Method for handling multicast broadcast service session related back-off timer and user equipment

Abstract

A method of processing and a user equipment for multicast broadcast service session related fallback timer are provided. Methods for handling joining and leaving a multicast broadcast service, MBS, session via a PDU session establishment or modification procedure are provided. When a fallback timer is received in a received MBS container IE (with an action / decision "reject MBS join" or "remove UE from MBS session"), the UE shall associate the MBS fallback timer with the MBS session ID (e.g., TMGI). If the timer value is neither zero nor disabled, the UE shall not request to join the MBS session with the same MBS session ID until expiry of the timer. If the timer value is disabled, the UE shall not request to join the MBS session with the same MBS session ID until the UE is turned off, the USIM is removed, an entry in the "list of subscribers data" for the current SNPN is updated, or an event / notification is triggered by the network.

Description

[0001] Cross-references to related applications

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 297,863, filed January 10, 2022, entitled “Handling of MBS Session Related Back-Off Timer,” the subject matter of which is incorporated herein by reference. Technical Field

[0003] The disclosed implementations generally relate to wireless communication, and more specifically, to methods for handling Multicast Broadcast Services (MBS) sessions in 5G systems. Background Technology

[0004] Wireless communication networks have grown exponentially over the years. Long-term evolution (LTE) systems offer high peak data rates, low latency, improved system capabilities, and low operating costs resulting from a simplified network architecture. LTE systems (also known as 4G systems) also provide seamless integration with older wireless networks such as GSM, CDMA, and the Universal Mobile Telecommunications System (UMTS). In LTE systems, the evolved universal terrestrial radio access network (E-UTRAN) comprises multiple evolved Node-Bs (eNodeBs / eNBs) that communicate with multiple mobile stations called user equipment (UEs). The 3rd Generation Partner Project (3GPP) network generally includes a hybrid of 2G / 3G / 4G systems. The Next Generation Mobile Network (NGMN) committee has decided to focus future NGMN activities on defining end-to-end requirements for 5G new radio (NR) systems.

[0005] In 5G / NR, a protocol data unit (PDU) session defines an association between a UE and a data network that provides PDU connectivity service. PDU session establishment is a parallel procedure to the PDN connection (bearer) procedure in 4G / LTE. Individual PDU sessions are identified by a PDU session ID (PSI) and can include multiple QoS flows and QoS rules. Individual PDU sessions can be established via a 5G access network (e.g., a 3GPP radio access network (RAN), or via a non-3GPP RAN). To manage PDU sessions, both the network and the UE can initiate different PDU session procedures, such as a PDU session establishment procedure, a PDU session modification procedure, and a PDU session release procedure.

[0006] Multimedia Broadcast and Multicast Service (MBMS) is a broadcast service provided via existing GSM and UMTS cellular networks. Recently, evolved MBMS (E-MBMS) has been introduced into the LTE specification for broadcasting or multicasting TV, movies, and other information such as overnight transmission of newspapers in digital form. In 5G networks, Multicast and Broadcast Services (MBS) is a point-to-multipoint service that can improve network efficiency and user experience when the same content is sent to multiple users. The design principle of 5G MBS is to minimize the implementation impact by reusing as much as possible the 5G unicast architecture and functions.

[0007] A UE can request to join an MBS by using a PDU session establishment procedure or a PDU session modification procedure with a requested MBS container IE for the following MBS operations: join an MBS session and leave an MBS session. The network can also apply a PDU session establishment procedure or a PDU session modification procedure with a received MBS container IE for the following operations / decisions: update MBS service area, accept MBS join, reject MBS join, and remove UE from MBS session. However, there is no definition of what the UE should do when it receives the operation / decision "reject MBS join" or "remove UE from MBS session" from the network.

[0008] A solution is sought. SUMMARY

[0009] A method for handling joining and leaving MBS sessions via PDU session establishment or modification procedures is provided. When a fallback timer is received in a received MBS container IE (with an operation / decision "reject MBS join" or "remove UE from MBS session"), the UE shall associate the MBS fallback timer with the MBS session ID (e.g., TMGI). If the timer value is neither zero nor disabled, the UE shall not request to join the MBS session with the same MBS session ID until the timer expires. If the timer value is disabled, the UE shall not request to join the MBS session with the same MBS session ID until the UE is powered off, the USIM is removed, an entry in the "list of subscriber data" for the current SNPN is updated, or an event / notification is triggered by the network.

