Patent Description:
Looking back on the development of wireless communication over the generations, technologies have been developed mainly for human-oriented services, such as voice, multimedia, and data services. It is expected that connected devices, which have been explosively increasing since the commercialization of a fifth-generation (<NUM>) communication system, will be connected to a communication network. Examples of things connected to a network may include vehicles, robot, drones, home appliances, display, smart sensors installed in various types of infrastructure, construction machines, and factory equipment. Mobile devices are expected to evolve into various form factors, such as augmented reality glasses, virtual reality headsets, and hologram devices. To provide various services by connecting hundreds of billions of devices and things in a <NUM>th-generation (<NUM>) era, efforts are being made to develop an improved <NUM> communication system. For this reason, a <NUM> communication system is referred to as a beyond <NUM> communication system.

In the <NUM> communication system, which is predicted to be realized around <NUM>, the maximum transmission speed corresponds to terabits per second (i.e., at least <NUM>,<NUM> gigabits per second), and the wireless latency time is <NUM> microseconds (µsec). For example, in the <NUM> communication system, the transmission speed is <NUM> times faster than that in the <NUM> communication system, and the wireless latency time is reduced by one-tenth.

In order to achieve a high data transmission rate and an ultra-low latency, implementing the <NUM> communication system in a terahertz band (e.g., a band from <NUM> gigahertz (<NUM>) to <NUM> terahertz (<NUM> THz)) is being considered. In the terahertz band, compared to a millimeter-wave (mmWave) band introduced in <NUM>, the importance of a technique for guaranteeing the range, i.e., the coverage, of a signal is expected to increase due to serious path loss and atmospheric absorption. As major techniques for guaranteeing coverage, multiple antenna transmission techniques, such as a new waveform, beamforming, massive multiple-input and multiple-output (massive MIMO), full dimensional MIMO (FD-MIMO), an array antenna, and a large scale antenna, which are superior in terms of coverage to a radio frequency (RF) device, an antenna, and orthogonal frequency division multiplexing (OFDM), need to be developed. In addition, new techniques, such as metamaterial-based lenses and antennas, high-dimensional spatial multiplexing using orbital angular momentum (OAM), and a reconfigurable intelligent surface (RIS), are under discussion in order to improve the coverage of a signal in a terahertz band.

Further, in the <NUM> communication system, to improve frequency efficiency and to enhance a system network, full duplex that enables an uplink and a downlink to simultaneously use the same frequency resource at the same time, a network technique of using a satellite and high-altitude platform stations (HAPS) in an integrated manner, a network structure innovation technique that supports a mobile base station and enables optimization and automation of a network operation, dynamic spectrum sharing through collision avoidance based on spectrum usage prediction, an AI-based communication technique that realizes system optimization by utilizing artificial intelligence (AI) from a design stage and internalizing an end-to-end AI support function, and a next-generation distributed computing technique that realizes a service of complexity beyond the limit of terminal computation capability by utilizing ultra-high-performance communication and computing resources (mobile edge computing (MEC), cloud, and the like) are under development. In addition, attempts to reinforce connectivity between devices, to optimize a network, to promote the softwarization of network entities, and to increase the openness of wireless communication continue by designing a new protocol to be used in the <NUM> communication system, by configuring a hardware-based security environment, by developing a mechanism for the safe use of data, and by developing a technology for maintaining privacy.

Due to the research and development of the <NUM> communication system, the next hyper-connected experience is expected to be possible through the hyper-connectivity of the <NUM> communication system, which includes not only connectivity between objects but also connectivity between a human and an object. Specifically, the <NUM> communication system is expected to provide services, such as truly immersive extended reality (truly immersive XR), high-fidelity mobile hologram, and digital replica services. Moreover, the <NUM> communication system provides services, such as remote surgery, industrial automation, and emergency response, through security and reliability enhancement are provided through, thus being applied to various fields, such as industry, medical care, automobiles, and home appliances.

The quality of a video call using a smartphone may be controlled by adjusting the resolution of an image or the bit rate of a sound related to the video call, based on smartphone-related conditions (e.g., the processing capability of the smartphone, an available resolution, or a network environment). The range of a negotiated call quality may be specified by negotiating the maximum capability (e.g., codec or resolution processing capability) of the smartphone with the counterpart of the call in the initial stage of connection for the video call, after which the call quality may be adjusted within the range of the negotiated call quality range according to the state change. The call counterpart may be a counterpart terminal or a call server.

