COMMUNICATION DEVICE, AMF, COMMUNICATION DEVICE METHOD, AND AMF METHOD

Abstract

To provide an access network node capable of guiding user equipment UE in connection mode, the user equipment, a network function node, and a control method.SOLUTION: An access network node according to one embodiment is configured to: receive at least one piece of first network slice information different from second network slice information used for a session with a protocol data unit (PDU) and user equipment (UE) from a network function node for mobility management; and execute a redirection procedure of the UE from the first cell to a second cell supporting one piece of at least one piece of first network slice information when the first cell cannot use the second network slice information.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present disclosure relates to an access network node, a user equipment, a network function node and a control method. [Background technology]

[0002] Regarding mobile communication technology, progress has been seen as shown in Non-Patent Documents 1 to 7. For example, Non-Patent Document 3 describes the 3GPP technical specifications (TS), particularly the 5G system. [Prior art documents] [Non-patent literature]

[0003] [Non-Patent Document 1] 3GPP Technical Report (TR) 21.905: "Vocabulary for 3GPP Specifications" V17.0.0 (2020-07) [Non-Patent Document 2] 3GPP TS 23.501: "System architecture for the 5G System (5GS)" V16.5.0 (2020-07) [Non-Patent Document 3] 3GPP TS 23.502: "Procedures for the 5G System (5GS)" V16.5.0 (2020-07) [Non-Patent Document 4] GSM Association Official Document NG.116 - Generic Network Slice Template, v2.0 https: / / www.gsma.com / newsroom / wp-content / uploads / NG.116-v2.0.pdf [Non-Patent Document 5] 3GPP TR 23.700-40: "Study on enhancement of network slicing; Phase 2" V0.4.0 (2020-06) [Non-Patent Document 6] 3GPP TS 38.300: "NR; NR and NG-RAN Overall Description; Stage-2" V16.2.0 (2020-07) [Non-Patent Document 7] 3GPP TS 38.423: "NG-RAN; Xn Application Protocol (XnAP)" V16.2.0 (2020-07) Summary of the Invention [Problem to be solved by the invention]

[0004] In consideration of the above situation, an object of the present disclosure is to provide an access network node, a user equipment, a network function node, and a control method capable of guiding a UE in a connected mode. [Means for solving the problem]

[0005] In a first exemplary aspect, an access network node comprises: A receiving means for receiving at least one first network slice information different from a protocol data unit (PDU) and a second network slice information used in a session with a user equipment (UE) from a network function node for mobility management; and an executing means for performing a redirection procedure for a UE from a first cell to a second cell supporting one of the at least one first network slice information, when the second network slice information is unavailable in the first cell.

[0006] In a second exemplary aspect, a user equipment (UE) A transmitting means for transmitting at least one network slice information and a second network slice information in a protocol data unit (PDU), a session establishment request or a service request message to a network function node for mobility management via an access network node, The second network slice information is used for a PDU session with the network function node for mobility management; each of the at least one first network slice information is different from the second network slice information; A redirection procedure of a UE from a first cell served by the access network node to a second cell supporting one of the at least one first network slice information is performed when the second network slice information is not available in the first cell.

[0007] In a third exemplary aspect, a user equipment (UE) A transmitting means for transmitting the application identity and the second network slice information in a protocol data unit (PDU), a session establishment request or a service request message to a network function node for mobility management via an access network node, The second network slice information is used for a PDU session with the network function node for mobility management; The application identity is used by the network function node for mobility management to obtain at least one first network slice information, each of which is different from the second network slice information; A redirection procedure for a UE from a first cell served by the access network node to a second cell supporting one of the at least one first network slice information is performed when the second network slice information is not available in the first cell.

[0008] In a fourth exemplary aspect, a network function node for mobility management comprises: A transmitting means for transmitting at least one first network slice information to an access network node, the first network slice information being different from a second network slice information used for a PDU session with a user equipment (UE), The at least one first network slice information is used by the access network node to perform a redirection procedure of a UE from a first cell to a second cell supporting one of the at least one first network slice information when the second network slice information is not available in the first cell.

[0009] In a fifth exemplary embodiment, a method for controlling an access network node includes: receiving at least one first network slice information different from a protocol data unit (PDU) and a second network slice information used for a session with a user equipment (UE) from a network function node for mobility management; A redirection procedure for the UE is performed from a first cell to a second cell supporting one of the at least one first network slice information, when the second network slice information is not available in the first cell.

[0010] In a sixth exemplary aspect, a method for controlling a user equipment (UE) includes: Sending at least one network slice information and a second network slice information in a protocol data unit (PDU), a session establishment request or a service request message to a network function node for mobility management via an access network node; The second network slice information is used for a PDU session with the network function node for mobility management; each of the at least one first network slice information is different from the second network slice information; A redirection procedure for a UE from a first cell served by the access network node to a second cell supporting one of the at least one first network slice information is performed when the second network slice information is not available in the first cell.

[0011] In a seventh exemplary aspect, a method for controlling a user equipment (UE) includes: Sending the application identity and the second network slice information in a protocol data unit (PDU), a session establishment request or a service request message to a network function node for mobility management via the access network node; The second network slice information is used for a PDU session with a network function node for mobility management; The application identity is used by the network function node for mobility management to obtain the at least one first network slice information, which is different from the second network slice information; A redirection procedure for a UE from a first cell served by the access network node to a second cell supporting one of the at least one first network slice information is performed when the second network slice information is not available in the first cell.

[0012] In an eighth exemplary aspect, a control method for a network function node for mobility management includes: Transmitting at least one first network slice information to an access network node, the first network slice information being different from a second network slice information used for a PDU session with a user equipment (UE); The at least one first network slice information is used by the access network node to perform a redirection procedure of the UE from a first cell to a second cell supporting one of the at least one first network slice information when the second network slice information is not available in the first cell. Effect of the Invention

[0013] According to the present disclosure, it is possible to provide an access network node, a user equipment, a network function node, and a control method capable of guiding a UE in a connected mode. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 illustrates a use case in which an active PDU session of a UE may be released during handover in a first embodiment. [Diagram 2] FIG. 2 is a schematic timing (signaling) diagram illustrating an exemplary method of UE assistance in the first embodiment. [Diagram 3] FIG. 3 is a schematic timing (signaling) diagram illustrating an exemplary method for UE assistance in the first embodiment. [Figure 4] FIG. 4 is a schematic timing (signaling) diagram illustrating an exemplary method for UE assistance in the first embodiment. [Diagram 5] FIG. 5 is a schematic timing (signaling) diagram illustrating an exemplary method of core network assistance in the first embodiment. [Figure 6] FIG. 6 is a schematic timing (signaling) diagram illustrating an exemplary method of core network assistance in the first embodiment. [Figure 7] FIG. 7 is a schematic timing (signaling) diagram illustrating an exemplary method of core network assistance in the first embodiment. [Figure 8]FIG. 8 is a diagram showing a mobile (cellular or wireless) communication system according to a first embodiment. [Figure 9] FIG. 9 is a block diagram illustrating the main components of the UE (Mobile Equipment) shown in FIG. 8 according to the first embodiment. [Figure 10] FIG. 10 is a block diagram illustrating the main components of an exemplary (R)AN node (base station) shown in FIG. 8 according to a first embodiment. [Figure 11] FIG. 11 is a block diagram illustrating the main components of a typical core network node (or function) shown in FIG. 8 according to the first embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Prior to describing aspects according to the present disclosure, the following remarks are given.

[0016] (abbreviation) For the purposes of this disclosure, the following abbreviations apply: 3GPP 3rd Generation Partnership Project 5G 5th Generation 5GC 5G Core Network 5GS 5G System 5G-AN 5G Access Network AMF Access and Mobility Management Function AS Application Server CAG Closed Access Group CDR Charging Data Record CHF Charging Function gNB Next Generation NodeB GSMA Global System for Mobile Communications Association NAS Non-Access Stratum NG-RAN Next Generation Radio Access Network NR New Radio NSSAA Network Slice Specific Authentication and Authorisation NSSAI Network Slice Selection Assistance Information NSSP Network Slice Selection Policy PCF Policy Control Function PDU Protocol Data Unit PLMN Public Land Mobile Network RACH Random Access Channel RAN Radio Access Network RAT Radio Access Technology RRC Radio Resource Control S-AMF Source AMF S-NSSAI Single Network Slice Selection Assistance Information S-RAN Source RAN SMF Session Management Function TA Tracking Area T-AMF Target AMF T-RAN Target RAN UDM Unified Data Management UDR Unified Data Repository UE User Equipment URLLC Ultra Reliable and Low Latency Communications URSP UE Route Selection Policy

[0017] (definition) For purposes of this disclosure, the terms and definitions set forth in 3GPP Technical Report (TR) 21.905: “Vocabulary for 3GPP Specifications” V17.0.0 (2020-07) (hereinafter referred to as 3GPP TR 21.905) apply. Even if the same term is defined in 3GPP TR 21.905, the term defined in this specification takes precedence.

[0018] (Related Technology) The network slice capabilities defined in 3GPP Release 15 and Release 16 enable a wide variety of communication services for operators and verticals. To increase the commercial viability of network slices, GSMA 5GJA introduces the GSM Association Official Document NG.116-Generic Network Slice Template, v2.0, from which several network slice type descriptions can be derived. Some parameters in the Generic Slice Template (GST) explicitly indicate the definition of parameters and boundaries of the services offered to the end customer. However, the implementation of some of these boundaries and parameters is not yet supported in 5GS.

[0019] Phase 2 of the SA2 study on network slicing expansion aims to identify the gaps that need to be filled in providing support for the implementation of GST parameters and appropriate solutions to address these gaps.

[0020] Following the progress of the SA2 research on extended network slicing, the RAN has agreed to an independent research item on extending RAN slicing, the objective of which is to explore extending RAN support for network slicing in the following areas: 1. Consideration of mechanisms that allow UEs to quickly access cells that support the intended slice a. Slice-based cell reselection under network control b. Slice-based RACH configuration or access barring It may also be considered whether existing mechanisms meet this scenario or requirement. 2. Consider the need and mechanisms for supporting service continuity a. Regarding service interruption due to intra-RAT handover. Consider slice remapping, fallback and data forwarding procedures, e.g. in case the target gNB does not support the UE's ongoing slice. Coordination with SA2 is required.

[0021] Figure 1 illustrates use cases in which an active PDU session of a UE is released during handover if the target cell does not support a network slice with an active PDU session on the network slice of the UE. The following use cases are possible: The UE is registered with S-NSSAI-1, S-NSSAI-2, S-NSSAI-3, and S-NSSAI-4 and the UE is in connected mode, i.e. the UE has an active PDU session with S-NSSAI-3. -S-NSSAI-3 is not uniformly supported across PLMNs (as per current agreement of 3GPP specifications). - The UE is moving towards the edge of its current registration area, towards the coverage of Cell-1 supporting S-NSSAI-1 and Cell-2 supporting S-NSSAI-4. Both cells, Cell-1 and Cell-2, are eligible as target cells for handover.

[0022] Problem: In the related art, as shown in FIG. 1, the target cell Cell-1 or Cell-2 does not support the network slice S-NSSAI-3 on which the UE has an active PDU session, so the PDU session on S-NSSAI-3 is released upon handover to the target cell Cell-1 or Cell-2. One of the problems for the present disclosure is how to direct a UE in a connected mode (e.g., handover) to a target cell to support service continuity when a network slice (e.g., S-NSSAI-3) with an active PDU session on the network slice is not supported by the target cell.

[0023] (Description of the Mode) The present disclosure describes several aspects and variations of each example, which can be combined with each other in any combination.

[0024] The present disclosure relates to communication systems. The present disclosure has particular, but not exclusive, relevance to wireless communication systems and devices thereof operating in accordance with 3rd Generation Partnership Project (3GPP) standards or equivalents or derivatives thereof. The present disclosure has particular, but not exclusive, relevance to network slicing and handover in so-called "5G" (or "next generation") systems.

