Inter-radio access technology network slice switching

Abstract

Example embodiments of the present disclosure are directed to inter-Radio Access Technology (inter-RAT) network slice switching. An Access and Mobility Management Function (AMF) receives a handover re

Description

[0002] Network slicing is a key 5th Generation Mobile Communication Technology (5G) feature to support different services using the same underlying mobile network infrastructure. Network slices can differ either in their service requirements like UltraReliable Low Latency Communication (URLLC) and enhanced Mobile Broadband (eMBB) or the tenant that provides those services. SUMMARY

[0003] In a first aspect of the present disclosure, there is provided an apparatus. The apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: in response to receiving a handover request associated with a handover procedure of a user equipment (UE), from a further radio access network (RAN), associated with a second RAT, to a first RAN associated with a first RAT, identify a core network node in charge of mobility and management functions associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to one or more slices supported by the second RAT; and send, to the identified core network node a handover request for the UE.

[0004] In a second aspect of the present disclosure, there is provided an apparatus. The apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: during a handover procedure of a UE from a second RAN associated with a second RAT to a first RAN associated with a first RAT, receive, from an AMF, a request to handover the UE; determine, based on the request, at least one slice supported by the first RAT associated with one or more further slices supported by the second RAN to which the UE is currently connected; and transmit, to the first RAN associated with the first RAT, a handover request indicating the at least one slice supported by the first RAT for the inter-RAT switching.

[0005] In a third aspect of the present disclosure, there is provided an apparatus. The apparatus comprises at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to: receive an association between at least one slice supported by a first RAT and one or more further slices supported by a second RAT during a registration procedure to the first RAT or the second RAT; during a handover procedure of the apparatus from a second RAN associated with the second RAT to a first RAN associated with the first RAT, determine an allowed network slice selection assistance information (NSSAI) associated with the RAT to be used by the UE based on the received information.

[0006] In a fourth aspect of the present disclosure, there is provided a method. The method comprises: in response to receiving a handover request associated with a handover procedure of a UE from a second RAN associated with a second RAT to a first RAN associated with a first RAT, identifying by an Access and Mobility Management Function (AMF), a core network node in charge of mobility and management functions associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to one or more slices supported by the second RAT; and sending, to the identified core network node a handover request for the UE.

[0007] In a fifth aspect of the present disclosure, there is provided a method. The method comprises: during a handover procedure of a UE from a second RAN associated with a second RAT to a first RAN associated with a first RAT, receive, at a core network node in charge of mobility and management (MM) functions from an AMF, a request to handover the UE; determining, based on the request, at least one slice supported by the first RAT associated with one or more further slices supported by the second RAN to which the UE is currently connected; and transmitting, to the first RAN associated with the first RAT, a handover request indicating the at least one slice supported by the first RAT for the inter-RAT switching.

[0008] In a sixth aspect of the present disclosure, there is provided a method. The method comprises: obtaining, by a UE, an association between at least one slice supported by a first RAT and one or more further slices supported by a second RAT during a registration procedure to the first or the second RAT; during a handover procedure of the UE from a second RAN associated with the second RAT to a first RAN associated with the first RAT, determining an allowed NSSAI associated with the RAT to be used by the UE based on the received information.

[0009] In a seventh aspect of the present disclosure, there is provided an apparatus. The apparatus comprises means for in response to receiving a handover request associated with a handover procedure of a UE from a second RAN associated with a second RAT, to a first RAN associated with a first RAT, identifying by an Access and Mobility Management Function (AMF), a core network node in charge of mobility and management functions associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to one or more slices supported by the second RAT; and means for sending, to the identified core network node a handover request for the UE.

[0010] In an eighth aspect of the present disclosure, there is provided an apparatus. The apparatus comprises means for during a handover procedure of a UE from a second RAN associated with a second RAT to a first RAN associated with a first RAT, receiving, from an AMF, a request to handover the UE; means for determining, based on the request, at least one slice supported by the first RAT associated with one or more further slices supported by the second RAN to which the UE is currently connected; and means for transmitting, to the first RAN associated with the first RAT, a handover request indicating the at least one slice supported by the first RAT for the inter-RAT switching.

[0011] In a ninth aspect of the present disclosure, there is provided an apparatus. The apparatus comprises means for obtaining an association between at least one slice supported by a first RAT and one or more further slices supported by a second RAT during a registration procedure to the first or the second RAT; means for during a handover procedure of the apparatus from a second RAN associated with the second RAT to a first RAN associated with the first RAT, determining an allowed NSSAI associated with the RAT to be used by the UE based on the received information.

[0012] In a tenth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fourth aspect.

[0013] In an eleventh aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the fifth aspect.

[0014] In a twelfth aspect of the present disclosure, there is provided a computer readable medium. The computer readable medium comprises instructions stored thereon for causing an apparatus to perform at least the method according to the sixth aspect.

[0015] It is to be understood that the Summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Some example embodiments will now be described with reference to the accompanying drawings, where:

[0017] FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

[0018] FIG. 2 illustrates a signaling chart of communication according to some example embodiments of the present disclosure;

[0019] FIG. 3 illustrates a signaling chart of communication according to some example embodiments of the present disclosure;

[0020] FIG. 4 illustrates a signaling chart of communication according to some example embodiments of the present disclosure;

[0021] FIG. 5 illustrates a flowchart of a method implemented at a apparatus in accordance with some example embodiments of the present disclosure;

[0022] FIG. 6 illustrates a flowchart of a method implemented at a apparatus in accordance with some example embodiments of the present disclosure;

[0023] FIG. 7 illustrates a flowchart of a method implemented at a apparatus in accordance with some example embodiments of the present disclosure;

[0024] FIG. 8 illustrates a simplified block diagram of a device that is suitable for implementing example embodiments of the present disclosure; and

[0025] FIG. 9 illustrates a block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

[0026] Throughout the drawings, the same or similar reference numerals represent the same or similar element. DETAILED DESCRIPTION

[0027] Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

[0028] In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which this disclosure belongs.

[0029] References in the present disclosure to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

[0030] It shall be understood that although the terms “first,” “second,”..., etc. in front of noun(s) and the like may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another and they do not limit the order of the noun(s). For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and / or” includes any and all combinations of one or more of the listed terms.

[0031] As used herein, “at least one of the following: ” and “at least one of ” and similar wording, where the list 5 of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

[0032] As used herein, unless stated explicitly, performing a step “in response to A” does not indicate that the step is performed immediately after “A” occurs and one or more intervening steps may be included. 10

[0033] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and / or “including”, when 15 used herein, specify the presence of stated features, elements, and / or components etc., but do not preclude the presence or addition of one or more other features, elements, components and / or combinations thereof.

[0034] As used in this application, the term “circuitry” may refer to one or more or all of the following: (a) hardware-only circuit implementations (such as implementations in only analog and / or digital circuitry) and (b) combinations of hardware circuits and software, such as (as applicable): (i) a combination of analog and / or digital hardware circuit(s) with software / firmware and (ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0035] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and / or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0036] As used herein, the term “communication network” refers to a network following any suitable communication standards, such as New Radio (NR), Long Term Evolution (LTE), LTE-Advanced (LTE-A), Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), Narrow Band Internet of Things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network device in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the first generation (1G), the second generation (2G), 2.5G, 2.75G, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G), 5.5G, the sixth generation (6G) communication protocols, and / or any other protocols either currently known or to be developed in the future. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future types of communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

[0037] As used herein, the term “network device” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network device may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), an NR NB (also referred to as a gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, an Integrated Access and Backhaul (IAB) node, a low power node such as a femto, a pico, a non-terrestrial network (NTN) or non-ground network device such as a satellite network device, a low earth orbit (LEO) satellite and a geosynchronous earth orbit (GEO) satellite, an aircraft network device, and so forth, depending on the applied terminology and technology. In some example embodiments, radio access network (RAN) split architecture comprises a Centralized Unit (CU) and a Distributed Unit (DU) at an IAB donor node. An IAB node comprises a Mobile Terminal (IAB-MT) part that behaves like a UE toward the parent node, and a DU part of an IAB node behaves like a base station toward the next-hop IAB node.

