Improvements in and relating to managing a slice deregistration inactivity timer

Abstract

A method of managing a slice deregistration inactivity timer in a telecommunication system, wherein if a User Equipment, UE or an Access and Mobility Management Function, AMF,releases a Protocol Data

Description

Fifth Generation (5G) telecommunication systems, at least, employ network slicing, so that a portion of network resources can be controlled at a slice level, enabling certain resources to be made available to users registered with a particular slice. The invention has particular relevance to a Multi-Access Protocol Data Unit, MA PDU, Session, which is a session that may have user-plane resources on two access networks e.g. both 3GPP access and non-3GPP access are allowed for the slice, S-NSSAI, of the PDU Session. 3rd Generation Partnership Project (3GPP) has developed several features related to network slicing, one of which uses a slice deregistration inactivity timer where the timer is per slice (Single - Network Slice Selection Assistance Information, 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 User Equipment (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 Protocol Data Unit (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 Access and Mobility management Function (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 NS SA I 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 from 3GPP TS 23.501): “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 6.3.3.3 of 3GPP TS 24.501 which describes that the deregistration inactivity timer is stopped upon the deactivation of a PDU session, noting that this deactivation is performed with explicit session management Non-Access Stratum (NAS) messages: “For a single access PDU session, upon receipt of a PDU SESSION RELEASE COMMAND message and a PDU session ID, using the NAS transport procedure as specified in subclause 5.4.5, the UE considers the PDU session as released and the UE shall create a PDU SESSION RELEASE COMPLETE message. [... SKIP ...] If the UE supports network slice usage control: a) all PDU session associated with an on-demand S-NSSAI are released and there is no MA PDU session associated with this on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer for this on-demand S-NSSAI over the corresponding access type; b) all MA PDU session associated with an on-demand S-NSSAI are released and there is no PDU session associated with this on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer for this on-demand S-NSSAI over both 3GPP access and non-3GPP access; or c) all PDU session and all MA PDU session associated with an on-demand S-NSSAI are released, the UE shall start the slice deregistration inactivity timer for this on-demand S-NSSAI over both 3GPP access and non-3GPP access.” To summarize, from the above, it can be observed that a slice is associated with a deregistration inactivity timer, where the timer is started when the PDU session is released using session management messages that are exchanged between the UE and the network. The UE and the network have the context e.g. PDU session ID, etc, of the PDU sessions that are active in the UE and the network. The UE or the network may determine to release a PDU session and this is normally performed with explicit session management NAS messages which can only be sent when the UE is in connected mode. However, it is possible that whilst a UE is in idle mode, any of the following can occur: • The UE may have locally deactivated a PDU session • The network may have locally deactivated a PDU session For each of these cases, there is no explicit session management NAS message. However, as it is important to keep both the UE and the network synchronized with respect to the PDU session status i.e. which sessions are still active and which have been deactivated. In order to synchronize, as described, the UE or the network uses the PDU session status IE which contains a bitmap representing the PDU session ID, where a bit value of one (i.e. 1) indicates that the session is active, and a value of zero (i.e. 0) indicates that the session is inactive. When a receiving entity processes the IE, the entity will synchronize the PDU sessions locally such that only those PDU sessions that are indicated as active will be maintained to be active, whereas all other PDU sessions will be set to be inactive. Hence both UE and network will be synchronized again with respect to PDU session context. Note that the IE is sent by the UE in an initial NAS message e.g. Service Request, Registration Request, or Control Plane Service Request. Therefore, the IE actually replaces the need for explicit session management NAS messages. Similarly, the network can send the IE in the NAS response message e.g. Registration Accept or Service Accept message. In summary, the PDU session status IE can be used for synchronization of PDU session status during initial NAS message procedures, where the IE portrays which sessions are active (and hence which others are inactive) and the recipient node will synchronize accordingly. The PDU session status IE replaces explicit session management messages to deactivate a PDU session. As set out above, the UE starts the deregistration timer when there is no PDU session which is active, noting that this description is captured as part of the PDU session release procedure which means that there are explicit session management NAS messages. Based on this, whenever a PDU session is released by means of the PDU session status IE there will be no impact to the slice deregistration inactivity timer i.e. the timer remains un-started and the slice remains in the UE’s allowed NSSAI indefinitely since the timer was never started. This is problematic as it contradicts the expectation and requirement for temporarily available slices. 