[0025] From another perspective, the present disclosure proposes providing an alternative network slice by a UE or a network to support service continuity during handover. A method is proposed for transferring a PDU session to an alternative network slice during handover when a current network slice having an active PDU session on the current network slice is not supported by a target cell. This can improve service continuity when a network slice having an active PDU session is not supported or permitted by a target cell.

[0026] (First embodiment) Hereinafter, the first embodiment of the present disclosure will be described with reference to the accompanying drawings. The following detailed description is merely exemplary in nature and is not intended to limit the present disclosure or the application and use of the present disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the present disclosure or the following detailed description.

[0027] (Solution 1 - Supporting UE with Alternate Network Slices for PDU Session Continuity) Solution 1 proposes PDU session transfer to an alternative network slice during handover if the current network slice with an active PDU session on the current network slice is not supported by the target cell. Service continuity can be improved by transferring active PDU sessions on the current network slice to an alternative network slice, thereby maintaining service continuity instead of releasing the PDU sessions. In this solution, alternative network slices for established PDU sessions are provided by the UE as new parameters in the PDU session establishment request message or service request message, and then the AMF further provides these alternative network slices to the RAN nodes to assist potential Xn and N2 handovers.

[0028] FIG. 2 is a schematic timing (signaling) diagram illustrating an exemplary method of UE assistance with alternative network slices for PDU session continuity in Xn handover.

[0029] 1) PDU Session Establishment Request / Service Request (S-NSSAI-3, Alternative S-NSSAI = S-NSSAI-1, S-NSSAI-2): An application of UE 101 requires a service. UE 101 checks the Network Slice Selection Policy (NSSP) in the UE Route Selection Policy (URSP) rule in UE policy and discovers the network slices (S-NSSAI-3, S-NSSAI-1, S-NSSAI-2, etc.) where the application can receive the service. UE 101 registers with all these network slices. Based on the request from the application, UE 101 sends a PDU Session Establishment Request message or a Service Request message, for example with network slice S-NSSAI-3, to AMF 104. In addition to the network slice S-NSSAI-3 included in the PDU Session Establishment Request message or the Service Request message (where the PDU session is established or reactivated), UE 101 also includes a new parameter "Alternative S-NSSAI" in the PDU Session Establishment Request message or the Service Request message. UE 101 deploys a network slice that is compatible with services other than S-NSSAI-3 that require applications in UE 101 (e.g., S-NSSAI-1 and S-NSSAI-2).

[0030] The new parameters may be configured with a priority or preferred order among the alternative S-NSSAIs. For example, if the "Alternative S-NSSAI" parameter is configured as Alternative S-NSSAI=S-NSSAI-1,S-NSSAI-2, it means that the UE 101 wants to use S-NSSAI-1 instead of S-NSSAI-2 as the alternative S-NSSAI for S-NSSAI-3. This new parameter may be called "Alternative S-NSSAI", "Alternative Network Slice", "Backup Network Slice", "Backup S-NSSAI", or any other name or notation of a parameter intended to convey information of a network slice that a service requiring application in the UE 101 can handle based on NSSP / URSP rules in the UE 101. The "Alternative Network Slice" may also be a default allowed S-NSSAI in the UE 101 if available. The "Alternative Network Slice" may be delivered by the UE 101 to the network via other NAS messages.

[0031] In one example, the AMF 104 may obtain an alternative S-NSSAI for each S-NSSAI in the subscribed NSSAI during the registration procedure or during the subscriber data update notification procedure to the AMF, as described in 3GPP Technical Specification (TS) 3GPP TS 23.502: “Procedures for the 5G System (5GS)” V16.5.0 (2020-07) (hereinafter referred to as 3GPP TS 23.502). In this case, the Nudm_SDM_Get service is used during the registration procedure, and the Nudm_SDM_Notification service is used during the subscriber data update notification procedure to the AMF.

[0032] In another example, the SMF 104 may obtain an alternative S-NSSAI for each S-NSSAI in the subscribed NSSAI during the registration procedure or during the subscriber data update notification procedure to the SMF 104, as described in 3GPP TS 23.502. In this case, the Nudm_SDM_Get service is used during the registration procedure and the Nudm_SDM_Notification service is used during the subscriber data update notification procedure to the SMF.

[0033] 2) PDU session establishment in S-NSSAI-3 based on 3GPP TS 23.502.

[0034] 3) N2 Message (S-NSSAI-3, Alternate S-NSSAI = S-NSSAI-1, S-NSSAI-2) - At the end of the PDU session establishment procedure on network slice S-NSSAI-3, the AMF 104 sends an N2 message (or other message on the N2 interface between the AMF 104 and the RAN node) to the source RAN (S-RAN) node 102 including parameters of the current network slice (e.g., S-NSSAI-3) on which the PDU session was established. If there is an alternative network slice, it includes, for example, S-NSSAI-1 and S-NSSAI-2, among the new "Alternative S-NSSAI" parameters.

[0035] The new parameters may be configured with a priority or preferred order among the alternative S-NSSAIs. This new parameter in the N2 message may be called "alternative S-NSSAI", "alternative network slice", "backup network slice", "backup S-NSSAI" or any other name or notation of a parameter intended to convey information of a network slice that an application in the UE 101 can handle. The alternative network slices S-NSSAI-1 and S-NSSAI-2 that the AMF 104 includes in the "alternative S-NSSAI" parameter of the N2 message are the ones that the AMF 104 received from the UE 101 in the PDU session establishment request message or the service request message. The "alternative network slice" may also be a default allowed S-NSSAI in the AMF 104 or UDM / UDR 105, if available. When the AMF 104 sends the N2 message including the alternative S-NSSAI to the S-RAN node 102, the AMF 104 can verify that the SMF 104 associated with the PDU session is accessible from any alternative S-NSSAI.

[0036] 4) At some stage, a handover is required: there is no target cell supporting S-NSSAI-3 for which UE 101 has an active PDU session, however there is a target cell supporting an alternative network slice, e.g., an alternative S-NSSAI=S-NSSAI-1.

[0037] 5) Handover to a target cell supporting an alternative network slice S-NSSAI-1. The S-RAN node 102 selects a target cell supporting one of the alternative network slices, for example the alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available in any of the target cells, the S-RAN node 102 must consider the priority between the alternative network slices when selecting a target cell. If both the alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available in the target cell, the S-RAN node 102 selects the alternative network slice S-NSSAI-1 taking the priority into consideration.

[0038] 6) PDU session modification with alternative network slice S-NSSAI-1 based on 3GPP TS 23.502. -AMF 104 triggers the PDU session modification procedure to replace the current S-NSSAI, i.e., S-NSSAI-3, with the alternative network slice S-NSSAI-1. Since the S-NSSAI is exchanged during this procedure, SMF 104 may contact the PCF and / or CHF (Charging Function) to issue separate CDRs for the original S-NSSAI-3 and the alternative network slice S-NSSAI-1.

[0039] 7) During the PDU session modification procedure, when the AMF 104 sends an N2 message to the T-RAN node 103, the N2 message includes the following parameters:

[0040] N2 Message (S-NSSAI-1, Original S-NSSAI = S-NSSAI-3, Alternate S-NSSAI = S-NSSAI-2, NAS Message (PDU Session ID, N1 SM Container (PDU Session Modification Command (New S-NSSAI = S-NSSAI-1)))) - During the PDU session modification procedure to exchange the network slice S-NSSAI-1, the AMF 104 may send an N2 message to the target RAN (T-RAN) node 103. Along with the network slice on which the PDU session is established, the AMF 104 includes two new parameters in the N2 message (or any other message on the N2 interface between the AMF 104 and the RAN node). - Original S-NSSAI - AMF 104 places in this parameter the initial network slice where the PDU session was transferred to one of the alternative network slices in the last handover, e.g. S-NSSAI-3. This new parameter can be called "Original S-NSSAI", "Original Network Slice", "Initial Network Slice", "Initial S-NSSAI", "UE Requested S-NSSAI", or any name or notation of a parameter intended to convey information of the network slice where the PDU session was established in the PDU Session Establishment procedure as described in 3GPP TS 23.502. Alternative S-NSSAI - the AMF 104 places in this parameter one of the remaining alternative network slices received with the PDU Session Establishment Request message or Service Request message from the UE 101, e.g. S-NSSAI-2. The alternative network slice can also be an S-NSSAI allowed by default in the AMF 104 or UDM / UDR 105 if available.

[0041] The alternative S-NSSAI may also indicate an alternative network slice to be used for the PDU session after a successful handover procedure.

[0042] 8) During the PDU session modification procedure, when the SMF 104 sends a PDU session modification command to the UE 101 via the AMF 104 and the T-RAN node 103 (in an N2 message on the AMF 104 to T-RAN node interface), the PDU session modification command includes a new S-NSSAI parameter (e.g. S-NSSAI-1) to inform the UE 101 that the S-NSSAI (e.g. S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g. S-NSSAI-1). The T-RAN node 103 sends the PDU session modification command received from the SMF 104 via the AMF 104 (in an N2 message on the AMF 104 to T-RAN node interface) to the UE 101. With this information, the UE 101 updates the network slice state at the UE 101.

[0043] In one example, instead of sending a PDU session modification message to UE 101, AMF 104 may send a UE configuration update message to UE 101 via T-RAN node 103 to inform UE 101 that the S-NSSAI (e.g., S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g., S-NSSAI-1).

[0044] 9) At some later stage, a handover is required. When selecting a target cell, if there are multiple eligible cells supporting different network slices, the T-RAN node 103 may select the target cell in the following order of priority: - "Original S-NSSAI" - The T-RAN node 103 may prefer the original network slice (e.g. S-NSSAI-3) first when selecting a target cell, which allows the PDU session to be moved back to the network slice where the PDU session was originally established, as this may be the best network slice for the PDU session (e.g. S-NSSAI-3). - Current network slice - If the target cell does not support the original network slice (e.g. S-NSSAI-3), the T-RAN node 103 preferably selects a target cell that supports the current network slice where the PDU session is currently active, e.g. S-NSSAI-1. - "Alternative S-NSSAI" - If there is no target cell supporting the original network slice (e.g. S-NSSAI-3) or the current network slice (e.g. S-NSSAI-1), the T-RAN node 103 may prioritize a target cell supporting an alternative network slice, e.g. S-NSSAI-2, if available.

[0045] It should be noted that the (source / target) RAN node may apply a different order in selecting a target cell, for example, giving priority first to a target cell supporting a current network slice (e.g., S-NSSAI-1) with an active PDU session, then the original S-NSSAI (e.g., S-NSSAI-3) if available, and finally another S-NSSAI (e.g., S-NSSAI-2) if available. The (source / target) RAN node may apply any other order of priority, for example, an operator-defined or configured order between the original, current, and alternative network slices.

[0046] While Figure 2 shows a solution for UE 101 assistance with alternative network slices for PDU session continuity during handover, it should also be noted that step 6 as well as steps 7 and 8 can only be used in the following cases to exchange S-NSSAI on an active PDU session without releasing the PDU session: - Slice congestion detected by AMF / SMF 104 or via NWDAF (Network Data Analytics Function). If the network slice indicated by the S-NSSAI used for an active PDU session becomes congested, the AMF / SMF 104 may initiate step 6 of replacing the S-NSSAI used for the PDU session with another S-NSSAI by indicating a less congested network slice. This action allows the AMF / SMF 104 to reduce traffic on the congested network slice. - Revocation of S-NSSAI from subscriber data: When an S-NSSAI associated with an active PDU session is derived from the subscriber data in the UDM 105, this subscriber data update is reported to the AMF 104. In this case, the AMF 104 may initiate step 6 to replace the S-NSSAI derived in the subscriber data with another S-NSSAI instead of releasing the associated PDU session. This action allows the AMF / SMF 104 to provide a better service experience since the active PDU session may survive. - Network slice specific authentication and authorization failure. If network slice specific (re)authentication and (re)authorization fails for an S-NSSAI associated with an active PDU session, the AMF 104 may initiate step 6 to replace the S-NSSAI that failed for network slice specific authentication and authorization with another S-NSSAI instead of releasing the associated PDU session. This action allows the AMF / SMF 104 to provide a better service experience since the active PDU session may survive. - Revocation of network slice specific authentication and authorization. When network slice specific (re)authentication and (re)authorization for an S-NSSAI associated with an active PDU session is revoked, the AMF 104 may initiate step 6 to replace the revoked S-NSSAI for network slice specific authentication and authorization with another S-NSSAI instead of releasing the associated PDU session. This action allows the AMF / SMF 104 to provide a better service experience since the active PDU session may survive.

