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 MAINTAINING CALL CONTINUITY
FOR A USER DEVICE”
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 MAINTAINING CALL CONTINUITY
FOR A USER DEVICE
FIELD OF THE DISCLOSURE
[0001] The present disclosure relates generally to the field of wireless communication systems. More particularly, the present disclosure relates to methods and systems for maintaining call continuity during network coverage issues in lower generation networks such as 4G network.
BACKGROUND
[0002] 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.
[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 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.
[0004] There may be a scenario where the user equipment may not be able to connect to the services of higher generation network due to issues such as low-quality signal, user equipment being not supported, and other various issues, in that scenario to facilitate the service or network functions, the user equipment has to fall back to lower generation network for availing the services. When a higher generation network (say a 5G) user equipment falls back to a lower generation network (say a 4G network) for voice calls, it is assumed that it should come back to the higher generation network after release of the voice call from the lower generation network But in real network scenario it is observed that due to poor RF (radio frequency) conditions, the user in lower generation such as 4G during an ongoing call attempts to connect to higher generation such as 5G. In such condition, the sessions management function (SMF) denies the evolved packet service (EPS) Fallback trigger from the gNodeB as the call is still ongoing. This results in call drops and poor customer experience. The EPS fallback is when a UE tries to use voice services in a 5G network that does not support Voice over New Radio (VoNR), the gNB redirects or performs a handover to the Long Term Evolution (LTE) network, and consequently the user equipment (UE) is able to use voice services via Voice over Long Term Evolution (VoLTE). After the voice session is terminated, the UE can move back to the 5G network.
[0005] Thus, there exists an imperative need in the art to provide a method and a system that allows for maintaining call continuity in 4G during network coverage issues in 4G network and enabling the user device to perform a smooth handover to 4G from 5G during the ongoing call, which the present disclosure aims to address.

[0006] Some of the objects of the present disclosure, which at least one implementation disclosed herein satisfies are listed herein below.
[0007] It is an object of the present disclosure to provide a system and a method that allows for maintaining call continuity for a user device in lower generation network such as 4G network during network coverage issues in the 4G network and enabling the user device to perform smooth handover to a lower generation network such as 4G network from a higher generation network such as 5G network during the ongoing call.
[0008] It is another object of the present disclosure to provide a solution that improves user experience by eliminating or reducing call drops and/or muting of the call by enabling call continuity during network coverage issues in the lower generation network such as 4G network.
[0009] It is yet another object of the present disclosure to provide a solution that enables the user device to perform a smooth handover to lower generation network such as 4G network from higher generation network such as 5G network during an ongoing call.
SUMMARY
[0010] 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.
[0011] An aspect of the present disclosure relates to a method for maintaining call continuity for a user device. The method comprises facilitating an establishment of a call for the user device in a higher generation network by a call establishment unit.

The method also comprises facilitating a fallback procedure for switching the call to a lower generation network by a switching unit. The method also comprises changing a state of the user device to an idle state by a transition unit in an event of occurrence of one or more network coverage issues. The method also comprises receiving a registration retry request for establishing connection of the user device with the higher generation network by a transceiver unit from the user device. The method also comprises triggering the fallback procedure upon receiving an establishment request from a session management entity by the call establishment unit for establishing a target call flow for establishing the call in the higher generation network. And finally, the method comprises facilitating the call continuity for the user device in the lower generation network based on the fallback procedure, by the session management entity.
[0012] According to another aspect of the present disclosure the triggering the fallback procedure further comprises rejecting, by the call establishment unit, the establishment request for establishing the target call flow for establishing the call in the higher generation network.
[0013] According to another aspect of the present disclosure, the triggering the fallback procedure further comprises receiving, by the session management entity from a base station, an indication for performing the fallback procedure.
[0014] According to another aspect of the present disclosure the session management entity is a session management function (SMF) module implementing a session management function in a 5G network.
[0015] According to another aspect of the present disclosure the target call flow is a 5G Quality of Service Identifiers (5QI) call flow.
[0016] Another aspect of the present disclosure relates to a system for maintaining call continuity for a user device. The system comprises a call establishment unit, a

