JP2009188868A - Communication system, relay apparatus, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To allow both relay apparatuses to carry out band measurement processing while avoiding the adverse influence from being exerted upon data communication between the relay apparatuses, under the environment where communication addresses are dynamically assigned to the relay apparatuses facing each other with a communication network therebetween. <P>SOLUTION: Each of relay apparatuses connecting different LANs to a broadband network, respectively, is allowed to carry out processing, when a packet transmitted from the LAN under control of the relay apparatus to the other LAN is received, for transmitting a response request packet calling transmission of a response packet to a destination of the received packet and to carry out processing, when the packet received via the broadband network is a response request packet, for transmitting the response packet to a transmission source of the received packet. Each of relay apparatus receiving the response request packet or the response packet via the broadband network is allowed to acquire a transmission source address of the packet as a communication address of the opposite-side relay apparatus and to carry out band measurement processing. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to data communication via a communication network, and more particularly to a technique for operating a plurality of relay apparatuses in cooperation with each other.

  2. Description of the Related Art In recent years, various communication services such as IP (Internet Protocol) telephones and video streaming distribution are generally provided through a wide area network that can be freely used by an unspecified number of users such as the Internet. In order to use the communication service using a communication device connected to a LAN (Local Area Network) or the like, it is necessary to connect the LAN to a wide area network using a relay device such as a router. However, since the bandwidth that can be used in the wide area network is generally narrower than the bandwidth that can be used in the LAN, there is a case in which a problem such as a break in call voice or video may occur. Therefore, in order to avoid the occurrence of such a problem, there is a case where the relay apparatus located at the boundary between the LAN and the wide area network performs communication control called QoS (Quality of Service).

  QoS is a plurality of types of packets transmitted from a LAN to a wide area network having a narrower usable bandwidth than the LAN (for example, a packet containing audio data, a packet containing video data, a packet containing text data). Etc.) is assigned in advance with a priority according to the type, and a higher priority packet is assigned a sufficient bandwidth in the wide area network. In order to execute such QoS, it is necessary to measure the bandwidth that can be allocated to packet communication in a wide area network, and various techniques for enabling such measurement have been proposed (for example, non- Patent Document 1). In the technique disclosed in Non-Patent Document 1, a plurality of bandwidth measurement packets are connected to a wide area network with a plurality of bandwidth measuring packets in a first relay device that connects the data transmission side LAN to the wide area network. A process of transmitting to the second relay apparatus at a constant transmission interval is executed. On the other hand, the second relay device has a bandwidth that can be used in the wide area network based on a comparison between the reception intervals of the plurality of band measurement packets transmitted via the wide area network and the original transmission intervals. A process of calculating the width and notifying the calculation result to the first relay device is executed. Thereby, the measurement of the bandwidth that can be used in the wide area network is realized.

  By the way, like the bandwidth measurement technique disclosed in Non-Patent Document 1, the relay devices (the first relay device and the second relay device described above) that face each other across the wide area network on the data communication path are linked. When performing some processing, it is necessary to store one communication address in the other in advance in order to enable communication between these relay apparatuses. There is no particular problem when the communication address of each relay device is unchanged (that is, when a unique communication address is assigned to each relay device). For example, the IP address of the relay device is determined by IPCP (Internet Protocol Control Protocol) or the like. When communication addresses are dynamically allocated, one communication address cannot be stored in advance in the other, and it is difficult to execute some processing in cooperation with each of the relay devices. Note that it is possible to detect all the relay devices existing on the data communication path by causing the first relay device to execute the traceroute command. Of the relay devices detected in this way, Therefore, it takes a lot of labor to specify the relay device (that is, the second relay device) facing each other across the wide area network. Thus, various technologies have been proposed that make it possible to identify a relay device that faces each other across a wide area network even under a situation in which the communication address of the relay device is dynamically allocated. The disclosed technology may be mentioned.

