CN112020111B - Method for avoiding network rollback executed by user equipment - Google Patents

Abstract

A method performed by a UE communicatively connected to a first third generation partnership project (3 GPP) network using a first Radio Access Technology (RAT) is provided. The method comprises the following steps: receiving a message from a first 3GPP network indicating that the first 3GPP network supports Packet Switched (PS) session based IP Multimedia Subsystem (IMS) voice; in response to receiving the message, providing, to the first 3GPP network, an indication that fallback of the UE to a second 3GPP network using a second RAT is disabled.

Description

Method for avoiding user equipment from executing network rollback

This application claims priority to U.S. provisional application No. 62/855,008, filed on 31/5/2019, the entire contents of which are incorporated herein by reference.

[ technical field ] A method for producing a semiconductor device

The present application relates generally to wireless communications, and more particularly, to a method of avoiding a User Equipment (UE) from performing network fallback.

[ background of the invention ]

In a typical Mobile communication environment, a User Equipment (UE) (also known as a Mobile Station (MS)), such as a Mobile phone (also known as a cellular phone or handset) or a tablet Personal Computer (PC) with wireless communication capabilities, may communicate voice and/or data signals with one or more serving networks. Wireless communication between the UE and the serving network may be performed using various Radio Access Technologies (RATs), such as Global system for mobile communications (GSM) Technology, general Packet Radio Service (GPRS) Technology, enhanced Data rates for Global Evolution (EDGE), wideband Code Division Multiple Access (WCDMA) Technology, code division multiple Access 2000 (CDMA-2000) Technology, time division synchronous code division multiple Access (TD-SCDMA) Technology, worldwide Interoperability for Microwave Access (WiMAX) Technology, long Term Evolution (LTE) Technology, advanced (advanced) LTE (LTE-a) Technology, and the like. In particular, the GSM/GPRS/EDGE technology is also known as 2G technology; WCDMA/CDMA-2000/TD-SCDMA technology is also called 3G technology; the LTE/LTE-A/TD-LTE technology is also referred to as 4G technology.

These RAT technologies have been used in various telecommunications standards to provide common protocols that enable different wireless devices to communicate on a municipal, national, regional, or even global level. One example of an emerging telecommunications standard is the 5G New Radio (NR). The 5G NR is a set of enhancements to the LTE mobile standard promulgated by the third Generation partnership project (3 GPP). It aims to better support mobile broadband internet access (internet access) by improving spectral efficiency, reducing costs and improving services.

According to 3GPP specifications and/or requirements that are compliant with 5G NR technology, if a 5G network supports IP Multimedia Subsystem (IMS) voice over Packet Switched (PS) session based IMS call service, but for some reason the IMS call service cannot be provided as usual (native), a UE residing on the 5G network may be triggered by the 5G network to fall back to the 4G network to receive a Mobile terminal called (MT) voice call. However, in some cases, the UE may be performing critical operations (critical operations) that require the UE to maintain a connection with the 5G network during the operations. As a result, fallback of the UE to the 4G network may result in disconnection from the 5G network and affect the critical operation.

[ summary of the invention ]

To address the above issues, the present application proposes a specific way to configure the UE and/or the serving network (e.g., 5G network) to avoid the UE performing network fallback (e.g., not performing a fallback of the UE to a legacy network (e.g., 4G)).

In one aspect of the present application, a method performed by a UE communicatively connected to a first third generation partnership project (3 GPP) network using a first Radio Access Technology (RAT) is provided. The method comprises the following steps: receiving a message from the first 3GPP network indicating that the first 3GPP network supports Packet Switched (PS) session based IP Multimedia Subsystem (IMS) voice; in response to receiving the message indicating that the first 3GPP network supports the PS session based IMS voice, providing an indication to the first 3GPP network that fallback of the UE to a second 3GPP network using a second RAT is disabled.

In another aspect of the present application, a method performed by a first 3GPP network that uses a first RAT and that is communicatively connected to a UE is provided. The method comprises the following steps: sending a message to a UE, the message indicating that the first 3GPP network supports IMS voice over PS session; in response to the first 3GPP network supporting the PS session based IMS voice, allowing IMS registration from the UE; and providing an indication that the incoming call is to be established in a second 3GPP network using a second RAT in response to initiating the incoming call (originating call) to the UE.

