Method and apparatus for broadcast session release

Abstract

Various embodiments of the present disclosure provide a method for broadcast session release. The method which may be performed by a first network node comprises: determining information about one or more radio access networks (RANs). The information about the one or more RANs indicates that a broadcast multicast and broadcast services (MBS) session is released in the one or more RANs. In accordance with an exemplary embodiment, the method further comprises: transmitting a message including the information about the one or more RANs which are using multicast transport over N3mb interface towards a second network node.

Description

METHOD AND APPARATUS FORBROADCAST SESSION RELEASEFIELD OF THE INVENTION

[0001] The present disclosure generally relates to communication networks, and more specifically, to a method and apparatus for broadcast session release.BACKGROUND

[0002] This section introduces aspects that may facilitate a better understanding of the disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art.

[0003] With the rapid development of networking and communication technologies, wireless communication networks such as long-term evolution (LTE)Zfourth generation (4G) network and new radio (NR) / fifth generation (5G) network are expected to achieve high traffic capacity and energy efficiency. In order to meet the diverse requirements of new services across a wide variety of industries, the 3rd generation partnership project (3GPP) is developing various network function (NF) services for the communication system architecture (e.g., 5G system (5GS) architecture, etc.). The service-based architecture under development for the next generation network can restructure the core network control plane and divide it into multiple independent modules with decoupled functions that can be updated individually. Considering the diversity of network capabilities and application scenarios, provision and management of various services with different transport configurations may become more challenging.SUMMARY

[0004] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0005] Multicast and broadcast services (MBS) is one of the most promising 5G applications / services, where the 5G network can be utilized to transmit contents to multiple user equipments (UEs). MBS may be a critical technology for public safety, the automotive industry, etc. Designing a meaningful and efficient system architecture to enable such a service may be important. Since there are usually different requirements and procedures if unicast or multicast applies in the core network, it may be desirable to provide solutions and implementation applicable for different transmission situations.

[0006] Various exemplary embodiments of the present disclosure propose a solution for broadcast session release, which can enable an event that a broadcast MBS session is released in one or more radio access networks (RANs)such as next generation-radio access networks (NG-RANs) to be informed to a network node (e.g., a multicast / broadcast session management function (MB-SMF), an application function (AF), a network exposure function (NEF), a multicast broadcast service function (MBSF), etc.) by another network node (e.g., an access and mobility management function (AMF), a MB-SMF, etc.), regardless of whether unicast transport or multicast transport is used over N3mb.

[0007] According to a first aspect of the present disclosure, there is provided a method performed by a first network node (e.g., AMF, etc.). The method comprises: determining information about one or more RANs. The information about the one or more RANs indicates that a broadcast MBS session is released in the one or more RANs. In accordance with an exemplary embodiment, the method further comprises: transmitting a message including the information about the one or more RANs which are using multicast transport over N3mb interface towards a second network node.

[0008] In accordance with an exemplary embodiment, the message may be an MBS context status notification. In accordance with another exemplary embodiment, the information about the one or more RANs may include an attribute indicating a RAN event related to a release of the broadcast MBS session.

[0009] In accordance with an exemplary embodiment, the attribute may be an OperationEvent attribute or a new attribute. In accordance with another exemplary embodiment, the attribute may indicate the RAN event related to the release of the broadcast MBS session by setting an OpEventType attribute or the new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

[0010] In accordance with an exemplary embodiment, the event information per RAN may include: an identifier of the RAN, a list of tracking area identifiers (TAIs) of one or more tracking areas served by the RAN, and / or an event indication for the RAN.

[0011] In accordance with an exemplary embodiment, the event indication may be set to a value which indicates an event that a NG-RAN has requested to release the broadcast MBS session in the NG-RAN.

[0012] In accordance with an exemplary embodiment, the attribute indicating the RAN event related to the release of the broadcast MBS session may also be applicable for a RAN using unicast transport over N3mb interface.

[0013] In accordance with an exemplary embodiment, the first network node may be configured to implement an AMF.

[0014] In accordance with an exemplary embodiment, the second network node may be configured to act as a NF service consumer.

[0015] In accordance with an exemplary embodiment, the second network node may be configured to implement an MB-SMF.

[0016] According to a second aspect of the present disclosure, there is provided an apparatus which may be implemented as a first network node. The apparatus may comprise one or more processors and one or more memoriesstoring computer program codes. The one or more memories and the computer program codes may be configured to, with the one or more processors, cause the apparatus at least to perform any step of the method according to the first aspect of the present disclosure.

[0017] According to a third aspect of the present disclosure, there is provided a computer-readable medium having computer program codes embodied thereon which, when executed on a computer, cause the computer to perform any step of the method according to the first aspect of the present disclosure.

[0018] According to a fourth aspect of the present disclosure, there is provided an apparatus which may be implemented as a first network node. The apparatus may comprise a determining unit and a transmitting unit. In accordance with some exemplary embodiments, the determining unit may be operable to carry out at least the determining step of the method according to the first aspect of the present disclosure. The transmitting unit may be operable to carry out at least the transmitting step of the method according to the first aspect of the present disclosure.

[0019] According to a fifth aspect of the present disclosure, there is provided a method performed by a second network node (e.g., an MB-SMF, etc.). The method comprises: receiving a first message transmitted by a first network node. The first message includes first information about one or more RANs which are using multicast transport over N3mb interface. The first information indicates that a broadcast MBS session is released in the one or more RANs. In accordance with an exemplary embodiment, the method further comprises: transmitting a second message including second information about the one or more RANs towards a third network node. The second information indicates that the broadcast MBS session is released in the one or more RANs.

[0020] In accordance with an exemplary embodiment, the first message may be an MBS context status notification. In accordance with another exemplary embodiment, the first information about the one or more RANs may include a first attribute indicating a RAN event related to a release of the broadcast MBS session.

[0021] In accordance with an exemplary embodiment, the first attribute may be an OperationEvent attribute or a new attribute. In accordance with another exemplary embodiment, the first attribute may indicate the RAN event related to the release of the broadcast MBS session by setting an OpEventType attribute or the new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

[0022] In accordance with an exemplary embodiment, the first attribute indicating the RAN event related to the release of the broadcast MBS session may also be applicable for a RAN using unicast transport over N3mb interface.

[0023] In accordance with an exemplary embodiment, the second message may be an MBS session event report. In accordance with another exemplary embodiment, the second information about the one or more RANs may include a second attribute indicating a RAN event related to a release of the broadcast MBS session.

[0024] In accordance with an exemplary embodiment, the second attribute may indicate the RAN event related to the release of the broadcast MBS session by setting an NgranEvent attribute or a new attribute to a value for a RANinitiated event together with event information per RAN in which the broadcast MBS session is released.

[0025] In accordance with an exemplary embodiment, the second attribute indicating the RAN event related to the release of the broadcast MBS session may also be applicable for a RAN using unicast transport over N3mb interface.

[0026] In accordance with an exemplary embodiment, the event information per RAN may include: an identifier of the RAN, a list of TAIs of one or more tracking areas served by the RAN, and / or an event indication for the RAN.

[0027] In accordance with an exemplary embodiment, the event indication may be set to a value which indicates an event that a NG-RAN has requested to release the broadcast MBS session in the NG-RAN.

[0028] In accordance with an exemplary embodiment, the second message may be transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation.

[0029] In accordance with an exemplary embodiment, the second message may be transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation and a Nnef_MBSSession_StatusNotify service operation.

