WO2022201980A1

WO2022201980A1 - Communication method, router, server, communication system, and communication program

Info

Publication number: WO2022201980A1
Application number: PCT/JP2022/006039
Authority: WO
Inventors: 貴洋原
Original assignee: ヤマハ株式会社
Priority date: 2021-03-25
Filing date: 2022-02-16
Publication date: 2022-09-29
Also published as: JP2022149654A

Abstract

According to one embodiment, a communication method involves a first terminal acquiring a range for port numbers that can be used for a first router, the first terminal transmitting the acquired range for the port numbers that can be used for the first router to a first server via the first router to allow a second terminal to acquire a port number for the first router, the first terminal acquiring information from the first server, the information being for specifying a port number for a prescribed second router that is selected on the basis of a transmission source port number for the second router and a range for the port numbers that can be used for the second router, and the first terminal attempting to connect to the second terminal via the first router using the port number for the second router as a destination port number.

Description

COMMUNICATION METHOD, ROUTER, SERVER, COMMUNICATION SYSTEM AND PROGRAM FOR COMMUNICATION

The present disclosure relates to communication methods, routers, servers, communication systems, and programs for communication.

Conventionally, network session systems have been known that enable musical sessions such as playing musical instruments (ensemble) and singing in chorus via communication networks such as the Internet. In this session system, two or more terminals mutually transmit performance information based on a performance performed by one's own terminal to other terminals via a wide area communication network, and two or more terminals including the own terminal It is intended to pronounce the performance sound of When performance information is transmitted and received via a network, there is a possibility that a delay may occur before the performance information reaches each terminal. In order to reduce such delays, P2P connections have been attempted in which two or more terminals communicate directly.

When a packet is sent from a communication device on the LAN (Local Area Network) side to a communication device on the WAN (Wide Area Network) side, the NAT router transfers the packet to the upper network. At this time, the NAT router converts the source IP address and source port in the communication packet to the WAN-side IP address of the NAT router and the newly assigned port number. Then, the packet returned as a reply is converted by the NAT router into the destination IP address and port number on the LAN side and transferred to the communication device on the LAN side. For example, Patent Literature 1 and Patent Literature 2 disclose a communication system that enables direct communication between two terminals even if there is a NAT router that converts the source port number to a different one when the destination port changes. there is

JP 2015-119217 A JP 2015-142217 A

In Patent Documents 1 and 2, two terminals attempt to establish a direct communication connection with each other using an inferred port number based on the source port number used for data transmission. If the speculated port number generated based on the source port number used to send the data is not included in the port numbers available to the router, the two terminals cannot communicate directly with each other.

One of the purposes of the present disclosure is to provide a communication method, a communication system, etc. that facilitate direct communication between terminals.

In a communication method according to an embodiment, in order for a first terminal to obtain a usable port number range of a first router and to cause a second terminal to obtain a port number of the first router, the first terminal and transmitting the obtained range of available port numbers of the first router to the first server via the first router, wherein the first terminal receives the source port number of the second router and the use of the second router. obtaining from the first server information for identifying a predetermined second router port number selected based on a range of possible port numbers, wherein the first terminal identifies the port number of the second router; Attempting a connection to the second terminal via the first router as a destination port number.

A router according to one embodiment includes a receiver that receives an inquiry about a range of usable port numbers from a first terminal, and transmits the range of usable port numbers to the first terminal in response to the inquiry. a transmitting unit, wherein the transmitting unit externally transmits the range of available port numbers and its own external port number based on a request from the first terminal.

A server according to one embodiment, based on a receiving unit that receives a range of available port numbers of a router from a terminal, and a source port number received from the router and a range of available port numbers of the router, A port selection unit for selecting a port number of a predetermined router, and a transmission unit for transmitting the port number of the predetermined router to another predetermined terminal.

A communication system according to one embodiment includes a first terminal under control of a first router, a second terminal under control of a second router, and a server not under control of a router. In a communication system in which terminals communicate with each other via the first router and the second router using a source address, a source port number, a destination address and a destination port number, the first terminal a first acquisition unit for acquiring a range of port numbers available for a router; and a first transmission unit for transmitting the acquired range of port numbers available for the first router to the server via the first router. a first receiving unit for receiving from the server a port number of a predetermined second router selected based on the transmission source port number of the second router and the range of usable port numbers of the second router; a first communication unit that attempts connection to the second terminal via the first router using the port number of the second router as the destination port number, wherein the second terminal is capable of using the second router. a first acquisition unit that acquires a range of port numbers that are suitable for use by the second router; a second transmission unit that transmits the acquired range of port numbers that can be used by the second router to the server via the second router; a second receiver for receiving from the server a predetermined port number of the first router selected based on the source port number of the router and the range of usable port numbers of the first router; a second communication unit that attempts connection to the first terminal via the second router using a port number as a destination port number, wherein the server is configured to allow the first router to be used from the first terminal. receiving a range of port numbers and a first source port number; receiving from the second terminal a range of port numbers available to the second router and a second source port number; transmitting to the second receiving unit information for identifying a predetermined port number of the first router selected based on the transmission source port number of the first router and the range of available port numbers of the first router; and the information for specifying the port number of a predetermined second router selected based on the transmission source port number of the second router and the range of usable port numbers of the second router is received by the first receiver. department.

A program according to one embodiment obtains a range of usable port numbers of a first router, and obtains a usable port number of the first router to cause a second terminal to obtain the port number of the first router. A predetermined second router that transmits a range of numbers to a first server via said first router and is selected based on the source port number of the second router and the range of available port numbers of the second router. acquiring from the first server information for specifying the port number of the second terminal, and attempting to connect to the second terminal via the first router using the port number of the second router as the destination port number; Let the first terminal execute.

A program according to one embodiment obtains a range of usable port numbers of a first router, and obtains a usable port number of the first router to cause a second terminal to obtain the port number of the first router. sending a range of numbers to a first server via said first router, and a predetermined second router selected based on the source port number of the second router and the range of available port numbers of the second router; and trying to connect to the second terminal through the first router using the port number of the second router as the destination port number.

According to the present disclosure, it is possible to provide a communication method, a communication system, and the like that facilitate direct communication between terminals.

