Improvements in and relating to methods for stopping inactivity timer in a user equipment

Abstract

Methods of operating a slice deregistration inactivity timer in a user equipment (UE). The slice deregistration timer is associated with a particular slice having an associated identifier (S-NSSAI). The slice deregistration inactivity timer is started when the particular slice is not used for a PDU session S101. In a first alternative the UE identifies the particular slice based on an S-NSSAI received in a PDU session establishment accept message and then stops the slice deregistration timer upon PDU session establishment S103. In a second alternative either the UE explicitly indicates the S-NSSAI of the particular slice (e.g. in a PDU session establishment request), or the S-NSSAI is received in a PDU session establishment accept message, and the UE stops the slice deregistration inactivity timer upon PDU session establishment. In a third alternative, if the UE did not indicate an S-NSSAI then no deregistration inactivity timer is stopped. In a fourth alternative, if the UE did not indicate an S-NSSAI then all deregistration inactivity timers are stopped upon PDU session establishment. The S-NSSAI may be an on-demand S-NSSAI.

Description

The present invention relates to methods for stopping an inactivity timer in a User Equipment. UE, the UE being arranged for communication with a telecommunication network. 3GPP has developed several features related to network slicing, one of which uses a slice deregistration inactivity timer where the timer is per slice (S-NSSAI) and per access type (i.e. 3GPP or non-3GPP). The timer guards the inactivity period for the slice in question such that if the timer expires and the UE has not used the slice, then the slice is deemed to be no longer available for the UE, and the slice is removed from the allowed NSSAI which enforces the lack of the slices availability since only slices in the allowed NSSAI can be used. The following is from 3GPP TS 23.501 which describes this concept: “The 5GC performs Network Slice usage monitoring to be able to enforce the release of inactive PDU Sessions, and deregistering of UEs from Network Slices with no PDU Sessions on them according to its own policies. In order to support usage monitoring for a Network Slice: the AMF runs a slice deregistration inactivity timer per S-NSSAI and access type to deregister the Network Slice which is started when the Network Slice is not used by any PDU Session over the corresponding access type. The slice deregistration inactivity timer is stopped and reset when at least a PDU Session associated with the Network Slice is successfully established or the Network Slice is removed form the Allowed NSSAI. When the slice deregistration inactivity timer for a Network Slice over an access type expires, the AMF removes the Network Slice from the Allowed NSSAI over the access type by sending the UE Configuration Update Command to impacted UE(s). ” The following is from section 4.6.2.9 of 3GPP TS 24.501 which describes the start of the timer and the outcome of its expiry (similar to what is shown above): “The slice deregistration inactivity timer is: a) started when there is no established PDU session, including any MA PDU session, associated with the S-NSSAI over the corresponding access type; and b) stopped and reset when at least a PDU session, including any MA PDU session, associated with the S-NSSAI is successfully established over the corresponding access type(s) or the S-NSSAI is removed from the allowed NSSAI." The following is from section 6.4.1.3 of 3GPP TS 24.501 which describes that the deregistration inactivity timer is stopped upon the successful establishment of a PDU session, noting that this is associated with explicit session management signaling that is exchanged with the network for the session to be established: “If the UE supports network slice usage control and: a) a PDU session is successfully established for the on-demand S-NSSAI, the UE shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over corresponding access type, if running; and b) an MA PDU session is successfully established for the on-demand S-NSSAI, the UE shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over both 3GPP access and non-3GPP access, if running." To summarize, the following key points can be observed from the above: • A slice is associated with a deregistration inactivity timer, where the timer guards the period of inactivity for the slice. The expiry of the timer means the slice is no longer available for use • The timer is per slice and access technology (i.e. 3GPP or non-3GPP) • The timer is stopped upon successful establishment of a PDU session, where this requires explicit session management signaling. A UE which requests a PDU session establishment may not necessarily indicate the actual slice or S-NSSAI for which the request is being sent. This may be due to the User Equipment Route Selection Policy, URSP, rules in the UE such that the default rule may be used which may not have an associated S-NSSAI. The NAS specification in 3GPP TS 24.501 clearly permits the scenario for which the UE can send a PDU session establishment request but without an S-NSSAL The following is from section 5.4.5.2.3 which describes the network behavior when no S-NSSAI is indicated by the UE, for which the selection is then made by the network: “If the S-NSSAI IE is not included, the UE does not have a partially allowed NSSAI, and the allowed NSSAI contains: one S-NSSAI, the AMF shall use the S-NSSAI in the allowed NSSAI as the