Improvements in and relating to location validity information and service area list in a telecommunication network

Abstract

Disclosed is a method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network

Description

The present invention relates to a method for handling location validity information and service area list in the context of a telecommunication network, particularly a Fifth Generation (5G) network. Network slicing is known in the art 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 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 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 information S-NSSAI location availability information defines additional restrictions to the usage of an S-NSSA / 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 an S-NSSAI) in a cell of a TA. Per the requirements from 3GPP TS 23.501 V18.2.1, 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, 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 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 3GPP TS 23.501 V18.2.1: 5.15.16 Optimized handling of temporarily available network A 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 CAM 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 network NOTE 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 the slice can only be used by a UE if the slice is deemed to be available, otherwise the UE is not allowed to get access to such a slice and the network takes certain actions to ensure this is the case. The 5G System (5GS) supports the concept of service area restrictions which define so called allowed areas, or non-allowed areas, where these areas are a list of tracking area identities (TAIs) that are provided by the network in the Service area list Information Element (IE). The details of the IE encoding and how the contents are to be used can be found in 3GPP TS 24.501 V18.3.0. The IE indicates whether the included TAIs are to be considered as allowed or non-allowed, and therefore: • when the list indicates that the TAIs are allowed, the UE would consider an area to be allowed if the TAI is part of the allowed list, and therefore the UE would be in a nonallowed area when it is in any TAI which is not part of the allowed list • when the list indicates that the TAIs are non-allowed, then the UE would consider an area to be allowed if the TAI is not part of the non-allowed list, and therefore the UE would be in a non-allowed area when it is in a TAI which is part of the list. As such, the UE would be in an allowed area if it is inside a list of TAIs that are considered to be allowed, or if it is outside the list of TAIs that are considered to be non-allowed. Similarly, the UE would be in a non-allowed area if it is inside the list of TAIs that are considered to be non-allowed, or it is outside of (or not inside) the list of TAIs that are considered to be allowed. The detailed UE behavior with regards to service area restrictions is provided below from section 5.3.5 in 3GPP TS 24.501 V18.3.0: The service area restrictions consist of tracking areas forming either an allowed area, or a non-allowed area. The tracking areas belong to the registered PLMN, its equivalent PLMNs in the registration area, or the registered SNPN. The allowed area can contain up to 16 tracking areas or include all tracking areas in the registered PLMN and its equivalent PLMN(s) in the registration area, or in the registered SNPN. The non-allowed area can contain up to 16 tracking areas. The network conveys the service area restrictions to the UE by including either an allowed area, or a non-allowed area, but not both, in the Service area list IE of a REGISTRATION ACCEPT message or a CONFIGURATION UPDATE COMMAND message. If the network does not convey the service area restrictions to the UE in the Service area list IE of a REGISTRATION ACCEPT message, the UE shall treat all tracking areas in the registered PLMN, its equivalent PLMN(s) in the registration area, or in the registered SNPN, as allowed area and delete the stored list of "allowed tracking areas" or the stored list of "non-allowed tracking areas". When the UE receives a Service area list IE with an allowed area indication during a registration procedure or a generic UE configuration update procedure: a) if the "Type of list" included in the Service area list IE does not indicate "all TAIs belonging to the PLMNs in the registration area are allowed area", the UE shall delete the old list of "allowed tracking areas" and store the tracking areas in the allowed area as the list of "allowed tracking areas". If the UE has a stored list of "non-allowed