Method and apparatus for enhancing session continuity of system interaction

Abstract

A method and apparatus for enhancing session continuity for interworking system interaction is presented. When a UE performs inter-system handover from A / Gb mode or Iu mode to S1 mode, the UE identifies some PDN connections that are not associated with a PDU session ID (PSI). In one novel aspect, the UE locally deactivates all EPS bearer contexts for such PDN connections, includes an EPS bearer context status IE in a tracking area update request message of a tracking area update (TAU) procedure upon inter-system handover from A / Gb mode or Iu mode to S1 mode, and then initiates a UE-requested PDN connection procedure for such PDN connection. Moreover, if there is no EPS bearer after local deactivation and the UE does not support EMM registration without PDN connection, the UE initiates a re-attach procedure for a subsequent UE-requested PDN connection procedure for this PDN connection.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority to U.S. Provisional Application No. 63 / 308,178, entitled “Enhanced Handling for Session Continuity,” filed February 9, 2022, pursuant to 35 USC §119, the subject matter of which is incorporated herein by reference. Technical Field

[0003] The disclosed implementations generally relate to wireless communication, and more particularly to methods for supporting session continuity when the UE performs system interaction work from A / Gb or Iu mode to S1 mode. Background Technology

[0004] Over the years, wireless communication networks have grown exponentially. Long-Term Evolution (LTE) systems offer high peak data rates, low latency, improved system capacity, and low operating costs due to their simpler network architecture. LTE systems, also known as 4th Generation (4G) systems, also provide seamless integration with older wireless networks such as Global System for Mobile Communications (GSM), Code Division Multiple Access (CDMA), and 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). 3rd Generation Partner Project (3GPP) networks typically include a hybrid of 2G / 3G / 4G systems. The Next Generation Mobile Network (NGMN) Board has decided to focus future NGMN activities on defining the end-to-end requirements for 5G New Radio (NR) systems (5GS).

[0005] In 4G Evolved Packet System (EPS), the PDN connection process is a crucial step when an LTE communication system accesses the Packet Data Network (PDN). The purpose of the PDN connection process is to establish a default EPS bearer between the UE and the PDN. In 5G, Protocol Data Unit (PDU) session establishment is a parallel process to the PDN connection process in 4G. The PDU session defines the association between the UE and the data network providing the PDU connection service. If the UE supports interactive operation and performs an intersystem change from S1 mode to A / Gb (2G) or Iu (3G, UMTS) mode, the UE uses parameters from the respective active EPS bearer contexts to enable the corresponding PDP context.

[0006] During system handover from A / Gb or Iu mode to S1 mode, for PDN connections that do not support 5GS interaction, the UE can initiate a PDN disconnection procedure and then initiate a UE-requested PDN connection procedure. However, this procedure may incur unnecessary signaling overhead, especially in cases where multiple PDN connections need to be re-established.

[0007] Seeking solutions. Summary of the Invention

[0008] A method to enhance session continuity in system interaction is proposed. During inter-system handover from A / Gb or Iu mode to S1 mode, for any transferred PDN connection, if the PDN connection is not associated with a PDU Session ID (PSI), and the UE supporting N1 mode decides to transfer the PDN connection from S1 mode to N1 mode, the UE can first initiate a UE-requested PDN disconnection procedure, and then initiate a UE-requested PDN connection procedure for such PDN connection. In a novel aspect, the UE locally deactivates all EPS bearer contexts for such PDN connection, includes the EPS bearer context state (IE) in the Tracking Area Update (TAU) request message during inter-system handover from A / Gb or Iu mode to S1 mode, and then initiates a UE-requested PDN connection procedure for such PDN connection. Furthermore, if there is no EPS bearer after local deactivation and the UE does not support EMM-REGISTERED without PDN connection, the UE initiates a reattachment procedure for the subsequent UE-requested PDN connection procedure for such PDN connection.

[0009] In one implementation, the UE performs an inter-system handover from A / Gb or Iu mode to S1 mode in a mobile communication network, wherein the UE maintains multiple Packet Data Network (PDN) connections in S1 mode. The UE identifies one or more PDN connections that do not support 5GS interoperability. The UE locally releases the one or more PDN connections and disables the evolved packet system (EPS) bearer contexts associated with the one or more PDN connections. The UE performs a tracking area update (TAU) procedure with the network to disable all EPS bearer contexts associated with the one or more PDN connections. The UE initiates one or more UE-requested PDN connection procedures to establish PDN connections that support 5GS interoperability.