In the technique disclosed in Patent Document 1, a relay device that transfers a packet adds history information including an identifier (for example, a communication address) indicating the relay device to the packet and performs the transfer. It is possible to track the transfer route of While applying the technology disclosed in Patent Document 1 to each relay device that connects the wide area network and the LAN, when sending packets received from the LAN side to the wide area network, the history information is added and transferred, When transferring a packet received from a wide area network to the LAN side, the history information is stored and then the history information is removed from the packet and transferred, and the communication address of the opposite relay device across the wide area network is stored in the history. A process of acquiring and storing the information is executed. In this way, it becomes possible to store the communication address of the other relay device in each of the relay devices facing each other via the wide area network.
Yamaha, Internet, [online], <URL: http: //www.rtpro.yamaha.co.jp/RT/docs/load-watch/index.html> JP 2007-28305 A

However, the technique disclosed in Patent Document 1 may adversely affect original data communication (for example, data communication related to IP phone communication or streaming distribution of video, etc.) performed via a wide area network. This is because, in the technique disclosed in Patent Document 1, a packet having a size larger than the original size is transmitted by adding history information, but the packet transmitted in the wide area network is transmitted. This is because, as the packet size increases, the packet transmission delay in the wide area network increases, and the possibility of packet loss due to the limitation of the MTU (Maximum Transmission Unit) on the route increases.
The present invention has been made in view of the above problems, and has an adverse effect on data communication between relay devices in an environment in which communication addresses are dynamically allocated to relay devices facing each other across a communication network. It is an object of the present invention to provide a technique that allows both relay apparatuses to execute cooperative processing while avoiding occurrence of the above-described problem.

  In order to solve the above problems, the present invention provides a first relay device that connects a first local area network to a wide area network, and a second local area network that is different from the first local area network. A second relay device connected to a network, wherein the first relay device transmits a packet transmitted to a communication device that is not a communication device in the first local area network. When received from the network, a response request packet for prompting transmission of a response packet is transmitted to the transmission destination of the received packet together with the received packet via the wide area network, and the second relay device When the response request packet is received via the wide area network, the response packet is transmitted to the transmission source of the response request packet On the other hand, when a packet that is not the response request packet is received via the wide area network, the received packet is transferred to the destination, and the first relay device is routed via the wide area network. The cooperative processing by communication with the transmission source of the response packet that is transmitted is executed, and the second relay device is caused to execute cooperative processing by communication with the transmission source of the response request packet. A communication system is provided.

  In such a communication system, the second relay device that has received the response request packet via the wide area network refers to the transmission source address of the response request packet, so that the relay device that is opposed across the wide area network (that is, , The communication address of the first relay device) is acquired, and a response packet is transmitted to the communication address. On the other hand, the first relay device that has received the response packet via the wide area network refers to the transmission source address of the response packet, thereby opposing the relay device across the wide area network (that is, the second relay device). Get the communication address. Then, both relay apparatuses communicate using the communication address of the opposite relay apparatus acquired as described above, and execute cooperative processing such as bandwidth measurement. In this communication system, since no modification is made to the packet related to the original data communication transmitted from one local area network to the other local area network through the wide area network, the data communication is adversely affected. There is nothing.

  In order to solve the above problem, the present invention includes a control unit, a first communication interface unit connected to a wide area network, and a second communication interface unit connected to a local area network, and the control A response request packet for prompting transmission of a response packet when the packet transmitted to a communication device in another local area network is received via the local area network, together with the received packet A first process for transmitting the received packet to the destination of the packet via the wide area network and a response request packet for prompting transmission of a response packet when the response request packet is received via the wide area network. A response packet is sent to the request packet source, while a packet that is not a response request packet is received via the wide area network. If a response request packet or a response packet is received via the wide area network, communication with the transmission source of the received packet is performed. And a relay apparatus that executes the third process performed in cooperation with each other, and a program that causes the computer apparatus to execute each of the above processes. As described above, the wide area network and the local area network are connected by the relay apparatus according to the present invention to construct the communication system, thereby enabling the relay apparatus to execute the cooperation process.

  In a more preferred aspect, the control unit of the relay device may execute the first process when the packet received via the local area network is a packet related to video or audio streaming distribution, The first process may be executed at regular time intervals. Each time a packet addressed to a communication device in another local area network is received, the first process and the second process are performed to transmit / receive the response request packet and the response packet. This is because there is a risk of using unnecessary communication bandwidth.

The best mode for carrying out the present invention will be described below.
(A: Configuration)
FIG. 1 is a block diagram illustrating a configuration example of a communication system 1 including a relay device according to an embodiment of the present invention. As shown in FIG. 1, the communication system 1 includes a server-side LAN 30 connected to a communication network 20 that is a wide area network such as the Internet, for example, via a relay device 10A, and a communication network 20 via a relay device 10B. The client-side LAN 40 is included. For example, a server device 31A and a server device 31B, which are computer devices such as personal computers, are connected to the server-side LAN 30, and a client device 41, which is also a computer device, is connected to the client-side LAN 40.

