Per-ue allowed slice dependent pdu-session handover to visited plmn

Abstract

Embodiments of the present disclosure relate to a method, device and computer readable storage medium for handover In the method, a network node causes selection of at least one allowed network slice identification from a set of home network slice identifications of a source network based on a set of subscribed network slice identifications of a target network. The set of home network slice identifications and the set of subscribed network slice identifications are associated with a user equipment (UE), and the at least one allowed network slice identification is available for the UE in the target network. Then, the network node causes execution of handover of the UE from the source network to the target network based on the at least one allowed network slice identification.

Description

PER-UE ALLOWED SLICE DEPENDENT PDU-SESSION HANDOVER TO VISITED PLMNFIELDS

[0001] Various embodiments of the present disclosure generally relate to the field of telecommunication and in particular, to a method, device and computer readable storage medium for handover.BACKGROUND

[0002] This section introduces aspects that may facilitate a better understanding of the 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.

[0003] In the third-generation partnership project (3GPP) TS 23.502, VERSION 18.1.1 (TS 23.502), two type of inter-public land mobile network (PLMN) handover are supported, which includes N2 based handover and evolved packet system (EPS) to the fifth-generation system (5GS) handover using an N26 interface. In the N2 based handover, user equipment (UE) context information from a source access and mobility management function (AMF) or S-AMF of a source network, which may be a visited PLMN (VPLMN), may include home PLMN (HPLMN) single network slice selection assistance information (S-NSSAI) corresponding to allowed NSSAI for each access type. As described in the chapter 4.9. 1.3 of TS 23.502, a target AMF or T-AMF of a target network, which may be a VPLMN, may determine the allowed NSSAI based on the HPLMN S-NSSAIs received from the source AMF. Alternatively, the target AMF may query a network slice selection function (NSSF) of the target network by invoking a Nnssf_NSSelection_Get service operation with the HPLMN S-NSSAIs and PLMN identity (ID) of a subscription permanent identifier (SUPI). Based on the query result returned from the NSSF, the target AMF may determine whether AMF reallocation needs be triggered and if needed reselect another target AMF. In this case, the target AMF selected by the S-AMF refers to an initial AMF (or l-AMF), and another reselected target AMF refers to a final target AMF (i.e., a T-AMF).

[0004] In the EPS to 5GS handover using an N26 interface, the initial AMF may receive the corresponding HPLMN S-NSSAIs for home routed (HR) packet data unit (PDU) session(s) from a session management function (SMF) and packet gateway (PGW) control plane (PGW-C). Based on the received S-NSSAI from the SMF and PGW-C (also called SMF+PGW-C), the initial AMF may reselect a target AMF, for example, as described in clause 5.15.5.2.1 of TS 23.501 , VERSION 18.1.0 (TS 23.501) and invoke a Namf_Communication_RelocateUEContext request to the selected target AMF with an SUPI, a target 5G access network (5G AN) Node ID, a PDU session ID and the S-NSSAI associated with N2 session management (SM) information received, a source to target transparent container, 5GS mobile management (MM) context, an MME Tunnel Endpoint Identifier for Control Plane, an MME Address for Control plane, aPDU session ID and its associated S-NSSAI of a VPLMN value for each PDU Session, the corresponding S-NSSAI of a HPLMN value for HR PDU session(s), SMF+PG W-C ID of each PDU session, a default visited SMF (V-SMF) ID and a SM Context ID of each PDU session, allocated EPS Bearer Identities (EBls) of each PDU session, an allowed NSSAI received from the NSSF, and / or the like.SUMMARY

[0005] 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.

[0006] As described above, in an inter-PLMN HR roaming scenario, the HPLMN S-NSSAIs may be received from the source AMF, or returned from the SMF+PGW-C in the HPLMN, and the NSSF will be contacted for selection of the target AMF by the initial AMF. The inter-PLMN handover could be performed between a HPLMN and a VPLMN or between VPLMNs. In roaming cases, as described in TS 23.501 , a unified data management (UDM) may provide to the VPLMN the S-NSSAIs from subscribed S-NSSAIs which the HPLMN allows for a UE in the VPLMN. Thus, it is possible for the UE to have different subscribed S-NSSAIs in the different PLMNs.

[0007] However, resources in a next generation radio access network (NG-RAN), a V-SMF, an AMF and a UPF in the VPLMN would be allocated for the PDU session (s) of the network slice which is finally no longer available in the VPLMN to this UE in the handover procedure, and then released in the registration procedure. This may cause a waste of resources in the different nodes of the VPLMN. Moreover, handover of the PDU session(s) for the network slice not available in the VPLMN may introduce a lot of signaling overhead.

[0008] To overcome or mitigate at least one of the above-mentioned problems or other problems or provide a useful solution, embodiments of the present disclosure propose communication methods, communication devices and storage medium.

[0009] In a first aspect of the present disclosure, there is provided a method implemented at a network node during handover of a UE from a source network to a target network. In the method, the network node causes selection of at least one allowed network slice identification from a set of home network slice identifications of the source network based on a set of subscribed network slice identifications of the target network. The set of home network slice identifications and the set of subscribed network slice identifications are associated with the UE, and the at least one allowed network slice identification is avail able for the UE in the target network. Then, the network node causes execution of the handover based on the at least one allowed network slice identification.

[0010] In an embodiment, the network node may comprise a first AMF of the target network.

[0011] In an embodiment, the network node may transmit the set of home network slice identifications and the set of subscribed network slice identifications to a NSSF of the target network . Then, the network node may receive the at least one allowed network slice identification from the NSSF of the target network.

[0012] In an embodiment, the network node may transmit a session management context request to the first SMF of the target network. The session management context request may include at least one home network slice identification of the set of home network slice identifications. The network node may receive a session management context response from the first SMF of the target network . The session management context response may include an indication whether the at least one home network slice identification is allowed by the target network.

[0013] In an embodiment, the network node may receive the set of subscribed network slice identifications from a UDM of a home network.

[0014] In an embodiment, the network node may transmit a subscription data management get message to the UDM of the home network. The set of subscribed network slice identifications is received from the UDM in response to transmitting the subscription data management get message.

[0015] In an embodiment, after receiving a create UE context request from a second AMF of the source network, the network node may transmit the subscription data management get message to the UDM.

[0016] In an embodiment, after receiving a create session management context response from a first session management function, SMF, of the target network, the network node may transmit the subscription data management get message to the UDM.

[0017] In an embodiment, the network node may receive the set of home network slice identifications from at least one of the second AMF of the source network, or an SMF and PGW-C of the home network.

[0018] In an embodiment, the network node may transmit an update session management context request to the first SMF of the target network. The update session management context request may include an indication for cancelling session resources associated with at least one home n etwork slice identification of the set of home network slice identifications unallowed by the target network.

[0019] In an embodiment, the network node may comprise the first SMF of the target network.

[0020] In an embodiment, the network node may receive a session management context request from the first AMF of the target network. The session management context request may include at least one home network slice identification of the set of home network slice identifications. The network node may transmit a session management context response to the first AMF of the target network . The session management context response may include an indication whether the at least one home network slice identification is allowed by the target network.

[0021] In an embodiment, the network node may transmit a session management context request to thesecond SMF or the SMF and PGW-C of the home network. The session management context request may include an identity of the target network. The network node may receive a session management context response from the second SMF or the SMF and PGW-C of the home network. The session management context response may include an indication whether the at least one home network slice identification is allowed by the target network.

[0022] In an embodiment, the network node may transmit a session update request to an SMF and PGW- C of the home network. The session update request may include an indication for cancelling session resources associated with at least one home network slice identification of the set of home network slice identifications unallowed by the target network.

[0023] In an embodiment, the network node may comprise the second SMF or the SMF and PGW-C of the home network.

[0024] In an embodiment, the network node may receive, from the UDM of the home network, information associated with the set of subscribed network slice identifications. The network node may determine, based on the received information, whether at least one home network slice identification of the set of home network slice identifications is available in the target network.

[0025] In an embodiment, the information associated with the set of subscribed network slice identifications may comprise an indication whether the at least one home network slice identification is available in the target network.

[0026] In an embodiment, the network node may transmit a subscription data management get message to the UDM of the home network. The subscription data management get message may include at least an identity of the target network. After transmitting the subscription data management get message, the network node may receive the indication whether the at least one home network slice identificatio n is available in the target network.

[0027] In an embodiment, the network node may comprise the first SMF of the target network. After receiving a create session management context request from the first AMF of the target network , the network node may transmit the subscription data management get message to the UDM.

[0028] In an embodiment, the network node comprises the first SMF of the target network. After receiving a session create response from the SMF and PGW-C of the home network, the network node may transmit the subscription data management get message to the UDM.

[0029] In an embodiment, the network node may comprise the second SMF of the home network. After receiving a session context request from the first SMF of the target network, the network node may transmit the subscription data management get message to the UDM.

[0030] In an embodiment, the network node may comprise the SMF and PGW-C of the home network. Afterreceiving a session create request from the first SMF of the target network, the network node may transmit the subscription data management get message to the UDM.

[0031] In an embodiment, the subscription data management get message further include at least one of: the at least one home network slice identification, or an indication for checking availability of the set of home network slice identifications in the target network.

[0032] In an embodiment, the selection of the at least one allowed network slice identification may be performed in a preparation phase of the handover.

[0033] In an embodiment, the handover may comprise at least one of: N2 based handover, or EPS to 5GS handover.

[0034] In an embodiment, the network slice identification may comprise NSSAI.

[0035] In an embodiment, the source network may comprise the home network, and the target network comprises a first visited network. In another embodiments, the source network comprises the first visited network, and the target network comprises a second visited network.

[0036] In a second aspect of the present disclosure, there is provided a network node. The traffic server comprises a processor and a memory coupled to the processor, the memory containing instructions executable by the processor, whereby the network node is operative to perform the method according to the first aspect.

[0037] In a third aspect of the present disclosure, there is provided an apparatus. The apparatus comprises means for performing the method according to the first aspect.

[0038] In a fourth aspect of the disclosure, there is provided a computer-readable storage medium having instructions stored thereon, the instructions, which, when executed by at least one processor of a device, cause the device to perform the method according to the first aspect.

[0039] With the present disclosure, a network slice no longer available in the target network may be identified early in the handover procedure. Further, session(s) of the network slice no longer available in the target network may be prevented to be handed over from the source network to the target network as soon as possible. Thus, resource saving may be achieved, and handover efficiency may be improved.BRIEF DESCRIPTION OF THE DRAWINGS

[0040] 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.

[0041] FIG. 1 is a diagram showing an example communication environment in which embodiments of thepresent disclosure can be implemented.

[0042] FIG. 2A is a signaling diagram showing an example handover process in accordance with some embodiments of the present disclosure.

[0043] FIG. 2B is a diagram showing an example process of early slice selection subscription data retrieval during the N2 based handover in accordance with some embodiments of the present disclosure .

