KR100546023B1 - Communication method between network devices - Google Patents

Abstract

According to the present invention, a first network device that can access the Internet selects a port accessible to itself and requests a connection to a connection relay server, and the connection relay server connects to the first network device according to a connection request of the first network device. And a registration step of registering, by the first network device, its connection information determined in accordance with the connection attempt result of the connection relay server to the connection relay server.

A retrieval step of retrieving the first network device from the connection relay server by the second network device that has registered the connection information in the connection relay server according to the registration step, and obtaining the connection information of the first network device;

The second network device includes a connection step of exchanging data in connection with the first network according to a communication method determined according to its connection information and the connection information of the first network device. About

Network device, firewall, TCP, UDP, connection relay server

Description

Method for communicating between network devices

1 is a diagram illustrating various network environments to which the present invention is applied.

2 is a flowchart illustrating a step in which a network device to which the present invention is applied registers access information in a connection relay server.

3 is a diagram illustrating a connection state in which network devices to which the present invention is applied are configured.

4 to 12 are diagrams illustrating a connection method between network devices to which the present invention is applied.

The present invention relates to a method for communication between network devices existing under various network environments, and more particularly, to a communication method for enabling two-way communication between network devices including network devices inside a firewall or using private IP. will be.

Unicast network communication refers to a communication in which one transmitting network device transmits video and audio data for e-mail and video conferencing to another receiving network device in a 1: 1 manner on the Internet. The concept corresponds to the multicast scheme of simultaneously transmitting information to two or more other receiving network devices without sending information.

If the sending and receiving network devices have different public IP addresses, there is no problem with these unicast network communications if they know each other's IP addresses regardless of whether the public IP addresses of the sending and receiving network devices are fixed or dynamic IP addresses. There is no.

However, not only is it expensive for each network device to obtain one public IP address, but there are a lot of cases of companies building private networks recently due to security and other problems. As the use of various network-equipped products such as web pads, network cameras, VoIP phones, Internet refrigerators, digital TVs, and set-top boxes increases, cases of building home networks using home gateways such as IP routers are increasing rapidly.

In the case of such a private network or a home network, a single public IP address is allocated to be shared by multiple network devices. In order to share a public IP address among multiple network devices and access an external network, a gateway (or a router or a gateway) is used. Collectively), and the network address port translation (NAT) technology is applied to these gateways.

According to this NAT technology, when there is a packet outgoing from inside the private network, the gateway converts the private IP address and port of the network device that sends the packet to the public IP address assigned to it and an arbitrary port. Write to NAT table.

This NAT technology allows network devices inside a private network to connect to any device on an external network. However, it is impossible for a network device in an external network to connect to any device inside the private network. Because in order to connect from external network to internal network, it is necessary to obtain information about private IP address and port of device in internal network by referring to NAT table recorded in gateway, but network device in internal network does not connect to external network. This is because such information is not recorded in the NAT table.

Even when operating a private network, in order to allow access from an external network, port forwarding can be performed at a gateway to access a network device having a specific private IP address. This is to route the packet to a network device with a specific private IP address inside. However, such port forwarding is possible only if the network administrator configures the function, and there are many security problems.

Also, in general homes and small offices, users connect to the Internet using xDSL modem or cable modem, and have been assigned a public IP address from the Internet service provider. In this case, the assigned floating IP address is used as the public IP address of the home network gateway. In addition, since the IP addresses of the network devices are assigned to the network devices in the home network through the DHCP function of the IP router or the gateway, the IP address of each network device may change every time it is connected to the network.

There are a number of conventional techniques proposed as a solution to these problems, and these techniques are not only to enable network communication in a specific case, but also have a problem in that the method is complicated and the efficiency of network communication is lowered.

In the case of JP 2002-44901, which uses a connection maintaining server called an AOIP server, any host computer A accesses an AOIP server, stores public access information (a public IP address and a port number), and continuously sends packets to the router. If the connection is maintained by updating the NAT table within the aging time, the external host computer B attempting to connect to the host computer A obtains the public connection information from the AOIP server and connects directly to the host computer A according to the connection information. I am doing it.

However, if there is a firewall that blocks access to the host computer A from the outside, such a connection method cannot be used. Because host computer A can make a TCP connection to the AOIP server through the firewall, but host computer B attempts to connect to host computer A, which has a different IP address than the AOIP server and the firewall does not allow, This is because the connection is blocked.

