KR20050005804A - Unconditional Call/Session Redirection Service using SIP - Google Patents

Abstract

The present invention provides a method for providing an unconditional call / session switching service in a network including a location server for storing registration and location information of a terminal, a session initiation protocol (SIP) server, and a SIP application server. A first step of confirming whether the subscriber subscribes to the call / session switching service unconditionally by referring to the profile information of the subscriber included in the first invitation message when receiving the invitation message; A second step of transmitting the first invitation message to the SIP application server if the subscriber unconditionally subscribes to the call / session switching service; The SIP application server analyzes the received first invitation message, checks the destination terminal information, extracts the call forwarding terminal information set by the subscriber corresponding to the called terminal information, and extracts the extracted call forwarding terminal information. Transmitting an included second invitation message to the SIP server; And after the SIP server checks the location information of the call forwarding terminal included in the second invitation message from the location server managing the location of the call forwarding terminal, the SIP server to which the call forwarding terminal belongs. The fourth step of transmitting to.

Description

Unconditional Call / Session Redirection Service using SIP}

The present invention relates to a method for providing an unconditional call / session switching service using a session initiation protocol and a recording medium recording the same. In particular, when a subscriber registers a service in a network based on a session initiation protocol (SIP), The present invention relates to a method of providing a call / session switching service for switching a call or a session to a terminal registered with the terminal and a recording medium recording the same.

In general, in a mobile communication network and a public switched telephone network (PSTN), a call forwarding service is provided for forwarding a call received from a user's terminal to a terminal having a predetermined specific number.

Incoming call forwarding service includes a call forwarding no reply service that transfers an incoming call when the subscriber station is not answering, and call forwarding during a call that transfers an incoming call when the subscriber station is busy. Busy) service, and Call Forwarding Unconditional service for switching the incoming call regardless of the state of the subscriber station.

Incoming call transfer service operation will be described using a mobile communication network as an example.

The incoming call transfer service is performed by the switching center 4, the visitor location register (VLR) 5, and the home location register (HLR) 6 shown in FIG. In more detail, when a subscriber applies for a service to receive an incoming call transfer service, it is registered in the HLR 6 that the subscriber has subscribed to the incoming call transfer service. At this time, the phone number of the terminal to be received is registered together, the terminal of the registered phone number may be a mobile station.

In the above state, when the first mobile station calls the destination mobile station, the call signal is transmitted to the switching station 4 through the base station 2 and the control station 3, and the switching station 4 receives the HLR 6 to which the subscriber belongs. The current location information of the subscriber. At this time, the exchange 4 checks the fact that the subscriber has registered the incoming call transfer service together with the location information of the subscriber. Accordingly, the switching center 4 determines the type of the call transfer service registered by the subscriber and the telephone number to be called. As a result of the determination, if it is determined that there is no incoming call forwarding service or that the call state of the subscriber is an incoming call event, the switching center transmits the incoming call through the call forwarding information of the mobile station 1 registered in the HLR 6 to which the mobile station 1 belongs. Deliver to the exchange. Accordingly, the originating mobile station makes a call with the mobile station designated by the subscriber.

In addition, the incoming call conversion to the PSTN can be known more easily than the mobile communication network because the location information of the destination can be known by the telephone number consisting of the area code, the station number and the individual number.

However, due to the development of the Internet and communication technology, various multimedia services such as teleconference, meeting, video call, and image data transmission are provided, and in the future, various multimedia communication services based on IP are provided through respective communication networks. Will be.

In accordance with the demands of the times, when various IP communication services are provided to each communication network, a new call forwarding service is required to allow service subscribers of each communication network to switch to a predetermined destination for a call that is directed to them. do.

Accordingly, the present invention provides a method for providing an unconditional call / session switching service for recording a service subscriber to a predetermined destination for an IP-based call or session received by the service subscriber when various multimedia communication services based on IP are provided. The purpose is to provide a medium.