1 is a diagram illustrating the configuration of a communication system according to an embodiment of the present disclosure; FIG. FIG. 4 is a diagram for explaining an example of procedures and operations up to direct communication between terminals according to an embodiment of the present disclosure; FIG. 4 is a diagram for explaining an example of procedures and operations up to direct communication between terminals according to an embodiment of the present disclosure; FIG. 4 is a diagram for explaining an example of procedures and operations up to direct communication between terminals according to an embodiment of the present disclosure; FIG. 4 is a diagram for explaining an example of procedures and operations up to direct communication between terminals according to an embodiment of the present disclosure; 6 is a flow chart showing an example of connection processing on the terminal side according to the present embodiment; 6 is a flow chart showing an example of connection processing on the terminal side according to the present embodiment; 6 is a flow chart showing an example of connection processing on the terminal side according to the present embodiment; 6 is a flow chart showing an example of connection processing on the terminal side according to the present embodiment; 6 is a flow chart showing an example of connection support processing on the router side according to the present embodiment; 6 is a flow chart showing an example of connection support processing on the router side according to the present embodiment; 7 is a flowchart showing an example of connection support processing on the server side according to the present embodiment; 2 is a block diagram showing the functional configuration of a terminal according to an embodiment of the present disclosure; FIG. 3 is a block diagram showing the functional configuration of a server according to an embodiment of the present disclosure; FIG. 2 is a block diagram showing the functional configuration of a router according to an embodiment of the present disclosure; FIG. FIG. 10 is a diagram for explaining a part of procedures and operations up to direct communication between terminals according to a modified example of the present disclosure; FIG. 10 is a block diagram showing a functional configuration of a terminal according to a modified example of the present disclosure;

Hereinafter, each embodiment of the present disclosure will be described with reference to the drawings and the like. However, the present disclosure can be implemented in various aspects without departing from the gist thereof, and should not be construed as being limited to the description of the embodiments illustrated below.

In this specification and each figure, elements having the same functions as those described with respect to the previous figures may be denoted by the same reference numerals, and overlapping descriptions may be omitted.

[First embodiment]
<Communication system configuration>
FIG. 1 is a diagram illustrating the configuration of a communication system 10 according to an embodiment of the present disclosure. The configuration of the communication system 10 will be described with reference to FIG.

The communication system 10 includes a first terminal 101, a second terminal 103, a first router 105, a second router 107, and a server 109. The first terminal 101, second terminal 103, first router 105, second router 107, and server 109 are communicably connected via a wide area communication network NW such as the Internet.

The first terminal 101 and the second terminal 103 are terminals capable of communicating with other devices via the network NW. Each of the first terminal 101 and the second terminal 103 may be a device capable of transmitting and receiving audio data in real time. Audio data transmitted from such a device may be, for example, audio data received from an external microphone, audio data received from an external electronic device, or audio data generated in response to an input performance operation. . In FIG. 1, only two terminals, a first terminal 101 and a second terminal 103, are shown as an example. However, the number of terminals is not limited to two, and may be two or more.

The first terminal 101 includes a control unit 111 and a storage unit 113. Control unit 111 includes an arithmetic processing circuit such as a CPU. The storage unit 113 includes storage devices such as RAM and ROM. The storage unit 113 stores a control program in which commands are described. The control unit 111 causes the CPU to execute the control program stored in the storage unit 113 to realize various functions in the first terminal 101 . Similarly, second terminal 103 also includes control unit 115 and storage unit 117 . The functions of the control unit 115 and the storage unit 117 are the same as those of the control unit 111 and the storage unit 113, so overlapping descriptions will be omitted.

The first router 105 and the second router 107 are NAT routers. The first router 105 has the first terminal 101 under its control. The second router 107 has the second terminal 103 under its control. Each of the first router 105 and the second router 107 has a plurality of host devices under its control in addition to the terminals shown in FIG. It has a NAT function that relays data and translates addresses and port numbers between both networks. That is, the first router 105 and the second router 107 have a local address and port number, such as a private IP address, which is valid only in the local network, and a global address and port number, such as a global IP address, on the network NW. are automatically converted to each other.

The NAT function provided in the first router 105 is such that when a packet is sent from under the router using the same source address and the same source port number as those used in past communication, if the destination address changes, the past Convert to a port number different from the one used for communication. The second router 107 also has the same functions as the first router 105 .

The first router 105 includes a control unit 119 and a storage unit 121. Control unit 119 includes an arithmetic processing circuit such as a CPU. The storage unit 121 includes storage devices such as RAM and ROM. The storage unit 121 stores a control program in which commands are described. The control unit 119 causes the CPU to execute the control program stored in the storage unit 121 to realize the NAT function described above in the first router 105 . Similarly, second router 107 also includes control unit 123 and storage unit 125 . The functions of the control unit 123 and the storage unit 125 are the same as those of the control unit 119 and the storage unit 121, so overlapping descriptions will be omitted.

The server 109 is not under the control of the first router 105 or the second router 107. The server 109 supports connection between the first terminal 101 and the second terminal 103, for example, performs connection procedures between the first terminal 101 and the second terminal 103 before starting a session. After the connection is established between the first terminal 101 and the second terminal 103, the connection is established between the first terminal 101 and the second terminal 103 via the first router 105 and the second router 107 without the intervention of the server 109. , and performance information such as audio data is directly transmitted and received.

The server 109 includes a control unit 127 and a storage unit 129. Control unit 127 includes an arithmetic processing circuit such as a CPU. The storage unit 129 includes storage devices such as RAM and ROM. The storage unit 129 stores a control program in which commands are described. The control unit 127 executes the control program stored in the storage unit 129 by the CPU, and performs various functions such as the above-described connection procedure between the first terminal 101 and the second terminal 103 before starting the session. Executes on server 109 .

[Communication procedure]
The communication system 10 according to the present embodiment includes a plurality of terminals (here, the first terminal 101 and the second terminal 103) under the control of the first router 105 and the second router 107, which are different from each other, and the first router 105 or the second router 107. It is composed of a server 109 that is not under the control of the router 103 . Each of the first terminal 101 and the second terminal 103 uses the source address, source port number, destination address and destination port number to identify the first router 105 to which the first terminal 101 and the second terminal 103 respectively belong. and direct communication via the second router 103 . Hereinafter, procedures and operation examples up to direct communication between two terminals according to the present embodiment will be described with reference to FIGS. 2 to 5. FIG. In the following, a case where communication is established between the first terminal 101 and the second terminal 103 will be described as an example.

2 to 5 are diagrams for explaining an example of procedures and operations up to direct communication between the first terminal 101 and the second terminal 103 according to this embodiment.

