Improvements in and relating to slice management in a telecommunication network

Abstract

If a current slice in a telecommunication network is to be replaced S101 by a replacement slice, then the network verifies S102 if the current slice is undergoing or scheduled to undergo an authentica

Description

The present invention relates to management of slices in a telecommunication network. It relates, in particular, to methods for replacing slices in certain circumstances. Embodiments of the invention find particular utility in Fifth Generation (5G) networks. The 5G System, 5GS, supports network slice replacement and network slice instance replacement as described in 5.15.19 and 5.15.20, respectively, of 3GPP TS 23.501 V18.2.1, both of which are described in the following from 3GPP TS 23.501 V18.2.1. 5.15.19 Support of Network Slice Replacement The Network Slice Replacement feature is used to replace a slice (identified by S-NSSAI) with an Alternative slice (S-NSSAI) when an S-NSSAI becomes unavailable or congested. The Network Slice Replacement may be triggered in the following cases: If the Network Slice Selection Function (NSSF) detects that an S-NSSAI becomes unavailable or congested (e.g. based on 0AM or NWDAF analytics output), it sends network slice availability notification for the S-NSSAI to the AMF. The notification may include an Alternative S-NSSAI which can be used by the Access and Mobility Management Function (AMF) to replace the S-NSSAI. The NSSF notifies the AMF when the S-NSSAI is available again. If the Policy Control Function (PCF) detects that an S-NSSAI becomes unavailable or congested for a UE (e.g. based on OAM or NWDAF analytics output), it sends access and mobility related policy notification to the AMF. The notification may include an Alternative S-NSSAI which can be used by the AMF to replace the S-NSSAI. The PCF notifies the AMF when the S-NSSAI is available again for the UE. The OAM sends notification to AMF when an S-NSSAI becomes unavailable or congested (and also when this S-NSSAI becomes available again) and provides the Alternative S-NSSAI to AMF. Based on the notification above from NSSF or PCF or OAM, the AMF may determine that an S-NSSAI is to be replaced with Alternative S-NSSAI. For roaming case, the AMF may receive network slice availability notification of the HPLMN S-NSSAI from NSSF in the HPLMN via NSSF in VPLMN, to trigger the Network Slice Replacement of the HPLMN S-NSSAI as described in clause 5.15.6. NOTE 1: It is recommended that, the operator configures to use only one mechanism when triggering the Network Slice Replacement for S-NSSAI. The AMF determines the Alternative S-NSSAI for a UE registered with the S-NSSAI based on the notification from NSSF or PCF, or based on local configuration if the NSSF or PCF do not provide an alternative S-NSSAI. The Alternative S-NSSAI shall be supported in the UE Registration Area. If AMF cannot determine the Alternative S-NSSAI for the S-NSSAI, e.g. PCF or NSSF doesn't provide Alternative S-NSSAI, the AMF may further interact with the PCF to determine the Alternative S-NSSAI. The event trigger in AMF for interacting with PCF is described in clause 6.1.2.5 of TS 23.503