[0038] The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of Things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and / or other wireless devices operating in an industrial and / or an automated processing chain contexts), a consumer electronics device, a device operating on commercial and / or industrial wireless networks, and the like. The terminal device may also correspond to a Mobile Termination (MT) part of an IAB node (e.g., a relay node). In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

[0039] As used herein, the term “resource,” “transmission resource,” “resource block,” “physical resource block” (PRB), “uplink resource,” or “downlink resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network device, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other combination of the time, frequency, space and / or code domain resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

[0040] FIG. 1 illustrates an example communication environment 100 in which example embodiments of the present disclosure can be implemented. In the communication environment 100, a plurality of communication devices, including a UE 110, a 6G RAN node 120, a 6G core network 130 having a node in charge of mobility and management (MM) functions, e.g., a 6G MM function 131 and a 5G RAN node 140, a 5G core network node, e.g., an Access and Mobility Management Functions (AMF) 150.

[0041] The LIE 110 may connect to the 6G RAN node 120 when accessing the 6G core network 130. The UE 110 may communicate with the 6G MM function 131 to perform a registration procedure with the 6G core network 130 for example.

[0042] Similarly, the UE 110 may connect to the 5G RAN node 140 when accessing the 6G core network. For example, the UE 110 after being registered with the 6G core network may handover and connect to a 5G RAN via the 5G core network. The UE 110 may communicate with the AMF 150 which is configured to provide various functions relating to security and access and mobility management and authorization.

[0043] The 6G MM function 131 in the 6G core network 130 may be responsible for a similar or same function as the AMF 150 in the 5G core network. The 6G MM function 131 may communicate with the AMF 150, e.g., when a handover of the UE 110 between 5G and 6G occurs.

[0044] It is to be understood that the number of devices and their connections shown in FIG. 1 are only for the purpose of illustration without suggesting any limitation. The communication environment 100 may include any suitable number of devices configured to implement example embodiments of the present disclosure.

[0045] Communications in the communication environment 100 may be implemented according to any proper communication protocol(s), comprising, but not limited to, cellular communication protocols of the first generation (1G), the second generation (2G), the third generation (3G), the fourth generation (4G), the fifth generation (5G), 5.5G, the sixth generation (6G), and the like, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and / or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplex (FDD), Time Division Duplex (TDD), Multiple-Input Multiple-Output (MIMO), Orthogonal Frequency Division Multiple (OFDM), Discrete Fourier Transform spread OFDM (DFT-s-OFDM) and / or any other technologies currently known or to be developed in the future.

[0046] As described above, network slicing is a key 5G feature to support different services using the same underlying mobile network infrastructure. A network slice is uniquely identified via the Single-Network Slice Selection Assistance Information (S-NSSAI). Current 3rd Generation Partnership Project (3GPP) specifications allow a UE 110 to be simultaneously connected and served by at most eight slices corresponding to eight network slices meaning eight S-NSSAIs. On the other hand, each cell may support tens or even hundreds of slices, e.g., in the current specifications a Tracking Area (TA) can have a support up to 1024 network slices.

[0047] The S-NSSAI may include both the Slice Service Type (SST) and the Slice Differentiator (SD) field with a total length of 32 bits or include only the SST field part in which case the length of S-NSSAI is 8 bits only.

[0048] The SST field may have standardized and non-standardized values. Values 0 to 127 belong to the standardized SST range. For example, a SST value of 1 may indicate that the slice is suitable for handling of 5G eMBB, while a SST value of 2 may indicate that the slice is suitable for handling of URLLC, etc. In addition, the SD is operator-defined only.

[0049] In the existing 5G system, the RAN nodes possess information regarding the slice support and slice availability of the neighboring RAN nodes through the Xn interface (i.e., “Tracking area identity (TAI) Support List” information element), which means that if the Xn interface exists between the RAN nodes, the RAN nodes may use the slice support information in their handover decisions for the UE 110.

[0050] Furthermore, in the NG interface, each RAN node exposes its slice support to the connected AMF 150, which means that AMF 150 also possesses slice support information for each connected RAN node (i.e., “TAI Slice Support List” information element within the NG Setup Request). However, if the RAN nodes do not have an Xn interface with each other they cannot know the respective slice support as the slice support is not exchanged between the NG interface among RAN nodes.

[0051] When two RAN nodes do not have an Xn interface established with each other, they do not possess information of each other’s slice support. When the source RAN node decides to perform a handover of the UE 110 to another target RAN node via the NG interface (i.e., via the AMF 150), the source RAN node will not know the slice support of the target RAN node.

[0052] In the Handover Required message sent by the source RAN node to AMF 150, the source RAN node indicates the Protocol Data Unit (PDU) session identification (ID) and target RAN ID to the AMF 150. Upon sending the handover request to the target RAN node, the AMF indicates additionally to the PDU session ID also the network slice ID (i.e. S-NSSAI) that pertains to that PDU session ID. If the target RAN node does not support the S-NSSAI then it rejects the handover of the PDU session of the UE and thus no PDU session continuity may be achieved.

[0053] The issue of the present network slicing mechanism will be described below with some example scenarios. Considering the advances of next generation 6G network compared to existing 5G network, it is envisioned that new services will be provided given the new capabilities that the 6G network will offer compared to the 5G. In that regard additional standardized values for network slices that may offer and support those additional services may be established. For instance, compared to existing 5G eMBB slices, there could be 6G extended reality (XR) slices that are not supported in 5G.

[0054] Given the above scenario, suppose that a UE 110 that has 6G capabilities, connects to a 6G network (e.g. accessed via the 6G RAN node 120 shown in FIG. 1) that supports the XR network slice and establishes a PDU session with that XR network slice. Due to connectivity issues, for instance lack of the 6G coverage, which especially may occur at the beginning of the 6G deployments, where 6G coverage limitation may exist, the UE 110 may have to be handed over from the 6G network to the 5G network (e.g. accessed via the 5G RAN node 140 shown in FIG. 1) to allow the UE to still be served.

[0055] In some scenarios, due to the fact that the 5G network may not support the standardized 6G XR network slice, the PDU session of the UE 110 will not be continued, and the UE 110 will lose the connectivity. Which means that the UE 110 might even go back to idle mode due to the connectivity issues, which may cause not only violation of Service Level Agreement (SLA) since the UE will not be provided with the service, but also increased battery consumption at the UE 110 side, as the UE 110 will have to perform the cell reselection again to re-connect to the 5G or 6G network.

[0056] In another example scenario, although the issue of PDU session connectivity while moving from 6G to the 5G network is more evident in the case of different 6G standardized slices compared to 5G standardizes slices, the issue may exist also in the case where the same standardized slice, for instance, eMBB slice has a different identification (i.e. S-NSSAI) in the 6G network compared to the 5G network.

[0057] Assuming that a 6G network UE is connected to a 6G network and establishes a PDU session in the 6G network with an 6G eMBB slice that uses a S-NSSAI ID x. The UE due to coverage issues may move to a 5G network, but in case the S-NSSAI x is not supported in the 5G target RAN node (e.g. 5G RAN node 140), where the UE 110 is to be re-directed, the PDU session continuity would not be maintained and eventually the UE 110 would lose its connectivity.

[0058] Overall, the following issues are identified: When a UE 110 moves between different RATs with a PDU session that is associated with a network slice (i.e. S-NSSAI) that is not supported in the target RAT, either due to difference in slice support between RATs or due to the particular S-NSSAI not supported in the area (e.g., target RAN node of the target RAT) where the UE 110 is handed over, then the UE 110 will lose the PDU session connectivity and may go to idle mode experiencing excessive interruption and consuming more energy due to extra signaling needed for re-connecting to the new RAT (e.g. 5G RAN node 140 or 6G RAN node 120 shown in FIG. 1).

