WO2024166063A2 - Mobility across limited slice area of service during intra-gnb and inter-gnb handovers - Google Patents

Abstract

A method performed by an apparatus for a base station is provided. The method comprises, after determining that a user equipment, UE, is leaving an area of service, AoS, of a network slice, releasing resources of a protocol data unit, PDU, session established for the network slice. The method further comprises storing a PDU session context for said PDU session, and notifying a core network that the network slice is not available or that the UE is outside the AoS of the network slice.

Description

MOBILITY ACROSS LIMITED SLICE AREA OF SERVICE DURING INTRA- GNB AND INTER-GNB HANDOVERS

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This patent application claims the benefit of priority of United States Provisional Patent Application No. 63/ 484,470 filed February 10, 2023, which is hereby incorporated by reference as if reproduced in its entirety.

TECHNICAL FIELD

[0002] The subject disclosure generally relates to wireless telecommunication networks and more particularly, to operating user equipment and network devices in a wireless telecommunications network.

BACKGROUND

[0003] Wireless telecommunication networks are under constant development. There is a constant need for higher data rates and high quality of service. Reliability requirements are constantly rising and ways and means to ensure reliable connections and data traffic while keeping transmission delays minimal are constantly under development.

[0004] Wireless telecommunication networks provide services to customers. For example, in 5G wireless telecommunication network, network slicing is a key feature which provide network slices for different services to customer. Network slicing enables an operator of a wireless telecommunication network to offer connectivity, quality of service and data processing solutions tailored to specific customers' requirements. A network slice is a logical end-to-end virtual network that can be dynamically created and that provides specific capabilities and characteristics. Multiple network slices may be created on top of a common shared physical network infrastructure to provide services that may have different requirements on latency, reliability, throughput and mobility.

SUMMARY

[0005] According to a first aspect, a method performed at a base station is provided. The method comprises, after determining that a user equipment, UE, is leaving an area of service, AoS, of a network slice: releasing resources of a protocol data unit, PDU, session established for the network slice; storing a PDU session context for said PDU session; and notifying a core network that the network slice is not available or that the UE is outside the AoS of the network slice.

[0006] For example, the UE may be in an RC connected state. In this case, the base station, e.g. the gNB, knows at any point in time in which cell is the UE, and whether it is inside or outside AoS. [0007] In some examples of the first aspect, the AoS comprises one or more cells in which the network slice is available, and the determining comprises determining that the UE is being subject to hand over from a first cell in which a network slice is available to a second cell in which the network slice is not available.

[0008] For example, the method may be for operating mobility of a UE leaving an AoS of a network slice. Leaving the AoS may mean that the UE is being subject to hand over from a cell inside the AoS into a cell outside the AoS.

[0009] In some examples of the first aspect, both the first cell and the second cell are served by the base station.

[0010] For example, the UE may leave the AoS of the network slice during an intra-gNB handover.

[0011] In some examples of the first aspect, the method further comprises setting up resources for a PDU session based on the stored PDU session context after determining that the UE has re-entered the AoS of the network slice; and notifying the core network of the availability of the network slice or that the UE has re-entered the AoS of the network slice.

[0012] For example, the method may be for operating mobility of a UE re-entering the AoS of the network slice.

[0013] In some examples of the first aspect, the determining comprises determining that the UE is being subject to hand over from a second cell in which a network slice is not available to a third cell in which the network slice is available.

[0014] In some examples of the first aspect, setting up resources of a PDU session comprises setting up Data Radio Bearers (DRBs) of the UE for the PDU session.

[0015] In some examples of the first aspect, setting up the resources for the PDU session comprises sending a Radio Resource Control, RRC, Reconfiguration message to the UE, the RRC Reconfiguration message comprising information which causes the UE to set up the DRBs of the UE for PDU session.

[0016] In some examples of the first aspect, the notifying comprises sending a Next Generation, NG, Application Protocol, NGAP, UE associated message to the core network, the message comprising an indication that the network slice is not available or that the UE is outside the AoS of the network slice or that the network slice is available or that the UE is inside the AoS of the network slice.

[0017] In some examples of the first aspect, the NGAP UE associated message is the NGAP PDU Session Notify message.

[0018] In some examples of the first aspect, the releasing the resources of the PDU session comprises sending a Radio Resource Control, RRC, reconfiguration message to the UE, the RRC configuration message comprising information which causes the UE to release resources of the PDU session. [0019] In some examples of the first aspect, the first cell is served by a first base station and the second cell is served by a second base station.

[0020] For example, the UE may leave the AoS of the network slice during an inter-gNB handover.

[0021] In some examples of the first aspect, the method further comprises transmitting, to the second base station, a handover, HO, request, the HO request comprising the PDU session context for the PDU session with the resources of the PDU session; and receiving, from the second base station, a HO request acknowledgement comprising an indication to be forwarded to the UE and which causes the UE to release resources of the PDU session.

[0022] In some examples of the first aspect, the method further comprises transmitting, from the base station to the second base station, a HO request comprising the PDU session context for the PDU session without the resources of the PDU session; and receiving, from the second base station, a HO request acknowledgement comprising an indication to be forwarded to the UE and which causes the UE to set up resources for the PDU session. .

[0023] In some examples of the first aspect, the HO request further comprises an indication that the PDU session had no resources established in at the first base station.

[0024] According to a second aspect, a method performed at a core network is provided. The method comprises determining that a protocol data unit, PDU, session established for a network slice is setup and in active state; receiving, from a base station, a message comprising an indication that the network slice is not available or that a user equipment, UE, is outside the area of service, AoS, of the network slice; and in response to said indication, determining to release PDU session resources for the PDU session or locally deactivate the PDU session resources for the PDU session.

[0025] In some examples of the second aspect, said message is an NGAP UE associated message.

[0026] In some examples of the second aspect, said message is a NGAP Path Switch Request message.

[0027] In some examples of the second aspect, said message is an NGAP PDU Session Notify message.

[0028] In some examples of the second aspect, the method further comprises determining that a protocol data unit, PDU, session established for a network slice is setup and in deactivated or inactive state; receiving, from a base station, a message comprising an indication that the network slice is available or that a user equipment, UE, is inside the area of service, AoS, of the network slice; and in response to said indication, determining that the PDU session is activated or in an active state based on the indication. [0029] In some examples of the second aspect, said message is an NGAP UE associated message.

[0030] In some examples of the second aspect, said message is an NGAP PDU Session Notify message.

[0031] In some examples of the second aspect, the method further comprises receiving, at the second base station, a handover, HO, request for a UE, from the base station, the HO request comprising PDU session context for a PDU session with the resources for the PDU session; determining, at the second base station, that a target cell for the handover is outside the AoS of the network slice associated to the PDU session; refraining from setting up the resources for the PDU session at the second base station; and transmitting, from the second base station to the base station, a HO request acknowledgement comprising an indication to be forwarded to the UE which causes the UE to release resources of the PDU session.

[0032] In some examples of the second aspect, the indication comprises an RRC reconfiguration message towards the UE including a request to release a list of DRBs which corresponds to the DRBs associated to the PDU session.

[0033] In some examples of the second aspect, the method further comprises transmitting, from the second base station to a core network, an NGAP, Path Switch Request message including an indication indicating that the network slice is not available or that the UE is outside the AoS.