tracking areas", the UE shall delete that list; or b) if the "Type of list" included in the Service area list IE indicates "all TAIs belonging to the PLMNs in the registration area are allowed area", the UE shall treat all tracking areas in the registered PLMN and its equivalent PLMN(s), or in the registered SNPN, as allowed area and delete the stored list of "allowed tracking areas" or the stored list of "non-allowed tracking areas". When the UE receives a Service area list IE with a non-allowed area indication during a registration procedure or a generic UE configuration update procedure, the UE shall delete the old list of "non-allowed tracking areas" and store the tracking areas in the non-allowed area as the list of "non-allowed tracking areas". If the UE has a stored list of "allowed tracking areas", the UE shall delete that list. If the UE is successfully registered to a PLMN or SNPN and has a stored list of "allowed tracking areas": a) while the current TAI is in the list of "allowed tracking areas", the UE shall stay in, or enter, the state 5GMM-REGISTERED.NORMAL-SERVICE and is allowed to initiate any 5GMM and 5GSM procedures; and b) while the UE is camped on a cell which is in the registered PLMN, a PLMN from the list of equivalent PLMNs, or the registered SNPN, and the current TAI is not in the list of "allowed tracking areas", the UE shall enter the state 5GMM-REGISTERED.NON-ALLOWED-SERVICE, and: 1) if the UE is in 5GMM-IDLE mode or 5GMM-IDLE mode with suspend indication over 3GPP access, the UE: i) shall not include the Uplink data status IE in the registration procedure for mobility and periodic registration update except for emergency services or for high priority access; ii) shall not perform the registration procedure for mobility and periodic registration update with Follow-on request indicator set to "Follow-on request pending", except for: emergency services; high priority access; indicating a change of 3GPP PS data off UE status; sending an SOR transparent container; sending a UE policy container; or sending a UE parameters update transparent container; Hi) shall not initiate a service request procedure or request the lower layers to resume a suspended connection, except for: emergency services; emergency services fallback; high priority access; responding to paging; responding to notification received over non-3GPP access; indicating a change of 3GPP PS data off UE status; sending an SOR transparent container; sending a UE policy container; or sending a UE parameters update transparent container; and 2) if the UE is in 5GMM-CONNECTED mode or 5GMM-CONNECTED mode with RRC inactive indication over 3GPP access, the UE: i) shall not perform the registration procedure for mobility and periodic registration update with Uplink data status IE except for emergency services or for high priority access; ii) shall not initiate a service request procedure except for: emergency services; emergency services fallback; high priority access; responding to paging or responding to notification received over non-3GPP access; Hi) shall not initiate a 5GSM procedure except for: emergency services; high priority access; or indicating a change of 3GPP PS data off UE status; and iv) shall not perform the NAS transport procedure except for the sending: - SMS; an LPP message; a location services message; an SOR transparent container; a UE policy container; a UE parameters update transparent container; or a CloT user data container. NOTE 1: The contents of CloT user data container can be data that is not for exception reports, or data that is for exception reports if allowed for the UE (see subclause 6.2.13). If the UE is successfully registered to a PLMN or an SNPN and has a stored list of "non-allowed tracking areas": a) while the UE is camped on a cell which is in the registered PLMN, a PLMN from the list of equivalent PLMNs, or the registered SNPN, and the current TAI is not in the list of "non-allowed tracking areas”, the UE shall stay in, or enter, the state 5GMM-REGISTERED.NORMAL-SERVICE and is allowed to initiate any 5GMM and 5GSM procedures; and b) while the current TAI is in the list of "non-allowed tracking areas", the UE shall enter the state 5GMM-REGISTERED.NON-ALLOWED-SERVICE, and: 1) if the UE is in 5GMM-IDLE mode or 5GMM-IDLE mode with suspend indication over 3GPP access, the UE: i) shall not include the Uplink data status IE in the registration procedure for mobility and periodic registration update except for emergency services or for high priority access; ii) shall not perform the registration procedure for mobility and