S-NSSAI. Additionally, for a UE for which the AMF has provided a NS-AoS, the AMF shall use the S-NSSAI in the allowed NSSAI if the UE is inside the NS-AoS with respect to the S-NSSAI; two or more S-NSSAIs and the user's subscription context obtained from UDM contains only one default S-NSSAI that is included in the allowed NSSAI, the AMF shall use the S-NSSAI in the allowed NSSAI that matches the default S-NSSAI as the S-NSSAI; or two or more S-NSSAIs and the user's subscription context obtained from UDM contains two or more default S-NSSAI(s) included in the allowed NSSAI, the AMF shall use an S-NSSAI in the allowed NSSAI selected based on operator policy as the S-NSSAI. ” In other cases, however, the UE may be aware of the S-NSSAI for which the PDU session is requested, and hence the UE will explicitly include the S-NSSAI in the NAS message. Note that only S-NSSAIs from the allowed NSSAI can be requested by the UE. Note that the PDU Session Establishment Accept message includes the S-NSSAI for which the PDU session is established, and this information is provided for all cases including the case when the UE did not explicitly indicate the S-NSSAI as part of the PDU session establishment procedure. The following key points can be highlighted: • A PDU session can be requested with an explicit S-NSSAI which is provided by the UE. The network uses this S-NSSAI for the session establishment; • A PDU session can be requested without an explicit S-NSSAI which is indicated by the UE. In this case, the network selects the S-NSSAI forthe UE (using the allowed NSSAI). The allowed NSSAI may have more than one entry which the AMF selects from; • This S-NSSAI is indicated in the PDU Session Establishment Accept message regardless of whether the S-NSSAI was indicated by the UE, or selected by the network when not provided by the UE. As set out above: “The slice deregistration inactivity timer is: a) started when there is no established PDU session, including any MA PDU session, associated with the S-NSSAI over the corresponding access type; and b) stopped and reset when at least a PDU session, including any MA PDU session, associated with the S-NSSAI is successfully established over the corresponding access type(s) or the S-NSSAI is removed from the allowed NSSAI.” Turning to the slice deregistration inactivity timer, the UE is supposed to stop a timer when a PDU session is established for a particular slice or S-NSSAI. However, this does not provide enough clarity about how the UE identifies the S-NSSAI in question since there are two options for a PDU session and an S-NSSAI as follows: • The UE explicitly indicated the S-NSSAI during the PDU session establishment procedure; or • The UE did not explicitly indicate the S-NSSAI during the PDU session establishment procedure and so the S-NSSAI was selected by the network. Note that in both cases the UE receives the S-NSSAI with which the session is associated in the PDU Session Establishment Accept message. A problem therefore becomes the following: it is not clear how the UE identifies the S-NSSAI for which the slice deregistration inactivity timer needs to be stopped after a session is established for an on-demand S-NSSAI. Without an explicit specification or description, different UEs can behave differently as follows: One UE implementation may associate the timer to what it explicitly provides. A subsequent problem then becomes related to the UE behavior when nothing is provided. Does it stop the deregistration timer for all slices or randomly picks the slice? One UE implementation may associate the timer to what it receives in the Session Establishment Accept message, and so this requires an additional check at the UE which is currently not specified. Finally, UEs that behave differently can lead to different results in the system, since at least some UEs may be unsynchronized with the network in terms of having a running deregistration inactivity timer especially when the UE did not indicate a slice in its request for a session. It is the aim of embodiments of this invention to clearly specify how the UE identifies an S-NSSAI for which a deregistration inactivity timer should be stopped. 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. In one aspect there is provided a method of operating a slice deregistration inactivity timer in a User Equipment, UE, the UE being in operative communication with a telecommunication network, wherein the slice deregistration inactivity timer is associated with a particular slice, S-NSSAI, and whereby the slice deregistration inactivity is started then the particular slice is not used for a PDU session, wherein: a) the UE determines the particular slice based on the S-NSSAI which is received in a PDU Session Establishment Accept message, and then stops the slice deregistration inactivity timer upon PDU session establishment; or b) the particular slice is the S-NSSAI which the UE explicitly indicated, otherwise it is what the UE receives in a PDU Session Establishment Accept message, and then stops the slice deregistration inactivity timer upon PDU session establishment; or c) if the UE did not indicate an S-NSSAI, then no deregistration inactivity timer is stopped; or d) if the UE did not indicate an S-NSSAI, then all deregistration inactivity timers are stopped upon PDU session establishment. In one aspect, the slice deregistration inactivity timer is further associated with an access type. In one aspect, the access type is one of 3GPP and non-3GPP. In one aspect, the expiry of the slice deregistration inactivity timer renders the associated