JP2005117587A - Communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To certainly realize P2P application even in connection environment using NAT function. <P>SOLUTION: The method is provided with a 1st step for transmitting two or more echo packets 51 from a host computer 11 to a router 13 in which setting value of TTL increases one by one from one, a 2nd step for responding to one out of a plurality of echo packets, receiving an echo packet 52 returned from the router 13, and extracting the setting value of the TTL for the returned echo packet 51, and a 3rd step for transmitting a port setting packet 53 making the TTL setting value to be α by adding 1 to the extracted setting value from the host computer 11 to the router 13. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a communication method, and more particularly to a communication method for performing P2P communication from a computer connected to a network device having a NAT function.

  In recent years, due to the increase in the number of host computers connected to the Internet, the problem of insufficient IP addresses has become prominent. Therefore, a NAT (Network Address Translator) function is used as one method for solving the shortage of IP addresses. The NAT function performs address conversion in order to perform communication between a host computer having a private address in a LAN, which is a closed network, and a host computer having a global address in the Internet.

  FIG. 1 shows a network connection diagram for explaining the NAT function. A private address A and a global address M are assigned to the host 11. The router 13 has a NAT function and stores a conversion table for converting a private address to a global address. Here, the IP packet is transmitted from the host 11 to the host 12 (global address N) in the Internet via the routers 13 and 14. In the header of the IP packet transmitted from the host 11, “N” is written as the destination address 21 and “A” is written as the source address 22, and “200” as the destination port number 23 is written in the TCP header or UDP header. “100” is written as the source port number 24. The router 13 refers to the conversion table, converts the private address A of the source address 22 to the global address M, and transmits the packet to the router 14.

  Next, an IP packet is transmitted from the host 12 to the host 11 via the routers 14 and 13. In the header of the IP packet transmitted from the host 12, "M" is written as the destination address 31, and "N" is written as the source address 32. In the TCP header or UDP header, "100" is set as the destination port number 33. “200” is written as the source port number 34. The router 13 refers to the conversion table, converts the global address M of the destination address 31 to the private address A, and transmits the packet toward the host 11 in the LAN.

  On the other hand, applications using P2P (peer to peer) type communication such as online games and video chat (hereinafter referred to as P2P applications) are increasing. P2P type communication directly communicates between terminals without going through a server. In order to use a P2P application in a connection environment using the NAT function, STUN (see Non-Patent Document 1, for example) technology that is a standard of IETF (Internet Engineering Task Force) is known.

REC3489 “STUN-Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs)” March 2003

  However, there is a problem that communication between terminals may not be possible even with the STUN technology. This is because the standard is not stipulated to the details, or the parts to be implemented differ depending on the router. A specific example will be described below.

  FIG. 2 shows a case where the block is performed by the ICMP packet. The host 11 sends a packet 41 to the host 12 with the port number “200” of the router 14 as the destination port number. At this time, if the router 14 does not use the port number “200”, an ICMP packet (destination unreachable message) 42 is returned to the router 13. When the router 13 receives the ICMP packet 42, the router 13 closes the port of the transmission source port number “100”. Therefore, even if the host 11 subsequently transmits the packet 43 toward the host 12, the router 13 does not accept the packet 43.

  In addition, the contents of the conversion table stored in the router are deleted when a certain time elapses after communication is interrupted. That is, the relationship between the destination address, the source address, the destination port number, and the source port number is cleared, and the router 13 does not accept packets with the same address and the same port number.

  Further, a router called a symmetric router changes its own port number, that is, the source port number every time the destination port number and the destination address change. Therefore, if a packet is transmitted to a different destination port number in the same session, the packet cannot be transmitted thereafter using the same source port number.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a communication method for reliably realizing a P2P application even in a connection environment using the NAT function. .

  In order to achieve such an object, the present invention provides a communication method for performing P2P type communication from a computer connected to a network device having a NAT function. A first step of transmitting a plurality of echo packets in which the TTL setting value is incremented by 1 to 1 to the network device; and an echo returned from the network device in response to one of the plurality of echo packets A second step of receiving a packet and the computer extracting a TTL setting value of the returned echo packet; and adding 1 to the extracted setting value from the computer to the network device. And a third step of transmitting a port setting packet with the determined value.

  According to a second aspect of the present invention, in the communication method according to the first aspect, a keep-alive packet in which a TTL setting value is added to the extracted setting value by 1 from the computer to the network device. The method further includes a fourth step of transmitting at regular intervals while communication is interrupted.

  According to a third aspect of the present invention, in a communication method for performing P2P communication from a computer connected to a network device having a NAT function, an echo packet is transmitted from the computer to the network device. Communication is interrupted in a first step of acquiring the number of hops to the network device, and a keep-alive packet having a value obtained by adding 1 to the acquired number of hops from the computer to the network device as a TTL setting value. And a second step of transmitting at regular time intervals.

  According to a fourth aspect of the present invention, the packet according to the first, second, or third aspect includes a flag indicating a packet type, and the computer and the network device include the port setting packet and the keep alive packet. And other packets are identified by the flag.

