WO2021229346A1

WO2021229346A1 - 5g multicast broadcast service procedures

Info

Publication number: WO2021229346A1
Application number: PCT/IB2021/053540
Authority: WO
Inventors: Hans Bertil RÖNNEKE; Joakim ÅKESSON; Juying GAN; Jie LING; Maria Belen PANCORBO MARCOS
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2020-05-13
Filing date: 2021-04-28
Publication date: 2021-11-18

Abstract

A method (1200) performed by a RAN function (104). The method includes the RAN function storing (s1202) a Multicast Broadcast Services (MBS) session context for an MBS service. The method also includes the RAN function detecting (s1204) that no user equipment, UE, is using the MBS service. The method also includes, as a result of detecting that no UE is using the MBS service, the RAN function transmitting (s1206) to a management function (106) a message that triggers the management function to initiate MBS Session stop towards the RAN.

Description

5G MULTICAST BROADCAST SERVICE PROCEDURES

TECHNICAL FIELD

[001] Disclosed are embodiments related to multicast broadcast services in a 5G network.

BACKGROUND

[002] The 3rd Generation Partnership Project (3 GPP) has developed the

Multicast/Broadcast Multimedia Subsystem (MBMS) (see, e.g. 3GPP TS 23.246 vl6.1.0) for 3G networks for video multicast/broadcasting and streaming services. Subsequently, 3GPP introduced the evolved MBMS (eMBMS) for the Evolved Packet System (EPS). In 3GPP release 13 (Rel-13) and release 14 (Rel-14), the MBMS system has been updated to support new services such as Public Safety, cellular Internet-of-things (CIoT) and vehicle-to-everything (V2X).

[003] The scope of a new Release- 17 study in the 3GPP SA2 working group is to study both multicast requirements and use cases for CIoT, Public Safety, V2X, etc., and dedicated broadcasting requirements and use cases. The study targets the 5G Release 17 and the New Radio (NR) radio access. The study results so far have been documented in the TR 23.757 V0.3.0.

[004] As used herein, “broadcast” means communication to a group of receivers,

“multicast” means communication to a group of receives who have announced an interest in the communication, and “unicast” means point-to-point (a.k.a., one-to-one) communication.

SUMMARY

[005] Certain challenges presently exist. For example multicast/broadcast services are so far not supported on 5G NR. With the enhanced characteristics of the 5G NR (e.g. short delays, high bandwidth, etc.), it is believed Mission Critical (MC) Services (e.g., MC Push-To- Talk (MCPTT), MC Data, and MC Video), as well as VTX services, will show an enhanced and much better performance on 5G NR. [006] For 5G MBS multicast support, the 5G System (5GS) must support user equipments (UEs) joining multicast groups (a UE is any device, such as smartphone, sensor, appliance, computer, tablet, vehicle, capable of wirelessly communicating with an access node (e.g., base station or other access point)). “Joining” is sometimes referred to as “Multicast Service Activation.” 5G Multicast Broadcast Sessions (5G MBS Sessions) (a.k.a., MBS Bearers) must also be possible to be started (i.e., transmission of data or media to the group of UEs is started). Compare with MBMS TS 23.246 V16.1.0 clause 8.2 “MBMS Multicast Service Activation” and clause 8.3 “MBMS Session Start Procedure.” One solution is described in TR 23.757 V0.3.0 (see e.g. fig. 6.2.2.1-1, fig. 6.3.2-1, fig. 6.4.2.2-1, fig. 6.6.2.1-1, etc) where various tentative proposals on Join and Session Start are outlined. These two procedures are lacking on how the 5G core (5GC) interacts with the Application Function (AF), how the Policy Control Function (PCF) is used, and in general how different 5GC entities and NG-RAN and UE interacts.

[007] Accordingly in one aspect there is provided a method performed by a RAN function. In one embodiment the method includes the RAN function storing a Multicast Broadcast Services (MBS) session context for an MBS service. The method also includes the RAN function detecting that no user equipment, UE, is using the MBS service. The method also includes, as a result of detecting that no UE is using the MBS service, the RAN function transmitting to a management function a message that triggers the management function to initiate MBS Session stop towards the RAN.

[008] In another embodiment the method performed by the RAN function includes the

RAN function receiving a first message transmitted by a management function, the first message comprising a group identifier associated with a multicast broadcast (MB) session. The method also includes the RAN function receiving a response message intended for a UE that has indicated its interest to join the MB session. The method also includes the RAN function determining whether or not it has an MB Session Context in an active state for the group identifier. The method also includes the RAN function establishing resources for the UE if the RAN function determines that it has an MB Session Context in the active state for the group identifier. [009] In another embodiment the method performed by the RAN function includes the

RAN function receiving a first message transmitted by a management function, the first message comprising a group identifier associated with a multicast broadcast (MB) session. The method also includes the RAN function receiving a response message intended for a UE that has indicated its interest to leave the MB session, wherein the RAN function has a UE context for the UE. The method also includes, after receiving the first message, the RAN function removing the group identifier from the UE context. The method also includes the RAN function determining whether the RAN function is serving any other UEs that are using the MB session. The method also includes, as a result of determining that the RAN function is not serving any other UEs that are using the MB session, the RAN function sending a Leave message to stop the media stream to the RAN function and deleting an MB Session Context associated with the MB session.

[0010] In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of a RAN node causes the RAN node to perform any one of the RAN function methods disclosed herein. In another aspect there is provided a carrier containing the computer program, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable medium. In another aspect there is provided a RAN node, where the RAN node is configured to perform any one of the RAN function methods disclosed herein. In some embodiments, the RAN node includes processing circuitry and a memory containing instructions executable by the processing circuitry, whereby the RAN node is configured to perform any one of the RAN function methods disclosed herein.

[0011] In another aspect there is provided a policy method performed by a policy function. The method includes the policy function receiving a first message transmitted by session management function, SMF, the first message comprising a group identifier for a multicast broadcast (MB) session and service requirement information. The method also includes the policy function transmitting a second message responsive to the first message, the second message comprising a 5G Quality-of-Service, QoS, profile.

[0012] In another aspect there is provided a computer program comprising instructions which when executed by processing circuitry of a core network (CN) node causes the CN node to perform the policy method. In another aspect there is provided a carrier containing the computer program, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable medium. In another aspect there is provided a CN node, where the CN node is configured to perform the policy method. In some embodiments, the CN node includes processing circuitry and a memory containing instructions executable by the processing circuitry, whereby the CN node is configured to perform the policy method disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments.

[0014] FIG. 1 illustrates the architecture for MBS in 5GS.