[0010] Other implementations and advantages are described in the following detailed description. This summary is not intended to define the invention. The invention is defined by the claims. BRIEF DESCRIPTION OF DRAWINGS

[0011] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the application and together with the description, serve to explain the principles of the application.

[0012] Figure 1 An exemplary 5G network supporting MBS and corresponding PDU session procedures is illustrated in accordance with one novel aspect.

[0013] Figure 2 Simplified block diagrams of a UE and network entity in accordance with embodiments of the application are illustrated.

[0014] Figure 3 A PDU session establishment procedure in which a UE requests to join an MBS session and corresponding handling for a rejection in accordance with one novel aspect is illustrated.

[0015] Figure 4 A PDU session modification procedure in which a UE requests to join an MBS session and corresponding handling for a rejection in accordance with one novel aspect is illustrated.

[0016] Figure 5 A PDU session modification procedure in which a UE requests to leave an MBS session and corresponding handling for a removal from an MBS session in accordance with another novel aspect is illustrated.

[0017] Figure 6 A PDU session modification procedure in which a network performs an MBS service area update with a rejection reason and a fallback timer in accordance with one novel aspect is illustrated.

[0018] Figure 7is a flowchart of a method of MBS session handling via PDU session establishment procedure according to a novel aspect of the present invention.

[0019] Figure 8 is a flowchart of a method of MBS session handling via PDU session modification procedure according to a novel aspect of the present invention. DETAILED DESCRIPTION

[0020] Reference will now be made in detail to some embodiments of the application, examples of which are illustrated in the accompanying drawings.

[0021] Figure 1 An exemplary 5G network 100 supporting MBS and corresponding PDU session procedures according to a novel aspect is illustrated. The 5G new radio (NR) network 100 includes a UE 101 and multiple base stations gNB 102, gNB 103, and gNB 104. An MBS service area 10 covers multiple MBS Single Frequency Network (MBSFN) areas (e.g., MBSFN area 1 and MBSFN area 2). An MBSFN area includes a set of cells within an MBSFN service area of the network that are coordinated to enable MBSFN transmission. An MBSFN service area is defined as a network area where all base stations (gNBs) can be synchronized to perform MBSFN transmission. An MBS service area can support one or more MBSFN areas. On a given frequency layer, an eNB can only belong to one MBS service area. Under an MBS service area, a cell can belong to one or more MBSFN areas and support MBS services of all the belonging MBSFN areas. In the example, gNB 102 belongs to MBSFN area 1 and serves cell 17 for MBS services over a component carrier (CC), gNB 103 belongs to both MBSFN area 1 and MBSFN area 2 and serves cell 18 for MBS services over a CC, and gNB 104 belongs to MBSFN area 2 and serves cell 19 for MBS services over a CC. UE 101 is registered to the PLMN and subscribes to a specific MBS service in cell 17 served by gNB 102. Figure 1

[0022] ​An EPS network is a packet-switched (PS) Internet Protocol (IP) network. When a UE joins an Evolved Packet System (EPS) network, a Packet Data Network (PDN) address (i.e., an address that can be used on a PDN) is allocated to the UE for its connection to a PDN. In 4G, the EPS defines a Default EPS Bearer to provide always-on IP connectivity. In 5G, the PDU Session establishment procedure is a parallel procedure to the PDN connection procedure in 4G. A PDU Session defines an association between a UE and a data network that provides PDU connectivity service. Individual PDU Sessions are identified by a PDU Session ID and can be established over 3GPP RAN and / or non-3GPP RAN for radio access. 5G session management (5GSM) for PDU Sessions over 3GPP access and non-3GPP access is managed by the AMF and SMF through NAS signaling.

[0023] Both the network and the UE can initiate different PDU Session procedures, e.g., PDU Session establishment procedure, PDU Session modification procedure, and PDU Session release procedure, to manage PDU Sessions. A UE can request to join an MBS by using a PDU Session establishment procedure or a PDU Session modification procedure with a requested MBS container IE for the following MBS operations: join an MBS session and leave an MBS session. The network can also apply a PDU Session establishment procedure or a PDU Session modification procedure with a received MBS container IE for the following operations / decisions: update MBS service area, accept MBS join, reject MBS join, and remove UE from MBS session. However, there is no definition of what a UE should do when it receives the operation / decision “reject MBS join” or “remove UE from MBS session” from the network.