[0030] According to a sixth aspect of the present disclosure, there is provided an apparatus which may be implemented as a second network node. The apparatus may comprise one or more processors and one or more memories storing computer program codes. The one or more memories and the computer program codes may be configured to, with the one or more processors, cause the apparatus at least to perform any step of the method according to the fifth aspect of the present disclosure.

[0031] According to a seventh aspect of the present disclosure, there is provided a computer-readable medium having computer program codes embodied thereon which, when executed on a computer, cause the computer to perform any step of the method according to the fifth aspect of the present disclosure.

[0032] According to an eighth aspect of the present disclosure, there is provided an apparatus which may be implemented as a second network node. The apparatus may comprise a receiving unit and a transmitting unit. In accordance with some exemplary embodiments, the receiving unit may be operable to carry out at least the receiving step of the method according to the fifth aspect of the present disclosure. The transmitting unit may be operable to carry out at least the transmitting step of the method according to the fifth aspect of the present disclosure.

[0033] According to a ninth aspect of the present disclosure, there is provided a method performed by a third network node (e.g., an AF / NEF / MBSF, etc.). The method comprises: receiving a message transmitted by a second network node. The message includes information about one or more RANs which are using multicast transport over N3mb interface. The information about the one or more RANs indicates that a broadcast MBS session is released in the one or more RANs. In accordance with an exemplary embodiment, the method further comprises: obtaining the information about the one or more RANs from the message.

[0034] In accordance with an exemplary embodiment, the message may be an MBS session event report. In accordance with another exemplary embodiment, the information about the one or more RANs may include an attribute indicating a RAN event related to a release of the broadcast MBS session.

[0035] In accordance with an exemplary embodiment, the attribute may indicate the RAN event related to the release of the broadcast MBS session by setting an NgranEvent attribute or a new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

[0036] In accordance with an exemplary embodiment, the event information per RAN may include: an identifier of the RAN, a list of TAIs of one or more tracking areas served by the RAN, and / or an event indication for the RAN.

[0037] In accordance with an exemplary embodiment, the event indication may be set to a value which indicates an event that a NG-RAN has requested to release the broadcast MBS session in the NG-RAN.

[0038] In accordance with an exemplary embodiment, the attribute indicating the RAN event related to the release of the broadcast MBS session may also be applicable for a RAN using unicast transport over N3mb interface.

[0039] In accordance with an exemplary embodiment, the message may be transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation.

[0040] In accordance with an exemplary embodiment, the message may be transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation and a Nnef_MBSSession_StatusNotify service operation.

[0041] In accordance with an exemplary embodiment, the third network node may be configured to implement one or more of an AF, a NEF and an MBSF.

[0042] According to a tenth aspect of the present disclosure, there is provided an apparatus which may be implemented as a third network node. The apparatus may comprise one or more processors and one or more memories storing computer program codes. The one or more memories and the computer program codes may be configured to, with the one or more processors, cause the apparatus at least to perform any step of the method according to the ninth aspect of the present disclosure.

[0043] According to an eleventh aspect of the present disclosure, there is provided a computer-readable medium having computer program codes embodied thereon which, when executed on a computer, cause the computer to perform any step of the method according to the ninth aspect of the present disclosure.

[0044] According to a twelfth aspect of the present disclosure, there is provided an apparatus which may be implemented as a third network node. The apparatus may comprise a receiving unit and an obtaining unit. In accordance with some exemplary embodiments, the receiving unit may be operable to carry out at least the receiving step of the method according to the ninth aspect of the present disclosure. The obtaining unit may be operable to carry out at leastthe obtaining step of the method according to the ninth aspect of the present disclosure.

[0045] According to various exemplary embodiments, an event that a broadcast MBS session is released in certain RAN (e.g., a NG-RAN using unicast transport or multicast transport over N3mb, etc.) may be notified by a first network node such as an AMF to a second network node such as an MB-SMF, so that the second network node may know that the broadcast session service in the area which is controlled by the RAN is stopped, and can further populate this event towards a third network node such as AF / NEF / MBSF. This can enhance the performance of broadcast session services and increase the flexibility of network function configurations.BRIEF DESCRIPTION OF THE DRAWINGSThe disclosure itself, the preferable mode of use and further objectives are best understood by reference to the following detailed description of the embodiments when read in conjunction with the accompanying drawings, in which:Fig.1 is a diagram illustrating an exemplary broadcast MBS session release require procedure according to an embodiment of the present disclosure;Fig.2 is a diagram illustrating an exemplary broadcast MBS session context status change notification procedure according to an embodiment of the present disclosure;Fig.3 is a flowchart illustrating a method according to an embodiment of the present disclosure;Fig .4 is a flowchart illustrating another method according to an embodiment of the present disclosure;Fig.5 is a flowchart illustrating yet another method according to an embodiment of the present disclosure;Fig.6 is a block diagram illustrating an apparatus according to an embodiment of the present disclosure; andFig.7A-7C are block diagrams illustrating various apparatus according to some embodiments of the present disclosure.DETAILED DESCRIPTION

[0046] The embodiments of the present disclosure are described in detail with reference to the accompanying drawings. It should be understood that these embodiments are discussed only for the purpose of enabling those skilled persons in the art to better understand and thus implement the present disclosure, rather than suggesting any limitations on the scope of the present disclosure. Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present disclosure should be or are in any single embodiment of the disclosure. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Furthermore, the described features, advantages, and characteristics of thedisclosure may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the disclosure.

[0047] As used herein, the term "communication network” refers to a network following any suitable communication standards, such as new radio (NR), long term evolution (LTE), LTE-Advanced, wideband code division multiple access (WCDMA), high-speed packet access (HSPA), and so on. Furthermore, the communications between a terminal device and a network node in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1 G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), 4G, 4.5G, 5G communication protocols, and / or any other protocols either currently known or to be developed in the future.

[0048] As used herein, the terms "first”, "second” and so forth refer to different elements. The singular forms "a” and "an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises”, "comprising”, "has”, "having”, "includes” and / or "including” as used herein, specify the presence of stated features, elements, and / or components and the like, but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof. The term "based on” is to be read as "based at least in part on”. The term "one embodiment” and "an embodiment” are to be read as "at least one embodiment”. The term "another embodiment” is to be read as "at least one other embodiment”. Other definitions, explicit and implicit, may be included below.

[0049] Broadcast MBS session release may be well-defined for unicast transport. 3GPP technical specification (TS) 38.413 V17.3.0 defines the MBS Session Release Response Transfer Information Element (IE) for unicast transport in clause 9.2.16.8. Such IE may be passed through an AMF and notified to an MB-SMF. Therefore, the MB-SMF can further notify an AF about the release procedure for the unicast broadcast MBS session.

