Method and apparatus for signaling recovery in wireless communication system

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. According to an embodiment of the present disclosure, a user equipment (UE) is provided, the UE comprising: a transceiver; and at least one processor coupled with the transceiver and configured to: receive a fallback indication in a connected mode, and determine whether the UE is in a network slice-area of service (NS-AoS) with respect to a single network slice selection assistance information (S-NSSAI), wherein the S-NSSAI is associated with a protocol data unit (PDU) session for which user plane (UP) resources were active prior to receiving the fallback indication, and in case that it is determined that the UE is in the NS-AoS, transmit, to an access and mobility management function (AMF) entity, a request message including an indication of the PDU session.

Description

METHOD AND APPARATUS FOR SIGNALING RECOVERY IN WIRELESS COMMUNICATION SYSTEMCertain examples of the present disclosure relate to methods, apparatus and / or systems for controlling NAS signalling recovery at a UE. In particular, various examples relate to methods, apparatus and / or systems for controlling such recovery based on slice support, for example located-based slice support and / or time-based slice-support. Various examples provide one or more operations for a UE in the event that a slice is supported based on location and / or time, and in the event that a slice is not supported based on location and / or time.5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.It is an aim of certain examples of the present disclosure to address, solve and / or mitigate, at least partly, at least one of the problems and / or disadvantages associated with the related art, for example at least one of the problems and / or disadvantages described herein. It is an aim of certain examples of the present disclosure to provide at least one advantage over the related art, for example at least one of the advantages described herein.According to an embodiment of the present disclosure, a user equipment (UE) is provided, the UE comprising: a transceiver; and at least one processor coupled with the transceiver and configured to: receive a fallback indication in a connected mode, and determine whether the UE is in a network slice-area of service (NS-AoS) with respect to a single network slice selection assistance information (S-NSSAI), wherein the S-NSSAI is associated with a protocol data unit (PDU) session for which user plane (UP) resources were active prior to receiving the fallback indication, and in case that it is determined that the UE is in the NS-AoS, transmit, to an access and mobility management function (AMF) entity, a request message including an indication of the PDU session.According to an embodiment of the present disclosure, an access and mobility management function (AMF) entity is provided, the AMF entity comprising: a transceiver; and at least one processor coupled to the transceiver and configured to: receive, from a user equipment (UE), a request message including an indication of a protocol data unit (PDU) session associated with a single network slice selection assistance information (S-NSSAI), in case that the UE is in a network slice-area of service (NS-AoS) with respect to the S-NSSAI, wherein the S-NSSAI is associated with the PDU session for which user plane (UP) resources were active before the UE receives a fallback indication in a connected mode.According to an embodiment of the present disclosure, a method of a user equipment (UE) is provided, the method comprising: receiving a fallback indication in a connected mode; and determining whether the UE is in a network slice-area of service (NS-AoS) with respect to a single network slice selection assistance information (S-NSSAI), wherein the S-NSSAI is associated with a protocol data unit (PDU) session for which user plane (UP) resources were active prior to receiving the fallback indication; and in case that it is determined that the UE is in the NS-AoS, transmitting, to an access and mobility management function (AMF) entity, a request message including an indication of the PDU session.According to an embodiment of the present disclosure, a method of an access and mobility management function (AMF) entity is provided, the method comprising: receiving, from a user equipment (UE), a request message including an indication of a protocol data unit (PDU) session associated with a single network slice selection assistance information (S-NSSAI), in case that the UE is in a network slice-area of service (NS-AoS) with respect to the S-NSSAI, wherein the S-NSSAI is associated with the PDU session for which user plane (UP) resources were active before the UE receives a fallback indication in a connected mode.Other aspects, advantages, and salient features of the disclosure will become apparent to those skilled in the art from the following detailed description taken in conjunction with the accompanying drawings.Embodiments / examples of the present disclosure are further described hereinafter with reference to the accompanying drawings, in which:Figure 1 illustrates a method flow diagram of examples according to the present disclosure.Figure 2 illustrates a block diagram of an example structure of a network entity in accordance with certain examples of the present disclosure.Figure 3 illustrates a flow diagram of a method in accordance with various examples of the present disclosure.Figure 4 illustrates an example of single-network slice assistance information (S-NSSAI) location validity information information element (IE) according to the present disclosure.Figure 5 illustrates an example of Per S-NSSAI location validity information for S-NSSAI according to the present disclosure.Figure 6 illustrates an example of network slice(NS) area of service(AoS) information according to the present disclosure.Figure 7 illustrates an example of new radio (NR) cell global identity (CGI) information according to the present disclosure.The following description of examples of the present disclosure, with reference to the accompanying drawings, is provided to assist in a comprehensive understanding of certain examples of the present disclosure. The description includes various specific details to assist in that understanding but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the examples described herein can be made without departing from the scope of the invention or disclosure.The same or similar components may be designated by the same or similar reference numerals, although they may be illustrated in different drawings.Detailed descriptions of techniques, structures, constructions, functions or processes known in the art may be omitted for clarity and conciseness, and to avoid obscuring the subject matter of the present disclosure.The terms and words used herein are not limited to the bibliographical or standard meanings, but are merely used to enable a clear and consistent understanding of the disclosure.Throughout the description of this specification, the words "comprise", "include" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does not) exclude other features, elements, components, integers, steps, processes, operations, functions, characteristics, properties and / or groups thereof.Throughout the description of this specification, the singular form, for example "a", "an" and "the", encompasses the plural unless the context otherwise requires. For example, reference to "an object" includes reference to one or more of such objects.Throughout the description, the expression "at least one of A, B and / or C" (or the like), the expression "and / or" and the expression "one or more of A, B and / or C" (or the like) should be seen to separately include all possible combinations, for example: A, B, C, A and B, A and C, A and B and C.Throughout the description of this specification, language in the general form of "X for Y" (where Y is some action, process, operation, function, activity or step and X is some means for carrying out that action, process, operation, function, activity or step) encompasses means X adapted, configured or arranged specifically, but not necessarily exclusively, to do Y.Features, elements, components, integers, steps, processes, operations, functions, characteristics, properties and / or groups thereof described or disclosed in conjunction with a particular aspect, embodiment or example are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.Certain examples of the present disclosure relate to methods, apparatus and / or systems for controlling NAS signalling recovery at a UE. In particular, various examples relate to methods, apparatus and / or systems for controlling such recovery based on slice support, for example located-based slice support and / or time-based slice-support. Various examples provide one or more operations for a UE in the event that a slice is supported based on location and / or time, and in the event that a slice is not supported based on location and / or time.The following examples are applicable to, and use terminology associated with, 3GPP 4G and 5G. However, the skilled person will appreciate that the techniques disclosed herein are not limited to these examples or to 3GPP 4G or 5G, and may be applied in any suitable system or standard, for example one or more existing and / or future generation wireless communication systems or standards. The skilled person will appreciate that the techniques disclosed herein may be applied in any existing or future releases of 3GPP 4G or 5G NR or any other relevant standard. For example, the functionality of the various network entities and other features disclosed herein may be applied to corresponding or equivalent entities or features in other communication systems or standards. Corresponding or equivalent entities or features may be regarded as entities or features that perform the same or similar role, function, operation or purpose within the network. In particular, the following disclosure should be considered at least in relation to 6G also, which is expected to use at least part of the 5G architecture, or equivalent, and to which the present disclosure also relates.A particular network entity may be implemented as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, and / or as a virtualised function instantiated on an appropriate platform, e.g. on a cloud infrastructure.The skilled person will appreciate that the present disclosure is not limited to the specific examples disclosed herein. For example:The techniques disclosed herein are not limited to 3GPP 4G, 5G, B5G or 6G.One or more entities in the examples disclosed herein may be replaced with one or more alternative entities performing equivalent or corresponding functions, processes or operations.One or more of the messages in the examples disclosed herein may be replaced with one or more alternative messages, signals or other type of information carriers that communicate equivalent or corresponding information.One or more further elements, entities and / or messages may be added to the examples disclosed herein.One or more non-essential elements, entities and / or messages may be omitted in certain examples.The functions, processes or operations of a particular entity in one example may be divided between two or more separate entities in an alternative example.The functions, processes or operations of two or more separate entities in one example may be performed by a single entity in an alternative example.Information carried by a particular message in one example may be carried by two or more separate messages in an alternative example.Information carried by two or more separate messages in one example may be carried by a single message in an alternative example.The order in which operations are performed may be modified, if possible, in alternative examples.The transmission of information between network entities is not limited to the specific form, type and / or order of messages described in relation to the examples disclosed herein.Certain examples of the present disclosure may be provided in the form of an apparatus / device / network entity configured to perform one or more defined network functions and / or a method therefor. Such an apparatus / device / network entity may comprise one or more elements, for example one or more of receivers, transmitters, transceivers, processors, controllers, modules, units, and the like, each element configured to perform one or more corresponding processes, operations and / or method steps for implementing the techniques described herein. For example, an operation / function of X may be performed by a module configured to perform X (or an X-module). Certain examples of the present disclosure may be provided in the form of a system (e.g., a network) comprising one or more such apparatuses / devices / network entities, and / or a method therefor.It will be appreciated that examples of the present disclosure may be realized in the form of hardware, software or a combination of hardware and software. Certain examples of the present disclosure may provide a computer program comprising instructions or code which, when executed, implement