 directly and / or via base stations 5 or other (R)AN nodes, as appropriate. The network interface 75 typically includes an appropriate base station interface (e.g., S1 / NG-C / NG-U). A controller 77 controls the operation of the core network node in accordance with software stored in memory 79. The software may be pre-installed in memory 79 and / or 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 81, a communication control module 83, and an MBS module 85 (optional).

[0059] The communication control module 83 is responsible for handling (generating / sending / receiving) signaling between the core network nodes and other nodes such as UE3, (R)AN nodes, and other core network nodes.

[0060] For example, when present in the MB-SMF or MB-UPF, the MBS module 85 is responsible for handling signaling related to multimedia broadcast services, which may include signaling related to MBS (control signaling and / or data traffic).

[0061] Detailed Description The following is a description of some exemplary procedures performed by the nodes of the systems shown in FIGS. 1 and 2, with reference to FIGS.

[0062] When a UE 3 joins an MBS session, a shared user plane tunnel is established for that session between the serving base station 5 and a user plane function 10 in the core network 7 for delivery of associated MBS traffic. The base station 5 can decide whether to use a point-to-point (PTP) tunnel / bearer or a point-to-multipoint (PTM) tunnel / bearer. A shared user plane tunnel (NG-U / F1-U tunnel) is used for PTM. In addition, a multicast radio bearer (MRB) is used for the MBS session. The MRB may be provided for the PTP leg, the PTM leg, or both. It will be appreciated that a shared user plane tunnel may also be configured for the PTP leg, if appropriate.

[0063] In either case, the source base station 5 is assumed to be aware of the MBS support of the target base station 5 before the handover. Beneficially, the base station 5 is configured to avoid full configuration at the new base station 5 (when the source and target base stations have different MBS support capabilities). Specifically, so-called full configuration involves re-establishing a Packet Data Convergence Protocol (PDCP) entity at the new base station 5, which is highly likely to result in data loss. Therefore, to avoid full configuration during the handover, the base station 5 ensures that only one PDCP entity is present during the handover. The concept of non-full configuration is to retain the PDCP entity at the source base station 5 and convert it into a DRB (or MRB) suitable for the target base station 5, regardless of whether this PDCP entity is from a DRB / multicast MRB / unicast MRB.

[0064] MBS support notification (via Xn setup) 6 is a schematic signaling (timing) diagram illustrating an exemplary Xn setup procedure to which the present invention may be applicable. In this example, the setup procedure (or a similar update procedure) is used to exchange MBS support information between base stations 5. The MBS information may be included in the request and / or the corresponding response. It will be appreciated that the MBS information may be provided on a per-base station basis. A base station 5 may indicate its own MBS support related information using appropriate messages, including but not limited to, an "XN Setup Request" message (based on 3GPP TS 38.423, current version 16.7.0, clause 9.1.3.1), an "XN Setup Response" message (based on 3GPP TS 38.423, clause 9.1.3.2), and an "NG-RAN Node Configuration Update" message (based on 3GPP TS 38.423, clause 8.4.2).

[0065] The message may include an appropriately formatted "MBS Supported" information element (or the like) to indicate whether the base station sending the message supports MBS. The message may include one or more information elements to identify the supported MBS services or sessions (by their respective MBS session identifiers / Temporary Mobile Group Identifiers (TMGIs)), the supported delivery modes, and the supported service areas, as shown below. [Table 1]

[0066] It will also be appreciated that MBS information may be provided on a cell-by-cell basis, in which case the MBS information for each cell (at least one cell) may be included in an appropriately formatted information element, such as a "Served Cell Information NR" information element (included in at least one of the above messages).

[0067] The Served Cell Information NR information element is based on clause 9.2.2.11 of 3GPP TS 38.423. However, the information element is adapted to include cell-specific MBS information as shown below. [Table 2]

[0068] MBS support notification (during handover) Alternatively, or in addition to the Xn setup, the base stations 5 may be configured to exchange MBS support information with each other during the handover preparation procedure. For example, if the target base station supports a previously unindicated or modified MBS session, delivery mode, or service area, the relevant MBS information may be provided during the handover.

[0069] FIG. 7 is a schematic signaling (timing) diagram illustrating an exemplary handover procedure to which the present invention may be applicable.

