Method and user equipment for managing registration failure of access network slice

Abstract

A method and a user equipment for managing registration failure of an access network slice. The method comprises: sending, to a first wireless network, a registration request message comprising a single network slice selection assistance information (S-NSSAI) corresponding to the network slice while the UE is in a tracking area of a registration area; receiving, from the first wireless network, a registration reject message indicating that the network slice is not available in one of the registration area, a public land mobile network (PLMN), or a standalone non-public network (SNPN); storing, based on a tracking area identifier (TAI) of the tracking area being included in the registration reject message, the TAI of the tracking area to a reject list; and responsive to the receiving, establishing a connection with a second wireless network.

Description

[0001] This application claims the benefit of Indian Provisional Patent Application No. 202041016700, filed April 17, 2020, in the Indian Patent Office, and Indian Patent Application No. 202041016700, filed April 15, 2021, in the Indian Patent Office, the disclosures of which are incorporated herein in their entirety by this reference. TECHNICAL FIELD

[0002] The present disclosure relates to a wireless communication system, and more particularly, to a method for managing registration failure of an access network slice and a user equipment (UE). BACKGROUND

[0003] A network slice is a logical network and partition of a Third Generation Partnership Project (3GPP) wireless network. A network slice is created to serve a specific purpose or a group of customers. A single network slice selection assistance information (S-NSSAI) can be used to identify a network slice. Thus, S-NSSAI can also be referred to as an S-NNSAI identifier. Further, the terms S-NNSAI and / or NNSAI can be used herein to refer to a plurality of S-NNSAI identifiers. Various types of S-NSSAI are “configured S-NSSAI,” “requested S-NSSAI,” “allowed S-NSSAI,” “rejected S-NSSAI for the current public land mobile network (PLMN) or standalone non-public network (SNPN),” “rejected S-NSSAI for the current registration area,” and “rejected S-NSSAI for failed or revoked network slice specific authentication and authorization (NSSAA).” Configured S-NSSAI is an S-NSSAI provided in a UE that is applicable for one or more PLMNs. Requested S-NSSAI is an S-NSSAI provided by a UE to a serving PLMN during a registration procedure.

[0004] Allowed S-NSSAI is an S-NSSAI provided by a serving PLMN during a registration procedure. Allowed S-NSSAI indicates a value of S-NSSAI that the UE can use in the serving PLMN for the current registration area. An access and mobility function (AMF) assigns a registration area to the UE during a registration procedure. A registration area is defined as a set of tracking areas (TAs), where each tracking area consists of one or more cells covering a geographical area. A tracking area is identified by a tracking area identifier (TAI) broadcasted in the cells of the tracking area. Rejected S-NSSAI for the current PLMN or SNPN is an S-NSSAI (e.g., an S-NSSAI included in a requested NSSAI) sent by the AMF to the UE with a rejection cause “S-NSSAI not available in the current PLMN or SNPN.”

[0005] The rejected S-NSSAI for the current registration area is the S-NSSAI (e.g., S-NSSAI included in the requested NSSAI) sent by the AMF to the UE with the rejection cause "S-NSSAI not available in the current registration area". The rejected S-NSSAI for the failed or revoked NSSAA is the S-NSSAI sent by the AMF to the UE with the rejection cause "NSSAI rejected due to failed or revoked NSSAA". When the UE does not have allowed S-NSSAI for the current PLMN, configured S-NSSAI for the current PLMN, and default configured S-NSSAI, the UE does not include the requested NSSAI in the registration message. SUMMARY

[0006] Embodiments herein provide a method and a UE for managing registration failure for accessing a network slice. The method allows the UE to enable and continue connection with a 4G network when the 5G network rejects the request of the UE for accessing the network slice.

[0007] Embodiments herein provide for aborting excessive handover of connection at the UE with the 4G network and the 5G network. Thus, the UE will get seamless connection with the 4G network which improves the user experience. A large amount of electrical energy is consumed at the UE for excessive handover of link (e.g., communication link). The power loss at the UE can be significantly reduced using the proposed method in response to aborting the excessive handover of connection at the UE.

[0008] Thus, embodiments herein provide a method performed by a user equipment (UE) for managing registration failure for accessing a network slice, the method comprising: sending, by the UE, a registration request message to a first wireless network while the UE is in a tracking area of a registration area, the registration request message including a single network slice selection assistance information (S-NSSAI) corresponding to a network slice, receiving, by the UE, a registration reject message from the first wireless network, the registration reject message indicating that the network slice is not available in one of the registration area, a public land mobile network (PLMN), or a standalone non-public network (SNPN), storing, by the UE, a tracking area identifier (TAI) of the tracking area into a rejection list based on the TAI of the tracking area being included in the registration reject message, and in response to the receiving, establishing, by the UE, a connection with a second wireless network.

[0009] In an embodiment, wherein the method comprises disabling, by the UE, N1 mode in response to the establishing, starting, by the UE, a timer, determining, by the UE, whether the UE is located in the tracking area, and performing, by the UE, one of the following operations: enabling N1 mode after expiration of the timer in response to determining that the UE is located in the tracking area, and terminating the timer and enabling N1 mode in response to determining that the UE is located in another tracking area.

[0010] In an embodiment, wherein the establishing step comprises disabling, by the UE, N1 mode, starting, by the UE, a timer, establishing, by the UE, a connection with the second wireless network, and enabling, by the UE, N1 mode after expiration of the timer.

[0011] In an embodiment, wherein the method comprises searching, by the UE, for a new tracking area according to a periodic time interval.

[0012] In an embodiment, wherein the registration reject message comprises an instruction to disable N1 mode of the UE.

[0013] In an embodiment, wherein the method comprises detecting, by the UE, a reset condition, wherein the reset condition is one of a change in a UE policy, a timer-based retry, a removal of a universal subscriber identity module (USIM) from the UE, a reboot of the UE, a movement of the UE to a new tracking area, or a user-triggered action, terminating, by the UE, the timer in response to detecting the reset condition, deleting, by the UE, the TAI from the reject list in response to detecting the reset condition, and enabling, by the UE, N1 mode in response to detecting the reset condition.

