FORM 2
THE PATENTS ACT, 1970 (39 OF 1970)
& THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
“SYSTEM AND METHOD FOR ENSURING CALL CONTINUITY DURING AN INTER-PUBLIC LAND MOBILE NETWORK HANDOVER”
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.

SYSTEM AND METHOD FOR ENSURING CALL CONTINUITY DURING AN INTER-PUBLIC LAND MOBILE NETWORK HANDOVER
FIELD OF THE DISCLOSURE
5
[0001] The present disclosure relates generally to the field of wireless
communication systems. More particularly, the present disclosure relates to methods and systems for ensuring call continuity during an inter public land mobile network (PLMN) handover. 10
BACKGROUND
[0002] The following description of related art is intended to provide
background information pertaining to the field of the disclosure. This section may
15 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.
20 [0003] 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 the second-generation (2G) technology, digital communication and data
25 services became possible, and text messaging was introduced. 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
30 deployed, promising even faster data speeds, low latency, and the ability to connect
multiple devices simultaneously. With each generation, wireless communication
2

technology has become more advanced, sophisticated, and capable of delivering more services to its users.
[0004] The existing art in mobile communication networks, particularly in the
5 context of handover processes between Public Land Mobile Networks (PLMNs),
faces several challenges that impact user experience and service continuity. One of the primary problems is the disruption of ongoing voice or video calls when a user moves from one PLMN to another, which is common in border areas where PLMN coverage overlaps. This issue is exacerbated in 5G networks, where users expect
10 high-quality and uninterrupted service. Another problem in the existing art is the
complexity of the handover process, which often involves multiple network elements and requires significant configuration and coordination. This complexity can lead to delays in the handover process, further degrading the user experience. Additionally, the existing solutions may not be fully aligned with the latest 3GPP
15 standards, limiting their compatibility and interoperability with other network
components. Furthermore, the existing art may not provide a seamless and simplified call flow during the handover process, leading to increased latency and potential call drops. The lack of a minimal touch solution that requires minimal configuration changes in the network elements (such as MME and SMF) also poses
20 a challenge, as it increases the operational complexity and costs for network
operators.
[0005] For example, when a user is moving from one serving PLMN to another
serving PLMN it should get detached from Network and freshly attach in target
25 PLMN. 5G User’s VOLTE call drops when the subscriber is moving from one
PLMN to another. Also, 5G customers residing at border areas have poor quality and ping pong due to coverage overlap between the bordering PLMN – in many cases just a road separates the two PLMN. Due to this reason ongoing voice calls get disconnected and user experience gets impacted.
30
3

[0006] Therefore, considering the foregoing discussion, there exists a need to
overcome the aforementioned drawbacks. Thus, there exists an imperative need in the art to provide a method and system for ensuring call continuity during an inter¬public land mobile network (PLMN) handover. 5
OBJECTS OF THE INVENTION
[0007] Some of the objects of the present disclosure, which at least one
embodiment disclosed herein satisfies are listed herein below. 10
[0008] It is an object of the present disclosure to provide system and method
for ensuring call continuity during an inter- Public land mobile network (PLMN) handover.
15 [0009] The objects of the present disclosure are to address the challenges and
limitations of the existing art in mobile communication networks, particularly in the context of handover processes between Public Land Mobile Networks (PLMNs). The following are some of the objects of the present disclosure:
20 [0010] It is another object of the present disclosure to provide a system and
method for ensuring call continuity during an inter-Public Land Mobile Network (PLMN) handover that minimizes the disruption of ongoing voice or video calls when a user moves from one PLMN to another.
25 [0011] It is another object of the present disclosure to provide a system and
method for ensuring call continuity during an inter-PLMN handover that offers a seamless user experience, especially in border areas where PLMN coverage overlaps.
30 [0012] It is another object of the present disclosure to provide a system and
method for ensuring call continuity during an inter-PLMN handover that simplifies
4

the call flow by using the same Session Management Function and Gateway (SMF+GW) to communicate with both the source and target Radio Access Networks (RANs).
5 [0013] It is another object of the present disclosure to provide a system and
method for ensuring call continuity during an inter-PLMN handover that requires minimal configuration changes in the existing deployed network elements, such as the Mobile Management Entity (MME) and SMF, and the enabled interfaces.
10 [0014] It is another object of the present disclosure to provide a system and
method for ensuring call continuity during an inter-PLMN handover that is fully aligned with the 3GPP standards, ensuring compatibility and interoperability with other network components.
15 [0015] It is yet another object of the present disclosure to provide a system and
method for ensuring call continuity during an inter-PLMN handover that reduces operational complexity and costs for network operators by offering a minimal touch solution.
20 SUMMARY
[0016] 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
25 of the claimed subject matter.
[0017] In a first aspect of the present disclosure, the present invention relates
to a method for ensuring call continuity during an inter-Public Land Mobile
Network (PLMN) handover in a mobile communication network. The method
30 includes detecting, by a processing unit, when a User Equipment (UE) passes
through a geographical area of a source PLMN (A) to a geographical area of a target
5

PLMN (B). The method further includes initiating, by the processing unit, a
handover request by the UE or a source RAN node associated with the source
PLMN (A). Further, the method encompasses, selecting, by the processing unit, a
target evolved node B (eNB) of the target PLMN (B), a Mobile Management Entity
5 (MME) of the target PLMN (B). Further, the method includes relocating, by the
processing unit, the MME in the target PLMN (B) and fetching a user context data
from the source PLMN (A) MME. The method further includes retaining, by the
processing unit, based on a configuration and the fetched user context data, a
combined Session Management Function and Gateway (SMF+GW) of the source
10 PLMN (A). The method further includes selecting, by the processing unit via the
target PLMN (B) MME, the source PLMN (A) combo SMF+GW.
[0018] In an aspect of the present disclosure, the geographical area of the
source PLMN (A) is different from the geographical area of the target PLMN (B). 15
[0019] In an aspect of the present disclosure, the source PLMN (A) combo
SMF + GW is selected via an S11 interface.
[0020] In an aspect of the present disclosure, a User Plane Function and
20 Gateway in a user plane (UPF+GW-U) anchors the user context data to achieve
audio/video call continuity during the inter-PLMN handover.
[0021] In an aspect of the present disclosure, the handover request comprises
information associated with the UE's current state, capabilities, and ongoing
25 communication sessions.
[0022] In an aspect of the present disclosure, the user context data is fetched
via an S10 interface, the user context data comprises subscription details, current location, and security parameters.
6

[0023] In an aspect of the present disclosure, a handover command, comprising
instructions for the UE to change the eNB, is sent from MME of the source PLMN (A) to the UE.
5 [0024] In an aspect of the present disclosure, the method further includes the
step of sending a handover complete message from the UE to the MME of the target PLMN (B), confirming successful change of eNB and completion of the handover.
[0025] In an aspect of the present disclosure, a Modify Bearer Request (MBR)
10 comprising a Forwarding Tunnelling Endpoint identifier (FTE ID) is sent from
MME of the target PLMN (B) to SMF to establish user plane connectivity.
[0026] In an aspect of the present disclosure, a Session Management Request
(SMR) is sent from the SMF to the UPF, instructing the UPF to prepare for user
15 data traffic.
[0027] In another aspect of the present disclosure, the present invention relates
to a system for ensuring call continuity during an inter- Public land mobile network (PLMN) handover in a mobile communication network. The system includes a
20 processor configured to detect when a User Equipment (UE) passes from a
geographical area of a source PLMN (A) to a geographical area of a target PLMN (B). The processor is further configured to initiate a handover request by the UE or a source RAN node associated with the source PLMN (A). Further the processor is configured to select a target eNB of the target PLMN (B), a Mobile Management
25 Entity (MME) of the target PLMN (B). The processor is further configured to
relocate, the MME in the target PLMN (B) and fetching a user context data from the source PLMN (A) MME. The processor is further configured to retain, based on a configuration and the fetched user context data, a combined Session Management Function and Gateway (SMF+GW) of the source PLMN (A). The
30 processor is further configured to select, via the target PLMN (B) MME, the source
PLMN (A) combo SMF+GW.
7