[0070] In this case, when initiating a handover procedure for the UE 3, the source base station 5A is configured to include the applicable MRB configuration for any MBS service used by the UE 3 in the "Handover Request" message sent to the target base station 5B. If the target base station 5B can understand the MRB configuration, or in other words, if the target base station 5B supports MBS, the target base station 5B will provide its MRB configuration / support indication in response (i.e., in the "Handover Request Confirm" message).

[0071] It will be appreciated that in this case the source base station 5A supports MBS, otherwise the source base station 5A may not have the ability (or need) to query the target base station 5B. If the target base station 5B supports MBS, the relevant MBS information / configuration is included in the response (i.e., in the "Handover Request Confirm" message).

[0072] MBS Support Notification (via ANR) It will be appreciated that the MBS support information for a given cell may be obtained from the UE 3 in an Automatic Neighbor Relation (ANR) procedure.

[0073] FIG. 8 is a schematic signaling (timing) diagram illustrating an exemplary ANR procedure to which the present invention may be applicable.

[0074] As can be seen from the figure, in step 3, UE 3 reports information about a neighboring cell (cell B) to its serving cell (cell A). However, in this case, the information reported by UE 3 includes information about MBS support in the neighboring cell. More specifically, UE 3 may send the following information about the cell of neighboring base station 5B (cell B) to serving base station 5A: MBS support (e.g., true / false), which MBS services are supported, and which delivery mode (e.g., multicast / unicast) is supported (per service or cell). In this case, using the CGI-InfoNR information element as an example, the MBS-related information of neighboring cells may be reported by UE 3 as follows: [Table 3]

[0075] Lossless Handover 9 is a schematic signaling (timing) diagram illustrating an exemplary handover procedure to which the present invention may be applicable. In this case, the source base station 5A is configured to convert the MRB configuration used by the UE 3 in the cell of the source base station 5A into an appropriate DRB. The source base station 5A reconfigures the MRB to a DRB in the UE 3 by sending an appropriately formatted RRCReconfiguration message to the UE 3 before initiating / performing a handover towards the target base station 5B.

[0076] Below is a description of the steps of this procedure, with reference to FIG. Step 1: In this example, the source base station 5A supports MBS (multicast) over MRB, and the target base station 5B supports only DRB (unicast). After making a handover decision but before sending a handover request to the target base station 5B, the source base station 5A sends an RRCReconfiguration message to the UE 3. The message includes at least one of an MRB identifier (MRB ID) and a corresponding DRB identifier (DRB ID), and an MRB configuration and a corresponding DRB configuration (per MRB ID). In effect, this information represents a mapping of MRB and DRB configurations applicable to the MBS service used by the UE 3 and assists the UE 3 to switch between MRB and DRB in preparation for handover to the target cell.

[0077] Step 2: The UE 3 converts the MRB into a corresponding DRB according to the configuration received from the source base station 5A.

[0078] Step 3: The UE 3 generates and sends an appropriate response (an "RRCReconfiguration Complete" message) to the source base station 5A. It will be appreciated that step 4 is not triggered until the RRCReconfiguration Complete message is received by the source base station 5A.

[0079] Steps 4 and 5: Handover procedure between source base station 5A and target base station 5B. As can be seen, the source base station 5A requests handover based on the converted DRB (instead of MRB, since the target base station 5B does not support MBS over MBS / MRB).

[0080] Step 6: The source base station 5A sends another RRCReconfiguration message to the UE 3, which includes a DRB configuration for the target base station 5B, to be used by the UE 3 after handover to the cell of the target base station 5B.

[0081] It will be appreciated that the mapping between the (old) MRB and the (new) DRB may be provided using an appropriate mapping table, as shown below, which may be included in the RRCReconfiguration message (step 1 in FIG. 9). [Table 4]

[0082] In a variation of the above procedure, the source base station 5A may be configured to convert the MRB to a DRB and send information indicating an appropriate DRB configuration to the target base station 5B in a suitably formatted handover request message (instead of sending it to the UE 3). After the target base station 5B accepts the DRB and indicates its own DRB configuration (by sending an appropriate handover request confirm message), the source base station 5A proceeds to send an RRCReconfiguration message to the UE 3. The RRCReconfiguration message includes information identifying the mapping between the old MRB configuration and the associated new DRB configuration from the target base station 5B.

[0083] This alternative is illustrated in FIG. Step 1: The source base station 5A converts the MRB used by the UE 3 into a DRB.

