JPH10285247A - Data communication equipment and communication terminal equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable normal communication even when only an IP address is assigned to a terminal and to simultaneously reduce the scale of a communication terminal connecting equipment. SOLUTION: Data from a CATV network 2 is provided with a communication terminal 13 with a transmission medium connecting part 15 and a communication terminal connecting part 16. The transmitted data is fetched in a communication terminal connecting equipment connecting part 25 with a communication line 14 and an identifier included in the data is detected by an identifier detecting part 21. An IP address of, for example, a server to be communicated by communication terminal connecting equipment 12 is held by an identifier holding part 30 and an original address of received data is judged by comparing the detected identifier and the IP address held in the identifier holding part 30 by an identifier comparing part 29. When the original address is the communication terminal connecting equipment 12, the data is returned to the communication terminal connecting equipment 12 by a route switching part 28. Consequently, communication to the communication terminal connecting equipment 12 and a communication terminal 13 is enabled by each server.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a data communication device and a communication terminal device suitable for a cable modem for performing communication using an existing CATV network.

[0002]

2. Description of the Related Art In recent years, CATV (cable television) using a coaxial cable, an optical fiber cable, or the like as a transmission path has become widespread. Paying attention to the large capacity and bidirectionality of CATV, the use of CATV for multimedia has recently been considered. In addition, CATV has been increased in scale and number of channels, and the CTAV network can be effectively used as a transmission path in a multimedia communication system such as the Internet.
A data communication system using a network is being constructed.

In a LAN (local area network) type data communication service system, each terminal is provided with a personal computer (hereinafter, also referred to as a PC) or a workstation as a communication terminal device in addition to a general CATV broadcast receiver. (Hereinafter, also referred to as WS), and the communication terminal device and the CATV network are connected by a cable modem (hereinafter, also referred to as CM) which is a communication terminal connection device.

[0004] The CM and the PC are connected via a communication line such as Ethernet (registered trademark). CM is CAT
The signal form between data flowing on the V network and data flowing on the Ethernet is converted. By the way, transmission data is encrypted on the Internet for security maintenance. When this encryption process is performed on a PC,
The burden on the PC increases. Therefore, a system for performing such encryption and decryption processing in a CM has been developed.

That is, in this case, the cable modem itself connecting the PC to the CATV network becomes one client on the network, like the PC or the like. With this, CM
Can independently communicate with each server on the backbone connected to the CATV network, and can perform encryption and decryption of data to be transmitted and received, and download control software for the cable modem.

FIG. 4 is a block diagram showing a conventional data communication device in which a communication terminal connection device such as a cable modem is configured as one client on a network.

A communication terminal connecting device 1 such as a cable modem is connected to a CATV network 2 such as HFC (Hybrid Fiber and Coaxial).
It is connected to the. When the communication network connection unit 3 of the communication terminal connection device 1 captures data addressed to the communication terminal device 6 from the CATV network 2, it transmits this data to the communication terminal device 6 via the communication terminal connection unit 4. The communication terminal connection unit 4 of the communication terminal connection device 1 and the CM device connection unit 7 of the communication terminal device 6
For example, data is transmitted and received via a communication line 9 such as an Ethernet cable.

The communication terminal device 6 processes the data received via the CM device connection unit 7 in the communication processing unit 8 and transmits the transmission data from the communication processing unit 8 via the CM device connection unit 7 to the communication terminal device. Output to device 1.

The communication terminal connection device 1 includes a communication terminal connection unit 4
The transmission data received from the communication terminal device 6 via the communication network unit 3 is transmitted to the CATV network 2 via the communication network connection unit 3. When data input via the CATV network 2 is encrypted, the communication network connection unit 3 performs the decryption processing. The communication network connection unit 3 can also output the data to the CATV network 2 after encrypting the data to be transmitted.

Further, when the communication terminal connecting device 1 receives data addressed to the communication terminal connecting device 1 itself via the CATV network 2 at the communication network connecting portion 3, the received data is processed by the information processing portion 5. Together with the information processing unit 5
Is transmitted to the CATV network 2 via the communication network connection unit 3.

By the way, in order for a PC provided in a terminal on a network to be recognized as one client on the network, the PC must use an identifier (for example, I
P address). When the cable modem is simply used for packet conversion between the CATV network and the PC, the cable modem is recognized as a part of the function of the PC on the network, so that the terminal only needs to set one identifier for the PC.

