WO2022161815A1

WO2022161815A1 - Ran control for local mbs and location-dependent mbs service

Info

Publication number: WO2022161815A1
Application number: PCT/EP2022/051022
Authority: WO
Inventors: Jie LING; Juying GAN; Alexander Vesely; Paul Schliwa-Bertling
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2021-01-26
Filing date: 2022-01-18
Publication date: 2022-08-04

Abstract

Embodiments of a method performed by a network node are disclosed herein. In one embodiment, a method performed by a network node in a radio access network (RAN) of a cellular communications system comprises detecting that a wireless communication device that has joined a first MBS session having a first service area has crossed a boundary of the first service area and, responsive to detecting that the wireless communication device has crossed the boundary of the first service area, triggering a procedure by which the wireless communication device is either switched to a second MBS session having a second service area that covers a location of the wireless communication device or removed from the first MBS session. In this manner, service switch and area restriction for location-dependent services are provided.

Description

RAN CONTROL FOR LOCAL MBS AND LOCATION-DEPENDENT MBS SERVICE

TECHNICAL FIELD

The present disclosure relates to Multicast/Broadcast Services (MBS) service in a cellular communications system.

BACKGROUND

The Third Generation Partnership Project (3GPP) previously developed the Multicast/Broadcast Multimedia Subsystem (MBMS) (see 3GPP TS 23.246 v16.1.0) for Third Generation (3G) networks for video multicast/broadcasting and streaming services and later introduced the evolved MBMS (eMBMS) for the Evolved Packet System (EPS). In Release 13 and Release 14, the MBMS system has been updated to support new services such as Public Safety, Cellular Internet of Things (CloT), and Vehicle to anything (V2X).

The scope of a new Release 17 study in 3GPP SA2 working group is to study both multicast requirements and use cases for CloT, Public Safety, V2X etc., and dedicated broadcasting requirements and use cases. The study targets the Fifth Generation (5G) Release 17 and the New Radio (NR) radio access. The study results so far have been documented in the 3GPP Technical Report (TR) 23.757 V1.2.0.

Multicast I Broadcast services (MBS) are so far not supported on 5G NR. With the enhanced characteristics of the 5G NR, e.g. short delays, bandwidth, etc., it is believed Mission Critical Services (Mission Critical Push To Talk (MCPTT), Mission Critical Data (MCData), and Mission Critical Video (MCVideo), as well as VTX services, will show an enhanced and much better performance on 5G NR.

In 5G MBS (5MBS) study, local MBS service is Key Issue #6, which brings the restriction of the delivery of MBS service based on area. It requires the delivery control not only in the 5G Core (5GC), but also in the Next Generation Radio Access Network (NG-RAN).

Besides that, location-dependent service is further developed. For location-dependent service, a User Equipment (UE) may receive different contents depending on its location area. A UE shall not be aware of its location area, but just receive different contents.

In 3GPP TR 23.757 V1.2.0, chapter 6.19.2, a solution for location-dependent service in 5MBS is proposed.

Specifically, in Solution #19, 3GPP TR 23.757 V1.2.0, chapter 6.19.2, describes the location dependent solution for Xn based handover as shown in the excerpt below:

********** _{start Excerpt from} 3GPP TR 23.757 ***********

For location-dependent service handover, the handover procedure in Solution #11 and Solution #12 need to be enhanced. For simplification, only Xn based handover is addressed below. It can be extended to N2 based handover and other handover solutions.

Figure 6.19.2-2 assumes Option.2 in Solution #11, which is executed after AMF sends Path Switch Acknowledge. As an alternative solution, it is possible to adopt Option.1 (i.e. embedding step 3 in handover procedure) to speed up user plane establishment in Target NG-RAN side. Figure 1

[REPRODUCED HEREIN AS FIGURE 1]

Figure 6.19.2-2: Inter-gNB Xn Handover for Location-Dependent Service

In the description below, compared with the Xn based handover, the differences specific for location dependent services are shown in Italic.

1. Inter-gNB Xn handover is triggered as in step 1 to step 9 in clause 6.11.2.1. AMF has sent Path Switch Request Ack to Target NG-RAN.

2. IfUE moves to a new location area and AMF does not have MB Service for the new location area, AMF will query MB-SMF via MB Session Request/Response to get MB Service based on TMGI. AMF provides UE's location information, and B-SMF return the proper MB service to AMF

3. Target NG-RAN join the receiving of the MB session and the resources in the Source NG-RAN may be released, if there are on other UEs receiving the content of the MB session. Refer to step 10a. to 11. in clause 6.11.2.1 for more details. Compared with non-location dependent service, there may be the following differences, if UE's location belongs to a different location dependent service from the original one:

When shared delivery and multicast N3 applies, Target NG-RAN may join a different SSM from the one joined by the source NG-RAN.

When shared delivery and unicast MB-N 3 applies, Target NG-RAN may establish N3 tunnel to another MB- UPF endpoint.

When individual delivery and multicast MB-N9 applies, UPF may join a different SSM from the original one.

When individual delivery and unicast MB-N9 applies, UPF may switch to another MB- UPF endpoint.

********** _{End Excerpt from 3Gpp TR} 23 757 ***********

In Solution #21 , 3GPP TR 23.757 V1.2.0, chapter 6.21.2.3, describes the location dependent solution for Xn based handover is described as shown in the excerpt below:

********** _{start Excerpt from} 3GPP TR 23.757 ***********

NOTE: For simplification, this figure is based on Solution #27 and only address the Xn based Handover. It can be extended to N2 based Handover and other Handover Solutions if needed.

Figures 2A-2B

[REPRODUCED HEREIN AS FIGURES 2A-2B]

Figure 6.21.2.3-1: Enhancement on Handover procedure.

Prerequisite: The UE is camping at Source RAN (S-RAN) and receiving multicast data a corresponding to the multicast session ID and location area ID.

1. Same as in clause 6.27.2.1

2. Same as in clause 6.27.2.1: S-RAN sends Handover request to T-RAN with including multicast session ID, location area ID and location area.

3-7. T-RAN determines whether to establish the forwarding resources and multicast distribution for multicast session ID and location area ID provided by S-RAN, based on multicast session ID, area session ID and location area. To determine the forwarding resources for location-dependent contents delivery, T-RAN may only check whether or not the location area ID is the same if T-RAN already established the session context of the multicast session ID. If a multicast distribution session needs to be established, T-RAN provides multicast session ID and location ID in step 3

8. T-RAN sends the Handover request Ack to S-RAN, with the accepted multicast session ID and area session ID. When the T-RAN supports multicast but the UE is no longer in the location area indicated in step 2, the T-RAN rejects to handover that multicast session with a cause indication that the UE moved out of the location area and the new UE location. Other info is same as step 8 in clause 6.27.2.1.

