Improvements in and relating to handling network slice access group (NSAG) information

Abstract

A user equipment (UE) receives network slice access group (NSAG) information from a network; the UE determines if there is a single-network slice selection assistance information (S-NSSAI) entry that

Description

The present invention relates to improvements in the management and operation of network slices. Such slices are known, particularly in Fifth Generation, 5G, telecommunication systems, but the teaching of this application may be applied in other systems also. A set of slices (known by the abbreviation S-NSSAI (Single - Network Slice Selection Assistance Information)) may be known to be part of a group, where the set of slices may be optionally valid with a set of Tracking Area Identities (TAIs), if available, and a certain priority level may also be associated with these slices and, hence, the group. If the list of TAIs is not available, then the slices are valid in the entire Public Land Mobile Network, PLMN. The following is an excerpt from section 4.6.2.6 of 3GPP TS 24.501 about Network Slice Access Group, NSAG: “NSAG Information provided by the network and stored in the UE includes a list of NSAGs each of which contains: a) an NSAG ID; b) a list of S-NSSAi(s), which are associated with the NSAG and shall be part of the configured NSSAI; c) optionally a list of TAIs in which the NSAG is valid. If it is not provided by the network, the NSAG is valid in the PLMN which has sent the NSAG Information; and d) a priority value that is associated with the NSAG. The UE NAS layer shall provide the lower layers with the most recent NSAG information stored in the UE (see subclause 4.6.2.2) to lower layers. NOTE: Along with the NSAG information, the UE provides to the lower layers with allowed NSSAI and requested NSSAI for the purpose of NSAG-aware cell reselection. ” As set out in the above, the list of TAIs in the NSAG is optional. Moreover, the list of S-NSSAIs of the NSAG must be part of the configured NSSAI. This means that there should not be any S-NSSAI in the NSAG information such that the S-NSSAI is not present in the configured NSSAI. Regarding the configured NSSAI, it should be noted that the maximum number of slices that can be present in this list is 16 as stated in section 4.6.2.2 in 3GPP TS 24.501 V18.0.1: “Each of the configured NSSAI stored in the UE is a set composed of at most 16 S-NSSA / s" However, if the UE actually receives more than 16 entries in the configured NSSAI, then the UE keeps the first 16 entries and deletes the rest as described in ‘Table 9.11.3.37.1: NSSAI information element’ of 3GPP TS 24.501 V18.0.1: “if the NSSAI information element conveys a configured NSSAI or pending NSSAI and more than 16 S-NSSAI values are included in this information element, the UE shall store the first 16 S-NSSAI values and ignore the remaining octets of the information element.” From the above, it cannot therefore be ruled out that the UE may actually receive more than 16 entries for the configured NSSAI. The following observation can be made from the above contents: the number of slices in the NSAG must not be more than the number of slices in the configured NSSAI. In other words, the number of slices in the configured NSSAI can be greater than those in the NSAG information but the opposite should not happen. Therefore, whenever there is NSAG information, it must be ensured and enforced that the slices In the NSAG must be part of the configured NSSAI. There are various problems identified In the prior art. Firstly, the UE may receive a number of S-NSSAIs in the NSAG information which is larger than the number of S-NSSAIs in the configured NSSAI. Just like the case referred to where the UE may receive more than 16 entries for the configured NSSAI even though only a maximum of 16 can be saved in the UE, it is then possible that the UE receives NSAG information such that the number of S-NSSAIs in this NSAG information exceeds the number of S-NSSAIs in the configured NSSAI. There is currently no provision made in the standard for handling this scenario. If not handled, then the outcome would be problematic for the reasons stated earlier. Secondly, the UE may become registered for emergency services after having previously received NSAG information, hence performing unnecessary reselections. The lower layers use NSAG information for cell reselection into TAIs which are associated with the NSAG group identifier of highest priority. However, all the principles and behaviours associated with the NSAG feature are supposed to be applicable to a UE which is registered with no restrictions and which is able to receive normal services. However, it is possible that a UE which was previously normally