Method and apparatus for avoiding a slice deregistration in a telecommunication system

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. A method performed by an access and mobility management function (AMF) entity includes transmitting, to a user equipment (UE) via a base station, a paging message for a packet data unit (PDU) session of a non-3rd generation partnership project (3GPP) access, wherein the paging message is transmitted over a 3GPP access; and receiving, from the UE via the base station, a non-access stratum (NAS) message including information on an allowed PDU session to be transferred to the 3GPP access, wherein the allowed PDU session is associated with a first S-NSSAI.

Description

METHOD AND APPARATUS FOR AVOIDING A SLICE DEREGISTRATION IN A TELECOMMUNICATION SYSTEM

[0001] The present invention relates to improved methods to avoid slice deregistration for transferred Protocol Date Unit, PDU, sessions.

[0002] 5G mobile communication technologies define broad frequency bands such that high transmission rates and new services are possible, and can be implemented not only in "Sub 6GHz" bands such as 3.5GHz, but also in "Above 6GHz" bands referred to as mmWave including 28GHz and 39GHz. In addition, it has been considered to implement 6G mobile communication technologies (referred to as Beyond 5G systems) in terahertz bands (for example, 95GHz to 3THz bands) in order to accomplish transmission rates fifty times faster than 5G mobile communication technologies and ultra-low latencies one-tenth of 5G mobile communication technologies.

[0003] At the beginning of the development of 5G mobile communication technologies, in order to support services and to satisfy performance requirements in connection with enhanced Mobile BroadBand (eMBB), Ultra Reliable Low Latency Communications (URLLC), and massive Machine-Type Communications (mMTC), there has been ongoing standardization regarding beamforming and massive MIMO for mitigating radio-wave path loss and increasing radio-wave transmission distances in mmWave, supporting numerologies (for example, operating multiple subcarrier spacings) for efficiently utilizing mmWave resources and dynamic operation of slot formats, initial access technologies for supporting multi-beam transmission and broadbands, definition and operation of BWP (BandWidth Part), new channel coding methods such as a LDPC (Low Density Parity Check) code for large amount of data transmission and a polar code for highly reliable transmission of control information, L2 pre-processing, and network slicing for providing a dedicated network specialized to a specific service.

[0004] Currently, there are ongoing discussions regarding improvement and performance enhancement of initial 5G mobile communication technologies in view of services to be supported by 5G mobile communication technologies, and there has been physical layer standardization regarding technologies such as V2X (Vehicle-to-everything) for aiding driving determination by autonomous vehicles based on information regarding positions and states of vehicles transmitted by the vehicles and for enhancing user convenience, NR-U (New Radio Unlicensed) aimed at system operations conforming to various regulation-related requirements in unlicensed bands, NR UE Power Saving, Non-Terrestrial Network (NTN) which is UE-satellite direct communication for providing coverage in an area in which communication with terrestrial networks is unavailable, and positioning.

[0005] Moreover, there has been ongoing standardization in air interface architecture / protocol regarding technologies such as Industrial Internet of Things (IIoT) for supporting new services through interworking and convergence with other industries, IAB (Integrated Access and Backhaul) for providing a node for network service area expansion by supporting a wireless backhaul link and an access link in an integrated manner, mobility enhancement including conditional handover and DAPS (Dual Active Protocol Stack) handover, and two-step random access for simplifying random access procedures (2-step RACH for NR). There also has been ongoing standardization in system architecture / service regarding a 5G baseline architecture (for example, service based architecture or service based interface) for combining Network Functions Virtualization (NFV) and Software-Defined Networking (SDN) technologies, and Mobile Edge Computing (MEC) for receiving services based on UE positions.

[0006] As 5G mobile communication systems are commercialized, connected devices that have been exponentially increasing will be connected to communication networks, and it is accordingly expected that enhanced functions and performances of 5G mobile communication systems and integrated operations of connected devices will be necessary. To this end, new research is scheduled in connection with eXtended Reality (XR) for efficiently supporting AR (Augmented Reality), VR (Virtual Reality), MR (Mixed Reality) and the like, 5G performance improvement and complexity reduction by utilizing Artificial Intelligence (AI) and Machine Learning (ML), AI service support, metaverse service support, and drone communication.

[0007] Furthermore, such development of 5G mobile communication systems will serve as a basis for developing not only new waveforms for providing coverage in terahertz bands of 6G mobile communication technologies, multi-antenna transmission technologies such as Full Dimensional MIMO (FD-MIMO), array antennas and large-scale antennas, metamaterial-based lenses and antennas for improving coverage of terahertz band signals, high-dimensional space multiplexing technology using OAM (Orbital Angular Momentum), and RIS (Reconfigurable Intelligent Surface), but also full-duplex technology for increasing frequency efficiency of 6G mobile communication technologies and improving system networks, AI-based communication technology for implementing system optimization by utilizing satellites and AI (Artificial Intelligence) from the design stage and internalizing end-to-end AI support functions, and next-generation distributed computing technology for implementing services at levels of complexity exceeding the limit of UE operation capability by utilizing ultra-high-performance communication and computing resources.

[0008] The present invention has been made to address at least the above problems and / or disadvantages and to provide at least the advantages described below. Accordingly, an aspect of the present invention provides a method and apparatus for avoiding a slice deregistration in a telecommunication system.

[0009] In one embodiment, a method performed by a user equipment (UE) in a wireless communication system is provided. The method comprising: maintaining a packet data unit (PDU) session of a non-3rdgeneration partnership project (3GPP) access, wherein the PDU session of the non-3GPP access is associated with a first S-NSSAI; receiving, from an access and mobility management function (AMF) entity via a base station, a paging message for the PDU session of the non-3GPP access, wherein the paging message is received over a 3GPP access; and transmitting, to the AMF entity via the base station, a non-access stratum (NAS) message including information on an allowed PDU session to be transferred to the 3GPP access, wherein the allowed PDU session is associated with the first S-NSSAI.

[0010] In one embodiment, a method performed by an access and mobility management function (AMF) entity in a wireless communication system is provided. The method comprising: transmitting, to a user equipment (UE) via a base station, a paging message for a packet data unit (PDU) session of a non-3rdgeneration partnership project (3GPP) access, wherein the paging message is transmitted over a 3GPP access; and receiving, from the UE via the base station, a non-access stratum (NAS) message including information on an allowed PDU session to be transferred to the 3GPP access, wherein the allowed PDU session is associated with a first S-NSSAI, wherein the UE maintains the PDU session of the non-3GPP access associated with the first S-NSSAI before transmitting the paging message.

[0011] In one embodiment, a user equipment (UE) in a wireless communication system is provided. The UE comprising: a transceiver; and a controller coupled with the transceiver, and configured to: maintain a packet data unit (PDU) session of a non-3rdgeneration partnership project (3GPP) access, wherein the PDU session of the non-3GPP access is associated with a first S-NSSAI, receive, from an access and mobility management function (AMF) entity via a base station, a paging message for the PDU session of the non-3GPP access, wherein the paging message is received over a 3GPP access, and transmit, to the AMF entity via the base station, a non-access stratum (NAS) message including information on an allowed PDU session to be transferred to the 3GPP access, wherein the allowed PDU session is associated with the first S-NSSAI.