[0044] FIG. 2C is a diagram showing an example process of early slice selection subscription data retrieval during the EPS to 5GS handover in accordance with some embodiments of the present disclosure .

[0045] FIG. 3A is a diagram showing another example handover process in accordance with some embodiments of the present disclosure.

[0046] FIG. 3B is a diagram showing an example session validation process during the N2 based handover in accordance with some embodiments of the present disclosure.

[0047] FIG. 3C is a diagram showing an example session validation process during the EPS to 5GS handover in accordance with some embodiments of the present disclosure .

[0048] FIG. 4A is a signaling diagram showing yet an example handover process in accordance with some embodiments of the present disclosure.

[0049] FIG. 4B is a signaling diagram showing another example session validation process during the N2 based handover in accordance with some embodiments of the present disclosure .

[0050] FIG. 4C is a signaling diagram showing another example session validation process during the EPS to 5GS handover in accordance with some embodiments of the present disclosure .

[0051] FIG. 5 is a diagram showing an example inter-PLMN N2 based handover process in accordance with some embodiments of the present disclosure.

[0052] FIG. 6 is a signaling diagram showing an example EPS to 5GS handover process in accordance with some embodiments of the present disclosure.

[0053] FIG. 7 is a block diagram showing a flowchart of an example handover method in accordance with some embodiments of the present disclosure.

[0054] FIG. 8 is a block diagram showing a device in accordance with some embodiments.

[0055] FIG. 9 is a block diagram showing a computer readable storage medium in accordance with some embodiments.

[0056] FIG. 10 is a block diagram showing an example of a communication system in accordance with some embodiments.

[0057] FIG. 11 is a block diagram showing a network node in accordance with some embodiments.

[0058] FIG. 12 is a block diagram illustrating a virtualization environment in which functions implemented by some embodiments may be virtualized.DETAILED DESCRIPTION

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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 notpreclude 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.

[0063] As used herein, the term "terminal device” refers to a device which is intended for accessing services via an access network and configured to communicate over the access network. The terminal device may be able to communicate with a network node, such as a base station, or with another terminal device by transmitting and / or receiving wireless signals. For instance, the terminal device may include, but is not limited to: a mobile phone, a smart phone, a sensor device, a meter, a vehicle, a household appliance, a medical appliance, a media player, a camera, or any type of consumer electronic, for instance, but not limited to, a television, radio, lighting arrangement, a tablet computer, a laptop, or a personal computer (PC). The terminal device may also include a portable, pocketstorable, hand-held, computer-comprised, or vehicle-mounted mobile device, enabled to communicate voice and / or data, via a wireless connection. In the following description, the terms "terminal device”, "user equipment” and "UE” may be used interchangeably.

[0064] As used herein, the term "network node” refers to a device in a communication network via which a terminal device receives services from the network. The terms "network node”, "network function” may be used interchangeably. A network function can be implemented either as a network element on a dedicated hardware, as a software instance running on a dedicated hardware, or as a virtualised function instantiated on an appropriate platform, e.g. on a cloud infrastructure. The network node comprises an access network node via which a terminal device accesses an access network. Examples of access network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs) and newNR NodeBs (gNBs)). In the following description, the terms "access network node”, "base station” and "BS” may be used interchangeably.

[0065] The network node may further comprise a core network node. Examples of core network nodes may include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), a Home Subscriber Server (HSS), an Access and Mobility Management Function (AMF), a Session Management Function (SMF), a Network Slice Selection Function (NSSF), a Packet Gateway (PGW), an Authentication Server Function (AUSF), a Subscription Identifier De-concealing function (SIDF), a Unified Data Management (UDM), a Security Edge Protection Proxy (SEPP), a Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0066] As described above, it is possible for the UE to have different subscribed S-NSSAIs in the different PLMNs. If the subscribed S-NSSAIs in the different PLMNs (e.g., a HPLMN and a VPLMN) are different, but slice mapping in the NSSF of a serving PLMN (e.g., a VPLMN) supports all HPLMN S-NSSAIs accordingto a roaming agreement, then the PDU session(s) of the S-NSSAI(s), which is no longer available in a target PLMN, might be existing in a preparation phase for the handover, and even most time of an execution phase of the handover. After the target AMF receives the subscribed NSSAI for this UE in the corresponding PLMN from the UDM in the execution phase, the target AMF may distinguish the S-NSSAI(s), which is no longer available in the VPLMN, based on the allowed NSSAI, which is recalculated with the subscribed S- NSSAIs.

[0067] By way of example, a UE registers in the HPLMN, and the subscribed S-NSSAIs is {slice-1 , slice-2, slice-3}. The UE establishes PDU Sessions on the S-NSSAIs {slice-1 , slice-2, slice-3}. Then, the N2 based handover happened for this UE, and the UE is handed over to a VPLMN. In the NSSF of VPLMN, the slice mapping is supported for HPLMN S-NSSAIs {slice-1 , slice-2, slice-3} based on the roaming agreement, which could be {{slice-1 ', slice-1}, {slice-2', slice-2}, {slice-1 ', slice-3}}. The slice-1' and the slice-2' are the values of S-NSSAI mapping from the HPLMN S-NSSAI in the serving PLMN.

[0068] For this UE, only subscribed S-NSSAIs of slice-1 and slice-2 are allowed to be used in the VPLMN. The PDU sessions established on HPLMN S-NSSAIs {slice-1 , slice-2, slice-3} will be handed over to the VPLMN, the corresponding resources will be created in the target next generation radio access network (NG-RAN), a V-SMF in the VPLMN, a UPF in the VPLMN and an AMF in the VPLMN for HR roaming in the preparation phase. In the execution phase, the signaling for PDU sessions {slice-1 , slice-2, slice-3} will be performed as well. For example, in the registration procedure, the AMF retrieves the subscribed S-NSSAIs {slice-1 , slice-2} from the UDM, and receives a new allowed NSSAI based on that from the NSSF. Thus, the AMF detects that HPLMN S-NSSAI slice-3 is no longer available with the new allowed NSSAI, then the PDU session release procedure will be triggered by the AMF for the PDU sessions on this slice.

[0069] As described above, resources in the NG-RAN, the V-SMF, the AMF and the UPF in the VPLMN would be allocated for the PDU sessions of the slice finally no longer available in the VPLMN to this UE in the handover procedure, and then released in the registration procedure. This will cause a waste of resources in the different nodes of the VPLMN. This might cause additional issue specially when the free resources are limited, e.g., resource pre-empt. Moreover, user plane data would be transferred for the PDU sessions no longer available in the target PLMN during most time of the handover procedure, which might impact various aspects, e.g., charging. In another aspect, it may also introduce a lot of signaling overhead for the PDU session(s) of the slice not available in the VPLMN.

[0070] Certain aspects of the disclosure and their embodiments may provide solutions to these or other challenges. Some embodiments of the present disclosure propose a handover scheme. The proposed scheme utilizes a set of home network slice identifications (such as HPLMN S-NSSAIs) and a set of subscribed network slice identifications (such as subscribed S-NSSAIs) early in a handover procedure of a UE to identify a network slice identification of the home network slice identifications which is not allowed in a target network. As such, the network slice no longer available in the target network, which correspondsto the unallowed network slice identification, may be found at an early phase (for example, a preparation phase) of the handover procedure.

[0071] In this way, the PDU session(s) of the network slice no longer available in the target network may be prevented to be handed over from the source network to the target network as soon as possible. Thus, there is no resources allocated in related nodes, thereby saving resources and improving handover efficiency.

[0072] Some example implementations will be described below with reference to the accompanying drawings.

[0073] FIG. 1 illustrates an example communication environment 100 in which embodiments of the present disclosure can be implemented.

[0074] As shown in FIG. 1 , the communication environment 100 comprises a UE 110 which is roaming from a source network 120 to a target network 130. As the UE 110 is roaming, handover is performed from the source network 120 to the target network 130. The source and target networks 120 and 130 may be any type of networks. In some embodiments, the source network 120 may be a home network (such as a HPLMN) of the UE 110, and the target network 130 may be a visited network (such as a VPLMN) of the UE 110. In some other embodiments, both the source and target networks 120 and 130 may be visited networks of the UE 110. In the context of the present disclosure, a home network refers to a network in which a UE originally registers and by which the UE has a subscription to services. A visited network refers to a network used by a UE while roaming outside of its home network. The home and visited networks may be provided by one or more operators.

[0075] The source and target networks 120 and 130 may comprise any suitable network nodes via which the UE 110 receives services from the source and target networks 120 and 130. Communications in the environment 100 may be implemented according to any communication protocols and technologies that already exist or is to be developed in the future.

[0076] It is to be understood that the deployments of the communication environment 100 are shown in FIG. 1 only for the purpose of illustration, without suggesting any limitations. In an example, in the case that the roaming occurs between two visited networks, the communication environment 100 may comprise a home network of the UE 1 10 which may provide UE context information during handover between the visited networks.

[0077] In various embodiments, during handover of the UE 110 from the source network 120 to the target network 130, a network node, which may be located in the source network 120, the target network 130, a home network or another network, causes selection of at least one allowed network slice identification from a set of home network slice identifications of a home network. The selection is performed based on a set of subscribed network slice identifications of the target network 130 before execution of the handover. Inan example, NSSAI may be used as the network slice identification, and HPLMN S-NSSAIs and subscribed S-NSSAIs may be used as the home network slice identifications and the subscribed network slice identifications, respectively. Other forms of network slice identifications are also possible.

[0078] In some embodiments, to implement the early selection of the allowed network slice identification, slice selection subscription data retrieval may be moved ahead such that the network slice no longer available in the target network 130 may be prevented to be handed over from the source network 120 to the target network 130 as soon as possible. Some embodiments in this regard will be described below with reference to FIGS. 2A to 2C.

[0079] FIG. 2A shows an example handover process 200 in accordance with some embodiments of the present disclosure.

[0080] In this example, the target network 130 may comprise an AMF 202 (referred to as a first AMF) which may be an initial AMF or l-AMF or a final target AMF or T-AMF. The target network 130 may further comprise an NSSF 204 and an SMF 206 (referred to as a first SMF 206). In the example embodiments where the target network 130 is a visited network, the first SMF 206 may be a visited SMF or V-SMF. In addition to the target network 130, the process 200 may involve a home network 208 which may comprise a UDM 210. In some embodiments, the home network 208 may act as the source network 120.

[0081] In some embodiments, the first AMF 202 may be adapted to cause the selection of the allowed network slice identification from the home network slice identifications to facilitate the handover of the UE 110. In an example, the first AMF 202 may cause the NSSF 204 to select the allowed network slice identification. For example, as shown in FIG. 2A, the first AMF 202 may transmit (213) the set of home network slice identifications and the set of subscribed network slice identifications to the NSSF 204 for network slice selection. Then, the first AMF 202 may receive (214) the at least one allowed network slice identification from the NSSF 204. In some embodiments, the AMF reallocation may be triggered if needed based on the result from the NSSF 204.

