Method for handling protocol data unit session establishment and user equipment

Abstract

Methods for handling protocol data unit session establishment and user equipment. Specifically, a method for handling 5G PDU session establishment procedure when the maximum number of active 5G PDU sessions has been reached. When the number of active 5G PDU sessions in the 5GS has reached the maximum number of active 5G PDU sessions as defined for the PLMN / SNPN, the UE needs to release existing 5G PDU sessions in order to add new 5G PDU sessions. In a novel aspect, the UE can select a 4G PDN connection and release the selected PDN connection to meet the requirement for the maximum number of active 5G PDU sessions. The selected 4G PDN connection is established as user plane resources for a 5G MA PDU session; by releasing the selected PDN connection, the UE is then able to establish new 5G PDU sessions, including emergency PDU sessions in the 5GS.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 296,016, filed January 3, 2022, entitled “ATSSS maximum number of PDU sessions has been reached,” and U.S. Patent Application No. 18 / 079,616, filed December 12, 2022, which are hereby incorporated by reference in their entirety. TECHNICAL FIELD

[0003] Embodiments of the present application relate generally to wireless communication, and more specifically, to methods of handling protocol data unit (PDU) session establishment when a maximum number of PDU sessions has been reached. BACKGROUND

[0004] Wireless communication networks have grown exponentially over the years. Long-Term Evolution (LTE) systems provide high peak data rates, low latency, improved system capacity, and low operating cost due to a simple network architecture. LTE systems, also referred to as 4th Generation (4G) systems, also provide seamless integration with older networks, such as Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), and Universal Mobile Telecommunications System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node-Bs (eNodeBs or eNBs) that communicate to multiple mobile stations referred to as user equipment (UE). The 3rd Generation Partnership Project (3GPP) defines the standards for LTE systems. The 3GPP is currently developing a new generation of wireless communication systems, referred to as 5th Generation (5G) systems or New Radio (NR) systems. The 3GPP is also referred to as the International Mobile Telecommunications-Advanced (IMT-Advanced) system. rdA 5G network (e.g., a 5G New Radio (NR) network) is a continuing project of the 3rd Generation Partnership Project (3GPP) to improve the UMTS, LTE and LTE-Advanced mobile phone standards and air interface used in most current cellular (wireless) telecommunication networks. A 5G network typically includes a mix of 2nd Generation (2G) / 3rd Generation (3G) / 4G systems. The Next Generation Mobile Network (NGMN) Board has decided to focus future NGMN activities on defining end-to-end requirements for the 5G NR system.

[0005] In a 5G system (5GS), a PDU session defines an association between a UE and a data network that provides a PDU connectivity service. PDU session establishment is a parallel procedure to the packet data network (PDN) connectivity (bearer) procedure in 4G / LTE. Each PDU session is identified by a PDU session ID (PSI) and includes multiple Quality of Service (QoS) flows and QoS rules. Each PDU session can be established through a 5G access network (e.g., a 3GPP radio access network (RAN) or a non-3GPP RAN). Different PDU session procedures, such as PDU session establishment, PDU session modification, and PDU session release, can be initiated by the network / UE for managing the activation and deactivation of 5G PDU sessions.

[0006] 3GPP has also introduced Multi-Access (MA) PDU Sessions in 5GS. A MA PDU Session can be configured to use one 3GPP access network or one non-3GPP access network at a time, or both a 3GPP access network and a non-3GPP access network simultaneously. In addition, Access Traffic Steering, Switching, Splitting (ATSSS) is an optional feature that can be supported by the UE and 5GC network to route data traffic for an established MA PDU Session across 3GPP access networks and non-3GPP access networks. At any given time, a MA PDU Session can have user-plane resources established on 3GPP access (also referred to as 3GPP 5GS leg) and non-3GPP access (also referred to as non-3GPP 5GS leg), or on only one access (3GPP access or non-3GPP 5GS access). Also, to take advantage of wider LTE coverage compared to NR, a 4G Evolved Packet System (EPS) PDN connection can be established as user-plane resources for the corresponding MA PDU Session on 3GPP access (also referred to as 3GPP PDN leg).