  A communication address is dynamically assigned to the relay device 10A and the relay device 10B by the above-described IPCP at the time of connection to the communication network 20. Each of the server devices 31A and 31B is assigned a unique communication address in advance, and an identifier (for example, a domain name) uniquely corresponding to the communication address is assigned in advance. For example, when the power is turned on, the client device 41 is dynamically assigned a communication address by a DHCP (Dynamic Host Configuration Protocol) server (not shown) connected to the client-side LAN 40. The client device 41 stores in advance an identifier that uniquely corresponds to the communication address of the server device 31A or the server device 31B. When requesting data transmission from the client device 41 to the server device 31A or the server device 31B and starting data communication, these identifiers are used for the server device 31A and the existing device such as DNS (Domain Name System). It converts into the communication address of the server apparatus 31B, and starts data communication using the communication address.

In the communication system 1 shown in FIG. 1, a predetermined communication protocol (for example, RTP (Real-time Transport) is transmitted from the server device 31A or the server device 31B.
Protocol)) is transmitted to the client device 41 through the relay device 10A, the communication network 20, and the relay device 10B in this order, and reaches the destination client device 41. Here, when different priorities are assigned to the packets transmitted from the server device 31A and the server device 31B, the above-described QoS is executed in the relay device 10A. As described above, in order to execute QoS, it is necessary to measure the bandwidth that can be used in the communication network 20, and in order to perform the bandwidth measurement, relay devices (see FIG. 1, it is necessary to store the other communication address in advance in each of the relay device 10A and the relay device 10B). On the other hand, in this embodiment, the other communication address is not stored in advance in each of the relay devices by causing the relay device 10A or the relay device 10B to execute processing that clearly shows the characteristics of the present invention. Also, it is possible to perform the band measurement. Hereinafter, the relay apparatus 10A and the relay apparatus 10B that clearly show the features of the present invention will be mainly described. Hereinafter, when there is no need to distinguish between the relay device 10A and the relay device 10B, they are referred to as “relay device 10”.

FIG. 2 is a block diagram illustrating a configuration example of the relay device 10.
As shown in FIG. 2, the relay device 10 includes a control unit 110, a first communication interface (hereinafter “I / F”) unit 120, a second communication I / F unit 130, a storage unit 140, and data between these components. A bus 150 that mediates transfer is included.

  The control unit 110 is, for example, a CPU (Central Processing Unit). The control unit 110 functions as a control center of the relay device 10 by executing a communication control program stored in the storage unit 140. Details of processing executed by the control unit 110 in accordance with the communication control program will be clarified later.

  The first communication I / F unit 120 and the second communication I / F unit 130 are both NICs (Network Interface Cards) and are connected to different communication networks. More specifically, the first communication I / F unit 120 is connected to the communication network 20, and the second communication I / F unit 130 is connected to the other communication network. For example, the second communication I / F unit 130 of the relay device 10A is connected to the server-side LAN 30, and the second communication I / F unit 130 of the relay device 10B is connected to the client-side LAN 40. Each of the first communication I / F unit 120 and the second communication I / F unit 130 delivers a packet received from the communication network to which the first communication I / F unit 120 is connected to the control unit 110, while each of the packets delivered from the control unit 110 To the communication network that is the connection destination.

  As illustrated in FIG. 2, the storage unit 140 includes a volatile storage unit 141 and a nonvolatile storage unit 142. The volatile storage unit 141 is, for example, a RAM (Random Access Memory), and is used as a work area when executing various programs. On the other hand, the nonvolatile storage unit 142 is a flash ROM (Flash Read Only Memory) or a hard disk. The non-volatile storage unit 142 stores data (not shown) such as a routing table used in a general relay device and a communication control program.

  As shown in FIG. 2, the processing executed by the control unit 110 according to the communication control program includes a transmission side control process 142S and a reception side control process 142R in addition to the band measurement process 142T for performing the band measurement described above. included. The transmission side control process 142S and the reception side control process 142R are processes for causing each of the relay apparatuses facing each other across the communication network 20 to notify the communication address of the own apparatus to the other. The transmission-side control process 142S is executed by a relay device that sends a packet to the communication network 20, and the reception-side control process 142R is executed by a relay device that receives a packet transmitted via the communication network 20. Is done. Hereinafter, taking the case where a packet is transmitted from the server-side LAN 30 to the client-side LAN 40 (that is, the case where the relay device 10A is a transmission-side relay device and the relay device 10B is a reception-side relay device), the transmission-side control is taken as an example. The process 142S and the receiving side control process 142R will be described in detail.