  According to a fifth aspect of the present invention, in a communication method for performing P2P communication from a computer connected to a network device having a NAT function, different socket pairs are transmitted from the computer to a session management server via the network device. A first step of transmitting a plurality of packets; and a response packet including a transmission source port number extracted from the packet by the session management server from the session management server, wherein the computer transmits the transmission source port of the response packet A second step of extracting a number and a third step of calculating an increment number from the plurality of extracted source port numbers are provided by the computer.

  According to a sixth aspect of the present invention, in the communication method according to the fifth aspect, a packet is transmitted from the computer to the session management server via the network device, and a port of the network device is transmitted from a response packet of the packet. A fourth step of acquiring a number, and transmitting a packet in which a value obtained by adding the increment number to the port number acquired in the fourth step is set as a transmission source port number from the computer to the session management server, Fifth step of acquiring the port number of the network device of the other party of the P2P communication from the response packet of the packet, and a value obtained by adding the increment number is set as a transmission source port number, and acquired in the fifth step Send a packet with the port number set as the destination port number. Characterized in that it further includes a step.

  According to a seventh aspect of the present invention, there is provided a program for causing a computer connected to a network device having a NAT function to execute each step according to any one of the first to sixth aspects in order to perform P2P communication. It is a recorded computer-readable recording medium.

  The invention according to claim 8 is a program for causing a computer connected to a network device having a NAT function to execute each step according to any one of claims 1 to 6 in order to perform P2P communication. It is characterized by being.

  As described above, according to the present invention, since a predetermined port in a network device can always be opened from the start to the end of communication, a P2P application can be reliably used even in a connection environment using the NAT function. It can be realized.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. As described above, in order to realize a P2P application in a connection environment using the NAT function, it is necessary to always open a predetermined port in the router from the start to the end of communication. Therefore, a method of opening a boat at the beginning of communication, a method of maintaining a port that has been opened once, and a method corresponding to a change in port number during communication will be described in order.

  FIG. 3 shows a P2P communication method according to the first embodiment of the present invention. When performing P2P communication between terminals, it is necessary to first open a router port to be used in a session, avoiding blocking by ICMP packets. Therefore, the number of hops to the router 13 is checked, and a UDP packet for opening a port is transmitted.

  Specifically, the host 11 generates an ICMP echo packet and transmits it with TTL (Time To Live) = 1. Sequentially increasing TTL = 2.3... And transmitting a plurality of echo packets. When an echo packet 51 having a TTL value equal to the number of hops of the router 13 is transmitted, the echo packet 52 is returned from the router 13 to the host 11. The host 11 can know the number of hops to the router 13 from the returned echo packet 52.

  Next, the host 11 sets a value α obtained by adding 1 to the number of hops of the router 13 to the TTL, and transmits the port setting packet 53 of the transmission source port number “100”. As a result, the port of the transmission source port number “100” of the router 13 is opened. Since the port setting packet 53 is deleted at the next hop of the router 13, it does not affect other communications.

  With such a configuration, communication between terminals using the packets 54 and 55 can be performed by opening the port of the transmission source port number “100” of the router 13. At this time, if the router 14 also has a function of blocking by the ICMP packet, the host 12 performs the same processing.

  FIG. 4 shows a P2P communication method according to the second embodiment of the present invention. In the same session, while the packet transmission / reception is interrupted, it is necessary to maintain the port once opened so that the router does not clear the conversion table. Therefore, keep-alive packets are transmitted at regular time intervals while packet transmission / reception is interrupted. For example, the number of hops to the router 13 is checked in advance using the ICMP echo packet described above. The host 11 sets a value α obtained by adding 1 to the number of hops of the router 13 to the TTL, and transmits the UDP packet 61 of the transmission source port number “100”. As a result, the contents of the conversion table stored in the router 13 are not deleted, and packets with the same port number set can be transmitted thereafter.

  In the first and second embodiments, transmission may be made only to a router having a function of blocking by an ICMP packet. This is because some routers have a function of discarding a packet and closing a port when the TTL setting value is α.

  When the port setting packet and the keep alive packet reach other hosts, communication disruption is prevented. For example, as shown in FIG. 4, flags 63 and 64 are added to the head of all packets, and “1” is set for a keep-alive packet and “0” is set for a normal packet. In this way, even when the host receives a keep-alive packet, it can be identified and discarded.

  FIG. 5 shows a P2P communication method according to the third embodiment of the present invention. A method for dealing with a change in port number during communication such as a symmetric router will be described. The router 13 is a symmetric router and increments its own port number by 2 each time the destination port number and the destination address change. The router 14 is also a symmetric router and increments its own port number by 5. In such a case, the hosts 11 and 12 communicate via the session management server 15 while predicting the port number.

  FIG. 6 shows a port number prediction method according to an embodiment of the present invention. The flow of the process of the prediction method in the hosts 11 and 12 is shown. First, the hosts 11 and 12 receive a port check 1 packet from the session management server 15 (S102). The port check 1 packet is an instruction packet for causing the hosts 11 and 12 to check the increment number of the port numbers of the routers 13 and 14. Receiving the port check 1 packet, the hosts 11 and 12 transmit a new socket pair, that is, a UDP packet in which at least one of the destination port number and the destination address is changed, to the session management server 15 (S104).