[0028] Another aspect of the present disclosure relates to a user equipment
(UE) for ensuring call continuity during an inter- Public land mobile network
(PLMN) handover in a mobile communication network, the UE comprising: a
5 processor configured to: detect when the UE passes from a geographical area of a
source PLMN (A) to a geographical area of a target PLMN (B); initiate a handover
request by the UE or a source RAN node associated with the source PLMN (A);
select a target eNB of the target PLMN (B), a Mobile Management Entity (MME)
of the target PLMN (B); relocate the MME in the target PLMN (B) and fetching a
10 user context data from the source PLMN (A) MME; retain, based on a configuration
and the fetched user context data, a combined Session Management Function and Gateway (SMF+GW) of the source PLMN (A); and select, via the target PLMN (B) MME, the source PLMN (A) combo SMF+GW.
15 [0029] Yet another aspect of the present disclosure relates to a non-transitory
computer-readable storage medium storing instruction for ensuring call continuity during an inter- Public land mobile network (PLMN) handover in a mobile communication network, the storage medium comprising executable code which, when executed by one or more units of a system, causes: a processing unit to: detect
20 when a User Equipment (UE) passes from a geographical area of a source PLMN
(A) to a geographical area of a target PLMN (B); initiate a handover request by the UE or a source RAN node associated with the source PLMN (A); select, a target eNB of the target PLMN (B), a Mobile Management Entity (MME) of the target PLMN (B); relocate, the MME in the target PLMN (B) and fetching a user context
25 data from the source PLMN (A) MME; retain, based on a configuration and the
fetched user context data, a combined Session Management Function and Gateway (SMF+GW) of the source PLMN (A); and select, via the target PLMN (B) MME, the source PLMN (A) combo SMF+GW.
30 BRIEF DESCRIPTION OF DRAWINGS
8

[0030] 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
5 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
10 circuitry commonly used to implement such components.
[0031] FIG. 1 illustrates a 5GC network architecture comprising a plurality of
network nodes.
15 [0032] FIG. 2 illustrates an exemplary system for ensuring call continuity
during an inter public land mobile network (PLMN) handover in a mobile communication network, in accordance with exemplary embodiments of the present disclosure.
20 [0033] FIG. 3 illustrates an exemplary architecture for implementing system
for ensuring call continuity during an inter public land mobile network (PLMN) handover in a mobile communication network, in accordance with exemplary embodiments of the present disclosure.
25 [0034] FIG. 4 illustrates an exemplary sequence diagram for ensuring call
continuity during an inter- public land mobile network (PLMN) handover in a mobile communication network, in accordance with exemplary embodiments of the present disclosure.
30 [0035] FIG. 5 illustrates an an exemplary block diagram of a computer system
upon which an embodiment of the present disclosure may be implemented for
9

ensuring call continuity during an inter-Public Land Mobile Network (PLMN) handover in a mobile communication network.
[0036] FIG. 6, illustrates an exemplary method flow diagram indicating the
5 process for ensuring call continuity during an inter- public land mobile network
(PLMN) handover in a mobile communication network, in accordance with the exemplary embodiments of the present invention.
[0037] The foregoing shall be more apparent from the following more detailed
10 description of the disclosure.
DETAILED DESCRIPTION
[0038] In the following description, for the purposes of explanation, various
15 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
20 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
25 drawings.
[0039] 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
30 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
10

function and arrangement of elements without departing from the spirit and scope of the disclosure as set forth.
[0040] It should be noted that the terms "mobile device", "user equipment",
5 "user device", “communication device”, “device” and similar terms are used
interchangeably for the purpose of describing the invention. These terms are not
intended to limit the scope of the invention or imply any specific functionality or
limitations on the described embodiments. The use of these terms is solely for
convenience and clarity of description. The invention is not limited to any particular
10 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 invention as defined herein.
[0041] Specific details are given in the following description to provide a
15 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
20 circuits, processes, algorithms, structures, and techniques may be shown without
unnecessary detail in order to avoid obscuring the embodiments.
[0042] 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
25 structure diagram, or a block diagram. Although a flowchart may describe the
operations as a sequential process, many of the operations can 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.
30
11

[0043] 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
5 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
10 similar to the term “comprising” as an open transition word—without precluding
any additional or other elements.
[0044] As used herein, an “electronic device”, or “portable electronic device”,
or “user device” or “communication device” or “user equipment” or “device” refers
15 to any electrical, electronic, electromechanical and computing device. The user
device is capable of receiving and/or transmitting one or parameters, performing function/s, communicating with other user devices and transmitting data to the other user devices. 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. The user
20 equipment may be capable of operating on any radio access technology including
but not limited to IP-enabled communication, Zig Bee, Bluetooth, Bluetooth Low 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,
25 a general-purpose computer, desktop, personal digital assistant, tablet computer,
mainframe computer, or any other device as may be obvious to a person skilled in the art for implementation of the features of the present disclosure.
[0045] Further, the user device may also comprise a “processor”
30 or “processing unit” includes processing unit, wherein processor refers to any logic
circuitry for processing instructions. The processor may be a general-purpose
12

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
5 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 disclosure. More specifically, the processor is a hardware processor.
10 [0046] 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
15 development, in this respect, has been incremental in the order of second 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.
[0047] Radio Access Technology (RAT) refers to the technology used by
20 mobile devices/ user equipment (UE) to connect to a cellular network. It refers to
the specific protocol and 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
25 transmitting and receiving data. Examples of RATs include GSM (Global System
for Mobile Communications), CDMA (Code Division 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.
30 Mobile devices often support multiple RATs, allowing them to connect to different
13

types of networks and provide optimal performance based on the available network resources.
[0048] As used herein, Modify Bearer Request (MBR) refers to a signalling
5 message that is utilized by the Mobile Management Entity (MME) to request
changes to the parameters of an existing bearer associated with a User Equipment
(UE). The request, which is sent from the MME of the target Public Land Mobile
Network (PLMN) to the Session Management Function (SMF), includes new or
updated attributes for the bearers that handle the user's traffic. The MBR message
10 contains information such as FTE ID for establishing and maintaining user plane
connectivity during inter-PLMN handovers.
[0049] As used herein, 'Forward Relocation Request (FRR)' refers to a
signalling message or procedure used to transfer UE context from one MME to
15 another MME during a handover procedure.
[0050] As used herein, Mobility Management Entity (MME) refers to a
network node in the Evolved Packet Core (EPC) for LTE (4G) and responsible for
the control-plane functions related to mobility management and session
20 management. It handles tasks such as the registration, authentication, and
authorization of user equipment (UE); bearer establishment and management; and the handover processes between LTE and other radio technologies.
[0051] As discussed in the background section, The existing art in mobile
25 communication networks, particularly in the context of handover processes
between Public Land Mobile Networks (PLMNs), faces several challenges that
impact user experience and service continuity. One of the primary problems is the
disruption of ongoing voice or video calls when a user moves from one PLMN to
another, which is common in border areas where PLMN coverage overlaps. This
30 issue is exacerbated in 5G networks, where users expect high-quality and
uninterrupted service. Another problem in the existing art is the complexity of the
14