[45] . The UE indicates the support of Network Slice Replacement feature during the UE Registration procedure. For supporting UE in CM-CONNECTED state and if there is a Protocol Data Unit (PDU) Sessions in the UE context associated with the S-NSSAI that needs to be replaced, the AMF provides the Alternative S-NSSAI for this S-NSSAI in the Allowed NSSAI and in the Configured NSSAI, if not included yet, and the mapping between S-NSSAI(s) to Alternative S-NSSAI(s) to the UE in UE Configuration Update message as follows: for non-roaming UEs, the AMF provides the mapping of the S-NSSAI to the Alternative S-NSSAI to the UE. for roaming UEs when the VPLMN S-NSSAI has to be replaced by a VPLMN Alternative S-NSSAI, the AMF provides the mapping of the VPLMN S-NSSAI to the Alternative VPLMN S-NSSAI to the UE. for roaming UEs when the HPLMN S-NSSAI has to be replaced by an Alternative HPLMN S-NSSAI, the AMF provides the mapping of the HPLMN S-NSSAI to the Alternative HPLMN S-NSSAI to the UE. NOTE 2: The Alternative S-NSSAI or Alternative HPLMN S-NSSAI does not have to be part of the Subscribed S-NSSAI as long as they can be mapped to a HPLMN S-NSSAI that is part of the Subscribed S-NSSA / s. For the supporting UE in CM-IDLE state, when the UE establishes a NAS signalling connection, e.g. through a Service Request procedure or through a UE registration procedure, if the AMF determines that the S-NSSAI is to be replaced and there is a PDU Session associated with the S-NSSAI in the UE context, the AMF sends the mapping of the S-NSSAI to the Alternative S-NSSAI to the UE in the UE Configuration Update message or in the Registration Accept message. NOTE 3: It is left to AMF local policy whether to send the mapping of the S-NSSAI to the Alternative S-NSSAI to the UE when there is no PDU session associated with the S-NSSAI or wait and send the mapping of the S-NSSAI to the Alternative S-NSSAI to the UE when the UE establishes a PDU Session associated with the S-NSSAI. During a new PDU Session establishment procedure towards an S-NSSAI, if the UE is provided with the mapping of the S-NSSAI to an Alternative S-NSSAI, the UE provides both the Alternative S-NSSAI and the S-NSSAI in the PDU Session Establishment message. When the AMF receives the Alternative S-NSSAI and the S-NSSAI in the PDU Session Establishment message, or when the AMF receives only the S-NSSAI in PDU Session Establishment message the AMF determines that the S-NSSAI is to be replaced with the Alternative S-NSSAI, the AMF includes both the Alternative S-NSSAI and the S-NSSAI to the Session Management Function (SMF). if the UE is not provided with the mapping of the S-NSSAI to the Alternative S-NSSAI, the UE provides the S-NSSAI in the PDU Session Establishment message. When the AMF determines that the requested S-NSSAI is to be replaced with the Alternative S-NSSAI and if the UE supports Network Slice Replacement, the AMF performs UE Configuration Update procedure to reconfigure the UE with the Alternative S-NSSAI. The AMF continues the PDU Session establishment procedure with the Alternative S-NSSAI and provides both the Alternative S-NSSAI and the S-NSSAI to the SMF. The SMF proceeds with the PDU Session establishment using the Alternative S-NSSAI. The SMF sends the Alternative S-NSSAI to NG-RAN in N2 SM information and to UE in PDU Session Establishment Accept message. For existing PDU Session associated with an S-NSSAI that is replaced with the Alternative S-NSSAI, after the AMF sends mapping of the S-NSSAI to the Alternative S-NSSAI to the supporting UE in UE Configuration Update message, the AMF sends updates to the SMF of the PDU Session, e.g. triggering Nsmf_PDUSession_UpdateSMContext service operation, that the PDU Session is to be transferred to Alternative S-NSSAI and includes the Alternative S-NSSAI as follows (see details in clause 4.3.3 of TS 23.502 [3]): If the SMF determines that the PDU Session needs to be retained (e.g. if the anchor UPF can be reused with the alternative S-NSSAI and SSC mode 1), the SMF sends the Alternative S-NSSAI to the UPF in the N4 message, to the NG-RAN in N2 message and to the supporting UE in PDU Session Modification Command message. If the SMF determines that the PDU Session needs to be re-established, the SMF sends the Alternative S-NSSAI to the supporting UE either in PDU Session Modification Command if the PDU Session is of SSC mode 3, or in PDU Session Release if the PDU Session is of SSC mode 2 or SSC mode 1, to trigger the re-establishment of the PDU Session. The UE includes both, the S-NSSAI and the Alternative S-NSSAI in the PDU Session Establishment message. When the AMF is notified that the S-NSSAI is available again or the congestion of the S-NSSAI has been mitigated, if the AMF has configured the supporting UE with the Alternative S-NSSAI, and the AMF determines for the UE to use the S-NSSAI again, the AMF reconfigures the supporting UE (e.g. by using UE Configuration Update message) to use the S-NSSAI. If there is an existing PDU Session associated with the Alternative S-NSSAI, the AMF sends updates to the SMF of the PDU Session, e.g. triggering Nsmf_PDUSession_UpdateSMContext service operation, that the PDU Session is to be transferred to the S-NSSAI. During a handover procedure, if an S-NSSAI has to be replaced with an Alternative S-NSSAI, the handover procedure (including any PDU session associated with the S-NSSAI to be replaced) shall continue unaffected by the Network Slice Replacement. Any Network Slice Replacement for the S-NSSAI shall not take place during the handover. 