Method for supporting session continuity and user equipment thereof

Abstract

A method for S-NSSAI processing of a 5GS-capable UE supporting session continuity in interworking between 3GPP and non-3GPP is proposed. The UE maintains a PDN connection / PDU session. The UE interworks between S1 mode, N1 mode (including 3GPP and non-3GPP access) and ePDG. Regardless of whether the S-NSSAI is provided by the network, the UE associates the existing S-NSSAI with the new PDN connection / PDU session after interworking. The UE may update the S-NSSAI when a new value is received from the network. When interworking to N1 mode, the UE applies the relevant S-NSSAI. The present invention achieves the technical effect of maintaining session continuity when switching between different modes.

Description

Technical Field

[0001] The disclosed embodiments relate generally to wireless network communications, and more particularly to methods for supporting session continuity between 3GPP and non-3GPP interworking. Background Art

[0002] Wireless communication networks have grown exponentially over the years. Long-term evolution (LTE) systems offer high peak data rates, low latency, improved system capacity, and low operating costs due to a simplified network architecture. LTE systems, also known as 4G systems, also offer seamless integration with legacy wireless networks, such as GSM, CDMA, and universal mobile telecommunication systems (UMTS). In LTE systems, the evolved universal terrestrial radio access network (E-UTRAN) includes multiple evolved Node Bs (eNodeBs or eNBs) that communicate with multiple mobile stations, known as user equipment (UE). The 3rd generation partner project (3GPP) networks typically include a mix of 2G / 3G / 4G systems. The Next Generation Mobile Network (NGMN) committee has decided to focus future NGMN activities on defining the end-to-end requirements for 5G new radio (NR) systems.

[0003] In the 4G evolved packet system (EPS), when the LTE communication system accesses the packet data network, the packet data network (PDN) connection process is an important process. The purpose of the PDN connection process is to establish a default EPS bearer between the UE and the packet data network. In 5G, the protocol data unit (PDU) session establishment is a parallel process of the PDN connection process in 4G. The PDU session defines the association between the UE and the data network that provides the PDU connection service. Each PDU session is identified by a PDU session ID (PSI) and can include multiple QoS flows and QoS rules.

[0004] After the inter-system transition from N1 (5GS) mode to S1 (4G, EPS) mode, if the corresponding default EPS bearer context includes PSI, single-network slice selection assistance information (S-NSSAI), session aggregation maximum bit rate (Aggregate Maximum Bit Rate, AMBR) and one or more QoS flow descriptions received in the protocol configuration options IE or extended protocol configuration options IE, or the default EPS bearer context is associated with PSI, S-NSSAI, session AMBR and one or more QoS flow descriptions, then the PDN connection supports interworking with 5GS.

[0005] Specifically, to ensure session continuity, the S-NSSAI should remain associated with the PDN connection that supports interworking with 5GS. The S-NSSAI can be provided to the UE by the evolved packet data gateway (ePDG) when the PDN connection is established, and the S-NSSAI is used to associate the PDN connection. When switching from ePDG to N1 mode, the stored S-NSSAI can be included in the PDU session establishment request message. In scenarios with and without N26, the MME may also provide the S-NSSAI to the UE during PDN connection establishment. When switching from S1 mode to N1 mode, in scenarios without N26, the stored S-NSSAI is used to be included in the PDU session establishment request. However, the maintenance and processing of S-NSSAI for session continuity is not clear when switching from S1 mode to ePDG, from ePDG to S1 mode, from N1 mode to ePDG, and from N1 mode to S1 mode. Summary of the Invention

[0006] A method for S-NSSAI handling for 5GS capable UEs supporting session continuity for interworking between 3GPP and non-3GPP is proposed. The UE maintains the PDN connection / PDU session. The UE interworks between S1 mode, N1 mode (including 3GPP and non-3GPP access) and ePDG. Regardless of whether the S-NSSAI is provided by the network, the UE associates the existing S-NSSAI with the new PDN connection / PDU session after interworking. The UE may update the S-NSSAI when a new value is received from the network. When interworking to N1 mode, the UE applies the relevant S-NSSAI.