[0050] For the case of multicast transport, there may be some similar requirements for the AMF to notify the MB- SMF while all NG-RANS involved in the MBS session have released the radio resource. Therefore, the solution for unicast may not be applicable here anymore.Figure 1

[0051] Fig.1 is a diagram illustrating an exemplary broadcast MBS session release require procedure according to an embodiment of the present disclosure. As shown in Fig.1 , the broadcast MBS session release require procedure initiated by a NG-RAN may include the following steps:1 . If the NG-RAN may not be able to continue to provide the broadcast MBS session, e.g., due to lack of radio resources, the NG-RAN may send Broadcast Session Release Require (MBS Session ID) to an AMF.2. The AMF may initiate Broadcast Session Release towards the NG-RAN (e.g., as described in steps 4 - 7 in clause 7.3.2 of 3GPP TS 23.247 V18.0.0).3. If unicast transport applies in N3mb interface, the AMF may receive the downlink (DL) tunnel information for the broadcast MBS session from the NG-RAN in step 2. The AMF may notify a MB-SMF about the DL tunnel release via Namf_MBSBroadcast_ContextStatusNotify. If multicast transport applies in N3mb interface, only when Broadcast Session Release Require is performed for all the NG-RANs involved in the MBS session which are managed by the AMF, the AMF may notify the MB-SMF about radio resource release via Namf_MBSBroadcast_ContextStatusNotify indicating radio resource release.3a-3b. This step may be applied if an AF subscribed to a Delivery Status Indication (e.g., as described in clause 7.3.5 of 3GPP TS 23.247 V18.0.0). If Broadcast Session Release Require is performed by all the NG-RANs, i.e. , for unicast N3mb transport, the MB-SMF may release all the DL tunnel information for the broadcast MBS session, and for multicast N3mb transport, the MB-SMF may receive radio resource release from all the AMFs for the broadcast MBS session. The MB-SMF may notify the AF directly of the situation by invoking Nmbsmf_MBSSession_StatusNotify, or the MB-SMF may notify the AF via NEF / MBSF (if deployed) by invoking Nmbsmf_MBSSession_StatusNotify service operation to the NEF / MBSF which then invokes Nnef_MBSSession_StatusNotify service operation to the AF.4. The MB-SMF may perform N4mb Session Modification to let a multicast / broadcast session management function (MB-UPF) stop the broadcast data forwarding towards the indicated DL tunnel and release the DL tunnel.

[0052] The protocol support for the broadcast MBS session release require procedure as specified in 3GPP TS 23.247 V18.0.0 may not be well supported in Namf_MBSBroadcast service. As described with respect to Fig.1 , the broadcast session release require procedure is triggered when the NG-RAN may not be able to continue to provide the broadcast MBS session (e.g., due to a lack of radio resources), and such event may need to be reported to the MB-SMF, so that the MB-SMF can know that the MBS session is released in the area covered by the NG-RAN.

[0053] However, such information can only be reported to the MB-SMF when the NG-RAN is using unicast transport over N3mb, e.g., when the NG-RAN triggers to send a broadcast session release require to release the broadcast MBS session, the AMF may in turn send a broadcast session release request, and the NG-RAN may answer with a broadcast MBS session release response.

[0054] When unicast transport is used, the NG-RAN may include the MBS Session Release Response Transfer IE, which can be included in the N2MbsSmlnfo, where the NG-RAN ID is included, so that the MB-SMF can derive that the MBS session has been released in the NG-RAN via the MBS Session Release Response Transfer IE.

[0055] However, when multicast transport is used by the NG-RAN, the MBS Session Release Response Transfer IE may not be present, and the AMF may not be able to include N2MbsSmlnfo since ngapleType and ngapData are mandatory IE in the N2MbsSmlnfo. In this case, the MB-SMF may not be able to get a report that the MBS session hasbeen released in one or more NG-RANs.

[0056] In order to address one or more issues mentioned above, various exemplary embodiments of the present disclosure propose solutions to enable an AMF to report to an MB-SMF an event that a broadcast MBS session has been released in one or more NG-RANs, and / or that the broadcast MBS session has been released in all NG-RANs which are managed by the AMF, regardless of unicast or multicast transport is used over N3mb. In addition, the MB-SMF may further populate the event (that the broadcast MBS session has been released in one or more NG-RANs) to an AF / MBSF / NEF.

[0057] In accordance with an exemplary embodiment, during one or more NG-RANs required broadcast MBS session release procedure, the existing attribute OperationEvent or a new attribute may be used by the AMF to report the broadcast MBS session release to the MB-SMF, e.g., by setting the OpEventType attribute or the new attribute to "NG_RAN_EVENT” or a value indicating NG_RAN_initiated_event together with a list of "ngranFailureEvent” or a corresponding new event (which may be called "ngranEvent”) for each NG-RAN which has required to release the broadcast MBS session. In an embodiment, the "ngranFailureEvent” or the new event may contain the NG-RAN ID to identify the NG-RAN (and optionally a list of TAIs for one or more tracking areas which the NG-RAN is serving) and an indication what is the event. A new NgranFailurelndication "NG_RAN_REQUIRED_RELEASE” may be introduced to indicate the event that the NG-RAN has requested to release the broadcast MBS session in the NG-RAN. It is noted that when a list of TAIs is contained in the "ngranFailureEvent” or the new event, the MB-SMF may not need to have a mapping between NG-RAN ID and TAI(s) that the NG-RAN is covering. In fact, the NEF (as a NF interfacing towards an external node) may be configured with the mapping between civil geographical area and 3GPP location, e.g., TAIs, etc.

[0058] In addition, "MBS_SESSION_RELEASE_COMPLETE” or a new indication may be introduced to the operationstatus IE to indicate all NG-RANs for the broadcast MBS session which are managed by the AMF has released the resource for the broadcast MBS session, so that the MB-SMF can further notify it to the AF.

[0059] According to the proposed solutions of the present disclosure, on the one hand, the OpEventType attribute may be used together with "ngranFailureEvent” to indicate a release of the broadcast MBS session of a NG-RAN; and on the other hand, "MBS_SESSION_RELEASE_COMPLETE” may be used to indicate the broadcast MBS session release of all NG-RANs. The joint mechanisms of broadcast MBS session release for each NG-RAN and for all NG-RANs may be applied to ensure that when multicast transport is used by NG-RANs, each NG-RAN may have its own operation event type and event list to indicate a release of the broadcast MBS session and the AMF can explicitly report to the MB-SMF about the MBS session release in all NG-RANs.

[0060] Many advantages may be achieved by applying the proposed solution. For example, the proposed solution may be applicable to a broadcast MBS session release procedure while multicast transport is used. In addition, the proposed solution is complete and can cover different cases of session release required by at least part of NG-RANs and also can provide further information on each NG-RAN, which may be a concrete solution that can be used further by the MB-SMF.

[0061] In accordance with an exemplary embodiment, the ContextStatusNotify service operation may be used byan AMF to notify status change of a broadcast MBS session context to a NF service consumer (e.g., an MB-SMF, etc.). For example, the ContextStatusNotify service operation may be used in the following procedures:- MBS Session Start for Broadcast (e.g., as described in clause 7.3.1 of 3GPP TS 23.247 V18.0.0);- MBS Session Update for Broadcast (e.g., as described in clause 7.3.3 of 3GPP TS 23.247 V18.0.0);- Broadcast MBS Session Release Require (e.g., as described in clause 7.3.6 of 3GPP TS 23.247 V18.0.0).- Broadcast MBS session restoration by MB-SMF (e.g., as described in clause 8.3.2.3 of 3GPP TS 23.527 V17.6.0).- Selecting an alternative AMF for a Broadcast MBS Session at AMF failure (e.g., as described in clause 8.3.2.4 of 3GPP TS 23.527 V17.6.0).Figure 2

