User equipment session restoration in radio access network-network functions

Abstract

Disclosed herein are an apparatus and method for restoring User Equipment (UE) session in Radio Access Network (RAN) Network Functions. The method (600) includes detecting (602), by a Network Function (NF) (102), an event at a subscriber handling component associated with the NF (102). In response to detecting the event, the method (600) includes transmitting (604), by the NF (102) to peer NFs (106), a User Equipment (UE) session audit request message to request active UE context information associated with corresponding active UE sessions. In response to the transmitted UE session audit request message, the method (600) receiving (606), by the NF (102), a UE session audit response message from the peer NFs (106). The method (600) includes determining, by the NF (102), whether to retain or clean up stored UE context information at the NF (102) based on the received UE session audit response message from the peer NFs.

Description

USER EQUIPMENT SESSION RESTORATION IN RADIO ACCESS NETWORKNETWORK FUNCTIONSCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to Indian Non-Provisional Application No.202411082445, filed on October 28, 2024, the entire contents of which are incorporated herein by reference.FIELD

[0002] The present disclosure relates to user equipment session restoration in radio access network-network functions.BACKGROUND

[0003] The information disclosed in this background section is only for an enhancement of understanding of the general background of the disclosure and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.

[0004] In a Radio Access Network (RAN), there are key Network Functions (NFs) such as a Centralized Unit Control Plane (CUCP), a Centralized Unit User Plane (CUUP), a Distributed Unit (DU), and a Master eNodeB that work together to handle network operations. The CUCP manages signaling and control messages, the CUUP handles user data traffic, and the DU manages radio communication with User Equipment (UE). The NFs work in synchronization for efficient service delivery, and any disruption or restart of components can lead to missed signaling messages and synchronization issues, potentially resulting in stale UE context across a network. When a subscriber handling component (such as a VirtualNetworking Function Component (VNFC) or a Containerized Network Function Component(CNFC) in the 5G-RAN’s NF restarts, the component may miss critical signaling messages. The critical signaling messages may include UE Release or DeRegister requests. Radio Link Failures (RLF) detected by the DU, inactivity notifications from the CUUP, and / or Secondary gNodeB (SgNB) release requests.

[0005] Since the signaling messages do not have retries specified in Third Generation Partnership Project (3GPP) standards, the NF fails to clean up the corresponding UE sessions while the UE sessions may get deleted from the peer NFs since the peer NF do not receive response from the recovering NF. The peer NFs may include the CUCP, the CUUP, the DU, and the SgNB. As a result, the NF holds stale or outdated UE contexts, while the peer NFs may have already cleaned up UE sessions after seeing no further progress in signaling. This inconsistency between the NF and peer NFs leads to synchronization issues and the potential for stale UE contexts persisting in the network, which could impact the performance and efficiency of the 5G-RAN system.

[0006] The current 3GPP standards adopt a reactive approach to handling stale UE sessions, where the NF leams about session clean-up in the peer NFs through error indication messages. For instance, when the CUCP receives a downlink NG signaling message from an Access and Mobility' Management Function (AMF), the CUCP forwards a corresponding Fl signaling message to the DU. If the DU has already cleaned up the associated UE context, the DU responds by sending an error indication to the CUCP. Upon receiving the error indication, the CUCP can reactively clean up the UE context, releasing the context in the CUUP and the AMF. This reactive method results in delays and inefficiencies, as the CUCP can only clean up sessions after being notified by the DU. There are no mechanisms to prevent the stale UE contexts proactively, leading to outdated session information in the NFand the peer NFs. This gap may cause network resource mismanagement and signaling inefficiencies.

[0007] Therefore, it is desired to address the above-mentioned disadvantages or other shortcomings or at least provide a useful alternative to overcome the above-mentioned disadvantages.SUMMARY

[0008] Disclosed herein are apparatus and methods for restoring user equipment session in Radio Access Network (RAN)-Network Functions (NFs).

[0009] Also disclosed herein is a method for determining whether to retain or clean up stored UE context information. The method includes detecting, by a Network Function (NF), an event at a subscriber handling component associated with the NF. In response to detecting the event, the method includes transmitting, by the NF, a User Equipment (UE) session audit request message. Transmission is directed to one or more peer NFs. The NF requests active UE context information associated with one or more corresponding active UE sessions. In response to the transmitted UE session audit request message, the method includes receiving, by the NF, a UE session audit response message. The NF receives the UE session audit response message from each of the one or more peer NFs. Further, the method includes determining, by the NF, whether to retain or clean up stored UE context information at the NF. Further, the determination is based on the received UE session audit response message from the one or more peer NFs.

[0010] Also disclosed herein is a method for determining whether to retain or clean up stored UE context information. The method may include detecting, by a Network Function (NF), an event at a subscriber handling component. The subscriber handling component isassociated with the NF. Further, the method includes activating, by the NF, an activity monitoring timer. The activity monitoring timer is associated with the NF. The activation occurs upon detecting the event. Furthermore, the method includes monitoring, by the NF, signaling activity. The monitoring occurs on one or more interfaces of the NF. The monitoring takes place upon activating the activity monitoring timer. In addition, the method includes determining, by the NF, whether to retain or clean up stored User Equipment (UE) context information. The stored UE context information is associated with one or more corresponding active UE sessions at the NF. Further, the determination is based on the monitored signaling activity.

[0011] Also disclosed herein is an apparatus for determining whether to retain or clean up stored UE context information. The apparatus is configured to detect an event at a subscriber handling component. The subscriber handling component is associated with a Network Function (NF). In response to detecting the event, the apparatus is configured to transmit a User Equipment (UE) session audit request message to one or more peer NFs. The UE session audit request message requests active UE context information. The active UE context information is associated with one or more corresponding active UE sessions. In response to the transmitted UE session audit request message, the apparatus is configured to receive a UE session audit response message. The UE session audit response message is received from each of the one or more peer NFs. Further, the apparatus is configured to determine whether to retain or clean up stored UE context information at the NF. Further, the determination is based on the received UE session audit response message from the one or more peer NFs.

[0012] Also disclosed herein is an apparatus for determining whether to retain or clean up stored UE context information. The apparatus is configured to detect a restart eventat a subscriber handling component. The subscriber handling component is associated with aNetwork Function (NF). The apparatus is configured to activate an activity monitoring timer. The activity monitoring timer.is associated with the NF. The activation occurs upon detecting the restart event. Further, the apparatus is configured to monitor signaling activity. The monitoring occurs on one or more interfaces of the NF. The monitoring takes place upon activating the activity monitoring timer. Furthermore, the apparatus is configured to determine whether to retain or clean up stored User Equipment (UE) context information at the NF. Further, the determination is based on the monitored signaling activity.