[0007] When the number of active 5GS PDU Sessions reaches the maximum number of 5GS PDU Sessions for a network (Public Land Mobile Network (PLMN) or Standalone Non-Public Network (SNPN)), a solution is needed on how to establish a new 5GS PDU Session. SUMMARY

[0008] A method for handling 5G PDU Session establishment procedures when the maximum number of active 5G PDU Sessions has been reached is presented. When the number of active 5G PDU Sessions in 5GS has reached the maximum number of active 5G PDU Sessions as defined for a PLMN / SNPN, the UE needs to release existing 5G PDU Sessions in order to add new 5G PDU Sessions. In a novel aspect, the UE can select a 4G PDN connection and release the selected PDN connection to meet the requirement for the maximum number of active 5G PDU Sessions. The selected 4G PDN connection is established as the only user-plane resource for a 5G MA PDU Session; by releasing the selected PDN connection, the UE is then able to establish new 5G PDU Sessions, including emergency PDU Sessions in 5GS.

[0009] In one embodiment, the UE maintains multiple active PDU sessions in the 5GS. The UE determines that the number of active PDU sessions has reached the maximum number of PDU sessions for a PLMN or SNPN in the 5GS. The UE selects a PDN connection from one or more PDN connections maintained by the UE, wherein the UE initiates a PDN connection release procedure to release the selected PDN connection. The UE establishes a new PDU session after releasing the selected PDU connection. The selected PDN connection is established as user plane resources for the MA PDU session over 3GPP access; and is counted as an active PDU session in the PLMN / SNPN. In one embodiment, the UE initiates a UE-requested PDN disconnection procedure by sending a PDN DISCONNECT REQUEST message to the network. In another embodiment, the UE releases the selected PDN connection locally and performs a regular and periodic tracking area update (TAU) with the network.

[0010] Traditionally, when the 5G active PDUs reach the upper limit, only one 5G PDU can be released before another 5G PDU can be established (e.g., the UE releases the PDU through a PDU release procedure). However, the present invention proposes a way for the UE to select to release one 4G PDN (e.g., the UE releases the PDN through a PDN disconnection procedure) to establish another 5G PDU. Therefore, the method for handling PDU session establishment when the maximum number of PDU sessions has been reached proposed by the present invention can improve the flexibility of UE processing (when the 5G PDUs reach the upper limit, there are more candidates that can be released).

[0011] Other embodiments 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

[0012] The accompanying drawings illustrate embodiments of the present invention, wherein like numbers refer to like parts.

[0013] FIG. 1 An exemplary PLMN or SNPN and a method for PDU session establishment when the maximum number of active PDU sessions has been reached in the PLMN / SNPN according to the novel aspect are illustrated.

[0014] FIG. 2 Simplified block diagrams of a UE and a network entity according to embodiments of the present invention are illustrated.

[0015] FIG. 3Different scenarios of MA PDU session with 3GPP 5GS / PDN leg and / or non-3GPP 5GS leg are exemplified, as well as the corresponding determination as active PDU session.

[0016] FIG. 4 is a sequence flow between UE and 5GS for determining active PDU session in 5GS and UE initiated PDN release procedure in EPS followed by PDU session establishment procedure in 5GS when maximum active PDU session to a PLMN / SNPN is reached according to a novel aspect.

[0017] FIG. 5 is a method flow chart for handling PDU session establishment procedure when maximum number of PDU sessions in 5GS has been reached according to a novel aspect. DETAILED DESCRIPTION

[0018] Reference will now be made in detail to some embodiments of the application, examples of which are illustrated in the accompanying drawings.

[0019] FIG. 1 Exemplified is an exemplary PLMN or SNPN and a method for PDU session establishment when maximum number of active PDU sessions in the PLMN / SNPN has been reached according to one novel aspect. A 5G new radio (NR) network 100 includes: a UE 101, a 3GPP access 102 (e.g., 3GPP RAN), a non-3GPP access 103 (e.g., non-3GPP RAN), an access and mobility management function (AMF) 110, a session management function (SMF) 111, a non-3GPP interworking function (N3IWF) 112, a user-plane function (UPF) 113, and a 5G core (5GC) data network 120. The AMF 110 communicates with base stations in the 3GPP access 102, the SMF 111, and the UPF 113 for access and mobility management of wireless access devices in the 5G NR network 100. The SMF 111 is mainly responsible for interacting with a separate data plane, creating, updating, and removing PDU sessions, and managing session contexts with the UPF 113. The N3IWF 112 interfaces with 5G core network control plane functions and is responsible for routing messages outside the 5G RAN.