[0012] In one embodiment, an access and mobility managmenet function (AMF) entity in a wireless communication system is provided. The AMF entity comprising: a transceiver; and a controller coupled with the transceiver, and configured to: transmit, to a user equipment (UE) via a base station, a paging message for a packet data unit (PDU) session of a non-3rdgeneration partnership project (3GPP) access, wherein the paging message is transmitted over a 3GPP access, and receive, from the UE via the base station, a non-access stratum (NAS) message including information on an allowed PDU session to be transferred to the 3GPP access, wherein the allowed PDU session is associated with a first S-NSSAI, wherein the UE maintains the PDU session of the non-3GPP access associated with the first S-NSSAI before transmitting the paging message.

[0013] Advantages, and salient features of the invention will become apparent to those skilled in the art from the following detailed description, which, taken in conjunction with the annexed drawings, discloses exemplary embodiments of the invention. For more enhanced communication system, there is a need for method and apparatus for avoiding a slice deregistration in a telecommunication system.

[0014] These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

[0015] Figure 1 illustrates an example wireless network according to embodiments of the present disclosure;

[0016] Figure 2 illustrates an example base station (BS) according to embodiments of the present disclosure;

[0017] Figure 3 illustrates an example user equipment (UE) according to embodiments of the present disclosure;

[0018] Figure 4 shows a flowchart illustrating an embodiment of the intention from a network perspective;

[0019] Figure 5 shows a flowchart illustrating an embodiment of the intention from a UE perspective;

[0020] Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps to improve understanding of aspects of the present invention. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.

[0021] For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

[0022] It will be understood by those skilled in the art that the foregoing general description and the following detailed description are explanatory of the invention and are not intended to be restrictive thereof.

[0023] Reference throughout this specification to "an aspect", "another aspect" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

[0024] The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components preceded by "comprises... a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

[0026] FIGURES 1-3 below describe various embodiments implemented in wireless communications systems and with the use of orthogonal frequency division multiplexing (OFDM) or orthogonal frequency division multiple access (OFDMA) communication techniques. The descriptions of FIGURES 1-3 are not meant to imply physical or architectural limitations to the manner in which different embodiments may be implemented. Different embodiments of the present disclosure may be implemented in any suitably-arranged communications system.

[0027] FIGURE 1 illustrates an example wireless network 100 according to embodiments of the present disclosure. The embodiment of the wireless network 100 shown in FIGURE 1 is for illustration only. Other embodiments of the wireless network 100 could be used without departing from the scope of this disclosure.

[0028] As shown in FIGURE 1, the wireless network 100 includes various gNodeB (gNB) such a base station, BS 101, a BS 102, and a BS 103. The BS 101 communicates with the BS 102 and the BS 103. The BS 101 also communicates with at least one network 130, such as the Internet, a proprietary Internet Protocol (IP) network, or other data network.

[0029] The BS 102 provides wireless broadband access to the network 130 for a first plurality of user equipment's (UEs) within a coverage area 120 of the BS 102. The first plurality of UEs includes a UE 111, which may be located in a small business; a UE 112, which may be located in an enterprise (E); a UE 113, which may be located in a WiFi hotspot (HS); a UE 114, which may be located in a first residence (R); a UE 115, which may be located in a second residence (R); and a UE 116, which may be a mobile device (M), such as a cell phone, a wireless laptop, a wireless PDA, or the like. The BS 103 provides wireless broadband access to the network 130 for a second plurality of UEs within a coverage area 125 of the BS 103. The second plurality of UEs includes the UE 115, the UE 116, the UE 117, and the UE 118. In some embodiments, one or more of the BSs 101-103 may communicate with each other and with the UEs 111-118 using 5G / NR, long term evolution (LTE), long term evolution-advanced (LTE-A), WiMAX, WiFi, or other wireless communication techniques.

[0030] In certain embodiments, multiple UEs (such as the UE 117, the UE 118, and the UE 119) may communicate directly with each other through device-2-device communication. In some embodiments, a UE, such as UE 119, is outside the coverage area of the network, but can communicate with other UEs inside the coverage area of the network, such as UE 118, or outside the coverage area of the network.

[0031] Dotted lines show the approximate extents of the coverage areas 120 and 125, which are shown as approximately circular for the purposes of illustration and explanation only. It should be clearly understood that the coverage areas associated with BSs, such as the coverage areas 120 and 125, may have other shapes, including irregular shapes, depending upon the configuration of the BSs and variations in the radio environment associated with natural and man-made obstructions.

[0032] As described in more detail below, one or more of BS　101, BS　102 and BS　103 include conditions and timelines for transmission of acknowledgment information as described in embodiments of the present disclosure. In some embodiments, one or more of BS　101, BS　102 and BS　103 conditions and timelines for transmission of acknowledgment information. Additionally, as described in more detail below, one or more of the UEs 111-119 include circuitry, circuitry, programing, or a combination thereof for conditions and timelines for transmission of acknowledgment information. In certain embodiments, and one or more of the BSs 101-103 includes circuitry, programing, or a combination thereof for conditions and timelines for transmission of acknowledgment information.

[0033] Although FIGURE 1 illustrates one example of a wireless network, various changes may be made to FIGURE 1. For example, the wireless network could include any number of BSs and any number of UEs in any suitable arrangement. Also, the BS 101 could communicate directly with any number of UEs and provide those UEs with wireless broadband access to the network 130. Similarly, each BS 102-103 could communicate directly with the network 130 and provide UEs with direct wireless broadband access to the network 130. Further, the BSs 101, 102, and / or 103 could provide access to other or additional external networks, such as external telephone networks or other types of data networks.

[0034] FIGURE 2 illustrates an example BS 102 according to embodiments of the present disclosure. The embodiment of the BS 102 illustrated in FIGURE 2 is for illustration only, and the BSs 101 and 103 of FIGURE 1 could have the same or similar configuration. However, BSs come in a wide variety of configurations, and FIGURE 2 does not limit the scope of this disclosure to any particular implementation of a BS.

[0035] As shown in FIGURE 2, the BS 102 includes multiple antennas 205a-205n, multiple radio frequency (RF) transceivers 210a-210n, transmit (TX) processing circuitry 215, and receive (RX) processing circuitry 220. The BS 102 also includes a controller / processor 225, a memory 230, and a backhaul or network interface 235.

[0036] The RF transceivers 210a-210n receive, from the antennas 205a-205n, incoming RF signals, such as signals transmitted by UEs in the wireless network 100. The RF transceivers 210a-210n down-convert the incoming RF signals to generate IF or baseband signals. The IF or baseband signals are sent to the RX processing circuitry 220, which generates processed baseband signals by filtering, decoding, and / or digitizing the baseband or IF signals. The RX processing circuitry 220 transmits the processed baseband signals to the controller / processor 225 for further processing.

[0037] The TX processing circuitry 215 receives analog or digital data (such as voice data, web data, e-mail, or interactive video game data) from the controller / processor 225. The TX processing circuitry 215 encodes, multiplexes, and / or digitizes the outgoing baseband data to generate processed baseband or IF signals. The RF transceivers 210a-210n receive the outgoing processed baseband or IF signals from the TX processing circuitry 215 and up-converts the baseband or IF signals to RF signals that are transmitted via the antennas 205a-205n.

