JP2005348107A - Data communication device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a data communication device capable of avoiding a sharp increase in the data transmission delay between end-to-end terminals, and relieving the tightness of buffer capacity. <P>SOLUTION: A reception buffer 13a retains data received from a transmission terminal side. A TCP module 75 determines the amount of data Tbuf2 to be held between the data communication device and a reception terminal, based on a congestion window cwnd. And the TCP module 75 determines the amount of data that can be advertized to a transmission side, according to the amount of data that a transmission buffer 13b should hold. A PEP process 76 reads data from the reception buffer 13a until the reception buffer 13a becomes empty or the amount of data held by the transmission buffer 13b reaches Tbuf2, and stores the data into the transmission buffer 13b. The transmission buffer 13b temporarily holds the stored data. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a data communication apparatus that optimizes communication based on TCP / IP (Transmission Control Protocol / Internet Protocol).

  TCP is widely used as a protocol for realizing reliable data transfer on the Internet. In the Internet, there is a case where a congestion state in which effective communication cannot be performed due to an increase in network traffic occurs, and matters related to congestion control for controlling communication so as not to become a congestion state are defined in TCP. ing. In TCP, matters relating to flow control for controlling the amount of communication data performed between the transmission side and the reception side are also defined.

The flow control and congestion control based on TCP have the following characteristics.
1. The amount of data (window size) that the transmitting terminal can transmit without an acknowledgment (ACK: ACKnowledgement) depends on the TCP implementation and settings of the terminal, and there is no guarantee that a sufficient window size is always secured.
2. A certain line bandwidth is required for returning the ACK in the direction opposite to the data transmission direction.
3. Assuming that packet loss is due to network congestion, the data transmission rate is suppressed when packets are lost.
For this reason, it is difficult to effectively use the line bandwidth in a line with a large delay, a line with a high asymmetry in which the transmission speed differs between the downlink and the uplink, a line with a large transmission error rate, and the like. It was.

  As a technique for solving this problem, there has been proposed a technique of installing various TCP communication relay device (PEP: Performance Enhanced Proxy) devices optimized for a line having the above characteristics (for example, Patent Literature 1). Most PEP devices are installed at both ends of a line having the above-mentioned characteristics or at an end point on the transmitting terminal side, and explicitly or transparently divide the TCP connection established at the end end between the transmitting terminal and the receiving terminal. .

The following two methods are generally used as the TCP connection division method.
1. It is divided into two TCP connections between the transmission terminal and the PEP device and between the PEP device and the reception terminal (two-connection division method).
2. Three TCP connections between the sending terminal and the first PEP device, between the first PEP device and the second PEP device, and between the second PEP device and the receiving terminal (in the case of a unique protocol between the two PEP devices) (3 connection division method).

  FIG. 3 is a schematic configuration diagram showing a configuration of a conventional communication system using a two-connection division method. Hereinafter, each component in the figure will be described. The server 1 distributes data such as moving image content data via the Internet 2. The transmitting earth station 3 communicates with the subscriber network 5 via the communication satellite 4. The transmitting earth station 3 includes a TCP gateway 31 that plays the role of the PEP device, a router 32 for data relay, and an antenna 33 that transmits and receives data to and from the communication satellite 4. The subscriber network 5 includes an antenna 51 that transmits / receives data to / from the communication satellite 4, a router 52 for data relay, and a client terminal 6 that receives moving image content data from the server 1.

  It is assumed that the transmission delay between the server 1 and the TCP gateway 31 is smaller than the transmission delay between the TCP gateway 31 and the client terminal 6. That is, the bandwidth delay product between the server 1 and the TCP gateway 31 is greater than the bandwidth delay product between the TCP gateway 31 and the client terminal 6.

  FIG. 4 shows a communication sequence by the conventional communication system. FIG. 4A shows a communication sequence when no PEP device is provided. Data (DT) transmitted by the server is received by the client terminal via the router. If the data is received without error, the client terminal returns an ACK to the server. The server waits until an ACK is returned from the client terminal, and transmits the next data when receiving an ACK from the client terminal.

  FIG. 4B shows a communication sequence by the communication system shown in FIG. The TCP gateway 31 receives data from the server 1, transfers the data to the client terminal 6, creates an ACK for this data on behalf of the client terminal 6, and transmits it to the server 1. When the server 1 receives this ACK, the server 1 determines that the data is normally received by the client terminal 6 and transmits the next data. The client terminal 6 receives data from the TCP gateway 31 and transmits an ACK corresponding to the data. The TCP gateway 31 receives the ACK, but does not transfer it to the server 1.

  The TCP gateway 31 holds the data until an ACK is received so that the data can be retransmitted when a data retransmission request is made from the client terminal 6. According to the communication system shown in FIG. 3, since the TCP gateway 31 is provided, the time from the transmission of data to the arrival of ACK in the server 1 can be reduced. Communication can be speeded up.