Editor's note: The handling at source gNB from step 8 to step 14 require confirmation from RAN WGs.

Editor's note: To minimize impact on the handover procedure, an alternative whether steps 9-13 and steps 15-

17 can be performed after handover is complete is FFS.

Steps 9 to 20 only apply if the UE moved out of the location area and target gNB supports multicast.

9-10 The S-RAN indicates the new UE location to the SMF via the AMF.

11. The SMF determines the location area, area session ID and MB-SMF ID for the new UE location. It may query the UDR for that information. If the SMF determines that there is no local content (and MB-SMF ID, area session ID, location area) for the UE's location, the SMF removes the UE from the multicast session.

12-13. The SMF sends the new location area, area session ID and MB-SMF ID to the S-RAN via the AMF. 14-20. Same as steps 2-7, but with new MB-SMF ID, area session ID and location area.

21-42. Same as steps 9-29 in clause 6.27.2.1. In steps 29, 35 and 36, the area session ID is indicated in addition to the multicast session ID.

********** End Excerpt from 3GPP TR 23.757 ***********

SUMMARY

Systems and methods for location dependent MBS service (also referred to here as MBMS service) for intrabase station handover are disclosed. In one embodiment, systems and methods for location dependent MBS service in 5MBS for Intra-gNB handover are disclosed. In one embodiment, the systems and methods disclosed herein can be applied to local MBS service (without location-dependent) about the area restriction part (i.e., remove UE from the distribution list when outside the service area).

In one embodiment, if there is a second MBS session having (a) a same MBS session ID as the first MBS session and (b) a second service area that covers the location of the wireless communication device, the procedure switches the wireless communication device to the second MBS session. Otherwise, the procedure removes the wireless communication device from the first MBS session. In one embodiment, the MBS session ID is a TMGI. In another embodiment, the MBS service ID comprises a TMGl.

In one embodiment, triggering the procedure comprises sending a Multicast/Broadcast (MB) switch request to a network function (NF) in a core network of the cellular communications system, the MB switch request comprising an MBS session ID of the first MBS session and information that indicates the location of the wireless communication device. In one embodiment, the method further comprises receiving a response from the NF that indicates that the wireless communication device is removed from the first MBS session. IN another embodiment, the method further comprises receiving a response from the NF that indicates that the wireless communication device is being moved to the second MBS session and performing one or more actions to move the wireless communication device to the second MBS session.

In one embodiment, the NF is an Access and Mobility Management Function (AMF). In one embodiment, the cellular communications system is a Fifth Generation System (5GS).

In one embodiment, a method performed by a network node in a core network of a cellular communications system comprises receiving, from a RAN node in a RAN of the cellular communications system, a MB switch request comprising a MBS, session ID of a first MBS session to which the wireless communication device is currently joined and location information that indicates a location of a respective wireless communication device and performing a procedure by which the wireless communication device is either switched to a second MBS session having a service area that covers the location of the wireless communication device or removed from the first MBS session.

In one embodiment, if there is a second MBS session having (a) a same MBS session ID as the first MBS session and (b) a service area that covers the location of the wireless communication device, the procedure switches the wireless communication device to the second MBS session. Otherwise, the procedure removes the wireless communication device from the first MBS session.

In one embodiment, the MBS session ID is a TMGI. In another embodiment, the MBS service ID comprises a TMGl.

In one embodiment, performing the procedure comprises determining whether there is a second MBS session having (a) a same MBS session ID as the first MBS session and (b) a service area that covers the location of the wireless communication device and, if so, sending a request to the RAN node to switch the wireless communication device to the second MBS session and, otherwise, sending a message to the RAN node that indicates that the wireless communication device is to be removed from the first MBS session.

In one embodiment, performing the procedure comprises sending, to a Session Management Function (SMF), a Protocol Data Unit (PDU) session modification request comprising the MBS session ID of the first MBS session and information that indicates the location of the wireless communication device.

In one embodiment, the network node is a network node that implements an AMF. In one embodiment, the cellular communications system is a 5GS.

In one embodiment, a method performed by a network node in a core network of a cellular communications system comprises receiving a PDU session modification request comprising a MBS session ID of a first MBS session to which a wireless communication device is currently joined and location information that indicates a location of a respective wireless communication device and performing a procedure by which the wireless communication device is either switched to a second MBS session having a service area that covers the location of the wireless communication device or removed from the first MBS session. In one embodiment, if there is a second MBS session having (a) a same MBS session ID as the first MBS session and (b) a service area that covers the location of the wireless communication device, the procedure switches the wireless communication device to the second MBS session. Otherwise, the procedure removes the wireless communication device from the first MBS session.

In one embodiment, performing the procedure comprises determining whether there is a second MBS session having (a) a same MBS session ID as the first MBS session and (b) a service area that covers the location of the wireless communication device. Is so, performing the procedure further comprises performing one or more actions to switch the wireless communication device to the second MBS session. Otherwise, performing the procedure further comprises performing one or more actions to remove the wireless communication device from the first MBS session.

In one embodiment, the network node is a network node that implements a Session Management Function (SMF). In one embodiment, the cellular communications system is a 5GS.

Corresponding embodiments of a network node are also disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawing figures incorporated in and forming a part of this specification illustrate several aspects of the disclosure, and together with the description serve to explain the principles of the disclosure.

Figure 1 is a reproduction of Figure 6.19.2-2 of 3GPP TR 23.757 V1 .2.0;

Figures 2A and 2B are a reproduction of Figure 6.21 .2.3-1 of 3GPP TR 23.757 V1 .2.0;

Figure 3 illustrates one example of a cellular communications system in which embodiments of the present disclosure may be implemented;

Figures 4 and 5 illustrate example embodiments in which the cellular communication system of Figure 3 is a Fifth Generation (5G) System (5GS);

Figure 6 illustrates a procedure in accordance with a first embodiment of the present disclosure;

Figure 7 illustrates a procedure in accordance with a second embodiment of the present disclosure;

Figure 8 is a schematic block diagram of a network node according to some embodiments of the present disclosure;

Figure 9 is a schematic block diagram that illustrates a virtualized embodiment of the network node of Figure 8 according to some embodiments of the present disclosure;

Figure 10 is a schematic block diagram of the network node of Figure 8 according to some other embodiments of the present disclosure;

Figure 11 is a schematic block diagram of a User Equipment device (UE) according to some embodiments of the present disclosure;

Figure 12 is a schematic block diagram of the UE of Figure 11 according to some other embodiments of the present disclosure. DETAILED DESCRIPTION

The embodiments set forth below represent information to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure.

Radio Node: As used herein, a "radio node” is either a radio access node or a wireless communication device.

