JP4677299B2 - Data communication system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data communication system which automatically performs the connection control of a plurality of devices by a communication terminal, improves convenience, and simplifies the system compared with one in which setting operation to the communication terminal at each device is troublesome if there are a plurality of devices of an end terminal in the conventional data communication system. <P>SOLUTION: The data communication system is provided with a server destination management database 9 which stores IP addresses of a plurality of servers 1 and a number of ports 32 in the communication terminal 3 as destination device information corresponding each other, and a device selector server 8 which transmits the destination device information responding to a request from the communication terminal 3. If the communication terminal 3 does not store the destination device information at the time of powering-on, it requests the information to the device selector server 8, receives the device information, and stores it. If the server 1 transmits a connection request, the communication terminal 3 refers the connection device information, specifies the port 32 corresponding to the IP address of the originator's server 1, and transmits the connection request from the port 32. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to a data communication system in which a terminal device is connected to a server on a LAN via a communication terminal on a wireless network, and in particular, one communication terminal without performing data setting operations on the communication terminal. Thus, the present invention relates to a data communication system that can connect a plurality of devices provided in a terminal device to a server, improve convenience, and simplify the system.

A data communication system using a LAN or a wireless LAN as a communication medium and connecting a server or a communication terminal is realized.
An apparatus will be described as an example of a general data communication system with reference to FIG. FIG. 7 is a schematic block diagram of a general data communication system.
As shown in FIG. 7, as a data communication system, for example, a server 1 that is connected to a LAN line and provides a service with various data, and a wireless that performs data conversion for connecting a wireless network and the LAN line. -Consists of a LAN conversion device 2, a communication terminal 3 'for connecting the terminal device 4 to a wireless network, and a terminal device 4 for the user to access the server 1 and receive various data and services. was there.

  Among these, the server 1 and the wireless-LAN converter 2 are connected by a LAN 51, the wireless-LAN converter 2 and the communication terminal 3 ′ are connected via a wireless network 52, and the communication terminal 3 ′ and the terminal device 4. Are connected by a serial cable 53.

  In other words, the system configured as described above is such that the LAN line network provided with the server 1 and the wireless network provided with the communication terminal 3 'are connected by the wireless-LAN converter 2 and connected to the communication terminal 3'. 4 is a system that enables communication between the server 4 and the server 1.

Next, the protocol stack in the data communication system having the above-described configuration will be described as an example in which data is transmitted from the server 1 to the terminal device 4. FIG. 8 is an explanatory diagram showing an example of a protocol stack in the data communication system.
As shown in FIG. 8, data transmitted from the server 1 to the wireless-LAN conversion device 2 via the LAN is transmitted from the wireless interface of the wireless-LAN conversion device 2 to the communication terminal 3 ′ via the wireless network 52. . And it transmits to the terminal device 4 by RS-232C from the radio | wireless interface of communication terminal 3 '. Further, transmission from the terminal device 4 to the server 1 is performed through the reverse route.

Next, in the communication between the server and the terminal device 4 in the above-described system, an operation when the terminal device 4 holds its own IP address will be described with reference to FIG. FIG. 9 is a schematic explanatory diagram illustrating communication when the terminal device holds an address.
As shown in FIG. 9, generally, in the network environment including the server 1, the IP address of the communication terminal 3 'directly connected to the network is preset in the server 1. In the example of FIG. 9, 192.168.1.1 is set in the server 1 as the IP address of the communication terminal 3 ′.

  However, the IP address of the communication terminal 3 ′ is often different from the IP address of the end device 4. For example, in FIG. 9, the IP address of the end device 4 is 172.16.1.1, and the IP address of the communication terminal 3 ′ is It does not match the address. In such a case, when the terminal device 4 tries to communicate with the server 1 using its own IP address as the source address, the server 1 cannot recognize the IP address and performs communication because the IP addresses do not match. I can't.

  Therefore, in order for the terminal device 4 and the server 1 to communicate, the terminal device 4 or the communication terminal 3 ′ replaces the IP address of the terminal device 4 with the IP address of the communication terminal 3 ′, and then transmits to the server 1. It was like that.