[0059] In accordance with some example embodiments of the present disclosure, there is provided a solution for inter-RAT network slice switching. In this solution, an indication that inter-RAT slice switching is supported by the apparatus is transmitted from the UE 110 to a 6G core network in charge of mobility and management functions for the UE 110 associated with the first RAT (e.g., 6G network / technology). Upon receiving the indication, the 6G core network node 131 determines an association between the at least one slice supported by a 6G RAN node 120 the UE 110 is currently connected and one or more further slices supported by a second RAT (e.g., 5G network / technology) and transmits, to the UE 110, an NSSAI at least indicating the association. In this way, the inter-RAT network slice switching can be achieved, and therefore the network slice mobility efficiency may be improved when the UE 110 is switching between different RAN nodes among different RATs (e.g. 5G and 6G).

[0060] Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0061] The term “inter-RAT slice switching” used hereinafter may refer to a procedure, caused by a mobility of the UE from the first RAT, to which the UE is currently connected, to the second RAT, during which a further slice supported by the second RAT provides a service for the UE instead of a slice supported by the first RAT, or a procedure, caused by a mobility of the UE from the second RAT, to which the UE is currently connected, to the first RAT, during which a slice supported by the first RAT provides a service for the UE instead of a further slice supported by the second RAT. The term “inter-RAT slice switching” may also be called as inter-RAT slice interworking / change / handover / mobility.

[0062] Hereinafter the first RAT may be referred to as a 6G network / technology. The second RAT may be referred to as a 5G network / technology. It is to be understood that the RAT used hereinafter may also be referred to as other RAT according to any other protocols currently known or to be developed in the future.

[0063] Specifically, the “inter-RAT slice switching” may be a switching mechanism involving both the 6G network and 5G network, which may be utilized to provide continuity of service when the UE 110 is switching between network slice of the 6G network and the network slice of the 5G network. The feature of the inter-RAT slice switching mechanism is that, the 6G network and 5G network share their information between each other and work in a corporate manner to perform the switching of network slices in different RATs. As an example, the communication between the 6G core network function in charge of mobility and management functions for the UE may communicate with AMF in the 5G core network via existing 5G network interfaces such as for instance the NG interface. It is to understood that new interfaces may be established with development of 6G networks.

[0064] Reference is now made to FIG. 2, which shows a signaling chart 200 for communication according to some example embodiments of the present disclosure. As shown in FIG. 2, the signaling chart 200 involves a UE 110, a 6G RAN node 120 and a 6G core network 130 which may include a node in charge of mobility and management (MM) functions, e.g., a 6G MM 131. For the purpose of discussion, reference is made to FIG. 1 to describe the signaling chart 200.

[0065] The UE 110 transmits (205), to a function of the 6G core network 130, for example, to the 6G MM 131, an indication that an inter-RAT slice switching between the first RAT and a second RAT is supported by the UE 110, which may indicate the UE 110 has a capability for supporting the inter-RAT slice switching. The 6G MM 131 may be considered as a 6G core network function responsible for the mobility management (e.g., which may correspond to the 5G AMF core network function). As shown, the indication may be transmitted from the UE 110 to the 6G core network 130 via the 6G RAN node 120 using for example Non-Access Stratum (NAS) signaling as performed in 5G networks. It is to be understood that this is just an example and not a limitation and it may change in 6G.

[0066] In some embodiments, the UE 110 may transmit the indication to the 6G core network 130 during a registration procedure to a 6G network. For example, the UE 110 may transmit the indication along with a request for one or more specific slices supported by 6G RAN node 120 the UE is connected during the registration procedure.

[0067] Specifically, for a 6G capable UE 110, when the UE 110 performs the registration procedure with the 6G core network 130, the UE 110 indicates the support of the inter-RAT slice switching feature. In this procedure, the UE 110 may register with the network and request a 6G network slice (e g., one or more specific slices supported by 6G RAN node 120).

[0068] Upon receiving the indication that the inter-RAT slice switching is supported by the UE 110, the 6GMM 131 may determine (210) an association between the at least one slice supported by the 6G RAN node 120 and one or more further slices supported by the 5G network. That is, the 6G MM 131 may determine the 6G to 5G network slice mapping / association if the UE 110 supports the feature of inter-RAT slice switching.

[0069] For example, the determination of the association can be based on Operation Administration and Maintenance (0AM) configuration at the 6G MM 131 or it can be based on communication with any other 6G core network function of the 6G core network 130 of shared / combo 6G / 5G core network functions such as Network Slice Selection Function (NSSF) and / or Policy Control Function (PCF) for instance.

[0070] As an option, once the 6G MM 131 determines the mapping / association between the 6G and 5G network slices used for inter-RAT slice switching, the 6G MM 131 may transmit (215), to the UE 110, the NSSAI at least indicating the determined association, e.g., via a registration accept message. In this case, the NSSAI may comprise a first allowed NSSAI list indicating the at least one slice supported by the 6G RAN node 120 and a second allowed NSSAI list indicating the one or more further slices supported by 5G network corresponding to the at least one slice.

[0071] That is to say, the 6G MM 131 provides to the UE 110 in addition to the 6G allowed NSSAI list where it includes the 6G S-NSSAI, also an additional 5G allowed NSSAI list where it includes the list of 5G S-NSSAIs. The UE shall store both allowed NSSAI lists and use them respective to the RAT where the UE 110 operates on.

[0072] The benefit of UE 110 having two allowed NSSAI lists which are RAT dependent could be such that the UE 110 does not have to be re-configured by the target RAT with a new allowed NSSAI list when the UE connects to the target RAT. Furthermore, it could be used for cell reselection purposes in other examples. Utilizing two lists compared to a shared list can also be due to the fact that currently the allowed NSSAI list has a limit of 8 S-NSSAIs based on 3GPP standardization and using the feature of inter-RAT switching the amount of S-NSSAI in the list can grow larger and eventually it may exceed the current limit of 8 S-NSSAIs.

[0073] As another option, the 6G MM 131 may transmit (220), to the UE 110, the NSSAI at least indicating the determined association eg., via a registration accept message. In this case, the NSSAI may comprise an allowed NSSAI list indicating the at least one slice supported by the 6G RAN node 120, and the one or more further slices supported by the 5G network corresponding to the at least one slice.

[0074] In this situation, the 6G MM 131 provides to the UE 110 one allowed NSSAI list, but additionally it includes in the allowed NSSAI list both the 6G and 5G slices and their mapping / association used for inter-RAT slice switching with additional information at the UE 110 that the mapping is to be used only when the UE 110 changes RAT and so the S-NSSAI has to be accompanied with the respective RAT identifier.

[0075] The benefit of UE 110 using one shared allowed NSSAI list among the two RATs could be due to the fact of UE 110 storing less information e.g. only one allowed NSSAI list is maintained at the UE 110 instead of two lists, however this comes to the expense of the need of extra information to associate the RAT for which the slice is valid and to be used from the UE.

[0076] It is to be understood that in addition to the registration accept message, it is also possible that the allowed NSSAI list(s) are transmitted to the UE via other signaling, e.g., a UE configuration update message. For example, if the association between the 6G slice(s) and 5G slice(s) has changed, the 6G MM 131 may provide to the UE 110 the updated allowed NSSAI list(s) via UE configuration update message or similar messages.

[0077] An example corresponding to a process shown in signaling chart 200 will be further described in detail as below.

[0078] The UE 110 initiates the registration procedure with the 6G core network 130 and 6G RAN node 120. During the registration procedure, the UE 110 may request 6G network slice 2 and indicate inter-RAT slice switching feature capability towards the 6G network.

[0079] Then the 6G MM 131 identifies that UE 110 supports inter-RAT slice switching feature capability and determines the 6G to 5G slice mapping / association information. For example, the 6G MM 131 may be configured from OAM with 6G to 5G slice ID mapping / association to be used by the UE 110 for inter-RAT slice switching.