5.15.20 Support of Network Slice Replacement The Network Slice Instance Replacement is used when a PDU Session for a given S-NSSAI is established using a selected Network Slice instance and the S-NSSAI corresponding to this Network Slice instance is associated with multiple Network Slice instances. In this case, the network may change the Network Slice instance for the S-NSSAI if the selected Network Slice instance is no longer available (e.g. due to overload). The AMF may subscribe with the NSSF for notifications when any of the Network Slice instances served by the AMF is congested or no longer available. In case of roaming, the NSSF of VPLMN subscribes with the NSSF of the HPLMN for notifications. When the NSSF notifies the AMF that a Network Slice instance is congested or no longer available, for some of PDU Sessions associated with the Network Slice instance that is no longer available, the AMF may delete old NSI ID corresponding to the Network Slice instance that is no longer available and the SMF of the PDU Session(s) selected by using such old NSI ID is informed by the AMF to release the PDU Session(s). Subsequently, the SMF triggers the impacted UE(s) to establish new PDU session(s) associated with the same S-NSSAI as described in clause 5.6.9.2 for PDU Session(s) of SSC Mode 2 and SSC Mode 3. The AMF selects a new Network Slice instance for the given S-NSSAI during PDU Session Establishment. From the above, it can be seen that one of the main reasons that a slice may be replaced is either when the slice is unavailable, or it is congested. However, it is not clear if the congestion is based on control plane congestion or user plane congestion. The 5GS supports the transport of data over the control plane for a UE which is using control plane Cellular Internet o Things (CloT) 5GS optimization as described in 3GPP TS 23.501 V18.2.1 and in 3GPP TS 24.501 V18.3.0. Data over Non-Access Stratum (NAS) - or data over the control plane (CP) - is sent by a UE using the Control Plane Service Request (CPSR) message (when the UE is in 5GMM-IDLE mode) or the UL NAS TRANSPORT message (when the UE is in 5GMM-CONNECTED mode). In some cases, a PDU session is deemed to be established as control plane only i.e. the session can never be switched to user plane, or the session will never admit user plane resources. Such a PDU session is identified by the inclusion of the Control plane only indication in the PDU Session Establishment Accept message which is sent by the SMF to the UE. The 5GS supports Network Slice-Specific Authentication &Authorization (NSSAA) as described in section 5.15.10 of 3GPP TS 23.501 V18.2.1. This occurs with a participation of the UE, the AMF and an external Authentication, authorization and accounting (AAA) server. After a slice is authenticated and authorized, the AAA server may perform re-authentication for the slice or S-NSSAI in question. Therefore, it should be noted that an S-NSSAI may be subject to another NSSAA procedure even after the slice has already succeeded an NSSAA procedure. A first problem with the prior art is a lack of other solutions when a slice is congested at the user plane level. It is most likely the case that the congestion is at the user plane level as otherwise control plane congestion would mean that an SMF is congested and this aspect is not listed in the description from 3GPP TS 23.501 V18.2.1. Even if it is not always the case, it is safe to assume that congestion can occur at the user plane level and hence the need for slice replacement arises. The prior art solution to congestion is to replace a slice or a slice instance. However, this is not the only solution, especially if the congestion is at the user plane level. Alternative solutions can be devised for this problem and seeking an alternative is one aim of an embodiment of the invention. A second problem is the handling of ongoing NSSAA procedure and slice replacement procedure. As stated in 3GPP TS 23.501 V18.2.1 : “During a handover procedure, if an S-NSSAI has to be replaced with an Alternative S-NSSAI, the handover procedure (including any PDU session associated with the S-NSSAI to be replaced) shall continue unaffected by the Network Slice Replacement. Any Network Slice Replacement for the S-NSSAI shall not take place during the handover.” However, it is also possible that the slice replacement may be triggered when there is an ongoing NSSAA procedure. It is not clear how the network should behave in this regard i.e. whether to perform the procedures together or put one of them on hold. It is an aim of an embodiment of the present invention to address the problems identified herein, as well as other problems not mentioned. 