[0010] According to the method and apparatus for enhancing session continuity of system interaction provided by the present invention, the TAU procedure can be used to disable all EPS bearer contexts of PDN connections that do not support interaction with 5GS, thereby reducing signaling overhead.

[0011] Other embodiments and advantages are described in the detailed description below. This invention is not intended to be limited. The invention is defined by the claims. Attached Figure Description

[0012] The accompanying drawings illustrate embodiments of the invention, wherein the same numbers denote the same components.

[0013] Figure 1 An exemplary mobile communication network and inter-system handover for multiple Packet Data Network (PDN) connections with session continuity is illustrated according to a novel aspect.

[0014] Figure 2 A simplified block diagram illustrating user equipment (UE) and network entities according to an embodiment of the present invention is shown.

[0015] Figure 3 This paper illustrates a novel aspect, specifically a first implementation of UE behavior during system handover from 2G / 3G to 4G for a PDN connection that does not support 5GS interaction.

[0016] Figure 4 This paper illustrates a novel aspect, a second implementation of UE behavior during system handover from 2G / 3G to 4G for PDN connections that do not support 5GS interaction.

[0017] Figure 5 This illustrates the sequential procedures for PDN connection establishment, EPS bearer activation, and deactivation between the UE and PLMN1 and PLMN2 during inter-system handover with session continuity.

[0018] Figure 6 This is a flowchart of a method for supporting interactive operation from 2G / 3G to 4G with session continuity for multiple PDN connections, according to a novel aspect of the present invention. Detailed Implementation

[0019] Reference will now be made in detail to some embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0020] Figure 1An exemplary mobile communication network 100 and inter-system handover for a PDN connection with session continuity are illustrated according to a novel aspect. The mobile communication network 100 includes: a user equipment (UE) 101, a base station gNB / eNB 102, an Access and Mobility Management Function (AMF), a Session Management Function (SMF), or a Mobility Management Entity (MME) 103, and a 5G / 4G core network 5GC / EPC 104. Figure 1 In the example, UE 101 and its serving base station gNB 102 are part of Radio Access Network (RAN) 120. In the Access Stratum (AS), RAN 120 provides radio access for UE 101 via Radio Access Technology (RAT). In the Non-Access Stratum (NAS), AMF / SMF / MME 103 communicates with gNB 102 and 5GC / EPC 104 for access and mobility management of radio access devices in network 100, as well as PDU session management. UE 101 may be equipped with a single Radio Frequency (RF) transceiver, or multiple RF transceivers via different RATs / CNs for different application services. UE 101 may be a smartphone, wearable device, Internet of Things (IoT) device, or tablet computer, etc.

[0021] EPS networks are packet-switched (PS) Internet Protocol (IP) networks. This means the network delivers all data traffic in IP packets and provides IP connectivity to users. When a UE joins a 5GS network, a Packet Data Network (PDN) address (i.e., an address that can be used on the PDN) is assigned to the UE to connect it to the PDN. In 4G, the PDN connection process is a crucial step in establishing a default EPS bearer between the UE and the packet data network. EPS has defined a default EPS bearer to provide IP connectivity. In 5G, the Protocol Data Unit (PDU) session establishment process is a parallel process to the PDN connection process in 4G. The PDU session defines the association between the UE and the data network providing PDU connectivity services.

[0022] If the UE supports interactive operation and performs an inter-system handover from S1 (4G) mode to A / Gb (2G) or Iu (3G, UMTS) mode, the UE uses parameters from each active EPS bearer context to enable the corresponding PDP context. During an inter-system handover from A / Gb or Iu mode to S1 mode, for PDN connections that do not support 5GS interactive operation (e.g., without PSI association), the UE can initiate a PDN disconnection procedure and then initiate a UE-requested PDN connection procedure. However, this procedure may incur unnecessary signaling overhead, especially in cases where multiple PDN connections need to be re-established.

[0023] exist Figure 1 In the example, UE 101 maintains multiple PDN connections in the EPS, each associated with a default EPS bearer identified by an EPS bearer ID (EBI). If UE 101 loses its 4G signal and only has 2G / 3G signal, UE 101 can perform an inter-system handover from S1 mode to A / Gb mode (2G) or Iu mode (3G) (141). Therefore, UE 101 can enable the 2G / 3G PDP context by using parameters from the EPS bearer context of the multiple PDN connections (142). Later, UE 101 can perform an inter-system handover from A / Gb mode (2G) or Iu mode (3G) back to S1 mode (143), and the enabled PDP context is converted back to multiple PDN connections (131). If some of the PDN connections do not support working with 5GS (e.g., without PSI association), UE 101 may want to switch the PDN connections from S1 mode to N1 mode.