[0047] Also note that this alternative is applicable to other use cases / solutions in this disclosure.

[0048] 3 is a schematic timing (signaling) diagram illustrating an example method of UE assistance with an alternative network slice for PDU session continuity in N2 handover (use case 1), in which the alternative network slice in the target cell is reconfirmed as an allowed network slice during the registration process in the target AMF (T-AMF) after N2 handover.

[0049] 1) PDU Session Establishment Request / Service Request (S-NSSAI-3, Alternative S-NSSAI = S-NSSAI-1, S-NSSAI-2): An application of UE 201 requires a service. UE 201 checks the Network Slice Selection Policy (NSSP) in the UE Route Selection Policy (URSP) rule in the UE policy and discovers the network slices (S-NSSAI-3, S-NSSAI-1, S-NSSAI-2, etc.) where the application can receive the service. UE 201 is registered in all these network slices. UE 201 sends a PDU Session Establishment Request message or a Service Request message on network slice S-NSSAI-3, for example, to source AMF (S-AMF) 204 based on the request from the application. In addition to the network slice S-NSSAI-3 included in the PDU session establishment request message or the service request message (where a PDU session is established or reactivated), the UE 201 also includes in the PDU session establishment request message or the service request message a new parameter "Alternative S-NSSAI", in which the UE 201 places in the UE 201 a network slice (e.g., S-NSSAI-1 and S-NSSAI-2) that is also compatible with the service requiring the application.

[0050] The new parameter may be configured with a priority or preferred order between the alternative S-NSSAIs. For example, if the "Alternative S-NSSAI" parameter is configured as Alternate S-NSSAI=S-NSSAI-1,S-NSSAI-2, it means that the UE 201 wants to use S-NSSAI-1 instead of S-NSSAI-2 as the alternative S-NSSAI for S-NSSAI-3. This new parameter may be called "Alternative S-NSSAI", "Alternative Network Slice", "Backup Network Slice", "Backup S-NSSAI", or any other name or notation of a parameter intended to convey information of a network slice that a service requiring application in the UE 201 can process based on the NSSP / URSP rules of the UE 201. The "Alternative Network Slice" may also be a default allowed S-NSSAI in the UE 201, if possible. The "Alternative Network Slice" may be delivered by the UE 201 to the network via other NAS messages.

[0051] In one example, the AMF 204 may obtain an alternative S-NSSAI for each S-NSSAI in the subscriber NSSAI during a registration procedure or during a subscriber data update notification procedure to the AMF, as described in 3GPP TS 23.502, in which case the Nudm_SDM_Get service is used during the registration procedure and the Nudm_SDM_Notification service is used during a subscriber data update notification to the AMF.

[0052] In another example, the SMF may obtain an alternative S-NSSAI for each S-NSSAI in the subscribed NSSAI during the registration procedure or during the subscriber data update notification procedure to the SMF, as described in 3GPP TS 23.502. In this case, the Nudm_SDM_Get service is used during the registration procedure and the Nudm_SDM_Notification service is used during the subscriber data update notification to the AMF.

[0053] 2) PDU session establishment in S-NSSAI-3 based on 3GPP TS 23.502.

[0054] 3) N2 message (S-NSSAI-3, Alternate S-NSSAI = S-NSSAI-1, S-NSSAI-2) - Upon completion of the PDU session establishment procedure on network slice S-NSSAI-3, the source AMF (S-AMF) 204 sends to the S-RAN node 202 an N2 message (or other message on the N2 interface between the S-AMF 204 and the S-RAN node 202) including parameters of the current network slice (e.g. S-NSSAI-3) on which the PDU session was established, and also includes the alternative network slice, if any, in the new "Alternative S-NSSAI" parameters, e.g. S-NSSAI-1 or S-NSSAI-2.

[0055] The new parameters may be configured with a priority or preferred order among the alternative S-NSSAIs. This new parameter in the N2 message may be called "alternative S-NSSAI", "alternative network slice", "backup network slice", "backup S-NSSAI", or any other name or notation of a parameter intended to convey information of a network slice that an application in the UE 201 can handle. The alternative network slices S-NSSAI-1 and S-NSSAI-2 that the S-AMF 204 includes in the "alternative S-NSSAI" parameter of the N2 message are the ones that the S-AMF 204 received from the UE 201 in the PDU session establishment request message or the service request message. The "alternative network slice" may also be an S-NSSAI that is allowed by default in the S-AMF 204 or the UDM / UDR 206, if available.

[0056] When the S-AMF 204 sends an N2 message including an alternative S-NSSAI to the S-RAN node 202, the S-AMF 204 can verify that the SMF associated with the PDU session is accessible from any alternative S-NSSAI.

[0057] 4) At some stage, a handover is required. There is no target cell supporting S-NSSAI-3 for which UE 201 has an active PDU session. However, there is a target cell supporting an alternative network slice, e.g., an alternative S-NSSAI=S-NSSAI-1.

[0058] 5) Handover to a target cell supporting an alternative network slice S-NSSAI-1. The S-RAN node 202 selects a target cell supporting one of the alternative network slices, for example, the alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available in any of the target cells, the S-RAN node 202 must consider the priority between the alternative network slices when selecting a target cell. If both the alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available in the target cell, the S-RAN node 202 selects the alternative network slice S-NSSAI-1 by considering the priority. During the N2 handover, the S-AMF 204 forwards the original S-NSSAI-3 and the alternative S-NSSAI-1 and S-NSSAI-2 to the T-AMF 205.

[0059] 6) Registration with T-AMF 205 based on 3GPP TS 23.502. During the registration procedure, S-NSSAI-1 is reconfirmed as an allowed network slice.

[0060] 7) PDU session modification with alternative network slice S-NSSAI-1 based on 3GPP TS 23.502. - T-AMF 205 triggers a PDU session modification change to replace the current S-NSSAI, i.e. S-NSSAI-3, with the alternative network slice S-NSSAI-1.

[0061] Since the S-NSSAI is exchanged during this procedure, the SMF may contact the PCF and / or CHF to issue separate CDRs for the original S-NSSAI-3 and the alternative network slice S-NSSAI-1.

[0062] 8) During the PDU session modification procedure, when the T-AMF 205 sends an N2 message to the T-RAN node 203, the N2 message includes the following parameters:

[0063] During the PDU session modification on the alternative network slice S-NSSAI-1, the T-AMF 205 may send the N2 message to the T-RAN node 203. Along with the network slice on which the PDU session is established, the T-AMF 205 also includes two new parameters in the N2 message to the T-RAN node 203 (or any other message on the N2 interface between the T-AMF 205 and the T-RAN node 203). -Original S-NSSAI - T-AMF 205 places in this parameter the initial network slice where the PDU session was transferred to one of the alternative network slices in the last handover, e.g. S-NSSAI-3. This new parameter can be called "Original S-NSSAI", "Original Network Slice", "Initial Network Slice", "Initial S-NSSAI", "UE Requested S-NSSAI", or any other name or notation of a parameter intended to convey information of the network slice where the PDU session was established in the PDU Session Establishment procedure as described in 3GPP TS 23.502. Alternative S-NSSAI - the T-AMF 205 places in this parameter one of the remaining alternative network slices, e.g. S-NSSAI-2, received with the PDU session establishment request message or service request message from the UE 201. The alternative network slice can also be an S-NSSAI allowed by default in the T-AMF 205 or UDM / UDR 206, if available.

[0064] The alternative S-NSSAI may also indicate an alternative network slice to be used for the PDU session after a successful handover procedure.

[0065] 9) During the PDU session modification procedure, when the SMF sends a PDU session modification command to the UE 201 via the T-AMF 205 and the T-RAN node 203 (in an N2 message to the T-RAN node interface on the T-AMF 205), the PDU session modification command includes a new S-NSSAI parameter (e.g., S-NSSAI-1) to inform the UE 201 that the S-NSSAI (e.g., S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g., S-NSSAI-1). The T-RAN node 203 sends the PDU session modification command received via the T-AMF 205 (in an N2 message to the T-RAN node interface on the T-AMF 205) from the SMF to the UE 201. With this information, the UE 201 updates the network slice state at the UE 201. In one example, instead of sending a PDU session modification message to the UE 201, the T-AMF 205 may send a UE configuration update message to the UE 201 via the T-RAN node 203 to inform the UE 201 that the S-NSSAI (e.g., S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g., S-NSSAI-1).

[0066] 10) At some later stage, a handover is required. When selecting a target cell, if there are multiple eligible cells, the T-RAN node 203 may select the target cell in the following order of priority: - "Original S-NSSAI" - The T-RAN node 203 may first prioritize the original network slice (e.g. S-NSSAI-3) when selecting a target cell, so that the PDU session can be moved back to the network slice where the PDU session was originally established, as this may be the best network slice for the PDU session. - Current network slice - If the target cell does not support the original network slice (e.g. S-NSSAI-3), the T-RAN node 203 preferably selects a target cell that supports the current network slice on which the PDU session is currently active, e.g. S-NSSAI-1. - "Alternative S-NSSAI" - If there is no target cell supporting the original or current network slice, the T-RAN node 203 may prioritize a target cell supporting an alternative network slice, e.g. S-NSSAI-2, if available.

[0067] It should be noted that the RAN nodes (both S-RAN and T-RAN) may apply alternative orders when selecting a target cell, for example, first giving priority to the target cell supporting the current network slice (e.g. S-NSSAI-1) with an active PDU session, then giving priority to the original S-NSSAI (e.g. S-NSSAI-3) if available, and finally giving priority to the alternative S-NSSAI (e.g. S-NSSAI-2) if available. The RAN node may also apply any other order of priority, for example, an operator-defined or configured order between the original, current, and alternative network slices.

[0068] 4 is a schematic timing (signaling) diagram illustrating an exemplary method of UE assistance with an alternative network slice for PDU session continuity in N2 handover (use case 2). In use case 2, during the registration process in the T-AMF 305 after N2 handover, the alternative network slice in the target cell is not reconfirmed as an allowed network slice. In this case, the T-AMF 305 may transfer the PDU session to another alternative S-NSSAI (e.g., S-NSSAI-2) if available or to the default network slice in the new registration area.

[0069] 1) PDU Session Establishment Request / Service Request (S-NSSAI-3, Alternative S-NSSAI = S-NSSAI-1, S-NSSAI-2) - An application in UE 301 requires a service. UE 301 checks the NSSP (Network Slice Selection Policy) in the URSP (UE Route Selection Policy) rule in the UE policy and discovers the network slices (e.g. S-NSSAI-3, S-NSSAI-1, S-NSSAI-2) from which the application can receive the service. UE 301 is registered in all these network slices. UE 301 sends a PDU Session Establishment Request message or a Service Request message in, for example, network slice S-NSSAI-3 to S-AMF 304 based on the request from the application. In addition to the network slice S-NSSAI-3 included in the PDU session establishment request message or service request message (where a PDU session is established or reactivated), the UE301 also includes a new parameter “Alternative S-NSSAI” in the PDU session establishment request message or service request message, and the UE301 configures a network slice (e.g., S-NSSAI-1 and S-NSSAI-2) that is also compatible with the service requiring the application in the UE301.