[0062] Fig.2 is a diagram illustrating an exemplary broadcast MBS session context status change notification procedure according to an embodiment of the present disclosure. As shown in Fig.2, an AMF may notify status change of a broadcast MBS session context to a NF Service Consumer (e.g., an MB-SMF, etc.) by using the HTTP POST method with the following steps:1. The AMF may send a POST request targeting the notification uniform resource identifier (URI) received from the NF Service Consumer. The payload body of the POST request may contain the following information:- MBS Session ID (e.g., temporary mobile group identity (TMGI), or TMGI and network identifier (NID) for an MBS session in a standalone non-public network (SNPN), etc.);- Area Session ID, if this is a location dependent broadcast MBS service;- one or more N2 MBS Session Management containers, if N2 MBS session management information (e.g., MBS Session Setup or Modification Response Transfer IE, MBS Session Setup or Modification Failure Transfer IE or MBS Session Release Response Transfer IE in 3GPP TS 38.413 V17.3.0) has been received from one or more NG-RANs that may need to be transferred to the NF Service Consumer; for each N2 MBS Session Management container sent towards the MB-SMF, the AMF may insert the identifier of the NG-RAN node that generated it in the corresponding entry of the n2MbsSmlnfoList attribute.- the operationstatus IE indicating the completion of the Broadcast MBS session establishment, update or release, if the NF Service Consumer has requested to establish or update the Broadcast MBS session context and a response has been received from all NG-RANs; and- the operationstatus IE indicating the incompletion of the Broadcast MBS session establishment or update, if the NF Service Consumer has requested to establish or update the Broadcast MBS session context including a maximum response time and the AMF has not received responses from all NG-RANs before the maximum response time elapses.During a Broadcast MBS Session Release Require procedure, one or more NG-RANs may request to release the Broadcast MBS session, in this case, the AMF may report the Broadcast MBS Session release to the MB- SMF by including an operationEvent attribute in the MBS Context Status Notification request and setting the OpEventType to "NG_RAN_EVENT” together with a list of "ngranFailureEvent” for each NG-RAN has required to release the Broadcast MBS Session.If all NG-RANs for the Broadcast MBS session which are managed by the AMF has released the Broadcast MBS session by sending a Broadcast Session Release Response message, the AMF may include the operationstatus IE and set it to "MBS_SESSION_RELEASE_COMPLETE” to report the Broadcast MBS session is released in the AMF.The AMF may include an operationEvent attribute in the MBS Context Status Notification request to report the MB-SMF:- a NG-RAN failure event, e.g., the NG-RAN failure with or without restart, as specified in clause 8.3.2.3 of 3GPP TS 23.527 V17.6.0);- that a new AMF has taken over the control of the broadcast MBS session upon an AMF failure as specified in clause 8.3.2.4 of 3GPP TS 23.527 V17.6.0).2a. On success, the NF Service Consumer may return a "204 No Content” response.2b. On failure or redirection, one of the HTTP status codes listed in Table 6.5.5.2.3.1-3 of 3GPP TS 29.518 V18.0.0 may be returned. For a 4xx / 5xx response, the message body may contain a ProblemDetails attribute with the "cause” attribute set to one of the application errors listed in Table 6.5.5.2.3.1-3 of 3GPP TS 29.518 V18.0.0.

[0063] In accordance with an exemplary embodiment, an exemplary definition of type ContextStatusNotification is shown in Table 1.Table 1

[0064] In accordance with an exemplary embodiment, an exemplary enumeration Operationstatus which may represent the status of a broadcast MBS session start or update operation is shown in Table 2.Table 2

[0065] In accordance with an exemplary embodiment, an exemplary enumeration NgranFailurelndication which may indicate a NG-RAN failure event (e.g., a release of the broadcast MBS session in a NG-RAN as required by the NG- RAN) is shown in Table 3.Table 3

[0066] In accordance with an exemplary embodiment, an exemplary Namf_MBSBroadcast application programming interface (API) may include the following contents:- skip for clarity -Operationstatus: description: Status of a Broadcast MBS session start or update operation. anyOf:- type: string enum:- MBS_SESSION_START_COMPLETE- MBS_SESSION_START_INCOMPLETE- MBS_SESSION_UPDATE_COMPLETE- MBS_SESSION_UPDATE_INCOMPLETE- MBS_SESSION_RELEASE_COMPLETE- type: string- skip for clarity -NgranFailurelndication: description: Indicates a NG-RAN failure event. anyOf:- type: string enum:- NG_RAN_RESTART_OR_START- NG_RAN_FAILURE_WITHOUT_RESTART- NG_RAN_NOT_REACHABLE- NG_RAN_REQUIRED_RELEASE- type: string- skip for clarity -

[0067] In accordance with an exemplary embodiment, the Nmbsmf_MBSSession_StatusNotify service may be able to notify an AF about the delivery status indication. When multicast transport is applied in N3mb, the broadcast session release require may be performed for all the NG-RANs involved in the MBS session. There may be no enough information for this case when parts of the NG-RANs are released. As described with respect to Fig.1 , for the scenario where at least part of the NG-RANs is released, such information may be passed through the Nmbsmf_MBSSession_StatusNotify toward the AF.

[0068] As described in 3GPP TS 29.532 V17.3.0, the status notification service may use StatusNotifyReqData and is further defined by MbsSessionEventResportList for MBS session related events. The MbsSessionEventResportList is further specified in 3GPP TS 29.571 V18.0.0. In an embodiment, a NEF may be able to get the notification from an MB- SMF and further pass it to an AF, e.g., the MbsSessionStatusNotify may be used as described in 3GPP TS 29.522 V18.0.0 to make the AF get the notification to the MBS session status. The MbsSessionStatusNotify may be further defined as theMbsSessionEventResportList, e.g., as described in 3GPP TS 29.571 V18.0.0.

[0069] In accordance with an exemplary embodiment, the definition of NG-RAN related information may be introduced into the MbsSessionEventReport to enable the status notification from the MB-SMF to the AF. Furthermore, it may be important for the NG-RAN to pass the event status towards the AF so that the AF may be aware of the status of the broadcast MBS session and can take further action. In an embodiment, the NG-RAN event may be passed towards the AF as well by introducing the ngranEventlndication attribute into the MbsSessionEventReport.

[0070] In accordance with an exemplary embodiment, an exemplary definition of type MbsSessionEventReport is shown in Table 4. The MbsSessionEventReport data type may be used to cover the scenario where the NG-RAN partially failed to release. Table 4

[0071] In accordance with an exemplary embodiment, an exemplary definition of type NgranEvent is shown in Table 5, and an exemplary enumeration NgranEventlndication which may indicate the NG-RAN status is shown in Table 6. NgranEvent and NgranEventlndication may be used to pass the NG-RAN event to the AF. Table 5Table 6

[0072] In accordance with an exemplary embodiment, the corresponding API may be updated as well. For example, the data related to common data types may include the following contents:- skip for clarity -MbsSessionEventReport: description: MBS session event report type: object properties: eventType:$ref: '# / components / schemas / MbsSessionEventType' timeStamp:$ref: '# / components / schemas / DateTime'IngressTunAddrlnfo:$ref: '# / components / schemas / lngressTunAddrlnfo' broadcastDel Status:$ref: '# / components / schemas / BroadcastDelivery Status' ngranEventList: type: array item:$ref: '# / components / schemas / NgranEvent' minltems: 1 required:- eventType- skip for clarity -NgranEvent: description: the event status of the NG-RAN type: object properties:ranld:$ref: '# / components / schemas / GlobalRanNodeld' taiList: type: array item:$ref: '# / components / schemas / Tai minltems: 1 ngranEventlndication: type: boolean required:- ranld- taiList- ngranEventlndication- skip for clarity -NgranEventlndication: anyOf:- anyOf:- type: string enum:- NG_RAN_RESTART_OR_START- NG_RAN_FAILURE_WITHOUT_RESTART- NG_RAN_NOT_REACHABLE- NG_RAN_REQUIRED_RELEASE- type: string- $ref: '# / components / schemas / NullValue' description: >The enumeration NgranEventlndication defines the NG-RAN event status.It shall comply with the provisions defined in Table 6.- skip for clarity -

[0073] It can be appreciated that network elements and signaling messages shown in Fig.1 and Fig.2 are just as examples, and more or less alternative network elements and signaling messages may be involved in the broadcast session release procedure according to various embodiments of the present disclosure. It also can be appreciated that the names, representations and values of the parameter / attributes used herein are exemplary, and other names, representations and values may also be used to indicate the same or similar information.Figure 3

[0074] Fig.3 is a flowchart illustrating a method 300 according to some embodiments of the present disclosure. The method 300 illustrated in Fig.3 may be performed by a first network node or an apparatus communicatively coupled to the first network node. In accordance with an exemplary embodiment, the first network node may be configured to implement an AMF or act as any other suitable network entity which may be configured to perform access and mobility management for one or more terminal devices (e.g., UEs, etc.). In accordance with another exemplary embodiment, the first network node may be configured to report a broadcast session status to a second network node (e.g., an MB-SMF, etc.).

