Improvements in and relating to using Radio Resources During Emergency Session Network Slicing

Abstract

A method of operating a User Equipment, UE, arranged for communication with a telecommunication network. A Non-Access Stratum, NAS, layer in the UE identifies a slice, identified by a Single Network S

Description

The present invention relates to improvements in network slicing in a telecommunication network. It applies particularly, but not exclusively, to Fifth Generation, 5G, networks, but has wider application. A set of slices, (each slice identified as Single Network Slice Selection Assistance Information S-NSSAI) may be known to be part of a group - Network Slice Access Group, NSAG - 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 regarding 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.” The UE lower layers use the NSAG information for cell reselection or for accessing a cell (e.g. Random Access via Random Access Channel - RACH). The following is from Section 16.3.1 in 3GPP TS 38.300 (V 17.2.0) on this topic: “Slice Availability Some slices may be available only in part of the network. The NG-RAN supported S-NSSAI(s), NSAG(s) and NSAG related information such as NSAG associated Cell Reselection Priority are configured by OAM. Awareness in the NG-RAN of the slices supported in the cells of its neighbours may be beneficial for inter-frequency mobility in connected mode. It is assumed that the slice availability does not change within the UE's registration area (see TS 23.501 [3]). The NG-RAN and the 5GC are responsible to handle a service request for a slice that may or may not be available in a given area. Admission or rejection of access to a slice may depend by factors such as support for the slice, availability of resources, support of the requested service by NG-RAN.” The following is from section 16.3.3a on this topic: “16.3.3a Slice-based cell reselection Slice-based cell reselection information can be included in SIB16 and in RRCRelease messages. The slice-based cell reselection information may include reselection priorities per NSAG per frequency and corresponding list(s) of cells where the slices of the NSAG are supported or not supported. In the UE, NAS provides the NSAG(s) and their priorities to be considered during cell reselection. In order to support the NSAG, the NG-RAN provides the AMF with the NSAG information per TA in the appropriate NG interface management procedures, as specified in TS 23.501 [3]. Awareness in the NG-RAN of the NSAG information supported in the list(s) of neighbour cells may be configured by OAM, or exchanged with neighbour NG-RAN nodes. When a UE supports slice-based cell reselection, and when slice-based cell reselection Information is provided to the UE, then the UE uses the slice-based cell reselection information. Valid cell reselection information provided in RRCRelease always has a priority over cell reselection information provided in SIB messages. When no slice-based reselection information is provided for any NSAG that UE AS received from NAS to be considered during cell reselection, then the UE uses the general cell reselection information, i.e., without considering the NSAG(s) and their priorities.” From the above, it can be seen that the UE uses slice-based cell reselection based on the information in the UE. The following is indicated in section 9.2.6 in 3GPP TS 38.300 (V 17.2.0): “The network can associate a set of RACH resources with feature(s) applicable to a Random Access procedure: Network Slicing (see clause 16.3), RedCap (see clause 16.13), SDT (see clause 18), and NR coverage enhancement (see clause 19). A set of RACH resources associated with a feature is only valid for random access procedures applicable to at least that feature; and a set of RACH resources associated with several features is only valid for random access procedures having at least all of these features. The UE selects the set(s) of applicable RACH resources, after uplink carrier (i.e. NUL or SUL) and BWP selection and before selecting the RA type.” From the above, it can be seen that the UE uses a set of RACH resources which are applicable to network slicing i.e. for NSAG. A problem in the prior art arises when UE behaviour can be unclear with respect to which resources will be used when there is an access attempt for an emergency PDU session. The NSAG feature uses specific resources for a set of slices (or S-NSSAIs) when the UE attempts access for the slices in the NSAG. The UE may attempt to establish a PDU session for emergency and hence the UE’s access attempt is for emergency. However, there is no slice (i.e. S-NSSAI) which is known to the UE to be a slice for emergency. This is because the slice for emergency is selected by the Access and Mobility Management Function, AMF, of the network, if any. This leads to one or more of the following problems: • Given a certain set of slices that are chosen to be used e.g. based on the current allowed NSSAI or current chosen NSAG information, when the UE needs to place an emergency call, how can the UE know which resources to use given that the slice for an emergency call is never part of the NSAG