[0070] The new parameter may be configured with a priority or preferred order between the alternative S-NSSAIs. For example, if the "Alternative S-NSSAI" parameter is configured as Alternate S-NSSAI=S-NSSAI-1,S-NSSAI-2, it means that UE301 wants to use S-NSSAI-1 instead of S-NSSAI-2 as the alternative S-NSSAI for S-NSSAI-3. This new parameter may be called "Alternative S-NSSAI", "Alternative Network Slice", "Backup Network Slice", "Backup S-NSSAI", or any other name or notation of a parameter intended to convey information of a network slice that a service requiring application in UE301 can process based on NSSP / URSP rules of UE301. The alternative network slice may also be an S-NSSAI that is allowed by default in UE301, if possible. The alternative network slice may be delivered by UE301 to the network via other NAS messages.

[0071] In one example, the S-AMF 304 may obtain an alternative S-NSSAI for each S-NSSAI in the subscribed NSSAI during the registration procedure or during the subscriber data update notification procedure to the AMF, as described in 3GPP TS 23.502, in which case the Nudm_SDM_Get service is used during the registration procedure and the Nudm_SDM_Notification service is used during the subscriber data update notification procedure to the AMF.

[0072] In another example, the SMF may obtain an alternative S-NSSAI for each S-NSSAI in the subscribed NSSAI during the registration procedure or during the subscriber data update notification procedure to the SMF, as described in 3GPP TS 23.502. In this case, the Nudm_SDM_Get service is used during the registration procedure and the Nudm_SDM_Notification service is used during the subscriber data update notification procedure to the AMF.

[0073] 2) PDU session establishment in S-NSSAI-3 based on 3GPP TS 23.502.

[0074] 3) N2 message (S-NSSAI-3, Alternate S-NSSAI = S-NSSAI-1, S-NSSAI-2) - Upon completion of the PDU session establishment procedure on network slice S-NSSAI-3, the S-AMF 304 sends to the S-RAN node 302 an N2 message (or other message on the N2 interface between the S-AMF 304 and the S-RAN node 302) including parameters of the current network slice (e.g. S-NSSAI-3) on which the PDU session was established, and also includes alternative network slices, if any, in the new "Alternate S-NSSAI" parameters, e.g. S-NSSAI-1 and S-NSSAI-2.

[0075] The new parameters may be configured with a priority or preferred order among the alternative S-NSSAIs. This new parameter in the N2 message may be called "alternative S-NSSAI", "alternative network slice", "backup network slice", "backup S-NSSAI", or any other name or notation of a parameter intended to convey information of a network slice that an application in the UE 301 can handle. The alternative network slices S-NSSAI-1 and S-NSSAI-2 that the AMF 304 includes in the "alternative S-NSSAI" parameter of the N2 message are the ones that the AMF 304 received from the UE 301 in the PDU session establishment request message or the service request message. The alternative network slices may also be S-NSSAIs that are allowed by default in the S-AMF 304 or UDM / UDR 306, if available. When the S-AMF 304 sends the N2 message including the alternative S-NSSAI to the S-RAN node 302, the S-AMF 304 may verify that the SMF related to the PDU session is accessible from any alternative S-NSSAI.

[0076] 4) At some stage, a handover is required. There is no target cell supporting S-NSSAI-3 for which UE 301 has an active PDU session. However, there is a target cell supporting an alternative network slice, e.g., an alternative S-NSSAI=S-NSSAI-1.

[0077] 5) Handover to a target cell supporting an alternative network slice S-NSSAI-1. The S-RAN node 302 selects a target cell supporting one of the alternative network slices, for example, the alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available in any of the target cells, the S-RAN node 302 must consider the priority between the alternative network slices when selecting a target cell. If both the alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available in the target cell, the S-RAN node 302 selects the alternative network slice S-NSSAI-1 by considering the priority. During the N2 handover, the S-AMF 304 forwards the original S-NSSAI-3 and the alternative S-NSSAI-1 and S-NSSAI-2 to the T-AMF 305.

[0078] 6) Registration with T-AMF 305 based on 3GPP TS 23.502. The registration procedure does not re-validate S-NSSAI-1 as an allowed network slice.

[0079] 7) PDU session modification with alternative network slice S-NSSAI-2 or default S-NSSAI based on 3GPP TS 23.502 - Since the alternative network slice S-NSSAI-1 is not an allowed network slice in the new registration area, the T-AMF 305 triggers a PDU session modification procedure with another alternative network slice (e.g. S-NSSAI-2) or default network slice. Since the S-NSSAI is exchanged during this procedure, the SMF may contact the PCF and / or CHF to issue separate CDRs for the original S-NSSAI-3 and the alternative network slice S-NSSAI-2 or default network slice.

[0080] 8) During the PDU session modification procedure, when the T-AMF 305 sends an N2 message to the T-RAN node 303, the N2 message includes the following parameters:

[0081] During the PDU session modification at the N2 Message (S-NSSAI-2 / Default S-NSSAI, Original S-NSSAI=S-NSSAI-3, Alternate S-NSSAI=S-NSSAI-1, NAS Message (PDU Session ID, N1 SM Container (PDU Session Modification Command (New S-NSSAI=S-NSSAI-1)))) - Network Slice S-NSSAI-2 / Default S-NSSAI, the T-AMF 305 may send the N2 message to the T-RAN node 303. Along with the network slice where the PDU session is established, the T-AMF 305 also includes two new parameters in the N2 message to the T-RAN node 303 (or any other message on the N2 interface between the AMF 305 and the RAN node 303). -Original S-NSSAI - T-AMF 305 places in this parameter the initial network slice where the PDU session was transferred to one of the alternative network slices in the last handover, e.g. S-NSSAI-3. This new parameter can be called "Original S-NSSAI", "Original Network Slice", "Initial Network Slice", "Initial S-NSSAI", "UE Requested S-NSSAI", or any other name or notation of a parameter intended to convey information of the network slice where the PDU session was established in the PDU Session Establishment procedure as described in 3GPP TS 23.502. Alternative S-NSSAI - the T-AMF 305 places in this parameter one of the remaining alternative network slices received with the PDU session establishment request message or service request message from the UE 301 (e.g. in this case the S-NSSAI-1 rejected upon registration to the T-AMF 305 can still act as an alternative S-NSSAI). The alternative S-NSSAI may also indicate an alternative network slice to be used for the PDU session after a successful handover procedure.

[0082] 9) During the PDU session modification procedure, when the SMF sends a PDU session modification command to the UE 301 via the T-AMF 305 (in an N2 message to the T-RAN node interface on the T-AMF 305) and the T-RAN node 303, the PDU session modification command includes a new S-NSSAI parameter (e.g. S-NSSAI-2) to inform the UE 301 that the S-NSSAI (e.g. S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g. S-NSSAI-2). The T-RAN node 303 sends the PDU session modification command received from the SMF via the T-AMF 305 (in an N2 message on the T-AMF 305) to the UE 301. With this information, the UE 301 updates the network slice state at the UE 301.

[0083] In one example, instead of sending a PDU session modification message to UE 301, T-AMF 305 may send a UE configuration update message to UE 301 via T-RAN node 303 to inform UE 301 that the S-NSSAI (e.g., S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g., S-NSSAI-2).

[0084] 10) A handover is also required at some later stage. When selecting a target cell, if there are multiple eligible cells, the T-RAN node 303 may select the target cell in the following order of priority: - "Original S-NSSAI" - The T-RAN node 303 may prefer the original network slice (e.g. S-NSSAI-3) first when selecting a target cell, thereby moving the PDU session back to the network slice where it was originally established, as this may be the best network slice for the PDU session. - Current network slice - If the target cell does not support the original network slice (e.g. S-NSSAI-3), the T-RAN node 303 preferably selects a target cell that supports the current network slice on which the PDU session is currently active, e.g. S-NSSAI-2 / Default S-NSSAI. - "Alternative S-NSSAI" - If there is no target cell supporting either the original or the current network slice, the T-RAN node 303 may prioritize a target cell supporting an alternative network slice, e.g. S-NSSAI-1, if available.

[0085] It should be noted that the RAN nodes (both S-RAN and T-RAN nodes) may apply alternative orders when selecting a target cell, e.g., first giving priority to the target cell supporting the current network slice (e.g., S-NSSAI-2) with an active PDU session, then giving priority to the original S-NSSAI (e.g., S-NSSAI-3) if available, and finally giving priority to the alternative S-NSSAI (e.g., S-NSSAI-1) if available. The RAN node may also apply any other order of priority, e.g., an operator-defined or configured order between the original, current, and alternative network slices.

[0086] (Solution 2 - Core Network Support Using Alternate Network Slices for PDU Session Continuity) Solution 2 proposes PDU session transfer to an alternative network slice at handover when the current network slice with active PDU sessions on the current network slice is not supported by the target cell. This allows to improve service continuity by transferring active PDU sessions on the current network slice to another network slice instead of releasing the PDU sessions. In this solution, an alternative network slice for the PDU session to be established is provided by the network. The NSSP rules of the UE are obtained from the URSP rules in the PCF by the AMF or SMF during the PDU session establishment / modification procedure. The AMF or SMF discovers alternative network slices, if they exist, that are compatible with the current PDU session from the NSSP / URSP rules of the UE. For example, the current PDU session can be transferred to them if necessary. The AMF or SMF then provides these alternative network slices to the RAN node in the core network assistance parameters in the N2 message or in the new parameters in the N2 message to assist potential Xn and N2 handovers.

[0087] FIG. 5 is a schematic timing (signaling) diagram illustrating an example method of core network assistance using alternative network slices for PDU session continuity in Xn handover.

[0088] 1) PDU Session Establishment Request / Service Request (Application ID, S-NSSAI-3, PDU Session ID, DNN ID) - An application of UE 401 requires a service. UE 401 checks the Network Slice Selection Policy (NSSP) in the UE Route Selection Policy (URSP) rules in the UE policy and discovers the network slices (S-NSSAI-3, S-NSSAI-1, S-NSSAI-2, etc.) where the application can receive the service. UE 401 registers with all these network slices. UE 401 sends a PDU Session Establishment Request message or a Service Request message on network slice S-NSSAI-3 to AMF 404 based on the request from the application. UE 401 may also include an application ID, e.g., the application ID in the PDU Session Establishment Request or Service Request message. This allows the application ID to assist AMF 404 or SMF 404 to find an alternative network slice for network slice S-NSSAI-3 from the NSSP / URSP rules of UE 401.

[0089] 2) Continue the PDU session establishment procedure or service request procedure with S-NSSAI-3 according to 3GPP TS 23.502.

[0090] 3) AMF / SMF Association with PCF (NSSP / URSP) - The AMF 404 or SMF 404 may interact with the PCF 405 during association with the PCF 405 to discover a compatible network slice instead of the network slice S-NSSAI-3 on which the PDU session is established.

[0091] The AMF 404 may do one of the following during UE policy association establishment with the PCF 405: a) Requesting URSP or NSSP rules for the UE 401 from the PCF 405 via an Npcf_UEPolicy_Contol_Create Request message. In this case, the AMF 404 includes new parameters (e.g., URSP flags, NSSP flags, or other names for parameters intended to request URSP or NSSP information from the PCF 405) in the Npcf_UEPolicy_Contol_Create Request message; or b) Request a list of network slices compatible with the current network slice S-NSSAI-3 via the Npcf_UEPolicy_Contol_Create Request message. In this case, AMF 404 may include in the Npcf_UEPolicy_Contol_Create Request message the identity of the application that triggered the PDU session establishment (e.g., App ID), the network slice identity (e.g., S-NSSAI-3) on which the PDU session is established, or a DNN ID to help PCF 405 find network slices compatible with network slice S-NSSAI-3.

[0092] The PCF 405 may provide the requested information (i.e., URSP or NSSP rules for the UE) or a list of network slices compatible with the network slice S-NSSAI-3 in the Npcf_UEPolict_Control_Create Response message.

[0093] It should be noted that the AMF 404 may also use any other existing procedures or services provided by the PCF 405 to retrieve URSP or NSSP related information from the PCF 405.

