JPH09191326A - Inter-work equipment and communication system using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make communication without the need for notifying communication between different kinds of networks by the user and to avoid useless line connection. SOLUTION: The system is provided with an incoming terminal information acquisition means 122a to acquire information to designate by (incoming call terminal equipment) among terminal equipments 131-133 on a LAN 102 among connection request message sent from a terminal equipment 111 (outgoing terminal) on an ISDN 101 at the connection request from the ISDN 101 to the LAN 102 and an incoming terminal equipment retrieval means 124a retrieving whether or not the incoming terminal equipment denoted by incoming terminal equipment information is connected to the LAN 102 at that point of time on the connection request. When a concerned incoming terminal equipment is found out as the retrieval, the connection to the caller terminal equipment is executed, and when not found out, the connection is rejected, then only when the object incoming terminal equipment is connected to the LAN 102, the line connection is conducted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interwork device and a communication system using the interwork device and a plurality of communication terminal devices.

[0002]

2. Description of the Related Art In recent years, communication technology has advanced, and when communication is performed between communication terminal devices (hereinafter referred to as terminals) and terminals, they differ not only between terminals connected in a single network but also between terminals. It is also possible to communicate between terminals connected to the type of network.

Usually, when communication is performed in a certain network, the communication is performed in accordance with a predetermined communication protocol (communication protocol) in order to secure the communication connectivity. IS
In a public line such as DN (Integrated Services Digital Network), the communication protocol is ITU (International Telecommunication).
Union: International Telecommunications Union) and other standardization bodies.

[0004] For example, in ISDN, the connection procedure and the disconnection procedure between terminals are defined in ITU-T Recommendation Q. 931. On the other hand, LAN (Local Area Network:
In a local area network), each vendor or organization uses its own communication protocol, and the communication protocol is often different for each network.

Therefore, when communication is performed between terminals connected to networks of different types such as ISDN and LAN, an interwork device generally called "gateway" or "router" is used. The interworking device is a device for performing interworking such as protocol conversion and address conversion between networks of different types.

Here, as a conventional example, a communication system for performing communication between terminals connected to different types of networks as described above will be described with reference to FIGS.

FIG. 8 is a diagram showing a configuration example of the conventional communication system. In the figure, 301 is a public line such as ISDN, and 302 is a LAN such as Ethernet. Reference numeral 311 is a first terminal connected to the ISDN 301 and has an interface with the ISDN 301. Reference numerals 312 to 314 denote second to fourth terminals connected to the LAN 302, and have an interface with the LAN 302.

Reference numeral 321 denotes an interworking device, which is an IS
Connected between DN301 and LAN302, ISDN
The interworking between 301 and the LAN 302 is performed. 331 is a user who is using the first terminal 311.

In FIG. 9, the first terminal 311 is the LAN 30
3 is a flowchart showing an operation when communicating with any of the second to fourth terminals 312 to 314 in FIG.
FIG. 10 is a sequence diagram showing an outline of a series of processes of steps S301 to S307 when Yes is determined in step S305 of FIG. Also, FIG.
It is a sequence diagram which shows the outline of a series of processes of step S301-S311 when it determines with No in step S305 of FIG.

The communication operation will be described below with reference to FIGS. First, in step S301 of FIG. 9, the user 331 makes a call from the first terminal 311 to the interworking device 321. At this time, the first
The terminal 311 of the I, as shown in FIG. 10 and FIG.
A call setup (SETUP) message is sent to the SDN 301, and a call setup acceptance (CALL PROC) message sent from the ISDN 301 is received correspondingly.

When a call is made in this manner, the first terminal 311 and the interwork device 321 are connected via the ISDN 301 in step S302.
The connection between the first terminal 311 and the interwork device 321 is performed as follows. That is, FIG.
And, as shown in FIG. 11, the interworking device 321 sends the ISD in response to the call made in step S301.
A response (CONN) message is sent to the first terminal 311 via N301.

