FORM 2
THE PATENTS ACT, 1970
(39 OF 1970)
AND
THE PATENT RULES, 2003
COMPLETE SPECIFICATION
(See section 10 and rule 13)
“METHOD AND SYSTEM FOR REDUCING A CALL SETUP TIME”
We, JIO PLATFORMS LIMITED, an Indian National, of address 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 REDUCING A CALL SETUP TIME
FIELD OF THE DISCLOSURE
The present disclosure relates generally to the field of wireless communication systems. More particularly, the present disclosure relates to methods and systems for reducing signalling and a call setup time in a higher radio access technology (RAT).
BACKGROUND
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.
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. 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. Further, reducing call drops and latency is of paramount importance in the telecommunications industry. Call drops can be frustrating for users, and they can also result in lost revenue for service providers. Latency, on the other hand, refers to the time it takes for data to travel from one device to another and can cause delays and disruptions in communication. The introduction of 5G technology promises to address these issues by delivering ultra-low latency and high-speed data transmission. With 5G, call drops are going to be minimized, and users are going to experience seamless, uninterrupted communication. Additionally, 5G technology may enable the development of new applications and services that require high-speed, low-latency communication, such as remote surgeries, autonomous vehicles, and virtual reality. The reduction of call drops and latency is crucial in ensuring that users have access to reliable and efficient communication services, and the 5G technology is a significant step towards achieving this goal.
Further, reducing call set-up time is essential in the telecommunications industry as it directly impacts the user experience. Call set-up time refers to the time it takes for a call to be initiated and connected. A lengthy call set-up time may cause frustration for users and may lead to a poor customer experience. In today's fast-paced world, people rely heavily on their smartphones for communication, and any delay or inconvenience during a call set-up process may have a negative impact on a telecom network operator/service provider. Additionally, long call set¬up times may result in lost revenue for service providers, as customers/users may switch to other service providers offering quicker call set-up times. Therefore, reducing call set-up time is crucial in ensuring that the users have access to reliable

and efficient communication services, and the service providers can retain their customers and generate revenue.
Further, over the period of time various solutions have been developed to improve the performance of communication devices and reduce call setup time in higher generation RATs after the communication devices fall back to a lower generation RAT to execute voice services. However, there may be certain challenges in enabling the communication devices to quickly return to the higher generation RAT in certain conditions. According to the known solutions, if there are issues with network coverage or interference, the communication device may struggle to establish a connection with the higher generation RAT, resulting in increased call setup time or call setup failure. Similarly, any failure during the signaling process can also lead to call setup failure or increased call setup time. Further, in another known solution for EPS Fall Back (EPSFB) calls for devices registered in 5G has shortcomings, for instance, during the EPS Fall Back (EPSFB) calls a device registered in 5G, gets RRC release with redirection (RWR) command from the 5G network to fallback to LTE after 183 session in progress. Call gets established in LTE and after call is disconnected, the device does fast return to 5G and does a Mobility Registration Update (MRU) process. To start registration process for doing the MRU takes around 1 second. Also, while performing the registration process i.e., Mobility Registration Update (MRU) in 5G, the device does not send any flag for Uplink (UL) data status to enable 5th generation mobile network QoS Identifier (5 QI) = 5 Packet Data Unit (PDU)/data radio bearer (DRB) for IP Multimedia Subsystem (IMS) calls. Also, the device does not send UL data status related to 5QI = 9 PDU (for data services) until it has any data to send in the buffer. Further in the known solution, the Uplink data status is set to 0 for 5QI=5 and 5QI=9, and the device gets RRC release immediately after the Registration process (MRU) completes. This MRU process may take around 1.5 seconds in good coverage. Also, the device is mandated to inform the IMS stack about a current

radio access technology (RAT) via Refresh Register in P-Access-Network-Info (PANI) header.
Therefore, after every MRU while coming back from a lower RAT to a higher RAT say for e.g., from 4G after Evolved Packet System Fallback (EPSFB) call to 5G or from normal 4G to 5G inter radio access technology (IRAT) reselection, or in case of handover to 5G NR, devices have to send refresh register with RAT details in P-Access-Network-Info (PANI) header. So, the problem in the known arts is that the device gets RRC release from the network as the device sends uplink data status (UDS) flag as 0 for both the 5QI=9 and the 5QI=5 in registration request (MRU). To send refresh register and get 200 OK response from the network, the device has to initiate service request with UDS data indication for 5QI=5 PDU (for IMS DRB) PSI as 1 (high).Therefore, the process of sending Refresh Register and getting the 200 OK response from the network requires the device to initiate a service request with UDS data indication for 5QI=5 PDU (for IMS DRB) PSI as 1 (high) (so the device has to go for Random Access Channel (RACH) procedure to make new RRC connection), which consumes more signaling and increases the chances of signaling failure, especially in poor coverage or mobility scenarios. A total time to do reselection, MRU, and service request for sending refresh register takes approximately 3 seconds in ideal good coverage, which can increase in case of retransmission in poor coverage, mobility scenario, radio link failure (RLF), RACH failure, registration (MRU) accept failure and retransmission of registration request (MRU) etc. These deficiencies may affect the call setup process by increasing the call setup time or by leading to call setup failure (in case any failure happens during the signaling process), and therefore these deficiencies may impact the user experience.