Recently, a large number of auxiliary devices (e.g., an AR device, a VR device, a smartwatch, and the like) linked to a smartphone are used. Some auxiliary devices may be used for a video call. When a specific auxiliary device is used for a video call, it is necessary for a mobile communication operator to recognize a main device and the auxiliary device (e.g., a smartphone) in combination as a single terminal. A group of terminals in which one or more devices are wired or wirelessly coupled to receive services may be referred to as a new terminal.

The commercialization of a new terminal enables a user to use voice and video calls of the related depending on the situation or to use an immersive video call based on 3D graphics (emoji) and a 3D realistic images when large-capacity information transmission and high processing capability are guaranteed.

<CIT> discloses a framework and method for realizing multimedia communication. <CIT> discloses signaling asymmetric media capabilities using SDP signaling. <CIT> discloses a method for session initiation in a conference. <CIT> discloses a method of replicating a media session in a Service Centralized and Continuity Application Server (SCC AS).

Accordingly, an aspect of the disclosure is to provide for supporting a call according to a plurality of modes.

The present invention is defined by the subject-matter of the appended set of claims.

In accordance with an aspect of the disclosure, a method for supporting, by a first terminal, switching between a plurality of modes for a call is provided. The method includes performing a capability negotiation for a call with a second terminal, and establishing a first connection between the first terminal and a call server according to a first mode among the plurality of modes for the call with the second terminal after performing the capability negotiation, wherein the performing of the capability negotiation includes transmitting a first message including information indicating a media attribute of each of two or more modes of the plurality of modes to the call server.

In accordance with another aspect of the disclosure, a method for supporting, by a call server, switching between a plurality of modes for a call is provided. The method includes performing a capability negotiation for a call between a first terminal and a second terminal, and establishing a first connection between the first terminal and the call server according to a first mode among the plurality of modes for the call between the first terminal and the second terminal after performing the capability negotiation, wherein the performing of the capability negotiation includes receiving a first message including information indicating a media attribute for each of two or more modes among the plurality of modes from the first terminal.

In accordance with another aspect of the disclosure, a first terminal for supporting switching between a plurality of modes for a call is provided. The first terminal includes a transceiver, and at least one processor configured to be connected to the transceiver, wherein the at least one processor is configured to perform a capability negotiation for a call with a second terminal, and establish a first connection between the first terminal and a call server according to a first mode among the plurality of modes for the call with the second terminal after performing the capability negotiation, and the at least one processor is configured to transmit a first message including information indicating a media attribute of each of two or more modes of the plurality of modes to the call server in order to perform the capability negotiation.

In accordance with another aspect of the disclosure, a call server for supporting switching between a plurality of modes for a call is provided. The call server includes a transceiver, and at least one processor configured to be connected to the transceiver, wherein the at least one processor is configured to perform a capability negotiation for a call between a first terminal and a second terminal, and establish a first connection between the first terminal and the call server according to a first mode among the plurality of modes for the call between the first terminal and the second terminal after performing the capability negotiation, and the at least one processor is configured to receive a first message including information indicating a media attribute for each of two or more modes among the plurality of modes from the first terminal in order to perform the capability negotiation.

Specific details of other embodiments are included in the detailed description and drawings.

Embodiments disclosed herein have at least the following effect.

For example, it is possible to provide a seamless service in a call according to a plurality of modes using a main device and an auxiliary device.

The above and other aspects, features, and advantages certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:.

Although the terms "first", "second", and the like are used to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element.

<FIG> is a block diagram illustrating a system for providing a call service according to an embodiment of the disclosure.

Referring to <FIG>, a terminal <NUM> may receive a call service with a different counterpart terminal <NUM> via a <NUM> network <NUM>. The terminal <NUM> may refer to a device capable of independently performing a call, such as a smartphone or a tablet PC. The terminal <NUM> may be referred to as a user equipment (UE), an electronic device, or the like and is not limited to the illustrated terms.

Although the <NUM> network <NUM> refers to a communication network according to a fifth-generation communication protocol specified by the 3rd Generation Partnership Project (3GPP), the <NUM> network <NUM> in <FIG> is merely an example of a communication network, and the disclosure is not necessarily applicable in the <NUM> network <NUM>. The disclosure may be applied not only in the <NUM> network <NUM> but also in various communication networks to which various communication techniques, such as LTE, LTE-A, and CDMA, are applied.