[0007] In one embodiment, a method for supporting session continuity is provided, comprising: maintaining, by a UE, an existing PDN connection in an EPC, wherein the existing PDN connection is established based on a first access type and is associated with an S-NSSAI; performing a first handover in the EPC from the existing PDN connection based on the first access type to a new PDN connection based on a second access type; associating the new PDN connection based on the second access type with the S-NSSAI of the existing PDN connection; and performing a second handover of a protocol data unit session in a 5G core from the new PDN connection based on the second access type in the EPC.

[0008] In another embodiment, a method for supporting session continuity is provided, comprising: maintaining, by a UE, an existing PDU session in a 5G core, wherein the existing PDU session is associated with an S-NSSAI; performing a first handover from the 5GC to a PDN connection in an EPC for the existing PDU session; associating the PDN connection in the EPC with the S-NSSAI of the existing PDU session; and performing a second handover from the EPC to a new protocol data unit session in the 5GC for the PDN connection.

[0009] In another embodiment, a user equipment supporting session continuity is provided, comprising: a PDU session and PDN connection processing circuit for maintaining an existing PDN connection in an EPC, wherein the existing PDN connection is established based on a first access type and is associated with an S-NSSAI; an inter-system processing circuit for performing a first switching in the EPC from the existing PDN connection based on the first access type to a new PDN connection based on a second access type; and a configuration and control circuit for associating the new PDN connection based on the second access type with the S-NSSAI of the existing PDN connection, wherein the user equipment performs a second switching from the new PDN connection based on the second access type in the EPC to a PDU session in a 5G core.

[0010] The present invention provides a method for supporting session continuity and user equipment thereof, which achieve the technical effect of maintaining session continuity when switching between different modes.

[0011] Other embodiments and advantages are described in the detailed description below. This summary is not intended to define the invention. The invention is defined by the claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The accompanying drawings, wherein like numerals indicate like components, illustrate embodiments of the present invention.

[0013] Figure 1According to one novel aspect, an exemplary 5G / 4G network and PDN connections supporting inter-system transitions and interworking sessions with 5GS are shown.

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

[0015] Figure 3 A first embodiment of a PDN connection supporting session continuity when switching from ePDG to N1 mode and corresponding S-NSSAI processing is shown.

[0016] Figure 4 A second embodiment of a PDN connection supporting session continuity when switching from ePDG to N1 mode and corresponding S-NSSAI processing is shown.

[0017] Figure 5 A first embodiment of a PDN connection supporting session continuity when switching from S1 mode to N1 mode and corresponding S-NSSAI processing is shown.

[0018] Figure 6 A second embodiment of a PDN connection supporting session continuity when switching from S1 mode to N1 mode and corresponding S-NSSAI processing is shown.

[0019] Figure 7 is a flow chart of a method for supporting session continuity of a PDN connection when switching between ePDG and S1 modes according to one novel aspect of the present invention.

[0020] Figure 8 is a flowchart of a method for supporting session continuity of a PDN connection when switching from N1 mode to ePDG or S1 mode according to one novel aspect of the present invention. DETAILED DESCRIPTION

[0021] Reference will now be made in detail to some embodiments of the present invention, examples of which are illustrated in the accompanying drawings.

[0022] Figure 1An exemplary 5G / 4G network and PDN connections supporting inter-system transitions and interworking sessions with 5GS are shown according to one novel aspect. A 5G New Radio (NR) network 100 includes a user equipment (UE) 101, a 3GPP access 102 (e.g., a 3GPP radio access network (RAN)), a non-3GPP access 103 (e.g., a 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) or evolved packet core (EPC) data network 120. The AMF 110 communicates with base stations in the 3GPP access 102, SMF 111, and UPF 113 for access and mobility management of wireless access devices in the 5G network 100. The SMF 111 is primarily responsible for interacting with the decoupled data plane, creating, updating, and deleting PDU sessions, and managing session contexts with the UPF 113. The N3IWF 112 interfaces with the 5GC / EPC network control plane functions and is responsible for routing messages outside the 3GPP RAN.