[0075] According to the exemplary method 300 illustrated in Fig.3, the first network node may determine information about one or more RANs, as shown in block 302. The information about the one or more RANs may indicate that a broadcast MBS session is released in the one or more RANs. In accordance with an exemplary embodiment, the first network node may transmit a message including the information about the one or more RANs which are using multicast transport over N3mb interface towards a second network node, as shown in block 304.

[0076] In accordance with an exemplary embodiment, the message may be an MBS context status notification. In accordance with another exemplary embodiment, the information about the one or more RANs may include an attribute indicating a RAN event related to a release of the broadcast MBS session.

[0077] In accordance with an exemplary embodiment, the attribute may be an OperationEvent attribute or a new attribute. In accordance with another exemplary embodiment, the attribute may indicate the RAN event related to the release of the broadcast MBS session by setting an OpEventType attribute or the new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

[0078] In accordance with an exemplary embodiment, the event information per RAN may include an identifier of the RAN, a list of TAIs of one or more tracking areas served by the RAN, and / or an event indication for the RAN. In an embodiment, the event indication for the RAN may be set to a value which indicates an event that a NG-RAN has requested to release the broadcast MBS session in the NG-RAN. For example, the first network node such as an AMF may report the broadcast MBS session release to the second network node such as an MB-SMF by including an operationEvent attribute in the MBS context status notification request and setting the OpEventType to "NG_RAN_EVENT” together with a list of "ngranFailureEvent” for each NG-RAN has required to release the broadcast MBS session.

[0079] In accordance with an exemplary embodiment, the attribute indicating the RAN event related to the release of the broadcast MBS session may also be applicable for a RAN using unicast transport over N3mb interface.Figure 4

[0080] Fig.4 is a flowchart illustrating a method 400 according to some embodiments of the present disclosure. The method 400 illustrated in Fig.4 may be performed by a second network node or an apparatus communicatively coupledto the second network node. In accordance with an exemplary embodiment, the second network node may be configured to act as a NF service consumer. For example, the second network node may be configured to implement an MB-SMF or act as any other suitable network entity which may be configured to perform a multicast / broadcast session management function. In accordance with another exemplary embodiment, the second network node may be configured to obtain a report of broadcast session status from a first network node (e.g., an AMF, etc.) and notify the broadcast session status to a third network node (e.g., an AF / NEF / MBSF, etc.).

[0081] According to the exemplary method 400 illustrated in Fig.4, the second network node may receive a first message transmitted by a first network node (e.g., the first network node as described with respect to Fig.3), as shown in block 402. The first message may include first information about one or more RANs which are using multicast transport over N3mb interface. The first information may indicate that a broadcast MBS session is released in the one or more RANs. In accordance with an exemplary embodiment, the second network node may transmit a second message including second information about the one or more RANs towards a third network node, as shown in block 404. The second information may indicate that the broadcast MBS session is released in the one or more RANs.

[0082] In accordance with an exemplary embodiment, the first message may be an MBS context status notification. In accordance with another exemplary embodiment, the first information about the one or more RANs may include a first attribute indicating a RAN event related to a release of the broadcast MBS session.

[0083] In accordance with an exemplary embodiment, the first attribute may be an OperationEvent attribute or a new attribute. In accordance with another exemplary embodiment, the first attribute may indicate the RAN event related to the release of the broadcast MBS session by setting an OpEventType attribute or the new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

[0084] In accordance with an exemplary embodiment, the first attribute indicating the RAN event related to the release of the broadcast MBS session may also be applicable for a RAN using unicast transport over N3mb interface.

[0085] In accordance with an exemplary embodiment, the second message may be an MBS session event report. In accordance with another exemplary embodiment, the second information about the one or more RANs may include a second attribute indicating a RAN event related to a release of the broadcast MBS session.

[0086] In accordance with an exemplary embodiment, the second attribute may indicate the RAN event related to the release of the broadcast MBS session by setting an NgranEvent attribute or a new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

[0087] In accordance with an exemplary embodiment, the second attribute indicating the RAN event related to the release of the broadcast MBS session may also be applicable for a RAN using unicast transport over N3mb interface.

[0088] In accordance with an exemplary embodiment, the event information per RAN may include: an identifier of the RAN, a list of TAIs of one or more tracking areas served by the RAN, and / or an event indication for the RAN. In anembodiment, the event indication may be set to a value which indicates an event that a NG-RAN has requested to release the broadcast MBS session in the NG-RAN.

[0089] In accordance with an exemplary embodiment, the second message may be transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation. In accordance with another exemplary embodiment, the second message may be transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation and a Nnef_MBSSession_StatusNotify service operation.Figure 5

[0090] Fig.5 is a flowchart illustrating a method 500 according to some embodiments of the present disclosure. The method 500 illustrated in Fig.5 may be performed by a third network node or an apparatus communicatively coupled to the third network node. In accordance with an exemplary embodiment, the third network node may be configured to implement one or more NFs such as AF, NEF and / or MBSF, or act as any other suitable network entity which may be configured to perform one or more application / service functions. In accordance with another exemplary embodiment, the third network node may be configured to obtain a report of broadcast session status from a second network node (e.g., an MB-SMF, etc.).

[0091] According to the exemplary method 500 illustrated in Fig.5, the third network node may receive a message transmitted by a second network node (e.g., the second network node as described with respect to Fig.4), as shown in block 502. The message may include information about one or more RANs which are using multicast transport over N3mb interface. The information about the one or more RANs may indicate that a broadcast MBS session is released in the one or more RANs. In accordance with an exemplary embodiment, the third network node may obtain the information about the one or more RANs from the message, as shown in block 504.

[0092] In accordance with an exemplary embodiment, the message may be an MBS session event report. In accordance with another exemplary embodiment, the information about the one or more RANs may include an attribute indicating a RAN event related to a release of the broadcast MBS session.

[0093] In accordance with an exemplary embodiment, the attribute may indicate the RAN event related to the release of the broadcast MBS session by setting an NgranEvent attribute or a new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

[0094] In accordance with an exemplary embodiment, the event information per RAN may include an identifier of the RAN, a list of TAIs of one or more tracking areas served by the RAN, and / or an event indication for the RAN. In an embodiment, the event indication may be set to a value which indicates an event that a NG-RAN has requested to release the broadcast MBS session in the NG-RAN.