However, as shown in the example of FIG. 4, when the cable modem not only has a packet exchange function between the CATV network and the PC but also communicates as one client on the network, Cable modems also need to be assigned an identifier on the network. That is, in this case, in order to connect one PC to the network and operate it, a communication terminal connection device such as a cable modem and a communication terminal device such as a PC require two identifiers on the network. . In addition, the cable modem needs to have a function of communicating with a server on the network, and the structure of the cable modem device is complicated.

[0013]

As described above, conventionally, it is necessary to assign an identifier on the network to both the communication terminal connecting device and the communication terminal device used in the data communication system, and the identifier tends to be exhausted. There was a problem. There is also a problem that the structure of the communication terminal connection device becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and a communication terminal connection device and a communication terminal device each perform communication as one client on a network only by assigning one identifier to one terminal. It is an object of the present invention to provide a data communication device and a communication terminal device capable of performing the above.

[0015]

According to a first aspect of the present invention, there is provided a data communication device comprising a communication terminal connecting device and a communication terminal device connected by a predetermined communication line. The connection device is set to a predetermined identifier of a network layer, performs an interface process between a predetermined transmission medium and the predetermined communication line, and performs data communication between the predetermined transmission medium and the communication terminal device. The communication terminal device is set to the same network layer identifier as the communication terminal connection device, and returns the information transferred by the transfer device to the communication terminal connection device. Based on the identifiers of the layers above the network layer included in the information transferred by the transfer unit, and transmitted through the predetermined transmission medium. Determination means for determining the destination of the report, and a path switching means for switching whether or not the information transferred by the transfer means is returned by the return means based on the determination result of the determination means, The communication terminal device according to claim 6 of the present invention is connected to a predetermined transmission medium by a communication terminal connection device,
The communication terminal device is set to the same network layer identifier as the communication terminal connection device, and is capable of returning information from the communication terminal connection device to the communication terminal connection device. Determining means for determining the destination of the information transmitted via the predetermined transmission medium, based on the identifier of the network layer or higher included in the information from the terminal connection device, and based on the determination result of the determining means Path switching means for switching whether or not information from the communication terminal connection device is returned by the return means.

In the first aspect of the present invention, the transfer means includes:
Information is transmitted and received between a predetermined transmission medium and a predetermined communication line, and communication between the predetermined transmission medium and the communication terminal device is enabled. The determining means determines whether the transmitted information is destined for the communication terminal connection device or the communication terminal device based on the identifier of the layer above the network layer included in the information transmitted via the communication line. judge. If the determination result indicates that the destination of the transmitted information is the communication terminal connection device, the path switching unit controls the return unit to return the transferred information to the communication terminal connection device. Let it.

In a sixth aspect of the present invention, the determining means comprises:
Based on the identifier of the layer above the network layer included in the information from the communication terminal connection device, it is determined whether this information is intended for the communication terminal connection device or the communication terminal device. If the determination result indicates that the destination is the communication terminal connection device, the path switching unit causes the return unit to return the information to the communication terminal connection device.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of a data communication device according to the present invention.

The data communication device 11 includes a communication terminal connection device 12
And the communication terminal device 13. The communication terminal connection device 12 and the communication terminal device 13 are connected to each other by a communication line 14, such as Ethernet. The communication terminal connection device 12 can be constituted by, for example, a cable modem (CM), and the communication terminal device 13 can be constituted by, for example, a PC or WS.

FIG. 2 is an explanatory diagram showing a data communication system in which a data communication apparatus according to the present embodiment is constituted by CM, PC, and WS, and uses a CATV network as a transmission medium.

In FIG. 2, the data communication device of each terminal is constituted by a CM 35, a PC, and a WS 36 which constitute the communication terminal connection device 12 and the communication terminal device 13. P
C and WS 36 are connected to the CATV network 2 via the CM 35. As the CATV network 2, an HFC or the like that performs transmission using an optical fiber and a coaxial cable is used. CATV
The network 2 is connected to a network such as the Internet via a cable modem management device 37.

The CM 35 of each terminal is centrally managed by a cable modem management device 37 configured as a part of a head end. The cable modem management device 37 is a CATV network 2
Is connected to the CM 35 of each terminal via the Internet, and is also connected to a backbone network line 38 such as the Internet, and enables data transmission between each terminal and the backbone via the CATV network 2 and the network line 38. .

The backbone network line 38 includes:
For example, security server 39, DHCP (Dynamic Ho
st Configuration Protocol) server 40 and TFTP (T
rivial File Transfer Protocol) server 41 and the like.