[0024] According to a novel aspect, UE 101 performs the following steps to transition a PDN connection from S1 mode to N1 mode (151). First, UE 101 locally disables all EPS bearer contexts of PDN connections that do not have PSI associations. Second, during inter-system handover from A / Gb mode or Iu mode to S1 mode, UE 101 includes the EPS bearer context state IE in the tracking area update request message of the TAU procedure. The EPS bearer state IE indicates which EPS bearer contexts should be disabled by the network. Third, UE 101 initiates one or more UE-requested PDN connection procedures for those PDN connections. Moreover, if no EPS bearer exists after local disabling and the UE does not support EMM registration without PDN connections, UE 101 initiates a reattachment procedure, followed by one or more UE-requested PDN connection procedures for those PDN connections. As a result, UE 101 does not need to disconnect each PDN connection individually, which reduces signaling overhead. When switching between systems from S1 mode to N1 mode (161), the newly established PDN connection (132) can be transferred to the corresponding PDU session (162).

[0025] Figure 2 A simplified block diagram illustrating a wireless device (e.g., UE 201) and network entity 211 according to an embodiment of the present invention is shown. Network entity 211 may be a base station and / or an AMF / SMF / MME / SGSN / RAN. Network entity 211 has an antenna 215 for transmitting and receiving radio signals. An RF transceiver module 214, coupled to the antenna, receives RF signals from the antenna 215, converts the RF signals into baseband signals, and transmits the baseband signals to a processor 213. The RF transceiver 214 also converts the baseband signals received from the processor 213, converts the baseband signals into RF signals, and transmits them to the antenna 215. The processor 213 processes the received baseband signals and invokes different functional modules to perform functions in the base station 211. Memory 212 includes volatile computer-readable storage media and non-volatile computer-readable storage media, storing program instructions and data 220 for controlling the operation of the base station 211. Figure 2 In the example, network entity 211 also includes a protocol stack 280 and a set of control function modules and circuits 290. PDU session or PDN connection or PDP context processing circuit 231 handles the PDU / PDN / PDP establishment and modification process. QoS and EPS bearer management circuit 232 creates, modifies, and deletes QoS and EPS bearers for the UE. Configuration and control circuit 233 provides various parameters to configure and control relevant UE functions, including mobility and session management, and PDU / PDN / PDP management.

[0026] Similarly, UE 201 includes memory 202, processor 203, and radio frequency (RF) transceiver module 204. RF transceiver 204 is connected to antenna 205, receives RF signals from antenna 205, converts the RF signals into baseband signals, and sends the baseband signals to processor 203. RF transceiver 204 also converts the baseband signals received from processor 203, converts the baseband signals into RF signals, and sends them to antenna 205. Processor 203 processes the received baseband signals and invokes different functional modules and circuits to perform functions in UE 201. Memory 202 includes volatile computer-readable storage media and non-volatile computer-readable storage media, storing data and program instructions 210 to be executed by the processor to control the operation of UE 201. For example, suitable processors include: dedicated processors, digital signal processors (DSPs), multiple microprocessors, one or more microprocessors associated with a DSP core, controllers, microcontrollers, application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), and other types of integrated circuits (ICs) and / or state machines. Software-associated processors can be used to implement and configure the functionality of UE 201.

[0027] UE 201 also includes a set of functional modules and control circuitry for performing the functional tasks of UE 201. Protocol stack 260 includes: a Non-Access-Stratum (NAS) layer for communicating with AMF / SMF / MME / SGSN entities connected to the 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. System modules and circuitry 270 can be implemented and configured through software, firmware, hardware, and / or combinations thereof. When executed by a processor via program instructions contained in memory, these functional modules and circuitry interact with each other to enable UE 201 to perform implementations and functional tasks and functions within the network.

[0028] In one example, system module and circuit 270 includes: PDU session, PDN connection, and PDP context processing circuitry 221 that performs the PDU session and PDN connection establishment and modification process with the network; session and mobility management circuitry 222 that manages session and mobility parameters; inter-system handover processing circuitry 223 that handles inter-system handover functions; and configuration and control circuitry 224 that handles configuration and control parameters for session and mobility management. In a novel aspect, during inter-system handover from 2G / 3G to 4G, UE 201 utilizes the TAU procedure to disable all EPS bearer contexts of PDN connections that do not support 5GS interaction, thereby reducing signaling overhead.