[0024] According to one novel aspect, a method (110) for handling joining and leaving MBS sessions via PDU session establishment or modification procedures is provided. Upon receiving a fallback timer in a received MBS Container IE (with an operation / decision “Reject MBS Join” or “Remove UE from MBS Session”), the UE shall associate the MBS fallback timer with the MBS session ID (e.g., TMGI). If the timer value is neither zero nor disabled, the UE shall not request to join the MBS session with the same MBS session ID until the timer expires. If the timer value is disabled, the UE shall not request to join the MBS session with the same MBS session ID until the UE is turned off, the USIM is removed, an entry in the “List of Subscribers Data” of the current SNPN is updated, or an event / notification is triggered by the network.

[0025] Figure 2 A simplified block diagram of a wireless device (e.g., UE 201 and network entity 211) according to embodiments of the present application is illustrated. The network entity 211 can be a base station and / or an AMF / SMF. The network entity 211 has an antenna 215 to send and receive radio signals. A radio frequency (RF) transceiver module 214 is coupled with the antenna to receive RF signals from the antenna 215, convert the RF signals to baseband signals and send the baseband signals to the processor 213. The RF transceiver 214 also converts baseband signals received from the processor 213, converts the baseband signals to RF signals, and sends the RF signals out to the antenna 215. The processor 213 processes the received baseband signals and invokes different functional modules to implement features in the base station 211. The memory 212 stores program instructions and data 220 used to control operation of the base station 211. In Figure 2 In an example, the network entity 211 also includes a protocol stack 280 and a set of control functional modules and circuits 290. The protocol stack 280 includes a Non-Access-Stratum (NAS) layer to communicate with an AMF / SMF / MME entity connected to a core network, a Radio Resource Control (RRC) layer for high layer configuration and control, a Packet Data Convergence Protocol / Radio Link Control (PDCP / RLC) layer, a Media Access Control (MAC) layer, and a Physical (PHY) layer. In one example, the control functional modules and circuits 290 include a PDU session handling circuit 291 to handle PDU establishment, modification, and release procedures, and a configuration and control circuit 292 to provide different parameters to configure and control related functions of the UE including PDU session management.

[0026] Similarly, the UE 201 has a memory 202, a processor 203, and a radio frequency (RF) transceiver module 204. The RF transceiver 204 is coupled with an antenna 205, receives RF signals from the antenna 205, converts the RF signals into baseband signals, and sends the baseband signals to the processor 203. The RF transceiver 204 also converts baseband signals received from the processor 203, converts the baseband signals into RF signals, and sends the RF signals outwards to the antenna 205. The processor 203 processes the received baseband signals and invokes different functional modules and circuits to perform features in the UE 201. The memory 202 stores data and program instructions 210 to be executed by the processor to control the operation of the UE 201. Suitable processors include, by way of example, a special-purpose processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) circuit, and other types of integrated circuits (ICs) and / or state machines. The features of the UE 201 can be implemented using the processor in association with software.

[0027] The UE 201 also includes a protocol stack 260 and a set of control functional modules and circuits 270. The protocol stack 260 includes a NAS layer for communication with an AMF / SMF / MME entity connected to a core network, an RRC layer for high layer configuration and control, a PDCP / RLC layer, a MAC layer, and a PHY layer. The control functional modules and circuits 270 can be implemented and configured by software, firmware, hardware, and / or combinations thereof. The control functional modules and circuits work with each other when executed by the processor via program instructions contained in the memory to allow the UE 201 to perform the embodiments and functional tasks and features in the network.

[0028] In one example, the control function module and circuitry 270 includes PDU session handling circuitry 271 that performs PDU session establishment, modification, and release procedures with the network, and configuration and control circuitry 272 that handles configuration and control parameters for mobility management and session management. Upon receiving the fallback timer in the received MBS Container IE (with operation / decision “Reject MBS Join” or “Remove UE from MBS Session”), the UE shall associate the MBS fallback timer with the MBS Session ID (e.g., TMGI). The received cause / reason / indication can indicate whether the UE can re-attempt to join the MBS session in the registered PLMN or in all PLMNs.

