Method and apparatus for NAS timer handling in store and forward mode in a communication network system

Abstract

The disclosure relates to a 5G or 6G communication system for supporting a higher data transmission rate. The invention pertains to a method and a UE (102) for handling timers in a Store and Forward (S&F) mode in a communication network system (100) by the UE (102). The method includes receiving a message without integrity protection with an Evolved Packet System Mobility Management (EMM) cause value from a network apparatus (114). The method includes detecting that an MME on-board a satellite (104, 104a, 104b) that is serving the UE (102) is operating in the S&F mode of operation. The method includes starting the timer with a duration when the MME on-board the satellite that is serving the UE (102) is operating in the S&F mode of operation and when the UE (102) receives the message without integrity protection with the EMM cause value before secure exchange of NAS messages has been established.

Description

METHOD AND APPARATUS FOR NAS TIMER HANDLING IN STORE AND FORWARD MODE IN A COMMUNICATION NETWORK SYSTEM

[0001] The present disclosure relates to a communication network system, and more specifically related to a Non-Access Stratum (NAS) timer handling in a Store and Forward (S&F) mode in the communication network system.

[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] Embodiments of the present disclosure is to provide an apparatus and method for effectively providing a service in a wireless communication system.

[0009] In an aspect, the objectives are achieved by providing a method for handling timers in a Store and Forward (S&F) mode in a communication network system. The method includes receiving by a User Equipment (UE) a message without integrity protection with an Evolved Packet System Mobility Management (EMM) cause value from a network apparatus. The method includes detecting by the UE that the MME on-board a satellite that is servicing the UE is operating in the S&F mode of operation. The method includes starting by the UE a timer with a duration when the MME on-board the satellite that is serving the UE is operating in the S&F mode of operation and when the UE receives the message without integrity protection with the EMM cause value before secure exchange of NAS messages has been established.

[0010] In another aspect, the objectives are achieved by providing a UE for handling timers in store and forward mode in a communication network system. The UE includes a timer duration controller coupled with a processor and a memory. The timer duration controller receives a message without integrity protection with an EMM cause value from a network apparatus. The timer duration controller detects that the MME on-board a satellite that is serving the UE is operating in the S&F mode of operation. The timer duration controller starts a timer with a duration when the MME on-board the satellite that is serving the UE is operating in the S&F mode of operation and when the UE receives the message without integrity protection with the EMM cause value before secure exchange of NAS messages has been established.

[0011] In an embodiment, a method performed by a user equipment (UE) in a wireless communication system is provided. The method includes: receiving, by the UE (102), a message without integrity protection with an Evolved Packet System Mobility Management (EMM) cause value from a network apparatus (114); detecting, by the UE (102), that a MME on-board a satellite (104, 104a, 104b) that is serving the UE (102) is operating in the store-and-forward mode of operation; and starting, by the UE (102), a timer with a duration, when the MME on-board the satellite (104, 104a, 104b) that is serving the UE (102) is operating in the store-and-forward mode of operation and when the UE (102) receives the message without integrity protection with the EMM cause value before secure exchange of NAS messages has been established.

[0012] In an embodiment, a user equipment (UE) in a wireless communication system is provided. The UE includes at least one transceiver; at least one processor communicatively coupled to the at least one transceiver; and at least one memory, communicatively coupled to the at least one processor, storing instructions executable by the at least one processor individually or in any combination to cause the UE to receive a message without integrity protection with an Evolved Packet System Mobility Management (EMM) cause value from a network apparatus (114), detect that an MME on-board a satellite (104, 104a, 104b) that is serving the UE (102) is operating in the store-and-forward mode of operation; and start a timer with a duration, when the MME on-board the satellite (104, 104a, 104b) that is serving the UE (102) is operating in the store-and-forward mode of operation and when the UE (102) receives the message without integrity protection with the EMM cause value before secure exchange of NAS messages has been established.

[0013] In an embodiment, starting by the UE the timer with the duration includes detecting by the UE whether the UE has stored S&F wait timer value or received an S&F wait timer value from the network apparatus and performing by the UE one of determining the duration for the timer based on the stored S&F wait timer value or received S&F wait timer value when the UE has the stored S&F wait timer value or has received the S&F wait timer value from the network apparatus and starting the timer with the determined duration wherein the S&F wait timer value does not exceed a UE implementation-specific maximum value or determining the duration for the timer based on a random value drawn between 30 to 60 minutes or a random value drawn between 12 to 24 hours when the UE does not have a saved S&F wait timer value or does not receive an S&F wait timer value from the network apparatus and starting the timer with the determined duration wherein the S&F wait timer value exceeds a UE implementation-specific maximum value.

[0014] In an embodiment, the S&F wait timer value for the timer is received by the UE from the network apparatus in at least one of a NAS message, a radio resource control (RRC) message, and an Operations Administration and Maintenance (OAM) mechanism.

[0015] In an embodiment, the random value is a value drawn between 30 to 60 minutes or a random value drawn between 12 to 24 hours or an S&F wait timer value indicated by the network apparatus.

[0016] In an embodiment, the UE implementation-specific maximum value can be 90 minutes.

[0017] In an embodiment, the message comprises at least one of an attach reject message, tracking area update reject message, and a service reject message.

[0018] In an embodiment, the EMM cause value comprises at least one of an EMM cause value #3, an EMM cause value #6, an EMM cause value #7, an EMM cause value #8, an EMM cause value #11, an EMM cause value #12, an EMM cause value #13, an EMM cause value #14, an EMM cause value #15, an EMM cause value #31, an EMM cause value #35, an EMM cause value #36 and an EMM cause value #83.

[0019] In an embodiment, the message is received prior to the establishment of secure exchange of NAS messages for the NAS signaling connection from the network apparatus.

[0020] In an embodiment, the timer is T3245 or T3247 or T3451 or T3452. The timer is a NAS timer.

[0021] These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications can be made within the scope of the embodiments herein, and the embodiments herein include all such modification.

[0022] The principal object of the embodiments herein is to provide a Non-Access Stratum (NAS) timer handling in an S&F mode in a communication network system.

[0023] Another object of the embodiments herein is to provide that the UE starts a timer with a duration when the UE and a satellite serving the UE are operating in the S&F mode of operation and when the UE receives the message without integrity protection with EMM cause value.

[0024] Yet another object of the embodiments herein is to provide a UE that adds a Public Land Mobile Network (PLMN) identity to a "forbidden PLMN list," the "forbidden PLMNs for attach in S101 mode" list, or a "forbidden PLMNs for General Packet Radio Service (GPRS) service" list, or sets the Universal Subscriber Identification Module (USIM) as invalid for non-Evolved Packet System (EPS) services or EPS services or both and perform PLMN selection, and the timer T3245 is not running. The UE shall start the timer T3245 with a value that is greater than the S&F wait timer value received from a Network (NW).

[0025] These and other features, aspects, and advantages of the present invention are illustrated in the accompanying drawings, throughout which like reference letters indicate corresponding parts in the various figures. The embodiments herein will be better understood from the following description with reference to the drawings, in which:

[0026] FIG. 1a is a schematic diagram that illustrates Normal / default Satellite operation mode according to prior art.

[0027] FIG. 1b is a schematic diagram that illustrates S&F Satellite operation mode according to prior art.

[0028] FIG. 2a is a sequence diagram that illustrates NAS timer handling in an S&F mode according to prior art.

[0029] FIG. 2b is a detailed sequence diagram that illustrates NAS timer handling in an S&F mode according to prior art.

[0030] FIG. 3 is a sequence diagram that illustrates the NAS timer handling in the S&F mode according to embodiments as disclosed herein.

[0031] FIG. 4 is a block diagram of a UE according to embodiments as disclosed herein.

