JP4384676B2 - Method for controlling data communication apparatus - Google Patents

Description

  The present invention relates to a data communication apparatus including a transmission control means for executing a transport layer protocol when performing communication via a packet switching network, and particularly involves generation of a temporary delay and transmission of a bursty packet. The present invention relates to a data communication apparatus that improves a load in communication including a communication path in the communication path.

  Conventionally, TCP (Transmission Control Protocol) is known as a transport layer protocol that guarantees reliability in Internet communication. TCP is documented in RFC793, RFC1122, RFC2581, RFC2582, etc., but research for improving it is continued. TCP is located in the transport layer in the OSI reference model, and controls connections, realizes stream-type communication, controls quality such as error control and flow control, communication between ports specified by port numbers, and congestion control ( (Technology for controlling communication so as not to be in a congested state in which effective communication cannot be performed due to an increase in network traffic).

  In communication based on TCP, data to be transmitted is divided into small data called segments, and the segments are stored in an IP (Internet Protocol) packet and transmitted. When the receiving side receives the IP packet, it extracts the segments based on TCP and concatenates them in order to restore the original data.

  The IP located in the network layer defines communication between hosts specified by IP addresses. A TCP connection is established between two ports specified by a port number in addition to an IP address. For this reason, even if a plurality of applications use a communication path at the same time, they can be distinguished by a difference in port numbers.

  TCP error control is realized by ACK (ACKnowledge: Acknowledgment, Acknowledgment), ACK is transmitted from the reception side to the transmission side, and the transmission side retransmits a data segment that does not return ACK. Further, the transmission side tries to transmit a data segment for a certain window size in order to increase the throughput based on TCP. This method is called sliding window flow control, and transmission of data segments for the window size is permitted. When an ACK for the data segment is returned from the receiving side, the sequence number of the window slides. This window of the transmission side is called a “congestion window” (cwnd: congestion window) and also serves as a congestion control.

  The TCP flow control is also performed by notifying the receiver window (rwnd) in the ACK returned from the receiving side to the transmitting side. This rwnd represents the amount of data that can be received by the receiving side, and transmission can be stopped by reporting 0 as rwnd. rwnd is determined depending on the buffer amount prepared on the receiving side. The transmission side suppresses transmission so that the smaller one of rwnd and cwnd is not exceeded.

  The purpose of the sliding window flow control is to avoid a situation where a buffer on the receiving side is insufficient and to improve throughput by performing retransmission control by ARQ (automatic retransmission request). Since communication is performed via a plurality of data links in the Internet, it is necessary to perform flow control in the transport layer without depending on a specific data link layer.

  Hereinafter, TCP congestion control will be described. In TCP congestion control, slow start and congestion avoidance operations are performed to avoid network congestion collapse. In slow start, cwnd is set small at the start of transmission, and cwnd is increased exponentially every time an ACK is returned from the receiving side. For example, every time an ACK is returned, cwnd increases by one.

  That is, two data segments can be transmitted for one ACK. Congestion avoidance is an operation of increasing cwnd little by little. In congestion avoidance, every time one ACK is returned, cwnd increases by 1 / cwnd. That is, when cwnd ACKs are returned, cwnd + 1 becomes the next cwnd value for the current cwnd. While flow control is a consideration for the receiving side, congestion control is a consideration for the network.

  With the spread of wireless data communication, usage forms including wireless communication paths in communication paths are increasing. In a high-speed wireless communication path, a temporary delay and bursty packet transmission may be involved. In the data link layer and the physical layer of the wireless communication path, reliability is enhanced by executing a protocol based on automatic repeat request (ARQ). When the receiving terminal in the wireless communication channel detects an error in the received data, it requests the transmitting side to retransmit the data, and temporarily stores the received data in the buffer until the requested data arrives. To delay.

  The base station on the transmission side of the wireless communication path holds data in preparation for retransmission until the receiving terminal returns an acknowledgment (ACK). Since the quality of the wireless communication channel may temporarily deteriorate, the base station adjusts the error rate so as not to become too low by changing the modulation method and the data transmission rate. Nevertheless, the error rate of the wireless communication path is larger than that of the wired communication path, and retransmission control is required in the wireless communication path.

  TCP has a mechanism called Delayed ACK. The Delayed ACK is described in RFC1122 and RFC813. In the Delayed ACK, the transmission of the ACK is delayed, and the ACK is transmitted when the next ACK is generated, timed out, or a transmission data segment is generated. When the next ACK is generated with the ACK being delayed, the number of ACKs to be transmitted is reduced at a rate of one in two. When a transmission data segment is generated, the ACK is added to the ACK. By doing so, the number of ACKs to be transmitted is reduced.