As shown in FIG. 2, first, prior to direct communication between the first terminal 101 and the second terminal 103, the first terminal 101 asks the first router 105 the range of port numbers that the first router 105 can use. Inquire. Here, the range of usable port numbers refers to all port numbers associated with global IPs that can be used by the first router 105 . Hereinafter, the range of port numbers that can be used by the first router 105 is referred to as first port range information. The first port range information is stored in storage unit 121 . The first router 105 receives an inquiry from the first terminal 101 under its control. First router 105 transmits first port range information to first terminal 101 in response to an inquiry from first terminal 101 . FIG. 2 shows, as an example, the case where the first port range information is 1024-1156, 4096-4224, and 59000-60000.

Similarly, the second terminal 103 inquires of the second router 107 about the range of port numbers that the second router 107 can use. Hereinafter, the range of port numbers that can be used by the second router 107 is referred to as second port range information. The second port range information is stored in storage unit 125 . The second router 107 receives an inquiry from the second terminal 103 under its control. The second router 107 transmits second port range information to the second terminal 103 in response to the inquiry. FIG. 2 shows a case where the second port range information is 1224-1256, 5096-5224, and 61000-62000 as an example.

Next, as shown in FIG. 3, the first terminal 101 uses "source address: 192.168.0.100.10" and "source port number: 5000" to obtain "destination address: 2 . 2.2.2” and “destination port number: 7000”, that is, data is packetized and transmitted to the server 109 . At this time, the data includes the first port range information.

Similarly, the second terminal 103 uses "source address: 192.168.100.20" and "source port number: 6000" to use "destination address: 2.2.2.2" and " Destination port number: 7000”, that is, the data is packetized and transmitted to the server 109 . At this time, the data includes the second port range information.

The server 109 receives packets from the first terminal 101 via the first router 105 . The server 109 receives the results of conversion by the first router 105 under the control of the first terminal 101, namely, "source address: 1.1.1.1", "source port number: 60000", and "first port range". Information: 1024-1156, 4096-4224, 59000-60000".

Similarly, the server 109 receives packets from the second terminal 103 via the second router 107 . The server 109 receives the results of conversion by the second router 107 under the second terminal 103, namely, "source address: 3.3.3.3", "source port number: 5224", and "second port range". Information: 1224-1256, 5096-5224, 61000-62000".

Next, server 109 determines “source address: 1.1.1.1” for confirmed first terminal 101 as the address of first terminal 101, and also determines “source port 1.1.1.1” for confirmed first terminal 101. number: 60000" and "first port range information: 1024 to 1156, 4096 to 4224, 59000 to 60000", it is assumed that the second terminal 103 will be used when attempting communication with the first terminal 101. Select a port number.

Here, a brief description will be given of the procedure by which the server 109 selects the port number presumed to be used when the second terminal 103 attempts to communicate with the first terminal 101. First, the server 109 determines whether or not the first port range information includes the number next to the source port number of the received packet, that is, the port number obtained by adding "+1" to the source port number of the received packet. Check whether If the port number obtained by adding "+1" to the source port number of the received packet is included in the first port range information, the server 109 adds "+1" to the "source port number". , is selected as the port number presumed to be used when the second terminal 103 attempts communication with the first terminal 101 . On the other hand, if the port number obtained by adding "+1" to the source port number of the received packet is not included in the first port range information, the server 109 selects the source port number of the received packet from the first port range information. Among one or more port numbers larger than the port number, the smallest port number is selected as the port number presumed to be used when the second terminal 103 attempts to communicate with the first terminal 101 . Further, the first port range information does not include the port number obtained by adding "+1" to the source port number of the received packet, and the port number greater than the source port number of the received packet is the first port number. If it does not exist in the port range information, the server 109 presumes that the smallest port number in the first port range information will be used when the second terminal 103 attempts to communicate with the first terminal 101. Select as port number.

A specific description will be given with reference to FIGS. 3 and 4. Server 109 selects the port number obtained by adding “+1” to the confirmed “source port number” of first terminal 101 as the port number used when second terminal 103 attempts communication with first terminal 101 . In the case of "source port number: 60000" for the first terminal 101, the port number obtained by adding "+1" is "60001". However, "60001" is not included in the first port range information. In this way, if the selected port number, that is, the port number obtained by adding "+1" to the "source port number" is not included in the first port range information, the server 109 selects the "first port range information: 1024 to 1156, 4096 to 4224, 59000 to 60000”, a predetermined port number that is presumed to be used when the second terminal 103 attempts communication with the first terminal 101 is selected. "Source port number: 60000" is the maximum port number in "first port range information: 1024 to 1156, 4096 to 4224, 59000 to 60000". Therefore, the server 109 uses the minimum port number “1024” in the “first port range information: 1024 to 1156, 4096 to 4224, 59000 to 60000” when the second terminal 103 attempts communication with the first terminal 101. Select as the port number that is assumed to be Then, the server 109 notifies the second terminal 103 that the address of the first terminal 101 is "1.1.1.1" and the port number of the first terminal 101 is "1024". .

Similarly, server 109 determines "source address: 3.3.3.3" for confirmed second terminal 103 as the address of second terminal 103, and also determines "source port 3.3.3.3" for confirmed second terminal 103. number: 5224” and “second port range information: 1224 to 1256, 5096 to 5224, 61000 to 62000”, it is assumed that the first terminal 101 is used when attempting communication with the second terminal 103. Select a port number. The server 109 adds "+1" to the confirmed "source port number" of the second terminal 103, which is the port number presumed to be used when the first terminal 101 attempts to communicate with the second terminal 103. Select as In the case of "source port number: 5224" for the second terminal 103, the port number obtained by adding "+1" is "5225". However, "5225" is not included in the second port range information. In this way, if the selected port number, that is, the port number obtained by adding "+1" to the "source port number" is not included in the second port range information, the server 109 selects the "second port range information: 1224 to 1256, 5096 to 5224, 61000 to 62000”, a predetermined port number that is presumed to be used when the first terminal 101 attempts communication with the second terminal 103 is selected. In the "second port range information: 1224 to 1256, 5096 to 5224, 61000 to 62000", the smallest port number is 61000 among the port numbers: 61000 to 62000 that are larger than the "source port number: 5224". Therefore, when the first terminal 101 attempts communication with the second terminal 103, the server 109 selects the port number "61000" from the "second port range information: 1224 to 1256, 5096 to 5224, 61000 to 62000". Select as the port number presumed to be used. Then, the server 109 notifies the first terminal 101 that the address of the second terminal 103 is "3.3.3.3" and the port number of the second terminal 103 is "61000". .