[0032] FIG. 5 is a flow chart illustrating a method for handling timers in an S&F mode in a communication network system according to embodiments as disclosed herein.

[0033] FIG. 6 is a detailed flow chart illustrating a method for handling timers in the S&F mode in the communication network system according to embodiments as disclosed herein.

[0034] Like reference numerals represent like elements in the drawing. Elements are illustrated for simplicity and may not be to scale; some dimensions can be exaggerated for clarity. Conventional symbols can be used, and only specific details pertinent to understanding the invention are shown to avoid obscuring the drawing with obvious details.

[0035] The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are 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. Also, the various embodiments described herein are not necessarily mutually exclusive, as some embodiments can be combined with one or more other embodiments to form new embodiments. The term "or" as used herein, refers to a non-exclusive or, unless otherwise indicated. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein can be practiced and to further enable those skilled in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein.

[0036] As is traditional in the field, embodiments can be described and illustrated in terms of blocks which carry out a described function or functions. These blocks, which can be referred to herein as units or modules or the like, are physically implemented by anolog or digital circuits such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits, or the like, and may optionally be driven by firmware. The circuits may, for example, be embodied in one or more semiconductor chips, or on substrate supports such as printed circuit boards and the like. The circuits constituting a block can be implemented by dedicated hardware, or by a processor (e.g., one or more programmed microprocessors and associated circuitry), or by a combination of dedicated hardware to perform some functions of the block and a processor to perform other functions of the block. Each block of the embodiments can be physically separated into two or more interacting and discrete blocks without departing from the scope of the invention. Likewise, the blocks of the embodiments can be physically combined into more complex blocks without departing from the scope of the invention

[0037] The accompanying drawings aid in understanding the technical features, but the embodiments are not limited to these drawings. The disclosure includes any alterations, equivalents, and substitutes beyond those shown. Terms like first, second, etc., are used for distinction and do not limit the elements.

[0038] The evolution of mobile communication network systems has progressed significantly with the integration of satellite communication capabilities into terrestrial networks, especially with the advent of fifth-generation (5G) technology. This integration aims to enhance coverage, particularly in remote and underserved areas, offering connectivity where terrestrial infrastructure can be limited or non-existent. In this context, a Store-and-Forward (S&F) satellite operation mode has been proposed to provide communication services to User Equipment (UE) under intermittent or temporary satellite connectivity conditions.

[0039] In a typical 5G system with satellite access, the normal / default operation mode requires simultaneous active connections between a UE, a satellite, and a ground network. This necessitates a continuous end-to-end connectivity path involving service links (between the UE and the satellite) and feeder links (between the satellite and the ground network). However, in scenarios where the satellite is not continuously connected to the ground network―due to its orbital position, lack of feeder link availability, or other factors―this mode of operation becomes impractical.

[0040] The S&F satellite operation mode addresses this issue by decoupling the connectivity requirements into two distinct steps. In the first step (step A), the UE exchanges signalling and data with the satellite without the satellite being connected to the ground network. In the second step (step B), the satellite establishes connectivity with the ground network to forward the stored signalling and data. This mode of operation is particularly beneficial for delay-tolerant communication services, such as non-real-time Internet of Things (IoT) applications, where immediate data transmission is not critical.

[0041] Despite its advantages, the S&F satellite operation mode introduces several challenges and limitations. One significant issue is the potential delay in communication, as the UE must wait for the satellite to establish a connection with the ground network before data can be forwarded. This delay can be problematic for applications requiring timely data delivery. Additionally, the intermittent connectivity complicates the management of network resources and the maintenance of consistent service quality.

[0042] Another challenge is the handling of UE procedures such as Attach and Tracking Area Update (TAU) in the context of the S&F operation. The UE must be capable of indicating its support for S&F mode and managing the rejection of Attach or TAU procedures due to the lack of immediate end-to-end connectivity. The network, in turn, must communicate to the UE the reasons for rejection and provide instructions for re-attempting these procedures. This includes the use of specific signalling messages, timers, and potentially lists of alternative satellite identifiers (IDs) for the UE to use in subsequent attempts.

[0043] Furthermore, the management of the UE states and NAS timers, such as T3247, and the handling of forbidden location areas and Public Land Mobile Network (PLMN)-specific attempt counters add complexity to the system. The UE must be able to process and act upon the information received from the network, including waiting for specified periods before re-attempting procedures and maintaining the validity of its Subscriber Identity Module (SIM) / Universal Subscriber Identity Module (USIM) for different services.

[0044] Given these challenges, there is a need to address the problems and disadvantages associated with the S&F satellite operation mode in a 5G system and next-generation systems.

[0045] Various definitions used in the proposed invention are as follows.

[0046] Visited PLMN (VPLMN):A Public Land Mobile Network (PLMN) that is not the Home PLMN (HPLMN). If an Equivalent HPLMN (EHPLMN) list is present and non-empty, a VPLMN is a PLMN that is not included in the EHPLMN list.

[0047] Allowable PLMN:A PLMN that is not indicated as forbidden by the UE. In one example, for a UE operating in operation mode A or B, an allowable PLMN is a PLMN that is not included in a "forbidden PLMNs" list stored in the UE. In another example, for a UE operating in operation mode C, or for a UE that does not support A / Gb mode and does not support Iu mode, an allowable PLMN is a PLMN that is not included in the "forbidden PLMNs" list and is also not included in a "forbidden PLMNs for General Packet Radio Service (GPRS) service" list stored in the UE.

[0048] Available PLMN:One or more PLMNs identified in a given area based on information broadcast by one or more cells (e.g., broadcast system information indicating PLMN identity), from which the UE can attempt to obtain wireless communication service.

[0049] Camped on a cell:A state in which the UE (or, if a Subscriber Identity Module (SIM) / Universal SIM (USIM) is not present, mobile equipment) has completed cell selection or cell reselection and has selected a cell on which it intends to monitor for service (e.g., system information and paging) and from which it may attempt to receive available services. Services can be limited, and the PLMN or a Standalone Non-Public Network (SNPN) may not be aware of the UE's presence in the selected cell.

[0050] EHPLMN:Any PLMN identity included in an Equivalent HPLMN list.

[0051] Equivalent HPLMN list:A list of PLMN identities stored on the USIM that allows provision for multiple HPLMN identities. When present, PLMN identities in the Equivalent HPLMN list are treated as equivalent to the HPLMN (e.g., for PLMN selection purposes) and may replace the HPLMN identity derived from an International Mobile Subscriber Identity (IMSI). The Equivalent HPLMN list may also include the HPLMN identity derived from the IMSI. If the HPLMN identity derived from the IMSI is not included in the Equivalent HPLMN list, the HPLMN identity derived from the IMSI is treated as a visited PLMN for PLMN selection purposes.

[0052] Home PLMN (HPLMN):A PLMN whose Mobile Country Code (MCC) and Mobile Network Code (MNC) match the MCC and MNC of the IMSI.

[0053] Registered PLMN (RPLMN):The PLMN on which a location registration (LR) outcome has occurred such that the UE is registered on that PLMN. In a shared network, the RPLMN is the PLMN identified by the PLMN identity of the core network (CN) operator that accepted the location registration.

[0054] Registration:A process in which the UE becomes registered with a PLMN or an SNPN. In one example, registration includes camping on a cell and performing one or more registration-related procedures (e.g., location registration and / or NAS registration signaling) as required for obtaining service.

[0055] UPLMN:A PLMN / access-technology combination in a "User Controlled PLMN Selector with Access Technology" data file stored on the SIM / USIM, in priority order.

[0056] OPLMN:A PLMN / access-technology combination in an "Operator Controlled PLMN Selector with Access Technology" data file stored on the SIM / USIM, in priority order, and / or stored in mobile equipment in priority order.