Other aspects and features of the present application will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of a method for avoiding fallback of a UE to a legacy network.

[ description of the drawings ]

The present application may be more completely understood in consideration of the following detailed description and examples in connection with the accompanying drawings, in which:

FIG. 1 is a block diagram of a wireless communication environment according to an embodiment of the present application;

fig. 2 is a block diagram illustrating a UE110 according to an embodiment of the application;

fig. 3 is a flowchart illustrating a method of avoiding a UE to fall back to a legacy network according to an embodiment of the present application;

fig. 4 is a message sequence chart illustrating a method of avoiding a UE fallback to a legacy network according to the embodiment of fig. 3;

fig. 5 is another message sequence chart illustrating a method of avoiding a UE fallback to a legacy network according to the embodiment of fig. 3;

fig. 6 is a flowchart illustrating a method of avoiding a UE to fall back to a legacy network according to another embodiment of the present application; and

fig. 7 is a message sequence chart illustrating a method of preventing the UE from falling back to the legacy network according to the embodiment of fig. 6.

[ detailed description ] A

The following description is made for the purpose of illustrating the general principles of this application and should not be taken in a limiting sense. It should be understood that embodiments may be implemented in software, hardware, firmware, or any combination thereof. The terms "comprises," "comprising," "includes," and/or "having," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

Fig. 1 is a block diagram of a wireless communication environment according to an embodiment of the present application.

As shown in fig. 1, a wireless communication environment 100 includes a User Equipment (UE) 110 and two 3GPP networks 120 and 130.

UE110 may be a feature phone, a smartphone, a tablet Personal Computer (PC), a laptop, or any wireless communication device that supports the RAT used by 3GPP networks 120 and 130. UE110 may be in wireless communication with one or both of 3GPP networks 120 and 130.

Specifically, the RAT used by 3GPP network 120 is more advanced than the RAT used by 3GPP network 130. That is, the 3GPP network 120 is a more advanced network than the 3GPP network 130 (for example, the 3GPP network 120 may be referred to as an advanced network, and the 3GPP network 130 may be referred to as a legacy network).

For example, 3GPP network 120 can be a 5G network (e.g., an NR network), and 3GPP network 130 can be a 4G network (e.g., an LTE/LTE-A/TD-LTE network) or a 3G network (e.g., a WCDMA/CDMA-2000/TD-SCDMA network) or a 2G network (e.g., a GSM/GPRS/EDGE network).

Specifically, 3GPP network 120 includes an access network 121 and a core network 122, while 3GPP network 130 includes an access network 131 and a core network 132. Access networks 121 and 131 are responsible for handling radio signals, terminating radio protocols, and connecting UE110 with core networks 122 and 132, respectively. The core networks 122 and 132 are responsible for performing mobility management, network-side authentication, and interfacing with public/external networks (e.g., the internet).

Access networks 121 and 131 and core networks 122 and 132 may each include one or more network nodes for performing the described functions. For example, if the 3GPP network 120 is an NR network, the Access network 121 may be a next generation radio Access network (NG-RAN) including at least a gNB or a Transmission Reception Point (TRP), and the core network 122 may be a next generation core network (NG-CN) including various network functions including Access and Mobility Functions (AMF), session Management Functions (SMF), policy Control functions (Policy Control Function, PCF), application functions (Application Function, AF), authentication Server functions (AUSF), user Plane Functions (UPF), and User Data Management (User Data Management, UDM), where each network Function may be implemented as a network element on dedicated hardware, or as an instance running on dedicated hardware, or as a virtual cloud Function (e.g., instantiated as a virtual cloud platform) on a suitable basis.

The AMF provides UE-based authentication, authorization, mobility management, etc. The SMF is responsible for session management and assigns an Internet Protocol (IP) address to the UE. The SMF also selects and controls the UPF for data transmission. If the UE has multiple sessions, different SMFs may be assigned to each session to manage them separately, and possibly to provide different functionality for each session.

The AF provides information on the packet flow to the PCF responsible for policy control to support Quality of Service (QoS). And the PCF determines a strategy related to mobility and session management according to the information so as to enable the AMF and the SMF to operate normally. The AUSF stores data for authentication of the UE, and the UDM stores subscription data (subscription data) of the UE.