FIG. 5 is a schematic configuration diagram showing a configuration of a conventional communication system using a three-connection division method. In FIG. 5, the same components as those in FIG. 4 are given the same reference numerals. In this communication system, a TCP gateway 53 is provided in the subscriber network 5. FIG. 6 shows a communication sequence by this communication system. Communication between the TCP gateway 31 and the TCP gateway 53 is performed based on a unique protocol. Similar to the communication by the communication system shown in FIG. 3, according to this communication system, the communication between the server 1 and the client terminal 6 can be speeded up.
Japanese Patent Laid-Open No. 11-252179

In particular, a PEP device for speeding up TCP communication on a line with a large delay requires the following operation.
1. A large number of packets are prefetched from the transmitting terminal and stored in the PEP device.
2. Packets prefetched from the transmitting terminal are sequentially transmitted to the receiving terminal.
3. Hold packet until ACK is returned.

  FIG. 7 hierarchically shows the functions of the PEP device for realizing this. In the figure, the connection between the transmitting terminal side and the PEP device is TCP connection # 1, and the connection between the receiving terminal side and the PEP device is TCP connection # 2. A NIC (Network Interface Card) 81 and a NIC 82 are physical interfaces of the PEP device.

  The driver 83 bridges data between the NICs 81 and 82 and the upper layer. The IP module 84 is software that executes IP. The TCP module 85 is software that executes TCP. The driver 83, the IP module 84, and the TCP module 85 are managed by Kernel, which is a core part of an OS (Operating System). The PEP process 86 controls application programs executed by the PEP device.

  One of the functions of the TCP module 85 is to manage the reception buffer 23a and the transmission buffer 23b. In a general PEP implementation, a reception buffer 23a (buffer size is Rbuf) corresponding to a general (small) window size is prepared between a transmission terminal and a PEP device. The reception buffer 23a temporarily holds data received from the transmission terminal side. A large-capacity transmission buffer 23b (buffer size is Tbuf) corresponding to a large window size is prepared between the PEP device and the receiving terminal. The transmission buffer 23b temporarily holds data transmitted to the receiving terminal.

  Data received from the transmission terminal side is stored in the reception buffer 23a. The PEP process 86 reads data from the reception buffer 23a and stores it in the transmission buffer 23b until the reception buffer 23a becomes empty or the transmission buffer 23b becomes full. The buffer sizes of the reception buffers 23a and 23b are fixed, and the window size (Rwin) advertised by the PEP device to the transmission terminal is not reduced until the transmission buffer 23b is full.

In particular, in a line with a large delay, transmission to the receiving terminal may be delayed due to fluctuations in the line bandwidth, existence of low-speed receiving terminals and applications, or unexpected packet loss. In such a case, a large amount of packets (for reception buffer 23a + transmission buffer 23b) stays in the PEP device in units of TCP connections, causing the following problems.
1. An unexpected transfer delay occurs between end-to-end terminals.
2. The buffer capacity in the PEP device is tight.

  The present invention has been made in view of the above-described problems, and provides a data communication device capable of avoiding a significant increase in data transfer delay between end-to-end terminals and alleviating buffer capacity tightness. The purpose is to provide.

  The present invention has been made to solve the above problems, and the invention according to claim 1 is provided between a transmission device and a reception device that perform data communication, and is provided between the transmission device and the reception device. In a data communication device that speeds up data communication to be performed, a receiving unit that receives data transmitted by the transmitting device, a transmitting unit that transmits the data received by the receiving unit to the receiving device, and the reception Receiving data holding means for holding the data received by the means, transmission data holding means for holding the data waiting for transmission transmitted by the transmitting means, and reading the data from the received data holding means, Communication control variable used for communication control in communication between data storing means for storing in transmission data holding means and said receiving device Depending on the value, the transmission data holding unit is a data communication apparatus characterized by comprising a data amount determination means for determining an amount of data to be held.

  According to a second aspect of the present invention, in the data communication device according to the first aspect, the data amount determining means may be further held by the received data holding means in accordance with a value of the communication control variable. It is characterized by determining the amount of data that can be generated.

  According to a third aspect of the present invention, in the data communication device according to the first aspect, the data amount determining means further includes a new reception data holding means according to a data amount held by the transmission data holding means. It is characterized by determining the amount of data that can be held.

  According to a fourth aspect of the present invention, in the data communication apparatus according to any one of the first to third aspects, the communication control variable is a congestion window.

  According to the present invention, the amount of data held by the transmission data holding means holding the data waiting for transmission is determined based on the value of the communication control variable, so that a large amount of data transfer between end-end terminals can be achieved. There is an effect that an increase in delay can be avoided and the buffer capacity can be alleviated.