[0057] Serving satellite:A satellite that provides satellite access to a UE. In a Non-Geostationary Satellite Orbit (NGSO) system, the serving satellite may change over time due to movement of satellites in the constellation relative to the UE.

[0058] Store-and-forward (S&F) satellite operation:An operation mode of a 5G system with satellite access in which the system provides communication service by storing data and forwarding the stored data when connectivity to another segment (e.g., a feeder link connection to a ground segment) becomes available. In some examples, S&F satellite operation supports service when satellite connectivity to the ground segment is intermittent or temporarily unavailable, including when a simultaneous active feeder link connection is not available while the satellite is interacting with the UE.

[0059] S&F data retention period:A validity period during which undelivered data stored for S&F satellite operation is retained, after which at least a portion of the undelivered stored data can be discarded.

[0060] UE-satellite-UE communication:For a 5G system with satellite access, communication between UEs under coverage of one or more serving satellites using satellite access without routing traffic through a ground segment.

[0061] NAS messages:Non-Access Stratum (NAS) signaling messages, including but not limited to: Registration Request, Deregistration Request, Service Request, Control Plane Service Request, Identity Request, Authentication Request, Authentication Result, Authentication Reject, Registration Reject, Registration Accept, Deregistration Accept, Service Reject, Service Accept, UE Configuration Update command, and UE Parameters Update command.

[0062] Radio access technology (RAT):A radio access technology used for network access, including but not limited to: NG-RAN, NR, NR in unlicensed bands, NR satellite access (LEO), NR satellite access (MEO), NR satellite access (GEO), NR satellite access (other satellite types), NR RedCap, E-UTRA, E-UTRA in unlicensed bands, NB-IoT, WB-IoT, LTE-M, and legacy radio access technologies (e.g., 2G, 3G, 4G, and 5G).

[0063] 5GS registration type:A registration type for 5G System (5GS) registration, including: initial registration, mobility registration updating, periodic registration updating, emergency registration, SNPN onboarding registration, disaster roaming initial registration, and disaster roaming mobility registration updating.

[0064] Non-disaster 5GS registration type:A 5GS registration type other than disaster roaming initial registration and disaster roaming mobility registration updating.

[0065] The PLMN selection as per 23.122 without RPLMN:The MS selects and attempts registration on any PLMN / access technology combinations, if available and allowable, in the following order:

[0066] a) either the HPLMN (if the EHPLMN list is not present or is empty) or the highest priority EHPLMN that is available (if the EHPLMN list is present);

[0067] b)_each PLMN / access technology combination in the "User Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order);

[0068] c) each PLMN / access technology combination in the "Operator Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order) or stored in the ME (in priority order);

[0069] d) other PLMN / access technology combinations with received high quality signal in random order; and

[0070] e) other PLMN / access technology combinations in order of decreasing signal quality.

[0071] The PLMN selection as per 23.122 with RPLMN: The MS selects and attempts registration on any PLMN / access technology combinations, if available and allowable, in the following order:

[0072] a) either the RPLMN or the Last registered PLMN;

[0073] b) either the HPLMN (if the EHPLMN list is not present or is empty) or the highest priority EHPLMN that is available (if the EHPLMN list is present);

[0074] c) each PLMN / access technology combination in the "User Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order);

[0075] d) each PLMN / access technology combination in the "Operator Controlled PLMN Selector with Access Technology" data file in the SIM (in priority order) or stored in the ME (in priority order);

[0076] e) other PLMN / access technology combinations with received high quality signal in random order; and

[0077] f) other PLMN / access technology combinations in order of decreasing signal quality.

[0078] For a 5G system with satellite access, the following requirements apply:

[0079] The 5G system shall support service continuity between NR terrestrial access network and New Radio (NR) satellite access networks owned by a same operator or owned by two different operators having an agreement. The Non-Terrestrial Network (NTN) and Terrestrial Network (TN) could either operate in two different frequency bands (e.g., FR1 vs FR2) or in the same frequency band (e.g., FR1 or FR2). The terms Satellite Third Generation Partnership Project (3GPP) access, Satellite access, Satellite Access Network, NR Satellite Access Network, Satellite Next Generation Radio Access Network (NG-RAN) Access Technology, and the NR Satellite access have been interchangeably. The methods, issues, or solutions disclosed in the embodiments are explained using NR satellite access or Satellite NG-RAN Access Technology as an example and are not restricted or limited to the NR Satellite access only. However, the solutions proposed in the embodiments are also applicable for Satellite E-UTRAN access Technology Narrow Band (NB)-S1 mode or Wide Band (WB)-S1 mode via satellite E-UTRAN access and / or Narrow Band Internet Of Things (NB-IOT) or Wide Band Internet Of Things (WB-IOT) Satellite Access / Architecture.

[0080] The solutions which are defined for NR (5GC) are also applicable to legacy RATs like E-UTRA / LTE. The corresponding CN entities need to be replaced by LTE entities, e.g., Access and Mobility Management Function (AMF) with Mobility Management Entity (MME), g-nodeB with e-nodeB, Unified Data Management Function (UDM( with HSS, etc. But the principles of the solution remain the same. In a similar way, the solutions or proposals which are defined for LTE (EPC) are also applicable to other RAT(s) (for example, 5G or 5GC and other RATs). An example list of NAS messages can be, but is not limited to, REGISTRATION REQUEST message, DEREGISTRATION REQUEST message, SERVICE REQUEST message, CONTROL PLANE SERVICE REQUEST, IDENTITY REQUEST, AUTHENTICATION REQUEST, AUTHENTICATION RESULT, AUTHENTICATION REJECT, REGISTRATION REJECT, DEREGISTRATION ACCEPT, SERVICE REJECT, SERVICE ACCEPT, and so on.

[0081] The Network used in the embodiments is explained using any 5G Core Network Function, e.g., AMF. However, the network could be any 5G / EUTRAN Core Network Entities like AMF / SMF / MME / UPF, or the Network could be any 5G / EUTRAN RAN Entity like eNodeB (eNB) or gNodeB (gNB) or NG-RAN, etc. The messages used or indicated in the embodiments are shown as an example. The messages could be any signalling messages between UE and the Network Functions / Entities or between different Network functions / entities. The term area / location / geographical area used in the embodiments may refer to any of cell / cell ID, Tracking Area Code (TAC) / Tracking Area Identity (TAI), PLMN, Mobile Country Code (MCC / ) Mobile Network Code (MNC), Latitude / longitude, Closed Access Group (CAG) cell, or any geographical location / coordinate.

[0082] The methods, issues, or solutions disclosed in the embodiments are explained using NR access or NG-RAN Access Technology as an example and are not restricted or limited to NR access only. However, the solutions proposed in the embodiments are also applicable for E-UTRAN access Technology NB-S1 mode or WB-S1 mode via E-UTRAN access and / or NB-IOT or WB-IOT Access / Architecture. The solutions which are defined for NR (5GC) are also applicable to legacy RATs like E-UTRA / LTE. The corresponding CN entities need to be replaced by LTE entities, e.g., AMF with MME, g-nodeB with e-nodeB, UDM with HSS, etc. But the principles of the solution remain the same.

[0083] The Network used in the embodiments is explained using any 5G Core Network Function, e.g., the AMF. However, the network could be any 5G / EUTRAN Core Network Entities like AMF / SMF / MME / UPF, or the Network could be any 5G / EUTRAN RAN Entity like eNB or gNB or NG-RAN, etc. The messages used or indicated in the embodiments are shown as an example. The messages could be any signalling messages between UE and the Network Functions / Entities or between different Network functions / entities.

[0084] The terms camp and register are used interchangeably and have the same meaning.