The first terminal 101 obtains notification from the server 109 that the address of the second terminal 103 is "3.3.3.3" and the port number of the second terminal 103 is "61000". Similarly, the second terminal 103 obtains a notification from the server 109 that the address of the first terminal 101 is "1.1.1.1" and the port number of the first terminal 101 is "1024". .

As shown in FIG. 5, the first terminal 101 secures a "source port number: 5001" different from the "source port number: 5000" used when the packet was first transmitted to the server 109. Then, the first terminal 101 uses the "source address: 192.168.100.10" and the "source port number: 5001" to use the "destination address: 3.3.3" notified from the server 109. .3” and “destination port number: 61000”, that is, the packet is transmitted to the second terminal 103 .

Similarly, the second terminal 103 secures a "source port number: 6001" that is different from the "source port number: 6000" used when the packet was first sent to the server 109. Then, the second terminal 103 uses the “source address: 192.168.100.20” and the “source port number: 6001” to use the “destination address: 1.1.1” notified from the server 109. .1” and “destination port number: 1024”, that is, the packet is transmitted to the first terminal 101 .

[motion]
Next, an example of a specific communication flow will be described. 6 to 9 show an example of connection processing on the terminal side according to this embodiment. Here, the terminal may be the first terminal 101 or the second terminal 103 . 10 and 11 show an example of connection support processing on the router side according to this embodiment. Here, the router may be the first router 105 or the second router 107 . FIG. 12 shows an example of connection support processing on the server (server 109) side according to this embodiment. The processing examples shown in FIGS. 6 to 9 are flowcharts of computer programs related to connection processing executed by the CPU of the terminal. The process examples shown in FIGS. 10 and 11 are flowcharts of computer programs related to connection support processing executed by the CPU of the router. Also, the processing example shown in FIG. 12 is a flowchart of a computer program relating to connection support processing executed by the CPU of the server (server 109).

In the following description, for the sake of convenience, notification of connection from one terminal to the server 109 will be described. However, other terminals that communicate with each other also execute the program processes shown in FIGS. 6 to 9, respectively.

　The terminal starts executing the program shown in FIG. A terminal first inquires of the router to which it belongs about the range of port numbers that can be used by the router, that is, the port range information corresponding to the router (S101).

On the other hand, when the router receives an inquiry for port range information from a terminal under its control, it starts executing the program shown in FIG. In response to the inquiry from the subordinate terminal, the router notifies the subordinate terminal of its own port range information (S301).

　Referring to FIG. 6 again, the terminal acquires the port range information corresponding to the router notified from the router (S102). Then, the terminal notifies the server 109 of the connection (S103). Next, the terminal determines whether or not an instruction to start connection has been received from the server 109, that is, whether or not another participant has appeared (S104). If the connection start instruction has not been received from the server 109 (S104; No), the terminal repeats the process of S104 and waits for a connection start instruction.

On the other hand, the server 109 starts executing the program shown in FIG. 12 upon receiving a connection notification from the terminal through the processing of S103 described above. The server 109 first determines whether or not there are two or more terminals TM waiting for connection (that is, whether or not another participant has appeared) (S201). If there are not two or more terminals waiting for connection (S201; No), the server 109 waits until there are two or more terminals TM waiting for connection. In the case of this embodiment, when two terminals, that is, the first terminal 101 and the second terminal 103, receive connection notifications, it is determined that there are two or more terminals TM waiting for connection (S201; Yes). be done.

When it is determined that there are two or more terminals TM waiting for connection (S201; Yes), the server 109 transmits a connection start instruction to all terminals waiting for connection (S202). Next, the server 109 determines whether or not packets to the port number P1 have been received from all terminals instructed to start connection (S203). In a state where packets to port number P1 have not been received from all terminals (S203; No), the server 109 waits for reception of packets from all terminals.

On the other hand, as shown in FIG. 6, each terminal waiting for a connection start instruction, while waiting for the process of S104, receives a connection start instruction from the server 109 (S104; Yes), and proceeds to the process of S105. The terminal transmits a packet addressed to port number P1 to server 109 using a predetermined source address and source port number (S105). Then, the terminal determines whether notification of the connection destination port number and address has been received from the server 109 (S106). If notification of the port number and address of the connection destination has not arrived (S106; No), the terminal waits for notification of the port number and address of the connection destination.

On the other hand, when the router receives a packet addressed to port number P1 from the terminal to the server 109 through the processing of S105 described above, the router starts executing the program shown in FIG. The router converts the source IP address and source port number of the received packet and transmits the packet to port number P1 (S302).

Refer to FIG. 12 again. The server 109 waiting to receive a packet receives the transmitted packet each time a packet is transmitted from the terminal in the process of S203. When the server 109 receives packets to the port number P1 from all the terminals notified of connection (S203; Yes), the process proceeds to S204. The server 109 is used when each terminal tries to communicate with a terminal to be connected based on the source port number of the packet received from each terminal and the port range information corresponding to the router to which the terminal that sent the packet belongs. Select the port number that is assumed to be Specifically, the server 109 adds the port number obtained by adding "+1" to the source port number of the packet received from each terminal when the terminal tries to communicate with the other terminal. Select as the port number presumed to be used. However, if the port number obtained by adding "+1" to the source port number of the received packet is not included in the port range information corresponding to the router to which the terminal attempting to connect belongs, the server 109 , selects a predetermined port number from the port range information as a port number presumed to be used when the terminal attempts communication with the terminal to be connected. The server 109 transmits the source address of the received packet and the selected port number to all terminals (S205).

Next, the server 109 determines whether or not any of the "connection complete", "connection retry notification", and "connection failure" packets have arrived from the terminal (S206). If the packet has not arrived at the terminal (S206; No), the server 109 waits for the packet to arrive at the terminal. Regarding "connection completed" in the determination of S206, it is determined whether or not notification has been received from all the terminals that have transmitted the connection start instruction by the processing of S205. On the other hand, regarding "retry notification of connection" and "failure to connect", it is determined whether or not there is a notification from any one of all the terminals.