[0029] Figure 3 An embodiment of PDU session establishment procedure for a UE requesting to join a MBS session and corresponding handling for rejection in accordance with one novel aspect is illustrated. In step 311, the UE 301 initiates a PDU session establishment procedure by sending a PDU session establishment request message (for PSI=5) to the network (e.g., session management function (SMF)). The PDU session establishment request message includes a “requested MBS Container IE” with MBS operation = “Join MBS Session” + MBS Session ID = TMGI or MBS Session ID Type = “Source Specific IP Multicast Address”. The network can accept the PDU session establishment request and accept or reject the request for the UE to join the MBS session. In a first scenario (step 321), the network sends a PDU session establishment accept message including a “received MBS Container IE” with MBS decision = “Accept MBS Join” + MBS Session ID = TMGI + “Source Specific IP Address and Destination IP Address”. The accept message can also include received MBS information: MBS start time, MBS security container, MBS service area = “MBS TAI list, NE CGI list, or both”.

[0030] In a second scenario (step 331), the network sends a PDU session establishment accept message including a “received MBS Container IE” with MBS decision = “Reject MBS Join” + MBS Session ID = TMGI + “Source Specific IP Address and Destination IP Address”. The accept message shall also include received MBS information: rejection cause, and if the rejection cause = “MBS session not started or not about to start”, a MBS fallback timer can be included. The accept message can also include MBS service area = “MBS TAI list, NE CGI list, or both”. Upon receiving the PDU session establishment accept message, the PDU session (PSI=5) is established for data communication (step 341).

[0031] If the network rejects the UE’s request to join the MBS session, the rejection cause with a reason or indication can indicate the subsequent UE behavior. For example, based on the rejection cause, the UE learns the reason why the request to join the MBS session is rejected, and the UE can forward such reason to upper layer / user. In one example, the rejection cause = “UE is outside the local MBS service area”, and if the UE is camping on a cell outside the received MBS service area, the UE shall not request to join the same MBS session. The UE can invoke a default or pre-configured fallback timer upon receiving the rejection cause. The UE can also learn whether the UE can re-attempt to join the MBS session in the registered PLMN or all PLMNs, depending on whether the re-attempt is set to “apply fallback timer in all PLMNs” or “apply fallback timer in registered PLMN only”. The UE will also learn when the UE can re-attempt to join the MBS session, e.g., when the UE is turned off, the USIM is removed, or the entry in the “list of subscriber data” for the current SNPN is updated, or an event / notification is triggered by the network (e.g., network initiated de-registration).

[0032] Figure 4 An embodiment of the PDU session modification procedure for a UE requesting to join a MBS session and the corresponding handling for rejection in accordance with one novel aspect is illustrated. In step 411, the UE 401 maintains a PDU session (PSI = 5) in the 5GS network. In step 421, the UE 401 initiates a PDU session modification procedure by sending a PDU session modification request message (PSI = 5) to the network (e.g., SMF). The PDU session modification request message includes a “requested MBS container IE” with MBS operation = “join MBS session” + MBS session ID = TMGI or MBS session ID type = “source specific IP multicast address”. The network can accept the PDU session modification request and accept or reject the request for the UE to join the MBS session. In a first scenario (step 431), the network sends a PDU session modification command message including a “received MBS container IE” with MBS decision = “accept MBS join” + MBS session ID = TMGI + “source specific IP address and destination IP address”. The command message can also include the received MBS information: MBS start time, MBS security container, MBS service area = “MBS TAI list, NE CGI list, or both”.

[0033] In the second scenario (step 441), the network sends a PDU session modification command message including the "Received MBS Container IE" with MBS decision = "Reject MBS Join" + MBS session ID = TMGI + "Source specific IP address and destination IP address". The command message should also include the received MBS information: reject cause, and if the reject cause = "MBS session not started or not about to start", the MBS fallback timer can be included. The accept message can also include the MBS service area = "MBS TAI list, NE CGI list, or both". Upon receiving the PDU session modification command message, the UE 401 determines its behavior based on the reject cause and the fallback timer.

[0034] Figure 5 Another implementation of the PDU session modification procedure for a UE requesting to leave a MBS session and the corresponding handling for removal from the MBS session in accordance with one novel aspect is illustrated. In step 511, the UE 501 maintains a PDU session in the 5GS network (PSI = 5). In step 521, the UE 501 initiates a PDU session modification procedure by sending a PDU session modification request message (PSI = 5) to the network (e.g., SMF). The PDU session modification request message includes the "Requested MBS Container IE" with MBS operation = "Leave MBS session" + MBS session ID = TMGI. In step 531, the UE 501 receives from the network a PDU session modification command message including the "Received MBS Container IE" with MBS decision = "Remove UE from MBS session" + MBS session ID = TMGI. The command message should also include the received MBS information: reject cause = "MBS session released" if the UE triggered or otherwise, and can include the MBS fallback timer. The command message can also include the received MBS information: MBS service area = "MBS TAI list, NE CGI list, or both".