[0085] The terms wait timer, DisCo wait timer, Discontinuous Coverage wait timer, Random timer, Random wait timer, DCW Timer are all used interchangeably and have the same meaning.

[0086] The terms wait range, Disco Wait Range, Discontinuous Coverage Wait Range, DCW Range are all used interchangeably and have the same meaning.

[0087] The terms area as used in the embodiments may refer to any of cell / cell ID, TAC / TAI, PLMN, MCC / MNC, Latitude / longitude, any CAG / CAG identifier, or any geographical location / coordinate.

[0088] The terms "Satellite store and forward operation", "Satellite store and forward mode of operation", "Satellite store and forward mode", and "Satellite store and forward operation mode" are used unteachably.

[0089] For the list of possible NAS messages please refer to 3GPP TS 24.501 or 3GPP TS 24.301, for list of AS messages please refer to 3GPP TS 38.331 or 3GPP TS 36.331. The cause names in the embodiments are for illustration purposes and can have any name. The NAS messages and access stratum (AS) messages described in the embodiments are only for illustration purposes; they can be any NAS or AS messages as per the defined protocol between UE and AMF / MME or UE and gNB (NG-RAN / any RAN node) / eNB. In an embodiment, the term Satellite is used interchangeably with 5G or 4G system with satellite access and is used to represent any Satellite(s) or constellation of the Satellites(s) or any aerial body / satellite in any of the Satellite orbits (for example, Low Earth Orbit (LEO) / Medium Earth Orbit (MEO) / Geostationary Orbit (GEO) / HEO, etc.) or any 5G system with Satellite Access or 4G System with Satellite Access or any RAN Entity or Core Network Entity or any Network Function(s) associated with the Satellite Access / RAT / PLMN / Network.

[0090] The embodiments herein disclose a method and system for managing NAS timers in S&F mode within a communication network. A UE initiates NAS procedures by sending a request to a network entity. The network entity responds with a downlink message that includes a list of satellite IDs for signaling and data exchange and an S&F wait timer indicating the wait time before further exchanges. If the NAS message lacks integrity protection and the UE is not set to use timer T3245, the NAS layer starts timer T3247 with a value greater than the S&F wait timer. Depending on the reject cause, a SIM or USIM is marked invalid for General Packet Radio Service (GPRS) or non-GPRS services, and the corresponding counter is incremented. The UE starts a timer with the S&F wait timer. The Timer T3247 expires only after the S&F wait timer has expired, allowing the NAS layer to re-initiate the procedure.

[0091] In an aspect the objects are achieved by providing a method and system for NAS timer handling in S&F mode is disclosed. The UE initiates an attach procedure, Tracking Area Update (TAU) procedure, Registration, or any NAS procedure or message, and sends an attach request, TAU request, Registration request, or any NAS message to the Mobility Management Entity (MME) on-board or any network entity on a satellite (SAT A) of a PLMN, such as first PLMN.

[0092] The MME on-board or any network entity sends a Downlink (DL) message, such as Attach Accept / Reject, Tracking Area Update Accept / Reject, or any other NAS message, to the UE. The MME on-board or any network entity provides a list of satellite IDs (e.g., SAT-ID 1, SAT-ID 2) over which the UE may exchange signalling and data. Additionally, an S&F wait timer is provided, indicating to the UE the time it should wait before attempting signalling and data exchanges on those satellites (e.g., SAT-ID 1, SAT-ID 2) in the DL NAS message.

[0093] If the NAS message is not integrity protected and the UE is not configured to use timer T3245, NAS starts timer T3247 with a value greater than the S&F wait timer value. Depending on the reject cause, the SIM / USIM is marked invalid for GPRS services / non-GPRS services, and the counter for SIM / USIM considered invalid for GPRS / non-GPRS services is increased. The UE also starts a timer with the S&F wait timer value. Timer T3247 expires only after the S&F wait timer has expired, and NAS re-initiates the procedure.

[0094] FIG. 1a is a schematic diagram illustrating the normal / default satellite operation mode in a communication network system (100) according to prior art. FIG. 1b is a schematic diagram illustrating the S&F Satellite operation mode according to prior art.

[0095] The S&F satellite operation in a 5G system, with access to a satellite (104, 104a, 104b), is intended to provide some level of communication service for UEs (102) under satellite coverage with intermittent / temporary satellite connectivity. This occurs, for example, when the satellite (104, 104a, 104b) is not connected via a feeder link or an Inter-Switch Link (ISL) to a ground network (106) for delay-tolerant communication service. The ground network (106) communicates with an external network (108).

[0096] An example of the S&F satellite operation is illustrated in FIG. 1b, contrasting with the current assumption for the normal / default satellite operation of the 5G system with satellite access. As shown in FIG. 1b, under normal / default satellite operation mode, signaling and data traffic exchange between the UE (102) with satellite access and the remote ground network (108) requires the service and feeder links to be active simultaneously. This ensures that when the UE (102) interacts over the service link with the satellite (104, 104a, 104b), there is a continuous end-to-end connectivity path between the UE (102), the satellite (104, 104a, 104b), and the ground network (106).

[0097] In contrast, under the S&F satellite operation mode, the end-to-end exchange of signaling / data traffic is handled as a combination of two steps, not concurrent in time (step A and B in FIG. 1b). In step A, signaling / data exchange between the UE (102) and the satellite (104, 104a, 104b) takes place without the satellite being simultaneously connected to the ground network (106). This means the satellite (104, 104a, 104b) can operate the service link without an active feeder link connection. In step B, connectivity between the satellite (104, 104a, 104b) and the ground network (106) is established, allowing communication between the satellite (104, 104a, 104b) and the ground network (106). Thus, the satellite (104, 104a, 104b) moves from being connected to the UE (102) in step A to being connected to the ground network (106) in step B.

[0098] The concept of the S&F service is widely used in the fields of delay-tolerant networking and disruption-tolerant networking. In the 3GPP context, a service that could be assimilated to an S&F service is Short Message Service (SMS), which does not require end-to-end connectivity between the end-points. Instead, connectivity is needed only between the end-points and a Short Message Service Center (SMSC), which acts as an intermediate node in charge of storing and relaying messages.

[0099] The support of the S&F satellite operation is especially suited for the delivery of delay-tolerant / non-real-time IoT satellite services with Non-Geostationary Satellite Orbit (NGSO) satellites. The MME functionality is split into two parts: an MME-onboard, which is onboard the satellite (104, 104a, 104b), and an MME-ground. When the UE (102) initiates an Attach or TAU procedure, the UE (102) indicates support for S&F mode to the MME following existing NAS capability. The MME sends an Attach or TAU Reject message to the UE (102) if these procedures cannot be completed due to S&F operation. The Attach or TAU Reject message includes:

[0100] a) A new information indicating to the UE (102) that the attach or TAU procedure cannot be completed because of the S&F operation and that the UE (102) can re-attempt the attach or TAU in the PLMN in the next satellite pass. This indicates to the UE (102) that the information contained in the Attach or TAU Request message is stored by the MME and the network will be available to the UE (102) after interaction with the ground network (106).

[0101] b) A wait timer indicating to the UE (102) the time it should wait before re-attempting the Attach / TAU procedure in the current or another satellite of the same PLMN.

[0102] c) Optionally, the list of the Satellite IDs over which the UE (102) may re-attempt the Attach / TAU procedure after the wait timer expires. The Satellite IDs are based on the system information block (SIB) information broadcasted by the eNB.

[0103] The processing of this information by the UE (102) is up to the UE implementation. During the wait timer, the UE (102) can search for another terrestrial or satellite PLMN to get the normal service. If the UE (102) receives a non-integrity protected reject message from the network, the UE (102) that is not configured to use T3245 shall start a timer T3247 with a timer value randomly drawn between 30 minutes to 60 minutes. Additionally, the UE (102) shall maintain a counter for "SIM / USIM considered invalid for non-GPRS services" or "SIM / USIM considered invalid for GPRS services" and an MS implementation-specific maximum value.