information? • If the expected UE behaviour is not defined in a standardized way, then different UEs will end up using different resources, where some resources may be inefficient or of lower priority and hence this may cause delays to the establishment of the emergency PDU session As such, well-defined and standardised UE behaviour is desirable, in order to solve one or more of the problems set out above. To state the problem another way, there may be one or more different reasons why the Non-Access Stratum, NAS, wants to go to connected mode and therefore the UE may need to use several different slices when it enters connected mode. However, each NAS procedure may be associated with a different slice (S-NSSAI) and so in order for the NSAG feature to work correctly, the lower layers in the UE must use the appropriate radio resources (e.g. RACH) which correspond to the NAS procedure and Information Elements, IE, that the NAS wants to send to the network. In the prior art, there is no clear description of how the NAS clearly and unambiguously indicates the slices (S-NSSAIs) that the UE wants to use when it enters into connected mode. Without this explicit description, the lower layers may use the wrong resources (e.g. for RACH) which may be of lower priority and hence can cause significant delay to the service. This can lead to undefined behaviour and consequent negative user experience. 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: a Non-Access Stratum, NAS, layer in the UE identifies a slice, identified by a Single Network Slice Selection Assistance Information, N-SSAI, for which an access attempt is made via a NAS message; wherein the step of identifying the slice is based on one of: • a slice that corresponds to a PDU session, indicated by an Uplink data status Information Element, IE, which is included in the NAS message; • a slice that corresponds toa PDU session, indicated by an Allowed PDU session status IE, which is included in the NAS message; or • a 5GSM procedure. In an embodiment, the identified slice is provided from the NAS layer to a lower layer of the UE. In an embodiment, the UE is in 5GMM-IDLE mode or in 5GMM-CONNECTED mode with RRC inactive indication. In an embodiment, if the access attempt is related to an emergency service, then the NAS layer does not provide any slice information to a lower layer. In an embodiment, the 5GSM procedure is one of a PDU session modification procedure, a PDU session establishment procedure or a PDU session release procedure. According to a second aspect of the present invention, there is provided a method of operating a User Equipment, UE, arranged for communication with a telecommunication network, wherein if an attempt is made to access the telecommunication network for emergency service, then a NAS layer in the UE does not pass any slice information to a lower layer. In an embodiment, the step of the UE not passing any slice information to the lower layer is either because the UE determines that there is no such slice information or that no such slice information should be passed. According to a third aspect of the present invention, there is provided apparatus arranged to perform the method of any preceding aspect. 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. An embodiment of the invention aims to define how the UE uses resources when there is a need to place an emergency PDU session, given that the UE is already using NSAG information. Note that throughout this specification the term “UE” may be referring to any layer or entity in the UE e.g. the NAS layer, or RRC layer or both or multiple layers or entities. As such, any detail provided herein may apply to any of these layers or entities in any combination or order, or may apply to more than one layer or entity. When the UE determines that there is an access attempt for emergency services (e.g. to establish a PDU session for emergency service, or to access the network for using an existing PDU session for emergency service, etc), then the UE should take any of the following actions in any order or combination: • The UE (e.g. RRC) should stop using any specific resources that were otherwise being used (e.g. for NSAG or slice specific random access or cell reselection) before this access attempt or before the emergency request is sent (e.g. before the PDU session for emergency services is established) • The UE (e.g. RRC) should use the resources related to the highest priority of the NSAG information • The UE randomly picks an NSAG and uses the priority and / or resources associated with the randomly picked NSAG Note that the UE (e.g. RRC) may determine that the access attempt is for emergency based on the established cause received from the NAS (e.g. indicating emergency) or based on a specific access category value as defined in 3GPP TS 24.501 e.g. value number 2, or based on any other method that points to an emergency session. The UE (e.g. RRC) should resume the use of NSAG information, and hence the resources related to slicing (S-NSSAIs, based on the NSAG information), and optionally the priority levels associated with these resources, etc, when a next (or new) access