For example, if 3GPP Network 130 is an LTE/LTE-a/TD-LTE Network, access Network 131 may be an Evolved UTRAN (E-UTRAN) that includes at least an Evolved NB (eNB) (e.g., macro, femto, or pico eNB), and Core Network 132 may be an Evolved Packet Core (EPC) that includes a Home Subscriber Server (HSS), a Mobility Management Entity (MME), a Serving Gateway (S-GW), and a Packet Data Network Gateway (PDN-GW or P-GW).

Alternatively, if the 3GPP network 130 is a WCDMA network, the access network 121 may be a Universal Terrestrial Radio Access Network (UTRAN) and the core network 122 may be a GPRS core comprising a Home Location Register (HLR), at least one Serving GPRS Support Node (SGSN) and at least one Gateway GPRS Support Node (GGSN).

More specifically, 3GPP networks 120 and 130 each support Packet Switched (PS) session based IP Multimedia Subsystem (IMS) voice, and 3GPP network 120 supports fallback procedures that are performed to fallback UE110 from 3GPP network 120 to 3GPP network 130 for IP Multimedia Subsystem (IMS) call services. For example, if 3GPP network 120 is an NR network and 3GPP network 130 is an LTE network, the fallback procedure is referred to as Evolved Packet System (EPS) fallback. Although not shown, each of the 3GPP networks 120 and 130 may include IMS servers that may be connected to the core network 122/132 or disposed in the core network 122/132.

However, for some reasons, 3GPP network 120 cannot provide IMS call services to UE110 as often (natively), so the method of the present application is introduced to avoid UE110 falling back from 3GPP network 120 to 3GPP network 130 when UE110 is performing critical operations.

It should be understood that the description of the wireless communication environment 100 is for illustrative purposes only and is not intended to limit the scope of the present application. For example, if 6G technology supports UE110 to fall back from a 6G network to a 5G network, 3GPP network 120 may be the 6G network and 3GPP network 130 may be the 5G network.

Fig. 2 is a block diagram illustrating UE110 according to an embodiment of the application.

The UE110 may include a wireless transceiver 10, a controller 20, a storage device 30, a display device 40, and an input/output (I/O) device 50.

The wireless transceiver 10 is configured to perform wireless transmission and reception with the access network 121 and/or the access network 131.

In particular, the wireless transceiver 10 may include a baseband processing device 11, a Radio Frequency (RF) device 12, and an antenna 13, where the antenna 13 may include one or more antennas for beamforming. The baseband processing device 11 is configured to perform baseband signal processing and control communication between a subscriber identity card (not shown) and the RF device 12. Baseband processing device 11 may contain a number of hardware components to perform baseband signal processing including analog-to-digital conversion (ADC)/digital-to-analog conversion (DAC), gain adjustment, modulation/demodulation, encoding/decoding, and the like. The RF device 12 may receive an RF wireless signal via the antenna 13, convert the received RF wireless signal into a baseband signal processed by the baseband processing device 11, or receive a baseband signal from the baseband processing device 11 and convert the received baseband signal into an RF wireless signal, and then transmit it through the antenna 13. The RF device 12 may also contain a number of hardware devices to perform radio frequency conversion. For example, the RF device 12 may include a mixer to multiply a baseband signal with a carrier oscillating in a radio frequency of a supported cellular technology, where the radio frequency may be 900MHz,1900MHz, or 2100MHz used in a 3G (e.g., WCDMA) system, or may be 900MHz,2100MHz, or 2.6GHz used in a 4G (e.g., LTE/LTE-A/TD-LTE) system, or may be any radio frequency used in a 5G (e.g., NR) system (e.g., 30GHz for millimeter waves)

300 GHz) or other radio frequency depending on the RAT used.

In another embodiment, the wireless transceiver 10 may include a plurality of sets of baseband processing devices, RF devices and antennas, wherein each set of baseband processing devices, RF devices and antennas is configured to perform wireless transmission and reception using a respective RAT.

The controller 20 may be a general purpose processor, a Micro Control Unit (MCU), an application processor, a Digital Signal Processor (DSP), a Graphics Processing Unit (GPU), a Holographic Processing Unit (HPU), a Neural Processing Unit (NPU), etc., which includes various circuits for providing data processing and computing functions, controls the wireless transceiver 10 to wirelessly communicate with the access network 121 and/or the access network 131, enables the storage device 30, and stores and retrieves data to and from the storage device 30, transmits a series of frame data (e.g., representing text messages, graphics, images, etc.) to the display device 40, and receives signals from/outputs signals to the I/O device 50 from the I/O device 50.

