JP4666173B2 - Relay device, relay method, and relay program - Google Patents

Description

  The present invention relates to a technology for communication using a mobile network, and particularly uses a packet communication method for end-to-end communication between a terminal device and a server device in a use environment where the communication quality of an intermediate route is unstable. The present invention relates to a technique for maintaining a communication session in a data communication system that performs data transmission.

  In recent years, the Internet has become widespread as a network for data communication between terminal devices such as computers. At the same time, usage forms called mobile computing and remote access have become widespread.

  A terminal device or router connected to the Internet is loaded with a program that operates according to a routing protocol called Internet Protocol (hereinafter referred to as IP) shown in Non-Patent Document 1. By using IP, packet communication can be performed between any terminal devices connected to different LANs.

  By the way, in packet switching by IP, when a packet has been transmitted via communication media, if some data content has an error, or if sufficient packet storage area cannot be secured in the router on the way Packet loss occurs during transmission. In addition, since packet arrival order is not guaranteed in IP packet switching, when sending a series of packets from any terminal device to a terminal device connected to a different LAN, the packet transmission order and arrival order May be different.

  In the Internet, reliable data communication is possible even when packets are lost or reordered along such a route, that is, there is no loss of the contents of transmitted packets, and they are received at the receiving side in the order in which they were sent. There is a transmission control protocol (Transmission Control Protocol, hereinafter referred to as TCP) communication method disclosed in Non-Patent Document 2, which is widely used.

  FIG. 1 is a block diagram showing a configuration example of a conventional packet communication system using a TCP / IP communication system. FIG. 2 is a diagram illustrating a configuration of packet data transmitted and received in the packet communication system illustrated in FIG. 1, and is a diagram illustrating a positional relationship of each protocol header. FIG. 3 is a block diagram showing the configuration of the IP header shown in FIG. FIG. 4 is a block diagram showing the configuration of the TCP header shown in FIG. FIG. 5 is a sequence diagram showing a connection maintenance procedure performed to maintain a TCP connection during a period when there is no application data to be transmitted / received in the TCP / IP communication system.

  A conventional packet communication system using the TCP / IP communication system shown in FIG. 1 includes a first terminal device 100, a second terminal device 200, a first relay device 300, a second relay device 400, and a first wire. The network 1001, the second wired network 1002, and the wireless network 1003 are configured. The first terminal device 100 and the first relay device 300 are each connected to the first wired network 1001. Also, the first relay device 300 and the second relay device 400 are each connected to the wireless network 1003. The second relay device 400 and the second terminal device 200 are connected to the second wired network 1002.

  The first terminal device 100 is, for example, an information processing device including a communication device that can be connected to the first wired network 1001, and includes a first processor 101, a first TCP module 102, a first IP module 103, And a first network access module 104.

  The second terminal device 200 is, for example, an information processing device including a communication device that can be connected to the second wired network 1001, and includes a second processor 201, a second TCP module 202, a second IP module 203, And a second network access module 204.

  The first relay device 300 is an information processing device including a communication device that can be connected to the first wired network 1001 and the wireless network 1003, and includes a third IP module 301, a third network access module 302, and a first network device. 4 network access modules 303 are provided.

  The second relay device 400 is an information processing device including a communication device that can be connected to the wireless network 1003 and the second wired network 1002, and includes a fourth IP module 401, a fifth network access module 402, and a second network device. 6 network access modules 403 are provided.

  Each of the first processor 101 and the second processor 201 executes processing according to an application program for performing communication. Here, the application program means an application program that exchanges data with each other and provides a communication service to the user.

  Application programs include FTP (File Transfer Protocol) client server, HTTP (Hyper Text Transfer Protocol) client server, telnet client server, POP (Post Office Protocol) client server, SMTP (Simple Mail Transfer Protocol) client server A known server or the like, or a user-created one is used. Hereinafter, data generated by processing of the application program and exchanged between the first processor 101 and the second processor 201 is referred to as application data.

  Each of the first TCP module 102 and the second TCP processing module 202 is a module that implements the TCP communication method.

  The first IP module 103, the second IP module 203, the third IP module 301, and the fourth IP module 401 are modules that implement a path control function based on IP.

  The state of application data transmission will be described with reference to FIG.

  The application data is first divided into a plurality of divided application data portions having a data size that can be transmitted as a packet, and a protocol control header necessary for the communication method is added to each divided application data and transmitted. The access line trailer in FIG. 2 is data indicating the end of a packet transmitted to the access line, and is defined for each access line to be used.

  When application data is transmitted and received between the first processor 101 and the second processor 201, first, a connection is established between the first processor 101 and the second processor 201, and then the established connection is established. Application data is transmitted through the network. In addition, when the transmission / reception of application data is completed or when a transmission / reception request for application data does not occur for a predetermined period or longer, the established connection is discarded. This predetermined period is generally called “time-out time”. However, depending on the application program that uses the connection, there may be a request to maintain the connection, although transmission / reception is not executed for a long time. In this case, by receiving the “connection maintenance” request, the connection is continuously maintained even when the transmission / reception request does not occur for a period exceeding the timeout time.

  The above functions are realized by the first TCP module 102 and the second TCP module 202 which are transport layer protocol modules that execute TCP protocol control for realizing the connection control function and the data transmission / reception function.

  Next, a connection control function in the conventional packet communication system shown in FIG. 1 will be described. Note that the connection control function is executed by the first TCP module 103 and the second TCP module 203, and each module or device located in the lower layer of the TCP module becomes the destination of the received data. It only performs the function of sending it to the module or device.

The operations described below are executed when an operation request for each function is made from the first processor 101 to the first communication interface management module 102. Alternatively, it is executed when an operation request for each function is made from the second processor 201 to the second communication interface management module 202.
(1) TCP Basic Operation First, a basic operation common to each TCP module shown in FIG. 1 and a method of using a TCP header in a TCP segment will be described.

  As described above, in TCP, a virtual connection is established between TCP modules at both ends, and TCP segments are transmitted and received. Here, in the TCP segment, information for associating the connection with the TCP segment is required.

  The correspondence between the TCP segment and the connection in each TCP module is determined by the combination of the Source Port field indicating the source port number and the Destination Port field indicating the destination port number in the TCP segment header shown in FIG. . Further, the correspondence between the TCP segment and the connection in the entire network is not only the Source Port field and Destination Port field in the TCP header described above, but also the Source Address field representing the source IP address in the IP header shown in FIG. It is determined by the combination of the Destination Address field indicating the destination IP address.

  That is, the TCP module of the device that holds the socket S1 with the IP address of one socket S1 constructing an arbitrary connection is A1, the port number is P1, the IP address of the other socket S2 is A2, and the port number is P2. When the TCP module M1 is the TCP module M1 and the TCP module M2 is the TCP module M2 of the apparatus holding the socket S2, the following operations are performed when a TCP segment is transmitted from the TCP module M1 to the TCP module M2.