[0035] When the operation / decision "Reject MBS Join" or the operation / decision "Remove UE from MBS session" in the received MBS Container IE (with MBS operation = "Leave MBS session" or with MBS operation = "Join MBS session") in the PDU session modification procedure is not supported by the network, the network sends a PDU session modification command message including the "Received MBS Container IE" with MBS decision = "MBS operation not supported" + MBS session ID = TMGI + "Source specific IP address and destination IP address". The command message should also include the received MBS information: reject cause = "MBS operation not supported", and if the reject cause = "MBS operation not supported", the MBS fallback timer can be included. The command message can also include the MBS service area = "MBS TAI list, NE CGI list, or both". Figure 4 Figure 5 ​When the UE receives a fallback timer in the "Remove UE from MBS Session" section, it should associate the MBS fallback timer with the MBS session ID (e.g., TMGI). If the timer value is neither zero nor disabled, the UE should not request to join an MBS session with the same MBS session ID (e.g., TMGI) until the timer expires, for example, any request to join an MBS session in the current PDU session (PSI=5) or any other PDU session is prohibited. If the timer value is disabled, the UE should not request to join an MBS session with the same MBS session ID (e.g., TMGI) until the UE is shut down, or the USIM is removed, or the entry in the current SNPN's "Subscriber Data List" is updated, or an event / notification is triggered by the NW (e.g., network-initiated deregistration). The MBS fallback timer is associated with the MBS session ID (and optionally with the PLMN when MBS roaming is supported). Therefore, the UE cannot attempt to join an MBS session in another PDU session (e.g., identified by TMGI), and / or after the UE is turned off (i.e., the MBS BO timer remains running when the UE is turned off), or the USIM is removed, or an entry in the current SNPN's "Subscriber Data List" is updated, or an event / notification is triggered by the NW (e.g., a network-initiated deregistration).

[0036] Figure 6 An implementation of a PDU session modification process according to a novel aspect is illustrated, wherein the network performs an MBS service area update using a denial reason and a fallback timer. In step 611, UE 601 maintains the PDU session (PSI=5) in the 5GS network. In step 612, as described above... Figure 4 As illustrated, UE 601 has joined the MBS session via the PDU session modification procedure. In step 621, the network initiates an MBS session service area update by sending a PDU session modification command message to UE 601. The PDU session modification command message includes "Received MBS Container IE", where MBS Decision = "MBS Service Area Update" + MBS Session ID = TMGI. The command message should also include received MBS information: MBS Service Area = "MBS TAI List, NE CGI List, or both".

[0037] Figure 7is a flowchart of a method of MBS session handling via a PDU session establishment procedure according to a novel aspect of the present application. In step 701, a UE initiates a protocol data unit (PDU) session establishment procedure and sends a PDU session establishment request message in a 5G network. In step 702, the UE requests to join a MBS session with a multicast broadcast service (MBS) session ID by using the PDU session establishment request message. In step 703, the UE receives a received MBS container IE from the network, wherein the received MBS container IE indicates that the network rejects the UE to join the MBS session, and wherein the received MBS container IE includes a rejection cause and a non-zero fallback timer value. In step 704, the UE starts a fallback timer with the fallback timer value in response to the received MBS container IE. The fallback timer is not deactivated before the fallback timer expires, and the UE refrains from requesting to join the same MBS session.

[0038] Figure 8 is a flowchart of a method of MBS session handling via a PDU session modification procedure according to a novel aspect of the present application. In step 801, a UE maintains a protocol data unit (PDU) session in a 5G network. In step 802, the UE receives a PDU session modification command message from the network, wherein the PDU session modification command message includes a received MBS container IE associated with a MBS session. In step 803, the UE determines that the received MBS container IE indicates that the network rejects the UE to join the MBS session or removes the UE from the MBS session, wherein the received MBS container IE includes a rejection cause and a non-zero fallback timer value. In step 804, the UE starts a fallback timer with the fallback timer value in response to the received MBS container IE. The fallback timer is not deactivated before the fallback timer expires and the UE refrains from requesting to join the same MBS session.

[0039] While the present application has been described for illustrative purposes with reference to certain illustrative embodiments thereof, it is not to be limited to the same. Therefore, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the present application as set forth in the claims.