In particular, the controller 20 coordinates the aforementioned operations of the wireless transceiver 10, the storage device 30, the display device 40, and the I/O device 50 to perform a method of preventing the UE110 from falling back to the conventional network.

In another embodiment, the controller 20 may be integrated into the baseband processing apparatus 11 to function as a baseband processor.

As will be understood by those skilled in the art, the circuitry of the controller 20 will typically include transistors configured to control the operation of the circuitry in accordance with the functions and operations described herein. As will be further appreciated, the specific structure or interconnection of the transistors will typically be determined by a compiler, such as a Register Transfer Language (RTL) compiler. An RTL compiler may be operated on scripts very similar to assembly language code by a processor to compile the scripts into a form for final circuit layout or fabrication. Indeed, RTL is known for its role and use in facilitating the design of electronic and digital systems.

Storage device 30 is a non-transitory machine-readable storage medium comprising memory such as FLASH memory or non-volatile random access memory (NVRAM), or magnetic storage devices such as hard disks or magnetic tape, optical disks, or any combination thereof, for storing instructions and/or program code for an operating system, application programs, communication protocols, and/or the methods of the present application (or the methods of the present application may be implemented as part of a communication protocol).

The display device 40 may be a Liquid Crystal Display (LCD), a Light Emitting Diode (LED) display, an Electronic Paper Display (EPD), or the like, for providing a display function. Alternatively, the display device 40 may further include one or more touch sensors disposed thereon or therebelow for sensing a touch, contact or proximity operation of an object such as a finger or a pen.

The I/O device 50 may include one or more buttons, a keyboard, a mouse, a touch pad, a camera, a microphone and/or a speaker, etc., to serve as a man-machine interface (MMI) to interact with a user, such as to receive user input and output prompts to the user.

It should be understood that the components described in the embodiment of FIG. 2 are for illustration purposes only and are not intended to limit the scope of the present application. For example, UE110 may include further components, such as a power supply or a Global Positioning System (GPS) device, where the power supply may be a mobile/replaceable battery that powers all other components of UE 110. The GPS device may provide location information for UE110 for certain location-based services or applications. Alternatively, UE110 may include fewer components. For example, UE110 may not include display device 40 and/or I/O device 50.

Fig. 3 is a flowchart illustrating a method of avoiding a UE to fall back to a legacy network according to an embodiment of the present application.

In this embodiment, the method of avoiding a UE fallback to a legacy network is applied to and performed by a UE (e.g., UE 110). Specifically, the UE is communicatively connected to a first 3GPP network (e.g., 3GPP network 120) that uses an advanced RAT (e.g., 5G NR).

First, the UE registers with the first 3GPP network by transmitting a request message to the first 3GPP network (step S310). In one embodiment, the REQUEST message may be a REGISTRATION REQUEST (REGISTRATION REQUEST) message.

After step S310, the UE receives a response message from the first 3GPP network, the response message indicating that the first 3GPP network supports PS session based IMS voice (step S320). In one embodiment, the response message may be a REGISTRATION ACCEPT (REGISTRATION ACCEPT) message.

After step S320, in response to receiving the response message indicating that the first 3GPP network supports IMS voice over PS session, the UE provides an indication to the first 3GPP network that fallback of the UE to the second 3GPP network using the legacy RAT is disabled (step S330), and the method ends.

In one embodiment, an indication is provided to a first 3GPP network that fallback of a UE to a second 3GPP network using a legacy RAT is disabled in response to detecting that an IMS voice session is initiated. Details of this embodiment will be given later in fig. 4.

In another embodiment, an indication that fallback of the UE to a second 3GPP network using a legacy RAT is disabled may be provided to the first 3GPP network when performing IMS registration on the first 3GPP network. Details of this embodiment will be given later in fig. 5.

Fig. 4 is a message sequence chart illustrating a method of avoiding a UE fallback to a legacy network according to the embodiment of fig. 3.

In step S401, UE110 sends a registration request message to core network 122 to register with 3GPP network 120.