Thus, there exists an imperative need in the art to continuously reduce signalling and call setup time in a network in various scenarios such as during mobility or IRAT scenarios etc., which the present disclosure aims to address.
OBJECTS OF THE INVENTION
Some of the objects of the present disclosure, which at least one embodiment disclosed herein satisfies are listed herein below.
It is an object of the present disclosure to provide a system and a method that facilitates for reducing a call setup time in a higher radio access technology (RAT).
It is another object of the present disclosure to provide a solution that addresses the issue of mobile terminal (MT) call setup delay/failure during Mobility Registration Update (MRU) to make default E-UTRAN Radio Access Bearer (ERAB) for IMS refresh registration and Session Initiation Protocol (SIP) signalling.
It is another object of the present disclosure to provide a solution to reduce a signalling part leading to reduction in call setup time and call setup failure and hence improving the network KPI and user experience.
It is also an object of the present disclosure to provide a system and a method that is able to maintain IP Multimedia Subsystem (IMS) Packet Data Unit (PDU) during Mobility Registration Update (MRU) to reduce signalling and call setup time in 5G during 4G to 5G IRAT scenario.
It is another object of the present disclosure to provide a solution that does not invoke Uplink data status (UDS) in service request, avoids the service request itself and includes the UDS during mobility registration request itself, to handle IMS

failure and to overcome the limitations of existing solutions that sends the UDS in service request in different scenario.
It is another object of the present disclosure to provide a system and a method to avoid Release with Redirection (RWR) delays in case of Mobile Terminated (MT) calls during Mobility Registration Update (MRU) is ongoing to return to 5G after an EPSFB call ends, for 4G to 5G reselection and/or for handover to 5G.
It is another object of the present disclosure to provide a solution that can enable a communication device to send an Uplink data status (UDS) field as 1 (high) for 5QI=5 PDU (IMS DRB) while doing Mobility Registration Update (MRU) in a registration request, so that the communication device remains in connected mode with 5QI=5 DRB maintained just after MRU complete and hence signalling and call setup time reduced and call failure is avoided in 5G during 4G to 5G IRAT scenario.
It is yet another object of the present disclosure to provide a system and a method to optimize the MRU process. Seamless inter-working between IMS calls in 5G, handover to 4G, and vice versa, is crucial for maintaining a high call success rate and ensuring a smooth user experience with a common IMS stack in both 4G and 5G networks.
SUMMARY
This section is intended to introduce certain aspects of the disclosed method and system in a simplified form and is not intended to identify the key advantages or features of the present disclosure.
An aspect of the present disclosure relates to a system for reducing a call setup time in a higher radio access technology (RAT). The system comprises a processing

unit, configured to transmit, from a user equipment (UE) to a network server, a UE register request to register the UE on the higher RAT from a lower RAT. Further, the processing unit is configured to transmit, from the UE to the network server, a Mobility Registration Update (MRU) with an additional information element, wherein the MRU is associated with the UE register request. The processing unit is further configured to receive, at the UE from the network sever, an MRU registration accept indication in response to the MRU with the additional information element. Further, the processing unit is configured to receive, at the user equipment from the network server, an indication of a configuration of data radio bearer (DRB) for an nth generation mobile network QoS Identifier based on the additional information element. Further, the processing unit is configured to transmit, from the UE to the network server, a refresh register message based on the configuration of the DRB. The processing unit further configured to receive, at the UE from the network sever, an acknowledgement response based on the refresh register message. Thereafter, the processing unit is configured to reduce, at the UE, the call setup time in the higher RAT based on the acknowledgement response.
Another aspect of the present disclosure relates to a method for reducing a call setup time in a higher radio access technology (RAT). The method comprises transmitting, by a processing unit from a user equipment (UE) to a network server, a UE register request to register the UE on the higher RAT from a lower RAT. The method further comprises transmitting, by the processing unit from the UE to the network server, a Mobility Registration Update (MRU) with an additional information element, wherein the MRU is associated with the UE register request. Further, the method comprises receiving, by the processing unit at the UE from the network sever, an MRU registration accept indication in response to the MRU with the additional information element. The method further encompasses receiving, by the processing unit at the user equipment from the network server,

an indication of a configuration of data radio bearer (DRB) for an nth generation mobile network QoS Identifier based on the additional information element. Further, the method encompasses transmitting, by the processing unit from the UE to the network server, a refresh register message based on the configuration of the DRB. The method further comprises receiving, by the processing unit at the UE from the network sever, an acknowledgement response based on the refresh register message. Thereafter, the method comprises reducing, by the processing unit at the UE, the call setup time in the higher RAT based on the acknowledgement response.
Yet another aspect of the present disclosure relates to a user equipment (UE) for reducing a call setup time in a higher radio access technology (RAT). The user equipment (UE) comprises a system, wherein the system comprises a processing unit configured to: transmit, from the user equipment (UE) to a network server a UE register request to register the UE on the higher RAT from a lower RAT; transmit, from the UE to the network server a Mobility Registration Update (MRU) with an additional information element, wherein the MRU is associated with the UE register request; receive, at the UE from the network sever an MRU registration accept indication in response to the MRU with the additional information element; receive, at the user equipment from the network server an indication of a configuration of data radio bearer (DRB) for an nth generation mobile network QoS Identifier based on the additional information element; transmit, from the UE to the network server a refresh register message based on the configuration of the DRB; receive, at the UE from the network sever an acknowledgement response based on the refresh register message, and reduce, at the UE the call setup time in the higher RAT based on the acknowledgement response.
BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated herein, and constitute a part of this disclosure, illustrate exemplary embodiments of the disclosed methods and systems in which like reference numerals refer to the same parts throughout the different drawings. Components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Some drawings may indicate the components using block diagrams and may not represent the internal circuitry of each component. It will be appreciated by those skilled in the art that disclosure of such drawings includes disclosure of electrical components, electronic components or circuitry commonly used to implement such components.
FIG.1 illustrates an exemplary block diagram depicting an exemplary network architecture diagram [100], in accordance with exemplary embodiments of the present disclosure.
FIG.2 illustrates an exemplary block diagram of a system [200] for reducing a call setup time in a higher radio access technology (RAT), in accordance with exemplary embodiments of the present disclosure.
FIG.3 illustrates an exemplary method flow diagram [300], for reducing a call setup time in a higher radio access technology (RAT), in accordance with exemplary embodiments of the present disclosure.
FIG.4 illustrates an exemplary process flow diagram [400] for reducing a call setup time in a higher radio access technology (RAT) in an exemplary scenario, in accordance with exemplary embodiments of the present disclosure.
The foregoing shall be more apparent from the following more detailed description of the disclosure.