[0038] The controller / processor 225 can include one or more processors or other processing devices that control the overall operation of the BS 102. For example, the controller / processor 225 could control the reception of uplink channel signals and the transmission of downlink channel signals by the RF transceivers 210a-210n, the RX processing circuitry 220, and the TX processing circuitry 215 in accordance with well-known principles. The controller / processor 225 could support additional functions as well, such as more advanced wireless communication functions. Any of a wide variety of other functions could be supported in the BS 102 by the controller / processor 225. In some embodiments, the controller / processor 225 includes at least one microprocessor or microcontroller.

[0039] The controller / processor 225 is also capable of executing programs and other processes resident in the memory 230, such as an OS. The controller / processor 225 can move data into or out of the memory 230 as required by an executing process. For example, the controller / processor 225 can move data into or out of the memory 230 according to a process that is being executed.

[0040] The controller / processor 225 is also coupled to the backhaul or network interface 235. The backhaul or network interface 235 allows the BS 102 to communicate with other devices or systems over a backhaul connection or over a network. The network interface 235 could support communications over any suitable wired or wireless connection(s). For example, when the BS 102 is implemented as part of a cellular communication system (such as one supporting 5G / NR, LTE, or LTE-A), the network interface 235 could allow the BS 102 to communicate with other BSs over a wired or wireless backhaul connection. When the BS 102 is implemented as an access point, the network interface 235 could allow the BS 102 to communicate over a wired or wireless local area network or over a wired or wireless connection to a larger network (such as the Internet). The network interface 235 includes any suitable structure supporting communications over a wired or wireless connection, such as an Ethernet or RF transceiver.

[0041] The memory 230 is coupled to the controller / processor 225. Part of the memory 230 could include a RAM, and another part of the memory 230 could include a Flash memory or other ROM.

[0042] As described in more detail below, the transmit and receive paths of the BS 102 (implemented using the RF transceivers 210a-210n, TX processing circuitry 275, and / or RX processing circuitry 270) support communication with aggregation of frequency division duplex (FDD) cells and time division duplex (TDD) cells.

[0043] Although FIGURE 2 illustrates one example of BS 102, various changes may be made to FIGURE 2. For example, the BS 102 could include any number of each component shown in FIGURE 2. As a particular example, an access point could include a number of network interfaces 235, and the controller / processor 225 could support routing functions to route data between different network addresses. As another particular example, while shown as including a single instance of TX processing circuitry 215 and a single instance of RX processing circuitry 220, the BS 102 could include multiple instances of each (such as one per RF transceiver). Also, various components in FIGURE 2 could be combined, further subdivided, or omitted and additional components could be added according to particular needs.

[0044] FIGURE 3 illustrates an example UE 116 according to embodiments of the present disclosure. The embodiment of the UE 116 illustrated in FIGURE 3 is for illustration only, and the UEs 111-115 and 117-119 of FIGURE 1 could have the same or similar configuration. However, UEs come in a wide variety of configurations, and FIGURE 3 does not limit the scope of this disclosure to any particular implementation of a UE.

[0045] As shown in FIGURE 3, the UE　116 includes an antenna 305, a RF transceiver 310, TX processing circuitry 315, a microphone 320, and receive (RX) processing circuitry 325. The UE　116 also includes a speaker 330, a processor 340, an input / output (I / O) interface (IF) 345, an input device 350, a display 355, and a memory 360. The memory 360 includes an operating system (OS) 361 and one or more applications 362.

[0046] The RF transceiver 310 receives, from the antenna 305, an incoming RF signal transmitted by a BS of the wireless network 100. The RF transceiver 310 down-converts the incoming RF signal to generate an intermediate frequency (IF) or baseband signal. The IF or baseband signal is sent to the RX processing circuitry 325 that generates a processed baseband signal by filtering, decoding, and / or digitizing the baseband or IF signal. The RX processing circuitry 325 transmits the processed baseband signal to the speaker 330 (such as for voice data) or to the processor 340 for further processing (such as for web browsing data).

[0047] The TX processing circuitry 315 receives analog or digital voice data from the microphone 320 or other outgoing baseband data (such as web data, e-mail, or interactive video game data) from the processor 340. The TX processing circuitry 315 encodes, multiplexes, and / or digitizes the outgoing baseband data to generate a processed baseband or IF signal. The RF transceiver 310 receives the outgoing processed baseband or IF signal from the TX processing circuitry 315 and up-converts the baseband or IF signal to an RF signal that is transmitted via the antenna 305.

[0048] The processor 340 can include one or more processors or other processing devices and execute the OS 361 stored in the memory 360 in order to control the overall operation of the UE 116. For example, the processor 340 could control the reception of uplink channel signals and the transmission of downlink channel signals by the RF transceiver 310, the RX processing circuitry 325, and the TX processing circuitry 315 in accordance with well-known principles. In some embodiments, the processor 340 includes at least one microprocessor or microcontroller.

[0049] The processor 340 is also capable of executing other processes and programs resident in the memory 360, such as processes for beam management. The processor 340 can move data into or out of the memory 360 as required by an executing process. In some embodiments, the processor 340 is configured to execute the applications 362 based on the OS 361 or in response to signals received from BSs or an operator. The processor 340 is also coupled to the I / O interface 345, which provides the UE 116 with the ability to connect to other devices, such as laptop computers and handheld computers. The I / O interface 345 is the communication path between these accessories and the processor 340.

[0050] The processor 340 is also coupled to the input device 350. The operator of the UE 116 can use the input device 350 to enter data into the UE 116. The input device 350 can be a keyboard, touchscreen, mouse, track ball, voice input, or other device capable of acting as a user interface to allow a user in interact with the UE 116. For example, the input device 350 can include voice recognition processing, thereby allowing a user to input a voice command. In another example, the input device 350 can include a touch panel, a (digital) pen sensor, a key, or an ultrasonic input device. The touch panel can recognize, for example, a touch input in at least one scheme, such as a capacitive scheme, a pressure sensitive scheme, an infrared scheme, or an ultrasonic scheme.

[0051] The processor 340 is also coupled to the display 355. The display 355 may be a liquid crystal display, light emitting diode display, or other display capable of rendering text and / or at least limited graphics, such as from web sites.

[0052] The memory 360 is coupled to the processor 340. Part of the memory 360 could include a random access memory (RAM), and another part of the memory 360 could include a Flash memory or other read-only memory (ROM).

[0053] Although FIGURE 3 illustrates one example of UE 116, various changes may be made to FIGURE 3. For example, various components in FIGURE 3 could be combined, further subdivided, or omitted and additional components could be added according to particular needs. As a particular example, the processor 340 could be divided into multiple processors, such as one or more central processing units (CPUs) and one or more graphics processing units (GPUs). Also, while FIGURE 3 illustrates the UE 116 configured as a mobile telephone or smartphone, UEs could be configured to operate as other types of mobile or stationary devices.

[0054] 3GPP has developed several features related to network slicing, one of which uses a slice deregistration inactivity timer where the timer is per slice (Single - Network Slice Selection Assistance Information, S-NSSAI) and per access type (i.e. 3GPP or non-3GPP). The timer guards the inactivity period for the slice in question such that if the timer expires and the User Equipment, UE, has not used the slice, then the slice is deemed to be no longer available for the UE, and the slice is removed from the allowed NSSAI which enforces the lack of the slices availability since only slices in the allowed NSSAI can be used.