[0023] In the Access Stratum (AS) layer, the RAN provides radio access to the UE 101 through a radio access technology (RAT). In the Non-Access Stratum (NAS) layer, the AMF 110 and SMF 111 communicate with the RAN and 5GC for access and mobility management of wireless access devices in the 5G network 100, as well as PDU session management. The 3GPP access 102 may include a base station (gNB or eNB) that provides radio access to the UE 101 through various 3GPP RATs, including 5G, 4G, and 3G / 2G. The non-3GPP access 103 may include an access point (AP) that provides radio access to the UE 101 via a non-3GPP RAT, including 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. UE 101 can obtain access to data network 120 through non-3GPP access 103, N3IWF 112, AMF 110, SMF 111 and UPF 113. UE 101 can be equipped with a single radio frequency (RF) module or transceiver or multiple RF modules or transceivers for services via different RATs / CNs. In some examples, UE 101 can be a smartphone, a wearable device, an Internet of Things (IoT) device, a tablet, etc.

[0024] The 5GS network is a packet-switched (PS) Internet Protocol (IP) network. This means that the network transmits all data traffic in the form of IP data packets and provides users with always-on IP connectivity. 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 for the UE to connect to the PDN. In 4G, the PDN connection process is to establish a default EPS bearer between the UE and the PDN. EPS has defined a default EPS bearer to provide always-on IP connectivity. In 5G, the PDU session establishment process is a parallel process to the PDN connection process in 4G. A PDU session defines the association between the UE and the data network that provides the PDU connection service. Each PDU session is identified by a PDU session ID and can be established on a 3GPP RAN and / or on a non-3GPP RAN for radio access. 5G session management (5GSM) for PDU sessions based on both 3GPP access and non-3GPP access is managed by AMF and SMF via NAS signaling. In 5G, a multi-access (MA) PDU session uses one 3GPP access network or one non-3GPP access network at a time, or uses one 3GPP access network and one non-3GPP access network at the same time.

[0025] like Figure 1 As shown, PDU sessions and PDN connections support interworking, for example, system transitions between 5G 3GPP (N1 mode), 5G non-3GPP (N1 mode), 4G 3GPP (S1 mode) and 4G non-3GPP (ePDG). Specifically, to ensure session continuity, the S-NSSAI should remain associated with the PDN connection that supports interworking with 5GS. The S-NSSAI can be provided to the UE by the ePDG during the PDN connection establishment process, where the S-NSSAI is used to associate with the PDN connection. When switching from ePDG to N1 mode, the stored S-NSSAI may be included in the PDU session establishment request message. In scenarios with and without N26, the MME may also provide the S-NSSAI to the UE during PDN connection establishment. However, when switching from S1 mode to N1 mode, in scenarios without N26, the stored S-NSSAI is used to be included in the PDU session establishment request. However, the S-NSSAI maintenance and handling of session continuity when switching from S1 mode to ePDG, from ePDG to S1 mode, from N1 mode to ePDG, and from N1 mode to S1 mode is not clear.

[0026] A method (130) for S-NSSAI handling of a 5GS-capable UE supporting session continuity in interworking between 3GPP and non-3GPP is proposed. The UE maintains a PDN connection / PDU session. The UE interworks between S1 mode, N1 mode (including 3GPP and non-3GPP access) and ePDG. Regardless of whether the S-NSSAI is provided by the network, the UE associates the existing S-NSSAI with the new PDN connection / PDU session after interworking. The UE may update the S-NSSAI when a new value is received from the network. When interworking to N1 mode, the UE applies the S-NSSAI to ensure session continuity during inter-system transition. The S-NSSAI is a mandatory parameter associated with the PDU session and should be in the allowed NSSAI list provided by the network. If the S-NSSAI associated with the PDU session is not in the allowed NSSAI list, the UE shall locally release the corresponding PDU session. Applying the same principle, if the PDU session has no S-NSSAI associated, the PDU session shall be released locally by the UE.