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 performing slice management in a telecommunication network, wherein if a current slice is to be replaced by a replacement slice via a replacement procedure, the telecommunication network verifies if the current slice is undergoing or scheduled to undergo an authentication procedure, and if so, the replacement procedure is halted and the authentication procedure is progressed. In an embodiment, if the current slice is successfully authenticated, then the replacement procedure proceeds to replace the current slice with the replacement slice. In an embodiment, if the current slice is not successfully authenticated, then the current slice is not replaced. In an embodiment, a session associated with the current slice is dropped. In an embodiment, an Access and Mobility Management Function, AMF, performs the slice replacement. In an embodiment, the current slice requires replacement due to congestion on one or more of a User Plane, UP, or a Control Plane, CP. In an embodiment, if the current slice comprises a plurality of Protocol Data Unit, PDU, sessions as Control Plane only sessions and this number reaches a predefined maximum number, then this triggers the slice replacement procedure. According to a second aspect of the present invention, there is provided apparatus arranged to perform the method of any preceding aspect. In an embodiment, when a slice is congested, optionally at the user plane level, or when the maximum number of PDU sessions has been reached, the network may permit a PDU session to be established as control plane only. During an NSSAA procedure, any network slice replace for an S-NSSAI should be put on hold until NSSAA is completed. 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 first embodiment of the invention. According to a first embodiment of the present invention, the network accepts PDU sessions as control plane only when congestion occurs. The network may determine that a slice is congested, optionally due to user plane congestion, but may also be due congestion at the control plane. Hereafter, the term congested may refer to user plane congestion only, or control plane congestion only, or user plane congestion and control plane congestion, or other forms of congestion. The determination may be based on a trigger for network slice replace as has been described in 3GPP TS 23.501 V18.2.1, where the AMF may be notified of a slice being unavailable or congested by the NSSF, or the PCF, based on OAM. The determination may also be because of an alternative S-NSSAI be provided to the AMF or by the AMF determining to use an alternative S-NSSAI using any mechanism. When any of the above occurs, using any methods e.g. the AMF determines that a slice is unavailable or is congested, where optionally the congestion is on the user plane level, the AMF may then decide to permit the establishment of new PDU sessions such that these PDU sessions are to be established as control plane only sessions or as control plane sessions (i.e. not necessarily being control plane only sessions). As such, when the AMF receives a new request for a PDU session e.g. the AMF receives an UL NAS TRANSPORT message which carries a 5GSM message and optionally the request type indicates that it is an initial request, i.e. the request is for a new PDU session, even though the associated slice is experiencing congestion (optionally at the user plane level), the AMF should accept the request and forward the 5GSM message to the SMF which is associated with the S-NSSAI in question (whether the S-NSSAI is selected by the AMF or the UE). However, the AMF should indicate to the SMF that the PDU session should be established as control plane only i.e. the AMF includes the Control Plane Only Indicator to the SMF. Similarly, the SMF should accept the PDU session as control plane only and indicate to the UE (in the PDU Session Establishment Accept message) that the session is established for control plane only. In another alternative, the AMF should accept the request and forward the 5GSM message to the SMF but indicates that the session should be established as a session for control plane CloT optimization i.e. as a session which uses control plane to send the data however not as a control plane only session. Moreover, whilst the congestion is ongoing or the AMF determines that the S-NSSAI in question is congested, any subsequent request to establish the user plane resources for this session should be rejected by the network (e.g. the AMF). The AMF may use any 5GMM cause value to indicate the reason for rejection. For example, the AMF may use 5GMM cause value #92 "insufficient user-plane resources for the PDU session". Note that the network (e.g. AMF or SMF) may be configured to accept a certain number of PDU sessions as control plane only sessions i.e. the proposal above may be for a certain well known number of PDU sessions that can be established as control plane only (or as control plane). When this maximum is reached, the network may then revert to apply slice replacement mechanism. When the AMF determines that the congestion is alleviated, or the slice is available, the network (e.g. AMF and / or SMF) may then accept a new request for PDU sessions as normal requests i.e. as requests with user plane accordingly. Note that the technique set out here can also apply for the case when the network determines to apply a maximum number of established PDU sessions for a slice in question. As such, the network (AMF or SMF or Network Slice Admission Control Function (NSACF)) may be configured to exempt a PDU session that is based on control plane (but not control plane only), or to exempt a PDU session that is to be used for control plane only, from network slice admission control optionally where the admission control may be based on any criterion such as a maximum quota on the number of PDU sessions that can be established. As such, when the quota is reached, the network may be configured to allow new PDU sessions as PDU sessions that