handover process, which often involves multiple network elements and requires
significant configuration and coordination. This complexity can lead to delays in
the handover process, further degrading the user experience. Additionally, the
existing solutions may not be fully aligned with the latest 3GPP standards, limiting
5 their compatibility and interoperability with other network components.
Furthermore, the existing art may not provide a seamless and simplified call flow
during the handover process, leading to increased latency and potential call drops.
The lack of a minimal touch solution that requires minimal configuration changes
in the network elements (such as MME and SMF) also poses a challenge, as it
10 increases the operational complexity and costs for network operators.
[0052] To overcome these and other inherent problems in the art, the present
disclosure proposes a solution of ensuring call continuity during an inter-Public Land Mobile Network (PLMN) handover in a mobile communication network. This
15 is achieved through a method and system that includes detecting when a User
Equipment (UE) passes from the geographical area of a source PLMN to that of a target PLMN, initiating a handover request, selecting a target eNB and a Mobile Management Entity (MME) of the target PLMN, relocating the MME in the target PLMN and fetching user context data from the source PLMN MME via an S10
20 interface, retaining a combined Session Management Function and Gateway
(SMF+GW) of the source PLMN based on a configuration and the fetched user context data, and selecting, via the target PLMN MME, the source PLMN combo SMF+GW. The present disclosure addresses the problem of call drops and poor quality experienced by users moving between PLMNs, especially in border areas,
25 by ensuring continuity of audio/video calls during the handover process. It
simplifies the call flow by using the same SGW(SMF) in both the source and target PLMNs, which reduces the complexity of the handover process and minimizes the need for extensive configuration changes in existing network elements. Additionally, the solution is fully aligned with 3GPP standards, ensuring
30 compatibility and interoperability with other network components.
15

[0053] Hereinafter, exemplary embodiments of the present disclosure will be
described with reference to the accompanying drawings.
[0054] Referring to FIG. 1, illustrating a 5th generation (5GC) network
5 architecture comprising a plurality of network nodes. As shown in FIG. 4, the 5GC
network architecture [100] includes a user equipment (UE) [102], a radio access network (RAN) [104], an access and mobility management function (AMF) [106], a Session Management Function (SMF) [108], a Service Communication Proxy (SCP) [110], an Authentication Server Function (AUSF) [112], a Network Slice
10 Specific Authentication and Authorization Function (NSSAAF) [114], a Network
Slice Selection Function (NSSF) [116], a Network Exposure Function (NEF) [118], a Network Repository Function (NRF) [120], a Policy Control Function (PCF) [122], a Unified Data Management (UDM) [124], an application function (AF) [126], a User Plane Function (UPF) [128], a data network (DN) [130], wherein all
15 the components are assumed to be connected to each other in a manner as obvious
to the person skilled in the art for implementing features of the present disclosure.
[0055] The User Equipment (UE) [102] interfaces with the network via the
Radio Access Network (RAN) [104]; the Access and Mobility Management
20 Function (AMF) [106] manages connectivity and mobility, while the Session
Management Function (SMF) [108] administers session control; the service communication proxy (SCP) [110] routes and manages communication between network services, enhancing efficiency and security, and the Authentication Server Function (AUSF) [112] handles user authentication; the NSSAAF [114] for
25 integrating the 5G core network with existing 4G LTE networks i.e., to enable Non-
Standalone (NSA) 5G deployments, the Network Slice Selection Function (NSSF) [116], Network Exposure Function (NEF) [118], and Network Repository Function (NRF) [120] enable network customization, secure interfacing with external applications, and maintain network function registries respectively; the Policy
30 Control Function (PCF) [122] develops operational policies, and the Unified Data
Management (UDM) [124] manages subscriber data; the Application Function (AF)
16

[126] enables application interaction, the User Plane Function (UPF) [128]
processes and forwards user data, and the Data Network (DN) [130] connects to
external internet resources; collectively, these components are designed to enhance
mobile broadband, ensure low-latency communication, and support massive
5 machine-type communication, solidifying the 5GC as the infrastructure for next-
generation mobile networks.
[0056] Radio Access Network (RAN) [104] is the part of a mobile
telecommunications system that connects user equipment (UE) [102] to the core
10 network (CN) and provides access to different types of networks (e.g., 5G network).
It consists of radio base stations and the radio access technologies that enable wireless communication.
[0057] Access and Mobility Management Function (AMF) [106] is a 5G
15 core network function responsible for managing access and mobility aspects, such
as UE registration, connection, and reachability. It also handles mobility management procedures like handovers and paging.
[0058] Session Management Function (SMF) [108] is a 5G core network
20 function 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.
[0059] Service Communication Proxy (SCP) [110] is a network function in
25 the 5G core network that facilitates communication between other network
functions by providing a secure and efficient messaging service. It acts as a mediator for service-based interfaces.
[0060] Authentication Server Function (AUSF) [112] is a network function
30 in the 5G core responsible for authenticating UEs during registration and providing
security services. It generates and verifies authentication vectors and tokens.
17

[0061] Network Slice Specific Authentication and Authorization Function
(NSSAAF) [114] is a network function that provides authentication and
authorization services specific to network slices. It ensures that UEs can access only
5 the slices for which they are authorized.
[0062] Network Slice Selection Function (NSSF) [116] 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. 10
[0063] Network Exposure Function (NEF) [118] is a network function that
exposes capabilities and services of the 5G network to external applications, enabling integration with third-party services and applications.
15 [0064] Network Repository Function (NRF) [120] 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.
[0065] Policy Control Function (PCF) [122] is a network function
20 responsible for policy control decisions, such as QoS, charging, and access control,
based on subscriber information and network policies.
[0066] Unified Data Management (UDM) [124] is a network function that
centralizes the management of subscriber data, including authentication,
25 authorization, and subscription information.
[0067] Application Function (AF) [26] is a network function that represents
external applications interfacing with the 5G core network to access network capabilities and services. 30
18

[0068] User Plane Function (UPF) [128] is a network function responsible
for handling user data traffic, including packet routing, forwarding, and QoS enforcement.
5 [0069] Data Network (DN) [130] refers to a network that provides data
services to user equipment (UE) in a telecommunications system. The data services
may include but are not limited to Internet services, private data network related
services.
[0070] PLMN: A Public Land Mobile Network is a wireless communication
10 system which comprises of all mobile wireless networks which use earth-based
stations instead of satellites. PLMN can stand alone but are often interconnected with a fixed system.
[0071] CIRCLES: Telecommunication circles are geographic regions which
can be utilized by telecommunication companies for regulatory and administrative
15 purposes. A telecommunication company has valid licenses issued by the
Department of Telecommunication (DoT).
[0072] SMF+GW: SMF+GW refers to a combined entity in a mobile
communication network, specifically within the context of 5G networks, that
20 includes the Session Management Function (SMF) and the Gateway (GW). This
combined entity plays a crucial role in managing both session and data aspects within the network. Together, SMF+GW forms an integrated entity that efficiently manages both the control plane (session management) and the user plane (data handling) aspects of the network. This combined approach allows for seamless
25 communication, efficient data transfer, and effective resource allocation within the
5G network, enhancing the overall performance and user experience.
[0073] SMF+GW-U: SMF+GW-U refers to a combined entity in a mobile
communication network, specifically within the context of 5G networks, that
30 includes the Session Management Function (SMF) and the User Plane Function and
Gateway (UPF+GW-U). Together, SMF+GW-U forms an integrated entity that
19