[0015] FIG. 2 illustrates an example how a group of UEs using an MBS service moves while receiving the service

[0016] FIG. 3 illustrates an architecture to which the procedures in this disclosure apply.

[0017] FIG. 4 illustrates the Session Join procedure.

[0018] FIG. 5 illustrates the Session Start procedure.

[0019] FIG. 6 illustrates the MCPTT New Group Call procedure.

[0020] FIG. 7 illustrates the MCPTT Ongoing Group Call procedure.

[0021] FIG. 8 illustrates the MCPTT Ongoing Group Call procedure.

[0022] FIG. 9 illustrates the Session Feave procedure.

[0023] FIG. 10 illustrates the Session Stop procedure.

[0024] FIG. 11 illustrates the Session Delete procedure.

[0025] FIG. 12 is a flowchart illustrating a process according to some embodiments.

[0026] FIG. 13 is a flowchart illustrating a process according to some embodiments.

[0027] FIG. 14 is a flowchart illustrating a process according to some embodiments.

[0028] FIG. 15 is a flowchart illustrating a process according to some embodiments.

[0029] FIG. 16 illustrates a RAN node according to some embodiments.

[0030] FIG. 17 illustrates a CN node according to some embodiments. DETAILED DESCRIPTION

[0031] This disclosure describes, among other features:

[0032] 1. The use of MB Session Contexts to control MBS procedures, how these are created and deleted, how the ‘inactive’ and ‘active’ states are used (also ‘deleted’ state), and how NG-RAN differs in that it only uses MB Session Context (Ctx) in ‘active’ state.

[0033] 2. How the PCF is enhanced for MBS and interworks with SMF (i.e. MB-SMF)

(see, e.g., step 3 in FIG. 5). The PCF translates “Service Requirement” information (that originates from the AF) to a 5G QoS Profile (which becomes 5G Authorized QoS Profile in SMF). This Service Requirement information (or “Service Requirement” for short) comprises or consists of Quality-of-Service (Qos) information (e.g., level of QoS that the 5GMBS service demands, such as low, medium or high QoS; a particular bit rate to be provided for the service and a particular traffic class; reservation priority value; priority sharing indicator; QoS class identifier; downlink (DL) maximum requested bandwidth; DL guaranteed bit rate; Allocation Retention Priority (ARP) value; etc.) (further examples of such QoS information can be found in section 5.3.16 of 3GPP TS 23.212 V16.3.0 as well as in 3 GPP TS 29.214 V16.0.0).

[0034] 3. How NG-RAN controls its MB Session resources, illustrated in clause 6.2.2.4

MCPTT: Ongoing Group Call; step 4 in FIG. 7 where RAN itself initiates PTM/PTP for the new UE (based on the existence of an active MB Session Context (Ctx)) and in FIG. 8 step 4 where instead AMF need to send an NG Application Protocol (NGAP) message to RAN to establish resources (based on that AMF discovers that NG-RAG has not setup any MB Resources for this TMGI. Furthermore, in FIG. 9 (Session Leave) step 5, where NG-RAN itself decides to release the resources for a MB Session. Conclusion: different AMFs requests NG-RAN to setup resources for a MB Session (identified by e.g. a Temporary Mobile Group Identity (TMGI)), whereas it is always NG-RAN itself (not any AMFs) that decide when it is time (based on UE Session Leave) to release the MB Session resources in NG-RAN.

[0035] 4. The handling of potentially a very large number of Acknowledge messages going back from many NG-RAN nodes to the AF. See step 13 in 6.2.2.2-1; step 8 in FIG. 10 (Session Stop); step 9 in FIG. 11 (Session Delete). Note that the AMF may send a response message for each response it receives from NG-RAN nodes (e.g. useful for small MCPTT areas). That is, steps 8 to 10 may be repeated multiple times (once for each involved NG RAN node). The AMF may also use an upper limit for the number of Responses sent and fallback to aggregated responses if # RAN responses go beyond the limit (to reduce signaling load). That is, collect status from all or a number of downstream nodes (with time out) and then make an aggregated report.

[0036] A2. Baseline architecture 2: 5G MBS system architecture based on dedicated

MBS Function

[0037] A.2.1 General

[0038] The 5GS architecture is enhanced with Multicast Broadcast Services (MBS) as described below. In addition, an AF engaged in MBS can also use 5GS unicast resources (i.e. PDU Sessions) to deliver MBS media to UEs. However, that is considered independent to the MBS architecture enhancements below. Enhancements to existing entities and new entities are described in the clause below.

[0039] A.2.2 Reference Architecture

[0040] To support MBS in 5GS, two modes of operation exist, Transport Only Mode and

Full Service Mode, as defined in TS 23.246 [4] clause 7.5.

[0041] FIG. 1 illustrates the architecture for MBS in 5GS.

[0042] In this FIG. 1 the SMF and UPF which have the roles to support MB Sessions are named "MB-SMF" and "MB-UPF". Nothing prevents the MB -SMF and MB-UPF to simultaneously support both PDU Sessions and MB Sessions, e.g. PDU Sessions and MB Sessions to the same DNN. However, MB-SMF and MB-UPF can also be deployed and configured to exclusively handle MB Sessions. It is believed it may reduce signaling and in some cases be simpler and more cost efficient to operate a limited number of MB-SMFs and MB-UPFs dedicated to MBS. This architecture makes that possible if preferred.

[0043] Enhancement to existing entities and new functional components are as follows:

[0044] 1. UE 102, NG-RAN 104, AMF 106, SMF 108, UPF 110, NEF 112 and PCF 114 are enhanced to support MBS.

[0045] 2. UE is enhanced to support 5G MBS services. [0046] 3. NG-RAN is enhanced to support Point-to-Multipoint (PTM) and Point-to-Point

(PTP) delivery of MBS media. NG-RAN independently controls switching between PTM and PTP for best service quality and resource efficiency.

[0047] 4. AMF is enhanced to coordinate resource setup in NG-RAN nodes on request from MB-SMF and from UEs.

[0048] 5. SMF is enhanced to control MB Sessions including TMGI allocation, signaling with an AF 118 (via NEF), QoS control using PCF, and provision of MB Session information on request from AMF.

[0049] 6. UPF is enhanced with an MBS user plane function.

[0050] 7. Multicast/Broadcast Service Function (MBSF) 120 is a function which is part of NEF 112. The MBSF supports NEF with MBS signaling for the service layer capability in the Transport-Only and the Full Service Mode. The NEF/MBSF also provides an interface to the Application Function or content provider in the Transport Only mode and it has an interface to the Multicast/Broadcast Service User plane (MBSU) 116.