slice unavailable. In one aspect there is provided an apparatus arranged to perform a method as herein-described. The invention focuses on how the UE identifies the on-demand S-NSSAI and hence how it associates the S-NSSAI to a PDU session so that the appropriate / corresponding slice deregistration timer is stopped. In one option, the on-demand S-NSSAI associated with the PDU session is determined to be the S-NSSAI which is received in the PDU Session Establishment Accept message. Once the on-demand S-NSSAI is determined, the UE stops and resets the deregistration timer which is associated with this determined on-demand S-NSSAI. In one option, if the UE did not indicate an S-NSSAI during PDU session establishment procedure, the the on-demand S-NSSAI associated with the PDU session is determined to be the S-NSSAI which is received in the PDU Session Establishment Accept message. Otherwise if the UE did indicate an S-NSSAI during PDU session establishment procedure, then the UE determines the on-demand S-NSSAI to be that which it provided. Once the on-demand S-NSSAI is deteremined, the UE stops and resets the deregistration timer which is associated with this determined on-demand S-NSSAI. In one option, if the UE did not provide an S-NSSAI during PDU session establishment procedure, then the UE does not stop any timer. The UE does not determine any on-demand S-NSSAI, or determines that there is no on-demand S-NSSAI which is associated with the established PDU session, and hence each deregistration timer is kept running In one option, if the UE did not provide an S-NSSAI during PDU session establishment procedure, then the UE stops all the deregistration inactivity timer for all on-demand S-NSSAIs that are running on this access technology over which the session is established, or over which the PDU session establishment accept message is received. 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 UE in operative communication with a telecommunication network; and Figure 2 shows a method according to an embodiment of the present invention. Figure 1 shows a UE 10, including a slice deregistration inactivity timer 12. The UE 10 is in operative communication with a telecommunication network 20. The UE and network may operate according to one or more telecom standards, such as 5G, 6G etc. Embodiments of the invention clearly specify how the UE identifies the on-demand S-NSSAI in order to stop the true or correct slice deregistration timer. As indicated earlier, the UE may provide an S-NSSAI during PDU session establishment, but sometimes it does not do so. Hence embodiments ensure that the UE correctly identifies the on-demand S-NSSAI so that the correct timer can be stopped, noting that the prior art does not address this issue. For any of the embodiments herein, the stopping of the timer may also mean that the UE first stops the timer and then resets it. As such in all the embodiments below, stopping a timer can also refer to a reset and stop of the timer. Note that the PDU session establishment procedure may mean that the UE sends a PDU Session Establishment Request message which is included in the UL NAS TRANSPORT message. The S-NSSAI may or may not be provided in the UL NAS TRANSPORT message. The deregistration inactivity timer may be a slice deregistration inactivity timer. Embodiments may include one or more of the Options set out below. Option 1: the UE determines the S-NSSAI based on the S-NSSAI which is received in the PDU Session Establishment Accept message This option provides the most consistent way to identify the on-demand S-NSSAI which is associated with the PDU session. In order to stop the correct slice deregistration inactivity timer, the UE considers the on-demand S-NSSAI for the PDU session as that which is received in the PDU Session Establishment Accept message. As such, for the purpose of identifying the on-demand S-NSSAI and for stopping the appropriate or correct timer that is associated with the on-demand S-NSSAI, the UE should determine the on-demand S-NSSAI to be the S-NSSAI received in the PDU Session Establishment Accept message and should stop the slice deregistration inactivity timer which is associated with this determined S-NSSAI. Optionally the timer is also associated with an access type which may be determined as the access type over which the session is established. In another alternative, the access type corresponding to the slice deregistration inactivity timer may be determined to be the access type over which the PDU Session Establishment Accept message is received. The UE can behave as described above when: • The UE did not provide any S-NSSAI (to the network) during the PDU session establishment procedure • The UE indicated or provided an S-NSSAI as part of the PDU session establishment procedure. Option 2: the on-demand S-NSSAI is the S-NSSAI which the UE explicitly indicated, otherwise it is what the UE receives in the PDU Session Establishment Accept message In this option, the UE uses different methods for determining the on-demand S-NSSAI for which there is a slice deregistration timer that is potentially running. In a first method, the on-demand S-NSSAI is determined to be the S-NSSAI which the UE provided in the NAS message during the PDU session establishment procedure, where the NAS message may be an UL NAS TRANSPORT message which can carry the S-NSSAI. Therefore, for the purpose of stopping the slice deregistration inactivity timer, if the UE had provided an S-NSSAI during PDU session establishment procedure, the UE determines the on-demand S-NSSAI that is associated with the PDU session as that which the UE provided (during PDU session establishment procedure), and hence the slice deregistration inactivity timer is the timer associated with this determined S-NSSAI. The access type corresponding to the slice deregistration inactivity timer may be determined to be the access type over which the PDU Session Establishment Accept message is received, or the access type over which the session is established. In the second method, if the UE did not provide any S-NSSAI during PDU session establishment procedure, then the on-demand S-NSSAI that is associated with the PDU session is determined to be the S-NSSAI that the UE receives in the PDU Session Establishment Accept message. The UE should stop the slice deregistration inactivity timer which is associated with this determined S-NSSAI. The access type corresponding to the slice deregistration inactivity timer may be determined to be the access type over which the PDU Session Establishment Accept message is received, or the access type over which the session is established. In this option, the UE operates with both methods described above based on whether the UE had provided an S-NSSAI during PDU session establishment or not. In another alternative, for the case when the UE does not provide an S-NSSAI during PDU session establishment procedure, if the UE has only one S-NSSAI in the allowed NSSAI, then the UE determines the on-demand S-NSSAI to be the single S-NSSAI in the allowed NSSAI, and hence the UE stops the deregistration inactivity timer which is associated with this single S-NSSAI (from the allowed NSSAI). The access type corresponding to the slice deregistration inactivity timer may be determined to be the access type over which the PDU Session Establishment Accept message is received, or the access type over which the session is established, or the access type for which there is only one entry in the allowed NSSAI. Option 3: no deregistration inactivity timer is stopped if the UE did not indicate an S-NSSAI In this option, if the UE did not provide an S-NSSAI during the PDU session establishment procedure, then the UE determines that there is no on-demand S-NSSAI which is associated with the PDU session that was established without any explicit S-NSSAI indication from the UE. As such, the UE does not stop any timer in this case and all the slice deregistration timers are maintained or kept running. In this solution, the stopping of a deregistration timer strictly requires that the UE provides an S-NSSAI during PDU session establishment procedure and hence an on-demand S-NSSAI can only be identified to be associated with a PDU session if the UE provided an S-NSSAI, and that S-NSSAI is determined to be the on-demand S-NSSAI. Option 4: all deregistration inactivity timers are stopped if the UE did not indicate an S-NSSAI In this option, if the UE did not provide an S-NSSAI during PDU session establishment procedure, then the UE determines that all the on-demand S-NSSAIs which have a timer running should be stopped, where the access type of each timer is determined to be the access type over which the session is established or to be the access type over which the PDU Session Establishment Accept message is received. Figure 2 shows a flowchart. At S101 a a slice deregistration inactivity timer is started. At S102, a determination is made whether or not to stop the timer or not in response to a PDU establishment activity. At S103, the timer is either stopped, not stopped or all slice deregistration inactivity timers are stopped, depending upon which options is in use. An embodiment of the invention may make use of only one or more than one of the options set out herein. In particular, provided there is a consistent use of one or more options, then certainty can be provided, thereby ensuring correct and predictable operation of the UE and network. By use of an embodiment of the present invention, the issues in the prior art associated with a lack of certainty can be avoided or at least ameliorated. 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 slice deregistration inactivity timer in a User Equipment, UE, the UE being in operative communication with a telecommunication network, wherein the slice deregistration inactivity timer is associated with a particular slice, S-NSSAI, and whereby the slice deregistration inactivity is started then the particular slice is not used for a PDU session, wherein:a) the UE determines the particular slice based on the S-NSSAI which is received in a PDU Session Establishment Accept message, and then stops the slice deregistration inactivity timer upon PDU session establishment; orb) the particular slice is the S-NSSAI which the UE explicitly indicated, otherwise it is what the UE receives in a PDU Session Establishment Accept message, and then stops the slice deregistration inactivity timer upon PDU session establishment; orc) if the UE did not indicate an S-NSSAI, then no deregistration inactivity timer is stopped; ord) if the UE did not indicate an S-NSSAI, then all deregistration inactivity timers are stopped upon PDU session establishment.

2. The method of claim 1 wherein the slice deregistration inactivity timer is further associated with an access type.

3. The method of claim 2 wherein the access type is one of 3GPP and non-3GPP.

4. The method of any preceding claim wherein the expiry of the slice deregistration inactivitytimer renders the associated slice unavailable.

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

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