FORM 2
THE PATENTS ACT, 1970 (39 OF 1970)
& THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
“METHOD AND SYSTEM FOR SERVICE FALLBACK IN 5G CORE
NETWORK”
We, Jio Platforms Limited, an Indian National, of Office - 101, Saffron, Nr. Centre Point, Panchwati 5 Rasta, Ambawadi, Ahmedabad - 380006, Gujarat, India.
The following specification particularly describes the invention and the manner in which it is to be performed.

METHOD AND SYSTEM FOR SERVICE FALLBACK IN 5G CORE NETWORK
FIELD OF THE DISCLOSURE
[001] The present disclosure relates generally to the field of wireless communication systems. In particular, the present disclosure relates to service fallback. More particularly, the present disclosure relates to method and system for service fallback ensuring uninterrupted service continuity in 5G core network.
BACKGROUND
[002] The following description of related art is intended to provide background information pertaining to the field of the disclosure. This section may include certain aspects of the art that may be related to various features of the present disclosure. However, it should be appreciated that this section be used only to enhance the understanding of the reader with respect to the present disclosure, and not as admissions of prior art.
[003] Wireless communication technology has rapidly evolved over the past few decades, with each generation bringing significant improvements and advancements. The first generation of wireless communication technology was based on analog technology and offered only voice services. However, with the advent of second-generation (2G) technology, digital communication and data services became possible, and text messaging was introduced. The third- generation (3G) technology marked the introduction of high¬speed internet access, mobile video calling, and location-based services. The fourth generation (4G) technology revolutionized wireless communication with faster data speeds, better network coverage, and improved security. Currently, the fifth generation (5G) technology is being deployed, promising even faster data speeds, low latency, and the ability to connect multiple devices simultaneously. With each generation, wireless communication technology has become more advanced, sophisticated, and capable of delivering more services to its users.
[004] One of the main problems with existing technology prior to this disclosure is that users (UE end) may need to manually switch their devices to the 4G network during an

outage in the 5GC network. The outage refers to a period during which a telecommunication network or service is unavailable or not functioning properly. This issue may arise due to various reasons such as technical issues, equipment failure, maintenance activities, or external factors like severe weather conditions or natural disasters. During the outage, the users may experience disruptions in their ability to make calls, send messages, access the internet, or utilize other network-dependent services. Further, the issue of manual intervention during network disruptions posed several drawbacks and inconveniences. Firstly, it introduced a delay in the restoration of connectivity for users, as they were required to actively switch their devices to an alternative network mode. This delay could be especially problematic in critical situations where swift access to communication and data services is imperative. Additionally, the manual switching process added complexity and potential confusion for users, particularly those less familiar with technical aspects of network management. This complexity could lead to errors in network configuration, further exacerbating downtime and connectivity issues. This could lead to loss of service, inconvenience, and a poor user experience. Prior systems may not have a method for dynamically adjusting the type of network used based on outages in specific nodes of the home network or visited network.
[005] In addition to this, a Home Subscriber Server (HSS) and a User Data Management (UDM) are core elements within telecommunications networks, responsible for managing subscriber data and facilitating seamless connectivity for mobile users. In existing systems, there is a potential limitation regarding the Home Subscriber Server/User Data Management (HSS/UDM) component's ability to include various UE Usage Type (UUT) values in the Update Location Answer (ULA). These UUT values represent different types of UE Usage Type values. The ULA message is a response from the HSS/UDM following a request to update a user's location within the network, indicating where the user's subscription is located (Home PLMN) or the network they are currently connected to (Visited PLMN). The issue arises from the fact that the HSS/UDM may not differentiate between these two scenarios when sending UUT values. This means that the ULA message might not accurately reflect the type of user traffic being experienced based on whether the user is in their home network or roaming in another network. This lack of distinction could potentially impact network management and quality of service (QoS) provisioning, as different types of traffic may require varying levels of resources or priority handling.

[006] In previous arts, when a user device attempts to register with the network through an Access and Mobility Management Function (AMF), the AMF sends a request to the HSS/UDM for subscriber information. In scenarios where the HSS/UDM does not recognize the subscriber's 5G subscription status, it does not explicitly indicate this "Unknown 5GS Subscription" status in its response to the AMF. Due to this reason the HSS/UDM might not send an "Unknown 5GS Subscription" in an AMF registration response to avoid 5GC attachment. The existing systems thus do not contain a mechanism to prevent further attempts to connect to the 5GC network when an outage is detected. Furthermore, prior systems do not have an efficient mechanism for detecting network failure through KPI degradation, leading to delays in implementing fallback procedures.
[007] Thus, there exists an imperative need in the art to provide a method and system for service fallback ensuring uninterrupted service continuity in 5G core network.
SUMMARY OF THE DISCLOSURE
[008] This section is provided to introduce certain aspects of the present disclosure in a simplified form that are further described below in the detailed description. This summary is not intended to identify the key features or the scope of the claimed subject matter.
[009] An aspect of the present disclosure may relate to a method for service fallback in 5G core (5GC) network. The method comprises monitoring, by a monitoring unit, one or more key performance indicators (KPIs) to detect an outage in the 5G5GC network. The method further comprises triggering, by a trigger unit, a first application programming interface (API) for an affected home public land mobile network (HPLMN) or a visited PLMN (VPLMN) based on detection of the outage. Further, the method encompasses sending, by a transmitter unit via a home subscriber server (HSS) or a user data management (UDM), an update UE Usage Type (UUT) value in an Update Location Answer (ULA) based on the affected HPLMN or VPLMN. Furthermore, the method encompasses sending, by the transmitter unit via the HSS or UDM, a first message in an access and mobility management function (AMF) registration response based on the affected HPLMN or VPLMN. Thereafter, the method encompasses selecting, by a

processing unit via a mobility management entity (MME), any or a combination of a 4G packet gateway (PGW), a session management function (SMF) based on the updated UUT value.
[010] In an exemplary aspect of the present disclosure, the transmitter unit sends, via the AMF, an "N1 mode not allowed" code in a non-access stratum (NAS) to prevent further attempts to connect to the 5GC network.
[011] In an exemplary aspect of the present disclosure, the one or more KPIs comprises at least one of a latency, a throughput, a packet loss rate, and a signal strength.
[012] In an exemplary aspect of the present disclosure, the triggering of the first application programming interface (API) is performed automatically based on a predefined network outage threshold.
[013] In an exemplary aspect of the present disclosure, the first message is an “Unknown 5GS Subscription” message.
[014] In an exemplary aspect of the present disclosure, the processing unit further provides an error code indicating the reason for the subscription status as “unknown.”
[015] In an exemplary aspect of the present disclosure, the selecting of at least one of the PGW and the SMF is based on an analysis of a type of data traffic specified by the updated UUT value.
[016] In an exemplary aspect of the present disclosure, the processing unit defines a time period for a user equipment (UE) to attempt to connect to the network, wherein the UE attempts to reconnect to the network on expiration of the defined time period.
[017] In an exemplary aspect of the present disclosure, the first API corresponds to a UUT API.

[018] Another aspect of the present disclosure may relate to a system for service fallback in 5G core (5GC) network. The system comprises a monitoring unit configured to monitor one or more key performance indicators (KPIs) to detect an outage in a 5GCore (5GC) network. Further, the system comprises of a trigger unit that is connected to the monitoring unit and is configured for triggering a first application programming interface (API) for an affected home public land mobile network (HPLMN) or visited PLMN (VPLMN) based on detection of the outage. Furthermore, the system comprises a transmitter unit that is connected to the trigger unit and is configured for sending, via a home subscriber server (HSS) or a user data management (UDM), an updated UUT value in an Update Location Answer (ULA) based on the affected HPLMN or VPLMN. Further, the transmitter unit is configured for sending, via the HSS or UDM, a first message in an access and mobility management function (AMF) registration response based on the affected HPLMN or VPLMN. The system also comprises a processing unit that is connected to the transmitter unit and is configured to selecting, via a mobility management entity (MME), any or a combination of a 4G packet gateway (PGW), and a session management function (SMF) based on the updated UUT value.
[019] Further, an aspect of the present disclosure relates to a user equipment (UE) for service fallback in 5G core (5GC) network, the UE comprising: a memory; and a process connected to the memory, wherein the processor is configured to: transmit, to the system, a request to monitor one or more key performance indicators (KPIs) to detect an outage in the 5GC network, and receive from the system, a response associated with the request. wherein the response is received based on: monitoring, by the system, the one or more key performance indicators (KPIs) to detect the outage in the 5GC network, triggering, by the system, a first application programming interface (API) for one of an affected home public land mobile network (HPLMN) and a visited public land mobile network (VPLMN) based on detection of the outage, sending, by the system, an updated UE Usage Type (UUT) value in an update location answer (ULA) based on the affected one of the HPLMN and VPLMN, sending, by the system, a first message in an access and mobility management function (AMF) registration response based on the one of affected HPLMN and VPLMN, and selecting, by the system, at least one of a 4G packet gateway (PGW) and a session management function (SMF) based on the updated UUT value.

