Patent ID: 12225415

DESCRIPTION OF EMBODIMENTS

Prior to explaining aspects according to this present disclosure, the following explanatory notes will be given.

Abbreviations

For the purposes of the present disclosure, the following abbreviations apply.3GPP 3rd Generation Partnership Project5G 5th Generation5GC 5G Core Network5GS 5G System5G-AN 5G Access NetworkAMF Access and Mobility Management FunctionAS Application ServerCAG Closed Access GroupCDR Charging Data RecordCHF Charging FunctiongNB Next Generation NodeBGSMA Global System for Mobile Communications AssociationNAS Non-Access StratumNG-RAN Next Generation Radio Access NetworkNR New RadioNSSAA Network Slice Specific Authentication and AuthorisationNSSAI Network Slice Selection Assistance InformationNSSP Network Slice Selection PolicyPCF Policy Control FunctionPDU Protocol Data UnitPLMN Public Land Mobile NetworkRACH Random Access ChannelRAN Radio Access NetworkRAT Radio Access TechnologyRRC Radio Resource ControlS-AMF Source AMFS-NSSAI Single Network Slice Selection Assistance InformationS-RAN Source RANSMF Session Management FunctionTA Tracking AreaT-AMF Target AMFT-RAN Target RANUDM Unified Data ManagementUDR Unified Data RepositoryUE User EquipmentURLLC Ultra Reliable and Low Latency CommunicationsURSP UE Route Selection Policy

Definitions

For the purposes of the present disclosure, the terms and definitions given in 3GPP Technical Report (TR) 21.905: “Vocabulary for 3GPP Specifications” V17.0.0 (2020-07) (hereinafter referred to 3GPP TR 21.905) and the following apply. A term defined in the present document takes precedence over the definition of the same term, if any, in 3GPP TR 21.905.

RELATED ARTS

The Network Slicing features defined in 3GPP release 15 and release 16 enable a great variety of communication services for the operators and the verticals alike. To enhance the commercial viability of the Network Slicing, GSMA 5GJA has introduced in GSM Association Official Document NG. 116-Generic Network Slice Template, v2.0, from which several Network Slice Types descriptions can be derived. Some of the parameters in the Generic Slice Template (GST) point explicitly to the definition of parameters and bounds on the service delivered to the end customer. However, the enforcement of some of these bounds and parameters are not supported by the 5GS yet.

The SA2 Study on Enhancement of Network Slicing Phase 2 aims at identifying the gaps that need to be filled in providing the support for the GST parameters enforcement and the suitable solutions to address these gaps.

RAN follows the progress of SA2 study on enhanced Network Slicing and RAN has agreed their own study item on RAN slicing enhancement. The aim is to investigate enhancements on RAN support of the network slicing with the following objectives:

1. Study mechanisms to enable UE fast access to the cell supporting the intended slice, includinga. Slice based cell reselection under network controlb. Slice based RACH configuration or access barring

Note: whether the existing mechanism can meet this scenario or requirement can be studied.

2. Study necessity and mechanisms to support service continuity, including a. For intra-RAT handover service interruption, e.g., target gNB doesn't support the UE's ongoing slice, study slice re-mapping, fall-back, and data forwarding procedures. Coordination with SA2 is needed.

FIG.1illustrates a use case where active PDU Session(s) of the UE may be released at a handover if a target cell does not support the network slice with the active PDU Session(s) on the network slice in the UE. The following use case is considered:The UE is registered on the S-NSSAI-1, S-NSSAI-2, S-NSSAI-3 and S-NSSAI-4 and the UE is in connected mode, i.e., with active PDU Session(s) on the S-NSSAI-3.The S-NSSAI-3 is not homogeneously supported in the whole PLMN (as per the current agreements in the 3GPP specifications).The UE is moving towards the edges of the current registration area into the coverage of the Cell-1 supporting the S-NSSAI-1 and of the Cell-2 supporting the S-NSSAI-4.Both cells, the Cell-1 and the Cell-2, are eligible for a target cell in a handover.

Problem: Based on the related art, the PDU Session(s) on the S-NSSAI-3 will be released at a handover to one of the target cells Cell-1 or Cell-2 as they do not support the network slice S-NSSAI-3 on which the UE has the active PDU Session(s), as shown inFIG.1. One of the problems for this disclosure is how to steer the UE in connected mode (e.g., handover) to a target cell in order to support the service continuity when the network slice with active PDU Session(s) on the network slice (e.g., S-NSSAI-3) is not supported by the target cells.

DESCRIPTION OF ASPECTS

This disclosure describes multiple aspects and variants for each instance. These aspects and variants can be arbitrarily combined with each other.

The present disclosure relates to a communication system. The disclosure has particular but not exclusive relevance to wireless communication systems and devices thereof operating according to the 3rd Generation Partnership Project (3GPP) standards or equivalents or derivatives thereof. The disclosure has particular although not exclusive relevance to network slices and handover in the so-called ‘5G’ (or ‘Next Generation’) systems.

From another point of view, this disclosure proposes alternative network slices provision by a UE or a network for service continuity assistance in a handover. It proposes methods for a PDU Session transfer to an alternative network slice at a handover when a current network slice with an active PDU Session on the current network slice is not supported by a target cell. This allows for an improved service continuity when the network slice with an active PDU Session is not supported or not allowed in the target cell.

First Example Aspect

A first example aspect of the disclosure is explained below referring to the accompanying drawings. The following detailed description is merely exemplary in nature and is not intended to limit this disclosure or the application and uses of this disclosure. Furthermore, there is no intention to be bound by any theory presented in the preceding background of this disclosure or the following detailed description.

(Solution 1—UE Assistance with Alternative Network Slice for PDU Session Continuity)

Solution 1 proposes PDU Session(s) transfer to an alternative network slice at a handover when the current network slice with active PDU Session(s) on the current network slice is not supported by the target cells. This allows for improved service continuity by transferring the active PDU Session(s) on the current network slice to an alternative network slice thus maintaining the service continuity, instead releasing the PDU Session(s). In this solution, the alternative network slices, for the PDU Session that is being established, are provided by the UE as a new parameter in the PDU Session Establishment Request message or Service Request message and then the AMF further provides these alternative network slices to the RAN node to assist a potential Xn and N2 handover.

FIG.2is a schematic timing (signalling) diagram illustrating an exemplary method for UE assistance with alternative network slice(s) for PDU Session(s) continuity in the Xn handover.

1) PDU Session Establishment Request/Service Request (S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2)—An Application in the UE101requires a service. The UE101checks with the NSSP (Network Slice Selection Policy) within the URSP (UE Route Selection Policy) rules in the UE Policy and finds out the network slice(s) on which the Application can receive a service, e.g., the S-NSSAI-3, S-NSSAI-1 and S-NSSAI-2. The UE101is registered to all these network slices. Based on the request from the Application, the UE101sends, to the AMF104, a PDU Session Establishment Request message or a Service Request message on the network slice S-NSSAI-3, for example. Along with the network slice S-NSSAI-3 inclusion in the PDU Session Establishment Request message or in the Service Request message (on which the PDU Session is to be established or reactivated), the UE101also includes in the PDU Session Establishment Request message or in the Service Request message a new parameter ‘alternative S-NSSAI’ in which the UE101places the network slice(s), other than the S-NSSAI-3, that are also compatible with the service requiring Application in the UE101, e.g. S-NSSAI-1 and S-NSSAI-2, if any.

The new parameter may be structured with priority order or preference order among alternative S-NSSAI(s). For example, if the “alternative S-NSSAI” parameter is set as the alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2, this means that the UE101wishes to use the S-NSSAI-1 as an alternative S-NSSAI for the S-NSSAI-3 rather than the S-NSSAI-2. This new parameter may be called ‘alternative S-NSSAI’, ‘alternative network slice’, ‘backup network slice’, ‘backup S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) that the service requiring Application in the UE101can work with based on the NSSP/URSP rules in the UE101. The ‘alternative network slice’ can also be the default allowed S-NSSAI in the UE101, if available. The ‘alternative network slice(s)’ can also be delivered by the UE101to the network via any other NAS message.

In one example, the AMF104may obtain alternative S-NSSAI(s) per S-NSSAI in the subscribed NSSAI during the Registration Procedure or during the Subscriber Data Update Notification to AMF procedure as described in 3GPP Technical Specification (TS) 3GPP TS 23.502: “Procedures for the 5G System (5GS)” V16.5.0 (2020-07) (hereinafter referred to 3GPP TS 23.502). In this case, the Nudm_SDM_Get service is used during the Registration Procedure and the Nudm_SDM_Notification service is used during the Subscriber Data Update Notification to AMF procedure.

In another example, the SMF104may obtain alternative S-NSSAI(s) per S-NSSAI in the subscribed NSSAI during the Registration Procedure or during the Subscriber Data Update Notification to SMF104procedure as described in 3GPP TS 23.502. In this case, the Nudm_SDM_Get service is used during the Registration Procedure and Nudm_SDM_Notification service is used during the Subscriber Data Update Notification to SMF procedure.

2) PDU Session Establishment on the S-NSSAI-3 as per 3GPP TS 23.502.

3) N2 message (S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2)—At the end of the PDU Session Establishment procedure on the network slice S-NSSAI-3, the AMF104sends, to the Source RAN (S-RAN) node102, the N2 message (or in any other message on the N2 interface between the AMF104and the RAN node), including a parameter for the current network slice on which the PDU Session was established (e.g. S-NSSAI-3), and also including the alternative network slice(s), if any, for example S-NSSAI-1 and S-NSSAI-2 within a new ‘alternative S-NSSAI’ parameter.

The new parameter may be structured with priority order or preference order among the alternative S-NSSAI(s). This new parameter in the N2 message may be called ‘alternative S-NSSAI’, ‘alternative network slice’, ‘backup network slice’, ‘backup S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) that the service requiring Application in the UE101can work with. The alternative network slices S-NSSAI-1 and S-NSSAI-2, which the AMF104includes in the ‘alternative S-NSSAI’ parameter in the N2 message, are the ones which the AMF104has received from the UE101in the PDU Session Establishment Request message or in the Service Request message. The ‘alternative network slice’ can also be the default allowed S-NSSAI in the AMF104or UDM/UDR105, if available. When the AMF104sends the N2 message including alternative S-NSSAI(s) to the S-RAN node102, the AMF104may confirm that the SMF(s)104associated to the PDU session(s) are accessible from any alternative S-NSSAIs.