a method, system and / or apparatus in accordance with any aspect, example and / or embodiment disclosed herein. Certain embodiments of the present disclosure provide a machine-readable storage storing such a program.The content of the following documents is referred to below:3GPP TS 23.501 - System architecture for the 5G System (5GS)3GPP TS 24.501 - Non-Access-Stratum (NAS) protocol for the 5G System (5GS)Wireless or mobile (cellular) communications networks in which a mobile terminal (e.g., user equipment (UE), such as a mobile handset) communicates via a radio link with a network of base stations, or other wireless access points or nodes, have undergone rapid development through a number of generations. The 3rdGeneration Partnership Project (3GPP) design, specify and standardise technologies for mobile wireless communication networks. Fourth (4th) Generation (4G) and Fifth Generation (5G) systems (5GS) are now widely deployed, while beyond 5G (B5G) and 6G systems are being considered.3GPP standards for 4G systems include an Evolved Packet Core (EPC) and an Enhanced-UTRAN (E-UTRAN: an Enhanced Universal Terrestrial Radio Access Network). The E-UTRAN uses Long Term Evolution (LTE) radio technology. LTE is commonly used to refer to the whole system including both the EPC and the E-UTRAN, and LTE is used in this sense in the remainder of this document. LTE should also be taken to include LTE enhancements such as LTE Advanced and LTE Pro, which offer enhanced data rates compared to LTE.In 5G systems a new air interface has been developed, which may be referred to as 5G New Radio (5G NR) or simply NR. NR is designed to support the wide variety of services and use case scenarios envisaged for 5G networks, though builds upon established LTE technologies. B5G systems, such as 6G, are currently being considered and developed, and are expected to at least partly build on 5G systems.New frameworks and architectures are being developed as part of 5G network (and beyond, such as 6G networks) in order to increase the range of functionality and use cases available through 5G networks.Support for slicing with heterogenous coverage / deploymentAs part of such frameworks and architectures, support is provided for network slicing. A Network Slice (NS), or slice, is defined as a logical network that provides specific network capabilities and network characteristics. A Network Slice Instance (NSI) is defined as a set of Network Function instances and the required resources (e.g. compute, storage and networking resources) which form a deployed NS. A Network Function (NF) is defined as a 3GPP adopted or 3GPP defined processing function in a network, which has defined functional behaviour and 3GPP defined interfaces. A NS may be identified by Single Network Slice Selection Assistance Information (S-NSSAI).Network slicing can be supported such that a slice may not be available in all the tracking areas (TAs) of a UE's registration area (RA), noting that an RA can contain a list of TAs identified by TA Identities (TAIs). The description of this can be found in section 5.15.18 of 3GPP TS 23.501 [1] from which the following excerpt is provided:5.15.18.1 GeneralThe network support for a Network Slice is defined on a per Tracking Area granularity. It may be beneficial to deploy some Network Slices such that the Network Slice have a limited geographical availability that is not matching existing Tracking Area boundaries.The operator can in this case decide to change the topology of the Tracking Areas so they match the boundaries of the Network Slice, or the operator may configure resources for the Network Slices in the cells of TAs where the Network Slices are to be available, and in areas of the TAs where the network slice is defined to be not available the cells are configured with zero resources.The AMF receives from the OAM the information on availability of a network slice when the granularity is smaller than TA, i.e. if the NS-AoS includes TAs where the network slice is not available in some cells of the TA.In order to optimize the end-to-end behaviour, the AMF can, based on NS-AoS information received from OAM, configure supporting UEs with S-NSSAI location availability information, and the network may need to monitor the S-NSSAI usage and enforce the NS-AoS e.g. if the UE does not support the S-NSSAI location availability information.5.15.18.2 S-NSSAI location availability informationS-NSSAI location availability information defines additional restrictions to the usage of an S-NSSAI in TAs where the Network Slice availability does not match the TA boundaries. The AMF is configured per S-NSSAI whether to send the S-NSSAI location availability information to supporting UEs.The S-NSSAI location availability information sent to the UE includes, for each applicable S-NSSAI of the Configured NSSAI, Location information indicating the cells of TAs in the RA where the related S-NSSAI is available if the S-NSSAI is not available in all the cells of the TA.If the UE has indicated that the UE supports S-NSSAI location availability information in the 5GMM Core Network Capability (see clause　5.4.4a), the AMF may, based on OAM configuration, configure the UE with S-NSSAI location availability information for one or more S-NSSAIs when the AMF allocates an RA where the Network Slice availability does not match whole TAs, by including the S-NSSAI location availability information in the Registration Accept message or the UE Configuration Command message. A UE that receives S-NSSAI location availability information applies the information as follows.1. If the S-NSSAI is rejected in the RA or rejected partially in the RA or rejected with a cause code that allows attempting to register the S-NSSAI again, the UE can request the S-NSSAI only if the S-NSSAI location availability information indicates that the S-NSSAI is available at the cell where the UE is camping.2. If the S-NSSAI is in the Partially Allowed NSSAI or in the Allowed NSSAI, the UE shall not activate User Plane for any already established PDU Session with that S-NSSAI if the UE is in a cell within the RA but outside the Location information of the S-NSSAI. The UE and SMF shall not exchange user data as payload of a NAS message in both uplink and downlink directions.3. If the S-NSSAI is in the Partially Allowed NSSAI or in the Allowed NSSAI, and the UE in CM-IDLE mode is moved to a cell outside the Location information of the S-NSSAI, and the UE has an established PDU Session with that S-NSSAI, the PDU Session is kept.NOTE 1: By Radio Resource Management and existing mechanisms in NG-RAN, handover can be used to keep the UE in the NS-AoS or steer the UE to enter the NS-AoS as long as radio conditions allow it.NOTE 2: Since the S-NSSAI location availability information is not a used as a trigger for the UE to perform MRU due to mobility, i.e. the UE performs MRU due to mobility upon changing to a new TA outside the UE's Registration Area, the S-NSSAI remains registered and is included in the Allowed NSSAI when the UE exits the NS-AoS. If the S-NSSAI is subject for NSAC, the S-NSSAI is counted towards NSAC as described in clause　5.15.11 also when the UE is outside the NS-AoS.5.15.18.3 Network based monitoring and enforcement of Network Slice Area of Service not matching deployed Tracking AreasOAM may configure RRM policies for S-NSSAIs on a per cell basis as defined in TS　28.541

[0149] , i.e. cells outside the Network Slice Area of Service while in a TA supporting the S-NSSAI are allocated with no RRM resources for the S-NSSAI.The network may enforce the NS-AoS for an S-NSSAI as follows:1. The network may monitor the validity of the S-NSSAI for UE in CM-CONNECTED state, i.e. the AMF subscribes to the AoI using the Location information of the S-NSSAI location availability information as described in TS　38.413

[0034] .2. If the non-supporting UE makes a PDU Session establishment request with an S-NSSAI that is not valid as per the S-NSSAI location availability information, the AMF may reject the NAS Transport message with a back-off timer using S-NSSAI based congestion control as described in clause　5.19.7.4.3. If the AMF determines that the UE in CM-CONNECTED has moved outside the NS-AoS, the AMF performs the following logic:a) If the non-supporting UE has other S-NSSAI(s) in the Allowed NSSAI, then the AMF may update the UE with a UE Configuration Update by removing the S-NSSAI from the Allowed NSSAI (which causes the UE to locally release the PDU Sessions) and optionally removing the S-NSSAI from the Configured NSSAI and then, the AMF requests the SMF to locally release in the network any PDU Sessions with that S-NSSAI as per step　1f in clause　4.2.3.4 in TS　23.502　[3]. Alternatively, the AMF requests the SMF to release PDU Sessions with that S-NSSAI.b) If the non-supporting UE does not have any other S-NSSAI in the Allowed NSSAI, then the AMF may update the UE with a UE Configuration Update by removing the S-NSSAI from the Allowed NSSAI (which causes the UE to locally release the PDU Sessions) and optionally removing the S-NSSAI from the Configured NSSAI, and adding a default S-NSSAI to the Allowed NSSAI and then, the AMF requests the SMF to locally release in the network any PDU Sessions with the removed S-NSSAI as per step　1f in clause　4.2.3.4 in TS　23.502　[3]. Alternatively, the AMF requests the SMF to release PDU Sessions with that S-NSSAI.NOTE: Whether the AMF removes the S-NSSAI from Allowed NSSAI and Configured NSSAI or only releases the associated PDU Sessions when the AMF enforces the NS-AoS is up to AMF configuration.c) For a non-supporting UE that does not have any other S-NSSAI in the Allowed NSSAI nor in the Configured NSSAI, then the AMF indicates to the SMF to release the PDU Session.4. If the AMF determines that the S-NSSAI becomes valid e.g. the UE has moved into the NS-AoS, the AMF may update the UE with a UCU e.g. including the S-NSSAI in the Configured NSSAI.From the above, it can be seen that the UE may be provided with location information regarding the applicability of a slice (or an S-NSSAI) in a cell of a TA. According to the requirements from TS 23.501 [1], the UE is only allowed to use a slice if the cell supports the slice in question. In particular, if the slice (or S-NSSAI) is in the Partially Allowed NSSAI or in the Allowed NSSAI (this being the set or list of NSSAI allowed by the 5GN operator for a particular NS), the UE shall not activate User Plane for any already established protocol data unit (PDU) Session with that S-NSSAI if the UE is in a cell within the RA but outside the location information of the S-NSSAI.Support for slices during a certain timeFurthermore, the network may only support a slice during a specific time after which the UE cannot get any service which is associated with the slice. This feature is described in section 5.15.16 of [1]:5.15.16 Optimized handling of temporarily available networkA network slice may be available for all UEs or a limited number of UEs only for a limited time that is known at the network in advance e.g. by OAM or subscription. The limited time duration may be due to, for example, the fact that network slice is only temporarily or periodically active in the deployment (e.g. for a limited time to serve an event or a UE may be only authorized to access the network slice for a limited time known in advance), or the network slice is being decommissioned at a known future time. This feature is enabled by S-NSSAI validity time that the network and the UE can handle to reduce the signalling load associated to the transitions in RM and SM states for the network slice.The UE may indicate its support for temporarily available network slices in the UE MM Core Network Capability (see clause 5.4.4a) in the Registration Request. The AMF, based on OAM configuration or information received from the UDM or NSSF, may indicate to a supporting UE the validity time for one or more S-NSSAIs in the Configured NSSAI in the Registration Accept message or via the UE Configuration Update procedure. In roaming case, the AMF my include the validity time for an S-NSSAI in the Configured NSSAI either because of limited availability of the VPLMN S-NSSAI or the mapped S-NSSAI of the HPLMN.NOTE 1: When the validity time changes or a validity time is determined for a S-NSSAI in the configured NSSAI, the PLMN provides the new validity time for the S-NSSAIs in the Configured NSSAI to a supporting UE.If a supporting UE is configured with validity time for an S-NSSAI:a) If the validity time indicates the S-NSSAI is available, the UE may request the S-NSSAI in a Requested NSSAI in a Registration request and, if the S-NSSAI is included in the Allowed NSSAI or in the Partially Allowed NSSAI, the UE may establish PDU sessions associated with the S-NSSAI.b) If the validity time indicates the S-NSSAI is not available- The UE shall not include the S-NSSAI in the Requested NSSAI;- If the S-NSSAI is already part of the Allowed NSSAI or Partially Allowed NSSAI, the UE shall remove the S-NSSAI from the locally stored Allowed NSSAI or Partially Allowed NSSAI and the UE shall also locally release any PDU sessions associated with the S-NSSAI.