ISDN3 that received the response message
01 and the first terminal 311 confirm the response to the interwork device 321 and the ISDN 301 (CONN A
CK) Return message. Thereby, the first terminal 311
Connection with the interwork device 321 is completed. Here, since the first terminal 311 and the interworking device 321 are connected, the first terminal 311 is connected to the LAN 3
It will be connected to 02.

Next, in step S303, the user 331 logs in to the LAN 302 from the first terminal 311. As a result, the user 331 becomes the first terminal 311.
Can be used to access the LAN 302. Next, in step S304, the first terminal 31
1 is a terminal (incoming terminal) that the user 331 wants to communicate with
Is connected to LAN 302 (or L
To see if it is running on AN 302).

Then, in step S305, it is determined whether or not a corresponding called terminal is found as a result of the search in step S304. When the corresponding called terminal is found, the process of step S306 is performed next. On the other hand, if the corresponding incoming terminal is not found, then the process of step S310 is performed.

In step S306, the user 331
The first terminal 311 gives an instruction to start the connection between the interworking device 321 and the receiving terminal. Then, step S
At 307, a connection is established between the interwork device 321 and the called terminal via the LAN 302. After that, it becomes possible to perform communication between the first terminal 311 and the called terminal through the protocol conversion mechanism of the interworking device 321 (see FIG. 10).

In step S310, the user 331 logs out from the LAN 302 using the first terminal 311. Then, in step S311,
The user 331 disconnects the connection between the first terminal 311 and the interwork device 321. This disconnection process is specifically performed as follows.

That is, first, as shown in FIG.
A disconnect (DISC) message is sent from the terminal 311 of the above to the interwork device 321 via the ISDN 301. Correspondingly, a release (REL) message is returned from ISDN 301 and interworking device 321 to first terminal 311 and ISDN 301, respectively. And
Upon receiving the release message, the first terminal 311 sends a release complete (REL COMP) message to the interwork device 321 via the ISDN 301, and the line disconnection process is completed.

[0018]

As described above, when the conventional interworking device 321 is used, the connection between the calling terminal and the called terminal is as shown by the thick arrow in FIG.
The connection has been divided into two stages, a first stage connection between the calling terminal and the interworking device and a second stage connection between the interworking device and the receiving terminal. for that reason,
The information on the LAN 302, which is the network beyond the interwork device 321, can be obtained only after the connection between the calling terminal and the interwork device is established.

Therefore, the search for whether or not the intended incoming terminal is on the LAN 302 is also performed after the connection between the outgoing terminal and the interworking device is established. At this time, if the intended receiving terminal is not connected to the LAN 302 or is not operating, there is a disadvantage that the public line connection between the calling terminal and the interworking device becomes useless as shown in FIG. It was

Further, since the user 331 on the calling terminal side has to instruct each of the above two-stage connection, the operation procedure is complicated. Also, the user 33
In the case of No. 1, it is necessary to be familiar with the knowledge and operation method of the two networks, so that there is a drawback that not everyone can easily connect terminals between networks of different types.

The present invention has been made in view of the above situation, and it is possible to easily perform communication in a procedure of connecting terminals between networks of different types without making the user aware of the configuration between the networks. The purpose is to prevent the line connection from being wasted.

[0022]

The interworking device of the present invention is designed to enable communication between terminal devices connected to first and second networks having different communication protocols. In an interworking device that interconnects the first and second networks and performs a predetermined protocol conversion, when a connection request is made from the first network to the second network, a calling terminal on the first network Called terminal information acquisition means for acquiring information for designating a called terminal on the second network from the transmitted connection request message, and a connection request from the first network to the second network. Sometimes, the receiving terminal indicated by the information obtained by the receiving terminal information obtaining means is the second network at that time. It is provided with a a receiving terminal search means for searching whether a connected.

