JP4925916B2 - Data transmission apparatus, data transmission method, and data transmission program - Google Patents

Description

  The present invention relates to a data communication technique involving retransmission control by TCP (Transmission Control Protocol).

  TCP is a transmission control protocol used for file transfer by Web access, FTP (File Transmission Protocol) or the like. TCP has retransmission control and congestion avoidance algorithms, and is characterized by being able to perform highly reliable communication.

  Regarding the retransmission control in TCP, matters relating to the general contents are disclosed in Non-Patent Document 1, and in TCP widely used in the Internet, as a form of retransmission control, the transmission side requests a retransmission request from the reception side. And a form in which retransmission is performed when a reception confirmation response from the receiving side is not received within a predetermined timeout period. In such a form of retransmission control, there is a case in which after the retransmission in response to the retransmission request, the transmission side may perform retransmission due to the lapse of the timeout time before receiving the reception confirmation response of the retransmission. Patent Document 2 proposes a method in which a node between a transmitting side and a receiving side such as a router sets up a bit called ECN (Explicit Congestion Notification) in order to avoid the retransmission.

For retransmission control in TCP, techniques as disclosed in Patent Documents 1 to 7 have also been proposed. Japanese Patent Application Laid-Open No. 2004-228561 discloses a technique related to initial value setting of a retransmission timeout for retransmitting a transmission packet without an acknowledgment. Patent Document 2 discloses a technique for setting a congestion window size or the like depending on whether the cause of retransmission timeout is a data loss or a confirmation response loss or delay. Patent Document 3 discloses a technique for calculating a retransmission time-out time according to a changing packet round-trip time when a wireless communication section and a wired communication section coexist. Patent Document 4 discloses a technique for adding a margin to a measurement time from message transmission to response reception in communication between terminal devices to obtain a retransmission process activation timeout time. Patent Document 5 discloses a technique for returning a response waiting time during measurement by a retransmission timer by the time length of a control packet when a control packet that is not a reception response packet is received. Patent Document 6 discloses a technique for re-counting a retransmission timeout time from the reception point of a retransmission request for a transmitted segment. Patent Document 7 discloses a technique for updating a retransmission timeout value based on a response time obtained from a transmission frame transmission time and a reception confirmation frame reception time.
TCP Illustrated Volume 1, W. Richard Stvens, ADDISON-WESLEY, 1994, Chapters 17-24 (especially Chapter 21 for TCP retransmission) The Addition of Explicit Congestion Notification (ECN) to IP, RFC3168 JP-A-5-28072 JP 2006-173961 A JP 2004-253934 A JP-A-6-121002 JP-A-10-93661 JP 2005-136636 A JP-A-8-8895

  By the way, the duplicate retransmission due to the elapse of the timeout time after the retransmission for the retransmission request described above occurs when the retransmission is actually performed for the retransmission request. Therefore, in order to prevent such redundant retransmission, it is necessary to consider control of the timeout time in relation to the retransmission actually performed in response to the retransmission request. On the other hand, none of the techniques of the above-mentioned patent documents considers the relation with the retransmission actually performed in response to the retransmission request for the control of the timeout time. On the other hand, since the technique of Non-Patent Document 2 tries to avoid duplicate retransmission according to a specific notification form, the technique is different from that for controlling the timeout time.

  The present invention has been made in view of such circumstances. In the retransmission control by TCP, the timeout time is appropriately controlled by paying attention to the relationship with the retransmission actually performed in response to the retransmission request. It is an object of the present invention to provide a data communication technique that can enable improvement of throughput and the like by preventing unnecessary retransmission.

  In order to achieve such an object, the data transmission device according to the present invention is a data transmission device that performs data packet transmission by TCP, and retransmits the data packet in response to a retransmission request from the reception side. Based on the transmission / reception state of the data packet at the time of retransmission with the receiving side, the transmission data packet that has not been acknowledged for reception from the receiving side is sent for retransmission over time of the transmitted data packet. It is intended to adjust the elapsed time.

  In this data transmitting apparatus, the maximum amount of time increase indicated by the change index of the elapsed time for performing retransmission with the passage of time acquired based on the transmission / reception status is transmitted until the retransmission indicated by the timing when receiving a retransmission request for the same data packet. In addition to the time, the time may be adjusted. In this case, the maximum increase amount of the elapsed time for performing retransmission with the passage of time may be the maximum time increase amount.

