KR20070104829A - Method for exchanging information required for csi service - Google Patents

Abstract

A method for exchanging necessary information for a CSI(Combination of CS(Circuit Switched) and IMS(IP Multimedia Subsystems)) service is provided to prevent a waste of radio resources by exchanging radio environment information and IMS status information in setting up a CS bearer in order to prevent IMS bearer setup procedures from being unnecessarily executed. A UE comprises a communication module(101), a storage unit(102), and a controller(103). The communication module(101) transmits and receives radio environment information and IMS status information in setting up a CS bearer. In case IMS status is changed after CS bearer setup or the UE(100) moves to a dead-service area for an IMS service, the communication module(101) transmits changed IMS status and radio environment information through UUS-3 protocol. The storage unit(102) stores the other party's radio environment information and IMS status information. The controller(103) controls the communication module(101) and the storage unit(102).

Description

Method of exchanging information required for CSI service {METHOD FOR EXCHANGING INFORMATION REQUIRED FOR CSI SERVICE}

1 is an exemplary diagram illustrating the concept of a CSI service.

2 is an exemplary diagram illustrating a configuration of a network for providing a CSI service.

3 is a flowchart illustrating a process of performing a CSI service.

4 is a flowchart illustrating a process according to a first embodiment of the present invention.

5 is a flowchart illustrating a process according to a second embodiment of the present invention.

6 is a diagram illustrating an entity in a UE and a CS or IMS network according to the present invention.

** Description of the major signs in the drawings **

110: first UE 120: second UE

210: first CS core network 220: second CS core network

310: first PS core network 320: second PS core network

410: First IMS Core Network 420: Second IMS Core Network

The present invention relates to a combination service, and more particularly, to a combination of CS and IMS (CSI) service.

Combination services are those that provide services over at least two networks. That is, the combination service simultaneously provides at least two or more services to the user in a first service based on a first network, a second service based on a second network, a third service based on a third network, and the like. Such a combination service not only provides services from two or more service providers to a single user, but also enables the use of at least two or more services simultaneously between two or more users.

An example of such a combination service will be described with a combination of CS and IMS services.

The CSI service is a service capable of simultaneously performing (combining) a service based on circuit switching (CS) between a first terminal and a second terminal and a service based on IP multimedia subsystems (IMS). Here, the IMS (IP multimedia subsystems) is a network technology that enables packet switching (PS) based on IP (Internet Protocol) not only to a terminal but also to a wireless terminal. It was proposed to connect everything via IP (All-IP). Accordingly, the CSI service simultaneously provides a CS-based voice call service and an IMS-based instant messaging (IM), video sharing, data delivery, and the like between wireless terminals. In order to use such a CSI service, the UE needs to support the CSI service. Such a UE is called a CSI UE (or CSI UE).

1 is an exemplary diagram illustrating the concept of a CSI service.

Referring to FIG. 1, an originating terminal such as a first UE 11 and a destination terminal such as a second UE 12 combine a CSI service, that is, a CS-based voice call service, and an IMS-based service. In order to simultaneously perform the service, the first and second UEs 11 and 12 set up a CS bearer for a voice call service, and set up an IMS bearer for the IMS service.

In this case, the first UE 11 may further configure an IMS bearer (or session) for an IMS service after establishing a CS bearer with the second UE 12, and the reverse thereof. In this case, the first UE 11 may further configure a CS bearer after configuring an IMS bearer.

The voice call service is performed through a bearer (indicated by a solid line) set via the first and second CS domains 21 and 22, and the first PS domain 31 and the first in the case of an IMS-based service. It is performed via an IMS bearer (indicated by the dashed line) set via the IMS domain 41, the second IMS domain 42, and the second PS domain 32.

2 is an exemplary diagram illustrating a configuration of a network for providing a CSI service.