In order to achieve the above object, the present invention provides a method for providing an unconditional call / session switching service in a network including a location server storing registration and location information of a terminal, a session initiation protocol (SIP) server, and a SIP application server. When the SIP server receives the first invitation message, checking whether the subscriber subscribes to the call / session switching service unconditionally by referring to the profile information of the subscriber included in the first invitation message. A second step of transmitting the first invitation message to the SIP application server if the subscriber unconditionally subscribes to the call / session switching service; The SIP application server analyzes the received first invitation message, checks the destination terminal information, extracts the call forwarding terminal information set by the subscriber corresponding to the called terminal information, and extracts the extracted call forwarding terminal information. Transmitting an included second invitation message to the SIP server; And after the SIP server checks the location information of the call forwarding terminal included in the second invitation message from the location server managing the location of the call forwarding terminal, the SIP server to which the call forwarding terminal belongs. The fourth step of transmitting to.

The present invention also provides a method for providing unconditional call / session switching service in a network including a location server storing registration and location information of a terminal and a session initiation protocol (SIP) server, the first invitation for session initiation. A first step of, when the message is received, by the SIP server, referring to the profile information of the subscriber included in the first invitation message, whether the subscriber subscribes to the call / session switching service unconditionally; If the subscriber unconditionally subscribed to the call / session switching service, the first invite message is analyzed, the call forwarding terminal information set by the subscriber corresponding to the called terminal information in the first invite message is extracted, and the extracted call forwarding is performed. Generating a second invitation message including the terminal information; And a third step of the SIP server confirming the location information of the call forwarding terminal from the location server managing the location of the call forwarding terminal, and then transmitting the second invitation message to the SIP server to which the call forwarding terminal belongs. do.

In addition, the present invention, in the method for providing unconditional call / session switching service in a network including a location server for storing the registration and location information of the terminal, a session initiation protocol (SIP) server and a SIP application server, Receiving a first invitation message, determining whether the subscriber has subscribed to the call / session switching service unconditionally by referring to the profile information of the subscriber included in the first invitation message; A second step of transmitting the first invitation message to the SIP application server if the subscriber unconditionally subscribes to the call / session switching service; The SIP application server analyzes the received first invitation message to check the destination terminal information, extracts the call forwarding terminal information set by the subscriber corresponding to the destination terminal, and includes the extracted call forwarding terminal information. Transmitting a response message to the SIP server; And a fourth step of transmitting, by the SIP server, the response message to the originating terminal that sent the first invitation message, so that the originating terminal processes the response message.

In addition, the present invention is a method for providing unconditional call / session switching service in a network including a location server storing registration and location information of a terminal and a session initiation protocol (SIP) server, the first invitation message for session initiation. Receiving a message, checking whether the subscriber has subscribed to the call / session switching service unconditionally by referring to the profile information of the subscriber included in the first invitation message; If the subscriber unconditionally subscribes to the call / session switching service, analyzing the first invitation message to obtain incoming information, and extracting the forwarding terminal information set by the subscriber using the incoming information; Generating a second invitation message including the extracted call forwarding terminal information; Checking a service mode and a type of the call forwarding terminal; If the service mode is a proxy mode and the call forwarding terminal is a SIP terminal, requesting location information of the call forwarding terminal to a location server in charge of the call forwarding terminal; When the location information of the call forwarding terminal is received, transmitting the second invitation message to a SIP server to which the call forwarding terminal belongs; If the service mode is a proxy mode and the call forwarding terminal is not a SIP terminal, sending the second invitation message to an MGCF node; And when the service mode is the redirection mode, transmitting a response message including the call forwarding terminal information to a calling terminal, so that the calling terminal can be processed by the calling terminal.

