Patent Publication Number: US-2022240173-A1

Title: Method and apparatus for managing network slice for terminal device

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to the technology of communication system, and in particular, to a method and an apparatus for managing network slice for terminal device. 
     BACKGROUND 
     This section introduces aspects that may facilitate better understanding of the present disclosure. Accordingly, the statements of this section are to be read in this light and are not to be understood as admissions about what is in the prior art or what is not in the prior art. 
     Network slicing concept is used to fulfill rich requirements from various use cases. Various network services with different characteristics will be exposed to third party applications/users/operators as capabilities to enable various new business models. A specific network service can be instantiated according to on demand requirements for third party users/operators and the business policy between the network service providers and the network service consumers. 
     Different policies, such as Network slicing selection Policy, NSSP may be used by a terminal device (such as a user equipment, UE) to associate the matching application with a specific network slice. As such, UE may run the application using the connection setup within the designated network slice which has pre-defined features, quality of service that can fulfill certain business model. 
     However, such NSSP is usually pre-configured in the UE, or provisioned to UE from core network e.g. via policy control function, PCF, and it is hard to be adjusted timely. For example, even when a server, or server function/application function, which provides service to the UE via the network, finds out the current network slice for the UE is not suitable for the current service obviously, there is no way to change the network slice for the UE timely. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     Certain aspects of the present disclosure and their embodiments may provide solutions to these or other challenges. There are, proposed herein, various embodiments which address one or more of the issues disclosed herein. Namely, according to embodiments of the present disclosure, a server may be able to change the network slice for a terminal device. 
     A first aspect of the present disclosure provides a method performed at a server function, comprising: determining to change a network slice for a terminal device; and transmitting, to an exposure function, a request to change the network slice for the terminal device. 
     In embodiments of the present disclosure, the terminal device is included in a group of terminal devices; the network slice is changed for each terminal device in the group of terminal devices. 
     In embodiments of the present disclosure, the request includes an identifier of the terminal device, and external information of network slice. 
     In embodiments of the present disclosure, the identifier comprises an external identifier; the external information of network slice comprises at least one of: an external slice type of a source network slice, or an external slice type of a target network slice; the external slice type includes at least one of: eMBB slice, URLLC slice, or eMTC slice; and eMBB refers to enhanced mobile broadband, URLLC refers to ultra reliable low latency communications, and eMTC refers to enhanced machine type communication. 
     In embodiments of the present disclosure, the method further comprises: transmitting, to the exposure function, a request for updating a UE route selection policy, URSP, or a network slicing selection policy, NSSP for the terminal device; UE refers to user equipment. 
     In embodiments of the present disclosure, the exposure function comprises: a network exposure function, NEF. 
     In embodiments of the present disclosure, the server function comprises: an application function, AF, or a service capability server/application server, SCS/AS. 
     In embodiments of the present disclosure, the terminal device comprises: a user equipment, UE. 
     A second aspect of the present disclosure provides a method performed at an exposure function, comprising: receiving, from a server function, a first request to change a network slice for a terminal device; transmitting, to a network function, a second request to change the network slice for the terminal device. 
     In embodiments of the present disclosure, the terminal device is included in a group of terminal devices; the network slice is changed for each terminal device in the group of terminal devices. 
     In embodiments of the present disclosure, the method further comprises: determining an authorization of the first request. 
     In embodiments of the present disclosure, the method further comprises: mapping the first request to the second request; the first request includes an external identifier of the terminal device, and external information of network slice; the external information of network slice comprises at least one of: an external slice type of a source network slice, or an external slice type of a target network slice; the external slice type includes at least one of: eMBB slice, URLLC slice, or eMTC slice; and eMBB refers to enhanced mobile broadband, URLLC refers to ultra reliable low latency communications, and eMTC refers to enhanced machine type communication; the second request includes an internal identifier of the terminal device, and internal information of network slice; and the internal information of network slice comprises at least one of: an identifier of the source network slice, an identifier of the target network slice, or a data network name, DNN. 
     In embodiments of the present disclosure, the method further comprises: obtaining context information about the terminal device; the context information comprises information about at least one of: an access and mobility management function instance, AMF instance, where the terminal device is registered with; a session management function instance, SMF instance, where the terminal device is registered with; a network slice, where the terminal device is attached to; a data network name, DNN; or subscription information. 
     In embodiments of the present disclosure, at least part of the context information is obtained from a unified data management, UDM. 
     In embodiments of the present disclosure, the subscription information is obtained from the UDM; and the subscription information comprises information about at least one of: a subscribed slice, or a subscribed data network name. 
     In embodiments of the present disclosure, the method further comprises: obtaining session information about the terminal device; the session information comprises information about at least one of: an identifier of the terminal device; a DNN; or a policy control function instance, PCF instance, that handles a data session of the terminal device. 
     In embodiments of the present disclosure, the network function comprises at least one of: a unified data management, UDM; a policy control function, PCF; a network slice selection function, NSSF; an access and mobility management function, AMF; or a session management function, SMF. 
     In embodiments of the present disclosure, the exposure function comprises: a network exposure function. 
     In embodiments of the present disclosure, the second request comprises: a reason code indicating that the notification is triggered by the server function. 
     In embodiments of the present disclosure, the reason code is optional. 
     A third aspect of the present disclosure provides a method performed at a network function, comprising: receiving, from an exposure function, a second request to change a network slice for a terminal device; transmitting, to another network function, a third request to change the network slice for the terminal device. 
     In embodiments of the present disclosure, the network function comprises: a UDM, or a PCF, or a NS SF; and the another network function comprises: an AMF, or a SMF 
     In embodiments of the present disclosure, the network function comprises: a UDM, and the another network function comprises: an AMF; the third request comprises an indication for the terminal device to perform a registration procedure. 
     In embodiments of the present disclosure, the third request comprises internal information of network slice; and the internal information of network slice comprises at least one of: an identifier of a source network slice, an identifier of a target network slice, or a data network name, DNN. 
     In embodiments of the present disclosure, the network function comprises: a UDM, and the another network function comprises: a SMF; the third request comprises an indication for the terminal device to release a session. 
     In embodiments of the present disclosure, the network function comprises: a PCF, and the another network function comprises: a SMF; the third request comprises an indication for the terminal device to release a session. 
     In embodiments of the present disclosure, the network function comprises: a NSSF, and the another network function comprises: an AMF; the third request comprises an indication for the terminal device to perform a registration procedure. 
     In embodiments of the present disclosure, the second request comprises: a reason code indicating that the notification is triggered by the server function. 
     In embodiments of the present disclosure, the third request comprises: the reason code; or the third request comprises another reason code, which is mapped from the reason code by the network function. 
     In embodiments of the present disclosure, the reason code is optional. 