[020] Further, an aspect of the present disclosure relates to a non-transitory computer readable storage medium storing instruction for service fallback in 5G core (5GC) network, the instructions include executable code which, when executed by a one or more units of a system, causes: a monitoring unit to monitor one or more key performance indicators (KPIs) to detect an outage in the 5GC network, a trigger unit to trigger a first application programming interface (API) for one of an affected home public land mobile network (HPLMN) and a visited public land mobile network (VPLMN) based on detection of the outage, a transmitter unit to send via one of a home subscriber server (HSS) and a user data management (UDM) unit, an updated UE Usage Type (UUT) value in an update location answer (ULA) based on the affected one of the HPLMN and VPLMN, the transmitter unit to send via one of the HSS and the UDM unit, a first message in an access and mobility management function (AMF) registration response based on the one of affected HPLMN and VPLMN, and a processing unit to select via a mobility management entity (MME), at least one of a 4G packet gateway (PGW) and a session management function (SMF) based on the updated UUT value.
OBJECTS OF THE DISCLOSURE
[021] Some of the objects of the present disclosure, which at least one embodiment disclosed herein satisfies are listed herein below.
[022] It is an object of the present disclosure to provide a method and system for service fallback ensuring uninterrupted service continuity in 5G core network.
[023] It is another object of the present disclosure to provide a method and system for service fallback ensuring uninterrupted service continuity in 5G core network that ensures that when there's an outage in the 5GC network, users automatically fall back to the existing 4G network without needing any manual intervention.
[024] It is another object of the present disclosure to provide a method and system for service fallback ensuring uninterrupted service continuity in 5G core network that introduces mechanisms for detecting a network failure through one or more key performance indicators (KPIs) degradation, enabling timely fallback procedures.

[025] It is another object of the present disclosure to provide a method and system for service fallback ensuring uninterrupted service continuity in 5G core network that aims to provide a more dynamic network adaptation, allowing home subscriber server (HSS) or a user data management (UDM) to send different UE Usage Type (UUT) values based on whether the user is on a home network (HPLMN) or a visited network (VPLMN).
[026] It is another object of the present disclosure to provide a method and system for service fallback ensuring uninterrupted service continuity in 5G core network that sends an "Unknown 5GS Subscription" in the AMF registration response based on the HPLMN or VPLMN to prevent further attempts to attach to the 5GC network in case of an outage.
[027] It is another object of the present disclosure to provide a method and system for service fallback ensuring uninterrupted service continuity in 5G core network that facilitates the automatic selection of the appropriate Packet Gateway (PGW) by the Mobility Management Entity (MME) based on the updated UUT value, ensuring uninterrupted services.
[028] It is yet another object of the present disclosure to provide a method and system for service fallback ensuring uninterrupted service continuity in 5G core network that improve the user experience by providing seamless service continuity and reliability, despite network outages or issues in the 5GC network.
BRIEF DESCRIPTION OF DRAWINGS
[029] The accompanying drawings, which are incorporated herein, and constitute a part of this disclosure, illustrate exemplary embodiments of the disclosed methods and systems in which like reference numerals refer to the same parts throughout the different drawings. Components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Some drawings may indicate the components using block diagrams and may not represent the internal circuitry of each component. It will be appreciated by those skilled in the art that disclosure of such

drawings includes disclosure of electrical components, electronic components or circuitry commonly used to implement such components.
[030] FIG. 1A illustrates an exemplary block diagram representation of 5th generation core (5GC) network architecture.
[031] FIG. 1B illustrates an exemplary block diagram of a system [100] for service fallback in 5G core network, in accordance with exemplary embodiments of the present disclosure.
[032] FIG. 2 illustrates an exemplary network architecture diagram [200] with implementation of system and method for service fallback in 5Gcore network in accordance with exemplary embodiments of the present disclosure.
[033] FIG. 3 illustrates an exemplary method flow diagram indicating the process [300] for service fallback in 5Gcore network, in accordance with exemplary embodiments of the present disclosure.
[034] FIG. 4 illustrates an exemplary block diagram of a computing device upon which an embodiment of the present disclosure may be implemented.
[035] The foregoing shall be more apparent from the following more detailed description of the disclosure.
DETAILED DESCRIPTION
[036] In the following description, for the purposes of explanation, various specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent, however, that embodiments of the present disclosure may be practiced without these specific details. Several features described hereafter can each be used independently of one another or with any combination of other features. An individual feature may not address any of the problems discussed above or might address only some of the problems discussed above. Some of the problems discussed above might

not be fully addressed by any of the features described herein. Example embodiments of the present disclosure are described below, as illustrated in various drawings in which like reference numerals refer to the same parts throughout the different drawings.
[037] The ensuing description provides exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the ensuing description of the exemplary embodiments will provide those skilled in the art with an enabling description for implementing an exemplary embodiment. It should be understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the disclosure as set forth.
[038] Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, circuits, systems, networks, processes, and other components may be shown as components in block diagram form in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments.
[039] Also, it is noted that individual embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations may be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged. A process is terminated when its operations are completed but could have additional steps not included in a figure.
[040] The word “exemplary” and/or “demonstrative” is used herein to mean serving as an example, instance, or illustration. For the avoidance of doubt, the subject matter disclosed herein is not limited by such examples. In addition, any aspect or design described herein as “exemplary” and/or “demonstrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs, nor is it meant to preclude equivalent exemplary structures and techniques known to those of ordinary skill in the art.

Furthermore, to the extent that the terms “includes,” “has,” “contains,” and other similar words are used in either the detailed description or the claims, such terms are intended to be inclusive—in a manner similar to the term “comprising” as an open transition word— without precluding any additional or other elements. 5
[041] As used herein, a “processing unit” or “processor” or “operating processor” includes one or more processors, wherein processor refers to any logic circuitry for processing instructions. A processor may be a general-purpose processor, a special purpose processor, a conventional processor, a digital signal processor, a plurality of
10 microprocessors, one or more microprocessors in association with a (Digital Signal
Processing) DSP core, a controller, a microcontroller, Application Specific Integrated Circuits, Field Programmable Gate Array circuits, any other type of integrated circuits, etc. The processor may perform signal coding data processing, input/output processing, and/or any other functionality that enables the working of the system according to the present
15 disclosure. More specifically, the processor or processing unit is a hardware processor.
[042] As used herein, “mobile device”, “a user equipment”, “a user device”, “a smart-user-device”, “a smart-device”, “an electronic device”, “a mobile device”, “a handheld device”, “a wireless communication device”, “a mobile communication device”, “a
20 communication device” may be any electrical, electronic and/or computing device or
equipment, capable of implementing the features of the present disclosure. The user equipment/device may include, but is not limited to, a mobile phone, smart phone, laptop, a general-purpose computer, desktop, personal digital assistant, tablet computer, wearable device or any other computing device which is capable of implementing the features of the
25 present disclosure. Also, the user device may contain at least one input means configured
to receive an input from at least one of a transceiver unit, a processing unit, a storage unit, and any other such unit(s) which are required to implement the features of the present disclosure. The user equipment may be capable of operating on any radio access technology including but not limited to IP-enabled communication, Zig Bee, Bluetooth, Bluetooth Low
30 Energy, Near Field Communication, Z-Wave, Wi-Fi, Wi-Fi direct, etc. For instance, the
user equipment may include, but not limited to, a mobile phone, smartphone, virtual reality (VR) devices, augmented reality (AR) devices, laptop, a general-purpose computer, desktop, personal digital assistant, tablet computer, mainframe computer, or any other
11

device as may be obvious to a person skilled in the art for implementation of the features of the present disclosure.
[043] As used herein, “storage unit” or “memory unit” refers to a machine or computer-
5 readable medium including any mechanism for storing information in a form readable by
a computer or similar machine. For example, a computer-readable medium includes read¬
only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media,
optical storage media, flash memory devices or other types of machine-accessible storage
media. The storage unit stores at least the data that may be required by one or more units
10 of the system to perform their respective functions.
[044] As used herein “interface” or “user interface refers to a shared boundary across
which two or more separate components of a system exchange information or data. The
interface may also be referred to a set of rules or protocols that define communication or
15 interaction of one or more modules or one or more units with each other, which also
includes the methods, functions, or procedures that may be called.
[045] One or more modules, units, components used herein may be software modules configured via hardware modules/processors, or hardware processors, the processors being
20 a general-purpose processor, a special purpose processor, a conventional processor, a
digital signal processor, a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits, Field Programmable Gate Array circuits, any other type of integrated circuits, etc.
25
[046] It should be noted that the terms "mobile device", "user equipment", "user device", “communication device”, “device” and similar terms are used interchangeably for the purpose of describing the disclosure. These terms are not intended to limit the scope of the disclosure or imply any specific functionality or limitations on the described embodiments.
30 The use of these terms is solely for convenience and clarity of description. The disclosure
is not limited to any particular type of device or equipment, and it should be understood that other equivalent terms or variations thereof may be used interchangeably without departing from the scope of the disclosure as defined herein.
12

[047] As used herein, an “electronic device”, or “portable electronic device”, or “user
device” or “communication device” or “user equipment” or “device” refers to any
electrical, electronic, electromechanical and computing device. The user device is capable
5 of receiving and/or transmitting one or parameters, performing function/s, communicating
with other user devices and/or systems, and transmitting data to the other user devices and/or the systems. The user equipment may have a processor, a display, a memory, a battery and an input-means such as a hard keypad and/or a soft keypad.
10 [048] As portable electronic devices and wireless technologies continue to improve and
grow in popularity, the advancing wireless technologies for data transfer are also expected to evolve and replace the older generations of technologies. In the field of wireless data communications, the dynamic advancement of various generations of cellular technology are also seen. The development, in this respect, has been incremental in the order of second
15 generation (2G), third generation (3G), fourth generation (4G), and now fifth generation
(5G), and more such generations are expected to continue in the forthcoming time.
[049] Radio Access Technology (RAT) refers to the technology used by mobile devices/ user equipment (UE) to connect to a cellular network. It refers to the specific protocol and
20 standards that govern the way devices communicate with base stations, which are
responsible for providing the wireless connection. Further, each RAT has its own set of protocols and standards for communication, which define the frequency bands, modulation techniques, and other parameters used for transmitting and receiving data. Examples of RATs include GSM (Global System for Mobile Communications), CDMA (Code Division
25 Multiple Access), UMTS (Universal Mobile Telecommunications System), LTE (Long-
Term Evolution), and 5G. The choice of RAT depends on a variety of factors, including the network infrastructure, the available spectrum, and the mobile device's/device's capabilities. Mobile devices often support multiple RATs, allowing them to connect to different types of networks and provide optimal performance based on the available
30 network resources.
[050] “gNodeB" (gNB) refers to the base station component in 5G (fifth generation) wireless networks. It is an essential element of the Radio Access Network (RAN)
13

responsible for transmitting and receiving wireless signals to and from user devices, such
as smartphones, tablets, and Internet of Things (IoT) devices. Like in 5G networks, there
are similar components in other generations of wireless networks. Here are a few examples:
Base Transceiver Station (BTS): In 2G (second-generation) networks, the BTS serves as
5 the base station responsible for transmitting and receiving wireless signals. It connects
mobile devices to the cellular network infrastructure. NodeB: In 3G (third generation) networks, the NodeB is the base station component that enables wireless communication. It facilitates the transmission and reception of signals between user devices and the network. eNodeB: In 4G (fourth generation) LTE (Long-Term Evolution) networks, the
10 eNodeB serves as the base station. It supports high-speed data transmission, low latency,
and improved network capacity. Access Point (AP): In Wi-Fi networks, an access point functions as a central hub that enables wireless devices to connect to a wired network. It provides a wireless interface for devices to access the network and facilitates communication between them. The examples illustrate the base station components in
15 different generations of wireless networks, such as BTS in 2G, NodeB in 3G, eNodeB in
4G LTE, and gNodeB in 5G. Each component plays a crucial role in facilitating wireless connectivity and communication between user devices and the network infrastructure.
[051] UE Usage Type (UUT) refers to a classification or categorization of network traffic
20 based on one or more characteristics, such as the type of data being transmitted, the
applications generating the traffic, or the services being utilized. Further the UUT classification helps in managing one or more network resources efficiently, implementing one or more quality of service (QoS) policies, and optimizing traffic routing and prioritization. 25
[052] Additionally, Update Location Answer (ULA) is part of a network procedure where the network updates the location of a mobile device (i.e. UE - User Equipment) in the network.
30 [053] As discussed in the background section, one of the main problems with the existing
technology prior to this disclosure is that users (UE end) may need to manually switch their devices to the 4G network during an outage in the 5GC network. This could lead to loss of service, inconvenience, and a poor user experience. Prior systems do not have a method for
14

dynamically adjusting the type of network used based on outages in specific nodes of the
home network or visited network. The existing systems also do not contain a mechanism
to prevent further attempts to connect to the 5GC network when an outage is detected.
Further, prior systems do not have a mechanism for detecting a network failure through
5 KPI degradation, thus leading to delays in implementing fallback procedures.
[054] To address these limitations, an improved methodology is required that addresses these challenges by introducing a method and system that effectively manages service transitions and provides uninterrupted connectivity during fallback scenarios.
10
[055] The present disclosure relates generally to the field of wireless communication systems. In particular, the present disclosure relates to seamless service fallback. More particularly, the present disclosure relates to method and system for seamless service fallback ensuring uninterrupted service continuity in5G core network.
15
[056] The present disclosure encompasses monitoring of one or more key performance indicators (KPIs) for detecting an outage in a 5G core network and upon detection of the outage a UE Usage Type (UUT) API is triggered for an affected Home Public Land Mobile Network (HPLMN) or Visited PLMN (VPLMN). Further an updated UUT value is send in
20 an Update Location Answer (ULA) based on the HPLMN or VPLMN affected by the
outage through a Home Subscriber Server/User Data Management (HSS/UDM). Thereafter, the HSS/UDM sends an "Unknown 5GS Subscription" in an Access and Mobility Management Function (AMF) registration response based on the HPLMN or VPLMN that are affected by the outage. Further the method comprises selection of a 4G
25 Packet Gateway (PGW) or a combination of Session Management Function and PGW
(SMF+PGW) based on the updated UUT value. Additionally, an "N1 mode not allowed" is transmitted in a Non-Access Stratum (NAS) code to prevent further attempts to connect to the 5GC network. Additionally, the above steps are performed without the need for user intervention, enabling users to consume services on the 4G network during an outage in the
30 5GC network.
[057] Hereinafter, exemplary embodiments of the present disclosure will be described with reference to the accompanying drawings.
15

[058] FIG. 1A illustrates an exemplary block diagram representation of 5th generation
core (5GC) network architecture. As shown in FIG. 1A, the 5GC network architecture [101]
includes a user equipment (UE) [101a], a radio access network (RAN) [101b], a 5G Core
5 Network and a Data Network [101p]. The 5G Core Network includes an access and
mobility management function (AMF) [101c], a Session Management Function (SMF)
[101d], a Service Communication Proxy (SCP) [101e], an Authentication Server Function
(AUSF) [101f], a Network Slice Specific Authentication and Authorization Function
(NSSAAF) [101g], a Network Slice Selection Function (NSSF) [101h], a Network
10 Exposure Function (NEF) [101i], a Network Repository Function (NRF) [101j], a Policy
Control Function (PCF) [101k], a Unified Data Management (UDM) [101l], an application function (AF) [101m], a User Plane Function (UPF) [101n].
[059] The User Equipment (UE) [101a] interfaces with the network via the Radio Access
15 Network (RAN) [101b]. The RAN [101b] in the 5G architecture is also called as New Radio
or nG-RAN, and these terms may be interchangeably used herein. Radio Access Network
(RAN) [101b] is the part of a mobile telecommunications system that connects user
equipment (UE) [101a] to the core network (CN) and provides access to different types of
networks (e.g., 5G, LTE). It consists of radio base stations and the radio access technologies
20 that enable wireless communication.
[060] The Access and Mobility Management Function (AMF) [101c] manages connectivity and mobility. When the UE [101a] is active, i.e. it is interacting with the 5G network, e.g., by using data/ call functionalities, the AMF [101c] knows and maintains the
25 location of the UE [101a] within the network. The AMF [101c] is configured to maintain
the tracking area or registration area of the UE [101a], in case the UE is inactive. The AMF [101c]is configured to communicate with other network functions/ elements such as the Session Management Function (SMF) [101d], etc. to ensure that the UE [101a] is allowed and is able to avail the services by the network.
30
[061] Particularly, the Access and Mobility Management Function (AMF) [101c] is a 5G core network function responsible for managing access and mobility aspects, such as UE
16

registration, connection, and reachability etc. It also handles mobility management procedures like handovers and paging.
[062] The Session Management Function (SMF) [101d] is a 5G core network function
5 responsible for managing session-related aspects, such as establishing, modifying, and
releasing sessions. It coordinates with the User Plane Function (UPF) for data forwarding and handles IP address allocation and QoS enforcement.
[063] The Service Communication Proxy (SCP) [101e] is a network function in the 5G
10 core that facilitates communication between other network functions by providing a secure
and efficient messaging service. It acts as a mediator for service-based interfaces.
[064] The Authentication Server Function (AUSF) [101f] is a network function in the
5G core responsible for authenticating UEs during registration and providing security
15 services. It generates and verifies authentication vectors and tokens.
[065] The Network Slice Specific Authentication and Authorization Function
(NSSAAF) [101g] is a network function that provides authentication and authorization
services specific to network slices. It ensures that UEs can access only the slices for which
20 they are authorized.
[066] The Network Slice Selection Function (NSSF) [101h] is a network function responsible for selecting the appropriate network slice for a UE based on factors such as subscription, requested services, and network policies. 25
[067] The Network Exposure Function (NEF) [101i] is a network function that exposes capabilities and services of the 5G network to external applications, enabling integration with third-party services and applications.
30 [068] The Network Repository Function (NRF) [101j] is a network function that acts as
a central repository for information about available network functions and services. It facilitates the discovery and dynamic registration of network functions.
17

[069] The Policy Control Function (PCF) [101k] is a network function responsible for policy control decisions, such as QoS, charging, and access control, based on subscriber information and network policies.
5 [070] The Unified Data Management (UDM) [101l] is a network function that centralizes
the management of subscriber data, including authentication, authorization, and subscription information.
[071] The Application Function (AF) [101m] is a network function that represents
10 external applications interfacing with the 5G core network to access network capabilities
and services.
[072] The User Plane Function (UPF) [101n] is a network function responsible for handling user data traffic, including packet routing, forwarding, and QoS enforcement. 15
[073] The Data Network (DN) [101p] represents external networks or services that users connect to through the mobile network, such as the internet or enterprise networks.
[074] FIG.1B illustrates an exemplary block diagram of a system [100] for service
20 fallback in 5G core (5GC) network, in accordance with exemplary embodiments of the
present disclosure. The present disclosure discloses that the system [100] comprises at least
a monitoring unit [102], a trigger unit [104], a transmitter unit [106], and a processing unit
[108]. The system [100] components may be present at a same location or may be
distributed at different locations. Also, a component of the system [100] may comprise one
25 or more sub-components which may be centralized or distributed at various locations and
may together be referred to as that particular component. For ease of reference, FIG. 1B
depicts units/components of the system [100] by way of representation of blocks and FIG.
1B do not represent the internal circuitry or connections of each component/unit of the
system [100]. It will be appreciated by those skilled in the art that disclosure of such
30 drawings/block diagrams includes disclosure of electrical components and connections
between said electronic components, and electronic components or circuitry commonly
used to implement such components.
18

[075] Further, in accordance with the present disclosure, it is to be acknowledged that
the functionality described for the various the components/units can be implemented
interchangeably. While specific embodiments may disclose a particular functionality of
these units for clarity, it is recognized that various configurations and combinations thereof
5 are within the scope of the disclosure. The functionality of specific units as disclosed in the
disclosure should not be construed as limiting the scope of the present disclosure. Consequently, alternative arrangements and substitutions of units, provided they achieve the intended functionality described herein, are considered to be encompassed within the scope of the present disclosure.
10
[076] Additionally, the monitoring unit [102], the trigger unit [104] and the processing unit [108] are processors. The processor may be a general-purpose processor, a special purpose processor, a conventional processor, a digital signal processor, a plurality of microprocessors, one or more microprocessors in association with a DSP (digital signal
15 processor) core, a controller, a microcontroller, Application Specific Integrated Circuits,
Field Programmable Gate Array circuits, any other type of integrated circuits, etc.
[077] Also, the transmitter unit [106] includes a transmitter having capabilities to
transmit data/signals and optionally also a receiver unit having capabilities to receive
20 data/signals.
[078] The system [100] may be configured for service fallback in 5G core (5GC)
network, with the help of the interconnection between the components/units of the system
[100]. The system [100] comprises the monitoring unit [102] that is configured to monitor
25 one or more key performance indicators (KPIs) to detect an outage in the 5GC network.
The monitoring used herein refers to a process of continuously observing or tracking the one or more KPIs within the 5Gcore (5GC) network.
[079] The disclosure encompasses that failure in 5GC network is detected by a KPI
30 degrade and the one or more KPIs are used to monitor a health and a performance of the
5G Core (5GC) network. If there's an outage or issue affecting the 5GC network, it is reflected in the one or more KPIs, resulting in their degradation. The disclosure encompasses that the system [100] continuously monitors the one or more KPIs to promptly
19

identify any network problems. Additionally, the disclosure encompasses that the one or
more KPIs are one or more measurable values that indicate how effectively the 5Gcore
(5GC) network or any telecommunications network is working. These KPIs are used to
assess and monitor one or more aspects of performance and functionality. Furthermore, the
5 disclosure encompasses that the one or more KPIs comprises at least one of a latency, a
throughput, a packet loss rate, and a signal strength.
[080] As used herein, ‘latency’ is a time taken for a data to travel from a source to a
destination in a network. Further, as used herein, ‘throughput’ is an amount of data
10 transferred over the network within a given time frame. Also, as used herein, ‘packet loss
rate’ is a percentage of one or more packets lost or dropped during transmission over the network. Further, as used herein, ‘signal strength’ or quality of the signal received by one or more devices (such as user equipment (UEs), within the network.
15 [081] When KPI degradation is detected by the monitoring unit [102] and it is determined
that an outage has occurred, the monitoring unit [102] is configured to provide this information with respect to outage to the trigger unit [104]. The trigger unit [104] is configured to trigger a first application programming interface (API) for an affected home public land mobile network (HPLMN) or visited public land mobile network (VPLMN)
20 based on detection of the outage. The affected HPLMN and the affected VPLMN
respectively refers to an HPLMN where the outage is detected and the VPLMN where the outage is detected. Also, the first API corresponds to a UE Usage Type (UUT) API. Additionally, the UUT values include a User Equipment (UE) Usage Type.
25 [082] Further, the UE Usage Type (UUT) refers to a classification assigned to each User
Equipment (UE) based on its intended usage. Said classification is stored in a central database called the Home Subscriber Server (HSS) in order to facilitate the network to decide which gateway to use for routing data for the UE in the network. Furthermore, each device is assigned only one UE Usage Type.
30
[083] Furthermore, the transmitter unit [106] is connected with the trigger unit [104], and the transmitter unit [106] is configured to send, via a home subscriber server (HSS) [206] or a user data management (UDM) unit [204], an updated UE Usage Type (UUT) value in
20

an update location answer (ULA) based on the affected HPLMN or VPLMN. The disclosure encompasses that after enabling the UUT, the HSS [206] starts sending the updated UUT value in the ULA as per the HPLMN or VPLMN.
5 [084] Therefore, disclosure encompasses that once a failure or outage is detected, the
trigger unit [104] triggers a UE Usage Type (UUT) API for the affected HPLMN/VPLMN.
The UUT API is triggered by for the public land mobile network (PLMN) that is affected,
and the API is triggered from the user data management provisioning system (UDMPS)
[202]. Additionally, the disclosure encompasses that the trigger unit [104] is configured to
10 trigger the first application programming interface (API) automatically based on a
predefined network outage threshold. This predefined network outage threshold may refer to a predefined level or a pre-determined benchmark, and once the predefined network outage threshold reached or exceeded, the trigger unit [104] initiates an automatic response.
15 [085] Next, the transmitter unit [106] is further configured to send, via the HSS [206] or
UDM unit [204], a first message in an access and mobility management function (AMF) registration response based on the affected HPLMN or VPLMN. The disclosure encompasses that the first message is an "Unknown 5GS Subscription" message. The disclosure also encompasses that the UDM unit [204] starts sending the code “Unknown
20 5GS Subscription” in the AMF registration response as per the HPLMN/VPLMN.
[086] The processing unit [108] is connected with the transmitter unit [106] and the processing unit [108] is configured to select, via a mobility management entity (MME) [210], any or a combination of a 4G packet gateway (PGW) [214] and a session
25 management function (SMF) based on the updated UUT value. Once the MME [210]
receives the updated UUT value, it initiates a decision-making process. This step determines whether to continue service provision using either the 4G PGW [214] or a combination of Session Management Function and PGW (SMF+PGW) based on the UUT value. For example, in an event the UUT value UT value is 200 then SMF+PGW may be
30 selected for service provisioning and in an event the UUT value is 254 then 4G PGW [214]
may be selected for service provisioning. The decision is made based on the received UUT value, which serves as a factor in selecting the appropriate network component for continued service delivery. Particularly, the processing unit [108] is configured to select at
21

least one of the PGW [214] and the SMF based on an analysis of a type of data traffic specified by the updated UUT value. Also, the processing unit [108] is configured to define a time period for a user equipment (UE) [212] to attempt to connect to the network, wherein the UE [212] attempts to reconnect to the network on expiration of the defined time period. 5
[087] Further, the present invention encompasses that, upon sending the code “Unknown 5GS Subscription” in the AMF registration response as per the HPLMN/VPLMN, the processing unit [108] is configured to provide an error code indicating the reason for the subscription status as "unknown." The disclosure encompasses that the transmitter unit
10 [106] is configured to send, via the AMF [208], an "N1 mode not allowed" code in a non-
access stratum (NAS) to prevent further attempts to connect to the 5GC network. The present disclosure encompasses that the “N1 mode” is a mode in 5G technology wherein the user equipment (UE) is allowed to access the 5G core network via a 5G access network. Hence, “N1 mode not allowed" indicates that the UE is not permitted to access the 5G core
15 network.
[088] For example, the system [100] works without the need for user intervention,
enabling users to consume services on the 4G network during an outage in the 5GC
network. As part of the seamless transition process, the AMF [208] takes a crucial step to
20 prevent any further attempts by the User Equipment (UE) to connect to the 5GC network
during the outage. It for instance achieves this by sending an "N1 mode not allowed" message in a Non-Access Stratum (NAS) code.
[089] Considering an example, there is a citywide outage of 5G network service provided
25 by the large telecommunications company, Network Provider X, due to unforeseen
circumstances such as extreme weather conditions or technical issues. Network Provider
X's system automatically monitors the network's health using Key Performance Indicators
(KPIs). The outage leads to a significant degradation in these KPIs, which alerts the system
to the problem. Upon detecting the outage, the system triggers an API called UE Usage
30 Type (UUT) for the affected Home Public Land Mobile Network (HPLMN), which in this
case is Network Provider X. Subsequently, the Home Subscriber Server (HSS) [206] starts to send an updated UUT value in an Update Location Answer (ULA), indicating that the HPLMN (Network Provider X) is experiencing an outage. At the same time, the User Data
22

Management (UDM) unit [204] begins to send an "Unknown 5GS Subscription" message
in the Access and Mobility Management Function (AMF) registration response, tailored
based on the HPLMN affected by the outage. Upon receiving the updated UUT value, the
Mobility Management Entity (MME) [210] makes a decision to select a 4G Packet
5 Gateway (PGW) [214] to continue providing service to the millions of users across the
country. Simultaneously, due to the "Unknown 5GS Subscription" message in the AMF
registration response, the AMF [208] sends a "N1 mode not allowed" code in the Non-
Access Stratum (NAS). This action ensures that users' devices across the country do not
make any further attempts to connect to the faulty 5GC network. As a result of these
10 automated responses to the detected outage, users nationwide are seamlessly switched from
the 5GC network to the existing 4G network. Thus, even in the event of a large-scale outage, users can continue to use mobile data services without any interruptions or need for manual intervention.
15 [090] FIG.2 illustrates an exemplary 5G network architecture on which the method
service fallback in 5G core (5GC) network is implemented, in accordance with exemplary embodiments of the present disclosure. The 5G network architecture [200] comprise of at least a user data management provisioning system (UDMPS) [202], a user data management (UDM) unit [204], a home subscriber server (HSS) [206], an access and
20 mobility management function (AMF) [208], a mobility management entity (MME) [210],
a user equipment [212] and a 4G packet gateway (PGW) [214]. Further, at least one of each unit or element mentioned above is typically present in the 5G network architecture [200], however any number of additional units may be added based on the specific requirements and scale of the network deployment.
25
[091] Referring to FIG. 3 an exemplary method flow diagram, depicting a process [300] of service fallback ensuring uninterrupted service continuity in 5G core (5GC) network, in accordance with exemplary embodiments of the present disclosure is shown. In an implementation the method [300] is performed by the server. In another implementation,
30 the method [300] is implemented over the 5G architecture depicted in FIG. 2.
[092] The method [300] initiates at step [302].
23

[093] At step [304], the method [300] as disclosed by the present disclosure comprises
monitoring, by a monitoring unit [102], one or more key performance indicators (KPIs) to
detect an outage in a 5GCore (5GC) network. The disclosure encompasses that failure in
5GC network is detected by a KPI degrade and the one or more KPIs are used to monitor
5 a health and a performance of the 5GCore (5GC) network. If there's an outage or issue
affecting the 5GC network, it is reflected in the one or more KPIs, resulting in their
degradation. The disclosure encompasses that the method via the system [100]
continuously monitors the one or more KPIs to promptly identify any network problems.
In one implementation, the monitoring may be performed periodically at regular time
10 intervals that may be predefined or configurable. Additionally, the disclosure encompasses
that the one or more KPIs comprises at least one of a latency, a throughput, a packet loss rate, and a signal strength.
[094] Further, monitoring of KPIs is an essential step in managing the health and
15 performance of any network, including a 5G Core (5GC) network. For example, the one or
more KPIs are one or more specific metrics that give one or more insights into how well the network is performing. The KPIs may also include one or more factors like, connection speed, latency, packet loss, error rates, the number of concurrent users, and more. For example, if there is a sudden increase in latency or packet loss, these could be signs of a
20 potential network problem or an outage. Constant monitoring of the one or more KPIs
allows network operators to detect issues in real-time and respond promptly to mitigate the impact on users. In the case of the 5GC network, a degradation in KPIs trigger a series of actions designed to maintain service for users, including activating a fallback to a 4G network if necessary.
25
[095] Regularly checking the one or more KPIs allows the network provider to anticipate potential issues, diagnose existing problems, and track the performance of the network over time. Further, proactive way to ensure that users have a consistent and reliable experience with their 5Gservice.
30
[096] Next, at step [306], the method [300] as disclosed by the present disclosure comprises triggering, by a trigger unit [104], a first application programming interface (API) for an affected home public land mobile network (HPLMN) or visited public land
24

mobile network (VPLMN) based on detection of the outage. The affected HPLMN and the affected VPLMN respectively refers to an HPLMN where the outage is detected and the VPLMN where the outage is detected. Also, the first API corresponds to a (UUT) API.
5 [097] Next, at step [308], the method [300] as disclosed by the present disclosure
encompassing sending, by a transmitter unit [106] via a home subscriber server (HSS) [206]
or a user data management (UDM) unit [204], an updated UUT value in an Update Location
Answer (ULA) based on the affected HPLMN or VPLMN. The HSS [206] or UDM unit
[204] plays a crucial role in managing network outages in a 5GCore (5GC) network. The
10 disclosure encompasses that after enabling the UUT, the HSS [206] starts sending the
updated UUT value in the ULA as per the HPLMN or VPLMN.
[098] Therefore, the disclosure encompasses that once a failure or outage is detected, the trigger unit [104] triggers a UE Usage Type (UUT) API for the affected HPLMN/VPLMN.
15 The UUT API is triggered by for the public land mobile network (PLMN) that is affected
and further the PLMN may be HPLMN or VPLMN and the API is triggered from the user data management provisioning system (UDMPS) [202]. Additionally, the disclosure encompasses that the trigger unit [104] triggers the first application programming interface (API) automatically based on a predefined network outage threshold. The first API
20 corresponds to a UUT API. Further, the predefined network outage threshold may refer to
a predefined level or a pre-determined benchmark, and once the predefined network outage threshold reached or exceeded, the trigger unit [104] initiates an automatic response.
[099] For example, upon detecting an outage in either the Home Public Land Mobile
25 Network (HPLMN) or the Visited Public Land Mobile Network (VPLMN), the HSS [206]
or the UDM unit [204] takes one or more action(s) to maintain service continuity for one
or more affected users. One of the actions performed by the HSS [206] or the UDM unit
[204] is to send an updated (UUT) value. This updated UUT value is communicated
through an Update Location Answer (ULA) message. The ULA message include important
30 information regarding the user's location and network preferences. In this case, the updated
UUT value is included in the ULA message, specifically tailored based on whether the outage is affecting the HPLMN or the VPLMN. By sending the updated UUT value in the ULA message, the HSS [206] or the UDM unit [204] provides one or more instructions to
25

the network elements involved, such as the Mobility Management Entity (MME) [210] and
the Packet Gateway (PGW) [214]. This enables them to make informed decisions and select
the appropriate one or more network components for continued service delivery. Overall,
the updated UUT value sent by the HSS [206] or the UDM unit [204] in the ULA message
5 ensures that the network elements are aware of the outage and adapt their operations,
accordingly, maintaining service continuity for the affected users in the 5GCore network.
[100] Accordingly, next at step [310], the method [300] as disclosed by the present disclosure comprises sending, by the transmitter unit [106] via the HSS [206] or UDM unit
10 [204], a first message in an access and mobility management function (AMF) registration
response based on the affected HPLMN or VPLMN. The disclosure encompasses that the first message is an "Unknown 5GS Subscription" message. The disclosure also encompasses that the UDM unit [204] starts sending the code “Unknown 5GS Subscription” in the AMF registration response as per the HPLMN/VPLMN. For example,
15 when an outage occurs in either the HPLMN or the VPLMN, the HSS [206] or the UDM
unit [204] takes action during the registration process. Specifically, when the AMF [208] requests registration from a user device, the HSS [206] or the UDM unit [204] includes an "Unknown 5GS Subscription" message in the AMF [208] registration response.
20 [101] Further, the content of this message is dependent on the HPLMN or VPLMN that
is affected by the outage. It indicates to the AMF [208], which is responsible for managing access and mobility within the network, that the subscription status for the user's 5Gservice is currently unknown due to the ongoing network issue. By sending this "Unknown 5GS Subscription" message, the HSS [206] or the UDM unit [204] communicates to the AMF
25 [208] that the user's 5Gsubscription cannot be confirmed at the moment because of the
outage. This ensures that the AMF [208] understands the need to prevent any further attempts to connect the user to the affected 5GCore (5GC) network.
[102] This approach helps avoid unnecessary signalling procedures and potential
30 disruptions caused by attempting to establish or maintain a connection to the affected 5GC
network. Instead, the AMF [208] focus on managing the user's connection in the fallback
mode, such as connecting the user to the 4G network, until the network outage is resolved.
26

[103] Overall, the inclusion of the "Unknown 5GS Subscription" message in the AMF [208] registration response by the HSS unit [206] or the UDM unit [204] allows for effective network management during an outage, ensuring a smooth user experience and maintaining service continuity while the network issue is being addressed. 5
[104] Thereby, the method [300] includes providing, by the processing unit [108], an error code indicating the reason for the subscription status as "unknown."
[105] Next, at step [312], the method [300] as disclosed by the present disclosure
10 comprises selecting, by the processing unit [108] via a mobility management entity (MME)
[210], any or a combination of a 4G packet gateway (PGW) [214] and a session management function (SMF) based on the updated UUT value. Further, the selecting, any or a combination of the PGW [214] and the SMF, is based on analysis of a type of data traffic specified by the updated UUT value. Once the updated UUT value is received, the
15 Mobility Management Entity (MME) [210] takes one or more action to ensure the
continuity of service for the user. Additionally, once the MME [210] receives the updated UUT value, it initiates a decision-making process. This step determines whether to continue service provision using either the 4G PGW [214] or a combination of Session Management Function and PGW (SMF+PGW). The decision is made based on the received UUT value,
20 which serves as a factor in selecting the appropriate network component for continued
service delivery. Particularly, the processing unit [108] selects at least one of the PGW [214] and the SMF based on an analysis of a type of data traffic specified by the updated UUT value. Also, the processing unit [108] defines a time period for a user equipment (UE) [212] to attempt to connect to the network, wherein the UE [212] attempts to reconnect to
25 the network on expiration of the defined time period.
[106] The disclosure encompasses that based on the updated UUT value, the MME [210]
evaluates the available one or more options for maintaining the user's service continuity. It
considers factors such as network capabilities, resource availability, and the network
30 architecture. If the UUT value suggests compatibility with the 4G network, the MME [210]
selects the 4G PGW [214] to handle the user's traffic. However, in certain scenarios where the UUT value indicates the need for additional functionalities provided by a combination of Session Management Function (SMF) and PGW [214], the MME [210] may choose the
27

SMF+PGW combination instead. This decision ensures that the user's specific traffic
requirements are adequately addressed and managed. By dynamically selecting either the
4G PGW [214] or the SMF+PGW combination based on the updated UUT value, the MME
[210] optimizes the network resources and ensures the appropriate handling of the user's
5 traffic during the network transition. This enables seamless service continuation and a
consistent user experience, despite the network outage in the 5GCore (5GC) network.
[107] The disclosure encompasses that the method [300] as disclosed by the present disclosure comprises sending, by the transmitter unit via the AMF [208], an "N1 mode not
10 allowed" code in a non-access stratum (NAS) to prevent further attempts to connect to the
5GC network. The present disclosure encompasses that the “N1 mode” is a mode in 5G technology wherein the user equipment (UE) is allowed to access the 5G core network via a 5G access network. Hence, “N1 mode not allowed" indicates that the UE is not permitted to access the 5G core network.
15
[108] The above steps are performed without the need for user intervention, enabling users to consume services on the 4G network during an outage in the 5GC network. As part of the seamless transition process, the AMF [208] takes a crucial step to prevent any further attempts by the User Equipment (UE) [212] to connect to the 5GC network during the
20 outage. It achieves this by sending an "N1 mode not allowed" message in a Non-Access
Stratum (NAS) code.
[109] The disclosure encompasses that the NAS is responsible for managing signalling procedures between the UE [212] and the core network. Within the NAS, the "N1 mode
25 not allowed" code serves as a specific instruction to the UE [212], indicating that the current
mode of operation for connecting to the 5GC network is not permitted. By sending this NAS code, the AMF [208] ensures that the UE [212] does not initiate any additional connection attempts to the affected 5GC network. This prevents unnecessary signalling procedures and minimizes disruptions or potential issues that may arise from unsuccessful
30 connection attempts during the outage. The importance of this step is to optimize network
resources and focus on the available alternative, which is the 4G network. By preventing further attempts to connect to the 5GC network, the AMF [208] directs the UE [212] to
28

utilize the fallback option, enabling users to consume services seamlessly on the 4G network without any manual intervention required.
[110] The disclosure encompasses that the mechanism ensures that users can continue to
5 access services without interruptions during the outage in the 5GC network. The AMF's
[208] instruction through the "N1 mode not allowed" NAS code guides the UE [212] to operate exclusively on the 4G network until the 5GC network is restored, providing a smooth user experience and maintaining service continuity.
10 [111] Thereafter, the method [300] terminates at step [314].
[112] For example, the method and system for service fallback in 5Gcore (5GC) network may be utilised or implemented by a telecommunication organization to enhance the reliability and resilience of their network infrastructure. By employing the method and
15 system, the organization may effectively handle network outages or disruptions, ensuring
uninterrupted service delivery to their customers. The method and system enable the organization to detect one or more network outages promptly and initiate appropriate fallback mechanisms, minimizing service downtime and ensuring continuous connectivity for their customers. By proactively addressing network disruptions, the organization can
20 mitigate the impact on customer experience, maintaining high levels of satisfaction and
loyalty among their subscriber bases. The method and system facilitate intelligent selection of alternative network components based on updated UE information, allowing the organization to optimize resource utilization and maintain efficient network operations during fallback scenarios. Through automated monitoring and triggering of fallback
25 procedures, the organization can streamline network management processes, reducing
manual intervention and operational overhead. By ensuring minimal service disruptions and meeting SLAs for service availability and reliability, the organization can uphold contractual commitments and maintain trust with their enterprise and individual customers. Further the method and system are adaptable to varying network conditions and can
30 accommodate future expansions or upgrades in the 5Gcore network architecture, providing
scalability and flexibility to meet evolving operational requirements.
29

[113] In addition to this example, the method involves monitoring key performance
indicators (KPIs) by a monitoring processing unit to detect network outages. Upon
detection, it triggers appropriate actions, updates user equipment (UE) information, and
selects alternative network components based on the updated information. The monitoring
5 unit continuously tracks one or more KPIs such as latency, throughput, packet loss rate,
and signal strength to identify any anomalies or outages in the 5GC network. Upon detecting a network outage surpassing a predefined threshold, the trigger processing unit initiates a first application programming interface (API) to notify the affected home public land mobile network (HPLMN) or visited public land mobile network (VPLMN). The
10 transmitter unit, via the Home Subscriber Server (HSS) or User Data Management (UDM)
unit, updates the UE Usage Type (UUT) value in the Update Location Answer (ULA) message corresponding to the affected HPLMN or VPLMN. Similarly, the transmitter unit sends a first message in the Access and Mobility Management Function (AMF) registration response, indicating the affected HPLMN or VPLMN, facilitating network registration.
15 The processing unit, via the Mobility Management Entity (MME), selects appropriate
components such as the 4G Packet Gateway (PGW), Session Management Function (SMF), or others, based on the updated UUT value, ensuring continued service availability. Optionally, the transmitter processing unit, via the AMF, may send an "N1 mode not allowed" code in a non-access stratum (NAS) message to prevent further connection
20 attempts to the 5GC network during the outage. In case of an "Unknown 5GS Subscription"
message, the method provides an error code indicating the reason for the subscription status as "unknown." The processing unit defines a time period for the UE to attempt reconnection to the network. Upon expiration of this period, the UE makes further attempts to reconnect to restore network connectivity. The first API corresponds to a UUT API, facilitating
25 communication between network elements for service fallback procedures. This method
ensures seamless service continuity and efficient network management in response to outages or disruptions in the 5Gcore network.
[114] Fig. 4 illustrates an exemplary block diagram of a computing device [1000] (also
30 referred herein as a computing system [1000]) upon which an embodiment of the present
disclosure may be implemented. In an implementation, the computing device implements the method for service fallback in 5G core (5GC) network using the system [100]. In another implementation, the computing device itself implements the method for service
30

fallback in 5G core (5GC) network by using one or more units configured within the computing device, wherein said one or more units are capable of implementing the features as disclosed in the present disclosure.
5 [115] The computing device [1000] may include a bus [1002] or other communication
mechanism for communicating information, and a hardware processor [1004] coupled with bus [1002] for processing information. The hardware processor [1004] may be, for example, a general purpose microprocessor. The computing device [1000] may also include a main memory [1006], such as a random access memory (RAM), or other dynamic storage
10 device, coupled to the bus [1002] for storing information and instructions to be executed
by the processor [1004]. The main memory [1006] also may be used for storing temporary variables or other intermediate information during execution of the instructions to be executed by the processor [1004]. Such instructions, when stored in non-transitory storage media accessible to the processor [1004], render the computing device [1000] into a
15 special-purpose machine that is customized to perform the operations specified in the
instructions. The computing device [1000] further includes a read only memory (ROM) [1008] or other static storage device coupled to the bus [1002] for storing static information and instructions for the processor [1004].
20 [116] A storage device [1010], such as a magnetic disk, optical disk, or solid-state drive
is provided and coupled to the bus [1002] for storing information and instructions. The computing device [1000] may be coupled via the bus [1002] to a display [1012], such as a cathode ray tube (CRT), for displaying information to a computer user. An input device [1014], including alphanumeric and other keys, may be coupled to the bus [1002] for
25 communicating information and command selections to the processor [1004]. Another type
of user input device may be a cursor controller [1016], such as a mouse, a trackball, or cursor direction keys, for communicating direction information and command selections to the processor [1004], and for controlling cursor movement on the display [1012]. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second
30 axis (e.g., y), that allow the device to specify positions in a plane.
[117] The computing device [1000] may implement the techniques described herein using customized hard-wired logic, one or more ASICs or FPGAs, firmware and/or
31

program logic which in combination with the computing device [1000] causes or programs
the computer system [1000] to be a special-purpose machine. According to one
embodiment, the techniques herein are performed by the computing device [1000] in
response to the processor [1004] executing one or more sequences of one or more
5 instructions contained in the main memory [1006]. Such instructions may be read into the
main memory [1006] from another storage medium, such as the storage device [1010].
Execution of the sequences of instructions contained in the main memory [1006] causes
the processor [1004] to perform the process steps described herein. In alternative
embodiments, hard-wired circuitry may be used in place of or in combination with software
10 instructions.
[118] The computing device [1000] also may include a communication interface [1018] coupled to the bus [1002]. The communication interface [1018] provides a two-way data communication coupling to a network link [1020] that is connected to a local network
15 [1022]. For example, the communication interface [1018] may be an integrated services
digital network (ISDN) card, cable modem, satellite modem, or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, the communication interface [1018] may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be
20 implemented. In any such implementation, the communication interface [1018] sends and
receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.
[119] The computing device [1000] can send messages and receive data, including
25 program code, through the network(s), the network link [1020] and the communication
interface 1018. In the Internet example, a server [1030] might transmit a requested code for
an application program through the Internet [1028], the Internet Service Provider (ISP)
[1026], the Host [1024], the local network [1022] and the communication interface [1018].
The received code may be executed by the processor [1004] as it is received, and/or stored
30 in the storage device [1010], or other non-volatile storage for later execution.
[120] The present disclosure may relate to a user equipment (UE) for service fallback in 5G core (5GC) network, the UE comprising: a memory; and a process connected to the
32

memory, wherein the processor is configured to: transmit, to the system [100], a request to
monitor one or more key performance indicators (KPIs) to detect an outage in the 5GC
network, and receive from the system [100], a response associated with the request. wherein
the response is received based on: monitoring, by the system [100], the one or more key
5 performance indicators (KPIs) to detect the outage in the 5GC network, triggering, by the
system [100], a first application programming interface (API) for one of an affected home public land mobile network (HPLMN) and a visited public land mobile network (VPLMN) based on detection of the outage, sending, by the system [100], an updated UE Usage Type (UUT) value in an update location answer (ULA) based on the affected one of the HPLMN
10 and VPLMN, sending, by the system [100], a first message in an access and mobility
management function (AMF) [208] registration response based on the one of affected HPLMN and VPLMN, and selecting, by the system [100], at least one of a 4G packet gateway (PGW) [214] and a session management function (SMF) based on the updated UUT value.
15
[121] The present disclosure may relate to a non-transitory computer readable storage medium storing instruction for service fallback in 5G core (5GC) network, the instructions include executable code which, when executed by a one or more units of a system, causes: a monitoring unit [102] to monitor one or more key performance indicators (KPIs) to detect
20 an outage in the 5GC network, a trigger unit [104] to trigger a first application programming
interface (API) for one of an affected home public land mobile network (HPLMN) and a visited public land mobile network (VPLMN) based on detection of the outage, a transmitter unit [106] to send via one of a home subscriber server (HSS) [206] and a user data management (UDM) unit [204], an updated UE Usage Type (UUT) value in an update
25 location answer (ULA) based on the affected one of the HPLMN and VPLMN, the
transmitter unit [106] to send via one of the HSS [206] and the UDM unit [204], a first message in an access and mobility management function (AMF) [208] registration response based on the one of affected HPLMN and VPLMN, and a processing unit [108] to select via a mobility management entity (MME) [210], at least one of a 4G packet gateway (PGW)
30 [214] and a session management function (SMF) based on the updated UUT value.
[122] The present disclosure introduces a technologically advanced solution for service fallback in 5Gcore networks, offering automated subscriber service recovery upon failure
33

detection at the network's end. This feature significantly reduces downtime and enhances
service availability. By automating subscriber services recovery upon failure detection, the
method and system significantly reduce downtime and enhance service availability. This
ensures that subscribers experience minimal disruptions in accessing network services.
5 Furthermore, the present disclosure presents a standardized approach to deregistering and
re-registering subscribers across different network types (4G and 5G), resulting in
improved consistency in handling network failures and minimized service disruptions for
subscribers. This streamlined approach ensures minimal disruption to users and makes the
recovery process seamless from their perspective. Additionally, the present disclosure aims
10 to efficiently manage network resources by introducing a new API to handle deregistration
and re-registration tasks during network failures. The solution introduced in the present disclosure also has the potential to reduce system overhead and enhance overall network performance.
15 [123] While considerable emphasis has been placed herein on the disclosed
embodiments, it will be appreciated that many embodiments can be made and that many changes can be made to the embodiments without departing from the principles of the present disclosure. These and other changes in the embodiments of the present disclosure will be apparent to those skilled in the art, whereby it is to be understood that the foregoing
20 descriptive matter to be implemented is illustrative and non-limiting.
34

I/We Claim:
1. A method [300] for service fallback in 5G core (5GC) network, comprising:
monitoring, by a monitoring unit [102], one or more key performance indicators (KPIs) to detect an outage in the 5GC network;
triggering, by a trigger unit [104], a first application programming interface (API) for one of an affected home public land mobile network (HPLMN) and a visited public land mobile network (VPLMN) based on detection of the outage;
sending, by a transmitter unit [106] via one of a home subscriber server (HSS) [206] and a user data management (UDM) unit [204], an updated UE Usage Type (UUT) value in an update location answer (ULA) based on the affected one of the HPLMN and VPLMN;
sending, by the transmitter unit [106] via one of the HSS [206] and the UDM unit [204], a first message in an access and mobility management function (AMF) [208] registration response based on the one of affected HPLMN and VPLMN; and
selecting, by a processing unit [108] via a mobility management entity (MME) [210], at least one of a 4G packet gateway (PGW) [214] and a session management function (SMF) based on the updated UUT value.
2. The method [300] as claimed in claim 1, wherein the method comprises sending, by the transmitter unit via the AMF [208], an "N1 mode not allowed" code in a non-access stratum (NAS) to prevent further attempts to connect to the 5GC network.
3. The method [300] as claimed in claim 1, wherein the one or more KPIs comprises at least one of a latency, a throughput, a packet loss rate, and a signal strength.
4. The method [300] as claimed in claim 1, wherein the triggering of the first application programming interface (API) is performed automatically based on a predefined network outage threshold.
5. The method [300] as claimed in claim 1, wherein the first message is an “Unknown 5GS Subscription” message.

6. The method [300] as claimed in claim 5, wherein the method includes providing, by the processing unit [108], an error code indicating a reason for a subscription status as “unknown.”
7. The method [300] as claimed in claim 1, wherein the selecting of at least one of the PGW [214] and the SMF is based on an analysis of a type of data traffic specified by the updated UUT value.
8. The method [300] as claimed in claim 1, wherein the method comprises defining, by the processing unit [108], a time period for a user equipment (UE) [212] to attempt to connect to the network, wherein the UE [212] attempts to reconnect to the network on expiration of a defined time period.
9. The method [300] as claimed in claim 1, wherein the first API corresponds to a UUT API.
10. A system [100] for service fallback in 5G core (5GC) network, the system comprises:
a monitoring unit [102] configured to monitor one or more key performance
indicators (KPIs) to detect an outage in the 5GC network;
a trigger unit [104] connected with the monitoring unit [102], the trigger unit
[104] configured to trigger a first application programming interface (API) for one
of an affected home public land mobile network (HPLMN) and a visited public land
mobile network (VPLMN) based on detection of the outage;
a transmitter unit [106] connected with the trigger unit [104], the transmitter
unit [106] configured to:
send, via one of a home subscriber server (HSS) [206] and a user data management (UDM) unit [204], an updated UUT value in an update location answer (ULA) based on the affected one of HPLMN and VPLMN;
send, via one of the HSS [206] and the UDM unit [204], a first message in an access and mobility management function (AMF) registration response based on one of the affected HPLMN and VPLMN; and a processing unit [108] connected with the transmitter unit [106], the
processing unit [108] configured to select, via a mobility management entity (MME)

[210], at least one of a 4G packet gateway (PGW) [214], and a session management function (SMF) based on the updated UE Usage Type (UUT) value.
11. The system [100] as claimed in claim 10, wherein the transmitter unit [106] is configured to send, via the AMF [208], an "N1 mode not allowed" code in a non-access stratum (NAS) to prevent further attempts to connect to the 5GC network.
12. The system [100] as claimed in claim 10, wherein the one or more KPIs comprises at least one of a latency, a throughput, a packet loss rate, and a signal strength.
13. The system [100] as claimed in claim 10, wherein the trigger unit [104] is configured to trigger the first application programming interface (API) automatically based on a predefined network outage threshold.
14. The system [100] as claimed in claim 10, wherein the first message is an "Unknown 5GS Subscription" message.
15. The system [100] as claimed in claim 14, wherein the processing unit [108] is configured to provide an error code indicating a reason for the subscription status as "unknown".
16. The system [100] as claimed in claim 10, wherein the processing unit [108] is configured to select at least one of the PGW [214] and the SMF based on an analysis of a type of data traffic specified by the updated UUT value.
17. The system [100] as claimed in claim 10, wherein the processing unit [108] is configured to define a time period for a user equipment (UE) [212] to attempt to connect to the network, wherein the UE [212] attempts to reconnect to the network on expiration of the defined time period.
18. The system [100] as claimed in claim 10, wherein the first API corresponds to a UUT API.

19. A user equipment (UE) for service fallback in 5G core (5GC) network, the UE comprising:
- a memory; and
- a processor connected to the memory, wherein the processor is configured to:
o transmit, to a system [100], a request to monitor one or more key performance indicators (KPIs) to detect an outage in the 5GC network, and o receive from the system [100], a response associated with the request. wherein the response is received based on:
monitoring, by the system [100], the one or more key performance indicators (KPIs) to detect the outage in the 5GC network,
triggering, by the system [100], a first application programming interface (API) for one of an affected home public land mobile network (HPLMN) and a visited public land mobile network (VPLMN) based on detection of the outage,
sending, by the system [100], an updated UE Usage Type (UUT) value in an update location answer (ULA) based on the affected one of the HPLMN and VPLMN,
sending, by the system [100], a first message in an access and mobility management function (AMF) [208] registration response based on the one of affected HPLMN and VPLMN, and
selecting, by the system [100], at least one of a 4G packet gateway (PGW) [214] and a session management function (SMF) based on the updated UUT value.