  Further, in the present data transmitting apparatus, when the retransmission request for the same data packet is received, the time until the retransmission indicated by the time measurement may be reset to the initial time of the time measurement to adjust the time measurement, or the same data packet It is also possible to adjust the timing by adding a certain time to the time until the retransmission indicated by the timing when receiving the retransmission request.

  The data transmission method according to the present invention is a data transmission method for transmitting a data packet by TCP, and confirms reception from the reception side when the data packet is retransmitted in response to a retransmission request from the reception side. For a transmitted data packet that has not been responded to, based on the transmission / reception state of the data packet at the time of the retransmission with the receiving side, the time of the elapsed time toward the retransmission due to the lapse of time of the transmitted data packet is adjusted. It has become a thing.

  The data transmission program according to the present invention is a data transmission program for transmitting a data packet by TCP, and confirms reception from the reception side when the data packet is retransmitted in response to a retransmission request from the reception side. For a transmitted data packet that has not been responded to, based on the transmission / reception state of the data packet at the time of the retransmission with the receiving side, the time of the elapsed time toward the retransmission due to the lapse of time of the transmitted data packet is adjusted. A data transmission program for causing a computer to realize the function.

  According to the present invention, when a data packet is retransmitted in response to a retransmission request from the receiving side, the data packet at the time of the retransmission is transmitted with respect to the already transmitted data packet that has not been acknowledged by the receiving side. Since it was decided to adjust the elapsed time for retransmission due to the passage of time based on the transmission / reception status, in TCP retransmission control, it is necessary to pay attention to the relationship with the retransmission actually performed for the retransmission request. It is possible to control the timeout time, and it is possible to prevent unnecessary retransmission and improve throughput.

<Configuration>
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a configuration of a communication system including a transmission device Tn that is a data transmission device according to an embodiment of the present invention. As shown in the figure, this communication system is composed of a transmission device Tn, a transmission device tn, a communication network NW, and a reception device Rn. As will be described below, a data packet (a data TCP indicating information to be exchanged) Compliant packets (generally called TCP packets or segments, etc., the same shall apply hereinafter) are transmitted and received to perform data communication with TCP retransmission control.

  The transmission device Tn is a data transmission device that performs data packet transmission according to the TCP communication standard. The transmission device Tn is composed of a computer in which a data transmission program defining processing operations such as packet transmission / reception, retransmission control and congestion avoidance algorithm necessary for the data packet transmission is installed, and is necessary for executing the data transmission program A computer, a storage device, a control device, a communication interface, and the like, and is connected to a communication network NW. In the data transmission program, as a retransmission control processing operation, a retransmission processing operation for a retransmission request, a retransmission processing operation due to elapse of a predetermined timeout time, and a specific retransmission time for adjusting the timeout time under specific conditions Processing operations by the control method are specified. As a result, the transmission apparatus Tn performs data packet transmission accompanied by a specific retransmission control. The specific contents of the retransmission control specific to the transmission apparatus Tn will be clarified in an operation description to be described later.

  The transmission device tn is a conventional data transmission device that transmits data packets according to the TCP communication standard. The transmission device tn is configured by a computer in which programs such as packet transmission / reception, retransmission control, and congestion avoidance algorithm for implementing general data packet transmission in TCP are installed, and is connected to the communication network NW. The retransmission control performed by the transmission device tn is related to the retransmission for the retransmission request and the retransmission due to the elapse of a predetermined timeout time. The transmission device tn is generally employed in TCP for the retransmission. The conventional retransmission control mode is used.

  The communication network NW is a communication network capable of data transmission conforming to the TCP communication standard. As a typical communication network constituting the communication network NW, the Internet can be cited, but the communication network NW may be configured by an arbitrary network having a communication line capable of transmitting and receiving packets by TCP. Other fixed and mobile communication networks, IP (Internet Protocol) telephone network, LAN (Local Area Network), MAN (Metropolitan Area Network), WAN (Wide Area Network), satellite communication network, submarine cable, leased line Etc. may be included as appropriate.

  The receiving device Rn is a data receiving device that receives data packets according to the TCP communication standard. The receiving device Rn is configured by a computer in which a data receiving program for executing the data packet reception is installed, and is connected to the communication network NW. The data reception program may define processing operations such as packet transmission / reception, reception confirmation response, and retransmission request for performing general data packet reception in TCP. For this reason, as the receiving device Rn, a conventional data receiving device that receives a data packet by TCP can be used as it is. Since the data packets transmitted by the transmission device Tn and the transmission device tn via the communication network NW both conform to the TCP communication standard, they are received by the reception device Rn using the conventional data reception device or the like. be able to.