can be used for control plane data transfer (but not as control plane only), or as PDU sessions for control plane only (with a session which is associated with the control plane only indicator). The details above can be applied for any UE or for UEs which indicate the support of control plane CloT 5GS optimization (e.g. in the 5GMM capability IE) and / or for networks which indicate the support of (and / or allowance for a UE to use) control plane CloT 5GS optimization (e.g. in the 5GS network feature support IE). The details set out above can be applied by an AMF, SMF or NSACF or any network function or any combination of network functions. A second embodiment relates to AMF behaviour for slice replacement during an NSSAA procedure. The AMF should not perform slice replacement during an ongoing NSSAA procedure optionally for the S-NSSAI that has to be replaced and for which NSSAA is ongoing. As such, if there is an ongoing NSSAA procedure for an S-NSSAI and the AMF needs to trigger or perform slice replacement for the same S-NSSAI, then the AMF should wait until the NSSAA procedure is completed before performing the slice replacement. As such, during an ongoing NSSAA procedure for an S-NSSAI, if the S-NSSAI (for which NSSAA is ongoing) has to be replaced with an Alternative S-NSSAI, the NSSAA procedure (including any PDU session associated with the S-NSSAI to be replaced) shall continue unaffected by the Network Slice Replacement. Any Network Slice Replacement for the S-NSSAI shall not take place during the NSSAA procedure. In one alternative, if the UE is aware of an ongoing NSSAA for an S-NSSAI, and the UE receives an alternative S-NSSAI that is mapped to the S-NSSAI for which NSSAA is ongoing, the UE should not initiate the establishment of a new PDU session for the alternative S-NSSAI until the ongoing NSSAA is completed (optionally where the S-NSSAI that the alternative S-NSSAI is associated with is an S-NSSAI for which NSSAA is ongoing), or optionally until the NSSAA is completed and is successful. For example, the NSSAA may be deemed to be successful if the related S-NSSAI is not removed from the allowed NSSAI or is it not in the rejected NSSAI. As such, the establishment of a new PDU session for an alternative S-NSSAI should not be performed (e.g. by a UE) if there is an associated S-NSSAI for which NSSAA is ongoing. Therefore, the UE should verify a new condition when determining to establish a new PDU session for an alternative S-NSSAI. The condition is to verify if there is an associated S-NSSAI (i.e. an S-NSSAI which is associated with the alternative S-NSSAI) for which NSSAA is ongoing. If yes, then the UE should not establish a new PDU session for the alternative S-NSSAI (optionally until the NSSAA completes or completes successfully). If not, then the UE can establish a new PDU session for the alternative S-NSSAI. In one alternative, the NSSAA may be continued along with the slice replacement procedure with an alternative S-NSSAI. Once the NSSAA is completed, if it is successful, then the network provides the alternative S-NSSAI in the allowed NSSAI (if not already provided) or provides it to the UE in the allowed NSSAI. If the NSSAA fails for the existing S-NSSAI, the network may perform NSSAA for the alternative S-NSSAI. Or the network may remove the alternative S-NSSAI from the allowed NSSAI if the alternative S-NSSAI has already been provided to the UE in the allowed NSSAI. The existing S-NSSAI may also be removed from the allowed NSSAI if the NSSAA procedure fails for this S-NSSAI. For completeness, Figure 1 illustrates an embodiment of the invention. It illustrates a method of performing slice management in a telecommunication network. At S101, it is determined if a current slice is to be replaced by a replacement slice via a replacement procedure. At S102, the telecommunication network verifies if the current slice is undergoing an authentication procedure, and if so, at S103 the replacement procedure is halted. 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 performing slice management in a telecommunication network, wherein if a current slice is to be replaced by a replacement slice via a replacement procedure, the telecommunication network verifies if the current slice is undergoing or scheduled to undergo an authentication procedure, and if so, the replacement procedure is halted and the authentication procedure is progressed.

2. The method of claim 1 wherein if the current slice is successfully authenticated, then the replacement procedure proceeds to replace the current slice with the replacement slice.

3. The method of claim 1 wherein if the current slice is not successfully authenticated, then the current slice is not replaced.

4. The method of claim 3 wherein a session associated with the current slice is dropped.

5. The method of claim 2 wherein an Access and Mobility Management Function, AMF,performs the slice replacement.

6. The method of any preceding claim wherein the current slice requires replacement due to congestion on one or more of a User Plane, UP, or a Control Plane, CP.

7. The method of any preceding claim wherein if the current slice comprises a plurality of Protocol Data Unit, PDU, sessions as Control Plane only sessions and this number reaches a predefined maximum number, then this triggers the slice replacement procedure.

8. Apparatus arranged to perform the method of any preceding claim.14

Images