attempt no longer indicates that the attempt is for emergency services. Note that the UE resuming the use of NSAG information means that the UE does not use the general cell reselection information or the general cell random access resources, but rather the UE would / should use the resources that are associated with the slices in the NSAG or that are associated with the NSAG information. Alternatively, the UE resumes the use of NSAG information (e.g. resources associated with certain slices, or NSAG, or priority, etc) when the PDU session is released or when the user plane resources for the emergency PDU session have been released. In another embodiment, the UE behaves as described above when the UE (e.g. RRC layer) does not know the slices for which an access attempt is being made. For example, the UE (e.g. RRC) behaves as described above when the UE (e.g. RRC) does not receive the slices for which an access attempt is being made or does not receive the NSAG priority information (and / or does not receive any NSAG information). In this case, the UE (e.g. RRC) may then use the general resources which are not specific to any NSAG or slicing information or priority or slicing resources, etc. While doing so, the UE may continue to save the NSAG information that was previously received e.g. until a new version or updated version is received. The RRC may behave as described above optionally when the RRC received NSAG information but does not receive the slices for which the access attempt is being made. In this case, the RRC may use the general resources for random access or for cell reselection or for both. The UE (e.g. RRC) may switch between using NSAG information (e.g. resources for specific slices, etc) and using general resources (e.g. resources not related to specific slices) based on any one or more of the following: • Whether or not the UE knows the slices for which the access attempt is being made. For example, if the slices for which the access attempt is being made are unknown, then the UE uses the general resources of the cell • For example, if the UE knows the slices for which the access attempt is being made, and the UE optionally has NSAG information which matches the slices for which the access attempt is being made, then the UE uses the resources for the slices for which the access is being made (e.g. based on the NSAG information). Note that if the NAS layer does not know the slices for which an access attempt is being made, then the NAS layer may take any one or more of the following actions in any order or combination: • When initiating an access attempt, e.g. the UE needs to transition to connected mode (e.g. to 5GMM-CONNECTED mode, optionally from any mode or state), then the NAS does not provide the NSAG information to the RRC layer. Optionally the NAS provides the NSAG information to the RRC layer but does not indicate the slices for which the access attempt in being made, and optionally the NAS may not provide any NSAG priority information. In one alternative, the NAS may provide an NSAG and / or an NSAG priority but no slice for which an access attempt is being made • The NAS layer selects a particular NSAG based on a certain preconfigured manner e.g. the NSAG with the highest priority is selected, the UE selects the NSAG with the lowest priority, or the UE selects a particular NSAG which is known to be associated with no slices, or the UE selects a particular NSAG randomly. The UE may provide the NSAG information and optionally indicate the slices corresponding to the selected NSAG as the slices for which the access attempt is being made. Alternatively, the UE does not provide the slices for which access attempt is being made (since they are not known) but rather provides the NSAG priority and / or the selected NSAG (and may provide the NSAG information as well) o If the lower layers e.g RRC, receive NSAG information and a particular NSAG priority and / or the selected NSAG, then the RRC may consider the selected NSAG as the NSAG that matches the received priority and / or that matches the received NSAG (optionally in addition to the NSAG priority). Once the RRC determines the selected NSAG and / or the selected NSAG priority, then the RRC uses the resources that are associated with this determined selected NSAG and / or NSAG priority Note that the NAS may consider that the slice for which an access attempt is being made is unknown (or the NAS may determine that the slice for which the access being made is unknown) either when: the UE is trying to establish a PDU session for emergency services, or the UE is trying to access the network and use an existing PDU session for emergency PDU session, or the UE is attempting to establish a PDU session but does not know which slice to use for the session. Alternatively, for an existing PDU session which the UE may have established without including a slices (e.g. without sending an S-NSSAI), the UE may determine (and optionally use) the slice for which an access attempt is being as follows: • The slice (or S-NSSAI) is the S-NSSAI that the UE has received in the PDU session establishment accept message, optionally even if the session is