  First, the TCP module M1 generates a TCP segment in which P1 is stored in the Source Port field in the TCP header and P2 is stored in the Destination Port field, and is passed to the IP module. Next, the IP module generates an IP datagram in which A1 is stored in the Source Address field in the IP header and A2 is stored in the Destination Address field, and is passed to the network access device.

  On the other hand, the TCP module M2 that has received the IP datagram including the TCP segment, the Source Port field value P1 in the TCP header, the Destination Port field value P2 in the TCP header, the Source Address field value A1 in the IP header, and From the Destination Address field value A2 in the IP header, it can be determined that the TCP segment corresponds to a connection constructed from a combination of the socket S1 and the socket S2.

  In TCP, control using a value called a sequence number is performed in order to realize reachability of the TCP segment to be transmitted and received.

  When sending a TCP segment from the TCP module M1 to the TCP module M2, the TCP module M1 uses a number in units of 1 byte for the application data received from the processor for each held connection (hereinafter referred to as a sequence number). And the value of the top sequence number of the sub application data stored in the TCP segment is stored in the Sequence Number field of the TCP header.

  The TCP module M2 records the value of the Sequence Number field extracted from the received TCP segment for each connection, and the sub application data included in the TCP segment received this time has already been received from that record. Or if it is a newly received one.

  In addition, when new sub application data is received, the TCP module M2 stores a value obtained by adding 1 to the sequence number of the last received sub application data in the Acknowledgment Sequence Number field, and the confirmation flag field (A). A TCP segment storing a value indicating “valid” in is generated and transmitted to the TCP module M1.

  When the TCP module M1 receives a TCP segment in which a value indicating "valid" is set in the confirmation flag field (A) of the TCP header, the TCP module M1 extracts the value (X) of the Acknowledgment Sequence Number field and continues to the sequence number X-1. It is determined that the sub application data has been confirmed to arrive.

  The TCP module M1 starts a retransmission timer when sending a TCP segment. If the above-mentioned arrival confirmation is not made when the value of the retransmission timer reaches the specified time (this is called retransmission timeout), it is considered that the transmission of the TCP segment has failed, and the TCP segment is Send it out.

  If retransmission timeouts occur continuously when sending the same TCP segment, the TCP module M1 determines that the TCP module M2 that establishes the connection has become incapable of communication, and forces the connection. Disconnect. In general TCP module implementation, the connection is forcibly disconnected when retransmission timeout occurs four times in succession.

  Similarly, if application data to be transmitted is not generated in the processing of the application program executed by the processor, and as a result, the TCP module does not trigger the transmission of the TCP segment for a certain period of time, the connection Forcibly disconnect.

Hereinafter, the connection maintaining operation will be described.
(2) TCP connection maintenance operation Connection maintenance operation TCP has a function of forcibly disconnecting a connection when there is no application data to be transmitted in an application program executed by a processor for a predetermined period. . On the other hand, there is a request for maintaining a connection even when there is no application data to be transmitted. For example, in the TELNET service, application data transmission requests do not occur unless the service user inputs data, but a request for maintaining the connection so that it can be dealt with regardless of input is common. In order to respond to such a request, TCP provides a function (generally referred to as a keepalive function) for maintaining a connection even during a period when application data transmission / reception requests are not generated. Hereinafter, an example in which connection maintenance control is performed from the first TCP module 103 to the second TCP module 203 will be described with reference to FIG.

  The first TCP module 102 is in a state where the sequence number of the sub-application data that has been transmitted by itself and the delivery confirmation has been completed is X, and the sequence number of the sub-application data received from the communication partner is Y When it is determined that it is necessary to execute the connection maintenance procedure, a TCP segment (Keepalive) D1 for maintaining the connection is generated and sent to the second TCP module 202. Here, in the TCP header of the TCP segment (Keepalive) D1, in addition to the normal TCP header field settings, the X value is stored in the Sequence Number field, the Y value is stored in the Acknowledgment Number field, and the confirmation flag In the field (A), a value meaning “valid” is set.

  Next, the second TCP module 202 that has received the TCP segment (Keepalive) D1 determines the value (X) of the Sequence Number field and the value (Y) of the Acknowledgment Number field from the TCP header of the received TCP segment (Keepalive) D1. And the value of the confirmation flag field (A) (“valid”), it is determined that the TCP segment is a session maintenance notification.

  Further, the second TCP module 202 generates a TCP segment (Keepalive-ack) D2 for the TCP segment (Keepalive) D1, and sends it to the first TCP module. Here, in the TCP header of the TCP segment (Keepalive-ack) D2, in addition to the normal TCP header field settings, the Sequence Number field has a Y value, the Acknowledgment Number field has an X value, and a confirmation flag field. In (A), a value meaning “valid” is set. Furthermore, the second TCP module 202 continues to maintain the session.

  Next, the first TCP module 102 that has received the TCP segment (Keepalive-ack) D2 determines the value (Y) of the Sequence Number field and the value of the Acknowledgment Number field (from the TCP header of the TCP segment (Keepalive-ack) D2 ( X) and the value of the confirmation flag field (A) (“valid”) are confirmed, it is determined that the TCP segment is a session maintenance notification response, and the maintenance of the session is continued.

  The first TCP module 102 starts a retransmission timer when sending the sent TCP segment (Keepalive) D1, and the TCP segment (Keepalive-ack) D2, which is an arrival response, has not been received before the retransmission timeout. In this case, retransmission of the TCP segment (Keepalive) D1 is executed. Here, when retransmission timeouts continuously occur in the same TCP segment (Keepalive) D1, the above-described forced connection disconnection is executed.

  Further, the connection continuation process from the second processor 201 to the first processor 101 is a symmetric operation of the connection continuation process from the first processor 101 to the second processor 201 described above.

IETF RFC 791 (Internet Protocol: IP) IETF RFC 793 (Transmission Control Protocol)

  However, the packet communication method between the two terminal devices as described above has the following problems.

  When the wireless communication path is included in the intermediate path as shown in FIG. 1, in the conventional technology, the connection is frequently disconnected in a situation where the wireless communication path is unstable, and the connection establishment process is executed again each time. Since it is necessary, the utilization efficiency of the communication system is reduced.

  The reason for this is that in a conventional packet communication system using TCP / IP, even if the relay device existing on the route is directly connected to the wireless communication route, an IP datagram including a TCP segment is simply used. This is because the data is only transferred according to the path control table, is not involved in maintaining the connection, and does not notify a communication path failure of the midway path.

  A wireless communication path using radio waves has a large fluctuation in the quality of the communication path due to interference between radio waves and disturbances such as obstacles, and depending on the situation, the communication path quality may deteriorate so that data transmission / reception cannot be achieved. For example, in FIG. 1, a case where a railway vehicle or bus on which the first terminal device 100 and the first relay device 300 are mounted enters a basement or a tunnel corresponds.

  Data sent to the wireless communication path in such a situation is lost while passing through the wireless communication path, and cannot reach the original destination.