[0080] As another example, the 6G MM 131 may receive the information of 6G to 5G slice ID mapping / association for inter-RAT slice switching to be used by the UE 110 via communication with shared / combo 5G / 6GNSSF.

[0081] Furthermore, it is possible that the 6G MM 131 may receive the information of 6G to 5G slice ID mapping / association for inter-RAT slice switching to be used by the UE 110 via communication with shared / combo 5G / 6G PCF.

[0082] Alternatively, the 6G MM 131 and 5G AMF 150 may be co-allocated functions and so the mapping / association between the 6G to 5G slice ID for inter-RAT slice switching for the UE 110 is obtained via internal function communications.

[0083] The 6G MM 131 provides to the UE 110 the registration accept message. In this registration accept message, the 6G MM 131 may provide to the UE 110 two RAT dependent allowed NSSAI lists. That is, the UE 110 receives a 6G allowed NSSAI list that contains 6G slice 2 and a 5G allowed NSSAI list that contains 5G slice 1 that is the mapping of 6G slice 2 used for inter-RAT slice switching.

[0084] As another option, in this registration accept message, the 6G MM 131 may provide to the UE 110 one shared allowed NSSAI list which is shared between the 5G and 6G RATs and where each S-NSSAI is associated with a RAT identifier.

[0085] In this case, the UE 110 receives an allowed NSSAI list that contains 6G network slice 2 and 5G network slice 1 as well as their mapping / association for inter-RAT slice switching and indication for which RAT they are relevant to be used.

[0086] In the following, the process of an inter-RAT slice switching due to a handover of the UE from 6G RAN to 5G RAN will be described.

[0087] Reference is now made to FIG. 3, which shows a signaling chart 300 for communication according to some example embodiments of the present disclosure. As shown in FIG. 3, the signaling chart 300 involves a UE 110, a 6G RAN node 120, a 6G core network 130 which may include a node in charge of mobility management functions, e.g., a 6G MM 131, a 5G RAN node 140, an AMF 150 and a 5G core network 160. The AMF 150 may be considered as a node in the 5G core network 160. It is to understood that the 5G core network 160 may also comprise other nodes / functions other than the AMF 150. For the purpose of discussion, reference is made to FIG. 1 to describe the signaling chart 300.

[0088] As shown in FIG. 3, the UE 110 is already registered with the 6G network as described in the examples above and therefore the NSSAI either including two allowed NSSAI lists (i.e., a 5G allowed NSSAI list and a 6G allowed NSSAI list) or a shared allowed NSSAI list which is shared between the 5G and 6G RATs is received (305) by the UE 110.

[0089] Then the UE 110 may establish (310) a PDU session with at least one 6G network slice.

[0090] After the PDU session with the at least one 6G network slice is established by a UE 110, the 6GMM 131 may store (315) an association between the at least one slice and one or more further slices supported by 5G corresponding to the at least one slice.

[0091] When the 6G RAN node 120 (i.e., a source RAN node) decides to handover the 6G capable UE 110 to a 5G RAN node 140 (i.e., a target RAN node) due to coverage issues, the 6G RAN node 120 may send (320) a handover required message to the 6G MM 131 including the PDU session ID and target RAN node ID for the handover.

[0092] The 6G MM 131 may identify the AMF 150 for the handover. The identification may be done via configuration from 0AM or via communication with other 6G core network functions such as Network Repository Function (NRF) for example. Since the 6G MM 131 contains the UE context, i.e., the 6G MM 131 may be aware of the mapped / associated 6G slice to 5G slice used for inter-RAT slice switching for that PDU session, the 6G MM 131 may identify the AMF 150 based on UE context and inter-RAT slice switching information. Then the 6G MM, during a handover procedure of UE from the 6G RAN node to 5G, may transmit (325) a request of UE context creation to the identified AMF 150.

[0093] As an option, the request of UE context creation may at least indicate an identifier of a UE PDU session associated with the 6G network and one or more further slices supported by 5G associated with an inter-RAT slice switching.

[0094] As another option, the request of UE context creation may at least indicate an identifier of a UE PDU session associated with the 6G network, and one or more further slices supported by 5G associated with an inter-RAT slice switching and also at least one slice supported by the 6G.

[0095] That is to say, the 6G MM 131 may send a message related to creation of UE context towards the AMF 150 indicating the PDU session ID and the mapped / associated 5G slice that corresponds to the 6G slice used by the UE 110 in the 6G network or alternatively 6G MM 131, once requesting the respective AMF 150 to create UE 110 context during the inter-RAT switching, may forward both 5G and 6G slice IDs to the AMF 150 for later use.

[0096] For example, if the AMF 150 obtains both 5G and 6G slice IDs, the AMF 150 may store (330) the association between the at least one slice supported by the 6G network and the one or more further slices supported by the 5G network and may use the association for identifying the 6G MM 131 if the UE will later return back to the 6G network. For example, the stored information can be used by the AMF 150 in the communication with Network Repository Function (NRF) to find the proper 6G MM 131 for the UE.

[0097] Then the AMF 150 may communicate (335) with other 5G core network functions part of the 5G core network 160 to perform the required handover preparation steps. The AMF 150 may additionally send (340) a handover request message to 5GRAN node 140 indicating the one or more further slices supported by the 5G network and the 5G RAN node 150 may reply (345) with a handover request acknowledge message.

[0098] Once handover execution has terminated and the UE 110 has completed (350) the handover to the 5G RAN node 140, as an option, the UE 110 uses (355) the one or more further slices supported by the 5G network as 5G allowed NS SAI after the completion of the handover procedure without requesting a new the allowed NSSAI from the AMF 150.

[0099] Alternatively, after the completion of the handover procedure, the UE 110 may obtain from the AMF 150, an update of 5G allowed NSSAI including at least one further slice supported by the 5G other than the one or more further slices.

[0100] As another example, after the completion (350) of the handover procedure, the UE 110 may initiate (365) a registration procedure with AMF 150. Then the AMF 150 may transmit (370) an update of 5G allowed NSSAI via a registration accept message to the UE. In this case, the UE 110 may maintain / store (375) the at least one slice supported by the 6G network, which may be previously obtained, even when receiving a new 5G allowed NSSAI from AMF.

[0101] That is, the UE 110 may either register with the AMF 150 but will not receive an updated 5G allowed NSSAI list since it already received one during its registration at the 6G network. Otherwise, the UE 110 may still perform registration again with the AMF 150 and UE 110 will receive the updated 5G allowed NSSAI list.

[0102] In the latter scenario, the UE 110 although it receives an updated 5G allowed NSSAI list it will still store the 6G allowed NSSAI list to be used in case that the UE 110 goes back to the 6G network again.

[0103] An example corresponding to a process shown in signaling chart 300 will be further described in detail as below.

[0104] The UE 110 has joined the 6G network and has either received a per RAT (5G and 6G) specific allowed NSSAI list or a shared allowed NSSAI list among RATs that includes, for example, the 6G slice 2 and the mapped 5G slice 1 for inter-RAT slice switching. Then the UE 110 establishes a PDU session with 6G Slice 2.

[0105] The 6G MM 131 stores in the UE context information regarding both 6G slice 2 and 5G slice 1. After some time based on UE radio measurements, the 6GRAN node 120 may determine a 5G RAN node 140 as a target RAN node the for the UE 110 and send handover required message to 6G MM 131. The handover required message may contain the PDU session ID of the UE 110 and the target RAN node ID (i.e., the ID of the 5G RAN node 140).

[0106] The 6G MM 131, based on UE context and inter-RAT slice switching information, may identify the proper AMF 150 and send a request to create UE context to the AMF. The 6G MM 131 may then indicate the PDU session ID and the mapped 5G slice 1 that corresponds to 6G slice 2 in the 6G network for inter-RAT slice switching. Alternatively, the 6G MM 131 may indicate both the 6G Slice 2 and the mapped 5G slice 1 for inter-RAT slice switching to AMF 150.