  As described above, the transmission device Tn and the transmission device tn are devices that transmit data packets, and the reception device Rn is a device that receives data packets. However, these devices only transmit or receive data packets. The transmission device Tn and the transmission device tn may receive data packets, and the reception device Rn may also transmit data packets. That is, the “transmission device” means a device on the transmission side that is a data packet sender in this embodiment, and the “reception device” is a reception that is a data packet receiver in this embodiment. This means the device on the side. Therefore, each of the transmission device Tn, the transmission device tn, and the reception device Rn may be a terminal device or a server that transmits and receives data packets as appropriate, or a device such as a router or a gateway. In this communication system, among such devices, the transmitting device Tn and the transmitting device tn transmit data packets as described below in the description of the operation as transmitting devices, and the receiving device Rn receives the data packets as receiving devices. Receive.

<Operation>
Next, the operation according to the above configuration will be described. In the transmission of data packets, the transmission device Tn has a specific retransmission control as described above, whereas the transmission device tn adopts a general conventional retransmission control form. Therefore, in the following description of operations, first, transmission / reception of data packets by the transmission device tn and the reception device Rn will be described, and after considering conventional retransmission control and the like in the transmission / reception operation, the transmission device Tn and the reception device By explaining the transmission / reception of the data packet by Rn, the specific contents of the retransmission control specific to the transmission apparatus Tn different from the conventional retransmission control will be clarified. Note that packet transmission / reception in the following description of operations is all performed via the communication network NW (therefore, the communication network NW is not referred to unless otherwise required).

(1) Data packet transmission / reception by the transmission device tn and the reception device Rn In TCP, the reception side confirms the reception of the data packet transmitted by the transmission side by transmitting an ACK (Acknowledgement) packet. A sequence number is assigned to the data packet, and the receiving side indicates how far the data packet of the sequence number has been received by the transmitted ACK packet. By receiving the ACK packet, the transmitting side can grasp how far the receiving side has received the data packet. Therefore, when an error occurs in a data packet or the like for some reason, the transmission side can grasp the error occurrence from the ACK packet from the reception side.

  The transmission side performs two types of retransmission control according to the reception status of the ACK packet. The first retransmission control is retransmission control called Fast Retransmit (high-speed retransmission), and the second retransmission control is retransmission control called timeout retransmission. Fast Retransmit corresponds to retransmission control for the transmission device Tn and the transmission device tn to perform retransmission in response to a retransmission request, and timeout retransmission performs retransmission when the transmission device Tn and the transmission device tn have passed a predetermined timeout time. This corresponds to retransmission control. In data packet transmission / reception between the transmission device tn and the reception device Rn, these retransmission controls are performed as follows.

・ Fast Retransmit (high-speed retransmission)
FIG. 2 is a diagram showing a data packet transmission / reception sequence accompanied by Fast Retransmit between the transmission device tn and the reception device Rn. In FIG. 2, if the sequence number is i (i = 1, 2, 3,...), “Data, SEQ = i” represents a data packet with the sequence number i, and “ACK SEQ = i” represents the sequence number i. (Hereinafter, “Data, SEQ = i” and “ACK SEQ = i” in other drawings showing transmission / reception sequences are also the same).

  As shown in FIG. 2, when the transmission device tn transmits the data packet “Data, SEQ = 1” and the reception device Rn receives the data packet, the reception device Rn transmits the ACK packet “ACK SEQ = 1” and the transmission device tn. Receives it and recognizes that the receiving device Rn has normally received the data packet of sequence number 1. On the other hand, if the transmission device tn transmits the following data packet “Data, SEQ = 2”, but the data packet “Data, SEQ = 2” disappears and cannot be received by the reception device Rn, the reception device Rn. Receives a data packet “Data, SEQ = 3” transmitted by the transmitting apparatus tn without transmitting an ACK packet.

  When the receiving device Rn is received in a state where only one data packet sequence number is missing in this manner (when the received data packet sequence number is missing), the sequence of the missing data packet is received. The number is notified to the transmission device tn and a retransmission is requested. The sequence number of the lost data packet is the Duplicate ACK packet that informs the ACK number immediately before that (the same ACK packet as the transmitted ACK packet that informs the sequence number of the data packet that was ACKed (acknowledged) immediately before) ) To send notifications. Now, since the sequence number of the lost data packet is 2 and the immediately preceding ACK number is 1, the receiving device Rn transmits a Duplicate ACK packet “ACK SEQ = 1” indicated by a dashed arrow in FIG. The sequence number 1 included in the Duplicate ACK packet “ACK SEQ = 1” indicates that the data packet with the subsequent sequence number 2 has been lost, and the receiving apparatus Rn thereby requests retransmission of the data packet with the sequence number 2 To do.