[0094] The SMF 404 may do any of the following during SM policy association establishment or SM policy association modification with the PCF 405: a) Request URSP or NSSP rules for the UE 401 from the PCF 405 via an Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF 404 includes a new parameter (e.g., a URSP or NSSP flag, or other name of the parameter intended to request URSP or NSSP information from the PCF 405) in the Npcf_SMPolicy_Contol_Create Request message; or b) Request a list of network slices compatible with the current network slice S-NSSAI-3 via the Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF 404 may include in the Npcf_SMPolicy_Contol_Create Request message the application identity (e.g., App ID) that triggered the PDU session establishment, the network slice ID (e.g., S-NSSAI-3) on which the PDU session is established, or a DNN ID to help the PCF 405 find network slices compatible with the network slice S-NSSAI-3.

[0095] The PCF 405 may provide the requested information (i.e., URSP or NSSP rules for the UE 401) or a list of network slices compatible with the S-NSSAI-3 in the Npcf_SMPolicy_Control_Create Response message.

[0096] It should be noted that the SMF 404 may also use any other existing procedures or services provided by the PCF 405 to retrieve URSP or NSSP related information from the PCF 405.

[0097] 4) N2 message (S-NSSAI-3, Alternate S-NSSAI = S-NSSAI-1, S-NSSAI-2) - At the end of the PDU session establishment procedure on network slice S-NSSAI-3, the AMF 404 sends an N2 message (or other message on the N2 interface between the AMF 404 and the RAN node) to the S-RAN node 402. This N2 message contains parameters regarding the current network slice (e.g. S-NSSAI-3) on which the PDU session was established, and further contains in the new "Alternative S-NSSAI" parameter the alternative network slices (e.g. S-NSSAI-1 and S-NSSAI-2) from which the UE 401's URSP or NSSP rules as described in step 3 were originally obtained either directly from the PCF 405 or from the URSP or NSSP rules of the UE 401.

[0098] The new parameters may be configured with a priority or preferred order among the alternative S-NSSAIs. This new parameter in the N2 message may be called "alternative S-NSSAI", "alternative network slice", "backup network slice", "backup S-NSSAI", or any other name or notation of a parameter intended to convey information of a network slice that the service requiring application in the UE 401 can handle. The alternative network slice may also be an S-NSSAI that is allowed by default in the AMF 404 or UDM / UDR 406, if available.

[0099] When the AMF 404 sends an N2 message including an alternative S-NSSAI to the S-RAN node 402, the AMF 404 can verify that the SMF 404 associated with the PDU session is accessible from any alternative S-NSSAI.

[0100] 5) At some stage, a handover is required. There is no target cell supporting S-NSSAI-3 for which UE 401 has an active PDU session. However, there is a target cell supporting an alternative network slice, e.g., an alternative S-NSSAI=S-NSSAI-1.

[0101] 6) Handover to a target cell supporting an alternative network slice S-NSSAI-1. The S-RAN node 402 selects a target cell supporting one of the alternative network slices, for example the alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available in any of the target cells, the S-RAN node 402 must consider the priority between the alternative network slices when selecting a target cell. If both the alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available in the target cell, the S-RAN node 402 selects the alternative network slice S-NSSAI-1 by considering the priority.

[0102] 7) PDU session modification on alternative network slice S-NSSAI-1 based on 3GPP TS 23.502 - AMF 404 triggers PDU session modification on alternative network slice S-NSSAI-1. Since the S-NSSAI is exchanged during this procedure, SMF 404 may contact PCF 405 and / or CHF (Charging Function) to issue separate CDRs for the original S-NSSAI-3 and the alternative network slice S-NSSAI-1.

[0103] 8) During the PDU session modification procedure, when the AMF 404 sends an N2 message to the T-RAN node 403, the N2 message includes the following parameters:

[0104] N2 Message (S-NSSAI-1, Original S-NSSAI = S-NSSAI-3, Alternate S-NSSAI = S-NSSAI-2, NAS Message (PDU Session ID, N1 SM Container (PDU Session Modification Command (New S-NSSAI = S-NSSAI-1)))) - At the end of the PDU session modification on network slice S-NSSAI-1, the AMF 404 may send an N2 message to the T-RAN node 403. Along with the network slice on which the PDU session is established, the AMF 404 also includes two new parameters in the N2 message (or any other message on the N2 interface between the AMF 404 and the RAN node 403). Original S-NSSAI - AMF 404 places in this parameter the initial network slice from which the PDU session will be transferred to one of the alternative network slices in the final handover, e.g. S-NSSAI-3. This new parameter can be called "Original S-NSSAI", "Original Network Slice", "Initial Network Slice", "Initial S-NSSAI", "UE Requested S-NSSAI", or any other name or notation of a parameter intended to convey information of the network slice at which the PDU session was established in the PDU session establishment procedure as described in 3GPP TS 23.502. Alternative S-NSSAI - the AMF 404 places one of the remaining alternative network slices, e.g. S-NSSAI-2, in this parameter. The alternative network slice may also be an S-NSSAI allowed by default in the AMF 404 or UDM / UDR 406, if available. The alternative S-NSSAI may also indicate an alternative network slice to be used for the PDU session after a successful handover procedure.

[0105] 9) During the PDU session modification procedure, when the SMF 404 sends a PDU session modification command to the UE 401 via the AMF 404 (in an N2 message to the T-RAN node interface on the AMF 404) and the T-RAN node 403, the PDU session modification command includes a new S-NSSAI parameter (e.g. S-NSSAI-1) to inform the UE 401 that the S-NSSAI (e.g. S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g. S-NSSAI-1). The T-RAN node 403 sends the PDU session modification command received from the SMF 404 via the AMF 404 (in an N2 message to the T-RAN node interface on the AMF 404) to the UE 401. With this information, the UE 401 updates the network slice state at the UE 401.

[0106] In one example, instead of sending a PDU session modification message to the UE 401, the AMF 404 may send a UE configuration update message to the UE 401 via the T-RAN node 403 to inform the UE 401 that the S-NSSAI (e.g., S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g., S-NSSAI-1).

[0107] 10) A handover is also required at some later stage. When selecting a target cell, if there are multiple eligible cells, the T-RAN node 403 may select the target cell in the following order of priority: - "Original S-NSSAI" - The T-RAN node 403 may first prioritize the original network slice (e.g. S-NSSAI-3) when selecting a target cell, thereby moving the PDU session back to the network slice where it was originally established, as this may be the best network slice for the PDU session. - Current network slice - If the target cell does not support the original network slice (e.g. S-NSSAI-3), the T-RAN node 403 preferably selects a target cell that supports the current network slice on which the PDU session is currently active, e.g. S-NSSAI-1. - "Alternative S-NSSAI" - If there is no target cell supporting the original or current network slice, the T-RAN node 403 may prioritize a target cell supporting an alternative network slice, e.g. S-NSSAI-2, if available.

[0108] It should be noted that the (source / target) RAN node may apply different priorities in selecting a target cell. For example, first give priority to the target cell supporting the current network slice with an active PDU session (e.g., S-NSSAI-1), then give priority to the original S-NSSAI (e.g., S-NSSAI-3) if available, and finally give priority to another S-NSSAI (e.g., S-NSSAI-2) if available. The (source / target) RAN node may apply any other order of priorities, e.g., an operator-defined or configured order between the original, current, and alternative network slices.

[0109] 6 is a schematic timing (signaling) diagram illustrating an example method of core network assistance with an alternative network slice for PDU session continuity in N2 handover (use case 1), in which the alternative network slice in the target cell is reconfirmed as an allowed network slice during the registration process in the T-AMF after N2 handover.

[0110] 1) PDU Session Establishment Request / Service Request (App ID, S-NSSAI-3, PDU Session ID, DNN ID) - An application in UE 501 requires a service. UE 501 checks the Network Slice Selection Policy (NSSP) in the UE Route Selection Policy (URSP) rule in the UE policy and discovers the network slices (S-NSSAI-3, S-NSSAI-1, S-NSSAI-2, etc.) on which the application can receive the service. UE 501 registers in all these network slices. The UE sends, for example, a PDU session establishment request message or a service request message on network slice S-NSSAI-3 to source AMF (S-AMF) 504 based on a request from an application. UE 501 may also include an application identity, for example, an App ID, in the PDU session establishment request or service request message, which may assist AMF 504 or SMF 504 in finding an alternative network slice for network slice S-NSSAI-3 from the NSSP / URSP rules for UE 501.

[0111] 2) Continue the PDU session establishment procedure or service request procedure with S-NSSAI-3 according to 3GPP TS 23.502.

[0112] 3) AMF / SMF Association with PCF 506 (NSSP / URSP) - The S-AMF 504 or SMF 504 can interact with the PCF 506 during association with the PCF 506 to discover a compatible network slice for the network slice S-NSSAI-3 on which the PDU session is established.

[0113] The S-AMF 504 may do one of the following during UE policy association establishment with the PCF 506: a) Request URSP or NSSP rules for the UE 501 from the PCF 506 via an Npcf_UEPolicy_Contol_Create Request message. In this case, the S-AMF 504 includes new parameters (e.g., URSP flags, NSSP flags, or other names for parameters intended to request URSP or NSSP information from the PCF 506) in the Npcf_UEPolicy_Contol_Create Request message; or b) Request a list of network slices compatible with the current network slice S-NSSAI-3 via an Npcf_UEPolicy_Contol_Create Request message. In this case, the S-AMF 504 may include in the Npcf_UEPolicy_Contol_Create Request message the application identity (e.g., App ID) that triggered the PDU session establishment, the network slice identity (e.g., S-NSSAI-3) on which the PDU session is established, or a DNN ID to help the PCF 506 find network slices compatible with the network slice S-NSSAI-3.

[0114] The PCF 506 may provide the requested information (i.e., URSP or NSSP rules for the UE 501) or a list of network slices compatible with the S-NSSAI-3 in the Npcf_UEPolict_Control_Create Response message.

[0115] It should be noted that the S-AMF 504 may also use any other existing procedures or services provided by the PCF 506 to obtain the URSP or NSSP related information from the PCF 506.

[0116] The SMF 504 may do one of the following during SM policy association establishment or SM policy association modification with the PCF 506: a) Request URSP or NSSP rules for the UE 501 from the PCF 506 via an Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF 504 includes a new parameter (e.g., a URSP or NSSP flag, or other name of the parameter intended to request URSP or NSSP information from the PCF 506) in the Npcf_SMPolicy_Contol_Create Request message; or b) Request a list of network slices compatible with the current network slice S-NSSAI-3 via the Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF 504 may include in the Npcf_SMPolicy_Contol_Create Request message the application identity (e.g., App ID) that triggered the PDU session establishment, the network slice identity (e.g., S-NSSAI-3) on which the PDU session is established, or a DNN ID to help the PCF 506 find network slices compatible with the network slice S-NSSAI-3.

[0117] The PCF 506 may provide the requested information (i.e., URSP or NSSP rules for the UE 501) or a list of network slices compatible with the S-NSSAI-3 in the Npcf_SMPolicy_Control_Create Response message.

[0118] It should be noted that the SMF 504 may also use any other existing procedures or services provided by the PCF 506 to obtain the URSP or NSSP related information from the PCF 506.

[0119] 4) N2 Message (S-NSSAI-3, Alternate S-NSSAI = S-NSSAI-1, S-NSSAI-2) - At the end of the PDU session establishment procedure on network slice S-NSSAI-3, the S-AMF 504 sends an N2 message (or any other message on the N2 interface between the AMF 504 and the RAN node) to the RAN node. This N2 message contains parameters regarding the current network slice (e.g. S-NSSAI-3) on which the PDU session was established, and further contains in the new "Alternate S-NSSAI" parameter the alternative network slices (e.g. S-NSSAI-1 and S-NSSAI-2) from which the UE 501's URSP or NSSP rules were originally obtained either directly from the PCF 506 or from the URSP or NSSP rules of the UE 501 described in step 3.