[0107] In case that AMF 150 receives both 6G and mapped 5G slice IDs then the AMF 150 may store them in the UE context and may utilize them for communicating with NRF and identifying the proper 6G MM 131 for the UE 110 when the UE 110 returns back to the 6G network.

[0108] After the UE 110 completes the handover to the 5G RAN, the UE 110 uses the already received 5G allowed NSSAI list or the 5G slice ID within the shared allowed NSSAI to utilize in the 5G network.

[0109] In this case, the UE 110 does not need to re-register with AMF 150. Alternatively, the UE 110 may still perform registration with AMF, but does not have to receive again a 5G allowed NSSAI list or does not have to receive the 5G slice ID included in the shared allowed NSSAI.

[0110] It is also possible that the UE 110, after the completion of the handover to the 5G RAN node 140, initiates a registration procedure with AMF 150. In this case, the UE 110 may receive an updated allowed NSSAI list and may still store the 6G allowed NSSAI list although it receives an updated 5G allowed NSSAI list.

[0111] Although the example mentioned above explaining with one-to-one mapping of the 5G and 6G slices, e.g., the 5G slice 1 may be mapped to 6G slice 2, one to N mapping of the 5G and 6G slices may also be possible. For example, the 6G slice 2 may be mapped to 5G slices 1 and 3.

[0112] If the AMF 150 receives two or more corresponding 5G slices for the inter-RAT slice switching, the AMF 150 may determine a 5G slice from the two or more corresponding 5G slices for carrying the PDU session during the handover procedure of UE from 6G to 5G network.

[0113] In some embodiments, if the UE PDU session associated with the 6G slice corresponds to a plurality of quality of service (QoS) flows and two or more corresponding 5G slices available for the inter-RAT slice switching are provided by 6GMM 131, as one option, the AMF 150 may determine a 5G slice from the two or more corresponding 5G slices for carrying the plurality of the QoS flows in the handover of the PDU session during the handover procedure.

[0114] As another option, the UE PDU session associated with the 6G may also be divided into more than one (e.g., two) UE PDU sessions associated with the 5G network. In this case, the AMF 150 may choose multiple slices supported by 5G. Each QoS flow corresponding to a UE PDU session associated with 5G is to be served by one target slice supported by 5G.

[0115] Reference is now made to FIG. 4, which shows a signaling chart 400 for communication according to some example embodiments of the present disclosure. As shown in FIG. 4, the signaling chart 400 involves a UE 110, a 6G RAN node 120, a 6G core network 130 which may include a node in charge of MM functions, e.g., a 6G MM 131, a 5G RAN node 140, an AMF 150 and a 5G core network 160. For the purpose of discussion, reference is made to FIG. 1 to describe the signaling chart 400.

[0116] A 6G capable UE 110 may fall back to a 5G network temporary and return to the 6G later for instance due to connectivity issues. In this situation, as shown in FIG. 4, the UE 110 had obtained (405) the NSSAI either including two allowed NSSAI lists (i.e., a 5G allowed NSSAI list and a 6G allowed NSSAI list) or a shared allowed NSSAI list which is shared between the 5G and 6G RATs when the UE 110 previously connected to the 6G network as described in the examples before.

[0117] Now the UE 110 is connected to the 5G network using 5G allowed slice(s).

[0118] When the 5G RAN node 140 (i.e., a source RAN node) decides to handover the UE 110 to a 6G RAN node 120 (i.e., a target RAN node), the 5GRAN node 140 may send (415) a handover required message to the AMF 150 which involves the PDU session ID and target RAN node ID for the handover.

[0119] The AMF 150 may utilize (420) the UE context, that may be stored in the AMF 150 as described above, to identify the proper 6G MM for the UE 110.

[0120] If the UE context comprises the mapped 6G slice(s) to 5G slice(s) used for inter-RAT slice switching, the AMF 150 may contact (425) a 5G core network function within the 5G core network 160, e.g., the NRF, with the 6G slice(s) IDs instead of the 5G slice ID used in the 5G network. The NRF in communication with other 5G core network functions (NFs) or in case it is a shared NRF with the 6G network, it may identify the proper 6G MM 131 and return (430) the result to the AMF 150.

[0121] If the UE context only contains the 5G slice(s), the 0AM may configure the AMF 150 with the proper 6G MM 131 to contact for the handover.

[0122] The AMF 150 then may indicate, to the identified 6G MM 131 relevant information for performing a handover for the UE. For example, the AMF 150 may transmit (435), to the 6G MM 131, a request of a UE context creation. As an example, the request of a UE context creation may at least indicate an identifier of a UE PDU session associated with the 5G network and one or more further slices supported by 5G associated with an inter-RAT slice switching.

[0123] As another option, the request of UE context creation may at least indicate an identifier of a UE PDU session associated with the 6G network, one or more further slices supported by 5G associated with an inter-RAT slice switching and also at least one slice supported by the 6G.

[0124] In this way, the AMF 150 may contact the proper 6G MM 131 to create the UE context indicating either the 5G slice ID or both 6G and mapped 5G slice ID for inter-RAT slice switching. In the former case, the 6GMM 131 may map / associate the received 5G slice ID to the respective 6G slice ID for inter-RAT slice switching.

[0125] Then the 6G MM 131 may communicate (440) with other 6G core network functions within the 6G core network 130 to perform the required handover preparation steps. Further, the 6G MM may additionally send (445) a handover request message to 6G RAN node 120 indicating the mapped / associated 6G slice used for inter-RAT slice switching. The 6G RAN node 120 may reply (450) with a handover request acknowledge message.

[0126] Once handover is executed (455) and the UE 110 completes the handover to the 6G RAN node 120, the UE 110 may use (460) the at least one slice supported by the 6G as 6G allowed NSSAI after the completion of the handover procedure without requesting a new allowed NSSAI from the 6G MM 131.

[0127] That is, the UE 110 does not have to perform again registration with 6G MM 131 or at least it performs limited registration without having to obtain a new allowed NSSAI list for 6G since it is assumed to already have it from an earlier registration or update.

[0128] An example corresponding to a process shown in signaling chart 400 will be further described in detail as below.

[0129] The UE 110 has joined the 6G network and has either received a per RAT (5G and 6G) specific allowed NSSAI list or a shared allowed NSSAI list among RATs that includes the 6G slice 2 and the mapped / associated 5G slice 1 for inter-RAT slice switching. The UE 110 is currently in the 5G network with a PDU session indicating a 5G slice 1 that is associated with the 6G slice 2.

[0130] After some time based on UE radio measurements, the source 5GRAN node 140 determines a target 6G RAN node 120 for the UE 110 and sends a handover required message to the AMF 150. The handover required message may contain the PDU session ID of the UE 110 and the target 6G RAN ID that corresponds to the 6G RAN node 120.

[0131] The AMF 150 based on UE context identifies the proper 6G MM 131 for the UE 110. In case that AMF 150 contains both 5G slice ID and the corresponding associated 6G slice ID then it may communicate the 6G slice ID to NRF to identify the proper 6G MM 131 for the UE 110. The NRF will return to AMF 150 the proper 6G MM 131.

[0132] Then AMF 150 will contact the identified 6G MM 131 to handover the UE 110 and the UE context will contain either the 5G slice ID in case AMF 150 does not have knowledge of the 6G slice ID, or both 5G and 6G slice IDs if AMF had it stored in the UE context. In the former case the 6G MM will have to do the mapping / association of the 5G Slice ID received from AMF to the respective 6G Slice ID used for inter-RAT slice switching.

[0133] After the UE 110 completes the handover to the 6G RAN, the UE 110 uses the already received 6G allowed NSSAI list or the 6G slice ID within the shared allowed NSSAI to utilize in 6G.

[0134] The UE 110 does not need to re-register with 6G MM 131 or at least performs registration but does not have to receive again a 6G allowed NSSAI list or does not have to receive the 6G slice ID included in the shared allowed NSSAI.