4) At some stage a handover is required. There is no target cell supporting the S-NSSAI-3 on which the UE101has an active PDU Session. However, there is a target cell supporting an alternative network slice, e.g., alternative S-NSSAI=S-NSSAI-1.

5) Handover to a target cell supporting the alternative network slice S-NSSAI-1. The S-RAN node102selects a target cell that supports one of the alternative network slices, e.g., alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available at any of the target cells, the priority among the alternative network slices should be considered at the S-RAN node102when selecting a target cell. If both alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available at a target cell, the S-RAN node102selects the alternative network slice S-NSSAI-1 taking the priority into account.

6) PDU Session Modification on the alternative network slice S-NSSAI-1 as per 3GPP TS 23.502—The AMF104triggers the PDU Session Modification procedure to replace the current S-NSSAI, i.e., S-NSSAI-3, with the alternative network slice S-NSSAI-1. As the S-NSSAI will be swapped during this procedure, the SMF104may contact the PCF and/or the CHF (Charging Function) to issue separate CDRs, one with the original S-NSSAI-3 and the other one with the alternative network slice S-NSSAI-1.

7) During the PDU Session Modification procedure, when the AMF104sends the N2 message to the T-RAN node103, the N2 message contains the following parameters.

N2 message (S-NSSAI-1, original S-NSSAI=S-NSSAI-3, alternative S-NSSAI=S-NSSAI-2, NAS message (PDU Session ID, N1 SM container (PDU Session Modification command (New S-NSSAI=S-NSSAI-1))))—During the PDU Session Modification procedure for replacing the network slice S-NSSAI-1, the AMF104may send the N2 message to the target RAN (T-RAN) node103. Along with the network slice on which the PDU Session(s) were established, the AMF104also includes in the N2 message (or in any other message on the N2 interface between the AMF104and the RAN node) two new parameters:Original S-NSSAI—The AMF104places in this parameter the initial network slice from which the PDU Session was transferred to one of the alternative network slices in the last handover, e.g., S-NSSAI-3. This new parameter may be called ‘original S-NSSAI’, ‘original network slice’, ‘initial network slice’, ‘initial S-NSSAI’, ‘UE requested S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) on which the PDU Session was established at the PDU Session Establishment procedure as described in 3GPP TS 23.502.Alternative S-NSSAI—The AMF104places in this parameter one of the remaining alternative network slices received with the PDU Session Establishment Request message or Service Request message from the UE101, e.g., S-NSSAI-2. The alternative network slice can also be the default allowed S-NSSAI in the AMF104or UDM/UDR105, if available.

The alternative S-NSSAI may also indicate alternative network slices that will be used for the PDU Session after the successful Handover procedure.

8) During the PDU Session Modification procedure, when the SMF104sends the PDU Session Modification command to the UE101via the AMF104(within the N2 message on the AMF104to the T-RAN node interface) and the T-RAN node103, the PDU Session Modification command includes a New S-NSSAI parameter (e.g., S-NSSAI-1) in order to let the UE101know that the S-NSSAI (e.g. S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g. S-NSSAI-1). The T-RAN node103sends the PDU Session

Modification command, received from the SMF104via the AMF104(within the N2 message on the AMF104to the T-RAN node interface), to the UE101. With this information, the UE101updates the network slice state in the UE101.

In one example, instead of sending the PDU Session Modification message to the UE101, the AMF104may send the UE Configuration Update message to the UE101via the T-RAN node103to let the UE101know that the S-NSSAI (e.g., S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g., S-NSSAI-1).

9) At some stage later again, a handover is required. When selecting a target cell and there are multiple qualifying cells supporting different network slice(s), the T-RAN node103may select the target cell in the following order of preference:The ‘original S-NSSAI’—the T-RAN node103may give preference to the original network slice first (e.g., S-NSSAI-3) in selecting a target cell. This would allow for the PDU Session to be transferred back to the network slice on which the PDU Session has been established at the very beginning as this network slice may be the most suitable network slice for the PDU Session(s), e.g., S-NSSAI-3;The current network slice-if no target cell supports the original network slice (e.g., S-NSSAI-3), then the T-RAN node103may prefer to select a target cell supporting the current network slice on which the PDU Session is currently active, e.g., S-NSSAI-1.The ‘alternative S-NSSAI’-If there is no target cell supporting the original network slice (e.g., S-NSSAI-3) nor the current network slice (e.g., S-NSSAI-1), then the T-RAN node103may prefer a target cell supporting the alternative network slice if available, e.g., S-NSSAI-2.

It should be noted that the (source/target) RAN node may apply an alternative order(s) in selecting the target cell for example, first giving priority to a target cell supporting the current network slice with active PDU Session on it (e.g., S-NSSAI-1) and then the original S-NSSAI (e.g., S-NSSAI-3) if available and last the alternative S-NSSAI (e.g., S-NSSAI-2) if available. The (source/target) RAN node may apply a preference in any other order, e.g., an operator defined or configured order of preference between the original network slice, the current network slice and the alternative network slice.

Although theFIG.2illustrates the Solution about the UE101assistance with alternative network slice for PDU Session continuity during the handover, it should also be noted that the step6, including step7and step8, can be solely used for the following cases in order to swap the S-NSSAI on active PDU session(s) without releasing the PDU sessions(s):Slice congestion detected by the AMF/SMF104or via the NWDAF (Network Data Analytics Function).

When the network slice indicated by an S-NSSAI that is used for active PDU session(s) gets congested, the AMF/SMF104may initiate the step6to swap the S-NSSAI being used for the PDU session(s) to another S-NSSAI by indicating less-congested network slice(s). This operation allows the AMF/SMF104to reduce traffics on congested network slice(s).

An S-NSSAI withdrawal from the subscriber data.

When an S-NSSAI associated to the active PDU session(s) is withdrawn from the subscriber data in the UDM105, this subscriber data update is reported to the AMF104. In this case, the AMF104may initiate the step6, rather than releasing the associated PDU session(s), to swap the S-NSSAI being withdrawn in the subscriber data to another S-NSSAI. This operation allows the AMF/SMF104to provide a better service experience since an active PDU session may survive.

Network Slice Specific authentication and authorization failure.

When the Network Slice Specific (re-)authentication and (re-)authorization to an S-NSSAI associated to the active PDU session(s) fails, the AMF104may initiate the step6, rather than releasing the associated PDU session(s), to swap the S-NSSAI that failed for Network Slice Specific Authentication and Authorization to another S-NSSAI. This operation allows the AMF/SMF104to provide a better service experience since an active PDU session may survive.

Network Slice Specific Authentication and Authorization revocation.

When the Network Slice Specific (re-)authentication and (re-)authorization to an S-NSSAI associated to the active PDU session(s) is revoked, the AMF104may initiate the step6, rather than releasing the associated PDU session(s), to swap the S-NSSAI that has been revoked for Network Slice Specific Authentication and Authorization to another S-NSSAI. This operation allows the AMF/SMF104to provide a better service experience since an active PDU session may survive.

It should also be noted that this alternative can be applied to the other use cases/solutions in the present disclosure.

FIG.3is a schematic timing (signalling) diagram illustrating an exemplary method for UE assistance with alternative network slice(s) for PDU Session continuity in the N2 handover (Use case1). In Use case1the alternative network slice in the target cell is re-confirmed as allowed network slice during the registration procedure in the target AMF (T-AMF) after the N2 handover.

1) PDU Session Establishment Request/Service Request (S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2)—An Application in the UE201requires a service. The UE201checks with the NSSP (Network Slice Selection Policy) within the URSP (UE Route Selection Policy) rules in the UE Policy and finds out the network slice(s) on which the Application can receive a service, e.g., the S-NSSAI-3, S-NSSAI-1 and S-NSSAI-2. The UE201is registered to all these network slices. Based on the request from the Application, the UE201sends, to the source AMF (S-AMF)204, a PDU Session Establishment Request message or Service Request message on the network slice S-NSSAI-3, for example. Along with the network slice S-NSSAI-3 inclusion in the PDU Session Establishment Request message or in the Service Request message (on which the PDU Session is to be established or reactivated), the UE201also includes in the PDU Session Establishment Request message or in the Service Request message a new parameter ‘alternative S-NSSAI’ in which the UE201places the network slice(s) that are also compatible with the service requiring Application in the UE201, e.g., S-NSSAI-1 and S-NSSAI-2, if any.

The new parameter may be structured with priority order or preference order among alternative S-NSSAI(s). For example, if the “alternative S-NSSAI” parameter is set as the alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2, this means that the UE201wishes to use the S-NSSAI-1 as an alternative S-NSSAI for the S-NSSAI-3 rather than the S-NSSAI-2. This new parameter may be called ‘alternative S-NSSAI’, ‘alternative network slice’, ‘backup network slice’, ‘backup S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) that the service requiring Application in the UE201can work with based on the NSSP/URSP rules of the UE201. The ‘alternative network slice’ can also be the default allowed S-NSSAI in the UE201, if available. The ‘alternative network slice(s)’ can also be delivered by the UE201to the network via any other NAS message.

In one example, the AMF204may obtain alternative S-NSSAI(s) per S-NSSAI in the subscribed NSSAI during the Registration Procedure or during the Subscriber Data Update Notification to AMF procedure as described in 3GPP TS 23.502. In this case, the Nudm_SDM_Get service is used during the Registration Procedure and Nudm_SDM_Notification service is used during the Subscriber Data Update Notification to AMF procedure.

In another example, the SMF may obtain alternative S-NSSAI(s) per S-NSSAI in the subscribed NSSAI during the Registration Procedure or during the Subscriber Data Update Notification to SMF procedure as described in 3GPP TS 23.502. In this case, the Nudm_SDM_Get service is used during the Registration Procedure and the Nudm_SDM_Notification service is used during the Subscriber Data Update Notification to AMF procedure.

2) PDU Session Establishment on the S-NSSAI-3 as per 3GPP TS 23.502.

3) N2 message (S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2)—At the end of the PDU Session Establishment procedure on the network slice S-NSSAI-3, the Source AMF (S-AMF)204sends, to the S-RAN node202, the N2 message (or in any other message on the N2 interface between the S-AMF204and the S-RAN node202), including a parameter for the current network slice on which the PDU Session was established (e.g. S-NSSAI-3), and also including the alternative network slice(s), if any, for example S-NSSAI-1 and S-NSSAI-2 within a new ‘alternative S-NSSAI’ parameter.