  As described above, TCP connection control is executed only by the TCP modules on both end devices that perform communication. In other words, if the source TCP module at the end point of the connection cannot confirm the arrival response for the sent TCP segment, it means that there is a problem with the destination TCP module and it is impossible to maintain the connection. It is impossible to distinguish whether the TCP segment is lost because the quality of the route is deteriorated.

  The source TCP module whose arrival response cannot be confirmed retransmits the TCP segment triggered by a retransmission timeout. If the communication quality of the route is not recovered, it is detected as a continuous retransmission failure in the source TCP segment and the connection is forced. Termination will be executed.

  After that, even if the channel quality of the radio channel improves, the TCP module re-executes the connection establishment process that has already been completed, and resumes transmission and reception of application data unless a new connection is established. I can't do it. For this reason, applying the conventional TCP connection control in a communication path environment in which connection disconnection frequently occurs reduces the utilization efficiency of the communication system.

  Therefore, the present invention has been invented in view of the above problems, and its purpose is to disconnect a connection even when a situation in which communication quality deteriorates so frequently that data transmission cannot be realized on a halfway path occurs. An object of the present invention is to provide a packet communication technique that does not occur.

  The present invention that solves the above-described problems provides a first terminal device and a second terminal connected to the first relay device via a first relay device and a second relay device connected via a network including a wireless line. The second terminal device connected to the relay device is a communication system in which packet data is transmitted and received, wherein the first relay device is a 4 of the IP address and port number of the first and second terminal devices. Means for storing connection information consisting of two combinations, a time when the TCP segment related to the connection was last relayed, and a TCP segment related to the connection for a predetermined period or more by comparing the stored relay time and the current time. Means for detecting that no relay has been performed, means for detecting that a packet from the second relay device has not been received, and the second relay device And a means for transmitting a connection maintenance notification to the first terminal device when detecting that the packet is not received and that the TCP segment related to the connection is not relayed, The second relay device stores connection information comprising four combinations of the IP addresses and port numbers of the first and second terminal devices, and time when the TCP segment related to the connection was last relayed And a means for detecting that the TCP segment related to the connection has not been relayed for a predetermined period or more by comparing the stored relay time with the current time, and a packet from the first relay device. Means for detecting that it has not been received, that it has not received a packet from said first relay device, and said connection When detecting that not performed relay TCP segment concerned, characterized in that it comprises means for transmitting a connection keep notification to the second terminal device.

The present invention that solves the above-described problems includes a first terminal device connected to a first relay device and a first terminal device connected to the first relay device via a first relay device and a second relay device connected via a network including a wireless line. A communication system for transmitting and receiving packet data to and from a second terminal device connected to a second relay device, wherein the first relay device transmits an alive monitoring packet to the second relay device Means, means for receiving a response packet of the life / death monitoring packet from the second relay device, means for measuring an elapsed time since the transmission of the life / death monitoring packet, and a result of the measurement, predetermined. Means for transmitting a connection maintenance notification to the first terminal device when a response packet to the alive monitoring packet has not been received even after a lapse of a given period, the second relay device Is Means for transmitting a life and death monitoring packet to the first relay device, means for receiving a response packet for the life and death monitoring packet from the first relay device, and after transmitting the life and death monitoring packet And a means for transmitting a connection maintenance notification to the second terminal device when a predetermined period of time has passed as a result of the measurement.

  The present invention for solving the above problems is a relay apparatus in a communication system for transmitting and receiving packet data between terminal apparatuses via two relay apparatuses connected by a network including a wireless line, and a terminal for transmitting and receiving packet data By means of storing connection information consisting of four combinations of the IP address and port number of the device, the time when the TCP segment related to the connection was last relayed, and comparing the stored relay time with the current time, Means for detecting that the TCP segment related to the connection has not been relayed for a predetermined period or more, and detecting that a packet from another relay device connected in the network including the wireless line has not been received. And packets from other relay devices connected by a network including the wireless line And a means for transmitting a connection maintenance notification to the connected terminal device when it is detected that the TCP segment related to the connection is not relayed. .

The present invention for solving the above-described problems is a relay apparatus in a communication system that transmits and receives packet data between terminal apparatuses via two relay apparatuses connected by a network including a wireless line, the network including the wireless line Means for transmitting a life / death monitoring packet to another relay apparatus connected in the network, means for receiving a response packet for the life / death monitoring packet from another relay apparatus connected in a network including the wireless line, and Means for measuring the elapsed time since transmitting the life-and-death monitoring packet; and as a result of the measurement, when a response packet for the life-and-death monitoring packet has not been received even after a predetermined period has elapsed, And a means for transmitting a connection maintenance notification to the connected terminal device.

  The present invention that solves the above-described problems provides a first terminal device and a second terminal connected to the first relay device via a first relay device and a second relay device connected via a network including a wireless line. A communication method in which a second terminal device connected to the relay device transmits and receives packet data, wherein the first relay device and the second relay device are the first and second terminal devices. Stores connection information consisting of four combinations of an IP address and a port number, and the time when the TCP segment related to the connection was last relayed, and a predetermined period by comparing the stored relay time with the current time As described above, it is detected that the TCP segment related to the connection is not relayed, and the first relay device has not received a packet from the second relay device, and the connection When it is detected that the TCP segment related to the network is not relayed, a connection maintenance notification is transmitted to the first terminal device, and the second relay device sends a connection from the first relay device. A connection maintenance notification is transmitted to the second terminal device when it is detected that a packet is not received and that a TCP segment related to the connection is not relayed.

The present invention that solves the above-described problems includes a first terminal device connected to a first relay device and a first terminal device connected to the first relay device via a first relay device and a second relay device connected via a network including a wireless line. A communication method for transmitting and receiving packet data to and from a second terminal device connected to a second relay device, wherein the first relay device transmits a life and death monitoring packet to the second relay device. , Receiving a response packet of the alive monitoring packet from the second relay device, measuring an elapsed time after transmitting the alive monitoring packet, and a predetermined period of time has passed as a result of the measurement In this case, a connection maintenance notification is transmitted to the first terminal device, the second relay device transmits a life / death monitoring packet to the first relay device, and the first relay device Alive monitoring packet from Receiving a packet, the measured time elapsed from the transmission of the life-and-death monitoring packet, the result of the measurement, do not receive a response packet even after a predetermined period with respect to the life-and-death monitoring packet In this case, a connection maintenance notification is transmitted to the second terminal device.

  The present invention for solving the above problems is a relay device program in a communication system for transmitting and receiving packet data between terminal devices via two relay devices connected by a network including a wireless line, and transmits and receives packet data. By storing the connection information consisting of four combinations of the IP address and port number of the terminal device to be processed, the time when the TCP segment related to the connection was last relayed, and the comparison between the stored relay time and the current time A process for detecting that the TCP segment related to the connection has not been relayed for a predetermined period or more and that a packet from another relay device connected in the network including the wireless line has not been received. Detecting process and other relay devices connected by the network including the wireless line A process of transmitting a connection maintenance notification to the connected terminal device when it is detected that the TCP segment related to the connection has not been relayed and the relay device is not relayed to the relay device. It is made to perform.