  This Delayed ACK operation has the advantage of reducing the number of ACK packets when executing the Telnet application. However, there is no particular advantage when downloading large data, but rather the variation in RTT (Round Trip Time). There is a demerit such as generating. Also, if the Delayed ACK scheme is expanded to increase the transmission delay of ACK and the reduction rate of the number of ACKs, the data segment transmitted from the transmission side becomes bursty accordingly, and the forward link ( Congestion is likely to occur on the downstream).

  The following techniques are disclosed as techniques for reducing ACK. In an asymmetric communication channel with a large forward link transmission rate and a small reverse link (uplink) transmission rate, when congestion occurs in the reverse link channel, the oldest stored in the queue A router is disclosed that reduces the number of ACKs based on drop-from-front buffer discipline by discarding ACK packets and storing the latest ACK packets in a queue. . This device pays attention to the fact that congestion is likely to occur on a reverse link with a low transmission speed in an asymmetric communication path, and among the ACK packets that cannot be transmitted in the router, there is the least adverse effect when discarded. The oldest ACK packet is discarded.

  Conventionally, even if a wireless terminal transmits a retransmission request to the data transmission side, if the requested data is not retransmitted, a delay determined by the communication protocol of the wireless communication path occurs. The wireless terminal waits for retransmission for a predetermined time, but if the retransmission times out, the wireless terminal receives the data and stores it in the buffer while waiting for retransmission of the data, assuming that the data has been lost. The data being processed is output downstream. The bandwidth of the forward link of the wireless communication channel has reached several hundred kbps, and it is assumed that it will become even larger in the future. For this reason, data packets are transmitted in bursts after a temporary delay occurring in the wireless communication path.

  A downstream data communication apparatus that has received such a bursty data segment transmits an ACK packet in bursts based on TCP. However, if some data segments are lost, the sequence number in the ACK does not increase. If this ACK arrives before the TCP retransmission timeout on the transmission side, it is recognized as a duplicate ACK, and high-speed retransmission is executed by the transmission side. Based on this, the data is retransmitted without waiting for the arrival of ACK.

  The state of communication described above is shown in FIG. FIG. 12 is a time sequence graph showing the operation on the reception side of the conventionally known TCP New Reno (RFC2582), where the horizontal axis represents time and the vertical axis represents the sequence number. Note that a normal time sequence graph is measured on the transmission side, but FIG. 12 shows a situation on the reception side. On the receiving side, it is assumed that there are a wireless terminal connected to the wireless communication path and a downstream data communication apparatus that performs data input / output with the wireless terminal. FIG. 12 plots the reception of the data segment 30 and the transmission of the ACK 31 corresponding thereto. In the section 32, when the data communication apparatus receives the data segment 30 via the wireless terminal, the data communication apparatus transmits the ACK 31 immediately after a slight delay, so that both marks are substantially overlapped.

  In the section 32, the data segment 30 has successfully arrived at the downstream data communication apparatus, but in the section 33, a large delay has occurred. During this time, the wireless terminal is waiting for the data requested to be retransmitted, and during this time, the wireless terminal receives data one after another and accumulates the data. When the data requested to be retransmitted on the wireless communication channel times out without being retransmitted, the wireless terminal releases the accumulated data downstream, so that a large number of data segments 30 can be Arriving at the data communication device, a large amount of ACK 31 is transmitted to them. However, since some data segments 30 have not arrived, a large number of duplicate ACKs are transmitted while the ACK sequence number remains constant.

  The transmitting side detects a duplicate ACK based on TCP, or resends the data segment when the retransmission request times out, and it is shown in section 35 that it has reached the wireless terminal and the downstream data communication device. Yes. Since the ACK for the retransmitted data segment is the sequence number of the data segment that should arrive next, the ACK number increases as shown in section 35. Thereafter, in the section 36, the communication is recovering smoothly.