For example, the communication protocol for data transmission over the CATV network 2 includes TCP / IP (Transmission Control Pro
tocol / Internet Protocol), CM35 and P
Ethernet is adopted as a communication protocol for data transmission between C and WS36.

By the way, in TCP / IP, any transmission medium can be used. This is TC
This is because P / IP uses a logical address (IP address) which is an identifier independent of the transmission medium. TCP / I
P relays based on the IP address in the network layer of the OSI (Open System Interconnection) reference model. On the other hand, in the data link layer below the network layer, a physical address (MAC) depending on each transmission medium, such as an ID of an Ethernet card, is used.
(Medium Access Control) address).

The physical layer and the data link layer provide a packet transfer function between hosts connected to the same transmission medium. The network layer (Internet layer in TCP / IP) provides a function of relaying a packet from a transfer source to a transfer destination. The data link layer is used for relaying packets in the network layer.

That is, in the transmission source network layer, an IP address indicating the transmission source and the transmission destination is added to the transmission data and given to the link layer, and in the link layer, a MAC address corresponding to the IP address is added. The link layer on the receiving side ignores the IP address and determines whether or not the data is transferred from the MAC address to itself. The link layer on the receiving side deletes the MAC address from the received data addressed to itself and gives it to the network layer.

In the present embodiment, each terminal connected to the CATV network 2 is assigned only one IP address as an identifier. That is, the same IP address is set for the communication terminal connecting device 12 and the communication terminal device 13 in the same terminal. Further, in the present embodiment, each server in the backbone uses the physical address of the communication terminal device 13 when transmitting data to the communication terminal connection device 12 and the communication terminal device 13 in the same terminal. . Therefore, the IP address and the physical address specified as the transmission destination are the same for the data from each server in the backbone to the communication terminal connection device 12 and the communication terminal device 13 in the same terminal.

In FIG. 1, the CATV network 2 is connected to a transmission medium connection unit 15 of the communication terminal connection device 12. The transmission medium connection unit 15 is a part that interfaces data transmitted through the CATV network 2 with data to be processed in the communication terminal connection device 12. In the present embodiment, the transmission medium connection unit 15 does not perform logical processing in the physical layer and the data link layer, and the CATV network 2 and the communication terminal connection device 12 do not perform logical processing.
Only the conversion of the electrical transmission form with the internal bus (not shown) is performed. The transmission medium connection unit 15 supplies data transmitted via the CATV network 2 to the communication terminal connection unit 16 and sends data from the path switching unit 17 to the CATV network 2.

The communication terminal connection section 16 is designed to perform data transmission with the communication terminal device 13 via the communication line 14. In the present embodiment, the data transmitted via the CATV network 2 can be transmitted regardless of whether the destination is the communication terminal connection device 12 or the communication terminal device 13.
Communication line via transmission medium connection unit 15 and communication terminal connection unit 16
The data is transmitted to the communication terminal device 13.

Communication terminal connection unit connection unit of communication terminal device 13
25 performs processing in the physical layer and the data link layer of the OSI reference model, and performs an interface between data transmitted via the communication line 14 and data processed in the communication terminal device 13. I have. The data received by the communication terminal connection device connection unit 25 is supplied to the identifier detection unit 27 and is also supplied to the information processing unit 31 via the path switching unit 28.

The functions of the communication terminal connecting device 12 and the communication terminal device 13 are different from each other. Thus, for example, these devices differ in the servers in the backbone that require communication. Also, the applications used in these devices are different from each other. So, for example,
The server in the backbone communicates with the communication terminal according to the IP address indicating the communication partner of the communication terminal connection device 12 and the communication terminal device 13 or the port number of the communication data thereof, that is, the identifier of the network layer or higher in the OSI reference model. It is possible to determine which of the connection device 12 and the communication terminal device 13 is the transmission partner.

The identifier holding unit 30 holds an identifier indicating that the communication destination of the server is the communication terminal connection device 12. For example, the identifier holding unit 30 holds the IP address of a server with which the communication terminal connection device 12 communicates. Further, for example, the identifier holding unit 30 holds a port number that is not normally used in the communication terminal device 13. In the case where the port number is stored in the identifier storage unit 30, the server stores the identifier number in the identifier storage unit 30 in order to be able to determine that the destination is the communication terminal connection device 12.
You need to specify the port number that is stored in.