for emergency, or optionally if the session is not for emergency, and optionally if the UE did not send any slice (or any S-NSSAI) when the session was established (or when the UE sent the PDU session establishment request message) However, when the UE determines that the slice, for which an access attempt is being made, Is unknown (i.e. the UE Is not able to determine the slice for which an access attempt Is being made), then the UE behaves as described above / herein. E.g. the NAS does not indicate (e.g. to the RRC) any slice for which the access attempt is being made, or the RRC does not use any slice specific resources (based on NSAG information) but rather uses the general resources of the cell or network or RAN. As such, when the NAS considers or determines that the slices for which an access attempt is being made are not known, or when the NAS determines that there are no slices for which the access attempt is being made (or when the NAS is not able to determine the slices for which an access attempt Is being made), then the NAS may behave as described earlier, e.g.: • The NAS does not provide any NSAG information to the RRC • The NAS does not provide (to the RRC) any slices for which access attempt is being made, or the NAS indicates to the RRC that there are no slices for which the access attempt is being made. The NAS may optionally provide NSAG information or NSAG or NSAG priority e.g. based on a selection that the NAS makes as proposed earlier. If the UE is able to determine at least one slice for which the access attempt is being made (e.g. due to a request associated with a known slice, or to use / request resources for an existing PDU session for which the slice was optionally requested / provided by the UE at the time of the establishment) but also cannot determine at least one other slice for which the same access is being made (e.g. where the pending procedure is for an emergency service or for any PDU session for which the UE cannot determine or does not include a slice), then the UE may behave in any of the following manners: • Since one slice is not known, the UE may conclude that no slice can be determined for the current access and hence may behave as described earlier. In one option, the UE may behave as described if the slice which is not known is related to a PDU session for emergency services. E.g. in this case, the NAS does not provide (to the RRC) the slices for which the access attempt is being made. The NAS may provide NSAG information or priority, etc if available. The RRC may behave as described earlier e.g. the RRC would use general resources if it does not receive slices for which the access attempt is being made • Since at least one slice is known, and optionally at least one other slice is not known, the UE may consider the known slices as the slices for which the access attempt is being made. The NAS provides that information to the lower layers (e.g. RRC) and optionally includes the NSAG information or priority, etc. In some cases, the UE gets paged and then the UE sends a NAS message (e.g. Service Request or Registration Request) with the Uplink data status IE and / or the Allowed PDU session status IE. The following describes a proposal that enables the UE to determine the slices for which the access attempt is being made: • The S-NSSAIs for which an access attempt is being made is the S-NSSAI which corresponds to each PDU session for which the UE requests the establishment of user plane resources by means of the Uplink data status IE (where optionally the UE intends to include or includes this IE in the NAS message). For example, a slice (or S-NSSAI) is determined to be a slice for which an access attempt is being made if the slice corresponds to a PDU session (identified by a PDU session ID) for which the UE sets the bit position to 1 in the Uplink data status IE, where the value 1 indicates e.g. “indicates that uplink data are pending for the corresponding PDU session identity and the user-plane resources for the corresponding PDU session are not established”. As such, if a bit position for a PDU session (identified by a PDU session ID) is set to the value 0, or is not set to the value 1, then the slice corresponding to this PDU session is not a slice for which an access attempt is being made • The S-NSSAIs for which an access attempt is being made is the S-NSSAI which corresponds to each PDU session for which the UE requests the establishment of user plane resources (or for which the UE requests to be transferred from non-3GPP access to 3GPP access) by means of the Allowed PDU session status IE (where optionally the UE intends to include or includes this IE in the NAS message). For example, a slice (or S-NSSAI) is determined to be a slice for which an access attempt is being made if the slice corresponds to a PDU session (identified by a PDU session ID) for which the UE sets the bit position to 1 in the Allowed PDU data status IE, where the value 1 indicates e.g. “indicates that the user-plane resources of corresponding PDU session can be re-established over 3GPP access”. As such, if a bit position for a PDU session (identified by a PDU session ID) is