[0082] The home network slice identifications may be received by the first AMF 202 from an AMF (referred to as a second AMF) of the source network 120, or an SMF+PGW-C of the home network 208, as will be detailed in the following paragraphs. The subscribed network slice identifications may be received by the UDM 210. In some embodiments, as shown in FIG. 2A, the first AMF 202 may transmit (211) a subscription data management get message such as a Nudm_SDM_Get request to the UDM 210 and then receive (212) the set of subscribed network slice identifications from the UDM 210.

[0083] The slice selection subscription data retrieval from the UDM 210 may be performed after the home network slice identifications are received from the second AMF of the source network 120 or the SMF+PGW- C of the home network 208 (not shown). Then, the first AMF 202 may use the home network slice identifications and the subscribed network slice identifications as the input to the NSSF 204 for the networkslice selection.

[0084] In an example, the first AMF 202 may transmit (211 ) the subscription data management get message to the UDM 210 after receiving a create UE context request such as a Namf_Communication_CreatedUEContext request from the second AMF of the source network. Alternatively, or in addition, the first AMF 202 may transmit (21 1) the subscription data management get message to the UDM 210 after receiving a create session management context response such as a Nsmf_PDUSession_CreateSMContext response from the first SMF 206 of the target network.

[0085] The NSSF 204 may build an allowed network slice identification based on the slice mapping in the NSSF 204 and the subscribed network slice identifications and the home network slice identifications from the first AMF 202. The NSSF 204 may then respond to the first AMF 202 with the allowed network slice identification. With the allowed network slice identification returned from the NSSF 204, the first AMF 202 may detect which slice is no longer available in the target network 130.

[0086] The slice selection subscription data retrieval may be triggered early in the handover procedure, for example, in any time of a preparation phase of the handover procedure. In an example, in the case of the N2 based handover, the first AMF 202 may retrieve the subscription data after receiving a create UE context request from the second AMF of the source network 120. In another example, in the case of the EPS to 5GS handover, the first AMF 202 may retrieve the subscription data after the session management context creation procedure for the network slices.

[0087] In some embodiments, the first AMF 202 further cause the execution of the handover based on the at least one allowed network slice identification. For example, in the case of the N2 based handover, the first AMF 202 may transmit (220) a session management context request to the first SMF 206 for the allowed network slice identification, or for the corresponding network slice which is available in the target network 130. As a response, the first SMF 206 may continue (222) the handover procedure based on the allowed network slice identification.

[0088] The session management context request may be any type of requests associated with the session management context. In an example, the request sent from the first AMF 202 to the first SMF 206 may comprise a create session management context request such as a Nsmf_PDUSession_CreateSMContext request for PDU session(s) of the available network slice. In this way, the PDU session(s) of the network slice no longer available in the target network 130 will be prevented to be handed over from the source network 120 to the target network 130. Thus, there is no resource allocated in the corresponding nodes, thereby improving resource efficiency.

[0089] In some embodiments, in the case of the EPS to 5GS handover, the first AMF 202 may clean up session resources created for the network slice in the first SMF 206 during session management context creation procedure. In an example, the first AMF 202 may utilize the handover cancel procedure towardsthe first SMF 206 to release the resource allocated before. In some embodiments, as shown in FIG. 2A, the first AMF 202 may transmit (220) an update session management context request to the first SMF 206. The update session management context request may include an indication for cancelling session resources associated with at least one home network slice identification of the set of home network slice identifications unallowed by the target network 130. In an example, a relocation cancel indication may be used as such an indication. The update session management context request may comprise any type of requests for updating session management context, including, for example, a Nsmf_PDUSession_UpdateSMContext request.

[0090] Accordingly, the first SMF 206 may release (222) the session management context of the PDU session(s) for the unallowed home network slice identification in the first SMF 206. In some embodiments, the first SMF 206 may further clean up the resources created for the network slice in the SMF+PGW-C of the home network 208, as will be detailed in the following paragraphs.

[0091] FIG. 2B show an example process 224 of early slice selection subscription data retrieval during the N2 based handover in accordance with some embodiments of the present disclosure. In the process 224, the target network 130 may be a VPLMN (referred to as a first VPLMN) of the UE 110, and the source network 120 may be a HPLMN or another VPLMN (referred to as a second VPLMN) of the UE 110. It is to be understood that PLMNs are only examples of networks, and the source network 120, the target network 130 and the home network 208 may be any suitable type of networks.

[0092] As shown in FIG. 2B, a source AMF or S-AMF 228 of the source network 120 may transmit (230) to an initial AMF or l-AMF 232 (as an example implementation of the first AMF 202 as shown in FIG. 2A) of the target network 130 a Namf_Communication_CreatedUEContext request with HPLMN S-NSSAIs (as example implementations of the home network slice identifications). The l-AMF 232 may retrieve subscribed S-NSSAIs (as example implementations of the subscribed network slice identifications) from the UDM 210 later after the HPLMN NSSAI is received from the S-AMF 228. For the slice selection subscription data retrieval, the l-AMF 232 may transmit (236) a Nudm_SDM_Get request to the UDM 210 with VPLMN ID. The UDM 210 may transmit (238) a response to the l-AMF 232 with subscribed NSSAI. As such, the network slice no longer available in the target network 130 may be found by the NSSF 204 based on the subscribed NSSAI and HPLMN S-NSSAIs.

[0093] Then, the l-AMF 232 may use it, together with the HPLMN S-NSSAIs received, as the input to the NSSF 204 for the network slice selection. As shown in FIG. 2B, the l-AMF 232 may transmit (240) a Nnssf_NSSelection_Get request to the NSSF 204 with the subscribed NSSAIs. The NSSF 204 may build an allowed NSSAI based on the slice mapping in the NSSF 204 and the subscribed NSSAI and HPLMN NSSAI from the l-AMF 232. The NSSF 204 may transmit (242) a Nnssf_NSSelection_Get response to the l-AMF 232 with the available information (e.g., allowed NSSAI(s), the mapping of allowed NSSAI(s)), together with the candidate AMF Set or AMF instances. Herein, the allowed NSSAI refers to a HPLMNNSSAI allowed in the VPLMN, and the mapping of allowed NSSAI refers to a VPLMN NSSAI mapped from the allowed NSSAI.

[0094] With the allowed NSSAI returned from the NSSF 204, the l-AMF 232 will detect which slice is no longer available in the target network 130. At 244, based on the query result returned from the NSSF 204, the l-AMF 232 determines whether the AMF re-allocation need be triggered. If needed, the result from the NSSF 204 will be included in the request to a selected target AMF or T -AMF 246. If not needed, the l-AMF 232 operates as the target AMF. The l-AMF 232 will mark the slice not longer available in the target network according to the allowed NSSAI from the NSSF 204 and the HPLMN NSSAI from the S-AMF 228. Then, the handover procedure continues. In an example, the l -AMF 232 will not send a Nsmf_PDUSession_CreateSMContext request for the PDU session(s) of the network slice no longer available in the target network 130.

[0095] It is to be understood that the network deployments as shown in FIG. 2B are only illustrative, but not limited. Any number and type of networks, nodes, and devices may be applied in the process 200 depending on the specific implementations. For example, in the case of a handover from a home network to a visited network, the home network 208 and the source network 120 may be the same network.

[0096] FIG. 2C shows an example process 245 of early slice selection subscription data retrieval during the EPS to 5GS handover in accordance with some embodiments of the present disclosure .

[0097] Different from the process 224 as shown in FIG. 2B, in the process 245, the slice selection subscription data retrieval is performed after the session management context creation for the network slice, for example, after the Initial AMF 232 receives (248) a Nsmf_PDUSession_CreateSMContext response from the default visited SMF or V-SMF 250.

[0098] In this case, the Initial AMF 232, which operates as the target AMF, may clean up the SMContext of PDU session in a default V-SMF 250, and the individual PDU session resource in an SMF+PGW-C 252 created in the previous steps for the PDU session(s) of the network slice no longer available in the target network 130. In an example, a handover cancel procedure 254 may be performed towards the default V- SMF 250 and the SMF+PGW-C 252 to release the resource allocated before.

[0099] As shown in FIG. 2C, the Initial AMF 232 may transmit (256) a Nsmf_PDUSession_UpdateSMContext request to the default V-SMF 250 with a relocation cancel indication as an example implementation of an indication for cancelling session resources associated with at least one home network slice identification of the set of home network slice identifications unallowed by the target network 130. The default V-SMF 250 may release the resources allocated before for the unavailable network slice. The default V-SMF 250 may further transmit (258) a Nsmf_PDUSession_Update request to the SMF+PGW-C 252 with a relocation cancel indication. Accordingly, the SMF+PGW-C 252 may release the allocated resource.

[0100] In some embodiments, the Initial AMF 232 may indicate a source AMF (not shown) or an MME 260 that the corresponding PDU session(s) of the network slice no longer available in the target network 130 cannot be transferred. The source AMF or the MME 260 will release the PDU session in the legacy approach.

[0101] Still with reference to FIG. 2A, instead of or in addition to causing the NSSF 204 to select the allowed network slice identification from the home network slice identifications, in some embodiments, the first AMF 202 may cause the first SMF 206 to select the allowed network slice identification or trigger the selection of the allowed network slice identification. In some embodiments, session validation for the target network 130 based on the session management subscription data may be introduced in the preparation phase of the handover of the UE 1 10. Some embodiments in this regard will be discussed below with reference to FIGS. 3A to 3C.

[0102] FIG. 3A shows an example handover process 300 in accordance with some other embodiments of the present disclosure.

[0103] In this example, the first SMF 206 may be adapted to or caused by the first AMF 202 to select the allowed network slice identification from the home network slice identifications to facilitate the handover of the UE 110.

[0104] In the process 300, the first AMF 202 may transmit (302) a session management context request to the SMF 204. The session management context request may include at least one home network slice identification of the set of home network slice identifications. The session management context request may be any type of requests for session management context, including, for example, a create session management context request such as a Nsmf_PDUSession_CreateSMContext request for PDU session(s) of the available network slice. After receiving this session management context request, the first SMF 206 may perform session validation for the target network 130.

[0105] In some embodiments, the first SMF 206 may check the session validation to the UDM 210. As shown in FIG. 3A, the first SMF 206 may transmit (304) a subscription data management get message (or request) to the UDM 210. The subscription data management get message may include at least an identity (ID) of the target network 130. The subscription data management get message may comprise any type of messages for getting session management subscription data. In an example, the subscription data management get message may comprise a Nudm_SDM_Get request.

[0106] In an example, the first SMF 206 may transmit (304) the subscription data management get message to the UDM 210 after receiving a create session management context request (such as a Nsmf_PDUSession_CreateSMContext request) from the first AMF 202 of the target network. In another example, the first SMF 206 may transmit (304) the subscription data management get message to the UDM 210 after receiving a session create response (such as a Nsmf_PDUSession_Create response) from the SMF and PGW-C of the home network 208 (not shown).

[0107] Then, the first SMF 206 may receive (306) information associated with the set of subscribed network slice identifications from the UDM 210. Based on the received information, the first SMF 206 may determine (308) whether at least one home network slice identification of the set of home network slice identifications is available in the target network 130. The received information may comprise any information associated with the subscribed network slice identifications. In some embodiments, the information may comprise session management subscription data for the target network 130. Based on the session management subscription data, the first SMF 206 may utilize the home network slice identifications to determine whether a home network slice identifications is available for the target network 130 or not.

[0108] In some embodiments, the information associated with the subscribed network slice identifications may comprise an indication whether the at least one home network slice identification is available in the target network 130. This indication may be determined by the UDM 210 based on the subscribed network slice identifications. In some embodiments, the subscription data management get message sent from the first SMF 206 to the UDM 210 may further include at least one home network slice identification. Based on the session management subscription data of the target network 130, the UDM 210 may determine whether the at least one home network slice identification is available in the target network 130 and then transmit the corresponding indication to the first SMF 206. In this way, the overhead may be reduced, and the resource efficiency may be improved.

[0109] In some embodiments, the subscription data management get message may comprise an indication for checking availability of the set of home network slice identifications in the target network 130. After receiving such a subscription data management get message, the UDM 210 may know that this message is only used to check the home network slice identifications is available for the target network 130 or not. In this case, other information (e.g., dnnConfigurations) in the session management subscription data is meaningless for this purpose. Thus, the corresponding attributes may be skipped in the response from the UDM 210. As such, the processing resources may be saved, and the processing efficiency may be improved in the UDM 210.

[0110] In some embodiments, the subscription data management get message sent from the first SMF 206 to the UDM 210 may not include a home network slice identification. In this case, such a message or request may be used to retrieve session management subscription data for all the home network slice identifications, and the session validation may be performed for all the home network slice identifications. Then, the UDM 210 may transmit an availability indication related to all the home network slice identifications to further reduce the signaling overhead and improve the communication efficiency.

[0111] Based on the indication from the UDM 210, the first SMF 206 may determine (232) whether at least one home network slice identification of the set of home network slice identifications is available in the target network 130. Then, the first SMF 206 may transmit (310) a session management context response to the first AMF 202. In an example, the session management context response may comprise a createsession management context response such as a Nsmf_PDUSession_CreateSMContext response. The session management context response may include an indication whether the at least one home network slice identification is allowed by the target network 130. The first AMF 202 may perform the subsequent operations to facilitate the handover of the UE 110.

[0112] In some embodiments, in the case of the EPS to 5GS handover, the session validation may be performed by the first SMF 206 during the session management context creation procedure. In an example, after the first AMF 202 transmits (302) the session management context request to the first SMF 206, the first SMF 206 may transmit a session creation request such as a Nsmf_PDUSession_create request to an SMF+PGW-C of the home network 208 (not shown) and then receive a session creation response from the SMF+PGW-C, for example, with the home network slice identifications. Using the home network slice identifications, the first SMF 206 may check the session validation to the UDM 210.

[0113] In some embodiments, in the case of the EPS to 5GS handover, the first SMF 206 may clean up the resource created for the network slice which is no longer available in the target network 130. In an example, the first SMF 206 may transmit a session update request to an SMF+PGW-C of the home network 208. The session update request may include an indication for cancelling session resources associated with at least one home network slice identification of the set of home network slice identifications unallowed by the target network 130. The session update request may comprise any type of requests for updating sessions, for example, which may comprise a Nsmf_PDUSession_Update request with a relocation cancel indication. Accordingly, the SMF+PGW-C may perform the cleanup of the resources created for the PDU session(s) which is invalid due to the network slice is not valid in the target network 130.

[0114] FIG. 3B show an example session validation process 312 during the N2 based handover in accordance with some embodiments of the present disclosure. In the process 312, the target network 130 may be the first VPLMN of the UE 110, and the source network 120 may be a HPLMN or the second VPLMN of the UE 110. The target network 130 may also referred to as a serving network.

[0115] As shown in FIG. 3B, session validation for the target network 130 is performed at a visited SMF or V-SMF 316 (as an example implementation of the first SMF 206 as shown in FIG. 3A) based on the session management subscription data. The V-SMF 316 in the serving network will check whether a network slice is valid in the target network 130 or not by checking it with the UDM 210 with VPLMN Identity as well as the HPLMN S-NSSAI.

[0116] As shown in FIG. 3B, after the T-AMF 246 (as an example implementation of the first AMF 202 as shown in FIG. 3A) may transmit (318) a Nsmf_PDUSession_CreateSMContext request to the V-SMF 316, the V-SMF 316 may find that it is an inter-PLMN handover. Then, the V-SMF 316 may check the session validation to the UDM 210 based on the session management subscription data with the specified VPLMN Identity as well as the Home S-NSSAI from the T-AMF 246, or a home SMF or H-SMF 320 of the home network 208. In an example, as shown in FIG. 3B, the V-SMF 316 may transmit (322) a Nudm_SDM_Getrequest to the UDM 210.

[0117] The Nudm_SDM_Get request may include VPLMN identity. In addition, the Nudm_SDM_Get request may include a parameter onlySnssai to indicate that this request is only used to check the network slice is available for the VPLMN or not. An example implementation of the parameter onlySnssai is shown in the following table.Table 1 : URI query parameters supported by the GET method on this resource

[0118] In this case, other information (e.g., dnnConfigurations) except the singleNssai attribute is meaningless for this purpose. Thus, the corresponding attributes can be skipped in a successful response if the parameter onlySnssai is included in the request.

[0119] The Nudm_SDM_Get request may be used to retrieve session management subscription data for all S-NSSAIs for the specific PLMN if no S-NSSAI is included in the request. Such a request may be used for the signaling optimization in the V-SMF 316 or the H-SMF 320 than a request per each S-NSSAI.

[0120] If the network slice is not valid in the target network 130, then the request will be rejected, otherwise, the handover procedure will continue. As shown in FIG. 3B, if a HPLMN S-NSSAI is not allowed, the UDM 210 may transmit (324) to the V-SMF 316 "404 Not Found” to indicate that the HPLMN S-NSSAI is not available. The V-SMF 316 may then transmit (326) to the T-AMF 246 a Nsmf_PDUSession_CreateSMContext response with SNSSAIJJENIED to indicate that the HPLMN S- NSSAI is not allowed in the target network 130.

[0121] In this way, the validation check of a network slice based on the subscribed NSSAI will be performed early in a preparation phase of the inter-PLMN handover procedure, to avoid the handover of PDU sessions of the slices no longer available in the target network 130. Such check may be performed for inter-PLMN handover, and other handover procedures (e.g., an intra-PLMN handover procedure) will not be impacted, for example, to reduce latency.

[0122] FIG. 3C shows an example session validation process 327 during the EPS to 5GS handover using the N26 interface in accordance with some embodiments of the present disclosure.

[0123] Different from the process 312 as shown in FIG. 3B, in the process 327, if the session is invalid due to the network slice is not valid in the target network 130, the cleanup to the SMF+PGW-C 252 for the PDU session created will be performed. As shown in FIG. 3C, the default V-SMF 250 may transmit (328) a Nsmf_PDUSession_Update request to the SMF+PGW-C 252 with a relocation cancel indication.

[0124] Still with reference to FIG. 3A, in some embodiments, the first SMF 206 may trigger an SMF (referredto as a second SMF) or an SMF+PGW-C of the home network 208 to perform the session validation. The session validation process at the second SMF or an SMF+PGW-C of the home network 208 will be described below with reference to FIG. 4A to 4D.

[0125] FIG. 4A shows an example handover process 400 in accordance with some embodiments of the present disclosure.

[0126] In this example, a second SMF 402 of the home network 208 may be adapted to perform the session validation for the home network slice identifications. The second SMF 402 may be an intermediate SMF (or l-SMF) or home SMF (or H-SMF) of the home network 208.

[0127] In the process 400, the first SMF 206 of the target network 130 may transmit (404) a session management context request to the second SMF 402 of the home network 208. The session management context request may include an ID of the target network 130. The session management context request may be any type of requests for session management context, including, for example, a session context request such as a Nsmf_PDUSession_Context request. After receiving this session management context request, the second SMF 402 of the home network 208 may check the session validation for the target network 130 to the UDM 210.

[0128] As shown in FIG. 4A, the second SMF 402 may transmit (406) a subscription data management get message (or request) (such as a Nudm_SDM_Get request) to the UDM 210. The subscription data management get message may include at least the ID of the target network 130. In an example, the second SMF 402 may transmit (406) the subscription data management get message to the UDM 210 after receiving a session context request (such as a Nsmf_PDUSession_Context request) from the first SMF 206 of the target network 130.

[0129] Then, the second SMF 402 may receive (408) information associated with the set of subscribed network slice identifications from the UDM 210. Based on the received information, the first SMF 206 may determine (410) whether at least one home network slice identification of the set of home network slice identifications is available in the target network 130.

[0130] Based on the determining result, the second SMF 402 may transmit (412) a session management context response (such as a Nsmf_PDUSession_Context response) to the first SMF 206. The session management context response may include an indication whether the at least one home network slice identification is allowed by the target network 130. The operations and features related to the session validation implemented at the first SMF 206 as described above with reference to FIGS. 3A to 3C are likewise applicable to the second SMF 402, and thus the details will be omitted.

[0131] Instead of the second SMF 402, an SMF+PGW-C of the home network 208 may be used to exchange with the first SMF 206 and the UDM 210 for the session validation. In this case, the first SMF 206 and the SMF+PGW-C may communicate a session create request and response such as aNsmf_PDUSession_create request and response. In an example, the SMF+PGW-C may transmit a subscription data management get message (such as a Nudm_SDM_Get request) to the UDM 210 after receiving a session create request (such as a Nsmf_PDUSession_create request) from the first SMF 206 of the target network 130. The session validation procedure is similar to the process 236, and thus the details thereof will be omitted.

[0132] FIG. 4B shows an example session validation process 414 in a case of the inter-PLMN N2 based handover in accordance with some embodiments of the present disclosure . In this example, the target network 130 may be a VPLMN, and the source network 120 may be a HPLMN or another VPLMN.

[0133] In the process 414 as shown in FIG. 4B, the H-SMF 320 (as an example implementation of the second SMF 402 as shown in FIG. 4A) in the home network 208 checks whether the slice is valid in the VPLMN or not by checking it with the UDM 210 with VPLMN identity and HPLMN S-NSSAI. In an example, as shown in FIG. 4B, the validation will be performed after the H-SMF 320 receives (418) a Nsmf_PDUSession_Context request from the V-SMF 316. After the H-SMF 320 finds that it is the inter-PLMN handover, the H-SMF 320 may check the session validation to the UDM 210 based on the session management subscription data with the specified VPLMN Identity sent by the V-SMF 316 and the Home S-NSSAI. As shown in FIG. 4B, the H-SMF 320 may transmit (420) a Nudm_SDM_Get request to the UDM 210.