[0020] In the Access Stratum (AS), the RAN provides radio access for the UE 101 via radio access technologies (RATs). In the Non-Access Stratum (NAS), the AMF 110 and the SMF 111 communicate with the RAN and the 5GC for access and mobility management of wireless access devices in the 5G NR network 100 and for PDU session management. The 3GPP access 102 can include base stations (gNBs or eNBs) that provide radio access for the UE 101 via various 3GPP RATs including 5G, 4G, and 3G / 2G. The non-3GPP access 103 can include access points (APs) that provide radio access for the UE 101 via non-3GPP RATs including Wireless Fidelity (WiFi). The UE 101 can obtain access to the data network 120 through the 3GPP access 102, the AMF 110, the SMF 111, and the UPF 113. The UE 101 can obtain access to the data network 120 through the non-3GPP access 103, the N3IWF 112, the AMF 110, the SMF 111, and the UPF 113. The UE 101 can be equipped with a single radio frequency (RF) module or transceiver or multiple RF modules or transceivers for service via different RATs / CNs. In some examples, the UE 101 can be a smartphone, a wearable device, an Internet of Thing (IoT) device, a tablet, etc.

[0021] In the 5GS, a PDU session defines an association between a UE and a data network that provides PDU connectivity service. Each PDU session is identified by a PSI and includes multiple QoS flows and QoS rules. Each PDU session can be established through a 3GPP RAN or a non-3GPP RAN. The 5G session management (5GSM) for PDU sessions on both 3GPP access and non-3GPP access is managed by the AMF and the SMF via NAS signaling. In the 5GS, a UE can be connected to both 3GPP access and non-3GPP access (using NAS signaling) simultaneously, and thus, the 5GS is able to leverage these multiple accesses to improve user experience and optimize traffic distribution across various accesses. Accordingly, 3GPP introduced MA PDU sessions in the 5GS. An MA PDU session uses one 3GPP access network or one non-3GPP access network at a time, or both a 3GPP access network and a non-3GPP access network at the same time.

[0022] In addition, ATSSS is an optional feature that can be supported by the UE and 5GC network to route data traffic for an established MA PDU session across 3GPP access networks and non-3GPP access networks. At any given time, a MA PDU session can have user plane resources established on both 3GPP access (also referred to as 3GPP 5GS leg) and non-3GPP access (also referred to as non-3GPP 5GS leg), or only on one access (3GPP access or non-3GPP 5GS access). Also, to take advantage of wider LTE coverage compared to NR, a 4G EPS PDN connection can be established as user plane resources for the corresponding MA PDU session on 3GPP access (also referred to as 3GPP PDN leg). When the number of active 5GS PDU sessions reaches the maximum 5GS PDU session number for a network (PLMN or SNPN), solutions are sought on how to establish a new 5GS PDU session.

[0023] According to one novel aspect, a method of handling PDU session establishment procedure when the maximum number of PDU sessions has been reached in 5GS is proposed. In FIG. 1 In an example, the UE 101 establishes and maintains multiple SA PDU sessions and MA PDU sessions (including MA PDU 130). The MA PDU 130 is established on both 3GPP access and non-3GPP access, and the MA PDU session has one 3GPP PDN leg and one non-3GPP WiFi leg. The PDN connection is established as the only user plane resource on 3GPP for the MA PDU session. If the UE 101 wants to establish more PDU sessions, the UE 101 needs to check whether the number of active PDU sessions has reached the maximum number of active PDU sessions as defined in 5GS for a PLMN / SNPN. In step 131, the UE 101 determines the number of PDU sessions established in the network and currently active, and detects that the number has reached the maximum PDU session number allowed in the PLMN / SNPN. Note that the MA PDU session with 3GPP PDN leg (e.g., MA PDU 130) is also counted as an active PDU session in 5GS.

[0024] In step 132, the UE 101 decides to release the selected PDN connection for the purpose of adding a new PDU session. To release the 5GS MA PDU session (which has an EPS PDN connection established as user plane resources over 3GPP access), two actions can be needed. The first action is to release the PDN connection that is established as user plane resources of the MA PDU session. The second action is to release the user plane resources (if any) established over non-3GPP access of the MA PDU session. For UE triggered MA PDU release, the UE initiates a PDN disconnect procedure under the first action, and initiates a PDU session release procedure under the second action. After releasing the PDN connection and the MA PDU session, the number of active PDU sessions becomes less than the maximum number of PDU sessions allowed in the PLMN / SNPN, and the UE 101 can successfully establish a new PDU session.