  In TCP, when the receiving side transmits a Duplicate ACK packet in this way, the sequence number included in the subsequent ACK packet is maintained at the same sequence number until the data packet of the sequence number for which retransmission is requested is received. Therefore, even when the receiving device Rn receives the data packet “Data, SEQ = 4” transmitted by the transmitting device tn, the receiving device Rn transmits the Duplicate ACK packet “ACK SEQ = 1” including the same sequence number. Upon receiving two Duplicate ACK packets “ACK SEQ = 1” having the same sequence number, the transmission device tn retransmits the requested data packet “Data, SEQ = 2” of sequence number 2. As a result, the receiving device Rn receives the data packet “Data, SEQ = 2” that has been missing, but has already received the data packets “Data, SEQ = 3” and “Data, SEQ = 4”. Therefore, up to the data packet of sequence number 4, “ACK SEQ = 4” is transmitted indicating that it has been successfully received, and the transmission device tn receives it and transmits a new data packet “Data, SEQ = 5”. .

  Fast Retransmit is a retransmission control in which retransmission is started when the transmitting side receives a Duplicate ACK packet (ACK packet requesting retransmission) having the same sequence number as described above twice. As a result, when receiving the retransmission data packet, the receiving side notifies the latest sequence number of the data packet received so far by the ACK packet, and the subsequent data packet transmission / reception is continued.

Timeout retransmission FIG. 3 is a diagram showing a data packet transmission / reception sequence involving timeout retransmission between the transmission device tn and the reception device Rn. As shown in FIG. 3, the transmission device tn transmits the data packet “Data, SEQ = 1” and is received by the reception device Rn, and the reception device Rn transmits the ACK packet “ACK SEQ = 1” and the transmission device tn. , The transmitting device tn knows that the receiving device Rn has received the data packet with the sequence number 1 normally. On the other hand, the transmitting device tn transmits the subsequent data packet “Data, SEQ = 2” and is received by the receiving device Rn, and the receiving device Rn transmits the ACK packet “ACK SEQ = 2”. If ACK SEQ = 2 ”disappears and the transmission device tn cannot receive the ACK packet, the transmission device tn does not return an ACK packet, so it is not known whether or not the data packet of sequence number 2 has been normally received. .

  In this case, when a predetermined timeout period elapses without receiving the ACK packet, the transmission device tn considers that the data packet “Data, SEQ = 2” has not been received, and the data packet “Data, SEQ = 2” resend. As a result, the transmission device tn receives the ACK packet “ACK SEQ = 2” which is received again by the reception device Rn and receives the data packet “Data, SEQ = 2”, and the reception device Rn receives the data packet with the sequence number 2. To know that it was successfully received.

The timeout retransmission is a retransmission control in a form in which, when an ACK packet cannot be received for some reason, a data packet that has not been acknowledged when a predetermined period called a timeout time elapses as described above. The timeout time RTO (Retransmission Time Out) is dynamically calculated by, for example, the following equation based on RTT (Round Trip Time) which is the time between the transmission time of the data packet and the reception time of the ACK packet for the data packet. ing.
M is the measured value of RTT, A is the smoothed RTT (RT calculated by [A ← 0.9A + 0.1M]
Smoothing average of T), D as the fluctuation part of RTT,
Err = MA
A ← A + 1/8 × Err
D ← D + 0.25 (| Err | -D)
RTO = A + 4D
The initial values of M, A, and D are set as appropriate.

(2) Consideration about conventional retransmission control etc. In TCP, the above-mentioned Fast Retransmit and timeout retransmission are adopted as general retransmission control methods. In data communication by TCP, congestion control for avoiding congestion is performed while performing these retransmission controls. As a form of congestion control, cwnd (abbreviation of Congestion Window. It means the number of packets to be transmitted at one time, also called window size. The same shall apply hereinafter) is initially made small and every time an ACK packet is received ( That is, the one that gradually increases cwnd (with every successful transmission) is adopted. This form of congestion control is called slow start. Since a larger number of packets can be transmitted at a time as cwnd is larger, it is useful for improving TCP throughput (throughput of data communication by TCP; the same applies hereinafter).