[0135] Although the example mentioned above explaining with one-to-one mapping of the 5G and 6G slices, e.g., the 5G slice 1 may be mapped to 6G slice 2, one to N mapping of the 5G and 6G slices may also be possible. For example, the 5G slice 1 may be mapped to 6G slices 2 and 3. In this case, 6G MM 131 may decide which one can be used for the handover of the PDU session.

[0136] It is also possible that a 5G PDU session of slice 1 has multiple QoS flows, some of which may be mapped into 6G slice 2 and some of which may be mapped into 6G slice 3 for inter-RAT slice switching. That is, the 5G PDU session may be divided into two or more 6G PDU sessions, and each corresponding 6G slice may carry a QoS flow associated with a divided 6G PDU session.

[0137] FIG. 5 shows a flowchart of an example method 500 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 500 will be described from the perspective of the AMF 150 in FIG. 1.

[0138] At block 510, in response to receiving a handover request associated with a handover procedure of a UE from a second RAN associated with a second RAT, to a first RAN associated with a first RAT, the AMF 150 identifies a core network node in charge of mobility and management functions associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to one or more slices supported by the second RAT.

[0139] At block 520, the AMF 150 sends, to the identified core network node a handover request for the UE.

[0140] In some example embodiments, the method 500 further comprises: obtaining, from a stored UE context, the at least one slice supported by the first RAT for the inter-RAT slice switching; communicating with a network repository function, NRF, by informing the at least one slice; and receive, from the NRF, an identifier of the core network node associated with the at least one slice.

[0141] In some example embodiments, the method 500 further comprises: configuring with an identifier of the core network node by an operation and management (0AM) system.

[0142] In some example embodiments, the method 500 further comprises: communicating with a network repository function, NRF, by informing the one or more slices supported by the second RAT; and receiving, from the NRF, an identifier of the core network node associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to the one or more slices supported by the second RAT.

[0143] In some example embodiments, the method 500 further comprises: sending, to the identified core network node a handover request for the UE via a request of a UE context creation.

[0144] In some example embodiments, the method 500 further comprises: communicating with a network repository function, NRF, by informing the one or more slices supported by the second RAT; and receiving, from the NRF, an identifier of the core network node associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to the one or more slices supported by the second RAT.

[0145] In some example embodiments, the method 500 further comprises: indicating, to the identified core network node an identifier of a UE PDU, session and the one or more further slices supported by a first RAN to which the UE is currently connected and associated with the second RAT.

[0146] In some example embodiments, the method 500 further comprises: indicating, to the identified core network node, the request of UE context creation in handover request at least indicating an identifier of a UE PDU session, the at least one slice supported by the first RAT and the one or more further slices supported by a first RAN to which the UE is currently connected and associated with the second RAT.

[0147] In some example embodiments, the inter-RAT slice switching refers to a procedure, caused by a mobility of the apparatus from the second RAT to which the UE is currently connected the first RAT, during which at least one slice supported by the first RAT provides a service for the UE instead of one or more further slices supported by the second RAT.

[0148] In some example embodiments, the first RAT refers to a 6G network / technology, and wherein the second RAT refers to a 5G network / technology.

[0149] FIG. 6 shows a flowchart of an example method 600 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 600 will be described from the perspective of the 6GMM 131 in FIG. 1.

[0150] At block 610, during a handover procedure of a UE from a second RAN associated with a second RAT to a first RAN associated with a first RAT, the 6G MM 131 receives, from an AMF, a request to handover the UE.

[0151] At block 620, the 6G MM 131 determines, based on the indication, at least one slice supported by the first RAT associated with one or more further slices supported by the second RAN to which the UE is currently connected.

[0152] At block 630, the 6G MM 131 transmits to the first RAN associated with the first RAT, a handover request indicating the at least one slice supported by the first RAT for the inter-RAT switching.

[0153] In some example embodiments, the method 600 further comprises: receiving the request from the AMF via a request of a UE context creation.

[0154] In some example embodiments, the method 600 further comprises: receiving, from the AMF, an identifier of a UE protocol data unit, PDU, session and the one or more further slices supported by the second RAN to which the UE is currently connected and associated with the second RAT.

[0155] In some example embodiments, the method 600 further comprises: receiving, from the AMF, an identifier of a UE PDU session, the at least one slice supported by the first RAT.

[0156] In some example embodiments, the method 600 further comprises: in accordance with a determination that a plurality of slices supported by the first RAT is available for the inter-RAT slice switching, determining a target slice from the plurality of slices for carrying the handover of the UE PDU session during the handover procedure of the UE.

[0157] In some example embodiments, the method 600 further comprises: in accordance with a determination that the UE PDU session associated with the second RAT corresponds to a plurality of quality of service, QoS flows and a plurality of associated slices supported by the first RAT is available for the inter-RAT slice switching; and determining at least one target slice from the plurality of slices to be used for carrying the plurality of the QoS flows in a handover of the PDU session during the handover procedure of the UE.

[0158] In some example embodiments, the UE PDU session associated with second first RAT is divided into more than one PDU sessions associated with the first RAT if a plurality of target slices supported by the first RAT are selected, and each QoS flow corresponding to a UE PDU session associated with the first RAT is to be served by a target slice supported by the first RAT.

[0159] In some example embodiments, the first RAT refers to a 6G network / technology, and wherein the second RAT refers to a 5G network / technology.

[0160] FIG. 7 shows a flowchart of an example method 700 implemented at an apparatus in accordance with some example embodiments of the present disclosure. For the purpose of discussion, the method 700 will be described from the perspective of the UE 110 m FIG. 1.

[0161] At block 710, the UE 110 obtains an association between at least one slice supported by a first RAT and one or more further slices supported by a second RAT during a registration procedure to the first or the second RAT.

[0162] At block 720, during a handover procedure of the apparatus from a second RAN associated with the second RAT to a first RAN associated with the first RAT, the UE 110 determines an allowed network slice selection assistance information, NSSAI, associated with the RAT to be used by the UE based on the received information.

[0163] In some example embodiments, the method 700 further comprises: using the at least one slice supported by the first RAT as allowed NSSAI associated with the first RAN after the completion of the handover procedure without requesting the allowed NSSAI from a core network node associated with the first RAT in charge of mobility management functions.

[0164] In some example embodiments, the method 700 further comprises: receiving, from a core network node associated with the first RAT after the completion of the handover procedure, an update of allowed NSSAI associated with the first RAN; and overriding the current allowed NSSAI associated with the first RAT by the updated information.

[0165] In some example embodiments, the first RAT refers to a 6G network / technology, and wherein the second RAT refers to a 5G network / technology.

[0166] In some example embodiments, an apparatus capable of performing any of the method 500 (for example, the AMF 150 in FIG. 1) may comprise means for performing the respective operations of the method 500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the AMF 150 in FIG. 1.

[0167] In some example embodiments, the apparatus comprises means for in response to receiving a handover request associated with a handover procedure of a UE from a second RAN, associated with a second RAT, to a first RAN associated with a first RAT, identifying a core network node in charge of mobility and management functions associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to one or more slices supported by the second RAT; and means for sending, to the identified core network node a handover request for the UE.

[0168] In some example embodiments, the apparatus comprises means for obtaining, from a stored UE context, the at least one slice supported by the first RAT for the inter-RAT slice switching; means for communicating with a network repository function, NRF, by informing the at least one slice; and means for receiving, from the NRF, an identifier of the core network node associated with the at least one slice.

[0169] In some example embodiments, the apparatus comprises means for configuring with an identifier of the core network node by an 0AM.

[0170] In some example embodiments, the apparatus comprises means for communicating with a network repository function, NRF, by informing the one or more slices supported by the second RAT; and means for receiving, from the NRF, an identifier of the core network node associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to the one or more slices supported by the second RAT.