In addition, the present invention, if the first invitation message for session initiation is received in the computer of the SIP-based network, the subscriber unconditionally subscribes to the call / session switching service with reference to the profile information of the subscriber included in the first invitation message Checking whether it is done; If the subscriber unconditionally subscribes to the call / session switching service, analyzing the first invitation message to obtain incoming information, and extracting the forwarding terminal information set by the subscriber using the incoming information; Generating a second invitation message including the extracted call forwarding terminal information; Checking a service mode and a type of the call forwarding terminal; If the service mode is a proxy mode and the call forwarding terminal is a SIP terminal, requesting location information of the call forwarding terminal to a location server in charge of the call forwarding terminal; When the location information of the call forwarding terminal is received, transmitting the second invitation message to a SIP server to which the call forwarding terminal belongs; If the service mode is a proxy mode and the call forwarding terminal is not a SIP terminal, sending the second invitation message to an MGCF node; And when the service mode is the redirection mode, transmitting a response message including the call forwarding terminal information to the calling terminal, and processing the processing by the calling terminal to read the computer readable recording medium recording the program. To provide.

1 is a view showing a brief configuration of a conventional mobile communication network.

2 is a block diagram of a SIP-based network to which the present invention is applied.

3 is a flowchart illustrating a call / session switching process using SIP according to the first embodiment of the present invention.

FIG. 4 is a process flowchart when the call forwarding terminal (terminal 3) is a non-SIP terminal in FIG. 3. FIG.

5 is a flowchart illustrating a call / session switching process using SIP according to a second embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 2 to 5.

The present invention utilizes a Session Initiation Protocol (SIP). As is known, SIP has been selected as the protocol on the User-Network Interface (UNI), i.e., the interface between the mobile subscriber and the Call State Control Function (CSCF). SIP was defined in the Internet Engineering Task Force (IETF) draft standard Request For Comments (RFC2543), issued in March 1999. The Session Initiation Protocol (SIP) is an application-layer control (signaling) protocol for creating, modifying and terminating sessions with one or more participants. These sessions include internet multimedia conferencing, internet phone calls and multimedia distribution. Members in a session can communicate over a multicast or unicast network or a combination thereof.

2 is a diagram illustrating a SIP-based network configuration to which the present invention is applied.

As shown in FIG. 2, the network includes a plurality of SIP servers 10, 20, 30, a plurality of location servers 11, 21, 31 corresponding to each SIP server 10, 20, 30, and SIP. An application server (AS) 40 is included.

Terminals include both non-SIP terminals as well as SIP terminals such as wireless terminals, wired terminals, web phones, and email. The terminal registers its incoming information (ie, IP information or URL information or telephone number or e-mail address) with the SIP server. It is preferable that one SIP server is registered with a subscriber profile of the terminal. A plurality of terminals are registered in one SIP server. In FIG. 2, terminals registered in the same SIP server are called terminal groups. That is, the terminals registered in the first SIP server 10 are registered in the first terminal group M1 and the second SIP server 20 in the second terminal group M1 and the third SIP server 20. The terminals are referred to as a third terminal group M1.

SIP server (10, 20, 30) stores the service profile of the terminal in charge thereof. And, the SIP server connects the call in response to the invitation (invite) message of the terminal in charge. At this time, the SIP server determines whether to switch the call / session according to the service profile information of the user.

Unconditional call forwarding service subscriber shall unconditionally send to other terminal for all calls received to him through operation using terminal (for example, inputting specific number and code to network) or service setting through web menu or customer center. Can be set to switch. This subscriber's configuration changes the subscriber's profile stored in the in-network subscriber database (database of the location server or home subscriber server). When the subscriber's profile is changed in this way, the changed subscriber's profile is transferred to the SIP server and the SIP application server currently responsible for the subscriber's service, so that the subscriber's profile is updated in real time. If the subscriber has not yet registered in the network, the subscriber profile and scripts are downloaded to the SIP server and the SIP application server when the registration process is performed to provide the corresponding service.

The SIP server 10, 20, 30 stores information such as incoming call information of a terminal in charge of itself and a phone number of a terminal in charge of another SIP server in a DB. Here, the DB containing the information of the terminal can be configured to be separated from the SIP server (10, 20, 30) as a separate independent device.

The location servers 11, 21, and 31 store the current location information, that is, routing information of the terminal in charge of its SIP server. SIP application server 40 includes call transfer service logic. Here, those skilled in the art can expect that the functions of the SIP application server 40 can be included in the SIP server 10, 20, 30.