The present invention for solving the above-described problem is a relay device program in a communication system for transmitting and receiving packet data between terminal devices via two relay devices connected by a network including a wireless channel, A process of transmitting a life / death monitoring packet to another relay apparatus connected in the network including the process, and a process of receiving a response packet of the life / death monitoring packet from another relay apparatus connected in the network including the wireless line And means for measuring an elapsed time since the transmission of the life and death monitoring packet; and as a result of the measurement, if a response packet for the life and death monitoring packet has not been received even after a predetermined period has elapsed And causing the relay device to execute a process of transmitting a connection maintenance notification to the connected terminal device.

  The effect of the present invention is that the use efficiency of the communication system is improved by reducing the frequency of disconnection in the packet communication system even when the communication quality of the intermediate route deteriorates.

  The reason for this is that, in the relay device located in the middle of the packet communication system, connection information necessary for establishing and maintaining the connection exchanged by the devices at both ends using the connection at the time of connection establishment and packet transmission / reception, and This is because the TCP segment relay time is stored, and when the transmission of the packet related to the connection is not observed for a certain time or longer, the connection maintenance process is performed on behalf.

  A first embodiment of the present invention will be described with reference to the drawings.

  FIG. 6 is a block diagram showing a system configuration of the packet communication system according to the first embodiment. 6, the packet communication system according to an embodiment of the present invention includes a first communication terminal 100, a second communication terminal 200, a first relay device 500, a second relay device 600, and a first wired network 1001. , A second wired network 1002 and a wireless network 1003.

  Each of the first communication terminal 100 and the second communication terminal 200 is an information terminal that establishes a connection and executes data transmission / reception by packet communication in the first embodiment of the present invention. Note that the detailed configurations of the first communication terminal 100 and the second communication terminal 200 are the same as those described with reference to FIG. The first wired network 1001, the second wired network 1002, and the wireless network 1003 are also the same as those described with reference to FIG.

  In the first embodiment of the present invention, each of the first relay device 500 and the second relay device 600 selects an output path from the IP header of the IP packet received by the IP protocol control, and creates an IP datagram. Manages and communicates with the connection through itself by analyzing the contents of the IP datagram to be relayed and analyzing the contents of the IP datagram to be relayed, and acquiring information identifying the connection from the TCP header of the TCP segment included in the IP datagram A function is provided that prevents disconnection of a connection by sending a TCP segment for notifying connection maintenance when packet reception from a communication path with unstable quality is delayed for a certain period of time.

  In FIG. 6, the first relay device 500 includes a third network access module 505, a fourth network access module 506, and a first connection monitoring module 511.

  Each of the third network access module 505 and the fourth network access module 506 generates a data frame according to the network access method of the connected network from the IP datagram received from the first connection monitoring module 511. And a function of sending the generated data frame to the connected communication path and a function of taking out an IP datagram from the data frame received from the network and passing it to the first connection monitoring module 511.

  The first connection monitoring module 511 manages the IP datagram relay function and the connection through the relay device, and performs the procedure for maintaining the connection when the communication quality of the connected wireless network deteriorates. Perform the function.

  As shown in FIG. 7, the first connection monitoring device 511 includes an IP processing module 5111, a session maintenance processing module 5112, an input / output status monitoring device 5113, and a storage device 5114.

  The input / output status monitoring device 5113 detects the reception of data from the fourth network access module 506 and the function of relaying IP datagram exchange between the IP processing module 5111 and the fourth network access module 506, and the session maintenance device 5112. It has a function to communicate with.

  The IP processing module 5111 receives the IP datagram from the third network access module and the input / output status monitoring device 5113, and from the information of the IP header and the held routing control table to the network access module corresponding to the destination of the IP datagram And a function for passing the received IP datagram to the session maintenance device when the value of the Protocol field of the IP header is a value meaning TCP.

  The session maintenance processing module 5112 uses a storage device 5114 to maintain a connection management table that passes through the first connection monitoring device 511, and transmission / reception of TCP segments related to each connection is not detected for a certain period of time, and input / output If it is determined that the reception of a packet from the fourth network access module, which is an unstable line in this embodiment, is stopped using the monitoring device 5113, the connection maintenance addressed to the first terminal device is maintained. It has a function to generate and send a TCP segment.

  Note that the configuration and function of the second relay device 600 are the same as those of the first relay device 500, and thus description thereof is omitted.

  FIG. 8 shows an example of the configuration of the connection management table held in each of the session maintenance processing module 5112 and the session maintenance processing module 6112. In the connection management table, the IP address of the relay device that is opposed via a stable wireless line, the connection information managed inside each relay device, the IP address of the relay device that is opposed via an unstable wireless line, and each Stores connection information managed in the relay device.

  Next, referring to FIG. 8, FIG. 9, FIG. 10, FIG. 11, FIG. 12, FIG. 13 and FIG. The operation will be described by taking as an example a case where a connection is established toward the terminal device 2. Thereafter, the IP address of the first terminal device 100 is A1, the port number prepared by the first terminal device 100 is P1, the IP address of the second terminal device 200 is A2, and the second terminal device 200 is prepared. The port number is P2. The IP address assigned to the fourth network access module 506 provided in the first relay device 500 is R1, and the IP address assigned to the fifth network access module 605 provided in the second relay device 600. The address is R2.

  First, the first terminal device 100 generates a TCP segment (SYN) requesting connection establishment, and sends it as an IP datagram to the second terminal device 200 (S1-1). Here, in the TCP header of the TCP segment (SYN), P1 is in the Source Port field, the value of P2 is in the Destination Port field, and the initial value X1 of the sequence number generated by the first terminal device 100 is in the Sequence Number field. Each value is stored. In the IP header of the IP datagram, the value of A1 is stored in the Source Address field, and the value of A2 is stored in the Destination Address field.

Description of S1-2 Next, when the content of the received IP datagram is a TCP segment, the first relay device 500 determines the source address (A1), source port (P1), and destination address of the TCP segment. Check if the connection consisting of the combination of (A2) and Destination Port (P2) (hereinafter referred to as “Connection (A1, P1, A2, P2)”) already exists in the connection management table shown in FIG. If it does not exist, it is created as a new entry in the connection management table, and the time T (S1-2) at the time of creation is recorded (S1-2). Here, the TCP segment is received from the third network access module 505 connected to the stable communication line and transmitted to the fourth network access module connected to the unstable communication line. The result of registration in the connection management table is as shown in FIG.

Description of S1-3 Further, the first relay device 500 transfers the IP datagram received according to the routing control table held therein to the second relay device 600 (S1-3).

