Improvements in and relating to slicing in a telecommunication network

Abstract

Disclosed is a method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein in the event of a trigger of a procedure which requires sending of a Non-Access

Description

The present invention relates to Non-Access Stratum (NAS) procedures used in slicing operations in a telecommunication network. Slicing is known as a technique for offering different configurations in so-called network slices. Network slicing can be supported such that a slice may not be available in all the tracking areas (TAs) of a User Equipment, 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 publication 3GPP TS 23.501 from which the following excerpt is taken: 5.15.18.1 General The 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 0AM the information on availability of a network slice when the granularity is smaller than TA, i.e. if the Network Slice Area of Service (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 0AM, 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 information S-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 CAM 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 Areas OAM may configure RRM policies for S-NSSAIs on a per cell basis as defined in TS 28.541

[149] , 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

[34] . 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 a Single - Network Slice Selection Assistance Information, S-NSSAI) in a cell of a TA. Per the requirements from above, 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, the UE shall not activate User Plane, UP, for any already established Protocol Date 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. The following relates to an overview of 5GMM-CONNECTED mode with RRC-inactive indication. RRC indicated Radio Resource Control. The Fifth Generation System (5GS) defined the 5GMM-CONNECTED mode with RRC-inactive indication as a state in which the UE is considered to be in 5GMM-CONNECTED mode from a NAS perspective but in RRC-inactive state from the RRC perspective. The detailed UE behaviour in this mode can be found in section 5.3.1.4 of 3GPP TS 24.501. The following is an example of the UE behaviour in this mode from the above mentioned publication: This subclause is only applicable for UE's 5GMM mode over 3GPP access. The 5GMM-CONNECTED mode with RRC inactive indication is not supported when the UE is in NB-N1 mode. ... SKIP ... Upon: a) a trigger of a procedure which requires sending of a NAS message different from a REGISTRATION REQUEST message with the NG-RAN-RCU bit of the 5GS update type IE set to "UE radio capability update needed"; b) an uplink user data packet to be sent for a PDU session with suspended userplane resources; c) a trigger to request resources for 5G ProSe direct discovery over PC5 or 5G ProSe direct communication over PC5; d) a trigger to request resources for V2X communication over PC5 (see 3GPP TS 23.287 [6C]); or e) a trigger to request resources for A2X communication over PC5 (see 3GPP TS 23.256 [6AB]); the UE in 5GMM-CONNECTED mode with RRC inactive indication over 3GPP access shall request the lower layers to transition to RRC_CONNECTED state (see 3GPP TS 38.300

