JP2000022744A - Packet communication system, packet communication device and packet communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent lowering of throughput in a network by controlling intervals of acknowledgement of transmission and reception (ACK) to be transmitted to received data when transmission/reception of data is performed between a terminal and other terminals. SOLUTION: Data reception quantity is received by a received data quantity calculating part 12 and average received data quantity is newly calculated by using the data reception quantity and average received data quantity regarding period during which the ACKs are transmitted at the same intervals stored in a data reception quantity storage table 14 at a control part 11 of a client 1. The average received data quantity (1) is compared with the average received data quantity (2) at transmission intervals one stage narrower than the transmission intervals of the ACKs with the average received data quantity in the data reception quantity storage table 14 by the control part 11. When difference between the average data reception quantity (1) and (2) exceeds a certain threshold, an instruction to set the transmission interval as the one to transmit one ACK when 4380 bytes re received is transmitted to an ACK generating part 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a packet communication system, a packet communication apparatus, and a packet communication method that support multimedia for performing voice, image, and data communication.

[0002]

2. Description of the Related Art As a transport layer protocol used for communication between terminals such as computers, TCP (Tr
ansmission Control Protocol). To start communication, the data sender establishes a connection with the partner terminal using a means called three-way handshake of TCP. Then, the terminal that has received the data performs error control by returning a delivery confirmation response to the terminal that has transmitted the data. Since data is not lost, it is mainly used for data communication requiring reliability.

FIG. 4 shows an example of TCP behavior when data is downloaded to an application between terminals connected by Ethernet having a transmission speed of 10 Mbps. The workstation 41 establishes a TCP connection with the workstation 42, downloads data, and returns a response to the workstation 2 to the workstation 42.

[0004] TCP uses window control as flow control. In FIG. 4, the window size is 87
Assume 60 bytes. In Ethernet, the maximum packet length that can be transmitted at one time is 1500 bytes, and usually TCP / IP (Inter
net protocol) overhead 1460 minus 40 bytes
The bytes are the amount of data that can be sent in one transmission. Workstation 42 is workstation 4
The data to be transmitted to 1 is divided into 1460 bytes by the TCP layer and
The data in the packet is transmitted to the workstation 41 as 1460 bytes. At that time, the workstation 41
The window size, which is the number of bytes that can be transmitted without a response from, is reduced by each transmitted byte.

In this case, since the window size of the workstation 41 is set to 8760, the workstation 4
The number of bytes that 2 can send is 8760 minus 1460, giving 7300
Byte. Thus, the workstation 42
Each time data is transmitted, the number of transmittable bytes is reduced. Then, the workstation 41 confirms that the correct data has been received, and returns a delivery confirmation for the data including the window size. When the workstation 42 receives the response from the workstation 41, the workstation 42 updates the transmittable byte count of the workstation 42 with the receivable byte count included in the response. In FIG. 5, since it is 8760 bytes, it is reset to the initial value.

This acknowledgment is based on the fact that the amount of data transmitted from the workstation 42, which is the data transmission side, is equal to the maximum segment size of two since the acknowledgment was transmitted before.
In this example, it is a mechanism that is transmitted when it receives 1460 × 2 and 2920 bytes. However, in the actual communication example,
It is not unusual for an acknowledgment to be transmitted after three or four maximum segment sizes have been received, depending on the circumstances of the internal processing.

As shown in FIG. 4, by returning one response to the data transmitted by a plurality of packets, the transmission path from the workstation 41 to the workstation 42 can be reduced more than the method of returning a response for each packet. It can be used effectively.

Now, consider a system in which the transmission path from the workstation 42 to the work station 41 and the transmission path from the workstation 41 to the workstation 42 are different as shown in FIG. 5, and the transmission speed is asymmetric. Here, when the transmission path speed from the workstation 41 to the workstation 42 is sufficiently smaller than the transmission speed from the workstation 42 to the workstation 41, the throughput from the workstation 42 to the workstation 41 is the same in both directions. The transmission speed is smaller than the transmission speed.

As described above, the TCP has a mechanism of transmitting a delivery confirmation upon receipt of two maximum segment sizes, and further, the transmitting side performs window control based on window information included in the delivery confirmation. , The amount of data that can be transmitted is determined. When a large amount of data is transmitted, the receiving side will transmit a considerable amount of acknowledgment accordingly. However, since the transmission speed from the receiving side to the transmitting side is low, a state of waiting for transmission of the delivery confirmation occurs.

[0010] Yet another problem is that TCP employs a technique of positive acknowledgment with retransmission to provide reliable transmission. This sends an acknowledgment message back to the sender each time the receiver receives data. The sender keeps a record of the sent packet, and waits for delivery confirmation before sending the next packet. The sender starts a timer when sending a packet, and retransmits the packet if the timer expires before an acknowledgment arrives.

[0011] The acknowledgment refers to a sequence value that is one greater than the position of the most significant octet of the received portion. Therefore, the sender needs to transmit data having a value smaller than the sequence value to the receiver and transmit data starting from the sequence value. And this mechanism is cumulative because it reports how much data has been collected. This is called a cumulative acknowledgment.