     A fourth aspect of the present disclosure provides a method performed at a network function, comprising: receiving, from another network function, a third request to change a network slice for a terminal device; transmitting, to the terminal device, a notification to change the network slice for the terminal device. 
     In embodiments of the present disclosure, the method further comprises: transmitting, to the terminal device, slices information about allowed network slices, configured network slices, or target network slices. 
     In embodiments of the present disclosure, the network function comprises: an AMF; and the notification comprises an indication for the terminal device to perform a registration procedure. 
     In embodiments of the present disclosure, the network function comprises: a SMF; and the notification comprises an indication for the terminal device to release a session. 
     In embodiments of the present disclosure, the third request comprises: a reason code indicating that the notification is triggered by the server function; and the notification comprises: the reason code. 
     In embodiments of the present disclosure, the reason code is optional. 
     A fifth aspect of the present disclosure provides a method performed at a terminal device, comprising: receiving a notification to change a network slice for the terminal device; changing the network slice for the terminal device. 
     In embodiments of the present disclosure, the notification comprises a reason code indicating that the notification is triggered by a server function. 
     In embodiments of the present disclosure, the reason code is optional. 
     In embodiments of the present disclosure, the notification comprises an indication for the terminal device to perform a registration procedure; or the notification comprises an indication for the terminal device to release a session; or the notification comprises an indication for the terminal device to reestablish a session. 
     In embodiments of the present disclosure, a target network slice for performing the registration procedure, or for reestablishing the session is determined based on a local configuration, a URSP or NSSP, or the notification. 
     In embodiments of the present disclosure, the terminal device comprises a user equipment, UE. 
     A sixth aspect of the present disclosure provides an apparatus for a server function, comprising: a processor; and a memory, containing instructions executable by the processor; the apparatus for the server function is operative to implement the method according to any of embodiments of the first aspect. 
     A seventh aspect of the present disclosure provides an apparatus for an exposure function, comprising: a processor; and a memory, containing instructions executable by the processor; the apparatus for the exposure function is operative to implement the method according to any of embodiments of the second aspect. 
     An eighth aspect of the present disclosure provides an apparatus for a network function, comprising: a processor; and a memory, containing instructions executable by the processor; the apparatus for the network function is operative to implement the method according to any of embodiments of the third aspect and the fourth aspect. 
     A ninth aspect of the present disclosure provides an apparatus for a terminal device, comprising: a processor; and a memory, containing instructions executable by the processor; the apparatus for the terminal device is operative to implement the method according to any of embodiments of the fifth aspect. 
     A tenth aspect of the present disclosure provides a computer readable storage medium having a computer program stored thereon, the computer program executable by an apparatus to cause the apparatus to carry out the method according to any of embodiments of the first aspect to the fifth aspect. 
     According to embodiments of the present disclosure, when the server function finds out the current network slice situation is not suitable for the service being provided/to be provided to the terminal device, the network slice for the terminal device may be changed/updated timely. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Through the more detailed description of some embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein the same reference generally refers to the same components in the embodiments of the present disclosure. 
         FIG. 1  is an exemplary diagram showing a simplified structure of a communication network; 
         FIG. 2  is an exemplary flow chart showing a method performed at a server function for managing a network slice for a terminal device, according to embodiments of the present disclosure; 
         FIG. 3  is an exemplary flow chart showing an additional step of the method shown in  FIG. 2 , according to embodiments of the present disclosure; 
         FIG. 4  is an exemplary flow chart showing a method performed at an exposure function for managing a network slice for a terminal device, according to embodiments of the present disclosure; 
         FIG. 5  is an exemplary flow chart showing additional steps of the method shown in  FIG. 4 , according to embodiments of the present disclosure; 
         FIG. 6  is an exemplary flow chart showing additional steps of the method shown in  FIG. 4 , according to embodiments of the present disclosure; 
         FIG. 7  is an exemplary flow chart showing methods performed at network functions for managing a network slice for a terminal device, according to embodiments of the present disclosure; 
         FIG. 8  is an exemplary flow chart showing a method performed at a terminal device for managing a network slice for a terminal device, according to embodiments of the present disclosure; 
         FIG. 9  is a first exemplary diagram showing more details about functions and procedures in the communication system for managing the network slice for the terminal device; 
         FIG. 10  is a second exemplary diagram showing more details about functions and procedures in the communication system for managing the network slice for the terminal device; 
         FIG. 11  is a third exemplary diagram showing more details about functions and procedures in the communication system for managing the network slice for the terminal device; 
         FIG. 12  is a block diagram showing apparatuses for functions/nodes in accordance with embodiments of the present disclosure; 
         FIG. 13  is a block diagram showing a computer readable storage medium in accordance with embodiments of the present disclosure; 
         FIG. 14  is a schematic showing units of the server function, according to embodiments of the present disclosure; 
         FIG. 15  is a schematic showing units of the exposure function, according to embodiments of the present disclosure; 
         FIG. 16  is a schematic showing units of the network functions, according to embodiments of the present disclosure; 
         FIG. 17  is a schematic showing units of the terminal device, according to embodiments of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Some of the embodiments contemplated herein will now be described more fully with reference to the accompanying drawings. Other embodiments, however, are contained within the scope of the subject matter disclosed herein, the disclosed subject matter should not be construed as limited to only the embodiments set forth herein; rather, these embodiments are provided by way of example to convey the scope of the subject matter to those skilled in the art. 
     Generally, all terms used herein are to be interpreted according to their ordinary meaning in the relevant technical field, unless a different meaning is clearly given and/or is implied from the context in which it is used. All references to a/an/the element, apparatus, component, means, step, etc. are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any methods disclosed herein do not have to be performed in the exact order disclosed, unless a step is explicitly described as following or preceding another step and/or where it is implicit that a step must follow or precede another step. Any feature of any of the embodiments disclosed herein may be applied to any other embodiment, wherever appropriate. Likewise, any advantage of any of the embodiments may apply to any other embodiments, and vice versa. Other objectives, features and advantages of the enclosed embodiments will be apparent from the following description. 
     Reference throughout this specification to features, advantages, or similar language does not imply that all of the features and advantages that may be realized with the present disclosure should be or are in any single embodiment of the disclosure. Rather, language referring to the features and advantages is understood to mean that a specific feature, advantage, or characteristic described in connection with an embodiment is included in at least one embodiment of the present disclosure. Furthermore, the described features, advantages, and characteristics of the disclosure may be combined in any suitable manner in one or more embodiments. One skilled in the relevant art will recognize that the disclosure may be practiced without one or more of the specific features or advantages of a particular embodiment. In other instances, additional features and advantages may be recognized in certain embodiments that may not be present in all embodiments of the disclosure. 