[0134] The session validation is based on the response from the UDM 210 to get the session management subscription data. If the network slice is available for the target network 130, then the UDM 210 will return (422) a successful response (e.g., "200 OK”); otherwise, it returns (424) a failure response with 404 Not Found to the H-SMF 320. Then, the H-SMF 320 may reject the corresponding request from the V-SMF 316 by transmitting (426) a Nsmf_PDUSession_Context response with SNSSAI_DENIED.

[0135] FIG. 4C shows an example session validation process 448 in a case of the EPS to 5GS handover using N26 interface in accordance with some embodiments of the present disclosure.

[0136] In the process 448, the SMF+PGW-C 252 in the home network 208 may perform the validation check. As shown in FIG. 4C, after the SMF+PGW-C 252 receives (450) a Nsmf_PDUSession_Create request from the default V-SMF 250, the SMF+PGW-C 252 may check the session validation to the UDM 210.

[0137] Some example implementations in the inter-PLMN N2 based handover and the EPS to 5GS handover using the N26 interface will be discussed with reference to FIGS. 5 and 6, respectively.

[0138] FIG. 5 shows an example inter-PLMN N2 based handover process 500 in accordance with some embodiments of the present disclosure.

[0139] The process 500 may involve the inter-PLMN N2 based handover from a HPLMN to a VPLMN without an l-SMF in the HPLMN. The process 500 may be also applied to other inter-PLMN N2 handover procedures (for example, between VPLMNs).

[0140] Compared to the procedure in clause 4.23.7.3.2 of TS 23.502, the process 500 has the following differences. In Alternative 1 , at step 1 a, the T-AMF 246 may retrieve the slice selection subscription data from the UDM 210, and then utilize the NSSF 204 for the network slice selection by additionally including the subscribed S-NSSAIs and HPLMN S-NSSAIs. Based on the result from the NSSF 204, the T-AMF 246 may perform the AMF reallocation if needed, or perform the creation of a PDU session only for the slices included allowed NSSAI returned from the NSSF 204. Thus, the PDU session on the slice no longer available may not be continued in the subsequent signaling flow.

[0141] This allowed NSSAI may be reused as well in the target AMF 246 even the AMF reallocation happens, and it may be transferred from an initial AMF to the target AMF 246. The network slice no longer available may be handled as legacy, for example, handled as the PDU session failed to handover due to the slice no longer available.

[0142] In Alternative 2-A, at step 3a, after the V-SMF 316 receives the Nsmf_PDUSession_CreateSMContext request from the T-AMF 246 at step 3, the V-SMF 316 checks whether the slice is valid in the VPLMN by sending a Nudm_SDM_Get request to the UDM 210 with the VPLMN Identity and the Home S-NSSAI received from the T-AMF 246 as well as an indication of only S- NSSAI in the response. If the slice is valid, then the V-SMF 316 may continue to handle the request, and the handover procedure continues.

[0143] If the slice is not valid, a Nsmf_PDUSession_CreateSMContext response with the application error "SNSSAI_DENIED” may be sent by the V-SMF 316. Then, the T-AMF 246 may know that this slice is not valid in the VPLMN, and handle it in the same way as the case that a slice is no longer available.

[0144] In Alternative 2-B, at step 5a-a, after the H-SMF 320 receives a Nsmf_PDUSession_Context request from the V-SMF 316, the H-SMF 320 checks whether the slice is valid in the VPLMN by sending to the UDM 210 a Nudm_SDM_Get request with VPLMN Identity, home S-NSSAI and the indication of only SNSSAI in the response. If the PDU session cannot be transferred to the VPLMN due to the slice no longer available in the VPLMN, then the H-SMF 320 may reject the request, and the V-SMF 316 may send the failure response with the application error “SNSSAI_DENIED" to the T-AMF 246 in a Nsmf_PDUSession_CreateSMContext response. The T-AMF 246 may know that this slice is not valid in the VPLMN, and handle it in the same way as the case that a slice is no longer available.

[0145] FIG. 6 shows an example EPS to 5GS handover process 600 in accordance with some embodiments of the present disclosure.

[0146] For handover from EPS to 5GS using N26 interface, the preparation procedure defined in clause 4.23.12.7.1 of TS 23.502 for the home routed-roaming case are re-used, with the following changes.

[0147] In Alternative 2-B, at step 4c, after the SMF+PGW-C 252 receives a Nsmf_PDUSession_Create request from the V-SMF 316, the SMF+PGW-C 252 checks whether the slice is valid in the VPLMN bysending a Nudm_SDM_Get with VPLMN Identity, Home S-NSSAI and the indication of only SNSSAI in the response to a home subscriber server (HSS) and UDM (HSS+UDM) 602, which is an example implementation of the UDM 210. If the PDU session cannot be transferred to the VPLMN due to the slice no longer available in the VPLMN, then the SMF+PGW-C 252 may reject the request. Then, the V-SMF 316 may send the failure response with the application error " SNSSAI_DENIED" to the target AMF 246 in a Nsmf_PDUSession_CreateSMContext response. The target AMF 246 may know that this slice is not valid in the PLMN, and handle it as in the case that the slice is no longer available.

[0148] In Alternative 2-A, at step 7b, after the V-SMF 316 receives a Nsmf_PDUSession_CreateSMContext response from the SMF+PGW-C 252. The V-SMF 316 checks whether the slice is valid in the VPLMN by sending a Nudm_SDM_Get request to the HSS+UDM 602 with the VPLMN Identity received from the target AMF 246, the Home S-NSSAI received from the SMF+PGW-C 252, and the indication of only S-NSSAI in the response. If the slice is valid, then the V-SMF 316 continues to handle the request, and the handover procedure continues.

[0149] If the slice is not valid, a Nsmf_PDUSession_CreateSMContext response with the application error “SNSSAIJJENIED" may be sent by the V-SMF 316. The target AMF 246 may know that this slice is not valid in the PLMN, and handle it as in the case that the slice is no longer available. Moreover, the V-SMF 316 may send a Nsmf_PDUSession_Update request with "Relocation Cancel Indication” to clean up the resource created after the request in the Step 4b is received.

[0150] In Alternative 1 , at step 8a-a, the target AMF 246 may retrieve the slice selection subscription data from the HSS+UDM 602, and then utilize the NSSF 204 for the network slice selection by additionally including the subscribed S-NSSAIs and HPLMN S-NSSAIs returned from the SMF+PGW-C 252. Based on the result from the NSSF 204, the target AMF 246 may perform the AMF reallocation if needed.

[0151] For the initial AMF 232, it may send a Nsmf_PDUSession_UpdateSMContext with "Relocation Cancel Indication” to clean up the resource created in steps 4a, and 4b for the PDU sessions of the slice no longer available in the VPLMN, i.e. , the corresponding NSSAI not included in the allowed NSSAI returned from the NSSF 204. This allowed NSSAI may be reused as well in the target AMF 246 even the AMF reallocation happens, and it may be transferred from the initial AMF 232 to the target AMF 246.Example Methods

[0152] FIG. 7 shows a flowchart of an example handover method 700 in accordance with some embodiments of the present disclosure. The method 700 can be implemented at a network node in the source network 120, the target network 130, the home network 208, or another network.

[0153] At block 710, the network node causes selection of at least one allowed network slice identification from a set of home network slice identifications of the source network based on a set of subscribed network slice identifications of the target network. The set of home network slice identifications and the set ofsubscribed network slice identifications are associated with the UE, and the at least one allowed network slice identification is available for the UE in the target network. At block 720, the network node causes execution of the handover based on the at least one allowed network slice identification.

[0154] In an embodiment, the network node may comprise a first AMF of the target network.

[0155] In an embodiment, the network node may transmit the set of home network slice identifications and the set of subscribed network slice identifications to a NSSF of the target network. Then, the network node may receive the at least one allowed network slice identification from the NSSF of the target network.

[0156] In an embodiment, the network node may transmit a session management context request to the first SMF of the target network. The session management context request may include at least one home network slice identification of the set of home network slice identifications. The network node may receive a session management context response from the first SMF of the target network. The session management context response may include an indication whether the at least one home network slice identification is allowed by the target network.

[0157] In an embodiment, the network node may receive the set of subscribed network slice identifications from a UDM of a home network.

[0158] In an embodiment, the network node may transmit a subscription data management get message to the UDM of the home network. The set of subscribed network slice identifications is received from the UDM in response to transmitting the subscription data management get message.

[0159] In an embodiment, after receiving a create UE context request from a second AMF of the source network, the network node may transmit the subscription data management get message to the UDM.

[0160] In an embodiment, after receiving a create session management context response from a first session management function, SMF, of the target network, the network node may transmit the subscription data management get message to the UDM.

[0161] In an embodiment, the network node may receive the set of home network slice identifications from at least one of the second AMF of the source network, or an SMF and PGW-C of the home network.

[0162] In an embodiment, the network node may transmit an update session management context request to the first SMF of the target network. The update session management context request may include an indication for cancelling session resources associated with at least one home network slice identification of the set of home network slice identifications unallowed by the target network.

[0163] In an embodiment, the network node may comprise the first SMF of the target network.

[0164] In an embodiment, the network node may receive a session management context request from the first AMF of the target network. The session management context request may include at least one homenetwork slice identification of the set of home network slice identifications. The network node may transmit a session management context response to the first AMF of the target network. The session management context response may include an indication whether the at least one home network slice identification is allowed by the target network.

[0165] In an embodiment, the network node may transmit a session management context request to the second SMF or the SMF and PGW-C of the home network. The session management context request may include an identity of the target network. The network node m ay receive a session management context response from the second SMF or the SMF and PGW-C of the home network. The session management context response may include an indication whether the at least one home network slice identification is allowed by the target network.

[0166] In an embodiment, the network node may transmit a session update request to an SMF and PGW- C of the home network. The session update request may include an indication for cancelling session resources associated with at least one home network slice identification of the set of home network slice identifications unallowed by the target network.

[0167] In an embodiment, the network node may comprise the second SMF or the SMF and PGW-C of the home network.

[0168] In an embodiment, the network node may receive, from the UDM of the home network, information associated with the set of subscribed network slice identifications. The network node may determine, based on the received information, whether at least one home network slice identification of the set of home network slice identifications is available in the target network.

[0169] In an embodiment, the information associated with the set of subscribed network slice identifications may comprise an indication whether the at least one home network slice identification is available in the target network.

[0170] In an embodiment, the network node may transmit a subscription data management get message to the UDM of the home network. The subscription data management get message may include at least an identity of the target network. After transmitting the subscription data management get message, the network node may receive the indication whether the at least one home network slice identification is available in the target network.

[0171] In an embodiment, the network node may comprise the first SMF of the target network. After receiving a create session management context request from the first AMF of the target network , the network node may transmit the subscription data management get message to the UDM.

[0172] In an embodiment, the network node comprises the first SMF of the target network. After receiving a session create response from the SMF and PGW-C of the home network, the network node may transmit the subscription data management get message to the UDM.