[0029] Figure 3 This paper illustrates a novel aspect of UE behavior during inter-system handover from 2G / 3G to 4G for PDN connections that do not support 5GS interoperability. In step 311, UE 301 maintains multiple PDP contexts in UMTS 303. In step 312, UE 301 performs an inter-system handover from UMTS 303 to EPS 302 (from 2G / 3G to 4G). The multiple PDP contexts are transferred to the EPS bearer of the corresponding PDN connection in the EPS (step 321). In step 331, UE 301 determines which PDN connections do not support 5GS interoperability, for example, PDN connections not associated with a PDU session ID (PSI). For example, UE 301 may identify at least three PDN connections (Internet, IMS, other services, etc.) that do not support 5GS interoperability. Since UE 301 supports N1 mode, UE 301 decides to transfer those PDN connections from S1 mode to N1 mode by first releasing those PDN connections and then re-establishing PDN connections with interactive working capabilities.

[0030] Traditionally, during system handover from A / Gb or Iu mode to S1 mode, for any transferred PDN connection, if the PDN connection is not associated with a PDU session ID, the UE can first initiate a UE-requested PDN disconnection procedure, followed by a UE-requested PDN connection procedure for each PDN connection within the PDN connection. For example, as depicted in box 340, in step 341, UE 301 initiates a first PDN disconnectivity procedure to disconnect the PDN connection for Internet services. In step 342, UE 301 initiates a second PDN disconnectivity procedure to disconnect the PDN connection for IMS services. In step 343, UE 301 initiates a third PDN disconnectivity procedure to disconnect the PDN connection for other services. After disconnecting the PDN connections, in step 343, UE 301 initiates a first UE-requested PDN connection procedure for Internet services. In step 344, UE 301 initiates a second UE-requested PDN connection procedure for IMS services. In step 345, UE 301 initiates a third UE-requested PDN connection procedure for other services. It can be seen that for each PDN connection that does not support interaction with 5GS, UE 301 needs to initiate both a PDN disconnection procedure and a PDN connection procedure.

[0031] According to a novel aspect, the UE can locally disable all EPS bearer contexts for this PDN connection, include the EPS bearer context state IE in the tracking area update request message during system handover from A / Gb mode or Iu mode to S1 mode, and then initiate a UE-requested PDN connection procedure for this PDN connection. For example... Figure 3As described, in step 351, UE 301 locally disables all EPS bearer contexts for those PDN connections that do not support 5GS interaction. In step 361, during / after an inter-system handover to S1 mode, UE 301 initiates a tracking area update procedure by sending a TAU request message to EPS 302 to synchronize with the EPS bearer context state of EPS 302. The TAU request message includes the EPS bearer context state IE, which contains all EBIs of the EPS bearer contexts of those PDN connections to be disconnected. After the PDN connection is disconnected (e.g., the EPS bearer context is disabled), in step 362, UE 301 initiates a first UE-requested PDN connection procedure for Internet service. In step 363, UE 301 initiates a second UE-requested PDN connection procedure for IMS service. In step 364, UE 301 initiates a third UE-requested PDN connection procedure for other services. As can be seen, compared to three separate PDN disconnection procedures, UE 301 only requires one Tracking Area Update Synchronization (TAU SYNC) procedure, which reduces signaling overhead.

[0032] Figure 4 This paper illustrates a novel aspect, a second implementation of UE behavior during system handover from 2G / 3G to 4G for PDN connections that do not support 5GS interaction. Figure 4 Steps 411 to 451 are similar Figure 3 Steps 311 to 351. In Figure 3 In the example, some PDN connections do not support working with 5GS, while the rest do. However, in Figure 4 In the example, none of the PDN connections support interaction with 5GS. As a result, after step 451, UE 401 has locally disabled all EPS bearer contexts, and UE 401 determines that there are no EPS bearers (e.g., all PDN connections have been released) (step 452). If the UE does not support EMM registration without PDN connections (EMM-RESIGERED), the UE needs to reattach to the EPS network to establish the first PDN connection. In step 461, UE 401 reattaches to EPS 402 to establish the first PDN connection for Internet services. In step 462, UE 401 initiates a UE-requested PDN connection procedure for IMS services. In step 463, UE 401 initiates another UE-requested PDN connection procedure for other services. It can be seen that compared to three separate PDN disconnection procedures, UE 401 only needs one reattachment procedure, and signaling overhead is reduced.