- If the validity time indicates the S-NSSAI will not be available again, the UE shall remove the S-NSSAI from the locally stored Configured NSSAI.NOTE 2: Subject to implementation decisions outside 3GPP scope, the UE may also use the validity time information to e.g. attempt to use another PDU sessions to continue supporting the connectivity with another connectivity option if possible according to the URSP rules, or, if not possible, e.g. provide implementation-dependent information on the availability of connectivity for specific applications affected by an impending connectivity loss, so the UE can let the end user prepare for the loss of connectivity.For a supporting UE, if validity time applies to an S-NSSAI, an AMF supporting temporarily available network slices shall:- If the S-NSSAI is provided in a Requested NSSAI in a Registration Request by the UE and the validity time indicates the S-NSSAI is not available, but it is going to become available again (i.e. the UE is detected as not having up to date validity time), then the AMF sends the Configured NSSAI to the UE including the validity time for the S-NSSAI in the Registration Accept message. If the validity time indicates the S-NSSAI is not available and will not become available again, then the AMF sends the Configured NSSAI to the UE, excluding the S-NSSAI from the Configured NSSAI.- If the S-NSSAI is in the Allowed NSSAI or the Partially Allowed NSSAI for the UE and the validity time indicates that the S-NSSAI is not available, then locally remove (i.e. without sending any signalling to the UE) the S-NSSAI from the Allowed NSSAI or Partially Allowed NSSAI. If there is any PDU session established for the S-NSSAI, the AMF requests the SMF to release the PDU session:- If the UE is in CM-CONNECTED state, the AMF releases the PDU session for the S-NSSAI by sending to the SMF, as per step 1f in clause 4.3.4.2 of TS 23.502 [3], a Nsmf_PDUSession_UpdateSMContext Request with a release indication to request the release of the PDU Session and then the AMF forwards the N2 SM request to release the AN resources associated with the PDU session- If the UE is in CM-IDLE state, the AMF locally releases the PDU session without paging the UE and causes the SMF to locally release the SM context for the UE by a Nsmf_PDUSession_ReleaseSMContext, as in step 1c in clause 4.3.4.2 of TS 23.502 [3]. The PDU Session status is synchronized at next time when the UE connects to the network.For a non-supporting UE, if validity time applies to an S-NSSAI, an AMF supporting temporarily available network slices shall:- If the validity time indicates the S-NSSAI is available, allow or partially allow the network slice when requested, establish PDU sessions when requested.- If the S-NSSAI is provided in a Requested NSSAI in a Registration Request by the UE and the validity time indicates the S-NSSAI is not available, reject the registration and remove the S-NSSAI from the Configured NSSAI by providing an updated Configured NSSAI in the Registration Accept message.- If the S-NSSAI is in the UE in the Allowed NSSAI or Partially Allowed NSSAI and the validity time indicates the S-NSSAI is not available, remove the S-NSSAI from the Configured NSSAI and the Allowed NSSAI or Partially Allowed NSSAI by a UE Configuration Update procedure. If there is any PDU session established for the S-NSSAI, the AMF requests the SMF to release the PDU session in the network:- If the UE is in CM-CONNECTED state, the AMF releases the PDU session for the S-NSSAI by sending to the SMF, as in step 1f in clause 4.3.4.2 of TS 23.502 [3], a Nsmf_PDUSession_UpdateSMContext Request with a release indication to request the release of the PDU Session and then the AMF forwards the N2 SM request to release the AN resources associated with the PDU session- If the UE is in CM-IDLE, the AMF locally releases the PDU session without paging the UE and causes the SMF to locally release the SM context for the UE by a Nsmf_PDUSession_ReleaseSMContext, as in step 1c in clause 4.3.4.2 of TS 23.502 [3]. The PDU Session status is synchronized at next time when the UE connects to the networkNOTE 3: If the network slice becomes unavailable, and a large number of UEs are impacted, the AMF can send the updates to the non-supporting UEs in a manner that avoids surge in signalling (e.g. next time the UE becomes connected).- If the AMF detects from the validity time of a S-NSSAI that it is available again, then update the Configured NSSAI to include the S-NSSAI via a UE Configuration Update procedure.NOTE 4: The AMF, for the case of UE not performing any actions despite the validity timing information provided by the network, can terminate PDU Session(s) associated with S-NSSAI subject to be terminated according to the validity time by explicitly releasing the PDU Sessions associated with the S-NSSAI.From the above, it is evident that a slice / slices can only be used by a UE if the slice(s) is deemed to be available otherwise the UE is not allowed to get access to these slice(s) and the network takes certain actions to ensure this is the case.Overview of NAS signaling recoveryIn addition to the above, a UE in 5GMM-CONNECTED mode may experience a loss of connection at the lower layers which then triggers a notification to the NAS. This in turn leads the NAS to enter 5GMM-IDLE mode from which the NAS attempts to re-establish the NAS connection by sending a corresponding NAS message. This is referred to as re-establishment of the NAS signaling connection which is described in section 5.3.1.2 of TS 24.501 [1]:When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has no pending NAS procedure and no pending uplink user data for PDU session(s) with user-plane resources already established, the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the registration procedure for mobility and periodic registration update and include the Uplink data status IE in the REGISTRATION REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause 5.5.1.3 for further details).When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has pending uplink user data for PDU session(s) with user-plane resources already established but no pending NAS procedure, the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication (see subclause 5.6.1 for further details).When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has a pending registration procedure, a service request procedure, or a de-registration procedure, the UE shall:a) enter 5GMM-IDLE mode;b) proceed with the pending procedure; andc) if the pending procedure is a service request or registration procedure and the SERVICE REQUEST message, the CONTROL PLANE SERVICE REQUEST message or the REGISTRATION REQUEST message does not include UE request type IE with Request type value set to "NAS signalling connection release", the UE shall include the Uplink data status IE in the SERVICE REQUEST message, or in the REGISTRATION REQUEST message, indicating the PDU session(s) for which user-plane resources were not active prior to receiving a fallback indication from the lower layers and the UE has pending user data to be sent over 3GPP access, if any, and the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclauses 5.5.1.3 and 5.6.1 for further details).When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has a pending NAS procedure other than a registration procedure, a service request procedure, or a de-registration procedure, the UE shall:a) enter 5GMM-IDLE mode;b) initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause 5.6.1 for further details); andc) upon successful service request procedure completion, proceed with any pending procedure.When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has no pending NAS procedure and no pending uplink user data for PDU session(s) with user-plane resources already established, and the UE was using network resources for 5G ProSe direct discovery over PC5 or 5G ProSe direct communication over PC5 (see 3GPP TS 23.304 [6E]), the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause 5.6.1 for further details).The cases above apply when the UE is in an allowed area or when the UE is not in a non-allowed area.When the UE:a) is in a non-allowed area or is not in an allowed area;b) is in 5GMM-CONNECTED mode over 3GPP access;c) receives a fallback indication from lower layers; andd) does not have signalling pending,the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the registration procedure for mobility and periodic registration update. The UE shall not include the Uplink data status IE in the REGISTRATION REQUEST message except if the PDU session for which user-plane resources were active is an emergency PDU session, or if the UE is configured for high priority access in selected PLMN or SNPN.In the above cases when the UE receives a fallback indication from lower layers, if the UE is in non-allowed area or not in allowed area, the UE shall behave as specified in subclause 5.3.5.Based on the above, whenever the UE attempts to re-establish its NAS signaling connection, the UE is supposed to send the Uplink data status IE and request user-plane (UP) resources for those PDU sessions that had UP resources before the fallback indication was received.When a UE re-establishes the NAS connection, the UE may have changed cells within a TA or it may have moved into a new TA within its RA - which contains the list of allowed TAs for the UE. According to the current specification (e.g., referring to TS 23.501 [1]), as part of the NAS signaling re-establishment, the UE shall request the establishment of UP resources for all those sessions that had UP resources before the fallback indication was received. However, the UE may be re-establishing its NAS connection from a cell or TA which does not support a slice for which UP resources were active, or were established, before the fallback indication was received. This contradicts the requirements for heterogenous slice support which necessitates that UP resources are only requested if the UE is in the area (cell or TA) where a slice is supported. A similar problem may arise if a slice is only available within a validity time.As described above, when a UE re-establishes the NAS connection, the UE may have changed cells within a TA or it may have moved into a new TA within its RA - which contains the list of allowed TAs for the UE. According to the current specification, as part of the NAS signaling re-establishment, the UE shall request the establishment of UP resources for all those sessions that had UP resources before the fallback indication was received. However, the UE may be re-establishing its NAS connection from a cell or TA which does not support a slice for which UP resources were active, or were established, before the fallback indication was received. This contradicts the requirements for heterogenous slice support which necessitates that UP resources are only requested if the UE is in the area (cell or TA) where a slice is supported. As such, the UE is currently not performing any check on slice availability as part of the NAS signaling re-establishment.A similar problem may arise if a slice is only available within a validity time. That is, when a UE re-establishes a NAS signaling connection the UE currently does not verify if the slice is available or not.In addition, it is not clear what the network will do or how the network may behave when the UE requests the establishment of UP resources for which the slice is not considered to be available.Accordingly, various examples of the present disclosure aim to address at least to some extent one or more of these issues. That is, various examples aim to provide behaviour for the UE and / or the network in the event of a situation corresponding to the above arising. Of course, other advantages may also arise from the examples described herein.It will be understood that all examples provided herein may be provided in any order or in any combination with one another. Furthermore, any feature(s) disclosed in relation to one example may be combined with any feature(s) disclosed in combination with one or more other examples.It will be appreciated that, in the present disclosure, a slice (or S-NSSAI) that is associated with or that corresponds to a PDU session may refer to, or may mean, a slice (or S-NSSAI) that is associated with or that corresponds to a PDU session identity. Similarly, in the present disclosure, a PDU session which is identified by a PDU session identity may be associated with a slice (or an S-NSSAI).According to various examples of the present disclosure, during re-establishment of a NAS signalling connection (optionally, after the (NAS in the) UE in 5GMM-CONNECTED mode receives a fallback indication from the lower layers), the UE may verify (or check, identify, determine etc.) for at least one condition.Various examples of the UE performing verification of (or checking for) a condition (e.g., a location-based condition) include: for each and / or every slice (or for each and / or every PDU session which is associated with a slice) which had UP resources established prior to receiving the fallback indication, the UE may verify if the slice (i.e., said slice) is supported in the UE's current location (where the location may be a cell or a TA) from where the UE is re-establishing (or is