[0027] Figure 2 A simplified block diagram of a wireless device (e.g., UE 201 and network entity 211) is shown according to an embodiment of the present invention. The network entity 211 can be a base station and / or an AMF / SMF. The network entity 211 has an antenna 215 for sending and receiving radio signals. The RF transceiver module 214 coupled to the antenna 215 receives an RF signal from the antenna 215, converts the RF signal into a baseband signal and sends the baseband signal to the processor 213. The RF transceiver module 214 also converts the baseband signal received from the processor 213 into an RF signal and sends it to the antenna 215. The processor 213 processes the received baseband signal and calls different functional modules to perform functional features in the base station 211. The memory 212 stores program instructions and data 220 to control the operation of the base station 211. In Figure 2 In the example shown in FIG. 2 , for example, network entity 211 further includes a protocol stack 280 and a set of control function modules and circuits 290. PDU session and PDN connection processing circuitry 231 handles PDU / PDN establishment and modification processes. QoS and EPS bearer management circuitry 232 creates, modifies, and deletes QoS and EPS bearers for the UE. Configuration and control circuitry 233 provides various parameters for configuring and controlling UE-related functions, including mobility management and PDU session management.

[0028] Similarly, UE 201 has memory 202, processor 203, and RF transceiver module 204. RF transceiver 204 is coupled to antenna 205, receives RF signals from antenna 205, converts the RF signals to baseband signals, and transmits them to processor 203. RF transceiver module 204 also converts baseband signals received from processor 203 to RF signals and transmits them to antenna 205. Processor 203 processes the received baseband signals and invokes various functional modules and circuits to perform functional features within UE 201. Memory 202 stores data and program instructions 210 for execution by the processor to control the operation of UE 201. Suitable processors include, by way of example, a dedicated processor, a digital signal processor (DSP), multiple microprocessors, one or more microprocessors associated with a DSP core, a controller, a microcontroller, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and other types of integrated circuits (ICs), and / or state machines. The processor in association with software may be used to implement and configure the features of UE 201 .

[0029] UE 201 also includes a set of functional modules and control circuits to perform the functional tasks of UE 201. The protocol stack 260 includes a NAS layer for communicating with the AMF / SMF / MME entity connected to the core network, a Radio Resource Control (RRC) layer for high-level configuration and control, a Packet Data Convergence Protocol (PDCP) / Radio Link Control (RLC) layer, a Media Access Control (MAC) layer, and a Physical (PHY) layer. The system modules and circuits 270 can be implemented and configured by software, firmware, hardware, and / or a combination thereof. The functional modules and circuits cooperate with each other when executed by the processor through program instructions contained in the memory to allow UE 201 to perform embodiments and functional tasks and features in the network. In one example, the system modules and circuits 270 include a PDU session and PDN connection processing circuit 221 that performs PDU session and PDN connection establishment and modification processes with the network, an EPS bearer management circuit 222 that manages, creates, modifies, and deletes mapped EPS bearer contexts and mapped 5GSM parameters, an inter-system processing circuit 223 that handles inter-system transformation functions, and a configuration and control circuit 224 that handles configuration and control parameters for mobility management and session management.

[0030] Figure 3 A first embodiment of PDN connection support for session continuity when switching from ePDG to N1 mode and corresponding S-NSSAI processing is shown. In step 311, UE 301 establishes a PDN connection via 3GPP access (S1 mode) in the EPC. The S-NSSAI is provided by the network (e.g., MME), where the S-NSSAI is associated with the established PDN connection. In step 312, UE 301 associates the S-NSSAI with the PDN connection and stores the S-NSSAI. In step 321, UE 301 performs a handover procedure from an existing PDN connection in S1 mode (3GPP access) to a new PDN connection in ePDG (non-3GPP access). The network (e.g., ePDG) may not provide an S-NSSAI for the new PDN connection. In step 322, regardless of whether the network (e.g., ePDG) provides any S-NSSAI, UE 301 associates the previously stored S-NSSAI with the new PDN connection.