Here, consider the case where the delivery confirmation is lost. It is assumed that the window size on the transmitting side and the data amount that can be transmitted at one time at a time are two for the maximum segment size. The transmitting side transmits this amount of data, but transmission of the next data must wait for acknowledgment from the receiving side.
It is assumed that the delivery confirmation from the receiving side has been lost for some reason. Since the transmission confirmation is not transmitted to the transmitting side, the transmitted data times out. This results in a significant decrease in throughput. If the receiving acknowledgment is sent more frequently than this, due to the nature of the cumulative acknowledgment,
Thus, the possibility of timeout is reduced. As described above, depending on the frequency of the delivery confirmation, a timeout occurs on the transmission side, and the throughput is reduced.

[0013]

As described in the conventional example, when the transmission path from the data receiving side to the data transmitting side is smaller than the transmission path from the data transmitting side to the data receiving side, There is a problem that the throughput decreases in both directions compared to the same transmission speed. On the other hand, there has also been a problem that reducing the frequency of delivery confirmation leads to a decrease in throughput.

[0014]

In order to solve the above-mentioned problems, a packet communication system according to the present invention transmits data from a first terminal to a second terminal via a network, In a packet communication system that transmits an acknowledgment for notifying the first terminal that the terminal has received the data, an interval at which the second terminal transmits the acknowledgment is defined as an interval of the network. It is characterized by being changed based on the state.

Further, the packet communication system according to the present invention comprises:
The acknowledgment is discarded based on a state of the network. Further, the packet communication device of the present invention includes: means for receiving data via a network;
Means for transmitting an acknowledgment for the data received by the receiving means to the terminal that transmitted the data; means for detecting the traffic state of the network; and means for responding to the traffic state of the network detected by the detecting means. Means for controlling an interval at which the transmission confirmation is transmitted by the transmitting means.

Further, in the packet communication apparatus according to the present invention, the control means discards the delivery confirmation according to a traffic state of the network. Also, the packet communication method of the present invention transmits data from a first terminal to a second terminal via a network, and notifies the first terminal that the second terminal has received the data. In the packet communication method for transmitting a delivery confirmation for performing the above, a step of detecting a traffic state of the network, and the second terminal is configured to respond to the traffic state of the network detected in the detecting step. Controlling the transmission interval of the delivery confirmation.

Further, in the packet communication method according to the present invention, the controlling step discards the delivery confirmation according to a traffic state of the network.

[0018]

1 and 2 show a system configuration diagram according to the present invention. 1 is a client, 2 is a server,
Reference numeral 3 denotes a gateway, 4 denotes a network, and 5 denotes an asymmetric transmission path in which the transmission speed from the gateway to the client is sufficiently higher than the transmission speed from the client to the gateway.

FIG. 2 is a configuration diagram of the client 1.
11 is a control unit, 12 is a received data amount generation unit, 13 is ACK
A generating unit, 14 is a data reception amount storage table, and 15 is a transmitting / receiving unit.

FIG. 3 is a diagram showing an example of the data reception amount storage table. It is assumed that an application for transmitting a large amount of data from the server 2 to the client 2 is started by the request of the client 1. Here, the maximum segment size of this connection is 1460 bytes. In client 1, the initial value of the ACK transmission interval is set to 292.
When 0 bytes (maximum two segment sizes) are received, the interval is set so that one ACK is transmitted.

In the client 1, the received data amount calculation unit 12 calculates the amount of data received in a certain time unit. Based on the above, the method of changing the ACK transmission interval will be described step by step.

First, based on FIGS. 1, 2 and 3, claim 1
A first embodiment of the present invention corresponding to FIG. The control unit 11 of the client 1 receives the data reception amount from the reception data amount calculation unit 12 and averages the data reception amount and the period during which the ACK is transmitted at the same interval stored in the data reception amount storage table 14. The average received data amount is newly calculated using the received data amount.

The control unit 11 controls the average received data amount (1) and the average received data amount at a transmission interval one step narrower than the ACK transmission interval based on the average received data amount in the data reception amount storage table 14 (2). Compare. If an asymmetric transmission path exists in a part of the network as shown in Fig. 1, (1) and
The difference between (2) becomes large, and in the case of symmetry, the difference between (1) and (2) becomes small. Therefore, if the difference between (1) and (2) exceeds a certain threshold, 4380 bytes (maximum segment size 3
When an ACK is received, an instruction to make the interval such that one ACK is transmitted is transmitted to the ACK generation unit 13.

As described above, since the transmission speed from the client 1 to the server 2 is low as asymmetric, the server 1
Even in a network where the throughput from the client 2 to the client 1 decreases, it is possible to stop the decrease in the throughput from the server 2 to the client 1.

Next, a second embodiment of the present invention corresponding to claim 1 will be described with reference to FIGS. As in the first embodiment, it is assumed that an application in which a large amount of data is transmitted from the server 2 to the client 1 is started.