3 is a flowchart illustrating an unconditional call / session switching process according to the first embodiment of the present invention. This is an example of operating in proxy mode.

In an exemplary embodiment of the present invention, reference numerals M1, M2, and M3 indicating a terminal group are used as quotation marks of terminals belonging to the terminal group.

First, the third terminal (M3) unconditionally for every call received by the subscriber by using the second terminal (M2), the Internet, or by calling the customer center directly. Register an unconditional call / session switching service that causes the call to switch. Then, the service profile for the second terminal M2 stored in the in-network subscriber DB is changed. In addition, the service profile for the changed second terminal M2 is provided in real time to the second SIP server 20 and the SIP application server in charge of the second terminal M2, so that the service profile of the second terminal M2 is changed. Is updated.

In this state, the first terminal M1 transmits an invitation message to the first SIP server for call setup with the second terminal M2. The first SIP server 10 then analyzes the invite message, confirms the incoming information, and manages the location information of the second terminal, which is the called party, with the second location server 21. Requires. Upon receiving a response to the request from the second location server, the first SIP server 10 transmits an invite message to the second SIP server 20.

The second SIP server 20 analyzes the invite message received from the first SIP server to determine that the incoming request message is sent to the second terminal M2 in charge thereof, and the service profile of the called subscriber. Check. In this case, the second SIP server performs service triggering based on filter criteria managed as part of the subscriber's service profile to determine that the second terminal M2 unconditionally registers with the call / session switching service. As a result, it is determined that the invite message needs to be relayed to the SIP application server (AS) 40. The filter criterion refers to all mechanisms corresponding to a service triggering criterion defined in advance in connection with providing a service of a subscriber.

Accordingly, the second SIP server 20 transmits an invite message to the SIP AS 40. Then, the SIP AS 40 analyzes the invite message received from the second SIP server, determines that the called subscriber needs to apply the unconditional call transfer service activated by the service, and the corresponding service logic. It is determined that the call should be switched to the third terminal (M3) by driving). Here, the service logic is implemented in a language such as Call Processing Language (CPL), service subscriber information, subscriber service type, operation mode (proxy mode, redirection mode, etc.) of the SIP AS 40, service application conditions, and the like. Refers to a code including an application result (call transfer destination information) and the like.

The SIP AS 40 modifies the terminating information of the existing invite message to the third terminal M3 to call the third terminal M3, which is a new destination, and then modifies the second invite message. Transfer to the second SIP server 20. Here, the SIP AS 40 may provide the first terminal M1 with information indicating that the subscriber's call is being switched, which is optional and may not be notified according to the operator's policy and terminal implementation. The call forwarding notification message may be, for example, 181 Call is being forwarded message among SIP standard messages.

Meanwhile, when the second SIP server 20 receives a second invite message destined for the third terminal M3 from the SIP AS 40, the second SIP server 20 is in charge of the third terminal M3. And (31) request position information of the third terminal. When the second SIP server receives the response, the second SIP server transmits a second invite message to the third SIP server 30. Then, the third SIP server 30 analyzes the second invitation message received from the second SIP server, and based on the connection information (that is, IP address) of the third terminal M3, the third terminal ( Send a second invite message to M3). As a result, the first terminal establishes a call with the third terminal which has been transferred.

Meanwhile, in the above description, a case in which the third terminal M3 has URL information, an e-mail address, or a general telephone number as a non-SIP terminal will be described with reference to FIG. 4.

As shown in Fig. 4, in this case, the third location server is replaced with a MGCF (Media Gateway Control Function), and the third SIP server is replaced with a PSTN or PLMN. The MGCF is a system that performs interworking between two networks by in charge of converting a common signaling signal (SS7) protocol such as a SIP signaling protocol of a packet network and an ISUP of a circuit network.