In some cases, the terminal device 4 holds a plurality of devices, and each device connects to a separate server for communication. Such a case will be described with reference to FIG. FIG. 10 is a schematic explanatory diagram when a plurality of devices are provided in a terminal device in a conventional data communication system.
As shown in FIG. 10, the terminal device 4 is provided with a plurality of devices (device 1 to device n) of devices 41-1 to 41-n. Since the conventional communication terminal 3 ′ has only one serial port, in order to communicate with the server for each device of the terminal device 4, the communication terminal 3 connected to each device in a one-to-one relationship. '-1 to 3'-n are required.

  Similarly to the above-described example, each of the communication terminals 3′-1 to 3′-n is assigned an individual IP address, and each of the devices 41-1 to 41-n is normally An IP address different from that of the connected communication terminal 3 'is held.

  In the case of the example shown in FIG. 10, when the server 1 communicates with the device 41-1 of the terminal device 4, the IP address (192.168.1.1) of the communication terminal 3-1 is specified as the transmission destination address. It is like that.

As a prior art of a system for performing communication between a terminal in a LAN and an external terminal on an external network, Japanese Patent Laid-Open No. 2005-20091 “Communication System and Transfer Server” (January 20, 2005) ( Applicant: Hitachi Kokusai Electric Inc., inventor: Shinya Kobayashi).
This prior art includes a transfer server that transfers application layer data of a VoIP packet to an internal terminal provided in the LAN when a VoIP packet is received from an external terminal, and can appropriately perform VoIP communication. Is.

Japanese Patent Laying-Open No. 2005-20091 (page 3-14)

  However, in the conventional data communication system, in order for the terminal device and the server to communicate, it is necessary to rewrite the IP address of the terminal device to the IP address of the communication terminal in the terminal device or the communication terminal. Has to be performed manually for each apparatus, and there is a problem that the work is complicated.

  Further, in the conventional data communication system, when there are a plurality of devices in the terminal device and each communicates with the server, a communication terminal must be provided for each device, and the data setting operation for each communication terminal is complicated. This is inconvenient, and the management of the IP address in the terminal device is complicated.

  The present invention has been made in view of the above circumstances, and the communication terminal can automatically perform setting of an IP address and connection control of a plurality of devices accompanying communication between a terminal device and a server, thereby reducing work complexity. An object of the present invention is to provide a data communication system that can be reduced to improve convenience and simplify the system.

  The present invention for solving the problems of the conventional example is connected to a plurality of servers provided on a LAN, a communication terminal connected to the LAN via a wireless network, and a different server via the communication terminal. A data communication system including a terminal device having a plurality of devices to be communicated, wherein a communication terminal includes a port connected to each of the plurality of devices on a one-to-one basis, and communicates with an IP address of each server on a LAN. A database that stores connection device information in which the port number of the terminal is associated; and a device selection server that reads the connection device information from the database in response to a request from the communication terminal and transmits the connection device information to the communication terminal. If the connected device information is not stored when the power is turned on, request the connected device information from the device selection server and select the device. The connection device information transmitted from the server is stored, and when a connection request from any server on the LAN to the terminal device is received, the server's IP address included in the connection request is read and the stored connection is stored. It is a communication terminal that outputs a connection request to a port having a port number corresponding to the read IP address with reference to the device information.

  According to the present invention, the communication terminal includes a port that is connected to each of the plurality of devices on a one-to-one basis, and the connection device information in which the IP address of each server is associated with the port number of the communication terminal on the LAN. And a device selection server that reads connection device information from the database and transmits it to the communication terminal in response to a request from the communication terminal, and the communication terminal does not store the connection device information when the power is turned on. Requesting connection device information from the device selection server, storing the connection device information transmitted from the device selection server, and receiving a connection request from any server on the LAN to the terminal device. Read the IP address of the included server, refer to the stored connection device information and match the read IP address. Since the data communication system outputs a connection request to the port with the port number to be connected, the connection device information for associating the device with the server can be automatically set in the communication terminal without any special operation. When a connection request is received from a device, a connection request is output to an appropriate device corresponding to the server, and a single communication terminal can securely connect a plurality of end device devices to separate servers, improving convenience. This has the effect of simplifying the system.

Embodiments of the present invention will be described with reference to the drawings.
The data communication system according to the present invention includes an IP grant server for assigning an IP address and a terminal management database for storing an IP address corresponding to a telephone number. The IP grant server requests the IP information, and the IP grant server reads the IP address corresponding to the phone number included in the request received from the terminal management database, and responds to the communication terminal to thereby send the IP address to the communication terminal. And the communication terminal rewrites the transmission destination IP address from its own IP address to the IP address of the end device for data received from the server, and transmits the transmission destination IP address for data received from the end device. The IP address of the server is rewritten to the IP address of the server and transmitted. And unnecessary operation of the data set of IP addresses to devices, is capable of improving the convenience.

  The data communication system according to the present invention is a system in which a terminal device includes a device connected to each of a plurality of servers, a communication terminal includes a plurality of device ports, and each device port is a device of the terminal device. And a server connection destination management database that stores connection port device port numbers (connection device information) corresponding to each server, and a device selector server that transmits connection device information in response to a request. The communication terminal requests connection device information from the device selector server when the power is turned on. The device selector server reads the connection device information from the server connection destination management database and responds to the communication terminal. Of the device port number corresponding to the server IP address A single communication terminal can connect a plurality of devices at the end device to the corresponding server without performing an operation for setting the association data between the server and the device. It is possible to improve convenience and simplify the system.

FIG. 1 is a configuration block diagram of a data communication system (first system) according to the first embodiment of the present invention. In addition, the same code | symbol is attached | subjected and demonstrated about the part which has the structure similar to FIG.
As shown in FIG. 1, the basic configuration of the first system is the same as that of the conventional data communication system shown in FIG. 7, and the server 1, the wireless-LAN converter 2, the communication terminal 3, A terminal device 4, the server 1 and the wireless-LAN conversion device 2 are connected via a LAN 51, the wireless-LAN conversion device 2 and a communication terminal 3 are connected via a wireless network 52, and the communication terminal 3 The terminal device 4 is connected by a serial cable 53.
Further, as a feature of this system, an IP grant server 6 is connected to the LAN 51, and the IP grant server 6 includes a terminal management database (terminal management DB) 7.

Each component will be specifically described.
The IP assigning server 6 which is a characteristic part of the first system assigns an IP address. When an IP address request including a telephone number is received from an arbitrary communication terminal 3, the IP management server 6 receives the request from the terminal management database 7. The IP address corresponding to the telephone number is read and transmitted to the communication terminal 3. Here, the IP assignment server 6 performs transmission / reception with the communication terminal 3 via the LAN 51, the wireless-LAN conversion device 2, and the wireless network 52.

  The terminal management database 7 stores a plurality of telephone numbers and IP addresses in association with each other. A set of a telephone number and an IP address is registered when the system is installed, but may be added or deleted as needed from an administrator terminal (not shown) or the like.

  The communication terminal 3 of the first system performs transmission / reception with the server 1 via the wireless network 52 as in the conventional communication terminal 3 ′. In the first system, transmission / reception with the IP grant server 6 is performed. Go and get a new IP address.

  The communication terminal 3 includes a control unit 31 that controls the entire communication terminal 3, a serial port 32 that is connected to the terminal device 4, a wireless module 33 that is connected to the wireless network 52 and performs transmission and reception, and its own telephone number and IP And a storage unit 34 for storing data such as addresses. In the storage unit 34, the IP address of the IP grant server 6 and its own telephone number are registered in advance, and data such as the IP address of the server 1 and the IP grant server 6 and the IP address of the terminal device 4 are stored. Yes.

  Furthermore, the communication terminal 3 of the first system accesses the control unit 31 to obtain the IP address by accessing the IP grant server 6 and receiving the IP address, and the IP address when the terminal device 4 and the server perform transmission / reception. IP rewriting means for rewriting.

The operation of the first system having the above configuration will be described with reference to FIG. FIG. 2 is a sequence diagram showing an operation when the communication terminal 3 acquires an IP address in the first system.
As shown in FIG. 2, when the communication terminal 3 is powered on, the IP acquisition unit of the control unit 31 of the communication terminal 3 determines whether or not its own IP address is stored in the storage unit 34, and stores it. If not, the telephone number stored in the storage unit 34 is read out, and an IP information request message (“IP information request” in the figure) is attached to the IP grant server 6 with its own telephone number. Send.

Upon receipt of the IP information request message, the IP grant server 6 accesses the terminal management database 7, reads the IP address corresponding to the telephone number received in the IP information request message from the terminal management database 7, and sends an IP information response It is transmitted to the communication terminal 3 as a message (“IP information response” in the figure).
Then, the communication terminal 3 stores the IP address received by the IP information response message in the storage unit 34. In this way, the operation at the time of IP address acquisition is performed. As a result, the communication terminal 3 itself automatically registers the IP address of the communication terminal that has been manually registered in the past, and the registration work can be eliminated.

Next, the IP address rewriting operation when the server 1 and the terminal device 4 communicate in the first system will be described with reference to FIG. FIG. 3 is a sequence diagram showing an IP address rewriting operation when the server 1 and the terminal device 4 communicate with each other in the first system.
As shown in FIG. 3, the IP address of the server 1 is 192.168.2.1, the IP address of the communication terminal 3 is 192.168.1.1, and the IP address of the end device is 172.16.1.1. When data is transmitted from the server 1 to the communication terminal 3, the server 1 writes its own IP address in the transmission source IP address and writes the IP address of the communication terminal 3 in the transmission destination IP address for transmission.

  When the IP rewriting means of the control unit 31 of the communication terminal 3 receives the data addressed to itself from the server 1, the end device 4 stored in the storage unit 34 stores its own IP address written in the destination IP address. The IP address is rewritten and transmitted to the end device 4.

  On the other hand, when data is transmitted from the terminal device 4 to the server 1, the terminal device 4 transmits its own IP address as the transmission source IP address and the IP address of the server 1 as the transmission destination IP address. To do.

When the IP rewriting means of the control unit 31 of the communication terminal 3 receives the data addressed to the server 1 from the terminal device 4, the IP address of the terminal device 4 written in the transmission source IP address is stored in the storage unit 34. It is rewritten to its own IP address and transmitted to the server 1.
As a result, the server 1 always performs transmission / reception with the communication terminal 3 in which the IP address is registered, and transmission / reception between the server 1 and the terminal device 4 is normally performed.

  According to the data communication system according to the first embodiment of the present invention, the IP grant server 6 for assigning an IP address in response to a request from the communication terminal, the telephone number and the IP address are stored in association with each other. The terminal management database 7 to be stored, and the communication terminal 3 determines whether or not its own IP address is stored when the power is turned on. An IP information request is transmitted with a telephone number attached, and the IP grant server 6 reads an IP address corresponding to the telephone number included in the received IP information request with reference to the terminal management database 7 as an IP information response. Since transmission to the communication terminal 3 is performed, an operation for setting an IP address in the communication terminal 3 is not required, and convenience can be improved and setting can be performed accurately. There is an effect that can.

  Further, according to the data communication system according to the first embodiment of the present invention, the communication terminal 3 to which the IP address is assigned ends the transmission destination IP address with respect to the data received from the server 1 from its own IP address. Since the IP address of the device 4 is rewritten and transmitted, and the data received from the terminal device 4 is transmitted by rewriting the source IP address from the IP address of the terminal device 4 to its own IP address, There is an effect that the rewriting is automatically performed and the server 1 and the terminal device 4 can communicate normally.

Next, a data communication system (second system) according to the second embodiment of the present invention will be described. FIG. 4 is a block diagram showing the configuration of the data communication system according to the second embodiment of the present invention.
As shown in FIG. 4, the basic configuration of the second system is substantially the same as that of the first system, but a plurality of servers 1-1 to 1-n, a wireless-LAN converter 2, and a LAN 51. And the wireless network 52, the communication terminal 3, and the terminal device 4, and as a feature of the second system, the device selector server 8 connected to the LAN 51, and the server connection destination management connected to the device selector server 8 And a database (server connection destination management DB) 9. Although not shown here, the IP grant server 6 and the terminal management database 7 described in the first system are provided on the LAN 51, and the same operation as in the first system is performed. Yes.

Each component will be specifically described.
In the second system, the terminal device 4 includes a plurality of devices 41-1 to 41-n, and each device 41-1 to 41-n communicates with a specific server 1-1 to 1-n. It has become.
The communication terminal 3 also includes a control unit 31 that controls the entire communication terminal 3, a wireless module 33 that performs transmission and reception with the wireless network 52, and a storage unit 34 that stores an IP address and connection device information described below. Further, as a feature of the second system, a plurality of serial ports 32-1 to 32-n are provided. Each serial port 32 is connected to the device 41 of the end device 4 in a one-to-one correspondence with a cable.

  The storage unit 34 of the communication terminal 3 stores in advance the IP address of the server connection destination management database 8 in addition to its own telephone number and the IP address of the terminal management database 6.

  In addition, as described later, the control unit 31 of the communication terminal 3 accesses the device selector server 8 to acquire the connected device information when the connected device information is not acquired, and the connected device information. And connection port selection means for connecting a connection request from the server 1 to an appropriate device. In addition, although description is abbreviate | omitted here, the control part 31 of the communication terminal 3 is provided with the same IP acquisition means and IP rewriting means as the communication terminal 3 in a 1st system.

  In response to a request from the communication terminal 3, the device selector server 8 connected to the LAN 51 receives device port number information (connection device information) for the terminal device 4 to connect to each of the servers 1-1 to 1-n. Is to provide. The device selector server 8 stores the IP address of the communication terminal 3 and performs transmission / reception with the communication terminal 3 via the LAN 51, the wireless-LAN conversion device 2, and the wireless network 52. The “device selection server” in the claims corresponds to the device selector server 8.

  In addition, the server connection destination management database 9 associates the IP address of each server 1 connected to the LAN 51 with the serial port (device port) 32 number of the communication terminal 3 corresponding thereto, as connection device information. It is something that is remembered. An example of data stored in the server connection destination management database 9 is shown in FIG. The data in the server connection destination management database 9 is normally registered at the time of system installation, but may be written and deleted as needed from an administrator terminal or the like (not shown). The “database” in the claims corresponds to the server connection destination management database 9.

Next, the operation in the second system will be described.
Although the description is omitted here, even in the second system, if the IP address is not stored when the communication terminal 3 is turned on, the communication terminal 3 accesses the IP grant server to obtain the IP address. It is supposed to be.

FIG. 5 is a sequence diagram showing an operation when the communication terminal 3 acquires device information in the second system.
As shown in FIG. 5, when power is turned on in the communication terminal 3, the device information acquisition unit of the control unit 31 of the communication terminal 3 refers to the storage unit 34 to determine whether the connected device information is stored. If the connection device information is not yet stored, a call is automatically made to the device selector server 8 and a connection device information request message (connection device information request in the figure) is transmitted to the device selector server 8.

  Upon receiving the device information request message, the device selector server 8 accesses the server connection destination management database 9 and stores the stored IP addresses of the servers 1-1 to 1-n and the serial numbers of the communication terminals 3 corresponding thereto. Data of the table in which the port 32 number is described is returned to the communication terminal 3 as connection device information. Note that the “device port number” in the table of FIG. 5 is an identification number of the serial port 32, and is indicated by a suffix (−1, −2,... -N) of the serial port 32 in FIG. Number. The communication terminal 3 that has received the connection device information stores the connection device information in the storage unit 34. In this way, the connection device information is acquired by the communication terminal 3.

Next, the operation when an arbitrary server 1 and the terminal device 4 communicate in the second system will be described with reference to FIG. FIG. 6 is a sequence diagram showing an operation when an arbitrary server 1 and a terminal device 4 are connected in the second system.
Through the above-described operation, the communication terminal 3 is connected to the storage unit 34 as connection device information to the IP address of the server 1-1 to server 1-n and the device of the terminal device 4 that is connected corresponding to each server. The device port number is stored.

  As shown in FIG. 6, when the server 1-1 (IP address 192.168.2.1) communicates with the terminal device 4, when the communication terminal 3 receives a connection request from the server 1-1, the connection of the control unit 31 is performed. The port selection unit reads the IP address of the transmission source server included in the connection request, refers to the connection device information stored in the storage unit 34, and specifies the device port number corresponding to the IP address of the server. Then, the control unit 31 transmits a connection request from the server 1-1 to the device 41-1 of the terminal device 4 via the serial port 32-1.

  In the terminal device 4, when the connection request from the server 1-1 is received by the device 41-1 via the serial port 32-1 of the communication terminal, the server 1- is connected from the device 41-1 via the communication terminal 3. Send a connection response to 1. Similar to the first system, the communication terminal 3 rewrites the source IP address with its own IP address and transmits a connection response to the server 1-1. When the connection response is received by the server 1-1, the server 1-1 and the terminal device 4 can communicate with each other.

  According to the data communication system (second system) according to the second embodiment of the present invention, the terminal device 4 is provided with a plurality of devices 41-1 to 41-n, each of which is a specific server 1- 1 to 1-n, a communication terminal 3 is provided with a plurality of serial ports 32-1 to 32-n, and each serial port 32-1 to 32-n is a device 41- of the terminal device 4. The serial port of the communication terminal 3 connected to the appropriate device 41 of the terminal device 4 corresponding to each IP address of the plurality of servers 1 while being connected to the 1 to 41-n one to one. A server connection destination management database 9 that stores the number of 32 as connection destination device information, and a device selector server 8 that reads out and sends out the connection device information from the server connection destination management database 9. In response to a request from the communication terminal 3, the connection destination device information is read from the server connection destination management database 9 and transmitted to the communication terminal 3, and the connection device information received by the communication terminal 3 is stored in the storage unit 34. Therefore, only one communication terminal 3 is conventionally provided for each of a plurality of devices, and the management of the IP address of the communication terminal 3 in the terminal device 4 is facilitated. It is not necessary to manually set the number of the serial port 32 for connecting to the device 41 of the appropriate terminal device 4 every 1 to 1-n, and there is an effect that convenience can be improved.

  Further, according to the data communication system according to the second embodiment of the present invention, when a call (connection request) is made from the server 1 to the terminal device 4, the control unit 31 of the communication terminal 3 performs the connection request. The serial port 32 corresponding to the IP address of the transmission source server 1 is identified by referring to the connection device information stored in the storage unit 34. Since the connection request is transmitted from the serial port 32, the serial port 32 connected to the appropriate device 41 for connecting the server 1 and the terminal device 4 is automatically set by one communication terminal 3. Thus, connection control of a plurality of devices can be performed by the communication terminal 3, and there is an effect that communication between the plurality of servers 1-1 to 1-n and the terminal device 4 can be realized smoothly.

  The present invention relates to a data communication system in which a terminal device is connected to a server on a LAN via a communication terminal on a wireless network, and performs a data setting operation on the communication terminal with one communication terminal. A plurality of devices provided in the apparatus can be respectively connected to a server, which is suitable for a data communication system capable of improving convenience and simplifying the system.

1 is a configuration block diagram of a data communication system (first system) according to a first embodiment of the present invention. It is a sequence diagram which shows operation | movement when the communication terminal 3 acquires an IP address in a 1st system. It is a sequence diagram which shows the operation | movement of IP address rewriting when the server 1 and the terminal device 4 communicate in a 1st system. It is a block diagram of the configuration of a data communication system (second system) according to a second embodiment of the present invention. It is a sequence diagram which shows operation | movement at the time of the communication terminal 3 acquiring device information in a 2nd system. It is a sequence diagram which shows operation | movement when the arbitrary servers 1 and the terminal device 4 in a 2nd system connect. It is a schematic block diagram of a general data communication system. It is explanatory drawing which shows an example of the protocol stack in a data communication system. It is a schematic explanatory drawing which shows communication when the terminal device hold | maintains an address. In the conventional data communication system, it is a schematic explanatory drawing in case a some apparatus is provided in the terminal device.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Server, 2 ... Wireless-LAN conversion apparatus, 3 ... Communication terminal, 31 ... Control part, 32 ... Serial port, 33 ... Wireless module, 34 ... Memory | storage part, 4 ... End device, 41 ... Device, 51 ... LAN, 52 ... Wireless network, 53 ... Serial cable, 6 ... IP grant server, 7 ... Terminal management database, 8 ... Device select server, 9 ... Server connection destination management database

Claims (1)

A data communication system comprising a plurality of servers provided on a LAN, a communication terminal connected to the LAN via a wireless network, and a terminal device having a plurality of devices connected to different servers via the communication terminal Because
The communication terminal includes a port connected to each of the plurality of devices on a one-to-one basis;
On the LAN,
A database that stores connection device information in which the IP address of each server and the port number of the communication terminal are associated with each other;
A device selection server that reads out the connected device information from the database in response to a request from the communication terminal and transmits it to the communication terminal;
If the communication terminal does not store the connection device information when the power is turned on, request the connection device information from the device selection server, store the connection device information transmitted from the device selection server, Upon receiving a connection request from any server on the LAN to the terminal device, the IP address of the server included in the connection request is read, and the read IP address is referenced with reference to the stored connection device information A data communication system that is a communication terminal that outputs the connection request to a port having a port number corresponding to.

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