[0014] In an embodiment, the storing step stores a plurality of TAIs corresponding to all tracking areas of the registration area based on a TAI of a tracking area being included in a registration reject message, the TAI of the tracking area being one of the plurality of TAIs.

[0015] In an embodiment, wherein the storing step comprises determining, by the UE, that all network slices in the first wireless network are rejected based on the registration reject message including one of “S-NSSAI is not available in the current PLMN or SNPN,” “S-NSSAI is not available in the current registration area,” or “S-NSSAI is not available due to failed or revoked network slice specific authentication and authorization (NSSAA),” and the reject list is usable for non-access stratum (NAS) and access stratum (AS) corresponding to the UE.

[0016] Accordingly, embodiments herein provide a UE for managing registration failure for accessing a network slice. The UE includes processing circuitry configured to, while the UE is in a tracking area of a registration area, send a registration request message to a first wireless network, the registration request message including a single network slice selection assistance information (S-NSSAI) corresponding to the network slice, receive a registration reject message from the first wireless network, the registration reject message indicating that the network slice is not available in one of the registration area, a public land mobile network (PLMN), or a standalone non-public network (SNPN), store a tracking area identifier (TAI) of the tracking area to a reject list based on the TAI of the tracking area being included in the registration reject message, and establish a connection with a second wireless network in response to receiving the registration reject message.

[0017] These and other aspects of embodiments herein will be better appreciated and understood when considered in connection with the following description and accompanying drawings. It is intended that the specification and examples be considered as illustrative of the embodiments and not in a limiting sense. It will be readily understood to those skilled in the art that many changes and modifications can be made to the embodiments described herein, and that BRIEF DESCRIPTION OF DRAWINGS

[0018] Embodiments are illustrated by way of example in the following drawings in which like references indicate similar elements, and in which:

[0019] Figures 1-3 is a timing diagram illustrating signaling of a UE for managing registration failure for accessing a network slice with a wireless network in accordance with embodiments disclosed herein;

[0020] Figure 4A is a block diagram of a UE for managing registration failure for accessing a network slice in accordance with embodiments disclosed herein;

[0021] Figure 4B is a block diagram of a registration message controller of a UE for establishing a connection with a second wireless network for registration failure for accessing a network slice in accordance with embodiments disclosed herein;

[0022] Figure 5 is a flow diagram illustrating a method for managing registration failure for accessing a network slice by a UE in accordance with embodiments disclosed herein;

[0023] Figure 6is a timing diagram illustrating signaling of a UE and a wireless network for managing registration failure due to idle mode inter radio access technology (IRAT) triggered by the UE without storing rejected S-NSSAI according to embodiments disclosed herein;

[0024] Figure 7 is a timing diagram illustrating signaling of a UE and a wireless network for managing registration failure due to idle mode IRAT triggered by the network with storing rejected S-NSSAI according to embodiments disclosed herein; and

[0025] Figure 8 is a timing diagram illustrating signaling of a UE and a wireless network for managing registration failure due to idle mode IRAT triggered by the network with storing rejected S-NSSAI according to embodiments disclosed herein; and DETAILED DESCRIPTION

[0026] Embodiments herein, and various features and advantageous details thereof, are explained more fully with reference to the non-limiting examples illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. Moreover, the various embodiments described herein are not necessarily mutually exclusive, as embodiments can be combined with one or more other embodiments to form new embodiments. The term "or" as used herein, unless otherwise indicated, is intended to mean any or all of the associated listed items. Examples used herein are intended to be illustrative only and are presented to facilitate understanding of the embodiments herein. Thus, described examples should not be construed as limiting the scope of the embodiments herein.

[0027] As is traditional in the art, embodiments can be described and demonstrated with reference to blocks that are configured to perform one or more functions. These blocks, which can be referred to herein as managers, units, modules, hardware components, and the like, are physically implemented by analog and / or digital circuitry (e.g., logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits, etc.) and can optionally be driven by firmware. For example, the circuitry can be implemented in one or more semiconductor chips, or on a substrate such as a printed circuit board. The circuitry making up a block can be implemented by specialized hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of specialized hardware and a processor adapted to execute one or more functions of the block. In embodiments, each block can be physically separated from, or combined with, two or more other blocks without departing from the scope of the disclosure. Likewise, in embodiments, blocks can be physically combined into a more complex block without departing from the scope of the disclosure.

[0028] Accordingly, the embodiments herein provide a method for managing registration failure for accessing a network slice at a UE. The method includes sending, by the UE in a tracking area of a registration area, a registration request message for accessing a network slice comprising a S-NSSAI to a first wireless network. The method includes receiving, by the UE, a registration reject message from the first wireless network, wherein the registration reject message indicates that the network slice corresponding to the S-NSSAI is not available in one of the registration area, a PLMN, and a SNPN. The method includes storing, by the UE, a TAI of the tracking area in the registration reject message to a rejection list, wherein the stored rejection list is available for NAS and AS. The method includes establishing, by the UE, a connection with a second wireless network.

[0029] Accordingly, the embodiments herein provide a UE for managing registration failure for accessing a network slice. The UE includes a registration message controller, a memory, a processor, wherein the registration message controller is coupled to the memory and the processor. The registration message controller is configured to send a registration request message for accessing a network slice comprising a S-NSSAI to a first wireless network, wherein the UE is in a tracking area of a registration area. The registration message controller is configured to receive a registration reject message from the first wireless network, wherein the registration reject message indicates that the network slice corresponding to the S-NSSAI is not available in one of the registration area, a PLMN, and a SNPN. The registration message controller is configured to store a TAI of the tracking area in the registration reject message to a rejection list, wherein the stored rejection list is available for NAS and AS. The registration message controller is configured to establish a connection with a second wireless network.