manages both the session management and user data aspects of the network, ensuring seamless communication and efficient data handling within the 5G network.
5 [0074] FIG.2 illustrates an exemplary block diagram of a system [200] for
ensuring call continuity during an inter-public land mobile network (PLMN)
handover in a mobile communication network, in accordance with exemplary
embodiments of the present disclosure. As shown in FIG. 2, the system [200]
comprises a processing Unit [202], and a memory [204]. In FIG. 2 only a few units
10 are shown, however, the system [200] may comprise multiple such units or the
system [200] may comprise any such numbers of said units, as required to implement the features of the present disclosure.
[0075] The system [200] for ensuring call continuity during an inter-PLMN
15 handover in a mobile communication network comprises the processing unit [202],
which is configured to detect when a User Equipment (UE) passes from a geographical area of a source PLMN (A) to a geographical area of a target PLMN (B). In an embodiment, the geographical area of the source PLMN(A) is different from the geographical area of the target PLMN(B). The detection of the UE's
20 movement across PLMN boundaries is typically based on signals received from the
UE or the network infrastructure, such as the source and target RAN nodes. Once the processing unit [202] identifies that the UE is moving into the coverage area of a different PLMN, it initiates a series of coordinated actions to ensure that the transition is seamless and does not disrupt the user's experience. This involves
25 initiating a handover request, selecting appropriate network elements in the target
PLMN, and managing the transfer of session and user context information between the source and target PLMNs. By accurately detecting the geographical transition of the UE and efficiently managing the handover process, the system [200] ensures that users experience uninterrupted voice and data services, even when moving
30 across different PLMN territories.
20

[0076] The processing unit [202] is further configured to initiate a handover
request by the User Equipment (UE) or a source Radio Access Network (RAN)
node associated with the source Public Land Mobile Network (PLMN A). The
handover request comprises information associated with but not limited only to the
5 UE's current state, capabilities, and ongoing communication sessions. When the UE
initiates the handover request, it typically does so based on its own measurements
of the signal quality from the surrounding networks. If the UE detects that the signal
from the target PLMN (B) is stronger than that of the current source PLMN (A), it
may decide to request a handover to the target PLMN. On the other hand, the source
10 RAN node may initiate the handover request on behalf of the UE based on its
assessment of the network conditions and the UE's location.
[0077] The UPF+GW-U is responsible for anchoring user context data, which
includes information about the subscriber's session such as IP addresses, QoS
15 profiles, and the state of the active data flows. By anchoring this data, the
UPF+GW-U maintains a persistent point of connectivity for the user’s data traffic, thereby ensuring that audio and video calls continue without interruption even as the User Equipment (UE) moves from one Public Land Mobile Network (PLMN) to another. During the handover process, the session and bearer management
20 functions of the SMF+GW in the source PLMN will cooperate with the UPF+GW-
U to sustain the active sessions despite the change in the radio access network connections, the data flow for ongoing calls or sessions is seamlessly transferred to the new PLMN. The data packets are thus continuously routed through the appropriate paths, providing an uninterrupted experience to the end-user. The
25 capability is vital for services that require real-time communication, such as Voice
over LTE (VoLTE) or video conferencing, where even brief disruptions can significantly degrade the quality of the communication. Anchoring refers to maintaining a consistent and stable data connection for the User Equipment (UE) as it transitions between different Public Land Mobile Networks (PLMNs). This is
30 achieved by retaining the same Session Management Function and serving/packet
data network (PDN) (S/P) Gateway (SMF+GW) from the source PLMN throughout
21

the handover to the target PLMN, ensuring seamless continuity of ongoing voice
and video calls. For example, if a 5G user is on a VoLTE call while crossing the
border between two PLMNs, the user’s context is transferred to the new PLMN’s
MME, which retains the same SMF+GW, ensuring the call remains uninterrupted.
5 Anchoring minimizes disruptions during inter-PLMN handovers, particularly in
border areas, simplifies the procedure, requires minimal configuration changes.
[0078] The processing unit [202] is further configured to select a target
eNodeB (eNB) of the target Public Land Mobile Network (PLMN B) and a Mobile
10 Management Entity (MME) of the target PLMN (B) as part of the handover process.
The target eNB is the base station in the target PLMN (B) that the UE will connect to after the handover is completed. The selection of the target eNB is based on various factors such as signal strength, network load, and the geographical location of the UE. The processing unit [202] ensures that the most suitable eNB is chosen
15 to provide optimal service to the UE in the target PLMN. The MME is a core
network element in the target PLMN (B) that is responsible for managing the UE's mobility and session states by coordinating the necessary signalling messages between the source and target networks. The processing unit [202] selects the appropriate MME in the target PLMN (B) to handle the UE's transition and maintain
20 the continuity of its services.
[0079] The processing unit [202] is further configured to relocate the Mobile
Management Entity (MME) in the target Public Land Mobile Network (PLMN B) and fetch user context data from the source PLMN (A) MME via an S10 interface.
25 Relocating the MME in the target PLMN (B) involves transferring the control and
management of the User Equipment (UE) from the MME in the source PLMN (A) to the MME in the target PLMN (B). The user context data includes important information such as the UE's subscription details, current location, and security parameters. This data ensures that the target network can provide uninterrupted
30 service to the UE, as it contains all the necessary information to continue the session
that was initiated in the source network.
22

[0080] The processing unit [202] is further configured to retain, based on a
configuration and the fetched user context data, a combined Session Management
Function and Gateway (SMF+GW) of the source Public Land Mobile Network
5 (PLMN A). Retaining the SMF+GW of the source PLMN (A) means that even
though the UE is moving to a new PLMN (B), the session management and gateway functions continue to be handled by the same network elements from the source PLMN (A). This approach simplifies the handover process by minimizing the number of changes needed in the network configuration and reducing the potential
10 for service disruption. The decision to retain the SMF+GW is based on the
configuration of the network and the user context data fetched from the source PLMN (A) MME via the S10 interface. This data includes important information such as subscription details, current location, and security parameters, which are used to determine the best way to maintain the UE's session continuity.
15
[0081] The processing unit [202] is further configured to select, via the target
Public Land Mobile Network (PLMN B) Mobile Management Entity (MME), the source PLMN (A) combo Session Management Function and Gateway (SMF+GW). The source PLMN (A) combo SMF + GW is selected via an S11
20 interface. By selecting the source PLMN (A) combo SMF+GW via the target
PLMN (B) MME, the processing unit [202] ensures that the same session management and gateway functions continue to handle the UE's session even after the handover to the target PLMN. This approach simplifies the handover process by minimizing the need for reconfiguring the network elements and reduces the
25 potential for service disruption. The decision to select the source PLMN (A) combo
SMF+GW is based on the configuration of the network and the user context data fetched from the source PLMN (A) MME via the S10 interface. This data includes important information such as subscription details, current location, and security parameters, which are used to determine the best way to maintain the UE's session
30 continuity. By selecting the source PLMN (A) combo SMF+GW via the target
PLMN (B) MME, the processing unit [202] facilitates a seamless handover
23