The transfer is performed smoothly, and the ACK transmission interval is
When an interval of sending one ACK is received after receiving 11680 bytes, some server 2
Suppose that one packet from client to client 1 is lost. The control unit 11 in the client 2 cannot confirm whether the packet has been lost, but detects that the order of the packets has changed, and interprets that some abnormality has occurred in the network.

Therefore, the control unit 11 considers that there is a possibility that the ACK is also lost, and instructs the ACK generation unit 13 to reduce the ACK transmission interval to half of the current transmission interval, that is, to receive the ACK transmission interval of 5840 bytes. Then, set the interval so that one ACK is transmitted. As a result, server 2 due to ACK loss
Therefore, it is possible to reduce the possibility of a decrease in the throughput in the client 1 direction.

FIG. 6 shows a stack of a network protocol inside the client 2. FIG.
Is a schematic representation of a state in which the ACK is waiting for transmission within the client 2.

Here, a third embodiment of the present invention corresponding to claim 2 will be described with reference to FIGS. Consider a case where a large amount of data is transmitted from the server 2 to the client 1 in FIG. At this time, the client 2 sends one ACK to the server 2 every time it receives a packet having a maximum segment size of two due to the behavior of TCP. This ACK is generated in the TCP layer 63 in FIG.
Processing is performed in the IP layer 64 and the data link layer 65, respectively, and transmitted from the physical layer (transmitter / receiver) 66.

Here, consider a case where the ACK generation speed is faster than the transmission speed of the transmission network. In this case, the ACK that cannot be transmitted is in a waiting state in the data link layer as shown in FIG.

When the number of ACKs waiting to be transmitted in the data link layer 65 exceeds a certain threshold, all ACKs except for the most recently generated ACK are discarded. Then, when there is room to transmit to the transmission network, the most recently generated ACK is transmitted.

Since ACKs in TCP are cumulative, the newest ACK can play the role of the oldest ACK. This makes it possible to avoid a decrease in the throughput from the server 2 to the client 1 due to the inability to transmit the ACK.

FIG. 8 is a diagram showing the configuration of the gateway according to the present invention. 81 is a receiving unit, 82 is a transmitting unit, 83 is a control unit, and 84 is an ACK storage unit. ACK storage unit 84
Is as shown in FIG. 9 and has a queue structure capable of storing ACK for each connection.

Here, the asymmetrical driving path as shown in FIG.
In the configuration of the third embodiment, when the gateway 3 exists between the gateway 3 and the server 2 instead of the part 5, the gateway 3 may perform the operation shown in the third embodiment.

That is, the ACK accumulating section 84 of the gateway 3 accumulates ACKs from the client 1, the client 11, and the client 12 separately in the queue as shown in FIG. ACK waiting for transmission
If exceeds a certain threshold, all but the most recently generated ACK are discarded. Then, when there is enough time to transmit to the transmission network, the most recently generated ACK is transmitted.

[0036]

As described above, according to the present invention, when a terminal connected via a network transmits / receives data to / from another terminal, an acknowledgment (ACK) transmitted for received data is transmitted. By controlling the interval, it is possible to prevent a decrease in throughput in the network. In particular, when the transmission and reception paths are asymmetric, it is possible to improve the reliability of data transmission / reception by transmitting only necessary acknowledgments.

[Brief description of the drawings]

FIG. 1 shows a communication system according to the present invention.

FIG. 2 is a diagram showing a configuration of a network system according to the present invention;

FIG. 3 is a diagram showing a data reception amount storage table;

Fig. 4 Diagram showing TCP behavior

FIG. 5 is a diagram showing an example of an asymmetric transmission line.

FIG. 6 shows a protocol stack.

FIG. 7 is a diagram showing a state of waiting for transmission of an ACK.

FIG. 8 is a diagram showing a configuration of a gateway according to the present invention.

FIG. 9 is a diagram showing a configuration of an ACK storage unit of the gateway;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Client 2 ... Server 3 ... Gateway 4 ... Network 5 ... Asymmetric transmission line

Claims (6)

[Claims] 1. A delivery confirmation for transmitting data from a first terminal to a second terminal via a network and notifying the first terminal that the second terminal has received the data. A packet communication system according to claim 1, wherein an interval at which said second terminal transmits said acknowledgment is changed based on a state of said network. 2. The packet communication system according to claim 1, wherein the acknowledgment is discarded based on a state of the network. Means for receiving data via a network, means for transmitting an acknowledgment for the data received by the receiving means to a terminal which has transmitted the data, and means for detecting a traffic state of the network. A packet communication device comprising: a unit that controls an interval at which the transmission unit transmits the acknowledgment in accordance with a traffic state of the network detected by the detection unit. 4. The packet communication device according to claim 3, wherein the control unit discards the delivery confirmation according to a traffic state of the network. 5. A delivery confirmation for transmitting data from a first terminal to a second terminal via a network, and notifying the first terminal that the second terminal has received the data. Detecting a traffic state of the network; and transmitting the acknowledgment by the second terminal according to the traffic state of the network detected in the detecting step. Controlling the interval. 6. The packet communication method according to claim 5, wherein in the packet communication method, the controlling step discards the delivery confirmation according to a traffic state of the network.