Another feature of the present invention is that, in the interworking device according to claim 1, when a corresponding called terminal is found as a result of the search by the called terminal searching means, connection with the calling terminal is made. Is executed, and when a corresponding incoming terminal is not found, a control means for controlling to refuse the connection with the outgoing terminal is further provided.

Another feature of the present invention is that, in the interworking device according to claim 1, when a corresponding incoming terminal is found as a result of the search by the incoming terminal searching means, the corresponding incoming terminal is found. As a result of the call by the receiving terminal calling means for calling the receiving terminal and the receiving terminal calling means, if there is a predetermined response from the receiving terminal, connection with the calling terminal is executed, and if there is no response from the receiving terminal, A control means is further provided for controlling so as to refuse the connection with the calling terminal when the corresponding called terminal is not found as a result of the search by the called terminal searching means.

Another feature of the interworking device of the present invention is that the first network is ISDN.
It is a line, and the second network is a LAN.

In the communication system of the present invention, the terminal device connected to the first network and the terminal device connected to the second network having a communication protocol different from that of the first network are the first device. , A communication system configured to perform communication through an interwork device for interconnecting the second networks and performing a predetermined protocol conversion, the terminal device connected to the first network is the first device. From the 1st network to the 2nd above
When the connection request to the network is made, the interworking apparatus has a transmission means for transmitting a connection request message including the reception terminal information for designating the reception terminal on the second network. Called terminal information acquisition means for acquiring the called terminal information from the connection request message transmitted from the calling terminal on the first network when a connection request is made from the network to the second network; When a connection request is made from this network to the second network, the receiving terminal which is indicated by the information acquired by the receiving terminal information acquiring means is searched for whether or not it is currently connected to the second network. A search means is provided.

Another feature of the present invention is that, in the communication system according to claim 5, when the interworking device finds a corresponding called terminal as a result of the search by the called terminal searching means, the above-mentioned It further comprises control means for executing a connection with the calling terminal and for denying the connection with the calling terminal when a corresponding called terminal is not found.

According to another feature of the present invention, in the communication system according to claim 5, the interwork device is a result of the search by the receiving terminal search means,
When the corresponding called terminal is found, the called terminal calling means for calling the applicable called terminal and the calling terminal when a specified response is given from the called terminal as a result of calling by the called terminal calling means. When a connection is executed and there is no response from the called terminal, or when a corresponding called terminal is not found as a result of the search by the called terminal searching means, a control means for controlling the connection with the calling terminal is rejected. Is further included.

Another feature of the communication system of the present invention is that the first network is an ISDN line and the second network is a LAN.

According to the present invention configured as described above, when the connection request from the first network to the second network is made, it is included in the connection request message sent from the calling terminal on the first network. Based on the incoming call terminal information, the search is made for whether the incoming call terminal specified by the incoming call terminal information is connected to the second network, and the target incoming call terminal is the second.
It is possible to perform a search process as to whether or not the terminal is connected to another network before connecting terminals on different networks.

Further, according to another feature of the present invention, as a result of the above-mentioned search, when a corresponding incoming terminal is found, a connection with the outgoing terminal is made, and when the corresponding incoming terminal is not found. Will not be connected to the calling terminal, and will be connected to the calling terminal only when the intended called terminal is connected to the second network.

Further, according to another feature of the present invention, as a result of the above-mentioned search, when a corresponding called terminal is found, a calling process of the called terminal is automatically performed and a response thereto is given. In this case, the connection with the calling terminal is made, and the connection with the calling terminal is made only when the intended called terminal is operating on the second network.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail. FIG. 1 is a block diagram showing the configuration of a communication system which is an embodiment of the present invention.

In FIG. 1, reference numeral 101 denotes a communication line such as ISDN, which is used for communication between the first terminal 111 and the interworking device 121. Reference numeral 102 denotes a LAN such as Ethernet, and the interwork device 12
This is for performing communication between the first terminal and the second to fourth terminals 131 to 133.