The new parameter may be structured with priority order or preference order among the alternative S-NSSAI(s). This new parameter in the N2 message may be called ‘alternative S-NSSAI’, ‘alternative network slice’, ‘backup network slice’, ‘backup S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) that the service requiring Application in the UE201can work with. The alternative network slices S-NSSAI-1 and S-NSSAI-2, which the S-AMF204includes in the ‘alternative S-NSSAI’ parameter in the N2 message, are the ones which the S-AMF204has received from the UE201in the PDU Session Establishment Request message or in the Service Request message. The ‘alternative network slice’ can also be the default allowed S-NSSAI in the S-AMF204or UDM/UDR206, if available.

When the S-AMF204sends the N2 message including alternative S-NSSAI(s) to the S-RAN node202, the S-AMF204may confirm that the SMF(s) associated to the PDU session(s) are accessible from any alternative S-NSSAIs.

4) At some stage a handover is required. There is no target cell supporting the S-NSSAI-3 on which the UE201has an active PDU Session. However, there is a target cell supporting an alternative network slice, e.g., alternative S-NSSAI=S-NSSAI-1.

5) Handover to a target cell supporting the alternative network slice S-NSSAI-1. The S-RAN node202selects a target cell that supports one of the alternative network slices, e.g., alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available at any of the target cells, the priority among the alternative network slices should be considered at the S-RAN node202when selecting a target cell. If both alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available at a target cell, the S-RAN node202selects the alternative network slice S-NSSAI-1 taking the priority into account. During the N2 handover the S-AMF204transfers the original S-NSSAI-3 and the alternative S-NSSAI-1 and S-NSSAI-2 to the T-AMF205.

6) Registration with the T-AMF205as per 3GPP TS 23.502. The registration procedure re-confirms the S-NSSAI-1 as an allowed network slice.

7) PDU Session Modification on the alternative network slice S-NSSAI-1 as per 3GPP TS 23.502—The T-AMF205triggers the PDU Session Modification procedure to replace the current S-NSSAI, i.e., S-NSSAI-3, with the alternative network slice S-NSSAI-1.

As the S-NSSAI will be swapped during this procedure, the SMF may contact the PCF and/or the CHF to issue separate CDRs, one with the original S-NSSAI-3 and the other one with the alternative network slice S-NSSAI-1.

8) During the PDU Session Modification procedure, when the T-AMF205sends the N2 message to the T-RAN node203, the N2 message contains the following parameters.

N2 message (S-NSSAI-1, original S-NSSAI=S-NSSAI-3, alternative S-NSSAI=S-NSSAI-2, NAS message (PDU Session ID, N1 SM container (PDU Session Modification command (New S-NSSAI=S-NSSAI-1)))) During the PDU Session Modification on the alternative network slice S-NSSAI-1, the T-AMF205may send the N2 message to the T-RAN node203. Along with the network slice on which the PDU Session(s) were established, the T-AMF205also includes in the N2 message (or in any other message on the N2 interface between the T-AMF205and the T-RAN node203) to the T-RAN node203two new parameters:Original S-NSSAI—The T-AMF205places in this parameter the initial network slice from which the PDU Session was transferred to one of the alternative network slices in the last handover, e.g., S-NSSAI-3. This new parameter may be called ‘original S-NSSAI’, ‘original network slice’, ‘initial network slice’, ‘initial S-NSSAI’, ‘UE requested S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) on which the PDU Session was established at the PDU Session Establishment procedure as described in 3GPP TS 23.502.Alternative S-NSSAI—The T-AMF205places in this parameter one of the remaining alternative network slices received with the PDU Session Establishment Request message or the Service Request message from the UE201, e.g., S-NSSAI-2. The alternative network slice can also be the default allowed S-NSSAI in the T-AMF205or UDM/UDR206, if available.

The alternative S-NSSAI may also indicate alternative network slices that will be used for the PDU Session after the successful Handover procedure.

9) During the PDU Session Modification procedure, when the SMF sends the PDU Session Modification command to the UE201(within the N2 message on the T-AMF205to the T-RAN node interface) via the T-AMF205and the T-RAN node203, the PDU Session Modification command includes a New S-NSSAI parameter (e.g., S-NSSAI-1) in order to let the UE201know that the S-NSSAI (e.g. S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g. S-NSSAI-1). The T-RAN node203sends the PDU Session Modification command, received from the SMF via the T-AMF205(within the N2 message on the T-AMF205to the T-RAN node interface), to the UE201. With this information, the UE201updates the network slice state in the UE201. In one example, instead of sending the PDU Session Modification message to the UE201, the T-AMF205may send the UE Configuration Update message to the UE201via the T-RAN node203to let the UE201know that the S-NSSAI (e.g., S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g., S-NSSAI-1).

10) At some stage later again, a handover is required. When selecting a target cell and there are multiple qualifying cells, the T-RAN node203may select the target cell in the following order of preference:The ‘original S-NSSAI’—the T-RAN node203may give a preference to the original network slice first (e.g., S-NSSAI-3) in selecting a target cell. This would allow for the PDU Session to be transferred back to the network slice on which the PDU Session has been established at the very beginning as this network slice may be the most suitable network slice for the PDU Sessions(s);The current network slice-if no target cell supports the original network slice (e.g., S-NSSAI-3), then the T-RAN node203may prefer to select a target cell supporting the current network slice on which the PDU Session(s) is currently active, e.g., S-NSSAI-1.The ‘alternative S-NSSAI’-If there is no target cell supporting the original network slice nor the current network slice, then the T-RAN node203may prefer a target cell supporting the alternative network slice if available, e.g., S-NSSAI-2.

It should be noted that RAN node (both, S-RAN and T-RAN) may apply an alternative order(s) in selecting the target cell, for example first giving priority to a target cell supporting the current network slice with active PDU Session(s) on it (e.g., S-NSSAI-1) and then the original S-NSSAI (e.g., S-NSSAI-3) if available and last the alternative S-NSSAI (e.g., S-NSSAI-2), if available. The RAN node may apply a preference in any other order, e.g., an operator defined or configured order of preference between the original network slice, the current network slice and the alternative network slice.

FIG.4is a schematic timing (signalling) diagram illustrating an exemplary method for UE assistance with alternative network slice(s) for PDU Session continuity in the N2 handover (Use case2). In Use case2the alternative network slice in the target cell is not re-confirmed as an allowed network slice during the registration procedure in the T-AMF305after the N2 handover. In this case the T-AMF305may transfer the PDU Session(s) to another alternative S-NSSAI, if available (e.g., S-NSSAI-2) or to a default network slice in the new registration area.

1) PDU Session Establishment Request/Service Request (S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2)—An Application in the UE301requires a service. The UE301checks with the NSSP (Network Slice Selection Policy) within the URSP (UE Route Selection Policy) rules in the UE Policy and finds out the network slice(s) on which the Application can receive a service, e.g., the S-NSSAI-3, S-NSSAI-1 and S-NSSAI-2. The UE301is registered to all these network slices. Based on the request from the Application, the UE301sends, to the S-AMF304, a PDU Session Establishment Request message or Service Request message on the network slice S-NSSAI-3, for example. Along with the network slice S-NSSAI-3 inclusion in the PDU Session Establishment Request message or Service Request message (on which the PDU Session is to be established or reactivated), the UE301also includes in the PDU Session Establishment Request message or in the Service Request message a new parameter ‘alternative S-NSSAI’ in which the UE301places the network slice(s) that are also compatible with the service requiring Application in the UE301, e.g., S-NSSAI-1 and S-NSSAI-2, if any.

The new parameter may be structured with priority order or preference order among alternative S-NSSAI(s). For example, if the “alternative S-NSSAI” parameter is set as the alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2, this means that the UE301wishes to use the S-NSSAI-1 as an alternative S-NSSAI for the S-NSSAI-3 rather than the S-NSSAI-2. This new parameter may be called ‘alternative S-NSSAI’, ‘alternative network slice’, ‘backup network slice’, ‘backup S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) that the service requiring Application in the UE301can work with based on the NSSP/URSP rules of the UE301. The alternative network slice can also be the default allowed S-NSSAI in the UE301, if available. The alternative network slice(s) can also be delivered by the UE301to the network via any other NAS message.

In one example, the S-AMF304may obtain alternative S-NSSAI(s) per S-NSSAI in the subscribed NSSAI during the Registration Procedure or during the Subscriber Data Update Notification to AMF procedure as described in 3GPP TS 23.502. In this case, the Nudm_SDM_Get service is used during the Registration Procedure and the Nudm_SDM_Notification service is used during the Subscriber Data Update Notification to AMF procedure.

In another example, the SMF may obtain alternative S-NSSAI(s) per S-NSSAI in the subscribed NSSAI during the Registration Procedure or during the Subscriber Data Update Notification to SMF procedure as described in 3GPP TS 23.502. In this case, the Nudm_SDM_Get service is used during the Registration Procedure and the Nudm_SDM_Notification service is used during the Subscriber Data Update Notification to AMF procedure.

2) PDU Session Establishment on the S-NSSAI-3 as per 3GPP TS 23.502.

3) N2 message (S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2)—At the end of the PDU Session Establishment procedure on the network slice S-NSSAI-3, the S-AMF304sends, to the S-RAN node302, the N2 message (or in any other message on the N2 interface between the S-AMF304and the S-RAN node302), including a parameter for the current network slice on which the PDU Session was established (e.g. S-NSSAI-3), and also including the alternative network slice(s), if any, for example S-NSSAI-1 and S-NSSAI-2 within a new ‘alternative S-NSSAI’ parameter.

The new parameter may be structured with priority order or preference order among the alternative S-NSSAI(s). This new parameter in the N2 message may be called ‘alternative S-NSSAI’, ‘alternative network slice’, ‘backup network slice’, ‘backup S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) that the service requiring Application in the UE301can work with. The alternative network slices S-NSSAI-1 and S-NSSAI-2, which the AMF304includes in the ‘alternative S-NSSAI’ parameter in the N2 message, are the ones which the AMF304has received from the UE301in the PDU Session Establishment Request message or in the Service Request message. The alternative network slice can also be the default allowed S-NSSAI in the S-AMF304or UDM/UDR306, if available. When the S-AMF304sends the N2 message including alternative S-NSSAI(s) to the S-RAN node302, the S-AMF304may confirm that the SMF(s) associated to the PDU session(s) are accessible from any alternative S-NSSAIs.

4) At some stage a handover is required. There is no target cell supporting the S-NSSAI-3 on which the UE301has an active PDU Session. However, there is a target cell supporting an alternative network slice, e.g., alternative S-NSSAI=S-NSSAI-1.

5) Handover to a target cell supporting the alternative network slice S-NSSAI-1. The S-RAN node302selects a target cell that supports one of the alternative network slices, e.g., alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available at any of the target cells, the priority among the alternative network slices should be considered at the S-RAN node302when selecting a target cell. If both alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available at a target cell, the S-RAN node302selects the alternative network slice S-NSSAI-1 taking the priority into account. During the N2 handover the S-AMF304transfers the original S-NSSAI-3 and the alternative S-NSSAI-1 and S-NSSAI-2 to the T-AMF305.

6) Registration with the T-AMF305as per 3GPP TS 23.502. The registration procedure does not re-confirm the S-NSSAI-1 as an allowed network slice.

7) PDU Session Modification on the alternative network slice S-NSSAI-2 or default S-NSSAI as per 3GPP TS 23.502—As the alternative network slice S-NSSAI-1 is not an allowed network slice in the new registration area, the T-AMF305triggers a PDU Session Modification procedure on another alternative network slice (e.g., S-NSSAI-2) or on a default network slice. As the S-NSSAI will be swapped during this procedure, the SMF may contact to the PCF and/or the CHF to issue separate CDRs, one with the original S-NSSAI-3 and the other one with the alternative network slice S-NSSAI-2 or the default network slice.

8) During the PDU Session Modification procedure, when the T-AMF305sends the N2 message to the T-RAN node303, the N2 message contains the following parameters.

N2 message (S-NSSAI-2/default S-NSSAI, original S-NSSAI=S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, NAS message (PDU Session ID, N1 SM container (PDU Session Modification command (New S-NSSAI=S-NSSAI-1))))—During the PDU Session Modification on the network slice S-NSSAI-2/default S-NSSAI, the T-AMF305may send the N2 message to the T-RAN node303. Along with the network slice on which the PDU Session(s) were established, the T-AMF305also includes in the N2 message (or in any other message on the N2 interface between the AMF305and the RAN node303) to the T-RAN node303two new parameters:Original S-NSSAI—The T-AMF305places in this parameter the initial network slice from which the PDU Session was transferred to one of the alternative network slices in the last handover, e.g., S-NSSAI-3. This new parameter may be called ‘original S-NSSAI’, ‘original network slice’, ‘initial network slice’, ‘initial S-NSSAI’, ‘UE requested S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) on which the PDU Session was established at the PDU Session Establishment procedure as described in 3GPP TS 23.502.Alternative S-NSSAI—The T-AMF305places in this parameter one of the remaining alternative network slices received with the PDU Session Establishment Request message or the Service Request message from the UE301, (e.g., in this case S-NSSAI-1 that was rejected at the registration with the T-AMF305can still play the role of the alternative S-NSSAI). The alternative S-NSSAI may also indicate alternative network slices that will be used for the PDU Session after the successful Handover procedure.

9) During the PDU Session Modification procedure, when the SMF sends the PDU Session Modification command to the UE301via the T-AMF305(within the N2 message on the T-AMF305to the T-RAN node interface) and the T-RAN node303, the PDU Session Modification command includes a New S-NSSAI parameter (e.g., S-NSSAI-2) in order to let the UE301knows that the S-NSSAI (e.g., S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g., S-NSSAI-2). The T-RAN node303sends the PDU Session Modification command, received from the SMF via the T-AMF305(within the N2 message on the T-AMF305to the T-RAN node interface), to the UE301. With this information, the UE301updates the network slice state in the UE301.

In one example, instead of sending the PDU Session Modification message to the UE301, the T-AMF305may send the UE Configuration Update message to the UE301via the T-RAN node303to let the UE301know that the S-NSSAI (e.g., S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g., S-NSSAI-2).

10) At some stage later again a handover is required. When selecting a target cell and there are multiple qualifying cells, the T-RAN node303may select the target cell in the following order of preference:The ‘original S-NSSAI’—the T-RAN node303may give preference to the original network slice first (e.g., S-NSSAI-3) in selecting a target cell. This would allow for the PDU Session(s) to be transferred back to the network slice on which the PDU Session has been established at the very beginning as this network slice may be the most suitable network slice for the PDU Session(s).The current network slice-if no target cell supports the original network slice (e.g., S-NSSAI-3), then the T-RAN node303may prefer to select a target cell supporting the current network slice on which the PDU Session(s) is currently active, e.g., S-NSSAI-2/default S-NSSAI.The ‘alternative S-NSSAI’-If there is no target cell supporting the original network slice nor the current network slice, then the T-RAN node303may prefer a target cell supporting the alternative network slice if available, e.g., S-NSSAI-1.

It should be noted that the RAN node (both, S-RAN node and T-RAN node) may apply an alternative order(s) in selecting the target cell, for example first giving priority to a target cell supporting the current network slice with active PDU Session(s) on it (e.g., S-NSSAI-2) and then the original S-NSSAI (e.g., S-NSSAI-3) if available and last the alternative S-NSSAI (e.g., S-NSSAI-1), if available. The RAN node may apply a preference in any other order, e.g., an operator defined or configured order of preference between the original network slice, the current network slice and the alternative network slice.

(Solution 2—Core Network Assistance with Alternative Network Slice for PDU Session Continuity)

Solution 2 proposes PDU Session transfer to an alternative network slice at a handover when the current network slice with active PDU Session(s) on the current network slice is not supported by the target cells. This allows for improved service continuity by transferring the active PDU Session(s) on the current network slice to an alternative network slice thus maintaining the service continuity, instead releasing the PDU Session(s). In this solution, the alternative network slices, for the PDU Session(s) that is being established, are provided by the network. The NSSP rules for the UE are retrieved by the AMF or the SMF from the URSP rules within the PCF during the PDU Session Establishment/Modification procedure. The AMF or the SMF finds out from the NSSP/URSP rules for the UE the alternative network slices (if any) that the current PDU Session is compatible with, e.g., the current PDU Session can be transferred to, if needed. Then the AMF or SMF provides these alternative network slices to the RAN node within the Core Network Assistance parameter in the N2 message or within a new parameter in the N2 message to assist a potential Xn and N2 handover.

FIG.5is a schematic timing (signalling) diagram illustrating an exemplary method for Core Network assistance with alternative network slice for PDU Session continuity in the Xn handover.

1) PDU Session Establishment Request/Service Request (App ID, S-NSSAI-3, PDU Session ID, DNN ID)—An Application in the UE401requires a service. The UE401checks with the NSSP (Network Slice Selection Policy) within the URSP (UE Route Selection Policy) rules in the UE Policy and finds out the network slice(s) on which the Application can receive a service, e.g., the S-NSSAI-3, S-NSSAI-1 and S-NSSAI-2. The UE401is registered to all these network slices. Based on the request from the Application, the UE401sends, to the AMF404, the PDU Session Establishment Request message or the Service Request message on the network slice S-NSSAI-3, for example. The UE401may also include in the Application identity e.g., App ID in the PDU Session Establishment Request or Service Request message as the App ID may assist the AMF404or the SMF404to find the alternative network slice(s) for network slice S-NSSAI-3 from the NSSP/URSP rules for the UE401.

2) Continue with the PDU Session Establishment procedure or the Service Request procedure on the S-NSSAI-3 as per 3GPP TS 23.502.

3) AMF/SMF association with PCF (NSSP/URSP)—The AMF404or the SMF404may interact with the PCF405during the association with the PCF405in order to discover the compatible network slices for the network slice S-NSSAI-3 on which a PDU Session is being established.

The AMF404, during the UE Policy Association Establishment with the PCF405, may either:a) request the URSP or NSSP rules for the UE401from the PCF405via the Npcf_UEPolicy_Contol_Create Request message. In this case, the AMF404would include a new parameter (e.g., URSP flag, NSSP flag or any other name for a parameter with the purpose of requesting URSP or NSSP information from the PCF405) in the Npcf_UEPolicy_Contol_Create Request message; ORb) request the list of the network slices that are compatible with the current network slice S-NSSAI-3 via the Npcf_UEPolicy_Contol_Create Request message. In this case, the AMF404may include, in the Npcf_UEPolicy_Contol_Create Request message, the identity of the Application (e.g., App ID) that has triggered the PDU Session Establishment, the network slice identity (e.g., S-NSSAI-3) on which the PDU Session is being established or the DNN ID in order to facilitate the PCF405in finding the network slices compatible to the network slice S-NSSAI-3.

The PCF405may provide the requested information (i.e., the URSP or NSSP rules for the UE) or the list of the network slices compatible with the network slice S-NSSAI-3 with the Npcf_UEPolict_Control_Create Response message.

It should be noted that the AMF404may make use of any other existing procedure or service provided by the PCF405in order to retrieve the URSP or NSSP related information from the PCF405.

The SMF404, during the SM Policy Association Establishment or SM Policy Association Modification with the PCF405, may either:

a) request the URSP or the NSSP rules for the UE401from the PCF405via the Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF404would include a new parameter (e.g., URSP flag or NSSP flag or any other name for a parameter with the purpose of requesting URSP or NSSP information from the PCF405) in the Npcf_SMPolicy_Contol_Create Request message; ORb) request the list of the network slices that are compatible with the current network slice S-NSSAI-3 via the Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF404may include, in the Npcf_SMPolicy_Contol_Create Request message, the identity of the Application (e.g., App ID) that has triggered the PDU Session Establishment, the network slice identity (e.g., S-NSSAI-3) on which the PDU Session is being established or the DNN ID in order to facilitate the PCF405in finding the network slices compatible to the network slice S-NSSAI-3.

The PCF405may provide the requested information (i.e., the URSP or NSSP rules for the UE401) or the list of the network slices compatible with the S-NSSAI-3 with the Npcf_SMPolicy_Control_Create Response message.

It should be noted that the SMF404may make use of any other existing procedure or service provided by the PCF405in order to retrieve the URSP or NSSP related information from the PCF405.

4) N2 message (S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2)—At the end of the PDU Session Establishment procedure on the network slice S-NSSAI-3, the AMF404sends, to the S-RAN node402, the N2 message (or in any other message on the N2 interface between the AMF404and the RAN node), including a parameter for the current network slice on which the PDU Session was established (e.g. S-NSSAI-3), and also including the alternative network slice(s) retrieved from the PCF405directly or first retrieving the URSP or NSSP rules for the UE401as described in step3(for example S-NSSAI-1 and S-NSSAI-2) within a new ‘alternative S-NSSAI’ parameter.

The new parameter may be structured with priority order or preference order among alternative S-NSSAI(s). This new parameter in the N2 message may be called ‘alternative S-NSSAI’, ‘alternative network slice’, ‘backup network slice’, ‘backup S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) that the service requiring Application in the UE401can work with. The alternative network slice can also be the default allowed S-NSSAI in the AMF404or UDM/UDR406, if available.

When the AMF404sends the N2 message including alternative S-NSSAI(s) to the S-RAN node402, the AMF404may confirm that the SMF(s)404associated to the PDU session(s) are accessible from any alternative S-NSSAIs.

5) At some stage a handover is required. There is no target cell supporting the S-NSSAI-3 on which the UE401has an active PDU Session. However, there is a target cell supporting an alternative network slice, e.g., alternative S-NSSAI=S-NSSAI-1.

6) Handover to a target cell supporting the alternative network slice S-NSSAI-1. The S-RAN node402selects a target cell that supports one of the alternative network slices, e.g. alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available at any of the target cells, the priority among the alternative network slices should be considered at the S-RAN node402when selecting a target cell. If both alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available at a target cell, the S-RAN node402selects the alternative network slice S-NSSAI-1 taking the priority into account.

7) PDU Session Modification on the alternative network slice S-NSSAI-1 as per 3GPP TS 23.502—The AMF404triggers PDU Session Modification on the alternative network slice S-NSSAI-1. As the S-NSSAI will be swapped during this procedure, the SMF404may contact the PCF405and/or the CHF (Charging Function) to issue separate CDRs, one with the original S-NSSAI-3 and the other one with the alternative network slice S-NSSAI-1.

8) During the PDU Session Modification procedure, when the AMF404sends the N2 message to the T-RAN node403, the N2 message contains the following parameters.

N2 message (S-NSSAI-1, original S-NSSAI=S-NSSAI-3, alternative S-NSSAI=S-NSSAI-2, NAS message (PDU Session ID, N1 SM container (PDU Session Modification command (New S-NSSAI=S-NSSAI-1))))—At the end of the PDU Session Modification on the network slice S-NSSAI-1, the AMF404may send the N2 message to the T-RAN node403. Along with the network slice on which the PDU Session(s) were established, the AMF404also includes in the N2 message (or in any other message on the N2 interface between the AMF404and the RAN node403) two new parameters:Original S-NSSAI—The AMF404places in this parameter the initial network slice from which the PDU Session was transferred to one of the alternative network slices in the last handover, e.g., S-NSSAI-3. This new parameter may be called ‘original S-NSSAI’, ‘original network slice’, ‘initial network slice’, ‘initial S-NSSAI’, ‘UE requested S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) on which the PDU Session was established at the PDU Session Establishment procedure as described in 3GPP TS 23.502.Alternative S-NSSAI—The AMF404places in this parameter one of the remaining alternative network slices, e.g., S-NSSAI-2. The alternative network slice can also be the default allowed S-NSSAI in the AMF404or UDM/UDR406, if available. The alternative S-NSSAI may also indicate alternative network slices that will be used for the PDU Session after the successful Handover procedure.

9) During the PDU Session Modification procedure, when the SMF404sends the PDU Session Modification command to the UE401via the AMF404(within the N2 message on the AMF404to the T-RAN node interface) and the T-RAN node403, the PDU Session Modification command includes a New S-NSSAI parameter (e.g., S-NSSAI-1) in order to let the UE401know that the S-NSSAI (e.g. S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g. S-NSSAI-1). The T-RAN node403sends the PDU Session Modification command, received from the SMF404via the AMF404(within the N2 message on the AMF404to the T-RAN node interface), to the UE401. With this information, the UE401updates the network slice state in the UE401.

In one example, instead of sending the PDU Session Modification message to the UE401, the AMF404may send the UE Configuration Update message to the UE401via the T-RAN node403to let the UE401know that the S-NSSAI (e.g., S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g., S-NSSAI-1).

10) At some stage later again a handover is required. When selecting a target cell and there are multiple qualifying cells, the T-RAN node403may select the target cell in the following order of preference:The ‘original S-NSSAI’—the T-RAN node403may give preference to the original network slice first (e.g., S-NSSAI-3) in selecting a target cell. This would allow for the PDU Session(s) to be transferred back to the network slice on which the PDU Session has been established at the very beginning as this network slice may be the most suitable network slice for that PDU Session(s);The current network slice-if no target cell supports the original network slice (e.g., S-NSSAI-3), then the T-RAN node403may prefer to select a target cell supporting the current network slice on which the PDU Session is currently active, e.g., S-NSSAI-1.The ‘alternative S-NSSAI’-If there is no target cell supporting the original network slice nor the current network slice, then the T-RAN node403may prefer a target cell supporting the alternative network slice if available, e.g., S-NSSAI-2.

It should be noted that the (source/target) RAN node may apply an alternative order(s) of preference in selecting the target cell, for example first giving priority to a target cell supporting the current network slice with active PDU Session on it (e.g., S-NSSAI-1) and then the original S-NSSAI (e.g., S-NSSAI-3) if available and last the alternative S-NSSAI (e.g., S-NSSAI-2) if available. The (source/target) RAN node may apply a preference in any other order, e.g., an operator defined or configured order of preference between the original network slice, the current network slice and the alternative network slice.

FIG.6is a schematic timing (signalling) diagram illustrating an exemplary method for Core Network assistance with alternative network slice for PDU Session continuity in the N2 handover (Use case1). In Use case1the alternative network slice in the target cell is re-confirmed as allowed network slice during the registration procedure in the T-AMF after the N2 handover.

1) PDU Session Establishment Request/Service Request (App ID, S-NSSAI-3, PDU Session ID, DNN ID)—An Application in the UE501requires a service. The UE501checks with the NSSP (Network Slice Selection Policy) within the URSP (UE Route Selection Policy) rules in the UE Policy and finds out the network slice(s) on which that Application can receive a service, e.g., the S-NSSAI-3, S-NSSAI-1 and S-NSSAI-2. The UE501is registered to all these network slices. Based on the request from the Application, the UE sends, to the source AMF (S-AMF)504, a PDU Session Establishment Request message or Service Request message on network slice S-NSSAI-3, for example. The UE501may also include the Application identity e.g., App ID in the PDU Session Establishment Request or Service Request message as the App ID may assist the AMF504or the SMF504to find the alternative network slice(s) for the network slice S-NSSAI-3 from the NSSP/URSP rules for the UE501.

2) Continue with the PDU Session Establishment procedure or the Service Request procedure on the S-NSSAI-3 as per 3GPP TS 23.502.

3) AMF/SMF association with the PCF506(NSSP/URSP)—The S-AMF504or the SMF504may interact with the PCF506during the association with the PCF506in order to discover the compatible network slices for the network slice S-NSSAI-3 on which a PDU Session is being established.

The S-AMF504, during the UE Policy Association Establishment with the PCF506, may either:a) request the URSP or NSSP rules for the UE501from the PCF506via the Npcf_UEPolicy_Contol_Create Request message. In this case, the S-AMF504would include a new parameter (e.g., URSP flag, NSSP flag or any other name for a parameter with the purpose of requesting URSP or NSSP information from the PCF506) in the Npcf_UEPolicy_Contol_Create Request message; ORb) request the list of the network slices that are compatible with the current network slice S-NSSAI-3 via the Npcf_UEPolicy_Contol_Create Request message. In this case, the S-AMF504may include, in the Npcf_UEPolicy_Contol_Create Request message, the identity of the Application (e.g., App ID) that has triggered the PDU Session Establishment, the network slice identity (e.g., S-NSSAI-3) on which the PDU Session is being established or the DNN ID in order to facilitate the PCF506in finding the network slices compatible to the network slice S-NSSAI-3.

The PCF506may provide the requested information (i.e., the URSP or NSSP rules for the UE501) or the list of the network slices compatible with the S-NSSAI-3 with the Npcf_UEPolict_Control_Create Response message.

It should be noted that the S-AMF504may make use of any other existing procedure or service provided by the PCF506in order to retrieve the URSP or NSSP related information from the PCF506.

The SMF504, during the SM Policy Association Establishment or SM Policy Association Modification with the PCF506, may either:a) request the URSP or NSSP rules for the UE501from the PCF506via the Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF504would include a new parameter (e.g., URSP flag or NSSP flag or any other name for a parameter with the purpose of requesting URSP or NSSP information from the PCF506) in the Npcf_SMPolicy_Contol_Create Request message; ORb) request the list of the network slices that are compatible with the current network slice S-NSSAI-3 via the Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF504may include, in the Npcf_SMPolicy_Contol_Create Request message, the identity of the Application (e.g., App ID) that has triggered the PDU Session Establishment, the network slice identity (e.g., S-NSSAI-3) on which the PDU Session is being established or the DNN ID in order to facilitate the PCF506in finding the network slices compatible to the network slice S-NSSAI-3.

The PCF506may provide the requested information (i.e., the URSP or NSSP rules for the UE501) or the list of the network slices compatible with the S-NSSAI-3 with the Npcf_SMPolicy_Control_Create Response message.

It should be noted that the SMF504may make use of any other existing procedure or service provided by the PCF506in order to retrieve the URSP or NSSP related information from the PCF506.

4) N2 message (S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2)—At the end of the PDU Session Establishment procedure on the network slice S-NSSAI-3, the S-AMF504sends, to the RAN node, the N2 message (or in any other message on the N2 interface between the AMF504and the RAN node), including a parameter for the current network slice on which the PDU Session was established (e.g. S-NSSAI-3), and also including the alternative network slice(s) retrieved from the PCF506directly or first retrieving the URSP or NSSP rules for the UE501as described in step3(for example S-NSSAI-1 and S-NSSAI-2) within a new ‘alternative S-NSSAI’ parameter.

The new parameter may be structured with priority order or preference order among the alternative S-NSSAI(s). This new parameter in the N2 message may be called ‘alternative S-NSSAI’, ‘alternative network slice’, ‘backup network slice’, ‘backup S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) that the service requiring Application in the UE501can work with. The alternative network slice can also be the default allowed S-NSSAI in the S-AMF504or UDM/UDR507, if available.

When the S-AMF504sends the N2 message including alternative S-NSSAI(s) to the S-RAN node502, the S-AMF504may confirm that the SMF(s)504associated to the PDU session(s) are accessible from any alternative S-NSSAIs.

5) At some stage a handover is required. There is no target cell supporting the S-NSSAI-3 on which the UE501has an active PDU Session. However, there is a target cell supporting an alternative network slice, e.g., alternative S-NSSAI=S-NSSAI-1.