As shown in FIG. 2, a network for providing a combination service, for example, a CSI service, to the first and second UEs 11 and 12 may include a first and second CS core network 21 for providing a CS service. 22, first and second IMS core networks 41 and 42 for providing IMS services, and a first PS (packet switching) packet network connected to the first IMS core network 41; 31 and a second PS core network 42 connected with the second IMS core network 42.

The UEs 11 and 12 are generally UEs capable of communicating by simultaneously opening a CS bearer and a PS bearer, and are also called CSI UEs. That is, the UEs 11 and 12 may communicate through a CS bearer through a CS domain for voice media and an IMS bearer through an IMS domain for an IMS service (eg, messaging, white board, etc.). Means the terminal. The UEs 11 and 12 are connected to the first and second CS core networks 21 and 22 and the first and second PS core networks 31 and 32 through a radio access network (RAN). Connected.

The first and second CS core networks 21 and 22 are located in the CS domain and include at least a mobile switching center (MSC), a visiting location register (VLR) and a home location register. Each HLR).

The first and second IMS core networks 41 and 42 are located in the IMS domain and include a home subscriber server (HSS), a call session control function (CSCF), And an application server (AS).

3 is a flowchart illustrating a process of performing a CSI service between a first UE and a second UE.

Referring to FIG. 3, a CS bearer is first established between a first UE 11 and a second UE 12, and then a process of configuring an IMS bearer is shown.

1-2) First, it is assumed that the first UE 11 is registered in the first IMS core network 41, and the second UE 12 is not registered in the second IMS core network 42. Assume a regulation. In this case, the term registration may mean logging in or accessing the IMS core network.

3) Then, the first UE 11 transmits a call origination message to the first CS core network 21 to perform a voice call service with the second UE 12. At this time, the current radio environment information for the first UE 11 is transmitted along with the call origination message. Here, the radio environment information is information on whether the second UE 11 supports the CSI service, and whether the first UE 11 is in an area where both the CSI service, that is, the CS service and the IMS service are available. Contains information about

4) Then, the first CS core network 21 sends a call origination message to the second CS core network 22. At this time, the radio environment information for the first UE 11 is transmitted with the call origination message.

5) Then, the second CS core network 22 sends a call origination message to the second UE 12. At this time, the radio environment information is transmitted together with the call origination message.

6) The second UE 12 receives the call origination message and stores the radio environment information. The second UE 12 determines whether to perform the requested voice call service, and if so, transmits an acceptance response message to the second CS core network 22. At this time, the radio environment information for the second UE 12 is transmitted together with the acceptance response message.

7) Then, the second CS core network 22 sends an accept response message to the first CS core network 21. At this time, the acceptance response message and the radio environment information are transmitted together.

8) The first CS core network 21 sends an accept response message to the first UE 11. At this time, the radio environment information is transmitted together with the acceptance response message. After performing this process, the first UE 11 performs a voice call service with the second UE 12.

9) Thereafter, the first UE 11 transmits a session invitation message to the first IMS core network 41 to perform an IMS service with the second UE 12 according to a user's request.

10) The first IMS core network 41 forwards the session invitation message to the second IMS core network 42.

11-12) However, since the second IMS core network 42 does not indicate that the IMS service cannot be performed because the second UE 12 is not currently registered, the first IMS core network 42 may fail. Transfer to 41. Then, the first IMS core network 41 forwards the failure message to the first UE 11.

As described above, since the calling terminal, that is, the first UE 11, does not know that the receiving terminal, that is, the second UE 12, is not registered in the IMS service, the procedure for performing the IMS service is unnecessary. The problem arises. In addition, by performing such an unnecessary procedure, there is a problem in that network resources are wasted.