When the terminal <NUM> performs a video call with a different counterpart terminal <NUM>, a call server <NUM> may be involved. The call server <NUM> is configured to process multimedia associated with the video call. For example, the call server <NUM> may provide a function of re-encoding or mixing a sound or an image or a function of splitting a screen for the video call. According to some embodiments of the disclosure, the call server <NUM> may be involved not only for the video call but also for a voice call.

The terminal <NUM> may be connected to an auxiliary terminal <NUM> via a cable or wirelessly. The auxiliary terminal <NUM> may be one of an AR device, such as AR glasses, a VR device, a head-mounted display (HMD), a tablet PC, a smartwatch, and a smartphone separate from the terminal <NUM> but is not limited thereto. A mobile communication operator or the counterpart terminal <NUM> may recognize the terminal <NUM> and the auxiliary terminal <NUM> as a single terminal and may perform a call. The terminal <NUM> and the auxiliary terminal <NUM> may be referred to as a new terminal as mentioned above. According to some embodiments of the disclosure, the mobile communication operator or the counterpart terminal <NUM> may recognize the new terminal as the terminal <NUM>. According to some embodiments of the disclosure, when the terminal <NUM> and the auxiliary terminal <NUM> can each independently perform a call and an agent of a call designated by a user or an agent of the call designated by the counterpart terminal <NUM> is the auxiliary terminal <NUM>, the mobile communication operator or the counterpart terminal <NUM> may recognize the new terminal as the auxiliary terminal <NUM>. For example, the auxiliary terminal <NUM> may actually function as a main terminal, and the terminal <NUM> may function as an auxiliary terminal. A main terminal and an auxiliary terminal may be relatively configured depending on a condition of an individual call.

A call between the new terminal and the counterpart terminal <NUM> may be distinguished through one of a plurality of modes. The plurality of modes may be distinguished according to whether the user directly uses the terminal <NUM> or the auxiliary terminal <NUM> for a call and a transmission method for media data used for the call, but conditions for distinguishing the plurality of modes are not limited thereto. Hereinafter, a plurality of modes for a call will be described with reference to <FIG>.

<FIG> illustrates a plurality of modes according to an embodiment of the disclosure.

Referring to <FIG>, the plurality of modes may include a phone mode <NUM>, a tethered mode <NUM>, and a standalone mode <NUM> but is not necessarily limited thereto.

In the phone mode <NUM>, the user may perform a call with a counterpart terminal <NUM> using a terminal <NUM>. In the phone mode <NUM>, the auxiliary terminal <NUM> may not be involved in the call between the terminal <NUM> and the counterpart terminal <NUM>.

In the tethered mode <NUM>, the user may perform a call with the counterpart terminal <NUM> using the auxiliary terminal <NUM>. In the tethered mode <NUM>, the terminal <NUM> may receive media data for the call and may transmit the received media data to the auxiliary terminal <NUM> by tethering.

In the standalone mode <NUM>, the user may perform a call with the counterpart terminal <NUM> using the auxiliary terminal <NUM>. In the standalone mode <NUM>, the auxiliary terminal <NUM> may directly receive media data for the call, not through the terminal <NUM>. The auxiliary terminal <NUM> may include a modem device (e.g., a <NUM> modem chip) to directly receive media data through the <NUM> network <NUM> in the standalone mode <NUM>.

Switching between modes may occur during a call. Switching between modes may occur by user manipulation. For example, switching between modes may occur by the user inputting a command to switch between modes to the terminal <NUM> or the auxiliary terminal <NUM>. Switching between modes may be determined by the terminal <NUM> or the auxiliary terminal <NUM>. In some embodiments of the disclosure, a device currently used by the user for a call among the terminal <NUM> and the auxiliary terminal <NUM> may determine switching. For example, the terminal <NUM> may determine switching during a call in the phone mode <NUM>, and the auxiliary terminal <NUM> may determine switching during a call in the tethered mode <NUM> or the standalone mode <NUM>. Whether to perform switching may be determined in view of the device capacity (e.g., the remaining capacity of a battery, the load of a processor, or the like) of the terminal <NUM> or the auxiliary terminal <NUM>. In some embodiments of the disclosure, when the auxiliary terminal <NUM> includes a mountable display, such as AR glasses or an HMD, the auxiliary terminal <NUM> may determine whether to switch from the tethered mode <NUM> or the standalone mode <NUM> to the phone mode <NUM> in response to detecting that the user demounts the auxiliary terminal <NUM>.