[0084] Steps 2 and 3: The source base station 5A initiates a handover towards the target base station 5B using the converted DRB and receives information identifying a corresponding DRB configuration applicable at the target base station 5B. The information may be provided in the form of an RRC context (or RRC configuration) to be applied by the UE 3 or by the source base station 5A on behalf of the UE 3. The target base station 5B may include this information in an appropriate information element of the handover request confirmation message, such as a "Target NG-RAN node to Source NG-RAN node transparent container".

[0085] Step 4: If the source base station 5A is able to decode the information received from the target base station 5B, it proceeds to generate and send (by applying the received RRC context) an appropriately formatted RRCReconfiguration message to the UE 3. Effectively, this message configures the UE 3 to convert its MRB to an appropriate DRB based on the information received from the target base station 5B (MRB ID, target gNB DRB configuration per MBS service).

[0086] Steps 4a and 5 (alternative to step 4): If the source base station 5A cannot decode the information received from the target base station 5B, the source base station 5A generates and sends to the UE 3 an RRCReconfiguration message including information associated with the source RRC context and the target RRC context. The source RRC context includes the converted DRBs associated with the respective MRBs, and the target RRC context includes the RRC configuration applicable to the target base station 5B for the respective DRBs to be used in the target base station 5B. The UE 3 is configured to first apply the source RRC context and then apply the target RRC context. Effectively, the UE 3 is configured to use a first DRB in the source base station 5A (instead of the MRBs) based on the source RRC context, and then switch to a second DRB in the target base station 5B to continue receiving the MBS service after the handover based on the target RRC context.

[0087] Handover from a non-supporting node to a supporting node 11 is a schematic signaling (timing) diagram illustrating an exemplary (Xn-based) NG-RAN inter-handover procedure to which the present invention may be applicable. In particular, the "N2 Path Switch Request" (in step 1b) may be adapted to include information about MBS services supported by the target base station 5B. The information may be included in an "MBS Service Supported List" field (or similar) and may also identify the MBS service area(s) and MBS session ID(s) associated with the supported MBS service(s).

[0088] More specifically, some multicast services may be localized services available only within a specific MBS service area. Such an MBS service area is typically defined as a list of cells or frequencies. Thus, a specific MBS service (or session) may be provided via unicast in some areas (e.g., in the cell of the UE's current base station 5A), and the same MBS service may be provided via multicast in other areas (e.g., in the cell of the target base station 5B). It will be understood that in some cells, a specific MBS service may be provided via both unicast and multicast (e.g., depending on the number of users). Also, there may be cells in which a specific MBS service is not provided, or in which no MBS service is provided at all. It will be understood that a specific MBS service may be represented by either an "MBS session" or a "TMGI," or both.

[0089] The path switch request message includes MBS session information for the MBS services supported by the target node 5B (e.g., as a list of MBS session IDs). The MBS session information (at least one MBS session ID / TMGI) is provided with MBS service area level granularity. Based on the MBS session ID / TMGI and the associated MBS service area, the AMF 9 can decide whether to establish a shared or dedicated MBS session in the cell of the target node 5B for each MBS service supported by the target node 5B.

[0090] Specifically, if the information included in the path switch request message indicates that the target cell supports a particular MBS service for multicast within the MBS service area of ​​the target cell, the AMF9 proceeds to establish a shared MBS session for the UE3 in that cell (or reuse an existing shared MBS session).

[0091] If the target cell does not support the particular MBS service for multicast (within the MBS service area of ​​the target cell), or if the information indicates that the target cell supports that MBS service by unicast, the AMF9 proceeds to establish a new unicast MBS session for the UE3 in that cell for that MBS service.

[0092] Further details of the relevant signaling messages and information elements are provided below. Path switch request (based on 3GPP TS 38.413 section 9.2.3.8) This message is sent by the NG-RAN node 5 to inform the AMF 9 of the new serving NG-RAN node 5 and to forward some NG-U DL tunnel termination points to the SMF 11 via the AMF 9 for one or more PDU session resources. Direction: NG-RAN node 5 to AMF9 [Table 5]

[0093] In this case, the "MBS Service Support List" field contains information about MBS services supported by the target base station 5B, such as a list of (at least one) MBS service area, and information about at least one MBS session corresponding to the supported MBS service (in this example, the "MBS Session Information List" field). Each MBS session information may be represented by an associated TMGI and / or MBS session ID. Path switch request confirmation (based on 3GPP TS 38.413 section 9.2.3.9) This message is sent by the AMF 9 to notify the (target) NG-RAN node 5 that the path switch has been successfully completed in the core network 7. Direction: AMF9 to NG-RAN node 5 [Table 6]

[0094] In this case, the 'Source AMF UE NGAP ID' field contains information identifying an existing shared multicast NG GTP tunnel (eg 'UE NGAP ID') to be used for the MBS session at the target base station 5B.

[0095] Modifications and Substitutions Detailed embodiments have been described above. Those skilled in the art will appreciate that numerous modifications and alternatives may be made to the above embodiments while still benefiting from the invention embodied therein. By way of example, only some of these alternatives and modifications are described herein.

[0096] Base stations in 5G / NR communication systems are commonly referred to as New Radio Base Stations ("NR-BSs"), or "gNBs," although it will be understood that they may also be referred to using the term "eNB" (or 5G / NR eNB), which is more commonly associated with Long Term Evolution (LTE) base stations (also commonly referred to as "4G" base stations). 3GPP TS 38.300 V16.7.0 and 3GPP 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 NR user plane and control plane protocol termination towards the UE and acts as a secondary node in E-UTRA-NR dual connectivity (EN-DC). NG-RAN node: Either a gNB or a ng-eNB.

[0097] The functionality of a gNB (referred to herein as a "distributed" gNB) may be divided between one or more distributed units (DUs) and a central unit (CU), where the CU typically performs higher-level functions and communication with the next-generation core, and the DU performs lower-level functions and communication over the air interface with nearby UEs (i.e., in the cell operated by the gNB). A distributed gNB 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) that controls the operation of one or more gNB-DUs. The gNB-CU terminates the F1 interface connected to the gNB-DU. 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 multiple cells. One cell is supported by only one gNB-DU. The gNB-DU terminates the F1 interface connected to the gNB-CU. gNB-CU-Control Plane (gNB-CU-CP): A logical node that hosts the control plane portion of the RRC and PDCP protocols of the en-gNB or gNB-CU for a gNB. The gNB-CU-CP terminates the E1 interface connected to the gNB-CU-UP and the F1-C interface connected to the gNB-DU. gNB-CU-User Plane (gNB-CU-UP): A logical node that hosts the user plane part of the PDCP protocol of the gNB-CU for the en-gNB, as well as the user plane parts of the PDCP and SDAP protocols 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 interface connected to the gNB-DU.

[0098] Although not shown in FIG. 4, if the base station includes a distributed gNB or en-gNB, the network interface 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 a gNB-CU-CP module, a gNB-CU-UP module, and a gNB-DU module. If present, the gNB-CU-CP module hosts the control plane portions of the RRC layer and PDCP layer of the distributed gNB or en-gNB. If present, the gNB-CU-UP module hosts the user plane portions of the PDCP layer and SDAP layer of the distributed gNB or the user plane portion of the PDCP layer of the distributed en-gNB. If present, the gNB-DU module hosts the RLC layer, MAC layer, and PHY layer of the distributed gNB or en-gNB.

[0099] Those skilled in the art will appreciate that the central unit may be implemented and physically located with the base stations, or may be implemented remotely as a single physical element or as a cloud-based or virtualized system. It will also be appreciated that a single central unit may serve multiple base stations.

[0100] It will be understood that the above embodiments may be applied to 5G New Radio System and LTE System (E-UTRAN), as well as any future generation system. A base station 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, and / or any other 3GPP or non-3GPP communication protocol.

[0101] In the above description, for ease of understanding, the UE, access network node, and data network node are described as having several separate modules (e.g., communication control modules). These modules may be provided in this manner for a particular application, such as when an existing system is modified to implement the present invention; however, in other applications, such as systems designed from the beginning with the features of the present invention in mind, these modules may not be identifiable as separate entities because they may be incorporated into an overall operating system or code. These modules may be implemented in software, hardware, firmware, or a combination thereof.

[0102] Each control unit may comprise 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.

[0103] 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 compiled or uncompiled form, or may be supplied to the UE, access network node, and data network node as signals via a computer network or 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 updating the UE, access network node, and data network node to update their functionality.

[0104] The above embodiments are also applicable to "non-mobile" or generally fixed user equipment. The mobile devices (UEs) mentioned above may comprise MTC / IoT devices, power-saving UEs, etc.