That is, as described above, in the prior art, the radio environment information is exchanged between the UEs when establishing the CS bearer, but this does not guarantee the successful establishment of the IMS bearer. Specifically, whether the counterpart terminal supports the CSI service, that is, supports both the CS-based service and the IMS-based service by exchanging radio environment information when setting up the CS bearer (MultiRAB / DTM (Multi radio access bearer / Does not support the IMS service registration process even if it knows whether it supports Dual Transfer Mode) and is located in an area where CSI services are available (i.e., where it is available for MultiRAB / DTM). If not, IMS service is not available. On the other hand, in order to overcome the above-mentioned problem, when setting the CS bearer, only when the originating terminal is registered in the IMS service and the receiving terminal is not registered in the IMS service, A technique for triggering the receiving terminal to register with the IMS service has been proposed. However, even with this, there are the following problems.

① Even if the receiving terminal is triggered to register with the IMS service, since the user of the receiving terminal does not want to perform the IMS registration procedure, the success of the subsequent IMS bearer setup procedure cannot be guaranteed.

② Also, even if the receiving terminal is triggered to register with the IMS service, since the radio environment information may not be exchanged when the CS bearer is set up, it is not known whether the other terminal supports the CSI service and thus triggering IMS registration. It may be unnecessary and may also lead to waste of unnecessary radio resources.

③ If the originating terminal or the receiving terminal is subscribed to a presence service, such as a messaging service, if it is triggered to register with the IMS service, the messaging service signals all other terminals connected to the originating terminal or the receiving terminal. Should be sent. However, if the CSI service fails, this causes a huge waste of radio resources.

On the other hand, when the second UE 12 was registered in the IMS service at the time of CS bearer setup, but later deregistration in the IMS service, or moved to an area where the CSI service is not possible (that is, When moving to an area where MultiRAB / DTM is not available (ie, when radio environment information is changed), since the first UE 11 does not know this, a procedure for performing an IMS service is unnecessary. There is a possibility. In addition, by performing such an unnecessary procedure, there is a problem in that network resources are wasted.

Accordingly, an object of the present invention is to exchange not only radio environment information but also information on whether to register IMS when setting up a CS bearer.

Another object of the present invention is to exchange information when IMS registration is changed in consideration of whether IMS registration can be changed later even if IMS registration is exchanged when setting up a CS bearer. Alternatively, another object of the present invention is to exchange information when radio environment information is changed in consideration of the fact that it may be changed later even if the radio environment information is exchanged during CS bearer setup. That is, even though both the first and second UEs 11 and 12 are in the IMS registration state at the time of the CS bearer setup, the second UE 12 deregisters the IMS service before the IMS bearer setup later. Or if the location is moved to an area where the IMS service is not available (ie, if the location is not supported by MultiRAB / DTM) (that is, if the radio environment information changes), the IMS bearer setup may fail. . Therefore, when the IMS registration status is changed, or when the radio environment information is changed, the information is to be exchanged.

In order to achieve the above object, the present invention provides a method for exchanging information in a terminal that can simultaneously use a CS (Circuit Switching) based service and an IMS (IP Multimedia Sub-system) based service, the target terminal and the CS call ( Circuit switched call); And transmitting information about the factor to the target terminal through the CS service when at least one factor necessary for performing the IMS service is changed during the CS call. Provide a method for exchanging information.

In addition, in order to achieve the above object, the present invention is a method of exchanging information in a server in the CS network, the CS call between the first terminal and the second terminal, the IMS service between the first terminal and the second terminal If the at least one factor necessary for additionally performing is changed by at least one terminal, the server recognizing it; The server provides the information exchange method comprising the step of transmitting information on the factor to at least one counterpart terminal.

Example

In the accompanying drawings, although a user equipment (UE) is illustrated as an example, the illustrated UE may be referred to in terms of terminal, mobile equipment (ME), and the like. In addition, the UE may be a portable device such as a laptop, a mobile phone, a PDA, a smart phone, a multimedia device, or a non-portable device such as a PC or a vehicle-mounted device.

Before describing with reference to the drawings, it will be described for the technical matters to help the technical understanding of the present invention.

(1) Radio environment information: Also called Radio Environment Information, information about whether the UE supports CSI service, that is, whether it supports both CS based service and IMS based service (ie, MultiRAB / Information on whether DTM is supported (ie, CSI Capabilities), and information indicating whether or not the CSI service is located in an area (ie, whether MultiRAB / DTM is located in an area).