[0095] In accordance with an exemplary embodiment, the attribute indicating the RAN event related to the releaseof the broadcast MBS session may also be applicable for a RAN using unicast transport over N3mb interface.

[0096] In accordance with an exemplary embodiment, the message may be transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation. In accordance with another exemplary embodiment, the message may be transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation and a Nnef_MBSSession_StatusNotify service operation.

[0097] The various blocks shown in Figs.3-5 may be viewed as method steps, and / or as operations that result from operation of computer program code, and / or as a plurality of coupled logic circuit elements constructed to carry out the associated function(s). The schematic flow chart diagrams described above are generally set forth as logical flow chart diagrams. As such, the depicted order and labeled steps are indicative of specific embodiments of the presented methods. Other steps and methods may be conceived that are equivalent in function, logic, or effect to one or more steps, or portions thereof, of the illustrated methods. Additionally, the order in which a particular method occurs may or may not strictly adhere to the order of the corresponding steps shown.

[0098] It can be appreciated that the network node according to various embodiments can be implemented either as a network element and / or a network entity on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform, e.g., on a cloud infrastructure.Figure 6

[0099] Fig.6 is a block diagram illustrating an apparatus 600 according to various embodiments of the present disclosure. As shown in Fig.6, the apparatus 600 may comprise one or more processors such as processor 601 and one or more memories such as memory 602 storing computer program codes 603. The memory 602 may be non-transitory machine / processor / computer readable storage medium. In accordance with some exemplary embodiments, the apparatus 600 may be implemented as an integrated circuit chip or module that can be plugged or installed into a first network node as described with respect to Fig.3, or a second network node as described with respect to Fig.4, or a third network node as described with respect to Fig.5. In such cases, the apparatus 600 may be implemented as a first network node as described with respect to Fig.3, or a second network node as described with respect to Fig.4, or a third network node as described with respect to Fig.5.

[0100] In some implementations, the one or more memories 602 and the computer program codes 603 may be configured to, with the one or more processors 601 , cause the apparatus 600 at least to perform any operation of the method as described in connection with Fig.3. In other implementations, the one or more memories 602 and the computer program codes 603 may be configured to, with the one or more processors 601 , cause the apparatus 600 at least to perform any operation of the method as described in connection with Fig.4. In other implementations, the one or more memories 602 and the computer program codes 603 may be configured to, with the one or more processors 601 , cause the apparatus 600 at least to perform any operation of the method as described in connection with Fig.5. Alternatively oradditionally, the one or more memories 602 and the computer program codes 603 may be configured to, with the one or more processors 601 , cause the apparatus 600 at least to perform more or less operations to implement the proposed methods according to the exemplary embodiments of the present disclosure.Figure 7A

[0101] Fig.7A is a block diagram illustrating an apparatus 710 according to some embodiments of the present disclosure. As shown in Fig.7A, the apparatus 710 may comprise a determining unit 711 and a transmitting unit 712. In an exemplary embodiment, the apparatus 710 may be implemented in a first network node (e.g., an AMF, etc.). The determining unit 711 may be operable to carry out the operation in block 302, and the transmitting unit 712 may be operable to carry out the operation in block 304. Optionally, the determining unit 711 and / or the transmitting unit 712 may be operable to carry out more or less operations to implement the proposed methods according to the exemplary embodiments of the present disclosure.Figure 7B

[0102] Fig.7B is a block diagram illustrating an apparatus 720 according to some embodiments of the present disclosure. As shown in Fig.7B, the apparatus 720 may comprise a receiving unit 721 and a transmitting unit 722. In an exemplary embodiment, the apparatus 720 may be implemented in a second network node (e.g., an MB-SMF, etc.). The receiving unit 721 may be operable to carry out the operation in block 402, and the transmitting unit 722 may be operable to carry out the operation in block 404. Optionally, the receiving unit 721 and / or the transmitting unit 722 may be operable to carry out more or less operations to implement the proposed methods according to the exemplary embodiments of the present disclosure.Figure 7C

[0103] Fig.7C is a block diagram illustrating an apparatus 730 according to some embodiments of the present disclosure. As shown in Fig.7C, the apparatus 730 may comprise a receiving unit 731 and an obtaining unit 732. In an exemplary embodiment, the apparatus 730 may be implemented in a third network node (e.g., an AF / NEF / MBSF, etc.). The receiving unit 731 may be operable to carry out the operation in block 502, and the obtaining unit 732 may be operable to carry out the operation in block 504. Optionally, the receiving unit 731 and / or the obtaining unit 732 may be operable to carry out more or less operations to implement the proposed methods according to the exemplary embodiments of the present disclosure.

[0104] In general, the various exemplary embodiments may be implemented in hardware or special purpose chips, circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the exemplary embodiments of this disclosure may be illustrated and described as block diagrams, flow charts, or using some otherpictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0105] As such, it should be appreciated that at least some aspects of the exemplary embodiments of the disclosure may be practiced in various components such as integrated circuit chips and modules. It should thus be appreciated that the exemplary embodiments of this disclosure may be realized in an apparatus that is embodied as an integrated circuit, where the integrated circuit may comprise circuitry (as well as possibly firmware) for embodying at least one or more of a data processor, a digital signal processor, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this disclosure.