Description of S1-4 Next, when the content of the received IP datagram is a TCP segment, the second relay device 600 determines the source address (A1), source port (P1), and destination address of the TCP segment. Check if the connection consisting of the combination of (A2) and Destination Port (P2) already exists in the connection management table shown in FIG. 8, and if not, create a new entry in the connection management table, Record T (S1-4) which is the time of creation (S1-4). Since the TCP segment is received from the fifth network access module 605 connected to the unstable communication line and transmitted to the sixth network access module 606 connected to the stable communication line, the path control is performed. The result of registration in the table is as shown in FIG.

Description of S1-5 Also, the second relay device 600 transfers the IP datagram received according to the routing control table held therein to the second terminal device 200 (S1-5).

Description of S1-6 Next, the second terminal device 200 generates a TCP segment (SYN, ACK) that is a response to the TCP segment (SYN) and sends it to the first terminal device 100 (S -6). Here, in the TCP header of the TCP segment (SYN, ACK), in addition to the normal setting, the Sequence Number field contains the initial value Y1 of the sequence number generated inside the second terminal device 200 as the Acknowledge Sequence Number. The field stores a value of X1 + 1, and the confirmation flag field (A) stores a value meaning “valid”.

Explanation of S1-7 Next, since the content of the received IP datagram is a TCP segment and the value of the confirmation flag field (A) of the TCP header is “valid”, For the entry corresponding to the connection (A1, P1, A2, P2) from the connection management table, the arrival confirmed sequence number of the first terminal device 100 (A1, P1) that is the transmission destination of the TCP segment (SYN, ACK) A value (X1) obtained by subtracting 1 from the value (X1 + 1) of the Acknowledge Sequence Number field is stored in the location (S1-7).

Description of S1-8 Also, the second relay device 600 transfers the received IP datagram according to the path control table held therein to the first relay device 500 (S1-8).

Description of S1-9 Next, since the content of the received IP datagram is a TCP segment and the value of the confirmation flag field (A) of the TCP header is “valid”, the first relay device 500 For the entry corresponding to the connection (A1, P1, A2, P2) from the connection management table, the arrival confirmed sequence number of the first terminal device 100 (A1, P1) that is the transmission destination of the TCP segment (SYN, ACK) A value (X1) obtained by subtracting 1 from the value (X1 + 1) in the Acknowledge Sequence Number field is stored in the location, and the time T (S1-9) at the time of update is recorded (S1-9).

Description of S1-10 Also, the first relay device 500 transfers the IP datagram received according to the routing control table held therein to the first terminal device 100 (S1-10).

Description of S1-11 Next, the first relay device 100 generates a TCP segment (ACK), which is an arrival response to the TCP segment (SYN, ACK), and sends it to the second terminal device 200 (S -11). Here, in the TCP header of the TCP segment (ACK), in addition to the normal setting, the value of X1 + 1 in the Sequence Number field, the value of Y1 + 1 in the Acknowledge Sequence Number field, and the confirmation flag field (A ) Stores a value meaning “valid”.

Description of S1-12 Next, since the content of the received IP datagram is a TCP segment and the value of the confirmation flag field (A) of the TCP header is “valid”, the first relay device 500 For the entry corresponding to the connection (A1, P1, A2, P2) from the connection management table, the arrival confirmed sequence number of the second terminal device 200 (A2, P2) that is the transmission destination of the TCP segment (ACK) A value (Y1) obtained by subtracting 1 from the value (Y1 + 1) in the Acknowledge Sequence Number field is stored, and the time T (S1-12) at the time of update is recorded (S1-12).

Description of S1-13 Further, the first relay device 500 transfers the IP datagram received according to the routing control table held therein to the second relay device 600 (S1-13).

Description of S1-14 Next, since the content of the received IP datagram is a TCP segment and the value of the confirmation flag field (A) of the TCP header is “valid”, the second relay device 600 For the entry corresponding to the connection (A1, P1, A2, P2) from the connection management table, the arrival confirmed sequence number of the second terminal device 200 (A2, P2) that is the transmission destination of the TCP segment (ACK) A value (Y1) obtained by subtracting 1 from the value (Y1 + 1) in the Acknowledge Sequence Number field is stored, and T (S1-14) that is the time at the time of update is recorded (S1-14).

Description of S1-15 Further, the second relay device 600 transfers the IP datagram received according to the routing control table held therein to the second terminal device 200 (S1-15).

  When establishing a new connection, the first relay device 500 and the second relay device 600 each acquire information necessary for maintaining the connection by executing the processing sequence described above. Here, FIG. 13 shows a state of the connection management table held by the first relay device 500 when the above-described connection establishment processing sequence is completed. FIG. 14 shows the state of the connection management table held by the second relay apparatus 600 when the above connection establishment processing sequence is completed.

  Thereafter, each time the first relay device 500 and the second relay device 600 detect the TCP segment passing through the own relay device, the contents of the TCP header are confirmed, and the value of the confirmation flag field (A) is set. If it is "valid", set the value of "Acknowledged Sequence Number" in the corresponding entry of the connection management table held to the value obtained by subtracting 1 from the value of the Acknowledge Sequence Number field of the TCP header, and Set the value of “last update time” to the time of update.

  Next, the operation for maintaining the connection in one embodiment of the present invention will be described with reference to the sequence diagram of FIG.

  In FIG. 15, the arrival confirmation up to sequence number X2 has been completed for the sub application data transmitted from the first terminal apparatus 100, and the sequence number Y2 for the sub application data transmitted from the second terminal apparatus. It is assumed that the arrival confirmation has been completed. In addition, the communication quality of the wireless network 1003 to which the first relay device 500 and the second relay device 600 are connected has deteriorated, and each of the first relay device 500 and the second relay device 600 sends out. It is assumed that the communication packet to be lost has been lost.

  The operation of maintaining the connection in the situation described above will be described below.

  First, the first relay device 500 lastly detects a TCP segment related to the connection (A1, P1, A2, P2) that has passed through its own relay device, and starts a preset period (hereinafter referred to as “T”). If passage of the TCP segment related to the connection (A1, P1, A2, P2) is not detected even after elapse of "Keepalive timeout 1"), execution of the connection maintenance process is determined (S2-2).

  FIG. 16 shows the contents of the connection management table held by the first relay device 500 at the time of S2-2.

  The first relay device 500 generates a TCP segment (Keepalive) for maintaining the connection, and sends it to the first terminal device 100 located on the stable line side (S2-3). Here, in the TCP header of the TCP segment (Keepalive) S2-3, in addition to the normal TCP header field settings, the Y2 value in the Sequence Number field, the X2 value in the Acknowledge Sequence Number field, and the confirmation flag field Each stores a value meaning “valid”.

  Next, when the first terminal device 100 that has received the TCP segment (Keepalive) S2-3 confirms that the TCP segment is a connection maintenance notification, the first terminal device 100 notifies the delivery confirmation of the TCP segment (Keepalive) S2-3. A TCP segment (Keepalive-ack) is transmitted (S2-4).