[0051] 8. MBSU is a new entity to handle the payload part to cater for the service layer capability in Full Service mode (not used in Transport Only mode).

[0052] 9. NEF is an existing NF, the role/functions associated with NEF are enhanced to support MBS. NEF has also an MBSF subfunction (see above).

[0053] 10. PCF is enhanced to handle QoS for MB Sessions and its group members.

[0054] Enhancement to existing interfaces and new interfaces are as follows:

[0055] 1. Uu interface is enhanced with group paging (NOTE: Uu, N2 and N3 interface enhancements are subject to RAN evaluation and decision).

[0056] 2. N2 interface is enhanced to control MB Sessions.

[0057] 3. N3 interface is enhanced with IP Multicast transport from UPF to NG-RAN.

[0058] 4. N4 interface is enhanced with control of N6 Tunnel to AF and IP Multicast source-router for N3 Multicast transport.

[0059] 5. N6 interface is enhanced with tunnelling for the MBS user plane to the AF. [0060] 6. N7 and N30 interfaces are enhanced for policy control of MB Sessions.

[0061] 7. N11 interface is enhanced with MBS control signaling.

[0062] 8. N29 interface is enhanced with MBS control signaling.

[0063] 9. N33 interface is enhanced with MBS control signaling.

[0064] 10. Ny new (optional) interface between the MBSF and MBSU to provide the service layer capability in Full Service Mode.

[0065] 11. NxMB-C new API on N33 for MBS control signaling with AF. Provides a unified interface for both Transport Only Mode and Full Service Mode.

[0066] 12. NxMB-U new interface between the new MBSU and AF for MBS user plane traffic in Full Service Mode. It e.g. enables support for file delivery in Full Service Mode.

[0067] Discussion

[0068] This disclosure details the following procedures: Session Join, Start, Leave, Stop, and Delete. This disclosure also provides two examples of MCPTT procedures - New group call and Ongoing group call.

[0069] 6.2 Solution #2: MBS Session setup using flexible radio resources

[0070] 6.2.1 Functional Description

[0071] This Solution assumes the architecture shown in FIG. 1 and described above. It is assumed that a UE can notify the network of the MBS Session in which the UE is interested.

[0072] In this solution for Multicast communication services:

> When no MBS Session context exists in NG-RAN for an MBS service:

> If a UE is interested in an MBS service, the UE notifies NG-RAN of the interested MBS, or a UE previously using MBS service in an old NG-RAN is moved to a new NG-RAN;

> for the first UE initiating the MBS service interest, the (new) NG-RAN notifies the M-

AMF for MBS service to initiate MBS Session creation towards the (new) NG-RAN; > if the MBS Session does not exist for the service in the M-AMF, the M-AMF notifies the

MB-SMF to initiate the MBS Session later.

> When MBS Session context exists in NG-RAN for an MBS service:

> NG-RAN detects that no UE is using the MBS service (e.g. due to UE moving to a different NG-RAN), it notifies the M-AMF, so that the M-AMF can initiate MBS Session stop towards the NG-RAN.

[0073] Based on the proposal above that NG-RAN can dynamically allocate the radio resource for MBS service, when UE moves from one NG-RAN to another, the multicast service can continue without switching to the unicast. FIG. 2 illustrates an example how a group of UEs using an MBS service moves while receiving the service, which results in that radio resources being used dynamically moves from the cells within the dotted circle to the cells within the solid circle.

[0074] FIG. 3 illustrates an architecture to which the procedures in this disclosure apply.

[0075] 6.2.2 Procedures

[0076] 6.2.2.0 General

[0077] The message names in the procedures below are descriptive. It is assumed that the names are updated with corresponding SBI based names where applicable during the normative phase. N2, N3 messages are dependent on RAN3 decisions.

[0078] 6.2.2.1 Session Join

[0079] The Session Join procedure is used by UEs to inform the 3GPP network of the UE interest in an MB Session. During the Session Join procedure, the distribution area of the multicast session is adjusted if needed. As such, the Session Join procedure together with other procedures, e.g. Session Leave procedure and Handover procedure, enables the dynamic and efficient use of radio resources. FIG. 4 is a message flow diagram illustrating the Session Join procedure. The steps of the procedure are described below.

0. The UE registers and a PDU Session is established. The UE and the AF uses the PDU Session e.g. to signal and establish a group on application level (see 3GPP TS 23.468). AF sends Allocate TMGI Request () message to NEF to request allocation of a TMGI to identify a new group. NEF selects based on local configuration an MB-SMF (if there are multiple) to handle the group and sends an Allocate TMGI Request () message to the MB-SMF. MB-SMF allocates a TMGI, a Lower Layer Multicast IP Address (LL MC addr), and N6 tunnel information and stores the information in a new MB Session Ctx set to 'inactive' state. MB SMF registers the TMGI and its MB SMF address in NRF to allow AMFs to discover the MB-SMF for the TMGI. MB-SMF returns the TMGI and the N6 tunnel information to the NEF. For large networks or for redundancy reasons, the NEF might use multiple MB-SMFs (and MB-UPFs). The NEF establishes a new MB Session Ctx set to 'inactive' state, stores received information and responds to the AF by sending a Allocate TMGI Response (TMGI) message. MB Session Announcement (see e.g. 3GPP TS 23.468). The AF informs the members in the group of various group info (e.g., TMGI, HL MC addr). The HL MC addr may be allocated by the AF for the group/TMGI. UE indicates its interest to join an MB Session by sending an UL NAS MB Session Join Request (TMGI) message (i.e., the Join Request message contains a TMGI). NG- RAN forwards the NAS message to the AMF. The AMF stores the TMGI in its UE Context. If the AMF does not already have a MB Session Ctx for the received TMGI (in step 6), the AMF selects an MB SMF for the TMGI by querying the NRF. A MB Session Request (TMGI, AMF ID) message is sent to the MB SMF to announce the AMF’s interest in the MB Session. When the MB-SMF has returned a MB Session Response () message, the AMF creates a MB Session Ctx in 'inactive' state for the TMGI. The AMF stores the TMGI and the NG RAN ID of the originating node of the N2 message in step 6 in the AMF MB Session Ctx. The AMF creates a DL NAS MB Session Join Response () message and piggy backs that on an N2 MB Session Join (NGAP ID, TMGI) message. The NG-RAN stores the TMGI in the UE context in NG- RAN.

NG-RAN only keeps active MB Session Ctxs, i.e. created during Session Start procedures.