[0055] The following is from 3GPP TS 23.501 which describes this concept:

[0056] "The 5GC performs Network Slice usage monitoring to be able to enforce the release of inactive PDU Sessions, and deregistering of UEs from Network Slices with no PDU Sessions on them according to its own policies. In order to support usage monitoring for a Network Slice:

[0057] - the AMF runs a slice deregistration inactivity timer per S-NSSAI and access type to deregister the Network Slice which is started when the Network Slice is not used by any PDU Session over the corresponding access type. The slice deregistration inactivity timer is stopped and reset when at least a PDU Session associated with the Network Slice is successfully established or the Network Slice is removed form the Allowed NSSAI. When the slice deregistration inactivity timer for a Network Slice over an access type expires, the AMF removes the Network Slice from the Allowed NSSAI over the access type by sending the UE Configuration Update Command to impacted UE(s)."

[0058] The following is from section 4.6.2.9 of 3GPP TS 24.501 which describes the start of the timer and the outcome of its expiry (similar to what is shown above):

[0059] "The slice deregistration inactivity timer is:

[0060] a) started when there is no established PDU session, including any MA PDU session, associated with the S-NSSAI over the corresponding access type; and

[0061] b) stopped and reset when at least a PDU session, including any MA PDU session, associated with the S-NSSAI is successfully established over the corresponding access type(s) or the S-NSSAI is removed from the allowed NSSAI."

[0062] The following is from section 6.4.1.3 of 3GPP TS 24.501 which describes that the deregistration inactivity timer is stopped upon the successful establishment of a PDU session, noting that this is associated with explicit session management signaling that is exchanged with the network for the session to be established:

[0063] "If the UE supports network slice usage control and:

[0064] a) a PDU session is successfully established for the on-demand S-NSSAI, the UE shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over corresponding access type, if running; and

[0065] b) an MA PDU session is successfully established for the on-demand S-NSSAI, the UE shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over both 3GPP access and non-3GPP access, if running."

[0066] To summarize, the following key points can be observed from the above:

[0067] ● A slice is associated with a deregistration inactivity timer, where the timer guards the period of inactivity for the slice. The expiry of the timer means the slice is no longer available for use

[0068] ● The timer is per slice and access technology (i.e. 3GPP or non-3GPP)

[0069] ● The timer is stopped upon successful establishment of a PDU session, where this requires explicit session management signaling.

[0070] A UE which supports non-3GPP access and 3GPP access may be registered to the network via both access technology types. The UE may have a PDU session which is already established over the non-3GPP access, say with PDU session ID 1.

[0071] The 3GPP supports the transfer of a session from across these access types as is described next using two methods, a) and b):

[0072] a) Transfer of a session between 3GPP access & non-3GPP access by means of session management messages

[0073] The UE can use explicit session management messages (referred to as 5GSM messages) in order to transfer an already established PDU session on one access to the other access. Note that this requires the sending of a 5GSM message to achieve the transfer. This method can be used to transfer a session from 3GPP access to non-3GPP access, or from non-3GPP access to 3GPP access.

[0074] b) Transfer of a session from non-3GPP access to 3GPP access by means of the Allowed PDU session status IE

[0075] Before describing how this works, it should be noted that this method only works for the transfer of a session from non-3GPP access to 3GPP access i.e. this cannot be used to transfer a session in the other direction i.e. from 3GPP access to non-3GPP access.

[0076] A UE may have a PDU session, say with PDU session ID 1, which is established over the non-3GPP access. The network may determine that the UE is not reachable over the non-3GPP where, in fact, paging is not supported.

[0077] However, since the UE is (assumed to be) also registered over the 3GPP access, the network (which determines that there is downlink data for PDU session ID 1) can page the UE over the 3GPP access and indicate in the paging message that the cause of the paging is related to the non-3GPP access.

[0078] When the UE receives the paging message and determines that the cause is for a service over the non-3GPP access, the UE is required to send the (Control Plane) Service Request, CPSR, message and include the Allowed PDU session status Information Element, IE. The IE contains bit positions that correspond to PDU session identities and therefore by setting a bit position to 1, then the UE "indicates that the user-plane resources of corresponding PDU session can be re-established over 3GPP access" as described above. In this case, the PDU session would have user plane established over the 3GPP access and hence is now considered to be associated with the 3GPP access as described above:

[0079] "If the PDU session reactivation result IE is included in the SERVICE ACCEPT message indicating that the user-plane resources have been successfully reactivated for a PDU session that was indicated by the UE in the Allowed PDU session status IE as allowed to be re-established over 3GPP access, the UE considers the corresponding PDU session to be associated with the 3GPP access. If the user-plane resources of a PDU session have been successfully reactivated over the 3GPP access, the AMF and SMF update the associated access type of the corresponding PDU session."

[0080] If the bit was set to 0, then the UE does not allow the transfer of the session from non-3GPP access to 3GPP access and so the session continues to be associated with the non-3GPP access.

[0081] The following key points can therefore be highlighted:

[0082] ● A PDU session can be transferred from non-3GPP access to 3GPP access by means of the Allowed PDU session status IE

[0083] ● This does not require any 5GSM signalling between the UE and the network.

[0084] A problem in the prior art is that the current mechanism to stop the slice deregistration inactivity timer has only considered PDU session establishment by means of explicit 5GSM messages, whereas PDU session transfer by means of the Allowed PDU session status IE is ignored. This can lead to the slice deregistration inactivity timer expiring, even though the session is active on the 3GPP access after being transferred from non-3GPP.

[0085] The following describes, in more detail, the problem experienced in the prior art.

[0086] Assume the UE:

[0087] ● has an allowed NSSAI for the 3GPP access which includes S-NSSAI X, the UE has started the slice deregistration inactivity timer for S-NSSAI X (as there is no active PDU session over the 3GPP access)

[0088] ● has an allowed NSSAI for the non-3GPP access which also includes S-NSSAI X, and the UE has a PDU session active for this slice over the non-3GPP access

[0089] ● the UE gets paged for non-3GPP access and the UE indicates in the Allowed PDU session status IE that the session (associated with S-NSSAI X) is to be transferred from non-3GPP access to 3GPP access

[0090] ● the user plane gets established over the 3GPP access for the PDU session with S-NSSAI X, and the session is now considered to be associated with the 3GPP access

[0091] ● the deregistration inactivity timer for S-NSSAI X over the 3GPP access is still running, and its expiry leads to removal of S-NSSAI X from the allowed NSSAI and hence an abrupt end to the active PDU session. This leads to a very negative user experience.

[0092] The reason why the problem exists is because the stopping of the deregistration inactivity timer is strictly dependent on a successful establishment of a PDU session for the access type in question by means of explicit 5GSM signaling. Therefore, any transfer of a session by means of the Allowed PDU session status IE will not lead to stopping of the timer and hence the PDU session will eventually be dropped.

[0093] It is an aim of embodiments of the present invention to address this problem and, therefore, to avoid negative user experience and possible network malfunction.