  Here, in the TCP header of the TCP segment (Keepalive-ack) S2-4, in addition to the normal TCP header field settings, the X2 value in the Sequence Number field, the Y2 value in the Acknowledge Sequence Number field, and the confirmation flag Each field stores a value meaning “valid”.

  Next, the first relay device 500 that has received the TCP segment (Keepalive-ack) S2-4 determines that the TCP segment is a delivery confirmation for the TCP segment (Keepalive) S2-3 transmitted by itself. The TCP segment (Keepalive-ack) S2-4 is received by terminating the TCP segment and receiving the “last update time” in the entry corresponding to the connection (A1, P1, A2, P2) in the connection management table shown in FIG. The time is updated to T (S2-4) (S2-5).

  Thereafter, when the passage of the TCP segment related to the connection (A1, P1, A2, P2) is not detected during the “Keepalive timeout 1” period, the TCP segment (Keepalive) for maintaining the connection is transmitted (S2- 6).

  According to the above procedure, even when the state where the channel quality between the first relay device 500 and the second relay device 600 deteriorates continues for a long period of time, the first terminal device 100 holds it. Existing TCP connections (A1, P1, A2, P2) can be maintained and maintained.

  In addition, the same operation as the connection maintenance procedure performed between the first relay device 500 and the first terminal device 100 described above also between the second relay device 600 and the second terminal device 200. (S2-7 to S2-12).

  FIG. 17 shows the contents of the connection management table held by the second relay device 600 at the time of S2-7.

  As a result, it is possible to keep the second terminal apparatus 200 maintaining the held TCP connections (A1, P1, A2, P2) in an established state.

  Note that the value of “Keepalive timeout 1” used by the first relay device 500 and the value of “Keepalive timeout 2” used by the second relay device 600 do not necessarily match, and the first relay device The connection maintenance procedures executed by each of the 500 and the second relay device 600 operate independently.

  As described above, even in a situation where the channel quality of the wireless network 1003 has deteriorated, the first relay device 500 performs a connection maintenance procedure on the first terminal device 100 as a proxy for the second relay device. In addition, when the second relay device 600 performs the connection maintenance procedure for the second terminal device 200 on behalf of the first relay device 500, the TCP module of each terminal device does not discard the connection. . Thereby, when the communication channel quality of the wireless network 1003 is improved, it is not necessary to perform connection establishment processing, and transmission / reception of application data can be immediately resumed.

  A second embodiment of the present invention will be described.

  In the first embodiment, the first relay device 500 and the second relay device 600 are respectively sent from the first terminal device 100 or the second terminal device 200 and passed through the TCP segment. In response to the fact that no connection period was detected for a predetermined period, execution of connection maintenance processing for only the TCP communication was determined. In the second embodiment, the first intermediate plan is triggered when a response to a life / death confirmation request exchanged between the first relay device 500 and the second relay device 600 is not confirmed for a certain period of time. The execution of the connection maintenance process is determined for all TCP communications via the device 500 and the second mid-range device 600.

  Hereinafter, the block diagram of FIG. 6, the sequence diagram of FIG. 18, and FIG. 19 are used to explain the relationship between the first relay device 500 and the second relay device 600 in the second embodiment of the present invention. The connection maintenance realizing means will be described.

  FIG. 19 shows an example of the configuration of the connection management table held by the first relay device 500 in the second embodiment of the present invention, and FIG. 20 shows the second relay in the second embodiment of the present invention. Each state of the connection management table held by the device 600 is shown.

  Here, there are already three connections Ca (A1, P1a, A2, P2a), Cb (A1, P1b, A2, P2b), Cc (A1) between the first terminal device 100 and the second terminal device 200. , P1c, A2, P2c). In connection Ca, it is assumed that the delivery confirmed sequence number on the first terminal device 100 side is X1a, and the delivery confirmed sequence number on the second terminal device 200 side is X2a. In connection Cb, the delivery confirmed sequence number on the first terminal device 100 side is assumed to be X1b, and the delivery confirmed sequence number on the second terminal device 200 side is assumed to be X2b. Furthermore, in connection Cb, it is assumed that the delivery confirmed sequence number on the first terminal device 100 side is X1c, and the delivery confirmed sequence number on the second terminal device 200 side is X2c.

  In this case, the registration status in the connection management table held by the first relay device 500 is as shown in FIG. 19, and the registration status in the connection management table held by the second relay device 600 is as shown in FIG. It becomes.

  The operation for maintaining the connection in the situation described above will be described below with reference to the sequence diagram of FIG.

  First, the first relay device 500 transmits a life / death confirmation request message to the IP address R2 assigned to the second relay device 600 (S12-1).

  The second relay device 600 that has received the alive confirmation request message (S12-1) sets the last update times of all the connections Ca to Cc registered in the connection management table shown in FIG. 20 to the alive confirmation request (S12-1). Is updated to T (S12-1) which is the reception time of (S12-2).

  Next, the second relay device 600 transmits a life / death confirmation response message to the first relay device 500 (S12-3).

  The first relay device 500 that has received the alive confirmation response message (S12-3) receives the alive confirmation response message (S12-3) with the last update times of all the connections registered in the connection management table shown in FIG. The time is updated to T (S12-3), which is the time (S12-4).

  In addition, the life and death confirmation procedure described above may be started from the second relay device 600. In this case, the operations described in S12-1 to S12-4 are switched between the first relay device 500 and the second relay device 600 (S12-5 to S12-8).

  In FIG. 18, after S12-8, the communication quality of the wireless network 1003 to which the first relay device 500 and the second relay device 600 are connected has deteriorated, and the alive confirmation request message has disappeared in the middle. And

  The first relay device 500 confirms the life and death between the first relay device 500 and the second relay device 600 even after the preset keepalive timeout 1 'has elapsed since the time T (S12-5) when the life and death confirmation was last performed. If not, the execution of the connection maintenance process is determined (S12-9).

  The first relay device 500 generates a TCP segment (Keepalive) for maintaining the connection for each of all the TCP connections Ca to Cc registered in FIG. 19, and the first terminal located on the stable line side The data is sent to the device 100 (S12-10).

  Here, in the TCP header of the TCP segment (Keepalive) for the connection Ca, in addition to the normal settings of each field of the TCP header, the value of Y1a in the Sequence Number field, the value of X1a in the Acknowledge Sequence Number field, Each field stores a value meaning “valid”. In addition, in the TCP header of the TCP segment (Keepalive) for connection Cb, in addition to the normal settings of each field of the TCP header, the value of Y1b in the Sequence Number field, the value of X1b in the Acknowledge Sequence Number field, and the confirmation flag field Each stores a value meaning “valid”. In addition, in the TCP header of the TCP segment (Keepalive) for the connection Cc, in addition to the normal settings of each field of the TCP header, the value of Y1c in the Sequence Number field, the value of X1c in the Acknowledge Sequence Number field, and the confirmation flag field Each stores a value meaning “valid”.