The first terminal 111 is connected to the ISDN1
01 is a communication terminal device connected to the ISDN 101
Interface. The second to fourth terminals 131 to 133 are connected to the LAN 102,
A LAN terminal configured to be able to communicate with each other and with the interwork device 121.
It has an interface with 02.

The first terminal 111 has a system controller 112 and a line controller 113. Here, the system control unit 112 controls the entire system of the first terminal 111. For example, the system control unit 112 includes a receiving terminal designating unit 112a, and performs processing such as transmitting the receiving terminal information and the receiving user information obtained by the designation by the user to the line control unit 113.

Further, the line control unit 113 uses the ISDN 10
1 is performed, and processing such as transmission of a call setup message, which is a connection request message, is performed according to an ISDN user / network interface such as the ITU-T Recommendation Q series. At this time, the receiving terminal information and the receiving user information transmitted from the system control unit 112 are included in the call setting message and transmitted.

Further, the interworking device 121 is
Connected between ISDN 101 and LAN 102, IS
Interworking between the DN 101 and the LAN 102 is performed. The interworking device 121 includes a line controller 122, a LAN controller 123, and a system controller 124.
And a LAN terminal information storage unit 125.

The line control unit 122 performs processing based on the communication protocol on the ISDN 101 side according to the ISDN user / network interface such as the ITU-T recommendation Q series. The line control unit 122 is provided with a called terminal information acquisition unit 122a, and the called terminal information is selected from the call setting messages sent from the line control unit 113 in the first terminal 111 via the ISDN 101. And processing to acquire the incoming user information.

Further, the LAN control unit 123 performs processing based on the communication protocol on the LAN 102 side according to the interface used in the LAN 102 connected thereto. The LAN control unit 123 includes a called terminal calling unit 123a, and the LAN 102
A process for calling the called terminal indicated by the called terminal information or the called user information from the second to fourth terminals 131 to 133 operating above is performed.

The system controller 124 controls the interworking device 121 as a whole. For example, the system control unit 124 uses the receiving terminal searching means 1
24a, the receiving terminal specified by the first terminal 111 on the LAN 102 based on the receiving terminal information and the receiving user information acquired by the receiving terminal information acquiring means 122a in the line control unit 122. Performs a search process to see if it is operating in.

Further, the LAN terminal information storage unit 125 stores L
Second to fourth terminals 131-connected to the AN 102
Each terminal 131 such as 133 LAN address and terminal number
~ 133 is stored. The search processing in the called terminal search means 124a is
Each terminal 13 stored in the AN terminal information storage unit 125
It is performed using the information regarding 1 to 133.

FIG. 2 is a conceptual diagram showing the data structure of the LAN terminal information storage unit 125 shown in FIG. As shown in FIG. 2, the LAN terminal information storage unit 125 stores the LAN 10
As the information about each terminal connected to 2, the terminal number No assigned from the ISDN 101 for identifying each terminal, the terminal name Name, and the LAN address information Address assigned to each terminal on the LAN 102 are included in each terminal. Are stored for each.

The operation procedure of the communication system according to the present embodiment configured as described above will be described below. As an outline of communication, the first terminal 111 makes a call to any of the second to fourth terminals 131 to 133 via the interwork device 121 to perform communication. Therefore, in the following, the first terminal 111 = the calling terminal and any of the second to fourth terminals 131 to 133 = the receiving terminal.

First, the operation of the first terminal 111, which is the calling terminal, will be described. FIG. 3 is a flowchart showing the operation of the first terminal 111. In the figure, the first terminal 111 first creates a call setup message in step S101. Note that call control messages such as call setup messages are ITU-T Recommendation Q. 931.

In this embodiment, a call setup message having the structure shown in FIG. 4 is created. That is, information for designating the called terminal (terminal number or terminal name for identifying the called terminal, that is, called terminal information) and ISDN address information of the interworking device 121 are sent to the line controller 113 by the system controller 112. The information is transmitted and each piece of information is encoded as a called sub address information element and a called number information element in the call setup message.