     As used herein, the term “network”, or “communication network/system” refers to a network/system following any suitable communication standards, such as new radio (NR), long term evolution (LTE), LTE-Advanced, wideband code division multiple access (WCDMA), high-speed packet access (HSPA), and so on. Furthermore, the communications between a terminal device and a network node in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), 4G, 4.5G, 5G communication protocols, and/or any other protocols either currently known or to be developed in the future. 
     The term “function”, “node”, “network node” or “network side node” refers to a network device/apparatus/entity with accessing capability in a communication network via which a terminal device accesses to the network and receives services therefrom. The node/function may include a base station (BS), an access point (AP), a multi-cell/multicast coordination entity (MCE), a server node/function (such as a service capability server/application server, SCS/AS, group communication service application server, GCS AS, application function, AF), an exposure node (such as a service capability exposure function, SCEF, network exposure function, NEF), a controller or any other suitable device in a wireless communication network. The BS may be, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), a next generation NodeB (gNodeB or gNB), a remote radio unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, a low power node such as a femto, a pico, and so forth. 
     Yet further examples of the network node comprise multi-standard radio (MSR) radio equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes, positioning nodes and/or the like. More generally, however, the network node may represent any suitable device (or group of devices) capable, configured, arranged, and/or operable to enable and/or provide a terminal device access to a wireless communication network or to provide some service to a terminal device that has accessed to the wireless communication network. 
     The term “terminal device” encompasses a device which is able to communicate with a network node/network function, such as a base station, or with another wireless device by transmitting and/or receiving wireless signals. Thus, the term terminal device encompasses, but is not limited to: a mobile phone, a stationary or mobile wireless device for machine-to-machine communication, an integrated or embedded wireless card, an externally plugged in wireless card, a vehicle, etc. 
     As yet another specific example, in an Internet of things (IoT) scenario, a terminal device may also be called an IoT device and represent a machine or other device that performs monitoring, sensing and/or measurements etc., and transmits the results of such monitoring, sensing and/or measurements etc. to another terminal device and/or a network equipment. The terminal device may in this case be a machine-to-machine (M2M) device, which may in a 3rd generation partnership project (3GPP) context be referred to as a machine-type communication (MTC) device. 
     As one particular example, the terminal device may be a UE implementing the 3GPP narrow band Internet of things (NB-IoT) standard. Particular examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, or home or personal appliances, e.g. refrigerators, televisions, personal wearables such as watches etc. In other scenarios, a terminal device may represent a vehicle or other equipment, for example, a medical instrument that is capable of monitoring, sensing and/or reporting etc. on its operational status or other functions associated with its operation. 
     As used herein, the terms “first”, “second” and so forth refer to different elements. The singular forms “a” and “an” are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises”, “comprising”, “has”, “having”, “includes” and/or “including” as used herein, specify the presence of stated features, elements, and/or components and the like, but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof. The term “based on” is to be read as “based at least in part on”. The term “one embodiment” and “an embodiment” are to be read as “at least one embodiment”. The term “another embodiment” is to be read as “at least one other embodiment”. Other definitions, explicit and implicit, may be included below. 
       FIG. 1  is an exemplary diagram showing a simplified structure of a communication network. 
     As shown in  FIG. 1 , a network includes a plurality of network functions, NF  300  (NF 1, NF 2 . . . NF n, n is an integer). The network provides network exposure capability to enable suitable access/exchange of network information to a server function or terminal device. The server function, SF, such as application function, AF  100  (AF 1, AF 2, AF 3), uses application program interfaces, API  500  (API 1, API 2, API 3 . . . API n, n is an integer) of the exposure functions, EF, such as network exposure function, NEF  200  (NEF 1, NEF 2), so as to access/exchange network information. 
     Namely, the Network Exposure Function (NEF) may support exposure of capabilities of network functions, using the information collected via network internal interfaces, and exposing them towards Application Function (AF) via proper APIs. 
     The terminal device, such as the user equipment, UE,  400  may receive service form the AF  100 . However, if the current network slice for the UE  400  is not suitable for the current service provided by the AF  100 , the quality of service might be affected, or the service might have to be stopped. 
     It is expected that there would be many different types of network slices for different usages. The relation between specific usage and the network service with special characteristics may be dynamic and flexible to support flexible/agile business model. For example, during initial period of special usage, it is possible that special usage traffic is still served by a common network slice for basic network service. With the increased numbers of special users or VIP users, a dedicated network slice is instantiated to support required features and enable the flexible business model. In addition, as mentioned by 3GPP, usually one default network slice is associated with one or more dedicated network slices. In case the dedicated network slice for the usage is not available or without sufficient information, the special usage UE can be directed to default network slice for basic network service or steered to a dedicated network slice, using serving operator specific policies. 
     The 5 th  generation core network, 5GC, provides policy information for the UE, such as UE Route Selection Policy (URSP). This policy is used by the UE to determine whether a detected application can be associated to an established packet data unit, PDU, Session, can be offloaded to non-3GPP access outside a PDU Session, or can trigger the establishment of a new PDU Session. 
     Part of URSP is Network slicing selection Policy (NSSP). This is used by the UE to associate the matching application with a specific network slice. The NSSP rules associate an application with one or more Single Network Slice Selection Assistance information, S-NSSAIs, in Configured NSSAI for the Home Public Land Mobile Network, HPLMN, of the UE. A default rule which matches all applications to an S-NSSAI in Configured NSSAI for the HPLMN may also be included. As such, UE can run the application using the connection setup within the designated network slice which has pre-defined features, quality of service that can fulfill certain business model. 
     URSP/NSSP may be pre-configured in the UE or may be provisioned to UE from 5GC, e.g. via PCF. When the Subscription Information changes and the network wants to control/modify the UE usage of those network slices, then the network provisions/updates the UE with NSSP as part of the URSP rules. 
     The establishment of User Plane connectivity to a Data Network via a network slice comprises two steps:
         performing a RM (registration management) procedure to select an AMF that supports the required Network Slices.   establishing one or more PDU Session to the required Data network via the Network Slice Instance(s).       

     When a UE registers with a Public Land Mobile Network, PLMN, it provides to the network a Requested NSSAI containing the S-NSSAI(s) corresponding to the slice(s) to which the UE wishes to register. UE associates Applications to S-NSSAIs based on NSSP of the URSP rules. 
     The selection of the set of Network Slice instances for the UE is triggered by the first contacted AMF in a registration procedure normally by interacting with the NSSF. 3GPP defined network slice selection flow, such as in 3GPP technical specification, TS, 23.502 V15.5.1, is shown below. 