[0106] It should be appreciated that at least some aspects of the exemplary embodiments of the disclosure may be embodied in computer-executable instructions, such as in one or more program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device. The computer executable instructions may be stored on a computer readable medium such as a hard disk, optical disk, removable storage media, solid state memory, random access memory (RAM), etc. As will be appreciated by one of skill in the art, the function of the program modules may be combined or distributed as desired in various embodiments. In addition, the function may be embodied in whole or partly in firmware or hardware equivalents such as integrated circuits, field programmable gate arrays (FPGA), and the like.Some EmbodimentsSome embodiments that have been described above can be summarized in the following manner:1 . A method (300) performed by a first network node, comprising: determining (302) information about one or more radio access networks, RANs, wherein the information about the one or more RANs indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and transmitting (304) a message including the information about the one or more RANs which are using multicast transport over N3mb interface towards a second network node.2. The method according to embodiment 1 , wherein the message is an MBS context status notification, and the information about the one or more RANs includes an attribute indicating a RAN event related to a release of the broadcast MBS session.3. The method according to embodiment 2, wherein the attribute is an OperationEvent attribute or a new attribute, and indicates the RAN event related to the release of the broadcast MBS session by setting an OpEventType attribute or the new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.4. The method according to embodiment 3, wherein the event information per RAN includes one or more of the following information: an identifier of the RAN; a list of tracking area identifiers, TAIs, of one or more tracking areas served by the RAN; and an event indication for the RAN.5. The method according to embodiment 4, wherein the event indication is set to a value which indicates an event that a next generation-radio access network, NG-RAN, has requested to release the broadcast MBS session in the NG-RAN.6. The method according to any of embodiments 2-5, wherein the attribute indicating the RAN event related to the release of the broadcast MBS session is also applicable for a RAN using unicast transport over N3mb interface.7. The method according to any of embodiments 1-6, wherein the first network node is configured to implement an access and mobility management function, AMF.8. The method according to any of embodiments 1-7, wherein the second network node is configured to act as a network function, NF, service consumer.9. The method according to any of embodiments 1-8, wherein the second network node is configured to implement a multicast / broadcast session management function, MB-SMF.10. A first network node (600), comprising: one or more processors (601); and one or more memories (602) comprising computer program codes (603), the one or more memories (602) and the computer program codes (603) configured to, with the one or more processors (601), cause the first network node (600) at least to: determine information about one or more radio access networks, RANs, wherein the information about the one or more RANs indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and transmit a message including the information about the one or more RANs which are using multicast transport over N3mb interface towards a second network node.11 . The first network node according to embodiment 10, wherein the one or more memories and the computer program codes are configured to, with the one or more processors, cause the first network node to perform the method according to any one of embodiments 2-9.12. A computer-readable medium having computer program codes (603) embodied thereon which, when executed on a computer, cause the computer to perform any step of the method according to any one of embodiments 1-9.13. A method (400) performed by a second network node, comprising: receiving (402) a first message transmitted by a first network node, wherein the first message includes first information about one or more radio access networks, RANs, which are using multicast transport over N3mb interface, and the first information indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and transmitting (404) a second message including second information about the one or more RANs towards a third network node, wherein the second information indicates that the broadcast MBS session is released in the one or more RANs.14. The method according to embodiment 13, wherein the first message is an MBS context status notification, and the first information about the one or more RANs includes a first attribute indicating a RAN event related to a release of the broadcast MBS session.15. The method according to embodiment 14, wherein the first attribute is an OperationEvent attribute or a new attribute, and indicates the RAN event related to the release of the broadcast MBS session by setting an OpEventType attribute or the new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.16. The method according to embodiment 14 or 15, wherein the first attribute indicating the RAN event related to the release of the broadcast MBS session is also applicable for a RAN using unicast transport over N3mb interface.17. The method according to any of embodiments 13-16, wherein the second message is an MBS session event report, and the second information about the one or more RANs includes a second attribute indicating a RAN event related to a release of the broadcast MBS session.18. The method according to embodiment 17, wherein the second attribute indicates the RAN event related to the release of the broadcast MBS session by setting an NgranEvent attribute or a new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.19. The method according to embodiment 17 or 18, wherein the second attribute indicating the RAN event related to the release of the broadcast MBS session is also applicable for a RAN using unicast transport over N3mb interface.20. The method according to embodiment 15 or 18, wherein the event information per RAN includes one or more of the following information:an identifier of the RAN; a list of tracking area identifiers, TAIs, of one or more tracking areas served by the RAN; and an event indication for the RAN.21. The method according to embodiment 20, wherein the event indication is set to a value which indicates an event that a next generation-radio access network, NG-RAN, has requested to release the broadcast MBS session in the NG- RAN.22. The method according to any of embodiments 13-21 , wherein the second message is transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation, or via invoking a Nmbsmf_MBSSession_StatusNotify service operation and a Nnef_MBSSession_StatusNotify service operation.23. The method according to any of embodiments 13-22, wherein the first network node is configured to implement an access and mobility management function, AMF.24. The method according to any of embodiments 13-23, wherein the second network node is configured to act as a network function, NF, service consumer.25. The method according to any of embodiments 13-24, wherein the second network node is configured to implement a multicast / broadcast session management function, MB-SMF.26. The method according to any of embodiments 13-25, wherein the third network node is configured to implement one or more of the following functions: an application function, AF; a network exposure function, NEF; and a multicast broadcast service function, MBSF.27. A second network node (600), comprising: one or more processors (601); and one or more memories (602) comprising computer program codes (603), the one or more memories (602) and the computer program codes (603) configured to, with the one or more processors (601), cause the second network node (600) at least to: receive a first message transmitted by a first network node, wherein the first message includes first information about one or more radio access networks, RANs, which are using multicast transport over N3mb interface, and the first information indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; andtransmit a second message including second information about the one or more RANs towards a third network node, wherein the second information indicates that the broadcast MBS session is released in the one or more RANs.28. The second network node according to embodiment 27, wherein the one or more memories and the computer program codes are configured to, with the one or more processors, cause the second network node to perform the method according to any one of embodiments 14-26.29. A computer-readable medium having computer program codes (603) embodied thereon which, when executed on a computer, cause the computer to perform any step of the method according to any one of embodiments 13-26.30. A method (500) performed by a third network node, comprising: receiving (502) a message transmitted by a second network node, wherein the message includes information about one or more radio access networks, RANs, which are using multicast transport over N3mb interface, and the information about the one or more RANs indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and obtaining (504) the information about the one or more RANs from the message.31 . The method according to embodiment 30, wherein the message is an MBS session event report, and the information about the one or more RANs includes an attribute indicating a RAN event related to a release of the broadcast MBS session.32. The method according to embodiment 31 , wherein the attribute indicates the RAN event related to the release of the broadcast MBS session by setting an NgranEvent attribute or a new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.33. The method according to embodiment 32, wherein the event information per RAN includes one or more of the following information: an identifier of the RAN; a list of tracking area identifiers, TAIs, of one or more tracking areas served by the RAN; and an event indication for the RAN.34. The method according to embodiment 33, wherein the event indication is set to a value which indicates an event that a next generation-radio access network, NG-RAN, has requested to release the broadcast MBS session in the NG- RAN.35. The method according to any of embodiments 31-34, wherein the attribute indicating the RAN event related to the release of the broadcast MBS session is also applicable for a RAN using unicast transport over N3mb interface.36. The method according to any of embodiments 30-35, wherein the message is transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation, or via invoking a Nmbsmf_MBSSession_StatusNotify service operation and a Nnef_MBSSession_StatusNotify service operation.37. The method according to any of embodiments 30-36, wherein the second network node is configured to act as a network function, NF, service consumer.38. The method according to any of embodiments 30-37, wherein the second network node is configured to implement a multicast / broadcast session management function, MB-SMF.39. The method according to any of embodiments 30-38, wherein the third network node is configured to implement one or more of the following functions: an application function, AF; a network exposure function, NEF; and a multicast broadcast service function, MBSF.40. A third network node (600), comprising: one or more processors (601); and one or more memories (602) comprising computer program codes (603), the one or more memories (602) and the computer program codes (603) configured to, with the one or more processors (601), cause the third network node (600) at least to: receive a message transmitted by a second network node, wherein the message includes information about one or more radio access networks, RANs, which are using multicast transport over N3mb interface, and the information about the one or more RANs indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and obtain the information about the one or more RANs from the message.41 . The third network node according to embodiment 40, wherein the one or more memories and the computer program codes are configured to, with the one or more processors, cause the third network node to perform the method according to any one of embodiments 31-39.42. A computer-readable medium having computer program codes (603) embodied thereon which, when executed on a computer, cause the computer to perform any step of the method according to any one of embodiments 30-39.

[0107] The present disclosure includes any novel feature or combination of features disclosed herein either explicitly or any generalization thereof. Various modifications and adaptations to the foregoing exemplary embodiments ofthis disclosure may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this disclosure.

Claims

CLAIMSWhat is claimed is:

1. A method (300) performed by a first network node, comprising: determining (302) information about one or more radio access networks, RANs, wherein the information about the one or more RANs indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and transmitting (304) a message including the information about the one or more RANs which are using multicast transport over N3mb interface towards a second network node.

2. The method according to claim 1, wherein the message is an MBS context status notification, and the information about the one or more RANs includes an attribute indicating a RAN event related to a release of the broadcast MBS session.

3. The method according to claim 2, wherein the attribute is an OperationEvent attribute or a new attribute, and indicates the RAN event related to the release of the broadcast MBS session by setting an OpEventType attribute or the new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

4. The method according to claim 3, wherein the event information per RAN includes one or more of the following information: an identifier of the RAN; a list of tracking area identifiers, TAIs, of one or more tracking areas served by the RAN; and an event indication for the RAN.