[0025] FIG. 2 A simplified block diagram of a wireless device (e.g., UE 201 and network entity 211) according to embodiments of the application is described. The network entity 211 can be a base station and / or an AMF / SMF. The network entity 211 has antennas 215 that send and receive radio signals. The RF transceiver 214 is coupled to the antennas 215, receives RF signals from the antennas 215, converts them to baseband signals, and sends them to the processor 213. The RF transceiver 214 also converts baseband signals received from the processor 213, converts them to RF signals, and sends them to the antennas 215. The processor 213 processes the received baseband signals and invokes different functional modules to perform the functions in the network entity 211. The memory 212 stores program instructions and data 220 to control the operation of the network entity 211. In FIG. 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: NAS for communication with an AMF / SMF / MME entity connected to a core network, a Radio Resource Control (RRC) layer for upper 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 system modules and circuits 290 include PDU session handling circuits 291 that handle PDU establishment, modification, and release procedures, and configuration and control circuits 292 that provide different parameters to configure and control the UE, including mobility management and PDU session management.

[0026] Similarly, the UE 201 has a memory 202, a processor 203, and an RF transceiver 204. The RF transceiver 204 is coupled with an antenna 205, receives RF signals from the antenna 205, converts them to baseband signals, and sends them to the processor 203. The RF transceiver 204 also converts baseband signals received from the processor 203, converts them to RF signals, and sends them to the antenna 205. The processor 203 processes the received baseband signals and invokes different functional modules and circuits to perform functions in the UE 201. The memory 202 stores program instructions and data 210 to control the operation of the UE 201 by the processor. Suitable processors include, for example, special purpose processors, digital signal processors (DSP), multiple microprocessors, one or more microprocessors in association with a DSP core, controllers, micro-controllers, application specific integrated circuits (ASICs), field programmable gate array (FPGA) circuits, and other types of integrated circuits (ICs) and / or state machines. The features of the UE 201 can be implemented using a processor associated with software, firmware, and / or software (e.g., stored in memory).

[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 that communicates with AMF / SMF / MME entities connected to a core network, an RRC layer for upper layer configuration and control, PDCP / RLC layers, a MAC layer, and a PHY layer. The control functional modules and circuits 270 can be implemented and configured by hardware, firmware, software, and any combination thereof. When the processor executes the functional modules and circuits through program instructions in the memory, they cooperate with each other to enable 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 MAPDU session establishment, modification, and release procedures with the network, configuration and control circuitry 272 that handles configuration and control parameters for mobility management and session management, and PDN connection handling circuitry 273 that performs PDN connection establishment, modification, and release procedures. When the UE determines that the number of active PDU sessions has reached the maximum number of active PDU sessions allowed in the PLMN / SNPN network, the UE releases the PDN connection of the user plane resources on 3GPP established as a MA PDU session. Thus, the UE can then establish a new PDU session, e.g., an emergency PDU session or a PDU session to a DNN, if needed. The UE can release the PDN connection via local release or via explicit signaling to the network.

[0029] FIG. 3 Different scenarios of a multi-access PDU (MA PDU) session with 3GPP 5GS / PDN leg and / or non-3GPP 5GS leg are exemplified, as well as the determination of active and maximum PDU sessions. Since a PDN connection can be used as user plane resources for a MA PDU session, for active MA PDU sessions, the possible scenarios are as follows, as depicted: FIG. 3 A) MA PDU session with only non-3GPP leg (user plane resources established on non-3GPP access); B) MA PDU session with only 3GPP leg (user plane resources established on 3GPP access); C) MA PDU session with 3GPP leg + non-3GPP leg (user plane resources established on 3GPP access and non-3GPP access); D) MA PDU session with only PDN leg (PDN connection established as user plane resources); and E) MA PDU session with PDN leg + non-3GPP leg (PDN connection established as user plane resources, and user plane resources established on non-3GPP access). For case (A), the MA PDU with only non-3GPP leg is counted as an active PDU session. For case (D), the MA PDU session with only PDN leg is counted in the number of active PDU sessions, even though it does not have a 5GS 3GPP leg nor a 5GS non-3GPP leg. Note also that the MA PDU session with only PDN leg, case D), is counted not only as an active PDU session, but also as an active PDN connection. For case (E), if the UE has reached the maximum number of PDU sessions, the UE needs to release the entire MA PDU in order to establish a new PDU.