     If there is a need for slice selection, e.g. the initial AMF cannot serve all the S-NSSAI(s) from the Requested NSSAI permitted by the subscription information, the initial AMF sends a Slice Selection Request to the NSSF. It sends to NSSF Requested NSSAI, Subscribed S-NSSAIs, PLMN ID of the Subscription Permanent Identifier, SUPI, and the Tracking Area Identity, TAI, of the UE. 
     The NSSF returns to initial AMF the Allowed NSSAI and the target AMF Set or, based on configuration, the list of candidate AMF(s). When multiple Network Slice instances in the registration area are able to serve a given S-NSSAI and the NSSF has selected one of them to serve the UE, the NSSF may return a Network Slice Instance, NSI, ID associated with that given S-NSSAI. The NSSF may return the Network Repository Function, NRF(s), to be used to select NFs/services within the selected Network Slice instance(s). Further, it may also return information regarding rejection causes for S-NSSAI(s) not included in the Allowed NSSAI. 
     As per 3GPP definition, NSSF makes the slice selection decision, based on this information, local configuration, and other locally available information including radio access network, RAN, capabilities in the current Tracking Area for the UE. 
     Moreover, NSSF may also take the additional input, like information from analytic platform, operational status of slice and NF, Service Level Agreement, SLA, management information, operation and maintenance, O&amp;M, and orchestration information etc., as for slice selection. I.e. NSSF may make use of lots of dynamic information available at decision point to make an optimized slice selection result. 
     The set of Network Slices for a UE can be changed at any time while the UE is registered with a network, and may be initiated by the network, or by the UE. 
     The network, based on local policies, subscription changes and/or UE mobility, operational reasons (e.g. a Network Slice instance is no longer available or load level information for a network slice instance is provided by the Network Data Analytics Function, NWDAF), may change the set of Network Slice(s) to which the UE is registered and provide the UE with a new Allowed NSSAI or Configured NSSAI. The network may perform such a change during a Registration procedure or trigger a notification towards the UE of the change of the Network Slices using a UE Configuration Update procedure as specified in 3GPP TS 23.502 V15.5.1, clause 4.2.4. 
     When the UE&#39;s subscription Information contains more than one S-NSSAI and the network wants to control/modify the UE usage of those S-NSSAIs, then the network may also provisions/updates the UE with NSSP as part of the URSP rules. 
     From UE side, when URSP rules are updated or their validity changes, the association of existing applications to PDU Sessions may need to be re-evaluated. The UE may also re-evaluate the application to PDU Session association due to the following reasons: periodic re-evaluation based on UE implementation; an existing PDU Session that is used for routing traffic of an application based on a URSP rule is released. 
     If the re-evaluation leads to a change of the application to PDU Session association, e.g. the application is to be associated with another PDU session or a new PDU session needs to be established, the UE may enforce such changes in a timely manner based on implementation. 
     However, in the situation that the external AF triggers URSP change and intends for network slice change for UE, it is still up to UE to decide when and how to enforce such changes. The slice change for UE(s) may take longer timer than expected. This can then lead to unwanted or inefficient network resource usage. 
     Embodiments to further improve the managing of a network slice for a terminal device will be further illustrated below. 
       FIG. 2  is an exemplary flow chart showing a method performed at a server function for managing a network slice for a terminal device, according to embodiments of the present disclosure. 
     As shown in  FIG. 2 , the method performed at a server function, such as the AF  100  comprises: S 101 , determining to change a network slice for a terminal device; and S 102 , transmitting, to an exposure function, a request to change the network slice for the terminal device. 
     The AF  100  may determine to change the network slice, when the current network slice for the terminal device, such as the UE  400 , is not suitable to the service to be provided to the UE  400 . It should be understood that the change of the network slice may include the change for a source network slice to a target network slice, or from no network slice to a target network slice. 
     According to embodiments of the present disclosure, a method is performed at the server function to change the network slice for the terminal device. Therefore, whenever the server function finds out the current network slice situation is not suitable for the service being provided/to be provided to the terminal device, the network slice for the terminal device may be changed/updated timely. By utilizing such managing method, it makes an effective usage of network slice resources. 
     In embodiments of the present disclosure, the terminal device is included in a group of terminal devices; the network slice is changed for each terminal device in the group of terminal devices. 
     In embodiments of the present disclosure, the request includes an identifier of the terminal device, and external information of network slice. 
     For example, the request to change the network slice for the terminal device may include an identifier of the UE  400 . Further, additionally or alternatively, the request to change the network slice for the terminal device may include a group identifier of a group of UE including the UE  400 . The external information of network slice may indicate a target network slice the UE  400  should change to. 
     In embodiments of the present disclosure, the identifier comprises an external identifier; the external information of network slice comprises at least one of: an external slice type of a source network slice, or an external slice type of a target network slice; the external slice type includes at least one of: eMBB slice, URLLC slice, or eMTC slice; and eMBB refers to enhanced mobile broadband, URLLC refers to ultra reliable low latency communications, and eMTC refers to enhanced machine type communication. 
     For example, the external information of network slice may indicate that the AF  100  wants the UE  400  to change from a source network slice with type of eMBB to URLLC, so as to support a service requiring low latency. It should be understood that the type of slice may be directly defined with the application purpose. For example, the external slice type of a target network slice may be “V2X”, when a V2X application needs to be served. Further, the external information of network slice may include slice instance level information, such as a specific network slice instance identifier. For example, AF  100  can request a slice change from a source network slice with an external identifier of “eMBB-1” to a target network slice with an external identifier of “eMTC-1”. Then, the source network slice with an external identifier of “eMBB-1” may be mapped to an internal slice instance with an internal identifier of “NSSAI-1” by the NEF  200 . 
       FIG. 3  is an exemplary flow chart showing an additional step of the method shown in  FIG. 2 , according to embodiments of the present disclosure. 
     As shown in  FIG. 3 , the method further comprises: S 103 , transmitting, to the exposure function, a request for updating a UE route selection policy, URSP, or a network slicing selection policy, NSSP for the terminal device; UE refers to user equipment. 
     For example, with the updated URSP/NSSP, the intention of AF  100  to change the network slice of the UE  400  can be preserved in the UE  400 . Namely, the network slice of URLLC/V2X may be configured as a default network slice type, whenever the UE  400  try to register in the network. 
     In embodiments of the present disclosure, the exposure function comprises: a network exposure function, NEF, such as NEF  200  in  FIG. 1 . 
     In embodiments of the present disclosure, the server function comprises: an application function, AF, such as AF  100  shown in  FIG. 1 , or a service capability server/application server, SCS/AS, not shown in  FIG. 1 . 
     In embodiments of the present disclosure, the terminal device comprises: a user equipment, UE, such as UE  400  shown in  FIG. 1 . 