According to some embodiments of the disclosure, the call server <NUM> may determine switching between modes in view of a network state, the states of the terminals <NUM>, <NUM>, and <NUM>, or whether mobile edge computing (MEC) can be supported. Whether MEC can be supported may be determined in view of a delay on a network or a 3D processing resource of the call server. When the call server <NUM> determines to switch, the server may notify the terminal <NUM> to change a mode and may prepare for simulcasting of media data according to a mode and media data of the related according to a changed mode. When receiving a response to the notification from the auxiliary terminal <NUM>, the call server <NUM> may initiate the simulcasting.

When switching between modes is performed, negotiations not only for an initially used mode but also for at least one different mode may be simultaneously conducted in an initial capability negotiation to prevent a call service from being disconnected in order to perform a capability negotiation according to the new mode. Table <NUM> shows at least part of a message transmitted by the terminal <NUM> during an illustrative capability negotiation according to embodiments.

The message of Table <NUM> may be a signaling message according to a session description protocol (SDP) and may be an SDP offer message or an SDP offer answer message. However, a protocol used for the capability negotiation in the embodiments is not necessarily limited to an SDP.

The message of Table <NUM> includes identifications (IDs) of two or more respective configurations and information indicating media attributes in the configurations. Each of the configurations refers to a configuration in one of the plurality of modes for a call. A media attribute refers to a media attribute or an optimal media attribute allowable in a mode indicated by a relevant configuration ID. The media attribute may include, for example, a codec, a resolution, a bit rate, and the like but is not necessarily limited thereto. According to an embodiment of Table <NUM>, negotiations for media attributes of two or more modes may be performed through a single message in an initial capability negotiation, making it possible to perform switching between modes without a new capability negotiation, thus supporting seamless switching between modes. For example, when the terminal <NUM> performs a capability negotiation for a call with the counterpart terminal <NUM>, even though an initial mode is the phone mode <NUM>, a capability negotiation for one or more of the tethered mode <NUM> and the standalone mode <NUM> may be performed together with a capability negotiation for the phone mode <NUM>, thereby switching to the tethered mode <NUM> and the standalone mode <NUM> without a subsequent additional capability negotiation.

The message of Table <NUM> may further include information indicating configuration IDs of modes in which simulcasting is performed during switching. When switching between modes associated with configuration IDs for simulcasting is performed, media data for both of a new mode and an existing mode may be simulcast during a period from when a connection according to the new mode is established to when a connection according to the existing mode is terminated. Accordingly, it is possible to provide a seamless service when switching between modes occurs during a call.

Table <NUM> is an example of a message configured for a capability negotiation.

Table <NUM> shows an illustrative message for a media attribute negotiation associated with a video media stream when a real-time transport protocol (RTP) is used as a transmission protocol. In the message of Table <NUM>, a configuration ID in the standalone mode is configured as <NUM>, and a configuration ID in the tethered mode is configured as <NUM>. Further, the illustrative message of Table <NUM> includes information indicating a maximum resolution for configuration ID <NUM> and information indicating a maximum resolution for configuration ID <NUM>. Additionally, the illustrative message of Table <NUM> includes information indicating that when switching between the standalone mode and the tethered mode is performed, media data according to the two modes need to be simulcast.

Table <NUM> is another example of a message configured for a capability negotiation.

Table <NUM> shows an illustrative message for a media attribute negotiation associated with a video media stream when the RTP is used as a transmission protocol. According to the message of Table <NUM>, different codecs are applied for configurations for the two modes. A stream of RTP payload type <NUM> based on an H. <NUM> codec is used in configuration <NUM> (rid <NUM>), and a stream of RTP payload type <NUM> based on an H. <NUM> codec is used in configuration <NUM> (rid <NUM>). "a=fallback_simlcast: send <NUM>,<NUM>" indicates that when switching between a mode associated with configuration <NUM> and a mode associated with configuration <NUM> is performed, media data of the two modes need to be simultaneously transmitted. Entries with "a = imageattr:. " indicate that different resolutions are applicable in configuration <NUM> and configuration <NUM>. For example, the example of Table <NUM> indicates that the message transmitted in the capability negotiation process includes information indicating a codec and at least one resolution available in each mode.