attempting to re-establish) its NAS connection.In some examples, if the verification is positive (or is successful), the UE may determine that a slice is supported in its current location, and (e.g., subsequently) the UE may request the UP resources to be (re-)established for the PDU session which is associated with the slice by requesting the PDU session ID in the Uplink data status IE, e.g. as part of the NAS message or procedure for re-establishing the NAS connection.In some examples, if the verification is negative (or is not successful), the UE may determine that a slice is not supported in its current location, and (e.g., subsequently) the UE may not request the UP resources to be (re-)established for the PDU session which is associated with the slice by requesting the PDU session ID in the Uplink data status IE, e.g. as part of the NAS message or procedure for re-establishing the NAS connection.According to various examples of the present disclosure, the UE may verify (or check, identify, determine etc.) for a condition which is related to the availability of a slice based on a validity time (e.g. a time-based condition).Various examples of the UE performing a verification (or check, determination etc.) of such a condition include: for each and / or every slice (or for each and / or every PDU session which is associated with a slice) which had UP resources established prior to receiving the fallback indication, the UE should verify if the slice is available based on a validity time configuration information (e.g., that the UE may have).In some examples, if the verification is positive (or is successful), the UE may determine that a slice is available in this current time, and (e.g., subsequently) the UE may request the UP resources to be (re-)established for the PDU session which is associated with the slice by requesting the PDU session ID in the Uplink data status IE, e.g. as part of the NAS message or procedure for re-establishing the NAS connection.In some examples, if the verification is negative (or is not successful), the UE may determine that a slice is not available in this current time, and (e.g., subsequently) the UE may not request the UP resources to be (re-)established for the PDU session which is associated with the slice by requesting the PDU session ID in the Uplink data status IE, e.g. as part of the NAS message or procedure for re-establishing the NAS connection.According to various examples, the UE may verify one or both of the conditions stated above. In further examples, the UE may be configured to act (e.g. operate) according to the behaviour described above, for example if both conditions are positive (e.g., verification result is positive) then the UE may request the re-establishment of UP resources. In further examples, if one or both of the conditions are negative (e.g., verification result is negative) then the UE may not request the re-establishment of UP resources as part of the NAS signalling re-establishment procedure.It will be appreciated that the procedures, examples etc. disclosed herein may apply for any NAS message that is used to recover, or to re-establish, the NAS signalling connection; e.g. the Registration Request, Service Request, Control Plane Service Request, etc.According to various examples of the present disclosure (e.g., a first set of examples), a UE is configured to verify slice availability when recovering its NAS signaling connection, where the verification is based on the UE's location.The following examples (e.g., examples in accordance with the first set of examples) may apply for a UE in 5GMM-CONNECTED mode which receives a fallback indication from the lower layers.According to an example, when sending a NAS message to re-establish an NAS signalling connection (optionally, after receiving a fallback indication from the lower layers), a UE may verify (e.g., determine, check, identify etc.) whether one or more slice (e.g. each slice corresponding to each PDU session for which there was UP resources established prior to the fallback indication being received from the lower layers) is available at the UE's current location, where the location may be a cell or a TA, or RA, etc. The verification may be based on the support of the slice and / or the granularity of the location.In various examples such as may be combined with any of the above, when verifying if the UE's current location supports a slice, or whether the slice is available in the UE's current location, the UE may do so by verifying if the UE's current location (e.g. cell or TA) is within (or is part of) the network slice area of service (NS-AoS) for the given slice (or S-NSSAI). If yes, then the UE may determine that the current location supports the slice, or that the slice is available in the UE's current location. If no, then the UE may determine that the current location does not support the slice, or that the slice is not available in the UE's current location.In various examples such as may be combined with any of the above, when verifying if the UE's current location supports a slice, or whether the slice is available in the UE's current location, the UE may do so by verifying if the slice (or S-NSSAI) in question is part of (or is supported in) the UE's network slice area of service (NS-AoS), optionally for the current location. If yes, then the UE may determine that the current location supports the slice, or that the slice is available in the UE's current location. If no, then the UE may determine that the current location does not support the slice, or that the slice is not available in the UE's current location.If the UE determines that the slice is supported in the UE's current location (e.g. cell or TA or RA, or that the slice is part of the UE's NS-AoS), then the UE may include, in a message (e.g. reestablishment message) such as the NAS message (which is used to re-establish the NAS signaling connection), the Uplink data status IE (or some other indication) indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication and which correspond to a slice (or S-NSSAI) that is determined to be supported (or to be available) in the UE's current location. For example, the UE may include, in a message used to re-establish the connection, an indication of the PDU session(s) associated with (or corresponding to) the supported slice(s).If the UE determines that no slice (or S-NSSAI) corresponding to any PDU session, for which there were UP resources established prior to the fallback indication, are supported in the UE's current location, then the UE may behave (e.g., be configured to operate) according to any one or more of the following examples:If the UE has user data pending for another PDU session, for which no UP resources were established prior to the fallback indication, then the UE may verify if the PDU session in question is associated with a slice (or S-NSSAI) which is supported in the UE's current location (e.g. as has been described above in relation to verifying if a slice for which UP resources were established is supported).Optionally, if at least one such PDU session exists, then the UE may include the Uplink data status IE (in the NAS message) and request UP resources for such a PDU session.Optionally, if no slice (or S-NSSAI) corresponding to such a PDU session is supported in the UE's location, then the UE may either:Re-establish the NAS signaling connection by sending a NAS message and, in this case, the UE may not include the Uplink data status IE in the NAS message, or may include the Uplink data status IE in the NAS message but may not request UP for any PDU session. Optionally, the UE may use the Registration Request message to re-establish the NAS signalling connection in this case.orThe UE may not re-establish the NAS signalling connection. Optionally, the UE may remain in 5GMM-IDLE mode.In any of the examples, the NAS message may be any of the following: Registration Request message, Service Request message, or Control Plane Service Request message.In various examples, the UE may behave / operate as described in any of the examples above (e.g. such as any example in the first set of examples) after a transition to 5GMM-IDLE mode following the fallback indication; e.g., the UE may first enter 5GMM-IDLE mode and then behave as described in any of the examples above.In various examples, the UE may behave as described in any of the examples above (e.g. such as any example in the first set of examples) when it is a UE which supports S-NSSAI location validity information (e.g., when the UE is a UE which has set the NS-AoS bit to "S-NSSAI location validity information supported" in the 5GMM capability IE of the REGISTRATION REQUEST message), and / or when the UE has received / stored S-NSSAI location validity information from the network (e.g. from the AMF) in any NAS message (e.g., in the Registration Accept message or the Configuration Update Command message, etc.).It will be appreciated that for a UE which supports S-NSSAI location validity information (e.g. the UE is a UE which has set the NS-AoS bit to "S-NSSAI location validity information supported" in the 5GMM capability IE of the REGISTRATION REQUEST message), but has not received S-NSSAI location validity information from the network (e.g. from the AMF) or does not have any valid S-NSSAI location validity information (e.g. which is stored and / or available in the UE), the UE may request UP resources for any PDU session which had resources established prior to the fallback indication. For instance, the UE may do so as described in TS 24.501 [2], such as by setting the PDU session ID (to the value which indicates that UP resources are requested, e.g. the bit value is set to 1) in the Uplink data status IE which should be sent in the NAS message that is used for NAS connection re-establishment.The present disclosure also includes examples in which the UE may behave as described above (e.g. according to any example describe above, such as any example in the first set of examples) for any S-NSSAI which is either in the partially allowed NSSAI or the allowed NSSAI.Note that any combination or order of conditions may be verified by the UE in examples of the present disclosure.The following is a non-limiting example of a change which may be made to TS 23.501 [1] (e.g. v 18.2.1) to implement one or more of the examples described above. It will be appreciated that this may be useful for illustrating examples of the present disclosure, but should not be seen to limit how the present disclosure may be implemented.Example of Potential Changes (where changes areunderlined)5.3.1.2 Re-establishment of the N1 NAS signalling connectionWhen the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has no pending NAS procedure and no pending uplink user data for PDU session(s) with user-plane resources already established, the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the registration procedure for mobility and periodic registration update and:1)if the UE does not support the S-NSSAI location validity information or the UE has not received any S-NSSAI location validity information from the AMF, the UE shall include the Uplink data status IE in the REGISTRATION REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause　5.5.1.3 for further details); or2)if the UE supports the S-NSSAI location validity information and the UE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the REGISTRATION REQUEST message (see subclause　5.5.1.3 for further details).When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has pending uplink user data for PDU session(s) with user-plane resources already established but no pending NAS procedure, the UE shall:a) enter 5GMM-IDLE mode; and1)if the UE does not support the S-NSSAI location validity information or the UE has not received any S-NSSAI location validity information from the AMF,the UE shall initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message,or the CONTROL PLANE SERVICE REQUEST message,indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication (see subclause　5.6.1 for further details); or2)if the UE supports the S-NSSAI location validity information and the UE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message (see subclause　5.6.1 for further details).When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has a pending registration procedure, a service request procedure, or a de-registration procedure, the UE shall:a) enter 5GMM-IDLE mode;b) proceed with the pending procedure; andc) if the pending procedure is a service request or registration procedure and the SERVICE REQUEST message, the CONTROL PLANE SERVICE REQUEST message or the REGISTRATION REQUEST message does not include UE request type IE with Request type value set to "NAS signalling connection release", and:1)if the UE does not support the S-NSSAI location validity information or the UE has not received any S-NSSAI location validity information from the AMF, the UE shall include the Uplink data status IE in the SERVICE REQUEST messageor Control Plane Service Request message, or in the REGISTRATION REQUEST message, indicating the PDU session(s) for which user-plane resources were not active prior to receiving a fallback indication from the lower layers and