JP2001186179A - Method for transferring packet data - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve throughput in the initial state of packet data transfer. SOLUTION: A receiving side has the estimate value of the transmission packet window of a transmitting side, and when the estimate value is smaller than a preliminarily calculated threshold, the opening of the transmission packet window of the transmitting side is decided as being insufficient, and acknowledgement is immediately returned, so that the transmission packet window can fast be promptly.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method of transferring packet data, and more particularly to a method of acknowledgment from a receiving side of packet data.

[0002]

2. Description of the Related Art A conventional packet data transfer method is shown in FIG.
This will be described with reference to the processing flowchart of FIG. As described in the publication “Detailed Explanation TCP / IP” (issued on March 31, 1997) at pages 299 to 355, the conventional packet data transfer method uses a transport layer widely used in the Internet and the like. This is a packet data transfer method accompanied by an acknowledgment such as a protocol (TCP), and a method in which the transmitting side performs flow control in order to realize control to avoid congestion occurring in a network.

[0003] FIG. 7 is a diagram showing a processing flowchart on the transmitting side of packet data. Since the transmitting side of the packet data includes a packet transmitting process and an acknowledgment receiving process thereof, each process is shown in a separate flowchart. FIG. 5 is a flowchart showing an acknowledgment transmission process on the receiving side of packet data. In these flowcharts, for the sake of simplicity of discussion, only processing relating to packet data transfer is shown, and connection connection / disconnection processing and the like are omitted. Also, assuming that the process of transferring the received data to the upper application is sufficiently fast as compared with the transfer speed of the packet data, the window control process on the receiving side is also omitted. Further, it is assumed that packet data is transmitted only from the transmitting side to the receiving side.
In other words, the receiving side needs to transmit packet data to the transmitting side before the timeout of the delay acknowledgment described below,
The assumption is that the acknowledgment will not be piggybacked (processing the data packet and the acknowledgment in the same packet) with the packet data.

[0004] Next, the operations of the transmitting side and the receiving side will be described in detail with reference to respective processing flowcharts.

[0005] In FIG. 7, a packet transmitting process 500 on the transmitting side first performs initialization 501. Here, the transmission packet window size is initialized to 1 and the transmission packet size for which no acknowledgment has been received is initialized to 0.

Next, it is determined 502 whether a transmission data packet has occurred. If the packet to be transmitted has not been generated, the condition is NO, so the process loops until a packet to be transmitted is generated. Conversely, if a packet has occurred, the condition is YES, and the flow proceeds to the next step 503.

In step 503, flow control is performed by the transmitting side. That is, if the size of the unacknowledged transmission packet is greater than or equal to the transmission packet window size,
That is, when the determination result is NO, the packet transmission is suspended, and the process waits in a loop until the determination result becomes YES. Due to the reception of the acknowledgment described later, the size of the transmission packet for which the acknowledgment has not been received is reduced, and the determination result of step 503 is YES
Then, in step 504, a packet to be transmitted is transmitted.

After the transmission of the packet, in step 505, the size of the transmission packet that has not been acknowledged is increased, and the process waits for the next packet to be transmitted.

On the other hand, the acknowledgment receiving process 600 on the transmitting side
Performs a determination 601 as to whether an acknowledgment has been received,
When an acknowledgment has not been received, that is, when the determination is NO, the process waits in a loop.

When an acknowledgment is received, that is, when the determination is YES, in step 602, the size of the outgoing packet that has not been acknowledged is reduced, and at the same time, the size of the outgoing packet window is increased. The size of reducing the size of the transmission packet that has not been received and the size of increasing the size of the transmission packet window depend on the content of the received acknowledgment. The transmitting side processes all data packets transmitted before the data packet acknowledged by the received acknowledgment, assuming that the acknowledgment has been received.

Next, the acknowledgment processing on the receiving side will be described with reference to FIG.

When receiving the packet data, the receiving side returns an acknowledgment to the transmitting side. The acknowledgment transmission process 200 on the receiving side first starts the delay acknowledgment timer 2
01. Next, the process waits in a loop while making a timeout determination at 202 until the delay acknowledgment timer times out. Since it is assumed that there is no data packet to be transferred from the receiving side, the user always waits for a timeout. When a timeout occurs, it is determined in step 203 whether a data packet to be acknowledged has been received for a period before the timeout. If no data packet has been received, that is, if the determination is NO, the process returns to step 201 to start the delay acknowledgment timer. Conversely, when a data packet is received, that is, when the determination is YES, an acknowledgment is transmitted to the transmitting side. Here, the acknowledgment to be transmitted is the latest data packet among the data packets received during the period before waiting for the timeout.