  In the data communication by TCP, when a packet loss occurs, if it is transmitted as it is, there is a possibility that further errors and congestion may occur. Therefore, a congestion avoidance algorithm for avoiding congestion operates. Congestion avoidance is performed by reducing cwnd. The cwnd control method is roughly divided into two types, one performed at time-out retransmission and the other performed at Fast Retransmit.

  When performing timeout retransmission, cwnd is set to the initial state (usually 1) when timeout retransmission occurs. In this control method, since it is necessary to gradually increase cwnd by a slow start thereafter, the TCP throughput is affected, and when a timeout retransmission occurs, the TCP throughput is considerably reduced. TCP Tahoe, which is the original TCP implementation, only had a timeout retransmission function for retransmission control (Fast Retransmit was not possible). However, since there is a problem that the TCP throughput is lowered as described above, there is a background that Fast Retransmit was devised by the implementation of TCP Reno in order to solve the problem.

  When retransmitted by Fast Retransmit, multiple data packets are not in error, so it is considered that a large error has not occurred in the network, so as a cwnd control method to be performed at Fast Retransmit No longer needed to return cwnd to its initial state. To deal with this, Fast Recovery was devised as an algorithm for increasing cwnd. Fast Recovery is a mechanism for setting cwnd to ½ immediately before retransmission only for retransmission by Fast Retransmit. According to this Fast Recovery, cwnd only needs to be increased by a slow start from a half value, so that the effect on TCP throughput is suppressed.

  FIG. 4 is a diagram illustrating fluctuations in cwnd when Fast Retransmit and timeout retransmission are performed, in which the horizontal axis represents the sequence number of data packets that are sequentially transmitted, and the vertical axis represents the value of cwnd. As shown in this figure, after the start of data packet transmission, cwnd gradually increases due to slow start, but when Fast Retransmit occurs, the Fast Recovery causes the cwnd value to become 1 / 2 Also, in TCP, if a ACK packet does not reach the transmission side within a timeout period for a data packet retransmitted by Fast Retransmit, timeout retransmission is performed. In this case, since the congestion avoidance algorithm at time-out retransmission is applied, cwnd becomes 1 due to time-out as shown by an ellipse in the figure, which greatly affects TCP throughput. Therefore, if a data packet retransmitted by Fast Retransmit is normally received on the receiving side, it is important to suppress a decrease in TCP throughput that an ACK packet for the data packet arrives within the timeout period. .

However, when retransmitting a data packet by TCP, the ACK packet does not reach the transmitting side within the timeout period even though the data packet can be correctly retransmitted from the transmitting side and successfully received at the receiving side. There is an event that timeout retransmission occurs from. The reason why such redundant retransmission occurs may be that it took time to transmit the data packet, and it is known that there are the following cases as the cause.
・ When there is a temporary increase in delay due to retransmission in a lower layer (layer 2 in the case of a radio link such as a mobile network or an OSI (Open Systems Interconnection) reference model) ・ Considering QoS (Quality of Service) When the priority control is performed, the TCP data packet is not prioritized and the data packet is not transmitted. The TCP data packet is scheduled by scheduling in a time division multiple access (TDMA) environment. When bandwidth cannot be obtained

  FIG. 5 is a diagram showing an example of a transmission / reception sequence of a data packet in which such duplicate retransmission occurs. In FIG. 5, the transmission of the data packet is indicated by a solid line arrow, the transmission of the ACK packet is indicated by a one-dot chain line arrow, and the transmission delay of the packet is indicated by hatching each (hereinafter referred to as another drawing expression format showing a transmission / reception sequence) Is the same).

  As shown in FIG. 5, if the transmission device tn transmits data packets “Data, SEQ = 1” to “Data, SEQ = 8”, but the data packet “Data, SEQ = 4” is lost, the reception device Rn receives the data packets “Data, SEQ = 1” to “Data, SEQ = 3” and returns the ACK packets “ACK SEQ = 1” to “ACK SEQ = 3” and then returns the data packet “Data, SEQ = 3”. 5 ”is received and the data packet“ Data, SEQ = 4 ”is not received. When the data packet“ Data, SEQ = 5 ”is received, the Duplicate ACK packet“ ACK SEQ = 3 ”is issued, and each data packet thereafter The Duplicate ACK packet “ACK SEQ = 3” is also transmitted during reception. As a result, the transmitting device tn retransmits the data packet “Data, SEQ = 4” by Fast Retransmit when the Duplicate ACK packet “ACK SEQ = 3” is received twice, and the receiving device Rn receives the retransmitted data packet. “Data, SEQ = 4” is received, and at this time, an ACK packet “ACK SEQ = 8” indicating that the data packet “Data, SEQ = 8” has been received is transmitted. However, as shown in the figure, if the ACK packet “ACK SEQ = 8” does not reach the transmission device tn within the timeout period from the retransmission of the data packet “Data, SEQ = 4”, the transmission device tn retransmits the packet. Although the ACK packet for the data packet “Data, SEQ = 4” has not been received yet, the time-out time has arrived, so that the data packet “Data, SEQ = 4” is re-transmitted by time-out retransmission.