periodic registration update with Follow-on request indicator set to "Follow-on request pending", except for: emergency services; high priority access; indicating a change of 3GPP PS data off UE status; sending an SOR transparent container; sending a UE policy container; or sending a UE parameters update transparent container; and Hi) shall not initiate a service request procedure or request the lower layers to resume a suspended connection, except for: emergency services; emergency services fallback; high priority access; responding to paging; responding to notification received over non-3GPP access; indicating a change of 3GPP PS data off UE status; sending an SOR transparent container; sending a UE policy container; or sending a UE parameters update transparent container; and 2) if the UE is in 5GMM-CONNECTED mode or 5GMM-CONNECTED mode with RRC inactive indication over 3GPP access, the UE: i) shall not perform the registration procedure for mobility and periodic registration update with the Uplink data status IE except for emergency services or for high priority access; ii) shall not initiate a service request procedure or request the lower layers to resume a suspended connection, except for: emergency services; emergency services fallback; high priority access; or responding to paging or responding to notification received over non-3GPP access; Hi) shall not initiate a 5GSM procedure except for: emergency services; high priority access; or indicating a change of 3GPP PS data off UE status; and iv) shall not perform the NAS transport procedure except for the sending: SMS; an LPP message; a location services message; an SOR transparent container; a UE policy container; a UE parameters update transparent container; or a CloT user data container. NOTE 2: The contents of CloT user data container can be data that is not for exception reports, or data that is for exception reports if allowed for the UE (see subclause 6.2.13). The list of "allowed tracking areas", as well as the list of "non-allowed tracking areas" shall be erased when: a) the UE is switched off; and b) the UICC containing the USIM is removed or an entry of the "list of subscriber data" with the SNPN identity of the SNPN is updated. When a tracking area is added to the list of "5GS forbidden tracking areas for roaming" or to the list of "5GS forbidden tracking areas for regional provision of service" as specified in the subclauses 5.5.1.2.5 or 5.5.1.3.5, the tracking area shall be removed from the list of "allowed tracking areas" if the tracking area is already present in the list of "allowed tracking areas" and from the list of "non-allowed tracking areas" if the tracking area is already present in the list of "non-allowed tracking areas". From the above, it is understood that when the UE is in an allowed area, it can continue to receive normal services and hence it is in 5GMM-REGISTERED.NORMAL-SERVICE. On the other hand, when the UE is in a non-allowed area, it enters the state 5GMM-REGISTERED.NON-ALLOWED-SERVICE, and it cannot obtain normal service e.g. it cannot request a PDU session to be established (except for emergency services, etc.). S-NSSAI location validity information is described in detail on 3GPP TS24.501 V18.6.0 and certain portions are reproduced below. Reference is made to certain figures which are reproduced in the accompanying figures. Figure 1a shows Fig 9.11.3.100.1; Figure 1b shows Fig 9.11.3.100.2; Figure Icshows Fig 9.11.3.100.3; and Figure Isshows Fig 9.11.3.100.4. 9.11.3.100 S-NSSAI location validity information The 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 figures 9.11.3.100.1, 9.11.3.100.2, 9.11.3.100.3, and 9.11.3.100.4 and table 9.11.3.100.1. The S-NSSAI location validity information information element can contain per-S-NSSAI location validity information for maximum 8 S-NSSA / s. 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 9.11.3.100.1 is reproduced below: S-NSSAI (octet 6 to e) S-NSSAI value is coded as the length and value part of S-NSSAI information element as specified in subclause 9.11.2.8 starting with the second octet. NS-AoS (octet e+1 to octet a) NS-AoS filed consists of the Number of NR cell IDs field and at least two NR CGIs. Number of NR CGIs (octet e+1 to octet e+2) The field indicates the number of NR CGIs included in octets e+3 to octet a. (NOTE). NR CGI (octet e+3 to e+10) The NR CGI globally identifies an NR cell. It contains the NR Cell ID and the PLMN ID of that cell. NR Cell ID (octet e+3 to e+7) The NR Cell ID consists of 36 bits identifying an NR Cell ID as specified in subclause 9.3.1.7 of 3GPP TS 38.413