experience for the UE, ensuring that the ongoing voice or data session is uninterrupted. This capability is particularly beneficial in scenarios where users frequently move between different network coverage areas, such as in border regions, and require a smooth transition between networks. 5
[0082] In the handover process, a handover command is an essential
component that facilitates the transition of the User Equipment (UE) from one network to another. The handover command contains instructions for the UE to switch its connection from the current eNodeB (eNB) in the source Public Land
10 Mobile Network (PLMN A) to a new eNB in the target PLMN. The handover
command is sent from the Mobile Management Entity (MME) of the source PLMN (A) directly to the UE. It typically includes information such as the target cell identifier, radio resource configuration, and any necessary security parameters. The UE uses the information to establish a connection with the new eNB in the target
15 PLMN, ensuring a seamless transition and continuity of service.
[0083] After the User Equipment (UE) receives the handover command and
successfully connects to the new eNodeB (eNB) in the target Public Land Mobile Network (PLMN B), it sends a handover complete message back to the Mobile
20 Management Entity (MME) of the target PLMN (B). This message serves as a
confirmation that the UE has successfully changed its connection to the new eNB and that the handover process has been completed. The handover complete message signals to the target network that the UE is now under its control and that the network can start routing data and signals to the UE through the new connection. It
25 also triggers the release of resources in the source network, as the UE is no longer
connected to the source eNB.
[0084] Once the handover process is nearing completion, a Modify Bearer
Request (MBR) is sent from the Mobile Management Entity (MME) of the target
30 Public Land Mobile Network (PLMN B) to the Session Management Function
(SMF) [108] to establish user plane connectivity for the User Equipment (UE). The
24

Modify Bearer Request includes a Forwarding Tunnelling Endpoint identifier (FTE
ID). The FTE ID is a unique identifier used to route user data packets to the correct
destination. The FTE ID is used by the network to establish a bearer, which is a
virtual data path that carries the user's data traffic between the UE and the external
5 data network. By sending the Modify Bearer Request with the FTE ID, the MME
informs the SMF [108] about the new data path that needs to be set up for the UE in the target PLMN (B). The SMF [108] then configures the User Plane Function (UPF) [128] accordingly to ensure that the user's data traffic is correctly routed through the network.
10
[0085] After the Modify Bearer Request (MBR) is sent to establish user plane
connectivity, a Session Management Request (SMR) is sent from the Session Management Function (SMF) to the User Plane Function (UPF) [128] in the target network. The SMR typically includes information such as the session context,
15 quality of service (QoS) parameters, and routing rules. This information enables the
UPF [128] to set up the necessary data paths and allocate the appropriate resources to ensure that the UE's data traffic is handled efficiently and according to the specified QoS requirements.
20 [0086] By sending the Session Management Request, the SMF ensures that the
UPF [128] is fully prepared to manage the user data traffic for the UE in the new network, providing a seamless and uninterrupted service experience for the user.
[0087] Referring to FIG. 3 an exemplary architecture [300] for implementing
25 system for ensuring call continuity during an inter public land mobile network
(PLMN) handover in a mobile communication network, in accordance with
exemplary embodiments of the present invention is shown. The architecture [300]
comprises a PLMN (A) user equipment (UE) [102], a PLMN (A) [306], a PLMN
(B) [308], a combo core A [310], a combo core B [312], a PLMN (A) eNB [314], a
30 PLMN (A) MME [316], a PLMN (B) MME [318], and PLMN (B) eNB [220]. In
an embodiment, the combo core A [310] includes the SMF [108], a serving gateway control (SGW-C) [310A], and packet gateway control (PGW-C) [310B]. In an
25

embodiment, the combo core B [312] includes the UPF [128], a serving gateway
user plane (SGW-U) [312A], and a packet gateway user plane (PGW-U) [312B],
wherein all the components are assumed to be connected to each other in a manner
as obvious to the person skilled in the art for implementing features of the present
5 disclosure. Also, in FIG. 3 only a few units are shown, however, the architecture
[300] may comprise multiple such units or the architecture [300] may comprise any such numbers of said units, as required to implement the features of the present disclosure.
10 [0088] Referring to FIG. 3, the PLMN (A) UE [102] represents the user
equipment that maintains an active connection with the source network, such as PLMN (A) [306], during the initial phase of handover. When the user equipment [102] moves and crosses into a different geographical area, specifically into the area covered by PLMN (B) [308], the system activates a handover procedure to maintain
15 continuous call connectivity. The transition is managed by the processing unit
[202], which is configured to detect the change in geographical location of the UE [102] and to initiate the necessary handover procedures to ensure that the call does not drop and the user experience remains seamless.
20 [0089] The procedure includes the selection of a new target eNB [214] in
PLMN (B) [308] and the initiation of a transfer of control to the MME [218] within the target PLMN (B) [308]. The user context comprises essential data for maintaining the ongoing call such as subscription details and security parameters, is relayed from the source PLMN (A) MME [316] to the target PLMN (B) MME
25 [218] through the S10 interface. To facilitate a smooth transition without changing
the session and gateway control elements, the same combined Session Management Function and Gateway (SMF+GW) [210] from the source PLMN (A) [306] is retained.
30 [0090] The architecture [300] includes a combo core A [310] that includes the
SMF [108], the SGW-C [310A], and the PGW-C [310B], for managing the control
26

plane of data sessions. Correspondingly, the combo core B [312] incorporates the UPF [128], the SGW-U [312A], and the PGW-U [312B], which are part of the user plane and handle the actual data traffic for the UE [102].
5 [0091] Further, a Modify Bearer Request (MBR) with a Forwarding
Tunnelling Endpoint identifier (FTE ID) is dispatched from the target PLMN (B)
MME [218] to the retained SMF [108] to solidify user plane connectivity.
Concurrently, a Session Management Request (SMR) is sent to the UPF [128] to
prepare for the incoming data traffic, thus ensuring the resources are in place to
10 support the continued communication.
[0092] For example, a user on a 5G voice call while traveling near the border
of two network coverage areas, known as PLMNs. As they cross from PLMN (A) into PLMN (B), typically, the call would drop due to the need to detach from the
15 old network (A) and reattach to the new network (B). However, with this invention,
the call continues seamlessly. As the user moves into PLMN (B)'s coverage, the system detects this movement and initiates a handover without dropping the call. The target network's eNB [320] and MME [318] are selected, but instead of establishing a new session, the system cleverly retains the session management and
20 control functions from PLMN (A) [306]. This means there's no need for the UE
[102] to reestablish these elements in PLMN (B) [308], which typically causes the call disruption. The user's context is transferred over to the new network via the S10 interface, and the SMF+GW from PLMN (A) [306] continues to manage the session as if nothing has changed. The UPF [128] in PLMN (B) [308] is prepared to handle
25 the data traffic, ensuring no interruption in service. The result is that the user
experiences no drop in their voice call, and the transition between networks is invisible to them, thanks to the inventive steps taken within the system's architecture to maintain call continuity.
30 [0093] FIG. 4 illustrates an exemplary sequence diagram for ensuring call
continuity during an inter- public land mobile network (PLMN) handover in a
27