       FIG. 4  is an exemplary flow chart showing a method performed at an exposure function for managing a network slice for a terminal device, according to embodiments of the present disclosure. 
     As shown in  FIG. 4 , the method performed at the exposure function comprises: S 201 , receiving, from a server function, a first request to change a network slice for a terminal device; S 202 , transmitting, to a network function, a second request to change the network slice for the terminal device. 
     According to the embodiments of the present disclosure, the utilization of the exposure function may improve the efficiency and the safety. For example, the exposure function may provide an interface, such as API  500  shown in  FIG. 1 , for the server function to utilize. 
     In embodiments of the present disclosure, the terminal device is included in a group of terminal devices; the network slice is changed for each terminal device in the group of terminal devices. 
       FIG. 5  is an exemplary flow chart showing additional steps of the method shown in  FIG. 4 , according to embodiments of the present disclosure. 
     In embodiments of the present disclosure, the method further comprises: S 203 , determining an authorization of the first request. For example, if the exposure function determines that the AF  100  is not authorized to manage the slice for the UE  400 , the request from the AF  100  to change the network slice for the UE  400  may be rejected. The safety of the network communication may be improved. 
     In embodiments of the present disclosure, the method further comprises: S 204 , mapping the first request to the second request; the first request includes an external identifier of the terminal device, and external information of network slice; the external information of network slice comprises at least one of: an external slice type of a source network slice, or an external slice type of a target network slice; the external slice type includes at least one of: eMBB slice, URLLC slice, or eMTC slice; and eMBB refers to enhanced mobile broadband, URLLC refers to ultra reliable low latency communications, and eMTC refers to enhanced machine type communication; the second request includes an internal identifier of the terminal device, and internal information of network slice; and the internal information of network slice comprises at least one of: an identifier of the source network slice, an identifier of the target network slice, or a data network name, DNN. 
     The mapping between above external parameters/information and above internal external parameters/information simplifies the access from AF, UE to the network and provides protection for the network. For example, the AF, and UE only needs to provide a slice type, such as V2X, without knowing a specific identifier of the network slice. 
       FIG. 6  is an exemplary flow chart showing additional steps of the method shown in  FIG. 4 , according to embodiments of the present disclosure. 
     As shown in  FIG. 6 , the method further comprises: S 205 , obtaining context information about the terminal device; the context information comprises information about at least one of: an access and mobility management function instance, AMF instance, where the terminal device is registered with; a session management function instance, SMF instance, where the terminal device is registered with; a network slice, where the terminal device is attached to; a data network name, DNN; or subscription information. 
     In embodiments of the present disclosure, at least part of the context information is obtained from a unified data management, UDM. 
     In embodiments of the present disclosure, the subscription information is obtained from the UDM; and the subscription information comprises information about at least one of: a subscribed slice, or a subscribed data network name. 
     In embodiments of the present disclosure, the method further comprises: S 206 , obtaining session information about the terminal device; the session information comprises information about at least one of: an identifier of the terminal device; a DNN; or a policy control function instance, PCF instance, that handles a data session of the terminal device. 
     In embodiments of the present disclosure, the network function comprises at least one of: a unified data management, UDM; a policy control function, PCF; a network slice selection function, NSSF; an access and mobility management function, AMF; or a session management function, SMF. 
     According to embodiments of the present disclosure, the exposure function may trigger any of the network functions/nodes, which is able to change the network slice for the terminal device. 
     In embodiments of the present disclosure, the exposure function comprises: a network exposure function, such as NEF  200  shown in  FIG. 1 . 
     In embodiments of the present disclosure, the second request comprises: a reason code indicating that the notification is triggered by the server function. 
     In embodiments of the present disclosure, the reason code is optional. 
       FIG. 7  is an exemplary flow chart showing methods performed at network functions for managing a network slice for a terminal device, according to embodiments of the present disclosure. 
     As shown in  FIG. 7 , a method performed at a network function, such as a first network function  3001 , comprises: S 301 , receiving, from an exposure function, a second request to change a network slice for a terminal device; S 302 , transmitting, to another network function, such as a second network function  3002 , a third request to change the network slice for the terminal device. 
     According to embodiments of the present disclosure, the first network function  3001  may be a network function which does not manage the UE directly. The first network  3001  triggers the change of the network slice for the terminal device via the second network function  3002 . The second network function  3002  may be a network function which manages the UE directly. 
     In embodiments of the present disclosure, the first network function  3001  comprises: a UDM, or a PCF, or a NSSF; and the second network function  3002  comprises: an AMF, or a SMF. 
     In embodiments of the present disclosure, the first network function  3001  comprises: a UDM, and the second network function  3002  comprises: an AMF; the third request comprises an indication for the terminal device to perform a registration procedure. 
     In embodiments of the present disclosure, the third request comprises internal information of network slice; and the internal information of network slice comprises at least one of: an identifier of a source network slice, an identifier of a target network slice, or a data network name, DNN. 
     According to embodiments of the present disclosure, the procedure to change the network slice for the terminal device may relates to AF  100 , NEF  200 , UDM, AMF, UE sequentially. The change of the network slice may be achieved by registration procedure of the terminal device. Namely, a target network slice is to be utilized by the terminal device during registration. 
     In embodiments of the present disclosure, the first network function  3001  comprises: a UDM, and the second network function  3002  comprises: a SMF; the third request comprises an indication for the terminal device to release a session. 
     According to embodiments of the present disclosure, the procedure to change the network slice for the terminal device may relates to AF  100 , NEF  200 , UDM, SMF, UE sequentially. The change of the network slice may be achieved by a session creation procedure of the terminal device after a current session is released. Namely, a target network slice is to be utilized by the terminal device during session creation procedure. 
     In embodiments of the present disclosure, the first network function  3001  comprises: a PCF, and the second network function  3002  comprises: a SMF; the third request comprises an indication for the terminal device to release a session. 
     In embodiments of the present disclosure, the first network function  3001  comprises: a NSSF, and the second network function  3002  comprises: an AMF; the third request comprises an indication for the terminal device to perform a registration procedure. 
     According to embodiments of the present disclosure, the procedure to change the network slice for the terminal device may relates to AF  100 , NEF  200 , PCF, SMF, UE sequentially, or AF  100 , NEF  200 , NSSF, AMF, UE sequentially. 
     In embodiments of the present disclosure, the second request comprises: a reason code indicating that the notification is triggered by the server function. 
     In embodiments of the present disclosure, the third request comprises: the reason code; or the third request comprises another reason code, which is mapped from the reason code by the first network function  3001 . 
     In embodiments of the present disclosure, the reason code is optional. 
     Further, a method performed at a network function, such as the second network function  3002  is illustrated. The method performed at the second network function  3002  comprises: S 401 , receiving, from another network function, such as the first network function  3001 , a third request to change a network slice for a terminal device; S 402 , transmitting, to the terminal device, a notification to change the network slice for the terminal device. 