The delay acknowledgment timer shown here is generally associated with a system clock based on the system start time. This is shown in FIG.
Can be expressed as That is, a timeout occurs at a timeout interval set based on the system activation time.

By performing data packet transfer according to the processing flow described above, the transmission packet window size prepared on the transmission side gradually increases,
Packet data transmission is continuously performed. FIG. 6 shows this state as a time run of a packet exchanged between the transmitting side and the receiving side. Here, the timeout period of the delay confirmation response on the receiving side was set to 200 msec. This is the range of 500 ms for the delay acknowledgment timeout time recommended by TCP.
c. In the figure, the value of cwnd shown on the right side of the transmission side is the transmission packet window size. The arrow from the transmitting side to the receiving side indicates the transfer of the data packet, and the arrow from the receiving side to the transmitting side indicates the acknowledgment.

[0015]

The above-mentioned prior art has a problem that a sufficient throughput cannot be obtained in an initial stage of packet data transfer. This is because transmission of packet data is suppressed by flow control on the transmission side. This is also because the receiving side performs the acknowledgment delay process even at the beginning of the packet data transfer.

An object of the present invention is to enable packet data transfer with sufficient throughput even at the beginning of packet data transfer.

[0017]

According to the present invention, at the beginning of a packet data transfer, the receiving side transmits an acknowledgment to the transmitting side earlier or more frequently than usual. That is, the transmission side of the transmission side of the transmission side is opened earlier when the reception side transmits the acknowledgment earlier or more than usual. This improves the throughput characteristics at the beginning of the packet data transfer.

[0018]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a flow chart of the acknowledgment transmission process on the receiving side in the packet data transfer method of the present invention. The acknowledgment transmission process 100 performs initialization in step 101. This is based on the two variables newly introduced in the present invention (the estimated value of the transmission side packet window size and the threshold value on the transmission side).
Is to be initialized. After the initialization in step 101, it is determined in step 102 whether or not the estimated value of the transmitting side transmission packet window size is equal to or smaller than a threshold value. If the result of the determination is YES, a determination is made in step 105 as to whether or not packet data to be immediately acknowledged has been received. Conversely, if the decision result in the step 102 is NO, the delay acknowledgment timer is started in the step 103 as in the past, and if a timeout is detected in the step 104, the process proceeds to the step 105. If there is no packet data to be acknowledged in step 105, that is, if the determination is NO, the process returns to step 102. Step 1
If the determination result in step 05 is YES, an acknowledgment is transmitted in step 106, and in step 107, the estimated value of the transmission side transmission packet window size is updated.

As described above, in the acknowledgment transmission process in the packet data transfer method of the present invention, the transmission side has an estimated value of the transmission packet window size, and the transmission of the acknowledgment is controlled based on the estimated value.

Next, the operation of the embodiment of the present invention will be described in detail with reference to the acknowledgment processing flowchart of FIG.

In an initial initialization step 101, a transmission side packet window size estimation value on the transmission side is initialized to 1. The threshold value is set to a value that can use the data transfer bandwidth from the transmitting side to the receiving side without waste. For example, if the data transfer bandwidth is 64 KBPS, the data packet size is 160 bytes, and the delay acknowledgment timeout time on the receiving side is 200 msec, the threshold is 10
Is set to

After initialization in step 101, the process enters a steady state of the acknowledgment transmission process. First, it is determined in step 102 whether or not the transmission side transmission packet window size estimation value is equal to or smaller than a threshold value. Since this condition is always satisfied at the beginning of the packet data transfer, the determination is YES. Accordingly, it is determined in step 105 whether or not packet data to be immediately acknowledged has been received without passing through the timer for the delayed acknowledgment and the process of waiting for timeout. If no packet data is received, that is, if the determination is NO, the process returns to step 102, but the flow of steps 102 and 105 is looped in the initial stage of packet data transfer. Conversely, if packet data to be acknowledged is received, step 105
Is determined to be YES, and the transmission processing of the confirmation response is performed in step 106. The acknowledgment sent in step 106 is
This is performed for the latest packet among the packets to be acknowledged received up to that point.

If the above-described operation is expressed by focusing on packets exchanged between the receiving side and the transmitting side, it can be described as a time run in FIG. Here, the transmission packet window size of the transmission side is cwnd, and the transmission side transmission packet window size estimation value of the reception side is ec.
wnd. When the transmitting side transmits the first data packet, cwnd = 1, so that only one data packet is transmitted. The receiving side immediately sends an acknowledgment for the first data packet,
-Increase cwnd to 2. Upon receiving the acknowledgment, the transmitting side sets cwnd = 2 and transmits the second and third data packets. The receiving side sends an acknowledgment for each of the two received data packets, and ec
wnd = 4. The transmitting side receives the confirmation response and opens the window until cwnd = 4.
Fourth to seven data packets are transmitted, and before the transmission of the seventh data packet is completed, an acknowledgment for the fourth data packet is received from the receiving side.
wnd = 5 is reached. Up to this point, the speed at which cwnd opens exceeds the actual data packet transmission speed, so that the transmitting side can quickly and continuously transmit data packets. When the receiving side reaches e-cwnd = 10, the cwnd size of the transmitting side has widened as much as possible even if the transmitting side has acknowledged using the delay acknowledgment timer. Move to operation.