After the call setup message is created in this way, in step S102, the line control unit 113 sends the created call setup message to the ISDN 10
1 to call the interworking device 121. In response to this, in the next step S103, a call (ALERT) message is received from the ISDN 101,
Appropriate processing is performed accordingly.

Then, in step S104, the ISD
If a response message is received from N101, the first
The connection between the terminal 111 and the interworking device 121 has been accepted. In this case, the next step S
At 105, a response confirmation message is sent to ISDN 101.
Then, the connection process with the interwork device 121 is completed.

When the response message is not received in step S104 and the disconnection message is received in step S110, it means that the connection between the first terminal 111 and the interworking device 121 is rejected. In this case, the release message is transmitted to the ISDN 101 in the next step S111. And step S
When the release completion message is received from the ISDN 101 at 112, the connection refused process with the interwork device 121 is completed.

Next, the operation of the interworking device 121 will be described. FIG. 5 shows the interworking device 12
3 is a flowchart showing the operation procedure of No. 1; FIG.
6 is a sequence diagram showing an outline of a series of processes of steps S201 to S210 when Yes is determined in step S205 of FIG. In addition, FIG.
FIG. 8 is a sequence diagram showing an outline of a series of processes of steps S201 to S217 when No is determined in step S205. The operation of the interworking device 121 will be described below with reference to FIGS.

In FIG. 5, first, in step S201, when the line control unit 122 receives a call setting message sent from the line control unit 113 in the first terminal 111 via the ISDN 101, the next step S20.
2, the first terminal 111 via the ISDN 101
A call message to (see FIGS. 6 and 7).

Next, in step S203, the called terminal information acquisition means 122a acquires called terminal information from the called subaddress information element in the call setup message received in step S201, and the system control unit 12 acquires it.
Communicate to 4.

In the next step S204, the system controller 124 having received the above-mentioned called terminal information uses the called terminal information acquired in the above step S203 as a search key to find the called terminal specified by the user in the LAN terminal information storage section 125. The above is searched and the LAN address of the corresponding receiving terminal is acquired. This incoming terminal search processing is performed by the incoming terminal search means 124a.

Then, in step S205, it is determined whether or not a corresponding called terminal is found as a result of the search in step S204. When the corresponding called terminal is found, the process of step S206 is performed next.
On the other hand, if the corresponding called terminal is not found,
Next, the process of step S215 is performed.

In step S206, the LAN controller 12
Under the control of 3, the connection between the interworking device 121 and the receiving terminal is established by using the LAN address of the receiving terminal acquired in step S204. Then, in step S207, the called terminal calling means 123a in the interworking device 121 performs a calling process for the called terminal (see FIG. 6).

Then, in step S208, if there is a response from the receiving terminal to the interwork device 121, the process of step S209 is performed. Step S2
In 09, the interwork device 121 uses the line control unit 1
22 from the first terminal 111 by transmitting a response message to the first terminal 111 via the ISDN 101.
Indicates that the connection with is accepted. Then, in the next step S210, the response confirmation message is sent to ISDN1.
By receiving from 01, the connection with the first terminal 111 is completed (see FIG. 6).

As described above, in the present embodiment, based on the call setup message sent from the first terminal 111 to the interworking device 121 at the time of requesting a line connection, it is determined whether or not the desired called terminal is on the LAN 102. Is done. When a corresponding called terminal is found, the called terminal is automatically called, and when there is a response to the calling, the connection between the calling terminal and the interworking device and the interworking device-calling are performed. Two connections with a connection between terminals are made.

Therefore, the user of the first terminal 111 need only specify a desired receiving terminal and make a call,
Since it is not necessary to repeatedly perform troublesome connection instructions and the like, the operation for connecting the line is simplified and the ISDN10
Thus, it becomes possible for the user to communicate with a desired incoming terminal without the user being aware of the configuration of the two networks of 1 and LAN 102.