[0031] Later, in step 323, the ePDG may update the associated S-NSSAI by providing an updated value of the S-NSSAI. For example, the network provides the S-NSSAI to the UE in the N1 Mode Information Notification (N1_MODE_INFORMATIONNotify) payload in the IKE_AUTH Response message. The UE shall delete the stored S-NSSAI and store the S-NSSAI provided by the network. In step 331, the new PDN connection in the ePDG supports handover from ePDG to N1 mode with session continuity. When switching from ePDG to N1 mode, the associated S-NSSAI is sent with the PDU Session Establishment Request message, regardless of whether the S-NSSAI is provided by the network. Note that if the associated S-NSSAI is not included in the allowed NSSAIs of the target access, the UE should not request handover of an existing PDN connection from ePDG to N1 mode.

[0032] Figure 4 A second embodiment of a PDN connection supporting session continuity when switching from ePDG to N1 mode and corresponding S-NSSAI processing is shown. In step 411, UE 401 establishes a PDU session in 5GC via 3GPP access (N1 mode). The S-NSSAI is provided by the network (e.g., SMF / AMF) and is associated with the established PDU session. In step 412, UE 401 associates the S-NSSAI with the PDU session and stores the S-NSSAI. In step 421, UE 401 performs a handover process from an existing PDU session in N1 mode (via 3GPP access) to a new PDN connection in ePDG (non-3GPP access). The network (e.g., ePDG) may not provide S-NSSAI for the new PDN connection. In step 422, regardless of whether the network (e.g., ePDG) provides any S-NSSAI, UE 401 associates the previously stored S-NSSAI with the new PDN connection.

[0033] Later, in step 423, the ePDG may update the S-NSSAI by providing an updated value of the S-NSSAI. For example, the network provides the S-NSSAI to the UE in the N1 Mode Information Notification payload in the IKE_AUTH Response message. The UE shall delete the stored S-NSSAI and store the S-NSSAI provided by the network. In step 431, the new PDN connection in the ePDG supports handover from ePDG to N1 mode with session continuity. Regardless of whether the S-NSSAI is provided by the network, the associated S-NSSAI is sent with the PDU Session Establishment Request message when switching from ePDG to N1 mode. Note that if the associated S-NSSAI is not included in the allowed NSSAIs of the target access, the UE should not request handover of an existing PDN connection from ePDG to N1 mode.

[0034] Figure 5 A first embodiment of a PDN connection and corresponding S-NSSAI processing that supports session continuity when switching from S1 mode to N1 mode is shown. In step 511, UE 501 maintains a PDN connection through non-3GPP access (ePDG) in the EPC. For example, the PDN connection is switched from S1 mode or N1 mode to ePDG, and the S-NSSAI is not provided by the network (e.g., ePDG). In step 512, UE 501 associates the S-NSSAI (from the previous PDN connection or PDU session) with the PDN connection and stores the S-NSSAI. In step 521, UE 501 performs a handover process from an existing PDN connection in ePDG (non-3GPP access) to a new PDN connection in S1 mode (3GPP access). The network (e.g., MME) may not provide the S-NSSAI for the new PDN connection. In step 522 , regardless of whether the network (eg, MME) provides any S-NSSAI, UE 501 associates the previously stored S-NSSAI with the new PDN connection.

[0035] Later, in step 523, the MME may update the associated S-NSSAI by providing an updated value of the S-NSSAI. For example, if the network provides the S-NSSAI to the UE in the protocol configuration options IE or extended protocol configuration options IE of the ACTIVATE DEFAULT EPS BEARER REQUEST message, the UE shall delete the stored S-NSSAI and shall store the S-NSSAI provided in the ACTIVATE DEFAULT EPS BEARER REQUEST message. In step 531, a new PDN connection in S1 mode supports handover from S1 mode to N1 mode with session continuity. When switching from S1 mode to N1 mode, the associated S-NSSAI shall be sent along with the PDU SESSION SETUP REQUEST message, regardless of whether the S-NSSAI is provided by the network. Note that if the associated S-NSSAI is not included in the allowed NSSAI of the target access, the UE shall not request to perform a handover of an existing PDN connection from S1 mode to N1 mode.