the UE has pending user data to be sent over 3GPP access, if any, and the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclauses　5.5.1.3 and 5.6.1 for further details); or2)if the UE supports the S-NSSAI location validity information and the UE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the the SERVICE REQUEST message or Control Plane Service Request message, or in the REGISTRATION REQUEST message (see subclause　5.5.1.3 and 5.6.1 for further details).When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has a pending NAS procedure other than a registration procedure, a service request procedure, or a de-registration procedure, the UE shall:a) enter 5GMM-IDLE mode;b) initiate the service request procedure and:1)if the UE does not support the S-NSSAI location validity information or the UE has not received any S-NSSAI location validity information from the AMF, the UE shall include the Uplink data status IE in the SERVICE REQUEST or the CONTROL PLANE SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause　5.6.1 for further details); or2)if the UE supports the S-NSSAI location validity information and the UE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message (see subclause　5.6.1 for further details);andc) upon successful service request procedure completion, proceed with any pending procedure.When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has no pending NAS procedure and no pending uplink user data for PDU session(s) with user-plane resources already established, and the UE was using network resources for 5G ProSe direct discovery over PC5 or 5G ProSe direct communication over PC5 (see 3GPP　TS　23.304　[6E]), the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the service request procedure and:1)if the UE does not support the S-NSSAI location validity information or the UE has not received any S-NSSAI location validity information from the AMF, the UE shall include the Uplink data status IE in the SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause　5.6.1 for further details); or2)if the UE supports the S-NSSAI location validity information and the UE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message (see subclause　5.6.1 for further details).The cases above apply when the UE is in an allowed area or when the UE is not in a non-allowed area.When the UE:a) is in a non-allowed area or is not in an allowed area;b) is in 5GMM-CONNECTED mode over 3GPP access;c) receives a fallback indication from lower layers; andd) does not have signalling pending,the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the registration procedure for mobility and periodic registration update. The UE shall not include the Uplink data status IE in the REGISTRATION REQUEST message except if the PDU session for which user-plane resources were active is an emergency PDU session, or if the UE is configured for high priority access in selected PLMN or SNPN.In the above cases when the UE receives a fallback indication from lower layers, if the UE is in non-allowed area or not in allowed area, the UE shall behave as specified in subclause　5.3.5.According to various examples of the present disclosure (e.g., a second set of examples), a UE is configured to verify slice availability when recovering its NAS signaling connection, where the verification is based on time (time validity).The following examples (e.g., examples in accordance with the second set of examples) may apply for a UE in 5GMM-CONNECTED mode which receives a fallback indication from the lower layers.According to an examples, when sending a NAS message to re-establish the NAS signalling connection (optionally after receiving a fallback indication from the lower layers), the UE may verify (e.g., determine, check, identify etc) whether one or more slices (e.g., each slice corresponding to each PDU session for which there was UP resources established prior to the fallback indication being received from the lower layers) is available based on an S-NSSAI time validity information (or, more generally, time information), where, in some examples, the UE may have received a stored S-NSSAI time validity information (or time information) from the network.In some examples, when verifying if the slice (or S-NSSAI) can be used at the current time, or whether the slice is available based on an S-NSSAI time validity information, the UE may do so by verifying if the S-NSSAI time validity information indicates whether the slice can be used at the current time (or not).If yes, then the UE may determine that the slice can be used at the current time, or that the slice is available for use e.g. based on the S-NSSAI time validity information. If no, then the UE may determines that the slice cannot be used at the current time, or that the slice is not available for use based on the S-NSSAI time validity information.If the UE determines that the slice can be used at the current time, or that the slice is available or can be used based on the S-NSSAI time validity information, then the UE may include, in a message (e.g. reestablishment message) such as the NAS message (which is used to re-establish the NAS signaling connection), the Uplink data status IE (or some other indication) indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication and which correspond to a slice (or S-NSSAI) that is determined to be supported (or to be available) at the current time and / or in the UE's current location. For example, the UE may include, in a message used to re-established the connection, an indication of the PDU session(s) associated with (or corresponding to) the supported slice(s).If the UE determines that no slice(s) (or S-NSSAI) corresponding to any PDU session, for which there were UP resources established prior to the fallback indication, may be used at the current time, or that the slice(s) is / are not available or cannot be used based on the S-NSSAI time validity information, then the UE may behave (e.g., be configured to operate) according to any of the following examples:If the UE has user data pending for another PDU session, for which no UP resources were established prior to the fallback indication, then the UE may verify if the PDU session in question is associated with a slice (or S-NSSAI) that can be used at the current time, or that the slice is available or can be used based on the S-NSSAI time validity information.-Optionally, if at least one such PDU session exists, then the UE may include the Uplink data status IE (in the NAS message) and may request UP resources for such a PDU session.-Optionally, if no slice (or S-NSSAI) corresponding to such a PDU session can be used at the current time, or that no slice is available or no slice can be used based on the S-NSSAI time validity information, then the UE may either:1)Re-establish the NAS signaling connection by sending a NAS message and, in this case, the UE may not include the Uplink data status IE in the NAS message, or may include the Uplink data status IE in the NAS message but may not request UP for any PDU session. Optionally the UE should use the Registration Request message to re-establish the NAS signalling connection in this case.or2)The UE may not re-establish the NAS signalling connection. Optionally, the UE should remain in 5GMM-IDLE mode.In any of the examples, the NAS message may be any of the following: Registration Request message, Service Request message, or Control Plane Service Request message.In various examples, the UE may behave / operate as described in any of the examples above (such as any example in the second set of examples) after a transition to 5GMM-IDLE mode following the fallback indication; e.g. the UE may first enter 5GMM-IDLE mode and then behave as described above.In various examples, the UE may behave / operate as described in any of the examples above (e.g. such as any example in the second set of examples) when it is a UE which supports S-NSSAI time validity information (e.g., when the UE is a UE which has set the S-NSSAI time validity information (TempNS) bit to "S-NSSAI time validity information supported" in the 5GMM capability IE of the REGISTRATION REQUEST message), and / or when the UE has received / stored S-NSSAI time validity information from the network (e.g. from the AMF).It will be appreciated that for a UE which supports S-NSSAI time validity information( e.g. the UE is a UE which has set the S-NSSAI time validity information (TempNS) bit to "S-NSSAI time validity information supported" in the 5GMM capability IE of the REGISTRATION REQUEST message), but has not received S-NSSAI time validity information from the network (e.g. from the AMF) or does not have any valid S-NSSAI location validity information (e.g. which is stored and / or available in the UE), the UE may request UP resources for any PDU session which had resources established prior to the fallback indication. For instance, the UE may do so as described in TS 24.501 [2], such as by setting the PDU session ID (to the value which indicates that UP resources are requested, e.g. the bit value is set to 1) in the Uplink data status IE which should be sent in the NAS message that is used for NAS connection re-establishment.The present disclosure also includes examples in which the UE may behave as described above (e.g. according to any example describe above, such as any example in the second set) for any S-NSSAI which is either in the partially allowed NSSAI or the allowed NSSAI.As mentioned earlier, that any combination or order of conditions (e.g. referring to those conditions given in the examples disclosed herein) may be verified by the UE. Additionally, all examples provided herein may also be provided in any order or combination with each other.It will be appreciated that, in various examples, the UE may verify both conditions related to slice support / availability in a location (such as described herein) and also slice availability based on a validity time (such as described herein). The UE may then request UP resources for the slice (corresponding to the PDU session which had UP resources established prior to the fallback indication) if a slice is both available in the UE's location and also available for use based on a validity time. If one or both conditions are not met, then the UE may not request the re-establishment of UP resources for the PDU session as part of the NAS signalling re-establishment request. Note that the request for UP resources can be done using the Uplink data status IE as have been described herein.Figure 1 is a flow diagram showing a method according to various examples of the present disclosureIn 110, the UE us in 5GMM-CONNECTED mode and has received a fallback indication from the lower layers. The UE also has a NAS message to re-establish an NAS signalling connection to send, or is in the process of sending such a message.In 120, the UE verifies if a slice (e.g., corresponding to each PDU session for which there was UP resources established prior to the fallback indication being received) is available at the UE's current location, such as a current cell, TA or RA (e.g., a location-based condition), or is available at the current time (e.g., time-based condition). Optionally, both conditions may be checked / verified (such as describe in various examples given above).If the outcome of the verification in 120 is positive (e.g., the slice(s) (or S-NSSAI(s)) are supported in the current location and / or may be used at the current time), the method follows the path indicated by "YES" to 130, in which the UE may include, in the NAS message, Uplink data status IE indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication and which correspond to the slice (or S-NSSAI) that is determined to be supported (or to be available) in the UE's current location or at the current time.If the outcome of the verification in 120 is negative, (e.g., (e.g. the slice(s) (or S-NSSAI(s)) are not supported in the current cell or TA and / or may not be used at the current time), the method follows the path indicated by "NO" to 140, in which the UE determines that the current location does not support the slice, or that the slice is not available in the UE's current location. Optionally, in this case, if the UE has user data pending for another PDU session, for which no UP resources were established prior to the fallback indication, then the UE may verify if the PDU session in question is associated with a slice (or S-NSSAI) which is supported in the UE's current location (e.g. as has been described above in relation to verifying if a slice for which UP resources were established is supported). Optionally, if at least one such PDU session exists, then the UE may include the Uplink data status IE (in the NAS message) and request UP resources for such a PDU session. Optionally, if no slice (or S-NSSAI) corresponding to such a PDU session is supported in the UE's location, then the UE may either: (i) re-establish the NAS signaling connection by sending a NAS message and, in this case, the UE may not include the Uplink data status IE in the NAS message, or may include the Uplink data status IE in the NAS message but may not request UP for any PDU session, and, optionally, the UE may use the Registration Request message to re-establish