[0120] The new parameters may be configured with a priority or preferred order among the alternative S-NSSAIs. This new parameter in the N2 message may be called "alternative S-NSSAI", "alternative network slice", "backup network slice", "backup S-NSSAI", or any other name or notation of a parameter intended to convey information of a network slice that the service requiring application in the UE 501 can handle. The alternative network slice may also be an S-NSSAI that is allowed by default in the S-AMF 504 or UDM / UDR 507, if available.

[0121] When the S-AMF 504 sends an N2 message including an alternative S-NSSAI to the S-RAN node 502, the S-AMF 504 can verify that the SMF 504 associated with the PDU session is accessible from any alternative S-NSSAI.

[0122] 5) At some stage, a handover is required. There is no target cell supporting S-NSSAI-3 with which UE 501 has an active PDU session. However, there is a target cell supporting an alternative network slice, e.g., an alternative S-NSSAI=S-NSSAI-1.

[0123] 6) Handover to a target cell supporting an alternative network slice S-NSSAI-1. The S-RAN node 502 selects a target cell supporting one of the alternative network slices, for example, the alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available in any of the target cells, the priority between the alternative network slices needs to be considered in the S-RAN node 502 when selecting a target cell. If both the alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available in the target cell, the S-RAN node 502 selects the alternative network slice S-NSSAI-1 by considering the priority. During the N2 handover, the S-AMF 504 forwards the original S-NSSAI-3 and the alternative S-NSSAI-1 and S-NSSAI-2 to the T-AMF 505.

[0124] 7) Registration with T-AMF 505 based on 3GPP TS 23.502. During the registration procedure, S-NSSAI-1 is reconfirmed as an allowed network slice.

[0125] 8) PDU session modification procedure based on 3GPP TS 23.502 to replace the current S-NSSAI, i.e. S-NSSAI-3, with the alternative network slice S-NSSAI-1. - The T-AMF 505 triggers the PDU session modification on the alternative network slice S-NSSAI-1. Since the S-NSSAI is exchanged during this procedure, the SMF 505 may contact the PCF 506 and / or the CHF to issue separate CDRs for the original S-NSSAI-3 and for the alternative network slice S-NSSAI-1.

[0126] 9) During the PDU session modification procedure, when the T-AMF 505 sends an N2 message to the T-RAN node 503, the N2 message contains the following parameters:

[0127] N2 Message (S-NSSAI-1, Original S-NSSAI = S-NSSAI-3, Alternate S-NSSAI = S-NSSAI-2, NAS Message (PDU Session ID, N1 SM Container (PDU Session Modification Command (New S-NSSAI = S-NSSAI-1)))) - During the PDU session modification on the alternate network slice S-NSSAI-1, the T-AMF 505 may send the N2 message to the T-RAN node 503. Along with the network slice on which the PDU session is established, the T-AMF 505 also includes two new parameters in the N2 message to the T-RAN node 503 (or any other message on the N2 interface between the T-AMF 505 and the T-RAN node 503). -Original S-NSSAI - T-AMF 505 places in this parameter the initial network slice where the PDU session was transferred to one of the alternative network slices during the last handover, e.g. S-NSSAI-3. This new parameter can be called "Original S-NSSAI", "Original Network Slice", "Initial Network Slice", "Initial S-NSSAI", "UE Requested S-NSSAI", or any other name or notation of a parameter intended to convey information of the network slice where the PDU session was established in the PDU Session Establishment procedure as described in 3GPP TS 23.502. Alternative S-NSSAI - the T-AMF 505 places one of the remaining alternative network slices, e.g. S-NSSAI-2, in this parameter. The alternative network slice may also be a default allowed S-NSSAI in the T-AMF 505 or UDM / UDR 507, if available. The alternative S-NSSAI may also indicate an alternative network slice to be used for the PDU session after a successful handover procedure.

[0128] 10) During the PDU session modification procedure, when SMF 505 sends a PDU session modification command to UE 501 via T-AMF 505 (in an N2 message to the T-RAN node interface on T-AMF 505) and T-RAN node 503, the PDU session modification command includes a new S-NSSAI parameter (e.g. S-NSSAI-1) to inform UE 501 that the S-NSSAI (e.g. S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g. S-NSSAI-1). T-RAN node 503 sends the PDU session modification command received from SMF 505 via T-AMF 505 (in an N2 message to the T-RAN node interface on T-AMF 505) to UE 501. With this information, UE 501 updates the network slice state at the UE.

[0129] In one example, instead of sending a PDU session modification message to UE 501, T-AMF 505 may send a UE configuration update message to UE 501 via T-RAN node 503 to inform UE 501 that the S-NSSAI (e.g., S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g., S-NSSAI-1).

[0130] 11) At some later stage, a handover is required. When selecting a target cell, if there are multiple eligible cells, the T-RAN node 503 may select the target cell in the following order of priority: - "Original S-NSSAI" - The T-RAN node 503 may prefer the original network slice (e.g. S-NSSAI-3) first when selecting a target cell, thereby moving the PDU session back to the network slice where it was originally established, as this may be the best network slice for the PDU session. - Current network slice - If the target cell does not support the original network slice (e.g. S-NSSAI-3), the T-RAN node 503 preferably selects a target cell that supports the current network slice on which the PDU session is currently active, e.g. S-NSSAI-1. - "Alternative S-NSSAI" - If there is no target cell supporting the original or current network slice, the T-RAN node 503 may prioritize a target cell supporting an alternative network slice, e.g. S-NSSAI-2, if available.

[0131] It should be noted that the RAN nodes (both S-RAN and T-RAN) may apply alternative orders when selecting a target cell, for example, first giving priority to the target cell supporting the current network slice (e.g. S-NSSAI-1) with an active PDU session, then giving priority to the original S-NSSAI (e.g. S-NSSAI-3) if available, and finally giving priority to the alternative S-NSSAI (e.g. S-NSSAI-2) if available. The RAN nodes may apply any other order of priority, for example, an operator-defined or configured order between the original, current, and alternative network slices.

[0132] 7 is a schematic timing (signaling) diagram illustrating an exemplary method of core network assistance with an alternative network slice for PDU session continuity in N2 handover (use case 2). In use case 2, during the registration process in the T-AMF after N2 handover, the alternative network slice of the target cell is not reconfirmed as an allowed network slice. In this case, the T-AMF may transfer the PDU session to another alternative S-NSSAI (e.g., S-NSSAI-2) or to the default network slice in the new registration area.

[0133] 1) PDU Session Establishment Request / Service Request (App ID, S-NSSAI-3, PDU Session ID, DNN ID) - An application of UE 601 requires a service. UE 601 checks the Network Slice Selection Policy (NSSP) in the UE Route Selection Policy (URSP) rules in the UE policy and discovers the network slices (S-NSSAI-3, S-NSSAI-1, S-NSSAI-2, etc.) where the application can receive the service. UE 601 registers with all these network slices. UE 601 sends a PDU Session Establishment Request message or a Service Request message on network slice S-NSSAI-3, for example, to S-AMF 604 based on the request from the application. UE 601 can also include an application identity, for example, App ID, in the PDU Session Establishment Request or Service Request message, and the application ID can assist S-AMF 604 or SMF 604 to find an alternative network slice for network slice S-NSSAI-3 from the NSSP / URSP rules of UE 601.

[0134] 2) Continue the PDU session establishment procedure or service request procedure with S-NSSAI-3 according to 3GPP TS 23.502.

[0135] 3) AMF / SMF Association with PCF 606 (NSSP / URSP) - The S-AMF 604 or SMF 604 can interact with the PCF 606 during association with the PCF to discover a network slice compatible with the network slice S-NSSAI-3 on which the PDU session is established.

[0136] The S-AMF 604 may do one of the following during UE policy association establishment with the PCF 606: a) Requesting URSP or NSSP rules for the UE 601 from the PCF 606 via an Npcf_UEPolicy_Contol_Create Request message, in which case the S-AMF 604 includes new parameters (e.g., URSP flags, NSSP flags, or other names for parameters intended to request URSP or NSSP information from the PCF 606) in the Npcf_UEPolicy_Contol_Create Request message; or b) Request a list of network slices compatible with the current network slice S-NSSAI-3 via the Npcf_UEPolicy_Contol_Create Request message. In this case, the S-AMF 604 may include in the Npcf_UEPolicy_Contol_Create Request message the application identity (e.g., App ID) that triggered the PDU session establishment, the network slice identity (e.g., S-NSSAI-3) on which the PDU session is established, or a DNN ID to help the PCF 606 find network slices compatible with the network slice S-NSSAI-3.

[0137] The PCF 606 may provide the requested information (i.e., URSP or NSSP rules of the UE 601) or a list of network slices compatible with the S-NSSAI-3 in the Npcf_UEPolict_Control_Create Response message.

[0138] It should be noted that the S-AMF 604 may also use any other existing procedures or services provided by the PCF 606 to obtain the URSP or NSSP related information from the PCF 606.

[0139] The SMF 604 may do one of the following during SM policy association establishment or SM policy association modification with the PCF 606: a) Request URSP or NSSP rules for the UE 601 from the PCF 606 via an Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF 604 includes a new parameter (e.g., a URSP or NSSP flag, or other name of the parameter intended to request URSP or NSSP information from the PCF 606) in the Npcf_SMPolicy_Contol_Create Request message; or b) Request a list of network slices compatible with the current network slice S-NSSAI-3 via the Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF 604 may include in the Npcf_SMPolicy_Contol_Create Request message the application identity (e.g., App ID) that triggered the PDU session establishment, the network slice ID (e.g., S-NSSAI-3) on which the PDU session is established, or a DNN ID to help the PCF 606 find network slices compatible with the network slice S-NSSAI-3.

[0140] The PCF 606 may provide the requested information (i.e., URSP or NSSP rules of the UE 601) or a list of network slices compatible with the S-NSSAI-3 in the Npcf_SMPolicy_Control_Create Response message.

[0141] It should be noted that the SMF 604 may also use any other existing procedures or services provided by the PCF 606 to obtain the URSP or NSSP related information from the PCF 606.

[0142] 4) N2 Message (S-NSSAI-3, Alternate S-NSSAI = S-NSSAI-1, S-NSSAI-2) - At the end of the PDU session establishment procedure on network slice S-NSSAI-3, the S-AMF 604 sends an N2 message (or any other message on the N2 interface between the S-AMF 604 and the S-RAN node 602) to the S-RAN node 602. This N2 message contains parameters regarding the current network slice (e.g. S-NSSAI-3) on which the PDU session was established, and further contains in the new "Alternate S-NSSAI" parameter the alternative network slices (e.g. S-NSSAI-1 and S-NSSAI-2) from which the UE 601 first obtained the URSP or NSSP rules for the UE 601 directly or as described in step 3.

[0143] The new parameters may be configured with a priority or preferred order among the alternative S-NSSAIs. This new parameter in the N2 message may be called "alternative S-NSSAI", "alternative network slice", "backup network slice", "backup S-NSSAI", or any other name or notation of a parameter intended to convey information of a network slice that the service requiring application in the UE 601 can handle. The alternative network slice may also be an S-NSSAI that is allowed by default in the S-AMF 604 or UDM / UDR 607 if available.

[0144] When the S-AMF 604 sends an N2 message including an alternative S-NSSAI to the S-RAN node 602, the S-AMF 604 can verify that the SMF 604 associated with the PDU session is accessible from any alternative S-NSSAI.

[0145] 5) At some stage, a handover is required. There is no target cell supporting S-NSSAI-3 for which UE 601 has an active PDU session. However, there is a target cell supporting an alternative network slice, e.g., an alternative S-NSSAI=S-NSSAI-1.

[0146] 6) Handover to a target cell supporting an alternative network slice S-NSSAI-1. The S-RAN node 602 selects a target cell supporting one of the alternative network slices, for example, the alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available in any of the target cells, the priority between the alternative network slices needs to be considered in the S-RAN node 602 when selecting a target cell. If both the alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available in the target cell, the S-RAN node 602 selects the alternative network slice S-NSSAI-1 by considering the priority. During the N2 handover, the S-AMF 604 forwards the original S-NSSAI-3 and the alternative S-NSSAI-1 and S-NSSAI-2 to the T-AMF 605.