[0104] Upon expiry of timer T3247, the MS shall:

[0105] erase the list of "forbidden location areas for regional provision of service" and the list of "forbidden location areas for roaming";

[0106] set the SIM / USIM to valid for non-GPRS services, if

[0107] the MS does not maintain a counter for "SIM / USIM considered invalid for non-GPRS services" events; or

[0108] the MS maintains a counter for "SIM / USIM considered invalid for non-GPRS services" events and this counter has a value less than an MS implementation-specific maximum value.

[0109] set the SIM / USIM to valid for GPRS services, if

[0110] the MS does not maintain a counter for "SIM / USIM considered invalid for GPRS services" events; or

[0111] the MS maintains a counter for "SIM / USIM considered invalid for GPRS services" events and this counter has a value less than an MS implementation-specific maximum value.

[0112] erase the list of "forbidden location areas for non-GPRS services" and the list of "forbidden location areas for GPRS services", if the MS maintains these lists;

[0113] if the MS maintains a list of PLMN-specific attempt counters, for each PLMN-specific attempt counter that has a value greater than zero and less than an MS implementation-specific maximum value, remove the respective PLMN from the extension of the "forbidden PLMNs" list; and

[0114] if the MS maintains a list of PLMN-specific PS-attempt counters, for each PLMN-specific PS-attempt counter that has a value greater than zero and less than an MS implementation-specific maximum value, remove the respective PLMN from the "forbidden PLMNs for GPRS service" list. If the resulting "forbidden PLMNs for GPRS service" list is empty and the MS is supporting S1 mode, the MS re-enables the E-UTRA capability as specified in 3GPP　TS　24.301

[0120] for the case when timer T3247 expires.

[0115] FIG 2a is a sequence diagram that illustrates the NAS timer handling in the S&F mode according to prior art. At step 1, the UE (102) sends an attach request / TAU request / registration request or any NAS Message to the satellite (MME on-board) (110). There is no feeder link established between the satellite (MME on-board) (110) and the ground network (MME ground) (112). At step 2, satellite (MME on-board) (110) sends the NAS message (e.g. Attach Accept / Reject, TAU Accept / Reject or any other NAS message with the list of Satellite IDs (e.g. SAT-ID 1, SAT-ID 2) and S&F wait timer value to the UE (102).

[0116] At step 3, if the NAS message is non integrity protected, the NAS shall start timer with a random value drawn between 30 to 60 minutes or 12 to 24 hours or with the S&F wait timer value provided by the network. At step 4, the NAS timer expires. At step 5, the UE (102) sends an attach request / TAU request / registration request or any NAS Message to the satellite (MME on-board) (110). At step 6, the satellite (MME on-board) (110) sends the NAS message (e.g. Attach Accept / Reject, TAU Accept / Reject or any other NAS message with the list of Satellite IDs (e.g. SAT-ID 1, SAT-ID 2) and S&F wait timer value to the UE (102).

[0117] FIG 2b is a detailed sequence diagram that illustrates the NAS timer handling in the S&F mode according to prior art. At step 1, the UE (102) starts an attach procedure / TAU procedure / Registration or any NAS procedure or message and sends an attach request / TAU request / registration request or any NAS message to the MME on-board (110) or any network entity on satellite (SAT A) of a PLMN (e.g., first PLMN). The UE (102) may utilize its internal transceiver to establish a communication link with the satellite, ensuring that the message is transmitted with the appropriate frequency and modulation scheme suitable for satellite communication. The attach request may include the UE's identity, capabilities, and current location information to facilitate the network's response.

[0118] At step 2, the MME on-board (110) or any network entity sends a DL message (e.g., Attach Accept / Reject, Tracking Area Update Accept / Reject, or any other NAS message) to the UE (102). The MME on-board (110) or any network entity shall provide the list of satellite IDs (e.g., SAT-ID 1, SAT-ID 2) over which the UE (102) may exchange the signaling and data and an S&F wait timer that indicates to the UE (102) the time it should wait before attempting signaling and data exchanges in those satellites (e.g., SAT-ID 1, SAT-ID 2) in the DL NAS message. The DL message may also include additional parameters such as the allowed frequency bands, power levels, and any specific instructions for the UE to follow during the S&F mode operation.

[0119] At step 3, if the NAS message is non-integrity protected and the UE (102) is not configured to use timer T3245, the NAS shall start the timer T3247, say for 60 minutes depending on the reject cause, mark the SIM / USIM invalid for GPRS services / non-GPRS services, and increase the counter for SIM / USIM considered invalid for GPRS / non-GPRS services. The UE (102) also starts a timer with the S&F wait timer value. The UE's internal logic ensures that the timer T3247 is set accurately, and the SIM / USIM status is updated in the device's memory, preventing any unauthorized access to network services during this period.

[0120] At step 4, when timer T3247 expires, the UE (102) marks the SIM / USIM as valid for GPRS / non-GPRS services again and retries the NAS procedure. The UE's software stack reinitializes the NAS procedure, ensuring that all previous states are cleared, and the device is ready to attempt a fresh connection. The retry mechanism may include a back-off algorithm to prevent network congestion and ensure efficient use of satellite resources.

[0121] At step 5, the UE (102) restarts the attach procedure / TAU procedure / Registration or any NAS procedure or message and sends an attach request / TAU request / registration request or any NAS message to the MME on-board or any network entity on satellite (SAT A) of the PLMN (e.g., PLMN1). The UE may perform a self-diagnostic check to ensure that all necessary parameters are correctly set before initiating the procedure, thereby increasing the chances of a successful connection.

[0122] At step 6, the MME on-board (110) or any network entity sends a DL message (e.g., Attach Accept / Reject, Tracking Area Update Accept / Reject, or any other NAS message) to the UE (102). The MME on-board (110) or any network entity shall provide the list of satellite IDs (e.g., SAT-ID 1, SAT-ID 2) over which the UE (102) may exchange the signaling and data and an S&F wait timer that indicates to the UE the time it should wait before attempting signaling and data exchanges in those satellites (e.g., SAT-ID 1, SAT-ID 2) in the DL NAS message. The DL message may also include error codes or additional instructions to guide the UE in case of specific network conditions or constraints.

[0123] At step 7, the steps 4 to 6 are repeated while the S&F wait timer is still running in the UE (102). Once the counter of the SIM / USIM considered invalid for GPRS / non-GPRS services reaches the MS / UE implementation-specific maximum value, the SIM / USIM is marked as invalid. The UE (102) and the MME on-board (110) communicate with the MME ground (112) and a 4G / 5G RAN (114). The communication between the UE and the ground network may include multiple hops and relays, ensuring that the message integrity and timing are maintained throughout the process.

[0124] Issue: Hence, it is not clear how to handle NAS timers such as timer T3247 or timer T3245 (if UE is configured to use timer T3245) when NAS receives a non-integrity protected message from the network when the UE (102) and satellite (104) are operating in S&F mode of operation. If the handling of such timers is not aligned or changed as per the design of the S&F mode of operation, there are possibilities of the SIM / USIM getting marked as invalid forever or a PLMN / tracking area code / tracking area being marked as forbidden forever. The handling of these timers needs to be updated accordingly for the S&F mode of operation. Neither is it clear how non-integrity protected messages should be handled while operating in S&F mode of operation. The example provided above is just an example to elaborate on the problem statement. But the problem is not limited to 4G / EPS; it is also applicable to other radio access technologies and hence applicable for all NAS procedures in different access technologies. The ambiguity in timer handling can lead to significant service disruptions, especially in remote or critical applications where satellite communication is the primary mode of connectivity.

[0125] FIG 3 is a sequence diagram that illustrates NAS timer handling in the S&F mode according to embodiments as disclosed herein. When the UE (102) and the satellite (104, 104a, 104b) are operating in S&F mode of operation, if the UE (102) receives the ATTACH REJECT, the TRACKING AREA UPDATE REJECT, or the SERVICE REJECT message without integrity protection with the EMM cause value #3, #6, #7, #8, #11, #12, #13, #14, #15, #31, #35, or #36 (not limited to these causes) before the network (e.g., 4G / 5G RAN (114)) has established secure exchange of NAS messages for the NAS signaling connection, the UE (102) shall start the timer T3247 (see 3GPP TS 24.008) with a random value which is at least bigger than the S&F wait timer value indicated by the network and proceed as already described in existing mechanisms in 3GPP TS 24.301, TS 24.008, or TS 24.501. For example, in the problem scenario described earlier at step 3, the UE (102) starts the timer T3247 with a value greater than the S&F wait timer value. The counter for the SIM / USIM considered invalid for GPRS / non-GPRS services is incremented once, and the UE (102) waits for the timer T3247 to expire. Once timer T3247 expires, the S&F Wait timer should have expired already. This ensures that the retries of NAS procedures occur only after the UE contexts have been synced across all available satellites. The retries in that case will not be too quick, and hence the SIM / USIM will not be marked as invalid / PLMN will not be marked as forbidden / TA will not be marked as forbidden too soon. The synchronization of UE contexts across satellites ensures that the network state is consistent, reducing the likelihood of repeated failures and improving overall service reliability.

[0126] The timer value for the timer T3247 can be calculated by the UE (102) based on the received S&F wait timer value from the network (114). The calculation may include adding a predefined offset to the S&F wait timer value to ensure that the retry attempts are spaced out adequately, preventing network congestion and allowing sufficient time for context synchronization.

[0127] The timer value for the timer T3247 can be provided to the UE (102) by the network (114) based on the S&F wait timer value via NAS or RRC messages or other OAM mechanisms. The network may dynamically adjust the timer values based on current network load, satellite availability, and other operational parameters to optimize the overall system performance.

[0128] If the UE (102) does not have a saved S&F wait timer value / does not receive an S&F wait timer value from the network (114), the UE (114) can use a timer T3247 value randomly drawn between 30 to 60 minutes and proceed with existing mechanisms for handling non-integrity protected messages described in 3GPP TS 24.008, TS 24.301, TS 24.501. The randomization of the timer value helps in distributing the retry attempts over time, reducing the chances of simultaneous retries by multiple UEs and thus avoiding network congestion.

[0129] If the UE (102) does not have a saved S&F wait timer value / does not receive an S&F wait timer value from the network (114), the UE (102) can use a timer T3247 value greater than at least 12 hours or uniformly drawn between 12 and 24 hours. This extended timer value ensures that the UE waits for a sufficiently long period before retrying, allowing ample time for any network issues to be resolved and reducing the likelihood of repeated failures.

[0130] If the UE (102) is configured to use timer T3245, the UE (102) shall behave as follows: When the UE (102) adds a PLMN identity to the "forbidden PLMN list," the "forbidden PLMNs for attach in S101 mode" list, or the "forbidden PLMNs for GPRS service" list, or sets the USIM as invalid for non-EPS services or EPS services or both, and the timer T3245 (see 3GPP TS 24.008) is not running, the UE (102) shall start the timer T3245 with a value that is greater than the S&F wait timer value received from the network. The UE's internal logic ensures that the timer T3245 is set accurately, and the forbidden PLMN lists are updated in the device's memory, preventing any unauthorized access to network services during this period.

[0131] The timer value for the timer T3245 can be calculated by the UE (102) based on the received S&F wait timer value from the network or can be provided to the UE (102) by the network (114) based on the S&F wait timer value via the NAS or RRC messages or other OAM mechanisms. The calculation may include adding a predefined offset to the S&F wait timer value to ensure that the retry attempts are spaced out adequately, preventing network congestion and allowing sufficient time for context synchronization.

[0132] If the UE (102) does not have a saved S&F wait timer value / does not receive an S&F wait timer value from the network, the UE (102) can use a timer T3245 value randomly drawn between 12 to 24 hours and proceed with existing mechanisms for handling NAS procedures described in 3GPP TS 24.008, TS 24.301, TS 24.501. The randomization of the timer value helps in distributing the retry attempts over time, reducing the chances of simultaneous retries by multiple UEs and thus avoiding network congestion.

[0133] At step 1, the UE (102) starts an attach procedure / TAU procedure / Registration or any NAS procedure or message and sends the attach request / TAU request / registration request or any NAS message to the MME on-board (110) or any network entity on satellite (SAT A) of the PLMN (e.g., PLMN1). The UE (102) may utilize its internal transceiver to establish a communication link with the satellite, ensuring that the message is transmitted with the appropriate frequency and modulation scheme suitable for satellite communication. The attach request may include the UE's identity, capabilities, and current location information to facilitate the network's response.

[0134] At step 2, the MME on-board (110) or any network entity sends a DL message (e.g., Attach Accept / Reject, Tracking Area Update Accept / Reject, or any other NAS message) to the UE (102). The MME on-board (110) or any network entity shall provide the list of satellite IDs (e.g., SAT-ID 1, SAT-ID 2) over which the UE (102) may exchange the signaling and data and an S&F wait timer that indicates to the UE (102) the time it should wait before attempting the signaling and data exchanges in those satellites (e.g., SAT-ID 1, SAT-ID 2) in the DL NAS message. The DL message may also include additional parameters such as the allowed frequency bands, power levels, and any specific instructions for the UE to follow during the S&F mode operation.

[0135] At step 3, if the NAS message is non-integrity protected and the UE (102) is not configured to use timer T3245, the NAS shall start the timer T3247 with a value > S&F wait timer value and depending on the reject cause mark the SIM / USIM invalid for GPRS services / non-GPRS services and increase the counter for SIM / USIM considered invalid for GPRS / non-GPRS services. The UE (102) also starts the timer with the S&F wait timer value. The UE's internal logic ensures that the timer T3247 is set accurately, and the SIM / USIM status is updated in the device's memory, preventing any unauthorized access to network services during this period.

[0136] At step 4, the timer T3247 expires only after the S&F wait timer has expired and NAS re-initiates the procedure. For example, if the UE (102) has the stored S&F wait timer value of say 12 hours after receiving the non-integrity protected NAS messages, the NAS starts T3247 with a value greater than 12 hours, say 13 hours as an example. Once the S&F Wait timer expires, the UE (102) is allowed to retry in the same satellite or in a satellite that matches the satellite ID provided by the network to the UE (102) in step 2. The UE (102) retries the NAS procedure after 13 hours, increases the counter for the SIM / USIM considered as invalid for GPRS / non-GPRS services. The UE (102) repeats the process for the UE / MS implementation-specific number of times, after which the SIM is marked as invalid for GPRS / non-GPRS services depending on the reject cause received from the network. The retry mechanism ensures that the UE does not repeatedly attempt to connect without allowing sufficient time for network conditions to stabilize, thereby improving the overall success rate of the connection attempts.

[0137] Further, in an embodiment, the system (100) includes hardware devices such as the UE (102), the Satellite (MME on-board) (110), the Ground Network (MME ground) (112), and the 4G / 5G RAN (114) that communicate with each other.

[0138] FIG. 4 illustrates a block diagram of a user equipment (UE) (102) configured for Non-Access Stratum (NAS) timer handling in Store-and-Forward (S&F) mode in a communication network system (or communication system) (100), according to one or more embodiments.