[0013] Also disclosed herein is a non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by a Network Function (NF), the NF comprising one or more processors, causes the one or more processors configured to detect a restart event at a subscriber handling component. The subscriber handling component is associated with the NF. In response to detecting the restart event, the one or more processors are configured to transmit a UE session audit request message to one or more peer NFs. The UE session audit request message requests active UE context information. The active UE context information is associated with one or more corresponding active UE sessions. In response to the transmitted UE session audit request message, the one or more processors are configured to receive a UE session audit response message. The UE session audit response message is received from each of the one or more peer NFs. Further, the one or more processors are configured to determine whether to retain or clean up stored UE context information at the NF. Further, the determination is based on the received UE session audit response message from the one or more peer NFs.

[0014] To further clarify the advantages and features of the present disclosure, a more particular description of the disclosure will be rendered by reference to specific embodimentsthereof, which is illustrated in the appended drawing. It is appreciated that these drawings depict only typical embodiments of the disclosure and are therefore not to be considered limiting its scope. The disclosure will be described and explained with additional specificity and detail with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Features, aspects, and advantages of embodiments of the disclosure will be described below with reference to the accompanying drawings, in which like reference numerals denote like elements, and wherein:Figure 1 illustrates an example block diagram of a User Equipment (UE) session restoration environment depicting Network Functions (NF), peer NFs, and UE, in accordance with an embodiment of the present disclosure;Figure 2 illustrates a diagram of example components of a system to retain or clean up stored UE context information at the NF, in accordance with an embodiment of the present disclosure;Figure 3A, Figure 3B, and Figure 3C illustrate signaling diagrams for a Standalone (SA) mode of 5G-the UE deregistration scenario, in accordance with an embodiment of the present disclosure;Figure 4A, Figure 4B, and Figure 4C illustrate signaling diagrams for the SA mode or a Non-Standalone (NSA) - data inactivity notification scenario, in accordance with an embodiment of the present disclosure;Figure 5A, Figure 5B, and Figure 5C illustrate signaling diagrams for the NSA modesecondary gNodeB (SgNB) release request scenario, in accordance with an embodiment of the present disclosure;Figure 6 illustrates a flowchart depicting a method for determining stored UE context information at the NF based on a received UE session audit response message, according to an embodiment of the present disclosure; andFigure 7 illustrates a flowchart depicting a method for determining stored UE context information at the NF based on monitored signaling activity, according to an embodiment of the present disclosure.DETAILED DESCRIPTION

[0016] The following detailed description of example embodiments refers to the accompanying drawings. The present disclosure provides illustrations and descriptions, but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the present disclosure or may be acquired from practice of the implementations. Further, one or more features or components of one embodiment may be incorporated into or combined with another embodiment (or one or more features of another embodiment). Additionally, the flowchart and description of operations provided below relate to at least one of the embodiments in the present disclosure. It should be noted that it is possible to make other embodiments that do not exactly match the flowchart and its description. It is understood that in other embodiments one or more operations may be omitted, one or more operations may be added, one or more operations may be performed simultaneously (at least in part).

[0017] It will be apparent that systems and / or methods described herein, may be implemented in different forms of hardware, software, or a combination of hardware and software. The actual specialized control hardware or software code used to implement these systems and / or methods should not limit their implementations. Thus, the operation and behavior of the systems and / or methods are described herein without reference to specific software code. It is understood that software and hardware may be designed to implement the systems and / or methods based on the description herein.

[0018] Even though particular combinations of features are recited in the claims and / or disclosed in the specification, the particular combinations are not intended to limit the disclosure of implementations. In fact, many of these features may be combined in ways not specifically recited in the claims and / or disclosed in the specification. Even if a dependent claim directly depends on only one claim, the present disclosure may indicate that the dependent claim is dependent on other claims in the claim set.

[0019] No element, act, or instruction used herein should be construed as critical or essential unless explicitly described as such. Also, as used herein, the articles "a" and "an" (in other words, nouns not mentioned in the plural) are intended to include one or more items and may be used interchangeably with “one or more.” Also, as used herein, the terms “has.” “have,” “having,” “include,” “including.” or the like are intended to be open-ended terms.Further, the phrase “based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise. Furthermore, expressions such as “at least one of [A] and [B],” “[A] and / or [B],” or “at least one of [A] or [B]” are to be understood as including only A, only B, or both A and B.

[0020] The foregoing disclosure provides illustration and description but is not intended to be exhaustive or to limit the implementations to the precise form disclosed. Modifications and variations are possible in light of the above disclosure or may be acquired from practice of the implementations.

[0021] Figure 1 illustrates an example block diagram of a User Equipment (UE) session restoration environment 100 depicting Network Functions (NF) 102, peer NF 106, and UE 108, in accordance with an embodiment of the present disclosure. The NF 102 and the peer NF 106 may be associated with a Radio Access Network (RAN). Each of the NF 102 and the peer NFs 106 may include, but are not limited to, a Centralized Unit Control Plane(CUCP), a Centralized Unit User Plane (CUUP), a Distributed Unit (DU), and the like. In an embodiment, the NF 102 and the peer NF 106 may include a Master eNodeB (MeNB), and the like. While Figure 1 depicts one peer NF 106, it may be apparent that there may be more than one peer NF. The NF 102 may refer to a logical entity in the network that performs specific tasks or services, such as handling user sessions, signaling, or traffic management. The peer NF 106 may refer to another NF that interacts with the NF 102 in question to complete specific tasks. For example, the CUCP of the NF 102 may interact with the peer NF 106 like the CUUP or DU to manage UE sessions, exchange signaling messages, or perform coordinated actions. The peer NF 106 may be typically responsible for maintaining synchronized states across interactions, ensuring that user sessions and network resources are managed seamlessly. The NF 102 and the peer NF 106 may lie in interdependency for session management, signaling, and network operations. For instance, in a 5G-RAN, if the CUCP of the NF 102 restarts, it may miss signaling messages from the peer NF 106 (like the CUUP or the DU), leading to stale UE contexts. Therefore, effective coordination between NF 102 and the peer NF 106 may be critical to ensure a consistent session state and avoid network disruptions.