  When such a duplicate retransmission occurs, there is a problem that the data packet is retransmitted again even though the data packet is normally retransmitted, and the increase in cwnd due to timeout retransmission occurs. In addition, although the method of the said nonpatent literature 2 can be utilized in order to avoid such a problem, since all of a node, a transmission side, and a reception side need to understand ECN (only on the transmission side) However, since all nodes including the receiving side need to have a function corresponding to ECN), it is not so popular.

(3) Data packet transmission / reception by the transmission device Tn and the reception device Rn According to the above consideration, in order to avoid duplicate timeout retransmission, the timeout time may be appropriately controlled. At the same time, it can be said that the occurrence of Fast Retransmit is a premise that the possibility of duplicate timeout retransmission occurs. Therefore, in the data packet transmission by the transmitting device Tn, paying attention to the occurrence of Fast Retransmit, the above-described duplication is performed by performing the timeout time control considering the relationship with Fast Retransmit from the time when Fast Retransmit actually occurs. Resolve the problem with retransmission.

(i) Scope of time-out adjustment algorithm for time-out time control In the transmitting apparatus Tn, in order to control the time-out time, a data packet existing on the current line and a retransmitted data packet after the sequence number where Fast Retransmit occurs Timeout adjustment that increases only the timeout time for data packets sent after the original transmission of the packet (after the first time the retransmitted data packet was sent first) while the ACK packet for the retransmission data packet was not answered Use algorithm. That is, the time-out adjustment algorithm of the transmitting apparatus Tn is to receive a data packet retransmitted by Fast Retransmit after the Fast Retransmit occurs and an ACK packet for the data packet from the original transmission before the data packet is retransmitted. Each data packet transmitted until the time is applied as an object, and the timeout time of each data packet is increased by a predetermined time according to the situation when Fast Retransmit occurs.

  FIG. 6 is a diagram illustrating an example of an application range of the timeout adjustment algorithm in a data packet transmission / reception sequence example by the transmission device Tn and the reception device Rn. As shown in FIG. 6, when the transmitting device Tn transmits data packets “Data, SEQ = 1” to “Data, SEQ = 8”, but the data packet “Data, SEQ = 4” is lost, the receiving device Rn receives the data packets “Data, SEQ = 1” to “Data, SEQ = 3” and returns the ACK packets “ACK SEQ = 1” to “ACK SEQ = 3” and then returns the data packet “Data, SEQ = 3”. 5 ”is received and the data packet“ Data, SEQ = 4 ”is not received. Therefore, when the data packet“ Data, SEQ = 5 ”is received, the Duplicate ACK packet“ ACK SEQ = 3 ”is transmitted. The Duplicate ACK packet “ACK SEQ = 3” is also transmitted at each reception of Data, SEQ = 6 ”to“ Data, SEQ = 8 ”. Thereby, the transmitting apparatus Tn retransmits the data packet “Data, SEQ = 4” by Fast Retransmit when the Duplicate ACK packet “ACK SEQ = 3” is received twice.

  Here, the retransmitted data packet “Data, SEQ = 4” is subject to timeout adjustment by the timeout adjustment algorithm (the original transmission data packet “Data, SEQ = 4” itself is cleared at the time of retransmission. Therefore, it is not a target.) The data packets “Data, SEQ = 5” to “Data, SEQ = 8” transmitted after the original transmission of the data packet “Data, SEQ = 4” are also subject to timeout time adjustment. Thereafter, the transmitting device Tn sequentially transmits subsequent data packets “Data, SEQ = 9” and “Data, SEQ = 10”, but receives an ACK packet for the retransmitted data packet “Data, SEQ = 4”. In the meantime, the data packets to be sequentially transmitted are also sequentially adjusted for the timeout time.