  The best mode for carrying out the present invention will be described below with reference to the drawings. In the present embodiment, a data communication device (PEP device) used in a communication system based on the two-connection division method is assumed. The data communication apparatus according to the present embodiment is, for example, a document (T. Hasegawa, two others, “TCP Gateway for Satellite-based Internet Consuming of Multiple Customers”, Information Processing Society of Japan, Journal of Information Processing Society of Japan, 43. Vol. 12, No. 12, p. 3869-3877), which performs TCP-Vegas based congestion control.

  FIG. 1 hierarchically shows functions of a data communication apparatus according to an embodiment of the present invention. In the figure, the connection between the transmitting terminal side and the PEP device is TCP connection # 1, and the connection between the receiving terminal side and the PEP device is TCP connection # 2. The NIC 71 and the NIC 72 are physical interfaces of this data communication apparatus.

  The driver 73 bridges data between the NICs 71 and 72 and the upper layer. The IP module 74 is software that executes IP. The TCP module 75 (data amount determining means) is software that executes TCP. In particular, the TCP module 75 performs management and congestion control of the reception buffer 13a (reception data holding means) and the transmission buffer 13b (transmission data holding means). The driver 73, the IP module 74, and the TCP module 75 are managed by Kernel which is a core part of the OS. The PEP process 76 (data storage means) controls an application program executed by the data communication apparatus.

The TCP module 75 has a data amount Tbuf2 that the transmission buffer 13b should hold between the data communication apparatus and the receiving terminal (the data amount already held by the transmission buffer 13b and the PEP process 76 newly writes the data to the transmission buffer 13b. Is determined based on a congestion window cwnd which is a congestion control variable (communication control variable) used for congestion control. The TCP module 75 increases or decreases the congestion window cwnd according to a delay variation between the data communication device and the receiving terminal. For example, the TCP module 75 measures the delay between the data communication apparatus and the receiving terminal, and decreases the congestion window cwnd when the delay increases. Alternatively, the congestion window cwnd is decreased when a packet transmitted to the receiving terminal side is lost. In this way, the congestion window cwnd reflects the change in the transmission rate in the TCP connection # 2. The TCP module 75 determines the data amount Tbuf2 held by the transmission buffer 13b based on the following equation.
Tbuf2 = C × cwnd (1)
Note that C is a positive constant (default value: 2).

Further, the TCP module 75 determines the reception window size (Rwin: the amount of data that can be newly held by the reception buffer 13a) to be advertised to the transmission terminal based on the following equation.
Rwin = min (max (0, Tbuf2-DTsum), Rbuf) (2)
However, min (X, Y) = X (X ≦ Y), min (X, Y) = Y (X> Y), max (X, Y) = Y (X ≦ Y), min (X, Y) = X (X> Y).

  DTsum is the amount of data currently held in the transmission buffer 13b. This data amount is the total amount of data packets that have been transmitted and are waiting to be transmitted from now on until the ACK is returned between the data communication device and the receiving terminal (the amount of stored packets). ). Rbuf represents the reception buffer amount (the maximum value of the window size that can be advertised to the transmission terminal). Thus, the reception window size Rwin is determined based on the data amount Tbuf2 that the transmission buffer 13b should hold. That is, the value of the congestion window cwnd is reflected in the reception window size Rwin between the transmission terminal and the data communication device.

  Next, the operation of the data communication apparatus will be described. When the TCP connection (TCP connection # 1 and TCP connection # 2) is established, the data transmitted from the transmission terminal is input via the NIC 71. This data is passed to the upper layer by the driver 73 and processed by the IP module 74. Subsequently, the data is passed to the TCP module 75, and the TCP module 75 checks the error of the data, and if there is no error in the data, stores the data in the reception buffer 13a and creates an ACK. This ACK is transmitted to the transmission terminal via the IP module 74, the driver 73, and the NIC 71.

  The TCP module 75 determines the congestion window cwnd according to the delay variation on the receiving terminal side, and determines the data amount Tbuf2 that the transmission buffer 13b should hold based on the equation (1). Further, the reception buffer size Rwin to be advertised to the transmission side is determined based on the equation (2). The PEP process 76 reads data from the reception buffer 13a and stores it in the transmission buffer 13b until the reception buffer 13a becomes empty or the amount of data held by the transmission buffer 13b reaches Tbuf2.

  The TCP module 75 reads data from the transmission buffer 13 b and transmits the data to the receiving terminal via the IP module 74, the driver 73, and the NIC 72. The data transmitted to the receiving terminal is copied by the TCP module 75 and held by the transmission buffer 13b until ACK is returned from the receiving terminal. When the ACK from the receiving terminal is received, the TCP module 75 deletes the data in the transmission buffer 13b corresponding to the ACK.