Next, a second embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 3 is a flowchart of the acknowledgment transmission process on the receiving side in the packet data transfer method of the present invention. The acknowledgment transmission process 150 is first performed in step 1
At 51, initialization is performed. This is for initializing two variables newly introduced in the present invention (the estimated value of the transmission side transmission packet window size and the threshold value), as in the first embodiment. After the initialization in step 151, the first data packet transmitted is waited for in the determination in step 152. If the packet data to be acknowledged has been received, the process exits the loop of step 152 and enters an acknowledgment process (steps 153 to 156). First, a sequence number to be acknowledged is calculated. In TCP, the sequence number is a serial number assigned to each data byte in a packet. Next, step 154 includes step 15
An acknowledgment is transmitted with the sequence number obtained in step 3. Next, in step 155, the transmission side transmission packet window size estimation value is updated. Then, in step 156,
The transmission side window size estimation value is compared with the threshold size, and when the transmission side window size estimation value is equal to or smaller than the threshold value, that is, when the determination is YES, step 153 is executed.
Return to and send an acknowledgment. Step 156
When the determination of NO is NO, the process proceeds to step 157. Steps 157 to 160 are the same as the conventional acknowledgment transmission processing. However, after the acknowledgment transmission in step 160, the transmission side transmission packet size estimation value is updated in step 161. Thereafter, steps 157 to 161 are repeated.

Next, the operation of the second embodiment of the present invention will be described in detail with reference to the acknowledgment processing flowchart of FIG.

In an initial initialization step 151, the transmitting side transmission packet window size estimation value is initialized to 1. The threshold value is set to a value that can use the data transfer bandwidth from the transmitting side to the receiving side without waste. The method of determining the threshold is the same as that described in the operation of the first embodiment.

After initialization in step 151, the process waits in a loop in step 152 until a data packet is received from the transmitting side. When the packet data to be acknowledged is received, a plurality of acknowledgments are transmitted according to the procedure of steps 153 to 156. First, in step 153, a sequence number for acknowledgment is calculated.
The sequence number is a number assigned to a data byte of a received data packet in TCP. When performing the process of step 153 for the first time, a value smaller than the latest value of the sequence number of the received data packet is selected. Using the selected sequence number, step 15
In step 155, an acknowledgment is transmitted. Then one
The condition is evaluated at 56, but is YES at the beginning of the operation.
Therefore, the process returns to step 153. In step 153, a value larger than the previously selected sequence number and smaller than the latest value of the sequence number of the received data packet is selected, and an acknowledgment is transmitted in step 154 with the sequence number.

Thereafter, an acknowledgment is transmitted until the determination in step 156 becomes NO, that is, until the estimated value of the transmission window size on the transmission side reaches the threshold value. At this time, the sequence number of each acknowledgment is selected so as to be less than the latest value of the sequence number of the data packet received up to that point and to be increased for each transmission. As a result, at the initial stage of data packet transfer, the transmission packet window on the transmission side is rapidly expanded.

After the determination in step 156 becomes NO, the operation is the same as the conventional operation except for the update of the transmission side transmission packet window size estimation value in step 161.

If the above-described operation is expressed by focusing on packets exchanged between the receiving side and the transmitting side, it can be described as a time run in FIG. Here, the transmission packet window size of the transmission side is cwnd, and the transmission side transmission packet window size estimation value of the reception side is ec.
wnd.

When the transmitting side transmits the first data packet, cwnd = 1, so that only one data packet is transmitted. The receiving side immediately sends an acknowledgment for the first data packet, and sets e-cwnd to 2
To increase. The receiving side also transmits two acknowledgments without waiting for the arrival of the next data packet. At this time, the sequence numbers included in the first to third acknowledgments transmitted from the receiving side to the transmitting side are equal to or less than the latest sequence number of the first data packet, and are the first to third. It is chosen to approach the latest sequence number value as it transitions to the third acknowledgment.