[31] , in hexadecimal representation. Bit 8 of octet e+3 is the most significant bit and bit 5 of octet e+7 is the least significant bit. Bits 1 to 4 of octet e+7 are spare and shall be coded as zero. MCC, Mobile country code (octet e+8 and bits 1 to 4 octet e+9) The MCC field is coded as in ITU-T Recommendation E.212

[42] , annex A. MNC, Mobile network code (bits 5 to 8 of octet e+9 and octet e+10) The coding of this field is the responsibility of each administration but BCD coding shall be used. The MNC shall consist of 2 or 3 digits. If a network operator decides to use only two digits in the MNC, bits 5 to 8 of octet e+9 shall be coded as "1111 The MCC and MNC digits are coded as octets 6 to 8 of the Temporary mobile group identity IE in figure 10.5.154 of3GPP TS 24.008

[12] . NOTE: In this version the specification, the maximum number of NR cell IDs is 300. In essence, the above provides that there is available a list of slices associated with a list of cell identities. 5 The service area list contains tracking area codes (TAC). Normally the cell broadcasts a TAC. So the overlap would mean that the cell of the NS-AoS would broadcast a TAC which is the same as the TAC in the service area list, details of which may be found in section 9.11.3.49 of 3GPP TS24.501 V18.6.0, partially reproduced below. Reference is made to certain figures which are reproduced in the accompanying figures. Figure 2a shows Fig 9.11.3.49.1; and 10 Figure 2b shows Fig 9.11.3.49.2. 9.11.3.49 Service area list The purpose of the Service area list information element is to transfer a list of allowed tracking areas for an allowed area or a list of non-allowed tracking areas for a nonallowed area from the network to the UE. The coding of the information element allows combining different types of lists. The lists of type "00" and "01" allow a more compact encoding, when the different TAIs are sharing the PLMN identity. The lists of type "11" indicate all TAIs of the PLMNs in the registration area are allowed area. The Service area list information element is coded as shown in figure 9.11.3.49.1, figure 9.11.3.49.2, figure 9.11.3.49.3, figure 9.11.3.49.4, figure 9.11.3.49.5 and table 9.11.3.49.1. The Service area list is a type 4 information element with a minimum length of 6 octets and a maximum length of 114 octets. The list can contain a maximum of 16 different tracking area identities. A problem with the prior art is best described with an example. Assume that a slice is indicated to be supported in a particular TAI, say TAI #1. Based on the S-NSSAI location availability information, the slice in question is indeed available for use in TAI #1. Assume also that the service area restriction information is received in the UE such that TAI #1 is deemed to be a non-allowed area. The above therefore creates a scenario in which the UE may find the information to be contradictory. A standardized behaviour for the UE is therefore required so that the UE would function in accordance to well defined rules - otherwise different UEs will behave differently and the network would then behave differently in response, which is extremely undesirable. It is an aim of an embodiment of the present invention to address this and other shortcomings in the prior art. 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 a first aspect of the invention, there is provided a method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network and there is an overlap in area between a Service Area information list and a slice location validity information list, including one or more of: location availability information and information regarding a cell inside NS-AoS, then evaluation of the Service Area list is prioritised. According to a second aspect of the invention, there is provided a method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network, the UE only uses S-NSSAI location availability information if the UE is in state / mode 5GMM-REGISTERED. NORMAL-SERVICE. According to a third aspect of the invention, there is provided a method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network, the UE does not use the S-NSSAI location availability information if the UE is in state / mode 5GMM-REGISTERED.NON-ALLOWED-SERVICE. According to a fourth aspect of the invention, there is provided a method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network, the UE only uses validity time information associated with the particular slice if the UE is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE. According to a fifth aspect of the invention, there is provided a method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network, the UE does not use validity time information associated with the particular slice if the UE is in state / mode 5GMM-REGISTERED.NON-ALLOWED-SERVICE. According to a third sixth of the invention, there is provided apparatus arranged to perform the method of any preceding aspect. According to one or more embodiments of the present invention, when there is a common TAI in the service area list and the S-NSSAI location availability information, then one or more of the following apply: • The UE prioritizes the service area restriction list over the S-NSSAI location availability information • The UE uses the S-NSSAI location availability information only when the UE is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE, and optionally the UE does not use the S-NSSAI location availability information when the UE is in state / mode 5GMM-REGISTERED.NON-ALLOWED. SERVICE • The UE deletes one of the lists, and / or performs MRU 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: Figures 1 and 2 provided details of certain Information Elements associated with an embodiment of the invention; Figure 3 illustrates a flowchart illustrating a method according to an embodiment of the invention; and Figure 4 illustrates a flowchart illustrating a method according to an embodiment of the invention. Note that in the following, the described steps may apply in any order or combination as long as they achieve the desired aim. Note also that throughout reference is made to the S-NSSAI location availability information, the same techniques can be applicable using the validity time for an S-NSSAI, where instead of the UE verifying if a slice is supported in a TAI which considered to be in an allowed area, the UE can instead verify if the slice can be used at the current time (based on the validity time for an S-NSSAI) and the UE is in an allowed service area (or the UE is in 5GMM-REGISTERED.NORMAL-SERVICE). In a first embodiment, the UE considers one