[0036] Figure 6 A second embodiment of a PDN connection supporting session continuity when switching from S1 mode to N1 mode and corresponding S-NSSAI processing is shown. In step 611, UE 601 maintains or establishes a PDU session in 5GC through 3GPP access (N1 mode). The S-NSSAI is provided by the network (e.g., SMF / AMF), where the S-NSSAI will be associated with the PDU session. In step 612, UE 601 associates the S-NSSAI with the PDU session and stores the S-NSSAI. In step 621, UE 601 performs a handover process from an existing PDU session in N1 mode (3GPP access) to a new PDN connection in S1 mode (3GPP access) without N26. When the network does not support the N26 interface, the SMF does not provide the UE with a mapped EPS bearer context (including the S-NSSAI) for the PDU session. In addition, the network (e.g., MME) may or may not provide the S-NSSAI for the new PDN connection. In step 622 , regardless of whether the network (eg, MME) provides any S-NSSAI, UE 601 associates the previously stored S-NSSAI with the new PDN connection.

[0037] Later, in step 623, the MME may update the S-NSSAI by providing an updated value of the S-NSSAI. For example, if the network provides the S-NSSAI to the UE in the Protocol Configuration Options IE or Extended Protocol Configuration Options IE of the Activate Default EPS Bearer Request message, the UE shall delete the stored S-NSSAI and shall store the S-NSSAI provided in the Activate Default EPS Bearer Request message. In step 631, a new PDN connection in S1 mode supports handover from S1 mode to N1 mode with session continuity. When switching from S1 mode to N1 mode, the relevant S-NSSAI is sent along with the PDU Session Establishment Request message, regardless of whether the S-NSSAI is provided by the network. Note that if the associated S-NSSAI is not included in the allowed NSSAI of the target access, the UE shall not request to perform a handover of an existing PDN connection from S1 mode to N1 mode.

[0038] Figure 7 7 is a flow chart of a method for supporting session continuity of a PDN connection when switching between ePDG and S1 modes according to a novel aspect of the present invention. In step 701, the UE maintains an existing packet data network (PDN) connection in an evolved packet core (EPC). The existing PDN connection is established based on a first access type and is associated with single network slice selection assistance information (S-NSSAI). In step 702, the UE performs a first handover in the EPC from the existing PDN connection based on the first access type to a new PDN connection based on a second access type. In step 703, the UE associates the new PDN connection based on the second access type with the S-NSSAI of the existing PDN connection. In step 704, the UE performs a second handover from the new PDN connection based on the second access type in the EPC to a protocol data unit (PDU) session in a 5G core (5GC).

[0039] Figure 8 804, 805, 814, 820, 826, 827, 828, 829, 830, 831, 832, 833, 834, 836, 837, 838, 839, 840, 841, 842, 843, 844, 845, 846, 847, 848, 849, 851, 852, 853, 854, 855, 856, 857, 858, 859, 860, 861, 862, 864, 865, 866, 867, 868, 869, 870, 871, 872, 873, 874, 875, 876, 877, 878, 879, 880, 881, 882, 883, 884, 877, 869, 880, 881, 882, 883, 884, 864, 846, 847, 848, 859, 880, 881, 882, 883, 884, 864, 865

[0040] Although the present invention has been described in conjunction with specific embodiments for illustrative purposes, it is not limited thereto. Therefore, various modifications, adaptations and combinations of the various features of the described embodiments may be implemented without departing from the scope of the invention as set forth in the appended claims.

Claims

1. A method for supporting session continuity, comprising: maintaining, by the user equipment, an existing packet data network connection in the evolved packet core, wherein the existing packet data network connection is established based on the first access type and is associated with the single network slice selection assistance information; performing, in the evolved packet core, a first handover from the existing packet data network connection based on the first access type to a new packet data network connection based on a second access type; Associating the new packet data network connection based on the second access type with the single network slice selection assistance information of the existing packet data network connection; as well as A second handover is performed from the new packet data network connection based on the second access type in the evolved packet core to a protocol data unit session in the 5G core.

2. The method for supporting session continuity according to claim 1, wherein: The first access type is a non-3rd Generation Partnership Project access type, and the second access type is a 3rd Generation Partnership Project access type.