[0022] The UE 108 may be connected to the RAN and use services of the RAN. In an embodiment, the UE 108 perceives a gNodeB (gNB) as a unified entity' and is unaware of internal disaggregation into NFs such as the DU, the CUCP, and the CUUP. To the UE 108, a single CUCP and one or more instances of the CUUP and the DU appear as cohesive gNB, seamlessly managing communication and coordination. The NF 102 may perform a specific role in handling network sendees, such as managing UE sessions, controlling connections, or forwarding user data. For example, when the UE 108 sends signaling messages (such as session setup, data transfer requests, or deregistration), the NF 102 is responsible for handlingand processing these requests to ensure that the UE 108 remains connected to the network and that services are provided. The peer NFs may refer to other NFs that interact with the NF 102 within a network. For instance, the CUCP of the NF 102 may communicate with the peer NFs 106. such as the CUUP. the DU, and the MeNB to manage the UE sessions, handle signaling messages, or route data. The peer NFs 106 may work together in a distributed manner to manage various aspects of a fifth-generation (5G) network, such as mobility, session handling, and data forwarding. The UE 108 may interact with the gNB or the MeNB which comprises the NFs and its peers, in a coordinated manner. For instance, during a handover or when the UE 108 moves between different network nodes, the UE’s session information may be seamlessly managed by peer NFs 106. The UE 108 may rely on the NF 102 and the peer NF 106 to manage the UE sessions effectively. The UE session may refer to the active communication state established between the UE 108 and the network, which enables the exchange of data and signaling information. The NF 102 may play a critical role in managing the UE session, ensuring that the UE 108 remains connected to the network for seamless sendees like data transmission, voice calls, and more. The NF 102 and peer NF 106 may be interconnected and work together to ensure that the UE’s session, data flows, and signaling are handled efficiently, even during disruptions or restarts of individual components.

[0023] When the UE 108 sends a deregister message to the peer NF 106 with a Non- Access Stratum (NAS) cause as sw itch off, the peer NF 106 may forward the NAS deregistration request and wait for the release of the resources associated with the UE 108 based on instructions from the NF 102. The deregister message may indicate that the UE 108 may be voluntarily disconnecting from the network, typically due to a user powering off theUE 108. The peer NF 106 may forward an uplink Radio Resource Control (RRC) message tothe NF 102 in the network. The uplink RRC message may include an uplink information transfer that includes a dedicated Non-Access Stratum (NAS) message such as a deregistration request.

[0024] In an embodiment, the NF 102 may be associated with a system 104. In another embodiment, the system 104 may be part of the NF 102. The system 104 may be configured to restore the UE session between the NF 102 and the peer NF 106. When an event occurs at the subscriber handling component of the NF 102, the NF 102 may disrupt the UE session, potentially leading to session loss or the creation of stale session data. The system 104 may be configured to detect the event at a subscriber handling component associated with the NF 102. The event may include, but is not limited to, a restart event, and the like. In response to detecting the event, the NF 102 may be configured to transmit a UE session audit request message to the peer NFs 106. The UE session audit request message may be a signaling message to request information about active UE sessions. The UE session audit request message may include, but is not limited to, a list of gNB CUCP Fl UE ID and gNB DU Fl UE ID pair, a list of gNB CUCP El UE ID and gNB CUUP El UE ID pair, a list of gNB CUCP Fl UE ID and gNB DU Fl UE ID pair, a list of gNB CUCP El UE ID and gNB CUUP El UE ID pair, a list of gNB SgNB X2 UE ID and eNB MeNB X2 UE ID pair, a list of gNB CUCP Fl UE ID and gNB DU Fl UE ID pair, list of gNB CUCP El UE ID and the gNB CUUP El UE ID pair, a list of gNB SgNB X2 UE ID and eNB MeNB X2 UE ID pair , and the like. For example, the UE session audit request message is used to verify whether the peer NF 106 still maintains the context of the UE sessions that are active or have been cleaned up. The NF 102 may be configured to request active UE context information associated with corresponding active UE sessions.

[0025] In response to the transmitted UE session audit request message, the NF 102 may be configured to receive a UE session audit response message from the peer NFs 106.The audit response message may include the active UE context information associated with the corresponding active UE sessions. The UE session audit response message may include, but is not limited to, a list of gNB DU Fl UE ID and gNB CUCP Fl UE ID pair, a list of gNB CUUP El UE ID and gNB CUCP El UE ID pair, a list of gNB DU Fl UE ID and gNB CUCP Fl UE ID pair, a list of gNB CUUP El UE ID and gNB CUCP El UE ID pair, a list of eNB MeNB X2 UE ID and gNB SgNB X2 UE ID pair, a list of gNB DU Fl UE ID and the gNB CUCP Fl UE ID pair, a list of gNB CUUP El UE ID, gNB CUCP El UE ID pair) , a list of eNB MeNB X2 UE ID and gNB SgNB X2 UE ID pair, and the like.

[0026] The NF 102 may be configured to determine whether to retain or clean up stored UE context information at the NF 102 based on the received UE session audit response message from the peer NFs 106. Further, the NF 102 may be configured to determine a plurality of UE Identifiers (IDs) associated with the UE session audit response message received at the NF 102. The plurality of UE identifiers may be used by the NF 102 to track and manage the active sessions associated with different UEs 108.

[0027] In an embodiment, the NF 102 may be configured to retain the stored UE context information upon determining that the plurality of UE IDs is received at the NF 102. In another embodiment, the NF 102 may be configured to clean up the stored UE context information in the NF 102 upon determining that the plurality of UE IDs is not received at the NF 102. Further, the NF 102 may be configured to update the stored UE context information based on the received active UE context information from the peer NFs 106.

[0028] In another embodiment, the NF 102 may be configured to detect the event at the subscriber handling component associated with the NF 102. The NF 102 may beconfigured to activate an activity monitoring timer 110 upon detecting the event. In an embodiment, the activity monitoring timer 110 may be a signaling inactivity timer. The NF 102 may be configured to monitor signaling activity on interfaces of the NF 102 upon activating the activity monitoring timer 110. The signaling activity may refer to an exchange of control messages between the NF 102 and the peer NFs 106 to manage and maintain communication sessions. The interfaces may include, but are not limited to, an Fl interface, an El interface, an Ng interface, an X2 interface, an Xn interface, and the like. If the signaling activity is detected, it indicates that the session is ongoing and resources may be maintained. If no signaling activity is detected within a specific period tracked by the activitymonitoring timer 110, the NF 102 may decide whether to clean or retain the session information.

[0029] Further, the NF 102 may be configured to monitor signaling activity on interfaces of the NF 102 upon activating the activity monitoring timer 110. Furthermore, the NF 102 may be configured to determine whether to retain or clean up stored UE context information. The stored UE context information may be associated with the corresponding active UE sessions at the NF 102 based on the monitored signaling activity. The NF 102 maybe configured to determine that the signaling activity- is detected within the duration of the activity- monitoring timer 110. The activity- monitoring timer 110 may be associated with the NF 102.

[0030] In an embodiment, the NF 102 may be configured to retain the UE context information upon determining that the signaling activity- is detected. In another embodiment, the NF 102 may be configured to clean up the stored UE context information in the NF 102 upon determining that no signaling activity is detected.