mobile communication network, in accordance with exemplary embodiments of the present disclosure.
[0094] At step S1, a handover request may be initiated by UE/RAN [402] to
5 MME1 [406] at circle 1. At the step S1 the handover process is initiated as the user
equipment (UE) [102] detects it is moving from one PLMN to another, signalling the need to switch from the current network (circle 1) to a new network (circle 2).
[0095] Next at step S2, a Forward Relocation Request (FRR) for context
10 transfer may take place from MME1 [406] at circle 1 to MME 2 [408] at circle 2.
This involves transferring user-specific information from the source MME (circle 1) to the target MME (circle 2), ensuring the target network has all necessary information to continue the ongoing session seamlessly.
15 [0096] Now at step S3, a handover request may be initiated from MME2 [408]
(circle 2) to UE/RAN [404] (circle 2). The MME2 [408] (circle 2) informs the UE/RAN [404] to prepare for the incoming UE, setting up the necessary resources in the target network to accommodate the handover.
20 [0097] Further, at step S4, a handover acknowledgement may be sent from
UE/RAN [404] (circle 2) to MME2 [408] (circle 2). The acknowledgement confirms that the UE [102] has received the handover request from the UE/RAN [402] and is ready to proceed with the handover process, ensuring synchronization between the UE [102] and the UE/RAN [404].
25
[0098] Furthermore, at step S5, an FRR (response) may be sent from MME2
[408] (circle 2) to MME1 [406] (circle 1). The FRR response confirms that the MME2 [408] has successfully received and processed the context information, providing the MME1 [406] with the necessary feedback to proceed with the next
30 steps of the handover.
28

[0099] Next at step S6, a handover command may be sent from MME1 [406]
(circle 1) to UE/RAN [402] (in circle 1). The command instructs the UE [102] to switch to the new eNB (UE/RAN [404]), directing the UE [102] to transition from the source network (such as circle 1) to the target network (such as circle 2). 5
[0100] Thereafter, at step S7 a handover complete may be sent from UE/RAN
[404] (circle 2) to MME2 [408] (in circle 2). The message indicates that the UE
[102] has successfully connected to the target RAN (such as UE/RAN [404]) and
completed the handover process, ensuring the MME2 [408] that the UE [102] is
10 now under its control.
[0101] Now at step S8, MBR comprising an FTE ID may be sent from MME2
[408] to SMF [108]. The MBR is sent to establish or modify bearer parameters to
ensure continuity of the data session having the FTE ID for identifying the correct
15 forwarding path for the user's data traffic in the new network (such as circle 2).
[0102] Next at step S9, a SMR may be sent from SMF [108] to UPF [128]. The
request instructs the User Plane Function (UPF) to prepare for handling the user
data traffic, ensuring that the data path is correctly set up and that ongoing sessions
20 (such as voice or video calls) continue without interruption.
[0103] FIG. 5 illustrates an an exemplary block diagram of a computer system
[500] upon which an embodiment of the present disclosure may be implemented. In an implementation, the computer system [500] implements the method for
25 ensuring call continuity during an inter- public land mobile network (PLMN)
handover in a mobile communication network using the system [200]. In another implementation, the computer system [500] itself implements the method for ensuring call continuity during an inter- public land mobile network (PLMN) handover in a mobile communication network using one or more units configured
30 within the computer system [500], wherein said one or more units are capable of
implementing the features as disclosed in the present disclosure.
29

[0104] The computer system [500] encompasses a wide range of electronic
devices capable of processing data and performing computations. Examples of
computer system [500] include, but are not limited only to, personal computers,
5 laptops, tablets, smartphones, servers, and embedded systems. The devices may
operate independently or as part of a network and can perform a variety of tasks
such as data storage, retrieval, and analysis. Additionally, computer system [500]
may include peripheral devices, such as monitors, keyboards, and printers, as well
as integrated components within larger electronic systems, showcasing their
10 versatility in various technological applications.
[0105] The computer system [500] may include a bus [502] or other
communication mechanism for communicating information, and a processor [504] coupled with bus [502] for processing information. The processor [504] may be, for
15 example, a general-purpose microprocessor. The computer system [500] may also
include a main memory [506], such as a random-access memory (RAM), or other dynamic storage device, coupled to the bus [502] for storing information and instructions to be executed by the processor [504]. The main memory [506] also may be used for storing temporary variables or other intermediate information
20 during execution of the instructions to be executed by the processor [504]. Such
instructions, when stored in non-transitory storage media accessible to the processor [504], render the computer system [500] into a special-purpose machine that is customized to perform the operations specified in the instructions. The computer system [500] further includes a read only memory (ROM) [508] or other static
25 storage device coupled to the bus [502] for storing static information and
instructions for the processor [504].
[0106] A storage device [510], such as a magnetic disk, optical disk, or solid-
state drive is provided and coupled to the bus [502] for storing information and
30 instructions. The computer system [500] may be coupled via the bus [502] to a
display [512], such as a cathode ray tube (CRT), for displaying information to a
30

computer user. An input device [514], including alphanumeric and other keys, may
be coupled to the bus [502] for communicating information and command
selections to the processor [504]. Another type of user input device may be a cursor
control [516], such as a mouse, a trackball, or cursor direction keys, for
5 communicating direction information and command selections to the processor
[504], and for controlling cursor movement on the display [512]. This input device [514] typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allow the device to specify positions in a plane.
10 [0107] The computer system [500] may implement the techniques described
herein using customized hard-wired logic, one or more ASICs or FPGAs, firmware and/or program logic which in combination with the computer system [500] causes or programs the computer system [500] to be a special-purpose machine. According to one embodiment, the techniques herein are performed by the computer system
15 [500] in response to the processor [504] executing one or more sequences of one or
more instructions contained in the main memory [506]. Such instructions may be read into the main memory [506] from another storage medium, such as the storage device [510]. Execution of the sequences of instructions contained in the main memory [506] causes the processor [504] to perform the process steps described
20 herein. In alternative embodiments, hard-wired circuitry may be used in place of or
in combination with software instructions.
[0108] The computer system [500] also may include a communication
interface [518] coupled to the bus [502]. The communication interface [518]
25 provides a two-way data communication coupling to a network link [520] that is
connected to a local network [522]. For example, the communication interface [518] 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
30 interface [518] may be a local area network (LAN) card to provide a data
communication connection to a compatible LAN. Wireless links may also be
31

implemented. In any such implementation, the communication interface [518] sends and receives electrical, electromagnetic or optical signals that carry digital data streams representing various types of information.
5 [0109] The computer system [500] can send messages and receive data,
including program code, through the network(s), the network link [520] and the
communication interface 518. In the Internet example, a server [530] might transmit
a requested code for an application program through the Internet [528], the ISP
[526], the local network [522] and the communication interface [518]. The received
10 code may be executed by the processor [504] as it is received, and/or stored in the
storage device [510], or other non-volatile storage for later execution.
[0110] Referring to FIG. 6 an exemplary method [600] flow diagram indicating
the process for ensuring call continuity during an inter- public land mobile network
15 (PLMN) handover in a mobile communication network, in accordance with
exemplary embodiments of the present invention is shown. In an embodiment, the method may be implemented by the system [200] or the processing unit [202]. The method [600] for ensuring call continuity during an inter-PLMN handover in a mobile communication network. The method may be implemented by a system
20 [200]. The method begins at step [602].
[0111] At step [604] the method includes: detecting, by a processing unit [202]
when a User Equipment (UE) [102] passes from a geographical area of a source PLMN (A) [106] to a geographical area of a target PLMN (B) [208]. In an
25 embodiment, the geographical area of the source PLMN(A) is different from the
geographical area of the target PLMN(B). The detection of the UE's movement across PLMN boundaries is typically based on signals received from the UE or the network infrastructure, such as the source and target RAN nodes. Once the processing unit [202] identifies that the UE is moving into the coverage area of a
30 different PLMN, it initiates a series of coordinated actions to ensure that the
transition is seamless and does not disrupt the user's experience. This involves
32

initiating a handover request, selecting appropriate network elements in the target
PLMN, and managing the transfer of session and user context information between
the source and target PLMNs. By accurately detecting the geographical transition
of the UE and efficiently managing the handover process, the system [200] ensures
5 that users experience uninterrupted voice and data services, even when moving
across different PLMN territories.
[0112] .
[0113] Further, at step [606] the method encompasses initiating, by the
processing unit [202], a handover request by the UE [102] or a source RAN node
10 associated with the source PLMN (A) [106]. The handover request comprises
information associated with but not limited only to the UE's current state, capabilities, and ongoing communication sessions. When the UE initiates the handover request, it typically does so based on its own measurements of the signal quality from the surrounding networks. If the UE detects that the signal from the
15 target PLMN (B) is stronger than that of the current source PLMN (A), it may
decide to request a handover to the target PLMN. On the other hand, the source RAN node may initiate the handover request on behalf of the UE based on its assessment of the network conditions and the UE's location.
20 [0114] The UPF+GW-U is responsible for anchoring user context data, which
includes information about the subscriber's session such as IP addresses, QoS profiles, and the state of the active data flows. By anchoring this data, the UPF+GW-U maintains a persistent point of connectivity for the user’s data traffic, thereby ensuring that audio and video calls continue without interruption even as
25 the User Equipment (UE) moves from one Public Land Mobile Network (PLMN)
to another. During the handover process, the session and bearer management functions of the SMF+GW in the source PLMN will cooperate with the UPF+GW-U to sustain the active sessions despite the change in the radio access network connections, the data flow for ongoing calls or sessions is seamlessly transferred to
30 the new PLMN. The data packets are thus continuously routed through the
appropriate paths, providing an uninterrupted experience to the end-user. The
33

capability is vital for services that require real-time communication, such as Voice
over LTE (VoLTE) or video conferencing, where even brief disruptions can
significantly degrade the quality of the communication. Anchoring refers to
maintaining a consistent and stable data connection for the User Equipment (UE)
5 as it transitions between different Public Land Mobile Networks (PLMNs). This is
achieved by retaining the same Session Management Function and Gateway
(SMF+GW) from the source PLMN throughout the handover to the target PLMN,
ensuring seamless continuity of ongoing voice and video calls. For example, if a
5G user is on a VoLTE call while crossing the border between two PLMNs, the
10 user’s context is transferred to the new PLMN’s MME, which retains the same
SMF+GW, ensuring the call remains uninterrupted. Anchoring minimizes disruptions during inter-PLMN handovers, particularly in border areas, simplifies the procedure, requires minimal configuration changes.
15 [0115] Further, at step [608] the method comprises selecting a target eNB [214]
of the PLMN (B) [208], a Mobile Management Entity (MME [218]) of the serving PLMN (B) [208]. The target eNB is the base station in the target PLMN (B) that the UE will connect to after the handover is completed. The selection of the target eNB is based on various factors such as signal strength, network load, and the
20 geographical location of the UE. The processing unit [202] ensures that the most
suitable eNB is chosen to provide optimal service to the UE in the target PLMN. The MME is a core network element in the target PLMN (B) that is responsible for managing the UE's mobility and session states by coordinating the necessary signalling messages between the source and target networks. The processing unit
25 [202] selects the appropriate MME in the target PLMN (B) to handle the UE's
transition and maintain the continuity of its services.
[0116] Next, at step [610], the method encompasses relocating, by the
processing unit [202], the MME [218] in the target PLMN (B) and fetching a user
30 context data from the source PLMN (A) MME [216] via an S10 interface.
Relocating the MME in the target PLMN (B) involves transferring the control and
34

management of the User Equipment (UE) from the MME in the source PLMN (A)
to the MME in the target PLMN (B). The user context data includes important
information such as the UE's subscription details, current location, and security
parameters. This data ensures that the target network can provide uninterrupted
5 service to the UE, as it contains all the necessary information to continue the session
that was initiated in the source network.
[0117] Now, at step [612] the method retaining, by the processing unit [202],
based on a configuration and the fetched user context data, a combined Session
10 Management Function and Gateway (SMF+GW) [210] of the source PLMN (A)
[206]. Retaining the SMF+GW of the source PLMN (A) means that even though the UE is moving to a new PLMN (B), the session management and gateway functions continue to be handled by the same network elements from the source PLMN (A). This approach simplifies the handover process by minimizing the
15 number of changes needed in the network configuration and reducing the potential
for service disruption. The decision to retain the SMF+GW is based on the configuration of the network and the user context data fetched from the source PLMN (A) MME via the S10 interface. This data includes important information such as subscription details, current location, and security parameters, which are
20 used to determine the best way to maintain the UE's session continuity.
[0118] Thereafter, at step [614], the method includes selecting, by the
processing unit [202] via the target PLMN (B) MME [218], the source PLMN (A) combo SMF+GW [210]. The source PLMN (A) combo SMF + GW is selected via
25 an S11 interface. By selecting the source PLMN (A) combo SMF+GW via the
target PLMN (B) MME, the processing unit [202] ensures that the same session management and gateway functions continue to handle the UE's session even after the handover to the target PLMN. This approach simplifies the handover process by minimizing the need for reconfiguring the network elements and reduces the
30 potential for service disruption. The decision to select the source PLMN (A) combo
SMF+GW is based on the configuration of the network and the user context data
35

fetched from the source PLMN (A) MME via the S10 interface. This data includes
important information such as subscription details, current location, and security
parameters, which are used to determine the best way to maintain the UE's session
continuity. By selecting the source PLMN (A) combo SMF+GW via the target
5 PLMN (B) MME, the processing unit [202] facilitates a seamless handover
experience for the UE, ensuring that the ongoing voice or data session is uninterrupted. This capability is particularly beneficial in scenarios where users frequently move between different network coverage areas, such as in border regions, and require a smooth transition between networks. 10
[0119] The method terminates [616].
[0120] As is evident from the above, the present disclosure provides a
technically advanced solution during Inter PLMN handover, call continuity may be
15 achieved and also ensures seamless user experience. Further, the present invention
encompasses a simplified call flow where same SMF+GW-U(UPF) communicates with source RAN as well as Target RAN, thereby ensuring most simple and minimal touch solution. Also, minimal configuration at existing deployed network elements (MME and SMF) and enabled interfaces and the present solution is fully
20 aligned with 3GPP standards.
[0121] Another aspect of the present disclosure relates to a user equipment
(UE) [102] for ensuring call continuity during an inter- Public land mobile network (PLMN) handover in a mobile communication network, the UE comprising: a
25 processor configured to: detect when the UE [102] passes from a geographical area
of a source PLMN (A) [306] to a geographical area of a target PLMN (B) [308]; initiate a handover request by the UE [102] or a source RAN node associated with the source PLMN (A) [306]; select a target evolved node B (eNB) [314] of the target PLMN (B) [308], a Mobile Management Entity (MME) [318] of the target
30 PLMN (B) [308]; relocate the MME [318] in the target PLMN (B) [308] and
fetching a user context data from the source PLMN (A) MME [316]; retain, based
36

on a configuration and the fetched user context data, a combined Session Management Function and Gateway (SMF+GW) [310] of the source PLMN (A) [106]; and select, via the target PLMN (B) MME [318], the source PLMN (A) [306] combo SMF+GW [310]. 5
[0122] Yet another aspect of the present disclosure relates to a non-transitory
computer-readable storage medium storing instruction for ensuring call continuity during an inter- Public land mobile network (PLMN) handover in a mobile communication network, the storage medium comprising executable code which,
10 when executed by one or more units of a system, causes: a processing unit [202] to:
detect when a User Equipment (UE) [102] passes from a geographical area of a source PLMN (A) [306] to a geographical area of a target PLMN (B) [308]; initiate a handover request by the UE [102] or a source RAN node associated with the source PLMN (A) [306]; select, a target eNB [314] of the target PLMN (B) [308],
15 a Mobile Management Entity (MME) [318] of the target PLMN (B) [308]; relocate,
the MME [318] in the target PLMN (B) [308] and fetching a user context data from the source PLMN (A) MME [316]; retain, based on a configuration and the fetched user context data, a combined Session Management Function and Gateway (SMF+GW) [310] of the source PLMN (A) [306]; and select, via the target PLMN
20 (B) MME [318], the source PLMN (A) [306] combo SMF+GW [310].
[0123] 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
25 particular functionality of these units for clarity, it is recognized that various
configurations and combinations thereof 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
30 functionality described herein, are considered to be encompassed within the scope
of the present disclosure.
37

[0124] 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
5 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 descriptive matter to be implemented is illustrative and non-limiting.
38

I/We Claim:
1. A method for ensuring call continuity during an inter- Public land mobile
network (PLMN) handover in a mobile communication network, the method
5 comprising:
detecting, by a processing unit [202] when a User Equipment (UE) [102] passes from a geographical area of a source PLMN (A) [306] to a geographical area of a target PLMN (B) [308];
initiating, by the processing unit [202], a handover request by the UE
10 [102] or a source RAN node associated with the source PLMN (A) [306];
selecting, by the processing unit [202], a target evolved node B (eNB) [314] of the target PLMN (B) [308], a Mobile Management Entity (MME) [318] of the target PLMN (B) [308];
relocating, by the processing unit [202], the MME [318] in the target
15 PLMN (B) [308] and fetching a user context data from the source PLMN (A)
MME [316];
retaining, by the processing unit [202], based on a configuration and the
fetched user context data, a combined Session Management Function and
Gateway (SMF+GW) [310] of the source PLMN (A) [106]; and
20 selecting, by the processing unit [202] via the target PLMN (B) MME
[318], the source PLMN (A) [306] combo SMF+GW [310].
2. The method as claimed in claim 1, wherein the geographical area of the source
PLMN(A) [306] is different from the geographical area of the target
25 PLMN(B) [308].
3. The method as claimed in claim 1, where the source PLMN (A) [306] combo
SMF + GW [310] is selected via an S11 interface.
39

4. The method as claimed in claim 1, wherein a User Plane Function and
Gateway in a user plane (UPF+GW-U) [312] anchors the user context data to achieve audio/video call continuity during the inter-PLMN handover.
5 5. The method as claimed in claim 1, wherein the handover request comprises
information associated with the UE's [102] current state, capabilities, and ongoing communication sessions.
6. The method as claimed in claim l, wherein the user context data is fetched via
10 an S10 interface, the user context data comprises at least one of subscription
details, current location, and security parameters.
7. The method as claimed in claim 1, wherein a handover command, comprising
instructions for the UE [102] to change the eNB [314], is sent from MME
15 [316] of the source PLMN (A) to the UE [102].
8. The method as claimed in claim 1, further comprising the step of sending a
handover complete message from the UE [102] to the MME [318] of the
target PLMN (B), confirming successful change of eNB [314] and completion
20 of the handover.
9. The method as claimed in claim 1, wherein a Modify Bearer Request (MBR)
comprising a Forwarding Tunnelling Endpoint identifier (FTE ID) is sent
from MME [318] of the target PLMN (B) to SMF [310] to establish user plane
25 connectivity.
10. The method as claimed in claim 4, wherein a Session Management Request
(SMR) is sent from the SMF [108] to the UPF [128], instructing the UPF
[128] to prepare for user data traffic.
40

11. A system [200] for ensuring call continuity during an inter- Public land mobile network (PLMN) handover in a mobile communication network, the system comprising a processing unit [202] configured to:
detect when a User Equipment (UE) [102] passes from a geographical
5 area of a source PLMN (A) [306] to a geographical area of a target PLMN
(B) [308];
initiate a handover request by the UE [102] or a source RAN node associated with the source PLMN (A) [306];
select, a target evolved node B (eNB) [314] of the target PLMN (B)
10 [308], a Mobile Management Entity (MME) [318] of the target PLMN (B)
[308];
relocate, the MME [318] in the target PLMN (B) [308] and fetching a user context data from the source PLMN (A) MME [316];
retain, based on a configuration and the fetched user context data, a
15 combined Session Management Function and Gateway (SMF+GW) [310] of
the source PLMN (A) [306]; and
select, via the target PLMN (B) MME [318], the source PLMN (A) [306] combo SMF+GW [310].
20 12. The system as claimed in claim 11, wherein the geographical area of the
source PLMN(A) [306] is different from the geographical area of the target PLMN(B) [308].
13. The system as claimed in claim 11, where the source PLMN (A) [306] combo
25 SMF + GW [310] is selected via an S11 interface.
14. The system as claimed in claim 11, wherein a User Plane Function and
Gateway in a user plane (UPF+GW-U) [312] anchors the user context data
to achieve audio/video call continuity during the inter-PLMN handover.
41

15. The system as claimed in claim 11, wherein the handover request comprises information associated with the UE's [102] current state, capabilities, and ongoing communication sessions.
5 16. The system as claimed in claim 1l, wherein the user context data is fetched
vinban S10 interface, the user context data comprises at least one of subscription details, current location, and security parameters.
17. The system as claimed in claim 11, wherein a handover command,
10 comprising instructions for the UE [102] to change the eNB [314], is sent
from MME [316] of the source PLMN (A) to the UE [102].
18. The system as claimed in claim 11, wherein a handover complete message is
sent from the UE [102] to the MME [318] of the target PLMN (B) to confirm
15 successful change of eNB [314] and completion of the handover.
19. The system as claimed in claim 11, wherein a Modify Bearer Request (MBR)
comprising a Forwarding Tunnelling Endpoint identifier (FTE ID) is sent
from MME [318] of the target PLMN (B) to SMF [310] to establish user plane
20 connectivity.
20. The system as claimed in claim 14, wherein a Session Management Request
(SMR) is sent from the SMF [108] to the UPF [128], instructing the UPF
[128] to prepare for user data traffic.
25
21. A user equipment (UE) [102] for ensuring call continuity during an inter¬
Public land mobile network (PLMN) handover in a mobile communication
network, the UE comprising:
a processor configured to:
30 detect when the UE [102] passes from a geographical area of a source
PLMN (A) [306] to a geographical area of a target PLMN (B) [308];
42

initiate a handover request by the UE [102] or a source RAN node associated with the source PLMN (A) [306];
select a target eNB [314] of the target PLMN (B) [308], a Mobile
Management Entity (MME) [318] of the target PLMN (B) [308];
5 relocate the MME [318] in the target PLMN (B) [308] and fetching a
user context data from the source PLMN (A) MME [316];
retain, based on a configuration and the fetched user context data, a
combined Session Management Function and Gateway (SMF+GW) [310] of
the source PLMN (A) [106]; and
10 select, via the target PLMN (B) MME [318], the source PLMN (A)
[306] combo SMF+GW [310].