[0173] In an embodiment, the network node may comprise the second SMF of the home network. After receiving a session context request from the first SMF of the target network, the network node may transmit the subscription data management get message to the UDM.

[0174] In an embodiment, the network node may comprise the SMF and PGW-C of the home network. After receiving a session create request from the first SMF of the target network, the network node may transmit the subscription data management get message to the UDM.

[0175] In an embodiment, the subscription data management get message further include at least one of: the at least one home network slice identification, or an indication for checking availability of the set of home network slice identifications in the target network.

[0176] In an embodiment, the selection of the at least one allowed network slice identification may be performed in a preparation phase of the handover.

[0177] In an embodiment, the handover may comprise at least one of: N2 based handover, or EPS to 5GS handover.

[0178] In an embodiment, the network slice identification may comprise NSSAI.

[0179] In an embodiment, the source network may comprise the home network, and the target network comprises a first visited network. In another embodiments, the source network comprises the first visited network, and the target network comprises a second visited network.

[0180] All operations and features related to the network node such as the first AMF 202 of the target network 130, the first SMF 206 of the target network 130, or the second SMF 402 or the SMF+PGW-C of the home network 208 as described above with reference to FIGS. 1 to 6 are likewise applicable to the method 700 and have similar effects. For the purpose of simplification, the details will be omitted.Example Device and Medium

[0181] FIG. 8 shows a network node 800 in accordance with some embodiments.

[0182] As shown in FIG. 8, the network node 800 may comprise a processor 805 and a memory 810. The memory 810 may contain instructions 815 executable by the processor 805, whereby the network node 800 may be operative to: cause selection of at least one allowed network slice identification from a set of home network slice identifications of a source network based on a set of subscribed network slice identifications of a target network, wherein the set of home network slice identifications and the set of subscribed network slice identifications are associated with the UE, and the at least one allowed network slice identification is available for the UE in the target network; and cause execution of handover from the source network to the target network based on the at least one allowed network slice identification .

[0183] In an embodiment, the network node 800 may be further operative to implement actions oroperations according to any of the above-mentioned embodiments described with reference to FIGS. 1 to 7.

[0184] The processor 805 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 memory 810 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.

[0185] FIG. 9 shows a computer readable storage medium 900 in accordance with some embodiments.

[0186] As shown in FIG. 9, the computer readable storage medium 900 comprising instructions 815 which when executed by a processor of a device, cause the device to perform any above-mentioned embodiments described with reference to FIGS. 1 to 7.

[0187] The computer readable storage medium 900 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.

[0188] In some embodiments, an apparatus capable of performing the method 700 may comprise means for performing the respective operations of the method 700. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.Example System, Network Node and Virtualization Environment

[0189] FIG. 10 shows an example of a communication system 1000 in accordance with some embodiments.

[0190] In the example, the communication system 1000 includes a telecommunication network 1002 that includes an access network 1004, such as a radio access network (RAN), and a core network 1006, which includes one or more core network nodes 1008. The access network 1004 includes one or more access network nodes, such as network nodes 1010a and 1010b (one or more of which may be generally referred to as network nodes 1010), or any other similar 3rdGeneration Partnership Project (3GPP) access nodes or non-3GPP access points. Moreover, as will be appreciated by those of skill in the art, a network node is not necessarily limited to an implementation in which a radio portion and a baseband portion are supplied and integrated by a single vendor. Thus, it will be understood that network nodes include disaggregated implementations or portions thereof. For example, in some embodiments, the telecommunication network 1002 includes one or more Open-RAN (ORAN) network nodes. An ORAN network node is a node in the telecommunication network 1002 that supports an ORAN specification (e.g., a specification published by the O-RAN Alliance, or any similar organization) and may operate alone or together with other nodes to implement one or more functionalities of any node in the telecommunication network 1002, including one or more network nodes 1010 and / or core network nodes 1008.

[0191] Examples of an ORAN network node include an open radio unit (O-RU), an open distributed unit (0- DU), an open central unit (O-CU), including an O-CU control plane (O-CU-CP) or an O-CU user plane (0- CU-UP), a RAN intelligent controller (near-real time or non-real time) hosting software or software plug-ins, such as a near-real time control application (e.g., xApp) or a non-real time control application (e.g., rApp), or any combination thereof (the adjective "open” designating support of an ORAN specification). The network node may support a specification by, for example, supporting an interface defined by the ORAN specification, such as an A1 , F1 , W1 , E1 , E2, X2, Xn interface, an open fronthaul user plane interface, or an open fronthaul management plane interface. Moreover, an ORAN access node may be a logical node in a physical node. Furthermore, an ORAN network node may be implemented in a virtualization environment (described further below) in which one or more network functions are virtualized. For example, the virtualization environment may include an O-Cloud computing platform orchestrated by a Service Management and Orchestration Framework via an 0-2 interface defined by the 0-RAN Alliance or comparable technologies. The network nodes 1010 facilitate direct or indirect connection of user equipment (UE), such as by connecting UEs 1012a, 1012b, 1012c, and 1012d (one or more of which may be generally referred to as UEs 1012) to the core network 1006 over one or more wireless connections.

[0192] Example wireless communications over a wireless connection include transmitting and / or receiving wireless signals using electromagnetic waves, radio waves, infrared waves, and / or other types of signals suitable for conveying information without the use of wires, cables, or other material conductors. Moreover, in different embodiments, the communication system 1000 may include any number of wi red or wireless networks, network nodes, UEs, and / or any other components or systems that may facilitate or participate in the communication of data and / or signals whether via wired or wireless connections. The communication system 1000 may include and / or interface with any type of communication, telecommunication, data, cellular, radio network, and / or other similar type of system.

[0193] The UEs 1012 may be any of a wide variety of communication devices, including wireless devices arranged, configured, and / or operable to communicate wirelessly with the network nodes 1010 and other communication devices. Similarly, the network nodes 1010 are arranged, capable, configured, and / or operable to communicate directly or indirectly with the UEs 1012 and / or with other network nodes or equipment in the telecommunication network 1002 to enable and / or provide network access, such as wireless network access, and / or to perform other functions, such as administration in the telecommunication network 1002.

[0194] In the depicted example, the core network 1006 connects the network nodes 1010 to one or more hosts, such as host 1016. These connections may be direct or indirect via one or more intermediary networks or devices. In other examples, network nodes may be di rectly coupled to hosts. The core network 1006 includes one more core network nodes (e.g., core network node 1008) that are structured with hardware and software components. Features of these components may be substantially similar to those described with respect to the UEs, network nodes, and / or hosts, such that the descriptions thereof aregenerally applicable to the corresponding components of the core network node 1008. Example core network nodes include functions of one or more of a Mobile Switching Center (MSC), Mobility Management Entity (MME), Home Subscriber Server (HSS), Access and Mobility Management Function (AMF), Session Management Function (SMF), Authentication Server Function (AUSF), Subscription Identifier Deconcealing function (SIDF), Unified Data Management (UDM), Security Edge Protection Proxy (SEPP), Network Exposure Function (NEF), and / or a User Plane Function (UPF).

[0195] The host 1016 may be under the ownership or control of a service provider other than an operator or provider of the access network 1004 and / or the telecommunication network 1002, and may be operated by the service provider or on behalf of the service provider. The host 1016 may host a variety of applications to provide one or more service. Examples of such applications incl ude live and pre-recorded audio / video content, data collection services such as retrieving and compiling data on various ambient conditions detected by a plurality of UEs, analytics functionality, social media, functions for controlling or otherwise interacting with remote devices, functions for an alarm and surveillance center, or any other such function performed by a server.

[0196] As a whole, the communication system 1000 of Figure 10 enables connectivity between the UEs, network nodes, and hosts. In that sense, the communication system may be configured to operate according to predefined rules or procedures, such as specific standards that include, but are not limited to: Global System for Mobile Communications (GSM); Universal Mobile Telecommunications System (UMTS); Long Term Evolution (LTE), and / or other suitable 2G, 3G, 4G, 5G standards, or any applicable future generation standard (e.g., 6G); wireless local area network (WLAN) standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.1 1 standards (WiFi); and / or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, Z-Wave, Near Field Communication (NFC) ZigBee, LiFi, and / or any low-power wide-area network (LPWAN) standards such as LoRa and Sigfox.

[0197] In some examples, the telecommunication network 1002 is a cellular network that implements 3GPP standardized features. Accordingly, the telecommunications network 1002 may support network slicing to provide different logical networks to different devices that are connected to the telecommunication network 1002. For example, the telecommunications network 1002 may provide Ultra Reliable Low Latency Communication (URLLC) services to some UEs, while providing Enhanced Mobile Broadband (eMBB) services to other UEs, and / or Massive Machine Type Communication (mMTC)ZMassive loT services to yet further UEs.

[0198] In some examples, the UEs 1012 are configured to transmit and / or receive information without direct human interaction. For instance, a UE may be designed to transmit information to the access network 1004 on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the access network 1004. Additionally, a UE may be configured for operating in single- or multi-RATor multi-standard mode. For example, a UE may operate with any one or combination of Wi -Fi, NR (New Radio) and LTE, i.e. being configured for multi-radio dual connectivity (MR-DC), such as E-UTRAN (Evolved-UMTS Terrestrial Radio Access Network) New Radio - Dual Connectivity (EN-DC).

[0199] In the example, the hub 1014 communicates with the access network 1004 to facilitate indirect communication between one or more UEs (e.g., UE 1012c and / or 1012d) and network nodes (e .g., network node 1010b). In some examples, the hub 1014 may be a controller, router, content source and analytics, or any of the other communication devices described herein regarding UEs. For example, the hub 1014 may be a broadband router enabling access to the core network 1006 for the UEs. As another example, the hub 1014 may be a controller that sends commands or instructions to one or more actuators in the UEs. Commands or instructions may be received from the UEs, network nodes 1010, or by executabl e code, script, process, or other instructions in the hub 1014. As another example, the hub 1014 may be a data collector that acts as temporary storage for UE data and, in some embodiments, may perform analysis or other processing of the data. As another example, the hub 1014 may be a content source. For example, for a UE that is a VR headset, display, loudspeaker or other media delivery device, the hub 1014 may retrieve VR assets, video, audio, or other media or data related to sensory information via a network node, which the hub 1014 then provides to the UE either directly, after performing local processing, and / or after adding additional local content. In still another example, the hub 1014 acts as a proxy server or orchestrator for the UEs, in particular if one or more of the UEs are low energy loT devices.

[0200] The hub 1014 may have a constant / persistent or intermittent connection to the network node 1010b. The hub 1014 may also allow for a different communication scheme and / or schedule between the hub 1014 and UEs (e.g., UE 1012c and / or 1012d), and between the hub 1014 and the core network 1006. In other examples, the hub 1014 is connected to the core network 1006 and / or one or more UEs via a wired connection. Moreover, the hub 1014 may be configured to connect to an M2M service provider over the access network 1004 and / or to another UE over a direct connection. In some scenarios, UEs may establish a wireless connection with the network nodes 1010 while still connected via the hub 1014 via a wired or wireless connection. In some embodiments, the hub 1014 may be a dedicated hub - that is, a hub whose primary function is to route communications to / from the UEs from / to the network node 1010b. In other embodiments, the hub 1014 may be a non-dedicated hub - that is, a device which is capable of operating to route communications between the UEs and network node 1010b, but which is additionally capable of operating as a communication start and / or end point for certain data channels.