Refer to Figure 6 again. When the terminal waiting for notification of the connection destination port number and address receives the connection destination address and port number from the server 109 via the router to which the terminal belongs (S106; Yes), the process proceeds to S107. Here, the port number received from the server 109 is the port number selected based on the source port number of the packet received by the server 109 from each terminal and the port range information corresponding to the router to which each terminal belongs. be. The terminal sets a new source port number different from the source port number used when executing the process of S105, that is, the source port number used when the packet was sent to the server 109 (S107). . In this case, a new source port number may be set by adding “+1” to the source port number used when the packet was sent to the server 109 . However, the terminal is not limited to this, and the terminal may set another port number as the source port number as long as it is different from the source port number used when transmitting the packet to the server 109 .

Next, the terminal transmits a trial packet to the port number and address of the communication partner terminal notified by the server 109 using the same predetermined source address as in the process of S105 and the newly set source port number. By doing so, connection with the terminal of the communication partner is attempted (S108).

It should be noted that the terminal not only tries to connect to the terminal to be connected using only the port number and address of the communication partner terminal notified from the server 109, but also attempts to connect to the communication partner terminal notified from the server 109. You may attempt to connect using multiple port numbers before and after the port number of . The preceding and succeeding port numbers are, for example, several port numbers obtained by adding "+1", "+2", "+3" to the notified port number, and "+1", "+1", " +2”, “+3” . . . are subtracted from each other. If the router to which the terminal to be connected belongs is being used for another communication, the router may change the port number before or after the port number notified from the server 109 . As a result, the trial packet may not reach the terminal attempting to connect only by trying the port number notified from the server 109 . In this case, the terminal attempts connection using a plurality of port numbers before and after the port number of the communication partner terminal notified from the server 109 .

After the process of S108, the terminal determines whether or not a trial packet has arrived from the other terminal to which it is trying to connect (S109). When the trial packet from the partner terminal does not arrive (S109; No), the terminal proceeds to the process of S110. The terminal determines whether or not the maximum time for waiting for a packet from the partner terminal to be connected has passed (S110). Then, while the maximum time has not elapsed (S110; No), the terminal returns to the processing of S109 and waits until a trial packet from the partner terminal to be connected arrives or until the maximum time has elapsed. The process of S110 is repeatedly executed.

When a trial packet arrives from the terminal to be connected (S109; Yes), the terminal proceeds to the processing of S111 shown in FIG. In this case, the terminal notifies the server 109 that the connection has been completed (S111). As a result, the terminal that has received the trial packet from the partner terminal to be connected establishes a direct connection with the partner terminal, and terminates this connection operation. Since the received trial packet includes the source address and source port number of the partner terminal, the terminal receiving the trial packet can recognize the address and port number of the partner terminal. After this, packets are sent and received directly between the two terminals.

On the other hand, when the maximum time elapses (S110; Yes) in a state where the trial packet from the partner terminal to be connected does not arrive (S109; No), the terminal performs the maximum number of trial times of packet transmission by the process of S108. (S112). When the number of packet transmission attempts has not reached the maximum number of attempts (S112; No), the terminal proceeds to the process of S113 shown in FIG. If the number of packet transmission attempts has not reached the maximum number of attempts (S112; No), the terminal notifies the server 109 of connection retry (S113), returns to S105, and performs the above-described processes S105 to S110, S112, and S113. Repeatedly performing connection retries consisting of Then, when the packet transmission has been tried for the maximum number of times (S112; Yes), the terminal notifies the server 109 that the connection has failed and abandons the connection, as shown in FIG. The operation ends (S114). In this case, the terminal is unable to establish a connection with the partner terminal to which it is trying to connect.

Refer to Figure 12 again. When the server 109, which is repeating the process of S206, receives any one of the packets of "connection complete", "connection retry notification" and "connection failure" from the terminal (S206; Yes), the server 109 receives the "connection Branch processing is executed according to "completion", "connection retry notification", or "connection failure" (S207).

When the "connection complete" packet is received, the server 109 proceeds to the process of S208, completes the connection, and deletes the terminal that received the packet from the terminals waiting for connection. Further, when the server 109 receives a “connection retry notification” packet, the server 109 returns to the process of S202 and repeats the above-described processes S202 to S207. Further, when a "connection failure" packet is received, the server 109 advances to the process of S209, determines that the connection has failed, and deletes the terminal that received the packet from the terminals waiting for connection. After the process of S208 or S209, the original standby state is restored.

[Device configuration]
FIG. 13 is a block diagram showing a functional configuration for executing connection processing in the first terminal 101 and the second terminal 103. As shown in FIG. Functional configurations of the first terminal 101 and the second terminal 103 will be described with reference to FIG.

The first terminal 101 includes a first acquisition section 203 , a first transmission section 205 , a first reception section 207 and a first communication section 209 .

The first acquisition unit 203 acquires first port range information from the first router 105 . The first acquisition unit 203 may inquire of the first router 105 about the first port range information and acquire the first port range information notified from the first router 105 . The connection method for Internet connection may be the IPv4 over IPv6 method.

The first transmission unit 205 packetizes and transmits data to the server 109 via the first router 105 . At this time, the data includes the acquired first port range information of the first router 105 .

The first receiving unit 207 receives the IP address and port number of the second terminal 103 for attempting communication with the second terminal 103, that is, the IP address of the second router 107 to which the second terminal 103 belongs, and the second Port number of predetermined second router 107 selected based on port number of router 107 (hereinafter also referred to as source port number of second router 107) and second port range information corresponding to second router 107 Receive notifications from server 109 .

The first communication unit 209 sets the IP address of the second router 107 and the selected predetermined port number of the second router 107 notified from the server 109 as the destination address and the destination port number, and the second terminal 103.

The second terminal 103 includes a second acquisition unit 213, a second transmission unit 215, a second reception unit 217, and a second communication unit 219.

The second acquisition unit 213 acquires second port range information from the second router 107 . The second acquisition unit 213 may inquire of the second router 107 about the second port range information and acquire the second port range information notified from the second router 107 . The connection method for Internet connection may be the IPv4 over IPv6 method.

The second transmission unit 207 packetizes and transmits data to the server 109 via the second router 107 . At this time, the data includes the acquired second port range information of the second router 107 .

The second receiving unit 217 receives the IP address and port number of the first terminal 101 for attempting communication with the first terminal 101, that is, the IP address of the first router 105 to which the first terminal 101 belongs, and the first A predetermined port number of the first router 105 selected based on the port number of the router 105 (hereinafter also referred to as the source port number of the first router 105) and the first port range information corresponding to the first router 105 Receive notifications from server 109 .