(B: transmission side control processing 142S)
The transmission-side control process 142S is executed in response to reception of a packet via the second communication I / F unit 130 (that is, reception of a packet from the LAN side). FIG. 3A is a flowchart showing the flow of the transmission side control process 142S. As shown in FIG. 3A, in the transmission-side control processing 142S, first, a packet received via the second communication I / F unit 130 is connected to the second communication I / F unit 130. A process (step S010) for determining whether the packet is transmitted to a communication device in another LAN different from the above (that is, a communication device connected to the other LAN) is executed. Here, whether or not the received packet is a packet transmitted to the communication device in the other LAN is determined by referring to the destination address written in the header portion of the packet. Just do it.

  When the determination result of step S010 is “Yes” (that is, when the packet is addressed to a communication device in another LAN), a special packet called a response request packet is generated, and the response request packet is set to the above-described response request packet. Processing for transmitting the received packet to the transmission destination via the communication network 20 (step S020) is executed. Here, the response request packet refers to a relay device (hereinafter referred to as a counter relay) facing the communication network 20 on the transfer path of a packet addressed to a communication device in another LAN received by the second communication I / F unit 130. It is a packet for prompting a response (transmission of a special packet called a response packet in this embodiment) to a device. In step S020, the destination address of the received packet is written in the destination address of the header part, the communication address assigned to the relay device is written in the source address of the header part, and the payload part is written. Creates a response request packet by writing the port number of the communication port that is the destination of the response packet (that is, the communication port when the response request packet source receives the response packet), and identifies the response request packet The process of transmitting to the communication port is executed. The communication port that is the transmission destination of the response request packet and the communication port that is the transmission destination of the response packet may be a specific communication port that is predetermined among communication ports other than the so-called well-known port. In step S030, which is executed subsequent to step S20, a process of transmitting the received packet to the transmission destination via the communication network 20 (that is, transferring to the destination) is executed.

  In step S020, the response request packet is sent to the destination of the received packet because the communication address of the opposite relay device is unknown at the time of execution of step S020, and the response request is sent to the opposite relay device. This is because packets cannot be transmitted directly. Although the response request packet cannot be directly transmitted to the counter relay device in this way, the response request packet is transmitted to the communication device in the LAN connected to the communication network 20 via the counter relay device. Then, since the response request packet always passes through the opposite relay device, the opposite relay device can receive the response request packet. If it is necessary to notify the opposite relay apparatus in advance about the transmission interval of the packet to be transmitted in the bandwidth measurement processing, data indicating the transmission interval may be written in the payload portion of the response request packet.

  The reason why the response request packet is transmitted to a specific communication port is to make the opposite relay device distinguish the response request packet from the packet related to the original data communication. In another preferable aspect, an identifier indicating that the packet is a response request packet is written in a predetermined area of the header portion, and whether or not the packet is a response request packet may be discriminated based on the presence or absence of the identifier. In short, any mode can be used as long as it can process the response request packet separately from the packet related to the original data communication in the opposite relay apparatus.

On the other hand, if the determination result in step S010 is “No”, as shown in FIG. 3A, the transmission side control process 142S is executed without executing the processes in steps S020 and S030. finish. This is because if communication is performed between communication devices in the LAN connected to the second communication I / F unit 130, it is not subject to QoS, so there is no need to perform bandwidth measurement and transmission of a response request packet is unnecessary. .
The above is the transmission-side control process 142S executed by the transmission-side relay device.

FIG. 4 is a diagram illustrating an example of a communication sequence in the communication system 1.
In the transmission-side control process 142S executed by the relay device 10A when a packet transmitted from the server device 31A to the server device 31B is received, both the server devices 31A and 31B are communication devices in the server-side LAN 30. Therefore, the determination result of step S010 is “No”, and the execution of the transmission side control process 142S is terminated without executing the processes of steps S020 and S030 described above. On the other hand, in the transmission side control process 142S executed by the relay apparatus 10A when a packet transmitted from the server apparatus 31B to the client apparatus 41 is received, the determination result of step S010 is “Yes”. Steps S020 and S030 are executed. Hereinafter, packets (packets and response request packets related to data communication between the server device 31B and the client device 41) sent from the relay device 10A to the communication network 20 are routed by the network device in the communication network 20, and the relay device 10B. To reach. Hereinafter, the reception-side control process 142R executed by the relay device 10B when these packets are received will be described.

(C: receiving side control processing 142R)
The reception-side control process 142R is executed in response to reception of a packet via the first communication I / F unit 120 (that is, reception of a packet from the communication network 20). FIG. 3B is a flowchart showing the flow of the reception-side control process 142R. As shown in FIG. 3B, in the receiving-side control process 142R, first, a process for determining whether or not the packet received via the first communication I / F unit 120 is a response request packet (step R010). ) Is executed. As described above, whether or not a packet received via the first communication I / F unit 120 is a response request packet is a packet transmitted to a predetermined communication port. This may be done by verifying whether or not.

  If the determination result in step R010 is “Yes” (that is, if the received packet is a response request packet), the received packet is analyzed and the source address is stored as the communication address of the opposite relay device. Processing (writing to the volatile storage unit 141), sending a response packet for notifying the opposite relay device of its own communication address to the opposite relay device, and discarding the response request packet (step R020) ) Is executed. Conversely, when the determination result in step R010 is “No” (that is, when the received packet is not a response request packet), the received packet is sent to the destination via the second communication I / F unit 130. The process of transferring to (step R030) is executed.

More specifically, in step R020, the communication address of the opposite relay device is written as the transmission destination address in the header portion of the response packet, and the communication address of the relay device is written as the transmission source address. Processing for transmitting to (the communication port indicated by the port number written in the payload portion of the response request packet) is executed.
The above is the reception-side control process 142R executed by the reception-side relay device.

  As shown in FIG. 4, in a situation where a response request packet transmitted from the relay apparatus 10A and a packet addressed to the client apparatus 41 related to the original data communication are transmitted via the communication network 20, these packets are When the relay device 10B receives, the response request is made after the communication address of the opposite relay device (that is, the relay device 10A) is stored and the response packet is transmitted to the opposite relay device by the process of R020. The packet is discarded, and the latter is transferred to its destination by the process of step R030. On the other hand, when receiving the response packet transmitted via the communication network 20, the relay device 10A acquires and stores the transmission source address of the response packet as the communication address of the opposite relay device (that is, the relay device 10B). . As a result, the other communication address is stored in each of the relay devices facing each other across the communication network 20, and the above-described band measurement process 142T can be executed.

  As described above, according to the present embodiment, even when a communication address is dynamically allocated to each of the relay devices facing each other across the communication network 20 (that is, the relay device 10A and the relay device 10B). In response to the relay of data communication between the server device 31A (or server device 31B) and the client device 41, each of the relay devices executes a process of notifying the communication address of the own device to the other, and causes the communication network 20 to Thus, the bandwidth allocated to the data communication can be measured. In addition, in this embodiment, since no modification is made to the packet related to the data communication between the server device 31A or the server device 31B and the client device 41, the data communication is not adversely affected. Also, in bandwidth measurement, it is generally known that the measurement result depends on the data size of the bandwidth measurement packet. Therefore, a bandwidth measurement packet having the same data size as the packet related to data communication is used. If used, bandwidth measurement can be performed more accurately than in the past.

(D: Other embodiments)
Although the embodiment of the present invention has been described above, it is needless to say that the embodiment may be modified as described below.
(1) In the above-described embodiment, the communication control process characteristic of the communication apparatus according to the present invention is realized by a software module. However, it may be realized by a hardware module.

(2) In the above-described embodiment, the transmission-side relay device executes the transmission-side control process 142S every time a packet is received from the LAN side. However, if response request packets and response packets are frequently transmitted and received, the communication band that can be used in the communication network 20 is compressed by the transmission of these packets, and there is a possibility that the original data communication is adversely affected. Therefore, when receiving and relaying a specific type of packet (for example, a packet indicating the start of data communication that requires QoS in particular) such as a VoIP packet or a packet requesting streaming delivery of video or the like. Only the transmission-side control process 142S may be executed. Further, the transmission side control process 142S may be executed at regular time intervals, and the transmission side control process 142S is executed when a specific type of packet is received and a predetermined time or more has elapsed since the previous execution point. You may make it do. Alternatively, the communication address of the opposite relay device that has been stored once may be deleted after a predetermined time has elapsed. In this way, the present invention can be applied even when the communication address of the opposing relay device changes within a short period of time or when there are a plurality of opposing relay devices.