registered subsequently becomes registered for emergency services. In this case, the UE is considered to be only allowed access to emergency service, hence the term ‘registered for emergency services’. However, this is currently not the case i.e. the UE continues to use NSAG information even though the UE becomes registered for emergency services. Thirdly, the UE may receive NSAG information with an invalid TAI. The UE may receive a TAI in the NSAG information such that the TAI is not part of the current registration area of the UE, or the TAI may be considered to be forbidden i.e. the TAI is part of the current forbidden TAI list that the UE already stores. How the UE behaves in this case is undefined and this may lead to unpredictable or inconsistent behaviour across different UEs in otherwise similar or identical conditions. Fourthly, the network - specially the Access and Mobility management Function, AMF - AMF has no defined means to stop the UE from using NSAG. The specification (3GPP TS 24.501 V18.0.1) defines how the UE receives NSAG information and then uses it. However, if the network e.g. the AMF, determines that the UE should no longer use NSAG e.g. due to local policies or due to subscription changes, or any other decision taken by an entity in the 5G core network, then the AMF has no means of doing so. It is an aim of embodiments of the present invention to address shortcomings in the prior art, whether mentioned herein or not. 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 present invention, there is provided a method of operating a User Equipment, UE, arranged for communication with a telecommunication network, comprising the steps of: • the UE receiving a Network Slice Access Group, NASG, information from the telecommunication network; • the UE determining if there is a Single - Network Slice Selection Assistance Information, S-NSSAI, entry which is in the NSAG information, which is not part of a configured NSSAI; and • the UE removing any S-NSSAI entry which is in the NSAG information but not in the configured NSSAI. In an embodiment, the NSAG is associated with a plurality of S-NSSAIs and a list of Tracking Area Identities, TAIs, and a priority value, wherein if the step of removing any S-NSSAI entry which is in the NSAG information but not in the configured NSSAI, results is no remaining S-NSSAI, then the UE deletes the NSAG Information. In an embodiment, the UE further deletes the list of TAIs and the priority values. According to a second aspect of the present invention, there is provided an apparatus arranged to perform the method of the first aspect. In an embodiment, the apparatus is a User Equipment arranged to communicate with the telecommunication network. 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 present invention. In an embodiment of the invention, the UE removes any S-NSSAI in the NSAG information which is not part of the configured NSSAI. In the case that the UE receives, or when the UE determines that, the NASG information contains S-NSSAI which is not part of the configured NSSAI, then the UE should behave as follows: • If there is any S-NSSAI which is not part of the configured NSSAI, then the UE should delete the S-NSSAI; and • Optionally, if an NSAG e.g. a set of S-NSSAIs which are associated with a NSAG identifier and optionally a list of TAI and optionally a priority value, would contain no S-NSSAI after deleting any S-NSSAI which is not part of the configured NSSAI (as described above), then the UE may also delete the rest of the NSAG information i.e. the UE may delete the NSAG identifier, and optionally delete the TAI list if any, and optionally delete the NSAG priority value. In other words, if the number of S-NSSAIs in the NSAG information is more than the number of S-NSSAIs in the configured NSSAI, then the UE should remove at least one S-NSSAI such that the total number of S-NSSAIs in the NSAG information does not exceed the number of S- NSSAIs in the configured NSSAI. The UE should always ensure that the slices or number of S-NSSAIs in the NSAG information does not exceed the number of slices or number of S-NSSAIs in the configured NSSAI. Note that the process above is relevant for any number of S-NSSAIs in the configured NSSAI, even if the UE received a configured NSSAI for which the number of S-NSSAIs does not exceed 16. Figure 1 shows a flowchart illustrating the first embodiment. At S101, the UE receives a Network Slice Access Group, NASG, information from the telecommunication network. At S102, the UE determines if there is a Single - Network Slice Selection Assistance Information, S-NSSAI, entry which is in the NSAG information, which is not part of a configured NSSAI. At S103, the UE removes any S-NSSAI entry which is in the NSAG