The primary purpose of the MB Session Ctx in the AMF is for the AMF to be able to manage forwarding of Session Start messages to NG-RAN nodes where members of the group are camping and to initiate Group paging for CM-IDFE group members.

[0080] 6.2.2.2 Session Start

[0081] FIG. 5 is a message flow diagram illustrating the Session Start procedure.

[0082] The Session Start procedure is used by the AF to activate an MB Session and start transmission of multicast/broadcast data. During the Session Start procedure, resources for the MB Session are setup in the MB-UPF and in the NG-RAN. The steps of the procedure are described below.

1. The AF requests activation of an MB Session by sending an Activate MBS Bearer Request (TMGI, HE MC addr, Service Requirement) message to the NEF. AF has allocated a Higher Fayer IP Multicast Address (HE MC addr). Service Requirement for the MB Session may be included.

2. The NEF checks if the input parameters e.g. HE MC addr are valid. NEF sets the MB Session Ctx to active. NEF sends a MB Session Start (TMGI, Service Requirement) message to the MB-SMF.

3. MB-SMF sends the TMGI for the MB Session and the Service Requirement to the PCF. The PCF then returns a 5G QoS Profile, which the MB-SMF uses as the 5G Authorized QoS Profile for the MB Session.

4. MB-SMF sets up the resources in the MB-UPF with a Packet Detection Rule for the FF MC address allocated for the TMGI and stored in the MB Session Ctx. Optionally Media reception in MB-UPF is untunnelled, in which case the MB-SMF also provides the HE MC addr so that the MB-UPF can join and receive the Media stream.

The MB-UPF allocates N6 tunnel information (e.g. UDP port and IP address) and returns to the MB-SMF. Optionally if N6 tunnel is not used, the MB-UPF instead joins the HE MC addr to receive the Media stream. MB-SMF stores the received info in the MB Session Ctx. . MB-SMF sets the MB Session Ctx to active and sends MB Session Start (TMGI, LL MC addr, 5G Authorized QoS Profile) messages to all AMFs that has earlier joined the MB Session.

When the AMF receives the MB Session Start message, AMF sets its MB Session Ctx to active state. The AMF proceeds with step 6 and step 10 onwards in parallel. . If the AMF has CM-IDLE UEs that have joined the MB Session, the AMF performs group paging including the Group Paging Identity (TMGI) in the Paging message in the registration areas of the CM-IDLE UEs. The NG-RAN node triggers group paging. NOTE: Details to be developed in TSG RAN, e.g. whether and how UEs listens to same paging channel, which identity is used for group paging, how to coordinate group paging identity among NG-RAN nodes etc. -9. UEs respond to the Group paging e.g. by sending UL NAS MB Session Join Request (TMGI) to AMF (see clause 6.2.2.1 step 6 to 8). Step 8 may be performed if the UE responds to paging to a different AMF. 0. The AMF sends a MB Session Resource Setup Request (TMGI, LL MC, 5G Authorized QoS Profile) message to all RAN nodes where CM CONNECTED UEs that has joined the TMGI resides. NG-RAN creates a MB Session Ctx (if it not already exists), sets it to 'active' state, stores the TMGI, the QoS Profile and and a list of AMF IDs in the MB Session Ctx. If a NG RAN node receives multiple MB Session Resource Setup Request messages for the same TMGI (e.g. from several AMFs the NG-RAN is connected to), NG-RAN stores each sender AMF ID in the MB Session Ctx, but only performs step 11 once (instead continues at step 12). 1. The NG-RAN joins the multicast group (i.e. LL MC addr) and establishes PTM or PTP DL resources for the MB Session. If there are UEs in CM-Connected with RRC_INACTIVE state with the TMGI in their UE Contexts, NG-RAN performs the Network triggered transition from RRC_INACTIVE to RRC_CONNECTED procedure for those UEs (see TS 38.300 [x]). 12. The NG-RAN reports successful establishment of the MB Session resources by sending MB Session Resource Setup Response (TMGI) message(s) to the AMF.

13. The AMF sends MB Session Start Ack (TMGI) to the MB-SMF.

NOTE: The AMF may send an Ack for each response it receives from NG-RAN nodes (e.g. useful for small MCPTT areas). That is, steps 13 to 15 may be repeated multiple times (once for each involved NG RAN node). The AMF may also use an upper limit for the number of Acks sent and fallback to aggregated Acks if # RAN acks go beyond the limit (to reduce signaling load). That is, collect status from all or a number of downstream nodes (with time out) and then make an aggregated report.

14-15. The MB-SMF sends the MB Session Start Ack (TMGI) message to the NEF. N6 Tunnel info is included in the response if not already provided to the AF. The NEF sends an Activate MBS Bearer Response including the N6 Tunnel Info to the AF.

16. The MB Session is now active. The AF starts transmitting the DL media stream using the N6 Tunnel Info, or optionally untunneled i.e. as an IP multicast stream using using the HL MC address.

17. The NG-RAN transmits the received DL media stream using DL PTM or PTP resources.

[0083] 6.2.2.3 MCPTT: New Group Call

[0084] FIG. 6 is a message flow diagram illustrating the MCPTT New Group Call

Procedure. This procedure is an example of the typical sequence when a new Mission Critical Push-To-Talk call is established. It includes group affiliation and session announcement using application level signaling, TMGI allocation, first UE joining the group call, and the start of MBS session media transmission by the application server (AF). Transport Only mode is used as an example in the flows. The steps of the procedure are described below.

1-8. The upper part steps 1 to 8 corresponds to the steps in the Session Join procedure clause

6.2.2.1.

1-17. The bottom part steps 1 to 17 corresponds to the steps in the Session Start procedure clause 6.2.2.2.

[0085] 6.2.2.4 MCPTT: Ongoing Group Call [0086] This procedure is described with respect to FIG. 7 and FIG. 8. FIG. 7 shows the second (or subsequent) UE in a cell joining an ongoing group call. That is, when another UE in the cell has already joined the same group call. This is probably the most common sequence for mission critical group calls. FIG. 8 shows the sequence for the first UE in a cell, i.e. when the MB Session resources has to be established in the cell before reception can commence. This requires slightly more signaling, but is probably a bit less frequent than the first for normal group calls.

[0087] The steps shown in FIG. 7 are described below:

0. A PTM or PTP transmission of media is ongoing to other UE in the cell.

1. The new UE indicates its interest to join the MB Session by sending an UL NAS MB Session Join Request (TMGI) message. The AMF stores the TMGI in its UE Context.