Radio Access Node: As used herein, a "radio access node” or "radio network node” or "radio access network node” is any node in a Radio Access Network (RAN) of a cellular communications network that operates to wirelessly transmit and/or receive signals. Some examples of a radio access node include, but are not limited to, a base station (e.g., a New Radio (NR) base station (gNB) in a Third Generation Partnership Project (3GPP) Fifth Generation (5G) NR network or an enhanced or evolved Node B (eNB) in a 3GPP Long Term Evolution (LTE) network), a high-power or macro base station, a low-power base station (e.g., a micro base station, a pico base station, a home eNB, or the like), a relay node, a network node that implements part of the functionality of a base station or a network node that implements a gNB Distributed Unit (gNB-DU)) or a network node that implements part of the functionality of some other type of radio access node.

Core Network Node: As used herein, a "core network node” is any type of node in a core network or any node that implements a core network function. Some examples of a core network node include, e.g., a Mobility Management Entity (MME), a Packet Data Network Gateway (P-GW), a Service Capability Exposure Function (SCEF), a Home Subscriber Server (HSS), or the like. Some other examples of a core network node include a node implementing an Access and Mobility Function (AMF), a User Plane Function (UPF), a Session Management Function (SMF), an Authentication Server Function (AUSF), a Network Slice Selection Function (NSSF), a Network Exposure Function (NEF), a Network Function (NF) Repository Function (NRF), a Policy Control Function (PCF), a Unified Data Management (UDM), or the like.

Communication Device: As used herein, a "communication device” is any type of device that has access to an access network. Some examples of a communication device include, but are not limited to: mobile phone, smart phone, sensor device, meter, vehicle, household appliance, medical appliance, media player, camera, or any type of consumer electronic, for instance, but not limited to, a television, radio, lighting arrangement, tablet computer, laptop, or Personal Computer (PC). The communication device may be a portable, hand-held, computer-comprised, or vehiclemounted mobile device, enabled to communicate voice and/or data via a wireless or wireline connection.

Wireless Communication Device: One type of communication device is a wireless communication device, which may be any type of wireless device that has access to (i.e., is served by) a wireless network (e.g., a cellular network). Some examples of a wireless communication device include, but are not limited to: a User Equipment device (UE) in a 3GPP network, a Machine Type Communication (MTC) device, and an Internet of Things (loT) device. Such wireless communication devices may be, or may be integrated into, a mobile phone, smart phone, sensor device, meter, vehicle, household appliance, medical appliance, media player, camera, or any type of consumer electronic, for instance, but not limited to, a television, radio, lighting arrangement, tablet computer, laptop, or PC. The wireless communication device may be a portable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and/or data via a wireless connection.

Network Node: As used herein, a "network node” is any node that is either part of the RAN or the core network of a cellular communications network/system.

Local Multicast/Broadcast Multimedia Subsystem (MBMS) Service or Local MBS Service: As used herein, a local MBMS service or local MBS service a multicast or broadcast communication service that is only available in a local service area (e.g., cell, Tracking Area (TA), or other geographic metric) and, optionally, only for a specific time period (e.g., during event hours, emergency situation, or operation hours).

Note that the description given herein focuses on a 3GPP cellular communications system and, as such, 3GPP terminology or terminology similar to 3GPP terminology is oftentimes used. However, the concepts disclosed herein are not limited to a 3GPP system.

Note that, in the description herein, reference may be made to the term "cell”; however, particularly with respect to 5G NR concepts, beams may be used instead of cells and, as such, it is important to note that the concepts described herein are equally applicable to both cells and beams.

For location-dependent Multicast/Broadcast Multimedia Subsystem (MBMS) service (also referred to herein as an MBS service), service switch and area restriction need to be performed not only in the Fifth Generation Core (5GC), but also in the Next Generation Radio Access Network (NG-RAN). Especially when the New Radio (NR) base station (gNB) utilizes a Central Unit (CU) I Distributed Unit (DU), it is possible that the gNB can manage many cells. In this case, different location-dependent MBS services with the same MBMS service identity (ID), which is in current 3GPP specifications the Temporary Mobile Group Identity (TMGI), may be delivered towards the same gNB.

It is possible that when a User Equipment (UE) moves from one cell to another cell, the UE crosses the boundary of between service areas of different location dependent MBS services. In this case, the NG-RAN needs to be able to trigger a service switch from one MBS service to another MBMS service.

It is also possible that when a UE moves from one cell to another cell, the UE moves out of the boundary of a location dependent MBMS service. In this case, the UE should be removed from the MBS service, as the location dependent MBS service will not be delivered to it.

In Solution #19 and Solution #21 in 3GPP TR 23.757, the service switch and the area restriction are coupled with the handover so the 5GC can be the one to deal with them. It is important to have a solution to enable the NG- RAN to trigger the service switch or the area restriction. It can be regarded as an Intra-gNB handover scenario.

Systems and methods for addressed the aforementioned and/or other issues are disclosed herein. Systems and methods for location dependent MBS service (also referred to here as MBMS service) for intra-base station handover are disclosed. In one embodiment, systems and method for location dependent MBS service in 5MBS for Intra-gNB handover are disclosed. In one embodiment, the systems and methods disclosed herein can be applied to local MBS service (without location-dependent) about the area restriction part (i.e., remove UE from the distribution list when outside the service area). In one embodiment, a NG-RAN node becomes aware of the local service area(s) associated with a local MBS Session of active shared MBS traffic. The active shared MBS traffic may be, e.g., active 5GC shared MBS traffic (5GC receives a single copy of MBS data packets and delivers a single copy of those MBS data packets to a RAN node). If the NG-RAN node does not have information about neighboring local service areas but is aware of the "overall” MBS Session Area (e.g., combination of two or more local service areas, e.g., in which the system is able to keep the same MBS session ID (e.g., TGMI) when a UE moves across those local service areas) and there is no ongoing shared MBS traffic outside that local MBS Session area:

• The NG-RAN triggers a MB Session Switch request to the AMF, when the NG-RAN node detects that the UE moves out of the coverage of the current MB Session.

• The "MBS Session Switch request to AMF” carries the UE's location (ULI) to let the 5GC know which Local MBS Session content to deliver to the NG-RAN node.

• The UE may move within the current serving NG-RAN node or to another NG-RAN node.

In one embodiment, an AMF-centric approach is used. In one embodiment, for the AMF-centric approach:

• The AMF sends a query for MB Session Context information towards the MB-SMF based on the new location of the UE.

• If there is no such MB Session (if the UE is outside the "overall” MBS Session area), the AMF removes the UE from the MB Session (e.g., via a NAS message to UE and a N2 message to NG-RAN).

• If there is another location dependent MBS service that covers the UE's location, the AMF sends a MB Session Update to the NG-RAN to move the UE to the new location dependent MBS service.