[27] ). For case b) above, the UE which supports S-NSSAI location validity information, and which has received S-NSSAI location validity information from the AMF, shall request the lower layers to transition to RRC_CONNECTED state only if the UE is inside the NS-AoS with respect to the S-NSSAI which is associated with the PDU session with suspended user-plane resources. ... SKIP... It should be noted that for case a), the NAS procedure which may be different from a REGISTRATION REQUEST message with the NG-RAN-RCU bit of the 5GS update type IE set to "UE radio capability update needed" can be any of the following: • A 5GSM procedure to establish or modify a PDU session which is associated with an S-NSSAI or a slice (using the PDU SESSION ESTABLISHMENT REQUEST message or PDU SESSION MODIFICATION REQUEST message, respectively) • A NAS transport procedure to send CloT user data (using the UL NAS TRANSPORT message) With respect to the slice not being available in all cells or all tracking areas (TAs), the UE is not supposed to perform any of the above listed procedures (i.e. 5GSM procedure to establish or modify a PDU session which is associated with an S-NSSAI, or NAS transport procedure to send Cellular Internet of Things, CloT, user data which is associated with a slice) unless the UE ensures that the associated slice (i.e. the slice associated with the PDU session which in turn is associated with the NAS procedure) is supported in the cell or the TA. However, as can be seen, the UE does not perform any verification with respect to slice support. This becomes a problem as it does not conform with the requirements. According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows. According to an aspect of the invention, there is provided a method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein in the event of a trigger of a procedure which requires sending of a Non-Access Stratum, NAS, message different from a REGISTRATION REQUEST message with the NG-RAN-RCU bit of the 5GS update type IE set to "UE radio capability update needed", and: a) if the trigger of the procedure is to request the establishment of a Protocol Data Unit, PDU, session associated with a Single - Network Slice Selection Assistance Information, S-NSSAI, included in the partially allowed NSSAI, the UE shall request lower layers to transition to RRC_CONNECTED state; or b) if the trigger of the procedure is to request the establishment of a PDU session associated with an S-NSSAI which has S-NSSAI location validity information, the UE shall request lower layers to transition to RRC_CONNECTED state. In an embodiment, in option a) the UE shall request lower layers to transition to RRC_CONNECTED state only if the current Tracking Area, TA, is in the list of TAs where the S-NSSAI is allowed. In an embodiment, in option b) only if the current cell is in the Network Slice Area of Service, NS-AoS, of the S-NSSAI. According to another aspect of the invention, a UE in 5GMM-CONNECTED mode with RRC inactive indication should verify if a pending NAS procedure is associated with a slice. If yes, then the UE should also verify if the slice is supported in the UE’s current location. In an embodiment, verifying if the slice is supported in a UE’s current location can mean verifying if the slice is supported based on the UE’s TA or cell and, optionally, comparing it with information in the partially allowed NSSAI or in the Network Slice Area of Service, NS-AoS. In an embodiment, if the UE determines that the slice is supported, then the UE can request the RRC layer to transition to RRC CONNECTED mode, otherwise the UE remains in 5GMM-CONNECTED mode with RRC Inactive indication. The NAS procedure may be any 5GSM NAS procedure (or message) or may be for sending CloT user data in any NAS message. Embodiments are also applicable to time validity information where the verification of support of a slice may be with regards to availability of the slice in a particular time based on the S-NSSAI time validity information. Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims. For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which: Figure 1 shows a flowchart illustrating an embodiment of the invention; and Figure 2 shows a UE according to an embodiment, communicatively coupled to a network. All the embodiments described herein apply to a UE which may have an allowed NSSAI or a partially allowed NSSAI or an on-demand NSSAI. The embodiments apply for the case when a slice is either supported on a cell level e.g. using NS-AoS, or on a TA level by means of the partially allowed NSSAI. In the embodiments herein, verifying the support of a slice or S-NSSAI in a location can mean any one or more of the following: • Verifying that an S-NSSAI (or slice) is supported in the current UE location based on the NS-AoS information e.g. this may be based on support of a slice on a cell level. However, the determination is made based on verifying (at least) the contents of the NS-AoS information • Verifying that an S-NSSAI (or slice) is supported in the current UE location based on the TA information e.g. this may be based on support of a slice on a TA level in relation to the partially allowed NSSAL However, the determination is made based on verifying (at least) the contents of the partially allowed NSSAI information, e.g. by verifying if the slice in question is supported in the current TA which can be compared to the TA information in the partially allowed NSSAI The embodiments relate to 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 Information Element, IE, of the REGISTRATION REQUEST message, and / or optionally the UE has received / stored S-NSSAI location validity information from the network (e.g. from the Access and Mobility Management Function, AMF) in any NAS message e.g. the Registration Accept message or the Configuration Update Command message, etc. Embodiments can relate to a UE which supports handling partially allowed NSSAI e.g. the UE which has indicated that the UE supports the partial network slice feature and optionally has a valid partially allowed NSSAI information. Embodiments can relate to a UE which is optionally in 5GMM-CONNECTED mode with RRC inactive indication, and optionally for the UE which receives a fallback indication as it attempts (or attempted) to enter RRC_CONNECTED state optionally due to a request from the NAS entity which needs to send a NAS message (or initiate a NAS procedure). Embodiments can relate to the case when the UE has a NAS procedure which is optionally related to a network slice (e.g. an S-NSSAI) or which is related to a PDU session that is in turn associated with a network slice (e.g. an S-NSSAI), where optionally the slice (or S-NSSAI) is either supported in some TA only (e.g. based on a partially allowed NSSAI) or supported in some cells (e.g. based on the NS-AoS information), where the NAS procedure can be any of the following: • A 5GSM procedure (or a 5GSM message) which is either for PDU session establishment or PDU session modification e.g. for which the UE wants (or needs or has) to send a PDU Session Establishment Request message or a PDU Session Modification Request message, or • A NAS procedure for sending CloT user data, where optionally the CloT user data is for a PDU session which is associated with the slice (or S-NSSAI) • any other NAS procedure which may be associated with an S-NSSAI (or a slice), where the procedure may be a related to any entity such as the mobility management entity or the session management entity Embodiments are applicable to any combination of the conditions listed herein and in any order. When the UE (optionally which is in 5GMM-CONNECTED mode with RRC inactive indication has a NAS procedure to initiate (e.g. as listed above) or a NAS message to send in relation to a NAS procedure, optionally where the NAS procedure or NAS message is associated with an S-NSSAI (or slice), the UE should verify if the slice is supported in the UE’s current location. The verification may use any of the following methods and / or use any of the following items of information: • for the S-NSSAI in question, the UE verifies if the slice is supported in the TA (of the cell the UE is currently in), where this may be done by verifying the information of the partially allowed NSSAI e.g. to ensure that the TA where the slice is supported (based on the partially allowed NSSAI) contains the same TA as the TA of the current cell the UE is in (or as the TA where the UE is currently in). For example: o with respect to a slice, if the UE is in a TA which is part of the partially allowed NSSAI information (i.e. the slice is indicated to be supported in the TA which is the same as the UE’s current TA or the same as the TA where the UE is in), then the UE determines that the slice is supported in the UE’s current location. Otherwise, the UE determines that the slice is not supported in the UE’s current location or TA • for the S-NSSAI in question, the UE verifies if the slice is supported in the cell the UE is in e.g. based on the NS-AoS. This may be done by verifying that the cell the UE is in is part of the NS-AoS information, optionally such that the slice is indicated to be supported in the current cell. For example: o If the UE is inside the NS-AoS, then the UE determines that the slice is supported for the corresponding PDU session or slice o If the UE is outside the NS-AoS (or the UE is not inside the NS-AoS), then the UE determines that the slice is supported for the corresponding PDU session or slice If the UE determines that it the S-NSSAI in question (e.g. which is associated or related to a NAS procedure or a NAS message as has been explained herein, e.g. for which the UE has a pending NAS procedure) is supported in the UE’s current location, then the UE which is in 5GMM-CONNECTED mode with RRC inactive indication over 3GPP access shall request the lower layers to transition to RRC_CONNECTED state. If the UE determines that it the S-NSSAI in question (e.g. which is associated or related to a NAS procedure or a NAS message as has been explained, e.g. for which the UE has a pending NAS procedure) is not supported in the UE’s current location, then the UE which is in 5GMM-CONNECTED mode with RRC inactive indication over 3GPP access shall not request the lower layers to transition to RRC_CONNECTED state. In this case, the UE should remain in 5GMM-CONNECTED mode with RRC inactive indication over 3GPP access, or optionally enter 5GMM-IDLE mode. Note that UE location may refer to a particular cell or a set of tracking areas, TAs, or a set of tracking area identities, TAIs. All the embodiments set out above also apply for the case of slices that are only supported at a given time i.e. the slices are not always available. For example, for all of the embodiments above, the UE can initiate a NAS procedure (as has been described herein) only if the S-NSSAI (e.g. which is associated with the NAS procedure or NAS message) can be used at the current time (or connection establishment) or is available or can be used based on the S-NSSAI time validity information. Similarly, when the UE has to send the UL NAS TRANSPORT message and the UE needs to send CloT user data, the UE should only send the NAS message (or include the CloT user data) if the slice corresponding to the PDU session is available for use at the current time e.g. based on the S-NSSAI time validity information. When the UE wants to send a NAS message or initiate a NAS procedure, optionally for the UE which is in 5GMM-CONNECTED mode with RRC inactive indication, the UE should verify if the slice (or S-NSSAI) for which the NAS procedure or NAS message is associated with is supported in the current time or based on the time validity information. If it is supported, then the UE (which is in 5GMM-CONNECTED mode with RRC inactive indication) shall request the lower layers to transition to RRC_CONNECTED state. If the UE determines that an S-NSSAI is not available for use at the current time e.g. based on the S-NSSAI time validity information, then the UE (which is in 5GMM-CONNECTED mode with RRC inactive indication) shall not request the lower layers to transition to RRC_CONNECTED state. The UE should remain in 5GMM-CONNECTED mode with RRC inactive indication, or optionally enter 5GMM-IDLE mode. All the previous details in terms of how the verification should be made or can be made are also applicable to this case. The UE may behave as described above optionally when it is 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, and / or optionally the UE has received / stored S-NSSAI time validity information from the network (e.g. from the AMF). For all the embodiments herein, after transitioning to RRC connected state, the UE may initiate the NAS procedure or send the NAS message which triggered the request to lower layers to transition to RRC connected state. The following shows exemplary changes to the applicable 3GPP standards text to illustrate how the embodiment herein may be reflected in the applicable standard. The exemplary changes are shown in underlined text. “Upon: a) a trigger of a procedure which requires sending of a NAS message different from a REGISTRATION REQUEST message with the NG-RAN-RCU bit of the 5GS update type IE set to "UE radio capability update needed"; b) an uplink user data packet to be sent for a PDU session with suspended userplane resources; c) a trigger to request resources for 5G ProSe direct discovery over PC5 or 5G ProSe direct communication over PC5; d) a trigger to request resources for V2X communication over PC5 (see 3GPP TS 23.287 [6C]); or e) a trigger to request resources for A2X communication over PC5 (see 3GPP TS 23.256 [6AB]); the UE in 5GMM-CONNECTED mode with RRC inactive indication over 3GPP access shall request the lower layers to transition to RRC_CONNECTED state (see 3GPP TS 38.300