A network device with a private IP address and a network device with a public IP address communicate with each other by mapping an IP address (server-aware IP) extracted from a network socket and an IP address delivered directly from each host computer into a pair. In the case of Patent No. 392206, the IP information mapped to the server must be preserved at all times, so a large amount of storage device is required, and between a network device having a private IP address and a network device having a public IP address or a different private network. There was a disadvantage that only TCP connection was allowed by communication between network devices in the network. In addition, if only one of the network devices uses a private IP address, the communication load is increased because the server must continuously relay the communication between both network devices, and thus a large capacity server is required and communication efficiency is deteriorated.

The present invention has been made to solve the above problems, and communication between network devices regardless of the presence of a firewall (IP / IP address, public / private IP address) and the presence of a firewall under various network environments Its main purpose is to make it possible.

According to the present invention, when an arbitrary network device requests registration of its own information to the access relay server, the access relay server attempts to access the network device requesting registration again and verifies whether the access is possible in advance. Another object is to provide a proven connection method when accessing a computer.                         

The present invention provides a UDP connection in order to avoid overloading the network in a network communication that exchanges data with a small amount of packet loss while allowing a large amount of processing such as image data, and provides a TCP connection when the UDP connection is impossible. It is another object of the present invention to provide a communication method.

Hereinafter, a method for communication between network devices existing in various network environments according to the present invention will be described with reference to the accompanying drawings.

1 is a diagram illustrating various network environments to which the present invention is applied, and includes a conventional network device such as a desktop computer, a web pad, a VoIP phone, a network camera, and a gateway in various network environments such as a home network or a private network. Connection relay server is further provided to implement the technical idea of.

According to the present invention, a first network device and a second network device, which can be connected to the Internet, respectively set ports for waiting for UDP reception and TCP connection from the outside, and notify the connection relay server of the port number to connect to each network device. Requesting,
The connection relay server extracts the port number and IP address requested from the requested packet, sends a confirmation packet to each network device, and attempts a new connection. Each network device receives the confirmation packet from the connection relay server. Sends a registration request packet back to the access relay server, or each network device that does not receive an acknowledgment packet from the access relay server, requests the access relay server to send a confirmation packet by selecting a different protocol and port number. When the packet is received, the registration request packet is sent to the connection relay server again. If the acknowledgment packet from the connection relay server fails even with the protocol selected again, the registration request packet including information indicating that a connection is not possible by establishing a TCP connection with the connection relay server Maintaining a TCP connection while transmitting a message;
The connection relay server includes: a registration step of storing connection information of each network device according to contents of a registration request packet received from each network device;
A retrieval step of retrieving the first network device from the connection relay server by the second network device that has registered the connection information in the connection relay server according to the registration step, and obtaining the connection information of the first network device;
If the second network device searches for the first network device from the connection relay server and attempts to connect, the second network device relays the connection if both the UDP port and the TCP port are set to 0 in the connection information of the first network device. Requesting transmission of data to the first network device via the server; otherwise, requesting transmission of data directly to the first network device;
The first network device receiving the transmission request packet transmits data to the connection relay server when the UDP port and the TCP port are both set to 0 according to the connection information of the second network device stored in the transmission request packet. And sending the data to the second network device, otherwise, directly sending the data to the second network device, and the second network device receiving the data.

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The registration step as described above will be described according to one embodiment. In this embodiment, the first network device is set to be the network camera 1 connected to the private network 1 using the gateway as shown in FIG.

As shown in FIG. 1, the network camera 1 connected to the private network 1 using the gateway sets the TCP connection standby port (hereinafter referred to as TCP port) and UDP reception standby port (hereinafter referred to as UDP port) (step R10). A UDP or TCP connection request is made to the connection relay server via the gateway (step R20).

In the following description, a method of attempting a UDP connection first and then a TCP connection when the UDP connection is preferred is described. However, it does not matter even if the UDP connection is attempted first. Also, Network Camera 1 can select either TCP or UDP connection according to user's setting.