In another embodiment, an SMF-centric approach is used. In one embodiment, for the SMF-centric approach:

• The AMF receives a "MB Session Switch” request from the gNB (e.g., via event notification), with UE's location (ULI). The AMF sends PDU Session Update SM Context request to the SMF to trigger the SMF to take one or more actions.

• The SMF determines an MBS Session Context and Area session ID via communication with the MB-SMF.

• If gNB does not support 5MBS, individual delivery applies. In this case, the SMF initiates path switching from the MB-UPF to a UPF (via communication with MB-SMF as well).

• If gNB support 5MBS, shared delivery applies. In this case, gNB initiates the user plane path switching from the MB-UPF to gNB.

Embodiments of the present disclosure may enable service switch and area restriction for location-dependent MBS services in a RAN such as, e.g., the NG-RAN. The area restriction can be applied to local MBS service as well. This is particularly well-suited for deployments in which the NG-RAN node (e.g., gNB) manages many cells.

Figure 3

Figure 3 illustrates one example of a cellular communications system 300 in which embodiments of the present disclosure may be implemented. In the embodiments described herein, the cellular communications system 300 is a 5G system (5GS) including a Next Generation RAN (NG-RAN) and a 5G Core (5GC); however, the embodiments disclosed herein are not limited to the 5GS and may be used in other similar types of systems. In this example, the RAN includes a base station 302-1 and 302-2, which in the 5GS may be NR base stations (gNBs) or optionally next generation eNBs (ng-eNBs) (e.g., LTE RAN nodes connected to the 5GC), controlling respective cell(s) 304-1 and 304-2. The base stations 302-1 and 302-2 are generally referred to herein collectively as base stations 302 and individually as base station 302. In some embodiments, each base station 302 may control multiple cells 304. The cellular communications system 300 also includes a core network 310, which in the 5G System (5GS) is referred to as the 5GC. The base stations 302 are connected to the core network 310.

The base stations 302 provide services to wireless communication devices 312-1 through 312-5 in the cells 304. The wireless communication devices 312-1 through 312-5 are generally referred to herein collectively as wireless communication devices 312 and individually as wireless communication device 312. In the following description, the wireless communication devices 312 are oftentimes UEs and thus sometimes referred to herein as UEs 312, but the present disclosure is not limited thereto.

Figure 4

Figure 4 illustrates a wireless communication system represented as a 5G network architecture composed of core Network Functions (NFs), where interaction between any two NFs is represented by a point-to-point reference poi nt/i nterface. Figure 4 can be viewed as one particular implementation of the system 300 of Figure 3.

Seen from the access side the 5G network architecture shown in Figure 4 comprises a plurality of UEs 312 connected to either a RAN 302 or an Access Network (AN) as well as an AMF 400. Typically, the R(AN) 302 comprises base stations, e.g. such as eNBs or gNBs or similar. Seen from the core network side, the 5GC NFs shown in Figure 4 include a NSSF 402, an AUSF 404, a UDM 406, the AMF 400, a SMF 408, a PCF 410, and an Application Function (AF) 412.

Reference point representations of the 5G network architecture are used to develop detailed call flows in the normative standardization. The N1 reference point is defined to carry signaling between the UE 312 and AMF 400. The reference points for connecting between the AN 302 and AMF 400 and between the AN 302 and UPF 414 are defined as N2 and N3, respectively. There is a reference point, N11 , between the AMF 400 and SMF 408, which implies that the SMF 408 is at least partly controlled by the AMF 400. N4 is used by the SMF 408 and UPF 414 so that the UPF 414 can be set using the control signal generated by the SMF 408, and the UPF 414 can report its state to the SMF 408. N9 is the reference point for the connection between different UPFs 414, and N14 is the reference point connecting between different AMFs 400, respectively. N15 and N7 are defined since the PCF 410 applies policy to the AMF 400 and SMF 408, respectively. N12 is required for the AMF 400 to perform authentication of the UE 312. N8 and N10 are defined because the subscription data of the UE 312 is required for the AMF 400 and SMF 408.

The 5GC network aims at separating UP and CP. The UP carries user traffic while the CP carries signaling in the network. In Figure 4, the UPF 414 is in the UP and all other NFs, i.e., the AMF 400, SMF 408, PCF 410, AF 412, NSSF 402, AUSF 404, and UDM 406, are in the CP. Separating the UP and CP guarantees each plane resource to be scaled independently. It also allows UPFs to be deployed separately from CP functions in a distributed fashion. In this architecture, UPFs may be deployed very close to UEs to shorten the Round Trip Time (RTT) between UEs and data network for some applications requiring low latency.

The core 5G network architecture is composed of modularized functions. For example, the AMF 400 and SMF 408 are independent functions in the CP. Separated AMF 400 and SMF 408 allow independent evolution and scaling. Other CP functions like the PCF 410 and AUSF 404 can be separated as shown in Figure 4. Modularized function design enables the 5GC network to support various services flexibly.

Each NF interacts with another NF directly. It is possible to use intermediate functions to route messages from one NF to another NF. In the CP, a set of interactions between two NFs is defined as service so that its reuse is possible. This service enables support for modularity. The UP supports interactions such as forwarding operations between different UPFs.

Figure 5

Figure 5 illustrates a 5G network architecture using service-based interfaces between the NFs in the CP, instead of the point-to-point reference poi nts/i nterfaces used in the 5G network architecture of Figure 4. However, the NFs described above with reference to Figure 4 correspond to the NFs shown in Figure 5. The service(s) etc. that a NF provides to other authorized NFs can be exposed to the authorized NFs through the service-based interface. In Figure 5 the service based interfaces are indicated by the letter “N” followed by the name of the NF, e.g. Namf for the service based interface of the AMF 400 and Nsmf for the service based interface of the SMF 408, etc. The NEF 500 and the NRF 502 in Figure 5 are not shown in Figure 4 discussed above. However, it should be clarified that all NFs depicted in Figure 4 can interact with the NEF 500 and the NRF 502 of Figure 5 as necessary, though not explicitly indicated in Figure 4.

Some properties of the NFs shown in Figures 4 and 5 may be described in the following manner. The AMF 400 provides UE-based authentication, authorization, mobility management, etc. A UE 312 even using multiple access technologies is basically connected to a single AMF 400 because the AMF 400 is independent of the access technologies. The SMF 408 is responsible for session management and allocates Internet Protocol (IP) addresses to UEs. It also selects and controls the UPF 414 for data transfer. If a UE 312 has multiple sessions, different SMFs 408 may be allocated to each session to manage them individually and possibly provide different functionalities per session. The AF 412 provides information on the packet flow to the PCF 410 responsible for policy control in order to support QoS. Based on the information, the PCF 410 determines policies about mobility and session management to make the AMF 400 and SMF 408 operate properly. The AUSF 404 supports authentication function for UEs or similar and thus stores data for authentication of UEs or similar while the UDM 406 stores subscription data of the UE 312. The Data Network (DN), not part of the 5GC network, provides Internet access or operator services and similar.

An NF may be implemented either as a network element 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., a cloud infrastructure.

Now, a description of some example embodiments of the present disclosure will be described. For the following examples, the base station 302 is a gNB and, as such, is referred to as a gNB 302, and the wireless communication device 312 is a UE and, as such, is referred to as a UE 312. BS (e.g., gNB) Detects Service Switch or Area Restriction for AMF-Centric Approach

Figure 6

Figure 6 illustrates a procedure for NG-RAN triggered MBS session switch or MBS session service area restriction in accordance with one example embodiment of the present disclosure. When the gNB 302 detects that the UE 312 moves from one cell 304 (referred to as cell 304-A) to another cell 304 (referred to as cell 304-B) and where the movement to cell 304-B corresponds to crossing the boundary of an MBS service area of a current locationdependent MBS service provided to the UE 312, this cell change triggers a MB Session Switch as illustrated in Figure 6. The steps of the procedure of Figure 6 are as follows:

• Step 1 : Location dependent MBS services have been established in the network.

• Step 2: The UE 312 joins a location dependent MBS service. The MBS service ID is TMGI A and Flow ID B, while the service area is Y.

• Step 3: The NG-RAN (e.g., the gNB 302) detects that the UE 312 moves out of the boundary of the service area Y. As a result, the UE 312 should either be served by another location dependent MBS service with TMGI A or be removed as the service can no longer be offered to it.

• Step 4: The NG-RAN (e.g., the gNB 302) sends a MB Session Switch to the AMF 400 to indicate the UE 312 (e.g., identified by NGAP ID), the TMGI of the MBS service, and the new location L of the UE 312 (e.g., L may be defined a cell, Tracking Area (TA), or another other geographical unit). If the AMF 400 has a MB Session context in hand for a MBS service whose service area covers the location L of the UE 312, step 10 can be skipped. Step 9 and 10 can be performed directly.

• Step 5: If the AMF 400 does not have such a MB Session context on hand, the AMF 400 sends a MB Session Request to the MB-SMF 408-MB with the TMGI of the MBS service, the AMF ID, and the new location L of the UE 312. Note that the "MB-SMF” may be the same as the SMF 408 or a different SMF that has MBS related capabilities. As such, the MB-SMF is given reference number "408-MB” in order to differentiate it from the SMF 408.

If there is no location dependent MBS service whose service area covers the location L, this means that the UE 312 has moved out of the boundary of the "overall” service area of the location-dependent MBS services. In this case:

• Step 6: The MB-SMF 408-MB sends a MB Session Response to the AMF 400 indicating that no MB Session is available (no MB Session with TMGI A covers location L).

• Step 7: The AMF 400 sends a NAS message MB Session Remove to the UE 312 along with a N2 message MB Session Remove to the NG-RAN (e.g., to the gNB 302). In this manner, the UE 312 is removed.

If there is another location dependent MBS service whose service area covers the location L of the UE 312, this means that the UE 312 has moved to the service area of another location-dependent MBS service. In this case:

• Step 8: The MB-SMF 408-MB sends a MB Session Response to the AMF 400 indicating, with the MB Session Context information, the new MBS session having TMGI A and Flow ID C with service area Z. • Step 9: The AMF 400 sends a NAS message MB Session Update to the NG-RAN (e.g., the gNB 302) to request the NG-RAN (e.g., the gNB 302) to update the UE 312 to the MB Session with TMGI A and Flow ID C and service area Z.

• Step 10: The NG-RAN (e.g., the gNB 302) establishes the user plane towards the 5GC. It can join the multicast group in which the MB-UPF 414-MB sends packets out for the MB Session with TMGI A and Flow ID C. As another alternative, it is also possible to trigger the N3 tunnel between the NG-RAN (e.g., the gNB 302) and the MB-UPF 414-MB for the MB Session. Note that the "MB-UPF” may be the same as the UPF 414 or a different UPF that has MBS related capabilities. As such, the MB-UPF is given reference number "414-MB” in order to differentiate it from the UPF 414.

BS (e.g., gNB) Detects Service Switch or Area Restriction for SMF-Centric Approach

Figure 7

Figure 7 illustrates a procedure for NG-RAN triggered MBS session switch or MBS session service area restriction in accordance with another example embodiment of the present disclosure. The steps of the procedure of Figure 7 are as follows:

• Step 1 : When the gNB 302 detects that the UE 312 moves out the service area of the current MBS session, the gNB 302 sends a MB Switching Request to the AMF 400 with MBS Session ID and new UE location. In one embodiment, this can be achieved by an event notification to the AMF 400.

• Step 2: The AMF 400 converts the request to a PDU Session Modification request that it sends to the SMF 408 with the MBS Session ID and the new UE location information.

• Step 3: The SMF 408 determines an MBS Session context based on the MBS Session ID and the new UE location. There are two options depending on how provisioning is done. o Option-1 : The MB-SMF 408-MB allocates the MBS Session ID and Area Session ID and stores the MBS Session context. In this case, the SMF 408 already has the MB-SMF ID, since when the UE 312 joins the first time, the SMF 408 already got the MB-SMF ID via NRF query. In this option, Step 3a can be skipped. o Option-2: The MB Session ID is an external ID (e.g., allocated by the AF 412) and Area Session ID is allocated by other entities (e.g., NEF 500 in this case). In this case, it is the NEF 500 who selects the MB-SMF 408-MB during the MBS session provisioning. In this case, step 3a is executed.

■ Step 3a: The SMF 408 queries the NEF 500 to get the MB-SMF ID by providing the MBS Session ID and new UE Location in the query. Based on the new UE location and MBS Session ID, the NEF 500 selects the corresponding MBS Session whose service area covers the new UE location and responds with the MB-SMF ID and Area Session ID. o Step 3b: The SMF 408 communicates with the MB-SMF 408-MB to get MB Session Information, providing MBS Session ID. Depending on the two options above, the SMF may provide new UE Location to let the MB-SMF 408-MB to find the proper MBS Session, or provide Area Session ID so that the MB-SMF 408-MB can get the proper MBS Session directly. If the gNB 302 does not support 5MBS, individual delivery applies in this case.

For this MBS Session, if the MB-UPF 414-MB delivers data to the UPF 414 1 NG-RAN via multicast tunnel, step 4 applies.

• Step 4: The SMF 408 sends N4 Session Modification to the UPF 414 to let the UPF 414 to join the SSM address. Steps 5-7 apply.

For this MBS Session, if the MB-UPF 414-MB delivers data to UPF 414 / NG-RAN via unicast tunnel:

• Steps 5-7: The SMF 408 triggers the MB-UPF 414-MB to deliver the session data to the UPF tunnel endpoint via the MB-SMF 408-MB.