In step S402, UE110 receives a registration accept message from core network 122, wherein the registration accept message indicates that 3GPP network 120 supports IMS voice over PS session.

In step S403, UE110 establishes one or more radio bearers with 3GPP network 120 to perform critical operations.

In particular, the critical operations may be associated with a Low-Latency Communication (LLC) application, such as a gaming application.

In step S404, in response to UE110 being configured to be "voice-centric" and 3GPP network 120 supporting IMS voice over PS Session, UE110 sends a Session Initiation Protocol (SIP) registration message to an IMS server of 3GPP network 120 to register for IMS call services.

In step S405, UE110 receives a SIP OK (SIP OK) message from the IMS server of 3GPP network 120 to complete IMS registration.

In step S406, UE110 receives a SIP INVITE (INVITE) message from an IMS server of 3GPP network 120, where the SIP INVITE message indicates an incoming call to UE 110.

In step S407, the UE sends a SIP183 message to an IMS server of the 3GPP network 120, where the SIP183 message includes a Feature-cap header (Feature-Caps header) field, where a specific tag (tag) is present in the Feature-Caps header field to provide an indication that fallback of the UE110 to a legacy 3GPP network (e.g., 3GPP network 130) is disabled.

For example, the specific tag may be a "g.3gpp. Epsfb-fordi" tag, a "g.3gpp. Epsfb-disallow" tag, a "g.3gpp. Nonepsfb" tag, or a "g.3gpp.ps-fallback-fordi" tag.

In step S408, in response to 3GPP network 120 not being able to support PS session based IMS voice as usual and receiving a SIP183 message including an indication that fallback of UE110 to a legacy 3GPP network (e.g., 3GPP network 130) is disabled, the IMS server of 3GPP network 120 rejects the incoming call. For some reasons, 3GPP network 120 may not be able to support PS session based IMS voice as usual (i.e., EPS fallback is the only option). For example, an IMS server of 3GPP network 120 is in maintenance (maintenance) when initiating an incoming call to UE110, or an operator of 3GPP network 120 may want to utilize IMS services of a legacy 3GPP network (e.g., 3GPP network 130) more frequently.

In another embodiment, if 3GPP network 120 natively supports IMS voice over PS session when initiating an incoming call to UE110, 3GPP network 120 may proceed with the call setup procedure.

Fig. 5 is another message sequence chart illustrating a method of avoiding a UE fallback to a legacy network according to the embodiment of fig. 3.

In step S501, the UE110 transmits a registration request message to the core network 122 to register with the 3GPP network 120.

In step S502, UE110 receives a registration accept message from core network 122, wherein the registration accept message indicates that 3GPP network 120 supports IMS voice over PS session.

In step S503, UE110 establishes one or more radio bearers with 3GPP network 120 to perform critical operations.

In particular, the critical operations may be associated with an LLC application (e.g., a gaming application).

In step S504, in response to UE110 being configured to be "voice-centric" and 3GPP network 120 supporting IMS voice over PS session, UE110 sends a SIP REGISTER message (SIP REGISTER) to an IMS server of 3GPP network 120 to REGISTER for IMS call services.

In particular, the SIP register message includes a Contact header (Contact header) field in which no or a specific tag is present to provide an indication that fallback of UE110 to a legacy 3GPP network (e.g., 3GPP network 130) is disabled.

In one embodiment, the particular tag may be a "g.3gpp.epsfb" tag or a "g.3gpp.ps-fallback" tag, and indicates that fallback of UE110 to a legacy 3GPP network is disabled when such tag is absent in the contact header field.

In another embodiment, the particular tag may be a "g.3gpp.epsfb-forbid" tag, a "g.3gpp.epsfb-disallow" tag, a "g.3gpp.nonepsfb" tag, or a "g.3gpp.ps-fallback-forbid" tag, and indicate that fallback of the UE110 to the legacy 3GPP network is disabled when such a tag is present in the contact header field. Note that if the embodiment is applied in which a positive (positive) indication is included in the SIP REGISTER message, UE110 may need to re-REGISTER for IMS call services to allow EPS fallback at the end of critical operations.

In step S505, UE110 receives a SIP OK message from the IMS server of 3GPP network 120 to complete IMS registration.