[0030] Unlike the existing methods and systems, the proposed method allows the UE to establish a connection with a 4G network (e.g., the second wireless network) for a time period when the 5G network (e.g., the first wireless network) rejects the request of the UE for accessing a network slice. Further, the UE suspends excessive handover of the connection at the UE with the 4G network and the 5G network until the time period expires. Accordingly, the UE will get seamless connectivity with the 4G network, which improves the user experience. The excessive handover of the connection at the UE consumes a significant amount of electrical energy of the UE. The electrical energy loss at the UE can be significantly reduced using the proposed method in response to suspending the excessive handover of the connection at the UE.

[0031] Figures 1-3 is a timing diagram illustrating signaling of a UE for managing registration failure for accessing a network slice with wireless networks (e.g., a fifth generation (5G) network and a fourth generation (4G) network). The UE includes a 5G stack and a 4G stack for enabling communication of the UE with the 5G network and the 4G network, respectively.

[0032] using Figure 1An example scenario is explained. The 5G stack sends (101) an initial / mobility registration request with S-NSSAI of“A” for accessing a network slice to the 5G network. The 5G network verifies the subscription of the UE for this particular network slice and considers this network slice as not allowed for the UE. Further, the 5G network sends (102) a registration reject message with a 5thGeneration System Mobility Management (5GMM) cause #62 (no network slice available) or “S-NSSAI not available in current PLMN or SNPN” to the UE.

[0033] The UE stores (103) the rejected S-NSSAI to a reject list. Further, the UE establishes (104-106, e.g., sends an attach request message 104, receives an attach accept message 105, and sends an attach complete message 106) a connection with the 4G network. The non-access stratum (NAS) (107) has information of the rejected slice, while the access stratum (AS) (108) does not have information of the rejected slice. Thus, once the connection with the 4G network is established, the 4G stack configures the UE to perform 5G cell measurements. Further, the 5G stack performs (109) 5G cell measurements, receives a request (110) from the 4G stack for reselecting to the 5G network, and confirms (111) that the UE will reselect to the 5G network. The UE detects (112) that there is no valid slice available for registration from the NAS. The UE is still allowed to perform (113) a registration procedure without including any requested S-NSSAI according to 3GPP specifications, even though no valid S-NSSAI is available.

[0034] The 5G network rejects (114) the registration request of the UE with any suitable cause (e.g., #62: no network slice available). Further, the UE camps back (115) to the 4G network and establishes (116-118, e.g., sends an attach request message 116, receives an attach accept message 117, and sends an attach complete message 118) a connection with the 4G network. Further, the operations (107-118) keep repeating in the UE, and the connection of the UE switches between the 5G network and the 4G network, which leads to battery drain and frequent loss of service at the UE.

[0035] Using Figure 2Let's explain another example scenario. The 5G stack sends an initial / mobility registration request (201) to the 5G network for an S-NSSAI with an "A" for accessing a network slice. The 5G network verifies the UE's subscription to that specific network slice and determines that the network slice is not allowed for the UE. Furthermore, the 5G network sends a registration rejection message (202) to the UE with 5GMM reason #62 (no available network slice) or "S-NSSAI is not available in the current registration area". The UE's registration area is only defined after successful registration. Therefore, after any registration rejection, the "registration area" will be invalid in the UE. Since the UE's registration area is not defined in the 5G network due to registration rejection, the UE does not store (203) the S-NSSAI in the rejection list.

[0036] Furthermore, the UE establishes (204-206, e.g., sending an attachment request message 204, receiving an attachment acceptance message 205, and sending an attachment completion message 206) a connection with the 4G network. Neither the NAS nor the AS (207) has information about rejected slices. Therefore, once the connection with the 4G network is established, the 4G stack configures the UE to perform 5G cell measurements. In addition, the 5G stack performs (208) 5G cell measurements, receives a request (209) from the 4G stack for reselection to the 5G network, and confirms (210) that the UE will reselect to the 5G network. Since the S-NSSAI is not stored in the rejection list, the UE assumes (211) that valid slices are still available for registration from the NAS. In addition, the UE initiates (212) the registration process by including the same rejected S-NSSAI or a similar S-NSSAI in the registration request message.

[0037] The 5G network rejects (213) the UE's registration request for the same 5GMM reason or a similar 5GMM reason #62 (no network slice available) or "S-NSSAI is not available in the current registration area". The UE's registration area is only defined after successful registration. Therefore, after any registration rejection, the "registration area" will be invalid in the UE. Since the UE's registration area is not defined in the 5G network due to registration rejection, the UE does not store (214) S-NSSAI in the rejection list. In addition, the UE camps back (215) to the 4G network and establishes (216-218, e.g., sending an attachment request message 216, receiving an attachment acceptance message 217, and sending an attachment completion message 218) a connection with the 4G network. In addition, the operations (207-218) are repeated in the UE, and the UE's connection switches between the 5G network and the 4G network, which leads to battery depletion and frequent loss of service at the UE.

[0038] use Figure 3Let's explain another example scenario. The 5G stack sends an initial / mobility registration request (301) to the 5G network for an S-NSSAI with an "A" for accessing a network slice. Additionally, the 5G network sends a registration rejection message (302) to the UE with either 5GMM reason #62 (no available network slice) or "S-NSSAI is not available in the current registration area". The UE's registration area is only defined after successful registration. Therefore, after any registration rejection, the "registration area" will be invalid in the UE. Since the UE's registration area is not defined in the 5G network due to registration rejection, the UE does not store (303) the S-NSSAI in the rejection list.

[0039] In addition, the UE establishes (304-306, e.g., sending an attachment request message 304, receiving an attachment acceptance message 305, and sending an attachment completion message 306) a connection with the 4G network. Furthermore, the 4G network sends (307) an RRC connection release request with 5G redirection information to the 4G stack. Additionally, the 4G stack configures the UE to redirect the connection from the 4G network (308) to the 5G network. The UE initiates (309) the registration process by including the same S-NSSAI (e.g., S-NSSAI = A) or a similar S-NSSAI in the registration request message.