[0139] Examples of the communication network system include, but are not limited to, Public Land Mobile Networks (PLMNs) supporting radio access technologies such as 2G, 3G, 4G, 5G, and beyond-5G / 6G, and may further include non-terrestrial network (NTN) access via satellite systems. In addition, the communication network system may include, in combination or alternatively, wireless local area networks and machine-type communication networks, wherein the UE performs NAS procedures and associated signaling over one or more access technologies.

[0140] Examples of the UE include, but are not limited to, mobile phones, smartphones, tablets, wearable devices, computing devices, Internet-of-Things (IoT) devices, vehicular platforms supporting vehicle-to-everything (V2X) communications, public safety devices, medical devices, and other equipment capable of executing NAS procedures.

[0141] In an embodiment, the UE (102) comprises a timer duration controller (410), a processor (420), a memory (430), and a communicator (440). The processor (420) is operatively coupled to the timer duration controller (410), the memory (430), and the communicator (440). The communicator (440) is configured to transmit and receive control-plane signaling including NAS signaling and to support at least one of terrestrial radio access and satellite radio access.

[0142] The UE (102) is configured to communicate, depending on coverage and connectivity, with at least one satellite-based network entity (e.g., an onboard network node or function) and at least one ground-based network entity (e.g., a ground-based core network node or function). The memory (430) stores information associated with the satellite-based network entity and the ground-based network entity, including at least identifiers, connectivity state information, and timer-related parameters applicable to NAS procedures when the UE operates in S&F mode.

[0143] The timer duration controller (410) is implemented as a microcontroller-based circuit arranged to control NAS timer behavior during S&F operation by applying timer-duration adaptation that is distinct from a non-S&F operation. In one embodiment, the timer duration controller (410) comprises a microcontroller core including an instruction decoder and an arithmetic logic unit (ALU), coupled with a non-transitory controller memory storing timer-control firmware, and further coupled with a hardware timer peripheral including at least one programmable counter / tick generator and an interrupt generation circuit. The timer duration controller (410) further includes a memory-mapped timer-parameter register set configured to store one or more NAS timer duration values and associated mode / selection parameters, and an interface circuit configured to receive at least an S&F mode indication and / or a satellite-to-ground connectivity status indication and to provide a timer expiry indication to the processor (420). In operation, the microcontroller executes the timer-control firmware to program the hardware timer peripheral and to control at least one NAS timer by starting, inhibiting, suspending, resuming, or restarting the at least one NAS timer based on the S&F mode indication and the connectivity status indication, while maintaining protocol-compliant NAS behavior under intermittent connectivity associated with satellite access and S&F operation.

[0144] The timer duration controller (410) receives the message without integrity protection with the EMM cause value from the network apparatus (e.g., 4G RAN, 5G RAN, or the like) (114). In an embodiment, the message comprises at least one of the attach reject message, the tracking area update reject message, and the service reject message. In an embodiment, the EMM cause value comprises at least one of the EMM cause value #3, the EMM cause value #6, the EMM cause value #7, the EMM cause value #8, the EMM cause value #11, the EMM cause value #12, the EMM cause value #13, the EMM cause value #14, the EMM cause value #15, the EMM cause value #31, the EMM cause value #35, the EMM cause value #36 and an EMM cause value #83. In an embodiment, the message is received prior to the establishment of secure exchange of NAS messages for the NAS signaling connection from the network apparatus (114).

[0145] The timer duration controller (410) detects that the MME on-board (110) the satellite (104, 104a, 104b) that is serving the UE (102) is operating in the S&F mode of operation. The timer duration controller (410) starts the timer with the duration when the MME on-board (110) the satellite (104, 104a, 104b) that is serving the UE (102) is operating in the S&F mode of operation and when the UE (102) receives the message without integrity protection with the EMM cause value before secure exchange of NAS messages has been established. In an embodiment, the timer is the NAS timer. In another embodiment, the timer is T3245 or T3247 or T3451 or T3452.

[0146] The timer duration controller (410) detects whether the UE (102) has stored S&F wait timer value or received the S&F wait timer value from the network apparatus (114). The timer duration controller (410) determines the duration for the timer based on the stored S&F wait timer value or received S&F wait timer value when the UE (102) has the stored S&F wait timer value or has received the S&F wait timer value from the network apparatus (114) and starts the timer with the determined duration wherein the S&F wait timer value does not exceed the UE implementation-specific maximum value.

[0147] The timer duration controller (410) detects whether the UE (102) has stored S&F wait timer value or received the S&F wait timer value from the network apparatus (114). The timer duration controller (410) determines the duration for the timer based on the random value drawn between 30 to 60 minutes or the random value drawn between 12 to 24 hours when the UE (102) does not have a saved S&F wait timer value or does not receive a S&F wait timer value from the network apparatus (114). The timer duration controller (410) starts the timer with the determined duration wherein the S&F wait timer value exceeds the UE implementation-specific maximum value.

[0148] In an embodiment, the S&F wait timer value for the timer is received by the UE (102) from the network apparatus (114) in at least one of the NAS message, the RRC message, and the OAM mechanism. In an embodiment, the random value is a value drawn between 30 to 60 minutes or a random value drawn between 12 to 24 hours or the S&F wait timer value indicated by the network apparatus (114).

[0149] In an embodiment, the UE implementation-specific maximum value is 90 minutes.

[0150] The memory (430) is configured to store instructions to be executed by the processor (420). The memory (430) may include non-volatile storage elements. Examples of such non-volatile storage elements may include magnetic hard disks, optical disks, floppy disks, flash memories, or forms of electrically programmable memories (EPROM) or electrically erasable and programmable (EEPROM) memories. In addition, the memory may in some examples be considered a non-transitory storage medium. The term non-transitory may indicate that the storage medium is not embodied in a carrier wave or a propagated signal. However, the term non-transitory should not be interpreted that the memory is non-movable. In some examples, the memory (430) can be configured to store larger amounts of information. In certain examples, a non-transitory storage medium may store data that can over time change (e.g., in Random Access Memory (RAM) or cache).

[0151] The processor (420) communicates with the memory (430), the communicator, and the controller (410). The processor (420) is configured to execute instructions stored in the memory (430) and to perform various processes. The processor (420) may include one or a plurality of processors, can be a general-purpose processor such as a central processing unit (CPU), an application processor (AP), or the like, a graphics-only processing unit such as a graphics processing unit (GPU), a visual processing unit (VPU), and / or an Artificial Intelligence (AI) dedicated processor such as a neural processing unit (NPU).

[0152] The communicator (440) includes an electronic circuit specific to a standard that enables wired or wireless communication. The communicator (440) is configured to communicate internally between internal hardware components of the network system and with external devices via one or more networks.

[0153] The timer duration controller (410) is implemented by processing circuitry such as logic gates, integrated circuits, microprocessors, microcontrollers, memory circuits, passive electronic components, active electronic components, optical components, hardwired circuits, or the like. The circuits may, for example, be embodied in one or more semiconductors. The timer duration controller (410) implements the solution as described above with respect to FIG. 3, FIG. 5, and FIG. 6.

[0154] FIG. 5 is a flow chart (500) illustrating a method for handling timers in the S&F mode in the communication network system (100) according to embodiments as disclosed herein. The operations 502-506 are handled by the timer duration controller (410).

[0155] At 502, the method includes receiving the message without integrity protection with the EMM cause value from the network apparatus (114). At 504, the method includes detecting that the MME on-boards the satellite (104, 104a, 104b) that is serving the UE (102) is operating in the S&F mode of operation. At 506, the method includes starting the timer with the duration when the MME on-board the satellite (104, 104a, 104b) that is serving the UE (102) is operating in the S&F mode of operation and when the UE (102) receives the message without integrity protection with the EMM cause value before secure exchange of NAS messages has been established.