[0147] 7) Registration with T-AMF605 based on 3GPP TS 23.502. The registration procedure does not re-validate S-NSSAI-1 as an allowed network slice.

[0148] 8) PDU session modification with alternative network slice S-NSSAI-2 or default S-NSSAI based on 3GPP TS 23.502 - When the alternative network slice S-NSSAI-1 is an unauthorized network slice in the new registration area, T-AMF 605 triggers the PDU session modification procedure with another alternative network slice (e.g. S-NSSAI-2) or default network slice. Since the S-NSSAI is exchanged during this procedure, SMF 605 may contact PCF 606 and / or CHF to issue separate CDRs for the original S-NSSAI-3 and the alternative network slice S-NSSAI-2 or default network slice.

[0149] 9) During the PDU Session Modification procedure, when the T-AMF 605 sends an N2 message to the T-RAN node 603, the N2 message includes the following parameters:

[0150] During the PDU session modification in the N2 Message (S-NSSAI-2 / Default S-NSSAI, Original S-NSSAI=S-NSSAI-3, Alternate S-NSSAI=S-NSSAI-1, NAS Message (PDU Session ID, N1 SM Container (PDU Session Modification Command (New S-NSSAI=S-NSSAI-1)))) - Network Slice S-NSSAI-2 / Default S-NSSAI, the T-AMF 605 may send the N2 message to the T-RAN node 603. Along with the network slice on which the PDU session is established, the T-AMF 605 also includes two new parameters in the N2 message to the T-RAN node (or any other message on the N2 interface between the AMF 605 and the RAN node). -Original S-NSSAI - T-AMF 605 places in this parameter the initial network slice where the PDU session was transferred to one of the alternative network slices in the last handover, e.g. S-NSSAI-3. This new parameter can be called "Original S-NSSAI", "Original Network Slice", "Initial Network Slice", "Initial S-NSSAI", "UE Requested S-NSSAI", or any other name or notation of a parameter intended to convey information of the network slice where the PDU session was established in the PDU Session Establishment procedure as described in 3GPP TS 23.502. Alternative S-NSSAI - the T-AMF 605 places one of the remaining alternative network slices in this parameter. For example, in this case the S-NSSAI-1, which was rejected upon registration to the T-AMF 605, can still act as an alternative S-NSSAI. The alternative S-NSSAI can also indicate an alternative network slice to be used for the PDU session after a successful handover procedure.

[0151] 10) During the PDU session modification procedure, when the SMF 605 sends a PDU session modification command to the UE 601 via the T-AMF 605 (in an N2 message to the T-RAN node interface on the T-AMF 605) and the T-RAN node 603, the PDU session modification command includes a new S-NSSAI parameter (e.g., S-NSSAI-2) to inform the UE 601 that the S-NSSAI (e.g., S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g., S-NSSAI-2). The T-RAN node 603 sends the PDU session modification command received from the SMF 605 via the T-AMF 605 (in an N2 message to the T-RAN node interface on the T-AMF 605) to the UE 601. With this information, the UE 601 updates the network slice state at the UE 601.

[0152] In one example, instead of sending a PDU session modification message to UE 601, T-AMF 605 may send a UE configuration update message to UE 601 via T-RAN node 603 to inform UE 601 that the S-NSSAI (e.g., S-NSSAI-3) used for the PDU session has been replaced with a new S-NSSAI (e.g., S-NSSAI-2).

[0153] 11) At some later stage, a handover is required. When selecting a target cell, if there are multiple eligible cells, the T-RAN node 603 may select the target cell in the following order of priority: - "Original S-NSSAI" - The T-RAN node 603 may prefer the original network slice (e.g. S-NSSAI-3) first when selecting a target cell, thereby moving the PDU session back to the network slice where the PDU session was originally established, as this may be the best network slice for the PDU session. - Current network slice - If the target cell does not support the original network slice (e.g. S-NSSAI-3), the T-RAN node 603 preferably selects a target cell that supports the current network slice on which the PDU session is currently active, e.g. NSSAI-2 / Default S-NSSAI. - "Alternative S-NSSAI" - If there is no target cell supporting the original network slice or the current network slice, the T-RAN node 603 may select a target cell supporting an alternative network slice, e.g. S-NSSAI-1, if available.

[0154] It should be noted that the RAN nodes (both S-RAN and T-RAN) may apply a different order in selecting a target cell, for example, first giving priority to the target cell supporting the current network slice (e.g. S-NSSAI-2) with an active PDU session, then giving priority to the original S-NSSAI (e.g. S-NSSAI-3) if available, and finally giving priority to the alternative S-NSSAI (e.g. S-NSSAI-1) if available. The RAN node may apply any other order of priority, for example, an operator-defined or configured order between the original, current, and alternative network slices.

[0155] Beneficially, the above aspects include one or more of the following features, but are not limited to these. New "Alternative Network Slice" parameter in PDU Session Establishment Request and Service Request messages from the UE. New "alternative network slice" and "original network slice" parameters in the N2 message from the AMF to the RAN node. · The 'alternative network slice' and 'original network slice' parameters are transferred between the source and target AMF in the N2 handover. · AMF / SMF obtains NSSP (Network Slice Selection Policy) or alternative network slice from PCF. To provide these functions, the above aspects describe an exemplary method that includes (at least some of) the following steps: Improved service continuity through PDU session transfer / mapping between network slices during handover based on "alternative network slice" provided by the UE. Improved service continuity through PDU session transfer / mapping between network slices during handover based on "alternate network slices" provided by the network (e.g. PCF). Improved service continuity through PDU session transfer / mapping between network slices during handover based on the "original network slice" maintained by AMF.

[0156] The present disclosure proposes methods for service continuity for a mobile terminal in connected mode, which enable PDU session transfer to an alternative network slice when a current network slice with a PDU session is not available in a target cell after a handover, thus maintaining service continuity by PDU session transfer on the alternative network slice.

[0157] (System Overview) FIG. 8 illustrates diagrammatically a mobile (cellular or wireless) communication system 1 to which the above aspects are applicable.

[0158] In this network, users of mobile devices 3 (UE) can communicate with each other and other users via respective base stations 5 and a core network 7 using an appropriate 3GPP radio access technology (RAT), e.g. E-UTRA and / or 5G RAT. It will be appreciated that many base stations 5 form a (radio) access network or (R)AN. As will be appreciated by those skilled in the art, although one mobile device 3 and one base station 5 (RAN) are shown in Figure 8 for illustrative purposes, when the system is implemented it will typically include other base stations and mobile devices (UE).

[0159] Each base station 5 controls (directly or via other nodes such as home base stations, relays, remote radio heads, distributed units, etc.) one or more associated cells. A base station 5 supporting the E-UTRA protocol for mobile devices 3 may be referred to as an "ng-eNB" and a base station 5 supporting next generation protocols for mobile devices 3 may be referred to as a "gNB". It will be appreciated that some base stations 5 may be configured to support both 4G and 5G, and / or any other 3GPP or non-3GPP communication protocols.

[0160] The mobile devices 3 and the serving base stations 5 are connected via suitable air interfaces (such as the so-called "Uu" interface). Adjacent base stations 5 are connected to each other via suitable base station-base station interfaces (such as the so-called "X2" interface, "Xn" interface, etc.). The base stations 5 / access networks are also connected to the core network nodes via suitable interfaces (such as the so-called "NG-U" interface (for user plane), the so-called "NG-C" interface (for control plane), etc.).

[0161] The core network 7 typically includes logical nodes (or "functions") for supporting communications in the communication system 1. Typically, for example, the core network 7 of a "next generation" / 5G system includes, among other functions, a control plane function (CPF) and a user plane function (UPF). It will be appreciated that the core network 7 may include, among other functions, an access and mobility management function (AMF) 10, a session management function (SMF) 11, a unified data management (UDM) / unified data repository (UDR) function 12, and a policy control function (PCF) 13. Although not shown in FIG. 8, the core network 7 may also be coupled to at least one application function (AF) / application server (AS), etc. A connection to an external IP network / data network 20 (such as the Internet) is also provided from the core network 7.

[0162] The components of this system 1 are configured to carry out one or more of the above-described aspects.

[0163] (User Equipment (UE)) FIG. 9 is a block diagram illustrating the main components of the UE (mobile equipment 3) shown in FIG. 8. As shown in the figure, the UE includes a transceiver circuit 31 operable to transmit and receive signals to and from connected nodes via one or more antennas 33. Although not necessarily shown in FIG. 9, the UE naturally has all the usual features of a conventional mobile device (such as a user interface 35), which may be provided by any one or any combination of hardware, software and firmware, as appropriate. A controller 37 controls the operation of the UE according to software stored in a memory 39. The software may be pre-installed in the memory 39 and / or may be downloaded, for example, via the communication system 1 or from a removable data storage device (RMD). The software includes, among others, an operating system 41 and a communication control module 43. The communication control module 43 is responsible for handling (generating / sending / receiving) signaling messages and uplink / downlink data packets between the UE 3 and other nodes, including the (R)AN node 5, application functions, and core network nodes. Such signaling includes appropriately formatted requests and responses related to the management of network slices and handovers.

[0164] ((R)AN node) FIG. 10 is a block diagram illustrating the main components of an exemplary (R)AN node 5 (base station) shown in FIG. 8. As shown in the figure, the (R)AN node 5 includes a transceiver circuit 51 operable to transmit and receive signals from a connected UE 3 via one or more antennas 53, and to transmit and receive signals to and from other network nodes (directly or indirectly) via a network interface 55. The network interface 55 typically includes an appropriate base station-base station interface (e.g., X2 / Xn) and an appropriate base station-core network interface (e.g., NG-U / NG-C). The controller 57 controls the operation of the (R)AN node 5 according to software stored in memory 59. The software may be pre-installed in the memory 59 and / or may be downloaded, for example, via the communication system 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 61 and a communication control module 63. The communication control module 63 handles signal processing (generation / transmission / reception) between the (R)AN node 5 and other nodes, such as the UE 3 and the core network nodes. Such signaling includes properly formatted requests and responses related to the management of network slicing and handovers.

[0165] (Core network node) FIG. 11 is a block diagram illustrating the main components of a generic core network node (or function) shown in FIG. 8, e.g., AMF 10, SMF 11, UDM / UDR 12, and PCF 13. As shown in the figure, the core network node includes a transceiver circuit 71 operable to transmit and receive signals to other nodes (including UE 3 and (R)AN node 5) via a network interface 75. A controller 77 controls the operation of the core network node according to software stored in a memory 79. The software may be pre-installed in the memory 79 and / or may be downloaded, for example, via the communication system 1 or from a removable data storage device (RMD). The software includes, among other things, an operating system 81 and at least a communication control module 83. The communication control module 83 is responsible for handling (generating / sending / receiving) signaling between the core network node and other nodes, such as UE 3, (R)AN node 5, and other core network nodes. Such signaling includes appropriately formatted requests and responses related to the management of network slices and handovers.

[0166] (Modifications and Substitutions) Although detailed aspects have been described above, those skilled in the art will appreciate that many modifications and alternatives can be made to the above-described embodiments while still benefiting from the invention embodied therein, and by way of example only a few of these alternatives and modifications are described herein.

[0167] In the above description, for ease of understanding, the UE, (R)AN node, and core network node are described as having a number of discrete modules (such as a communications control module). While these modules may be provided in this manner in certain applications, for example where an existing system is modified to implement the above aspects, in other applications, for example in systems designed with the features of the invention in mind from the outset, these modules may be incorporated into an overall operating system or code and therefore may not be recognized as separate entities. These modules may also be implemented in software, hardware, firmware, or a combination thereof.

[0168] Each controller may be comprised of any suitable form of processing circuitry including, but not limited to, one or more hardware-implemented computer processors, microprocessors, central processing units (CPUs), arithmetic logic units (ALUs), input / output (IO) circuitry, internal memory / cache (program and / or data), processing registers, communications buses (such as control, data and / or address buses), direct memory access (DMA) facilities, hardware or software implemented counters, pointers and / or timers, etc.