[0094] According to the present invention there is provided an apparatus and method as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

[0095] According to a first aspect of the invention, in a telecommunication network, operatively connected to a User Equipment, there is a method of transferring a Protocol Data Unit, PDU, session from a non-3GPP access to a 3GPP access, wherein the UE or the network take account of an "Allowed PDU status" Information Element, IE, in order to determine if a particular slice is being used via the 3GPP access, then the network or the UE should stop a deregistration inactivity timer associated with the slice over the 3GPP access.

[0096] In an embodiment, after the transferring of the PDU session, the UE and the network consider that the slice associated with the transferred PDU session to be active and, if necessary, to remove any indication contrary to this status.

[0097] In an embodiment, wherein the method is performed by either the UE individually, the telecommunication network individually or both the network and UE together.

[0098] According to a second aspect, there is provided apparatus arranged to perform the method of the first aspect.

[0099] Certain aspects of the invention are:

[0100] ● The UE and the network should consider the Allowed PDU status IE in order to determine if a slice is being used or not via the 3GPP access

[0101] ● If a PDU session is transferred over to the 3GPP access using the Allowed PDU session status IE, then the network should stop (and optionally reset) any deregistration inactivity timer for that slice over the 3GPP access

[0102] ● If a PDU session is transferred over to the 3GPP access using the Allowed PDU session status IE, then the UE should stop (and optionally reset) any deregistration inactivity timer for that slice over the 3GPP access

[0103] ● After the transfer of the PDU session from non-3GPP to 3GPP by means of the Allowed PDU session status IE, both the UE and network should consider that the slice associated with the transferred PDU session is active i.e. is being used, and hence remove or delete any flag or local indication that states otherwise, if any

[0104] ● After the transfer of a PDU session from a source access to a target access, either by means of the Allowed PDU session status IE or by means of explicit signalling, the deregistration inactivity timer should be started for the S-NSSAI associated with the source access, and the deregistration inactivity timer should be stopped for the S-NSSAI associated with the target access

[0105] ● The establishment of a PDU session which leads to stopping of the deregistration inactivity timer should consider both the establishment of a new PDU session or the transfer of a PDU session, where this distinction can be made based on the value indicated in the Request type IE.

[0106] Although a few preferred embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes and modifications might be made without departing from the scope of the invention, as defined in the appended claims.

[0107] For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example only, to the accompanying diagrammatic drawings in which:

[0108] Figure 4 shows a flowchart illustrating an embodiment of the intention from a network perspective; and

[0109] Figure 5 shows a flowchart illustrating an embodiment of the intention from a UE perspective.

[0110] Note that herein, any relevant method steps, where appropriate, may be performed in in any order or combination. Whenever NAS message names are listed, they can be considered as examples but not restrictions. As such the proposals can apply to other NAS messages which are either existing or new. Wherever reference is made to the Access and Mobility management Function, AMF, these may also be applied to the Session Management Function, SMF, or other suitable network entity. Reference is primarily made to Fifth Generation, 5G, systems, but embodiments may find use in other systems (e.g. 6G, 4G, etc) where similar network functions are available.

[0111] Embodiments may apply for a UE and the network support network slice usage control (where for example this may be for a UE and / or network that exchange related capability indications using any IE or NAS message).

[0112] Herein, the S-NSSAI in question may be referred to as an on-demand S-NSSAI, and optionally the S-NSSAI may be associated with a deregistration inactivity timer and optionally an access type. The deregistration inactivity timer may refer to a slice deregistration inactivity timer. A slice may refer to an S-NSSAI. For any embodiment which involves stopping of the deregistration inactivity timer, this may also involve resetting of the timer, optionally, after stopping of the timer.

[0113] The following relates to AMF behaviour with respect to the deregistration inactivity timer and the Allowed PDU session status IE

[0114] The network may page the UE and indicate that the access for which the paging is performed is the non-3GPP access. The network may use the AMF, which has triggered the paging via the NG-RAN.

[0115] The AMF may receive a NAS message, e.g. a Registration Request, Service Request, or Control Plane Service Request, where the Allowed PDU session status IE is included, the AMF may determine to establish (e.g. activate or reactive) the user plane resources for a PDU session which the UE has indicated that should / can be transferred to the 3GPP access (e.g. the Allowed PDU session status IE has at least one bit which is set to the value 1 - "indicates that the user-plane resources of corresponding PDU session can be re-established over 3GPP access"). When the AMF determines that a PDU session has been transferred from the non-3GPP access to the 3GPP access, where this is done by means of the Allowed PDU session status IE, then the AMF should stop and optionally reset slice deregistration inactivity timer for the slice (or for the S-NSSAI) which is associated with the PDU session that has been transferred over to the 3GPP access (from the non-3GPP access). The timer that is stopped and reset is associated with the slice (or S-NSSAI) in question and the 3GPP access.

[0116] The AMF may behave as described above (when or after any of the above occurs) in any of the following ways:

[0117] ● After the AMF receives (optionally from the UE) the Allowed PDU session status IE such that the PDU session associated with the slice (or S-NSSAI) for which there is a running deregistration inactivity timer, has an associated bit position whose value is set to 1 (i.e. the UE is requesting the reactivation of user plane resources over the 3GPP access)

[0118] ● After the AMF establishes (or reactivates) the user plane resources for the PDU session which is associated with the slice (or S-NSSAI), for which there is a running deregistration inactivity timer

[0119] ● After the AMF (and / or SMF) updates the associated access type of the corresponding PDU session e.g. when the AMF (and / or SMF) updates the associated access type of the session such that the PDU session is now considered to be associated with the 3GPP access (optionally when or after any of the previous proposals occur) for e.g. when user plane resources are established on the 3GPP access.

[0120] Note that for any of the above the AMF stops and, optionally, resets a (slice) deregistration inactivity timer for the slice (or S-NSSAI) in question and the 3GPP access, if any is running.

[0121] In addition to the above, the AMF should also behave as follows:

[0122] ● After a session has been transferred from non-3GPP access to 3GPP access, either by means of explicit 5GSM signalling or by means of the Allowed PDU session status, the AMF should (optionally reset and) start the deregistration inactivity timer for the slice (or S-NSSAI) in question and the non-3GPP access i.e. the timer is that which is associated with the non-3GPP access. As such, when a PDU session is transferred from non-3GPP access to 3GPP access, the AMF behaves as described above (e.g. resets and stops the timer associated with the slice and the 3GPP access) and optionally also (resets and) starts the deregistration inactivity timer for the same slice (or S-NSSAI) and the non-3GPP access.

[0123] ● Similarly, when a PDU session is transferred from 3GPP access to non-3GPP access by means of explicitly 5GSM signalling, the AMF should start the deregistration inactivity timer for the slice (or S-NSSAI) and 3GPP access i.e. the timer which is associated with the slice (or S-NSSAI) and the 3GPP access

[0124] ○ The AMF may behave as set out above (i.e. with regards to stopping of a deregistration inactivity timer) when:

[0125] ● the access type of the PDU session is updated to the new access type i.e. when the access type of the PDU session is changed / updated from 3GPP access to non-3GPP access

[0126] ● the PDU session establishment procedure (optionally where the Request type IE is set to the value '010' "existing PDU session") completes successfully

[0127] ● In general, after a session has been transferred from a source access (e.g. 3GPP access or non-3GPP access) to a target access (e.g. non-3GPP access or 3GPP access, respectively) by means of explicit 5GSM signalling, then the UE should (optionally reset and) start the deregistration inactivity timer for the slice (or S-NSSAI) in question and the source access i.e. the timer is that which is associated with the source access. As such, when a PDU session is transferred from a source access to a target access, the UE behaves as described herein (e.g. resets and stops the timer associated with the slice and the target access) and optionally also (resets and) starts the deregistration inactivity timer for the same slice (or S-NSSAI) and source access.