2. If the AMF does not already have a MB Session Ctx for the received TMGI (the first UE in the cell for this group may be served by a different AMF), the AMF selects an MB SMF for the TMGI by querying the NRF. A MB Session Request (TMGI, AMF ID) message is sent to the MB SMF to announce the AMF’s interest in the MB Session.

When the MB-SMF has returned a MB Session Response (active) message, the AMF creates a MB Session Ctx in 'active' state for the TMGI.

3. The AMF stores the TMGI and the NG RAN ID of the originating node of the N2 message in step 6 in the AMF MB Session Ctx. The AMF creates a DL NAS MB Session Join Response () message and piggy backs that on an N2 MB Session Join (NGAP ID, TMGI) message. The NG-RAN stores the TMGI in the UE context in NG RAN.

4. NG-RAN determines that it has an MB Session Ctx in active state for the TMGI. Therefore NG-RAN establishes PTM or PTP DL resources for the UE.

5. The transmission of the DL media stream to the UE commences.

[0088] The steps shown in FIG. 8 are described below:

0-3 Corresponds to step 0-3 in FIG. 7.

4. When the NG-RAN has received the N2: MB Session Join (NGAP ID, TMGI) message, the NG-RAN determines that it does not have any MB Session Ctx (in active state) for the TMGI. However, after having sent the N2 MB Session Join message to NG-RAN, the AMF determines that the MB Session is in active state and that AMF has not already requested NG-RAN to setup resources for the MB Session. Therefore, AMF sends an MB Session Resource Setup Request (TMGI, LL MC, 5G Authorized QoS Profile) message to the NG-RAN node. If a NG RAN node receives multiple MB Session Resource Setup Request messages for the same TMGI (e.g. for an MB Session Ctx in active state), the NG-RAN only performs the resource setup once.

5-6. Corresponds to step 11 & 12 in Session Start procedure in clause 6.2.2.2. Note, after step 6, the AMF does not send any MB Session Start Ack to MB-SMF (like in clause 6.2.2.2).

7. Corresponds to step 17 in Session Start procedure in clause 6.2.2.2.

[0089] 6.2.2.5 Session Leave

[0090] FIG. 9 is a message flow diagram illustrating the Session Leave procedure. The

Session Leave procedure is used by UEs to inform the 3GPP network that the UE interest in an MB Session has ceased. During the Session Leave procedure, the distribution area of the multicast session is adjusted if needed. This enables a dynamic and efficient use of radio resources.

[0091] The steps of the Session Leave procedure are described below.

0. Potential decision on application level for UE to leave the group.

1. There may be a media stream before the UE has left. UE receives the media by PTM or PTP.

2. The UE sends a UL NAS MB Session Leave Request (TMGI) message to the AMF. The AMF removes the TMGI from the UE Context.

3. The AMF creates a DL NAS MB Session Leave Response () message and piggy backs that on an N2 MB Session Leave (NGAP ID, TMGI) message. The NG-RAN removes the TMGI from the UE context in NG-RAN.

4. The NG-RAN adjusts the PTM/PTP transmission if necessary.

5. If this UE is the last UE in this NG-RAN using the MB Session, the NG-RAN sends a Leave message (LL MC addr) to stop the media stream to this NG-RAN node and then deletes the MB Session Ctx.

6. If this UE is the last UE in this AMF being part of the MB Session, the AMF sends an MB Session Release Request (TMGI, AMF ID) to the MB-SMF, for AMF to unsubscribe to the MB Session. The MB-SMF removes the AMF in the MB-SMF MB Session Ctx. 7. The MB-SMF sends an MB Session Release Response message to the AMF. AMF deletes its MB Session Ctx.

[0092] 6.2.2.6 Session Stop

[0093] FIG. 10 is a message flow diagram illustrating the Session Stop procedure. The

Session Stop is used to stop media delivery for a MB Session i.e. to all UEs in a group defined by a TMGI. Afterwards the MB Session will still remain, and the Session can later be restarted again with limited amount of signaling. The resources in the NG-RAN are however released and the NG-RAN MB Session Ctx is deleted. The MB Session Ctx in AMF, MB-SMF and NEF are kept but set to inactive state. This preserves the MBS distribution tree, and reduces the response time to restart the MB Session if needed. The Session Stop procedure is intended for MB Sessions in active state, using it on an inactive MB Session does not change anything. The steps of the Session Stop procedure are described below.

0. Decision on application level for the Session to be stopped.

1. The AF may stop the media stream before sending the Deactivate MBS Bearer Request (TMGI) message to the 3 GPP network.

2. The AF sends a Deactivate MBS Bearer Request (TMGI) message to the NEF.

3. The NEF sends a MB Session Stop Request (TMGI) message to the MB-SMF(s) that has been involved in the MB Session. The NEF sets its MB Session Ctx to inactive state.

4. MB-SMF sends a MB Session Stop Request (TMGI) message to the AMF(s) that has been involved in the MB Session. The MB-SMF sets its MB Session Ctx to inactive state. The N6 Tunnel is kept.

5. The AMF sends a MB Session Resource Release Request (TMGI) message to all RAN nodes where CM CONNECTED UEs that has joined the TMGI resides. If a NG RAN node receives multiple MB Session Resource Release Request messages for the same TMGI (e.g. from several AMFs the NG-RAN is connected to), NG-RAN only performs step 6 once. The AMF sets its MB Session Ctx to inactive state.

6. The NG-RAN stops the PTM/PTP transmission. The NG-RAN sends a Leave message (LL MC addr) to stop the media stream to this NG-RAN node. NG-RAN deletes its MB Session Ctx. 7. The NG-RAN reports successful release of resources for the MB Session by sending MB Session Resource Release Response (TMGI) message(s) to the AMF(s).

8. The AMF sends MB Session Stop Response (TMGI) to the MB-SMF.

NOTE: The AMF may send a response message for each response it receives from NG- RAN nodes (e.g. useful for small MCPTT areas). That is, steps 8 to 10 may be repeated multiple times (once for each involved NG RAN node). The AMF may also use an upper limit for the number of Responses sent and fallback to aggregated responses if # RAN responses go beyond the limit (to reduce signaling load). That is, collect status from all or a number of downstream nodes (with time out) and then make an aggregated report.

9. The MB-SMF sends the MB Session Stop Response (TMGI) message to the NEF.

10. The NEF sends a Deactivate MBS Bearer Response (TMGI) to the AF.

[0094] 6.2.2.Ί Session Delete

[0095] FIG. 11 is a message flow diagram illustrating the Session Delete procedure. The

Session Delete is used to stop media delivery for a MB Session and to delete all resources including MB Session Ctxs in NG-RAN and in 5GC for the MB Session. The MB Session Ctxs are deleted from all nodes, the distribution tree removed and the TMGI is deallocated. The MB Session cannot be restarted (i.e. using the Session Start procedure). The Session Delete procedure can be used both on active (ongoing) Sessions and on inactive (stopped) Sessions. The steps of the Session Delete procedure are described below.

