JPH02149157A - Transmission control method - Google Patents

Abstract

PURPOSE:To prevent the occurrence of an oscillating state by controlling the revision timing of information to control a flow even when either the case of the number of reception buffers in use in excess of an upper limit threshold level or the case of the number reaching a lower limit threshold level or below takes place. CONSTITUTION:A means sending back reply information including independently information informing a sequence number of a data received correctly at a receiver side RU to a sender side SU and information to control a flow is provided to the method. Then if number of received buffers in use exceeds an upper threshold level limit (n), for example, a flag ful is in use and the data transmission is interleaved while the timing is controlled tentatively (for a time in response to a delay time equivalent nearly to reciprocation of a length of a communication line l) to decrease the data stored in the reception buffer one by one each. Thus, the number of reception buffers in use is kept to a steady-state without causing oscillation and stable transmission control is attained while suppressing the limit to the threshold level or below.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmission control method for data communication between convenience stores included in a computer network or the like.

[Conventional technology]

Data communication between computers is different from voice communication.
High quality is required. For example, when transferring a program from one computer to another, if even one bit is erroneously transferred, the result is the same as transferring a program with a bug. Furthermore, even when rewriting bank data from a remote terminal, it can be a big problem if it is rewritten incorrectly.

Therefore, in order to guarantee high quality in data communication between computers, the following transmission control method is usually implemented.

■If the receiving side receives the data correctly, it sends back response information indicating that it was received correctly, and the transmitting side transmits the data according to the response information from the receiving side.

■If a response is returned and confirmation cannot be obtained, resend the same data again.

In other words, the data is sent while confirming that it has correctly arrived at the receiving end.

The prior art will be explained with reference to the sequence diagram shown in FIG. In Fig. 4, D (h) indicates the data of the sequence number, and RR (i, j> is the receivable response information, i is the sequence number, and the data up to i-1 is correctly received. The sender is able to send data up to a predetermined maximum outstanding number k without confirmation, and j has a sequence number up to +j-1. This indicates that data transmission is permitted.Incidentally, when k=1, when one data is transmitted, the transmission of the next data must be waited until the confirmation information for that data is returned. In the case of FIG. 4, 2=4.

In this case, RR(1,1) correctly receives data D(0) and also notifies the sending side that it is okay to send data up to data D(4) because +j-1=4. There will be. When the sending side receives RR (1, 1), it can send up to data D (4), but cannot send any more. Next, when one reception buffer becomes empty, it updates the value of j by 1. , requesting to send one piece of data (
(Refer to RR (5, 2) in Figure 4), as we will see below, the response information is returned to the sending side at the timing when data is taken from the receive buffer, so the capacity of the receive buffer can be set to the maximum outstanding number k. For example, it can be seen that no data is sent beyond the receive buffer.

However, in systems with large delays, such as satellite lines, the value of k is generally made extremely large to enable continuous transfer. If the receiving side is slower than the transmitting side, data will always accumulate in the receiving buffer, but it is difficult to always secure such a large number of receiving buffers. In addition, with conventional transmission control methods, if the transmission delay is large, the receive buffer becomes empty when the receiving speed increases, making it impossible to continuously transfer data and reducing throughput. be. The following proposals have been made as improvement plans to deal with these problems.

First, on the receiving side, the number of receiving buffers in use bu
Constantly count f, and compare buf with the upper threshold value n and lower threshold value O of the receive buffer immediately after data is taken from the receive buffer, and if buf=o, then j=j+2
If O<bur<n, then j−j+1, and bur≧
If n, the value of j is not updated. However, in order to prevent excess data from accumulating in the reception buffer, j is not updated so that i<j. After calculating the value of j by the above comparison process, the receivable response information R accompanying this value is calculated.
Send R(i,j). Note that updating of 1 is performed in the same manner as in the conventional method.On the other hand, when the transmitting side receives RR(i,D), it is possible to transmit data up to k+j-1 (modulo m).

Figures 5 and 6 show sequence examples of this improvement plan. This is an example showing that the number of uses is suppressed to n or less in a steady state.

When the transmitting side receives RR(1,1), it has data D(
You can send up to 4), but you cannot send any more.

When the number of used reception buffers becomes less than the upper threshold value n, the value of ``' is updated by 1 and a request to send one piece of data is started (see RR (5, 2)).

On the other hand, FIG. 6 shows that the lower threshold allows for increased throughput in response to speed changes on the receiving side. When data D(8) is taken from the receive buffer and buf=0 for the first time, update the value of j two at a time,
In the previous conventional example, RR (9, 8) is sent, but R
It is requesting that R(9,9) be sent and one more piece of data be sent.

[Problems to be Solved by the Invention] As shown in FIGS. 5 and 6, as shown in FIGS. 5 and 6, throughput can be improved while reducing the number of reception buffers used.

However, in the above-mentioned improvement plan, when the receive buffer exceeds the upper threshold value n, j is not updated until the next data is taken from the receive buffer and the number of used receive buffers buf becomes smaller than n; When the number of data used falls below the lower threshold O, transmission control is required to reach a steady state depending on conditions such as the maximum outstanding number, transmission delay, and threshold. may start to oscillate. That is, the sender continues to send data until the upper threshold of the receive buffer is exceeded, then no data is sent until the receive buffer is empty, and then data is sent again until the upper threshold of the receive buffer is exceeded. The zero oscillation state is unstable and causes a problem because a large amount of data repeatedly flows through the transmission path and sometimes no data flows at all.

An object of the present invention is to prevent the occurrence of such an oscillation condition.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the present invention allows a receiver to send data to a sender via a communication line.
In a transmission control method including a procedure for sending back response information that independently includes (a) information informing the transmitting side of the sequence number of data correctly received on the receiving side, and (b) information for controlling the flow, ■The result of comparing the number of reception buffers in use with the upper and lower thresholds of the reception buffer, and ■Controlling the flow in (b) above when the number of reception buffers in use exceeds the upper threshold. A flag that temporarily controls the timing of thinning out updates of information for controlling the flow, and a flag that temporarily controls the timing of thinning out updates of information for controlling the flow in (b) above when the number of reception buffers in use falls below the lower threshold. Is the flow in (b) controlled based on the state of one of the temporarily controlled flags?
Information for I is calculated, and response information including this information is transmitted to the transmitting side, for example, when the reception buffer becomes empty.

(Function) When the number of reception buffers in use exceeds the upper threshold, updating of the information for controlling the flow in (b) is always stopped, and the number of reception buffers in use falls below the lower threshold. If the update amount of the information for controlling the flow in (b) is always increased by a predetermined value in such a case, the effect of returning to the steady state becomes too large, increasing the risk of falling into an oscillation state. In the transmission control method of the present invention, a flag for temporarily controlling the timing of thinning out updates of information for controlling the flow in the above (b) when the number of used reception buffers exceeds an upper threshold; Checking the state of one of the flags that temporarily controls the timing of increasing the update of the information for controlling the flow in (b) when the number of buffers in use falls below the lower threshold; In either case (b) above, if the number of reception buffers in use exceeds the upper threshold or falls below the lower threshold.
The occurrence of an oscillation state is prevented by controlling the timing of updating information for controlling the flow of information.

(Example) Next, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sequence diagram of an embodiment of the transmission control method of the present invention, and the transmission side device SU shown in the figure is connected to a communication surface vAf! from a computer to a satellite line, for example. .

This is the case when data is transmitted to the receiving side device RU, for example, another computer, via the transmission control method according to the present invention.

In FIG. 1, in the receiving unit 2RU, the number of used receiving buffers buf is counted as follows.

That is, in the initial state, buf=o, when data is received from the communication line 2, buf=buf+l, and when data is taken from the reception buffer, bur'=buf-1. In addition, the receiving device RU transmits response information RR (i, D) indicating that data can be received by the value of buf to the transmitting device SO at the timing when data is retrieved from the receiving buffer. Here, i is the sequence number i-1 The value of j is 0 in the initial state. Also, in order to control the timing of updating the value of ``, the flag ful is set to the receiving device RU.
The flag ful is set to 1 in the initial state. After receiving the data from the receiving buffer and decrementing bur, the receiving device RU compares bur with the upper threshold value n and the lower threshold value O of the receiving buffer, and further checks the state of the flag ful. ■but≧n
And if ful=1, the value of j is not updated and RR(i, j
) and set ful=0.

Note that when the sending device SU receives the next data D(j+k) to be sent after receiving the RR(i, j), ru1=
Return to 1.

(2) If buf=0, set j=j+2.

■In cases other than ■ and ■ above, set j=j+1.

However, in both (1) and (2), in order to prevent excess data from accumulating in the reception buffer, j is not updated such that i becomes j. When the receiving device RU calculates the value of j according to the conditions (1) to (2) above, it transmits the receivable response information fill along with the value to the transmitting device SU via the communication line 2. Note that i is updated in the same manner as in the conventional method.

In FIG. 1, k=7. n-2, and the receive buffer is 5
As shown in FIG. 1, the data D
When (6) is received, buf=3>n. At this time, when data D (4) is received from the 0th order reception buffer with flag rul = 1, buf = 2 = n, which is ful-1, so the receiving device RU does not update j = 4. RR(7,4) is sent to , and ful=0. Therefore, even if the sending device SU receives the RR(7,4), it does not send the next data, thereby thinning out the data transmission. The receiving device RU then retrieves the data D(5), D(6), D(7) from the receiving buffer.
, D When (8) is taken over, buf≧n is satisfied, but since ful, = 0, the update of j is not stopped as in the past, but RR(8,5LRR(10,6),
Send RR(11,7), Rrl(11,8). Therefore, data transmission is never thinned out.

The sending device SU sends the next data D (11) when it receives RR (8, 5), but the receiving device RU sets the flag ful=1 again when it receives the next data D (11).
shall be. Therefore, the receiving side device r2U receives data D(9).
is taken from the receive buffer, bur≧n and ru
l-17, the receiving device RU updates R without updating j again.
R(12,8) is transmitted and set to ful"o. Even when the transmitting device SU receives RR(12,8), it does not transmit the next data, so the transmission will be thinned out again. In this way, when the number of used reception buffers becomes equal to or less than the upper threshold value and the reception side device RU receives data D (15) and becomes f u l=1, a steady state is reached.

In this way, when the number of used reception buffers exceeds the upper threshold value n, the flag ful is used to temporarily (in this embodiment, only for a period corresponding to the round-trip delay time of the communication line l) By thinning out the data transmission while controlling the timing and freezing the data accumulated in the receive buffer one by one, the number of receive buffers used is kept to n or less in a steady state without causing oscillation, resulting in stable operation. transmission control can be performed.

FIG. 2 is a flowchart of the processing of one embodiment of the receiving device RU that performs the operations described above. In the receiving side device RU, when data is received, the data reception processing 100 is started, and the sequence number of the received data is checked in the sequence number check processing 11O, and the data is sent to the RR transmission processing 200 and 220. When the sequence number check process 110 is finished, the buf value is incremented by one in the buf addition process 120, the data is accumulated in the reception buffer in the buffer accumulation process 130, and the pause process 2 is executed.
Enter 50. On the other hand, a transfer process 140 sequentially transfers the data stored in the reception buffer to a necessary location.

When the transfer is completed, buf subtraction processing 150 reduces the value of bur to 1.
buf comparison processing 160 compares the value of buf with the upper threshold value n and the lower threshold value 0 of the receiving buffer. If buf-0, j update process 170. j update processing 1
After executing step 80, RR (i, j
) to send. At this time, i is the sequence number + 1 sent from the sequence number check/reprocessing 110.j
The value of j is incremented by 1 in the j update processes 170 and 180, but j is not updated to exceed the value of i.

When 0<bur<n, only the j update processing 180 is executed and then the RR transmission processing 200 is entered. If bur≧n, the value of the flag ful is checked in flag comparison processing 190. f
If ul=0, j update processing 180 is executed and RR transmission processing 200 is entered. When the RR transmission process 200 is completed, the pause process 250 is entered. When ful=1, j memory processing 21
0 stores the value j1 of j at that time, and performs the RR transmission process 22
0 sends RR (i, j) and flag reset processing 23
0 is the flag ful=o.

The operation of the RR transmission process 220 is exactly the same as the RR transmission process 200. After the flag ful is reset, the sequence number check and flag set processing 240 monitors the sequence number of the arriving data D (h), and the j storage processing 210 sets the maximum outstanding value to the value j1 recorded ↑ and α. When the value becomes equal to the sum of the number k, that is, when the data D(jl+k) arrives, the flag ful is set to 1. After the flag ful is set, a pause process 250 is entered.

FIG. 3 is a flowchart of the processing of one embodiment of the sending device SU. At the sending device SU, the receiving device RU receives RR(i
, j), the RR reception process 300 is activated,
Parameters i, j in RR are examined. In retransmission buffer release processing 310, data up to sequence number i-1 is erased from the retransmission buffer, and the buffer is released. In the transmittable number update process 320, the transmittable number is set to j+ by -1, and then the pause process 330 is entered. k is the maximum outstanding number. At the same time, the transmission buffer is constantly monitored in a transmission buffer check process 340, and if data exists in the transmission buffer, the data is extracted, a sequence number is added in a sequence number addition process 350, and the data is compared with the transmittable number. At this time, if the sequence number is larger than the sendable number, the process waits until it becomes equal to or smaller than the sendable number. If it is equal to or smaller than the transmittable number, it is passed to the transmit and retransmit buffer storage process 360, and the data is transmitted. It is also stored in the retransmission buffer at the same time. The retransmission mechanism is performed in the same manner as before.

The above embodiment uses the flag j1 to control the timing of thinning updates of j when the number of used reception buffers buf exceeds the upper threshold value n for a time corresponding to the delay time of the communication line l. But instead of that flag fulO,
A flag emp may be used to temporarily control the timing of increasing the update of j when the number of used reception buffers falls below the lower threshold. After buf is decremented, compare buf with the upper threshold value n and lower threshold value 0 of the receive buffer, and further check the state of flag fu1. If bur≧n, do not update the value of j. Zuni RR (i, j)
Send.

(2) If buf=0 and emp-1, update j=j+2, transmit RR (i, j), and set emp=Q.

Note that when the transmitting side receives the next data D (j - 1) to be sent after receiving the RR (i, j), emp = 1.
shall be.

■In cases other than ■ and ■ above, j=j+1 is updated and sent. However, in both ■ and ■, j is not updated so that °C becomes i less than j. Even with this method,
It is possible to prevent oscillation conditions.

〔Effect of the invention〕

As explained above, in the transmission control method of the present invention, the number of reception buffers used is compared with the upper threshold and lower threshold, and furthermore, a flag newly provided on the reception side is checked, and the results are By calculating information for controlling the flow on the receiving side and feeding it back to the sending side, it is possible to limit the number of receive buffers used to below the upper threshold in a steady state and perform continuous data transfer. , it is possible to prevent the transmission control from falling into an oscillation state, without having the advantage of the above-mentioned conventional improvement plan that it is possible to improve the throughput in response to speed changes on the receiving side by using the lower threshold, Transmission side 1 with stable steady state
It becomes possible to perform 2tl.

Therefore, high-speed data communication, such as high-speed packet communication, can be realized even in systems with large delay times such as satellite lines.

[Brief explanation of the drawing]

FIG. 1 is a sequence diagram of an embodiment of the present invention, FIG. 2 is a flowchart of processing of an embodiment of the receiving device RU, FIG. 3 is a flowchart of processing of an embodiment of the transmitting device SU, and FIG. 5 and 6 are sequence diagrams of the conventional method. In the figure, SU... Sending device RU... Receiving device L... Communication line D (h)... Data RR with sequence number (i,
j)...Response information ful...Flag k...Maximum outstanding number

Claims (1)

[Claims] In response to data transmitted by the transmitting side via a communication line, the receiving side provides the transmitting side with (a) information that informs the transmitting side of the sequence number of the data correctly received by the receiving side; and (b) flow. In a transmission control method that includes a procedure for sending back response information that independently includes information for controlling the and [2] If the number of reception buffers used exceeds the upper threshold, the above (b
), a flag that temporarily controls the timing of thinning out updates of information for controlling the flow of (b), and information for controlling the flow of (b) above when the number of reception buffers in use falls below the lower threshold. The information for controlling the flow in (b) above is calculated based on the state of one of the flags that temporarily controls the timing of increasing the update of A transmission control method characterized by transmitting to.