When the transmitting side receives the first acknowledgment, it sets cwnd = 2 and transmits a new data packet. Since the receiving side continues to send an acknowledgment until e-cwnd = 10, the transmission packet window of the transmission side is opened faster than the actual data packet transmission, so that the transmission side also continues immediately. Data packet transmission can be performed. When e-cwnd reaches 10, the receiving side responds using the delay acknowledgment timer in the same manner as the conventional acknowledgment transmission. At this time, since the transmission side has also reached cwnd = 10, by transmitting the data packet within the window size, the data transfer can be performed by sufficiently utilizing the line bandwidth.

[0035]

The first effect is that high-speed data transfer can be realized even at the beginning of data transfer. The reason is that an acknowledgment is transmitted immediately without performing the delay acknowledgment process at the beginning of data transfer.

A second effect is that there is little change in using the packet data transfer method of the present invention. The reason is that only the acknowledgment process on the receiving side is changed, and the transmitting side does not need to change. For example, only by implementing the acknowledgment method of the present invention in a protocol stack of a PC or a mobile terminal used by a general user, the protocol stack in a server on the Internet does not need to be changed.

A third effect is that data can be transferred at a high speed from the beginning of data transfer even when the bandwidth of an access line is narrow, such as a dial-up terminal or a mobile terminal using wireless communication. The reason is that the most efficient window size of the transmitting side is estimated from the line bandwidth and the packet size, and the transmitting side operates so as to transmit packet data with the window size.

[Brief description of the drawings]

FIG. 1 is a flowchart showing an acknowledgment transmission process on a packet data receiving side in a packet data transfer method according to a first embodiment of the present invention.

FIG. 2 is a time run diagram showing a state of packet data exchanged between a transmitting side and a receiving side in the packet data transfer method according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing an acknowledgment transmission process on the packet data receiving side in the packet data transfer method according to the second embodiment of the present invention.

FIG. 4 is a time run diagram showing a state of packet data exchanged between a transmitting side and a receiving side in the packet data transfer method according to the second embodiment of the present invention.

FIG. 5 is a flowchart showing an acknowledgment transmission process on the packet data receiving side in the conventional packet data transfer method.

FIG. 6 is a time run diagram showing a state of packet data exchanged between a transmitting side and a receiving side in a conventional packet data transfer method.

FIG. 7 is a flowchart of a transmission process on the packet data transmission side and a flowchart of an acknowledgment reception process.

FIG. 8 is an explanatory diagram showing a system clock and a timing of a timeout.

Claims (9)

[Claims] The receiving side returns an acknowledgment to the transmitting side after a predetermined time has elapsed since receiving the packet data from the transmitting side, and the transmitting side sets the upper limit of the size of the transmitting packet window. A packet data transfer method for transmitting a number of packet data, wherein the receiving side returns the acknowledgment before the predetermined time elapses in an initial stage of the packet data transfer. Method. 2. The reception side returns an acknowledgment to the transmission side after a predetermined time has elapsed after receiving the packet data from the transmission side, and the transmission side sets an upper limit of the size of the transmission packet window. In the packet data transfer method for transmitting the number of packet data, the size of the transmission packet window is determined by the number of acknowledgments from the receiving side, and the receiving side is configured to perform the A packet data transfer method, wherein the acknowledgment is returned before a predetermined time has elapsed. 3. The receiving side estimates a size of the transmission packet window, and changes a time at which the return of the acknowledgment is started according to the estimated value. Packet data transfer method. 4. The receiving side compares the estimated packet window size with a predetermined threshold value, and when the estimated packet window size is smaller than the threshold value, immediately after receiving the packet data. 4. The packet data transfer according to claim 3, wherein the acknowledgment is returned, and when the size of the estimated packet window is larger than the threshold, the acknowledgment is returned after the predetermined time has elapsed. Method. 5. The receiving side compares the estimated packet window size with a predetermined threshold value, and when the estimated packet window size is smaller than the threshold value, immediately after receiving the packet data. 4. The method according to claim 3, wherein the plurality of acknowledgments are returned, and when the estimated packet window size is larger than the threshold, the acknowledgments are returned after the predetermined time has elapsed.
Described packet data transfer method. 6. The packet data transfer method according to claim 4, wherein the threshold value is obtained from a data transfer speed between a transmission side and a reception side and a packet size. 7. The packet data transfer method according to claim 4, wherein the predetermined time is a time from when a delay acknowledgment timer is activated to when the delay acknowledgment timer times out. 8. The acknowledgment in the order in which the sequence numbers included in the plurality of acknowledgments are equal to or less than the latest sequence number of the packet data received by the receiving side up to that point and the receiving side transmits the acknowledgment. 6. The packet data transfer method according to claim 5, wherein the included sequence number changes from an old value to a new value. 9. The method according to claim 3, wherein the estimated value is increased by an accumulated number of acknowledgments transmitted by the receiving side.
9. The packet data transfer method according to any one of items 1 to 8.