[0034] In some examples of the second aspect, the method further comprises receiving, at the second base station, a handover, HO, request from the base station for the UE, the HO request comprising the PDU session context for a PDU session without the resources of the PDU session; determining, at the second base station, that a target cell for the handover is inside the AoS of the network slice associated to the PDU session; setting up, at the second base station, resources for the PDU session corresponding to the received PDU session context; and transmitting, from the second base station to the base station, a HO request acknowledgement comprising an indication to be forwarded to the UE and which causes the UE to set up resources for the PDU session.

[0035] In some examples of the second aspect, the HO request acknowledgement includes setting up the DRBs at the second base station.

[0036] In some examples of the second aspect, setting up PDU session resources for the PDU session at the second base station comprises setting up the DRBs which correspond to the received PDU session context.

[0037] In some examples of the second aspect, the indication to be forwarded to the UE comprises an RRC reconfiguration message towards the UE including a request to set up a list of DRBs which corresponds to the DRBs associated to the received PDU session context. [0038] In some examples of the second aspect, the method further comprises sending an NGAP Path Switch Request message to a core network including an indication indicating that the slice is available or that the UE is inside the AoS of the network slice.

[0039] In some examples of the second aspect, the core network comprises at least one of an Access Management Function, AMF, and a Session Management Function, SMF.

[0040] In some examples of the second aspect, said releasing the resources of the PDU session includes releasing of Data Radio Bearers, DRBs.

[0041] In some examples of the second aspect, the PDU session context comprises one or more quality-of-service (QoS) profile(s) for one or more QoS Flows for the PDU session.

[0042] In some examples of the second aspect, the network slice is available in a cell means that the base station has configured more than zero resources for the network slice in the cell and the cell belongs to a tracking area where the network slice is supported.

[0043] In some examples of the second aspect, the UE is in RRC_CONNECTED state in the base station.

[0044] According to a third aspect, an apparatus for a base station is provided. The apparatus comprises a processor, and a memory. The memory comprises instructions which, when executed by the processor, cause the apparatus, after determining that a user equipment, UE, is leaving an area of service, AoS, of a network slice, to: release resources of a protocol data unit, PDU, session established for the network slice; store a PDU session context of said PDU session; and notify a core network that the network slice is not available or that the UE is outside the AoS of the network slice.

[0045] According to a fourth aspect, a core network is provided. The core network comprises a processor, and a memory. The memory comprises instructions which, when executed by the processor, cause the core network to: determine that a protocol data unit, PDU, session established for a network slice is setup and in active state; receive, from a base station, a message comprising an indication that the network slice is not available or that a user equipment, UE, is outside the area of service, AoS, of the network slice; and in response to said indication, determine to release PDU session resources for the PDU session or to locally deactivate the PDU session resources for the PDU session.

[0046] The above-noted aspects and features may be implemented in systems, apparatuses, methods, articles and/or non-transitory computer-readable media depending on the desired configuration. The subject disclosure may be implemented in and/or used with a number of different types of devices, including but not limited to cellular phones, tablet computers, wearable computing devices, portable media players, and any of various other computing devices.

[0047] This summary is intended to provide a brief overview of some of the aspects and features according to the subject disclosure. Accordingly, it will be appreciated that the above-described features are merely examples and should not be construed to narrow the scope of the subject disclosure in any way. Other features, aspects, and advantages of the subject disclosure will become apparent from the following detailed description, drawings and claims.

LIST OF ABBREVIATIONS

[0048] In the subject disclosure, the following abbreviations are used and should be understood in accordance with the given definitions:

3GPP 3^rd Generation Partnership Project

5G 5^th Generation (Mobile Communication Network)

5GC 5G Core

5GS 5G System

AF Application Function

AMF Access and Mobility Function

AN Access Network

APN Access Point Name

AoS Area of Service

BS Base Station

CDMA Code Division Multiple Access

CN Core Network

CP Control Plane

DL Downlink

DNN Data Network Name

DRB Data Radio Bearer eNB Evolved NodeB

EPC Evolved Packet Core

EPS Evolved Packet System

ETSI European Telecommunications Standards Institute

E-UTRAN Evolved UMTS Terrestrial Radio Access gNB Next Generation Node B / 5G Base Station

HO Handover

IE Information Element

IMS IP Multimedia Subsystem

IP Internet Protocol LTE Long Term Evolution

MME Mobility Management Entity

NAS Non-Access Stratum

NR New Radio

NSSAI Network Slice Selection Assistance Information

PCF Policy Control Function

PCO Protocol Configuration Options

PDN Packet Data Network

PDP Packet Data Protocol

PDU Protocol Data Unit

PGW PDN Gateway

PGW-C PGW Control Function

PLMN Public Land Mobile Network

QoS Quality of Service

RA Registration Area

RAN Radio Access Network

RCS Rich Communication Services

RRC Radio Resource Control (Protocol)

SGW Serving Gateway

SIB System Information Block

SIM Subscriber Identity Module

SM Session Management

SMF Session Management Function

S-NSSAI Single NSSAI

TA Tracking Area

TAI Tracking Area Identifier

TS Technical Specification

UDM Unified Data Management

UE User Equipment / Mobile Terminal

UL Uplink

URLLC Ultra-Reliable Low Latency Communication

VoNR Voice over NR

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] A better understanding of the subject disclosure can be obtained when the following detailed description of various embodiments is considered in conjunction with the following drawings, in which:

[0050] FIG. 1 shows a schematic diagram of an example communication system comprising a base station and a plurality of communication devices; [0051] FIG. 2 shows a schematic diagram of an example mobile communication device;

[0052] FIG. 3 shows a schematic diagram of an example control apparatus;

[0053] FIG. 4 shows the method in its simplest embodiment;

[0054] FIG. 5 shows an embodiment with a UE moving outside the AoS of an intra-gNB case;

[0055] FIG. 6 illustrates an embodiment with a UE moving into the AoS of an intra-gNB case;

[0056] FIG. 7 depicts an embodiment with a UE moving outside the AoS of an inter-gNB case;

[0057] FIG. 8 shows an embodiment with a UE moving into the AoS of an inter- gNB case.

DETAILED DESCRIPTION

[0058] Before explaining the examples in detail, certain general principles of a wireless telecommunication network and mobile communication devices are briefly explained with reference to FIGS. 1 to 3 to assist in understanding the technology underlying the described examples.

[0059] In a wireless telecommunication network 100, such as that shown in FIG. 1, communication devices 102, 104, 105 (otherwise referred to as user devices or user equipments (UEs)) are provided wireless access via base stations 106, 107 (e.g., next generation NB, gNB), or a similar wireless transmitting and/or receiving node or access node and a core network 112 to a data network 113. Base stations 106, 107 may be controlled or assisted by at least one appropriate controller apparatus, so as to enable operation thereof and management of communications of the communication devices 102, 104, 105 with the base stations 106, 107. The controller apparatus may be located in a radio access network 100 and may be implemented as one central apparatus or its functionality may be distributed over several apparatuses. The controller apparatus may be part of the base station and/or provided by a separate entity such as a Radio Network Controller (RNC). In FIG. 1 control apparatus 108 and 109 are shown to control the respective base stations 106 and 107 for providing macro cells. The control apparatus of a base station can be interconnected with other control entities. The control apparatus includes at least one memory capacity and at least one processor.