[0031] In an embodiment, in a Standalone (SA) mode of 5G scenario, missed uplink RRC messages carrying UE deregistration or RLF triggered release when the NF 102 such as the gNBCUCP subscriber handling component is restarting. In another embodiment, in the SA or Non-Standalone NSA mode-data inactivity notification scenario 405, missed UE inactivity indication from the peer NF such as the CUUP. when the NF 102 such as the gNBCUCP subscriber handling component is restarting. In another embodiment, in the NSA mode-secondary gNodeB (SgNB) release request scenario, Missed SgNB Release Request from the peer NF 106 such as the MeNB or MgNB (for ENDC / NRDC cases) when the NF 102 such as the gNBCUCP subscriber handling component is restarting.

[0032] Figure 2 illustrates an embodiment of a system 200 (UE) connected to the NF 102. The example components of the system to determine whether to retain or clean up the stored UE context information at the NF 102. The system discussed here corresponds to an apparatus to retain or clean the stored UE context information at the NF 102. As show n in Figure 2, the device 200 includes processor 210, a memory 220, a storage component 230, an input component 240, an output component 250, a communication interface 260, and a bus 270.

[0033] The processor 210, as used herein, means any type of computational circuit that may comprise hardware elements and software elements. The processor 210 may be embodied as a multi-core processor, a single-core processor, or a combination of one or more multi-core processors and / or one or more single-core processors, a distributed processing system, or the like. The processor 210 may be a Central Processing Unit (CPU), a graphics processing unit (GPU), an accelerated processing unit (APU). an application-specific integrated circuit (ASIC), or another t pe of processing component.

[0034] Memory 220 includes a non-transitory computer-readable medium. Memory220 includes a random- access memory (RAM), a read only memory (ROM), and / or another A pe of dynamic or static storage device (e.g., a flash memory, a magnetic memory, and / or an optical memory) that stores information and / or instructions for use by processor 210. The memory 220 comprises machine-readable instructions which are executable by the processor 210. These machine-readable instructions when executed by the processor 210 cause the processor 210 to perform one or more method steps of an embodiment described above.

[0035] The storage component 230 stores information and / or software related to the operation and use of the device 200. For example, the storage component 230 may include a hard disk (e.g., a magnetic disk, an optical disk, a magneto-optic disk, and / or a solid-state disk), a compact disc (CD), a digital versatile disc (DVD), a floppy disk, a cartridge, a magnetic tape, and / or another type of non-transitory computer-readable medium, along with a corresponding drive.

[0036] Input component 240 is configured to receive information, such as user input. For example, the input component 240 may include, but not be limited to, a touchscreen display, a keyboard, a keypad, a mouse, a button, a switch, and / or a microphone.Additionally, or alternatively, the input component 240 may include a sensor for sensing information (e.g., a global positioning system (GPS), an accelerometer, a gyroscope, and / or an actuator).

[0037] Output component 250 is configured to provide output information from the device 200. For example, the output component 250 may be, but not limited to, a display, a speaker, an instruction device to an external device, and / or one or more light-emitting diodes (LEDs).

[0038] Communication interface 260 is an interface that provides a communication connection to other devices, such as external devices and internal devices. The connection by the communication interface 260 can be a wired connection, a wireless connection, or a combination of wired and wireless connections, and can be a direct connection or an indirect connection via a communication network that exists between the device 200 and other devices. In other words, the standard of the communication interface 260 is not limited.

[0039] The bus 270 acts as an interconnect between the processor 210, the memory 220, the storage component 230. the input component 240, the output component 250, and the communication interface 260 of the device 200. The bus 270 may include a wired interconnection or a wireless interconnection.

[0040] The number and arrangement of components shown in FIG. 2 are provided as an example. In practice, device 200 may include additional components, fewer components, different components, or differently arranged components than those shown in FIG. 2 Additionally, or alternatively, a set of components (e.g., one or more components) of device 200 may perform one or more functions described as being performed by another set of components of device 200. Further, one or more method steps described in any of the embodiments may be performed utilizing a plurality of devices 200 in communication with one another.

[0041] In an embodiment, the system 104 may include the processor 210 and the memory 220 configured to perform the functions as described in the present disclosure. The memory 220 may include executable instructions that, when executed by the processor 210, cause the system 104 to perform the functions as described in the present disclosure. As an example, the processor 210 may be a single processing unit or a number of units, all of which could include multiple computing units. The processor 210 may be implemented as one ormore microprocessors, microcomputers, microcontrollers, digital signal processors, central processing units, state machines, logic circuitries, and / or any devices that manipulate signals based on operational instructions. Among other capabilities, the processor 210 is configured to fetch and execute computer-readable instructions and data stored in the memory 220. The processor 210 may include one or a plurality of processors.

[0042] The memory 220 may include any non-transitory computer-readable medium known in the art including, for example, volatile memory, such as static random-access memory (SRAM) and dynamic random-access memory (DRAM), and / or non-volatile memory, such as read-only memory (ROM), erasable programmable ROM, flash memories, hard disks, optical disks, and magnetic tapes. In an embodiment, the system 104 of the NF 102 may be implemented as dedicated hardware units. In another embodiment, the system 104 of the NF 102 may be implemented in the form of virtualized software units in hardware or cloud environments.

[0043] Further, the processor 210 may be configured to detect the event at the subscriber handling component associated with the NF 102. In response to detecting the event. The processor 210 may be configured to transmit the UE session audit request message to the peer NFs 106. The processor 210 may be configured to request the active UE context information associated with the corresponding active UE sessions. In response to the transmitted UE session audit request message, the processor 210 may be configured to receive the UE session audit response message from the peer NFs 106. Further, the processor 210 may be configured to determine whether to retain or clean up the stored UE context information at the NF 106. The determination may be based on the received UE session audit response message from the peer NFs 106.

[0044] In an embodiment, the processor 210 may be configured to detect the restart event at the subscriber handling component associated with the NF 102. In response to detecting the restart event, the processor 210 may be configured to transmit the UE session audit request message to the peer NFs 106. The processor 210 may be configured to request the active UE context information associated with the corresponding active UE sessions from the peer NFs 106. In response to the transmitted UE session audit request message, the processor 210 may be configured to receive the UE session audit response message from the peer NFs 106. Further, the processor 210 may be configured to determine whether to retain or clean up the stored UE context information at the NF 102 based on the received UE session audit response message from the peer NFs 106.