switching unit, a transition unit, and a transceiver unit connected to each other. The system is connected to a session management entity. The call establishment unit is configured to facilitate an establishment of a call for the user device in a higher generation network. The switching unit is configured to facilitate a fallback procedure for switching the call to a lower generation network. The transition unit is configured to change a state of the user device to an idle state, in an event of occurrence of one or more network coverage issues. The transceiver unit is configured to receive a registration retry request for establishing connection of the user device with the higher generation network from the user device. The call management entity is also configured to trigger the fallback procedure upon receiving an establishment request from a session management entity for establishing a target call flow for establishing the call in the higher generation network. The session management entity of the system is configured to facilitate the call continuity for the user device in the lower generation network based on the fallback procedure.
[0017] Another aspect of the present disclosure relates to a non-transitory computer readable storage medium storing instruction for maintaining call continuity for a user device. The instructions comprising executable code which, when executed by one or more units of a system, causes: a call establishment unit of the system to facilitate an establishment of a call for the user device in a higher generation network; a switching unit of the system to facilitate a fallback procedure for switching the call to a lower generation network; a transition unit of the system to change a state of the user device to an idle state in an event of occurrence of one or more network coverage issues; a transceiver unit of the system to receive a registration retry request for establishing connection of the user device with the higher generation network from the user device; the call establishment unit of the system to trigger the fallback procedure upon receiving an establishment request from a session management entity for establishing a target call flow for establishing the call in the higher generation network; the session management entity to facilitate

the call continuity for the user device in the lower generation network based on the fallback procedure by the session management entity.
BRIEF DESCRIPTION OF DRAWINGS
5
[0018] The accompanying drawings, which are incorporated herein, and constitute a part of this disclosure, illustrate exemplary implementations 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
10 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
15 used to implement such components.
[0019] FIG. 1 illustrates an exemplary block diagram representation of 5th generation core (5GC) network architecture.
20 [0020] FIG. 1A illustrates an exemplary block diagram of a computing device upon
which the features of the present disclosure may be implemented in accordance with exemplary implementation of the present disclosure.
[0021] FIG. 1B illustrates an exemplary block diagram of a system [100A] for
25 maintaining call continuity for a user device, in accordance with exemplary
implementations of the present disclosure.
[0022] FIG. 2 illustrates an exemplary method flow diagram indicating the process
[200] for maintaining call continuity for a user device, in accordance with
30 exemplary implementations of the present disclosure.
7

[0023] FIG. 3 illustrates an exemplary call flow diagram for maintaining call continuity for a user device during network coverage issues, in accordance with exemplary implementation of the present disclosure.
5 [0024] The foregoing shall be more apparent from the following more detailed
description of the disclosure.
DETAILED DESCRIPTION
10 [0025] In the following description, for the purposes of explanation, various
specific details are set forth in order to provide a thorough understanding of implementations of the present disclosure. It will be apparent, however, that implementations of the present disclosure may be practiced without these specific details. Several features described hereafter can each be used independently of one
15 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 implementations of the present disclosure are described below, as illustrated in various drawings in
20 which like reference numerals refer to the same parts throughout the different
drawings.
[0026] The ensuing description provides exemplary implementations only, and is not intended to limit the scope, applicability, or configuration of the disclosure.
25 Rather, the ensuing description of the exemplary implementations will provide
those skilled in the art with an enabling description for implementing an exemplary implementation. 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.
30
8

[0027] 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
5 limitations on the described implementations. 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.
10
[0028] Specific details are given in the following description to provide a thorough understanding of the implementations. However, it will be understood by one of ordinary skill in the art that the implementations may be practiced without these specific details. For example, circuits, systems, networks, processes, and other
15 components may be shown as components in block diagram form in order not to
obscure the implementations 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 implementations.
20 [0029] Also, it is noted that individual implementations 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 can be performed in parallel or concurrently. In addition, the order of the operations may be re-arranged.
25 A process is terminated when its operations are completed but could have additional
steps not included in a figure.
[0030] The word “exemplary” and/or “demonstrative” is used herein to mean
serving as an example, instance, or illustration. For the avoidance of doubt, the
30 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
9

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
5 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.
[0031] As used herein, an “electronic device”, or “portable electronic device”, or
10 “user device” or “communication device” or “user equipment” or “device” refers
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,
15 a battery and an input-means such as a hard keypad and/or a soft keypad. 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
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,
20 virtual reality (VR) devices, augmented reality (AR) devices, laptop, 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.
25 [0032] Further, the user device may also comprise a “processor” or “processing
unit” includes processing unit, wherein processor refers to any logic circuitry for processing instructions. 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
30 DSP core, a controller, a microcontroller, Application Specific Integrated Circuits,
Field Programmable Gate Array circuits, any other type of integrated circuits, etc.
10