In the description of FIG. 3, when the second SIP server 20 receives the second invitation message modified from the SIP application server 40 with the third terminal (which is a non-SIP terminal) information, the second SIP server invites the second invitation. The destination number of the message is analyzed to determine whether this call should be routed to a circuit-switched network, such as a PSTN or PLMN. Accordingly, the second SIP server 20 transmits an invitation message to a node that performs the MGCF function, which is an interworking function with the PSTN / PLMN, in the network.

When the MGCF node receives the invitation message from the second SIP server, it analyzes the called number included in the invitation message, converts the invitation message into an ISUP message (IAM), and sends it to the PSTN exchange for establishing a call with the PSTN or PLMN. do. Accordingly, a call is established between the first terminal and the third terminal.

5 is a diagram illustrating an unconditional call / session switching process according to a second embodiment of the present invention. This is an example of operating in redirection mode.

Similarly, in the second embodiment, the subscriber registers an unconditional call / session switching service requesting that the incoming call / session to the second terminal M2 is unconditionally received by the third terminal M3.

In this state, the first terminal M1 transmits an invitation message to the first SIP server for call setup with the second terminal M2. Then, an invitation message is delivered to the SIP AS 40 through the same process as described above in the first embodiment.

Then, the SIP AS 40 analyzes the received invite message and recognizes that it is necessary to apply an unconditional call transfer service activated by the called subscriber, and drives the corresponding service logic to drive the third service. It is determined that the call should be transferred to the terminal M3. In addition, the SIP AS 40 transmits a response message including the third terminal M3 information to the second SIP server in order to call the third terminal M3, which is a new destination. Thereafter, the response message transmitted to the second SIP server is transmitted to the first terminal M1 through the first SIP server. Here, the response message may be, for example, a 302 Moved Temporarily message.

The first terminal M1 recognizes that the call should be transferred to a new destination (that is, the third terminal) through the received response message, and accordingly invites to request the incoming call to the third terminal M3. The message is automatically generated and transmitted to the first SIP server 10. Of course, the first terminal may automatically perform the following process by receiving the response message, but may optionally perform a call processing after asking the subscriber whether to try to transfer the call through the display.

The first SIP server 10 analyzes the destination number of the invitation message received from the first terminal and transmits to the third location server that manages registration and location information of the third terminal for routing to the third terminal. 3 Request location information of terminal. Upon receiving the response from the third location server, the first SIP server 10 transmits an invitation message to the third SIP server 30 according to the obtained information. The third SIP server 30 analyzes the invitation message received from the first SIP server and transmits the invitation message to the third terminal M3.

Meanwhile, also in the second embodiment, the third terminal may be a non-SIP terminal, which will be described.

The first terminal analyzes the received response message and automatically sets up a call with the third terminal by automatically driving the circuit switched mobile telephone function when the third terminal to be forwarded is a terminal having a general telephone number.

The first terminal analyzes the received response message and, when the third terminal to be forwarded to is the URL of an Internet site, automatically drives a web browser in the terminal to establish a session for receiving the URL.

The first terminal analyzes the received response message, and automatically drives the E-mail program in the terminal that receives the E-mail address when the third terminal to be forwarded is the E-mail address. Of course, the first terminal may also attempt to process the call after receiving confirmation from the subscriber according to the call transfer attempt.

Meanwhile, in the description of the first and second embodiments of the present invention, after the invite message is transmitted to the device, a message for the invite message, that is, 180 RINGING indicating call status information, 200 OK indicating a successful connection, and an error to the terminal 404 NOT FOUND, etc. indicating that there is an additional message should be used, but for the sake of understanding, it is assumed that all devices and terminals are in a normal state and that the connection is successful as soon as a call arrives. Described.

In addition, as described above, the SIP server and the SIP application server may be installed in one system, and the processing in this case will be described.

First, when the first invitation message for initiating a session is received by the system, the system refers to the profile information of the subscriber included in the first invitation message and checks whether the user has subscribed to the call / session switching service. Its confirmation process is the same as described above.