  Next, when the first relay device 100 receiving the TCP segment (Keepalive) confirms that the TCP segment is a connection maintenance notification, the first relay device 100 notifies the delivery confirmation for each of the connections Ca to Cc (Keepalive-ack). ) Are sent individually (S12-11).

  Here, in the TCP header of the TCP segment (Keepalive-ack) for the connection Ca, in addition to the settings of the normal TCP header fields, the value of X1a in the Sequence Number field, the value of Y1a in the Acknowledge Sequence Number field, In the confirmation flag field, a value meaning “valid” is stored. In addition, in the TCP header of the TCP segment (Keepalive-ack) for connection Cb, in addition to the settings of the normal TCP header fields, the X1b value is confirmed in the Sequence Number field, and the Y1b value is confirmed in the Acknowledge Sequence Number field. Each flag field stores a value meaning “valid”. In addition, in the TCP header of the TCP segment (Keepalive-ack) for connection Cc, in addition to the settings of the normal TCP header fields, the X1c value is confirmed in the Sequence Number field, and the Y1c value is confirmed in the Acknowledge Sequence Number field. Each flag field stores a value meaning “valid”.

  Next, when the first relay device 500 that has received each TCP segment (Keepalive-ack) determines that each TCP segment is a delivery confirmation for the TCP segment (Keepalive) S12-10 transmitted from itself, the first TCP segment (Keepalive-ack) As shown in FIG. 19, the last update time of each connection in the connection management table is updated to T (S12-11) which is the reception time of the TCP segment (Keepalive-ack) S12-11 (S12-12). ).

Thereafter, if the confirmation of life and death with the second relay device 600 is not detected during the “Keepalive timeout 1 ′” period, the procedure for maintaining the connection with the first terminal device 100 is repeated.
According to the above procedure, even when the state where the channel quality between the first relay device 500 and the second relay device 600 deteriorates continues for a long period of time, the first terminal device 100 holds it. TCP connections Ca (A1, P1a, A2, P2a), Cb (A1, P1b, A2, P2b), Cc (A1, P1c, A2, P2c) can be maintained and maintained. .

  In addition, the same operation as the connection maintenance procedure performed between the first relay device and the first terminal device 100 described above is performed between the second relay device 600 and the second terminal device 200. Thus, the TCP connection Ca (A1, P1a, A2, P2a), Cb (A1, P1b, A2, P2b), Cc (A1, P1c, A2, P2c) held for the second terminal device 200 ) Can be maintained in the established state.

  As in the first embodiment of the present invention, the value of “Keepalive timeout 1 ′” used by the first relay device 500 and the value of “Keepalive timeout 2 ′” used by the second relay device 600 are The connection maintaining procedures executed by each of the first relay device 500 and the second relay device 600 operate independently of each other.

  As described above, even in the second embodiment of the present invention, even in a situation where the communication channel quality of the wireless network 1003 is deteriorated, the first relay device 500 is compared with the first terminal device 100 in the second state. Each terminal device is configured such that the connection maintenance procedure is performed on behalf of the relay device, and the second relay device 600 performs the connection maintenance procedure on the second terminal device 200 on behalf of the first relay device 500. The TCP module no longer discards the connection. Thereby, when the communication channel quality of the wireless network 1003 is improved, it is not necessary to perform connection establishment processing, and transmission / reception of application data can be immediately resumed.

  In this embodiment, the ICMP ECHO message is used as the life / death confirmation request and the ICMP REPLY message is used as the life / death confirmation response. However, the present invention is not limited to this.

  As described above, according to the present invention, in a packet communication system in which there is a line with unstable communication quality such as a wireless network on a midway route, when a communication method for transmitting and receiving data after establishing a connection in advance is used. Even when the communication quality of the route on the way deteriorates and packet transmission / reception becomes impossible, disconnection of the connection is avoided and communication efficiency of the packet communication system is not reduced.

It is a block diagram which shows the example of 1 structure of the conventional packet communication system. It is a figure which shows the structure of the information transmitted / received by the packet communication system shown in FIG. 1, and is a figure which shows the positional relationship of each protocol header. FIG. 3 is a diagram illustrating a configuration of an IP header illustrated in FIG. 2. FIG. 3 is a diagram illustrating a configuration of a TCP header illustrated in FIG. 2. FIG. 2 is a sequence diagram illustrating a connection maintenance procedure in the packet communication system illustrated in FIG. 1. It is a block diagram which shows the example of 1 structure of the packet communication system of this invention. It is a figure which shows embodiment of the packet communication system of this invention, and is a block diagram which shows the structure of the 1st connection monitoring module shown in FIG. It is a figure which shows embodiment of the packet communication system of this invention, and is the figure which showed the example of 1 structure of the connection management table which each storage apparatus of a 1st connection monitoring module and a 2nd connection monitoring module has. It is a figure which shows embodiment of the packet communication system of this invention, and is a sequence diagram which shows the procedure at the time of connection establishment. It is a figure which shows embodiment of the packet communication system of this invention, and is a sequence diagram which shows the procedure at the time of connection establishment. It is a figure which shows embodiment of the packet communication system of this invention, and showed the internal state of the management table which the memory | storage device of a 1st connection monitoring module has shown in the procedure at the time of the connection establishment operation | movement shown in FIG. FIG. It is a figure which shows embodiment of the packet communication system of this invention, and showed the internal state of the management table which has in the memory | storage device of a 2nd connection monitoring module in the procedure at the time of the connection establishment operation | movement shown in FIG. FIG. FIG. 11 is a diagram showing an embodiment of the packet communication system of the present invention, and shows the inside of the management table possessed by the storage device of the first connection monitoring module when the procedure at the time of the connection establishment operation shown in FIGS. It is the figure which showed the state. FIG. 11 is a diagram showing an embodiment of the packet communication system of the present invention, and shows the inside of the management table held in the storage device of the second connection monitoring module when the procedure at the time of the connection establishment operation shown in FIGS. It is the figure which showed the state. It is a figure which shows embodiment of the packet communication system of this invention, and is a sequence diagram which shows the procedure at the time of connection maintenance execution. FIG. 16 is a diagram showing an embodiment of the packet communication system of the present invention, and is a diagram showing an internal state of a management table included in the storage device of the first connection monitoring module in the procedure at the time of connection establishment shown in FIG. is there. FIG. 16 is a diagram illustrating an embodiment of the packet communication system of the present invention, and is a diagram illustrating an internal state of a management table included in the storage device of the second connection monitoring module in the procedure at the time of connection establishment illustrated in FIG. 15. is there. It is a figure which shows another embodiment of the packet communication system of this invention, and is a sequence diagram which shows the procedure at the time of connection maintenance execution. It is a figure which shows another embodiment of the packet communication system of this invention, and is the figure which showed the example of 1 structure of the connection management table which has in the memory | storage device of a 1st connection monitoring module.