(3) In the above-described embodiment, the band measurement process is described as an example of the process that is executed in cooperation with the relay apparatuses that are opposed to each other across the communication network 20. However, other processes may be used. is there. For example, when a packet requesting the start of streaming delivery of video or the like is relayed from a LAN to a wide area network, a setting change such as an increase in buffer size is urged from the transmission side relay device to the opposite relay device A control packet in which data or a command is written in the payload portion may be transmitted, and the opposite relay apparatus may be caused to change the setting according to the data or command stored in the control packet. In addition, when a packet transmitted to a destination that should not be accessed is relayed from the LAN to the wide area network, it is urged to suspend transfer of the packet from the transmitting relay device to the opposite relay device. It is also possible to transmit a control packet in which a command to this effect is written, and cause the opposite relay apparatus to execute the injunction process according to the control packet. According to such an aspect, it becomes possible to stop damage caused by spyware or computer viruses. In these aspects, the control packet and the response request packet are not transmitted separately, but the data and command are written in the payload portion of the response request packet, and the response request packet also serves as the control packet. May be.

(4) In the above-described embodiment, the communication control program for causing the control unit 110 to execute the communication control processing (reception side control processing 142R or transmission side control processing 142S) characteristic of the communication device according to the present invention is the relay device 10's. It was previously stored in the nonvolatile storage unit 142. However, the communication control program may be distributed by being written on a computer-readable recording medium such as a CD-ROM (Compact Disk-Read Only Memory), or the communication is performed by downloading via a telecommunication line such as the Internet. A control program may be distributed. The communication control program distributed in this way is installed in an existing relay device, and the control unit of the relay device is operated according to the communication control program. This is because the same function can be given.

It is a figure which shows the structural example of the communication system 1 containing the relay apparatus 10 which concerns on one Embodiment of this invention. 3 is a block diagram illustrating a configuration example of the relay device 10. FIG. It is a flowchart which shows each flow of the transmission side control process 142S and the reception side control process 142R which the control part 110 of the relay apparatus 10 performs according to a communication control program, respectively. 3 is a diagram showing an example of a communication sequence in the communication system 1. FIG.

Explanation of symbols

  10A, 10B, 10 ... Relay device, 20 ... Communication network, 30 ... Server side LAN, 31A, 31B, 31 ... Server device, 40 ... Client side LAN, 41 ... Client device, 110 ... Control unit, 120 ... First communication I / F unit, 130 ... second communication I / F unit, 140 ... storage unit, 141 ... nonvolatile storage unit, 142 ... volatile storage unit, 150 ... bus.

Claims (5)

A first relay device for connecting the first local area network to the wide area network;
A second relay device for connecting a second local area network different from the first local area network to the wide area network;
Including
The first relay device urges transmission of a response packet when a packet transmitted to a communication device that is not a communication device in the first local area network is received from the first local network. The response request packet is sent to the destination of the received packet together with the received packet via the wide area network,
When the second relay device receives the response request packet via the wide area network, the second relay device transmits the response packet to the transmission source of the response request packet, while the response device transmits the response packet via the wide area network. If a packet that is not a request packet is received, the received packet is forwarded to its destination,
The first relay device is caused to execute cooperation processing by communication with the transmission source of the response packet transmitted via the wide area network, and the second relay device is configured to transmit the response request packet. A communication system, characterized in that it performs cooperative processing by communication with the original. A control unit;
A first communication interface unit connected to the wide area network;
A second communication interface unit connected to the local area network;
With
The controller is
When a packet transmitted to a communication device in another local area network is received via the local area network, a response request packet for prompting transmission of a response packet is received together with the received packet. A first process for transmitting to the destination of the transmission via the wide area network;
When a response request packet for prompting transmission of a response packet is received via the wide area network, a response packet is transmitted to the transmission source of the received response request packet, while a packet that is not a response request packet is A second process of forwarding the received packet to its destination when received via a wide area network;
When a response request packet or a response packet is received via the wide area network, a third process performed in cooperation with the transmission source of the received packet is executed. The said control part performs a said 1st process, when the packet received via the local area network is a packet which concerns on a predetermined kind of data communication. The said 1st process is characterized by the above-mentioned. Relay device.   4. The relay device according to claim 2, wherein the control unit executes the first process at a constant time interval. 5. Computer equipment,
A response request for prompting transmission of a response packet when a packet transmitted to a communication device in another local area network connected to the wide area network together with the local area network is received via the local area network A first process for transmitting a packet to the destination of the received packet together with the received packet via the wide area network;
When a response request packet for prompting transmission of a response packet is received via the wide area network, a response packet is transmitted to the transmission source of the received response request packet, while a packet that is not a response request packet is A second process of forwarding the received packet to its destination when received via a wide area network;
When a response request packet or a response packet is received via the wide area network, a program is executed to execute a third process that is performed in cooperation with a transmission source of the received packet.

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