The identifier detecting section 27 constituting the judging section 26 detects an IP address or a port number as an identifier from the data received by the communication terminal connecting apparatus connecting section 25 and outputs the same to the identifier comparing section 29. The identifier comparing unit 29 compares the detected identifier with the identifier held in the identifier holding unit 30 so that the received data is destined to the communication terminal connection device 12 or the communication terminal device 13. Is determined. For example, the identifier comparing unit 29 compares the IP address held in the identifier holding unit 30 with the source IP address included in the received data received by the communication terminal connection unit connection unit 25, so that the received data is It is determined whether the destination is the connection device 12. The determination result of the identifier comparing unit 29 is provided to the path switching unit 28.

When the identifier comparison unit 29 determines that the received data is destined for the communication terminal device 13, the path switching unit 28 supplies the output of the communication terminal connection device connection unit 25 to the information processing unit 31. If it is determined that the received data is destined for the communication terminal connection device 12, the reception data is supplied to the communication terminal connection device connection unit 25.

The information processing section 31 performs a predetermined process on the data received from the path switching section 28, creates predetermined transmission data, and outputs it to the communication terminal connection device connection section 25.

From the path switching unit 28 to the communication terminal connection unit connection unit
The data returned to 25, that is, the data determined to be destined for the communication terminal connection device 12 and the transmission data from the information processing unit 31 are transmitted from the communication terminal connection device connection unit 25 to the communication terminal connection via the communication line 14. It is supplied to the device 12. In the present embodiment, the communication terminal connection device connection unit
25, the data from the path switching unit 28 is added with the physical address of the communication terminal connection device 12 at the beginning and output to the communication line 14, and the data from the information processing unit 31 is output to the communication line 14 as it is. It has become.

The data from the communication terminal device 13 is supplied to the communication terminal connection unit 16 of the communication terminal connection device 12 via the communication line 14 and also to the identifier detection unit 20 constituting the determination unit 19. The communication terminal connecting unit 16 outputs the data received via the communication line 14 to the path switching unit 17. The identifier detector 20 detects the physical address of the data transmitted via the communication line 14 and outputs the physical address to the identifier comparator 24. The identifier holding unit 22 holds the physical address of the communication terminal connection device 12 itself.
The identifier comparing unit 21 compares the physical address detected by the identifier detecting unit 20 with the physical address held in the identifier holding unit 22, and determines that the destination of the data transmitted via the communication line 14 is the communication terminal connection device. 12 It is determined whether it is itself. The determination result of the identifier comparing unit 21 is provided to the path switching unit 17.

The route switching unit 17 determines, based on the determination result of the identifier comparison unit 21, that the data input via the communication line 14 is destined for the communication terminal connection device 12 itself. Is supplied to the information processing unit 18 from the communication terminal connection unit 16, and otherwise, the data from the communication terminal connection unit 16 is transmitted to the CATV network 2 via the transmission medium connection unit 15. I have. The information processing section 18 performs predetermined signal processing on the input data.

Next, the operation of the embodiment configured as described above will be described with reference to the explanatory diagram of FIG. FIG. 3 is an explanatory diagram for explaining the flow of data from the server on the backbone to the communication terminal connection device 12.

Now, in the identifier 30, the communication terminal connection device
The description will be made on the assumption that the IP address of the server 12 with which communication is performed is held. The server with which the communication terminal connection device 12 communicates among the servers in the backbone and the communication terminal device
13 is different from a server that communicates, for example, the communication terminal connection device 12 is a TFT that stores a file to be downloaded.
P server 41 and DHCP for assigning IP addresses
The communication terminal device 13 communicates with the server 40 and the like, for example,
It communicates with a WWW server or the like that holds various information.

First, a case where a data packet is transmitted from a server in the backbone will be described. When transmitting a data packet to the communication terminal connection device 12 or the communication terminal device 13, the server connected to the backbone uses the same IP as the destination address in the network layer in common for the communication terminal connection device 12 and the communication terminal device 13. An address is specified, and the IP address of each server is used as a source address. The physical address of the communication terminal device 13 is specified as the physical address.

Here, it is assumed that the WWW server on the backbone transmits data to the communication terminal device 13.
In this case, the WWW server uses the MAC address of the communication terminal device 13 as the destination address in the data link layer.
Specify an address. In addition, a common destination IP address is used for the communication terminal connection device 12 and the communication terminal device 13. That is, in the output data from the WWW server, the MAC addresses of the transmission source and the destination are arranged at the head, the IP addresses of the transmission source and the destination are arranged next, and the data is arranged at the end.