(2) IMS registration status: Also referred to as IMS status, this information indicates the presence or absence of registration for IMS.

(3) User to User Signaling (UUS): A protocol defining signaling required when exchanging information (or IMS status) on whether the IMS is registered through CS (Circuit Switch). UUS-1 is a protocol used when the calling terminal transmits a call origination message (SETUP message) and exchanges information on whether IMS is registered with UUS-1. More specifically, this is a protocol used when a receiving terminal transmits an acknowledgment message (CONNECT message) and wants to exchange information on whether or not IMS is registered. UUS-3 is a protocol used to register IMS after a CS bearer is already set up. This protocol is used to exchange information.

(4) User-to-User Information (UUI): Information transmitted through UUS.

Hereinafter, with reference to the accompanying drawings an embodiment according to the present invention will be described in detail.

4 is a flowchart illustrating a process according to a first embodiment of the present invention.

As can be seen with reference to Figure 4, the first embodiment of the present invention, in order to solve the above-mentioned problems of the prior art, the information on the IMS registration as well as the radio environment information when setting up the CS bearer (IMS Status ) Is exchanged. In addition, in the first embodiment of the present invention, after the CS bearer is set up, when the IMS registration state of either the receiving terminal or the originating terminal is changed, or when the CSI service is moved to an area where the CSI service is not possible (that is, MultiRAB) When moving to an area where / DTM is not possible (ie, when the radio environment information is changed), the changed state is notified to the counterpart terminal. Specifically, it is as follows.

1-2) First, the first UE 110 registers with the first IMS core network 410. Specifically, the first UE 110 transmits a registration message, eg, a SIP-based REGISTER message, to the first IMS core network 410. Then, after confirming whether the first IMS core network 410 is a legitimate user, the first IMS core network 410 transmits a positive response message, for example, a SIP-based 200 OK message, to the first UE 110.

3-4) The second UE 120 registers with the second IMS core network 420. Specifically, the process is the same as 1) to 2).

5) Then, in order for the first UE 110 to perform a voice call service with the second UE 120, a call origination message (or a service request message) to the first CS core network 210 is shown, for example, shown. Send the SETUP message. At this time, information on the current radio environment (radio environment information) for the first UE (110) and information on whether or not IMS registration (or IMS Status) is delivered together. Here, the radio environment information may include information on whether the second UE 110 supports the CSI service, and information on whether the first UE 110 is located in an area where both the CS service and the IMS service are available. Include. The IMS registration information is transmitted through the UUS-1 protocol described above.

6) Then, the first CS core network 210 sends a call origination message, such as the illustrated IAM message, to the second CS core network 220. At this time, the radio environment information about the current radio environment for the first UE 110 and the IMS registration information are transmitted together with the IAM message.

7) Then, the second CS core network 220 sends a call origination message, eg, the illustrated SETUP message, to the second UE 120. At this time, the wireless environment information and information on whether or not IMS registration is delivered together.

8) The second UE 120 receives the call origination message and stores the radio environment information and the IMS registration information transmitted together. In addition, the second UE 120 determines whether to perform the requested voice call service, and if so, transmits an acceptance response message, for example, a CONNECT message, to the second CS core network 220. At this time, the information on the radio environment of the second UE 120 and the information on whether to register the IMS are transmitted together with the acceptance response message. In addition, the second UE 120 uses the radio environment information and the IMS registration information of the first UE 110 to determine whether IMS service is available, and the capability with the first UE 110. Determine whether to exchange information.

9) Then, the second CS core network 220 sends an acknowledgment message, eg, the CON / ANM message shown, to the first CS core network 210. At this time, the radio environment information and the IMS registration information are transmitted together with the acceptance response message.