[0060] In FIG. 1, base stations 106 and 107 are shown as connected to a data network 113 via a core network 112 (e.g., via a gateway or a user plane function of the core network 112).

[0061] As used herein, the term "base station" has the full breadth of its ordinary meaning, and at least includes a wireless communication station installed at a fixed location and used to communicate as part of a wireless telephone system or radio system. The communication area (or coverage area) of the base stations may be referred to as a "cell." The base stations and the mobile communication devices may be configured to communicate wireless over an air interface using any of various radio access technologies (RATs) specified in telecommunication standards described hereinbelow. As illustrated in FIG. 1, while one of the base stations may act as a "serving cell" for mobile communication devices (i.e., UEs), each mobile communication device (i.e., UE) may also be capable of receiving wireless signals (i.e., radio signals) from (and possibly within communication range of) one or more other cells (which might be provided by the base stations and/or any other base stations), which may be referred to as "neighboring cells".

[0062] The smaller base stations 116, 118 and 120 may also be connected to the core network 112, for example via a separate controller apparatus and/or via the controller apparatuses of the macro level stations. The base stations 116, 118 and 120 may provide pico or femto cells. In the example, base stations 116 and 118 are connected via a controller apparatus 111 to the core network 112 whilst base station 120 connects via the controller apparatus 108 to the core network 112. In some embodiments, the smaller base stations may not be provided. Smaller base stations 116, 118 and 120 may be part of a second radio access network. The mobile communication devices 102, 104, 105 may access the base stations of the radio access network using on various access techniques, such as code division multiple access (CDMA), or wideband CDMA (WCDMA). Other non-limiting examples comprise time division multiple access (TDMA), frequency division multiple access (FDMA) and various schemes thereof such as the interleaved frequency division multiple access (IFDMA), single carrier frequency division multiple access (SC-FDMA) and orthogonal frequency division multiple access (OFDMA), space division multiple access (SDMA) and so on. [0063] An example of an architecture of the core network 112 wireless telecommunication network is described in TS 23.501 of the 3rd Generation Partnership Project (3GPP) for new radio (NR). The core network 112 may utilize network functions virtualization (NFV) which is a concept that proposes virtualizing network functions of the core network 112 into "building blocks" or entities that may be operationally connected or linked together to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program codes using standard or general type servers instead of customized hardware or a container. A cloud computing may be utilized to provide or instantiate various VNFs. In some implementations, VNFs of a core network 112 may be distributed among a plurality of distributed computing systems, such as servers.

[0064] An example of the core network 112 is a 5G core network (5GC) which comprises various VNFs. The 5GC is connected to a communication device via a base station (e.g., base station 106, 107, 118, 116, 120). The base stations are part of a radio access network (RAN). An UPF (User Plane Function) is a VNF of the core network 112 whose role is called PSA (PDU Session Anchor) may be responsible for forwarding traffic back and forth between the data network 113 and one or more PDU sessions established between the core network 112 and the communication devices 102, 104, 105.

[0065] The UPF is controlled by an SMF (Session Management Function) that receives policies from a PCF (Policy Control Function). The SMF and the PCF are both VNFs of the core network 112. The core network 112 also other VNFs, including an AMF (Access & Mobility Function).

[0066] A communication device 200 will now be described in more detail with reference to FIG. 2 showing a schematic, partially sectioned view. Communication devices 102, 104, and 105 shown in FIG. 1 are examples of communication device 200. Communication device 200 is often referred to as user equipment (UE), user device or terminal device. An appropriate communication device 200 may be provided by any device capable of sending and receiving radio signals. Non-limiting examples comprise a mobile station (MS) or mobile device such as a mobile phone or what is known as a smart phone, a computer provided with a wireless interface card or other wireless interface facility (e.g., USB dongle), personal data assistant (PDA) or a tablet provided with wireless communication capabilities, or any combinations of these or the like. The communication device 200 may provide, for example, communication of data for carrying communications such as voice, electronic mail (e-mail), text message, multimedia and so on. Users may thus be offered and provided numerous services via their communication devices. Non-limiting examples of these services comprise two- way or multi-way calls, data communication or multimedia services or simply an access to a data communications network system, such as the Internet. Users may also be provided broadcast or multicast data. Non-limiting examples of the content comprise downloads, television and radio programs, videos, advertisements, various alerts and other information.

[0067] In an industrial application the communication device 200 may be a modem integrated into an industrial actuator (e.g., a robot arm) and/or a modem acting as an Ethernet-hub that will act as a connection point for one or several connected Ethernet devices (which connection may be wired or un wired).

[0068] The communication device 200 is typically provided with at least one processor 201, at least one memory 202 and other possible components 203 for use in software and hardware aided execution of tasks it is designed to perform, including control of access to and communications with base stations and other communication devices. The at least one processor processing, the at least one memory 202, and possible components 203 can be provided on an appropriate circuit board and/or in chipsets 204. A user may control the operation of the communication device 200 by means of a suitable user interface such as keypad 205, voice commands, touch sensitive screen or pad, combinations thereof or the like. A display 208, a speaker and a microphone can be also provided. Furthermore, the communication device 200 may comprise appropriate connectors (either wired or wireless) to other devices and/or for connecting external accessories, for example hands-free equipment, thereto.

[0069] The communication device 200 may receive radio signals over an air or radio interface 207 transmitted by base stations (e.g., base stations 106, 107, 116, 118, 120) and may transmit radio signals to base stations (e.g., base stations 106, 107, 116, 118, 120) using a transceiver apparatus 206. The transceiver apparatus 206 may be provided for example by means of a radio part and associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the communication device 200 and may comprise one or more antenna elements.

[0070] The communication device 200 may also comprises a device or alternatively be configured to communicate with one or more global navigational satellite systems (GNSS, e.g., GPS or GLONASS), one or more mobile television broadcasting standards (e.g., ATSC-M/H or DVB-H), and/or any other wireless communication protocol. [0071] Generally, the communication device 200 illustrated in FIG. 2 includes a set of components configured to perform core functions. For example, this set of components may be implemented as a system on chip (SoC), which may include portions for various purposes. Alternatively, this set of components may be implemented as separate components or groups of components for the various purposes. The set of components may be coupled (e.g., communicatively; directly or indirectly) to various other circuits of the communication device 200.

[0072] The communication device 200 may include at least one antenna in communication with a transmitter and a receiver (e.g., the transceiver apparatus 206). Alternatively, transmit and receive antennas may be separate. The at least one processor 201 may be configured to provide signals to and receive signals from the transmitter and receiver, respectively, and to control the functioning of the communication device 200. The at least one processor 201 may be configured to control the functioning of the transmitter and receiver by effecting control signaling via electrical leads to the transmitter and receiver. Likewise, the at least one processor 201 may be configured to control other components of the communication device 200 by effecting control signaling via electrical leads connecting the at least one processor 201 to the other components of the communication device 200, such as the display 208 the at least one memory 202. The at least one processor 201 may, for example, be embodied in a variety of ways including circuitry, at least one processing core, one or more microprocessors with accompanying digital signal processor(s), one or more processor(s) without an accompanying digital signal processor, one or more coprocessors, one or more multicore processors, one or more controllers, processing circuitry, one or more computers, various other processing elements including integrated circuits (for example, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), and/or the like), or some combination thereof. Accordingly, in some examples, the at least one processor 201 may comprise a plurality of processors or processing cores. [0073] The communication device 200 may be capable of operating with one or more air interface standards, communication protocols, modulation types, access types, and/or the like. Signals sent and received by the processor may include signaling information in accordance with an air interface standard of an applicable cellular system, and/or any number of different wireline or wireless networking techniques, comprising but not limited to Wi-Fi, WLAN techniques, such as Institute of Electrical and Electronics Engineers (IEEE) 802.11, 802.16, 802.3, ADSL, DOCSIS, and/or the like. In addition, these signals may include speech data, user generated data, user requested data, and/or the like.