Data from the WWW server is transmitted to the CATV network 2
Is transmitted to the communication terminal connection device 12 via This data is received by the transmission medium connection unit 15, and the transmission form is converted. The transmission medium connection unit 15 outputs the received data to the communication terminal connection unit 16. The communication terminal connection unit 16 converts the input data into a transmission form of the communication line 14 and transfers the data to the communication terminal device 13.

Communication terminal connection unit connection unit of communication terminal device 13
25 receives data via the communication line 14. When detecting that the received data is data addressed to the communication terminal device 13 from the MAC address included in the received data, the communication terminal connection device connection unit 25 removes the MAC address portion and removes the MAC address.
Outputs address and data parts.

The identifier detection unit 27 is a communication terminal connection device connection unit.
25 detects the IP address of the received data and outputs it to the identifier comparing unit 29. The identifier holding unit 30 is a communication terminal connection device
12 holds the IP addresses of the TFTP server and DHCP server with which communication is performed. Since the detected IP address does not match the IP address stored in the identifier storage unit 30, the identifier comparison unit 29 determines that the received data is destined for the communication terminal device 13, and Control 28. Thereby, the communication terminal connection device connection unit
The output of 25 is supplied to the information processing section 31 via the path switching section 28. The information processing section 31 performs predetermined data processing using the received data.

Next, it is assumed that a TFTP server or a DHCP server transmits data to the communication terminal connection device 12. Even in this case, for the same terminal, the server uses the same IP address and physical address as the destination address when the communication terminal device 13 is used as the destination.

The data packet from the server is a CATV
The data is transmitted via the network 2 and is taken in the transmission medium connection unit 15 of the communication terminal connection device 12 as shown by an arrow A in FIG. The data packet is transmitted from the transmission medium connection unit 15 to the communication line 14 via the communication terminal connection unit 16 (arrow B in FIG. 3), and is received by the communication terminal connection unit connection unit 25 of the communication terminal device 13. Upon detecting that the received data is data destined for its own terminal from the MAC address included in the received data, the communication terminal connection device connection unit 25
The address part is removed and the IP address and the data part are output.

The identifier detecting section 27 detects the IP address included in the data received by the communication terminal connecting apparatus connecting section 25, and outputs it to the identifier comparing section 29. The identifier comparing unit 29 compares the source IP address included in the received data with the IP address held by the identifier holding unit 30. Since the identifier holding unit 30 holds the IP addresses of the TFTP server and the DHCP server, the identifier comparing unit 30
29 determines that the received data is originally destined for the communication terminal connection device 12, and returns the determination result to the path switching unit 28.
Output to

The path switching unit 28 is a communication terminal connection unit connection unit 25
Is returned to the communication terminal connection device connection unit 25. The communication terminal connection device connection unit 25 adds the MAC address of the communication terminal connection device 12 of the own terminal to the input data to reconfigure the data of the data link layer, and the communication terminal connection device 12 (arrow C in FIG. 3). Data from the communication line 14 is provided to the communication terminal connection unit 16 and the identifier detection unit 20.

The identifier detecting section 20 detects a physical address arranged at the head of the data input via the communication line 14 and gives the physical address to the identifier comparing section 21. The identifier comparing unit 21 detects whether the physical address indicates its own communication terminal connection device 12 by comparing it with the physical address stored in the identifier storing unit 22. In this way, the identifier comparison unit 21 determines that the data input via the communication line 14 indicates the communication terminal connection device 12 of the own device.
The data received by the communication terminal connection unit 16 is supplied to the information processing unit 18 by the path switching unit 17. The information processing section 18 performs predetermined signal processing on the input data.

Next, it is assumed that the communication terminal device 13 sends a data packet to a server on the backbone.
The communication terminal device 13 creates data addressed to, for example, a WWW server in the information processing section 31. This data is supplied to the communication terminal connection device connection unit 25, and the MAC address in the link layer is added before the IP address in the network layer. That is, the communication terminal connection device connection unit 25
Outputs data in which the source and destination MAC addresses and the source and destination IP addresses are arranged at the beginning. In this case, the destination MAC address and IP address indicate the WWW server.