[0105] The first access network node may receive MBS support information from the second access network node (e.g., in an "Xn Setup Request", "Handover Request", "Xn Setup Response", or "Handover Request Confirm" message from the second access network node) or from the user equipment (e.g., in a message forming part of the ANR procedure). The MBS support information may indicate that the second access network node supports MBS using multicast mode or unicast mode, or both. The MBS support information may be included in the "CGI-InfoNR" information element.

[0106] The MBS support information may include at least one of information indicating whether the second access network node supports MBS (e.g., true / false), information identifying at least one MBS service supported by the second access network node, and information identifying an MBS mode (e.g., multicast, unicast, both) supported by the second access network node. The MBS support information may indicate whether a particular cell of the second access network node supports MBS (e.g., using the "Served Cell Information NR" information element included in the "Xn Setup Request" / "Xn Setup Response" or using the "CGI-InfoNR" information element in the ANR procedure).

[0107] Reconfiguring the UE may include sending a radio resource control (RRC) message (e.g., an "RRCReconfiguration" message) to the UE. The RRC message may indicate a mapping between the MRB and the first DRB. The RRC message may include at least one of an MRB identifier and a corresponding DRB identifier of the MRB, an MRB identifier and a corresponding DRB configuration for the first DRB, and an MRB configuration for the MRB and a corresponding DRB configuration for the first DRB.

[0108] The method performed by the first access network node may further include reconfiguring the UE to use the first DRB for MBS services before initiating a procedure for handover of the UE to the second access network node, and after the handover, the MBS services may be provided to the UE via the second DRB.

[0109] The method performed by the first access network node may further include initiating a procedure for handover of the UE to the second access network node after receiving confirmation from the UE that the reconfiguration is complete.

[0110] The method performed by the first access network node may further include, after initiating a procedure for handover of the UE to the second access network node, reconfiguring the UE to use the first DRB for MBS services, wherein after the handover, the MBS services may be provided to the UE via the second DRB.

[0111] The reconfiguring may include reconfiguring the UE to apply a first RRC context associated with a first access network node, and the procedure for handover includes reconfiguring the UE to apply a second RRC context associated with a second access network node. The first RRC context may be adapted to reconfigure the UE to use a first DRB for the MBS service, and the second RRC context may be adapted to reconfigure the UE to change from the first DRB to the second DRB.

[0112] The method may further include receiving a second RRC context from the second access network node, and reconfiguring the UE to apply the first RRC context upon receipt of the second RRC context.

[0113] The method may further include, upon receiving an RRC context from the second access network node, reconfiguring the UE to use a DRB at the second access network node.

[0114] If the first MBS service is not supported within an associated MBS service area by the first access network node acting as the target node for handover, the message sent by the network node may be adapted to include information for providing the first MBS service to the UE via the first access network node using an individual MBS traffic delivery method.

[0115] The information for providing the first MBS service using the shared MBS traffic delivery method may include information identifying a multicast tunnel associated with the first MBS session.

[0116] The information identifying the at least one MBS service supported by the access network node may include a respective MBS session identifier or a Temporary Mobile Group Identifier (TMGI) for each supported MBS service.

[0117] The information identifying the at least one MBS service supported by the access network node may include information identifying a respective service area of ​​each supported MBS service.

[0118] The request to switch paths may form part of an Xn-based NG-RAN inter-handover procedure (e.g., the request may be an "N2 Path Switch Request"). A network node for handling connectivity and mobility management may comprise an Access and Mobility Management Function (AMF).

[0119] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0120] This application claims the benefit of priority to UK Patent Application No. 2119032.7 filed on December 24, 2021, the disclosure of which is incorporated herein by reference in its entirety. [Explanation of symbols]

[0121] 3UE 5 base station 7 Core Network 9 AMF 10 UPF 11 SMF

Claims

1. An access network node, means for transmitting a handover request message to a further access network node, the handover request message including Multicast and Broadcast Services (MBS) session configuration information; means for receiving a handover request confirmation message from the further access network node, wherein if the further access network node or a cell of the further access network node supports MBS, the handover request confirmation message includes information indicating that the further access network node or the cell of the further access network node supports MBS; means for controlling a handover for the MBS between the access network node and the further access network node based on the information; If the further access network node does not support the MBS on a Multicast Radio Bearer (MRB), means for switching the MRB to a further Data Radio Bearer (DRB); means for sending configuration information for the further DRB to a mobile device before transmitting the handover request message; The handover request message includes configuration information for the further DRB, the access network node.