set to the value 0, or is not set to the value 1, then the slice corresponding to this PDU session is not a slice for which an access attempt is being made • Any S-NSSAI for which the UE intends to establish a PDU session, or for which there is a pending NAS procedure (e.g. PDU session modification procedure or PDU session establishment procedure or PDU session release procedure). • Any combination of the above In one alternative, if the UE is accessing the network to release at least one PDU session, then the UE may behave as if the slice for which the access attempt in being made is not known. In one alternative, if the UE needs to establish a PDU session but does not know the slice that should be used with the request (e.g. with the PDU session establishment request message), and if the UE only has one S-NSSAI in the allowed NSSAI, then the UE determines that the slice for which the access attempt is being made is the (only) S-NSSAI which is part of the allowed NSSAI. In one alternative, if the UE has no S-NSSAI in the allowed NSSAI, and the UE has a pending NSSAI (which is not empty), then when responding to paging, the UE considers that the slice for which the access attempt is being made is not known i.e. the UE determines that there is no identified S-NSSAI for which the access attempt is being made. As such, the UE behaves as described earlier e.g. the NAS does not provide, to the lower layers (e.g. RRC), the slice for which an access attempt is being made, or the RRC does not use resources related to NSAG information, etc. Note: once the UE knows the slices for which the access is attempt is being made, then the UE provides this information to the lower layers when the UE is using NSAG information. Note that in one alternative, the network may send to the UE e.g. as part of the NSAG information, an NSAG (i.e. a network slice access group) which contains no S-NSSAI and may contain a priority level. As such, anytime the UE needs to establish a PDU session, or perform an access to the network, such that the slice (for which the access is being made) is not known, then the UE uses the associated NSAG and / or NSAG priority and provides it to the lower layers. The lower layers e.g. RRC, may use it as described herein for the case when the slice for which the access is being made) is not known. E.g. the RRC uses general resources in this cases, or the resources corresponding to the received priority or NSAG (although no particular S-NSSAI may have been received). Note: NSAG information may refer to a set of: network slice access group (NSAG), and / or a priority level, and / or a list of TAI where the information is valid, or any combination of these. Note: NSAG may refer to the group that is associated with a set of slices (where the set of slices may be empty) Note: priority level, or NSAG priority, may refer to a priority associated with the NSAG The details presented above can be applied in any order or combination, and may apply for a UE which is in 5GMM-IDLE mode or 5GMM-CONNECTED mode with RRC inactive indication, or for a UE which is trying to transition from these modes / states to the 5GMM-CONNECTED mode. Figure 1 shows a representation of an embodiment of the present invention. At S101, a Non-Access Stratum, NAS, layer in the UE identifies a slice, identified by a Single Network Slice Selection Assistance Information, N-SSAI, for which an access attempt is made via a NAS message. At S102, the step of identifying the slice is based on one of: a slice that corresponds to a PDU session, indicated by an Uplink data status Information Element, IE, which is included in the NAS message; a slice that corresponds toa PDU session, indicated by an Allowed PDU session status IE, which is included in the NAS message; or a 5GSM procedure. At S103, optionally, the identified slice is provided from the NAS layer to a lower layer of the UE. 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. 20 01 25

Claims

1. A method of operating a User Equipment, UE, arranged for communication with a telecommunication network, comprising the steps of:5a Non-Access Stratum, NAS, layer in the UE identifies a slice, identified by a Single Network Slice Selection Assistance Information, N-SSAI, for which an access attempt is made via a NAS message;10 wherein the step of identifying the slice is based on one of:• a slice that corresponds to a PDU session, indicated by an Uplink data status Information Element, IE, which is included in the NAS message; or• a slice that corresponds to a PDU session, indicated by an Allowed PDU session 15 status IE, which is included in the NAS message.

2. The method of claim 1 wherein the identified slice is provided from the NAS layer to a lower layer of the UE.20 3. The method of claim 1 or 2 wherein the UE is in 5GMM-IDLE mode or in 5GMM-CONNECTED mode with RRC inactive indication.

4. The method of any preceding claim wherein if the access attempt is related to an emergency service, then the NAS layer does not provide any slice information to a lower layer.

5. Apparatus arranged to perform the method of any preceding claim.

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