[0156] FIG. 6 is a detailed flow chart (600) illustrating a method for handling timers in the S&F mode in the communication network system (100) according to embodiments as disclosed herein. The operations 602-610 are handled by the timer duration controller (410).

[0157] At 602, the method includes receiving the message without integrity protection with the EMM cause value from the network apparatus (114). At 604, the method includes detecting that the MME on-board the satellite (104, 104a, 104b) that is serving the UE (102) is operating in the S&F mode of operation. At 606, the method includes detecting whether the UE (102) has stored S&F wait timer value or received the S&F wait timer value from the network apparatus (114).

[0158] At 608, the method includes determining the duration for the timer based on the stored S&F wait timer value or received S&F wait timer value when the UE (102) has the stored S&F wait timer value or has received the S&F wait timer value from the network apparatus (114) and starting the timer with the determined duration wherein the S&F wait timer value does not exceed the UE implementation-specific maximum value.

[0159] At 610, the method includes determining the duration for the timer based on a random value drawn between 30 to 60 minutes or a random value drawn between 12 to 24 hours when the UE (102) does not have the saved S&F wait timer value or does not receive an S&F wait timer value from the network apparatus (114) and starting the timer with the determined duration wherein the S&F wait timer value exceeds the UE implementation-specific maximum value.

[0160] Based on the proposed method, the NAS timer can be started with the random value if the UE (102) does not trust in the S&F wait timer value provided by the network (114) and no previously configured value of the NAS timer is configured in the UE (102). The UE (102) can also choose to trust in the value provided by the network (114) and start the NAS timer with the corresponding value. This results in handling the re-initiating NAS signaling without wasting the resources (e.g., bandwidth, signaling usage, or the like).

[0161] The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and / or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the scope of the embodiments as described herein.

Claims

1.A method performed by a user equipment (UE) (102) for handling timers in a store-and-forward mode in a communication network system (100), comprising:receiving, by the UE (102), a message without integrity protection with an Evolved Packet System Mobility Management (EMM) cause value from a network apparatus (114);detecting, by the UE (102), that a MME on-board a satellite (104, 104a, 104b) that is serving the UE (102) is operating in the store-and-forward mode of operation; andstarting, by the UE (102), a timer with a duration, when the MME on-board the satellite (104, 104a, 104b) that is serving the UE (102) is operating in the store-and-forward mode of operation and when the UE (102) receives the message without integrity protection with the EMM cause value before secure exchange of NAS messages has been established.2.The method of claim 1, wherein starting, by the UE (102), the timer with the duration comprises:detecting, by the UE (102), whether the UE (102) has stored store-and-forward wait timer value or received a store-and-forward wait timer value from the network apparatus (114); andperforming, by the UE (102), one of:determining the duration for the timer based on the stored store-and-forward wait timer value or received store-and-forward wait timer value when the UE (102) has the stored store-and-forward wait timer value or have received the store-and-forward wait timer value from the network apparatus (114), and starting the timer with the determined duration, wherein the store-and-forward wait timer value　does not exceed a UE implementation-specific maximum value, ordetermining the duration for the timer based on a random value drawn between 30 to 60 minutes or a random value drawn between 12 to 24 hours when the UE (102) does not have a saved store-and-forward wait timer value or does not receive a store-and-forward wait timer value from the network apparatus, and starting the timer with the determined duration, wherein the store-and-forward wait timer value　exceeds a UE implementation-specific maximum value.3.The method of claim 2, wherein the store-and-forward wait timer value for the timer is received by the UE (102) from the network apparatus (114) in at least one of: a NAS message, a radio resource control (RRC) message, and an Operations, Administration, and Maintenance (OAM) mechanism, andwherein the UE implementation-specific maximum value is 90 minutes.4.The method of claim 2, wherein the random value is a value drawn between 30 to 60 minutes or a random value drawn between 12 to 24 hours or a store-and-forward wait timer value indicated by the network apparatus (114).5.The method of claim 1, wherein the message comprises at least one of: an attach reject message, tracking area update reject message, and a service reject message.6.The method of claim 1, wherein the EMM cause value comprises at least one of: an EMM cause value #3, an EMM cause value #6, an EMM cause value #7, an EMM cause value #8, an EMM cause value #11, an EMM cause value #12, an EMM cause value #13, an EMM cause value #14, an EMM cause value #15, an EMM cause value #31, an EMM cause value #35, an EMM cause value #36 and an EMM cause value #83.7.The method of claim 1, wherein the message is received prior to the establishment of secure exchange of NAS messages for the NAS signalling connection from the network apparatus (114).8.The method of claim 1, wherein the timer is a NAS timer.9.A user equipment (UE) (102) for handling timers in store and forward mode in a communication network system (100), the UE (102) comprising:at least one transceiver;at least one processor communicatively coupled to the at least one transceiver; andat least one memory, communicatively coupled to the at least one processor, storing instructions executable by the at least one processor individually or in any combination to cause the UE (102) to:receive a message without integrity protection with an Evolved Packet System Mobility Management (EMM) cause value from a network apparatus (114),detect that an MME on-board a satellite (104, 104a, 104b) that is serving the UE (102) is operating in the store-and-forward mode of operation, andstart a timer with a duration, when the MME on-board the satellite (104, 104a, 104b) that is serving the UE (102) is operating in the store-and-forward mode of operation and when the UE (102) receives the message without integrity protection with the EMM cause value before secure exchange of NAS messages has been established.10.The UE (102) of claim 9, wherein the instructions executable by the at least one processor individually or in any combination further cause the UE (102) to:detect, by the UE (102), whether the UE (102) has stored store-and-forward wait timer value or received a store-and-forward wait timer value from the network apparatus (114), andperform, by the UE (102), one of:determine the duration for the timer based on the stored store-and-forward wait timer value or received store-and-forward wait timer value when the UE (102) has the stored store-and-forward wait timer value or have received the store-and-forward wait timer value from the network apparatus (114), and starting the timer with the determined duration, wherein the store-and-forward wait timer value　does not exceed a UE implementation-specific maximum value, ordetermine the duration for the timer based on a random value drawn between 30 to 60 minutes or a random value drawn between 12 to 24 hours when the UE (102) does not have a saved store-and-forward wait timer value or does not receive a store-and-forward wait timer value from the network apparatus, and starting the timer with the determined duration, wherein the store-and-forward wait timer value　exceeds a UE implementation-specific maximum value.11.The UE (102) of claim 10, wherein the store-and-forward wait timer value for the timer is received by the UE (102) from the network apparatus (114) in at least one of: a NAS message, a radio resource control (RRC) message, and an Operations, Administration, and Maintenance (OAM) mechanism,wherein the random value is a value drawn between 30 to 60 minutes or a random value drawn between 12 to 24 hours or a store-and-forward wait timer value indicated by the network apparatus (114), andwherein the UE implementation-specific maximum value is 90 minutes.12.The UE (102) of claim 9, wherein the message comprises at least one of: an attach reject message, tracking area update reject message, and a service reject message.13.The UE (102) of claim 9, wherein the EMM cause value comprises at least one of: an EMM cause value #3, an EMM cause value #6, an EMM cause value #7, an EMM cause value #8, an EMM cause value #11, an EMM cause value #12, an EMM cause value #13, an EMM cause value #14, an EMM cause value #15, an EMM cause value #31, an EMM cause value #35, an EMM cause value #36 and an EMM cause value #83.14.The UE (102) of claim 9, wherein the message is received prior to the establishment of secure exchange of NAS messages for the NAS signalling connection from the network apparatus (114).15.The UE (102) of claim 9, wherein the timer is a NAS timer.

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