According to some embodiments of the disclosure, the message for capability negotiation may be transmitted again by the terminal <NUM> to the call server <NUM> for additional capability negotiation or a change of capability negotiation details after the initial capability negotiation is performed.

According to some embodiments of the disclosure, when the terminal <NUM> determines whether to switch, the terminal <NUM> may change a media attribute of media data transmitted in simulcasting. For example, when switching is performed from the standalone mode <NUM> having a maximum resolution of <NUM> * <NUM> to the tethered mode <NUM> having a maximum resolution of <NUM> * <NUM>, the terminal <NUM> may change the resolution of media data for the standalone mode <NUM>, which is transmitted to the auxiliary terminal <NUM> in simulcasting, to <NUM> * <NUM>.

When the call server <NUM> determines whether to switch, a media attribute changed according to mode switching may be determined by the call server <NUM> but is not limited thereto, and the terminal <NUM> may automatically determine whether to switch according to a predefined method.

To perform switching between modes, a procedure of performing negotiations for the modes in advance, determining a mode change during a call, establishing a new connection according to a new mode with an existing connection maintained, performing simulcasting for both the new connection and existing connection, and terminating the existing connection is needed.

The procedure for the mode change may be performed using various transmission periods and protocols. For example, a mode may be changed by temporarily performing point-to-multipoint (PtM) transmission before/after the mode change through point-to-point (PtP)/PtM switching. However, in this case, PtM radio resources need to be allocated only for the two modes, thus causing inefficiency in resources and not individually guaranteeing QoS in a PtM configuration period according to the modes.

The procedure for the mode change may be performed by configuring a connection path according to the new mode as a proxy so that media data needs to be transmitted necessarily through the connection path for the new mode, which will be described with reference to <FIG>.

<FIG> illustrates a mode switch method using a proxy according to an embodiment of the disclosure.

Referring to <FIG>, when switching to a new configuration mode <NUM> is determined while a call service according to an existing configuration mode <NUM> is in progress (<NUM>), a connection path according to the new configuration mode <NUM> is configured as a proxy for the existing configuration mode <NUM> (<NUM>). Accordingly, media data to a counterpart terminal (or call server) <NUM> or from the counterpart terminal (or call server) <NUM> according to the existing configuration mode <NUM> passes through the connection path of the new configuration mode <NUM> configured as the proxy (<NUM>). Subsequently, transmission of the media data according to the existing configuration mode <NUM> using the connection path of the new configuration mode <NUM> as the proxy is suspended (<NUM>), an optimal media attribute for the new configuration mode <NUM> is re-determined (<NUM>), and the media data is transmitted in the new configuration mode according to the determined optimal media attribute (<NUM>).

According to embodiments of the disclosure, to implement a procedure for changing modes, an existing connection between two points (or between a terminal and a call server) may be temporarily changed to a mode similar to that of a point-to-multipoint call, thereby adding a connection according to a new mode and subsequently releasing a connection according to an existing mode. According to this method, the connection according to the new mode may be added with the existing connection maintained, and the existing connection may be released when the new connection is completely added, thereby enabling efficient and seamless switching between the modes while continuously ensuring the QoS of each individual connection. A relevant embodiment will be described with reference to <FIG> and <FIG>.

<FIG> illustrates a flow of media data for a call service according to an embodiment of the disclosure.

Referring to <FIG>, it shows that media data is transmitted from a home UE <NUM> to a visitor UE <NUM> via a home IP multimedia system (IMS) <NUM>, a media resource function (MRF) <NUM>, and a visitor IMS <NUM>. On the contrary, media data may also be transmitted from the visitor UE <NUM> to the home UE <NUM> for a two-way call.

The home UE <NUM> refers to a UE (calling UE) making a call, and the visitor UE <NUM> refers to a UE (called UE) receiving the call. An IMS refers to a system to control IP multimedia flow in a communication operator network to which each terminal is connected. The IMS may be classified as a proxy-call session control function (P-CSCF), a serving-CSCF (S-CSCF), or an interrogation-CSCF (I-CSCF) according to functions. The home IMS <NUM> refers to an IMS of a communication operator to which the home UE <NUM> is connected, and the visitor IMS <NUM> is an IMS of a communication operator to which the visitor UE <NUM> is connected.