DETAILED DESCRIPTION
In the following description, for the purposes of explanation, various specific details are set forth in order to provide a thorough understanding of embodiments of the present disclosure. It will be apparent, however, that embodiments of the present disclosure may be practiced without these specific details. Several features described hereafter can each be used independently of one another or with any combination of other features. An individual feature may not address any of the problems discussed above or might address only some of the problems discussed above. Some of the problems discussed above might not be fully addressed by any of the features described herein. Example embodiments of the present disclosure are described below, as illustrated in various drawings in which like reference numerals refer to the same parts throughout the different drawings.
The ensuing description provides exemplary embodiments only, and is not intended to limit the scope, applicability, or configuration of the disclosure. Rather, the ensuing description of the exemplary embodiments will provide those skilled in the art with an enabling description for implementing an exemplary embodiment. It should be understood that various changes may be made in the function and arrangement of elements without departing from the spirit and scope of the disclosure as set forth.
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 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 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.
Specific details are given in the following description to provide a thorough understanding of the embodiments. However, it will be understood by one of ordinary skill in the art that the embodiments may be practiced without these specific details. For example, circuits, systems, networks, processes, and other components may be shown as components in block diagram form in order not to obscure the embodiments in unnecessary detail. In other instances, well-known circuits, processes, algorithms, structures, and techniques may be shown without unnecessary detail in order to avoid obscuring the embodiments.
Also, it is noted that individual embodiments may be described as a process which is depicted as a flowchart, a flow diagram, a data flow diagram, a structure diagram, or a block diagram. Although a flowchart may describe the operations as a sequential process, many of the operations 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.
The word “exemplary” and/or “demonstrative” is used herein to mean serving as an example, instance, or illustration. For the avoidance of doubt, the subject matter disclosed herein is not limited by such examples. In addition, any aspect or design described herein as “exemplary” and/or “demonstrative” is not necessarily to be construed as preferred or advantageous over other aspects or designs, nor is it meant to preclude equivalent exemplary structures and techniques known to those of ordinary skill in the art. Furthermore, to the extent that the terms “includes,” “has,” “contains,” and other similar words are used in either the detailed description or the claims, such terms are intended to be inclusive—in a

manner similar to the term “comprising” as an open transition word—without precluding any additional or other elements.
As used herein, an “electronic device”, or “portable electronic device”, or “user device” or “communication device” or “user equipment” or “device” refers to any electrical, electronic, electromechanical and computing device. The user device is capable 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 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, 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.
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 DSP core, a controller, a microcontroller, Application Specific Integrated Circuits, Field Programmable Gate Array circuits, any other type of integrated circuits, etc. The processor may perform signal coding data processing, input/output processing, and/or any other functionality that enables the working of the system

according to the present disclosure. More specifically, the processor is a hardware processor.
As portable electronic devices and wireless technologies continue to improve and grow in popularity, the advancing wireless technologies for data transfer are also expected to evolve and replace the older generations of technologies. In the field of wireless data communications, the dynamic advancement of various generations of cellular technology are also seen. The development, in this respect, has been incremental in the order of second 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.
Radio Access Technology (RAT) refers to the technology used by mobile devices/ user equipment (UE) to connect to a cellular network. It refers to the specific protocol and standards that govern the way devices communicate with base stations, which are responsible for providing the wireless connection. Further, each RAT has its own set of protocols and standards for communication, which define the frequency bands, modulation techniques, and other parameters used for transmitting and receiving data. Examples of RATs include GSM (Global System for Mobile Communications), CDMA (Code Division Multiple Access), UMTS (Universal Mobile Telecommunications System), LTE (Long-Term Evolution), and 5G. The choice of RAT depends on a variety of factors, including the network infrastructure, the available spectrum, and the mobile device's/device's capabilities. Mobile devices often support multiple RATs, allowing them to connect to different types of networks and provide optimal performance based on the available network resources.
Mobility Registration Update (MRU) is a process in mobile communication networks where a mobile device informs a network of its new location after