[0201] FIG. 1 1 shows a network node 1100 in accordance with some embodiments. As used herein, network node refers to equipment capable, configured, arranged and / or operable to communicate directly or indirectly with a UE and / or with other network nodes or equipment, in a telecommunication network. Examples of network nodes include, but are not limited to, access points (APs) (e.g., radio access points), base stations (BSs) (e.g., radio base stations, Node Bs, evolved Node Bs (eNBs) and NR NodeBs (gNBs)), O-RAN nodes or components of an O-RAN node (e.g., O-RU, O-DU, O-CU).

[0202] Base stations may be categorized based on the amount of coverage they provide (or, stated differently, their transmit power level) and so, depending on the provided amount of coverage, may be referred to as femto base stations, pico base stations, micro base stations, or macro base stations. A base station may be a relay node or a relay donor node controlling a relay. A network node may also include one or more (or all) parts of a distributed radio base station such as centralized d igital units, distributed units (e.g., in an O-RAN access node) and / or remote radio units (RRUs), sometimes referred to as Remote Radio Heads (RRHs). Such remote radio units may or may not be integrated with an antenna as an antenna integrated radio. Parts of a distributed radio base station may also be referred to as nodes in a distributed antenna system (DAS).

[0203] Other examples of network nodes include multiple transmission point (multi -TRP) 5G access nodes, multi-standard radio (MSR) 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, multi-cell / multicast coordination entities (MCEs), Operation and Maintenance (O &M) nodes, Operations Support System (OSS) nodes, Self-Organizing Network (SON) nodes, positioning nodes (e.g., Evolved Serving Mobile Location Centers (E-SMLCs)), and / or Minimization of Drive Tests (MDTs).

[0204] The network node 1100 includes a processing circuitry 1102, a memory 1104, a communication interface 1106, and a power source 1 108. The network node 1100 may be composed of multiple physically separate components (e.g., a NodeB component and a RNC component, or a BTS component and a BSC component, etc.), which may each have their own respective components. In certain scenarios in which the network node 1100 comprises multiple separate components (e.g., BTS and BSC components), one or more of the separate components may be shared among several network nodes. For example, a single RNC may control multiple NodeBs. In such a scenario, each unique NodeB and RNC pair, may in some instances be considered a single separate network node. In some embodiments, the network node 1100 may be configured to support multiple radio access technologies (RATs). In such embodiments, some components may be duplicated (e.g., separate memory 1104 for different RATs) and some components may be reused (e.g., a same antenna 1110 may be shared by different RATs). The network node 1100 may also include multiple sets of the various illustrated components for different wireless technologies integrated into network node 1100, for example GSM, WCDMA, LTE, NR, WiFi, Zigbee, Z-wave, LoRaWAN, Radio Frequency Identification (RFID) or Bluetooth wireless technologies. These wireless technologies may be integrated into the same or different chip or set of chips and other components within network node 1100.

[0205] The processing circuitry 1102 may comprise a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application -specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, software and / or encoded logic operable to provide, either alone or in conjunction with other network node 1100 components, such as the memory 1104, to provide network node 1100 functionality.

[0206] In some embodiments, the processing circuitry 1102 includes a system on a chip (SOC). I n some embodiments, the processing circuitry 1102 includes one or more of radio frequency (RF) transceiver circuitry 1 112 and baseband processing circuitry 1114. In some embodiments, the radio frequency (RF) transceiver circuitry 1112 and the baseband processing circuitry 1 114 may be on separate chips (or sets of chips), boards, or units, such as radio units and digital units. In alternative embodiments, part or all of RF transceiver circuitry 1112 and baseband processing circuitry 11 14 may be on the same chip or set of chips, boards, or units.

[0207] The memory 1104 may comprise any form of volatile or non-volatile computer-readable memory including, without limitation, persistent storage, solid-state memory, remotely mounted memory, magnetic media, optical media, random access memory (RAM), read-only memory (ROM), mass storage media (for example, a hard disk), removable storage media (for example, a flash drive, a Compact Disk (CD) or a Digital Video Disk (DVD)), and / or any other volatile or non-volatile, non-transitory device-readable and / or computer-executable memory devices that store information, data, and / or instructions that may be used by the processing circuitry 1102. The memory 1104 may store any suitable instructions, data, or information, including a computer program, software, an application including one or more of logic, rules, code, tables, and / or other instructions capable of being executed by the processing circuitry 1 102 and utilized by the network node 1100. The memory 1104 may be used to store any calculations made by the processing circuitry 1102 and / or any data received via the communication interface 1106. In some embodiments, the processing circuitry 1102 and memory 1104 is integrated.

[0208] The communication interface 1106 is used in wired or wireless communication of signaling and / or data between a network node, access network, and / or UE. As illustrated, the communication interface 1106 comprises port(s) / terminal(s) 1116 to send and receive data, for example to and from a network over a wired connection. The communication interface 1106 also includes radio front-end circuitry 1118 that may be coupled to, or in certain embodiments a part of, the antenna 1110. Radio front-end circuitry 1 118 comprises filters 1120 and amplifiers 1122. The radio front-end circuitry 1118 may be connected to an antenna 1110 and processing circuitry 1102. The radio front-end circuitry may be configured to condition signals communicated between antenna 11 10 and processing circuitry 1102. The radio front-end circuitry 1118 may receive digital data that is to be sent out to other network nodes or UEs via a wireless connection. The radio front-end circuitry 11 18 may convert the digital data into a radio signal having the appropriate channel and bandwidth parameters using a combi nation of filters 1120 and / or amplifiers 1122. The radio signal may then be transmitted via the antenna 1 110. Similarly, when receiving data, the antenna 1 110 may collect radio signals which are then converted into digital data by the radio front-end circuitry 1118. The digital data may be passed to the processing circuitry 1 102. In other embodiments, the communication interface may comprise different components and / or different combinations of components.

[0209] In certain alternative embodiments, the network node 1100 does not include separate radio frontend circuitry 1118, instead, the processing circuitry 1102 includes radio front-end circuitry and is connectedto the antenna 11 10. Similarly, in some embodiments, all or some of the RF transceiver circuitry 111 2 is part of the communication interface 1106. In still other embodiments, the communication interface 1106 includes one or more ports or terminals 1116, the radio front-end circuitry 1118, and the RF transceiver circuitry 1112, as part of a radio unit (not shown), and the communication interface 1106 communicates with the baseband processing circuitry 1114, which is part of a digital unit (not shown).

[0210] The antenna 1110 may include one or more antennas, or antenna arrays, configured to send and / or receive wireless signals. The antenna 1110 may be coupled to the radio front-end circuitry 1118 and may be any type of antenna capable of transmitting and receiving data and / or signals wirelessly. In certain embodiments, the antenna 1 110 is separate from the network node 1100 and connectable to the network node 1100 through an interface or port.

[0211] The antenna 1110, communication interface 1106, and / or the processing circuitry 1102 may be configured to perform any receiving operations and / or certain obtaining operations described herein as being performed by the network node. Any information, data and / or signals may be received from a UE, another network node and / or any other network equipment. Similarly, the antenna 1110, the communication interface 1106, and / or the processing circuitry 1102 may be configured to perform any transmitting operations described herein as being performed by the network node. Any information, data and / or signals may be transmitted to a UE, another network node and / or any other network equipme nt.

[0212] The power source 1108 provides power to the various components of network node 1100 in a form suitable for the respective components (e.g., at a voltage and current level needed for each respective component). The power source 1108 may further comprise, or be coupled to, power management circuitry to supply the components of the network node 1100 with power for performing the functionality described herein. For example, the network node 1100 may be connectable to an external power source (e.g., the power grid, an electricity outlet) via an input circuitry or interface such as an electrical cable, whereby the external power source supplies power to power circuitry of the power source 1108. As a further example, the power source 1 108 may comprise a source of power in the form of a battery or battery pack which is connected to, or integrated in, power circuitry. The battery may provide backup power should the external power source fail.

[0213] Embodiments of the network node 1100 may include additional components beyond those shown in Figure 11 for providing certain aspects of the network node's functionality, including any of the functionality described herein and / or any functionality necessary to support the subject matter described herein. For example, the network node 1100 may include user interface equipment to allow input of information into the network node 1100 and to allow output of information from the network node 1100. This may allow a user to perform diagnostic, maintenance, repair, and other administrative functions for the network node 1100.

[0214] FIG. 12 is a block diagram illustrating a virtualization environment 1200 in which functionsimplemented by some embodiments may be virtualized. In the present context, virtualizing means creating virtual versions of apparatuses or devices which may include virtualizing hardware platforms, storage devices and networking resources. As used herein, virtualization can be applied to any device described herein, or components thereof, and relates to an implementation in which at least a portion of the functionality is implemented as one or more virtual components. Some or all of the functions described herein may be implemented as virtual components executed by one or more virtual machines (VMs) implemented in one or more virtual environments 1200 hosted by one or more of hardware nodes, such as a hardware computing device that operates as a network node, UE, core network node, or host. Further, in embodiments in which the virtual node does not require radio connectivity (e.g., a core network node or host), then the node may be entirely virtualized. In some embodiments, the virtualization environment 1200 includes components defined by the O-RAN Alliance, such as an O-Cloud environment orchestrated by a Service Management and Orchestration Framework via an 0-2 interface.

[0215] Applications 1202 (which may alternatively be called software instances, virtual appliances, network functions, virtual nodes, virtual network functions, etc.) are run in the virtualization environment Q400 to implement some of the features, functions, and / or benefits of some of the embodiments disclosed herein.

[0216] Hardware 1204 includes processing circuitry, memory that stores software and / or instructions executable by hardware processing circuitry, and / or other hardware devices as described herein, such as a network interface, input / output interface, and so forth. Software may be executed by the processing circuitry to instantiate one or more virtualization layers 1206 (also referred to as hypervisors or virtual machine monitors (VMMs)), provide VMs 1208a and 1208b (one or more of which may be generally referred to as VMs 1208), and / or perform any of the functions, features and / or benefits described in relation with some embodiments described herein. The virtualization layer 1206 may present a virtual operating platform that appears like networking hardware to the VMs 1208.

[0217] The VMs 1208 comprise virtual processing, virtual memory, virtual networking or interface and virtual storage, and may be run by a corresponding virtualization layer 1206. Different embodiments of the instance of a virtual appliance 1202 may be implemented on one or more of VMs 1208, and the implementations may be made in different ways. Virtualization of the hardware is in some contexts refe rred to as network function virtualization (NFV). NFV may be used to consolidate many network equipment types onto industry standard high volume server hardware, physical switches, and physical storage, which can be located in data centers, and customer premise equipment.