6) Handover to a target cell supporting the alternative network slice S-NSSAI-1. The S-RAN node502selects a target cell that supports one of the alternative network slices, e.g., alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available at any of the target cells, the priority among the alternative network slices should be considered at the S-RAN node502when selecting a target cell. If both alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available at a target cell, the S-RAN node502selects the alternative network slice S-NSSAI-1 taking the priority into account. During the N2 handover the S-AMF504transfers the original S-NSSAI-3 and the alternative S-NSSAI-1 and S-NSSAI-2 to the T-AMF505.

7) Registration with the T-AMF505as per 3GPP TS 23.502. The registration procedure re-confirms the S-NSSAI-1 as an allowed network slice.

8) PDU Session Modification procedure to replace the current S-NSSAI, i.e., S-NSSAI-3, with the alternative network slice S-NSSAI-1 as per 3GPP TS 23.502

The T-AMF505triggers PDU Session Modification on the alternative network slice S-NSSAI-1. As the S-NSSAI will be swapped during this procedure, the SMF505may contact the PCF506and/or the CHF to issue separate CDRs, one with the original S-NSSAI-3 and the other one with the alternative network slice S-NSSAI-1.

9) During the PDU Session Modification procedure, when the T-AMF505sends the N2 message to the T-RAN node503, the N2 message contains the following parameters.

N2 message (S-NSSAI-1, original S-NSSAI=S-NSSAI-3, alternative S-NSSAI=S-NSSAI-2, NAS message (PDU Session ID, N1 SM container (PDU Session Modification command (New S-NSSAI=S-NSSAI-1))))—During the PDU Session Modification on the alternative network slice S-NSSAI-1, the T-AMF505may send the N2 message to the T-RAN node503. Along with the network slice on which the PDU Session(s) were established, the T-AMF505also includes in the N2 message (or in any other message on the N2 interface between the T-AMF505and the T-RAN node503) to the T-RAN node503two new parameters:Original S-NSSAI—The T-AMF505places in this parameter the initial network slice from which the PDU Session was transferred to one of the alternative network slices in the last handover, e.g., S-NSSAI-3. This new parameter may be called ‘original S-NSSAI’, ‘original network slice’, ‘initial network slice’, ‘initial S-NSSAI’, ‘UE requested S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) on which the PDU Session was established at the PDU Session Establishment procedure as described in 3GPP TS 23.502.Alternative S-NSSAI—The T-AMF505places in this parameter one of the remaining alternative network slices e.g., S-NSSAI-2. The alternative network slice can also be the default allowed S-NSSAI in the T-AMF505or UDM/UDR507, if available. The alternative S-NSSAI may also indicate alternative network slices that will be used for the PDU Session after the successful Handover procedure.

10) During the PDU Session Modification procedure, when the SMF505sends the PDU Session Modification command to the UE501via the T-AMF505(within the N2 message on the T-AMF505to the T-RAN node interface) and the T-RAN node503, the PDU Session Modification command includes a New S-NSSAI parameter (e.g., S-NSSAI-1) in order to let the UE501know that the S-NSSAI (e.g. S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g. S-NSSAI-1). The T-RAN node503sends the PDU Session Modification command, received from the SMF505via the T-AMF505(within the N2 message on the T-AMF505to the T-RAN node interface), to the UE501. With this information, the UE501updates the network slice state in the UE.

In one example, instead of sending the PDU Session Modification message to the UE501, the T-AMF505may send the UE Configuration Update message to the UE501via the T-RAN node503to let the UE501know that the S-NSSAI (e.g., S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g., S-NSSAI-1).

11) At some stage later again a handover is required. When selecting a target cell and there are multiple qualifying cells, the T-RAN node503may select the target cell in the following order of preference:The ‘original S-NSSAI’—the T-RAN node503may give preference to the original network slice first (e.g., S-NSSAI-3) in selecting a target cell. This would allow for the PDU Session to be transferred back to the network slice on which the PDU Session has been established at the very beginning as this network slice may be the most suitable network slice for that PDU Session(s);The current network slice-if no target cell supports the original network slice (e.g., S-NSSAI-3), then the T-RAN node503may prefer to select a target cell supporting the current network slice on which the PDU Session is currently active, e.g., S-NSSAI-1.The ‘alternative S-NSSAI’-If there is no target cell supporting the original network slice nor the current network slice, then the T-RAN node503may prefer a target cell supporting the alternative network slice if available, e.g., S-NSSAI-2.

It should be noted that RAN node (both, S-RAN and T-RAN) may apply an alternative order(s) in selecting the target cell, for example first giving priority to a target cell supporting the current network slice with active PDU Session on it (e.g., S-NSSAI-1) and then the original S-NSSAI (e.g., S-NSSAI-3) if available and last the alternative S-NSSAI (e.g., S-NSSAI-2), if available. The RAN node may apply a preference in any other order, e.g., an operator defined or configured order of preference between the original network slice, the current network slice and the alternative network slice.

FIG.7is a schematic timing (signalling) diagram illustrating an exemplary method for Core Network assistance with alternative network slice for PDU Session continuity in the N2 handover (Use case2). In Use case2the alternative network slice in the target cell is not re-confirmed as allowed network slice during the registration procedure in the T-AMF after the N2 handover. In this case the T-AMF may transfer the PDU Session to another alternative S-NSSAI, if available (e.g., S-NSSAI-2) or to a default network slice in the new registration area.

1) PDU Session Establishment Request/Service Request (App ID, S-NSSAI-3, PDU Session ID, DNN ID)—An Application in the UE601requires a service. The UE601checks with the NSSP (Network Slice Selection Policy) within the URSP (UE Route Selection Policy) rules in the UE Policy and finds out the network slice(s) on which the Application can receive a service, e.g., the S-NSSAI-3, S-NSSAI-1 and S-NSSAI-2. The UE601is registered to all these network slices. Based on the request from the Application, the UE601sends, to the S-AMF604, a PDU Session Establishment Request message or Service Request message on the network slice S-NSSAI-3, for example. The UE601may also include the Application identity e.g., App ID in the PDU Session Establishment Request or Service Request message as the App ID may assist the S-AMF604or the SMF604to find the alternative network slice(s) for network slice S-NSSAI-3 from the NSSP/URSP rules for the UE601.

2) Continue with the PDU Session Establishment procedure or the Service Request procedure on the S-NSSAI-3 as per 3GPP TS 23.502.

3) AMF/SMF association with the PCF606(NSSP/URSP)—The S-AMF604or the SMF604may interact with the PCF606during the association with PCF in order to discover the compatible network slices for the network slice S-NSSAI-3 on which a PDU Session is being established.

The S-AMF604, during the UE Policy Association Establishment with the PCF606, may either:a) request the URSP or NSSP rules for the UE601from the PCF606via the Npcf_UEPolicy_Contol_Create Request message. In this case, the S-AMF604would include a new parameter (e.g., URSP flag, NSSP flag or any other name for a parameter with the purpose of requesting URSP or NSSP information from the PCF606) in the Npcf_UEPolicy_Contol_Create Request message; ORb) request the list of the network slices that are compatible with the current network slice S-NSSAI-3 via the Npcf_UEPolicy_Contol_Create Request message. In this case, the S-AMF604may include, in the Npcf_UEPolicy_Contol_Create Request message, the identity of the Application (e.g., App ID) that has triggered the PDU Session Establishment, the network slice identity (e.g., S-NSSAI-3) on which the PDU Session is being established or the DNN ID in order to facilitate the PCF606in finding the network slices compatible to the network slice S-NSSAI-3.

The PCF606may provide the requested information (i.e., the URSP or NSSP rules for the UE601) or the list of the network slices compatible with the S-NSSAI-3 with the Npcf_UEPolict_Control_Create Response message.

It should be noted that the S-AMF604may make use of any other existing procedure or service provided by the PCF606in order to retrieve the URSP or NSSP related information from the PCF606.

The SMF604, during the SM Policy Association Establishment or SM Policy Association Modification with the PCF606, may either:a) request the URSP or NSSP rules for the UE601from the PCF606via the Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF604would include a new parameter (e.g., URSP flag or NSSP flag or any other name for a parameter with the purpose of requesting URSP or NSSP information from the PCF606) in the Npcf_SMPolicy_Contol_Create Request message; ORb) request the list of the network slices that are compatible with the current network slice S-NSSAI-3 via the Npcf_SMPolicy_Contol_Create Request message. In this case, the SMF604may include, in the Npcf_SMPolicy_Contol_Create Request message, the identity of the Application (e.g., App ID) that has triggered the PDU Session Establishment, the network slice identity (e.g., S-NSSAI-3) on which the PDU Session is being established or the DNN ID in order to facilitate the PCF606in finding the network slices compatible to the network slice S-NSSAI-3.

The PCF606may provide the requested information (i.e., the URSP or NSSP rules for the UE601) or the list of the network slices compatible with the S-NSSAI-3 with the Npcf_SMPolicy_Control_Create Response message.

It should be noted that the SMF604may make use of any other existing procedure or service provided by the PCF606in order to retrieve the URSP or NSSP related information from the PCF606.

4) N2 message (S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, S-NSSAI-2)—At the end of the PDU Session Establishment procedure on the network slice S-NSSAI-3, the S-AMF604sends, to the S-RAN node602, the N2 message (or in any other message on the N2 interface between the S-AMF604and the S-RAN node602), including a parameter for the current network slice on which the PDU Session was established (e.g. S-NSSAI-3), and also including the alternative network slice(s) retrieved from the PCF606directly or first retrieving the URSP or NSSP rules for the UE601as described in step3(for example S-NSSAI-1 and S-NSSAI-2) within a new ‘alternative S-NSSAI’ parameter.

The new parameter may be structured with priority order or preference order among the alternative S-NSSAI(s). This new parameter in the N2 message may be called ‘alternative S-NSSAI’, ‘alternative network slice’, ‘backup network slice’, ‘backup S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) that the service requiring Application in the UE601can work with. The alternative network slice can also be the default allowed S-NSSAI in the S-AMF604or UDM/UDR607, if available.

When the S-AMF604sends the N2 message including alternative S-NSSAI(s) to the S-RAN node602, the S-AMF604may confirm that the SMF(s)604associated to the PDU session(s) are accessible from any alternative S-NSSAIs.

5) At some stage a handover is required. There is no target cell supporting the S-NSSAI-3 on which the UE601has an active PDU Session. However, there is a target cell supporting an alternative network slice, e.g., alternative S-NSSAI=S-NSSAI-1.