Since the bandwidth of a wireless communication path is relatively narrow, it is often a bottleneck in the communication path. The bursty ACK packet as described above places a load on the reverse link of the wireless communication path. In many cases, the bandwidth of the reverse link of the wireless communication path is only about 1/10 of the bandwidth of the forward link, and the ACK packet generated in a burst manner is accumulated in the transmission queue of the wireless terminal. Note that Patent Document 1 describes a line interface device based on TCP / IP.
JP-A-7-67088

  However, this temporary and large delay of data packets and the subsequent occurrence of bursty ACK packets occur when the quality of the wireless communication channel deteriorates. However, there is a problem that it takes a long time to transmit all bursty ACKs accumulated in the transmission queue of the wireless terminal. In this case, there is also a problem that it takes much time for other packets to pass through the reverse link. In addition, there is a problem that the transmission queue of the wireless terminal may overflow and ACK packets and other packets may be lost.

The present invention has been made in view of the above-described problems, and it is an object of the present invention to provide a method for controlling a data communication apparatus that can prevent the occurrence of bursty ACK and reduce the load on the reverse link. And

The present invention has been made to solve the above-described problems, and the invention according to claim 1 generates transmission / reception means for transmitting / receiving data, and confirmation response information corresponding to data received by the transmission / reception means. And a transmission control means for outputting the confirmation response information via the transmission / reception means, the data communication apparatus control method comprising: a data reception interval received by the transmission / reception means; and the transmission control means The confirmation response generated by the transmission control means is detected until the generation interval at which the confirmation response information is generated is detected and the detected reception interval exceeds a predetermined interval until the detected generation interval exceeds the predetermined interval. It is characterized by deleting information.

The invention according to claim 2 stores only the latest acknowledgment information generated by the transmission control means when the detected reception interval exceeds a predetermined interval in the invention according to claim 1. Thus, the confirmation response information generated by the transmission control means is deleted.

According to a third aspect of the present invention, in the first aspect of the invention, when duplication of identification information in the confirmation response information generated by the transmission control means is further detected, and duplication of the identification information is detected a predetermined number of times Further, the confirmation response information is deleted.

  According to the present invention, it is possible to prevent the occurrence of bursty ACK and reduce the load on the reverse link.

  The best mode for carrying out the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of a communication system according to the first embodiment of the present invention. Hereinafter, each component in the figure will be described. The data communication apparatus 20 according to the present embodiment is connected to the wireless terminal 21 via a LAN (Local Area Network) defined in IEEE802.3.

  The wireless terminal 21 is a default gateway for the data communication device 20. The wireless terminal 21 forms a data link with the wireless base station 22 via a wireless communication path. In this data link, a data link layer protocol that performs ARQ (automatic retransmission request) is executed in order to realize reliable communication with few errors. IP packets are carried on this data link. The radio base station 22 is connected to the Internet 23.

  An information server 24 (external device) connected to the Internet 23 operates as an http (Hyper Text Transfer Protocol) server or an ftp (File Transfer Protocol) server, and provides information in response to a request from the data communication device 20. To do. Although the information server 24 also executes TCP, it does not have to have the same function as the data communication apparatus 20, and a commonly used OS (Operating System) function may be used. . Of course, the information server 24 may have the function of the data communication device 20.

  FIG. 2 is a block diagram showing a functional configuration of the data communication apparatus 20 according to the first embodiment of the present invention. Hereinafter, each component in the figure will be described. The transmission / reception means 1 is hardware and software that uses a physical layer / data link layer defined in IEEE 802.3 and uses IP as a network layer to realize communication via a packet switching network. The transmission / reception means 1 performs transmission / reception of packets with other communication devices on the communication path, and extracts and processes IP packets from the packets.

  When the IP packet is related to itself and uses the TCP protocol, the transmission / reception means 1 outputs the IP packet to the transmission control means 2 and requests processing related to the packet. Note that, regarding a received packet using a protocol other than TCP, for example, UDP (User Datagram Protocol) or ICMP (Internet Control Message Protocol), the transmission / reception means 1 requests processing to software (not shown) responsible for the received packet.

  The transmission control means 2 performs communication control such as error control and flow control based on TCP. In particular, when a data segment is received by the transmission / reception unit 1, the transmission control unit 2 generates an ACK (acknowledgment response information) for notifying the information server 24 of the reception of the data segment. The transmission control unit 2 allocates resources such as a memory and a timer for each TCP connection. The transmission control means 2 exchanges data with a function means of an upper protocol (not shown) such as an application layer. The transmission control means 2 delivers received data output from the transmission / reception means 1 to the function means of the upper protocol and The passed transmission data is output to the transmission / reception means 1.