     In embodiments of the present disclosure, the method further comprises: S 403 , transmitting, to the terminal device, slices information about allowed network slices, configured network slices, or target network slices. 
     In embodiments of the present disclosure, the second network function  3002  comprises: an AMF; and the notification comprises an indication for the terminal device to perform a registration procedure. 
     In embodiments of the present disclosure, the second network function  3002  comprises: a SMF; and the notification comprises an indication for the terminal device to release a session. 
     In embodiments of the present disclosure, the third request comprises: a reason code indicating that the notification is triggered by the server function; and the notification comprises: the reason code. 
     In embodiments of the present disclosure, the reason code is optional. 
       FIG. 8  is an exemplary flow chart showing a method performed at a terminal device for managing a network slice for a terminal device, according to embodiments of the present disclosure. 
     As shown in  FIG. 8 , a method performed at a terminal device, such as the UE  400  shown in  FIG. 1 , comprises: S 501 , receiving a notification to change a network slice for the terminal device; S 502 , changing the network slice for the terminal device. 
     In embodiments of the present disclosure, the notification comprises a reason code indicating that the notification is triggered by a server function. 
     In embodiments of the present disclosure, the reason code is optional. 
     In embodiments of the present disclosure, the notification comprises an indication for the terminal device to perform a registration procedure; or the notification comprises an indication for the terminal device to release a session; or the notification comprises an indication for the terminal device to reestablish a session. 
     In embodiments of the present disclosure, a target network slice for performing the registration procedure, or for reestablishing the session is determined based on a local configuration, a URSP or NSSP, or the notification. 
     In embodiments of the present disclosure, the terminal device comprises a user equipment, UE. 
       FIG. 9  is a first exemplary diagram showing more details about functions and procedures in the communication system for managing the network slice for the terminal device. 
     As shown in  FIG. 9 , the procedure to change the network slice for the terminal device relating to AF  100 , NEF  200 , UDM  3001   a , AMF  3002   b /SMF  3002   a , UE  400  sequentially is illustrated. The procedure may be also named as a UDM anchored solution. The underlines in the figure are used for emphasizing. 
     Step  90  refers to a UE registration over a selected network slice. 
     In steps  91 - 92 , the AF  100  determines that there is a need to change the slice(s) for the target UE(s) specified by an identifier, e.g. UE ID or UE group ID, and triggers a request to NEF  200  to change the slice for those UE(s). 
     AF  100  may provide additional information (named as external slice information), e.g. the source slice(s), the target slice(s), slice tenant information, action indicator (immediate, delayed), NSSP. 
     As to the NSSP, AF  100  may trigger network to update URSP/NSSP to UE(s) in a separate procedure or together with this procedure. 
     For example, AF  100  with an ID of “AFid-1” orders a slice change for one of its enterprise user UE  400 . 
     The request may include: UE id: “GPSI=1”, UE addr: “Ipaddr=10.0.0.1”, Source Slice: “eMBB”, Target Slice: v2x”, Slice tenant: Application-1, Action indicator: “Immediate”, URSP: “NSSP-1; NSSP-2”. 
     In step  92   b , NEF  200  determines UE&#39;s session binding information. 
     In step  93 , NEF  200  checks the request and authorize that the AF  100  can trigger such request as well as the request conditions, e.g. the AF  100  can changes UE(s) attaching on a specific network slice, based on operator policy and/or subscription information from UDM  3001   a.    
     NEF  200  may map the external slice information provided by AF  100  to the internal slice information such as Network Slice Selection Assistance Information, NSSAI, Slice/Service type, SST, Slice Differentiator, SD, Network Slice Instance ID, NSI ID etc. 
     NEF  200  may also fetch the UE context information such as AMF, SMF instances where UE  400  is registered with and also the network slice(s) where UE  400  is attached to, DNN(s) that UE is connected with, and/or subscription from UDM  3001   a , such as subscribed slices, subscribed DNN(s) etc. 
     NEF  200  may additionally trigger session binding discovery procedure via Nbsf interface as defined in 3 rd  generation partnership project technical specification, 3GPP TS, 23.501 V15.5.0 &amp;23.502 V15.5.1; to get UE session information, including, UE id information (e.g Subscription Permanent Identifier, SUPI, Generic Public Subscription Identifier, GPSI), DNN, and also the PCF instance that handles the UE  400 &#39;s data session. 
     E.g. NEF  200  authorize “AFid-1” with slice tenant “Application-1” can change slice for UE  400  from Slice“eMBB” to slice “v2x”; NEF maps “eMBB” and “V2x” to “S-NSSAI=1”&amp;“S-NSSAI=2” accordingly; NEF fetch UE  400 &#39;s context information and subscription information from UDM, and discover the active slice which UE is attached to i.e. “S-NSSAI=1” and the NFs instances, i.e. AMF-1,SMF-1 where UE  400  is registered with. 
     In steps  94 - 95 , NEF  200  determines that slice “S-NSSAI=1” which UE  400  is attached to is the source slice indicated by the AF  100  to change. S-NSSAI refers to Single-Network Slice Selection Assistance Information. NEF  200  then triggers slice change towards 5 th  generation core network function, 5GC NF(s), e.g. 5GC NF can be any of UDM  3001   a , AMF  3002   b , SMF  3002   a , NSSF  3001   b , PCF; NEF  200  may trigger such request directly towards these 5GC NF(s), or indirectly via intermediate 5GC NF(s) 
     E.g. NEF  200  sends slice change request to UDM  3001   a , including: UE ID: GPSI=1; Source Slice: “S-NSSAI=1”, Target Slice: “S-NSSAI=2”, DNN=“internet”, Action indicator: “Immediate”, Reason: “AF triggered slice change”. 
     In step  96   a , after receiving the request from NEF  200 , UDM  3001   a  determines, based on the operator&#39;s policy, AMF  3002   b  with ID of “AMF-1” shall be notified about slice change for UE  400 ; UDM  3001   a  may also adjust the subscription information for UE  400  accordingly. 
     For example, UDM  3001   a  maps UE  400 &#39;s ID “GPSI=1” to 5GC internal ID “SUPI=1”, and send slice change request, e.g., “Nudm_UECM_DeregistrationNotification” to AMF  3002   b , including: UEID: SUPI=1; Source Slice: “S-NSSAI=1”; Target Slice: “S-NSSAI=2”; DNN=“internet”; Action indicator: “Immediate”; Reason: “network triggered slice change” or “AF triggered slice change”. 