moving from one location area to another. When a mobile device moves to a new location area, it needs to register with the network to receive incoming calls and messages. The MRU process involves sending a message to the serving network to update location information of the mobile device. The network then updates the location of the mobile device in its database and forwards any incoming calls or messages to the new location. The frequency of MRU updates depends on the network and the mobile device's mobility parameters. In some networks, the mobile device is required to update its location every time it moves to a new location area, while in others, the mobile device is only required to update its location after a certain amount of time or after a certain distance has been travelled. The MRU is an important function of mobile communication networks as it ensures that incoming calls and messages are correctly routed to the mobile device, regardless of its location. It also helps the network optimize its resources and manage the allocation of network resources based on the location of the mobile devices.
Further, in mobile communication networks, a Data Radio Bearer (DRB) is a logical channel that is used to transport data between the mobile device and the network. It is a type of channel that is established between the mobile device and the network's Radio Access Network (RAN) to carry user data. A DRB is established when a mobile device establishes a connection with the network, such as during the process of setting up a data session. The DRB is used to transport data packets between the UE and the network, providing a reliable and efficient means of transmitting user data. Multiple DRBs can be established between a mobile device and the network to support different types of data traffic, such as voice, video, and data. The network can also dynamically allocate and release DRBs based on the traffic demand and available network resources. The use of DRBs is an important function of mobile communication networks as it ensures efficient and

reliable transport of user data while also allowing for the optimization of network resources.
Mobile Network QoS Identifier (for e.g., 5QI) is a parameter used in mobile communication networks to define the Quality of Service (QoS) characteristics for a specific type of data traffic. It is used to determine the priority, reliability, and other QoS parameters for data packets being transmitted over the network. Each 5QI value corresponds to a specific set of QoS characteristics, such as the maximum bit rate, delay, and packet loss rate. The network uses the 5QI value to allocate network resources and to ensure that the QoS requirements for the data traffic are met. The use of 5QI is an important function of mobile communication networks, as it ensures that different types of data traffic receive the appropriate level of QoS, based on their requirements. This helps to optimize network resources and ensure that data traffic is transmitted efficiently and reliably over the network.
As discussed in the background section, the current known solutions for reducing a call setup time in a higher radio access technology (RAT) have several shortcomings such as the total time to do reselection, MRU, and Service request for sending Refresh register takes approximately 3 seconds in ideal good coverage, which can increase in case of retransmission or failure in the registration process. Furthermore, in the known solutions of device mobility registration update while transitioning from 4G to 5G with the User Data Source (UDS) field set to 0 "low" has certain shortcomings. In this approach, a device needs to establish a fresh Radio Resource Control (RRC) connection setup with UDS for 5QI=5 as 1, which triggers a Refresh Register procedure. However, this process introduces delays and requires additional signalling, which can increase the chances of call failure. The need for a fresh RRC connection setup and the associated Refresh Register procedure can add complexity and overhead to mobility registration update

(MRU) process, resulting in potential delays and increased signalling load on the network.
With this background and the new evolving generations, in the context of 5G networks, one of the options for sustaining voice calls is to use the IP Multimedia Subsystem (IMS) stack to work on New Radio (NR) for Voice over NR (VoNR). However, in scenarios where 5G coverage is weak, service providers with both 4G and 5G network systems may need to fallback to legacy 4G for voice calls using Voice over LTE (VoLTE) through a feature known as Evolved Packet System Fallback (EPSFB). EPSFB calls are initiated by the network to redirect the device / User Equipment (UE) to LTE via Radio Resource Control (RRC) release with Redirection (RWR) command for call setup. To avoid delays in case of Mobile Terminated (MT) calls during Mobility Registration Update (MRU), to return to 5G after an EPSFB call ends and/or for 4G to 5G reselection and/or for handover to 5G, the present application provides a novel solution to optimize the MRU process. Further, the present solution also discloses a novel solution for seamless inter-working between IMS calls in 5G, handover to 4G, and vice versa, which is crucial for maintaining a high call success rate and ensuring a smooth user experience with a common IMS stack in both 4G and 5G networks.
The present disclosure aims to overcome the above-mentioned and other existing problems in this field of technology by providing methods and systems for reducing call setup time in a higher radio access technology (RAT). The present disclosure proposes transmitting to a network server from a user equipment (UE), a Mobility Registration Update (MRU) with an additional information element, wherein the MRU is associated with a UE register request to register the UE on the higher RAT from a lower RAT, when the UE is moving from the higher RAT to the lower RAT. Also, the additional information element enables the UE to receive an indication of a configuration of 5QI=5 (IMS) data radio bearer (DRB). Additionally,

the present disclosure proposes to use Refresh Register immediately without the requirement of a fresh RRC connection setup based on the configuration of the DRB.
Hereinafter, exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the solution provided by the present disclosure.
Referring to Figure 1, the Figure 1 illustrates an exemplary block diagram depicting an exemplary network architecture diagram [100], in accordance with exemplary embodiments of the present disclosure. As shown in Figure 1, the exemplary network architecture diagram [100] comprises at least one user equipment (UE) [102] connected to at least one network server [104], wherein in an implementation the UE [102] further comprises a system [200] configured to implement the feature of the present invention. Also, in an implementation the system [200] may reside partially in either the network server [104] or the user device [102] or may be in connection with the network server [104] and the user device [102], in a manner as obvious to a person skilled in the art to implement the features of the present disclosure.
Also, in Figure 1 only the single user equipment (or may be referred to as user device) [102] and the single network server [104] are shown, however, there may be multiple such user equipment [102] and/or network servers [104] or there may be any such numbers of said user equipment [102] and/or network server [104] as obvious to a person skilled in the art or as required to implement the features of the present disclosure. Further, in the implementation where the system [200] is present in the UE [102], based on the implementation of the features of the present disclosure, a call setup time is reduced in a higher radio access technology (RAT) (e.g., in 5G RAT) by the system [200], by transmitting to the network server