  The reception interval detection unit 3 detects (measures) a time interval at which the data segment is received by the transmission / reception unit 1. The reception interval detection means 3 has a timer that times out at the first predetermined value. In the present embodiment, the first predetermined value is set to 500 ms. This value matches the timeout value until the data link protocol of the wireless communication path gives up retransmission. This timer is reset by an instruction from the transmission / reception means 1 when the data segment is transferred from the transmission / reception means 1 to the transmission control means 2. When the timer of the reception interval detection unit 3 times out, the reception interval detection unit 3 sets the ACK reduction unit 4 to the operating state, thereby causing the ACK reduction unit 4 to perform an ACK reduction operation for reducing the number of ACKs. Instruct the start.

  The ACK reduction unit 4 reduces the number of ACKs transmitted to the wireless terminal 21 via the transmission / reception unit 1 when the reception interval detection unit 3 is instructed to start the ACK reduction operation. The ACK reduction means 4 has a buffer 5. The buffer 5 temporarily stores the ACK input to the ACK reduction unit 4. When the buffer 5 is empty and the ACK reduction unit 4 is performing the ACK reduction operation, when ACK is input from the transmission control unit 2 to the ACK reduction unit 4, the ACK reduction unit 4 stores the ACK in the buffer 5. It is temporarily stored and not output to the transmission / reception means 1.

  When an ACK is further input in this state, the ACK reduction unit 4 overwrites the buffer 5 with a new ACK and does not output it to the transmission / reception unit 1. If this is repeated, the buffer 5 always stores only one latest ACK. This ACK is then output to the transmission / reception means 1 when the ACK reduction means 4 is stopped and transmitted to the wireless terminal 21. That is, only the latest one of the continuously generated ACKs is transmitted.

  The ACK interval detection means 6 detects (measures) the time interval of occurrence of ACK by the transmission control means 2. The ACK interval detection means 6 also has a timer, which times out with a second predetermined value. In the present embodiment, the second predetermined value is set to 10 ms. With respect to this value, a value that is large enough to detect the end of occurrence of bursty ACK and that is as small as possible is set. The transmission control means 2 instructs the ACK interval detection means 6 to reset the timer when an ACK is generated. Receiving this instruction, the ACK interval detection means 6 resets the timer.

  When the timer of the ACK interval detection unit 6 times out, the ACK interval detection unit 6 stops the ACK reduction operation by the ACK reduction unit 4. At this time, when the ACK is stored in the buffer 5, the ACK reduction unit 4 outputs the ACK in the buffer 5 to the transmission / reception unit 1, and the transmission / reception unit 1 transmits the ACK to the wireless terminal 21. When the ACK reduction unit 4 stops the ACK reduction operation, the input ACK is immediately stored and transmitted to the transmission / reception unit 1 without being stored in the buffer 5. Note that the values of the first predetermined value and the second predetermined value are not limited to the values described above.

  Next, the operation of the data communication apparatus 20 according to the present embodiment will be described. In order to receive content data and the like from the information server 24, the data communication device 20 first establishes a connection. The transmission control unit 2 creates a SYN (connection start request) packet and transmits it to the wireless terminal 21 via the transmission / reception unit 1. This SYN packet is transmitted from the wireless terminal 21 to the wireless base station 22 by wireless communication, and is transmitted from the wireless base station 22 to the information server 24 via the Internet 23. The information server 24 recognizes that the packet is a TCP SYN packet, creates a packet (SYN + ACK) with the ACK flag and SYN flag in the TCP header set to 1, and transmits the packet to the data communication apparatus 20. The SYN + ACK packet is delivered to the data communication device 20 in the opposite direction to the SYN packet.

  The connection establishment by TCP is called three-way handshake. The data communication apparatus 20 transmits a SYN packet, the information server 24 that receives the SYN packet transmits a SYN + ACK packet, and the data communication apparatus 20 that receives the packet subsequently receives an ACK. The connection is established by sending At this time, SYN + ACK received by the transmission / reception unit 1 is processed by the transmission control unit 2, and ACK generated by the transmission control unit 2 is transmitted to the information server 24 via the transmission / reception unit 1. At this point, the ACK reduction unit 4 has not been operated yet. When the information server 24 receives and recognizes the ACK, the connection is established, and thereafter, the information server 24 transmits a data segment to the data communication device 20.