[0030] The maximum number of PDU sessions (that a UE can establish in a PLMN / SNPN) is limited to the lowest of the following: the maximum number of PDU session IDs allowed by the protocol, the maximum number of PDU sessions for the PLMN or SNPN, and the maximum number of PDU sessions specific to the UE's implementation. If the UE receives an indication from the 5GS during a PDU session establishment procedure requested by the UE that the maximum number of PDU sessions has been reached, the UE determines the maximum number of PDU sessions as the number of active PDU sessions it has.

[0031] The maximum number of PDU sessions for a PLMN / SNPN applies to the PLMN / SNPN that receives the 5GSM cause #65 "Maximum number of PDU sessions reached". If the maximum number of PDU sessions established is reached at the UE and the upper layers of the UE request connectivity to a Data Network Name (DNN), the UE shall not send a PDU session establishment request (SESSION ESTABLISHMENT REQUEST) message unless an established PDU session is released. If the UE needs to release an established PDU session, it is implementation specific which PDU session is released. If the UE needs to release a PDU session to request an emergency PDU session, it shall perform a local release of the PDU session; or release the PDU session via explicit 5G (SM) signaling (5G UE requested PDU session release procedure).

[0032] In a novel aspect, if the UE has a PDN connection used as user plane resources for a MA PDU session, the UE can release the 4G PDN connection to establish a new PDU session when the maximum number of PDU sessions has been reached. In FIG. 3 In the example, the UE has established two PDU sessions, one SA PDU session 310 and one MA PDU session 320. The MA PDU session 320 has a 3GPP PDN leg, so it counts as an active PDU session and an active PDN connection. If the maximum number of PDU sessions is two, the UE cannot establish more PDU sessions (even an emergency PDU session). In response, the UE can release the PDN connection for the MA PDU session, and then the UE should be able to establish a new PDU session.

[0033] FIG. 4is a sequence flow between the UE and the 5GS for determining active PDU sessions in the 5GS and the UE-initiated PDN release procedure in the EPS followed by the PDU session establishment procedure in the 5GS when the maximum active PDU sessions to a PLMN / SNPN is reached according to one novel aspect. In step 411, the UE 401 maintains multiple SAPDU sessions. In step 412, the UE 401 maintains a MA PDU session with a PDN connection (e.g., a 3GPP PDN leg) established as a user plane resource over 3GPP for the MA PDU session. In step 421, the UE 401 determines whether the UE needs to establish another PDU session and whether the number of active PDU sessions has reached the maximum active PDU sessions allowed in the PLMN / SNPN. If yes, the UE 401 shall not send a PDU session establishment request unless an existing PDU session is released.

[0034] In one novel aspect, the UE 401 selects a 4G PDN connection of the MA PDU session and decides to release the selected 4G PDN connection to establish a new 5G PDU session. The UE 401 can release the selected 4G PDN connection under two options. Under option #1, the UE 401 releases the 4G PDN connection using explicit 4G ESM signaling. In step 431, the UE 401 sends a 4G PDN disconnect request message to the network. In step 432, the UE 401 receives a 4G DEACTIVATE EPS BEARER message from the network to release the 4G PDN connection. Under option #2, the UE 401 performs a local release of the MA PDU with the PDN leg (step 441). In step 442, the UE 401 performs a 4G TAU procedure with the network to indicate the 4G EPS bearer context status to the network. The EPS bearer context status IE is included in the TAU request message. In step 451, the UE 401 establishes a new 5G PDU session in the 5GS after releasing the 4G PDN connection. In one example, the new 5G PDU session is an emergency PDU session. In another example, the new 5G PDU session is a PDU session to a DNN.

[0035] FIG. 5 FIG. 5is a flowchart of a method of handling PDU session establishment procedure when maximum number of PDU sessions has been reached in 5GS according to a novel aspect of the present application. In step 501, the UE maintains multiple active PDU sessions in 5GS. In step 502, the UE determines that the number of active PDU sessions has reached the maximum number of PDU sessions for the PLMN or SNPN in 5GS. In step 503, the UE determines that a new 5G PDU session is needed based on a request from upper layers. In step 504, the UE selects a PDN connection from one or more PDN connections maintained by the UE, wherein the UE initiates a PDN connection release procedure to release the selected PDN connection; or the UE releases the PDN connection locally. In step 504, the UE establishes a new PDU session after releasing the selected PDU connection. The selected PDN connection is established as user plane resources for a MAPDU session over 3GPP access; and is counted as an active PDU session in the PLMN / SNPN. In one embodiment, the UE initiates a UE-requested PDN disconnect procedure by sending a PDN disconnect request message to the network. In another embodiment, the UE releases the selected PDN connection locally and performs a regular and periodic TAU with the network.