The second communication unit 219 sets the IP address of the first router 105 and the selected predetermined port number of the first router 105 notified from the server 109 as the destination address and the destination port number, and A connection to the terminal 101 is attempted.

[Server configuration]
FIG. 14 is a block diagram showing a functional configuration for executing connection support processing in the server 109. As shown in FIG. A functional configuration of the server 109 will be described with reference to FIG. Server 109 includes receiver 303 , port selector 305 , and transmitter 307 .

The receiving unit 303 receives packets from the first terminal 101 via the first router 105 . Similarly, receiving section 303 also receives packets from second terminal 103 via second router 107 . The data sent from the first terminal 101 includes first port range information corresponding to the first router 105 . The data sent from the second terminal 103 includes second port range information corresponding to the second router 107 .

The port selection unit 305 selects a predetermined port number of the first router 105 from the first port range information based on the transmission source port number of the first router 105 and the first port range information. The selected port number is a newly set port number that is used when the destination address is changed. Here, the selected port number is a port number different from the port number used when the first terminal 101 sent the packet to the server 109, and the first terminal 101 tries to connect to the second terminal 103. This is the newly set port number used when

Similarly, the port selection unit 305 selects a predetermined port number of the second router 107 from the second port range information based on the transmission source port number of the second router 107 and the second port range information. . The selected port number is a newly set port number that is used when the destination address is changed. Here, the selected port number is a port number different from the port number used when the packet was transmitted from the second terminal 103 to the server 109, and the second terminal 103 tries to connect to the first terminal 101. This is the newly set port number used when The port number selection procedure executed by the port selection unit 305 is as described above, and redundant description will be omitted.

The transmission section 307 transmits the port number selected by the port selection section 305 to a predetermined terminal. For example, the transmission unit 307 transmits the source port number of the first router 105 and the port number selected based on the first port range information to the second terminal 103 via the second router 107 . Similarly, transmitting section 307 transmits the source port number of second router 107 and the port number selected based on the second port range information to first terminal 101 via first router 105 .

The first terminal 101 attempts to connect to the second terminal 103 using the transmission source port number of the second router 107 obtained from the server 109 and the predetermined port number selected from the second port range information. do. Similarly, the second terminal 103 uses the transmission source port number of the first router 105 obtained from the server 109 and the predetermined port number selected from the first port range information to send to the first terminal 101. Attempt to connect. The connection method between the first terminal 101 and the second terminal 103 is P2P connection.

[Router configuration]
FIG. 15 is a block diagram showing a functional configuration for executing connection support processing in the first router 105. As shown in FIG. A functional configuration of the first router 105 will be described with reference to FIG. Since the second router 107 has substantially the same functional configuration as the first router 105, illustration and detailed description of the functional configuration of the second router 107 are omitted here.

The first router 105 includes a receiver 401 , a transmitter 403 and a port changer 405 . The receiving unit 401 receives an inquiry requesting notification of the first port range information corresponding to the first router 105 from the first terminal 101 under its control.

In response to this inquiry, the transmission unit 403 notifies the first terminal 105 of the first port range information. The transmission unit 403 may read the first port range information stored in the storage unit 121 . Also, when a packet is transmitted from the first terminal 101 to the server 109, the transmission unit 403 transmits the IP address and port number of itself, that is, the first router 105, together with the first port range information. It is transmitted to the server 109 as the source port.

When the destination IP address is changed, the port changing unit 405 changes the port number used as the transmission source to another port number selected from the range of port numbers that can be used by itself.

As described above, in this embodiment, prior to direct communication between two terminals (first terminal 101 and second terminal 103), first terminal 101 and second terminal 103 send to server 109, Packetized data is sent that includes the first port range information or the second port range information. The server 109 selects a predetermined port number of the partner terminal to which each terminal tries to connect, based on the source port number used for packet transmission, the first port range information, and the second port range information. and notify each terminal. After that, the first terminal 101 and the second terminal 103 receive a source port number different from the source port number used for transmission to the server 109, the IP address of the partner terminal notified from the server 109, and the selected port number. Numbers can be used to communicate directly with each other. That is, in this embodiment, when the destination address is changed, the first router 105 and the second router 107 control the first terminal 101 by using the property of sequentially changing the source port number. Regardless of the type of first router 105 and second router 107 governing the second terminal 103, the first terminal 101 and the second terminal 103 will be able to communicate directly. Therefore, according to this embodiment, the first terminal 101 and the second terminal 103 can be used for transmission to the server 109 regardless of what type of NAT router the first router 105 and the second router 107 are. By simply changing the source port number, they can communicate directly with each other.

[Modification 1]
In the above embodiment, prior to direct communication between the first terminal 101 and the second terminal 103, the first terminal 101 queries the first router 105 for the first port range information. Similarly, the second terminal 103 inquires the second router 107 about the second port range information. However, each terminal may inquire of another server different from the server 109 described above for port range information corresponding to the router to which the terminal belongs. Such a server can calculate the range of port numbers assigned to IPv6 addresses to IPv4 addresses, that is, port range information, using a predetermined calculation method. The server notifies each terminal of the calculated port range information.

[Modification 2]
In the above embodiment, the server 109 changes the destination address from the first port range information based on the source port number and the first port range information of the packet received from the first terminal 101. A predetermined port number of the first router 105 that is used at the time is selected. Similarly, the server 109 is used when the destination address is changed from the second port range information based on the source port number of the packet received from the second terminal 103 and the second port range information. The port number of the predetermined second router 107 is selected. However, the port number used by the terminal when attempting to communicate with another terminal may be selected by the terminal.

FIG. 16 is a diagram for explaining a part of the procedure and operation up to direct communication between the first terminal 101 and the second terminal 103 according to Modification 2. As shown in FIG. As described with reference to FIG. 3, server 109 receives packets from first terminal 101 via first router 105 . The server 109 receives the results of conversion by the first router 105 under the control of the first terminal 101, namely, "source address: 1.1.1.1", "source port number: 60000", and "first port range". information: 1024-1156, 4096-4224, 59000-60000". Server 109 also receives packets from second terminal 103 via second router 107 . The server 109 receives the results of conversion by the second router 107 under the second terminal 103, namely, "source address: 3.3.3.3", "source port number: 5224", and "second port range". information: 1224-1256, 5096-5224, 61000-62000".