5. The method according to claim 4, wherein the event indication is set to a value which indicates an event that a next generation-radio access network, NG-RAN, has requested to release the broadcast MBS session in the NG-RAN.

6. The method according to any of claims 2-5, wherein the attribute indicating the RAN event related to the release of the broadcast MBS session is also applicable for a RAN using unicast transport over N3mb interface.

7. The method according to any of claims 1-6, wherein the first network node is configured to implement an access and mobility management function, AMF.

8. The method according to any of claims 1-7, wherein the second network node is configured to act as a network function, NF, service consumer.

9. The method according to any of claims 1-8, wherein the second network node is configured to implement a multicast / broadcast session management function, MB-SMF.

10. A first network node (600), comprising: one or more processors (601); and one or more memories (602) comprising computer program codes (603), the one or more memories (602) and the computer program codes (603) configured to, with the one or more processors (601), cause the first network node (600) at least to: determine information about one or more radio access networks, RANs, wherein the information about the one or more RANs indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and transmit a message including the information about the one or more RANs which are using multicast transport over N3mb interface towards a second network node.11 . The first network node according to claim 10, wherein the one or more memories and the computer program codes are configured to, with the one or more processors, cause the first network node to perform the method according to any one of claims 2-9.

12. A computer-readable medium having computer program codes (603) embodied thereon which, when executed on a computer, cause the computer to perform any step of the method according to any one of claims 1-9.

13. A method (400) performed by a second network node, comprising: receiving (402) a first message transmitted by a first network node, wherein the first message includes first information about one or more radio access networks, RANs, which are using multicast transport over N3mb interface, and the first information indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and transmitting (404) a second message including second information about the one or more RANs towards a third network node, wherein the second information indicates that the broadcast MBS session is released in the one or more RANs.

14. The method according to claim 13, wherein the first message is an MBS context status notification, and the first information about the one or more RANs includes a first attribute indicating a RAN event related to a release of the broadcast MBS session.

15. The method according to claim 14, wherein the first attribute is an OperationEvent attribute or a new attribute, and indicates the RAN event related to the release of the broadcast MBS session by setting an OpEventType attribute or thenew attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

16. The method according to claim 14 or 15, wherein the first attribute indicating the RAN event related to the release of the broadcast MBS session is also applicable for a RAN using unicast transport over N3mb interface.

17. The method according to any of claims 13-16, wherein the second message is an MBS session event report, and the second information about the one or more RANs includes a second attribute indicating a RAN event related to a release of the broadcast MBS session.

18. The method according to claim 17, wherein the second attribute indicates the RAN event related to the release of the broadcast MBS session by setting an NgranEvent attribute or a new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

19. The method according to claim 17 or 18, wherein the second attribute indicating the RAN event related to the release of the broadcast MBS session is also applicable for a RAN using unicast transport over N3mb interface.

20. The method according to claim 15 or 18, wherein the event information per RAN includes one or more of the following information: an identifier of the RAN; a list of tracking area identifiers, TAIs, of one or more tracking areas served by the RAN; and an event indication for the RAN.

21. The method according to claim 20, wherein the event indication is set to a value which indicates an event that a next generation-radio access network, NG-RAN, has requested to release the broadcast MBS session in the NG-RAN.

22. The method according to any of claims 13-21 , wherein the second message is transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation, or via invoking a Nmbsmf_MBSSession_StatusNotify service operation and a Nnef_MBSSession_StatusNotify service operation.

23. The method according to any of claims 13-22, wherein the first network node is configured to implement an access and mobility management function, AMF.

24. The method according to any of claims 13-23, wherein the second network node is configured to act as a network function, NF, service consumer.

25. The method according to any of claims 13-24, wherein the second network node is configured to implement amulticast / broadcast session management function, MB-SMF.

26. The method according to any of claims 13-25, wherein the third network node is configured to implement one or more of the following functions: an application function, AF; a network exposure function, NEF; and a multicast broadcast service function, MBSF.

27. A second network node (600), comprising: one or more processors (601); and one or more memories (602) comprising computer program codes (603), the one or more memories (602) and the computer program codes (603) configured to, with the one or more processors (601), cause the second network node (600) at least to: receive a first message transmitted by a first network node, wherein the first message includes first information about one or more radio access networks, RANs, which are using multicast transport over N3mb interface, and the first information indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and transmit a second message including second information about the one or more RANs towards a third network node, wherein the second information indicates that the broadcast MBS session is released in the one or more RANs.

28. The second network node according to claim 27, wherein the one or more memories and the computer program codes are configured to, with the one or more processors, cause the second network node to perform the method according to any one of claims 14-26.

29. A computer-readable medium having computer program codes (603) embodied thereon which, when executed on a computer, cause the computer to perform any step of the method according to any one of claims 13-26.

30. A method (500) performed by a third network node, comprising: receiving (502) a message transmitted by a second network node, wherein the message includes information about one or more radio access networks, RANs, which are using multicast transport over N3mb interface, and the information about the one or more RANs indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and obtaining (504) the information about the one or more RANs from the message.31 . The method according to claim 30, wherein the message is an MBS session event report, and the information about the one or more RANs includes an attribute indicating a RAN event related to a release of the broadcast MBS session.

32. The method according to claim 31, wherein the attribute indicates the RAN event related to the release of the broadcast MBS session by setting an NgranEvent attribute or a new attribute to a value for a RAN initiated event together with event information per RAN in which the broadcast MBS session is released.

33. The method according to claim 32, wherein the event information per RAN includes one or more of the following information: an identifier of the RAN; a list of tracking area identifiers, TAIs, of one or more tracking areas served by the RAN; and an event indication for the RAN.

34. The method according to claim 33, wherein the event indication is set to a value which indicates an event that a next generation-radio access network, NG-RAN, has requested to release the broadcast MBS session in the NG-RAN.

35. The method according to any of claims 31-34, wherein the attribute indicating the RAN event related to the release of the broadcast MBS session is also applicable for a RAN using unicast transport over N3mb interface.

36. The method according to any of claims 30-35, wherein the message is transmitted towards the third network node by the second network node via invoking a Nmbsmf_MBSSession_StatusNotify service operation, or via invoking a Nmbsmf_MBSSession_StatusNotify service operation and a Nnef_MBSSession_StatusNotify service operation.

37. The method according to any of claims 30-36, wherein the second network node is configured to act as a network function, NF, service consumer.

38. The method according to any of claims 30-37, wherein the second network node is configured to implement a multicast / broadcast session management function, MB-SMF.

39. The method according to any of claims 30-38, wherein the third network node is configured to implement one or more of the following functions: an application function, AF; a network exposure function, NEF; and a multicast broadcast service function, MBSF.

40. A third network node (600), comprising: one or more processors (601); and one or more memories (602) comprising computer program codes (603), the one or more memories (602) and the computer program codes (603) configured to, with the one or more processors (601), cause the third network node (600) at least to:receive a message transmitted by a second network node, wherein the message includes information about one or more radio access networks, RANs, which are using multicast transport over N3mb interface, and the information about the one or more RANs indicates that a broadcast multicast and broadcast services, MBS, session is released in the one or more RANs; and obtain the information about the one or more RANs from the message.41 . The third network node according to claim 40, wherein the one or more memories and the computer program codes are configured to, with the one or more processors, cause the third network node to perform the method according to any one of claims 31-39.

42. A computer-readable medium having computer program codes (603) embodied thereon which, when executed on a computer, cause the computer to perform any step of the method according to any one of claims 30-39.

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