[0045] Reference is now made to Figure 3A, Figure 3B, and Figure 3C depicting signaling diagrams 300a, 300b, and 300c for a Standalone (SA) UE deregistration scenario (SA-UE deregistration scenario), in accordance with an embodiment of the present disclosure. The UE 108 operating in a 5G SA mode initiates the process of deregistration from the network. The signalling diagrams 300a and 300b depict the exchange of signals and messages between the NF 102 such as the CUCP 302 and the peer NF 106 such as the DU 304, and the CUUP 306 .

[0046] The SA-UE deregistration scenario 305 may include missed uplink RRC messages. The missed uplink RRC messages carry either UE deregistration or RLF-triggered release. The missed uplink RRC messages occur when the gNBCUCP subscriber handling component is restarting.

[0047] Initially, as seen in Figure 3A, at step 310a, the UE 108 may send the deregister message to the DU 304 with the NAS cause as switched off 310b. At step 315, based on the received deregister message, the DU 304 may forward the uplink RRC messageto the CUCP 302. The uplink RRC message may include an uplink information transfer that includes a dedicated Non-Access Stratum (NAS) message such as a deregistration request.

[0048] At step 320, as the application of the CUCP 302 is restarting, the deregistration request message from the UE 108 may not be handled, and there may be no retransmission.

[0049] At step 325, the DU 304 may locally clean up the UE context information due to no response from the CUCP 302.

[0050] As seen in Figure 3B, at step 330, stale UE context may remain in the CUCP 302 until any new message initiates a process to address the stale UE context information.

[0051] At step 335, the CUCP 302 may come up and initialize an audit procedure.

[0052] At step 340, the CUCP 302 may transmit an active UE session audit request to the DU 304. The active UE session audit request may include the list of gNB CUCP Fl UE ID and gNB DU Fl UE ID pair.

[0053] At step 345, the CUCP 302 may receive an active UE session audit response.The active UE session audit response may include the list of gNB DU Fl UE ID and gNB CUCP Fl UE ID pair.

[0054] At step 350, the CUCP 302 may transmit the active UE session audit request to the CUUP 306. The active UE session audit request may include the list of gNB CUCP El UE ID and gNB CUUP El UE ID pair.

[0055] At step 355, the CUCP 302 may receive the active UE session audit response. The active UE session audit response may include the list of gNB CUUP El UE ID and gNB CUCP El UE ID pair.

[0056] At step 360, the CUCP 302 may locally clean up the UE context information whose UE IDs are not received from the peer NFs 106 in the audit procedure.

[0057] At step 365, the CUCP 302 may come to an operational state.

[0058] As seen in Figure 3C, at step 370, the CUCP 302 may come up and initialize the alternate procedure to clean up or retain the UE context information.

[0059] At step 375, the CUCP 302 may activate the activity monitoring timer 110.

[0060] At step 380, the CUCP 302 may monitor the signaling activity on the interfaces of the CUCP 302 upon activating the activity monitoring timer 110. The interfaces may include but are not limited to. the Fl interface, the El interface, the Ng interface, the X2 interface, the Xn interface, and the like. If no signaling is detected within the activity’ monitoring timer 110, the CUCP 302 may clean up the UE context information.

[0061] Reference is now made to Figure 4A, Figure 4B, and Figure 4C depicting signaling diagrams 400a, 400b, and 400c for SA / NSA data inactivity notification scenario 405, in accordance with an embodiment of the present disclosure. In the SA / NSA data inactivity notification scenario 405, the UE 110 operating in either the SA or NSA 5G networks enters a state where UE 110 no longer sends or receives data for a certain period of time, triggering the network to handle the inactivity. The signaling diagrams 400a, 400b, and 400c depict the exchange of signals and messages between the NF 102 and the peer NF 106, in particular, among the CUCP 302, the DU 304, and the CUUP 306 .

[0062] The SA or NSA mode-data inactivity notification scenario 405 may include a missed UE inactivity' indication from the CUUP 306 when the gNBCUCP subscriber handling component is restarting.

[0063] Initially, as seen in Figure 4A, at step 410, the CUUP 306 may detect the UE level inactivity’.

[0064] At step 415, the CUCP 302 may receive an inactivity notification from theCUUP 306.

[0065] At step 420, as the application of the CUCP 302 is restarting, the inactivity notification from the CUUP 306 may not be handled, and there may be no retransmission.

[0066] At step 425, the CUUP 306 may locally clean up UE context information due to no response from the CUCP 302. As a result, at step 430. the stale UE context may remain in the CUCP 302 until any new message initiates the process to address the stale UE context information.

[0067] At step 435, the CUCP 302 may come up and initialize an audit procedure.

[0068] At step 440, the CUCP 302 may transmit the active UE session audit request to the DU 304. The active UE session audit request may include the list of gNB CUCP Fl UE ID and gNB DU Fl UE ID pair.

[0069] At step 445, the CUCP 302 may receive the active UE session audit response. The active UE session audit response may include the list of gNB DU Fl UE ID and gNB CUCP Fl UE ID pair.

[0070] As seen in Figure 4B, At step 450, the CUCP 302 may transmit the active UE session audit request to the CUUP 306. The active UE session audit request may include the list of gNB CUCP El UE ID and gNB CUUP El UE ID pair.

[0071] At step 455, the CUCP 302 may receive the active UE session audit response from the CUUP 306. The active UE session audit response may include the list of gNB CUUP El UE ID and gNB CUCP El UE ID pair.

[0072] At step 460, the CUCP 302 may transmit the active UE session audit request to the MeNB 308. The active UE session audit request may include a list of gNB SgNB X2 UE ID and eNB MeNB X2 UE ID pair.

[0073] At step 465, the CUCP 302 may receive the active UE session audit response from the MeNB 308. The active UE session audit response may include a list of eNB MeNB X2 UE ID and gNB SgNB X2 UE ID pair.

[0074] At step 470, the CUCP 302 may update the locally built UE sessions within the audited UE sessions.

[0075] At step 475, the CUCP 302 may come to the operational state.

[0076] As seen in Figure 4C, at step 480, the CUCP 302 may come up and initialize the alternate procedure to clean up or retain the UE context information.

[0077] At step 485, the CUCP 302 may activate the activity monitoring timer 110.

[0078] At step 490, the CUCP 302 may monitor the signaling activity on the interfaces of the CUCP 302 upon activating the activity monitoring timer 110. If no signaling is detected within the activity' monitoring timer 110. the CUCP 302 may clean up the UE context information.

[0079] Figure 5A, Figure 5B, and Figure 5C illustrate signaling diagrams 500a, 500b, 500c for the NSA-sgNB release request scenario 505, in accordance with an embodiment of the present disclosure. The MeNB 308, which serves as the primary anchor in the NSA 5G networks, decides to release the sgNB or the associated UE context information. The NSA mode-secondary' gNodeB (SgNB) release request scenario 505 may include a missed SgNB release request from the MeNB or MgNB when the gNBCUCP subscriber handling component is restarting. The missed SgNB release request may be applied to an E- UTRA New Radio Dual Connectivity7(ENDC). The missed SgNB release request may be applied to a New Radio Dual Connectivity (NRDC).