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.
5 [0033] 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
10 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.
[0034] Radio Access Technology (RAT) refers to the technology used by mobile
15 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
20 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.
25 Mobile devices often support multiple RATs, allowing them to connect to different
types of networks and provide optimal performance based on the available network
resources.
[0035] As discussed in the background section, due to poor RF conditions in lower
30 generation network such as 4G network, the user equipment in lower generation
network such as 4G during an ongoing call attempts to move to the higher
11

generation network such as 5G network and the current known solutions do not
allow smooth EPS fallback trigger from the higher generation network such as 5G
network to lower generation network such as 4G network during the call is ongoing.
The EPS fallback trigger is when a UE tries to use voice services in a 5G network
5 that does not support Voice over New Radio (VoNR), the gNB redirects or performs
a handover to the Long Term Evolution (LTE) network, and consequently the user equipment (UE) is able to use voice services via Voice over Long Term Evolution (VoLTE). After the voice session is terminated, the UE can move back to the 5G network. 10
[0036] The present disclosure aims to overcome the above-mentioned and other existing problems in this field of technology by enabling call continuity in 4G network during network coverage issues in 4G network.
15 [0037] According to the disclosure, when user equipment tries to move from a
lower generation network such as 4G to a higher generation network such as 5G while an ongoing audio call, due to any radio frequency (RF) coverage issue, a fallback indication is received from radio access network (RAN) for maintaining call continuity and to avoid disconnection. In such case, a system as disclosed in
20 the present disclosure handles the fallback procedure such as an Evolved Packet
Service Fallback (EPS FB) Trigger from the gNodeB and smoothly allows changing state of the user equipment to idle state or idle mobility and then retrying the registration for establishing connection with higher generation network such as 5G network, and then triggering the fallback procedure with session management entity
25 for establishing call in higher generation network such as 5G network to ensure call
continuity of the user equipment. The idle state or idle mobility state is when the user equipment is not actively connected with the network and is not transmitting or receiving any data from the gNodeB.
30 [0038] Hereinafter, exemplary implementations of the present disclosure will be
described with reference to the accompanying drawings.
12

[0039] FIG. 1 illustrates an exemplary block diagram representation of 5th
generation core (5GC) network architecture [100], in accordance with exemplary
implementation of the present disclosure. As shown in FIG. 1, the 5GC network
5 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 Specific Authentication and Authorization Function (NSSAAF) [114], a Network Slice
10 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 the components are assumed to be connected to each other in a manner as obvious to
15 the person skilled in the art for implementing features of the present disclosure.
[0040] The User Equipment (UE) [102] interfaces with the network via the Radio Access Network (RAN) [104]; the Access and Mobility Management Function (AMF) [106] manages connectivity and mobility, while the Session Management
20 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 Network Slice Specific Authentication and Authorization Function (NSSAAF) [114] for integrating the 5G core network with
25 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 Control Function (PCF) [122] develops
30 operational policies, and the Unified Data Management (UDM) [124] manages
subscriber data; the Application Function (AF) [126] enables application
13

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 machine-type communication,
5 solidifying the 5GC as the infrastructure for next-generation mobile networks.
[0041] Radio Access Network (RAN) [104] is the part of a mobile
telecommunications system that connects user equipment (UE) [102] to the core
network (CN) and provides access to different types of networks (e.g., 5G network).
10 It consists of radio base stations and the radio access technologies that enable
wireless communication.
[0042] Access and Mobility Management Function (AMF) [106] is a 5G core
network function responsible for managing access and mobility aspects, such as UE
15 registration, connection, and reachability. It also handles mobility management
procedures like handovers and paging.
[0043] Session Management Function (SMF) [108] is a 5G core network function
responsible for managing session-related aspects, such as establishing, modifying,
20 and releasing sessions. It coordinates with the User Plane Function (UPF) for data
forwarding and handles IP address allocation and QoS enforcement.
[0044] Service Communication Proxy (SCP) [110] is a network function in the 5G
core network that facilitates communication between other network functions by
25 providing a secure and efficient messaging service. It acts as a mediator for service-
based interfaces.
[0045] Authentication Server Function (AUSF) [112] is a network function in the
5G core responsible for authenticating UEs during registration and providing
30 security services. It generates and verifies authentication vectors and tokens.
14

[0046] 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 the slices for which they are authorized. 5
[0047] 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 [0048] 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.
[0049] Network Repository Function (NRF) [120] is a network function that acts
15 as a central repository for information about available network functions and
services. It facilitates the discovery and dynamic registration of network functions.
[0050] Policy Control Function (PCF) [122] is a network function responsible for
policy control decisions, such as QoS, charging, and access control, based on
20 subscriber information and network policies.
[0051] Unified Data Management (UDM) [124] is a network function that centralizes the management of subscriber data, including authentication, authorization, and subscription information. 25
[0052] Application Function (AF) [126] is a network function that represents external applications interfacing with the 5G core network to access network capabilities and services.
15