[0128] Note that it is specified that the AMF stops and resets the deregistration inactivity timer for a slice after the successful establishment of the PDU session over the corresponding access and for the slice in question. However, there is no distinction regarding whether the PDU session establishment is for a new PDU session or for an existing PDU session. The successful completion of the PDU session establishment can hint that this is for a new session only. As such, according to an embodiment:

[0129] ● after the successful completion of a PDU session establishment, where the Request type IE is set to the value '001' "initial request" , or is set to '010' "existing PDU session", then the AMF should reset and stop the deregistration inactivity timer

[0130] ● after the successful completion of a PDU session establishment, where the Request type IE is set to the value '001' "initial request" , or is set to '010' "existing PDU session", then the UE should reset and stop the deregistration inactivity timer

[0131] ○ Note that herein, the PDU session transfer can occur for the case when the:

[0132] ● PDU session is first associated with the 3GPP access, the PDU session has been transferred to the non-3GPP access, and optionally the PDU session is now considered to be associated with the non-3GPP access, or

[0133] ● PDU session is first associated with the non-3GPP access, the PDU session has been transferred to the 3GPP access, and optionally the PDU session is now considered to be associated with the 3GPP access.

[0134] Note that for all of the above, if the AMF determines that a PDU session has not been successfully transferred from the non-3GPP access to the 3GPP access, e.g. by means of the Allowed PDU session status IE, where for example the Allowed PDU session status IE indicates that the user-plane resources of corresponding PDU session is not allowed to be re-established over 3GPP access (e.g. the bit position corresponding to the PDU session is set to the value '0'), then the AMF:

[0135] ● does not reset or stop the deregistration inactivity timer for the slice and 3GPP access, e.g. the AMF maintains the timer running

[0136] ● does not reset or start the deregistration inactivity timer for the slice and the non-3GPP access, e.g. the AMF maintains the timer not running for the non-3GPP access (except if the slice is removed from the allowed NSSAI for the non-3GPP access, or the PDU session is released over the non-3GPP access).

[0137] Note that for all of the above, if the AMF determines that a PDU session has not been successfully transferred from a source access (which may be 3GPP or non-3GPP access) to target access (which may be non-3GPP or 3GPP access, respectively), e.g. user plane resources could not be established successfully on target access and identified this e.g. by means of explicit 5GSM signalling, where the Request type IE indicates "existing PDU session" then the AMF:

[0138] ● does not reset or stop the deregistration inactivity timer for the slice and the target access, e.g. the AMF maintains the timer running

[0139] ● does not reset or start the deregistration inactivity timer for the slice and the source access, e.g. the AMF maintains the timer not running for the source access (except if the slice is removed from the allowed NSSAI for the source access, or the PDU session is released over the source access).

[0140] Figure 4 shows an example of how the AMF should behave based on the details set out above. It shows steps 1) to 5):

[0141] 1) A PDU session exists for the UE on non-3GPP access, say for S-NSSAI K. The AMF has a deregistration inactivity timer running for S-NSSAI K for 3GPP access.

[0142] 2) The AMF initiates paging over 3GPP access bit for non-3GPP access PDU session(s) e.g. the access type in the paging indicates non-3GPP access.

[0143] 3) The AMF receives a NAS message with Allowed PDU session status IE indicating that at least one PDU is to be transferred to 3GPP access. This includes the PDU session ID associated with S-NSSAI K.

[0144] 4) The AMF stops (and optionally resets) the deregistration inactivity timer for S-NSAAI K and the 3GPP access. Optionally, if the PDU session for S-NSSAI K is indicated in the IE, or after the establishment of UP resources, or after the AMF (and / or SMF) updates the access type for the PDU session with S-NSSAI K to be 3GPP access.

[0145] 5) The AMF starts the deregistration inactivity timer for S-NSSAI K and the non-3GPP access. This step applies to any PDU session transfer with explicit 5GSM signalling.

[0146] The following relates to UE behaviour with respect to the deregistration inactivity timer and the Allowed PDU session status.

[0147] The UE should also reset and stop any timer, where the timer is the deregistration inactivity timer, that is associated with a slice (e.g. an S-NSSAI) and the 3GPP access when a PDU session is transferred from the non-3GPP access to the 3GPP access by means of the Allowed PDU session status IE.

[0148] When the UE sends a NAS message, a Registration Request, Service Request, or Control Plane Service Request, where the Allowed PDU session status IE is included such that the user plane resources for a PDU session is indicated (by the UE) to be transferred to the 3GPP access (e.g. the Allowed PDU session status IE has at least one bit which the UE has set to the value 1 - "indicates that the user-plane resources of corresponding PDU session can be re-established over 3GPP access"), then the UE should reset and stop the deregistration inactivity timer for the slice (e.g. S-NSSAI) and the 3GPP access.

[0149] The UE can behave as described above when (or after) any of the following occurs:

[0150] ● The UE determines that the PDU session has been transferred from the non-3GPP access to the 3GPP access optionally by means of the Allowed PDU session status IE

[0151] ● The UE determines that the user plane resources have been established, for example:

[0152] ○ The UE determines this locally by means of interaction with the lower layers

[0153] ○ The UE receives the PDU session reactivation result IE in any NAS message indicating that the user plane resources have been successfully reactivated for a PDU session that was indicated by the UE in the Allowed PDU session status IE (as allowed to be re-established over 3GPP access)

[0154] ○ The user plane resources are established on the 3GPP access for the corresponding PDU session.

[0155] ● The UE updates the access type of the PDU session such that there is a new access type associated with the PDU session, where for example the new access type is the 3GPP access (and optionally the previous access type was the non-3GPP access)

[0156] ● For any of the above, the slice associated with the transferred PDU session optionally has a deregistration inactivity timer which is running.

[0157] As indicated previously, a PDU session can be transferred from one access type to another access type by means of explicit 5GSM signalling. The process to do so is the PDU session establishment procedure. The specification indicates that the UE should stop the timer i.e. the deregistration inactivity timer, which is associated with a slice (e.g. S-NSSAI) and access type after the successful establishment of the PDU session. However, it is not explicitly indicated if the establishment procedure is for a new PDU session or for the transfer of a PDU session. In an embodiment, both options are addressed and the means to do so would be dependent on the value of the Request type IE that the UE includes in the NAS message:

[0158] ● after the successful completion of a PDU session establishment, where the Request type IE is set to the value '001' "initial request" , or is set to '010' "existing PDU session", then the AMF should reset and stop the deregistration inactivity timer

[0159] ● after the successful completion of a PDU session establishment, where the Request type IE is set to the value '001' "initial request" , or is set to '010' "existing PDU session", then the UE should reset and stop the deregistration inactivity timer

[0160] ○ Note that herein, the PDU session transfer can occur for the case when the:

[0161] ● PDU session is first associated with the 3GPP access, the PDU session has been transferred to the non-3GPP access, and optionally the PDU session is now considered to be associated with the non-3GPP access, or

[0162] ● PDU session is first associated with the non-3GPP access, the PDU session has been transferred to the 3GPP access, and optionally the PDU session is now considered to be associated with the 3GPP access.