[104] from the user equipment [102], a Mobility Registration Update (MRU) with an additional information element, wherein the additional information element comprises an uplink data status (UDS) for the nth generation (e.g., 5th generation) mobile network QoS Identifier, wherein the UDS is associated with a first value and the nth generation mobile network QoS Identifier (e.g. 5QI) is associated with a second value. Also, the first value is 1 (i.e., UDS is 1) and the second value is 5 (i.e., 5QI=5).
Referring to Figure 2, an exemplary block diagram of a system [200] for reducing a call setup time in a higher radio access technology (RAT) is shown, in accordance with the exemplary embodiments of the present invention. The system [200] comprises at least one processing unit [202] and at least one storage unit [204]. Also, all of the components/ units of the system [200] are assumed to be connected to each other unless otherwise indicated below. Also, in Fig. 2 only a few units 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. Further, in an implementation, the system [200] may be present in a user device to implement the features of the present invention. The system [200] may be a part of the user device / or may be independent of but in communication with the user device (may also referred herein as a UE [102]).
The system [200] is configured for reducing a call setup time in a higher radio access technology (RAT), with the help of the interconnection between the components/units of the system [200].
In order to reduce the call setup time in the higher RAT, the processing unit [202] of the system [200] is configured to transmit, from the user equipment (UE) [102] to a network server [104], a UE register request to register the UE [102] on the

higher RAT from a lower RAT, when the UE is moving from the higher RAT to the lower RAT. In a preferred implementation of the present invention, the higher RAT is associated with a 5th generation mobile network, and the lower RAT is associated with a 4th generation mobile network.
Further, the processing unit [202] is configured to transmit from the UE [102] to the network server [104] a Mobility Registration Update (MRU) with an additional information element, wherein the MRU is associated with the UE register request. The additional information element comprises an uplink data status (UDS) for nth generation mobile network QoS Identifier, wherein the UDS is associated with a first value and the nth generation mobile network QoS Identifier is associated with a second value. In a preferred implementation of the present invention, the additional information element comprises an uplink data status (UDS) for the 5th generation mobile network QoS Identifier (5QI), wherein the UDS is associated with the first value and the 5QI is associated with the second value. In said preferred implementation of the present invention, the first value associated with UDS is 1, and the second value associated with 5QI is 5. Therefore, in said preferred implementation, the UE [102] sends to the network server [104], the uplink data status field as 1 (high) for 5QI=5 PDU (IMS ERAB) while doing Mobility Registration Update (MRU) in registration request.
Further, the processing unit [202] is configured to receive, at the UE [102] from the network server [104], an MRU registration accept indication in response to the MRU in the registration request with the additional information element. Particularly, in the above-mentioned preferred implementation, the MRU registration accept indication is received when the UE [102] sends to the network server [104], the uplink data status field as 1 (high) for 5QI=5 PDU (IMS ERAB) while doing Mobility Registration Update (MRU) in registration request. Further, the processing unit [202] is configured to receive at the user equipment [102] from

the network server [104] an indication of a configuration of data radio bearer (DRB) for an nth generation mobile network QoS Identifier based on the additional information element, wherein the nth generation mobile network QoS Identifier is the 5th generation mobile network QoS Identifier (5QI). Therefore, the UE [102] receives from the network server [104] the indication of the configuration of the DRB for 5QI based on the setting of uplink data status field as 1 (high) for 5QI=5 PDU (IMS ERAB). In this scenario, the Access and Mobility Management Function (AMF) will not send the Radio Resource Control (RRC) release as the UE [102] has already informed the AMF via the UDS (i.e., via the uplink data status set as 1) that it has to send an IMS packet to the network server [104]. Thus, the UE [102] will remain in connected mode just after the MRU is complete.
Further, the processing unit [202] is configured to transmit from the UE [102] to the network server [104] a refresh register message based on the configuration of the DRB (i.e., 5QI=5 DRB). Further, the processing unit [202] is configured to receive at the UE [102] from the network server [104] an acknowledgement response based on the refresh register message, wherein the acknowledgement response comprises a refresh register 200 OK response and a resume Session Initiation Protocol (SIP) signalling response. Thereafter, the processing unit [202] is configured to reduce, at the UE [102], the call setup time in the higher RAT based on the acknowledgement response, wherein the higher RAT is associated with the 5th generation mobile network. Continuing from the above preferred implementation, once the UE [102] has informed the AMF via the UDS that it has to send the IMS packet to the network server [104], the UE [102] therefore remains in connected mode just after the MRU is complete. Now, the UE [102] can do Refresh Register immediately without the requirement of fresh RRC connection setup, thereby facilitating incoming Session Initiation Protocol (SIP) messages for the MT call to start immediately without further delay. Also, as the UE [102] can do Refresh Register immediately without the requirement of fresh RRC connection