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 invention, there is provided a method of managing a slice deregistration inactivity timer in a telecommunication system, wherein if: a) a User Equipment, UE, releases a Protocol Data Unit, PDU, session locally, and if there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI, then the UE starts the slice deregistration inactivity timer; or b) an Access and Mobility Management Function, AMF, releases a PDU session locally, and if there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI, then the AMF starts the slice deregistration inactivity timer; or c) the UE receives a PDU session status Information Element, IE, including a PDU session ID, which is in an inactive state, in registration accept or service accept, the UE starts the slice deregistration inactivity timer if the PDU session is associated with on-demand slice, S-NSSAI, and there is no established PDU session, including any MultiAccess, MA, PDU session, associated with the slice, S-NSSAI; or d) the AMF receives a PDU session status IE including a PDU session ID, which is in an inactive state, in registration request or service request, the AMF starts the slice deregistration inactivity timer if the PDU session is associated with on-demand slice, S-NSSAI, and there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI. In an embodiment, in c) or d), the PDU session associated with the PDU session ID was previously in an active state. In an embodiment, in c) or d) wherein the PDU session ID is associated with on-demand slice, S-NSSAI, for which the UE received a PDU session inactive notification. According to a second aspect of the invention, there is provided apparatus comprising one or more of a UE or a telecommunication system arranged to perform the method of the first aspect. Embodiments of the invention provide that the slice deregistration inactivity timer should be started when there is a local release of the PDU session i.e. even if there is no explicit session management NAS message exchange. The timer may be started when the local release is performed, or after the indication of the local release (or the indication of the PDU session being inactive) by means of the PDU session status IE. Solutions apply to both the UE and / or the network. Alternatively, for a UE which supports use of on-demand NSSAI, or which has received a slice deregistration inactivity timer, the UE should trigger a NAS connection i.e. the UE should send a NAS message, after a local release of a PDU session in order to synchronize the release of the PDU session with the network. The UE and the network can then start the slice deregistration inactivity timer after synchronization by means of PDU session status IE. 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 a method according to an embodiment of the invention. Figure 1 shows a flowchart illustrating an embodiment of the invention. At step S10, a User Equipment, UE, releases a Protocol Data Unit, PDU, session locally, and if there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI then, at step S11 the UE starts the slice deregistration inactivity timer. Alternatively, at step S20 an Access and Mobility Management Function, AMF, releases a PDU session locally, and if there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI then, at step S21, the AMF starts the slice deregistration inactivity timer. Alternatively, at step S30, the UE receives a PDU session status Information Element, IE, including a PDU session ID, which is in an inactive state, in registration accept or service accept then, at step S31, UE starts the slice deregistration inactivity timer if the PDU session is associated with on-demand slice, S-NSSAI, and there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI. Alternatively, at step S40, the AMF receives a PDU session status IE including a PDU session ID, which is in an inactive state, in registration request or service request then, at step S41, the AMF starts the slice deregistration inactivity timer if the PDU session is associated with on-demand slice, S-NSSAI, and there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI. A feature of an embodiment of the invention is to clearly specify how the UE and / or the network handles the slice deregistration inactivity timer when a PDU session is locally released and optionally after the PDU session context synchronization is performed by means of the PDU session status IE. The UE and / or the AMF should handle the slice deregistration inactivity timer as follows: • At any time when there is a local release of the PDU session, the entity should start the slice deregistration inactivity timer o The entity may be a UE or the AMF o In the case of the AMF, the AMF may determine that the PDU session has been released when so informed by the Session Management Function (SMF) which is service a particular slice (S-NSSAI) and hence the slice is associated with the PDU session in question. The AMF then starts the slice deregistration inactivity timer ■ Therefore, determination of local release at the AMF may be based on an indication from the SMF, optionally where the UE in question is known to be in 5GMM-IDLE mode (or in 5GMM-IDLE mode with suspend indication • Optionally, an entity may start the slice deregistration inactivity timer for a slice (or S-NSSAI) after sending the PDU session status IE where the sending entity indicates that the PDU session in question (e.g. where the PDU session is referred to by a PDU session ID) is indicated to be inactive o Optionally, the timer is started for a PDU session for which there has been a change in status i.e. in particular for a PDU session which was previously active and is now considered to be inactive ■ Optionally where the change in the PDU session status (e.g. from being active to inactive) has not yet been reported by means of the PDU session status IE, or where the PDU session in question has not been released or deactivated using explicit session management NAS messages o The entity may start a slice deregistration inactivity timer after sending the PDU session status IE as set out above but optionally after receiving an indication from the lower layers that the carrying message (i.e. the message which carries the IE, where the message may be a NAS message or any other message that may further encapsulate a NAS message) has been sent, optionally successfully ■ E.g. for a UE, the UE starts the timer as set out after indication is received from the lower layers (e.g. RRC) that the NAS message (e.g. Service Request, Registration Request, etc.) has been successfully sent, where the NAS message included the PDU session status IE as described herein ■ E.g. for the AMF, the AMF starts the timer after the AMF receives a confirmation from the Next Generation Radio Access Network (NG-RAN) that the message has been sent to a UE o The entity may be a UE or an AMF o In the case of a UE, the UE may start the slice deregistration inactivity timer as set out above (i.e. after sending the PDU session status IE as has been described above, using any NAS message), where the UE should optionally start the timer after receiving a NAS response message e.g. Registration Accept, Service Accept, or any NAS message In one embodiment, the UE may behave as follows after sending the PDU session status IE (in any NAS message) such that the UE indicates that there is at least one PDU session which is inactive in the UE: • Optionally if the UE supports network slice usage control and a PDU session which is indicated as inactive is associated with an on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer corresponding to this on-demand S-NSSAI and over the current access type • Optionally, if the UE supports network slice usage control and a PDU session which is indicated as inactive is associated with an on-demand S-NSSAI, and optionally all Multi-Access (MA) PDU session associated with an on-demand S-NSSAI are released and optionally there is no PDU session associated with this on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer for this on-demand S-NSSAI over both 3GPP access and non-3GPP access The embodiments set out above may also be further enhanced with the following alternatives: • When the UE performs a local release of a PDU session, the UE should initiate the establishment of a NAS connection and include the PDU session status IE to indicate the PDU session which has been deactivated. Hence, the local release of a PDU session should trigger a NAS message or procedure and the inclusion of the PDU session status IE. The UE then takes the actions set out above. The importance of this enhancement is that it further enables both the UE and the network to be synchronized with respect to when the slice deregistration inactivity timer becomes started o For example, if the UE starts the timer after a local release but the UE does not immediately send the PDU session status IE, then the network would receive the indication of the deactivation of the PDU session at a much later time and only then would the network start the slice deregistration inactivity timer. Therefore, the duration of the running timer on the UE side (i.e. the remaining duration of the timer) and that on the network side would be very different. • Optionally when the UE performs a local release of a PDU session, the UE should not start the slice deregistration inactivity timer immediately. The UE may behave as described earlier e.g. the UE starts the timer after sending the PDU session status IE with an indication that the PDU session is inactive (where e.g. the PDU session is associated with the S-NSSAI for which there is a slice deregistration inactivity timer) • Alternatively, the UE should not perform local release and hence should only release a PDU session using explicit session management messages. This then forces the UE and the network to release a session by means of signalling and then both entities would start the slice deregistration inactivity timer at around the same time. Note that this behaviour is not normally expected of the UE i.e. the UE does need to enter connected mode just to release a PDU session. As such the proposal is that for a UE which supports the slice deregistration inactivity feature, the UE may always perform release of a PDU session by means of explicit session management NAS messages o This may be for a UE which supports the related feature o This may be for a UE which has received a slice deregistration inactivity timer value from the network • When the AMF receives an indication from the SMF that a PDU session is released, the AMF may page the UE and send the PDU session status IE in a NAS message. The AMF and the UE may then take any of the actions set out earlier regarding the start of the slice deregistration inactivity timer o Alternatively, the network (e.g. SMF) should optionally perform PDU session release by means of explicit session management NAS message so that both the UE and the network would start the necessary slice deregistration inactivity timer at around the same time If a PDU session status IE is included in a NAS message which is received by the AMF e.g. the REGISTRATION REQUEST message, Service Request message or Control Plane Service Request message, when the AMF performs local release of a PDU session which is indicated by the UE as being in in 5GSM state PDU SESSION INACTIVE (where this PDU session was previously considered to be in 5GSM state PDU SESSION ACTIVE in the network e.g. in the AMF), and if the PDU session which is indicated by the UE as being in 5GSM state PDU SESSION INACTIVE is associated with an on-demand S-NSSAI, the AMF shall start the slice deregistration inactivity timer corresponding to this on-demand S-NSSAI and the current access type (over which the NAS message is received). If a PDU session status IE is included in a NAS message which is received by the UE e.g. the REGISTRATION ACCEPT message, or SERVICE ACCEPT message, when the UE performs local release of a PDU session which is indicated by the AMF as being in in 5GSM state PDU SESSION INACTIVE (where this PDU session was previously considered to be in 5GSM state PDU SESSION ACTIVE in the UE), and if the PDU session which is indicated by the AMF as being in 5GSM state PDU SESSION INACTIVE is associated with an on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer corresponding to this on-demand S-NSSAI and the current access type (over which the NAS message is received). For all the embodiments and variants thereof herein, starting the timer by any entity may be performed (as set out herein) if the timer is not already running. • The details herein may apply for a UE which supports (or has indicated that the UE supports) the network slice replacement feature, e.g. the proposals apply for a UE as follows: o Optionally the details apply for a UE which supports network slice usage control o Optionally the details apply for a UE which has received a slice deregistration inactivity timer, or which has received on-demand NSSAI consists of one or more on-demand S-NSSAIs and, optionally, the slice deregistration inactivity timer per on-demand S-NSSAI o This information may be received in any NAS message e.g. in the REGISTRATION ACCEPT message or the CONFIGURATION UPDATE COMMAND message • Optionally the details herein are for a UE which is not in 5GMM-CONNECTED mode when the local release was performed, or the proposal is for a UE which has performed a local release for is in 5GMM-IDLE mode or 5GMM-IDLE mode with suspend indication, or 5GMM-CONNECTED mode with RRC inactive indication • Indicating that the PDU session is inactive can refer to setting of the PSI bit of the PDU session status IE to the value 0, indicating that the 5GSM state of the corresponding PDU session is PDU SESSION INACTIVE • The PDU session status IE may be included in any NAS message such as CONTROL PLANE SERVICE REQUEST, SERVICE REQUEST, REGISTRATION REQUEST The following represents an exemplary means by which the applicable standards document(s) may be amended to reflect the operation of one or more embodiments of the present invention: “When the registration procedure for mobility and periodic registration update is initiated in 5GMM-IDLE mode, the UE may include a PDU session status IE in the REGISTRATION REQUEST message, indicating: which single access PDU sessions associated with the access type the REGISTRATION REQUEST message is sent over are not inactive in the UE. If the UE supports network slice usage control and a PDU session which is indicated as inactive is associated with an on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer, if not running corresponding to this on-demand S-NSSAI and over the current access type; and which MA PDU sessions are not inactive and having the corresponding user plane resources being established or established in the UE on the access the REGISTRATION REQUEST message is sent over. If the UE supports network slice usage control and a PDU session which is indicated as inactive is the UE MA PDU session, is associated with an on-demand S-NSSAI and the user plane resources being established or established on the access where registration request is sent, and there is no PDU session associated with this on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer, if not running for this on-demand S-NSSAI over the access where registration request is sent. If a PDU session status IE is included in the REGISTRATION REQUEST message: a) for single access PDU sessions, the AMF shall: 1) perform a local release of all those PDU sessions which are not in 5GSM state PDU SESSION INACTIVE on the AMF side associated with the access type the REGISTRATION REQUEST message is sent over, but are indicated by the UE as being in 5GSM state PDU SESSION INACTIVE. If the PDU session which is indicated by the UE as being in 5GSM state PDU SESSION INACTIVE is associated with an on-demand S-NSSAI, the AMF shall start the slice deregistration inactivity timer corresponding to this on-demand S-NSSAI and the current access type. If any of those PDU sessions is associated with one or more MBS multicast sessions, the SMF shall consider the UE as removed from the associated multicast MBS sessions; and 2) include a PDU session status IE in the REGISTRATION ACCEPT message to indicate which PDU sessions associated with the access type the REGISTRATION ACCEPT message is sent over are not in 5GSM state PDU SESSION INACTIVE in the AMF; and b) for MA PDU sessions: 1) for all those PDU sessions which are not in 5GSM state PDU SESSION INACTIVE and have user plane resources being established or established on the access the REGISTRATION REQUEST message is sent over on the AMF side, but are indicated by the UE as no user plane resources are being established or established: i) for PDU sessions having user plane resources being established or established only on the access the REGISTRATION REQUEST message is sent over, the AMF shall perform a local release of all those PDU sessions. If the MA PDU session is associated with one or more multicast MBS sessions, the SMF shall consider the UE as removed from the associated multicast MBS sessions. If the UE supports network slice usage control and the MA PDU session is associated with an S-NSSAI which is an on-demand NSSAI and no PDU session associated with S-NSSAI is active then AMF shall start the slice deregistration inactivity timer, if not running, for the access where the REGISTRATION REQUEST message is received and the optionally the on-demand S-NSSAI ii) for PDU sessions having user plane resources being established or established on both accesses, the AMF shall perform a local release on the user plane resources associated with the access type the REGISTRATION REQUEST message is sent over. If the REGISTRATION REQUEST message is sent over 3GPP access and the MA PDU session is associated with one or more multicast MBS sessions, the SMF shall consider the UE as removed from the associated multicast MBS sessions; and 2) the AMF shall include a PDU session status IE in the REGISTRATION ACCEPT message to indicate which MA PDU sessions having the corresponding user plane resources are being established or established on the AMF side on the access the REGISTRATION ACCEPT message is sent over. If the AMF needs to initiate PDU session status synchronization the AMF shall include a PDU session status IE in the REGISTRATION ACCEPT message to indicate the UE: which single access PDU sessions associated with the access the REGISTRATION ACCEPT message is sent over are not in 5GSM state PDU SESSION INACTIVE in the AMF. If the AMF indicates that a PDU session is now in 5GSM state PDU SESSION INACTIVE in the AMF, and the PDU session is associated with an on-demand S-NSSAI, the AMF shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI and the current access type over which the REGISTRATION ACCEPT message is sent; and which MA PDU sessions are not in 5GSM state PDU SESSION INACTIVE and having user plane resources established in the AMF on the access the REGISTRATION ACCEPT message is sent over. If the AMF indicates that a PDU session is now in 5GSM state PDU SESSION INACTIVE in the AMF, and the MA PDU session is associated with an on-demand S-NSSAI and there is no other PDU session associated with the on-demand S-NSSAI, the AMF shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI over the current access type over which the REGISTRATION ACCEPT message message is sent. If the PDU session status IE is included in the REGISTRATION ACCEPT message: a) for single access PDU sessions, the UE shall perform a local release of all those PDU sessions associated with the access type the REGISTRATION ACCEPT message is sent over which are not in 5GSM state PDU SESSION INACTIVE or PDU SESSION ACTIVE PENDING on the UE side, but are indicated by the AMF as being in 5GSM state PDU SESSION INACTIVE. If the PDU session which is indicated by the AMF as being in 5GSM state PDU SESSION INACTIVE is associated with an on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI and the current access type (where or over which the REGISTRATION ACCEPT message is received). If a locally released PDU session is associated with one or more multicast MBS sessions, the UE shall locally leave the associated multicast MBS sessions; and b) for MA PDU sessions, for all those PDU sessions which are not in 5GSM state PDU SESSION INACTIVE and have the corresponding user plane resources being established or established in the UE on the access the REGISTRATION ACCEPT message is sent over, but are indicated by the AMF as no user plane resources are being established or established: 1) for MA PDU sessions having the corresponding user plane resources being established or established only on the access the REGISTRATION ACCEPT message is sent over, the UE shall perform a local release of those MA PDU sessions. If a locally released MA PDU session is associated with one or more multicast MBS sessions, the UE shall locally leave the associated multicast MBS sessions. If the MA PDU