In step S506, in response to 3GPP network 120 being unable to support PS session based IMS voice as usual and receiving a SIP register message that includes an indication indicating that fallback of UE110 to a legacy 3GPP network (e.g., 3GPP network 130) is disabled, an IMS server of 3GPP network 120 rejects the incoming call. For some reasons, 3GPP network 120 may not be able to support PS session based IMS voice as usual (i.e., EPS fallback is the only option). For example, an IMS server of 3GPP network 120 is in maintenance when initiating an incoming call to UE110, or an operator of 3GPP network 120 may want to utilize IMS services of a legacy 3GPP network (e.g., 3GPP network 130) more frequently.

In another embodiment, if 3GPP network 120 natively supports IMS voice over PS session when initiating an incoming call to UE110, 3GPP network 120 may continue the call setup procedure.

In view of the foregoing embodiments of fig. 3-5, it will be appreciated that the present invention enables avoiding fallback of a UE from an advanced 3GPP network to a legacy 3GPP network by allowing the UE to provide an indication that fallback of the UE to the legacy 3GPP network is disabled. Advantageously, the UE may maintain a connection with the advanced 3GPP network to keep critical operations ongoing without being interrupted by an IMS incoming call that may trigger a fallback to a legacy 3GPP network.

Fig. 6 is a flowchart illustrating a method of avoiding a UE to fall back to a legacy network according to another embodiment of the present application.

In this embodiment, the method of avoiding a fallback of a UE to a legacy network is applied to and performed by a first 3GPP network (e.g., 3GPP network 120). In particular, a first 3GPP network is communicatively connected to a UE (e.g., UE 110).

First, the first 3GPP network receives a request message from the UE (step S610). In one embodiment, the request message may be a registration request message.

After step S610, the first 3GPP network replies to the UE with a response message indicating that the first 3GPP network supports IMS voice over PS session (step S620). In one embodiment, the response message may be a registration accept message.

After step S620, in response to the first 3GPP network supporting IMS voice over PS session, the first 3GPP network allows IMS registration from the UE (step S630).

After step S630, in response to initiating the incoming call to the UE, the first 3GPP network provides an indication that the incoming call is to be established in a second 3GPP network that uses the legacy RAT (step S640), and the method ends.

In one embodiment, if the first 3GPP network is unable to provide IMS call services locally for some reason, the first 3GPP network may provide an indication that an incoming call to the UE will be established in the second 3GPP network. For example, an IMS server of the first 3GPP network may be in maintenance when initiating an incoming call to the UE, or the operator of the first 3GPP network may want to utilize IMS services of the second 3GPP network more frequently.

In one embodiment, an indication may be provided to the UE in a SIP message that an incoming call to the UE is to be established in the second 3GPP network. Details of this embodiment will be given later in fig. 7.

Fig. 7 is a message sequence chart illustrating a method of preventing the UE from falling back to the conventional network according to the embodiment of fig. 6.

In step S701, the core network 122 receives a registration request message from the UE 110.

In step S702, core network 122 replies to UE110 with a registration accept message to indicate that 3GPP network 120 supports IMS voice over PS session.

In step S703, UE110 establishes one or more radio bearers with 3GPP network 120 to perform critical operations.

In particular, the critical operations may be associated with an LLC application (e.g., a gaming application).

In step S704, in response to UE110 being configured to be "voice-centric" and 3GPP network 120 supporting IMS voice over PS session, UE110 sends a SIP register message to an IMS server of 3GPP network 120 to register for IMS call service.

In step S705, UE110 receives a SIP invite message from the IMS server of 3GPP network 120 to complete IMS registration.

In step S706, the IMS server of 3GPP network 120 sends a SIP invite message to UE110, where the SIP invite message indicates that an incoming call to UE110 is to be established in legacy 3GPP network 130.

In step S707, the IMS server of 3GPP network 120 receives the SIP 403 message from UE110, where the SIP 403 message indicates that UE110 rejects the incoming call.

In response to receiving the SIP 403 message indicating rejection of the incoming call, the IMS server of the 3GPP network 120 rejects the incoming call in step S708.

In view of the foregoing embodiments of fig. 6-7, it will be appreciated that the present application avoids fallback of a UE from an advanced 3GPP network to a legacy 3GPP network by allowing the advanced 3GPP network to provide an indication that an incoming call to the UE will be established in the legacy 3GPP network. Advantageously, the UE may choose to reject the incoming call and maintain a connection with the advanced 3GPP network to keep ongoing critical operations from being interrupted by IMS incoming calls that may trigger a fallback to legacy 3GPP networks.