[0074] For example, the communication device 200 and/or a cellular modem therein may be capable of operating in accordance with various protocols of fourth generation (4G) or fifth generation (5G) radio access technologies. For example, the communication device 200 may be capable of operating in accordance with 4G wireless communication protocols, such as LTE Advanced protocols, 5G, and/or the like as well as similar wireless communication protocols that may be subsequently developed. [0075] It is understood that the processor may include circuitry for implementing audio/video and logic functions of the communication device 200. For example, the processor may comprise a digital signal processor device, a microprocessor device, an analog-to-digital converter, a digital-to-analog converter, and/or the like. Control and signal processing functions of the communication device 200 may be allocated between these devices according to their respective capabilities. The processor may additionally comprise an internal voice coder (VC), an internal data modem (DM), and/or the like. Further, the processor may include functionality to operate one or more software programs, which may be stored in memory. In general, the processor and stored software instructions may be configured to cause the communication device 200 to perform actions. For example, the processor may be capable of operating a connectivity program, such as a web browser. The connectivity program may allow the communication device 200 to transmit and receive web content, such as location-based content, according to a protocol, such as wireless application protocol (WAP), hypertext transfer protocol (HTTP), and/or the like.

[0076] The communication device 200 may also comprise a user interface including, for example, an earphone or speaker, a ringer, a microphone, a display, a user input interface, and/or the like, which may be operationally coupled to the processor. The display may, as noted above, include a touch sensitive display, where a user may touch and/or gesture to make selections, enter values, and/or the like. The processor may also include user interface circuitry configured to control at least some functions of one or more elements of the user interface, such as the speaker, the ringer, the microphone, the display, and/or the like. The processor and/or user interface circuitry comprising the processor may be configured to control one or more functions of one or more elements of the user interface through computer program instructions, for example, software and/or firmware, stored on a memory accessible to the processor, for example, volatile memory, non-volatile memory, and/or the like. The communication device 200 may include a battery for powering various circuits related to the mobile terminal, for example, a circuit to provide mechanical vibration as a detectable output. The user input interface may comprise devices allowing the communication device 200 to receive data, such as a keypad (e.g., keypad 206) and/or other input devices. The keypad can also be a virtual keyboard presented on display or an externally coupled keyboard.

[0077] The communication device 200 may also include one or more devices or components for sharing and/or obtaining data. For example, the communication device 200 may include a short-range radio frequency (RF) transceiver and/or interrogator, so data may be shared with and/or obtained from electronic devices in accordance with RF techniques. The communication device 200 may include other short-range transceivers, such as an infrared (IR) transceiver, a Bluetooth™ (BT) transceiver operating using Bluetooth™ wireless technology, a wireless universal serial bus (USB) transceiver, a Bluetooth™ Low Energy transceiver, a ZigBee transceiver, an ANT transceiver, a cellular device-to-device transceiver, a wireless local area link transceiver, and/or any other short-range radio technology. The communication device 200 and more specifically, the short-range transceiver may be capable of transmitting data to and/or receiving data from electronic devices within the proximity of the apparatus, such as within 10 meters, for example. The communication device 200 including the Wi-Fi or wireless local area networking modem may also be capable of transmitting and/or receiving data from electronic devices according to various wireless networking techniques, including 6LoWpan, Wi-Fi, Wi-Fi low power, WLAN techniques such as IEEE 802.11 techniques, IEEE 802.15 techniques, IEEE 802.16 techniques, and/or the like.

[0078] The communication device 200 may comprise memory, such as one or more Subscriber Identity Modules (SIM), one or more Universal Subscriber Identity Modules (USIM), one or more removable User Identity Modules (R-UIM), one or more eUICC, one or more UICC, and/or the like, which may store information elements related to a mobile subscriber. In addition, the at least one memory 202 of the communication device 200 may include other removable and/or fixed memory. The communication device 200 may include volatile memory and/or non-volatile memory. For example, the volatile memory may include Random Access Memory (RAM) including dynamic and/or static RAM, on-chip or off-chip cache memory, and/or the like. The non-volatile memory, which may be embedded and/or removable, may include, for example, readonly memory, flash memory, magnetic storage devices, for example, hard disks, floppy disk drives, magnetic tape, optical disc drives and/or media, non-volatile random-access memory (NVRAM), and/or the like. Like volatile memory, the non-volatile memory may include a cache area for temporary storage of data. At least part of the volatile and/or non-volatile memory may be embedded in the processor. The memories may store one or more software programs, instructions, pieces of information, data, and/or the like which may be used by the apparatus for performing operations disclosed herein. [0079] The at least one memory 202 may comprise or store an identifier, such as an International Mobile Equipment Identification (IMEI) code, capable of uniquely identifying the communication device 200. The at least one memory 202 may comprise an identifier, such as an international mobile equipment identification (IMEI) code, capable of uniquely identifying the communication device 200. In the example embodiment, the processor may be configured using computer code stored at memory to cause the processor to perform operations disclosed herein.

[0080] Some of the embodiments disclosed herein may be implemented in software, hardware, application logic, or a combination of software, hardware, and application logic. The software, application logic, and/or hardware may reside on the memory, the processor, or electronic components, for example. In some example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a "computer-readable medium" may be any non-transitory media that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer or data processor circuitry, with examples depicted at FIG. 2, computer-readable medium may comprise a non-transitory computer-readable storage medium that may be any media that can contain or store the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer.

[0081] FIG. 3 shows an example embodiment of a controller apparatus 300, for example to be coupled to and/or for controlling a base station of a radio access network. Controller apparatuses 108, 109, and 111 shown in FIG. 1 are examples of the controller apparatus 300. As noted above, a base station may be an eNB, a gNB, an access node, or a radio access network node. The control apparatus 300 may be integrated with or external to a base station (e.g., base station 106, 107, 118). As noted above, each base station may comprise a separate controller apparatus 300. The controller apparatus 300 can be a radio network controller or a spectrum controller. In some embodiments, each base station may have a control apparatus 300 as well as a radio network controller. The control apparatus 300 can be arranged to control communications with communication devices (e.g., communication devices 102, 104, 105) located in a service area of the wireless telecommunication network 100. The control apparatus 300 comprises a memory 301, a processor 302 and an input/output interface 304. Via the input/output interface 304, the control apparatus 300 can be coupled to a receiver and a transmitter of a base station. The receiver and/or the transmitter of a base station may be a radio front end or a remote radio head.