The network camera 1 transmits a specific packet including its identification ID to the connection relay server through a UDP socket, and the gateway sends a private IP address and a UDP port of the network camera 1 (for example, The private IP address is converted to 192.168.123.5, UDP port: 5050, and converted into a public IP address and a gateway access port (for example, public IP address is 211.104.124.158, port: 19144) in the NAT table. (Step R30), information about the public IP address and the gateway connection port (hereinafter referred to as a connection port) is transmitted to the connection relay server, and the connection relay server requests that the connection relay server be connected to the public IP address and the connection port. The access relay server sends a UDP acknowledgment packet to the gateway using the public IP address and access port of the UDP packet sent by the network camera 1, and the gateway sends a UDP acknowledgment packet to the network camera 1 based on the mapping information stored in the NAT table. do. Network camera 1 receives the UDP acknowledgment packet sent by the access relay server, and then sends a UDP registration request packet to the access relay server (step R40), and the connection relay server receives the public IP address existing at the head of the UDP registration request packet. Is registered as an IP address, a UDP port number, a connection port number, a TCP port number 0, and an identification ID included in a registration request packet.

At this time, the information of the network camera 1 registered in the access relay server includes the following contents.

      ID: Network Camera 1 MAC

       IP: 211.104.124.158

       TCP port: 0

       UDP port: 19194

Hereinafter, setting the UDP port or TCP port number to 0 means that the connection to the port is not possible.

Here, the identification ID of the network camera 1 may use an ID arbitrarily selected by the user as well as the MAC address or GUID of the own network interface card, and the identification ID is used when searching for the network camera 1 in the access relay server. Done. This identification ID need not necessarily be unique, and if it is unique then only one network camera 1 will be searched, otherwise other network devices with the same identification ID will be searched simultaneously. The user may select the desired network device appropriately by referring to the IP address.

When mapping information such as a NAT table should be stored in the gateway by using a UDP connection, it is preferable that the network camera 1 or the connection relay server send a dummy packet to the gateway within the aging time so that the mapping information is not deleted. In order to prevent the mapping information from being deleted, the gateway may be configured not to delete the mapping information of the network camera 1, or the first network camera may periodically access the connection relay server and update the registration information.

If the network camera 1 does not receive the UDP confirmation packet within a certain time period due to the firewall, etc., the UDP packet is sent to the connection relay server several times, requesting that the connection relay server send the UDP confirmation packet to the network camera 1, and continue to connect. If the UDP confirmation packet is not received from the relay server, the network camera 1 determines that the connection is not possible through the UDP connection method. Again, network camera 1 transmits a packet containing a request for the connection relay server to send a TCP confirmation packet to the TCP port of network camera 1 (step R50).

The connection relay server attempts a TCP connection to the transmitted IP address and connection port of the network camera 1. The network camera 1 using the public IP address receives the TCP confirmation packet from the access relay server, and requests the access relay server to register its information with the access relay server (step R60).

At this time, the information of the network camera 1 registered in the access relay server includes the following contents.

      ID: Network Camera 1 MAC

       Authorized IP: 211.104.124.158

       TCP port: 9090

       UDP port: 0

If the gateway is configured to forward port to network camera 1, external network devices can directly connect to network camera 1 using the information of network camera 1 registered in the access relay server.

If the network camera 1 does not receive the TCP connection request from the connection relay server within a certain time due to the presence of a firewall, the network camera 1 is again unable to receive UDP and the TCP connection itself to the connection relay server. A request to register is sent (step R70). At this time, the network camera 1 establishes and maintains a TCP connection to the connection relay server. Even if there is a firewall or a private IP address, it is already known that a TCP connection is possible in the case of first accessing from the inside through the relay of the inside of the firewall and the gateway. The connection relay server registers the information of network camera 1 and maintains the TCP connection.

At this time, the information of the network camera 1 registered in the connection relay server is as follows.

      ID: Network Camera 1 MAC

       Authorized IP: 211.104.124.158

       TCP port: 0

       UDP port: 0

On the other hand, when the network camera 1 has a public IP address, it is obvious that the connection can be made by providing a public IP address and a connection port to the access relay server. It does not matter whether the IP address of Network Camera 1 is a static IP address or a dynamic IP address. This is because the assigned IP address does not change when the network camera 1 is connected to the network and is waiting for a call from another network device even for a dynamic IP address.

On the other hand, the connection relay server has a public / fixed IP address, and is capable of TCP connection and UDP connection to respond to registration requests of various network devices, store connection information of the network devices, and to search requests of other network devices. In response, provide access information of the discovered network device.

Next, a connection step in which the second network device is connected to the first network device and exchanges data according to a communication method determined according to its connection information and the connection information of the first network device will be described.