[0080] As seen in Figure 5A, at step 510, the MeNB 308 may decide to release theSgNB or release the UE context.

[0081] At step 515, the MeNB 308 may send an X2 Application Protocol (X2AP) SgNB release request to the CUCP 302.

[0082] At step 520, as the application of the CUCP 302 is restarting, the X2AP SgNB release request may not be handled, and there may be no retransmission.

[0083] At step 525, the stale UE context may remain in the CUCP 302 until any new message initiates the process to address the stale UE context information.

[0084] At step 530, the CUCP 302 may come up and initialize an audit procedure.

[0085] At step 535, the CUCP 302 may transmit the active UE session audit request to the DU 304. The active UE session audit request may include the list of gNB CUCP Fl UE ID and gNB DU Fl UE ID pair.

[0086] At step 540, the CUCP 302 may receive the active UE session audit response. The active UE session audit response may include the list of gNB DU Fl UE ID and the gNB CUCP Fl UE ID pair.

[0087] At step 545, the CUCP 302 may transmit the active UE session audit request to the CUUP 306. The active UE session audit request may include the list of gNB CUCP El UE ID and the gNB CUUP El UE ID pair .

[0088] At step 550, the CUCP 302 may receive the active UE session audit response from the CUUP 306. The active UE session audit response may include a list of gNB CUUP El UE ID, gNB CUCP El UE ID pair) .

[0089] At step 555, the CUCP 302 may transmit the active UE session audit request to the MeNB 308. The active UE session audit request may include the list of gNB SgNB X2 UE ID and eNB MeNB X2 UE ID pair .

[0090] At step 560, the CUCP 302 may receive the active UE session audit response from the MeNB 308. The UE session audit response may include the list of eNB MeNB X2 UE ID and gNB SgNB X2 UE ID pair.

[0091] At step 565, the CUCP 302 may update the local built UE sessions within the audited UE sessions.

[0092] At step 570, the CUCP 302 may come to the operational state.

[0093] As seen in Figure 5C, at step 575, the CUCP 302 may come up and initialize the alternate procedure to clean up or retain the UE context information.

[0094] At step 580, the CUCP 302 may activate the activity monitoring timer 110.

[0095] At step 585, the CUCP 302 may monitor the signaling activity on the interfaces of the CUCP 302 upon activating the activity monitoring timer 110. If no signaling is detected within the activity' monitoring timer 110. the CUCP 302 may clean up the UE context information.

[0096] Figure 6 illustrates a flowchart depicting a method 600 for determining stored UE context information at the NF 102 based on the received UE session audit response message, according to an embodiment of the present disclosure. In an embodiment of the present disclosure, the method 600 may be performed by the NF 102, as explained concerning Figure 1. For the sake of brevity, technical implementations as explained in Figure 1, Figure 2, and Figure 3A-5C are omitted herein.

[0097] At step 602, the method 600 may include detecting the event at the subscriber handling component associated with the NF 102.

[0098] At step 604, the method 600 may include transmitting the UE session audit request message to the peer NFs 106 from the NF 102. The NF 102 may request the active UE context information associated with the corresponding active UE sessions.

[0099] At step 606, the method 600 may include receiving the UE session audit response message from the peer NFs 106 to the NF 102.

[0100] At step 608, the method 600 may include Determining whether to retain or clean up stored UE context information at the NF 102 based on the received UE session audit response message from the peer NFs 106.

[0101] The method 600 may include determining the plurality’ of UE IDs associated with the UE session audit response message received at the NF 102. Further, the method 600 may include the NF 102 may include retaining the stored UE context information upon determining that the plurality’ of UE IDs is received at the NF 102. Further, the method 600 may include cleaning up the stored UE context information in the NF 102 upon determining that the plurality of UE IDs is not received at the NF 102.

[0102] The method 600 may include updating, by the NF 102, the stored UE context information based on the received active UE context information from the peer NFs 106. The NF 102 and the peer NFs 106 may include the CUCP 302, the CUUP 306, the DU 304, and the MeNB 308.

[0103] Figure 7 illustrates a flowchart depicting a method 700 for determining stored UE context information at the NF based on monitored signaling activity', according to an embodiment of the present disclosure. In an embodiment of the present disclosure, the method 700 may be performed by the NF 102, as explained concerning Figure 1. For the sake of brevity', technical implementations as explained in Figure 1, Figure 2, and Figure 3A-5C are omitted herein.

[0104] At step 702, the method 700 may include detecting the event at the subscriber handling component associated with the NF 102.

[0105] At step 704, the method 700 may include activating the activity monitoring timer 110 associated with the NF 102 upon detecting the event.

[0106] At step 706, the method 700 may include monitoring signaling activity on the interfaces of the NF 102 upon activating the activity monitoring timer 110.

[0107] At step 708, the method 700 may include determining whether to retain or clean up the stored UE context information associated with the corresponding active UE sessions at the NF 102 based on the monitored signaling activity.

[0108] The method 700 may include determining, by the NF 102. that the signaling activity is detected within the duration of the activity monitoring timer 110 associated with the NF 102. The method 700 may include retaining, by the NF 102. the UE context information upon determining that the signaling activity is detected. Further, method 700 cleans up the stored UE context information in the NF 102 upon determining that no signaling activity is detected. The NF 102 may include the CUCP 302, the CUUP 306, the DU 304, and the MeNB 308.

[0109] The present disclosure provides the apparatus and method for restoring the user equipment session in RAN-NFs. The stale UE context information may be cleaned up proactively, ensuring that all the RAN NFs 102 remain synchronized regarding UE context information. The apparatus implements a systematic approach to clean up stale UE context information, the apparatus minimizes the risk of outdated or incorrect information being retained, leading to more efficient network resource management. The apparatus ensures that all RAN NFs remain synchronized regarding UE contexts, improving the overall coherence and reliability of session management. The apparatus addresses the issue of missed signaling messages during component restarts. The apparatus reduces unnecessary signaling traffic, optimizing the use of netw ork resources. The apparatus maintains accurate UE contextinformation and minimizes stale entries. The apparatus enhances network performance, leading to improved user experience and lower latency in service delivery. The audit request and response mechanism provide a clear framework for recovering UE context information, facilitating quicker recovery from component failures or restarts. The apparatus aligns with existing 3 GPP standards while introducing enhancements to session management, ensuring compatibility and ease of integration into current networks. The apparatus provides the network operators with greater flexibility in managing UE sessions, allowing for tailored strategies based on real-time network conditions. The apparatus effectively manages the UE context information during component restarts, the apparatus helps minimize service disruptions, maintaining continuous connectivity for end users.