[0171] In some example embodiments, the apparatus comprises means for sending, to the identified core network node a handover request for the UE via a request of a UE context creation.

[0172] In some example embodiments, the apparatus comprises means for communicating with a network repository function, NRF, by informing the one or more slices supported by the second RAT; and means for receiving, from the NRF, an identifier of the core network node associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to the one or more slices supported by the second RAT.

[0173] In some example embodiments, the apparatus comprises means for indicating, to the identified core network node an identifier of a UE protocol data unit, PDU, session and the one or more further slices supported by a first RAN to which the UE is currently connected and associated with the second RAT.

[0174] In some example embodiments, the apparatus comprises means for indicating, to the identified core network node, the request of UE context creation in a handover request at least indicating an identifier of a UE PDU session, the at least one slice supported by the first RAT and the one or more further slices supported by a first RAN to which the UE is currently connected and associated with the second RAT.

[0175] In some example embodiments, the inter-RAT slice switching refers to a procedure, caused by a mobility of the apparatus from the second RAT to which the UE is currently connected the first RAT, during which at least one slice supported by the first RAT provides a service for the UE instead of one or more further slices supported by the second RAT.

[0176] In some example embodiments, the first RAT refers to a 6G network / technology, and wherein the second RAT refers to a 5G network / technology.

[0177] In some example embodiments, an apparatus capable of performing any of the method 600 (for example, the 6G MM 131 in FIG. 1) may comprise means for performing the respective operations of the method 600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module. The apparatus may be implemented as or included in the 6G MM 131 in FIG. 1.

[0178] In some example embodiments, the apparatus comprises means for during a handover procedure of a UE from a second RAN associated with a second RAT to a first RAN associated with a first RAT, receiving, from an AMF, a request to handover the UE; means for determining, based on the request, at least one slice supported by the first RAT associated with one or more further slices supported by the second RAN to which the UE is currently connected; and means for transmitting, the first RAN associated with the first RAT, a handover request indicating the at least one slice supported by the first RAT for the inter-RAT switching.

[0179] In some example embodiments, the apparatus comprises means for receiving the indication from the AMF via a request of a UE context creation.

[0180] In some example embodiments, the apparatus comprises means for receiving, from the AMF, an identifier of a UE protocol data unit, PDU, session and the one or more further slices supported by the second RAN to which the UE is currently connected and associated with the second RAT.

[0181] In some example embodiments, the apparatus comprises means for receiving, from the AMF, an identifier of a UE PDU session, the at least one slice supported by the first RAT and the one or more further slices supported by the second RAN to which the UE is currently connected and associated with the second RAT.

[0182] In some example embodiments, the apparatus comprises means for in accordance with a determination that a plurality of slices supported by the first RAT is available for the inter-RAT slice switching, determining a target slice from the plurality of slices for carrying the handover of the UE PDU session during the handover procedure of the UE.

[0183] In some example embodiments, the apparatus comprises means for in accordance with a determination that the UE PDU session associated with the second RAT corresponds to a plurality of quality of service, QoS flows and a plurality of associated slices supported by the first RAT is available for the inter-RAT slice switching; and means for determining at least one target slice from the plurality of slices to be used for carrying the plurality of the QoS flows in a handover of the PDU session during the handover procedure of the UE.

[0184] In some example embodiments, the UE PDU session associated with second first RAT is divided into more than one PDU sessions associated with the first RAT if a plurality of target slices supported by the first RAT are selected, and each QoS flow corresponding to a UE PDU session associated with the first RAT is to be served by a target slice supported by the first RAT.

[0185] In some example embodiments, the first RAT refers to a 6G network / technology, and wherein the second RAT refers to a 5G network / technology.

[0186] In some example embodiments, an apparatus capable of performing any of the method 700 (for example, the UE 110 in FIG. 1) 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. The apparatus may be implemented as or included in the UE 110 in FIG. 1.

[0187] In some example embodiments, the apparatus comprises means for obtaining an association between at least one slice supported by a first RAT and one or more further slices supported by a second RAT during a registration procedure to the first or the second RAT; means for during a handover procedure of the apparatus from a second RAN associated with the second RAT to a first RAN associated with the first RAT, determining an allowed NSSAI, associated with the RAT to be used by the UE based on the received information.

[0188] In some example embodiments, the apparatus comprises means for using the at least one slice supported by the first RAT as allowed NSSAI associated with the first RAN after the completion of the handover procedure without requesting the allowed NSSAI from a core network node associated with the first RAT in charge of mobility management functions.

[0189] In some example embodiments, the apparatus comprises means for receiving, from a core network node associated with the first RAT after the completion of the handover procedure, an update of allowed NSSAI associated with the first RAN; and means for overriding the current allowed NSSAI associated with the first RAT by the updated information.

[0190] In some example embodiments, the first RAT refers to a 6G network / technology, and wherein the second RAT refers to a 5G network / technology.

[0191] FIG. 8 is a simplified block diagram of a device 800 that is suitable for implementing example embodiments of the present disclosure. The device 800 may be provided to implement a communication device, for example, the UE 110 or the AMF 150 OR the 6G MM 131 as shown in FIG. 1. As shown, the device 800 includes one or more processors 810, one or more memories 820 coupled to the processor 810, and one or more communication modules 840 coupled to the processor 810.

[0192] The communication module 840 is for bidirectional communications. The communication module 840 has one or more communication interfaces to facilitate communication with one or more other modules or devices. The communication interfaces may represent any interface that is necessary for communication with other network elements. In some example embodiments, the communication module 840 may include at least one antenna.

[0193] The processor 810 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 800 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

[0194] The memory 820 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a Read Only Memory (ROM) 824, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), an optical disk, a laser disk, and other magnetic storage and / or optical storage. Examples of the volatile memories include, but are not limited to, a random-access memory (RAM) 822 and other volatile memories that will not last in the power-down duration.

[0195] A computer program 830 includes computer executable instructions that are executed by the associated processor 810. The instructions of the program 830 may include instructions for performing operations / acts of some example embodiments of the present disclosure. The program 830 may be stored in the memory, e.g., the ROM 824. The processor 810 may perform any suitable actions and processing by loading the program 830 into the RAM 822.

[0196] The example embodiments of the present disclosure may be implemented by means of the program 830 so that the device 800 may perform any process of the disclosure as discussed with reference to FIG. 2 to FIG. 7. The example embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

[0197] In some example embodiments, the program 830 may be tangibly contained in a computer readable medium which may be included in the device 800 (such as in the memory 820) or other storage devices that are accessible by the device 800. The device 800 may load the program 830 from the computer readable medium to the RAM 822 for execution. In some example embodiments, the computer readable medium may include any types of non-transitory storage medium, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. The term “non-transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e g., RAM vs. ROM).

[0198] FIG. 9 shows an example of the computer readable medium 900 which may be in form of CD, DVD or other optical storage disk. The computer readable medium 900 has the program 830 stored thereon.

[0199] Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, and other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. Although various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0200] Some example embodiments of the present disclosure also provide at least one computer program product tangibly stored on a computer readable medium, such as a non-transitory computer readable medium. The computer program product includes computerexecutable instructions, such as those included in program modules, being executed in a device on a target physical or virtual processor, to carry out any of the methods as described above. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

[0201] Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. The program code may be provided to a processor or controller of a general-purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program code, when executed by the processor or controller, cause the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

[0202] In the context of the present disclosure, the computer program code or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like.

[0203] The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random-access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

[0204] Further, although operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, although several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Unless explicitly stated, certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, unless explicitly stated, various features that are described in the context of a single embodiment may also be implemented in a plurality of embodiments separately or in any suitable sub-combination.

[0205] Although the present disclosure has been described in languages specific to structural features and / or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features 5 or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

1. An apparatus comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:in response to receiving a handover request associated with a handover procedure of a user equipment, UE, from a second radio access network, RAN, associated with a second radio access technology, RAT, to a first RAN associated with a first RAT, identify a core network node in charge of mobility and management functions associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to one or more slices supported by the second RAT; andsend, to the identified core network node a handover request for the UE.