     In step  97   a , after receiving the request from the UDM  3001   a , AMF  3002   b  determines based on the operator&#39;s policy, UE  400  with ID of “UE-1” shall be notified about slice change. AMF  3002   b  may determine that the previous slice related information sent to UE  400  need be updated, e.g. allowed NSSAI(s), configured NSSAI(s), target NSSAI(s); AMF  3002   b  triggers UE  400  configuration update procedure. 
     For example, AMF  3002   b  may indicate UE  400  to perform an immediate registration; AMF  3002   b  may trigger network resource release procedure accordingly; AMF  3002   b  may indicate UE  400  with the reason for slice change, which is “network triggered slice change” or “AF triggered slice change”. 
     In step  96   b , alternatively for step  96   a , after receiving the request from the NEF  200 , UDM  3001   a  determines, based on the operator&#39;s policy, only specific data connection shall be released, e.g. SMF  3002   a  with ID of “SMF-1” shall be notified about slice change for UE  400 . 
     For example, UDM  3001   a  maps UE ID “GPSI=1” to 5GC internal ID “SUPI=1”, and send slice change request, e.g. “Nudm_UECM_DeregistrationNotification” to SMF  3002   a , including: UE ID: SUPI=1; Source Slice: “S-NSSAI=1”; Target Slice: “S-NSSAI=2”; DNN: “internet”; Action indicator: “Immediate”; Reason: “network triggered slice change” or “AF triggered slice change”. 
     In step  97   b , after receiving the request from UDM  3001   a , SMF  3002   a  determines based on the operator policy, the PDU session(s) shall be released; SMF  3002   a  triggers PDU session release procedure accordingly; SMF  3002   a  may indicate UE  400  the reason, which is “network triggered slice change” or “AF triggered slice change”. 
     In step  98 , the UE  400  then re-evaluates the application to PDU Session association with the current slice, trigger attach to network (as per  97   a ) and or establish new PDU session (s) (as per  97   b ), with new requested NSSAI based on the latest received slice related information (e.g. allowed NSSAIs, Configured NSSAI, target NSSAI etc.) and/or URSP/NSSP. 
       FIG. 10  is a second exemplary diagram showing more details about functions and procedures in the communication system for managing the network slice for the terminal device. 
     As shown in  FIG. 10 , the procedure to change the network slice for the terminal device relating to AF  100 , NEF  200 , PCF  3001   c , SMF  3002   a , UE  400  sequentially is illustrated. The procedure may be also named as a PCF anchored solution. 
     Steps S 10 -S 14  may be the same with the steps  90 - 94  in the  FIG. 9 . 
     For example, NEF  200  may additionally trigger session binding discovery procedure via Nbsf interface as defined in 3GPP 23.501 V15.5.0 &amp;23.502 V15.5.1; to get UE  400 &#39;s session information, including, UE id information (e.g SUPI, GPSI), DNN, and also the PCF instance that handles the UE&#39;s data session. 
     In step S 15 , NEF  200  determines that slice “S-NSSAI=1” which UE  400  with ID of “UE1” is attached to is the source slice indicated by the AF  100  to change. NEF  200  then triggers slice change towards PCF  3001   c , e.g. NEF  200  sends slice change request, via Npcf service to PCF  3001   c , including UE ID: GPSI=1 or SUPI=1; Source Slice: “S-NSSAI=1”; Target Slice: “S-NSSAI=2”; DNN: “internet”; Action indicator=“Immediate”; Reason: “AF triggered slice change”. 
     In step S 16 , after receiving the request from the NEF  200 , PCF  3001   c  determines, based on the operator policy, the PDU session(s) to be released, e.g. SMF  3002   a  with ID of “SMF-1” shall be notified about slice change for UE  400 . PCF  3001   c  sends slice change request, e.g. “Npcf_SMPolicyControl_UpdateNotify” to SMF  3002   a , including: UE ID: GPSI=1 or SUPI=1; Source Slice: “S-NSSAI=1”; Target Slice: “S-NSSAI=2”; DNN: “internet”; Action indicator: “Immediate”; Reason: “network triggered slice change” or “AF triggered slice change”. 
     In step S 17 , after receiving the request from the PCF  3001   c , SMF  3002   a  determines, based on the operator&#39;s policy, the PDU session(s) shall be released; SMF  3002   a  triggers PDU session release procedure accordingly. SMF  3002   a  may indicate UE  400  the reason, which is “network triggered slice change” or “AF triggered slice change”. 
     In step S 18 , the UE  400  then re-evaluate the application to PDU Session association with the current slice and trigger establish new PDU session (s) with new requested NSSAI, based on the latest received slice related information (e.g. allowed NSSAIs, Configured NSSAI, target NSSAIs etc.) and/or URSP/NSSP. 
       FIG. 11  is a third exemplary diagram showing more details about functions and procedures in the communication system for managing the network slice for the terminal device. 
     As shown in  FIG. 11 , the procedure to change the network slice for the terminal device relating to AF  100 , NEF  200 , NSSF  3001   b , AMF  3002   b , UE  400  sequentially is illustrated. The procedure may be also named as a NSSF anchored solution. 
     Steps S 20 -S 24  may be the same as the step  90 - 94  in  FIG. 9 . 
     In step S 25 , NEF  200  determines that slice “S-NSSAI=1” which UE  400  with ID of “UE1” is attached to is the source slice indicated by the AF  100  to change. NEF  200  then triggers slice change towards NSSF  3001   b . E.g., NEF  200  sends slice change request, via Nssf service to NSSF  3001   b , including UE ID: GPSI=1 or SUPI=1; Source Slice: “S-NSSAI=1”; Target Slice: “S-NSSAI=2”; DNN=“internet”; Action indicator=“Immediate”; Reason: “AF triggered slice change”. 
     In step S 26 , after receiving the request from NEF  200 , NSSF  3001   b  determines, based on the operator&#39;s policy, AMF  3002   b  with ID of “AMF-1” shall be notified about slice change for UE1&amp; “S-NSSAI=1”. This implies that when AMF  3002   b  performs network slice selection, AMF  3002   b  sends UE ID in Slice Selection request; NSSF  3001   b  keeps association between UE(s) and AMFs for the accepted slices. 
     NSSF  3001   b  then sends slice change request to AMF  3002   b , including: UEID: SUPI=1; Source Slice: “S-NSSAI=1”; Target Slice: “S-NSSAI=2”; DNN=“internet”; Action indicator: “Immediate”; Reason: “network triggered slice change” or “AF triggered slice change”. 
     Steps S 27 -S 28  may be the same as the step  97   a  and  98  in  FIG. 9 . 
       FIG. 12  is a block diagram showing apparatuses for functions/nodes in accordance with embodiments of the present disclosure. 