[0169] The above-mentioned memory may be configured as a volatile memory or a non-volatile memory, or may be configured as a combination of a volatile memory and a non-volatile memory.

[0170] In the above embodiments, a number of software modules have been described. As will be appreciated by those skilled in the art, the software modules may be provided in compiled or uncompiled form and may be provided to the UE, the (R)AN node, and the core network node as a signal via a computer network or on a recording medium. Furthermore, the functions performed by some or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as they facilitate updating the functionality of the UE, the (R)AN node, and the core network node.

[0171] The above aspects are also applicable to "non-mobile" or generally stationary user equipment.

[0172] Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

[0173] A part or all of the above-described embodiments can be described as, but is not limited to, the following supplementary notes. (Appendix 1) A receiving means for receiving at least one first network slice information different from a protocol data unit (PDU) and a second network slice information used in a session with a user equipment (UE) from a network function node for mobility management; and performing a redirection procedure for a UE from a first cell to a second cell supporting one of the at least one first network slice information, when the second network slice information is unavailable in the first cell. (Appendix 2) 2. The access network node of claim 1, wherein one of the at least one first network slice information is granted after a registration procedure of the UE. (Appendix 3) An access network node as described in Supplementary Note 1 or 2, wherein one of the at least one first network slice information is determined based on a priority among the at least one first network slice. (Appendix 4) The access network node according to any one of Supplementary Notes 1 to 3, wherein the executing means is configured to execute a redirection procedure of the UE from the first cell to the second cell during handover from an access network node serving the first cell to another access network node serving the second cell. (Appendix 5) An access network node as described in any one of Supplementary Notes 1 to 4, wherein the at least one network slice information and the second network slice information are transmitted from the UE to the network function node for mobility management by a PDU session establishment request or a service request message. (Appendix 6) The at least one network slice information is selected by the network function node for mobility management by obtaining it from a network function node for policy control using an application identity; The access network node according to any one of Supplementary Notes 1 to 4, wherein the application identity is sent from the UE to the network function node for mobility management by a PDU session establishment request or a service request message. (Appendix 7) An access network node as described in any one of Supplementary Notes 1 to 5, which, after the redirection procedure, performs re-establishment of a PDU session from a second network slice indicated in the second network slice information to a first network slice indicated in one of the at least one first network slice information. (Appendix 8) A transmitting means for transmitting at least one network slice information and a second network slice information in a protocol data unit (PDU), a session establishment request or a service request message to a network function node for mobility management via an access network node, The second network slice information is used for a PDU session with the network function node for mobility management; each of the at least one first network slice information is different from the second network slice information; A user equipment (UE) is provided, wherein a redirection procedure of the UE from a first cell served by the access network node to a second cell supporting one of at least one first network slice information is performed when the second network slice information is not available in the first cell. (Appendix 9) A transmitting means for transmitting the application identity and the second network slice information in a protocol data unit (PDU), a session establishment request or a service request message to a network function node for mobility management via an access network node, The second network slice information is used for a PDU session with the network function node for mobility management; The application identity is used by the network function node for mobility management to obtain at least one first network slice information, each of which is different from the second network slice information; A user equipment (UE), wherein a redirection procedure of the UE from a first cell served by the access network node to a second cell supporting one of the at least one first network slice information is performed when the second network slice information is not available in the first cell. (Appendix 10) A transmitting means for transmitting at least one first network slice information to an access network node, the first network slice information being different from a second network slice information used for a PDU session with a user equipment (UE), A network function node for mobility management, wherein the at least one first network slice information is used by the access network node to perform a redirection procedure of a UE from a first cell to a second cell supporting one of the at least one first network slice information when the second network slice information is not available in the first cell. (Appendix 11) receiving at least one first network slice information different from a protocol data unit (PDU) and a second network slice information used for a session with a user equipment (UE) from a network function node for mobility management; A method for controlling an access network node to perform a redirection procedure for a UE from a first cell to a second cell supporting one of the at least one first network slice information, when the second network slice information is unavailable in the first cell. (Appendix 12) The control method of claim 11, wherein one of the at least one first network slice information is permitted after a registration procedure of the UE. (Appendix 13) The control method according to claim 11 or 12, wherein one of the at least one first network slice information is determined based on a priority among the at least one first network slice. (Appendix 14) The control method according to any one of Supplementary Notes 11 to 13, wherein the executing step includes a step of executing a redirection procedure of a UE from the first cell to the second cell during handover from an access network node providing the first cell to another access network node providing the second cell. (Appendix 15) The at least one network slice information and the second network slice information are transmitted from the UE to the network function node for mobility management by a PDU session establishment request or a service request message. (Appendix 16) The at least one network slice information is selected by the network function node for mobility management by obtaining it from a network function node for policy control using an application identity; The control method according to any one of Supplementary Notes 11 to 14, wherein the application identity is sent from the UE to the network function node for mobility management by a PDU session establishment request or a service request message. (Appendix 17) A control method described in any one of Supplementary Notes 11 to 15, comprising, after the redirection procedure, re-establishing a PDU session from a second network slice indicated in the second network slice information to a first network slice indicated in one of the at least one first network slice information. (Appendix 18) Sending at least one network slice information and a second network slice information in a protocol data unit (PDU), a session establishment request or a service request message to a network function node for mobility management via an access network node; The second network slice information is used for a PDU session with the network function node for mobility management; each of the at least one first network slice information is different from the second network slice information; A method for controlling a user equipment (UE), wherein a redirection procedure of the UE from a first cell served by the access network node to a second cell supporting one of the at least one first network slice information is performed if the second network slice information is not available in the first cell. (Appendix 19) Sending the application identity and the second network slice information in a protocol data unit (PDU), a session establishment request or a service request message to a network function node for mobility management via the access network node; The second network slice information is used for a PDU session with a network function node for mobility management; The application identity is used by the network function node for mobility management to obtain the at least one first network slice information, which is different from the second network slice information; A method for controlling a user equipment (UE), wherein a redirection procedure of the UE from a first cell served by the access network node to a second cell supporting one of the at least one first network slice information is performed if the second network slice information is not available in the first cell. (Appendix 20) Transmitting at least one first network slice information to an access network node, the first network slice information being different from a second network slice information used for a PDU session with a user equipment (UE); A method for controlling a network function node for mobility management, wherein the at least one first network slice information is used by the access network node to perform a redirection procedure of the UE from a first cell to a second cell supporting one of the at least one first network slice information when the second network slice information is not available in the first cell.

[0174] It will be appreciated by those skilled in the art that numerous variations and / or modifications may be made to the present disclosure as set forth in the specific embodiments without departing from the spirit or scope of the disclosure as broadly described. The present embodiments are therefore considered in all respects to be illustrative and not restrictive.

[0175] This application claims the benefit of priority to European Patent Application No. EP20189550.5, filed August 5, 2020, the disclosure of which is incorporated herein by reference in its entirety. [Explanation of symbols]

[0176] 101UE 102 S-RAN nodes 103 T-RAN nodes 104 AMF / SMF 105 UDM / UDR 201UE 202 S-RAN nodes 203 T-RAN nodes 204 S-AMF 205 T-AMF 206 UDM / UDR 301UE 302 S-RAN nodes 303 T-RAN nodes 304 S-AMF 305 T-AMF 306 UDM / UDR 401UE 402 S-RAN nodes 403 T-RAN Node 404 AMF / SMF 405 PCF 406 UDM / UDR 501UE 502 S-RAN nodes 503 T-RAN nodes 504 S-AMF / SMF 505 T-AMF / SMF 506 PCF 507 UDM / UDR 601UE 602 S-RAN Node 603 T-RAN Node 604 S-AMF / SMF 605 T-AMF / SMF 606 PCF 607 UDM / UDR 1. Communication Systems 3. Mobile devices 5 base station 7 Core Network 10 AMF 11 SMF 12 UDM / UDR 13 PCF 20 External IP Networks / Data Networks 31 Transceiver Circuit 33 Antenna 35 User Interface 37 Controller 39 Memory 41 Operating Systems 43 Communication Control Module 51 Transceiver Circuit 53 Antenna 55 Network Interface 57 Controller 59 Memory 61 Operating Systems 63 Communication Control Module 71 Transceiver Circuit 75 Network Interface 77 Controller 79 Memory 81 Operating Systems 83 Communication Control Module 91 Access Network Node 911 Receiver 912 Executive Department 93 User Equipment 931 Transmitter 95 Network Function Nodes 951 Transmitter

Claims

1. Sending a first signal to an Access and Mobility Management Function (AMF), the first signal including the first information and the second information; the first information is information about Single-Network Slice Selection Assistance Information (S-NSSAI) for a Protocol Data Unit (PDU) session; A transmission unit, wherein the second information is information regarding an Alternative S-NSSAI for the PDU session; A receiving unit that receives a second signal including information regarding the Alternative S-NSSAI for the PDU session from the AMF that has determined to replace the S-NSSAI for the PDU session with the Alternative S-NSSAI for the PDU session. Communications equipment.

2. The first signal is a PDU session establishment request message. The communication device according to claim 1 .

3. sending a Protocol Data Unit (PDU) session establishment request message including the first information to an Access and Mobility Management Function (AMF); A transmission unit, the first information being information regarding Single-Network Slice Selection Assistance Information (S-NSSAI) for a PDU session; A receiving unit that receives, from the AMF that has determined to replace the S-NSSAI for the PDU session with an Alternative S-NSSAI for the PDU session, a signal that executes a User equipment (UE) configuration update procedure for reconfiguring a communication device with the Alternative S-NSSAI for the PDU session. Communications equipment.

4. receiving a first signal from a communication device, the first signal including first information and second information; the first information is information about Single-Network Slice Selection Assistance Information (S-NSSAI) for a Protocol Data Unit (PDU) session; The second information is information regarding an Alternative S-NSSAI for the PDU session, If the processing unit determines to replace the S-NSSAI for the PDU session with the Alternative S-NSSAI for the PDU session, The transmitter transmits a second signal including information about the Alternative S-NSSAI for the PDU session to the communication device. Access and Mobility Management Function (AMF).

5. The first signal is a PDU session establishment request message. The AMF of claim 4.

6. receiving a Protocol Data Unit (PDU) session establishment request message including first information from the communication device; The first information is information regarding Single-Network Slice Selection Assistance Information (S-NSSAI) for a PDU session, When the receiving unit receives information regarding an Alternative S-NSSAI for the PDU session from a Policy Control Function (PCF), The processing unit determines to replace the S-NSSAI for the PDU session with the Alternative S-NSSAI for the PDU session; The transmitter transmits to the communication device a signal for performing a User equipment (UE) configuration update procedure for reconfiguring the communication device in the Alternative S-NSSAI for the PDU session. Access and Mobility Management Function (AMF).

7. Sending a first signal to an Access and Mobility Management Function (AMF), the first signal including the first information and the second information; the first information is information about Single-Network Slice Selection Assistance Information (S-NSSAI) for a Protocol Data Unit (PDU) session; The second information is information about an Alternative S-NSSAI for the PDU session, receiving a second signal including information regarding the Alternative S-NSSAI for the PDU session from the AMF that has determined to replace the S-NSSAI for the PDU session with the Alternative S-NSSAI for the PDU session; Method of communication device.

8. The first signal is a PDU session establishment request message. The method of claim 7.

9. receiving a first signal from a communication device, the first signal including first information and second information; the first information is information about Single-Network Slice Selection Assistance Information (S-NSSAI) for a Protocol Data Unit (PDU) session; The second information is information about an Alternative S-NSSAI for the PDU session, If it is determined to replace the S-NSSAI for the PDU session with the Alternative S-NSSAI for the PDU session, transmitting a second signal to the communication device, the second signal including information regarding the Alternative S-NSSAI for the PDU session; Access and Mobility Management Function (AMF) methods.

10. The first signal is a PDU session establishment request message.

10. The AMF method of claim 9.

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