[0218] In the context of NFV, a VM 1208 may be a software implementation of a physical machine that runs programs as if they were executing on a physical, non-virtualized machine. Each of the VMs 1208, and that part of hardware 1204 that executes that VM, be it hardware dedicated to that VM and / or hardware shared by that VM with others of the VMs, forms separate virtual network elements. Still in the context of NFV, a virtual network function is responsible for handling specific network functions that run in one or more VMs1208 on top of the hardware 1204 and corresponds to the application 1202.

[0219] Hardware 1204 may be implemented in a standalone network node with generic or specific components. Hardware 1204 may implement some functions via virtualization. Alternatively, hardware 1204 may be part of a larger cluster of hardware (e.g. such as in a data center or CPE) where many hardware nodes work together and are managed via management and orchestration 1210, which, among others, oversees lifecycle management of applications 1202. In some embodiments, hardware 1204 is coupled to one or more radio units that each include one or more transmitters and one or more receivers that may be coupled to one or more antennas. Radio units may communicate directly with other hardware nodes via one or more appropriate network interfaces and may be used in combination with the virtual components to provide a virtual node with radio capabilities, such as a radio access node or a base station. In some embodiments, some signaling can be provided with the use of a control system 1212 which may alternatively be used for communication between hardware nodes and radio units.

[0220] Although the computing devices described herein (e.g., UEs, network nodes, hosts) may include the illustrated combination of hardware components, other embodiments may comprise computing devices with different combinations of components. It is to be understood that these computing devices may comprise any suitable combination of hardware and / or software needed to perform the tasks, features, functions and methods disclosed herein. Determining, calculating, obtaining or similar operations described herein may be performed by processing circuitry, which may process information by, for example, converting the obtained information into other information, comparing the obtained information or converted information to information stored in the network node, and / or performing one or more operations based on the obtained information or converted information, and as a result of said processing making a determination. Moreover, while components are depicted as single boxes located within a larger box, or nested within multiple boxes, in practice, computing devices may comprise multiple different physical components th at make up a single illustrated component, and functionality may be partitioned between separate components. For example, a communication interface may be configured to include any of the components described herein, and / or the functionality of the components may be partitioned between the processing circuitry and the communication interface. In another example, non-computationally intensive functions of any of such components may be implemented in software or firmware and computationally intensive functions may be implemented in hardware.

[0221] In certain embodiments, some or all of the functionality described herein may be provided by processing circuitry executing instructions stored on in memory, which in certain embodiments may be a computer program product in the form of a non-transitory computer-readable storage medium. In alternative embodiments, some or all of the functionality may be provided by the processing circuitry without executing instructions stored on a separate or discrete device-readable storage medium, such as in a hard-wired manner. In any of those particular embodiments, whether executing instructions stored on a non -transitory computer-readable storage medium or not, the processing circuitry can be configured to perform thedescribed functionality. The benefits provided by such functionality are not limited to the processing circuitry alone or to other components of the computing device, but are enjoyed by the computing device as a whole, and / or by end users and a wireless network generally.

Claims

WHAT IS CLAIMED IS:

1. A method (700) implemented at a network node (800) during handover of a user equipment, UE(110) from a source network (120) to a target network (130) , the method (700) comprising: causing (710) selection of at least one allowed network slice identification from a set of home network slice identifications of the source network (120) based on a set of subscribed network slice identifications of the target network (130), wherein the set of home network slice identifications and the set of subscribed network slice identifications are associated with the UE (110), and the at least one allowed network slice identification is available for the UE (110) in the target network (130); and causing (720) execution of the handover based on the at least one allowed network slice identification.

2. The method (700) of claim 1 , wherein the network node (800) comprises a first access and mobility management function, AMF (202) of the target network (130).

3. The method (700) of claim 2, wherein causing (710) the selection of the at least one allowed network slice comprises: transmitting (213) the set of home network slice identifications and the set of subscribed network slice identifications to a network slice selection function, NSSF (204) of the target network (130); an d receiving (214) the at least one allowed network slice identification from the NSSF (204) of the target network (130).

4. The method (700) of claim 2, wherein causing (710) the selection of the at least one allowed network slice comprises: transmitting (302) a session management context request to a first session management function, SMF (206) of the target network (130), wherein the session management context request includes at least one home network slice identification of the set of home network slice identifications; and receiving (310) a session management context response from the first SMF (206) of the target network (130), wherein the session management context response includes an indication whether the at least one home network slice identification is allowed by the target network (130).

5. The method (700) of any of claims 1 -4, further comprising: receiving (212) the set of subscribed network slice identifications from a unified data management, UDM (210) of a home network (208).

6. The method (700) of claim 5, further comprising: transmitting (211 ) a subscription data management get message to the UDM (210) of the home network (208), wherein the set of subscribed network slice identifications is received (212) in response to transmitting (211) the subscription data management get message.

7. The method (700) of claim 6, wherein transmitting (304) the subscription data management get message comprises: in response to receiving a create UE (110) context request from a second AMF of the source network (120), transmitting (304) the subscription data management get message to the UDM (210).

8. The method (700) of claim 6, wherein transmitting (304) the subscription data management get message comprises: in response to receiving a create session management context response from a first session management function, SMF, of the target network (130), transmitting (211) the subscription data management get message to the UDM (210).

9. The method (700) of any of claims 2-8, further comprising: receiving the set of home network slice identifications from at least one of: a second AMF of the source network (120), or a session management function, SMF, and packet gateway control plane, PGW-C (252) of a home network (208).

10. The method (700) of any of claims 2-9, wherein causing (710) the execution of the handovercomprises: transmitting (220) an update session management context request to a first session management function, SMF (206) of the target network (130), wherein the update session m anagement context request includes an indication for cancelling session resources associated with at least one home network slice identification of the set of home network slice identifications unallowed by the target network (130).1 1. The method (700) of claim 1 , wherein the network node (800) comprises a first session management function, SMF (206) of the target network (130).

12. The method (700) of claim 11 , wherein causing (710) the selection of the at least one allowed network slice comprises: receiving (302) a session management context request from a first access and mobility management function, AMF (202) of the target network (130), wherein the session management context request includes at least one home network slice identification of the set of home network slice identifications; and transmitting (310) a session management context response to the first AMF (202) of the target network (130), wherein the session management context response includes an indication whether the at least one home network slice identification is allowed by the target network (130).

13. The method (700) of claim 11 , wherein causing (710) the selection of the at least one allowed network slice comprises: transmitting (404) a session management context request to a second SMF (402) or a SMF and packet gateway control plane, PGW-C (252) of a home network (208), wherein the session management context request includes an identity of the target network (130); and receiving (412) a session management context response from the second SMF (402) or the SMF and PGW-C (252) of the home network (208), wherein the session management context response includes an indication whether the at least one home network slice identification is allowed by the target network (130).

14. The method (700) of any of claims 1 1 -13, wherein causing (720) the execution of the handover comprises:transmitting a session update request to a session management function, SMF, and packet gateway control plane, PGW-C (252) of a home network (208), wherein the session update request includes an indication for cancelling session resources associated with at least one home network slice identification of the set of home network slice identifications unallowed by the target network (130).

15. The method (700) of claim 1 , wherein the network node (800) comprises a second session management function, SMF (402) or a SMF and packet gateway control plane, PGW-C (252) of a home network (208).

16. The method (700) of claim 11 or 15, wherein causing (710) the selectio n of the at least one allowed network slice comprises: receiving (306, 408), from a unified data management, UDM (210), of a home network (208), information associated with the set of subscribed network slice identifications; and determining (308, 410), based on the retrieved information, whether at least one home network slice identification of the set of home network slice identifications is available in the target network (130).

17. The method (700) of claim 16, wherein the information associated with the set of subscribed network slice identifications comprises an indication whether the at least one home network slice identification is available in the target network (130).

18. The method (700) of claim 17, further comprising: transmitting (304, 406) a subscription data management get message to the UDM (210) of the home network (208), wherein the subscription data management get message includes at least an identity of the target network (130), wherein the indication is received (306, 408) in response to transmitting (304, 406) the subscription data management get message.

19. The method (700) of claim 18, wherein the network node (800) comprises the first SMF (206) of the target network (130), and transmitting (304) the subscription data management get message comprises:after receiving a create session management context request from a first access and mobility management function, AMF, of the target network (130), transmitting (304) the subscription data management get message to the UDM (210).

20. The method (700) of claim 18, wherein the network node (800) comprises the first SMF (206) of the target network (130), and transmitting (304) the subscription data management get message comprises: after receiving a session create response from the SMF and PGW-C (252) of the home network (208), transmitting (304) the subscription data management get message to the UDM (210).

21. The method (700) of claim 18, wherein the network node (800) comprises the second SMF (402) of the home network (208), and transmitting (406) the subscription data management get message comprises: after receiving a session context request from the first SMF (206) of the target network (130) , transmitting (406) the subscription data management get message to the UDM (210).

22. The method (700) of claim 18, wherein the network node (800) comprises the SMF and PGW-C (252) of the home network (208), and transmitting the subscription data management get message comprises: after receiving a session create request from the first SMF (206) of the target network (130) , transmitting the subscription data management get message to the UDM (210).

23. The method (700) of any of claims 18-22, wherein the subscription data management get message further includes at least one of: the at least one home network slice identification, or an indication for checking availability of the set of home network slice identifications in the target network (130).

24. The method (700) of any of claims 1 -23, wherein the selection of the at least one allowed network slice identification is performed in a preparation phase of the handover.

25. The method (700) of any of claims 1 -24, wherein the handover comprises at least one of:N2 based handover, or evolved packet system, EPS, to the fifth-generation system, 5GS, handover.

26. The method (700) of any of claims 1 -25, wherein the network slice identification comprises network selection assistance information, NSSAI.

27. The method (700) of any of claims 1 -26, wherein the source network (120) comprises a home network (208), and the target network (130) comprises a first visited network; or the source network (120) comprises the first visited network, and the target network (130) comprises a second visited network.

28. A network node (800), comprising: a processor (805); and a memory (810), the memory (810) containing instructions (815) executable by the processor (805), whereby the network node (800) is operative to: cause (710) selection of at least one allowed network slice identification from a set of home network slice identifications of a source network (120) based on a set of subscribed network slice identifications of a target network (130), wherein the set of home network slice identifications and the set of subscribed network slice identifications are associated with a user equipment, UE (1 10), and the at least one allowed network slice identification is available for the UE (110) in the target network (130) ; and cause (710) execution of handover of the UE (110) from the source network (120) to the target network (130) based on the at least one allowed network slice identification.

29. The network node (800) of claim 28, wherein the network node (800) is fu rther operative to implement the method (700) according to any of claims 2-27.

30. A computer-readable storage medium (900) having instructions (815) stored thereon, the instructions (805), which, when executed by at least one processor of a device, causes the device to perform the method (700) according to any of claims 1 -27.

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