[27] ). For case b) above, the UE which supports S-NSSAI location validity information, and which has received S-NSSAI location validity information from the AMF, shall request the lower layers to transition to RRC_CONNECTED state only if the UE is inside the NS-AoS with respect to the S-NSSAI which is associated with the PDU session with suspended user-plane resources. For case a) above, if the NAS procedure is associated with a PDU session which is associated with an S-NSSAI that is included in the partially allowed NSSAI, the UE shall request the lower layers to transition to RRC CONNECTED state only if the UE is in a TA within the list of TAs where the S-NSSAI is allowed. The NAS procedure may be a 5GSM procedure (e.q. PDU session establishment procedure, or a PDU session modification procedure, or any other 5GSM procedure), or a NAS transport procedure for sending CloT user data. For case a) above, if the NAS procedure is associated with a PDU session which is associated with an S-NSSAI that is supported in the UE’s current location based on the NS-AoS, or if the UE is inside the NS-AoS with respect to the S-NSSAI for which the NAS procedure is associated with, the UE shall request the lower layers to transition to RRC CONNECTED state. The NAS procedure may be a 5GSM procedure (e.q. PDU session establishment procedure, or a PDU session modification procedure, or any other 5GSM procedure), or a NAS transport procedure for sending CloT user data. For case a) above, if the NAS procedure is associated with a PDU session which is associated with an S-NSSAI that is included in the partially allowed NSSAI or the on-demand NSSAI, the UE shall reguest the lower layers to transition to RRC CONNECTED state only if the UE is in a cell where the slice is supported based on the NS-AoS. The NAS procedure may be a 5GSM procedure (e.g. PDU session establishment procedure, or a PDU session modification procedure, or any other 5GSM procedure), or a NAS transport procedure for sending CloT user data. Note that the condition “only if the UE is in a cell where the slice is supported based on the NS-AoS” can also be achieved by verifying if the UE is inside the NS-AoS with respect to the S-NSSAI for which the NAS procedure is associated with.” For completeness, Figure 1 shows a flowchart illustrating an embodiment of the invention. At step S101, a trigger is received at the UE of a procedure which reguires sending of a Non-Access Stratum, NAS, message different from a REGISTRATION REQUEST message with the NG-RAN-RCU bit of the 5GS update type IE set to "UE radio capability update needed". At step S102, a determination is made of the type of trigger. If the trigger is to reguest the establishment of a Protocol Data Unit, PDU, session associated with a Single - Network Slice Selection Assistance Information, S-NSSAI, included in the partially allowed NSSAI, then flow continues to step S103, where the UE shall reguest lower layers to transition to RRC_CONNECTED state, optionally, only if the current Tracking Area, TA, is in the list of TAs where the S-NSSAI is allowed. At step S102, if it is determined that the trigger of the procedure is to reguest the establishment of a PDU session associated with an S-NSSAI which has S-NSSAI location validity information, then flow continues to step S104 where the UE shall reguest lower layers to transition to RRC_CONNECTED state, optionally, only if the current cell is in the Network Slice Area of Service, NS-AoS, of the S-NSSAI. Figure 2 illustrates a UE 10, configured according to an embodiment of the invention, communicatively coupled to a network 20. At least some of the example embodiments described herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as ‘component’, ‘module’ or ‘unit’ used herein may include, but are not limited to, a hardware device, such as circuitry in the form of discrete or integrated components, a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks or provides the associated functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. These functional elements may in some embodiments include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term “comprising” or “comprises” means including the component(s) specified but not to the exclusion of the presence of others. 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. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein in the event of a trigger of a procedure which requires sending of a Non-Access Stratum, NAS, message different from a REGISTRATION REQUEST message with the NG-RAN-RCU bit of the 5GS update type IE set to "UE radio capability update needed", and:a) if the trigger of the procedure is to request the establishment of a Protocol Data Unit, PDU, session associated with a Single - Network Slice Selection Assistance Information, S-NSSAI, included in the partially allowed NSSAI, the UE shall request lower layers to transition to RRC_CONNECTED state; orb) if the trigger of the procedure is to request the establishment of a PDU session associated with an S-NSSAI which has S-NSSAI location validity information, the UE shall request lower layers to transition to RRC_CONNECTED state.

2. The method of claim 1 wherein in option a) the UE shall request lower layers to transition to RRC_CONNECTED state only if the current Tracking Area, TA, is in the list of TAs where the S-NSSAI is allowed.

3. The method of claim 1 wherein in option b) only if the current cell is in the Network Slice Area of Service, NS-AoS, of the S-NSSAI.

4. A UE arranged to perform the method of any preceding claim.

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