More specifically, the connection step of the present invention includes the steps of requesting the first network device to transmit data to the IP address and port that the second network device can receive, and the first network device that is requested to transmit the data. It consists of sending data and receiving it by the second network.

More specifically, when the second network device attempts to connect by searching for the first network device from the access relay server, if both the UDP port and the TCP port of the connection information of the first network device are set to 0, Causing the second network device to request the transmission of the data to the first network device via the connection relay server; otherwise, requesting the transmission of the data directly to the first network device;

 The first network device receiving the transmission request packet transmits data to the connection relay server when the UDP port and the TCP port are both set to 0 according to the connection information of the second network device stored in the transmission request packet. Send the data to the second network device, otherwise, send the data directly to the second network device, and the second network device receives the data.

This will be described in more detail with reference to the drawings in accordance with an embodiment of the present invention.

In this embodiment, as shown in Fig. 1, a description will be given of a process in which desktop computer 3 connected to private network 2 receives image data from network camera 1 connected to private network 1. FIG. The first network device is network camera 1 connected to private network 1, and the second network device is desktop computer 3 connected to private network 2.

The desktop computer 3 connected to the private network 2 registers its connection information with the connection relay server in the same way as the network camera 1 registers itself with the connection relay server.

The desktop computer 3 and the network camera 1 are registered in the connection relay server in one of three states: UDP, TCP, and UDP / TCP. There is a case.

First, when both the desktop computer 3 and the network camera 1 can receive UDP (case 1), the communication is performed as follows (see FIG. 4). ① The desktop computer 3 searches for the network camera 1 to which the connection relay server connects using information such as an IP address or identification ID, and requests that the connection information of the network camera 1 be sent from the connection relay server. ② The connection relay server provides the desktop computer 3 with information about the public IP address and connection port of the network camera 1. At this time, the desktop computer 3 recognizes that the UDP port must be used to connect to the network camera 1 from the network camera 1 connection information registered as 19194 and the TCP port number is 0 as described above. do. Accordingly, ③ the desktop computer 3 requests the network camera 1 to send a UDP packet to itself, and ④ the network camera 1 responds to the request, thereby communicating UDP packets.

When the network camera 1 is capable of TCP connection only, and the desktop computer 3 is capable of UDP reception (case 2), the communication is performed as follows (see FIG. 5). ① The desktop computer 3 searches for the network camera 1 to which the connection relay server connects using information such as an IP address or identification ID, and requests that the connection information of the network camera 1 be sent from the connection relay server. ② The connection relay server provides the desktop computer 3 with information about the public IP address and connection port of the network camera 1. At this time, as shown above, the UDP port number is 0 and the TCP port number is 9090. From the connection information of the network camera 1, the desktop computer 3 recognizes that the TCP port must be used to access the network camera 1. . ③ The desktop computer 3 connects the network camera 1 to the TCP port first and sends a UDP packet to the desktop computer 3's UDP port. ④ The network camera 1 responds to the request from the desktop computer 3 to the desktop computer 3. By transmitting data, communication is made with each other. Since the network camera 1 can not receive the UDP packet but can transmit the UDP packet, the network camera 1 can transmit the UDP packet that the desktop computer 3 can receive.

Network camera 1 is not able to receive UDP connection as well as TCP connection, and desktop computer 3 can perform communication when UDP connection is available (case 3) as follows.

In the following drawings, a network camera 1 or a desktop computer 3 connected with a connection relay server and a dotted line indicates that a TCP connection is maintained with the connection relay server.

 ① The desktop computer 3 searches for the network camera 1 to which the connection relay server connects using information such as an IP address or identification ID, and requests that the connection information of the network camera 1 be sent from the connection relay server. ② The connection relay server judges that the desktop computer 3 cannot send a packet directly to the network camera 1 according to the connection information of the network camera 1 registered with the UDP port number 0 and the TCP port number 0. It sends 3 connection relay server's own connection information. (3) The desktop computer 3 recognizes that the connection relay server is the network camera 1 and requests to send a packet, but the request is actually sent to the connection relay server. ④ Upon receiving this request, the connection relay server notifies the network camera 1 of the registered connection information of the desktop computer 3 and requests the UDP packet to be sent to the desktop computer 3, and ⑤ the network camera 1 notifies from the connection relay server. Based on the connection information received, UDP packets are sent directly to the desktop computer 3.