[0082] The radio front end or a remote radio head of a base station comprises an antenna configured to transmit and receive radio frequency (RF) signals and a RF transceiver module, coupled with the antenna arrangement receives RF signals from antenna, converts them to baseband signals and sends them to a baseband processor. RF transceiver also converts baseband signals received from the baseband processor, converts them to RF signals, and sends the RF signals to a communication device using the antenna. Baseband processor processes the received baseband signals.

[0083] In some embodiments, the processor comprises any suitable processor includes, by way of example, a special purpose processor, a digital signal processor (DSP), a plurality of micro-processors, one or more micro-processor associated with a DSP core, a controller, a microcontroller, application specific integrated circuits (ASICs), file programmable gate array (FPGA) circuits, a tensor processing unit, a central processing unit, a graphical processing unit, integrated circuits (ICs), and/or state machines. The memory 302 includes computer program code causing the control apparatus 300 to perform processing according to the method described further below. Although only one processor 301 and one memory 302 is shown in FIG. 2, the controller apparatus may include multiple processors 301 and multiple memories 302. [0084] As mentioned, network slicing is a concept where network resources of an end-to-end connection between a communication device (e.g., 102, 104, 105) and an end point (e.g., a N6 interface between the core network 112 and the data network 113) in a wireless telecommunication network (e.g., wireless telecommunication network 100 which may be a public land mobile network or a standalone private network) are sliced. A network slice may be understood as a logical end-to-end network that can be dynamically created and/or modified by an operator of a wireless telecommunication network. The network(s) between the end devices may all be sliced from one end device to the other end device, the slices thus forming logical pipelines within the network(s). User devices may access a slice over a radio interface. As described in 3GPP TS 38.300 (e.g., version 16.8.0 Release 16, 2022-01), network slicing will be a key feature in 5G to support different services using the same underlying mobile network infrastructure.

[0085] A network slice may provide or server a particular type of service (“service type”). So far, three different network slice/service types have been standardized: eMBB (slice suitable for the handling of 5G enhanced Mobile Broadband), URLLC (slice suitable for the handling of Ultra-Reliable Low Latency Communication) and MIoT (slice suitable for the handling of massive Internet of Things). Communications Service Providers (CSPs) are able to define additional network slice/service types if needed. A given communication device may access to multiple networks slices over a same access network (over a same radio interface, for example).

[0086] Thus, network slicing enables a network operator to provide dedicated virtual networks over a common network infrastructure. The different virtual or logical networks may have different networking characteristics such as different qualities of service (QoS) in order to host services with diverse requirements based on service level agreements (SLAs) with customers. For example, the virtual networks may be customized to meet specific needs of various applications, services, devices, customers and/or network operators. Thus, network slicing enables provision of different services to communication devices (e.g., UEs). In an example, network slices may differ either in their service requirements for services like URLLC and eMBB or the tenant that provides those services.

[0087] A network slice is uniquely identified by Single-Network Slice Selection Assistance Information (S-NSSAI). Current 3GPP specifications (e.g., 3GPP TS 38.300 version 17.3.0 Release 17, 2023-01) allow a communication device (e.g., UE) to be simultaneously connected and served by at most eight network slices corresponding to eight S-NSSAIs. On other hand, each cell may support (i.e., is capable of providing) tens or even hundreds of S-NSSAIs. In current 3GPP specifications (e.g., 3GPP TS 38.423 version 17.3.0 Release 17 2023-01), a tracking area (TA) can support (i.e., is capable of handling) up to 1024 network slices.

[0088] The format of the S-NSSAI may include both Slice Service Type (SST) and Slice Differentiator (SD) fields with a total length of 32 bits or include only SST field part in which case the length of S-NSSAI is 8 bits only. Examples of the format of a S- NSSAI are described in 3GPP specifications such as 3GPP TS 23.501 or 3GPP TS 23.003. The SST field may have standardized and non-standardized values. Values 0 to 127 belong to the standardized SST range. For instance, SST value of 1 may indicate that the slice is suitable for handling of 5G eMBB, 2 for handling of URLLC, etc. SD is defined by a network operator only.

[0089] Other concepts concern defining a tracking area (TA) and a registration area (RA). The TA is a logical concept of an area where a user can move around without updating the MME and is the LTE, EPS or 5GS counterpart of the location area and routing area of GSM, WCDMA and GPRS. The TA consists of a set of cells. TAs can be grouped into lists of tracking areas (TA lists), which can be configured on the UE. For example, the network allocates a list with one or more TAs to the user. In certain operations, the UE may move freely in all TAs of the list without updating the MME. The RA is a list consisting of tracking areas (TAs), which is configured to the UE by the network. The RA are used to track the UE for paging purposes. If the UE leaves the RA, the UE will let the network know through NAS registration request (referred to as mobility registration update) such that the correct RA can be configured to the UE. [0090] In 5G wireless telecommunication networks, the RA also has the role to maintain allowed network slices (alternatively allowed NSSAI) of the communication device (e.g., UE). The allowed NSSAI is provided to the communication device (e.g., UE) by a core network (e.g., the AMF of the core network 112). Throughout the subject disclosure, an allowed S-NSSAI can refer to an S-NSSAI included in the allowed NSSAI. The communication device (e.g., UE) can request an S-NSSAI during registration (e.g., by including a request S-NSSAI in a NAS message sent by the communication device to the core network) and the core network would decide whether or not to add the request S-NSSAI to the list of allowed S-NSSAIs for the communication device (e.g., UE).

[0091] In recent developments, the 3GPP has agreed to have homogenous network slice support within a TA, as well as RA. This means that the same network slices are to be supported throughout a TA, and the allowed NSSAI is valid throughout the RA of the communication device (e.g., UE).

[0092] However, the RA may comprise multiple TAs that are not supporting all allowed network slices of a communication device (e.g., UE), allowing a more flexible registration area configuration including non-homogenous network slice support for the TAs comprising the RA.

[0093] Network slices are deployed for services over an Area of Service (AoS) which may match the existing TAs or for which the AoS can be different. Currently, the network slice availability (i.e., where the network slices are defined to be supported or provided) is designed to match deployed TA boundaries. In addition, the communication devices (e.g., UEs) and network configuration can be impacted when network slices are deployed and decommissioned over certain time interval (e.g., the Configured NSSAI can change when a network slice is no longer available or becomes available, this can affect the Allowed NSSAI and other parameters and in turn the RA may need to change, etc.).

[0094] From this arises the problem that the AoS does not necessarily map to existing TA boundaries and temporary network slices. Furthermore, when a communication device (e.g., UE) in RRC_Connected mode having a PDU session associated with a specific network slice that is active moves out of the AoS, i.e., the communication device (e.g., UE) is physically moving away from the AoS and/or TA, the PDU session is subject to be deactivated.

[0095] Deactivation of a PDU session normally means that there are no more RAN resources assigned to the PDU session and no more PDU session context in the base station (e.g., gNB). If the PDU session is deactivated in the part of the RA outside the AoS it is undefined how the PDU session can be reactivated when the UE re-enters the AoS in the RA.

[0096] Additionally, the problem becomes more complex depending on whether the border of the AoS matches the border of a base station (e.g., gNB), i.e., whether crossing a border of the AoS involves changing gNB and an inter-gNB handover is done, or crossing a border of the AoS is done within the same gNB and an intra-gNB handover is done.