Claims

1. A method of handling a multicast broadcast service session related back-off timer, the method comprising the steps of: initiating, by a user equipment (UE), a protocol data unit (PDU) session establishment procedure and sending a PDU session establishment request message in a 5G network; requesting to join a multicast broadcast service (MBS) session with an MBS session ID by using the PDU session establishment request message; receiving a received MBS container IE from the network, wherein the received MBS container IE indicates that the network rejects the UE to join the MBS session, and wherein the received MBS container IE includes a rejection cause and a non-zero back-off timer value, the rejection cause indicating that the MBS session is not started or not about to start; and starting, in response to the received MBS container IE, a back-off timer with the back-off timer value, wherein the back-off timer is not deactivated and the UE refrains from requesting to join the same MBS session before the back-off timer expires.

2. The method of claim 1, wherein, the PDU session establishment request message includes a MBS operation set to request to join the MBS session.

3. The method of claim 1, wherein, the back-off timer is deactivated, and wherein the UE is prohibited to request to join the same MBS session until the UE is closed, the USIM is removed, an entry in a subscriber data list is updated, or an event or notification is triggered by the network.

4. The method of claim 1, wherein, the UE attempts to join an MBS session in another PLMN when the back-off timer only applies to a registered PLMN.

5. A method of handling a multicast broadcast service session related back-off timer, the method comprising the steps of: maintaining, by a user equipment (UE) in a 5G network, a protocol data unit (PDU) session; receiving a PDU session modification command message from the network, wherein the PDU session modification command message includes a received MBS container IE associated with a multicast broadcast service (MBS) session; determining that the received MBS container IE indicates that the network rejects the UE to join the MBS session or removes the UE from the MBS session, wherein the received MBS container IE includes a rejection cause and a non-zero back-off timer value, the rejection cause indicating that the MBS session is not started or not about to start for a duration of time; and starting, in response to the received MBS container IE, a back-off timer with the back-off timer value, wherein the back-off timer is not deactivated and the UE refrains from requesting to join the same MBS session before the back-off timer expires.

6. The method of claim 5, wherein, the PDU session modification command message is in response to a PDU session modification request message sent by the UE.

7. The method of claim 6, wherein, the PDU session modification request message includes a MBS operation set to request to join the MBS session.

8. The method of claim 6, wherein, the PDU session modification request message includes a MBS operation set to request to leave the MBS session.

9. The method of claim 8, wherein, the rejection cause indicates that the MBS session is released.

10. The method of claim 5, wherein, the PDU session modification command message is initiated by the network without any UE request.

11. The method of claim 5, wherein, The back-off timer is deactivated, and wherein the UE is prohibited from requesting to join the same MBS session until the UE is turned off, the USIM is removed, an entry in a subscriber data list is updated, or an event or notification is triggered by the network.

12. A user equipment (UE) for multicast broadcast service session related back-off timer handling, the UE comprising: a protocol data unit (PDU) session handling circuit that maintains a PDU session in a 5G network; a receiver that receives a PDU session modification command message from the network, wherein the PDU session modification command message includes a received multicast broadcast service (MBS) container IE associated with an MBS session; a control circuit that determines that the received MBS container IE indicates that the network rejects the UE from joining the MBS session or removing the UE from the MBS session, wherein the received MBS container IE includes a rejection cause and a non-zero back-off timer value, the rejection cause indicating that the MBS session is not started or is not about to start for a duration of time; and a back-off timer having a back-off timer value, wherein the UE starts the back-off timer in response to the received MBS container IE and refrains from requesting to join the same MBS session until the timer expires.

13. The UE of claim 12, wherein, The PDU session modification command message is in response to a PDU session modification request message sent by the UE.

14. The UE of claim 13, wherein, The PDU session modification request message includes an MBS operation set to request to join the MBS session.

15. The UE of claim 13, wherein, The PDU session modification request message includes an MBS operation set to request to leave the MBS session.

16. The UE of claim 15, wherein, The rejection cause indicates that the MBS session is dismissed.

17. The UE of claim 12, wherein, The PDU session modification command message is initiated by the network without any UE request.

18. The UE of claim 12, wherein, The back-off timer is deactivated, and wherein the UE is prohibited from requesting to join the same MBS session until the UE is turned off, the USIM is removed, an entry in a subscriber data list is updated, or an event or notification is triggered by the network.

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