the NAS signalling connection in this case; or (ii) the UE may not re-establish the NAS signalling connection, and, optionally, the UE may remain in 5GMM-IDLE mode.It will be appreciated that the examples described earlier in the present disclosure provide other examples of cases / scenarios / conditions in which the outcome of 120 (i.e., the verification of whether the slice(s) are supported or may be used) is positive and / or is negative. These other examples may also be regarded in combination with the method of Fig. 1, so as to define individual methods based on each example.Similarly, the examples described earlier in the present disclosure provide other examples of UE behaviour in the event that the outcome of the verification (i.e. of 120) is positive and / or is negative. These other examples may also be regarded in combination with the method of Fig. 1, so as to define individual methods based on each example. Of course, it will also be appreciated that the present disclosure envisages all combinations of such methodsIn accordance with a first example of the present disclosure, there is provided a UE (or other network entity), wherein, in a case where the UE is in an initial state or mode in which a first connection is to be re-established, the UE is configured to: determine if a first slice satisfies a condition, wherein the first slice corresponds to a first protocol data unit (PDU) session for which user plane (UP) resources were previously established; and, if the first slice satisfies the condition, include an indication of the first PDU session in a message for re-establishing the first connection.In accordance with a second example, there is provided the UE of the first example, wherein the first connection is a NAS signalling connection.In accordance with a third example, there is provided the UE of the first example or the second example, wherein the initial state or mode is 5GMM-CONNECTED mode.In accordance with a fourth example, there is provided the UE of any of the first example to the third example, wherein in the initial state or mode the UE has received a fallback indication from lower layers.In accordance with a fifth example, there is provided the UE of any of the first example to the fourth example, wherein, if it is determined that the slice does not satisfy the condition, the UE is configured to: if the UE has user data pending for a second PDU session, determine if a second slice associated with the second PDU session satisfies the condition.In accordance with a sixth example, there is provided the UE of the fifth example, wherein, if the second slice satisfies the condition, the UE is configured to transmit a message including a request for UP resources for the second PDU session; and / or of the second slice does not satisfy the condition, the UE is configured to: transmit a message for re-establishing the first connection without a request for UP resources for any PDU session including the first PDU session and the second PDU session; or determine not to re-establish the first connection.In accordance with a seventh example, there is provided the UE of the fifth example or the sixth example, wherein UP resources were not previously established for the second PDU session.In accordance with an eighth example, there is provided the UE of any of the first example to the seventh example, wherein the condition includes a time-based condition and / or a location-based condition.In accordance with a ninth example, there is provided the UE of any of the first example to the eighth example, wherein the UE is configured to: determine if the first slice is available in a current location of the UE, and, if so, determine the condition to be satisfied; and / or determine if the first slice is available at a current time, and, if so, determine the condition to be satisfied.In accordance with a tenth example, there is provided the UE of the ninth example, wherein the condition is only satisfied if the first slice is available in the current location and is available at the current time.In accordance with an eleventh example, there is provided the UE of the ninth example or the tenth example, wherein the current location corresponds to, or is, a cell, a tracking area (TA) or a registration area (RA).In accordance with a twelfth example, there is provided the UE of any of the first example to the eleventh example, wherein the message is a NAS message for re-establishing the first connection (e.g., the first connection is an NAS connection).In accordance with a thirteenth example, there is provided the UE of any of the first example to the eleventh twelfth, wherein the indication corresponds to an Uplink (UL) data status information element (IE).It will be appreciated that the above first to thirteenth examples may also be provided in the form of a method performed by the network entity, and / or in the form of a set of computer-readable instructions (e.g., arranged to perform said method / operations when executed by at least one processor).Figure 2 is a block diagram of an exemplary apparatus, or network entity, that may be used in examples of the present disclosure. The skilled person will appreciate said entity may be implemented, for example, as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, and / or as a virtualised function instantiated on an appropriate platform, e.g. on a cloud infrastructure.The entity 1000 may include a processor (or controller) 1001, a transmitter 1003 and a receiver 1005. The receiver 1005 is configured for receiving one or more messages from one or more other network entities, for example as described above. The transmitter 1003 is configured for transmitting one or more messages to one or more other network entities, for example as described above. In an embodiment, the entity 1000 may include a transceiver comprising the receiver 1005 and the transmitter 1003. The processor 1001 is configured for performing one or more operations, for example according to the operations as described above. The processor may include at least one processor.Figure 3 is a flow diagram illustrating a method according to various examples of the present disclosure. The method is performed by a UE.In operation S310, while the UE is in 5GMM-CONNECTED mode, the UE receives a fallback indication. In various examples, the UE enters 5GMM-IDLE mode, in response.In operation S320, the UE verifies whether a network slice (NS) is available based on a location of the UE and / or time information, wherein the NS is associated with a protocol data unit (PDU) session for which user plane (UP) resources were established prior to the fallback indication being received.It will be appreciated that, in each example / embodiment / aspect etc. described above, one or more features or operations may be omitted, modified or moved (e.g., to change the order of the features or the operations), if desired and appropriate. Additionally, one or more features or operations from any example / embodiment may be combined with features or operations from any other example / embodiment. In particular, regardless of whether or not a pointer towards a combination of features / examples is found herein, the present disclosure should be considered to include all combinations of two or more of the embodiments, examples etc. disclosed herein, and all combinations of two or more of the features disclosed herein.The techniques described herein may be implemented using any suitably configured apparatus and / or system. Such an apparatus and / or system may be configured to perform a method according to any aspect, embodiment or example disclosed herein. Such an apparatus may comprise one or more elements, for example one or more of receivers, transmitters, transceivers, processors, controllers, modules, units, and the like, each element configured to perform one or more corresponding processes, operations and / or method steps for implementing the techniques described herein. For example, an operation / function of X may be performed by a module configured to perform X (or an X-module). The one or more elements may be implemented in the form of hardware, software, or any combination of hardware and software.It will be appreciated that examples of the present disclosure may be implemented in the form of hardware, software or any combination of hardware and software. Any such software may be stored in the form of volatile or non-volatile storage, for example a storage device like a ROM, whether erasable or rewritable or not, or in the form of memory such as, for example, RAM, memory chips, device or integrated circuits or on an optically or magnetically readable medium such as, for example, a CD, DVD, magnetic disk or magnetic tape or the like.It will be appreciated that the storage devices and storage media are embodiments of machine-readable storage that are suitable for storing a program or programs comprising instructions that, when executed, implement certain examples of the present disclosure. Accordingly, certain examples provide a program comprising code for implementing a method, apparatus or system according to any example, embodiment and / or aspect disclosed herein, and / or a machine-readable storage storing such a program. Still further, such programs may be conveyed electronically via any medium, for example a communication signal carried over a wired or wireless connection.While the present disclosure has been shown, illustrated and described with reference to certain examples, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the scope of the disclosure.The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.Further examples of the present disclosure, which may be considered alone or in combination with any other example(s) disclosed herein, are in accordance with the following.TS 23.501 [1] states:"If the UE has indicated that the UE supports S-NSSAI location availability information in the 5GMM Core Network Capability (see clause　5.4.4a), the AMF may, based on OAM configuration, configure the UE with S-NSSAI location availability information for one or more S-NSSAIs when the AMF allocates an RA where the Network Slice availability does not match whole TAs, by including the S-NSSAI location availability information in the Registration Accept message or the UE Configuration Command message. A UE that receives S-NSSAI location availability information applies the information as follows....2. If the S-NSSAI is in the Partially Allowed NSSAI or in the Allowed NSSAI,the UE shall not activate User Plane for any already established PDU Session with that S-NSSAI if the UE is in a cell within the RA but outside the Location information of the S-NSSAI.The UE and SMF shall not exchange user data as payload of a NAS message in both uplink and downlink directions."(emphasis added byunderline)The UE may have PDU sessions with UP resources that have already been established but then experiences fallback. Per section 5.3.1.2 of TS 24.501, the UE shall include the Uplink data status IE indicating the PDU session(s) for which UP resources were active prior to receiving the fallback indication (if any). However, the NAS signaling recovery may happen from a cell or TA within the UE's RA which does not support a corresponding slice. As such the UE should only request the UP resources if the slice is supported in the NS-AoS (Network slice area of service).According to various examples, when re-establishing a NAS connection following fallback indication, the UE should only request UP resource re-establishment if the slice corresponding to the PDU session is supported in the UE. A technical advantage of this is that the UE may not request UP resources for a slice which is not supported in the UE's location, hence preventing contradicting the requirements from SA2.Examples in accordance with this may be implemented according to the following changes to TS 23.501 (where the changes areunderlined):****** START CHANGES ******5.3.1.2 Re-establishment of the N1 NAS signalling connectionWhen the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has no pending NAS procedure and no pending uplink user data for PDU session(s) with user-plane resources already established, the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the registration procedure for mobility and periodic registration update and:1) if the UE does not support the S-NSSAI location validity informationor the UE has not received any S-NSSAI location validity information from the AMF, the UE shall include the Uplink data status IE in the REGISTRATION REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause　5.5.1.3 for further details); or2) if the UE supports the S-NSSAI location validity information and theUE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the REGISTRATION REQUEST message (see subclause　5.5.1.3 for further details).When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has pending uplink user data for PDU session(s) with user-plane resources already established but no pending NAS procedure, the UE shall:a) enter 5GMM-IDLE mode; and1) if the UE does not support the S-NSSAI location validity informationor the UE has not received any S-NSSAI location validity information from the AMF, the UE shall initiate the