[0040] Furthermore, the 5G network sends a registration rejection message (310) to the UE with 5GMM reason #62 (no available network slice) or "S-NSSAI is not available in the current PLMN or SVPN" (e.g., the same 5GMM reason or a similar 5GMM reason). Since the UE's registration area is not defined in the 5G network due to the registration rejection, the UE does not store (311) S-NSSAI in the rejection list. Additionally, the UE camps back on the 4G network and establishes (312-314, e.g., sending an attachment request message 312, receiving an attachment acceptance message 313, and sending an attachment completion message 314) a connection with the 4G network. Furthermore, operations (307-314) are repeated at the UE, and the UE's connection switches between the 5G and 4G networks, leading to battery depletion and frequent service loss at the UE. Therefore, a useful alternative is desired.

[0041] Now refer to the accompanying drawings, and more specifically to... Figures 4A to 8 An example is shown.

[0042] Figure 4AThis is a block diagram of a UE (400) for managing registration failures in accessing a network slice, according to embodiments disclosed herein. Examples of the UE (400) include, but are not limited to, smartphones, tablet computers, personal digital assistants (PDAs), desktop computers, Internet of Things (IoT) devices, wearable devices, etc. In embodiments, the UE (400) may include a registration message controller (410), a memory (420), a processor (430), and / or a communicator (440). The registration message controller (410) may be operatively coupled to the memory (420) and the processor (430). The registration message controller (410) may be implemented by processing circuitry. As used herein, the term "processing circuitry" may refer to, for example, hardware including logic circuitry; a hardware / software combination such as a processor executing software; or a combination of both. For example, the processing circuitry may more specifically include, but is not limited to, logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hard-wired circuits, central processing units (CPUs), arithmetic logic units (ALUs), digital signal processors, microcomputers, field-programmable gate arrays (FPGAs), systems-on-chips (SoCs), programmable logic units, application-specific integrated circuits (ASICs), etc., and may optionally be driven by firmware. For example, the circuitry may be implemented in one or more semiconductor chips, or on a substrate support such as a printed circuit board. Furthermore, according to embodiments, the operations described herein, such as those performed by the UE (400), processor (430), and / or communicator (440), may be performed by the processing circuitry.

[0043] The registration message controller (410) can be configured to send a registration request message including S-NSSAI for accessing a network slice to a first wireless network (100), wherein the UE (400) is located in the tracking area of ​​a PLMN. An example of the first wireless network (100) is a 5G network. The registration message controller (410) can be configured to receive a registration rejection message from the first wireless network (100). In an embodiment, the registration rejection message may be a deregistration request. The registration rejection message indicates to the UE (400) that the network slice corresponding to S-NSSAI is unavailable in the registration area or in the PLMN or SNPN.

[0044] In an embodiment, the registration rejection message includes an instruction to disable or restrict the N1 mode of the UE (400). The N1 mode is a mode that allows the UE (400) to access a 5G network via a 5G access network. In an embodiment, when the UE (400) does not have a valid registration area, the S-NSSAI of rejection from the current registration area applies to the tracking area on which the UE (400) receives the registration rejection message (e.g., where the UE (400) receives the tracking area). The valid registration area may include at least one TAI, where the UE (400) receives information about the valid registration area from the first wireless network (100) during the registration acceptance message. The registration message controller (410) may be configured to store the TAI of the tracking area in the registration rejection message (e.g., corresponding to the registration rejection message) into a rejection list (e.g., stored in a rejection list), where the stored rejection list is available for both NAS and AS. In an embodiment, the registration message controller (410) may be configured to maintain a new list of "prohibited N1 TAIs for rejected Network Slice Selection Assistance Information (NSSAI)" in the rejection list for storing TAIs, where the NSSAI includes a set of S-NSSAIs. The registration message controller (410) can be configured to start a timer after an entry is added to the "Prohibited N1 TAIs for Rejected Network Slice Selection Assistance Information (NSSAI)" list. According to an embodiment, the registration message controller (410) can store all TAIs corresponding to the registration region of a specific TAI included in the registration rejection message in the "Prohibited N1 TAIs for Rejected Network Slice Selection Assistance Information (NSSAI)" list. Furthermore, the registration message controller (410) can be configured to delete entries from the "Prohibited N1 TAIs for Rejected Network Slice Selection Assistance Information (NSSAI)" list upon timer expiration.

[0045] In an embodiment, the registration message controller (410) may be configured to determine, based on a registration rejection message, that all possible network slices in the first wireless network (100) are rejected by the first wireless network (100) for one of the following reasons: "S-NSSAI is unavailable in the current PLMN or SNPN", "S-NSSAI is unavailable in the current registration area", and / or "S-NSSAI is unavailable due to failed or revoked Network Slice Specific Authentication and Authorization (NSSAA)". Furthermore, the registration message controller (410) may be configured to store the TAI from the registration rejection message into a rejection list. The registration message controller (410) may be configured to establish a connection with a second wireless network (200). An example of the second wireless network (200) is a 4G network. In an embodiment, the registration message controller (410) may be configured to disable or restrict N1 mode when storing the TAI. Furthermore, the registration message controller (410) may be configured to start a timer for a period of time (e.g., 10 minutes). In this scenario, the current TAI or the stored TAI is blocked locally by the UE's NAS for a period of time, and the current TAI or the stored TAI is shared with the UE's AS so that the AS does not select them for camping. Furthermore, the registration message controller (410) can be configured to establish a connection with the second wireless network (200). The registration message controller (410) can be configured to enable N1 mode after a timer expires. The timer expires after the stated period of time.

[0046] In this embodiment, the registration message controller (410) can be configured to disable or restrict N1 mode in response to establishing a connection with the second wireless network (200). Furthermore, the registration message controller (410) can be configured to start a timer (e.g., in response to storing a TAI and / or establishing a connection with the second wireless network). Additionally, the registration message controller (410) can be configured to determine whether the UE (400) has (e.g., has) moved to a new tracking area. The registration message controller (410) can be configured to enable N1 mode after the timer expires in response to determining that the UE (400) is in a new tracking area. The registration message controller (410) can also be configured to terminate the timer and enable N1 mode in response to determining that the UE (400) is in another tracking area.