information but not in the configured NSSAI. In a second embodiment, The UE and / or the network stop(s) using NSAG when the UE has an emergency PDU session. A UE may be normally registered and may have received NSAG information. The UE may also have a PDU session for emergency services. The UE, at any time, or regardless of its registration type, may receive a Configuration Update Command message with the 5GS registration result Information Element, IE, value set to "Registered for emergency services". When this occurs, the UE may take any of the following actions: • The UE may behave as if NSAG is not supported by the UE • The UE may delete the NSAG Information • The UE may inform the lower layers to stop using NSAG Information • The UE may request the lower layers to delete the NSAG information and / or the allowed NSSAI and / or the requested NSSAI which the UE may have provided to the lower layers (optionally where this information may have been previously provided to the lower layers) For a UE which has indicated that it supports NSAG (e.g. for a UE which had set the NSAG bit to "NSAG supported" in the 5GMM capability IE of the REGISTRATION REQUEST message), if the AMF sends the Configuration Update Command message with the 5GS registration result IE value to "Registered for emergency services", then the AMF may behave as if NSAG information is not sent to the UE, or the AMF may behave as if the UE does not support NSAG information. Note that the process above also applies for the case when the UE is normally registered but has established, or is attempting to establish, a PDU session for emergency services. Therefore, all the actions set out above also apply for the case when the UE is normally registered but has a PDU session for emergency services. For example, if the UE and / or the network behave as if NSAG information is not supported when a UE has established a PDU session for emergency services (as set out earlier), then the UE and the network may consider that NSAG information is supported, and hence can be used, after the PDU session for emergency services is released or deactivated. In another embodiment, when a UE is registering for emergency services, the UE which supports NSAG (information) should indicate in the 5GMM capability IE (of the Registration Request message) that NSAG is not supported. In other words, the UE should set the NSAG bit in the 5GMM capability IE to the value ‘NSAG not supported’ (l.e. value 0) even though the UE supports NSAG. For a UE which is registering for emergency services, e.g. when the 5GS registration type IE indicates ‘emergency registration’, the AMF should not provide NSAG information to the UE even if the UE indicates that NSAG is supported in the 5GMM capability IE (of the Registration Request message). In a further embodiment, a new UE behaviour is defined for handling NSAG information with a TAI that is either not part of the UE’s registration area, or that is part of any forbidden TAI list. If the UE receives NSAG information where any TAI, which is part of the NSAG information, is not part of the UE’s current registration area (i.e. not part of the of 5GS TAIs that the UE received from the network), then the UE should take any one or more of the following actions in any combination: • The UE should remove / delete from the NSAG information any TAI(s) which is (are) in the NSAGI information but which is (are) not part of the UE’s registration area • The UE should the NSAG information associated with that TAI i.e. the slices, NSAG identifier and priority, if any of these are available, which are associated with the TAI in question. In other words, the UE need not delete the entire NSAG information but rather the parameters that are associated with the TAI in question i.e. the TAI which is not part of the UE’s registration area If the UE receives NSAG information where any TAI, which is part of the NSAG information, is also present in either the list of "5GS forbidden tracking areas for roaming" or the list of "5GS forbidden tracking areas for regional provision of service", then the UE may take one or more of the following actions: • The UE may behave as stated above i.e. remove the TAI (and optionally any related parameter which is associated with this TAI) from the NSAG information (i.e. the UE may take the same behaviour as described above for the case when a TAI in the NSAG information is not part of the UE’s registration area) • The UE may remove the TAI from the list of "5GS forbidden tracking areas for roaming" or from the list of "5GS forbidden tracking areas for regional provision of service" In a further embodiment, new AMF behaviour is defined to revoke (or start) the use of NSAG information. The AMF may decide to revoke the use of NSAG