  The subsequent operation of the data communication device 20 is as shown in the flowcharts of FIGS. Hereinafter, the operation of the data communication apparatus 20 will be described with reference to FIGS. Each time the data communication device 20 receives a data segment from the wireless terminal 21, the data communication device 20 performs the processing shown in FIG. The transmission / reception means 1 receives the data segment from the wireless terminal 21 and outputs the data segment to the transmission control means 2 (step S31). The transmission control unit 2 allocates resources to the timers of the reception interval detection unit 3 and the ACK interval detection unit 6 for each TCP connection. As a result, the transmission control means 2 can process a plurality of connections simultaneously. The transmission control means 2 instructs the reception interval detection means 3 to measure the first reception interval, and the reception interval detection means 3 that has received the instruction starts a timer (step S32).

  FIG. 4 shows an operation when the timer of the reception interval detection means 3 times out. When the timer of the reception interval detecting means 3 times out without being reset, it is detected that the second time interval is 500 ms or more, an interrupt is generated with respect to the operation of FIG. 3, and the operation of FIG. 3 is executed, and after the execution of this operation is completed, the operation following FIG. 3 is performed. In FIG. 4, the reception interval detection unit 3 causes the ACK reduction unit 4 to start an ACK reduction operation (step S41).

  Returning to FIG. 3, following step S32, the transmission control means 2 checks (confirms) whether there is an error in the data segment output from the transmission / reception means 1 (step S33). This process is illustrated in FIG. The transmission control means 2 checks the data segment for errors (step S331). If there is no error, the transmission control means 2 concatenates the data segments in the order indicated by the sequence number based on TCP and waits for the arrival of data. Data is transferred to the application or the like (step S332). Subsequently, the transmission control unit 2 updates the sequence number of the data segment held therein (step S333), and ends the processing related to error checking. If there is an error in step S331, the sequence number is not updated, and the error check process is terminated.

  Then, it progresses to step S34 of FIG. The transmission control means 2 generates an ACK corresponding to the arrived data segment, outputs it to the ACK reduction means 4, and instructs the ACK interval detection means 6 to reset the timer. This ACK stores the sequence number of the data segment that should arrive next to the confirmed data segment. The ACK interval detection means 6 that has received the instruction from the transmission control means 2 resets the timer (step S34).

  Subsequently, the ACK reduction unit 4 determines whether or not an ACK reduction operation is being performed (step S35). Immediately after the TCP connection is started, the ACK reduction unit 4 stops the ACK reduction function, and the ACK reduction unit 4 outputs the input ACK to the transmission / reception unit 1 as it is. The transmission / reception means 1 stores this ACK in the IP packet and transmits it to the wireless terminal 21 (step S36). On the other hand, when the ACK reduction unit 4 is performing the ACK reduction operation in step S35, the process proceeds to step S37.

  The process in step S37 is shown in FIG. The transmission control means 2 instructs the ACK interval detection means 6 to measure the ACK generation interval, and the ACK interval detection means 6 that has received the instruction starts a timer (step S371). Subsequently, the ACK reduction unit 4 reduces the number of ACKs input from the transmission control unit 2 (step S372).

  In this process, if the ACK is not stored in the buffer 5, the ACK reduction unit 4 temporarily stores the input ACK in the buffer 5 and does not output it to the transmission / reception unit 1. If no ACK is stored in the buffer 5, the ACK reduction unit 4 overwrites the buffer 5 with a new ACK and does not output it to the transmission / reception unit 1. With this operation, the buffer 5 always stores only one latest ACK. This ACK is then output to the transmission / reception means 1 when the ACK reduction means 4 is stopped and transmitted to the wireless terminal 21. In other words, only the latest one of the continuously generated ACKs is transmitted. Thereafter, the process ends.

  FIG. 7 shows an operation when the timer of the ACK interval detection means 6 times out. When the timer of the ACK interval detection unit 6 times out without being reset, an interrupt occurs with respect to the operation of FIG. 3 or FIG. 5, and the operation of FIG. 7 is executed. Or the operation | movement of a continuation of FIG. 5 is performed. When the timer of the ACK interval detection unit 6 times out, the ACK interval detection unit 6 causes the ACK reduction unit 4 to stop the ACK reduction operation (step S71).

  Subsequently, the ACK reduction unit 4 determines whether or not ACK is stored in the buffer 5 (step S72). When ACK is stored in the buffer 5, the ACK reduction unit 4 outputs the ACK to the transmission / reception unit 1. The transmission / reception means 1 transmits the ACK to the wireless terminal 21 (step S73). On the other hand, if no ACK is stored in the buffer 5, the process ends.