[0097] The methods and apparatus described herein address the problems described above.

[0098] Reference is now made to FIG. 4, to describe a method of the present disclosure in its simplest embodiment. In FIG. 4, the UE 400 is a communication device, such as the communication device 102, 104, or 105.

[0099] The method is performed by an apparatus (e.g., controller apparatus 300) of a base station and comprises after determining that a user equipment, UE 400, is leaving an area of service, AoS 402, of a network slice, the base station releases the resources of a protocol data unit, PDU, session established for the network slice. A PDU session context is stored for said PDU session and the base station notifies a core network that the network slice is not available or that the UE 400 is outside the AoS 402 of the network slice.

[0100] The UE 400 which is connected to a cell 401 using a specific slice is moving outside the AoS 402. The UE 400 moves near the cell 404 outside the AoS 402 but still inside the TA 403, so this embodiment refers to an intra-gNB embodiment, meaning there is no handover to another gNB. When the UE 400 is leaving the AoS, the gNB releases its resources and saves a PDU session context for the return of the UE 400. Later, when the UE 400 re-enters the AoS 402 again, the PDU session context may be used to reactivate the PDU session. Leaving the AoS may mean that the UE is being subject to hand over from a cell inside the AoS into a cell outside the AoS, while entering the AoS may mean that the UE is being subject to hand over from a cell outside the AoS to a cell inside the AoS.

[0101] Through this method, some advantages arise compared to the previous stated problems. Firstly, it drastically reduces the signaling involved in this procedure for an intra-gNB handover case and even more for an inter-gNB handover case. Secondly, the UE does not need double RRC reconfiguration in inter-gNB handover case, i.e., the UE resumes the PDU session by activating the PDU session again and therefore does not need to go through the signaling steps of a full mobility registration procedure to register again the network slice. Thirdly, the method avoids the need to support in all nodes the 3GPP the location reporting procedure, together with the configuration and reporting of the Area of Interest which is part of this procedure, which introduces additional signaling and complexity. [0102] Additionally, the complexity of managing multiple simultaneous Area of Interests for multiple UEs which overlap and create lots of signaling towards AMF is less and provides means to avoid the interaction between UE-context level concepts like UE mobility reporting and PDU-session-context level concepts like activation/deactivation of PDU sessions.

[0103] With reference to FIG. 5, an embodiment of an intra-gNB handover case is shown with a UE moving outside the AoS, i.e., the handover of the UE is performed from a cell inside the AoS to a cell outside the AoS, but still in the same gNB, which will now be described in more detail.

[0104] A UE 500 is in RRC_Connected mode to a cell of a gNBl 501 inside an AoS of a network slice, e.g., network slice 1. Then, at 504, a PDU session 1 with context and corresponding resources is setup. Likewise, for the AMF 502 or SMF 503 the PDU session 1 is setup and in active state (e.g., is activated or activeO.

[0105] Next, at 506, after detecting that the UE 500 leaves the AoS of network slice 1, i.e. that the UE 500 is subject to hand over from a cell inside the AoS of network slice 1 to a cell outside the AoS of network slice 1, the gNBl 501 releases the resources of the PDU session 1 including releasing the Data Radio Bearers (DRB)s of the UE 500 by sending a RRC Reconfiguration at 507 that includes an indication that cause the UE 500 to release its DRBs), but the gNBl 501 still keeps storing the PDU session context of the PDU session 1. In this situation, the context of the PDU session (generally referred to as PDU session context) still exists and/or remains for a PDU session without PDU resources established (i.e., set up) for the PDU session.

[0106] At 508, the gNBl 501 notifies the AMF 502 of the core network (e.g., core network 112) that network slice 1 is unavailable or alternatively that the UE 500 is out of AoS of network slice 1 by sending a NG Application Protocol (NGAP) PDU session Notify message including an indication that network slice 1 is unavailable or alternatively that the UE 500 is out of AoS of network slice 1.

[0107] Finally, at 509 and 510, after receiving the new indication that the network slice 1 is unavailable or alternatively that the UE is out of AoS of network slice 1 , the AMF 502 and the SMF 503 of the core network decide either to behave as if the PDU sessions associated with network slice 1 are deactivated (e.g., buffer traffic of the PDU session 1) or to release PDU session 1. The AMF 502 and the SMF 503 may decide whether to keep or release the PDU context based on previous UE behavior, UE mobility behaviour the traffic of the gNB or else.

[0108] FIG. 6 illustrates an embodiment of an intra-gNB handover case with a UE moving into the AoS, meaning there is a handover between two cells in the same gNB, from one cell which is outside the AoS and the other cell which is inside the AoS. This embodiment assumes that a UE has already moved at least once out from this AoS, so that the following method applies accordingly. [0109] At 600, the UE 500 is outside the AoS of network slice 1 and the PDU session 1 has no resources established (i.e., set up) for PDU session 1, but gNBl 501 has however a context for PDU session 1 with a corresponding Quality-of Service (QoS) profile for the QoS flows of the PDU session 1 of the UE 500. Likewise for the AMF 502 and the SMF 503 at 601, the PDU session 1 is setup but in a deactivated state or inactive state (i.e., has been deactivated or inactivated)

[0110] At 602, after the gNBl 501 detects that re-entry of UE 500 in the AoS of network slice 1, i.e., that the UE is being subject to hand over from a cell outside the AoS of network slice 1 to a cell inside the AoS of network slice 1, the gNBl 501 sets up the resources of PDU session 1 including setting up the DRBs of gNBl 501 towards UE 500. At 603, the DRBs are setup in a RRC Reconfiguration message from the gNBl 501 to the UE 500.

[0111] Next, at 604, the gNBl 501 then sends a NGAP PDU session Notify message including the newly indication that the slice 1 is available or alternatively that the UE is now inside the AoS of slice 1.

[0112] At 605 and 606, upon receiving the new indication that the slice 1 is available or alternatively that the UE is now inside the AoS of network slice 1 , the AMF 502 and the SMF 503 behave as if the PDU sessions associated with network slice 1 are activated again (e.g., deliver traffic of the PDU session 1).

[0113] In the following embodiments, the UE is leaving and/or re-entering the AoS and involves a change of gNB i.e., during an inter-gNB handover.

[0114] FIG. 7 depicts an embodiment of an inter-gNB handover case with a UE moving outside the AoS.

[0115] At first, at 701, the UE 500 is inside an AoS of slice 1 in RRC connected mode to gNBl 501, and a PDU session 1 has context and resources setup. At 702, for the AMF 502 and SMF 503, the PDU session 1 is setup and in active state (i.e., PDU session 1 is active). The UE 500 leaves the AoS from gNBl 501 at inter-gNB handover at 703. Leaving the AoS means that the UE is being subject to hand over from gNBl to gNB2.

[0116] Now at 704, the source gNBl 501 sends a handover request to gNB2 700, as in any common handover, but including the PDU session context for the PDU session with the resources for the PDU session established at source gNBl 501, such as the DRBs for PDU session 1.