[0163] In addition to the above, the UE should also behave as follows:

[0164] ● After a session has been transferred from non-3GPP access to 3GPP access, either by means of explicit 5GSM signalling or by means of the Allowed PDU session status, for e.g. user plane resources are established on 3GPP access, the UE should (optionally reset and) start the deregistration inactivity timer for the slice (or S-NSSAI) in question and the non-3GPP access i.e. the timer is that which is associated with the non-3GPP access. As such, when a PDU session is transferred from non-3GPP access to 3GPP access, the UE behaves as described above (e.g. resets and stops the timer associated with the slice and the 3GPP access) and optionally also (resets and) starts the deregistration inactivity timer for the same slice (or S-NSSAI) and the non-3GPP access

[0165] ● After a session has been transferred from a source access (e.g. 3GPP access or non-3GPP access) to a target access (e.g. non-3GPP access or 3GPP access, respectively) by means of explicit 5GSM signalling, then the UE should (optionally reset and) start the deregistration inactivity timer for the slice (or S-NSSAI) in question and the source access i.e. the timer is that which is associated with the source access. As such, when a PDU session is transferred from a source access to a target access, the UE behaves as described herein (e.g. resets and stops the timer associated with the slice and the target access) and optionally also (resets and) starts the deregistration inactivity timer for the same slice (or S-NSSAI) and source access.

[0166] For all the details and procedures herein (for the UE and / or the AMF), where the Request type IE is mentioned, the described techniques can be applied for the case when the Request type IE is included in the UL NAS TRANSPORT message, where optionally the message includes a 5GSM message, e.g. where the Payload container type IE indicates "N1 SM information" (i.e. the value is set to '0001') and optionally where the payload container contents contain a 5GSM message.

[0167] Note that for all of the above, if the UE determines that a PDU session has not been successfully transferred from a source access (which may be 3GPP or non-3GPP access) to target access (which may be non-3GPP or 3GPP access, respectively), e.g. by means of explicit 5GSM signalling, where the Request type IE indicates "existing PDU session" or if the user plane resources could not be established on target access, then the UE:

[0168] ● does not reset or stop the deregistration inactivity timer for the slice and the target access, e.g. the UE maintains the timer running

[0169] ● does not reset or start the deregistration inactivity timer for the slice and the source access, e.g. the UE maintains the timer not running for the source access (except if the slice is removed from the allowed NSSAI for the source access, or the PDU session is released over the source access).

[0170] Figure 5 shows an example of how the UE should behave based on the details herein. It shows steps 11) to 15).

[0171] 11) a PDU session exists for the UE on non-3GPP access, say of S-NSSAI K. The UE has a deregistration inactivity timer running for S-NSSAI K for 3GPP access.

[0172] 12) the UE receives a paging message over the 3GPP access but for non-3GPP access PDU session(s) e.g. the access type indicates non-3GPP.

[0173] 13) the UE sends a NAS message with Allowed PDU session status IE indicating that at least one PDU session to be transferred to 3GPP access. This includes PDU session ID associated with S-NSSAI K.

[0174] 14) The UE stops (and optionally resets) the deregistration inactivity timer for S-NSAAI K and the 3GPP access. Optionally, if the PDU session reactivation result IE is received and indicates that that the UP resources for the PDU session with S-NSSAI K are established, or after establishment of the UP resources for the PDU session for S-NSSAI K over the 3GPP access.

[0175] 15) the UE starts the deregistration inactivity timer for S-NSSAI K and the non-3GPP access. This step applies to any PDU session transfer with explicit 5GSM signalling.

[0176] It should be noted that the flowcharts shown in Figures 4 and 5, provided for the AMF and the UE, respectively, may also be used together although this is not shown explicitly herein.

[0177] The following provides examples of how the 3GPP specification(s) can be updated based on the details herein, noting that these are examples only and are not to be considered as restrictions.

[0178] For example, the following paragraph in section 4.6.2.9 of 3GPP TS 24.501 can be updated as follows, where the update is shown with underlined text:

[0179] "The slice deregistration inactivity timer is:

[0180] a) started when there is no established PDU session, including any MA PDU session, associated with the S-NSSAI over the corresponding access type, or when a PDU session is transferred from one access type to another; and

[0181] b) stopped and reset when at least a PDU session, including any MA PDU session, associated with the S-NSSAI is successfully established over the corresponding access type(s) or the S-NSSAI is removed from the allowed NSSAI."

[0182] For example, the following paragraph in section 5.5.1.3.4 of 3GPP TS 24.501 can be updated as follows, where the update is shown with underlined text:

[0183] "If the PDU session reactivation result IE is included in the REGISTRATION ACCEPT message indicating that the user-plane resources have been successfully reactivated for a PDU session that was indicated by the UE in the Allowed PDU session status IE as allowed to be re-established over 3GPP access, the UE considers the corresponding PDU session to be associated with the 3GPP access,and optionally the UE shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over the 3GPP access (optionally if any is running). The UE shall (optionally reset and) start the slice deregistration inactivity timer for the on-demand S-NSSAI over the non-3GPP access. If the user-plane resources of a PDU session have been successfully reactivated over the 3GPP access, the AMF and SMF update the associated access type of the corresponding PDU session.Optionally the AMF shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over the 3GPP access (optionally if any is running). The AMF shall (optionally reset and) start the slice deregistration inactivity timer for the on-demand S-NSSAI over the non-3GPP access."

[0184] For example, the following paragraph in section 5.6.1.4.1 of 3GPP TS 24.501 can be updated as follows, where the update is shown with underlined text:

[0185] "If the PDU session reactivation result IE is included in the SERVICE ACCEPT message indicating that the user-plane resources have been successfully reactivated for a PDU session that was indicated by the UE in the Allowed PDU session status IE as allowed to be re-established over 3GPP access, the UE considers the corresponding PDU session to be associated with the 3GPP access, andoptionally the UE shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over the 3GPP access(optionally if any is running). The UE shall (optionally reset and) start the slice deregistration inactivity timer for the on-demand S-NSSAI over the non-3GPP access. If the user-plane resources of a PDU session have been successfully reactivated over the 3GPP access, the AMF and SMF update the associated access type of the corresponding PDU session."

[0186] Note that the above can also be applied to the case when the UE sends the Control Plane Service Request message i.e. when the UE receives Service Accept message after sending the Control Plane Service Request message.

[0187] For example, the following paragraph in section 6.3.3.3 of 3GPP TS 24.501 can be updated as follows, where the update is shown with underlined text:

[0188] "If the UE supports network slice usage control:

[0189] a) all PDU session associated with an on-demand S-NSSAI are releasedor transferred to another access type, and there is no MA PDU session associated with this on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer for this on-demand S-NSSAI over the corresponding access type;

[0190] b) all MA PDU session associated with an on-demand S-NSSAI are released and there is no PDU session associated with this on-demand S-NSSAI, the UE shall start the slice deregistration inactivity timer for this on-demand S-NSSAI over both 3GPP access and non-3GPP access; or

[0191] c) all PDU session and all MA PDU session associated with an on-demand S-NSSAI are released, the UE shall start the slice deregistration inactivity timer for this on-demand S-NSSAI over both 3GPP access and non-3GPP access."