     An apparatus for a server function  100  comprises: a processor  101 ; and a memory  102 , containing instructions executable by the processor  101 ; the apparatus for the server function  100  is operative to implement the method according to any of embodiments above mentioned, such as shown in  FIGS. 2, 3, 9, 10, 11 . 
     An apparatus for an exposure function  200  comprises: a processor  201 ; and a memory  202 , containing instructions executable by the processor  201 ; the apparatus for the exposure function  200  is operative to implement the method according to any of embodiments above mentioned, such as shown in  FIGS. 4, 5, 6, 9, 10, 11 . 
     An apparatus for a network function  300  comprises: a processor  301 ; and a memory  302 , containing instructions executable by the processor  301 ; the apparatus for the network function  300  is operative to implement the method according to any of embodiments above mentioned, such as shown in  FIGS. 7, 9, 10, 11 . 
     An apparatus for a terminal device (UE)  400  comprises: a processor  401 ; and a memory  402 , containing instructions executable by the processor  401 ; the apparatus for the terminal device  400  is operative to implement the method according to any of embodiments above mentioned, such as shown in  FIGS. 8, 9, 10, 11 . 
     The processors  101 ,  201 ,  301 ,  401  may be any kind of processing component, such as one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The memories  102 ,  202 ,  302 ,  402  may be any kind of storage component, such as read-only memory (ROM), random-access memory, cache memory, flash memory devices, optical storage devices, etc. 
       FIG. 13  is a block diagram showing a computer readable storage medium in accordance with embodiments of the present disclosure. 
     The computer readable storage medium  1300  has a computer program  1301  stored thereon, the computer program  1301  is executable by an apparatus to cause the apparatus to carry out the method according to any of embodiments above mentioned, such as shown in  FIGS. 2-11 . 
     The computer readable storage medium  1300  may be configured to include memory such as RAM, ROM, programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic disks, optical disks, floppy disks, hard disks, removable cartridges, or flash drives. 
       FIG. 14  is a schematic showing units of the server function, according to embodiments of the present disclosure. 
     The apparatus for a server function (AF)  100  comprises: a determining unit  1001 , configured to determine (S 101 ) to change a network slice for a terminal device; and a transmitting unit  1002 , configured to transmit (S 102 ), to an exposure function, a request to change the network slice for the terminal device. 
       FIG. 15  is a schematic showing units of the exposure function, according to embodiments of the present disclosure. 
     The apparatus for an exposure function (NEF)  200  comprises: a receiving unit, configured to receive (S 201 ), from a server function, a first request to change a network slice for a terminal device; and a transmitting unit  2002 , configured to transmit (S 202 ), to a network function, a second request to change the network slice for the terminal device. 
       FIG. 16  is a schematic showing units of the network functions, according to embodiments of the present disclosure. 
     The apparatus for a first network function  3001  comprises: a receiving unit  3011 , configured to receive (S 301 ), from an exposure function, a second request to change a network slice for a terminal device; and a transmitting unit  3012 , configured to transmit (S 302 ), to another network function, a third request to change the network slice for the terminal device. 
     The apparatus for a second network function  3002  comprises: a receiving unit  3021 , configured to receive (S 401 ), from another network function, a third request to change a network slice for a terminal device; and a transmitting unit  3012 , configured to transmit (S 402 ), to the terminal device, a notification to change the network slice for the terminal device. 
       FIG. 17  is a schematic showing units of the terminal device, according to embodiments of the present disclosure. 
     The apparatus for a terminal device (UE)  400  comprises: a receiving unit  4001 , configured to receive (S 501 ) a notification to change a network slice for the terminal device; and a changing unit  4002 , configured to change (S 502 ) the network slice for the terminal device. 
     The term unit may have conventional meaning in the field of electronics, electrical devices and/or electronic devices and may include, for example, electrical and/or electronic circuitry, devices, modules, processors, memories, logic solid state and/or discrete devices, computer programs or instructions for carrying out respective tasks, procedures, computations, outputs, and/or displaying functions, and so on, as such as those that are described herein. 
     With these units, the server function, e.g. application function  100 , exposure function, e.g. network exposure function  200 , network function  300 , or terminal device, e.g. user equipment  400  may not need a fixed processor or memory, any computing resource and storage resource may be arranged from at least one network node/device/entity/apparatus in the communication system. The virtualization technology and network computing technology may be further introduced, so as to improve the usage efficiency of the network resources and the flexibility of the network. 
     Particularly, these network functions, e.g. application function  100 , exposure function, e.g. network exposure function  200 , network function  300 , or terminal device, e.g. user equipment  400 , may be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualized function instantiated on an appropriate platform, e.g. on a cloud infrastructure. 
     According to embodiments of the present disclosure, a method is performed at the server function to change the network slice for the terminal device. Therefore, whenever the server function finds out the current network slice situation is not suitable for the service being provided/to be provided to the terminal device, the network slice for the terminal device may be changed/updated timely. 
     According to embodiments of the present disclosure, the exposure function may trigger any of the network functions/nodes, which is able to change the network slice for the terminal device. 
     According to embodiments of the present disclosure, the first network function  3001  may be a network function which does not manage the UE directly. The first network  3001  triggers the change of the network slice for the terminal device via the second network function  3002 . The second network function  3002  may be a network function which manages the UE directly. 
     In general, the various exemplary embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. For example, some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor or other computing device, although the disclosure is not limited thereto. While various aspects of the exemplary embodiments of this 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. 
     As such, it should be appreciated that at least some aspects of the exemplary embodiments of the disclosure may be practiced in various components such as integrated circuit chips and modules. It should thus be appreciated that the exemplary embodiments of this disclosure may be realized in an apparatus that is embodied as an integrated circuit, where the integrated circuit may include circuitry (as well as possibly firmware) for embodying at least one or more of a data processor, a digital signal processor, baseband circuitry and radio frequency circuitry that are configurable so as to operate in accordance with the exemplary embodiments of this disclosure. 
     It should be appreciated that at least some aspects of the exemplary embodiments of the disclosure may be embodied in computer-executable instructions, such as in one or more program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types when executed by a processor in a computer or other device. The computer executable instructions may be stored on a computer readable medium such as a hard disk, optical disk, removable storage media, solid state memory, RAM, etc. As will be appreciated by those skilled in the art, the functionality of the program modules may be combined or distributed as desired in various embodiments. In addition, the functionality may be embodied in whole or in part in firmware or hardware equivalents such as integrated circuits, field programmable gate arrays (FPGA), and the like. 
     The present disclosure includes any novel feature or combination of features disclosed herein either explicitly or any generalization thereof. Various modifications and adaptations to the foregoing exemplary embodiments of this disclosure may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings. However, any and all modifications will still fall within the scope of the non-limiting and exemplary embodiments of this disclosure.