service request procedure and include the Uplink data status IE in the SERVICE REQUEST message, or the CONTROL PLANE SERVICE REQUEST message, indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication (see subclause　5.6.1 for further details); or2) if the UE supports the S-NSSAI location validity information and theUE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message (see subclause　5.6.1 for further details).When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has a pending registration procedure, a service request procedure, or a de-registration procedure, the UE shall:a) enter 5GMM-IDLE mode;b) proceed with the pending procedure; andc) if the pending procedure is a service request or registration procedure and the SERVICE REQUEST message, the CONTROL PLANE SERVICE REQUEST message or the REGISTRATION REQUEST message does not include UE request type IE with Request type value set to "NAS signalling connection release", and:1) if the UE does not support the S-NSSAI location validity informationor the UE has not received any S-NSSAI location validity information from the AMF, the UE shall include the Uplink data status IE in the SERVICE REQUEST message or Control Plane Service Request message, or in the REGISTRATION REQUEST message, indicating the PDU session(s) for which user-plane resources were not active prior to receiving a fallback indication from the lower layers and the UE has pending user data to be sent over 3GPP access, if any, and the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclauses　5.5.1.3 and 5.6.1 for further details); or2) if the UE supports the S-NSSAI location validity information and theUE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the the SERVICE REQUEST message or Control Plane Service Request message, or in the REGISTRATION REQUEST message (see subclause　5.5.1.3 and 5.6.1 for further details).When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has a pending NAS procedure other than a registration procedure, a service request procedure, or a de-registration procedure, the UE shall:a) enter 5GMM-IDLE mode;b) initiate the service request procedure and:1) if the UE does not support the S-NSSAI location validity informationor the UE has not received any S-NSSAI location validity information from the AMF, the UE shall include the Uplink data status IE in the SERVICE REQUEST or the CONTROL PLANE SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause　5.6.1 for further details); or2) if the UE supports the S-NSSAI location validity information and theUE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message (see subclause　5.6.1 for further details); andc) upon successful service request procedure completion, proceed with any pending procedure.When the UE in 5GMM-CONNECTED mode over 3GPP access receives a fallback indication from lower layers, and the UE has no pending NAS procedure and no pending uplink user data for PDU session(s) with user-plane resources already established, and the UE was using network resources for 5G ProSe direct discovery over PC5 or 5G ProSe direct communication over PC5 (see 3GPP　TS　23.304　[6E]), the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the service request procedure and:1) if the UE does not support the S-NSSAI location validity informationor the UE has not received any S-NSSAI location validity information from the AMF, the UE shall include the Uplink data status IE in the SERVICE REQUEST message indicating the PDU session(s) for which user-plane resources were active prior to receiving the fallback indication, if any (see subclause　5.6.1 for further details); or2) if the UE supports the S-NSSAI location validity information and theUE has received S-NSSAI location validity information from the AMF, then for any PDU session for which user-plane resources were active prior to receiving the fallback indication, if the corresponding S-NSSAI is part of the UE's NS-AoS, the UE shall indicate the PDU session in the Uplink data status IE and include this IE in the SERVICE REQUEST message or the CONTROL PLANE SERVICE REQUEST message (see subclause　5.6.1 for further details).The cases above apply when the UE is in an allowed area or when the UE is not in a non-allowed area.When the UE:a) is in a non-allowed area or is not in an allowed area;b) is in 5GMM-CONNECTED mode over 3GPP access;c) receives a fallback indication from lower layers; andd) does not have signalling pending,the UE shall:a) enter 5GMM-IDLE mode; andb) initiate the registration procedure for mobility and periodic registration update. The UE shall not include the Uplink data status IE in the REGISTRATION REQUEST message except if the PDU session for which user-plane resources were active is an emergency PDU session, or if the UE is configured for high priority access in selected PLMN or SNPN.In the above cases when the UE receives a fallback indication from lower layers, if the UE is in non-allowed area or not in allowed area, the UE shall behave as specified in subclause　5.3.5.****** END CHANGES ******The above should not be regarded as limiting - the examples may be implemented through other changes to the standards.There now follows an excerpt from TS 24.501, section 9.11.3.100:9.11.3.100 S-NSSAI location validity informationThe purpose of the S-NSSAI location validity information information element is to provide the S-NSSAI location validity information to the UE.The S-NSSAI location validity information information element is coded as shown in Figure　4, Figure 5, Figure 6, and Figure 7 and Table　1.The S-NSSAI location validity information information element can contain per-S-NSSAI location validity information for maximum 8 S-NSSAIs.The S-NSSAI location validity information information is a type 6 information element with a minimum length of 25 octets and a maximum length of 19307 octets.[Table　1]S-NSSAI location validity information information elementHere, it may be described that the PDU session is associated with a slice i.e. S-NSSAI. As shown, the NS-AoS includes a list of:-S-NSSAI, and-Cell identities (cell global identity - CGI)According to various examples of the present disclosure, the UE verifies that the S-NSSAI for a given PDU session is part of (e.g. included in, associated with, related to etc.) the NS-AoS and, if so, verifies whether the current UE cell location matches any of the CGI which is associated with the S-NSSAI.If there is a match then UE considers that the slice is available in the current UE location.In other words, in addition to the above examples of determining whether a NS is available based on a location of the UE, there is also disclosed examples whereby said determination is made by, or based on: verifying whether the S-NSSAI associated with (e.g. for) a PDU session (e.g. a PDU session for which UP resources were established prior to a fallback indication being received (while the UE is in 5GMM-CONNECTED mode, as discussed in other examples above) is part of the NS-AoS, and verifying whether a current UE cell location matches (e.g. corresponds to) any of the cell identities in the NS-AoS (e.g. that are associated with the S-NSSAI).In various examples, the performance of these two verifications is conditional upon the result of the other. For instance, when it is verified that the S-NSSAI if part of the NS-AoS, then (e.g. only then) is it verified whether the current UE cell location matches any of the CGI associated with the S-NSSAI. Alternatively, the two verifications are performed concurrently.If the result of both verifications is positive (e.g. with verification of the S-NSSAI being part of the NS-AoS leading to verifying whether the current UE cell location matches any of the associated CGI), then the UE determines (or considers, or verifies etc.) that the slice is available in the current location.According to an aspect of the present disclosure, there is provided a user equipment (UE) comprising: a transmitter; a receiver; and at least one processor configured to: while the UE is in 5GMM-CONNECTED mode, receive a fallback indication; and verify whether a network slice (NS) is available based on a location of the UE and / or time information, wherein the NS is associated with a protocol data unit (PDU) session for which user plane (UP) resources were established prior to the fallback indication being received.According to various examples, the at least one processor is configured to: if the NS is available, request the UP resources to be re-established by transmitting an indication of the PDU session or the UP resources to a core network.According to various examples, the indication is included in a message, the message being one of a NAS message, a Registration Request message, a Service Request message, or a Control Plane Service Request message.According to various examples, the indication is included in uplink data status information element (IE).According to various examples, the at least one processor is configured to: if the NS is unavailable, determine not to request the UP resources to be re-established for the PDU session.According to various examples, the at least one processor is configured to: verify whether the NS is available in a cell or a tracking area (TA) of the UE; and / or verify whether the NS is available based on a current time or S-NSSAI time validity information.According to various examples, the at least one processor is configured to: verify whether the cell or the TA is within a NS area of service (NS-AoS) for the NS and, if so, verify that the NS is available; and / or verify whether the NS can be used at the current time or based on the S-NSSAI time validity information and, if so, verify that the NS is available.According to various examples, the at least one processor is configured to: if it is verified that the cell of the TA is not within the NS-AoS, determine the NS is not available; and / or if it is verified that the NS cannot be used at the current time or based on the S-NSSAI time validity information, determine the NS is not available.According to various examples, the at least one processor is configured to: verify whether a single network slice selection assistance information (S-NSSAI) for the NS is part of a NS area of service (NS-AoS); if so, verify whether the location of the UE corresponds to a cell identity included in the NS-AoS; and if so, verify that the NS is available in the location of the UE.According to various examples, the UE is configured to support S-NSSAI location validity information, and optionally, the UE is configured to receive the S-NSSAI location validity information from an access and mobility management function (AMF).According to various examples, the at least one processor is configured to: verify whether at least one other NS is available based on the location of the UE or the time information, wherein each of the at least one other NS is associated with another PDU session for which UP resources were established prior to the fallback indication being received; and if the at least one other NS is available, include uplink data status indicating the other PDU session for each of the at least one other NS in the message transmitted to a core network.According to various examples, the at least one processor is configured to: enter 5GMM-IDLE mode in response to receiving the fallback indication.According to another aspect of the present disclosure, there is provided a method of a user equipment (UE), the method comprising: while the UE is in 5GMM-CONNECTED mode, receiving a fallback indication from lower layers; and verifying whether a network slice (NS) is available based on a location of the UE and / or time information, wherein the NS is associated with a protocol data unit (PDU) session for which user plane (UP) resources were established prior to the fallback indication being received.According to various examples, the method further comprises: if the NS is available, requesting the UP resources to be re-established by transmitting an indication of the PDU session or the UPO resources to a core network.According to various examples, the indication is included in a message, the message being one of a NAS message, a Registration Request message, a Service Request message, or a Control Plane Service Request message.According to various examples, the indication is included in uplink data status information element (IE).According to various examples, the method further comprises: if the NS is unavailable, determining not to request the UP resources to be re-established for the PDU session.According to various examples, verifying whether the NS is available based on the location of the UE comprises verifying whether the NS is available in a cell or a tracking area (TA) of the UE; and / or wherein verifying whether the NS is available based on the time information comprises verifying whether the NS is available based on a current time or S-NSSAI time validity information.According to various examples, verifying whether the NS is available in the cell or the TA comprises verifying whether the cell or the TA is within a NS area of service (NS-AoS) for the NS; and / or wherein verifying whether the NS is available based on the current time or S-NSSAI time validity information comprises verifying whether