As a result of the check, when the subscriber unconditionally subscribes to the call / session switching service, the first invitation message is analyzed to obtain the incoming information, and the called forwarding terminal information set by the subscriber is extracted using the incoming information. In addition, a second invitation message including the extracted call forwarding terminal information is generated.

Then, it is checked whether the service mode is the proxy mode or the redirection mode, and in the case of the proxy mode, whether the call forwarding terminal included in the second invitation message is the SIP terminal. As a result of the check, in case of the SIP terminal, the location server in charge of the call forwarding terminal requests the location information of the call forwarding terminal. When the response is received, the second invitation message is transmitted to the SIP server to which the call forwarding terminal belongs. On the other hand, if it is not confirmed that the SIP terminal transmits the second invitation message to the MGCF node.

Meanwhile, when the service mode is the redirection mode, the response message including the call forwarding terminal information is transmitted to the first terminal which is the calling terminal. Accordingly, the first terminal transmits the response message to the first SIP server, or when the terminal to be forwarded is a non-SIP terminal, the first terminal performs the above-described processing according to the type of the terminal.

Although the above-described embodiment of the present invention has been described with a call as an example, even if the IP information of the terminal is changed to a SIP URL (Uniform Resource Location), when applied to the above-described embodiment of the present invention, an unconditional session incoming service method for a session Is about.

Although the technical spirit of the present invention has been described above with reference to the accompanying drawings, this is intended to describe exemplary embodiments of the present invention by way of example and not to limit the present invention. In addition, it will be apparent to those skilled in the art that various modifications and imitations can be made without departing from the scope of the technical idea of the present invention.

As described above, the present invention can provide a service that allows a service subscriber to switch to a destination designated in advance for a call that is received by the user when various multimedia communication services based on IP are provided through the Hyangwoo mobile communication network.

Claims (11)