10) Then, the first CS core network 210 transmits an acknowledgment message, for example, the CONNECT message shown to the first UE (110). At this time, the radio environment information and the IMS registration information are transmitted together with the acceptance response message. After performing such a process, the first UE 110 performs a voice call service with the second UE 120.

11 to 12) the second UE 120 deregistration from the IMS service. Specifically, the second UE 120 transmits a deregistration message to the second IMS core network 420. Alternatively, the second UE 120 includes an expiry indicator, such as expire = 0, in a registration message, eg, a SIP-based REGISTER message, and transmits it to the second IMS core network 420. Then, after canceling registration, the second IMS core network 420 transmits an acknowledgment message, such as a 200 OK message based on SIP, to the second UE 210.

Meanwhile, although the second UE 120 has not canceled IMS registration, the second UE 120 may move to an area where IMS service is not available, and thus connection may be lost. As such, the first UE 11 does not know about the fact that the second UE 120 cancels registration from the IMS service or is moved to an area where the IMS service is unavailable.

13) Then, the second UE 120 transmits information (IMS Status) on whether the changed IMS is registered to the second CS core network 220. Alternatively, the second UE 120 transmits changed radio environment information, that is, not located in an area where an IMS service is available. At this time, the information on whether the IMS registration and the radio environment information may be transmitted in a USER INFORMATION message shown through the UUS-3 protocol.

14) The second CS core network 220 transmits information on whether IMS is registered and radio environment information to the first CS core network 210.

15) The first CS core network 210 transmits information on whether IMS is registered and radio environment information to the first UE 110.

16) Then, the first UE 110 can know that the second UE 120 is deregistered IMS or that the IMS service is not available. Thus, the second UE 110 may not unnecessarily send a session invitation message, thereby preventing waste of network resources.

Meanwhile, according to the first embodiment of the present invention described above, even when the second UE 120 is not registered in the IMS service at the time of establishing the CS bearer, the first UE 110 may be registered in the subsequent IMS service. This may be immediately known, and may send a session invitation message (or service request message) such as a SIP-based INVITE message to perform the IMS service if necessary. In addition, after receiving an acknowledgment message such as a 200 OK or a negative response message such as a SIP-based 4xx Error message from the second UE 120, an IMS service may be performed.

5 is a flowchart illustrating a process according to a second embodiment of the present invention.

As can be seen with reference to FIG. 5, in the second embodiment of the present invention, when the IMS registration status changes or moves to an area where CSI service is unavailable, the CS core network notifies the counterpart terminal of the changed status. It is characterized by.

1) to 10) process is the same as in FIG.

11) The second UE 120 deregistration from the IMS service. Specifically, the second UE 120 transmits a deregistration message to the second IMS core network 420. Alternatively, the second UE 120 includes an expiry indicator, such as expire = 0, in a registration message, eg, a SIP-based REGISTER message, and transmits it to the second IMS core network 420. Then, after canceling registration, the second IMS core network 420 transmits an acknowledgment message, such as a 200 OK message based on SIP, to the second UE 210.

Meanwhile, although the second UE 120 has not canceled IMS registration, the second UE 120 may move to an area where IMS service is not available, and thus connection may be lost. As such, the first UE 11 does not know about the fact that the second UE 120 cancels registration from the IMS service or is moved to an area where the IMS service is unavailable.

12) When the second UE 120 deregistration from the IMS service, an entity of the second IMS core network 420 notifies the second CS core network 220.

13) Then, the IMS status of whether the specific entity of the second CS core network 220 has changed is transmitted to the first CS core network 210.

Alternatively, when the second UE 120 is moved to an area where IMS service is not available, even if there is no notification from the second IMS core network 420, a specific entity of the second CS core network 220 may be used. Transmits the changed wireless environment information, that is, the location where the second UE 120 is not available to the IMS service.

At this time, the information on whether the IMS registration and the radio environment information may be transmitted in a USER INFORMATION message shown through the UUS-3 protocol.

14) The second CS core network 220 transmits information on whether IMS is registered and radio environment information to the first CS core network 210.