  The receiving device Rn receives the retransmitted data packet “Data, SEQ = 4”, and at that time, the ACK packet “ACK SEQ = 8” indicating that the data packet “Data, SEQ = 8” has been received. ". The ACK packet “ACK SEQ = 8” is not the ACK number that is the sequence number of the retransmitted data packet “Data, SEQ = 4”, but has not been received until then (the retransmission request was made) ) As a result of receiving the data packet “Data, SEQ = 4”, it indicates that the data packet up to sequence number 8 is received at that time. That is, since the ACK packet “ACK SEQ = 8” indicates that the Fast Retransmit retransmission of the data packet “Data, SEQ = 4” has been completed, the transmitter Tn retransmits the ACK packet “ACK SEQ = 8”. Received as an ACK packet for the data packet “Data, SEQ = 4”. As a result, the transmission apparatus Tn finishes adjusting the timeout time by the timeout adjustment algorithm, and adjusts the subsequent data packets “Data, SEQ = 11” and the subsequent data packets transmitted from the reception time point of the ACK packet “ACK SEQ = 8”. A normal timeout period (such as the above timeout period RTO) is applied.

  Therefore, in the transmission / reception sequence example of FIG. 6, the data packets “Data, SEQ = 4” to “Data, SEQ = 10” are the adjustment targets of the timeout time by the timeout adjustment algorithm. That is, the application range of the timeout adjustment algorithm is, in terms of sequence numbers, from the sequence number of the data packet retransmitted by Fast Retransmit to the sequence number of the data packet transmitted last before the completion of Fast Retransmit. The transmission device Tn adjusts the timeout time for each data packet with a sequence number in the range. However, since these data packets are data packets that have not been ACKed, the transmission device Tn can easily grasp them. It is possible to acquire these sequence numbers and use them for the timeout time control in the retransmission control in the transmission device Tn.

(ii) Timeout Time Control FIG. 7 is a flowchart showing a processing procedure for timeout time control executed by the transmission apparatus Tn. The processing operation according to this processing procedure corresponds to a part of the processing operation based on a specific retransmission time control method for adjusting the timeout time under a specific condition in the above-described data transmission program of the transmission device Tn. While performing packet transmission / reception by other parts, retransmission control such as Fast Retransmit and timeout retransmission, congestion avoidance algorithm, etc., timeout time control by the processing procedure of FIG. 7 is performed, and data packet transmission with specific retransmission control is performed. carry out.

  In the timeout time control of the transmitting device Tn, it is determined whether or not retransmission by Fast Retransmit has occurred (step S1), and if it does not occur (the determination result in step S1 is “NO”), the process is terminated. If it occurs (the determination result in step S1 is “YES”), the process proceeds to the process for adjusting the timeout time (process after step S2). Thereby, in the timeout time control, the occurrence of Fast Retransmit is monitored at any time (for example, at regular time intervals).

  Here, in the transmission / reception of the data packet between the transmitting device Tn and the receiving device Rn, if the transmitting device Tn retransmits by Fast Retransmit (the determination result in Step S1 is “YES”), in the timeout time control, Fast Retransmit is used. The sequence number X of the retransmitted data packet is acquired (step S2). At this time (here, when Fast Retransmit occurs), the sequence number of the data packet that has not yet been ACKed (the sequence number of the data packet that has not yet been confirmed to be normally received by the receiving device Rn depending on the received ACK packet) Hereinafter, a range of “UnACKed sequence number” and the data packet thereof is referred to as “UnACKed data packet”) is acquired (step S3).

  The data packet retransmitted by Fast Retransmit has not been ACKed yet, and each data packet already transmitted after sequence number X has not been ACKed yet, but the sequence number which is the ACK number in the Duplicate ACK packet immediately before sequence number X Up to the data packet is ACKed. Therefore, the range of the UnACKed sequence number is from the sequence number X to the sequence number of the latest transmitted data packet. The transmitting apparatus Tn uses the range of the UnACKed sequence number as the application range of the timeout adjustment algorithm, and adjusts the timeout value indicating the timeout period of each UnACKed data packet (step S4).