On the other hand, if the response from the receiving terminal is rejected in step S208, the process of step S215 is performed. In step S215, which is a transition from steps S205 and S208, the interworking device 121
From the line controller 122 via the ISDN 101
By sending a disconnection message to the terminal 111 of
Indicates that the connection with the first terminal 111 is refused (FIG. 7).
reference).

Then, in the next step S216, I
While receiving the release message from SDN 101,
By transmitting a release confirmation message to the ISDN 101 in step S217, the connection refusal process with the first terminal 111 is completed (see FIG. 7).

As described above, in this embodiment, when the above-described search is performed before the line connection and the corresponding called terminal is not found, the connection between the calling terminal and the interwork apparatus and the interwork apparatus- 2 with the connection between the receiving terminals
No connection is made, and the connection between the calling terminal and the called terminal is rejected. Therefore, the intended receiving terminal is LAN1
No line is wasted because the line is connected only when the line connection is established.

In the above embodiment, the search is executed using the information stored in the LAN terminal information storage unit 125 in order to obtain the LAN address of the called terminal in step S204 of FIG. , LAN102
Depending on the communication protocol and application used above, each terminal 131 to 13 currently connected
Each LAN address information of No. 3 can be dynamically collected. For example, DNS (Domain Name Se) in UNIX
rver) is applicable. Therefore, it is also possible to search using this.

[0063]

As described above, according to the interworking apparatus and the communication system of the present invention, when the connection request from the first network to the second network is made,
Information for designating a called terminal on the second network is acquired from the connection request message transmitted from the calling terminal on the first network, and the called terminal indicated by the acquired information is Since the search is made to see if it is connected to the second network, it is possible to check whether the intended called terminal is connected to the second network before actually connecting between terminals on different networks. You can search.

Further, according to another feature of the present invention, as a result of the above-mentioned search, if a corresponding called terminal is found, connection with the calling terminal is executed, and if no corresponding called terminal is found, calling is made. Since the connection with the terminal is rejected, the line between the calling terminal and the interworking device can be connected only when the intended receiving terminal is connected to the second network. It is possible to prevent the connection fee of the line from being wasted due to the fact that the intended incoming terminal cannot be found despite the connection of.

Further, according to another feature of the present invention, when a corresponding called terminal is found as a result of the above-mentioned search, the called terminal is called and, as a result of the calling, a predetermined terminal is called from the called terminal. When there is a response, the connection with the calling terminal is executed, and if there is no response from the called terminal or if the corresponding called terminal cannot be found, the connection with the calling terminal is rejected. Originating terminal-interworking device only if the terminal is connected to a second network and the call is answered, i.e. if the intended terminating terminal is operating on the second network. Connection between the interworking device and the receiving terminal can be automatically performed, and the user is aware of the configurations of the first and second networks. It is possible to communicate without, it is possible to connection fee of line is not wasted.

[Brief description of the drawings]

FIG. 1 is a block diagram showing configurations of an interworking apparatus and a communication system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a data structure in a LAN terminal information storage unit in the present embodiment.

FIG. 3 is a flowchart showing an operation procedure of a transmitting terminal of the communication system according to the present embodiment.

FIG. 4 is a diagram showing a data structure of a call setup message according to the present embodiment.

FIG. 5 is a flowchart showing an operation procedure of the interworking device of the communication system according to the present embodiment.

FIG. 6 is a sequence diagram showing an operation situation when a calling terminal and a called terminal are connected in the present embodiment.

FIG. 7 is a sequence diagram showing an operation situation in the case where a calling terminal and a called terminal are not connected in the present embodiment.

FIG. 8 is a diagram showing configurations of a conventional interworking device and a communication system.

FIG. 9 is a flowchart showing an operation procedure of a conventional communication system.