6) Handover to a target cell supporting the alternative network slice S-NSSAI-1. The S-RAN node602selects a target cell that supports one of the alternative network slices, e.g., alternative network slice S-NSSAI-1. If only the alternative network slice S-NSSAI-1 or the alternative network slice S-NSSAI-2 is available at any of the target cells, the priority among the alternative network slices should be considered at the S-RAN node602when selecting a target cell. If both alternative network slice S-NSSAI-1 and the alternative network slice S-NSSAI-2 are available at a target cell, the S-RAN node602selects the alternative network slice S-NSSAI-1 taking the priority into account. During the N2 handover the S-AMF604transfers the original S-NSSAI-3 and the alternative S-NSSAI-1 and S-NSSAI-2 to the T-AMF605.

7) Registration with the T-AMF605as per 3GPP TS 23.502. The registration procedure does not re-confirm the S-NSSAI-1 as an allowed network slice.8) PDU Session Modification on the alternative network slice S-NSSAI-2 or default S-NSSAI as per 3GPP TS 23.502—As the alternative network slice S-NSSAI-1 is not allowed network slice in the new registration area, the T-AMF605triggers a PDU Session Modification procedure on another alternative network slice (e.g., S-NSSAI-2) or on a default network slice. As the S-NSSAI will be swapped during this procedure, the SMF605may contact to the PCF606and/or the CHF to issue separate CDRs, one with the original S-NSSAI-3 and the other one with the alternative network slice S-NSSAI-2 or the default network slice.

9) During the PDU Session Modification procedure, when the T-AMF605sends the N2 message to the T-RAN node603, the N2 message contains the following parameters.

N2 message (S-NSSAI-2/default S-NSSAI, original S-NSSAI=S-NSSAI-3, alternative S-NSSAI=S-NSSAI-1, NAS message (PDU Session ID, N1 SM container (PDU Session Modification command (New S-NSSAI=S-NSSAI-1))))—During the PDU Session Modification on the network slice S-NSSAI-2/default S-NSSAI, the T-AMF605may send the N2 message to the T-RAN node603. Along with the network slice on which the PDU Session(s) were established, the T-AMF605also includes in the N2 message (or in any other message on the N2 interface between the AMF605and the RAN node) to the T-RAN node two new parameters:Original S-NSSAI—The T-AMF605places in this parameter the initial network slice from which the PDU Session was transferred to one of the alternative network slices in the last handover, e.g., S-NSSAI-3. This new parameter may be called ‘original S-NSSAI’, ‘original network slice’, ‘initial network slice’, ‘initial S-NSSAI’, ‘UE requested S-NSSAI’ or any other name or notation for a parameter with the purpose to carry information for the network slice(s) on which the PDU Session was established at the PDU Session Establishment procedure as described in 3GPP TS 23.502.Alternative S-NSSAI—The T-AMF605places in this parameter one of the remaining alternative network slices, e.g., in this case S-NSSAI-1 that was rejected at the registration with the T-AMF605can still play the role of the alternative S-NSSAI. The alternative S-NSSAI may also indicate alternative network slices that will be used for the PDU Session after the successful Handover procedure.

10) During the PDU Session Modification procedure, when the SMF605sends the PDU Session Modification command to the UE601via the T-AMF605(within the N2 message on the T-AMF605to the T-RAN node interface) and the T-RAN node603, the PDU Session Modification command includes a New S-NSSAI parameter (e.g., S-NSSAI-2) in order to let the UE601know that the S-NSSAI (e.g. S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g. S-NSSAI-2). The T-RAN node603sends the PDU Session Modification command, received from the SMF605via the T-AMF605(within the N2 message on the T-AMF605to the T-RAN node interface), to the UE601. With this information, the UE601updates the network slice state in the UE601.

In one example, instead of sending the PDU Session Modification message to the UE601, the T-AMF605may send the UE Configuration Update message to the UE601via the T-RAN node603to let the UE601know that the S-NSSAI (e.g., S-NSSAI-3) being used for the PDU Session has been replaced with the New S-NSSAI (e.g., S-NSSAI-2).

11) At some stage later again a handover is required. When selecting a target cell and there are multiple qualifying cells, the T-RAN node603may select the target cell in the following order of preference:The ‘original S-NSSAI’—the T-RAN node603may give preference to the original network slice first (e.g., S-NSSAI-3) in selecting a target cell. This would allow for the PDU Session to be transferred back to the network slice it has been established on at the very beginning as this network slice may be the most suitable network slice for that PDU Session(s);The current network slice-if no target cell supports the original network slice (e.g., S-NSSAI-3), then the T-RAN node603may prefer to select a target cell supporting the current network slice on which the PDU Session is currently active, e.g., NSSAI-2/default S-NSSAI.The ‘alternative S-NSSAI’-if there is no target cell supporting the original network slice nor the current network slice, then the T-RAN node603may prefer a target cell supporting the alternative network slice if available, e.g., S-NSSAI-1.

It should be noted that RAN node (both, S-RAN and T-RAN) may apply an alternative order(s) in selecting the target cell, for example first giving priority to a target cell supporting the current network slice with active PDU Session on it (e.g., S-NSSAI-2) and then the original S-NSSAI (e.g., S-NSSAI-3) if available and last the alternative S-NSSAI (e.g., S-NSSAI-1), if available. The RAN node may apply a preference in any other order, e.g., an operator defined or configured order of preference between the original network slice, the current network slice and the alternative network slice.

Beneficially, the above described aspects include, although they are not limited to, one or more of the following functionalities:A new ‘alternative network slice’ parameter in the PDU Session Establishment Request and Service Request messages from the UE.A new ‘alternative network slice’ and ‘original network slice’ parameters in the N2 message from the AMF to the RAN node.The ‘alternative network slice’ and the ‘original network slice’ parameters transfer between source and target AMFs in the N2 handover.NSSP (Network Slice Selection Policy) or alternative network slices retrieval from the PCF by the AMF/SMF.

In order to provide these functionalities, the above aspects describe exemplary methods comprising (at least some of) the following steps:Service continuity improvement via PDU Session transfer/mapping across network slices in a handover based on the ‘alternative network slice’ provided by the UE.Service continuity improvement via PDU Session transfer/mapping across network slices in a handover based on the ‘alternative network slice’ provided by the network (e.g., PCF).Service continuity improvement via PDU Session transfer/mapping across network slices in a handover based on the ‘original network slice’ maintained by the AMF.

The present disclosure proposes methods for service continuity for mobile terminals in connected mode. These methods allow for PDU Session transfer to an alternative network slice when the current network slice with PDU Session on it is not available in the target cell after a handover. Thus, the service continuity is maintained by PDU Sessions transfer on alternative network slices.

(System Overview)

FIG.8schematically illustrates a mobile (cellular or wireless) telecommunication system1to which the above aspects are applicable.

In this network, users of mobile devices3(UEs) can communicate with each other and other users via respective base stations5and a core network7using an appropriate 3GPP radio access technology (RAT), for example, an E-UTRA and/or 5G RAT. It will be appreciated that a number of base stations5form a (radio) access network or (R)AN. As those skilled in the art will appreciate, whilst one mobile device3and one base station5(RAN) are shown inFIG.8for illustration purposes, the system, when implemented, will typically include other base stations and mobile devices (UEs).

Each base station5controls one or more associated cells (either directly or via other nodes such as home base stations, relays, remote radio heads, distributed units, and/or the like). A base station5that supports E-UTRA protocols to the mobile devices3may be referred to as an ‘ng-eNB’ and a base station5that supports Next Generation protocols to the mobile devices3may be referred to as a ‘gNB’. It will be appreciated that some base stations5may be configured to support both 4G and 5G, and/or any other 3GPP or non-3GPP communication protocols.

The mobile device3and its serving base station5are connected via an appropriate air interface (for example the so-called ‘Uu’ interface and/or the like). Neighbouring base stations5are connected to each other via an appropriate base station to base station interface (such as the so-called ‘X2’ interface, ‘Xn’ interface and/or the like). The base station5/access network is also connected to the core network nodes via an appropriate interface (such as the so-called ‘NG-U’ interface (for user-plane), the so-called ‘NG-C’ interface (for control-plane), and/or the like).

The core network7typically includes logical nodes (or ‘functions’) for supporting communication in the telecommunication system1. Typically, for example, the core network7of a ‘Next Generation’/5G system will include, amongst other functions, control plane functions (CPFs) and user plane functions (UPFs). It will be appreciated that the core network7may also include, amongst others: an Access and Mobility Management Function (AMF)10, a Session Management Function (SMF)11, a Unified Data Management (UDM)/Unified Data Repository (UDR) function12, and a Policy Control Function (PCF)13. Although not shown inFIG.8, the core network7may also be coupled to at least one application function (AF)/application server (AS), and/or the like. From the core network7, connection to an external IP network/data network20(such as the Internet) is also provided.

The components of this system1are configured to perform one or more of the above-described aspects.

(User Equipment (UE))

FIG.9is a block diagram illustrating the main components of the UE (mobile device3) shown inFIG.8. As shown, the UE includes a transceiver circuit31which is operable to transmit signals to and to receive signals from the connected node(s) via one or more antenna33. Although not necessarily shown inFIG.9, the UE will of course have all the usual functionality of a conventional mobile device (such as a user interface35) and this may be provided by any one or any combination of hardware, software and firmware, as appropriate. A controller37controls the operation of the UE in accordance with software stored in a memory39. The software may be pre-installed in the memory39and/or may be downloaded via the telecommunication system1or from a removable data storage device (RMD), for example. The software includes, among other things, an operating system41and a communications control module43. The communications control module43is responsible for handling (generating/sending/receiving) signalling messages and uplink/downlink data packets between the UE3and other nodes, including (R)AN nodes5, application functions, and core network nodes. Such signaling includes appropriately formatted requests and responses relating to management of network slices and handover.

((R)AN Node)

FIG.10is a block diagram illustrating the main components of an exemplary (R)AN node5(base station) shown inFIG.8. As shown, the (R)AN node5includes a transceiver circuit51which is operable to transmit signals to and to receive signals from connected UE(s)3via one or more antenna53and to transmit signals to and to receive signals from other network nodes (either directly or indirectly) via a network interface55. The network interface55typically includes an appropriate base station-base station interface (such as X2/Xn) and an appropriate base station-core network interface (such as NG-U/NG-C). A controller57controls the operation of the (R)AN node5in accordance with software stored in a memory59. The software may be pre-installed in the memory59and/or may be downloaded via the telecommunication system1or from a removable data storage device (RMD), for example. The software includes, among other things, an operating system61and a communications control module63. The communications control module63is responsible for handling (generating/sending/receiving) signalling between the (R)AN node5and other nodes, such as the UE3, and the core network nodes. Such signaling includes appropriately formatted requests and responses relating to management of network slices and handover.