  Next, a hardware configuration of the data communication apparatus that realizes the above functions and operations will be described. FIG. 2 is a block diagram showing the configuration of the data communication apparatus according to the present embodiment. Hereinafter, each component in the figure will be described. The I / F units 10a and 10b are interfaces through which data is input and output, and have a configuration corresponding to the NICs 71 and 72 in FIG. The transmission / reception unit 11 (transmission means, reception means) performs processing related to data transmission / reception and has functions corresponding to the driver 73 and the IP module 74 in FIG.

  The buffer / window management unit 12 (data amount determination means, data storage means) has a function corresponding to a part of the TCP module 75 and the PEP process 76. In particular, the buffer / window management unit 12 manages the buffer 13, and performs congestion control, flow control, error control (inspection of errors in data, creation of ACK, etc.), and the like. The buffer 13 is a buffer including the reception buffer 13a and the transmission buffer 13b in FIG. 1, and temporarily stores received data.

  In this embodiment, the description has been made on the assumption that it is applied to a communication system using the two-connection division method. is there. The data communication apparatus according to the present embodiment performs TCP-Vegas-based congestion control. However, another TCP (TCP-Reno or the like) may be applied to the data communication apparatus. Further, the value of the constant C in the expression (1) is not limited to 2, but another fixed value may be used, or a value that changes depending on the congestion window cwnd or the like.

  As described above, in this embodiment, the TCP module 75 (buffer / window management unit 12) uses the data amount Tbuf2 held by the transmission buffer 13b as the value of the congestion window cwnd used for communication control in communication with the receiving terminal. To be decided. In this case, the TCP module 75 increases Tbuf2 when the congestion window cwnd increases, and decreases Tbuf2 when the congestion window cwnd decreases. As a result, the data communication device does not accumulate a large amount of data in spite of the occurrence of a large delay on the receiving terminal side, so avoid an unexpected transfer delay between end-to-end terminals. Can do. In addition, the buffer capacity can be alleviated.

  Further, the TCP module 75 (buffer / window management unit 12) determines the data amount that can be newly held by the reception buffer 13a according to the data amount Tbuf2 (or the congestion window cwnd) to be held by the transmission buffer 13b. Thereby, said effect can be heightened more. The data communication apparatus according to the present embodiment is particularly suitable for a line having a large delay, a line having a high asymmetry, a line having a large transmission error rate, and the like such as a wireless communication path.

  As described above, the embodiments of the present invention have been described in detail with reference to the drawings, but the specific configuration is not limited to these embodiments, and includes design changes and the like within a scope not departing from the gist of the present invention. It is.

It is a reference figure showing the function of the data communication device by one embodiment of the present invention. It is a block diagram which shows the structure of the data communication apparatus by the embodiment. It is a schematic block diagram which shows schematic structure of the conventional communication system. It is a reference figure which shows the sequence of communication by the conventional communication system. It is a schematic block diagram which shows schematic structure of the conventional communication system. It is a reference figure which shows the sequence of communication by the conventional communication system. It is a reference figure which shows the function of the conventional PEP apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Server, 2 ... Internet, 3 ... Transmitting earth station, 4 ... Communication satellite, 5 ... Subscriber network, 6 ... Client terminal, 10a, 10b ... I / F part, 11 ... transmission / reception part, 12 ... buffer / window management part, 13 ... buffer, 13a, 23a ... reception buffer, 13b, 23b ... transmission buffer, 31, 53 ... TCP gateway, 32, 52 ... router, 33, 51 ... antenna, 71, 72, 81, 82 ... NIC, 73, 83 ... driver, 74, 84 ... IP module, 75, 85: TCP module, 76, 86: PEP process.

Claims (4)

In a data communication apparatus that is provided between a transmission apparatus and a reception apparatus that perform data communication, and that speeds up data communication performed between the transmission apparatus and the reception apparatus,
Receiving means for receiving data transmitted by the transmitting device;
Transmitting means for transmitting the data received by the receiving means to the receiving device;
Received data holding means for holding the data received by the receiving means;
Transmission data holding means for holding the data waiting for transmission transmitted by the transmission means;
Data storage means for reading the data from the received data holding means and storing it in the transmission data holding means;
Data amount determining means for determining a data amount held by the transmission data holding means according to a value of a communication control variable used for communication control in communication with the receiving device;
A data communication apparatus comprising:   2. The data communication apparatus according to claim 1, wherein the data amount determining unit further determines a data amount that can be newly held by the received data holding unit in accordance with a value of the communication control variable. .   2. The data amount determination unit further determines a data amount that can be newly held by the reception data holding unit according to a data amount held by the transmission data holding unit. Data communication equipment. The data communication apparatus according to any one of claims 1 to 3, wherein the communication control variable is a congestion window.

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