particular list (or information) to take precedence over the other. Note: the term “information” may refer to any format of information that can be either a list, or contents of an information element (IE), or message. As such, the service area information may refer to the service area list in the Service area list IE or the general (or particular e.g. at least one TAI) content of the Service area list IE. Similarly, the slice location availability information may refer to the contents of the corresponding IE in its entirety or it may refer to at least one TAI which is represented by the information. It should be noted that the TAIs may be either provided as part of the slice location information or may be determined by the UE based on the cells where the slice is supported. For example, if a cell is known to support a particular slice, the UE can determine that TAI where the slice is supported as the TAI that is broadcast (or represented) by that cell. As such, the TAI information in the slice location validity information is expected to be known in the UE and the details herein apply regardless of the method by which the UE makes the determination about this the TAI where a slice is supported. The following solution options apply optionally when the UE receives service area restriction information and slice location availability information from the network. The UE may verify if there is at least one TAI which is present (or is common) in both the service area information (list) and the S-NSSAI location availability information, optionally such that the TAI is considered to be non-allowed (or part of a non-allowed service area). The UE may behave as set out next if indeed there is such a TAI which is considered to be common in both information set, or optionally is common in both information such and also it is considered to be a non-allowed TAI. Or the common TAI is considered to be part of a non-allowed service area, and the TAI is also part of the S-NSSAI location availability information. Note that the UE considers a TAI to be part of the non-allowed service area using any of the following ways: • The service area list indicates that the TAI type is allowed and the TAI in question is not part of the allowed TAI list, (and optionally the UE is in such a TAI that is not part of the allowed area) • The service area list indicates that the TAI type is non-allowed and the TAI in question is part of the non-allowed TAI list, (and optionally the UE is in such a TAI that is part of the nonallowed area) Note that the TAI in question may be the TAI that is part of the S-NSSAI location availability information which the UE may be considering when determining if a slice can be used or not in its current location. The UE may verify if a slice can be used based on the S-NSSAI location availability information, where the UE may verify if a TAI (e.g. related to a cell) supports the slice. The UE should verify if the TAI (associated with this slice) is considered to be part of the allowed service area or part of the non-allowed service area. The UE may behave in any of the following manner (described below) if the TAI (in question) is deemed to be part of a nonallowed service area, or when the TAI in question is common across the service information list and the S-NSSAI location availability information. Option 1: the UE prioritizes the service area information over the S-NSSAI location availability information. In this option, the UE considers one of the information type to be of higher priority than the other, or to have higher precedence over the other. By doing so, the UE behaves according to the information that is considered to have higher priority or higher precedence, and consequently the information which has lower priority or lower precedence will basically have no effect on the UE behaviour. As such, the UE follows the requirements of the information that is deemed to be of higher priority or of higher precedence. The UE should consider the service area information to have higher precedence over the slice location availability information. The UE may do so for any TAI that is part of the service area list and that is also part of the S-NSSAI location availability information. Alternatively, the UE may do so when any TAI that is considered to be part of a non-allowed area is also part of the S-NSSAI location availability information. By considering the service area information to have higher precedence as proposed above, the UE would therefore refrain from using the slice (or S-NSSAI) when the UE is in the TAI where the slice is supported, and the TAI is also part of the non-allowed area. Note that based on this option, the UE can optionally only use an S-NSSAI, which is subject to S-NSSAI location availability information, if the TAI where the S-NSSAI is supported is considered to be part of the allowed service area (or as part of an allowed area). Option 2: the UE prioritizes the S-NSSAI location availability information over the service area information. In this option, the UE can always use an S-NSSAI, which is supported in a TAI, if the UE in the TAI (or in the cell which is part of that TAI) regardless of whether the TAI is in the service area list or not, or regardless of whether the TAI is in a non-allowed area or not. The UE may optionally behave as described above if the UE is considered to be a high priority access UE or if the UE wants to use any high priority service, where for example the slice is known to be associated with (a PDU session for) a high priority service. The UE may behave as set out above if the UE is configured for multimedia priority service (MPS) or if the UE is configured for mission critical service (MCS) or if the slice is associated with a PDU session that is used for MPS or MCS. In a second embodiment, the UE considers (or uses) the S-NSSAI location availability information when the UE is in 5GMM-REGISTERED.NORMAL-SERVICE state. Optionally, the UE should only use the S-NSSAI location availability information if the UE is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE. Alternatively, the UE can only use an S-NSSAI, optionally to either establish a PDU session or modify a PDU session which is associated with / for the S-NSSAI, only when the UE is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE. Alternatively, when the UE is in state / mode 5GMM-REGISTERED.NON-ALLOWED-SERVICE, the UE should stop using the S-NSSAI location availability information or should stop using (or should not use) the S-NSSAI which is part of (or associated with) the S-NSSAI location availability