setup, and the incoming Session Initiation Protocol (SIP) messages for the MT call starts immediately without further delay, the call setup time in the higher RAT is reduced.
Referring to Figure 3 an exemplary method flow diagram [300], for reducing a call setup time in a higher radio access technology (RAT), in accordance with exemplary embodiments of the present invention is shown. In an implementation the method [300] is performed by the system [200]. Further, in an implementation, the system [200] may be present in a user equipment [102] to implement the features of the present invention. Also, as shown in Figure 3, the method [300] starts at step [302].
At step [304], the method [300] as disclosed by the present disclosure comprises transmitting, by a processing unit [202] from the user equipment (UE) [102] to a network server [104], a UE register request to register the UE [102] on the higher RAT from a lower RAT, when the UE is moving from the higher RAT to the lower RAT. In a preferred implementation of the present invention, the higher RAT is associated with a 5th generation mobile network, and the lower RAT is associated with a 4th generation mobile network.
Next, at step [306], the method [300] as disclosed by the present disclosure comprises transmitting, by the processing unit [202] from the UE [102] to the network server [104], a Mobility Registration Update (MRU) with an additional information element, wherein the MRU is associated with the UE register request. The additional information element comprises an uplink data status (UDS) for nth generation mobile network QoS Identifier, wherein the UDS is associated with a first value and the nth generation mobile network QoS Identifier is associated with a second value. In a preferred implementation of the present invention, the additional information element comprises an uplink data status (UDS) for the 5th

generation mobile network QoS Identifier (5QI), wherein the UDS is associated with the first value and the 5QI is associated with the second value. In said preferred implementation of the present invention, the first value associated with UDS is 1, and the second value associated with 5QI is 5. Therefore, in said preferred implementation, the UE [102] sends to the network server [104], the uplink data status field as 1 (high) for 5QI=5 PDU (IMS ERAB) while doing Mobility Registration Update (MRU) in registration request.
Next, at step [308], the method [300] as disclosed by the present disclosure comprises receiving, by the processing unit [202] at the UE [102] from the network sever [104], an MRU registration accept indication in response to the MRU in the registration request with the additional information element. Particularly, in the above-mentioned preferred implementation, the MRU registration accept indication is received when the UE [102] sends to the network server [104], the uplink data status field as 1 (high) for 5QI=5 PDU (IMS ERAB) while doing Mobility Registration Update (MRU) in registration request.
Next, at step [310], the method [300] as disclosed by the present disclosure comprises receiving, by the processing unit [202] at the user equipment [102] from the network server [104], an indication of a configuration of data radio bearer (DRB) for an nth generation mobile network QoS Identifier based on the additional information element, wherein the nth generation mobile network QoS Identifier is the 5th generation mobile network QoS Identifier (5QI). Therefore, the UE [102] receives from the network server [104] the indication of the configuration of the DRB for 5QI based on the setting of uplink data status field as 1 (high) for 5QI=5 PDU (IMS ERAB). In this scenario, the Access and Mobility Management Function (AMF) will not send the Radio Resource Control (RRC) release as the UE [102] has already informed the AMF via the UDS (i.e., via the uplink data status set as 1) that

it has to send an IMS packet to the network server [104]. Thus, the UE [102] will remain in connected mode (for example for 5QI=5) just after the MRU is complete.
Next, at step [312], the method [300] as disclosed by the present disclosure comprises transmitting, by the processing unit [202] from the UE [102] to the network server [104], a refresh register message based on the configuration of the DRB (i.e., 5QI=5 DRB). Next, at step [314], the method [300] as disclosed by the present disclosure comprises receiving, by the processing unit [202] at the UE [102] from the network sever [104], an acknowledgement response based on the refresh register message, wherein the acknowledgement response comprises a refresh register 200 OK response and a resume Session Initiation Protocol (SIP) signalling response. Next, at step [316], the method [300] as disclosed by the present disclosure comprises reducing, by the processing unit [202] at the UE [102], the call setup time in the higher RAT based on the acknowledgement response, wherein the higher RAT is associated with the 5th generation mobile network. Continuing from the above preferred implementation, once the UE [102] has informed the AMF via the UDS status 1 that it has to send the IMS packet to the network server [104], the UE [102] therefore remains in connected mode just after the MRU is complete. Now, the UE [102] can do Refresh Register immediately without the requirement of fresh RRC connection setup, thereby facilitating incoming Session Initiation Protocol (SIP) messages for the MT call to start immediately without further delay. Also, as the UE [102] can do Refresh Register immediately without the requirement of fresh RRC connection setup, and the incoming Session Initiation Protocol (SIP) messages for the MT call starts immediately without further delay, the call setup time in the higher RAT is reduced.
Thereafter, the method terminates at step [318].

Referring to Figure 4 an exemplary process flow diagram [400] for reducing a call setup time in a higher radio access technology (RAT) in an exemplary scenario, in accordance with exemplary embodiments of the present invention, is shown. In an implementation the method/process [400] is performed by the system [200]. Further, in an implementation, the system [200] may be present in a user equipment (UE) [102] to implement the features of the present invention. Also, as shown in Figure 4, the method [400] starts at step [402].
At step [404], the exemplary process as disclosed by the present disclosure comprises receiving, from the UE [102] at a network server [104] of the higher RAT, a device register request for the higher RAT network (i.e., 5G network) from the lower RAT network (i.e., 4G network).
Next, at step [406], the exemplary process as disclosed by the present disclosure comprises receiving at the network server [104] from the UE [102] a Mobility Registration Update (MRU), wherein the MRU is received with an uplink data status (UDS) for the 5th generation mobile network QoS Identifier (5QI=5). Further, if the UDS value received is equal to 0 (i.e., low) then the process moves to step [422] and follows a currently known method of call establishment. At step [422], the MRU registration is accepted.
Next, at step [424] to follow the currently known method, the network server [104] sends RRC release message. In an implementation of the currently known method once the MRU registration is accepted and the network server [104] sends RRC release message approx. 2.5 seconds is consumed in ideal good coverage condition. Further, the time consumed in this process can increase substantially in case of any failure during MRU from 4G to 5G due to RACH failure, RLF, Beam failure, and lower layer failures etc.