[0047] In an embodiment, the registration message controller (410) can be configured to detect a reset condition for terminating a timer. The reset condition can be a change in UE policy and / or subscription, a timer-based retry (e.g., resetting the timer, or the UE (400) periodically retrying after the timer expires), removal of the Global Subscriber Identity Module (USIM) from the UE (400), a reboot of the UE (400), a change in TAI (e.g., determining that the UE (400) has moved to a new tracking area), and / or a user-triggered action. An example of a change in UE policy / subscription: When a user recharges a service (e.g., for a previously recharged service), the UE's subscription information can change. Furthermore, the UE (400) can now (after the user recharges the service) be allowed access to slices. An example of a user-triggered action: When a user manually selects a 5G network from the manual search option, the UE (400) can attempt to register on that network even if the UE (400) already has the 5G PLMN and tracking area stored in the rejection list. Furthermore, the registration message controller (410) can be configured to terminate the timer upon detecting a reset condition. Additionally, the registration message controller (410) can be configured to remove TAIs and / or registration rejection messages from a rejection list (e.g., a list of "Banned N1 TAIs for Rejected NSSAIs"). Furthermore, the registration message controller (410) can be configured to enable N1 mode. In embodiments, the registration message controller (410) can be configured to search for new tracking areas of the registration area at periodic time intervals (e.g., 5 minutes) using information from background activity or another USIM in the UE (400), and is not limited to these examples. According to embodiments, the registration message controller (410) can be configured to establish a connection with the first wireless network (100) in response to enabling N1 mode, for example, by retransmitting a registration request message including an S-NSSAI for accessing a network slice to the first wireless network (100). According to embodiments, retransmitting the registration request message can result in successful registration for accessing the network slice. According to an embodiment, the UE (400) can generate signals for (e.g., encoding, modulation, decoding, demodulation, etc.) and perform communication (e.g., voice calls, data communications, etc.) with another device (e.g., another UE, base station, etc.) via a connection with the first wireless network (100) and / or network slice.

[0048] The memory (420) may include (e.g., store) a rejection list. The memory (420) may store TAIs. The memory (420) may include a non-volatile storage element. Examples of such a non-volatile storage element may include magnetic hard disks, optical disks, floppy disks, flash memory, or electrically programmable memory (EPROM) or electrically erasable programmable memory (EEPROM). Additionally, in some examples, the memory (420) may be considered a non-transitory storage medium. The term "non-transitory" may indicate that the storage medium is not implemented in a carrier wave or propagating signal. However, the term "non-transitory" should not be construed as meaning that the memory (420) is non-removable. In some examples, the memory (420) may be configured to store a larger amount of information than the memory (420) itself. In certain examples, a non-transitory storage medium may store data that may change over time (e.g., in random access memory (RAM) or cache memory).

[0049] The processor (430) can be configured to execute instructions stored in memory (420). The processor (430) can be a general-purpose processor (such as a central processing unit (CPU), application processor (AP)), graphics-specific processing unit (such as a graphics processing unit (GPU) and / or visual processing unit (VPU)), etc. The processor (430) can include multiple cores for executing instructions. The communicator (440) can be configured to perform internal communication between hardware components in the UE (400). In addition, the communicator (440) can be configured to facilitate communication between the UE (400) and a first wireless network (100) and a second wireless network (200). The communicator (440) can include electronic circuitry specific to standards that enable wired and / or wireless communication.

[0050] although Figure 4A The hardware components of the UE (400) are shown, but it is to be understood that the embodiments are not limited thereto. In embodiments, the UE (400) may include fewer or more components. Furthermore, the labels or names of the components are for illustrative purposes only and do not limit the scope of the embodiments. One or more components may be combined to perform the same or substantially similar functions to manage registration failures of access network slices.

[0051] Figure 4BThis is a block diagram of a registration message controller (410) for a UE (400) establishing a connection to a second wireless network (200) due to a registration failure of an access network slice, according to embodiments disclosed herein. In embodiments, the registration message controller (410) may include a registration request message transmitter (411), a registration request message receiver (412), and / or a wireless connectivity controller (413). The registration request message transmitter (411), the registration request message receiver (412), and / or the wireless connectivity controller (413) may be implemented by processing circuitry such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuitry, etc., and may optionally be driven by firmware. For example, the circuitry may be implemented in one or more semiconductor chips, or on a substrate support such as a printed circuit board.

[0052] A request message sender (411) can send a registration request message, including S-NSSAI, for accessing a network slice to a first wireless network (100). A registration request message receiver (412) can receive a registration rejection message from the first wireless network (100). The registration request message receiver (412) can store the TAI of the tracking area in the registration rejection message into a rejection list in memory (420) (e.g., the rejection list is stored in memory (420)), wherein the stored rejection list is available for NAS and AS. In an embodiment, the registration request message receiver (412) can determine, based on the registration rejection message, that all possible network slices in the first wireless network (100) are rejected by the first wireless network (100) for reasons including "S-NSSAI is not available in the current PLMN or SNPN", "S-NSSAI is not available in the current registration area", and / or "S-NSSAI is unavailable due to a failed or withdrawn NSSAA". Furthermore, the registration request message receiver (412) can store the TAI into a rejection list, wherein the stored rejection list is available for NAS and AS. The wireless connection controller (413) can establish a connection with the second wireless network (200).

[0053] In this embodiment, the wireless connectivity controller (413) can disable or limit N1 mode when storing TAI. Furthermore, the wireless connectivity controller (413) can start a timer for a period of time (e.g., 10 minutes). Additionally, the wireless connectivity controller (413) can establish a connection with a second wireless network (200). The wireless connectivity controller (413) can enable N1 mode after the timer expires.

[0054] In this embodiment, the wireless connectivity controller (413) may disable or restrict N1 mode in response to establishing a connection with the second wireless network (200). Furthermore, the wireless connectivity controller (413) may start a timer. Additionally, the wireless connectivity controller (413) may determine whether the UE (400) has (e.g., has) moved to a new tracking area. In response to determining that the UE (400) is in a tracking area, the wireless connectivity controller (413) may enable N1 mode after the timer expires. In response to determining that the UE (400) is in another tracking area, the wireless connectivity controller (413) may terminate the timer and enable N1 mode.