The data packet transmitted from the communication terminal device 13 is input to the communication terminal connection unit 16 of the communication terminal connection device 12. The identifier detection unit 20 detects the MAC address arranged at the top of the data input via the communication line 14 and outputs the detected MAC address to the identifier comparison unit 21. The identifier comparison unit 21 determines whether the data input via the communication line 14 is the communication terminal of the own communication terminal by determining whether the MAC address detected by the identifier detection unit 20 matches the MAC address stored in the identifier storage unit 22. It is determined whether the data is addressed to the connection device 12.

In this case, the detected MAC address is different from the MAC address stored in the identifier storage unit 22, and the output of the communication terminal connection unit 16 is supplied to the transmission medium connection unit 15 via the path switching unit 17. You. The transmission medium connection unit 15 sends out the input data to the CATV network 2.

As described above, in this embodiment, the common IP address is used for the communication terminal connection device and the communication device, and the MAC address of the communication terminal device is always used for the server on the backbone. And
The server on the backbone recognizes the communication terminal connection device and the communication terminal device as one terminal device. Then, it is possible to determine whether the transmission destination is the communication terminal connection device or the communication terminal device by the identifier of the layer above the network layer and return the data addressed to the communication terminal connection device, Both the connection device and the communication terminal device can communicate with the server on the backbone. For this reason, as the communication terminal connection device, TC
It is not necessary to have a configuration corresponding to the P / IP protocol, and the software configuration of the communication terminal connection device can be significantly reduced.

[0056]

As described above, according to the present invention, 1
By allocating only one identifier to the terminal, the communication terminal connection device and the communication terminal device can each perform communication as one client on the network.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of a data communication device according to the present invention.

FIG. 2 shows a data communication device according to the present embodiment as a CM,
FIG. 1 is an explanatory diagram showing a data communication system constituted by PCs and WSs and using a CATV network as a transmission medium.

FIG. 3 shows a backbone server to a communication terminal connection device 12
FIG. 4 is an explanatory diagram for explaining a data flow destined for.

FIG. 4 is a block diagram showing a conventional data communication device in which a communication terminal connection device such as a cable modem is configured as one client on a network.

[Explanation of symbols]

11 data communication device, 12 communication terminal connection device, 13 communication terminal device, 14 communication line, 25 communication terminal connection device connection portion,
26: determination unit, 27: identifier detection unit, 28: path switching unit, 29 ...
Identifier comparison unit, 30 ... Identifier holding unit

Claims (6)

[Claims] 1. A data communication device comprising a communication terminal connection device and a communication terminal device connected by a predetermined communication line, wherein the communication terminal connection device is set to a predetermined identifier of a network layer, The communication terminal device includes a transfer unit that performs an interface process between a predetermined transmission medium and the predetermined communication line to enable data communication between the predetermined transmission medium and the communication terminal device. A return unit configured to be set to the same network layer identifier as the communication terminal connection device and capable of returning the information transferred by the transfer unit to the communication terminal connection device; and the information transferred by the transfer unit. Determining means for determining a destination of information transmitted through the predetermined transmission medium, based on an identifier of a network layer or a higher layer included in the determination means; The determination result data communication apparatus characterized by comprising a path switching means for switching whether to return by the returning means the information transferred by said transfer means on the basis of. 2. The communication device according to claim 1, wherein the determination unit is configured to detect an identifier of a layer above a network layer from the information transferred by the transfer unit; Identifier holding means for holding the identifiers of the layers above the layer, and determining the destination of the information transferred by the transfer means by comparing the identifier detected by the identifier detecting means with the identifier held by the identifier holding means. The data communication device according to claim 1, further comprising a comparison unit. 3. The data communication device according to claim 1, wherein the return unit adds an identifier of a physical layer of the communication terminal connection device to data returned to the communication terminal connection device. 4. The communication terminal connection device according to claim 3, wherein a destination of information transmitted from said communication terminal device via said communication line is determined by an identifier of a physical layer included in the information. A data communication device according to claim 1. 5. The data communication device according to claim 1, wherein the identifier of the layer above the network layer is a source address of the network layer or a port number of the transport layer. 6. A communication terminal device connected to a predetermined transmission medium by a communication terminal connection device, wherein said communication terminal device is set to the same network layer identifier as said communication terminal connection device, Return means capable of returning information from the terminal connection device to the communication terminal connection device, and the predetermined transmission medium based on an identifier of a network layer or higher included in the information from the communication terminal connection device. Determining means for determining the destination of the information transmitted via the control means, and path switching means for switching whether or not to return the information from the communication terminal connection device by the returning means based on the determination result of the determining means. A communication terminal device comprising: