JP2000115241A - Data transfer control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a data transfer control method by which a high speed hyper text transport protocol(HTTP) is available without decreasing a window size just after start of transfer. SOLUTION: This data transfer control method that uses a communication network of packet exchange type to transfer file data has steps (S1-S3) where own transmission control protocol(TCP) window sizes are informed between transmission reception terminals to decide the TCP window size, steps (S4, S5) where transfer of data is started by the decided TCP window size, and steps (S6-S12) where transmission of data is continued by decreasing the TCP window size on the occurrence of a communication fault and the TCP window size is increased stepwise when the communication fault is recovered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a data transfer control method suitable for a packet-switched communication network,
The present invention relates to a data transfer control method that enables high-speed flow control in a P (Transmission Control Protocol) session.

[0002]

2. Description of the Related Art Widely used in the Internet,
HT, a WWW (World Wide Web) transfer protocol
TP (Hyper Text Transport Protocol) is TCP /
It is implemented on TCP located in the transport layer of IP (Internet Protocol). In this TCP, for example, when a router or a low-speed link is interposed between the transmitting and receiving terminals, the throughput is not reduced. Richard S
tevens, "TCP / IP Illustrated, Volume 1
"Slow start" (s
Flow control called low-start) is performed.

In the flow control based on the slow start method, the receiving side transmits its own T
The CP window size is declared. The TCP window size W is an amount of data that can be continuously transmitted until the transmitting side obtains an acknowledgment (ACK) packet. Since the transmitting side needs to reduce the amount of data transferred at one time to the TCP window size or less, the TCP window size W
Is larger, the data transfer speed is improved.

Further, when a connection is established between the receiving side and the transmitting side, a congestion control window size called cwnd (congestion window) is added to TCP on the transmitting side. cwnd represents the amount of data that can be transferred from the transmission side to the reception side at one time by the number of segments, and is set to “1” at the start of communication. One segment is set to, for example, about 500 bytes.

[0005] The transmitting side can transmit data at one time until the data amount of the transfer data reaches the smaller one of the TCP window size W or cwnd. The number of segments is set to “2” each time a normal response confirmation packet (ACK signal) is received from the receiving side.
"4", "8",...

[0006] Figure 4 is a diagram showing the transition of the data transfer amount in the flow control in slow start mode described above, after the transfer has been started at time t _0, ACK
Each time a signal is received, the number of segments of the cwnd increases, thereby substantially improving the transfer rate. cwnd number of segments, continue to increase until it reaches the current TCP window size W at time _{t 1.}

[0007] When congestion is detected during transfer by the slow start method, for example, W.W. Richard Ste
vens, "TCP / IP Illustrated, Volume 1
As described in Chapter 21.6, a flow control for avoiding congestion called "congestion avoidance" is performed.

[0008] In flow control congestion-Aboidansu method, as shown in FIG. 4, when congestion is detected at the time t _2, the threshold level ssthre
sh is set to half of the current TCP window size W, and data transfer is continued with the ssthresh as an initial value. After that, every time an ACK signal is received,
Since the number of segments increases linearly, the communication speed gradually increases.

[0009]

The slow start described above prevents congestion beforehand for a protocol such as FTP (file transfer protocol) in which a transfer file is relatively large and a long time TCP session is frequent. It is effective from the viewpoint of However, in the HTTP used in the WWW, the number of sporadic and short-time TCP sessions increases. Therefore, if the above-described slow start control is adopted, the session ends before the TCP window size becomes sufficiently large. Therefore, there is a problem that a sufficient throughput cannot be obtained.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and to provide a one-shot, short-time TC like HTTP.
An object of the present invention is to provide a data transfer control method capable of speeding up a protocol having many P sessions.

[0011]

According to the present invention, there is provided a data transfer control method for transferring file data using a packet-switched communication network. A procedure of notifying a window size to determine a TCP window size, a procedure of starting data transfer with the determined TCP window size, and, when a communication error occurs, reducing the TCP window size and continuing data transfer; When the communication abnormality is resolved, a procedure is provided for increasing the TCP window size stepwise.

According to the above feature, data transfer is started with a relatively large TCP window size determined according to the capability of the transmitting and receiving terminal without previously limiting the TCP window size to a small value, and only when congestion is detected, T
Since the CP window size is reduced and the actual transfer speed is reduced, a protocol such as HTTP that transfers a file having a relatively small size and a transfer time originally shorter enables high-speed transfer.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. FIG. 1 is a flowchart showing a data transfer control method according to an embodiment of the present invention.
FIG. 3 is a diagram showing a transition of a data transfer amount per time according to the present embodiment.

In step S1, the transmitting terminal transmits a SYN packet to the receiving terminal. This SYN packet stores the TCP window size Ws of the own station and the maximum segment length MSSs. The window size Ws depends on the capacity of a buffer memory for temporarily storing data to be processed. In step S2, the process waits for a response from the receiving terminal, and returns (SYN
+ ACK) When the packet is received, in step S3,
In response, the SYN packet is transmitted to the receiving terminal.

In step S4, the TCP window size W of the receiving terminal registered in the received packet
r and the maximum segment length MSSr. Further, the window size Ws of the own station is compared with the window size Wr of the receiving terminal, and the smaller window size (here, Ws> Wr) Wr is registered as a congestion window cwnd. Step S
In 5, the transmitting terminal transfers data for the number of segments defined by the cwnd to the receiving terminal.

In steps S6 and S7, it is determined whether or not congestion has occurred on the line. The occurrence of congestion on the line means that an ACK signal for transfer data has not been received within a predetermined time and a timeout has occurred (step S6), or that an ACK signal for the same packet has been received in duplicate (step S7). Can be recognized by detecting any of the following.

In step S7, when duplication of the ACK signal is detected, and based on this, occurrence of congestion is recognized,
In step S8, a threshold level ssthresh, which is an initial value of cwnd when starting the congestion and avoidance control, is set to the current window size Wr.
Is registered as Wr / 2, which is half the value of

In step S9, as shown in FIG.
Examples cwnd ssthresh is set, the flow control by the congestion-Aboidansu method is started at time _{t 1.} So after that,
At time _{t 2} until cwnd reaches the TCP window size Wr, every time when receiving the normal ACK signal, the number of segments cwnd increases linearly.

On the other hand, if the timeout of the ACK signal is detected in step S6 and the occurrence of congestion is recognized based on the timeout, the process proceeds to step S10 in step S8.
Similarly to the above, a value Wr / 2 that is half the current window size Wr is registered in the threshold level ssthresh.

In step S11, the number of segments of cwnd is set to "1". In step S12, FIG.
As indicated, at time t ₁ the slow start control from the number of segments "1" is started, normal A
Each time the CK signal is received, the number of segments of cwnd increases exponentially.

In the slow start control in step S12, every time the number of segments of cwnd increases, cwnd and ssthre are set in step S12a.
sh is compared. Then, as time _{t 2} before 3, but cwnd slow start control is continued if less than ssthresh, at time _{t 2,} when the cwnd exceeds ssthresh, the process is slow start From the control, the process proceeds to step S9 to shift to the congestion and avoidance control. Thus, then, at time _{t 3} cwnd is TC
Each time a regular ACK signal is received, the number of segments of cwnd increases linearly until the P window size Wr is reached.

[0022]

As described above, according to the present embodiment,
A relatively large TC determined according to the capabilities of the transmitting and receiving terminals without previously limiting the TCP window size to a small value.
The data transfer is started with the P window size, and only after the congestion is detected, the TCP window size is reduced to reduce the actual transfer speed, so that the transfer time is originally shorter with a relatively small size like HTTP. With the protocol for transferring files, the transfer speed can be increased.

[Brief description of the drawings]

FIG. 1 is a flowchart showing the operation of an embodiment of the present invention.

FIG. 2 is a diagram showing a transition of a data transfer amount per time according to the present invention.

FIG. 3 is a diagram showing a transition of a data transfer amount per one time according to the present invention.

FIG. 4 is a diagram showing a transition of a data transfer amount per one time according to a conventional technique.

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Claims (4)

[Claims] 1. A data transfer control method for transferring file data using a packet-switched communication network, comprising: a step of notifying a TCP window size between transmitting and receiving terminals to determine a TCP window size; Starting the data transfer with the set TCP window size, and, when a communication error occurs, reducing the TCP window size to continue the data transfer, and when the communication error is resolved, gradually changing the TCP window size. And a data transfer control method. 2. The data transfer control method according to claim 1, wherein the procedure for increasing or decreasing the TCP window size is flow control by a slow-start method. 3. The method of increasing or decreasing the TCP window size, the method comprising the steps of:
2. The data transfer control method according to claim 1, wherein the flow control is performed by an avoidance method. 4. The data transfer control method according to claim 2, wherein the flow control based on the slow start method includes a flow control based on a congestion and avoidance method.