[0053] User Plane Function (UPF) [128] is a network function responsible for handling user data traffic, including packet routing, forwarding, and QoS enforcement.
5 [0054] 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.
[0055] FIG. 1A illustrates an exemplary block diagram of a computing device
10 [1000] upon which the features of the present disclosure may be implemented in
accordance with exemplary implementation of the present disclosure. In an
implementation, the computing device [1000] may also implement a method [200]
for maintaining call continuity for a user device by utilising the system [100A]. In
another implementation, the computing device [1000] itself implements the method
15 [200] for maintaining call continuity for a user device using one or more units
configured within the computing device [1000], wherein said one or more units are capable of implementing the features as disclosed in the present disclosure.
[0056] The computing device [1000] may include a bus [1002] or other
20 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 device, coupled to the
25 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
30 [1000] into a special-purpose machine that is customized to perform the operations
specified in the instructions. The computing device [1000] further includes a read
16

only memory (ROM) [1008] or other static storage device coupled to the bus [1002] for storing static information and instructions for the processor [1004].
[0057] A storage device [1010], such as a magnetic disk, optical disk, or solid-state
5 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), Liquid crystal Display (LCD), Light Emitting Diode (LED) display, Organic LED (OLED) display, etc. for displaying information to a computer user. An input device [1014], including
10 alphanumeric and other keys, touch screen input means, etc. may be coupled to the
bus [1002] for 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
15 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 axis (e.g., y), that allow the device to specify positions in a plane.
[0058] The computing device [1000] may implement the techniques described
20 herein using customized hard-wired logic, one or more ASICs or FPGAs, firmware
and/or program logic which in combination with the computing device [1000]
causes or programs the computing device [1000] to be a special-purpose machine.
According to one implementation, the techniques herein are performed by the
computing device [1000] in response to the processor [1004] executing one or more
25 sequences of one or more 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 implementations of the
30 present disclosure, hard-wired circuitry may be used in place of or in combination
with software instructions.
17

[0059] 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
5 to a local network [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
10 communication connection to a compatible LAN. Wireless links may also be
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.
15 [0060] The computing device [1000] can send messages and receive data, including
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 ISP [1026], the local network [1022], host [1024] and the communication
20 interface [1018]. The received code may be executed by the processor [1004] as it
is received, and/or stored in the storage device [1010], or other non-volatile storage for later execution.
[0061] Referring to FIG. 1B, an exemplary block diagram of a system [100A] for
25 maintaining call continuity for a user device is shown, in accordance with the
exemplary implementations of the present disclosure. The system [100A]
comprises at least one of a call establishment unit [102A], a switching unit [104A],
a transition unit [106A], and a transceiver unit [108A]. The system [100A] is
connected to a session management entity [110A]. Also, all of the components/
30 units of the system [100A] are assumed to be connected to each other unless
otherwise indicated below. Also, in FIG. 1B only a few units are shown, however,
18

the system [100A] may comprise multiple such units or the system [100A] may
comprise any such numbers of said units, as required to implement the features of
the present disclosure. Further, in an implementation, the system [100A] may reside
in a session management entity [110A] or may also be operably connected to the
5 session management entity [110A]. Maintaining call continuity may refer to as the
keeping the connection between the user device and the network to be stable in order to achieve no interruptions or disconnection during calls.
[0062] Particularly, for maintaining call continuity for the user device, initially the
10 call establishment unit [102A] is configured to facilitate an establishment of a call
for the user device in a higher generation network. The establishment of the call may be referred to as a voice call or a video call in which a connection between two parties i.e., a caller party and a callee party has been established. The higher generation network with respect to a lower generation network stands for a type of
15 generation of telecommunication technology standards which is newer as compared
to the lower generation network such as the 5G network is higher generation network with respect to the 4G network. It is pertinent to note that the lower generation network and the higher generation network as used herein may include any other telecommunication network that can facilitate implementation of
20 technical features as disclosed in the present disclosure and shall not be considered
to be limited to only the referred terms. The higher generation network stands for the generation of telecommunication network which may be higher or latest when compared to the lower generation network. For example, if the user is in the 4G communication network then the higher generation network would be 5G or 6G.
25 The call establishment unit [102A] is a unit capable of establishing the call and may
also be a processor capable of processing data and establishing the call.
[0063] Further, the switching unit [104A] may be connected at least to the call
establishment unit [102A] for facilitating communication of data, and is configured
30 to facilitate a fallback procedure for switching the call to the lower generation
network. The switching unit [104A] may be a processor capable of switching the
19