Network camera 1 can receive UDP and desktop computer 3 can communicate only when TCP connection is available (case 4). (See Fig. 7) ① Desktop computer 3 is connected to the connection relay server. The network camera 1 which it connects to is searched using information such as an IP address or an identification ID, and a request is made to send the network camera 1 access information from the access relay server. ② The connection relay server provides the desktop computer 3 with information about the public IP address and connection port of the network camera 1. At this time, the UDP port number is 19194, and the TCP port number is 0, so that the desktop computer 3 recognizes that the UDP port must be used to access the network camera 1 from the connection information of the network camera 1. do. ③ The desktop computer 3 requests to connect to the TCP port of the desktop computer 3 while sending a UDP packet to the public IP address and connection port of the network camera 1, and the network camera 1 to the desktop computer 3 according to the request of the desktop computer 3. By connecting through TCP port, communication is established.

First, when both desktop computer 3 and network camera 1 can only connect to TCP from the outside (case 5), the communication method is as follows. (See Fig. 8) ① Desktop computer 3 connects itself to the connection relay server. Search for the network camera 1 using information such as an IP address or identification ID, and then obtain information on the authorized IP address and access port of the searched network camera 1. At this time, the desktop computer 3 recognizes that the TCP port must be used to access the network camera 1 from the connection information of the network camera 1 registered with the UDP port number as 0 and the TCP port number as 9090. do. Therefore, ③ desktop computer 3 connects to TCP port of network camera 1 and establishes TCP connection with network camera 1, and communication is performed in the form of exchanging TCP packets with each other.

Network camera 1 is not capable of TCP connection as well as TCP connection, and desktop computer 3 can perform communication when only TCP connection is available (case 6). (See Fig. 9) ① Desktop computer 3, the connection relay server searches for the network camera 1 to which it connects using information such as an IP address or an identification ID, and requests the connection relay server to send the connection information of the network camera 1. ② The connection relay server judges that the desktop computer 3 cannot send a packet directly to the network camera 1 according to the connection information of the network camera 1 registered with the UDP port number 0 and the TCP port number 0. It sends 3 connection relay server's own connection information. (3) The desktop computer 3 recognizes that the connection relay server is the network camera 1 and requests to send a packet, but the request is actually sent to the connection relay server. ④ Upon receiving such a request, the connection relay server notifies the network camera 1 of the registered connection information of the desktop computer 3 and sends a TCP packet to the desktop computer 3. The network camera 1 notifies the relay server from the relay server. Based on the connection information received, a TCP connection is attempted to the desktop computer 3 and a TCP packet is sent directly.

If Network Camera 1 is able to receive UDP and Desktop Computer 3 is unable to receive both UDP and UDP connections as well (case 7), the communication can be performed as follows. (See Fig. 10) ① Desktop Computer 3 In the connection relay server, the network camera 1 to which it connects is searched using information such as an IP address or an identification ID, and requests to send the connection information of the network camera 1 from the connection relay server. ② The connection relay server provides the desktop computer 3 with information about the public IP address and connection port of the network camera 1. At this time, the desktop computer 3 recognizes that the UDP port should be used to connect to the network camera 1 from the connection information of the network camera 1 registered as 19194 and the TCP port number is 0 as described above. . ③ The desktop computer 3 sends a UDP packet to the public IP address and connection port of the network camera 1 and requests that the data be sent to itself via the connection relay server. ④ The network camera 1 sends the requested data to the connection relay server and requests that the data be relayed to the desktop computer 3. ⑤ The connection relay server sends the data received from the network camera 1 to the desktop computer 3 through the TCP connection established with the desktop computer 3.

When network camera 1 is able to connect to TCP and desktop computer 3 is not able to receive both TCP connection and UDP connection (case 8), communication is performed as follows (see Fig. 11). The connection relay server searches for the network camera 1 to which it connects using information such as an IP address or an identification ID, and requests the connection relay server to send the connection information of the network camera 1. ② The connection relay server provides the desktop computer 3 with information about the public IP address and connection port of the network camera 1. At this time, as shown above, the UDP port number is 0 and the TCP port number is 9090. From the connection information of the network camera 1, the desktop computer 3 recognizes that the TCP port must be used to access the network camera 1. . ③ The desktop computer 3 connects to the TCP port of the network camera 1, and the network camera 1 permits this connection so that communication between the TCP packets is performed.