[0055] In this embodiment, the wireless connectivity controller (413) can detect a reset condition for terminating the timer. Furthermore, the wireless connectivity controller (413) can terminate the timer upon detecting the reset condition. Additionally, the wireless connectivity controller (413) can remove TAIs from the rejection list and / or register rejection messages. Furthermore, the wireless connectivity controller (413) can enable N1 mode. In this embodiment, the wireless connectivity controller (413) can search for new tracking areas at periodic time intervals.

[0056] although Figure 4B The hardware components of the registration message controller (410) are shown, but it is to be understood that the embodiments are not limited thereto. In embodiments, the registration message controller (410) may include fewer or more components. Furthermore, the labels or names of the components are for illustrative purposes only and do not limit the scope of the embodiments. One or more components may be combined together to perform the same or substantially similar functions for establishing a connection to a second wireless network (200) due to registration failure of an access network slice.

[0057] Figure 5 This is a flowchart 500 illustrating a method for managing registration failure of an access network slice by a UE (400) according to embodiments disclosed herein. In operation 501, the method may include sending a registration request message including S-NSSAI for accessing a network slice to a first wireless network (100), wherein the UE (400) is in a tracking area of ​​the registration area. In an embodiment, the method allows a registration request message sender (411) to send a registration request message including S-NSSAI for accessing a network slice to the first wireless network (100), wherein the UE (400) is in a tracking area of ​​the registration area. In operation 502, the method may include receiving a registration rejection message from the first wireless network (100), wherein the registration rejection message indicates that the network slice corresponding to the S-NSSAI is unavailable in the registration area or in a PLMN or SNPN.

[0058] In an embodiment, the method allows a registration request message receiver (412) to receive a registration rejection message from a first wireless network (100), wherein the registration rejection message indicates that the network slice corresponding to S-NSSAI is unavailable in the registration area or PLMN or SNPN. In operation 503, the method may include storing the TAI of the tracking area in the registration rejection message into a rejection list, wherein the stored rejection list is available for both NAS and AS. In an embodiment, the method allows the registration request message receiver (412) to store the TAI of the tracking area in the registration rejection message into a rejection list. In operation 504, the method may include establishing a connection with a second wireless network (200). In an embodiment, the method allows a wireless connectivity controller (413) to establish a connection with the second wireless network (200). According to an embodiment, the UE (400) may generate signals for (e.g., encoding, modulation, decoding, demodulation, etc.) and perform communication (e.g., voice calls, data communications, etc.) with another device (e.g., another UE, base station, etc.) via the connection with the second wireless network (200).

[0059] The various actions, behaviors, blocks, operations, etc. in flowchart 500 can be executed in the presented order, in different orders, or simultaneously. Furthermore, in the embodiments, some of the actions, behaviors, blocks, operations, etc., can be omitted, added, modified, skipped, etc., without departing from the scope of the embodiments.

[0060] Figure 6This is a timing diagram illustrating signaling between a UE (400) and wireless networks (100, 200) that has failed to register due to an idle mode IRAT triggered by the UE, according to embodiments disclosed herein, without storing a rejected S-NSSAI. The UE (400) may include a 5G stack (440A) and a 4G stack (440B) for enabling communication between the UE (400) and the 5G network (100) and the 4G network (200), respectively. According to embodiments, processing circuitry may be used to perform the operations described herein as performed by the 5G stack (440A) and / or the 4G stack (440B). The 5G stack (440A) may send (601) an initial / mobility registration request (e.g., a registration request message) with S-NSSAI=A for accessing a network slice to the 5G network (100), wherein the UE (400) is located in the tracking area (TA) of the PLMN. The 5G network (100) can detect that the UE (400) does not have an allowed S-NSSAI for the current PLMN, a configured S-NSSAI for the current PLMN, and / or a default configured S-NSSAI. Furthermore, the 5G network (100) can send the UE (400) a registration rejection message (602) with 5GMM reason #62 (e.g., no available network slice) or "S-NSSAI is unavailable in the current PLMN or SNPN" (or "S-NSSAI is unavailable in the current registration area"). The UE (400) can store (603) the rejected S-NSSAI along with the camped 5G TAI in the rejection list. Additionally, the UE (400) can add (604) the TAI to the "Banned TAIs for Rejected NSSAIs" list in the rejection list and start a timer.

[0061] The “Banned TAIs for Rejected NSSAIs” list is a new list not defined in the 3GPP specifications. The “Banned TAIs for Rejected NSSAIs” list is also shared with the AS. The AS can consider any TAI present in the “Banned TAIs for Rejected NSSAIs” list as unsuitable for normal service. Furthermore, the UE (400) can establish (605-607, e.g., send an attach request message 605, receive an attach accept message 606, and send an attach complete message 607) a connection to the 4G network (200). The UE (400) can block or restrict (608) inter-Radio Access Technology (IRAT) handover to the 5G network (100) until the UE (400) detects a timer expiration or a change in the Tracking Area (TA). Consider an example where the UE (400) remains in the TA and detects (609) a timer expiration. In this example, the UE (400) can allow / unblock (610) an IRAT handover from the 4G network (200) to the 5G network (100). Consider another example where the UE (400) moves to another TA. In this example, the UE (400) can terminate (611) the timer and allow / unblock (612) an IRAT handover from the 4G network (200) to the 5G network (100).

[0062] Unlike existing methods and systems, the proposed method allows the UE (400) to camp on the 4G network (200) until the timer expires or the TA changes after receiving a registration rejection message. Furthermore, the UE (400) does not initiate an excessive reselection and registration process to the 5G network (100) until the timer expires or the TA changes, which reduces power consumption at the UE. In addition, the proposed method achieves seamless connectivity between the UE (400) and the 4G network (200), improving the user experience.