[0117] At 705, after detecting that the target cell is outside AoS of network slice 1, the target gNB2 700 decides to create and store a context for PDU session 1 based on the PDU session 1 context received from gNBl 501. The target gNB2 700 however refrains from setting up the resources of the PDU session 1 in the target gNB and also builds an RRC container containing an RRC reconfiguration message aiming at releasing the DRBs of the UE 500 corresponding to the PDU session 1. [0118] At 706 and 707, the target gNB2 700 sends the handover request acknowledge message including a command (or indication) to release of the DRBs of the UE encapsulated in a RRC reconfiguration message (transferred to the UE as an the RRC container transparently to the source gNBl 501), even though it has kept (i.e., stored) a PDU session 1 context with QoS profile for the QoS flows of the PDU session 1. The UE 500 receives the RRC reconfiguration message and releases the DRBs, then the UE 500 accesses the target cell at 708.

[0119] At 709, the target gNB2 700 sends a NGAP Path Switch Request message to complete the handover, in which the gNB2 700 includes an indication that the slice 1 is unavailable or alternatively that the UE is out of AoS of slice 1.

[0120] Finally, at 710, after receiving the new indication via the path switch request that the network slice 1 is unavailable or alternatively that the UE 500 is now outside the AoS of network slice 1 , the AMF 502 and the SMF 503 decide whether to behave as if the PDU sessions associated with network slice 1 are deactivated (or inactive) (e.g., buffer traffic of the PDU sessions) or to release the PDU sessions. The AMF 502 and the SMF 503 may decide whether to keep or release the PDU context based on the previous UE behavior, UE mobility behaviour, the traffic pattern or else.

[0121] FIG. 8 shows an embodiment of an inter-gNB handover case with a UE moving into the AoS, i.e., when entering the AoS again. In this case, the source gNB (e.g., gNBl) sends a handover request for the UE to the target gNB (e.g., gNB2) in which the selected target cell (included in the handover request message) indicates a cell inside the AoS. Moving into the AoS or entering the AoS means that the UE 500 is subject to handover from a cell outside the AoS to a cell inside the AoS. In an inter-gNB handover case, the cell outside the AoS is served by a base station, e.g., gNBl, and the cell inside the AoS is served by another base station, e.g., gNB2.

[0122] At 800, the UE is outside the AoS of network slice 1 and the gNBl 501 has kept an existing context for PDU session 1 even though all resources of PDU session 1 have been previously released. For the AMF 502 and the SMF 503 at 801, the PDU session 1 is setup and in inactive state or deactivated state (i.e., PDU session 1 is inactive or deactivated).

[0123] Now the UE 500 moves from a cell of gNBl 501 to another cell which belongs to gNB2 700 at 802, leading to a handover in an inter-gNB handover case. [0124] At 803, the gNBl 501 sends a handover request to gNB2 700 including the context of PDU session 1 without associated PDU sessions resources setup such as associated established DRBs and optionally an explicit indication to inform that the PDU session 1 had no associated resources established in source gNB 1.

[0125] At 804, after detecting that the selected target cell is now inside the AoS of network slice 1, the target gNB2 700 decides to create a context for PDU session 1 based on received PDU session context from gNB 1 500 (even though it has no resources associated with PDU session 1, e.g., no associated DRBs) and set up resources for PDU session 1 including setting up the DRBs of the target gNG2 700 towards the UE 500.

[0126] At 805 and 806, the target gNB2 700 sends the handover request acknowledge message including a command to set up the DRBs of the UE 500 decided at 804 encapsulated in an RRC reconfiguration message (transferred to the UE 500 as an RRC container transparently via the source gNBl 501). The UE 500 receives the RRC reconfiguration message and sets up the DRBs. Consequently, the UE 500 accesses the target cell, at 807, via the RRC HO complete message.

[0127] At 808, the target gNB2 700 sends a NGAP Path Switch Request message to complete the handover in which the target gNB2 700 includes an indication that the network slice 1 is available or alternatively that the UE is now inside the AoS of slice 1. [0128] Finally at 809, upon receiving the new indication via the path switch request that the network slice 1 is available or alternatively that the UE 500 is now inside the AoS of network slice 1 , the AMF 502 and the SMF 503 behave as if the PDU sessions associated with network slice 1 are activated (e.g., deliver traffic of the PDU session associated with network slice 1).

[0129] The core network 112 may be an apparatus comprising network function virtualization infrastructure for providing various network functions of the core network 112, including the AMF 502 and the SMF 503 shown in FIGs. 5-8. Alternatively, the core network 112 may comprises an apparatus implementing an AMF and an apparatus implementing the SMF that are configured to communicate with each other. An apparatus of the core network 112 may comprise one or more processors and one or more memories storing instructions, which when executed by the one or more processors cause the apparatus to perform the functionality of the AMF 502 and the SMF 503, including the operations or actions of the AMF 502 and SMF 503 described herein with respect to FIGs. 5-8.

[0130] It should be understood that the apparatuses may comprise or be coupled to other units or modules etc., such as radio parts or radio heads, used in or for transmission and/or reception. Although the apparatuses have been described as one entity, different modules and memory may be implemented in one or more physical or logical entities.

[0131] It is noted that whilst embodiments have been described in relation to ETE and 5G NR, similar principles can be applied in relation to other networks and communication systems where enforcing fast connection re-establishment is required. Therefore, although certain embodiments were described above by way of example with reference to certain example architectures for wireless networks, technologies and standards, embodiments may be applied to any other suitable forms of communication systems than those illustrated and described herein. [0132] It is also noted herein that while the above describes exemplary embodiments, there are several variations and modifications which may be made to the disclosed solution without departing from the scope of the subject disclosure.

[0133] In general, the various exemplary embodiments may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects of the subject disclosure may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device, although the subject disclosure is not limited thereto. While various aspects of the subject disclosure may be illustrated and described as block diagrams, flow charts, or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0134] Example embodiments of the subject disclosure may be implemented by computer software executable by a data processor of the mobile device, such as in the processor entity, or by hardware, or by a combination of software and hardware. Computer software or program, also called program product, including software routines, applets and/or macros, may be stored in any apparatus-readable data storage medium and they comprise program instructions to perform particular tasks. A computer program product may comprise one or more computer- executable components which, when the program is run, are configured to carry out embodiments. The one or more computer-executable components may be at least one software code or portions of it.

[0135] Example embodiments of the subject disclosure may be practiced in various components such as integrated circuit modules. The design of integrated circuits is by and large a highly automated process. Complex and powerful software tools are available for converting a logic level design into a semiconductor circuit design ready to be etched and formed on a semiconductor substrate.

[0136] The foregoing description has provided by way of non-limiting examples a full and informative description of the exemplary embodiment of the subject disclosure. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of the subject disclosure as defined in the appended claims. Indeed, there is a further embodiment comprising a combination of one or more embodiments with any of the other embodiments previously discussed.

Claims

1. A method performed by an apparatus for a base station, the method comprising: after determining that a user equipment, UE, is leaving an area of service, AoS, of a network slice: releasing resources for a protocol data unit, PDU, session established for the network slice; storing a PDU session context for said PDU session; and notifying a core network that the network slice is not available or that the UE is outside the AoS of the network slice.

2. The method of claim 1, wherein the AoS comprises one or more cells in which the network slice is available, and wherein the determining comprises determining that the UE is being subject to hand over from a first cell in which the network slice is available to a second cell in which the network slice is not available.