Next, at step [426] to follow the currently known method, the UE [102] sends refresh register.
Next, at step [428] according to the currently known method, the UE [102] sends service request with UDS for 5QI=5 as 1.
Next, at step [430] according to the currently known method, the process [400] moves to RRC connection setup request.
Next, at step [432] the process [400] follows the currently known method, and evokes contention based random-access channel (RACH) procedure.
Next, at step [434] according to the currently known method, the process [400] receives refresh register 200 OK and resumes SIP signalling. Further, in an implementation of the currently known method to execute step [430] - step [434] approx. 1 second is consumed in ideal good coverage condition. Further, the time consumed in this process can again increase substantially in case of any failure during fresh RRC connection setup due to RACH failure, RLF, Beam failure, and lower layer failure etc. Furthermore, in an implementation an IMS SIP Invite timer is 14 seconds with 3 retries of 2, 4, 8 seconds of interval and an IMS SIP Non-Invite timer is 6 seconds with 3 retries of 2 seconds of interval each.
Next, at step [436] according to the currently known method, the process [400] receives Release with Redirection (RWR) command.
More particularly, at step [436] if the UE [102] and network server [104] supports VoNR, the UE [102] receives PDU modification command for 5QI=1 for establishing VoNR calls otherwise the method [400] follows EPSFB process.
Next, at step [438] according to the currently known method, the UE [102] moves to the lower RAT.

Next, at step [440] as per the currently known method, a dedicated EPS bearer is established.
Next, at step [442] a call is established based on the establishment of the dedicated EPS bearer.
Furthermore, if at step [406] the UDS value received is equal to 1 (i.e., MRU with additional information element is received at the network server [104] from the UE [102]), then the process moves to step [408] in accordance with the implementation of the features of the present disclosure. At step [408], the MRU registration is accepted.
Next, at step [410] of the exemplary process [400] as disclosed by the present disclosure, the network server [104] reconfigure the Data Radio Bearer (DRB) for 5QI=5.
Next, at step [412] of the exemplary process [400] as disclosed by the present disclosure, the UE [102] sends a refresh register message.
Next, at step [414] of the exemplary process [400] as disclosed by the present disclosure, the UE [102] receives a refresh register 200 OK message and resumes the SIP signalling.
Next, at step [416] of the exemplary process [400] as disclosed by the present disclosure, the UE [102] receives from the network server [104] a Release with Redirection (RWR) command.
More particularly, at step [416] if the UE [102] and network server [104] supports VoNR, the UE [102] receives PDU modification command for 5QI=1 for establishing VoNR calls otherwise the method [400] follows EPSFB process.

Next, at step [418] of the exemplary process [400] as disclosed by the present disclosure, the UE [102] moves to the lower RAT. In a preferred implementation of the present invention the lower RAT is 4G RAT.
Next, at step [420] of the exemplary process [400] as disclosed by the present disclosure, a dedicated Evolved Packet System (EPS) bearer is established and the process [400] leads to step [442] from step [420].
Next, at step [442] of the exemplary process [400] as disclosed by the present disclosure, the call is established at the lower RAT based on the establishment of the dedicated EPS bearer. The process [400] terminates after the step [442].
Furthermore, an aspect of the present disclosure relates to a user equipment (UE) for reducing a call setup time in a higher radio access technology (RAT). The user equipment (UE) comprises a system [200], wherein the system [200] comprises a processing unit [202] configured to: transmit, from the user equipment (UE) [102] to a network server [104], a UE register request to register the UE [102] on the higher RAT from a lower RAT; transmit, from the UE [102] to the network server [104], a Mobility Registration Update (MRU) with an additional information element, wherein the MRU is associated with the UE register request; receive, at the UE [102] from the network sever [104], an MRU registration accept indication in response to the MRU with the additional information element; receive, at the user equipment [102] from the network server [104], an indication of a configuration of data radio bearer (DRB) for an nth generation mobile network QoS Identifier based on the additional information element; transmit, from the UE [102] to the network server [104], a refresh register message based on the configuration of the DRB; receive, at the UE [102] from the network sever [104], an acknowledgement response based on the refresh register message; and

reduce, at the UE [102], the call setup time in the higher RAT based on the acknowledgement response.
It is evident from the above disclosure, that the solution provided by the disclosure is technically advanced as compared to the prior known solutions. The present disclosure enables reducing the signalling, call setup time, and avoiding call failures during the Mobility Registration Update process for IMS PDU. The novel solution as disclosed by the present disclosure transmits from devices the Uplink data status (UDS) field as 1 (high) for 5QI=5 PDU (IMS DRB)) in the Registration request, and the devices inform the AMF that they have to send IMS packets to the network, and therefore, RRC release is not necessary. The technical effect of the disclosed novel solution is that the devices remain in connected mode just after the MRU complete, and the IMS ERAB is configured by the network during the Registration process itself. Moreover, Refresh Register can be done immediately without requiring a fresh RRC connection setup. Further, the invention as disclosed by the present disclosure specifically addresses the IMS PDU to reduce the call setup time and the chances of call failure in the case of Non-Invite retries, thereby improving the user experience. The proposed solution in case of IMS SIP Invite timer i.e., 14 seconds with 3 retries of 2, 4, 8 seconds of interval, significantly increases chances of receiving the 1st Invite retry after 2 seconds (i.e., total delay of 2 seconds) in ideal scenario and, even in poor coverage scenarios, the proposed solution increases chances of receiving the 2nd Invite retry after 4 seconds (i.e., total delay of 6 seconds), therefore the 3rd retry is saved based on the implementation of the features of the present invention. By saving the 3rd retry, the solution disclosed in the present disclosure reduces call setup time and increases chances of successful call setup, thereby demonstrating a significant technical advancement in the field of telecommunications.
While considerable emphasis has been placed herein on the disclosed embodiments, it will be appreciated that many embodiments can be made and