0. Decision on application level to dissolve a group and deallocate the group TMGI.

1. The AF sends a Deallocate TMGI Request (TMGI) message to the NEF.

2. The NEF sends a Deallocate TMGI Request (TMGI) message to the MB-SMF(s) that has been involved in the MB Session. The NEF sets its MB Session Ctx to deleted state (for delayed deletion to when procedure ought to be terminated).

3.-4. MB-SMF request the MB-UPF to release the resources allocated for the MB Session (e.g. designated by the TMGI), including the N6 tunnel. The MB-UPF responds to the MB- SMF when resources are released.

5. MB-SMF sends a MB Session Delete Request (TMGI) message to the AMF(s) that has been involved in the MB Session. The MB-SMF sets its MB Session Ctx to deleted state. 6. If the MB Session is still ongoing (i.e. if the MB Session Ctx in the AMF is still in active state), the AMF sends a MB Session Resource Release Request (TMGI) message to all RAN nodes where CM CONNECTED UEs that has joined the TMGI resides. If a NG RAN node receives multiple MB Session Resource Release Request messages for the same TMGI (e.g. from several AMFs the NG-RAN is connected to), NG-RAN only performs step 7 once.

The AMF sets its MB Session Ctx to deleted state.

If the MB Session is not ongoing (i.e. if the MB Session Ctx in the AMF is in inactive state), the procedure skips steps 6 to 8 and the AMF continues with step 9.

7. The NG-RAN stops the PTM/PTP transmission. The NG-RAN sends a Feave message (FF MC addr) to stop the media stream to this NG-RAN node. NG-RAN deletes its MB Session Ctx.

8. The NG-RAN reports successful release of resources for the MB Session by sending MB Session Resource Release Response (TMGI) message(s) to the AMF(s).

9. The AMF sends MB Session Delete Response (TMGI) to the MB-SMF.

NOTE: The AMF may send a response message for each response it receives from NG- RAN nodes (e.g. useful for small MCPTT areas). That is, steps 9 to 11 may be repeated multiple times (once for each involved NG RAN node). The AMF may also use an upper limit for the number of Responses sent and fallback to aggregated responses if # RAN responses go beyond the limit (to reduce signaling load). That is, collect status from all or a number of downstream nodes (with time out) and then make an aggregated report.

10. The MB-SMF sends the Deallocate TMGI Response (TMGI) message to the NEF.

11. The NEF sends a Deallocate TMGI Response (TMGI) to the AF.

[0096] 6.2.3 Impacts on services, entities and interfaces

[0097] UE:

[0098] > Reception of multicast data using PTM /PTP in RRC Connected.

[0099] > MBS control client which can exchange Session Join, and Session Feave messages.

[00100] NG-RAN: [00101] > Support for MB Sessions and MBS related signaling on N2 with AMF and on

N3 with UPF.

[00102] > Transmission of multicast data using PTM /PTP in RRC Connected.

[00103] AMF:

[00104] > MBS control function which can maintain the MBS signaling tree and control

MBS resources in NG-RAN.

[00105] > Support selection of SMFs that have MBS capabilities using NRF.

[00106] SMF:

[00107] > MBS control function which can maintain the MBS signaling tree and respond to session requests from the NEF/MBSF, PCF and AF including allocation of TMGIs.

[00108] > Optionally support deployments with SMFs dedicated to MBS services.

[00109] NEF:

[00110] > MBS control function (i.e. MBSF) which can maintain the MBS signaling tree and respond to session requests from the AF.

[00111] > Support selection of SMFs that have MBS capabilities and registering selected

SMF for an MB Session in NRF.

[00112] UPF:

[00113] > MBS user plane function with southbound IP Multicast tunnelling/transport interface and northbound interface with N6 tunnelling of MBS DL media streams.

[00114] > Support MBS operations on the N4 interface for MB Session setup and release.

[00115] PCF:

[00116] > MBS control function with 5G QoS Profiles for MB Sessions.

[00117] GCS Server:

[00118] > Support for using the NEF API. The API should be largely equivalent as the eMBMS BM-SC API, but with some 5G enhancements. [00119] N6:

[00120] > Support for N6 tunneling for AF to UPF transmission of DL MBS media.

Support for N6 IP Multicast in the untunnelled ditto.

[00121] FIG. 16 is a block diagram of a RAN node 1600, according to some embodiments, for implementing RAN function 104. As shown in FIG. 16, RAN node 1600 may comprise: processing circuitry (PC) 1602, which may include one or more processors (P) 1655 (e.g., one or more general purpose microprocessors and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (i.e., RAN node 1600 may be a distributed computing apparatus); at least one network interface 1668 comprising a transmitter (Tx) 1665 and a receiver (Rx) 1667 for enabling RAN node 1600 to transmit data to and receive data from other nodes connected to a network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1668 is connected; communication circuitry 1648, which is coupled to an antenna arrangement 1649 comprising one or more antennas and which comprises a transmitter (Tx) 1645 and a receiver (Rx) 1647 for enabling RAN node 1600 to transmit data and receive data (e.g., wirelessly transmit/receive data); and a local storage unit (a.k.a., “data storage system”) 1608, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC 1602 includes a programmable processor, a computer program product (CPP) 1641 may be provided. CPP 1641 includes a computer readable medium (CRM) 1642 storing a computer program (CP) 1643 comprising computer readable instructions (CRI) 1644. CRM 1642 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1644 of computer program 1643 is configured such that when executed by PC 1602, the CRI causes RAN node 1600 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, RAN node 1600 may be configured to perform steps described herein without the need for code. That is, for example, PC 1602 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software. [00122] FIG. 17 is a block diagram of an core network (CN) node 1700, according to some embodiments, for implementing any one of the CN functions (e.g., AMF, PCF, SMF, NEF, UPF, etc.). As shown in FIG. 17, CN node 1700 may comprise: processing circuitry (PC) 1702, which may include one or more processors (P) 1755 (e.g., a general purpose microprocessor and/or one or more other processors, such as an application specific integrated circuit (ASIC), field-programmable gate arrays (FPGAs), and the like), which processors may be co-located in a single housing or in a single data center or may be geographically distributed (i.e., CN node 1700 may be a distributed computing apparatus); at least one network interface 1748 comprising a transmitter (Tx) 1745 and a receiver (Rx) 1747 for enabling CN node 1700 to transmit data to and receive data from other nodes connected to a network 110 (e.g., an Internet Protocol (IP) network) to which network interface 1748 is connected (directly or indirectly) (e.g., network interface 1748 may be wirelessly connected to the network 110, in which case network interface 1748 is connected to an antenna arrangement); and a storage unit (a.k.a., “data storage system”) 1708, which may include one or more non-volatile storage devices and/or one or more volatile storage devices. In embodiments where PC 1702 includes a programmable processor, a computer program product (CPP) 1741 may be provided. CPP 1741 includes a computer readable medium (CRM) 1742 storing a computer program (CP) 1743 comprising computer readable instructions (CRI) 1744. CRM 1742 may be a non-transitory computer readable medium, such as, magnetic media (e.g., a hard disk), optical media, memory devices (e.g., random access memory, flash memory), and the like. In some embodiments, the CRI 1744 of computer program 1743 is configured such that when executed by PC 1702, the CRI causes CN node 1700 to perform steps described herein (e.g., steps described herein with reference to the flow charts). In other embodiments, CN node 1700 may be configured to perform steps described herein without the need for code. That is, for example, PC 1702 may consist merely of one or more ASICs. Hence, the features of the embodiments described herein may be implemented in hardware and/or software.