  The session management server 15 extracts the transmission source port number, that is, the changed port number of the routers 13 and 14 from the received UDP packet, and transmits a response packet to the hosts 11 and 12 (S106). Further, the hosts 11 and 12 repeat the n times with the new socket pair and transmit the UDP packet to the session management server 15 (S108).

  After sending the UDP packet n times, the hosts 11 and 12 obtain n port numbers of the routers 13 and 14 from the received response packet. The hosts 11 and 12 calculate the increment number from the obtained port number (S110). The calculation method is, for example, the average value of the differences between the acquired port numbers. It is also possible to use a calculation method such as calculating an average by removing the maximum value and the minimum value of the difference.

  FIG. 7 shows a P2P communication method based on the predicted port number. First, the hosts 11 and 12 transmit a port check 2 packet to the session management server 15 (S202). The port check 2 packet is an instruction packet for checking the port numbers of the routers 13 and 14. The session management server 15 that has received the port check 2 packet extracts the transmission source port number from the received UDP packet and transmits it to the hosts 11 and 12 (S204).

  The hosts 11 and 12 add the increment number acquired by the prediction method shown in FIG. 6 to the received transmission source port number, and transmit the port check 3 packet to the session management server 15 (S206). Receiving the port check 3 packet, the session management server 15 extracts the port number of the corresponding router as the communication partner and transmits it to the hosts 11 and 12 (S208). The hosts 11 and 12 set the source port number used in step S206 and the port number received in step S208 as destination port numbers, and perform normal packet transmission / reception.

  According to this configuration, the hosts 11 and 12 that perform communication can always predict an accurate port number via the session management server 15, so that a P2P application via a symmetric router can be realized. .

  According to this embodiment, since a predetermined port in the router is always opened from the start to the end of communication, it is possible to avoid blocking by an ICMP packet and open a boat at the beginning of communication. It is also possible to maintain a new port and cope with changes in the port number during communication.

  The present invention can be applied to network devices such as routers and gateways that can reliably realize a P2P application even in a connection environment using the NAT function.

It is a network connection diagram for demonstrating a NAT function. It is a network connection diagram for demonstrating the function to perform a block by an ICMP packet. It is a network connection figure which shows the P2P communication method concerning the 1st Embodiment of this invention. It is a network connection figure which shows the P2P communication method concerning the 2nd Embodiment of this invention. It is a network connection figure which shows the P2P communication method concerning the 3rd Embodiment of this invention. It is a flowchart which shows the prediction method of the port number concerning one Embodiment of this invention. It is a flowchart which shows the P2P communication method based on the estimated port number.

Explanation of symbols

11, 12 Host 13, 14 Router 15 Session management server

Claims (8)

In a communication method for performing P2P communication from a computer connected to a network device having a NAT function,
A first step of transmitting a plurality of echo packets in which a TTL setting value is increased by 1 from 1 to the network device;
A second step of receiving an echo packet returned from the network device in response to one of the plurality of echo packets, and wherein the computer extracts a TTL setting value of the returned echo packet;
And a third step of transmitting a port setting packet having a TTL setting value obtained by adding 1 to the extracted setting value to the network device from the computer.   A fourth step of transmitting a keep-alive packet having a TTL setting value obtained by adding 1 to the extracted setting value from the computer to the network device at regular intervals while communication is interrupted; The communication method according to claim 1, further comprising: In a communication method for performing P2P communication from a computer connected to a network device having a NAT function,
A first step of transmitting an echo packet from the computer to the network device to obtain a hop number from the computer to the network device;
A second step of transmitting a keep-alive packet having a value obtained by adding 1 to the acquired number of hops from the computer to the network device at a predetermined time interval while communication is interrupted; A communication method comprising:   The packet includes a flag indicating a packet type, and the computer and the network device identify the port setting packet, the keep-alive packet, and other packets by the flag. The communication method according to 1, 2, or 3. In a communication method for performing P2P communication from a computer connected to a network device having a NAT function,
A first step of transmitting a plurality of packets of different socket pairs from the computer to the session management server via the network device;
A second step in which the session management server receives a response packet including the source port number extracted from the packet from the session management server, and the computer extracts the source port number of the response packet;
And a third step of calculating an increment number from the plurality of extracted source port numbers. A fourth step of transmitting a packet from the computer to the session management server via the network device, and obtaining a port number of the network device from a response packet of the packet;
A packet in which a value obtained by adding the increment number to the port number acquired in the fourth step is set as a transmission source port number is transmitted from the computer to the session management server. From the response packet of the packet, the P2P type A fifth step of acquiring a port number of a network device of a communication partner;
And a sixth step of transmitting a packet in which the value obtained by adding the increment number is set as a transmission source port number and the port number acquired in the fifth step is set as a destination port number. The communication method according to claim 5.   A computer-readable recording medium storing a program for causing a computer connected to a network device having a NAT function to execute each step according to any one of claims 1 to 6 in order to perform P2P communication. A program for causing a computer connected to a network device having a NAT function to execute each step according to any one of claims 1 to 6 in order to perform P2P type communication.

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