[0063] Figure 7This is a timing diagram illustrating signaling between a UE (400) and a wireless network (100, 200) for managing a registration failure due to an idle mode IRAT triggered by the UE in the case of a stored S-NSSAI rejection. The 5G stack (440A) may send (701) an initial / mobility registration request (e.g., a registration request message) with S-NSSAI=A for accessing a network slice to the 5G network (100), wherein the UE (400) is located in the TA of the PLMN. The 5G network (100) may detect that the UE (400) does not have an S-NSSAI allowed for the current PLMN, an S-NSSAI configured for the current PLMN, and / or a default configured S-NSSAI. Furthermore, the 5G network (100) may send (702) a registration rejection message to the UE (400) with 5GMM reason #62 (e.g., no available network slice) or "S-NSSAI is not available in the current registration area". The UE (400) can store the rejected S-NSSAI along with the camped 5G TAI in the rejected list (703). Furthermore, the UE (400) can mark the TA as an invalid registration area in the rejected list for the current registration area. Therefore, the UE (400) can maintain the awareness that the current TAI does not have a valid S-NSSAI. Additionally, the UE (400) can establish (704-706, e.g., send an attach request message 704, receive an attach accept message 705, and send an attach complete message 706) a connection with the 4G network (200). The UE (400) can avoid initiating an excessive reselection and registration process with the 5G network (100) until the TA is changed, which reduces power consumption at the UE (400) and provides seamless connectivity to the UE (400).

[0064] The AS corresponding to the first wireless network (100) of the UE (400) can use the "Banned TAIs for Rejected NSSAIs" list to suspend the IRAT process, including idle mode reselection, redirection, and / or handover, under all conditions (e.g., various methods of the UE (400) from a 4G network to a 5G network, such as reselection, redirection, handover, cell selection, etc.), until the timer expires. Therefore, the UE (400) can disable or restrict N1 mode without suspending the IRAT process. When the timer expires, the TAIs stored in the "Banned TAIs for Rejected NSSAIs" list can be deleted by the UE (400). Furthermore, the UE (400) can initiate the IRAT process and register.

[0065] Figure 8This is a timing diagram illustrating signaling between a UE (400) and a wireless network (100, 200) that has failed to register due to a network-triggered IRAT, according to embodiments disclosed herein, without storing a rejected S-NSSAI. The 5G stack (440A) may send (801) an initial / mobility registration request (e.g., a registration request message) to the 5G network (100) for accessing a network slice with S-NSSAI=A, where the UE (400) is located in the TA of the PLMN. The 5G network (100) may detect that the UE (400) does not have an S-NSSAI allowed for the current PLMN, an S-NSSAI configured for the current PLMN, and / or a default configured S-NSSAI. Furthermore, the 5G network (100) may send (802) a registration rejection message to the UE (400) with 5GMM reason #62 (e.g., no available network slice) or "S-NSSAI is not available in the current PLMN or SNPN". The UE (400) can store (803) the rejected S-NSSAI along with the camped 5G TAI into a rejection list. Furthermore, the UE (400) can identify (e.g., determine) all requested S-NSSAIs rejected by the 5G network (100) in the current TA. Therefore, as long as the UE (400) operates in the same or a similar TA, the UE (400) can disable or limit (804) N1 mode and start a timer. Additionally, when N1 mode is disabled or limited, the UE (400) can reselect to any 5G cell without measurement.

[0066] Furthermore, the UE (400) can reselect (805-807, for example, send an attachment request message 805 with N1 support = false, receive an attachment acceptance message 806, and send an attachment completion message 807) to the 4G network (200) and perform a registration process, wherein the UE (400) can indicate to the 4G network (200) that N1 mode is disabled or restricted during the registration process (805). Additionally, the UE (400) can establish a connection with the 4G network (200). The 4G network (200) can send (808) an RRC connection release to the UE (400) instructing the UE (400) not to redirect or switch to the 5G network (100). Later, the timer can expire, and the UE (400) can detect (809) the expiration of the timer. Furthermore, the UE (400) can enable N1 mode and send (810) a Tracking Area Update (TAU) request to the 4G network (200) indicating that N1 mode is enabled. In addition, the 4G network (200) can perform TAU procedures (811-812, e.g., receiving a TAU acceptance message 811 and sending a TAU completion message 812) and allow / unblock (813) the UE (400) from the 4G network (200) to the 5G network (100) for IRAT handover. The UE (400) can be allowed to retry registration for the network slice.

[0067] Unlike existing methods and systems, the proposed method allows the UE (400) to camp on the 4G network (200) until N1 mode is enabled at the UE (400). Therefore, the UE (400) can avoid initiating an excessive reselection and registration process to the 5G network (100) until N1 mode is enabled, which reduces power consumption at the UE. Furthermore, the proposed method achieves seamless connectivity between the UE (400) and the 4G network (200), improving the user experience.

[0068] In the embodiments, the method of disabling or limiting and enabling N1 mode based on timers can be used alternatively for scenarios where "S-NSSAI is not available in the current registered area" and when a new TA- / registered area is detected and N1-related processes are enabled.

[0069] When a legacy UE receives a registration rejection message corresponding to the requested S-NSSAI from the 5G network, it connects to the 4G network and, upon connecting to the 4G network, re-attempts to connect to the S-NSSAI on the 5G network. The legacy UE cannot use the recognition of the received registration rejection message to prevent or reduce further connection attempts for the same or similar S-NSSAI. Therefore, the legacy UE performs excessive handover between 4G and 5G networks, resulting in excessive resource consumption (e.g., power, processor, memory, etc.) and / or service loss.

[0070] However, embodiments provide an improved UE that uses the awareness of received registration rejection messages to prevent or reduce further connection attempts to the same S-NSSAI or similar S-NSSAI. For example, the improved UE can disable or restrict access to the 5G network for a period of time until the UE moves to a new tracking area or until a reset condition is detected. Therefore, the improved UE overcomes the shortcomings of conventional UEs in avoiding or reducing excessive handover between 4G and 5G networks, thereby reducing resource consumption (e.g., power, processor, memory, etc.) and / or avoiding or limiting service loss.

[0071] The foregoing description of the embodiments so fully reveals the general nature of the embodiments herein that others can readily modify and / or adapt the embodiments for various applications by applying present knowledge without departing from the overall concept, and therefore, such modifications and alterations should and are intended to be understood within the meaning and scope of equivalents of the embodiments. It is to be understood that the wording or terminology used herein is for descriptive purposes and not for limitation. Therefore, those skilled in the art will recognize that the embodiments described herein can be practiced with modifications within the scope of the embodiments as described herein.