3. The method for supporting session continuity according to claim 1, wherein: The first access type is a 3rd Generation Partnership Project access type, and the second access type is a non-3rd Generation Partnership Project access type.

4. The method for supporting session continuity according to claim 1, wherein: When the evolved packet data gateway in the evolved packet core does not provide any single network slice selection assistance information to the new packet data network connection, the user equipment associates the single network slice selection assistance information with the new packet data network connection.

5. The method for supporting session continuity according to claim 1, wherein: The single network slice selection assistance information of the new packet data network connection is updated by the evolved packet data gateway in the evolved packet core.

6. The method for supporting session continuity according to claim 1, wherein: When performing the second handover to the N1 mode in the 5G core, the user equipment applies the associated single network slice selection assistance information.

7. The method for supporting session continuity according to claim 1, wherein: If the single network slice selection assistance information is not included in the allowed network slice selection assistance information list of the target access in the 5G core, the user equipment does not perform the second handover.

8. A method for supporting session continuity, comprising: maintaining, by the user equipment, an existing protocol data unit session in the 5G core, wherein the existing protocol data unit session is associated with the single network slice selection assistance information; performing a first handover of the existing protocol data unit session from the 5G core to a packet data network connection in an evolved packet core; associating the packet data network connection in the evolved packet core with the single network slice selection assistance information of the existing protocol data unit session; as well as A second handover is performed for the packet data network connection from the evolved packet core to a new protocol data unit session in the 5G core.

9. The method for supporting session continuity according to claim 8, wherein: The packet data network connection is established via a non-3GPP access type in the Evolved Packet Core.

10. The method for supporting session continuity according to claim 8, wherein: The packet data network connection is established via a 3GPP access type in the Evolved Packet Core.

11. The method for supporting session continuity according to claim 8, wherein: When the evolved packet data gateway in the evolved packet core does not provide any single network slice selection assistance information to the packet data network connection, the user equipment associates the single network slice selection assistance information with the packet data network connection.

12. The method for supporting session continuity according to claim 8, wherein: The single network slice selection assistance information of the packet data network connection is updated by the evolved packet data gateway in the evolved packet core.

13. The method for supporting session continuity according to claim 8, wherein: When performing the second handover to the N1 mode in the 5G core, the user equipment applies the associated single network slice selection assistance information.

14. The method for supporting session continuity according to claim 8, wherein: If the single network slice selection assistance information is not included in the allowed network slice selection assistance information list of the target access in the 5G core, the user equipment does not perform the second handover.

15. A user equipment supporting session continuity, comprising: a protocol data unit session and packet data network connection processing circuit configured to maintain an existing packet data network connection in the evolved packet core, wherein the existing packet data network connection is established based on the first access type and is associated with the single network slice selection assistance information; an inter-system processing circuit for performing a first handover in the evolved packet core from the existing packet data network connection based on the first access type to a new packet data network connection based on a second access type; as well as Configuration and control circuitry for associating the new packet data network connection based on the second access type with the single network slice selection assistance information of the existing packet data network connection, wherein the user equipment performs a second handover from the new packet data network connection based on the second access type in the evolved packet core to a protocol data unit session in the 5G core.

16. The user equipment supporting session continuity according to claim 15, wherein: The first access type is a non-3rd Generation Partnership Project access type, and the second access type is a 3rd Generation Partnership Project access type.

17. The user equipment supporting session continuity according to claim 15, wherein: The first access type is a 3rd Generation Partnership Project access type, and the second access type is a non-3rd Generation Partnership Project access type.

18. The user equipment supporting session continuity according to claim 15, wherein: When the evolved packet data gateway in the evolved packet core does not provide any single network slice selection assistance information to the new packet data network connection, the user equipment associates the single network slice selection assistance information with the new packet data network connection.

19. The user equipment according to claim 15, wherein: The single network slice selection assistance information of the new packet data network connection is updated by the evolved packet data gateway in the evolved packet core.

20. The user equipment supporting session continuity according to claim 15, wherein: When performing the second handover to the N1 mode in the 5G core, the user equipment applies the associated single network slice selection assistance information.

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