  In the present embodiment, the ACK generated in bursts is reduced to one ACK as a result. At this time, the ACK number (sequence number) notified by ACK increases rapidly after a blank of about 500 ms on the transmission side, which may cause bursty transmission. Burst transmission may cause congestion on the forward link, but if congestion does not occur, the effect of preventing a decrease in throughput by compensating for the previously generated blank of about 500 ms can be expected. Even in the forward link, the bottleneck is often a wireless communication path, so whether the forward link of the wireless communication path is likely to be congested is a problem.

  Such congestion is unlikely to occur in a wireless base station of a high-speed wireless communication channel that is currently in widespread use. If congestion is a problem, the ACK reduction means 4 should keep the rate of ACK reduction small. Also good. That is, the ACK reduction unit 4 counts the number of input ACKs with a counter, and when the number reaches a certain number, clears the ACK stored in the buffer 5 and replaces the input ACK with this time. Is transmitted to the transmission / reception means 1 without being stored in the buffer 5. When the threshold value of the counter is M, the transmission ratio occupied by the ACK transmitted to the wireless terminal 21 among the ACKs generated by the transmission control unit 2 is 1 / M. By transmitting ACK at a certain rate, burstiness on the transmission side can be relaxed.

  In the present embodiment, the ACK reduction means 4 including the buffer 5 for storing ACK is shown, but the number of ACKs can be reduced without the buffer 5. For example, the ACK reduction unit 4 may discard all input ACKs while performing the ACK reduction operation, or may include a counter and output one ACK for M inputs. However, the number of ACKs may be reduced to 1 / M by discarding the others.

  FIG. 8 is a time sequence graph showing the operation of this embodiment, where the horizontal axis represents time and the vertical axis represents the sequence number. FIG. 8 shows the situation on the receiving side. In the section 32, the data segment 30 has arrived at the data communication apparatus 20 smoothly, but a large delay has occurred in the section 33. During this time, the wireless terminal 21 waits for the data requested to be retransmitted, and data is accumulated in the wireless terminal 21 one after another. When the data requested to be retransmitted on the wireless communication channel times out without being retransmitted, the wireless terminal 21 releases the accumulated data.

  Therefore, a large amount of data segments 30 arrive at the data communication device 20 in a short time as indicated by the section 34 in FIG. However, some data segments have not arrived. Conventionally, as shown in the section 34 of FIG. 12, a large amount of ACK 31 is generated in a burst manner. On the other hand, in the present embodiment, the timer of the reception interval detection unit 3 times out at the first predetermined value in the section 33, and the ACK reduction operation by the ACK reduction unit 4 is started. In the section 34, the data segment arrives at a time interval shorter than the second predetermined value until the timer of the ACK interval detection unit 6 times out, and an ACK for the data segment is generated by the transmission control unit 2. For this reason, since the ACK interval detection means 6 is reset before time-out, the ACK reduction operation by the ACK reduction means 4 is continued, and ACK is not transmitted in the section 34.

  In the section 35, one ACK 31 is transmitted. In this case, the timer of the ACK interval detection means 6 times out when 10 ms elapses, the ACK reduction operation by the ACK reduction means 4 is stopped, and the ACK stored in the buffer 5 is transmitted. The information server 24 retransmits the data segment based on the TCP, and it is shown that this has reached the data communication terminal 20 in the section 35. Since the ACK number of the ACK for the retransmitted data segment is the sequence number of the data segment that should arrive next, the ACK number increases rapidly. Thereafter, communication has been smoothly recovered in the section 36.

  Next, a second embodiment of the present invention will be described. FIG. 9 is a block diagram showing a functional configuration of the data communication apparatus 20 according to the present embodiment. In the figure, the same components as those in FIG. In the present embodiment, duplicate ACK detection means 7 is provided. This duplicate ACK detection means 7 detects duplicate ACK based on the ACK number which is the identification number of ACK. The duplicate ACK detection means 7 is also assigned a resource by the transmission control means 2 when the TCP connection is started.

  A duplicate ACK is an ACK with duplicate ACK numbers. When the receiving side receives a subsequent data segment without receiving a data segment, multiple ACKs are sent with the ACK number fixed to the sequence number of the lost data segment. The side detects this and retransmits. This operation is called high-speed retransmission. The transmission side performs high-speed retransmission when three ACKs having the same ACK number are received in duplicate. The duplicate ACK indicates that the subsequent data segment continues to be received even after the data segment is lost. Because of this duplicate ACK, it can be considered that the congestion is minor or a loss due to an error that is not congestion, etc. Therefore, the transmission side operates based on TCP so as not to drop the congestion window cwnd too much.