session is associated with an on-demand S-NSSAI and there is no other PDU session associated with the on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI over the current access type over which the REGISTRATION ACCEPT message is received. ; and 2) for MA PDU sessions having user plane resources being established or established on both accesses, the UE shall perform a local release on the user plane resources on the access the REGISTRATION ACCEPT message is sent over. If the user plane resources over 3GPP access are released and the MA PDU session is associated with one or more multicast MBS sessions, the UE shall locally leave the associated multicast MBS sessions. The PDU session status information element may be included in the SERVICE REQUEST message to indicate: the single access PDU session(s) not in 5GSM state PDU SESSION INACTIVE in the UE associated with the access type the SERVICE REQUEST message is sent over. For any PDU session that was previously in 5GSM state PDU SESSION ACTIVE in the UE but is now indicated by the UE as being in 5GSM state PDU SESSION INACTIVE, if the UE supports network slice usage control and a PDU session which is indicated as inactive is associated with an on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI and over the current access type (where the Service Request message is sent); and the MA PDU session(s) not in 5GSM state PDU SESSION INACTIVE and having the corresponding user plane resources being established or established in the UE on the access the SERVICE REQUEST message is sent over. The UE may include the PDU session status IE in the CONTROL PLANE SERVICE REQUEST message to indicate which PDU session(s) associated with the access type the CONTROL PLANE SERVICE REQUEST message is sent over are active in the UE. For any PDU session that was previously in 5GSM state PDU SESSION ACTIVE in the UE but is now indicated by the UE as being in 5GSM state PDU SESSION INACTIVE, if the UE supports network slice usage control and a PDU session which is indicated as inactive is associated with an on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI and over the current access type (over which the Control Plane Service Request is sent). If the PDU session status information element is included in the SERVICE REQUEST message, then: a) for single access PDU sessions, the AMF shall: 1) perform a local release of all those PDU sessions which are not in 5GSM state PDU SESSION INACTIVE on the AMF side associated with the access type the SERVICE REQUEST message is sent over, but are indicated by the UE as being in 5GSM state PDU SESSION INACTIVE. If the PDU session which is indicated by the UE as being in 5GSM state PDU SESSION INACTIVE is associated with an on-demand S-NSSAI, the AMF shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI and the current access type; and 2) request the SMF to perform a local release of all those PDU sessions. If any of those PDU sessions is associated with one or more multicast MBS sessions, the SMF shall consider the UE as removed from the associated multicast MBS sessions; and b) for MA PDU sessions, the AMF shall: 1) for MA PDU sessions having user plane resources established in the AMF only on the access the SERVICE REQUEST message is sent over, but are indicated by the UE as no user plane resources established: i) for all those MA PDU sessions without a PDN connection established as a userplane resource, perform a local release of all those MA PDU sessions and request the SMF to perform a local release of all those MA PDU sessions. If the MA PDU session is associated with one or more multicast MBS sessions, the SMF shall consider the UE as removed from the associated multicast MBS sessions. If the PDU session which is indicated as inactive is the UE MA PDU session, is associated with an on-demand S-NSSAI and there is no other PDU session associated with this on-demand S-NSSAI, the AMF shall start the slice deregistration inactivity timer, if not running for this on-demand S-NSSAI over access where service request is received, If the AMF needs to initiate PDU session status synchronization or a PDU session status IE was included in the SERVICE REQUEST message, the AMF shall include a PDU session status IE in the SERVICE ACCEPT message to indicate: which single access PDU sessions associated with the access type the SERVICE ACCEPT message is sent over are not in 5GSM state PDU SESSION INACTIVE in the AMF. If the AMF indicates that a PDU session is now in 5GSM state PDU SESSION INACTIVE in the AMF, and the PDU session is associated with an on-demand S-NSSAI, the AMF shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI and the current access type over which the message is sent; and which MA PDU sessions are not in 5GSM state PDU SESSION INACTIVE and having user plane resources established in the AMF on the access the SERVICE ACCEPT message is sent over. If the PDU session status information element is included in the SERVICE ACCEPT message, then: a) for single access PDU sessions, the UE shall perform a local release of all those PDU sessions which are not in 5GSM state PDU SESSION INACTIVE or PDU SESSION ACTIVE PENDING on the UE side associated with the access type the SERVICE ACCEPT message is sent over, but are indicated by the AMF as in 5GSM state PDU SESSION INACTIVE. If the PDU session which is indicated by the AMF as being in 5GSM