[0033] Figure 5 This example illustrates the sequential procedures for PDN connection establishment, EPS bearer activation, and deactivation between the UE and PLMN1 and PLMN2 during inter-system handover with session continuity. Figure 5 In the example, UE 501 selects a RAT (4G) in PLMN1 that does not support 5G (step 510). In step 511, UE 501 initiates a UE-requested PDN connection procedure for Internet services, for example, by sending a PDN connection request message (APN: Internet) in PLMN1. In step 512, in response to the PDN connection procedure, UE 501 receives an ACTIVATE DEFAULT_EPS_BEARER_CONTEXT_REQUEST message (APN: Internet, EBI=5). In step 513, UE 501 sends an ACTIVATE DEFAULT_EPS_BEARER_CONTEXT_ACCEPT message to PLMN1 to complete the PDN connection procedure for Internet services in PLMN1. Similarly, in step 521, UE 501 initiates a UE-requested PDN connection procedure for IMS services, for example, by sending a PDN connection request message (APN: IMS) to PLMN1. In step 522, in response to the PDN connection procedure, UE 501 receives an ACTIVATE DEFAULT_EPS_BEARER_CONTEXT_REQUEST message (APN: IMS, EBI=6). In step 523, UE 501 sends an ACTIVATE_DEFAULT_EPS_BEARER CONTEXT_ACCEPT message to PLMN1 to complete the PDN connection procedure for the IMS service. UE 501 can follow the same procedure to establish more PDN connections for other services in PLMN1.

[0034] In step 531, UE 501 reselects the RAT from 4G (PLMN1) to 2G / 3G. For inter-system handover from S1 mode to A / Gb mode or Iu mode, the UE uses parameters from each active EPS bearer context to enable the corresponding PDP context. For example, the SM uses the following parameters from each active EPS bearer context: EPS bearer identifier for mapping to NSAPI; linked EPS bearer identifier for mapping to linked TI (if available); PDP address and APN of the default EPS bearer context for mapping to the PDP address and APN of the default PDP context; TFT of the default EPS bearer context (if any) for mapping to the TFT of the default PDP context; TFT of the dedicated EPS bearer context for mapping to the TFT of the secondary PDP context; and GERAN / UTRAN parameters provided by the MME during E-UTRAN access. The MME performs the mapping from EPS to R99 QoS parameters.

[0035] exist Figure 5 In the example, PLMN2 supports 5G (540). Later, in step 541, UE 501 reselects from 2G / 3G back to 4G with 5G capability (PLMN2). During the inter-system handover to 4G, the PDP context in 2G / 3G is transferred to the EPS bearer of the PDN connection in 4G. Since some PDN connections may not support 5GS interaction, UE 501 needs to transfer those PDN connections from S1 mode to N1 mode. In step 551, UE 501 locally disables the EPS bearer context corresponding to those PDN connections that do not support 5GS interaction. In a novel aspect, instead of initiating a PDN disconnection procedure to individually release each PDN connection, UE 501 initiates a Tracking Area Update procedure, for example, by sending a TAU request message to the network (step 561). The TAU request message includes the EPS bearer context state IE, which indicates that all EPS bearer contexts corresponding to those PDN connections need to be disabled (e.g., EPS bearers with EBI=5 and EBI=6). Then, UE 501 establishes a PDN connection by sending a PDN connection request message (APN: Internet) in step 562 and a PDN connection request message (APN: IMS) in step 563.

[0036] Figure 6This is a flowchart of a method for supporting interoperability from 2G / 3G to 4G with session continuity for multiple PDN connections, according to a novel aspect of the present invention. In step 601, the UE performs an inter-system handover from A / Gb or Iu mode to S1 mode in the mobile communication network, wherein the UE maintains multiple PDN connections in S1 mode. In step 602, the UE identifies one or more PDN connections that do not support interoperability with 5GS. In step 603, the UE locally releases the one or more PDN connections and disables the EPS bearer context associated with the one or more PDN connections. In step 604, the UE performs a TAU procedure with the network to disable all EPS bearer contexts associated with the one or more PDN connections. In step 605, the UE initiates one or more UE-requested PDN connection procedures to establish a PDN connection that supports interoperability with 5GS. In one embodiment, after the UE locally disables the EPS bearer context associated with the one or more PDN connections, no EPS bearer exists, and the UE initiates a reattach procedure to establish a first PDN connection that supports interoperability with 5GS.