[00123] Summary of Various Embodiments

[00124] Al. A method 1200 (see FIG. 12) performed by a radio access network (RAN) (e.g., NG-RAN) function 104, the method comprising: storing sl202 an MBS session context for an MBS service; detecting sl204 that no UE is using the MBS service; and as a result of detecting that no UE is using the MBS service, transmitting sl206 to a management function 106 (e.g., an M-AMF) a message (e.g., a notification that no UE is using the MBS service) that triggers the management function to initiate MBS Session stop towards the RAN.

[00125] Bl. A method 1400 (see FIG. 14) performed by a radio access network (RAN) (e.g., NG-RAN) function 104, the method comprising: the RAN function receiving sl402 a first message (e.g., an N2 MB Session Join message) transmitted by a management function 106, the first message comprising a group identifier (e.g., TMGI) associated with an MB session; the RAN function receiving sl404 a response message intended for a UE that has indicated its interest to join the MB Session (e.g., the response message is a NAS MB Session Join Response message intended for the UE) (the first message may include the response message - - i.e. the response message may be “piggy backed” on the first message); and the RAN function determining sl406 whether or not it has an MB Session Context in an active state for the group identifier, wherein if the RAN function determines that it has an MB Session Context in the active state for the group identifier, then the RAN function establishes sl408 resources (e.g., PTM or PTP DL resources) for the UE.

[00126] B2. The method of embodiment Bl, wherein the RAN function has determined that it does not have an MB Session Context in the active state for the group identifier, and the method further comprises: after receiving the first message; the RAN function receiving a second message transmitted by the management function (e.g., the second message is an MB Session Resource Setup Request (TMGI, LL MC, 5G Authorized QoS Profile) message); and as a result of receiving the second message, the RAN function establishes DL resources for the MB Session.

[00127] Cl. A method 1500 (see FIG. 15) performed by a radio access network (RAN) (e.g., NG-RAN) function 104, the method comprising: the RAN function receiving sl502 a first message (e.g., an N2 MB Session Leave message) transmitted by a management function 106, the first message comprising a group identifier (e.g., TMGI) associated with an MB session; the RAN function receiving si 504 a response message intended for a UE that has indicated its interest to leave the MB Session (e.g., the response message is a NAS MB Session Leave Response message intended for the UE) (the first message may include the response message - - i.e. the response message may be “piggy backed” on the first message), wherein the RAN function has a UE context for the UE; after receiving the first message, the RAN function removing si 506 the group identifier from the UE context; the RAN function determining si 508 whether the RAN function is serving any other UEs that are using the MB session (that is, the RAN function determines if the UE is the last UE in this NG-RAN using the MB Session); and as a result of determining that the RAN function is not serving any other UEs that are using the MB session, the RAN function sending s 1510 a Leave message to stop the media stream to the RAN function and deleting s 1512 an MB Session Context associated with the MB session.

[00128] Dl. A method 1300 (see FIG. 13) performed by PCF 114, the method comprising: receiving sl302 a first message transmitted by SMF 108, the first message comprising a group identifier (e.g., a Temporary Mobile Group Identity (TMGI)) for an MB Session and service requirement information; and transmitting si 304 a second message responsive to the first message, the second message comprising a 5G QoS Profile.

[00129] D2. The method of embodiment D 1 , wherein the MB-SMF is configured to use the 5G QoS Profile as a 5G Authorized QoS Profile for the MB Session.

[00130] El. A computer program 1643 comprising instructions 1644 which when executed by processing circuitry 1602 of a RAN node 1600 causes the RAN node 1600 to perform the method of any one of embodiments Al-Cl.

[00131] E2. A computer program 1743 comprising instructions 1744 which when executed by processing circuitry 1702 of a CN node 1700 causes the CN node 1700 to perform the method of any one of embodiments D1-D2.

[00132] E3. A carrier containing the computer program of embodiment El or E2, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium 1642, 1742.

[00133] FI. A RAN node 1600, the RAN node 1600 being adapted to perform the method of any one of embodiments Al-Cl.

[00134] Gl. A RAN node 1600, the RAN node 1600 comprising: processing circuitry 1602; and a memory 1642, the memory containing instructions 1644 executable by the processing circuitry, whereby the RAN node is operative to perform the method of any one of the embodiments Al-Cl.

[00135] HI. A CN node 1700, the CN node 1700 being adapted to perform the method of any one of embodiments D 1 -D2.

[00136] II. A CN node 1700, the CN node 1700 comprising: processing circuitry 1702; and a memory 1742, the memory containing instructions 1744 executable by the processing circuitry, whereby the CN node is operative to perform the method of any one of the embodiments D1-D2.

[00137] While various embodiments are described herein, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of this disclosure should not be limited by any of the above -described exemplary embodiments. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the disclosure unless otherwise indicated herein or otherwise clearly contradicted by context.

[00138] Additionally, while the processes described above and illustrated in the drawings are shown as a sequence of steps, this was done solely for the sake of illustration. Accordingly, it is contemplated that some steps may be added, some steps may be omitted, the order of the steps may be re-arranged, and some steps may be performed in parallel.