2. The apparatus of claim 1, wherein the apparatus is caused to:obtain, from a stored UE context, the at least one slice supported by the first RAT for the inter-RAT slice switching;communicate with a network repository function, NRF, by informing the at least one slice; andreceive, from the NRF, an identifier of the core network node associated with the at least one slice.

3. The apparatus of claim 1, wherein the apparatus is caused to:configure with an identifier of the core network node by an operation and management, OAM, system.

4. The apparatus of claim 1, wherein the apparatus is caused to:communicate with a network repository function, NRF, by informing the one or more slices supported by the second RAT; andreceive, from the NRF, an identifier of the core network node associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to the one or more slices supported by the second RAT.

5. The apparatus of any of claims 1-4, wherein the apparatus is caused to:indicate, to the identified core network node an identifier of a UE protocol data unit, PDU, session and the one or more further slices supported by the second RAN to which to which the UE is currently connected and associated with the second RAT.

6. The apparatus of any of claims 1-5, wherein the apparatus is caused to:indicate, to the identified core network node, the request of UE context creation in handover request at least indicating an identifier of a UE PDU session, the at least one slice supported by the first RAT and the one or more further slices supported by a first RAN to which the UE is currently connected and associated with the second RAT.

7. The apparatus of any of claims 1-6, wherein the inter-RAT slice switching refers to a procedure, caused by a mobility of the apparatus from the second RAT to which the UE is currently connected into the first RAT, during which at least one slice supported by the first RAT provides a service for the UE instead of one or more further slices supported by the second RAT.

8. The apparatus of any of claims 1-7, wherein the first RAT refers to a 6G network / technology, and wherein the second RAT refers to a 5Gnetwork / technology.

9. The apparatus of any of claims 1-8, wherein the apparatus comprises an Access and Mobility Management Function, AMF.

10. An apparatus comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:during a handover procedure of a UE from a second RAN associated with a second RAT to a first RAN associated with a first RAT, receive, from an AMF, a request to handover the UE;determine, based on the request, at least one slice supported by the first RAT associated with one or more further slices supported by the second RAN to which the UE is currently connected; andtransmit, to the first RAN associated with the first RAT, a handover requestindicating the at least one slice supported by the first RAT for the inter-RAT switching.

11. The apparatus of claim 10, wherein the apparatus is caused to:receive the request from the AMF via a request of a UE context creation.

12. The apparatus of claim 10 or 11, wherein the apparatus is caused to:receive, from the AMF, an identifier of a UE protocol data unit, PDU, session and the one or more further slices supported by the second RAN to which the UE is currently connected and associated with the second RAT.

13. The apparatus of claim 10 or 12, wherein the apparatus is caused to:receive, from the AMF, an identifier of a UE PDU session and the at least one slice supported by the first RAT.

14. The apparatus of claim 10 or 13, wherein the apparatus is caused to:in accordance with a determination that a plurality of slices supported by the first RAT is available for the inter-RAT slice switching, determine a target slice from the plurality of slices for carrying the handover of the UE PDU session during the handover procedure of the UE.

15. The apparatus of claim 10 or 11, wherein the apparatus is caused to:in accordance with a determination that the UE PDU session associated with the second RAT corresponds to a plurality of quality of service, QoS, flows and a plurality of associated slices supported by the first RAT is available for the inter-RAT slice switching; anddetermine at least one target slice from the plurality of slices to be used for carrying the plurality of the QoS flows in a handover of the PDU session during the handover procedure of the UE.

16. The apparatus of claim 15, wherein the UE PDU session associated with second RAT is divided into more than one PDU sessions associated with the first RAT if a plurality of target slices supported by the first RAT are selected, and each QoS flow corresponding to a UE PDU session associated with the second RAT is to be served by a target slice supported by the first RAT.

17. The apparatus of any of claims 10-16, wherein the first RAT refers to a 6G network / technology, and wherein the second RAT refers to a 5Gnetwork / technology.

18. The apparatus of any of claims 10-17, wherein the apparatus comprises a core network node associated with the first RAT in charge of mobility management functions.

19. An apparatus comprising:at least one processor; andat least one memory storing instructions that, when executed by the at least one processor, cause the apparatus at least to:receive at least one slice supported by a first RAT and one or more further slices supported by a second RAT during a registration procedure to the first or the second RAT;during a handover procedure of the apparatus from a second RAN associated with the second RAT to a first RAN associated with the first RAT, determine an allowed network slice selection assistance information, NSSAI, associated with the first RAT to be used by the UE based on the received information.

20. The apparatus of claim 19, wherein the apparatus is caused to:use the at least one slice supported by the first RAT as allowed NSSAI associated with the first RAN after the completion of the handover procedure without requesting the allowed NSSAI from a core network node associated with the first RAT in charge of mobility management functions.

21. The apparatus of claim 19, wherein the apparatus is caused to:receive, from a core network node associated with the first RAT after the completion of the handover procedure, an update of allowed NSSAI associated with the first RANoverride the current allowed NSSAI associated with the first RAT by the updated information.

22. The apparatus of any of claims 19-21, wherein the first RAT refers to a 6G network / technology, and wherein the second RAT refers to a 5G network / technology.

23. The apparatus of any of claims 19-22, wherein the apparatus comprises a UE.

24. A method comprising:in response to receiving a handover request associated with a handover procedure of a user equipment, UE from a further radio access network, RAN, associated with a second radio access technology, RAT, to a first RAN associated with a first RAT, identifying a core network node in charge of mobility and management functions associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to one or more slices supported by the second RAT; andsending, to the identified core network node a handover request for the UE.

25. A method comprising:during a handover procedure of a UE from a second RAN associated with a second RAT to a first RAN associated with a first RAT, receiving, from an AMF, a request to handover the UE;determining, based on the request, at least one slice supported by the first RAT associated with one or more further slices supported by the second RAN to which the UE is currently connected; andtransmitting, to the first RAN associated with the first RAT, a handover request indicating the at least one slice supported by the first RAT for the inter-RAT switching.

26. A method comprising:obtaining an association between at least one slice supported by a first RAT and one or more further slices supported by a second RAT during a registration procedure to the first or the second RAT; andduring a handover procedure of the apparatus from a second RAN associated with the second RAT to a first RAN associated with the first RAT, determining an allowed network slice selection assistance information, NSSAI, associated with the RAT to be used by the UE based on the received information.

27. An apparatus comprising:means for in response to receiving a handover request associated with a handover procedure of a user equipment, UE from a further radio access network, RAN, associated with a second radio access technology, RAT, to a first RAN associated with a first RAT, identifying a core network node in charge of mobility and management functions associated with the first RAT supporting the at least one slice for an inter-RAT slice switching corresponding to one or more slices supported by the second RAT; andmeans for sending, to the identified core network node a handover request for the UE.

28. An apparatus comprising:means for during a handover procedure of a UE from a second RAN associated with a second RAT to a first RAN associated with a first RAT, receiving, from an AMF, a request to handover the UE;means for determining, based on the request, at least one slice supported by the first RAT associated with one or more further slices supported by the second RAN to which the UE is currently connected; andmeans for transmitting, to the first RAN associated with the first RAT, a handover request indicating the at least one slice supported by the first RAT for the inter-RAT switching.

29. An apparatus comprising:means for obtaining an association between at least one slice supported by a first RAT and one or more further slices supported by a second RAT during a registration procedure to the first or the second RAT; andmeans for, during a handover procedure of the apparatus from a second RAN associated with the second RAT to a first RAN associated with the first RAT, determining an allowed network slice selection assistance information, NSSAI, associated with the RAT to be used by the UE based on the received information.

30. A computer readable medium comprising instructions stored thereon for causing an apparatus at least to perform the method of claim 24 or the method of claim 25 or the method of claim 26.43

Images