(Core Network Node)

FIG.11is a block diagram illustrating the main components of a generic core network node (or function) shown inFIG.8, for example, the AMF10, the SMF11, the UDM/UDR12, and the PCF13. As shown, the core network node includes a transceiver circuit71which is operable to transmit signals to and to receive signals from other nodes (including the UE3and the (R)AN node5) via a network interface75. A controller77controls the operation of the core network node in accordance with software stored in a memory79. The software may be pre-installed in the memory79and/or may be downloaded via the telecommunication system1or from a removable data storage device (RMD), for example. The software includes, among other things, an operating system81and at least a communications control module83. The communications control module83is responsible for handling (generating/sending/receiving) signaling between the core network node and other nodes, such as the UE3, (R)AN node5, and other core network nodes. Such signaling includes appropriately formatted requests and responses relating to management of network slices and handover.

(Modifications and Alternatives)

Detailed aspects have been described above. As those skilled in the art will appreciate, a number of modifications and alternatives can be made to the above aspects whilst still benefiting from the inventions embodied therein. By way of illustration only a number of these alternatives and modifications will now be described.

In the above description, the UE, the (R)AN node, and the core network node are described for ease of understanding as having a number of discrete modules (such as the communication control modules). Whilst these modules may be provided in this way for certain applications, for example where an existing system has been modified to implement the above aspects, in other applications, for example in systems designed with the inventive features in mind from the outset, these modules may be built into the overall operating system or code and so these modules may not be discernible as discrete entities. These modules may also be implemented in software, hardware, firmware or a mix of these.

Each controller may comprise any suitable form of processing circuitry including (but not limited to), for example: one or more hardware implemented computer processors; microprocessors: central processing units (CPUs); arithmetic logic units (ALUs); input/output (IO) circuits; internal memories/caches (program and/or data); processing registers; communication buses (e.g. control, data and/or address buses); direct memory access (DMA) functions; hardware or software implemented counters, pointers and/or timers; and/or the like.

The memories shown above may be formed by a volatile memory or a nonvolatile memory, however, the memories may be formed by a combination of a volatile memory and a nonvolatile memory.

In the above aspects, a number of software modules were described. As those skilled in the art will appreciate, the software modules may be provided in compiled or un-compiled form and may be supplied to the UE, the (R)AN node, and the core network node as a signal over a computer network, or on a recording medium. Further, the functionality performed by part or all of this software may be performed using one or more dedicated hardware circuits. However, the use of software modules is preferred as it facilitates the updating of the UE, the (R)AN node, and the core network node in order to update their functionalities.

The above aspects are also applicable to ‘non-mobile’ or generally stationary user equipment.

Various other modifications will be apparent to those skilled in the art and will not be described in further detail here.

Part of or all the foregoing aspects can be described as in the following appendixes, but the present disclosure is not limited thereto.

(Supplementary Note 1)

An access network node, comprising:means for receiving, from a network function node for mobility management, at least one first network slice information, each of which is different from a second network slice information being used for a Protocol Data Unit, PDU, session with a user equipment, UE; andmeans for performing a redirection procedure for the UE from a first cell to a second cell which supports one of the at least one first network slice information in a case where the second network slice information is not available in the first cell.
(Supplementary Note 2)

The access network node according to Supplementary Note 1, wherein the one of the at least one first network slice information is allowed after a registration procedure of the UE.

(Supplementary Note 3)

The access network node according to Supplementary Note 1 or 2, wherein the one of the at least one first network slice information is determined based on a priority among the at least one first network slice.

(Supplementary Note 4)

The access network node according to any one of Supplementary Notes 1 to 3, whereinthe means for performing is configured to perform the redirection procedure for the UE from the first cell to the second cell during the handover from the access network node serving the first cell to another access network node serving the second cell.
(Supplementary Note 5)

The access network node according to any one of Supplementary Notes 1 to 4, whereinthe at least one network slice information and the second network slice information are transmitted by a PDU session establishment request or a service request message, from the UE to the network function node for mobility management.
(Supplementary Note 6)

The access network node according to any one of Supplementary Notes 1 to 4, whereinthe at least one network slice information is selected, by the network function node for mobility management, by retrieving from a network function node for policy control using an application identity, andthe application identity is transmitted by a PDU session establishment request or a service request message, from the UE to the network function node for mobility management.
(Supplementary Note 7)

The access network node according to any one of Supplementary Notes 1 to 5, whereinre-establishment of the PDU session from a second network slice indicated by the second network slice information to a first network slice indicated by the one of the at least one first network slice information is performed after the redirection procedure.
(Supplementary Note 8)

A user equipment, UE, comprising:means for transmitting, to a network function node for mobility management via an access network node, at least one network slice information and second network slice information in a Protocol Data Unit, PDU, session establishment request or a service request message, whereinthe second network slice information is used for a PDU session with the network function node for mobility management,each of the at least one first network slice information is different from the second network slice information, anda redirection procedure for the UE from a first cell served by the access network node to a second cell which supports one of the at least one first network slice information is performed in a case where the second network slice information is not available in the first cell.
(Supplementary Note 9)

A user equipment, UE, comprising:means for transmitting, to a network function node for mobility management via an access network node, an application identity and second network slice information in a Protocol Data Unit, PDU, session establishment request or a service request message, whereinthe second network slice information is used for a PDU session with the network function node for mobility management,the application identity is used by the network function node for mobility management for retrieving at least one first network slice information, each of which is different from the second network slice information, anda redirection procedure for the UE from a first cell served by the access network node to a second cell which supports one of the at least one first network slice information is performed in a case where the second network slice information is not available in the first cell.
(Supplementary Note 10)

A network function node for mobility management, comprising:means for sending, to an access network node, at least one first network slice information, each of which is different from a second network slice information being used for a PDU session with a user equipment, UE, whereinthe at least one first network slice information is used, by the access network node, for performing a redirection procedure for the UE from a first cell to a second cell which supports one of the at least one first network slice information in a case where the second network slice information is not available in the first cell.
(Supplementary Note 11)

A control method for an access network node, comprising:receiving, from a network function node for mobility management, at least one first network slice information, each of which is different from a second network slice information being used for a Protocol Data Unit, PDU, session with a user equipment, UE; andperforming a redirection procedure for the UE from a first cell to a second cell which supports one of the at least one first network slice information in a case where the second network slice information is not available in the first cell.
(Supplementary Note 12)

The control method according to Supplementary Note 11, wherein the one of the at least one first network slice information is allowed after a registration procedure of the UE.

(Supplementary Note 13)

The control method according to Supplementary Note 11 or 12, wherein the one of the at least one first network slice information is determined based on a priority among the at least one first network slice.

(Supplementary Note 14)

The control method according to any one of Supplementary Notes 11 to 13, whereinthe performing includes performing the redirection procedure for the UE from the first cell to the second cell during the handover from the access network node serving the first cell to another access network node serving the second cell.
(Supplementary Note 15)

The control method according to any one of Supplementary Notes 11 to 14, whereinthe at least one network slice information and the second network slice information are transmitted by a PDU session establishment request or a service request message, from the UE to the network function node for mobility management.
(Supplementary Note 16)

The control method according to any one of Supplementary Notes 11 to 14, whereinthe at least one network slice information is selected, by the network function node for mobility management, by retrieving from a network function node for policy control using an application identity, andthe application identity is transmitted by a PDU session establishment request or a service request message, from the UE to the network function node for mobility management.
(Supplementary Note 17)

The control method according to any one of Supplementary Notes 11 to 15, whereinre-establishment of the PDU session from a second network slice indicated by the second network slice information to a first network slice indicated by the one of the at least one first network slice information is performed after the redirection procedure.
(Supplementary Note 18)

A control method for a user equipment, UE, comprising:transmitting, to a network function node for mobility management via an access network node, at least one network slice information and second network slice information in a Protocol Data Unit, PDU, session establishment request or a service request message, whereinthe second network slice information is used for a PDU session with the network function node for mobility management,each of the at least one first network slice information is different from the second network slice information, anda redirection procedure for the UE from a first cell served by the access network node to a second cell which supports one of the at least one first network slice information is performed in a case where the second network slice information is not available in the first cell.
(Supplementary Note 19)

A control method for a user equipment, UE, comprising:transmitting, to a network function node for mobility management via an access network node, an application identity and second network slice information in a Protocol Data Unit, PDU, session establishment request or a service request message, whereinthe second network slice information is used for a PDU session with the network function node for mobility management,the application identity is used by the network function node for mobility management for retrieving at least one first network slice information, each of which is different from the second network slice information, anda redirection procedure for the UE from a first cell served by the access network node to a second cell which supports one of the at least one first network slice information is performed in a case where the second network slice information is not available in the first cell.
(Supplementary Note 20)

A control method for a network function node for mobility management, comprising:sending, to an access network node, at least one first network slice information, each of which is different from a second network slice information being used for a PDU session with a user equipment, UE, whereinthe at least one first network slice information is used, by the access network node, for performing a redirection procedure for the UE from a first cell to a second cell which supports one of the at least one first network slice information in a case where the second network slice information is not available in the first cell.

It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present disclosure as shown in the specific aspects without departing from the spirit or scope of this disclosure as broadly described. The present aspects are, therefore, to be considered in all respects to be illustrative and not restrictive.

This application is based upon and claims the benefit of priority from European patent application No. EP20189550.5, filed on Aug. 5, 2020, the disclosures of which are incorporated herein in its entirety by reference.

REFERENCE SIGNS LIST

101UE102S-RAN node103T-RAN node104AMF/SMF105UDM/UDR201UE202S-RAN node203T-RAN node204S-AMF205T-AMF206UDM/UDR301UE302S-RAN node303T-RAN node304S-AMF305T-AMF306UDM/UDR401UE402S-RAN node403T-RAN node404AMF/SMF405PCF406UDM/UDR501UE502S-RAN node503T-RAN node504S-AMF/SMF505T-AMF/SMF506PCF507UDM/UDR601UE602S-RAN node603T-RAN node604S-AMF/SMF605T-AMF/SMF606PCF607UDM/UDR1telecommunication system3mobile device5base station7core network10AMF11SMF12UDM/UDR13PCF20external IP network/data network31transceiver circuit33antenna35user interface37controller39memory41operating system43communications control module51transceiver circuit53antenna55network interface57controller59memory61operating system63communications control module71transceiver circuit75network interface77controller79memory81operating system83communications control module91access network node911receiving unit912performing unit93user equipment931transmitting unit95network function node951sending unit