15) Then, the first CS core network 210 transmits the information on whether the IMS registration and the radio environment information to the first UE (110). Then, the first UE 110 may know that the second UE 120 is deregistered IMS or IMS service is unavailable.

The method according to the invention described thus far can be implemented in software, hardware, or a combination thereof. For example, the method according to the present invention may be stored in a storage medium (eg, mobile terminal internal memory, flash memory, hard disk, etc.) and may be stored in a processor (eg, mobile terminal internal microprocessor). It may be implemented as codes or instructions in a software program that can be executed by.

6 is a block diagram illustrating a UE and a network entity according to the present invention.

The UE 100 according to the present invention shown in FIG. 6 shows the configuration of the first UE 110 and the second UE 120 shown in FIGS. 4 to 5.

The UE 100 may simultaneously use the CSI service, that is, the CS service and the IMS service, and store the basic hardware, that is, the communication module 101 required for exchanging radio environment information and IMS registration information (or IMS status). Means 102 and a controller 103.

The communication module 101 may transmit and receive radio environment information and IMS status information (IMS status) when the CS bearer is set up. In addition, the communication module 101 is characterized in that the IMS registration status is changed after the CS bearer is set up, or the IMS registration information (IMS Status) and the wireless environment information changed through the UUS-3 protocol when the IMS service is moved to an area where it is not available. Can be transmitted. In addition, the communication module 101 may receive IMS status information and wireless environment information from the counterpart terminal.

 The storage unit 102 may store the radio environment information and the IMS registration information (IMS Status) of the counterpart terminal.

The controller 103 controls the communication module 101 and the storage means 102. In particular, the controller 103 may transmit radio environment information and IMS status information (IMS status) through the communication module 101 when establishing a CS bearer. In addition, when the controller 103 characteristically deregisters from the IMS service or moves to a region where the IMS service is impossible, the communication module 101 registers the changed IMS through the UUS-3 protocol. Whether to send information (IMS Status) or wireless environment information. In addition, when receiving the IMS status information (IMS Status) and radio environment information from the counterpart terminal, the controller 103 determines whether to perform an IMS service with the counterpart terminal based on the information.

Other matters about the communication module 101, the storage means 102, and the controller 103 can be easily implemented by those skilled in the art with reference to the present specification. This will not be described in more detail.

Meanwhile, the illustrated entity 200 or 400 may exist in the first or second CS core network 210, 220 or in the first or second IMS core network 410, 420.

The entity 200 or 400 includes a basic configuration necessary for exchanging radio environment information and IMS registration information (or IMS status), that is, a communication module 201, a storage unit 202, and a controller 203. .

The communication module 201 is characterized in that, after the CS bearer is established between the first UE 110 and the second UE 120, whether or not IMS registration for one UE is changed or moves to an area where IMS service is unavailable. In this case, the changed IMS status information (IMS Status) and radio environment information can be transmitted to the counterpart UE through the UUS-3 protocol.

 The storage unit 202 may store radio environment information and IMS status information (IMS Status) for the first UE 110 and the second UE 120.

The controller 203 controls the communication module 201 and the storage means 202. In particular, when at least one of the first UE 110 and the second UE 120 cancels registration from the IMS service, or when the controller 203 is moved to an area where the IMS service is impossible, In addition, the communication module 201 transmits the changed IMS status information (IMS Status) or radio environment information to another UE through the UUS-3 protocol.

Other matters of the communication module 201, the storage means 202, and the controller 203 can be easily implemented by those skilled in the art with reference to the present specification. It will not be described in detail.

The configuration and operation of the UE 100 and the network entity 200 or 400 including the technical features according to the present invention have been described above, but other necessary configurations are obvious to those skilled in the art. This is a matter of omission.

In the above description of the preferred embodiments of the present invention by way of example, the scope of the present invention is not limited only to these specific embodiments, the present invention is in various forms within the scope of the spirit and claims of the present invention Can be modified, changed, or improved.