The MRF <NUM> may correspond to the call server <NUM> of <FIG>. The MRF <NUM> may provide various multimedia processing functions, such as mixing of a sound or an image related to the call and screen splitting. The MRF <NUM> may be divided into an MRF processor (MRFP) responsible for substantial multimedia processing and an MRF controller (MRFC) to control the MFRP.

<FIG> illustrates a mode switch procedure according to an embodiment of the disclosure.

Referring to <FIG>, although a home UE in an existing configuration mode (hereinafter, referred to as an existing home UE) <NUM> may correspond to the terminal <NUM> of <FIG> and a home UE in a new configuration mode (hereinafter, referred to as a new home UE) <NUM> may correspond to the auxiliary terminal <NUM> of <FIG>, the embodiment is not necessarily limited thereto. For example, when the existing mode is the standalone mode <NUM> and the new mode that is switched is the phone mode <NUM>, the existing home UE <NUM> may correspond to the auxiliary terminal <NUM>, and the new home UE <NUM> may correspond to the terminal <NUM>. In some embodiments of the disclosure, when the existing mode is the tethered mode <NUM>, the existing home UE <NUM> may correspond to the terminal <NUM>.

First, to perform a call, operation <NUM> of negotiating a terminal capability in advance between the existing home UE <NUM> and the visitor UE <NUM> may be performed. A capability negotiation may be performed according to a session initiation protocol (SIP)/SDP but is not limited thereto. Negotiating the terminal capability may include the existing home UE <NUM> transmitting a capability negotiation message mentioned in Table <NUM> to Table <NUM> to the MRF <NUM>. As described above, since the capability negotiation message includes pieces of information indicating media attributes for two or more modes, negotiations for not only the existing mode initially used for the call but also the new mode that is switched may be performed at once. In some embodiments of the disclosure, the capability negotiation message may be transmitted to not only the MRF <NUM> but also the visitor UE <NUM>.

When the capability negotiation is completed, an AR call may be established between the existing home UE <NUM> and the visitor UE <NUM> according to the initial call mode (i.e., the existing mode) in operation <NUM>. Although <FIG> illustrates the AR call, the disclosure may be applied to not only the AR call but also general video and voice calls. The call may be established based on the capability negotiation for the existing mode. For example, the call may be established based on information indicating a media attribute for the existing mode included in the capability negotiation message.

After the call is established between the existing home UE <NUM> and the visitor UE <NUM>, a media stream (i.e., media data) may be exchanged between the existing home UE <NUM> and the visitor UE <NUM> via the MRF <NUM> according to the existing mode.

When a mode switch is determined, a switch preparation operation <NUM> may be performed. The mode switch may be determined by the existing home UE <NUM> in view of the load of a processor associated with the existing home UE <NUM> or the new home UE <NUM>, a battery state, a network state, or the like, may be determined by the MRF <NUM> in view of whether MEC can be supported, a delay on a network, or a 3D processing resource of the MRF <NUM>, or may be determined based on a user input or command.

The switch preparation operation <NUM> includes an operation in which the existing home UE <NUM> notifies the new home UE <NUM> of an address (e.g., a uniform resource indicator (URI) or a uniform resource locator (URL)) of the MRF <NUM> in operation <NUM>. The existing home UE <NUM> may transmit a message including information indicating the address of the MRF <NUM> to the new home UE <NUM>, and in some embodiments of the disclosure, the message may be transmitted through an REFER method of the SIP. The message may be transmitted from the existing home UE <NUM> to the new home UE <NUM> through a home IMS <NUM> without passing through the MRF <NUM>. Table <NUM> shows an illustrative SIP request message or SIP response message according to the REFER method as an illustrative message for the existing home UE <NUM> to notify the new home UE <NUM> of the address of the MRF <NUM>.

The switch preparation operation <NUM> may further include an operation <NUM> in which the new home UE <NUM> transmits an acknowledgment of the message including the address of the MRF <NUM> to the existing home UE <NUM>. A message including the acknowledgment may be transmitted from the new home UE <NUM> to the existing home UE <NUM> through the home IMS <NUM> without passing through the MRF <NUM>.