  Since the duplicate ACK is important for early execution of retransmission, the duplicate ACK detection means 7 prevents the duplicate ACK from being lost by the ACK reduction means 4 in this embodiment. The data communication apparatus 20 according to the present embodiment performs the same operation as that of the first embodiment except that the operation shown in FIG. 10 is performed as the operation in step S37 of FIG. Hereinafter, the operation in step S37 in FIG. 3 will be described with reference to FIG.

  The transmission control means 2 instructs the ACK interval detection means 6 to measure the ACK generation interval, and the ACK interval detection means 6 that has received the instruction starts a timer (step S373). The ACK reduction unit 4 stores the ACK in the buffer 5 and stores the ACK in the buffer 5 when the ACK is not stored in the buffer 5 regarding the ACK output from the transmission control unit 2 in step S34. In that case, the buffer 5 is overwritten with ACK (step S374).

  The transmission control means 2 notifies the duplicate ACK detection means 7 of the ACK number of the ACK generated in step S34 in FIG. The duplicate ACK detection means 7 stores the notified ACK number and determines whether or not the ACK number is the same as the ACK number of the previous ACK stored previously (step S375). When the ACK number notified by the transmission control means 2 is not the same as the ACK number of the previous ACK stored previously, the process returns to FIG. 3 and the process ends.

  On the other hand, if the ACK number notified by the transmission control means 2 is the same as the previous ACK number stored previously, the duplicate ACK detection means 7 instructs the ACK interval detection means 6 to stop the timer. To do. Receiving this instruction, the ACK interval detection means 6 stops the timer (step S376). The duplicate ACK detection unit 7 stops the ACK reduction operation of the ACK reduction unit 4, and the ACK reduction operation by the ACK reduction unit 4 is stopped (step S377).

  When the ACK reduction operation by the ACK reduction unit 4 is stopped, if ACK is stored in the buffer 5 in step S377, the ACK reduction unit 4 outputs the ACK to the transmission / reception unit 1, and the ACK reduction unit 4 thereafter. The input ACK is output to the ACK transmission / reception means 1 as it is. The transmission / reception means 1 transmits this ACK to the wireless terminal 21. That is, the duplicate ACK is transmitted without being lost. Since the first three ACKs are meaningful, the fourth and subsequent duplicate ACKs should be reduced. Therefore, the counter for counting the number of detected duplicate ACKs is provided in the duplicate ACK detection unit 7, and when the fourth duplicate ACK is detected, the duplicate ACK detection unit 7 starts the ACK reduction operation for the ACK reduction unit 4. You may make it make it.

  FIG. 11 is a time sequence graph showing the operation of this embodiment, where the horizontal axis represents time and the vertical axis represents the sequence number. Similar to FIG. 8, FIG. 11 shows the situation on the receiving side. In FIG. 11, three ACKs 31 are transmitted in the section 34. This is a duplicate ACK whose ACK number remains constant because some data segments 30 are missing. The duplicate ACK detection means 7 detects this, and the ACK reduction operation of the ACK reduction means 4 is stopped, so that a duplicate ACK is transmitted.

  If there are three duplicate ACKs, the information server 24 performs high-speed re-transmission based on TCP. Therefore, in order to reduce unnecessary duplicate ACKs, the duplicate ACK detection means 7 detects the fourth duplicate ACK and reduces ACK. The ACK reduction operation is started for the means 4 to avoid bursty ACK transmission. If the duplicate ACK arrives at the information server 24 and high-speed retransmission is performed, the retransmission of the data segment in the section 35 in FIG. 11 may arrive earlier than in the case of FIG. 8, which contributes to an improvement in throughput. .

  The data communication device 20 and the wireless terminal 21 according to the first or second embodiment described above are configured as an integrated device, and the device is a PC (Personal Computer), PDA (Personal Digital Assistance), or the like according to a standard such as USB. Or the device may be built in a PC or PDA.

  Further, the connection between the data communication device 20 and the wireless terminal 21 is not limited to the above embodiment, and may be connected through a serial interface such as a USB. Further, when the wireless terminal 21 is a data communication card, a connection conforming to PCMCIA may be used. The data communication apparatus 20 includes an information processing apparatus such as a PC or a PDA, and the wireless terminal 21 includes a wireless communication apparatus such as a mobile phone, a data communication device, or a communication module. Further, when the data communication device 20 and the wireless terminal 21 are integrated into a data communication device, examples of the data communication device include a mobile phone, a PDA, and a PC with a built-in wireless connection means.