[0110] Further, the present disclosure also describes non-transitory computer program products (i.e., physically embodies computer program products) or non-transitory computer- readable mediums encoded with executable instructions that store instructions. The executable instructions, when executed by one or more processors, such as the processors 210, cause the one or more processors to perform a method for determining whether to retain or clean up the stored UE context information at the NF 102 based on the received UE session audit response message from the peer NFs as described in the present disclosure, as elaborated in preceding paragraphs. Examples of computer-readable mediums include nonvolatile, hard-coded type mediums such as read-only memories (ROMs) or erasable, electrically programmable read-only memories (EEPROMs), and user-recordable type mediums such as floppy disks, hard disk drives and compact disk read-only memories (CD- ROMs) or digital versatile disks (DVDs).[OH l] [1] A method (600) comprising:detecting (602), by a Network Function (NF) (102), an event at a subscriber handling component associated with the NF (102); in response to detecting the event, transmitting (604), by the NF (102) to one or more peer NFs (106), a User Equipment (UE) session audit request message to request active UE context information associated with one or more corresponding active UE sessions; in response to the transmitted UE session audit request message, receiving (606), by the NF (102), a UE session audit response message from each of the one or more peer NFs (106); and determining, by the NF (102), whether to retain or clean up stored UE context information at the NF (102) based on the received UE session audit response message from the one or more peer NFs (106).

[0112] [2] The method (600) as described in [1] further comprising: determining a plurality of UE Identifiers (IDs) associated with the UE session audit response message received at the NF (102); and performing, by the NF (102), one of: retaining the stored UE context information upon determining that the plurality' of UE IDs is received at the NF (102); and cleaning up the stored UE context information in the NF (102) upon determining that the plurality of UE IDs is not received at the NF (102).

[0113] [3] The method as described in any of [l]-[2] further comprising: updating, by the NF (102), the stored UE context information based on the received active UE context information from the one or more peer NFs (106).

[0114] [4] The method as described in any of [l]-[3], wherein each of the NF (102) and the one or more peer NFs (106) comprise at least one of a Centralized Unit Control Plane(CUCP) (302), a Centralized Unit User Plane (CUUP) (306), a Distributed Unit (DU) (304), and a Master eNodeB (308).

[0115] [5] The method as described in any of [l]-[4], wherein the event at the subscriber handling component comprises a restart event.

[0116] [6] The method as described in any of

[0001] -[5] , wherein the audit response message comprises the active UE context information associated with the one or more corresponding active UE sessions.

[0117] [7] A method comprising: detecting, by aNetwork Function (NF) (102), an event at a subscriber handling component associated with the NF (102); activating, by the NF (102), an activity monitoring timer associated w ith the NF (102) upon detecting the event; monitoring, by the NF (102), signaling activity on one or more interfaces of the NF upon activating the activity monitoring timer; and determining, by the NF (102), whether to retain or clean up stored User Equipment (UE) context information associated with one or more corresponding active UE sessions at the NF (102) based on the monitored signaling activity.

[0118] [8] The method as described in [7], further comprising: determining, by the NF (102), that the signaling activity is detected within duration of the activity monitoring timer associated with the NF (102); and performing, by the NF (102), one of: retaining the UE context information upon determining that the signaling activity is detected; and cleaning up the stored UE context information in the NF (102) upon determining that no signaling activity is detected.

[0119] [9] The method as described in any of [7]-[8], wherein each of the NF (102) comprises at least one of a Centralized Unit Control Plane (CUCP) (302), a Centralized Unit User Plane (CUUP) (306), a Distributed Unit (DU) (304), and a Master eNodeB (308).

[0120]

[0010] The method as described in any of [7] -[9], wherein the event at the subscriber handling component comprises a restart event.

[0121]

[0011] An apparatus (100) configured to:detect an event at a subscriber handling component associated with a Network Function (NF) (102); in response to detecting the event, transmit a User Equipment (UE) session audit request message to one or more peer NFs (106) to request active (UE context information associated with one or more corresponding active UE sessions; in response to the transmitted UE session audit request message, receive a UE session audit response message from each of the one or more peer NFs (106); and determine whether to retain or clean up stored UE context information at the NF (102) based on the received UE session audit response message from the one or more peer NFs (106).

[0122]

[0012] The apparatus (100) as described in

[0011] , wherein the apparatus (100) is further configured to: determine a plurality of UE Identifiers (IDs) associated with the UE session audit response message received at the NF (102); and perform one of: retain the stored UE context information upon determining that the plurality of UE IDs is received at the NF (102); and clean up the stored UE context information in the NF (102) upon determining that the plurality of UE IDs is not received at the NF (102).

[0123]

[0013] The apparatus (100) as described in any of

[0011] -

[0012] , wherein the apparatus (100) is further configured to: update the stored UE context information based on the received active UE context information from the one or more peer NFs (106).

[0124]

[0014] The apparatus (100) as described in any of

[0011] -

[0013] , wherein each of theNF (102) and the one or more peer NFs (106) comprise at least one of a Centralized UnitControl Plane (CUCP) (302), a Centralized Unit User Plane (CUUP) (306), a DistributedUnit (DU) (304), and a Master eNodeB (308).

[0125]

[0015] The apparatus (100) as described in any of

[0011] -

[0014] , wherein the event at the subscriber handling component comprises a restart event.

[0126]

[0016] The apparatus (100) as described in any of

[0011] -

[0015] , wherein the audit response message comprises the active UE context information associated with the one or more corresponding active UE sessions.

[0127]

[0017] An apparatus (100) configured to: detect a restart event at a subscriber handling component associated with a Network Function (NF) (102); activate an activity monitoring timer associated with the NF (102) upon detecting the restart event; monitor signaling activity on one or more interfaces of the NF (102) upon activating the activity monitoring timer; and determine whether to retain or clean up stored User Equipment (UE) context information at the NF (102) based on the monitored signaling activity7.

[0128]

[0018] The apparatus (100) as described in

[0017] , wherein the apparatus (100) is further configured to: determine that the signaling activity is detected within duration of the activity monitoring timer; and perform one of: retain the stored UE context information upon determining that the signaling activity is detected; and clean up the stored UE context information in the NF (102) upon determining that no signaling activity is detected.

[0129]

[0019] The apparatus (100) as described in any of

[0017] -

[0018] , wherein the NF(102) comprises at least one of a Centralized Unit Control Plane (CUCP) (302), a Centralized Unit User Plane (CUUP) (306), a Distributed Unit (DU) (304), and a Master eNodeB (308).

[0130]

[0020] A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by a Network Function (NF) (102), the NF (102) comprising one or more processors (202), cause the one or more processors (202) to:detect a restart event at a subscriber handling component associated with the NF(102); in response to detecting the restart event, transmit a UE session audit request message to one or more peer NFs (106) to request active User Equipment (UE) context information associated with one or more corresponding active UE sessions; in response to the transmitted UE session audit request message, receive a UE session audit response message from each of the one or more peer NFs (106); and determine whether to retain or clean up stored UE context information at the NF (102) based on the received UE session audit response message from the one or more peer NFs (106).

[0131] The embodiments disclosed herein can be implemented through at least one software program running on at least one hardware device and performing network management functions to control the elements. The elements can be at least one of a hardware device, or a combination of hardware devices and software modules.

[0132] It is understood that terms including "unit" or “module” at the end may refer to the unit for processing at least one function or operation and may be implemented in hardware, software, or a combination of hardware and software.

[0133] While specific language has been used to describe the disclosure, any limitations arising on account of the same are not intended. As would be apparent to a person in the art, various working modifications may be made to the method in order to implement the inventive concept as taught herein.

[0134] The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to anotherembodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein.

[0135] Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

[0136] Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.

[0137] 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 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 at least one embodiment, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the embodiments as described herein.

Claims

We Claim:

1. A method comprising: detecting, by a Network Function (NF), an event at a subscriber handling component associated with the NF; in response to detecting the event, transmitting, by the NF to one or more peer NFs, a User Equipment (UE) session audit request message to request active UE context information associated with one or more corresponding active UE sessions; in response to the transmitted UE session audit request message, receiving, by the NF, a UE session audit response message from each of the one or more peer NFs; and determining, by the NF, whether to retain or clean up stored UE context information at the NF based on the received UE session audit response message from the one or more peer NFs.

2. The method as claimed in claim 1 further comprising: determining a plurality of UE Identifiers (IDs) associated with the UE session audit response message received at the NF; and performing, by the NF, one of: retaining the stored UE context information upon determining that the plurality' of UE IDs is received at the NF; and cleaning up the stored UE context information in the NF upon determining that the plurality of UE IDs is not received at the NF.

3. The method as claimed in claim 1 further comprising: updating, by the NF, the stored UE context information based on the received active UE context information from the one or more peer NFs.

4. The method as claimed in claim 1, wherein each of the NF and the one or more peer NFs comprise at least one of a Centralized Unit Control Plane (CUCP), a Centralized Unit User Plane (CUUP), a Distributed Unit (DU), and a Master eNodeB.

5. The method as claimed in claim 1, wherein the event at the subscriber handling component comprises a restart event.

6. The method as claimed in claim 1, wherein the audit response message comprises the active UE context information associated with the one or more corresponding active UE sessions.

7. A method comprising: detecting, by a Network Function (NF), an event at a subscriber handling component associated with the NF; activating, by the NF, an activity monitoring timer associated with the NF upon detecting the event; monitoring, by the NF, signaling activity' on one or more interfaces of the NF upon activating the activity monitoring timer; and determining, by the NF, whether to retain or clean up stored User Equipment (UE) context information associated with one or more corresponding active UE sessions at the NF based on the monitored signaling activity7.

8. The method as claimed in claim 7. further comprising: determining, by the NF, that the signaling activity is detected within duration of the activity monitoring timer associated with the NF; and performing, by the NF, one of: retaining the UE context information upon determining that the signaling activity is detected; and cleaning up the stored UE context information in the NF upon determining that no signaling activity is detected.

9. The method as claimed in claim 7, wherein each of the NF comprises at least one of a Centralized Unit Control Plane (CUCP), a Centralized Unit User Plane (CUUP), a Distributed Unit (DU), and a Master eNodeB.

10. The method as claimed in claim 7, wherein the event at the subscriber handling component comprises a restart event.

11. An apparatus configured to: detect an event at a subscriber handling component associated with a Network Function (NF); in response to detecting the event, transmit a User Equipment (UE) session audit request message to one or more peer NFs to request active (UE context information associated with one or more corresponding active UE sessions; in response to the transmitted UE session audit request message, receive a UE session audit response message from each of the one or more peer NFs; and determine whether to retain or clean up stored UE context information at the NF based on the received UE session audit response message from the one or more peer NFs.

12. The apparatus as claimed in claim 11, wherein the apparatus is further configured to: determine a plurality of UE Identifiers (IDs) associated with the UE session audit response message received at the NF; and perform one of: retain the stored UE context information upon determining that the plurality of UE IDs is received at the NF; and clean up the stored UE context information in the NF upon determining that the plurality of UE IDs is not received at the NF.

13. The apparatus as claimed in claim 11, wherein the apparatus is further configured to: update the stored UE context information based on the received active UE context information from the one or more peer NFs.

14. The apparatus as claimed in claim 1 1 , wherein each of the NF and the one or more peer NFs comprise at least one of a Centralized Unit Control Plane (CUCP), a Centralized Unit User Plane (CUUP), a Distributed Unit (DU), and a Master eNodeB.

15. The apparatus as claimed in claim 11, wherein the event at the subscriber handling component comprises a restart event.

16. The apparatus as claimed in claim 11, wherein the audit response message comprises the active UE context information associated with the one or more corresponding active UE sessions.

17. An apparatus configured to: detect a restart event at a subscriber handling component associated with a Network Function (NF); activate an activity monitoring timer associated with the NF upon detecting the restart event; monitor signaling activity on one or more interfaces of the NF upon activating the activity monitoring timer; and determine whether to retain or clean up stored User Equipment (UE) context information at the NF based on the monitored signaling activity.

18. The apparatus as claimed in claim 17, wherein the apparatus is further configured to: determine that the signaling activity is detected within duration of the activity monitoring timer; and perform one of: retain the stored UE context information upon determining that the signaling activity is detected; and clean up the stored UE context information in the NF upon determining that no signaling activity is detected.

19. The apparatus as claimed in claim 17, wherein the NF comprises at least one of a Centralized Unit Control Plane (CUCP), a Centralized Unit User Plane (CUUP), a Distributed Unit (DU), and a Master eNodeB.

20. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by a Network Function (NF), the NF comprising one or more processors, cause the one or more processors to:detect a restart event at a subscriber handling component associated with theNF; in response to detecting the restart event, transmit a UE session audit request message to one or more peer NFs to request active User Equipment (UE) context information associated with one or more corresponding active UE sessions; in response to the transmitted UE session audit request message, receive a UE session audit response message from each of the one or more peer NFs; and determine whether to retain or clean up stored UE context information at the NF based on the received UE session audit response message from the one or more peer NFs.

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