Explanation of symbols

100 first terminal device 101 first processor 102 first TCP module 103 first IP module 104 first network access module 200 second terminal device 201 second processor 202 second TCP module 203 second IP module 204 Second network access module 300 First relay device 301 in the prior art Third IP module 302, 505 Third network access module 303, 506 Fourth network access module 400 Second in the prior art Relay device 401 Fourth IP module 402, 605 Fifth network access module 403, 606 Sixth network access module 500 First relay device 511 in the packet communication system of the present invention First connector Monitoring module 600 Second relay device 611 in the packet communication system of the present invention Second connection monitoring module 1001 First wired network 1002 Second wired network 1003 Wireless networks 5111 and 6111 IP processing modules 5112 and 6112 Session maintenance processing Modules 5113 and 6113 Input / output status monitoring devices 5114 and 6114 Storage devices

Claims (8)

A first terminal device connected to the first relay device and a second terminal connected to the second relay device via a first relay device and a second relay device connected by a network including a wireless line A communication system in which the terminal device transmits and receives packet data,
The first relay device is
Means for storing connection information comprising four combinations of IP addresses and port numbers of the first and second terminal devices, and a time when the TCP segment related to the connection was last relayed;
Means for detecting that the TCP segment is not relayed for the connection over a predetermined period by comparing the stored relay time with the current time;
Means for detecting that no packet is received from the second relay device;
A connection maintenance notification is transmitted to the first terminal device when it is detected that a packet from the second relay device has not been received and that a TCP segment related to the connection has not been relayed. And means for
The second relay device is
Means for storing connection information comprising four combinations of IP addresses and port numbers of the first and second terminal devices, and a time when the TCP segment related to the connection was last relayed;
Means for detecting that the TCP segment is not relayed for the connection over a predetermined period by comparing the stored relay time with the current time;
Means for detecting that no packet is received from the first relay device;
A connection maintenance notification is transmitted to the second terminal device when it is detected that a packet from the first relay device has not been received and that a TCP segment related to the connection has not been relayed. And a communication system. The first terminal device connected to the first relay device and the second relay device connected to the second relay device via the first relay device and the second relay device connected by a network including a wireless line A communication system in which packet data is transmitted and received between two terminal devices,
The first relay device is
Means for transmitting a life and death monitoring packet to the second relay device;
Means for receiving a response packet of the alive monitoring packet from the second relay device;
Means for measuring an elapsed time after transmitting the alive monitoring packet;
A means for transmitting a connection maintenance notification to the first terminal device when a response packet to the alive monitoring packet has not been received after a predetermined period of time as a result of the measurement; ,
The second relay device is
Means for transmitting a life and death monitoring packet to the first relay device;
Means for receiving a response packet of the alive monitoring packet from the first relay device;
Means for measuring an elapsed time after transmitting the alive monitoring packet;
A communication system comprising: means for transmitting a connection maintenance notification to the second terminal device when a predetermined period of time has passed as a result of the measurement. A relay device in a communication system that transmits and receives packet data between terminal devices via two relay devices connected by a network including a wireless line,
Means for storing connection information comprising four combinations of the IP address and port number of a terminal device for transmitting and receiving packet data, and the time when the TCP segment related to the connection was last relayed;
Means for detecting that the TCP segment is not relayed for the connection over a predetermined period by comparing the stored relay time with the current time;
Means for detecting that a packet is not received from another relay device connected by a network including the wireless line;
A terminal device connected when it is detected that a packet from another relay device connected by a network including the wireless line is not received and that a TCP segment related to the connection is not relayed. And a means for transmitting a connection maintenance notification to the relay device. A relay device in a communication system that transmits and receives packet data between terminal devices via two relay devices connected by a network including a wireless line,
Means for transmitting an alive monitoring packet to another relay apparatus connected by a network including the wireless line;
Means for receiving a response packet of the alive monitoring packet from another relay apparatus connected in a network including the wireless line;
Means for measuring an elapsed time after transmitting the alive monitoring packet;
A unit for transmitting a connection maintenance notification to a connected terminal device when a response packet to the alive monitoring packet has not been received after a predetermined period of time as a result of the measurement; A relay device characterized by that. A first terminal device connected to the first relay device and a second terminal connected to the second relay device via a first relay device and a second relay device connected by a network including a wireless line The terminal device is a communication method for transmitting and receiving packet data,
The first relay device and the second relay device are:
Storing connection information consisting of four combinations of IP addresses and port numbers of the first and second terminal devices, and the time when the TCP segment related to the connection was last relayed;
By comparing the stored relay time with the current time, it is detected that the TCP segment related to the connection has not been relayed for a predetermined period or longer,
The first relay device is
A connection maintenance notification is transmitted to the first terminal device when it is detected that a packet from the second relay device has not been received and that a TCP segment related to the connection has not been relayed. And
The second relay device is
A connection maintenance notification is transmitted to the second terminal device when it is detected that a packet from the first relay device has not been received and that a TCP segment related to the connection has not been relayed. A communication method characterized by: The first terminal device connected to the first relay device and the second relay device connected to the second relay device via the first relay device and the second relay device connected by a network including a wireless line A communication method in which packet data is transmitted and received between two terminal devices,
The first relay device is
Send a life and death monitoring packet to the second relay device,
Receiving a response packet of the alive monitoring packet from the second relay device;
Measure the elapsed time since sending the alive monitoring packet,
As a result of the measurement, when a predetermined period has elapsed, a connection maintenance notification is transmitted to the first terminal device,
The second relay device is
Send a life and death monitoring packet to the first relay device,
Receiving a response packet of the alive monitoring packet from the first relay device;
Measure the elapsed time since sending the alive monitoring packet,
As a result of the measurement, when a response packet for the alive monitoring packet has not been received even after a predetermined period has elapsed, a connection maintenance notification is transmitted to the second terminal device, Communication method. A relay device program in a communication system for transmitting and receiving packet data between terminal devices via two relay devices connected by a network including a wireless line,
Processing for storing connection information consisting of four combinations of the IP address and port number of the terminal device that transmits and receives packet data, and the time when the TCP segment related to the connection was last relayed;
A process of detecting that the TCP segment related to the connection is not relayed over a predetermined period by comparing the stored relay time with the current time;
A process of detecting that a packet from another relay apparatus connected by a network including the wireless line is not received;
A terminal device connected when it is detected that a packet from another relay device connected by a network including the wireless line is not received and that a TCP segment related to the connection is not relayed. A program for a relay apparatus, which causes the relay apparatus to execute processing for transmitting a connection maintenance notification to the relay apparatus. A relay device program in a communication system for transmitting and receiving packet data between terminal devices via two relay devices connected by a network including a wireless line,
A process of transmitting a life / death monitoring packet to another relay apparatus connected by a network including the wireless line;
A process of receiving a response packet of the alive monitoring packet from another relay apparatus connected by a network including the wireless line;
Means for measuring an elapsed time after transmitting the alive monitoring packet;
As a result of the measurement, when a response packet for the alive monitoring packet has not been received even after a predetermined period of time has elapsed, a process of transmitting a connection maintenance notification to the connected terminal device is relayed A relay device program that is executed by a device.

Images