• Step 9: The SMF 408 sends a PDU Session Modification Response to the AMF 400 with the MBS session information.

• Step 10: The AMF 400 sends a MB Session Switch Response to the gNB 302 with the MBS session information.

If the gNB 302 supports 5MBS, shared delivery applies in this case.

For this MBS Session, if the MB-UPF 414-MB delivers data to the UPF 414 1 NG-RAN via multicast tunnel, the gNB 302 joins the SSM address.

For this MBS Session, if the MB-UPF 414-MB delivers data to the UPF 414 / NG-RAN via unicast tunnel, steps 11-15 apply.

• Steps 11-15: The gNB 302 triggers the MB-UPF 414-MB to deliver the session data to its tunnel endpoint via the AMF 400 and the MB-SMF 408-MB.

Additional Description

Figure 8

Figure 8 is a schematic block diagram of a network node 800 according to some embodiments of the present disclosure. Optional features are represented by dashed boxes. The network node 800 may be, for example, a base station 302 or 306 or a network node that implements all or part of the functionality of the base station 302 or gNB described herein or a network node that implements the functionality of a core NF (e.g., the AMF 400, the SMF 408, the UPF 414, the PCF 410, the NEF 500, the MBSF, the AF 412, the MB-SMF 408-MB, the MB-UPF 414-MB, or the like). As illustrated, the network node 800 includes a control system 802 that includes one or more processors 804 (e.g., Central Processing Units (CPUs), Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), and/or the like), memory 806, and a network interface 808. The one or more processors 804 are also referred to herein as processing circuitry. In addition, if the network node 800 is a radio access node (e.g., base station 302), the network node 800 may include one or more radio units 810 that each includes one or more transmitters 812 and one or more receivers 814 coupled to one or more antennas 816. The radio units 810 may be referred to or be part of radio interface circuitry. In some embodiments, the radio unit(s) 810 is external to the control system 802 and connected to the control system 802 via, e.g., a wired connection (e.g., an optical cable). However, in some other embodiments, the radio unit(s) 810 and potentially the antenna(s) 816 are integrated together with the control system 802. The one or more processors 804 operate to provide one or more functions of a network node 800 as described herein (e.g., one or more functions of the base station 302 or gNB described herein or one or more functions of a core NF (e.g., the AMF 400, the SMF 408, the UPF 414, the PCF 410, the NEF 500, the MBSF, the AF 412, the MB-SMF 408-MB, the MB-UPF 414-MB, or the like) as described herein). In some embodiments, the function(s) are implemented in software that is stored, e.g., in the memory 806 and executed by the one or more processors 804.

Figure 9

Figure 9 is a schematic block diagram that illustrates a virtualized embodiment of the network node 800 according to some embodiments of the present disclosure. Again, optional features are represented by dashed boxes. As used herein, a "virtualized” network node is an implementation of the network node 800 in which at least a portion of the functionality of the network node 800 is implemented as a virtual component(s) (e.g., via a virtual machine(s) executing on a physical processing node(s) in a network(s)). As illustrated, the network node 800 includes one or more processing nodes 900 coupled to or included as part of a network(s) 902. Each processing node 900 includes one or more processors 904 (e.g., CPUs, ASICs, FPGAs, and/or the like), memory 906, and a network interface 908. If the network node 800 is a radio access node (e.g., a base station 302), the network node 800 may include the control system 802 and/or the one or more radio units 810, as described above. The control system 802 may be connected to the radio unit(s) 810 via, for example, an optical cable or the like. If present, the control system 802 or the radio unit(s) are connected to the processing node(s) 900 via the network 902.

In this example, functions 910 of the network node 800 described herein (e.g., one or more functions of the base station 302 or gNB described herein or one or more functions of a core NF (e.g., the AMF 400, the SMF 408, the UPF 414, the PCF 410, the NEF 500, the MBSF, the AF 412, the MB-SMF 408-MB, the MB-UPF 414-MB, or the like) as described herein) are implemented at the one or more processing nodes 900 or distributed across the one or more processing nodes 900 and the control system 802 and/or the radio unit(s) 810 in any desired manner. In some particular embodiments, some or all of the functions 910 of the network node 800 described herein are implemented as virtual components executed by one or more virtual machines implemented in a virtual environment(s) hosted by the processing node(s) 900. As will be appreciated by one of ordinary skill in the art, additional signaling or communication between the processing node(s) 900 and the control system 802 is used in order to carry out at least some of the desired functions 910. Notably, in some embodiments, the control system 802 may not be included, in which case the radio unit(s) 810 communicate directly with the processing node(s) 900 via an appropriate network interface(s).

In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of network node 800 or a node (e.g., a processing node 900) implementing one or more of the functions 910 of the network node 800 in a virtual environment according to any of the embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

Figure 10

Figure 10 is a schematic block diagram of the network node 800 according to some other embodiments of the present disclosure. The network node 800 includes one or more modules 1000, each of which is implemented in software. The module(s) 1000 provide the functionality of the network node 800 described herein (e.g., one or more functions of the base station 302 or gNB described herein or one or more functions of a core NF (e.g., the AMF 400, the SMF 408, the UPF 414, the PCF 410, the NEF 500, the MBSF, the AF 412, the MB-SMF 408-MB, the MB-UPF 414-MB, or the like) as described herein). This discussion is equally applicable to the processing node 900 of Figure 9 where the modules 1000 may be implemented at one of the processing nodes 900 or distributed across multiple processing nodes 900 and/or distributed across the processing node(s) 900 and the control system 802.

Figure 11

Figure 11 is a schematic block diagram of a wireless communication device 312 (or UE or UE 312) according to some embodiments of the present disclosure. As illustrated, the wireless communication device 312 includes one or more processors 1102 (e.g., CPUs, ASICs, FPGAs, and/or the like), memory 1104, and one or more transceivers 1106 each including one or more transmitters 1108 and one or more receivers 1110 coupled to one or more antennas 1112. The transceiver(s) 1106 includes radio-front end circuitry connected to the antenna(s) 1112 that is configured to condition signals communicated between the antenna(s) 1112 and the processor(s) 1102, as will be appreciated by on of ordinary skill in the art. The processors 1102 are also referred to herein as processing circuitry. The transceivers 1106 are also referred to herein as radio circuitry. In some embodiments, the functionality of the wireless communication device 312 described above may be fully or partially implemented in software that is, e.g., stored in the memory 1104 and executed by the processor(s) 1102. Note that the wireless communication device 312 may include additional components not illustrated in Figure 11 such as, e.g., one or more user interface components (e.g., an input/output interface including a display, buttons, a touch screen, a microphone, a speaker(s), and/or the like and/or any other components for allowing input of information into the wireless communication device 312 and/or allowing output of information from the wireless communication device 312), a power supply (e.g., a battery and associated power circuitry), etc.

In some embodiments, a computer program including instructions which, when executed by at least one processor, causes the at least one processor to carry out the functionality of the wireless communication device 312 according to any of the embodiments described herein is provided. In some embodiments, a carrier comprising the aforementioned computer program product is provided. The carrier is one of an electronic signal, an optical signal, a radio signal, or a computer readable storage medium (e.g., a non-transitory computer readable medium such as memory).

Figure 12

Figure 12 is a schematic block diagram of the wireless communication device 312 according to some other embodiments of the present disclosure. The wireless communication device 312 includes one or more modules 1200, each of which is implemented in software. The module(s) 1200 provide the functionality of the wireless communication device 312 described herein. SOME EMBODIMENTS

Some embodiments described above may be summarized in the following manner:

1. A method performed by a network node (302; 800) in a radio access network, RAN, of a cellular communications system (300), the method comprising: detecting (Fig. 6, step 3; Fig. 7, step 1) that a wireless communication device (312) that has joined a first M ul ticast/Broadcast Service, MBS, session having a first service area has crossed a boundary of the first service area; and responsive to detecting that the wireless communication device (312) has crossed the boundary of the first service area, triggering (Fig. 6, step 4; Fig. 7, step 1) a procedure by which the wireless communication device (312) is either switched to a second MBS session having a second service area that covers a location of the wireless communication device (312) or removed from the first MBS session.

2. The method of embodiment 1 wherein: if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a second service area that covers the location of the wireless communication device (312), the procedure switches the wireless communication device (312) to the second MBS session; otherwise, the procedure removes the wireless communication device (312) from the first MBS session.

3. The method of embodiment 2 wherein the MBS session ID is a Temporary Group Mobile Identity, TMGI.

4. The method of embodiment 2 wherein the MBS service ID comprises a Temporary Group Mobile Identity, TMGI.

5. The method of any one of embodiment 1 to 4 wherein triggering (Fig. 6, step 4; Fig. 7, step 1) the procedure comprises sending (Fig. 6, step 4; Fig. 7, step 1) a Multicast/Broadcast, MB, switch request to a network function, NF, (400) in a core network (310) of the cellular communications system (300), the MB switch request comprising a MBS session ID of the first MBS session and information that indicates the location of the wireless communication device (312).

6. The method of embodiment 5 further comprising receiving (Fig. 6, step 7; Fig. 7, step 10) a response from the NF (400) that indicates that the wireless communication device (312) is removed from the first MBS session.

7. The method of embodiment 5 further comprising: receiving (Fig. 6, step 7; Fig. 7, step 10) a response from the NF (400) that indicates that the wireless communication device (312) is being moved to the second MBS session; and performing (Fig. 6, step 10; Fig. 7, step 11) one or more actions to move the wireless communication device (312) to the second MBS session. 8. The method of any one of embodiment 5 to 7 wherein the NF (400) is an Access and Mobility Management Function, AMF, (400).

9. The method of any one of embodiment 1 to 8 wherein the cellular communications system (300) is a Fifth Generation System, 5GS.

10. A method performed by a network node (400; 800) in a core network (310) of a cellular communications system (300), the method comprising: receiving (Fig. 6, step 4; Fig. 7, step 1), from a radio access network, RAN, node (302) in a RAN of the cellular communications system (300), a Multicast/Broadcast, MB, switch request comprising a Multicast/Broadcast Service, MBS, session identifier, ID, of a first MBS session to which the wireless communication device (312) is currently joined and location information that indicates a location of a respective wireless communication device (312); performing (Fig. 6, steps 5-10; Fig. 7, steps 2, 9) a procedure by which the wireless communication device (312) is either switched to a second MBS session having a service area that covers the location of the wireless communication device (312) or removed from the first MBS session.

11. The method of embodiment 10 wherein: if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312), the procedure switches the wireless communication device (312) to the second MBS session; otherwise, the procedure removes the wireless communication device (312) from the first MBS session.

12. The method of embodiment 10 or 11 wherein the MBS session ID is a Temporary Group Mobile Identity, TMGI.

13. The method of embodiment 10 or 11 wherein the MBS service ID comprises a Temporary Group Mobile Identity, TMGI.

14. The method of any one of embodiment 10 to 13 wherein performing (Fig. 6, steps 5-10) the procedure comprises: determining (Fig. 6, steps 4, 5, 6, and 8) whether there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312); and if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312), sending (Fig. 6, step 9) a request to the RAN node (302) to switch the wireless communication device (312) to the second MBS session; and otherwise, sending (step 6, step 7) a message to the RAN node (302) that indicates that the wireless communication device (312) is to be removed from the first MBS session. 15. The method of any one of embodiment 10 to 13 wherein performing (Fig. 6, steps 5-10) the procedure comprises: sending (Fig. 7, step 2), to a Session Management Function, SMF, (408), a Protocol Data Unit, PDU, session modification request comprising the MBS session ID of the first MBS session and information that indicates the location of the wireless communication device (302).

16. The method of any one of embodiment 10 to 15 wherein the network node (400; 800) is a network node (Q200) that implements an Access and Mobility Management Function, AMF, (400).

17. The method of any one of embodiment 10 to 16 wherein the cellular communications system (300) is a Fifth Generation System, 5GS.

18. A method performed by a network node (400; 800) in a core network (310) of a cellular communications system (300), the method comprising: receiving (Fig. 7, step 2) a Protocol Data Unit, PDU, session modification request comprising a Multicast/Broadcast Service, MBS, session identifier, ID, of a first MBS session to which a wireless communication device (312) is currently joined and location information that indicates a location of a respective wireless communication device (312); performing (Fig. 7, steps 3, 4, 5, 7, 9) a procedure by which the wireless communication device (312) is either switched to a second MBS session having a service area that covers the location of the wireless communication device (312) or removed from the first MBS session.

19. The method of embodiment 18 wherein: if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312), the procedure switches the wireless communication device (312) to the second MBS session; otherwise, the procedure removes the wireless communication device (312) from the first MBS session.

20. The method of embodiment 18 or 19 wherein the MBS session ID is a Temporary Group Mobile Identity, TMGI.

21. The method of embodiment 18 or 19 wherein the MBS service ID comprises a Temporary Group Mobile Identity, TMGI.

22. The method of any one of embodiment 18 to 20 wherein performing (Fig. 7, steps 3, 4, 5, 7, 9) the procedure comprises: determining (Fig. 7, step 3) whether there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312); and if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312), performing (Fig. 7, step 4, 5, 7, 9) one or more actions to switch the wireless communication device (312) to the second MBS session; and otherwise, performing (step 7, step 4, 5, 7, 9) one or more actions to remove the wireless communication device (312) from the first MBS session.

23. The method of any one of embodiment 18 to 22 wherein the network node (400; 800) is a network node (Q200) that implements a Session Management Function, SMF, (408).

24. The method of any one of embodiment 18 to 23 wherein the cellular communications system (300) is a Fifth Generation System, 5GS.

25. A network node (800) adapted to perform the method of any one of embodiment 1 to 24.

26. A network node (800) comprising processing circuitry (804; 904) configured to cause the network node (800) to perform the method of any of claims 1 to 24.

Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include Digital Signal Processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as Read Only Memory (ROM), Random Access Memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and/or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more embodiments of the present disclosure.

While processes in the figures may show a particular order of operations performed by certain embodiments of the present disclosure, it should be understood that such order is exemplary (e.g., alternative embodiments may perform the operations in a different order, combine certain operations, overlap certain operations, etc.).

At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used above. If listed multiple times below, the first listing should be preferred over any subsequent listing(s).

3GPP Third Generation Partnership Project

5G Fifth Generation 5GC Fifth Generation Core

5GS Fifth Generation System

AF Application Function

AMF Access and Mobility Function

AN Access Network

AP Access Point

AUSF Authentication Server Function

DCI Downlink Control Information

DN Data Network eNB Enhanced or Evolved Node B

EPS Evolved Packet System

E-UTRA Evolved Universal Terrestrial Radio Access gNB New Radio Base Station

HSS Home Subscriber Server loT Internet of Things

IP Internet Protocol

LTE Long Term Evolution

MAC Medium Access Control

MB Multicast/Broadcast

MBS Multicast/Broadcast Service(s) (when used as a prefix, the term MBS is sometimes used interchangeably with MB)

MME Mobility Management Entity

NEF Network Exposure Function

NF Network Function

NRF Network Function Repository Function

NSSF Network Slice Selection Function

OTT Over-the-Top

PCF Policy Control Function

P-GW Packet Data Network Gateway

QoS Quality of Service

RAN Radio Access Network

SCEF Service Capability Exposure Function

SMF Session Management Function

TCI Transmission Configuration Indicator

UDM Unified Data Management

UE User Equipment • UPF User Plane Function

Those skilled in the art will recognize improvements and modifications to the embodiments of the present disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein.

Claims

CLAIMS What is claimed is:

2. The method of claim 1 wherein: if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a second service area that covers the location of the wireless communication device (312), the procedure switches the wireless communication device (312) to the second MBS session; otherwise, the procedure removes the wireless communication device (312) from the first MBS session.

3. The method of claim 2 wherein the MBS session ID is a Temporary Group Mobile Identity, TMGI.

4. The method of claim 2 wherein the MBS service ID comprises a Temporary Group Mobile Identity, TMGI.

5. The method of any one of claim 1 to 4 wherein triggering (Fig. 6, step 4; Fig. 7, step 1) the procedure comprises sending (Fig. 6, step 4; Fig. 7, step 1) a Multicast/Broadcast, MB, switch request to a network function, NF, (400) in a core network (310) of the cellular communications system (300), the MB switch request comprising a MBS session ID of the first MBS session and information that indicates the location of the wireless communication device (312).

6. The method of claim 5 further comprising receiving (Fig. 6, step 7; Fig. 7, step 10) a response from the NF (400) that indicates that the wireless communication device (312) is removed from the first MBS session.

7. The method of claim 5 further comprising: receiving (Fig. 6, step 7; Fig. 7, step 10) a response from the NF (400) that indicates that the wireless communication device (312) is being moved to the second MBS session; and performing (Fig. 6, step 10; Fig. 7, step 11) one or more actions to move the wireless communication device (312) to the second MBS session.

22

8. The method of any one of claim 5 to 7 wherein the NF (400) is an Access and Mobility Management Function, AMF, (400).

9. The method of any one of claim 1 to 8 wherein the cellular communications system (300) is a Fifth Generation System, 5GS.

11. The method of claim 10 wherein: if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312), the procedure switches the wireless communication device (312) to the second MBS session; otherwise, the procedure removes the wireless communication device (312) from the first MBS session.

12. The method of claim 10 or 11 wherein the MBS session ID is a Temporary Group Mobile Identity, TMGI.

13. The method of claim 10 or 11 wherein the MBS service ID comprises a Temporary Group Mobile Identity, TMGI.

14. The method of any one of claim 10 to 13 wherein performing (Fig. 6, steps 5-10) the procedure comprises: determining (Fig. 6, steps 4, 5, 6, and 8) whether there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312); and if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312), sending (Fig. 6, step 9) a request to the RAN node (302) to switch the wireless communication device (312) to the second MBS session; and otherwise, sending (step 6, step 7) a message to the RAN node (302) that indicates that the wireless communication device (312) is to be removed from the first MBS session.

15. The method of any one of claim 10 to 13 wherein performing (Fig. 6, steps 5-10) the procedure comprises: sending (Fig. 7, step 2), to a Session Management Function, SMF, (408), a Protocol Data Unit, PDU, session modification request comprising the MBS session ID of the first MBS session and information that indicates the location of the wireless communication device (302).

16. The method of any one of claim 10 to 15 wherein the network node (400; 800) is a network node (Q200) that implements an Access and Mobility Management Function, AMF, (400).

17. The method of any one of claim 10 to 16 wherein the cellular communications system (300) is a Fifth Generation System, 5GS.

19. The method of claim 18 wherein: if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312), the procedure switches the wireless communication device (312) to the second MBS session; otherwise, the procedure removes the wireless communication device (312) from the first MBS session.

20. The method of claim 18 or 19 wherein the MBS session ID is a Temporary Group Mobile Identity, TMGI.

21. The method of claim 18 or 19 wherein the MBS service ID comprises a Temporary Group Mobile Identity, TMGI.

22. The method of any of claim 18 to 20 wherein performing (Fig. 7, steps 3, 4, 5, 7, 9) the procedure comprises: determining (Fig. 7, step 3) whether there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312); and if there is a second MBS session having (a) a same MBS session identifier, ID, as the first MBS session and (b) a service area that covers the location of the wireless communication device (312), performing (Fig. 7, step 4, 5, 7, 9) one or more actions to switch the wireless communication device (312) to the second MBS session; and otherwise, performing (step 7, step 4, 5, 7, 9) one or more actions to remove the wireless communication device (312) from the first MBS session.

23. The method of any one of claim 18 to 22 wherein the network node (400; 800) is a network node (Q200) that implements a Session Management Function, SMF, (408).

24. The method of any one of claim 18 to 23 wherein the cellular communications system (300) is a Fifth Generation System, 5GS.

25. A network node (800) adapted to perform the method of any one of claim 1 to 24.

26. A network node (800) comprising processing circuitry (804; 904) configured to cause the network node (800) to perform the method of any one of claim 1 to 24.

25