The switch preparation operation <NUM> may further include an operation <NUM> in which the new home UE <NUM> transmits a message for reporting that it is ready to establish a new connection with the MRF <NUM> to the existing home UE <NUM> after the operation <NUM> of transmitting the acknowledgement. The message for reporting that it is ready to establish the new connection with the MRF <NUM> may be may be transmitted from the new home UE <NUM> to the existing home UE <NUM> through the home IMS <NUM> without passing through the MRF <NUM>.

After the switch preparation operation <NUM>, a new connection configuration and simulcasting operation <NUM> may be performed. In the new connection configuration and simulcasting operation <NUM>, the new connection is configured according to the switched new mode, and media data is simulcast until the existing connection is terminated.

The new connection configuration and simulcasting operation <NUM> may include an operation <NUM> in which the new home UE <NUM> transmits a message for connection to the MRF <NUM>. The new home UE <NUM> may transmit an INVITE message to the MRF <NUM> in order to connect to the MRF <NUM>. Connection of the new home UE <NUM> to the MRF <NUM> may be based on the address of the MRF <NUM> received from the existing home UE <NUM>.

In response to receiving the message for the connection from the new home UE <NUM>, the MRF <NUM> may allocate a resource for the connection according to the new mode to the new home UE <NUM> in operation <NUM>.

The MRF <NUM> may transmit a message for reporting the allocated resource to the new home UE <NUM> in operation <NUM>.

In response to receiving the message for reporting the allocated resource from the MRF <NUM>, the new home UE <NUM> may allocate the resource for the new connection according to the new mode in operation <NUM>.

After transmitting the message for reporting the allocated resource to the new home UE <NUM> in operation <NUM>, the MRF <NUM> may transmit a message for reporting to the new home UE <NUM> that the new connection according to the new mode has been established in operation <NUM>.

Subsequently, a media stream for the new mode may be transferred between the new home UE <NUM> and the MRF <NUM> in operation <NUM> through the new connection. Here, since the media stream for the existing mode is transmitted through the existing connection, simulcasting through both the new connection and the existing connection may be performed.

Next, the new home UE <NUM> may transmit a message for reporting to the existing home UE <NUM> that the new connection according to the new mode has been established in operation <NUM>. The message for reporting that the new connection has been established may be transmitted from the new home UE <NUM> to the existing home UE <NUM> through the home IMS <NUM> without passing through the MRF <NUM>.

After the new connection configuration and simulcasting operation <NUM>, an existing connection termination and switch completion operation <NUM> may be performed.

In the switch completion operation <NUM>, the existing home UE <NUM> may transmit a message for releasing the existing connection to the MRF 530in operation <NUM>. The message for releasing the connection may further include information for reporting that the new connection has been completely established. For example, the message for releasing the existing connection may be a BYE message according to a BYE method of the SIP but is not necessarily limited thereto. Table <NUM> is an illustrative BYE message including a request to terminate the connection according to the existing mode and to change to the connection according to the new mode.

In response to receiving the message for releasing the existing connection from the existing home UE <NUM>, the MRF <NUM> may release resource allocation for the existing connection in operation <NUM>.

After releasing the resource allocation for the existing connection in operation <NUM>, the MRF <NUM> may report to the existing home UE <NUM> that the existing connection has been released in operation <NUM>.

After releasing the resource allocation for the existing connection in operation <NUM>, the MRF <NUM> may transmit a message for reporting to the visitor UE <NUM> that a home UE has been changed from the existing home UE <NUM> to the new home UE <NUM> in operation <NUM>. Table <NUM> shows an illustrative NOTIFY message according to the SIP for reporting a change of a home UE.

When a multilateral call is in progress, the message for reporting that the home UE has been changed from the existing home UE <NUM> to the new home UE <NUM> may be transmitted to all visitor UEs.

<FIG> is a flowchart illustrating an operation of a terminal according to an embodiment of the disclosure.

Referring to <FIG>, a method for supporting, by a first terminal, switching between a plurality of modes for a call may include an operation <NUM> of performing a capability negotiation for a call with a second terminal and an operation <NUM> of establishing a first connection between the first terminal and a call server according to a first mode among the plurality of modes for the call with the second terminal after performing the capability negotiation. The operation of performing the capability negotiation may include an operation of transmitting a first message including information indicating a media attribute for each of two or more modes among the plurality of modes to a communication server.