Claims

1. A method performed by a user equipment (UE) for managing registration failure for an access network slice, the method comprising: sending, by the UE, a registration request message to a first wireless network while the UE is in a tracking area of a registration area, wherein the registration request message includes a single network slice selection assistance information (S-NSSAI) corresponding to the network slice; receiving, by the UE, a registration reject message from the first wireless network, wherein the registration reject message indicates that the network slice is not available in one of the registration area, a public land mobile network (PLMN), or a standalone non-public network (SNPN); storing, by the UE, a tracking area identifier (TAI) of the tracking area to a reject list based on the TAI of the tracking area being included in the registration reject message; and establishing, by the UE, a connection with a second wireless network in response to the receiving, wherein the method further comprises: disabling, by the UE, N1 mode in response to the establishing; starting, by the UE, a timer in response to the establishing; determining, by the UE, whether the UE is located in the tracking area; and performing, by the UE, one of: enabling N1 mode after expiration of the timer in response to determining that the UE is located in the tracking area, or terminating the timer and enabling N1 mode in response to determining that the UE is located in another tracking area, wherein the first wireless network is a 5G network and the second wireless network is a 4G network.

2. The method of claim 1, wherein, the method further comprises: searching, by the UE, for a new tracking area according to a periodic time interval.

3. The method of claim 1, wherein, the registration reject message includes an instruction to disable N1 mode of the UE.

4. The method of claim 1, wherein, the method further comprises: detecting, by the UE, a reset condition, wherein the reset condition is one of: a change in a UE policy, a timer-based retry, a removal of a universal subscriber identity module (USIM) from the UE, a reboot of the UE, a movement of the UE to a new tracking area, or a user-triggered action; terminating, by the UE, the timer in response to detecting the reset condition; deleting, by the UE, the TAI from the reject list in response to detecting the reset condition; and enabling, by the UE, N1 mode in response to detecting the reset condition.

5. The method of claim 1, wherein, the storing step stores a plurality of TAIs corresponding to all tracking areas of the registration area based on the TAI of the tracking area being included in a registration accept message, wherein the TAI of the tracking area is one of the plurality of TAIs.

6. The method of claim 1, wherein The storing step comprises: determining, by the UE, that all network slices in the first wireless network are rejected based on the registration reject message including one of: "S-NSSAI not available in current PLMN or SNPN," "S-NSSAI not available in current registration area," or "S-NSSAI not available due to failed or revoked network slice specific authentication and authorization (NSSAA); and the reject list is usable for a non-access stratum (NAS) and an access stratum (AS) corresponding to the UE.

7. The method of claim 1, wherein, The method further comprises: performing, by the UE, a voice call or data communication with another device via the connection with the second wireless network.

8. The method of claim 1, wherein, The method further comprises: establishing, by the UE, the connection with the first wireless network by resending the registration request message to the first wireless network and successfully registering access to the network slice; and performing, by the UE, a voice call or data communication with another device via the connection with the first wireless network.

9. A user equipment (UE) for managing registration failure for accessing a network slice, comprising: processing circuitry configured to: send, to a first wireless network, a registration request message while the UE is in a tracking area of a registration area, wherein the registration request message includes a single network slice selection assistance information (S-NSSAI) corresponding to the network slice, receive, from the first wireless network, a registration reject message, wherein the registration reject message indicates that the network slice is not available in one of the registration area, a public land mobile network (PLMN), or a standalone non-public network (SNPN), store, to a reject list, a tracking area identifier (TAI) of the tracking area based on the TAI of the tracking area being included in the registration reject message, and establish a connection with a second wireless network in response to receiving the registration reject message, wherein the processing circuitry is further configured to: disable N1 mode in response to establishing the connection with the second wireless network; start a timer in response to establishing the connection with the second wireless network; determine whether the UE is located in the tracking area; and perform one of: enable N1 mode after expiration of the timer in response to determining that the UE is located in the tracking area, or terminate the timer and enable N1 mode in response to determining that the UE is located in another tracking area, wherein the first wireless network is a 5G network and the second wireless network is a 4G network.

10. The UE of claim 9, wherein, The processing circuitry is further configured to search for a new tracking area according to a periodic time interval.

11. The UE of claim 9, wherein, The registration reject message includes an instruction to disable N1 mode of the UE.

12. The UE of claim 9, wherein, The processing circuitry is further configured to: detect a reset condition, wherein the reset condition is one of: a change in a UE policy, a timer-based retry, a removal of a universal subscriber identity module (USIM) from the UE, a reboot of the UE, a movement of the UE to a new tracking area, or a user-triggered action; terminate the timer in response to detecting the reset condition; delete the TAI from the reject list in response to detecting the reset condition; and enable N1 mode in response to detecting the reset condition.

13. The UE of claim 9, wherein, The processing circuitry is further configured to store a plurality of TAIs corresponding to all tracking areas of the registration area based on the TAI of the tracking area being included in a registration accept message, wherein the TAI of the tracking area is one of the plurality of TAIs.

14. The UE of claim 9, wherein, The processing circuitry is configured to store the TAI of the tracking area to the rejection list, the storing operation comprising: determining that all network slices in the first wireless network are rejected based on the registration rejection message including one of "S-NSSAI is not available in current PLMN or SNPN", "S-NSSAI is not available in current registration area", or "S-NSSAI is not available due to failed or revoked Network Slice Specific Authentication and Authorization, NSSAA"; and The rejection list can be used for non-access stratum, NAS, and access stratum, AS, corresponding to the UE.

15. The UE of claim 9, wherein, The processing circuitry is further configured to perform a voice call or data communication with another device via the connection with the second wireless network.

16. The UE of claim 9, wherein, The processing circuitry is further configured to: establish the connection with the first wireless network by resending the registration request message to the first wireless network and successfully registering access to the network slice; and perform a voice call or data communication with another device via the connection with the first wireless network.

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