FIG. 10 is a sequence diagram showing an operation situation in the case where a calling terminal and a called terminal are connected in a conventional communication system.

FIG. 11 is a sequence diagram showing an operation situation in the case where a calling terminal and a called terminal are not connected in a conventional communication system.

[Explanation of symbols]

 101 ISDN Line 102 LAN 111 First Communication Terminal Device (Calling Terminal) 112 System Control Unit 112a Called Terminal Designating Unit 113 Line Control Unit 121 Interworking Device 122 Line Control Unit 122a Called Terminal Information Acquisition Means 123 LAN Control Unit 123a Called Terminal Calling unit 124 System control unit 124a Receiving terminal searching unit 125 LAN terminal information storage unit 131 Second communication terminal device (reception terminal) 132 Third communication terminal device (reception terminal) 133 Fourth communication terminal device (reception terminal)

Claims (8)

[Claims] 1. The first and second networks are interconnected to enable communication between terminal devices connected to the first and second networks having different communication protocols. In an interworking device for performing a predetermined protocol conversion, when a connection request from the first network to the second network is made, the connection request message transmitted from the calling terminal on the first network is selected from the connection request messages. Two
The receiving terminal information acquiring means for acquiring information for designating the receiving terminal on the network, and the information acquired by the receiving terminal information acquiring means at the time of requesting connection from the first network to the second network. An interworking device comprising: a called terminal searching means for searching whether the called terminal shown is currently connected to the second network. 2. The interworking apparatus according to claim 1, wherein when a corresponding called terminal is found as a result of the search by the called terminal searching means, connection with the calling terminal is executed and the called terminal is The interworking device further comprising control means for controlling so as to reject the connection with the calling terminal when the device is not found. 3. The interworking apparatus according to claim 1, wherein when a corresponding called terminal is found as a result of the search by the called terminal searching means, a called terminal calling means that calls the applicable called terminal, As a result of the call by the called terminal calling means, if there is a predetermined response from the called terminal, the connection with the calling terminal is executed, if there is no response from the called terminal, and the result of the search by the called terminal searching means. An interworking apparatus further comprising: a control unit that controls to reject the connection with the calling terminal when a corresponding called terminal is not found. 4. The interworking device according to claim 1, wherein the first network is an ISDN line, and the second network is a LAN. 5. A terminal device connected to a first network and a terminal device connected to a second network having a communication protocol different from that of the first network are connected between the first and second networks. In a communication system configured to perform communication via an interworking device for mutually connecting and performing a predetermined protocol conversion, the terminal device connected to the first network includes the terminal device connected to the first network and the second device. When the connection request to the network is made, the interwork apparatus has a transmission means for transmitting a connection request message including the reception terminal information for designating the reception terminal on the second network. When a connection request is made from the network to the second network, the first
Destination terminal information acquisition means for acquiring the destination terminal information from the connection request message transmitted from the source terminal on the network, and the incoming call when the connection request from the first network to the second network is made. A communication system comprising: a receiving terminal searching means for searching whether or not the receiving terminal indicated by the information acquired by the terminal information acquiring means is currently connected to the second network. 6. The communication system according to claim 5, wherein the interwork device executes a connection with the calling terminal when a corresponding called terminal is found as a result of the search by the called terminal searching means, A communication system, further comprising control means for controlling so as to reject the connection with the calling terminal when a corresponding called terminal is not found. 7. The communication system according to claim 5, wherein the interwork device, when a corresponding called terminal is found as a result of the search by the called terminal searching means,
As a result of the call by the called terminal calling means for calling the applicable called terminal and the called terminal calling means, if there is a predetermined response from the called terminal, the connection with the calling terminal is executed and a response is made from the called terminal. If there is not, or if the corresponding called terminal is not found as a result of the search by the called terminal searching means, the communication system further comprises control means for controlling to reject the connection with the calling terminal. . 8. The communication system according to claim 5, wherein the first network is an ISDN line and the second network is a LAN.