As shown in FIG. 16, the server 109 receives the received "source address: 1.1.1.1", "source port number: 60000", and "first port range information: 1024" of the first terminal 101. ~ 1156, 4096 ~ 4224, 59000 ~ 60000” to the second terminal 103 . Similarly, the server 109 receives the second terminal's "source address: 3.3.3.3", "source port number: 5224", and "second port range information: 1224 to 1256, 5096 to 5224, 61000 to 62000” to the first terminal.

The first terminal 101 receives the second port range information based on the "source port number: 5224" and "second port range information: 1224 to 1256, 5096 to 5224, 61000 to 62000" of the second terminal. From among them, a predetermined port number of the second router 107 that is used when the destination address is changed may be selected. Similarly, the second terminal 103, based on the received "source port number: 60000" and "first port range information: 1024 to 1156, 4096 to 4224, 59000 to 60000" of the first terminal, A predetermined first router 107 port number to be used when the destination address is changed may be selected from the range information. The port number selection procedure may be similar to the port number selection procedure performed by the server 109 .

FIG. 17 is a diagram for explaining the functional configurations of the first terminal 101A and the second terminal 103A according to Modification 2. As shown in FIG.

The first terminal 101A includes a first acquisition section 203, a first transmission section 205, a first reception section 207, a first communication section 209 and a first port selection section 221. The first acquisition unit 203, the first transmission unit 205, the first reception unit 207, and the first communication unit 209 shown in FIG. 17 are the first acquisition unit 203, the first transmission unit 205, and It is similar to the first receiving section 207 and the first communication section 209 .

The first port range selection unit 221 selects the second port based on the received "source port number: 5224" and "second port range information: 1224 to 1256, 5096 to 5224, 61000 to 62000" of the second terminal. A port number of a predetermined second router 107 to be used when the destination address is changed is selected from the range information. The port number selection procedure is similar to the port number selection procedure performed by the server 109 .

The second terminal 103A includes a second acquisition section 213, a second transmission section 215, a second reception section 217, a second communication section 219 and a second port selection section 223. In the second terminal 103A, the functions of the second acquisition unit 213, the second transmission unit 215, the second reception unit 217, the second communication unit 219, and the second port selection unit 223 are the functions of the first acquisition unit 203, the first transmission unit 205, the first receiving unit 207, the first communication unit 209, and the first port selection unit 221, so redundant description will be omitted.

[Modification 3]
In the above embodiment, the server 109, based on the source port number and the first port range information of the packet received from the first terminal 101, selects the first router 105 from the first port range information. A port number is selected and the selected port number of the first router 105 is transmitted to the second terminal 103 . Similarly, based on the source port number of the packet received from the second terminal 103 and the second port range information, the server 109 extracts the port number of the second router 107 from the second port range information. The selected port number of the second router 107 is transmitted to the first terminal 101 . However, the server 109 may transmit the source port number and the first port range information of the packet received from the first terminal 101 to another server that can communicate with the server 109 . Another server selects the port number of a predetermined first router 105 from the first port range information based on the received source port number and the first port range information, and selects the selected first router 105 may be sent to the second terminal 103 . Similarly, the server 109 may transmit the source port number and the second port range information of the packet received from the second terminal 103 to another server that can communicate with the server 109 . Another server selects the port number of a predetermined second router 107 from the second port range information based on the received source port number and the second port range information, and selects the selected second router 107 107 port number may be transmitted to the first terminal 101 . Instead of the other server, the server 109 transmits the source port number and the first Port range information is transmitted, and based on the transmission source port number received by the terminal and the first port range information, a predetermined port number of the first router 105 is selected from the first port range information and selected. The port number of the first router 105 that has been received may be transmitted to the second terminal 103 . Similarly, the server 109 transmits the source port number and the second port range information of the packet received from the second terminal 103 to the terminal (third terminal) of the server 109, and the terminal receives the packet. Based on the transmitted source port number and the second port range information, a predetermined port number of the second router 107 is selected from the second port range information, and the selected port number of the second router 107 is converted to the second port range information. It may be transmitted to one terminal 101 .

The above is the description of the modified example.

As described above, according to an embodiment of the present disclosure, in order to acquire the range of available port numbers of the first router and to cause the second terminal to acquire the port number of the first router, the acquired first router to the first server via the first router, and a predetermined range selected based on the source port number of the second router and the range of available port numbers of the second router acquires from the first server information for specifying the port number of the second router, and attempts to connect to the second terminal via the first router using the port number of the second router as the destination port number. A program is provided for execution by the first terminal. The program can also be configured as follows.

Cause the first terminal to execute the process of inquiring the first router about the range of port numbers that can be used by the first router, and obtain the range of port numbers that can be used by the first router from the first router.

Cause the first terminal to execute a process of inquiring the second server about the range of port numbers that can be used by the first router, and obtain the range of port numbers that can be used by the first router from the second server.

The information for identifying the port number of the predetermined second router is the predetermined port number selected by the first server based on the source port number of the second router and the range of available port numbers of the second router. 2 is the port number of the router.

A port number of a predetermined second router based on the source port number of the second router and the range of available port numbers of the second router included in the information for specifying the port number of the predetermined second router. including selecting

The range of port numbers that can be used by the first router is the range of port numbers for Internet connection.

The connection method for Internet connection is IPv4 over IPv6.

The connection to the second terminal is a P2P connection.

Further, according to an embodiment of the present invention, a receiving unit for receiving an inquiry about a range of usable port numbers from a first terminal; a transmitting unit for transmitting, the transmitting unit externally transmitting the range of available port numbers and its own external port number based on a request from the first terminal. The router can also be configured as follows.

It further comprises a port change unit that changes the port number used as the source to another port number selected from the range of usable port numbers when the destination address is changed.

Further, according to an embodiment of the present invention, a receiving unit for receiving a range of port numbers available for a router from a terminal, and a receiving unit based on the source port number received from the router and the range of port numbers available for the router. Accordingly, a server is provided that includes a port selection unit that selects a port number of a predetermined router, and a transmission unit that transmits the port number of the predetermined router to another predetermined terminal.