call. The fallback procedure refers to a fallback solution to prevent the total failure
leading to disconnection of the user device from the network or disconnection of
the ongoing call between the user devices. The lower generation network refers to
the earlier or previous generation of telecommunication technology. For example,
5 in case the user device is connected to 5G then lower generation would be 4G or
3G.
[0064] The transition unit [106A] may be connected at least to the switching unit [104A] for facilitating communication of data. The transition unit [106A] is
10 configured to change a state of the user device to an idle state, in an event of
occurrence of one or more network coverage issues. The state of the user device refers to the condition of usage of network at the user device, either active state or idle state. The active state refers to the state where the user device is actively connected to the network. The idle state refers to the state where the user device is
15 currently not actively using the network services. The event of occurrence of one
or more network coverage issues refers to the event where the one or more network issues such as connectivity issues, poor signal reception, etc. are occurred at the network due to which certain issues in connectivity between the user device and the network occurs. This case of occurrence of the issues in the network is the event of
20 one or more network issues. In case of network issues, the state of the user device
is changed to idle state and then new connection may be established between the user device and network. The transition unit [106A] as used herein may be a processor capable of transition of data for changing the state of the user device.
25 [0065] The transceiver unit [108A] may be connected at least to the transition unit
[106A] for facilitating communication of data. The transceiver unit [108A] is configured to receive a registration retry request for establishing connection of the user device with the higher generation network, from the user device. The registration retry request is a request for establishing the connection of the user
30 device with the higher generation network again from the user device. The
20

transceiver unit [108A] is a device which is capable of transmitting and receiving data and/or signals.
[0066] The call establishment unit [102A] may be connected at least to the
5 transceiver unit [108A] for facilitating communication of data. The call
establishment unit [102A] is further configured to trigger the fallback procedure
upon receiving from the session management entity [110A], an establishment
request for establishing a target call flow for establishing the call in the higher
generation network. It is to be noted that when the call establishment unit [102A]
10 triggers the fallback procedure upon receiving the establishment request, the call
establishment unit [102A] is configured to reject the establishment request for establishing the target call flow for establishing the call in the higher generation network.
15 [0067] Also, according to the present disclosure the call establishment unit [102A]
is configured to trigger the fallback procedure upon receiving the establishment request comprises receiving by the session management entity [110A] from a base station, an indication for performing the fallback procedure. The establishment request is a request for establishing the target call flow for establishment of the call
20 in the higher generation network. The target call flow is a 5G Quality of Service
Identifiers (5QI) call flow. The indication of the performing the fallback procedure is the indication that there may be several issues in the network connection and the connection should fallback to previous generation or lower generation network for more stable calls.
25
[0068] The session management entity [110A] is connected at least to the system [100A] to facilitate communication of data, and the system [100A] may also reside within the session management entity [110A]. The session management entity [110A] is then configured to facilitate the call continuity for the user device in the
30 lower generation network based on the fallback procedure. The session
management entity [110A] may be a session management function (SMF) module
21

implementing a session management function in the 5G network or future generation networks. The session management function is the core network elements which is responsible for managing the sessions between the user devices and the network. 5
[0069] In a preferred implementation of the disclosure, the system [100A] is
configured for maintaining call continuity during network coverage issues in 4G
network and performing smooth handover from 5G radio access network (RAN) to
4G RAN, with the help of the interconnection between the components/units of the
10 system [100A].
[0070] The present disclosure further discloses, the user attached to a 5G network
initiates establishing a call in the 5G network using the user device. Further, the call
is established in the 4G network through EPS-FB (evolved packet system –
15 fallback) procedure. During the ongoing call, due to RF issue or any other issue
related to the poor coverage in 4G network, user device moves to idle state. Therefore, the user device attempts mobility on 5G radio due to poor 4G radio conditions, i.e., the user equipment (UE) retries to register in 5G through 5G RAN.
20 [0071] In this case the SMF module retries to establish 5QI 1/2 flow for audio
and/or video call by sending resources to 5G RAN. The 5G RAN however, rejects the resources as it is an EPS-FB call. The radio access network (RAN) again triggers EPS-FB. In operation, a packet data unit (PDU) session may be established at this point.
25
[0072] SMF module is further configured to handle this EPS-FB trigger and allows call continuity in 4G again. This handling includes SMF module rejecting set-up of quality of service (QoS) flow for IP Multimedia system (IMS) voice session and/or IMS PDU session in 5G network. This results in EPS fallback for IMS voice session
30 and the call continues in 4G network.
22

[0073] In an implementation, a storage unit may also be connected to the call establishment unit [102A] and may be configured to facilitate the implementation of the features as disclosed in the present disclosure, by storing data related to the implementation of the present disclosure. 5
[0074] Referring to FIG. 2 an exemplary method flow diagram [200], for
maintaining call continuity for a user device during network coverage issues, in
accordance with exemplary implementation of the present disclosure. For example,
in a lower generation network (preferably 4G) and performing smooth handover
10 from a higher generation network (preferably 5G) radio access network (RAN) to
4G RAN, in accordance with exemplary implementations of the present disclosure is shown. In an implementation the method [200] is performed by the system [100A]. As shown in FIG. 2, the method [200] starts at step [202].
15 [0075] At step [204], the method [200] as disclosed by the present disclosure
comprises facilitating an establishment of a call for the user device in a higher generation network, by the call establishment unit [102A]. The establishment of the call may be referred to as a voice call or a video call in which a connection between two parties i.e., a caller party and a callee party has been established. The higher
20 generation network with respect to a lower generation network stands for type of
generation of telecommunication technology standards which is newer as compared to the lower generation network such as the 5G network is higher generation network with respect to the 4G network. It is pertinent to note that the lower generation network and the higher generation network as used herein may include
25 any other telecommunication network that can facilitate implementation of
technical features as disclosed in the present disclosure and shall not be considered to be limited to only the referred terms. The higher generation network stands for the generation of telecommunication network which may be higher or latest when compared to the lower generation network. For example, if the user is in the 4G
30 communication technology then the higher generation network would be 5G or 6G.
23

The call establishment unit [102A] is a unit capable of establishing the call, and may also be a processor capable of processing data and establishing the call.
[0076] Next, at step [206], the method [200] as disclosed by the present disclosure
5 comprises facilitating a fallback procedure for switching the call to the lower
generation network by the switching unit [104A]. The switching unit [104A may be
a processor capable of switching the call. The fallback procedure refers to a fallback
solution to prevent the total failure leading to disconnection of the user device from
the network or disconnection of the ongoing call between the user devices. The
10 lower generation network refers to the earlier or previous generation of
telecommunication technology. For example, in case the user device is connected to 5G then lower generation would be 4G or 3G.
[0077] Next, at step [208], the method [200] as disclosed by the present disclosure
15 comprises changing a state of the user device to an idle state by the transition unit
[106A] in an event of occurrence of one or more network coverage issues. The state of the user device refers to the condition of usage of network at the use device, either active state or idle state. The active state refers to the state where the user device is actively connected to the network. The idle state refers to the state where
20 the user device is currently not actively using the network services. The event of
occurrence of one or more network coverage issues refers to the event where the one or more network issues such as connectivity issues, poor signal reception, etc. have occurred at the network due to which certain issues in connectivity between the user device and the network occurs. This case of occurrence of the issues in the
25 network is the event of one or more network issues. In case of network issues, the
state of the user device is changed to idle state and then new connection may be established between the user device and network. The transition unit [106A] as used herein may be a processor capable of transition of data for changing the state of the user device.
30
24

[0078] Next, at step [210], the method [200] as disclosed by the present disclosure
comprises receiving a registration retry request for establishing connection of the
user device with the higher generation network by the transceiver unit [108A] from
the user device. The registration retry request is a request for establishing the
5 connection of the user device with the higher generation network again from the
user device. The transceiver unit [108A] is a device which is capable of transmitting and receiving data and/or signals.
[0079] Next, at step [212], the method [200] as disclosed by the present disclosure
10 comprises triggering, by the call establishment unit [102A], a fallback procedure
upon receiving an establishment request from a session management entity [110A]
for establishing a target call flow for establishing the call in the higher generation
network. It is further noted that during triggering of the fallback procedure upon
receiving the establishment request, rejecting, by the call establishment unit [102A],
15 the establishment request for establishing the target call flow for establishing the
call in the higher generation network.
[0080] Further, according to the present disclosure, the triggering, by the call establishment unit [102A], the fallback procedure upon receiving the establishment
20 request further comprises receiving by the session management entity [110A] from
a base station, an indication for performing the fallback procedure. The establishment request is a request for establishing the target call flow for establishment of the call in the higher generation network. The target call flow is a 5G Quality of Service Identifiers (5QI) call flow. The indication of the performing
25 the fallback procedure is the indication that there may be several issues in the
network connection and the connection should fallback to previous generation or lower generation network for more stable calls.
[0081] Next, at step [214], the method [200] as disclosed by the present disclosure
30 comprises facilitating the call continuity for the user device in the lower generation
network based on the fallback procedure by the session management entity [110A].
25

The session management entity [110A] may be a session management function
(SMF) module implementing a session management function in the 5G network or
future generation networks. The session management function is the core network
elements which is responsible for managing the sessions between the user devices
5 and the network.
[0082] Thereafter, the method terminates at step [216].
[0083] Referring to FIG. 3 an exemplary call flow diagram [300], for maintaining
10 call continuity for a user device during network coverage issues, in accordance with
exemplary implementation of the present disclosure. For example, in a lower
generation network (preferably 4G) and performing smooth handover from a higher
generation network (preferably 5G) radio access network (RAN) to 4G RAN, in
accordance with exemplary implementations of the present disclosure is shown. In
15 an implementation the call flow diagram is performed by the system [100A].
[0084] The call flow diagram [300] is performed in presence of a user equipment [102], a next generation radio access network (NG-RAN) [502], an evolved universal terrestrial radio access (E-UTRA) [504], an access and mobility
20 management function (AMF) [106], a mobility management entity (MME) [506],
and a session management entity (SME) [110A]. The NG-RAN [502] is the radio access network that provides the wireless connectivity between the user equipment (UE) [102] and the 5G core network. E-UTRA [504] is the radio access network or air interface of 3rd Generation Partnership Project (3GPP) for a Long-Term
25 Evolution (LTE) upgrade path for mobile networks. The AMF [106] is a 5G core
network function responsible for managing access and mobility aspects, such as UE registration, connection, and reachability and handles mobility management procedures like handovers and paging. The MME [506] provides mobility session management for the LTE network and supports subscriber authentication, roaming
30 and handovers to other networks. The session management entity (SME) [110A]
26

may be a session management function (SMF) module implementing a session management function in the 5G network or future generation networks.
[0085] The call flow diagram [300] is initiated by an ongoing call or a call session
5 in a lower generation network. Thereafter, due to occurrence of one or more
network coverage issues, changing a state of the user device to an idle state. The changing of the state of the user device to an idle state further comprises certain steps. At step 1, the changing of the state of the user device refers to an S1 release procedure. The S1 release procedure involves the E-UTRA [504] sending the S1
10 release to the MME [506], and releasing the connection between the user device
and the lower generation network (such as E-UTRA [504] in the present example). Then at step 2, the MME [506] sends a release access bearer request to the SME [110A] for release procedure after which at step 3, the SME [110A] releases the access bearer on receipt of release access bearer request and sends to the MME
15 [506] a response comprising information associated with releasing access bearer.
Then the user device sends a registration retry request for establishing a connection of the user device with the higher generation network (such as NG-RAN [502] in the present example). The registration retry request may be sent by the UE [102] connected with the lower generation network, to the higher generation network.
20 Then the SME [110A] sends an establishment request for establishing a target call
flow for establishing the call in the higher generation network. Then triggering the fallback procedure upon receiving the establishment request. Further, an indication for performing the fallback procedure may also be received at the SME [110A]. Thereafter, the call flow diagram [300] comprises rejecting the establishment
25 request for establishing the target call flow for establishing the call in the higher
generation network. Further, the call flow diagram [300] discloses facilitating the call continuity for the user device in the lower generation network based on the fallback procedure.
30 [0086] The present disclosure further discloses a non-transitory computer readable
storage medium storing instruction for maintaining call continuity for a user device.
27