[0036] While the application has been described in connection with certain specific embodiments thereof, the application is not limited to such specific embodiments. Thus, various modifications, adaptations, and combinations of various features of the described embodiments can be practiced without departing from the scope of the application as set forth in the claims.

Claims

1. A method for establishing a protocol data unit session, characterized in that, include: Multiple active 5G protocol data unit sessions are maintained by user equipment in the 5G system; Determine that the number of active 5G protocol data unit sessions has reached the maximum number of 5G protocol data unit sessions in the public terrestrial mobile network or independent non-public network of the 5G system; Based on the request from the upper layer, it was determined that a new fifth-generation protocol data unit session was needed; A fourth-generation packet data network connection is selected from one or more fourth-generation packet data network connections maintained by the user equipment, and the selected fourth-generation packet data network connection is established as the sole user plane resource for a multi-access protocol data unit session, wherein the user equipment releases the fourth-generation packet data network connection; as well as After releasing the selected fourth-generation packet data network connection, the new fifth-generation protocol data unit session is established.

2. The method for establishing a processing protocol data unit session as described in claim 1, characterized in that, The The user equipment initiates a packet data network disconnection process by sending a packet data network disconnection request message to the network, thereby releasing the selected fourth-generation packet data network connection.

3. The method for establishing a protocol data unit session as described in claim 2, characterized in that, The user equipment receives a Deactivate Evolved Packet System Bearer Context message from the network in response to the Packet Data Network Disconnection Request message.

4. The method for establishing a protocol data unit session as described in claim 1, characterized in that, The user equipment locally releases the selected fourth-generation packet data network connection and performs regular and periodic tracking area updates with the network.

5. The method for establishing a protocol data unit session as described in claim 4, characterized in that, The Evolved Group System carries context state information elements, which are included in the Tracking Area Update Request message.

6. The method for establishing a processing protocol data unit session as described in claim 1, characterized in that, The new protocol data unit session is either an emergency protocol data unit session or a protocol data unit session to a data network name.

7. The method for establishing a processing protocol data unit session as described in claim 1, characterized in that, The user equipment establishes the new fifth-generation protocol data unit session by initiating the protocol data unit session establishment process through the fifth-generation non-third-generation partner program access.

8. A user equipment for processing protocol data unit session establishment, comprising: The protocol data unit session processing circuit maintains multiple active fifth-generation protocol data unit sessions in the fifth-generation system. The configuration and control circuitry determines that the number of active fifth-generation protocol data unit sessions has reached the maximum number of fifth-generation protocol data unit sessions in the public terrestrial mobile network or independent non-public network of the fifth-generation system. The configuration and control circuitry determines that a new 5G protocol data unit session is needed based on a request from the upper layer. as well as A packet data network connection processing circuit selects a fourth-generation packet data network connection from one or more fourth-generation packet data network connections maintained by the user equipment, wherein the selected fourth-generation packet data network connection is established as the sole user plane resource for a multi-access protocol data unit session, wherein the user equipment releases the fourth-generation packet data network connection, and after releasing the selected fourth-generation packet data network connection, the user equipment establishes the new fifth-generation protocol data unit session.

9. The user equipment as claimed in claim 8, characterized in that, The user equipment initiates a packet data network disconnection process by sending a packet data network disconnection request message to the network, thereby releasing the selected fourth-generation packet data network connection.

10. The user equipment as claimed in claim 9, characterized in that, The user equipment receives a Deactivate Evolved Packet System Bearer Context message from the network in response to the Packet Data Network Disconnection Request message.

11. The user equipment as claimed in claim 8, characterized in that, The user equipment locally releases the selected fourth-generation packet data network connection and performs regular and periodic tracking area updates with the network.

12. The user equipment as claimed in claim 11, characterized in that, The Evolved Group System carries context state information elements, which are included in the Tracking Area Update Request message.

13. The user equipment as claimed in claim 8, characterized in that, The new protocol data unit session is either an emergency protocol data unit session or a protocol data unit session to a data network name.

14. The user equipment as claimed in claim 8, characterized in that, The user equipment establishes the new fifth-generation protocol data unit session by initiating the protocol data unit session establishment process through the fifth-generation non-third-generation partner program access.

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