Further, according to one embodiment of the present invention, the first terminal under the control of the first router, the second terminal under the control of the second router, and the server not under the control of the router comprise In a communication system in which a second terminal communicates with each other via a first router and a second router using a source address, a source port number, a destination address and a destination port number, the first terminal A first acquisition unit that acquires a range of available port numbers, a first transmission unit that transmits the acquired range of available port numbers of the first router to a server via the first router, and a second router. a first receiver for receiving from a server a predetermined second router port number selected based on a source port number and a range of available port numbers for the second router; a first communication unit that tries to connect to the second terminal via the first router as the port number, and the second terminal acquires a range of port numbers that can be used by the second router. a second transmitter for transmitting the obtained range of available port numbers of the second router to the server via the second router; the source port number of the first router and the available port number of the first router; a second receiving unit for receiving from the server the port number of the predetermined first router selected based on the range of and the port number of the first router to the first terminal via the second router using the port number of the first router as the destination port number a second communication unit that attempts connection, wherein the server receives from the first terminal the range of usable port numbers of the first router and the first source port number; receiving a range of available port numbers of two routers and a second source port number, selected based on the source port number of the first router and the range of available port numbers of the first router; transmitting information to a second receiver for specifying a predetermined first router port number, and selecting based on the second router's source port number and the second router's usable port number range; A communication system is provided for transmitting information to a first receiver for identifying a port number of a predetermined second router to be connected to the first receiver.

The first terminal is based on the source port number of the second router and the range of available port numbers of the second router, which are included in the information for specifying the port number of the predetermined second router received from the server. The second terminal includes a first port selection unit for selecting a port number of a predetermined second router by using the first router and a second port selection unit for selecting a port number of a predetermined first router based on the source port number and the range of available port numbers of the first router.

DESCRIPTION OF SYMBOLS 10... Communication system, 101,101A... 1st terminal, 103, 103A... 2nd terminal, 105... 1st router, 107... 2nd router, 109... Server, 111... Control part, 113... Storage part, 115... Control Unit 117 Storage unit 119 Control unit 121 Storage unit 123 Control unit 125 Storage unit 127 Control unit 129 Storage unit 203 First acquisition unit 205 First transmission unit , 207 first receiving unit 209 first communication unit 213 second acquisition unit 215 second transmission unit 217 second reception unit 219 second communication unit 221 first port selection unit , 223 second port selection unit 303 reception unit 305 port selection unit 401 reception unit 403 transmission unit 405 port change unit

Claims

the first terminal obtains a range of usable port numbers of the first router;
In order to cause the second terminal to acquire the port number of the first router, the first terminal transmits the acquired range of usable port numbers of the first router to the first server via the first router. death,
The first terminal sends information to the first terminal for specifying a port number of a predetermined second router selected based on the source port number of the second router and the range of available port numbers of the second router. 1 obtained from the server,
the first terminal attempting to connect to the second terminal via the first router using the port number of the second router as the destination port number;
communication methods, including
Further, the first terminal inquires of the first router about the range of port numbers available for the first router, and obtains the range of port numbers available for the first router from the first router. 2. The communication method of claim 1, comprising:
The first terminal further includes inquiring a second server about a range of port numbers available for the first router, and obtaining a range of port numbers available for the first router from the second server. , a communication method according to claim 1.
The information for identifying the port number of the predetermined second router is selected by the first server based on the source port number of the second router and the range of available port numbers of the second router. 4. The communication method according to any one of claims 1 to 3, wherein the port number of a predetermined second router.
the first terminal based on the source port number of the second router and the range of available port numbers of the second router, which are included in the information for specifying the port number of the predetermined second router; 4. The communication method according to any one of claims 1 to 3, further comprising selecting a port number of said predetermined second router by using a second router.
The communication method according to claim 1, wherein the range of port numbers available for said first router is a range of port numbers for Internet connection.
The communication method according to claim 6, wherein the connection method of the Internet connection is IPv4 over IPv6.
The communication method according to claim 1, wherein the connection to the second terminal is a P2P connection.
a receiving unit that receives an inquiry about a range of usable port numbers from the first terminal;
a transmission unit that transmits the range of usable port numbers to the first terminal in response to the inquiry;
with
The router, wherein the transmitting unit externally transmits the usable port number range and its own external port number based on a request from the first terminal.
The router according to claim 9, further comprising a port changing unit that changes a port number used as a source to another port number selected from the range of usable port numbers when the destination address is changed.
a receiver that receives a range of available port numbers of the router from the terminal;
a port selection unit that selects a port number of a given router based on the source port number received from the router and the range of available port numbers of the router;
a transmitting unit that transmits the port number of the predetermined router to another predetermined terminal;
A server with
It consists of a first terminal under the control of a first router, a second terminal under control of a second router, and a server not under the control of a router. In a communication system that communicates with each other through said first router and said second router using a source port number, a destination address and a destination port number,
The first terminal is
a first acquisition unit that acquires a range of port numbers that can be used by the first router;
a first transmission unit that transmits the obtained range of available port numbers of the first router to the server via the first router;
a first receiver that receives from the server a predetermined port number of the second router selected based on the transmission source port number of the second router and the range of usable port numbers of the second router;
a first communication unit that attempts connection to the second terminal via the first router using the port number of the second router as a destination port number;
the second terminal,
a first acquisition unit that acquires a range of port numbers that can be used by the second router;
a second transmission unit configured to transmit the obtained range of available port numbers of the second router to the server via the second router;
a second receiver that receives from the server a predetermined port number of the first router selected based on the transmission source port number of the first router and the range of usable port numbers of the first router;
a second communication unit that attempts connection to the first terminal via the second router using the port number of the first router as a destination port number;
The server is
receiving a range of available port numbers of the first router and a first source port number from the first terminal, and a range of available port numbers of the second router from the second terminal; receiving a second source port number;
information for specifying a port number of a predetermined first router selected based on a transmission source port number of the first router and a range of available port numbers of the first router to the second receiver; information for specifying a port number of a predetermined second router to be transmitted and selected based on the source port number of the second router and the range of usable port numbers of the second router; 1 receiver.
The first terminal receives from the server the source port number of the second router and the usable port number of the second router included in the information for specifying the port number of the predetermined second router. a first port selection unit that selects a port number of a predetermined second router based on the range,
The second terminal receives from the server the source port number of the first router and the available port number of the first router included in the information for specifying the port number of the predetermined first router. 13. The communication system according to claim 12, further comprising a second port selector that selects a predetermined first router port number based on the range.
obtain the range of available port numbers for the first router;
transmitting the obtained range of usable port numbers of the first router to the first server via the first router, in order to cause the second terminal to obtain the port number of the first router;
obtaining information from the first server for specifying a port number of a predetermined second router selected based on a source port number of the second router and a range of usable port numbers of the second router;
Attempting connection to the second terminal via the first router using the port number of the second router as the destination port number;
A program for causing the first terminal to execute processing.