While the present application has been described by way of example and in accordance with preferred embodiments, it is to be understood that the application is not so limited. Various changes and modifications may still be made by those skilled in the art without departing from the scope and spirit of the present application (e.g., the present application is equally applicable to avoid fallback of a UE from a legacy 3GPP network to an advanced 3GPP network. For example, in the embodiment shown in FIG. 3, the first 3GPP network may be a 2G, 3G or 4G network, and the second 3GPP network may be a 5G network, and in step S330, in response to receiving an indication that the first 3GPP supports PS session based IMS voice, an indication is provided indicating that fallback of the UE to the second 3GPP network using an advanced RAT (e.g., 5G NR) is disabled. Further, as in the embodiment shown in FIG. 6, the first 3GPP network may be a 2G, 3G or 4G network, the second 3GPP network may be a 5G network, and in step S640, in response to initiating an incoming call to the UE, an indication is provided indicating that the incoming call is to be established in the second 3GPP network using an advanced RAT (e.g., 5G NR). Accordingly, the scope of the application should be defined and protected by the following claims and their equivalents.

Use of ordinal terms such as "first," "second," etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

Claims (14)

1. A method of avoiding a user equipment performing network fallback, performed by a user equipment communicatively connected to a first 3GPP network using a first radio access technology, wherein the user equipment supports the first radio access technology and a second radio access technology, the method comprising:

receiving a message from the first 3GPP network indicating that the first 3GPP network supports voice over IP multimedia subsystem for packet switched sessions; and

in response to receiving the message indicating that the first 3GPP network supports the packet switched session based IP multimedia subsystem Voice, providing an indication to the first 3GPP network that fallback of the user equipment to a second 3GPP network using the second radio access technology is disabled.

2. The method of claim 1, wherein an indication that fallback to the second 3GPP network for the user equipment is disabled is provided in response to detecting that an IP multimedia subsystem voice session is being initiated.

3. The method of claim 1, wherein an indication that fallback of the user equipment to the second 3GPP network is disabled is provided when an IP multimedia subsystem registration is performed on the first 3GPP network.

4. The method of claim 1, wherein the indication that fallback of the user equipment to the second 3GPP network is disabled is provided in a session initiation protocol message.

5. The method of claim 4, wherein the session initiation protocol message is a SIP183 message.

6. The method of claim 5, wherein the SIP183 message comprises a feature cap field, and wherein the feature cap field comprises an indication that fallback of the user equipment to the second 3GPP network is disabled.

7. The method of claim 6, wherein the indication that fallback of the user equipment to the second 3GPP network is disabled is that a "g.3gpp.epsfb-forbid" or a "g.3gpp.epsfb-disallow" or a "g.3gpp.nonepsfb" or a "g.3gpp.ps-fallback-forbid" tag is present in a feature cap header field of a SIP183 message.

8. The method of claim 4, wherein the session initiation protocol message is a session initiation protocol registration message.

9. The method of claim 8, wherein the session initiation protocol registration message comprises a contact header field, and wherein the contact header field comprises an indication that fallback of the user equipment to the second 3GPP network is disabled.

10. The method of claim 9, wherein the indication that fallback of the user equipment to the second 3GPP network is disabled refers to an absence of a "g.3gpp.epsfb" or "g.3gpp.ps-fallback" tag in a contact header field of the session initiation protocol registration message, or to a presence of a "g.3gpp.epsfb-forward" or "g.3gpp.epsfb-display" or "g.3gpp.nonepsfb" or "g.3gpp.fbpsfb-fallback" tag in a contact header field of the session initiation protocol registration message.

11. The method of claim 1, wherein an indication that fallback of the user equipment to the second 3GPP network is disabled is provided in response to the usage setting of the user equipment being "Voice centric" and a predetermined operation being performed between the user equipment and the first 3GPP network.

12. The method of claim 11, wherein the predetermined operation is associated with a low latency communication application.

13. The method of claim 1, wherein the message is a registration accept message.

14. The method of claim 1, wherein the first radio access technology is a more advanced radio access technology than the second radio access technology.

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