that many changes can be made to the embodiments without departing from the principles of the present disclosure. These and other changes in the embodiments of the present disclosure will be apparent to those skilled in the art, whereby it is to be understood that the foregoing descriptive matter to be implemented is illustrative and non-limiting.

We claim:
1. A method for reducing a call setup time in a higher radio access technology
(RAT), the method comprising:
- transmitting, by a processing unit [202] from a user equipment (UE) [102] to a network server [104], a UE register request to register the UE on the higher RAT from a lower RAT;
- transmitting, by the processing unit [202] from the UE [102] to the network server [104], a Mobility Registration Update (MRU) with an additional information element, wherein the MRU is associated with the UE register request;
- receiving, by the processing unit [202] at the UE [102] from the network server [104], an MRU registration accept indication in response to the MRU with the additional information element;
- receiving, by the processing unit [202] at the user equipment [102] from the network server [104], an indication of a configuration of data radio bearer (DRB) for an nth generation mobile network QoS Identifier based on the additional information element;
- transmitting, by the processing unit [202] from the UE [102] to the network server [104], a refresh register message based on the configuration of the DRB;
- receiving, by the processing unit [202] at the UE [102] from the network server [104], an acknowledgement response based on the refresh register message; and
- reducing, by the processing unit [202] at the UE [102], the call setup time in the higher RAT based on the acknowledgement response.
2. The method as claimed in claim 1, wherein the nth generation mobile
network QoS Identifier is a 5th generation mobile network QoS Identifier
(5QI).

3. The method as claimed in claim 2, wherein the additional information element comprises an uplink data status (UDS) for the 5th generation mobile network QoS Identifier (5QI), wherein the UDS is associated with a first value and the 5QI is associated with a second value.
4. The method as claimed in claim 3, wherein the first value is 1 and the second value is 5.
5. The method as claimed in claim 1, wherein the acknowledgement response comprises a refresh register 200 OK response and a resume Session Initiation Protocol (SIP) signalling response.
6. The method as claimed in claim 1, wherein the higher RAT is associated with a 5th generation mobile network and the lower RAT is associated with a 4th generation mobile network.
7. A system for reducing a call setup time in a higher radio access technology (RAT), the system comprising:
- a processing unit [202], configured to:
transmit, from a user equipment (UE) [102] to a network server
[104], a UE register request to register the UE on the higher RAT
from a lower RAT,
transmit, from the UE [102] to the network server [104], a Mobility
Registration Update (MRU) with an additional information
element, wherein the MRU is associated with the UE register
request,
receive, at the UE [102] from the network sever [104], an MRU
registration accept indication in response to the MRU with the
additional information element,
receive, at the user equipment [102] from the network server
[104], an indication of a configuration of data radio bearer (DRB)

for an nth generation mobile network QoS Identifier based on the
additional information element,
transmit, from the UE [102] to the network server [104], a refresh
register message based on the configuration of the DRB,
receive, at the UE [102] from the network sever [104], an
acknowledgement response based on the refresh register message,
and
reduce, at the UE [102], the call setup time in the higher RAT based
on the acknowledgement response.
8. The system as claimed in claim 7, wherein the nth generation mobile network QoS Identifier is a 5th generation mobile network QoS Identifier (5QI).
9. The system as claimed in claim 8, wherein the additional information element comprises an uplink data status (UDS) for the 5th generation mobile network QoS Identifier (5QI), wherein the UDS is associated with a first value and the 5QI is associated with a second value.
10. The system as claimed in claim 9, wherein the first value is 1 and the second value is 5.
11. The system as claimed in claim 7, wherein the acknowledgement response comprises a refresh register 200 OK response and a resume Session Initiation Protocol (SIP) signalling response.
12. The system as claimed in claim 7, wherein the higher RAT is associated with a 5th generation mobile network and the lower RAT is associated with a 4th generation mobile network.
13. A user equipment (UE) for reducing a call setup time in a higher radio access technology (RAT), the user equipment (UE) comprising:
- a system, wherein the system comprises a processing unit [202] configured to:

transmit, from the user equipment (UE) [102] to a network server
[104], a UE register request to register the UE on the higher RAT
from a lower RAT,
transmit, from the UE [102] to the network server [104], a Mobility
Registration Update (MRU) with an additional information
element, wherein the MRU is associated with the UE register
request,
receive, at the UE [102] from the network sever [104], an MRU
registration accept indication in response to the MRU with the
additional information element,
receive, at the user equipment [102] from the network server
[104], an indication of a configuration of data radio bearer (DRB)
for an nth generation mobile network QoS Identifier based on the
additional information element,
transmit, from the UE [102] to the network server [104], a refresh
register message based on the configuration of the DRB,
receive, at the UE [102] from the network sever [104], an
acknowledgement response based on the refresh register message,
and
reduce, at the UE [102], the call setup time in the higher RAT based
on the acknowledgement response.