[0037] Although the invention has been described in conjunction with certain specific embodiments for guiding purposes, the invention is not limited thereto. Therefore, various modifications, adjustments, and combinations of features of the described embodiments can be made without departing from the scope of the invention as set forth in the claims.

Claims

1. A method for enhancing session continuity in system interaction, the method comprising: The user equipment (UE) performs an inter-system handover from A / Gb or Iu mode to S1 mode in the mobile communication network, wherein the UE maintains multiple packet data network (PDN) connections in S1 mode; The identifier does not support one or more PDN connections that interact with 5GS; Locally release the one or more PDN connections and deactivate the Evolved Packet System (EPS) bearer context associated with the one or more PDN connections; Perform a Tracking Area Update (TAU) procedure with the network to disable all EPS bearer contexts associated with the one or more PDN connections; and Initiate one or more PDN connection procedures requested by the UE to establish a PDN connection that supports interaction with 5GS.

2. The method according to claim 1, wherein, One or more PDN connections identified do not have a PDN session IDPSI association.

3. The method according to claim 1, wherein, Each of the identified one or more PDN connections is associated with a corresponding EPS bearer having an EPS bearer ID EBI.

4. The method according to claim 1, wherein, The UE sends a TAU request message, which includes the EPS bearer ID (EBI) of all EPS bearer contexts associated with the one or more PDN connections.

5. The method according to claim 4, wherein, The UE releases the one or more PDN connections without sending a separate PDN disconnect request for each of the one or more PDN connections.

6. The method according to claim 1, wherein, After the UE locally disables the EPS bearer context associated with the one or more PDN connections, no EPS bearer exists.

7. The method according to claim 6, wherein, The UE initiates a reattachment process to establish a first PDN connection that supports interaction with 5GS.

8. The method according to claim 1, wherein, During the system handover from A / Gb mode or Iu mode to S1 mode, the UE performs the TAU procedure.

9. The method according to claim 1, wherein, After the system handover from A / Gb mode or Iu mode to S1 mode is completed, the UE executes the TAU procedure.

10. A user equipment (UE) for enhancing session continuity in system interaction, the UE comprising: Inter-system handover processing circuit, which performs inter-system handover from A / Gb or Iu mode to S1 mode in the mobile communication network, wherein the UE maintains multiple packet data network (PDN) connections in S1 mode; Configuration and control circuitry, wherein the control circuitry identifies one or more PDN connections that do not support 5GS interaction, wherein the UE locally releases the one or more PDN connections and disables the Evolved Packet System EPS bearer context associated with the one or more PDN connections; Session and mobility management circuitry, the mobility management circuitry performing a Tracking Area Update (TAU) procedure with the network to disable all EPS bearer contexts associated with the one or more PDN connections; and The PDN connection processing circuit initiates one or more PDN connection procedures requested by the UE to establish a PDN connection that supports interaction with 5GS.

11. The UE according to claim 10, wherein, One or more PDN connections identified do not have a PDN session IDPSI association.

12. The UE according to claim 10, wherein, Each of the identified one or more PDN connections is associated with a corresponding EPS bearer having an EPS bearer ID EBI.

13. The UE according to claim 10, wherein, The UE sends a TAU request message, which includes the EPS bearer ID (EBI) of all EPS bearer contexts associated with the one or more PDN connections.

14. The UE according to claim 13, wherein, The UE releases the one or more PDN connections without sending a separate PDN disconnect request for each of the one or more PDN connections.

15. The UE according to claim 10, wherein, After the UE locally disables the EPS bearer context associated with the one or more PDN connections, no EPS bearer exists.

16. The UE according to claim 15, wherein, The UE initiates a reattachment process to establish a first PDN connection that supports interaction with 5GS.

17. The UE according to claim 10, wherein, During the system handover from A / Gb mode or Iu mode to S1 mode, the UE performs the TAU procedure.

18. The UE according to claim 10, wherein, After the system handover from A / Gb mode or Iu mode to S1 mode is completed, the UE executes the TAU procedure.

19. A non-volatile computer-readable storage medium storing program instructions and data that, when executed by a processor of a user equipment used to enhance session continuity of system interaction, cause the user equipment to perform operations according to any one of claims 1 to 9.

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