According to the present invention, by exchanging not only radio environment information but also information on whether to register IMS when setting up a CS bearer, it is possible to prevent unnecessary IMS bearer setup procedure and to prevent waste of radio resources. have.

In addition, the present invention requires that the IMS bearer setup procedure is unnecessary by exchanging IMS registration information or wireless environment information when the IMS registration status is changed after the CS bearer setup or when the IMS service is moved to an unavailable area. There is an advantage that can be prevented from performing, thereby preventing the waste of radio resources.

Claims (20)

A method of exchanging information in a terminal that can simultaneously use a CS (Circuit Switching) based service and an IMS (IP Multimedia Sub-system) based service, Performing a CS call (circuit switched call) with the target terminal; And transmitting information about the factor to the target terminal through the CS service when at least one factor necessary for performing the IMS service is changed during the CS call. Information exchange method. The method of claim 1, wherein the CS call proceeding step And establishing a session for the CS call with the target terminal. The method of claim 2, wherein the session establishment step And exchanging information on at least one factor necessary to perform the IMS service with the target terminal. The method of claim 1, wherein changing the factor is The terminal registers or deregisters the IMS service, or An information exchange method, characterized in that occurs when the terminal moves to a location where the IMS service is impossible. The method of claim 1, wherein changing the factor is The at least one terminal registers or deregisters the IMS service, or And when the at least one terminal moves to a coverage or an impossible region in which MultiRAB / DTM (Multi radio access bearer / dual transfer mode) is possible. The method of claim 1, If the factor is changed by deregistration of the terminal to the IMS service, The transmitting step is: Sending a cancellation message to the IMS service; Receiving an acknowledgment message from the IMS service; And transmitting the status of whether the IMS is registered to the target terminal through the CS service. The method of claim 1, wherein the information is Radio environment information, and And at least one or more of an IMS registration status. The method of claim 7, wherein the wireless environment information Information on whether the target terminal supports the IMS service, and And at least one of information on whether the terminal is located in an area accessible to the IMS service. The method of claim 7, wherein the wireless environment information Information on whether the target terminal supports MultiRAB / DTM, and And at least one of information on whether the terminal is located in an area where the MultiRAB / DTM is possible. The method of claim 1, wherein the information is Information exchange method characterized in that the transmission via the UUS-3 protocol. The method of claim 1, wherein the information is Information exchange method characterized in that the transmitted in the USER INFORMATION message. A method of exchanging information at a server in a CS network, If at least one factor required for additionally performing an IMS service between the first terminal and the second terminal during the CS call between the first terminal and the second terminal is changed by at least one terminal, the server Recognizing this; And transmitting, by the server, information about the factor to at least one counterpart terminal through a CS network. The method of claim 12, wherein the recognition step Receiving a notification from the particular entity in the IMS network that the factor has changed. 13. The method of claim 12, wherein changing the factor is The at least one terminal registers or deregisters the IMS service, or And the at least one terminal moves to a location where the IMS service is impossible. 13. The method of claim 12, wherein changing the factor is The at least one terminal registers or deregisters the IMS service, or And when the at least one terminal moves to a coverage or an impossible region in which MultiRAB / DTM (Multi radio access bearer / dual transfer mode) is possible. The method of claim 12, wherein the information is Radio environment information, and And at least one or more of an IMS registration status. The method of claim 16, wherein the wireless environment information Information on whether the target terminal supports the IMS service, and And at least one of information on whether the terminal is located in an area accessible to the IMS service. The method of claim 16, wherein the wireless environment information Information on whether the target terminal supports MultiRAB / DTM, and And at least one of information on whether the terminal is located in an area where the MultiRAB / DTM is possible. The method of claim 12, wherein the information is Information exchange method characterized in that the transmission via the UUS-3 protocol. The method of claim 12, wherein the information is Information exchange method characterized in that the transmitted in the USER INFORMATION message.

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