the NS can be used at the current time.According to various examples, the method comprises: if it is verified that the cell or the TA is within the NS-AoS, verifying that the NS is available; and / or if it is verified that the NS can be used at the current time or is available based on the S-NSSAI time validity information, verifying that the NS is available.According to various examples, the method comprises: if it is verified that the cell of the TA is not within the NS-AoS, determining the NS is not available; and / or if it is verified that the NS cannot be used at the current time or based on the S-NSSAI time validity information, determining the NS is not available.According to various examples, verifying whether the NS is available based on the location of the UE comprises: verifying whether a single network slice selection assistance information (S-NSSAI) for the NS is part of a NS area of service (NS-AoS); if so, verifying whether the location of the UE corresponds to a cell identity included in the NS-AoS; and if so, verifying that the NS is available in the location of the UE.According to various examples, the UE is configured to support S-NSSAI location validity information; and optionally, the method comprises receiving the S-NSSAI location validity information from an access and mobility management function (AMF).According to various examples, the method comprises: verifying whether at least one other NS is available based on the location of the UE or the time information, wherein each of the at least one other NS is associated with another PDU session for which UP resources were established prior to the fallback indication being received; and if the at least one other NS is available, including uplink data status indicating the other PDU session for each of the at least one other NS in the message transmitted to a core network.According to another aspect of the present disclosure, there is provided a computer readable storage medium comprising instructions which, when executed by at least one processor of a user equipment (UE), cause the UE to perform a method according to any of the above aspect(s) and / or example(s).According to another aspect of the present disclosure, there is provided a network or a system comprising a UE in accordance with any of the aspect(s) and / or example(s) disclosed above.Furthermore, "at least one item / at least one" described in this disclosure includes any and / or all possible combinations of listed items, and various embodiments and examples in the embodiments described in this disclosure can be changed and combined in any suitable form, and " / "described in this disclosure means "or".The various illustrative logic blocks, modules, and circuits described in this disclosure may be implemented or performed by a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA) or other programmable logic devices, discrete gates or transistor logics, discrete hardware components, or any combination thereof designed to perform the functions described herein. The general purpose processor may be a microprocessor, but in an alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors cooperating with a DSP core, or any other such configuration.The steps of the method or algorithm described in this disclosure may be embodied directly in hardware, in a software module executed by a processor, or in a combination thereof. The software module may reside in a RAM memory, a flash memory, a ROM memory, an EPROM memory, an EEPROM memory, a register, a hard disk, a removable disk, or any other form of storage medium known in the art. An exemplary storage medium is coupled to a processor to enable the processor to read and write information from / to the storage medium. In an alternative, the storage medium may be integrated into the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user equipment. In an alternative, the processor and the storage medium may reside in a user equipment as discrete components.In one or more exemplary designs, the functions may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, each function may be stored as one or more instructions or codes on a computer-readable medium or delivered through it. The computer-readable medium includes both a computer storage medium and a communication medium, the latter including any medium that facilitates the transfer of computer programs from one place to another. The storage medium may be any available medium that can be accessed by a general purpose or special purpose computer.The descriptions set forth herein, taken in conjunction with the drawings, describe example configurations, methods and apparatuses, and does not represent all examples that can be realized or are within the scope of the claims. As used herein, the term "example" means "serving as an example, instance or illustration" rather than "preferred" or "superior to other examples". The detailed description includes specific details in order to provide an understanding of the described technologies. However, these technologies may be practiced without these specific details. In some cases, well-known structures and devices are shown in a block diagram form to avoid obscuring the concepts of the described examples.Although this specification contains many specific implementation details, these should not be interpreted as limitations on any invention or the claimed protection scope, but as descriptions of specific features of specific embodiments of specific inventions. Some features described in this specification in the context of separate embodiments can also be combined in a single embodiment. On the contrary, various features described in the context of a single embodiment can also be implemented separately in a plurality of embodiments or in any suitable sub-combination. Furthermore, although features may be described above as functioning in some combinations, and even initially claimed as such, in some cases, one or more features from the claimed combinations may be deleted from the combinations, and the claimed combinations may be directed to a sub-combination or a variation of a sub-combination.It should be understood that a specific order or hierarchy of steps in the method of this disclosure is illustrative of an exemplary process. Based on design preferences, it can be understood that the specific order or hierarchy of the steps in the method can be rearranged to achieve the functions and effect disclosed in this disclosure. The appended method claims present elements of various steps in an example order, and are not meant to be limited to the particular order or hierarchy presented, unless otherwise stated. Furthermore, although elements may be described or claimed in the singular, the plural is also contemplated unless the limitation on the singular is explicitly stated. Therefore, this disclosure is not limited to the illustrated examples, and any apparatus for performing the functions described herein are included in various aspects of this disclosure.The text and drawings are provided as examples only to help readers understand the disclosure. They are not intended and should not be interpreted as limiting the scope of the disclosure in any way. Although certain embodiments and examples have been provided, based on the content disclosed herein, it will be apparent to those skilled in the art that changes may be made to the illustrated embodiments and examples without departing from the scope of the disclosure.Although the present disclosure has been described with various embodiments, various changes and modifications may be suggested to one skilled in the art. It is intended that the present disclosure encompass such changes and modifications as fall within the scope of the appended claims.

Claims

1.A user equipment (UE) in a wireless communication system, the UE comprising:a transceiver; andat least one processor coupled with the transceiver and configured to:receive a fallback indication in a connected mode, anddetermine whether the UE is in a network slice-area of service (NS-AoS) with respect to a single network slice selection assistance information (S-NSSAI), wherein the S-NSSAI is associated with a protocol data unit (PDU) session for which user plane (UP) resources were active prior to receiving the fallback indication, andin case that it is determined that the UE is in the NS-AoS, transmit, to an access and mobility management function (AMF) entity, a request message including an indication of the PDU session.2.The UE of claim 1, wherein the at least one processor is configured to:receive, from the AMF entity, S-NSSAI location validity information, anddetermine whether the UE is in the NS-AoS based on the S-NSSAI location validity information.3.The UE of claim 1, wherein the request message includes a registration request message, a service request message, and a control plane service request message.4.The UE of claim 1, wherein the indication is included in an uplink data status information element (IE) in the request message.5.The UE of claim 1, wherein the at least one processor is configured to:determine whether the S-NSSAI is available in a cell or a tracking area (TA) of the UE; ordetermine whether the S-NSSAI is available based on a current time or S-NSSAI time validity information.6.The UE of claim 1, wherein the at least one processor is configured to:enter an idle mode in response to receiving the fallback indication, andwherein the UE is configured to support the S-NSSAI location validity information.7.An access and mobility management function (AMF) entity in a wireless communication system, the AMF entity comprising:a transceiver; andat least one processor coupled to the transceiver and configured to:receive, from a user equipment (UE), a request message including an indication of a protocol data unit (PDU) session associated with a single network slice selection assistance information (S-NSSAI), in case that the UE is in a network slice-area of service (NS-AoS) with respect to the S-NSSAI,wherein the S-NSSAI is associated with the PDU session for which user plane (UP) resources were active before the UE receives a fallback indication in a connected mode.8.The AMF entity of claim 7, wherein the at least one processor is configured to:transmit, to the UE, S-NSSAI location validity information for determining whether the UE is in the NS-AoS.9.The AMF entity of claim 7,wherein the request message includes a registration request message, a service request message, and a control plane service request message, andwherein the indication is included in an uplink data status information element (IE) in the request message.10.A method of a user equipment (UE) in a wireless communication system, the method comprising:receiving a fallback indication in a connected mode; anddetermining whether the UE is in a network slice-area of service (NS-AoS) with respect to a single network slice selection assistance information (S-NSSAI), wherein the S-NSSAI is associated with a protocol data unit (PDU) session for which user plane (UP) resources were active prior to receiving the fallback indication; andin case that it is determined that the UE is in the NS-AoS, transmitting, to an access and mobility management function (AMF) entity, a request message including an indication of the PDU session.11.The method of claim 10, further comprising:entering an idle mode in response to receiving the fallback indication;receiving, from the AMF entity, S-NSSAI location validity information;determining whether the UE is in the NS-AoS based on the S-NSSAI location validity information,wherein the UE is configured to support the S-NSSAI location validity information.12.The method of claim 10, wherein the request message includes a registration request message, a service request message, and a control plane service request message, andwherein the indication is included in an uplink data status information element (IE) in the request message.13.The method of claim 10, further comprising:determining whether the S-NSSAI is available in a cell or a tracking area (TA) of the UE; ordetermining whether the S-NSSAI is available based on a current time or S-NSSAI time validity information.14.A method of an access and mobility management function (AMF) entity in a wireless communication system, the method comprising:receiving, from a user equipment (UE), a request message including an indication of a protocol data unit (PDU) session associated with a single network slice selection assistance information (S-NSSAI), in case that the UE is in a network slice-area of service (NS-AoS) with respect to the S-NSSAI,wherein the S-NSSAI is associated with the PDU session for which user plane (UP) resources were active before the UE receives a fallback indication in a connected mode.15.The method of claim 14, further comprising:transmitting, to the UE, S-NSSAI location validity information for determining whether the UE is in the NS-AoS,wherein the request message includes a registration request message, a service request message, and a control plane service request message, andwherein the indication is included in an uplink data status information element (IE) in the request message.

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