[00139] References:

[00140] [1] 3 GPP Technical Specification (TS) 23.246 MBMS (3G & 4G)

[00141] [2] 3GPP TS 23.501 5G system architecture

[00142] [3] 3GPP TS 23.5025G system procedures

[00143] [4] 3 GPP TS 38.3005G NR architecture

[00144] [5] 3 GPP TS 38.413 NGAP Protocol

Claims

1. A method (1200) performed by a radio access network, RAN, function (104), the method comprising: storing (sl202) a Multicast Broadcast Services, MBS, session context for an MBS service; detecting (sl204) that no user equipment, UE, is using the MBS service; and as a result of detecting that no UE is using the MBS service, transmitting (sl206) to a management function (106) a message that triggers the management function to initiate MBS Session stop towards the RAN.

2. The method of claim 1 , wherein the message comprises a notification indicating that no UE is using the MBS service.

3. A method (1400) performed by a radio access network, RAN, function (104), the method comprising: the RAN function receiving (sl402) a first message transmitted by a management function (106), the first message comprising a group identifier associated with a multicast broadcast (MB) session; the RAN function receiving (sl404) a response message intended for a UE that has indicated its interest to join the MB session; and the RAN function determining (sl406) whether or not it has an MB Session Context in an active state for the group identifier, wherein if the RAN function determines that it has an MB Session Context in the active state for the group identifier, then the RAN function establishes (sl408) resources for the UE.

4. The method of claim 3, wherein the first message comprises an N2 MB Session Join message.

5. The method of claim 3 or 4 wherein the response message comprises a Non-Access Stratum, NAS, MB Session Join Response message intended for the UE.

6. The method of any one of claims 3-5, wherein the response message is included in the first message.

7. The method of any one of claims 3-6, wherein the RAN function has determined that it does not have an MB Session Context in the active state for the group identifier, and the method further comprises: after receiving the first message, the RAN function receiving a second message transmitted by the management function; and as a result of receiving the second message, the RAN function establishes DL resources for the MB Session.

8. The method of claim 7, wherein the second message comprises an MB Session Resource Setup Request.

9. A method (1500) performed by a radio access network, RAN, function (104), the method comprising: the RAN function receiving (si 502) a first message transmitted by a management function (106), the first message comprising a group identifier associated with a multicast broadcast (MB) session; the RAN function receiving (si 504) a response message intended for a UE that has indicated its interest to leave the MB session, wherein the RAN function has a UE context for the UE; after receiving the first message, the RAN function removing (si 506) the group identifier from the UE context; the RAN function determining (si 508) whether the RAN function is serving any other UEs that are using the MB session; and as a result of determining that the RAN function is not serving any other UEs that are using the MB session, the RAN function sending (si 510) a Feave message to stop the media stream to the RAN function and deleting (si 512) an MB Session Context associated with the MB session.

10. The method of claim 9, wherein the first message comprises an N2 MB Session Leave message.

11. The method of claim 9 or 10, wherein the response message is a NAS MB Session Leave Response message intended for the UE.

12. The method of any one of claims 9-11, wherein the first message includes the response message.

13. A method (1300) performed by a policy function (114), the method comprising: receiving (si 302) a first message transmitted by session management function, SMF

(108), the first message comprising a group identifier for a multicast broadcast (MB) session and service requirement information; and transmitting (si 304) a second message responsive to the first message, the second message comprising a 5G Quality-of-Service, QoS, profile.

14. The method of claim 13, wherein the SMF is configured to use the 5G QoS Profile as a 5G Authorized QoS Profile for the MB session.

15. A computer program (1643) comprising instructions (1644) which when executed by processing circuitry (1602) of a radio access network, RAN, node (1600) causes the RAN node (1600) to perform the method of any one of claims 1-12.

16. A computer program (1743) comprising instructions (1744) which when executed by processing circuitry (1702) of a core network, CN, node (1700) causes the CN node (1700) to perform the method of any one of claims 13-14.

17. A carrier containing the computer program of claim 15 or 16, wherein the carrier is one of an electronic signal, an optical signal, a radio signal, and a computer readable storage medium (1642, 1742).

18. A radio access network, RAN, node (1600), the RAN node (1600) being configured to: store (sl202) a Multicast Broadcast Services, MBS, session context for an MBS service; detect (sl204) that no user equipment, UE, is using the MBS service; and as a result of detecting that no UE is using the MBS service, transmit (sl206) to a management function (106) a message that triggers the management function to initiate MBS Session stop towards the RAN.

19. The RAN node of claim 18, wherein the message comprises a notification indicating that no UE is using the MBS service.

20. A radio access network, RAN, node (1600), the RAN node (1600) being configured to: receive (sl402) a first message transmitted by a management function (106), the first message comprising a group identifier associated with a multicast broadcast (MB) session; receive (sl404) a response message intended for a UE that has indicated its interest to join the MB session; and determine (sl406) whether or not it has an MB Session Context in an active state for the group identifier, wherein the RAN node is configured such that, if the RAN node determines that it has an MB Session Context in the active state for the group identifier, then the RAN node establishes (sl408) resources for the UE.

21. The RAN node of claim 20, wherein the RAN node is further configured to perform the method of any one of claims 4-8.

22. A radio access network, RAN, node (1600), the RAN node (1600) being configured to: receive (si 502) a first message transmitted by a management function (106), the first message comprising a group identifier associated with a multicast broadcast (MB) session receive (si 504) a response message intended for a UE that has indicated its interest to leave the MB session, wherein the RAN node has a UE context for the UE; after receiving the first message, remove (si 506) the group identifier from the UE context; determine (si 508) whether the RAN node is serving any other UEs that are using the MB session; and as a result of determining that the RAN node is not serving any other UEs that are using the MB session, send (sl510) a leave message to stop the media stream to the RAN node and delete (s 1512) an MB Session Context associated with the MB session.

23. The RAN node of claim 22, wherein the RAN node is further configured to perform the method of any one of claims 10-12.

24. A radio access network, RAN, node (1600), the RAN node (1600) comprising: processing circuitry (1602); and a memory (1642), the memory containing instructions (1644) executable by the processing circuitry, whereby the RAN node is operative to perform the method of any one of the claims 1-12.

25. A core network, CN, node (1700), the CN node (1700) being configured to. receive (sl302) a first message transmitted by session management function, SMF (108), the first message comprising a group identifier for a multicast broadcast (MB) session and service requirement information; and transmit (si 304) a second message responsive to the first message, the second message comprising a 5G Quality-of-Service, QoS, profile.

27. A core network, CN, node (1700), the CN node (1700) comprising: processing circuitry (1702); and a memory (1742), the memory containing instructions (1744) executable by the processing circuitry, whereby the CN node is operative to perform the method of any one of the claims 13-14.