  As described above, according to the first embodiment, when the time interval at which data is received is greater than or equal to a predetermined value, the ACK reduction means is used until the time interval at which ACK is generated exceeds the predetermined value. When 4 performs the ACK reduction operation, it is possible to prevent the occurrence of bursty ACK and reduce the load on the reverse link. That is, a shortage of reverse link bandwidth can be avoided, and reverse link packet delay and packet discard due to congestion can be avoided.

  Further, according to the second embodiment, when the duplicate ACK detection unit 7 detects a duplicate ACK, the duplicate ACK necessary for high-speed retransmission is transmitted by stopping the ACK reduction operation of the ACK reduction unit 4. Therefore, high-speed retransfer can be executed earlier, and throughput can be improved. Furthermore, when the duplicate ACK detection unit 7 detects the fourth and subsequent duplicate ACKs, the ACK reduction unit 4 starts the ACK reduction operation to prevent unnecessary duplicate ACKs from being generated in bursts. Can do.

  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. For example, the data communication device 20 in the above-described embodiment records a program for realizing the operation and function in a computer-readable recording medium, causes the computer to read the program recorded in the recording medium, and executes the program. You may implement | achieve by doing.

  Here, the “computer” includes a homepage providing environment (or display environment) if the WWW system is used. The “computer-readable recording medium” refers to a storage device such as a portable medium such as a flexible disk, a magneto-optical disk, a ROM, and a CD-ROM, and a hard disk built in the computer. Further, the “computer-readable recording medium” refers to a volatile memory (RAM) in a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line. In addition, those holding programs for a certain period of time are also included.

  The above-described program may be transmitted from a computer storing the program in a storage device or the like to another computer via a transmission medium or by a transmission wave in the transmission medium. Here, the “transmission medium” for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. Further, the above-described program may be for realizing a part of the above-described function. Furthermore, what can implement | achieve the function mentioned above in combination with the program already recorded on the computer, what is called a difference file (difference program) may be sufficient.

It is a block diagram which shows the structure of the communication system by the 1st Embodiment of this invention. It is a block diagram which shows the function structure of the data communication apparatus by the embodiment. It is a flowchart which shows operation | movement of the data communication apparatus by the embodiment. It is a flowchart which shows operation | movement of the data communication apparatus when the timer of the receiving interval detection means by the embodiment times out. 4 is a flowchart showing an operation at the time of error checking of the data communication apparatus according to the embodiment. 5 is a flowchart showing the operation of the data communication apparatus when the ACK reduction means according to the embodiment is performing an ACK reduction operation. It is a flowchart which shows operation | movement of the data communication apparatus when the timer of the ACK space | interval detection means by the embodiment times out. It is a time sequence graph which shows the data reception condition in the embodiment. It is a block diagram which shows the function structure of the data communication apparatus by the 2nd Embodiment of this invention. 5 is a flowchart showing the operation of the data communication apparatus when the ACK reduction means according to the embodiment is performing an ACK reduction operation. It is a time sequence graph which shows the data reception condition in the embodiment. It is a time sequence graph which shows the data reception condition in the conventional data communication.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Transmission / reception means, 2 ... Transmission control means, 3 ... Reception interval detection means (1st detection means), 4 ... ACK reduction means (deletion means), 5 ... Buffer, 6. .. ACK interval detection means (second detection means), 7 ... duplicate ACK detection means (duplication detection means), 20 ... data communication device, 21 ... wireless terminal, 22 ... wireless base station, 23 ... Internet, 24 ... Information server.

Claims (3)

Control of a data communication apparatus having transmission / reception means for performing data transmission / reception, and transmission control means for generating confirmation response information corresponding to the data received by the transmission / reception means and outputting the confirmation response information via the transmission / reception means A method,
Detecting a reception interval of data received by the transmission / reception unit and a generation interval at which the acknowledgment information is generated by the transmission control unit;
When the detected reception interval exceeds a predetermined interval, the confirmation response information generated by the transmission control unit is deleted until the detected generation interval exceeds a predetermined interval.
A method for controlling a data communication apparatus.   When the detected reception interval exceeds a predetermined interval, only the latest confirmation response information generated by the transmission control unit is stored, thereby deleting the confirmation response information generated by the transmission control unit. The method of controlling a data communication apparatus according to claim 1, wherein The identification information of the confirmation response information generated by the transmission control unit is further detected, and the identification information is deleted when the identification information is detected a predetermined number of times. The control method of the data communication apparatus described.

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