information for a UE which supports NSAG (i.e. for a UE which had indicated that NSAG is supported in the 5GMM capability IE of the Registration Request message) and / or optionally for a UE for which the AMF had previously provided NSAG information. Note that the decision to revoke or stop the use of NSAG for a UE may be based on the following determination in the AMF: • Local policies that determine that NSAG should no longer be used (optionally for a UE in question) • Change of subscription information indicating that NSAG should no longer be used (optionally for a UE in question) • Indication from any other network entity (either new or existing) such that NSAG should no longer be used (optionally for a UE in question) To stop or revoke the use of NSAG information for this UE, the AMF may take one or more of the following actions: • The AMF should send the Configuration Update Command and include the NSAG information IE where the IE is set to include empty contents o For example, empty content of the IE may be achieved by setting the length field (i.e. the “Length of NSAG information contents” field) of the NSAG information IE to zero • The AMF should send the Configured NSSAI IE in the Configuration Update Command message but without including the NSAG information IE in the message o Note that in this case, the contents of the Configured NSSAI IE need not be new S-NSSAIs and may indeed be the same (or possibly partly new) S-NSSAIs which the AMF may have previously provided to the UE, or may be exactly the same set of S-NSSAIs that the AMF has previously provided to the UE, or may be partly new or totally new • The AMF should trigger a registration procedure for the UE using the current NAS connection i.e. without the UE entering into 5GMM-IDLE mode. The AMF can do so by setting the "registration requested" in the Registration requested bit of the Configuration update indication IE and "release of N1 NAS signalling connection not required" in the Signalling connection maintain request bit of the Additional configuration indication IE in the CONFIGURATION UPDATE COMMAND message. Furthermore, during the registration procedure that follows, the AMF should send the Configured NSSAI IE in the Registration Accept message, but the message should not include the NSAG information IE For any of the actions above that lead the UE to receiving a Configured NSSAI IE but not the NSAG information IE, this will lead the UE to delete the NSAG information and hence the UE cannot use NSAG anymore. Note that for a UE which supports NSAG (e.g. the UE indicates that NSAG is supported in the 5GMM capability IE of the Registration Request message), the AMF may use the same mechanisms above to enforce the use of NSAG or to start the use of NSAG in the UE. The determination to do so may be similar to the events listed above e.g. local policies, subscription change, etc, such that the AMF now determines that NSAG should be used. The AMF may send the Configuration Update Command message and include the NSAG information IE optionally with the configured NSSAI, when the AMF determines to allow the use of NSAG at the UE. Alternatively, the AMF can trigger a registration procedure for the UE, while still in connected mode i.e. without entering idle mode and while using the current NAS connection (as described above), and during the registration procedure the AMF may provide the NSAG information IE in the Registration Accept message, optionally with a configured NSSAI as well. The AMF may also determine to provide NSAG information to the UE, which is already registered, when another network function provides an indication to do so. 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, arranged for communication with a 5 telecommunication network, comprising the steps of:• the UE receiving a Network Slice Access Group, NSAG, information from the telecommunication network;• the UE determining if there is a Single - Network Slice Selection Assistance Information, 10 S-NSSAI, entry which is in the NSAG information, which is not part of a configured NSSAI; and• the UE removing any S-NSSAI entry which is in the NSAG information but not in the configured NSSAI.

2. The method of claim 1 wherein the NSAG is associated with a plurality of S-NSSAIs and15 a list of Tracking Area Identities, TAIs, and a priority value, wherein if the step of removing anyS-NSSAI entry which is in the NSAG information but not in the configured NSSAI, results is no LO remaining S-NSSAI, then the UE deletes the NSAG information.CM3. The method of claim 2 wherein the UE further deletes the list of TAIs and the priority20 values.CO4. A User Equipment, UE, arranged to perform the method of any preceding claim.

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