The first terminal may correspond to the terminal <NUM> of <FIG> or the existing home UE <NUM> of <FIG>. The second terminal may correspond to the counterpart terminal <NUM> of <FIG> or the visitor UE <NUM> of <FIG>.

The media attribute may include at least one of a resolution and a codec supported in each of the modes.

The plurality of modes may include a phone mode in which a user performs the call using the first terminal, a tethered mode in which the first terminal transmits data associated with the call to a third terminal by tethering and the user performs the call using the third terminal, and a standalone mode in which the third terminal directly receives the data associated with the call. Here, the third terminal may correspond to the auxiliary terminal <NUM> of <FIG> or the new home UE <NUM> of <FIG>.

The first message may further include information indicating modes in which simulcasting is performed when switching between the modes among the two or more modes.

<FIG> is a flowchart illustrating an operation of a call server according to an embodiment of the disclosure.

Referring to <FIG>, a method for supporting, by a call server, switching between a plurality of modes for a call according to an embodiment includes an operation <NUM> of performing a capability negotiation for a call between a first terminal and a second terminal and an operation <NUM> of establishing a first connection between the first terminal and the call server according to a first mode among the plurality of modes for the call between the first terminal and the second terminal after performing the capability negotiation. The operation of performing the capability negotiation may include an operation of receiving a first message including information indicating a media attribute for each of two or more modes among the plurality of modes from the first terminal.

The plurality of modes may include a phone mode in which a user performs a call using the first terminal, a tethered mode in which the first terminal transmits data associated with the call to a third terminal by tethering and the user performs the call using the third terminal, and a standalone mode in which the third terminal directly receives data associated with the call. Here, the third terminal may correspond to the auxiliary terminal <NUM> of <FIG> or the new home UE <NUM> of <FIG>.

The first message may further include information indicating modes in which simulcasting is performed when switching between modes among the two or more modes.

<FIG> is a block diagram illustrating an electronic device according to an embodiment of the disclosure.

Referring to <FIG>, the electronic device <NUM> may correspond to one of the electronic devices mentioned herein. For example, the electronic device <NUM> may correspond to any one of the terminal <NUM>, the auxiliary terminal <NUM>, the call server <NUM>, the counterpart terminal <NUM>, which are illustrated in <FIG>, the existing home UE <NUM>, the new home UE <NUM>, the home IMS <NUM>, the MRF <NUM>, the visitor IMS <NUM>, and the visitor UE <NUM>, which are illustrated in <FIG>.

The electronic device <NUM> may include a transceiver <NUM> and a controller <NUM>. The transceiver <NUM> may be configured to transmit or receive a signal or data to or from a different device via a cable or wirelessly. The transceiver <NUM> may perform communication using various communication methods, such as known Wi-Fi, LTE, LTE-A, CDMA, orthogonal frequency division multiplexing (OFDM), and coded OFDM (COFDM), but communication methods available for the transceiver <NUM> are not necessarily limited thereto.

The controller <NUM> may be connected to the transceiver <NUM>. The controller <NUM> may control overall operations of the electronic device <NUM>, and thus an operation of the electronic device <NUM> may be construed as an operation of the controller <NUM>.

Claim 1:
A method for supporting, by a first terminal (<NUM>), switching between a plurality of modes for a call, the method comprising:
performing (<NUM>) a capability negotiation for a call with a second terminal (<NUM>); and
establishing (<NUM>) a first connection between the first terminal (<NUM>) and a call server (<NUM>) according to a first mode among the plurality of modes for the call with the second terminal (<NUM>) after performing the capability negotiation,
wherein the performing of the capability negotiation comprises transmitting a first message comprising information indicating a media attribute of each of two or more modes of the plurality of modes to the call server (<NUM>), and information indicating modes in which simulcasting is performed when switching between the modes of the two or more modes,
wherein the plurality of modes comprises a phone mode in which the call is performed using the first terminal (<NUM>), a tethered mode in which the first terminal (<NUM>) transmits data related to the call to a third terminal (<NUM>) associated with the first terminal (<NUM>) by tethering and the call is performed using the third terminal (<NUM>), and a standalone mode in which the third terminal (<NUM>) directly receives the data related to the call.