In the method for providing an unconditional call / session switching service in a network including a location server for storing registration and location information of a terminal, a session initiation protocol (SIP) server, and a SIP application server, When the SIP server receives the first invitation message, checking whether the subscriber subscribes to the call / session switching service unconditionally by referring to profile information of the subscriber included in the first invitation message; A second step of transmitting the first invitation message to the SIP application server if the subscriber unconditionally subscribes to the call / session switching service; The SIP application server analyzes the received first invitation message, checks the destination terminal information, extracts the call forwarding terminal information set by the subscriber corresponding to the called terminal information, and extracts the extracted call forwarding terminal information. Transmitting an included second invitation message to the SIP server; And After the SIP server checks the location information of the call forwarding terminal included in the second invitation message from the location server managing the location of the call forwarding terminal, the SIP server sends the second invitation message to the SIP server to which the call forwarding terminal belongs. Unconditional call / session switching service providing method comprising the fourth step of transmitting. Claims [1] A method for providing an unconditional call / session switching service in a network including a location server storing registration and location information of a terminal and a session initiation protocol server. A first step of, if the first invitation message for starting the session is received, by the SIP server, referring to the profile information of the subscriber included in the first invitation message, whether the subscriber has subscribed to the call / session switching service unconditionally; If unconditionally subscribed to the call / session switching service, the first invitation message is analyzed, the call forwarding terminal information set by the subscriber corresponding to the destination terminal information in the first invitation message is extracted, and the extracted call forwarding terminal information A second step of generating a second invitation message including a; And And checking, by the SIP server, the location information of the call forwarding terminal from the location server managing the location of the call forwarding terminal, and transmitting the second invitation message to the SIP server to which the call forwarding terminal belongs. How to provide call / session switching service. The method according to claim 1 or 2, Checking, by the SIP server, call forwarding terminal information included in the second invitation message, and transmitting the second invitation message to a Media Gateway Control Function (MGCF) node when the call forwarding terminal is a non-SIP terminal. Unconditional call / session switching service providing method characterized in that it further comprises. In the method for providing an unconditional call / session switching service in a network including a location server for storing registration and location information of a terminal, a session initiation protocol (SIP) server, and a SIP application server, When the SIP server receives the first invitation message, checking whether the subscriber subscribes to the call / session switching service unconditionally by referring to profile information of the subscriber included in the first invitation message; A second step of transmitting the first invitation message to the SIP application server if the subscriber unconditionally subscribes to the call / session switching service; The SIP application server analyzes the received first invitation message to check the destination terminal information, extracts the call forwarding terminal information set by the subscriber corresponding to the destination terminal, and includes the extracted call forwarding terminal information. Transmitting a response message to the SIP server; And And a fourth step of transmitting, by the SIP server, the response message to the calling terminal that has sent the first invitation message, so that the calling terminal processes the response message based on the response message. The method according to claim 1 or 4, The SIP server and the SIP application server is unconditional call / session switching service providing method characterized in that implemented in one system. The method according to claim 1 or 2 or 4, After the SIP server performs triggering based on the filter criteria managed as part of the service profile of the called subscriber obtained from the first invitation message, the subscriber confirms that the subscriber subscribes to the call / session switching service. 1 unconditional call / session switching service providing method characterized in that the transmission of the invitation message to the SIP application server. The method according to claim 1 or 2, And transmitting a message to the calling terminal, informing that the SIP application server is transferring a call before transmitting the second invitation message to the SIP server. The method according to claim 1 or 4, The SIP application server extracts the call forwarding terminal information of the called terminal included in the first invitation message by referring to the service subscriber information, the subscription service type, the operation mode of the application server, the service application condition, and the call forwarding destination information. Unconditional call / session switching service providing method characterized by. The method of claim 4, wherein Analyzing, by the calling terminal, the response message in the fourth step, checking whether the call forwarding terminal included in the response message is a SIP terminal; If the call forwarding terminal is a SIP terminal, transmitting an invitation message including the call forwarding terminal information to the SIP server; And And if the call forwarding terminal is a non-SIP terminal, performing the process for connecting with the non-SIP terminal. Claims [1] A method for providing an unconditional call / session switching service in a network including a location server storing registration and location information of a terminal and a session initiation protocol server. When the first invitation message for starting the session is received, checking whether the subscriber subscribes to the call / session switching service unconditionally by referring to the profile information of the subscriber included in the first invitation message; If the subscriber unconditionally subscribes to the call / session switching service, analyzing the first invitation message to obtain incoming information, and extracting the forwarding terminal information set by the subscriber using the incoming information; Generating a second invitation message including the extracted call forwarding terminal information; Checking a service mode and a type of the call forwarding terminal; If the service mode is a proxy mode and the call forwarding terminal is a SIP terminal, requesting location information of the call forwarding terminal to a location server in charge of the call forwarding terminal; When the location information of the call forwarding terminal is received, transmitting the second invitation message to a SIP server to which the call forwarding terminal belongs; If the service mode is a proxy mode and the call forwarding terminal is not a SIP terminal, sending the second invitation message to an MGCF node; And And transmitting the response message including the call forwarding terminal information to the calling terminal to be processed by the calling terminal when the service mode is the redirection mode. On a computer in a SIP-based network, When the first invitation message for starting the session is received, checking whether the subscriber subscribes to the call / session switching service unconditionally by referring to the profile information of the subscriber included in the first invitation message; If the subscriber unconditionally subscribes to the call / session switching service, analyzing the first invitation message to obtain incoming information, and extracting the forwarding terminal information set by the subscriber using the incoming information; Generating a second invitation message including the extracted call forwarding terminal information; Checking a service mode and a type of the call forwarding terminal; If the service mode is a proxy mode and the call forwarding terminal is a SIP terminal, requesting location information of the call forwarding terminal to a location server in charge of the call forwarding terminal; When the location information of the call forwarding terminal is received, transmitting the second invitation message to a SIP server to which the call forwarding terminal belongs; If the service mode is a proxy mode and the call forwarding terminal is not a SIP terminal, sending the second invitation message to an MGCF node; And And transmitting the response message including the call forwarding terminal information to the calling terminal when the service mode is the redirection mode, so as to be processed by the calling terminal.