2. If the further access network node does not support the MBS on a Multicast Radio Bearer (MRB), means for receiving, from the further access network node, information of a configuration for a DRB in the further access network node; means for transmitting the configuration information for the DRB to the mobile device to provide the MBS to the mobile device over the DRB; 2. The access network node of claim 1, comprising:

3. 3. The access network node of claim 2, wherein the information of the configuration for the DRB is included in a Radio Resource Control (RRC) message.

4. The access network node of claim 3 , wherein the RRC message indicates a mapping between the MRB and the DRB.

5. 2. The access network node of claim 1, wherein the information of the configuration for the further DRB is included in a Radio Resource Control (RRC) message.

6. The access network node of claim 5 , wherein the RRC message indicates a mapping between the MRB and the further DRB.

7. The RRC message an MRB identifier and a corresponding DRB identifier for the MRB; an MRB identifier for the MRB and corresponding DRB configuration information for the DRB; MRB configuration information for the MRB and corresponding DRB configuration information for the DRB; The access network node according to claim 4, comprising at least one of:

8. a further access network node, means for receiving a handover request message from an access network node, the handover request message including Multicast and Broadcast Services (MBS) session configuration information; means for sending a handover request confirmation message to the access network node, wherein if the further access network node or a cell of the further access network node supports MBS, the handover request confirmation message includes information indicating that the further access network node or the cell of the further access network node supports MBS; means for controlling a handover for the MBS between the access network node and the further access network node based on the information; If the further access network node does not support the MBS on a Multicast Radio Bearer (MRB), The MRB on the access network node is switched to a further Data Radio Bearer (DRB); configuration information for the further DRB is transmitted from the access network node to the mobile device before receiving the handover request message; The handover request message includes configuration information for the further DRB to a further access network node.

9. means for receiving Multicast and Broadcast Services (MBS) using a Multicast Radio Bearer (MRB) via an access network node acting as a source node in a handover; means for performing the handover from said access network node to a further access network node acting as a target node; means for receiving the MBS from the further access network node if the further access network node or a cell of the further access network node supports the MBS; if the further access network node does not support the MBS on the MRB, The MRB on the access network node is switched to a further Data Radio Bearer (DRB); means for receiving, from the further access network node, configuration information for the further DRB before the further access network node receives a handover request message; The handover request message includes configuration information for the further DRB.

10. A method in an access network node, comprising: sending a handover request message to a further access network node, the handover request message including Multicast and Broadcast Services (MBS) session configuration information; receiving a handover request confirmation message from the further access network node, wherein if the further access network node or a cell of the further access network node supports MBS, the handover request confirmation message includes information indicating that the further access network node or the cell of the further access network node supports MBS; controlling a handover for the MBS between the access network node and the further access network node based on the information; If the further access network node does not support the MBS on a Multicast Radio Bearer (MRB), switching the MRB to a further Data Radio Bearer (DRB); sending configuration information for the further DRB to the mobile device before sending the handover request message; the handover request message includes configuration information for the further DRB; A method in an access network node.

11. A method in a further access network node, comprising: receiving a handover request message from an access network node, the handover request message including Multicast and Broadcast Services (MBS) session configuration information; sending a handover request confirmation message to the access network node, wherein if the further access network node or a cell of the further access network node supports MBS, the handover request confirmation message includes information indicating that the further access network node or the cell of the further access network node supports MBS; controlling a handover for the MBS between the access network node and the further access network node based on the information; If the further access network node does not support the MBS on a Multicast Radio Bearer (MRB), The MRB on the access network node is switched to a further Data Radio Bearer (DRB); configuration information for the further DRB is transmitted from the access network node to the mobile device before receiving the handover request message; the handover request message includes configuration information for the further DRB; A method in a further access network node.

12. receiving Multicast and Broadcast Services (MBS) using a Multicast Radio Bearer (MRB) via an access network node acting as a source node in the handover; performing the handover from the access network node to a further access network node acting as a target node; receiving the MBS from the further access network node if the further access network node or a cell of the further access network node supports the MBS; if the further access network node does not support the MBS on the MRB, The MRB on the access network node is switched to a further Data Radio Bearer (DRB); receiving, from the access network node before the further access network node receives a handover request message, configuration information for the further DRB; the handover request message includes configuration information for the further DRB; A method in a mobile device.

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