information. As such, the UE should optionally now verify for a new condition in order to determine if the S-NSSAI location availability information should be used or not, and that is based on whether the UE is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE or the UE is in state / mode 5GMM-REGISTERED.NON-ALLOWED-SERVICE as described above. Note that the same details set out above would apply for the validity time for an S-NSSAI i.e. when the UE is configured with a validity time for an S-NSSAI and / or when the UE indicates its support for temporarily available network slices. The UE can instead verify if the slice can be used at the current time (based on the validity time for an S-NSSAI) and the UE is in an allowed service area (or the UE is in 5GMM-REGISTERED.NORMAL-SERVICE). As such, the UE can only use an S-NSSAI if it is permitted according to the validity time for an S-NSSAI, and also the UE is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE. If the UE is in state / mode 5GMM-REGISTERED.NON-ALLOWED-SERVICE, the UE should stop using the validity time for an S-NSSAI information. As such, the UE should optionally now verify for a new condition in order to determine if the validity time for an S-NSSAI information should be used or not, and that is based on whether the UE is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE or the UE is in state / mode 5GMM-REGISTERED.NON-ALLOWED-SERVICE as described above. In a third embodiment, the AMF ensures that a TAI is either available in one of the information list but not both. In this solution option, the responsibility is on the AMF to ensure that a TAI is not part of the service area list and the S-NSSAI location availability information. Therefore, when sending this information to the UE, the AMF should ensure that the service area restriction information and the S-NSSAI location availability information should not contain the same TAI entries, or should not contain a common TAI. Alternatively, the AMF should ensure that the service area restriction information and the S-NSSAI location availability information should not contain the same TAI entries (or should not contain a common TAI) optionally when the TAI in question is considered to be part of a nonallowed area. Alternatively, the AMF should not send both lists when the S-NSSAI location availability information feature is used, where the UE and the AMF may have exchanged the relevant capabilities for this feature. As such the AMF either sends the service information list or the S-NSSAI location availability information list, but not both. In one alternative, if the UE receives a service area information and an S-NSSAI location availability information, the UE should verify if there is a common TAI in both information sets (or lists), or the UE should verify if there is a common TAI in both information sets (or lists) such that the common TAI is considered to be part of a non-allowed area. If this is the case, the UE may behave as follows: • The UE may delete one of the lists locally and the UE may perform a registration procedure (by sending a REGISTRATION REQUEST message). The UE either deletes the service area information list, or the S-NSSAI location availability information. In one option, the UE may delete both lists or both sets of information • The UE deletes the TAI entry from the service area list, optionally when the TAI is considered to be a non-allowed area • The UE deletes the TAI entry from the S-NSSAI location availability information • The UE deletes the S-NSSAI entry from the S-NSSAI location availability information, where the S-NSSAI entry in question is associated with the TAI that is common. The UE may delete the TAI in that information as well • The UE may ignore one or both of the information sets received. The UE may perform a registration procedure (e.g. the UE sends the Registration Request message) to get the information again from the network • The UE may send a 5GMM STATUS message when it receives a NAS message such that the message contains both information with a common TAI, optionally when the TAI is considered to be a non-allowed area. The UE may include an existing or new 5GMM cause value in the 5GMM STATUS message • The UE may take any combination of the above proposed actions For completeness, Figure 3 illustrates a flowchart representing a first embodiment of the invention. At S101, a UE wishes to access a particular slice on the telecommunication network. At S102, the UE it is determined if there is an overlap in area between a Service Area information list and a slice location validity information list, including one or more of: location availability information and information regarding a cell inside NS-AoS. At S103, if there is such an overlap, then evaluation of Service Area list is prioritised. Figure 4 shows a flowchart representing a second embodiment of the invention. At S201, a UE wishes to access a particular slice on the telecommunication network. At S202, the UE verifies if it is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE. At S203, if it so determined, then S-NSSAI location availability information is used. 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 if the UE wishes to access a particular slice on the telecommunication network and there is an overlap in area between a Service Area information list and a slice location validity information list, including one or more of: location availability information and information regarding a cell inside NS-AoS, then evaluation of the Service Area list is prioritised.

2. A method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network, the UE only uses S-NSSAI location availability information if the UE is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE.

3. A method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network, the UE does not use the S-NSSAI location availability information if the UE is in state / mode 5GMM-REGISTERED.NON-ALLOWED-SERVICE.

4. A method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network, the UE only uses validity time information associated with the particular slice if the UE is in state / mode 5GMM-REGISTERED.NORMAL-SERVICE.

5. A method of operating a User Equipment, UE, communicatively coupled to a telecommunication network, wherein if the UE wishes to access a particular slice on the telecommunication network, the UE does not use validity time information associated with the particular slice if the UE is in state / mode 5GMM-REGISTERED.NON-ALLOWED-SERVICE.6.Apparatus arranged to perform the method of any preceding claim.

Images