[0192] For example, the following paragraph in section 6.4.1.3 of 3GPP TS 24.501 can be updated as follows, where the update is shown with underlined text:

[0193] "If the UE supports network slice usage control and:

[0194] a) a new PDU session is successfully established for the on-demand S-NSSAI, the UE shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over corresponding access type, if running;

[0195] b)an existing PDU session is successfully transferred for the on-demand S-NSSAI, the UE shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over corresponding access type, if running; and

[0196] b) an MA PDU session is successfully established for the on-demand S-NSSAI, the UE shall stop and reset the slice deregistration inactivity timer for the on-demand S-NSSAI over both 3GPP access and non-3GPP access, if running."

[0197] Note that the transfer of a PDU session may refer to a PDU session that is not for emergency services.

[0198] At least some of the example embodiments described herein may be constructed, partially or wholly, using dedicated special-purpose hardware. Terms such as 'component', 'module' or 'unit' used herein may include, but are not limited to, a hardware device, such as circuitry in the form of discrete or integrated components, a Field Programmable Gate Array (FPGA) or Application Specific Integrated Circuit (ASIC), which performs certain tasks or provides the associated functionality. In some embodiments, the described elements may be configured to reside on a tangible, persistent, addressable storage medium and may be configured to execute on one or more processors. These functional elements may in some embodiments include, by way of example, components, such as software components, object-oriented software components, class components and task components, processes, functions, attributes, procedures, subroutines, segments of program code, drivers, firmware, microcode, circuitry, data, databases, data structures, tables, arrays, and variables. Although the example embodiments have been described with reference to the components, modules and units discussed herein, such functional elements may be combined into fewer elements or separated into additional elements. Various combinations of optional features have been described herein, and it will be appreciated that described features may be combined in any suitable combination. In particular, the features of any one example embodiment may be combined with features of any other embodiment, as appropriate, except where such combinations are mutually exclusive. Throughout this specification, the term "comprising" or "comprises" means including the component(s) specified but not to the exclusion of the presence of others.

[0199] Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

[0200] All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive.

[0201] Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

[0202] The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1.A method performed by a user equipment (UE) in a wireless communication system, the method comprising:maintaining a packet data unit (PDU) session of a non-3rdgeneration partnership project (3GPP) access, wherein the PDU session of the non-3GPP access is associated with a first S-NSSAI;receiving, from an access and mobility management function (AMF) entity via a base station, a paging message for the PDU session of the non-3GPP access, wherein the paging message is received over a 3GPP access; andtransmitting, to the AMF entity via the base station, a non-access stratum (NAS) message including information on an allowed PDU session to be transferred to the 3GPP access, wherein the allowed PDU session is associated with the first S-NSSAI.2.The method of claim 1,wherein a first deregistration inactivity timer associated with the 3GPP access and the first S-NSSAI is running while maintaining the PDU session of the non-3GPP access.3.The method of claim 2,wherein the first deregistration inactivity timer associated with the 3GPP access and the first S-NSSAI is stopped,after transmitting the NAS message, orreceiving information on a PDU session reactivation result indicating that the user plane (UP) resources for the PDU session is established, orafter establishing user plane (UP) resources for the PDU session for the first S-NSSAI over the 3GPP access.4.The method of claim 1, the method further comprising:starting a second inactivity timer associated with the non-3GPP access and the first S-NSSAI.5.A method performed by an access and mobility management function (AMF) entity in a wireless communication system, the method comprising:transmitting, to a user equipment (UE) via a base station, a paging message for a packet data unit (PDU) session of a non-3rdgeneration partnership project (3GPP) access, wherein the paging message is transmitted over a 3GPP access; andreceiving, from the UE via the base station, a non-access stratum (NAS) message including information on an allowed PDU session to be transferred to the 3GPP access, wherein the allowed PDU session is associated with a first S-NSSAI,wherein the UE maintains the PDU session of the non-3GPP access associated with the first S-NSSAI before transmitting the paging message.6.The method of claim 5,wherein a first deregistration inactivity timer associated with the 3GPP access and the first S-NSSAI is running while the UE maintains the PDU session of the non-3GPP access.7.The method of claim 6,wherein the first deregistration inactivity timer associated with the 3GPP access and the first S-NSSAI is stopped,after receiving the NAS message, ortransmitting information on a PDU session reactivation result indicating that the user plane (UP) resources for the PDU session is established, orafter establishing user plane (UP) resources for the PDU session for the first S-NSSAI over the 3GPP access.8.The method of claim 5,wherein a second inactivity timer associated with the non-3GPP access and the first S-NSSAI is started.9.A user equipment (UE) in a wireless communication system, the UE comprising:a transceiver; anda controller coupled with the transceiver, and configured to:maintain a packet data unit (PDU) session of a non-3rdgeneration partnership project (3GPP) access, wherein the PDU session of the non-3GPP access is associated with a first S-NSSAI,receive, from an access and mobility management function (AMF) entity via a base station, a paging message for the PDU session of the non-3GPP access, wherein the paging message is received over a 3GPP access, andtransmit, to the AMF entity via the base station, a non-access stratum (NAS) message including information on an allowed PDU session to be transferred to the 3GPP access, wherein the allowed PDU session is associated with the first S-NSSAI.10.The UE of claim 9,wherein a first deregistration inactivity timer associated with the 3GPP access and the first S-NSSAI is running while maintaining the PDU session of the non-3GPP access.11.The UE of claim 10,wherein the first deregistration inactivity timer associated with the 3GPP access and the first S-NSSAI is stopped,after transmitting the NAS message, orreceiving information on a PDU session reactivation result indicating that the user plane (UP) resources for the PDU session is established, orafter establishing user plane (UP) resources for the PDU session for the first S-NSSAI over the 3GPP access.12.The UE of claim 9, wherein the controller is further configured to:start a second inactivity timer associated with the non-3GPP access and the first S-NSSAI.13.An access and mobility management function (AMF) entity in a wireless communication system, the AMF entity comprising:a transceiver; anda controller coupled with the transceiver, and configured to:transmit, to a user equipment (UE) via a base station, a paging message for a packet data unit (PDU) session of a non-3rdgeneration partnership project (3GPP) access, wherein the paging message is transmitted over a 3GPP access, andreceive, from the UE via the base station, a non-access stratum (NAS) message including information on an allowed PDU session to be transferred to the 3GPP access, wherein the allowed PDU session is associated with a first S-NSSAI,wherein the UE maintains the PDU session of the non-3GPP access associated with the first S-NSSAI before transmitting the paging message.14.The AMF entity of claim 5,wherein a first deregistration inactivity timer associated with the 3GPP access and the first S-NSSAI is running while the UE maintains the PDU session of the non-3GPP access.15.The AMF entity of claim 14,wherein the first deregistration inactivity timer associated with the 3GPP access and the first S-NSSAI is stopped,after receiving the NAS message, ortransmitting information on a PDU session reactivation result indicating that the user plane (UP) resources for the PDU session is established, orafter establishing user plane (UP) resources for the PDU session for the first S-NSSAI over the 3GPP access.

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