3. The method of claim 2, wherein both the first cell and the second cell are served by the base station.

4. The method of any of claims 1 to 3, further comprising: setting up resources for a PDU session based on the stored PDU session context after determining that the UE has re-entered the AoS of the network slice; and notifying the core network of the availability of the network slice or that the UE has re-entered the AoS of the network slice

5. The method of claim 4, wherein the determining comprises determining that the UE is being subject to hand over from a second cell in which the network slice is not available to a third cell in which the network slice is available.

6. The method of any of claims 4 or 5, wherein the setting up resources for a PDU session comprises setting up Data Radio Bearers, DRBs, of the UE for the PDU session.

7. The method of claim 6, wherein setting DRBs of the UE for the PDU session comprises sending a Radio Resource Control, RRC, Reconfiguration message to the

UE, the RRC Reconfiguration message comprising a command which causes the UE to set up the DRBs of the UE for the PDU session.

8. The method of any of the preceding claims, wherein the notifying comprises sending a Next Generation, NG, Application Protocol, NGAP, UE associated message to the core network, the message comprising an indication that the network slice is not available or that the UE is outside the AoS of the network slice or that the network slice is available or that the UE is inside the AoS of the network slice.

9. The method of claim 8 wherein the NGAP UE associated message is the NGAP PDU Session Notify message.

10. The method of any of the preceding claims, wherein the releasing the resources of the PDU session comprises sending a Radio Resource Control, RRC, reconfiguration message to the UE, the RRC configuration message comprising a command which causes the UE to release data radio bearers of the UE for the PDU session.

11. The method of claim 2, wherein the first cell is served by the base station and the second cell is served by a second base station.

12. The method of claim 11, further comprising: transmitting, to the second base station, a handover, HO, request, the HO request comprising the PDU session context for the PDU session with the resources for the PDU session; receiving, from the second base station, a HO request acknowledgement comprising a command to be forwarded to the UE and which causes the UE to release the DRBs of the UE for PDU session.

13. The method of claim 11, further comprising: transmitting, from the base station to the second base station, a HO request comprising the PDU session context for the PDU session without the resources for the PDU session; receiving, from the second base station, a HO request acknowledgement comprising a command to be forwarded to the UE and which causes the UE to set up the DRBs for the UE for PDU session.

14. The method of claim 13, wherein the HO request further comprises an indication that the PDU session had no resources established in at the first base station.

15. A method performed by a core network, the method comprising: determining that a protocol data unit, PDU, session established for a network slice is setup and in active state; receiving, from a base station, a message comprising an indication that the network slice is not available or that a user equipment, UE, is outside the area of service, AoS, of the network slice; and in response to said indication, determining to either release PDU session resources for the PDU session or locally deactivate the PDU session resources for the PDU session.

16. The method of claim 15, wherein said message is an NGAP UE associated message.

17. The method of claim 16, wherein said message is a NGAP Path Switch Request message.

18. The method of claim 16, wherein said message is an NGAP PDU Session Notify message.

19. The method of claims 15 to 18 performed at a core network, further comprising: determining that a protocol data unit, PDU, session established for a network slice is setup and in deactivated or inactive state; receiving, from a base station, a message comprising an indication that the network slice is available or that a user equipment, UE, is inside the area of service, AoS, of the network slice; and in response to said indication, determining that the PDU session is activated or in an active state based on the indication.

20. The method of claim 19, wherein said message is an NGAP UE associated message.

21. The method of claim 20, wherein said message is an NGAP PDU Session Notify message.

22. The method of claim 20, wherein said message is an NGAP Path Switch Request message.

23. A method performed at a target base station, the method comprising: receiving a handover, HO, request for a UE, from a base station, the HO request comprising PDU session context for a PDU session with the resources for the PDU session; determining that a target cell for the handover is outside the AoS of the network slice associated to the PDU session; refraining from setting up the resources for the PDU session at the second base station; transmitting, to the base station, a HO request acknowledgement comprising an indication to be forwarded to the UE which causes the UE to release resources of the PDU session.

24. The method of claim 23 wherein the indication comprises an RRC reconfiguration message towards the UE including a request to release a list of DRBs which corresponds to the DRBs associated to the PDU session.

25. The method of any of claims 23 to 24, further comprising transmitting to a core network an NGAP, Path Switch Request message including an indication indicating that the network slice is not available or that the UE is outside the AoS.

26. A method performed at a target base station, the method comprising: receiving a handover, HO, request from a base station for the UE, the HO request comprising the PDU session context for a PDU session without the resources of the PDU session. determining that a target cell for the handover is inside the AoS of the network slice associated to the PDU session, setting up resources for the PDU session corresponding to the received PDU session context, transmitting to the base station, a HO request acknowledgement comprising an indication to be forwarded to the UE and which causes the UE to set up resources for the PDU session.

27. The method of claim 26, wherein transmitting the HO request acknowledgement includes setting up the DRBs at the target base station.

28. The method of claim 26 wherein setting up PDU session resources for the PDU session comprises setting up the DRBs which correspond to the received PDU session context.

29. The method of any of claims 26 to 28, wherein the indication to be forwarded to the UE comprises an RRC reconfiguration message towards the UE including a request to set up a list of DRBs which corresponds to the DRBs associated to the received PDU session context.

30. The method of any of claims 26 to 29, further comprising sending an NGAP Path Switch Request message to a core network including an indication indicating that the slice is available or that the UE is inside the AoS of the network slice.

31. The method of any of the preceding claims, wherein the core network comprises at least one of an Access Management Function, AMF, and a Session Management Function, SMF.

32. The method of any of the preceding claims, wherein said releasing the resources of the PDU session includes releasing of Data Radio Bearers, DRBs.

33. The method of any of the preceding claims, wherein the PDU session context comprises one or more quality-of-service (QoS) profile(s) for one or more QoS flows for the PDU session.

34. The method of any previous claims, wherein the network slice is available in a cell means that the base station has configured more than zero resources for the network slice in the cell and the cell belongs to a tracking area where the network slice is supported.

35. The method of any previous claims, wherein the UE is in RRC_CONNECTED state in the base station.

36. An apparatus for a base station, the apparatus comprising a processor, and a memory comprising instructions which, when executed by the processor, cause the apparatus to perform operations, the operations comprising: after determining that a user equipment, UE, is leaving an area of service, AoS, of a network slice, to: release resources of a protocol data unit, PDU, session established for the network slice; store a PDU session context of said PDU session; and notify a core network that the network slice is not available or that the UE is outside the AoS of the network slice.

37. The apparatus of claim 36, wherein the instructions, when executed by the processor, further cause the apparatus to perform a method according to any of the claims 2 to 14 and 23 to 30.

38. A core network, comprising a processor, and a memory comprising instructions which, when executed by the processor, cause the core network at least to: determine that a protocol data unit, PDU, session established for a network slice is setup and in active state; receive, from a base station, a message comprising an indication that the network slice is not available or that a user equipment, UE, is outside the area of service, AoS, of the network slice; and in response to said indication, determine to either release PDU session resources for the PDU session or to locally deactivate the PDU session resources for the PDU session.

39. The core network of claim 38, wherein the instructions, when executed by the processor, further cause the network element to perform a method according to any of the claims 15 to 22.