If network camera 1 and desktop computer 3 are not able to receive TCP connection as well as UDP connection (in case 9), communication is performed as follows. (See Fig. 12.) The network camera 1 to be accessed is searched using information such as an IP address or an identification ID, and a request is made to send the connection information of the network camera 1 from the connection relay server. ② The connection relay server judges that the desktop computer 3 cannot send a packet directly to the network camera 1 according to the connection information of the network camera 1 registered with the UDP port number 0 and the TCP port number 0. It sends 3 connection relay server's own connection information. (3) The desktop computer 3 recognizes that the connection relay server is the network camera 1 and requests to send a packet, but the request is actually sent to the connection relay server. ④ The connection relay server receiving such a request requests network camera 1 to send a packet to the connection relay server. ⑤ When network camera 1 sends a packet to the connection relay server, ⑥ the connection relay server sends the received packet to the desktop computer 3. By sending a message, the desktop computer 3 receives a packet from the network camera 1.

Through the present invention having the configuration as described above can be applied to monitor the status of their home or office at a remote location using a network camera. In addition, the network device 2 may receive data from the plurality of network devices 1 by setting a receivable IP address and a plurality of identification IDs and ports, in which case the present invention can be used in buildings or security fields.

However, the data exchanged through the present invention is not limited to the image data of the above embodiment, and all data types applying the Internet can be exchanged between network devices through the present invention and include instructions for receiving network devices in packets. can do.

Therefore, it may be variously applied to P2P applications such as video medical care, Internet telephony and messenger.

When searching for a network device in the access relay server, a security device such as searching only a limited network device according to login information may be configured together.

As described above with reference to the preferred embodiment of the present invention, the scope of protection of the present invention is not limited to the above embodiment, it should be determined by the matter described in the claims.

According to the present invention, the following effects can be obtained in addition to achieving the above object of the present invention.

According to the present invention, the access relay server registers the access information after confirming whether the access relay server can be connected according to its access information. Therefore, the registered network device can be connected in any case.

In addition, according to the present invention, in most cases, since data is directly transmitted between network devices, the load of the connection relay server of the connection relay server can be reduced and the transmission efficiency can be increased.

According to the present invention, it is possible to save the storage capacity of the connection relay server because only the minimum connection information that can be received by the connection relay server is stored.

Claims (6)

delete delete delete Setting up ports for UDP reception and TCP connection from the outside, respectively, for the first network device and the second network device that can access the Internet, and notifying the connection relay server of the port number to request access to each network device; ,  The connection relay server extracts the port number and IP address requested from the requested packet, sends a confirmation packet to each network device, and attempts a new connection. Each network device receives the confirmation packet from the connection relay server. Sends a registration request packet back to the access relay server, or each network device that does not receive an acknowledgment packet from the access relay server, requests the access relay server to send a confirmation packet by selecting a different protocol and port number. When the packet is received, the registration request packet is sent to the connection relay server again. If the acknowledgment packet from the connection relay server fails even with the protocol selected again, the registration request packet including information indicating that a connection is not possible by establishing a TCP connection with the connection relay server. Maintaining a TCP connection while transmitting a message; The connection relay server includes: a registration step of storing connection information of each network device according to contents of a registration request packet received from each network device; A retrieval step of retrieving the first network device from the connection relay server by the second network device that has registered the connection information in the connection relay server according to the registration step, and obtaining the connection information of the first network device; If the second network device searches for the first network device from the connection relay server and attempts to connect, the second network device relays the connection if both the UDP port and the TCP port are set to 0 in the connection information of the first network device. Requesting transmission of data to the first network device via the server; otherwise, requesting transmission of data directly to the first network device;  The first network device receiving the transmission request packet transmits data to the connection relay server when the UDP port and the TCP port are both set to 0 according to the connection information of the second network device stored in the transmission request packet. And a connection step of sending and sending data to the second network device, or otherwise transmitting data directly to the second network device and receiving the second network device. The network device of claim 4, wherein the second network device registers a receivable IP address, a plurality of identification IDs, and ports in the access relay server, and receives data from the plurality of first network devices, respectively. Communication method. The method of claim 4 or 5, wherein when the first network device or the second network device accesses the Internet through a gateway to receive a UDP packet, sending a dummy packet to the gateway so that the NAT table is not deleted. Communication method between the network device further comprises.

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