The instructions comprising executable code which, when executed by one or more
units of a system [100A], causes: a call establishment unit [102A] of the system
[100A] to facilitate an establishment of a call for the user device in a higher
generation network; a switching unit [104A] of the system [100A] to facilitate a
5 fallback procedure for switching the call to a lower generation network; a transition
unit [106A] of the system [100A] to change a state of the user device to an idle state in an event of occurrence of one or more network coverage issues; a transceiver unit [108A] of the system [100A] to receive a registration retry request for establishing connection of the user device with the higher generation network from
10 the user device; the call establishment unit [102A] of the system [100A] to trigger
the fallback procedure upon receiving an establishment request from a session management entity [110A] for establishing a target call flow for establishing the call in the higher generation network; the session management entity [110A] to facilitate the call continuity for the user device in the lower generation network
15 based on the fallback procedure.
[0087] As is evident from the above, the present disclosure provides a technically advanced solution for maintaining call continuity during network coverage issues in lower network such as 4G and performing smooth handover from higher
20 generation network such as 5G radio access network (RAN) to the lower generation
network such as 4G RAN. Implementing the features of the present disclosure enables one to improve user experience by eliminating or reducing call drops and/or muting of the call by enabling call continuity during network coverage issues in lower generation network 4G. The implementation of the solution provided in the
25 present disclosure improves user experience by eliminating or reducing call drops
and/or muting of the call. The muting of the call refers to the situation where the one or more parties of an ongoing call are unable to hear each other, the major reasons for muting may be network problems and user equipment problems., etc.
30 [0088] While considerable emphasis has been placed herein on the disclosed
implementations, it will be appreciated that many implementations can be made and
28

that many changes can be made to the implementations without departing from the
principles of the present disclosure. These and other changes in the implementations
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
5 and non-limiting.
[0089] Further, in accordance with the present disclosure, it is to be acknowledged that the functionality described for the various components/units can be implemented interchangeably. While specific embodiments may disclose a
10 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
15 functionality described herein, are considered to be encompassed within the scope
of the present disclosure.
29

We Claim:
1. A method for maintaining call continuity for a user device, the method
comprising:
- facilitating, by a call establishment unit [102A], an establishment of a call for the user device in a higher generation network;
- facilitating, by a switching unit [104A], a fallback procedure for switching the call to a lower generation network;
- changing, by a transition unit [106A], a state of the user device to an idle state, in an event of occurrence of one or more network coverage issues;
- receiving, by a transceiver unit [108A] from the user device, a registration retry request for establishing a connection of the user device with the higher generation network;
- triggering, by the call establishment unit [102A], the fallback procedure upon receiving, from a session management entity [110A], an establishment request for establishing a target call flow for establishing the call in the higher generation network; and
- facilitating, by the session management entity [110A], the call continuity for the user device in the lower generation network based on the fallback procedure.
2. The method as claimed in claim 1, wherein the triggering, by the call
establishment unit [102A], the fallback procedure upon receiving the
establishment request comprises:
- rejecting, by the call establishment unit [102A], the establishment
request for establishing the target call flow for establishing the call in
the higher generation network.
3. The method as claimed in claim 1, wherein the triggering, by the call
establishment unit [102A], the fallback procedure upon receiving the
establishment request comprises:

- receiving, by the session management entity [110A] from a base station,
an indication for performing the fallback procedure.
4. The method as claimed in claim 1, wherein the session management entity [110A] is a session management function (SMF) module implementing a session management function in a 5G network.
5. The method as claimed in claim 1 wherein the target call flow is a 5G Quality of Service Identifiers (5QI) call flow.
6. A system [100A] for maintaining call continuity for a user device, the system comprising:

- a call establishment unit [102A] configured to facilitate an establishment of a call for the user device in a higher generation network;
- a switching unit [104A] connected to at least the call establishment unit [102A], the switching unit [104A] configured to facilitate a fallback procedure for switching the call to a lower generation network;
- a transition unit [106A] connected to at least the switching unit [104A], the transition unit [106A] configured to change a state of the user device to an idle state, in an event of occurrence of one or more network coverage issues; and
- a transceiver unit [108A] connected to at least the transition unit [106A], the transceiver unit [108A] configured to receive, from the user device, a registration retry request for establishing a connection of the user device with the higher generation network,
wherein the call establishment unit [102A] is further configured to trigger the fallback procedure upon receiving an establishment request from a session management entity [110A] for establishing a target call flow for establishing the call in the higher generation network, wherein:

the session management entity [110A] is configured to facilitate the call continuity for the user device in the lower generation network based on the fallback procedure.
7. The system [100A] as claimed in claim 6, wherein the call establishment unit [102A] for triggering the fallback procedure, is configured to reject the establishment request for establishing the target call flow for establishing the call in the higher generation network.
8. The system [100A] as claimed in claim 6, wherein the session management entity [110A] is a session management function (SMF) module implementing a session management function in a 5G network.
9. The system [100A] as claimed in claim 6, wherein the target call flow is a 5G Quality of Service Identifier (5QI) call flow.
10. The system [100A] as claimed in claim 6, wherein prior to the call establishment unit [102A] triggering the fallback procedure upon receiving the establishment request, the session management entity [110A] is configured to:
- receive, from a base station, an indication for performing the fallback procedure.