state PDU SESSION INACTIVE is associated with an on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI and the current access type. If a locally released PDU session is associated with one or more multicast MBS sessions, the UE shall locally leave the associated multicast MBS sessions; and b) for MA PDU sessions, for all those PDU sessions which are not in 5GSM state PDU SESSION INACTIVE or PDU SESSION ACTIVE PENDING and have user plane resources established on the UE side associated with the access the SERVICE ACCEPT message is sent over, but are indicated by the AMF as no user plane resources established: 1) for MA PDU sessions having user plane resources established only on the access type the SERVICE ACCEPT message is sent over, the UE shall perform a local release of those MA PDU sessions. If a locally released MA PDU session is associated with one or more multicast MBS sessions, the UE shall locally leave the associated multicast MBS sessions. If the MA PDU session is associated with an on-demand S-NSSAI and there is no other PDU session associated with the on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI over the current access type over which the SERVICE ACCEPT message is received; and 2) for MA PDU sessions having user plane resources established on both accesses, the UE shall perform a local release on the user plane resources on the access type the SERVICE ACCEPT message is sent over. If the user plane resources over 3GPP access are released and the MA PDU session is associated with one or more multicast MBS sessions, the UE shall locally leave the associated multicast MBS sessions. If the PDU session status information element is included in the CONTROL PLANE SERVICE REQUEST message, then the AMF: a) shall perform a local release of all those PDU sessions which are not in 5GSM state PDU SESSION INACTIVE on the AMF side associated with the access type the CONTROL PLANE SERVICE REQUEST message is sent over, but are indicated by the UE as being inactive. If the PDU session which is indicated by the UE as being in 5GSM state PDU SESSION INACTIVE is associated with an on-demand S-NSSAI, the AMF shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI and the current access type (over which the Control Plane Service Request message is received), and b) request the SMF to perform a local release of all those PDU sessions. If any of those PDU sessions is associated with one or more multicast MBS sessions, the SMF shall consider the UE as removed from the associated multicast MBS sessions. If the PDU session status information element is included in the SERVICE ACCEPT message, then the UE shall perform a local release of all those PDU sessions which are not in 5GSM state PDU SESSION INACTIVE or PDU SESSION ACTIVE PENDING on the UE side associated with the 3GPP access but are indicated by the AMF as being inactive. If a locally released PDU session: a) is associated with one or more multicast MBS sessions, the UE shall locally leave the associated multicast MBS sessions; b) has the same PDU session identity value as that used by the UE in the CONTROL PLANE SERVICE REQUEST message, and the message contained CloT user data, then the UE determines that the CloT user data was not successfully sent; or c) is a single access PDU session and the PDU session is associated with an on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer, if not running, corresponding to this on-demand S-NSSAI and the current access type (over which the Service Accept message is received).” 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 managing a slice deregistration inactivity timer in a telecommunication system, wherein if:a) a User Equipment, UE, releases a Protocol Data Unit, PDU, session locally, and if there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI, then the UE starts the slice deregistration inactivity timer; orb) an Access and Mobility Management Function, AMF, releases a PDU session locally, and if there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI, then the AMF starts the slice deregistration inactivity timer; orc) the UE receives a PDU session status Information Element, IE, including a PDU session ID, which is in an inactive state, in registration accept or service accept, the UE starts the slice deregistration inactivity timer if the PDU session is associated with on-demand slice, S-NSSAI, and there is no established PDU session, including any MultiAccess, MA, PDU session, associated with the slice, S-NSSAI; ord) the AMF receives a PDU session status IE including a PDU session ID, which is in an inactive state, in registration request or service request, the AMF starts the slice deregistration inactivity timer if the PDU session is associated with on-demand slice, S-NSSAI, and there is no established PDU session, including any Multi-Access, MA, PDU session, associated with the slice, S-NSSAI.

2. The method of claim 1 wherein in c) or d), the PDU session associated with the PDU session ID was previously in an active state.

3. The method of claim 1 or 2 wherein in c) or d) wherein the PDU session ID is associated with on-demand slice, S-NSSAI, for which the UE received a PDU session inactive notification.

4. Apparatus comprising one or more of a UE or a telecommunication system arranged to perform the method of any preceding claim.

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