In the timeout adjustment algorithm, the timeout value of each UnACKed data packet is adjusted as follows.
(a) In the first adjustment when Fast Retransmit occurs, the timeout value of each UnACKed data packet is cleared, and the timeout time (such as the above timeout time RTO) calculated at the time of Fast Retransmit occurrence is cleared. Each UnACK
Set to timeout value of ed data packet.
(b) In the second and subsequent adjustments, the maximum increment of the previous timeout value is added to the timeout value of each UnACKed data packet.
Since the timeout time in TCP is dynamically calculated like the above-mentioned timeout time RTO, the amount of increase (maximum increase value) when the timeout time has increased the most in the timeout time sequentially calculated in the past is transmitted. It is stored in a storage device such as the RAM of the device Tn, a cache memory, or a hard disk, and in the second and subsequent adjustments, the maximum increase amount is added to the time-out value during counting of each UnACKed data packet. However, when a new UnACKed data packet is added in the second and subsequent adjustments (when a new data packet is transmitted), the time-out value calculated at that time is set to the timeout value of the UnACKed data packet. The time-out value of other UnACKed data packets is maintained as it is, and the adjustment of (b) is performed for each UnACKed data packet including the UnACKed data packet in the subsequent adjustments.

  At the present time, since Fast Retransmit has occurred and this is the first adjustment, the calculated time-out value is set to the time-out value of each UnACKed data packet, and transmission of a data packet or reception of an ACK packet is awaited (step S5). When either the transmission or reception event occurs, the generated event is determined (step S6). When the data packet is transmitted, the range of the UnACKed sequence number is acquired again to adjust the timeout value. (If the determination result in step S6 is "Data transmission", the process returns to step S3, and then proceeds to step S4). In this case, the data packet transmitted by the event is newly added as one of the UnACKed data packets, a timeout value is set, and becomes the adjustment target of the above (b) in the subsequent adjustment. That is, when a transmission event of a data packet occurs, the data packet transmitted thereby is newly added to the scope of application of the timeout adjustment algorithm, and new data packets that are sequentially transmitted are sequentially added as targets for adjusting the timeout time. It will be.

  On the other hand, when the generated event is reception of an ACK packet (when the determination result in step S6 is “ACK reception”), the sequence number of the data packet ACKed by the ACK packet is X or more. It is determined whether or not there is (step S7). If the ACK data packet is not greater than or equal to the sequence number X, the data packet with the sequence number immediately before the sequence number X is ACKed, so the ACK packet is the same as the Duplicate ACK packet that caused the Fast Retransmit retransmission. This is a Duplicate ACK packet with an ACK number. Thus, when the same Duplicate ACK packet is received after the occurrence of Fast Retransmit (when the judgment result in Step S7 is “NO”), the range of the UnACKed sequence number is acquired (proceeds to Step S3), respectively. The timeout value of the UnACKed data packet is adjusted (step S4).

  The adjustment of the timeout value here is the adjustment of the above (b) by the timeout adjustment algorithm. That is, in the timeout time control of the transmitting apparatus Tn, when the same Duplicate ACK packet is received after the occurrence of Fast Retransmit, the maximum increase amount of the previous timeout value is added to the time-out value of each UnACKed data packet. Thereafter, similarly, every time a Duplicate ACK packet is received, the maximum increase amount of the previous timeout value is added to the timeout value of each UnACKed data packet.

  The increase amount of the timeout time calculated dynamically reflects the transmission / reception state of the data packet in TCP. Therefore, adding the maximum increase amount to the timeout value of the UnACKed data packet increases the time corresponding to the worst value of the increase in packet transmission delay according to the transmission / reception status of the data packet when Fast Retransmit occurs. It is to let you. The worst value here is the minimum necessary value that is expected to return an ACK packet if the timeout time is increased at the worst, and varies depending on the transmission / reception state of the data packet. After the occurrence of Fast Retransmit, the maximum increase amount of the timeout time is regarded as the worst value, and each time a Duplicate ACK packet is received, the timeout time of each UnACKed data packet is extended by the worst value.

  In the timeout time control of the transmission device Tn, the timeout time is adjusted in this way, and after each adjustment, the transmission of the data packet or the reception of the ACK packet is waited as described above (step S5). When an ACK packet with an ACK number indicating completion of Fast Retransmit retransmission is X or more is received (when the determination result at step S6 is “ACK reception” and the determination result at step S7 is “YES”), transmitting apparatus Tn. Finishes the timeout time control process.

(iii) Example of Data Packet Transmission / Reception with Timeout Retransmission Control FIG. 8 is a diagram showing an example of a data packet transmission / reception sequence by the transmission device Tn and the reception device Rn when the above timeout time control is performed. As shown in FIG. 8, if the transmitting device Tn transmits data packets “Data, SEQ = 1” to “Data, SEQ = 8”, but the data packet “Data, SEQ = 4” is lost, the receiving device Rn receives the data packets “Data, SEQ = 1” to “Data, SEQ = 3” and returns the ACK packets “ACK SEQ = 1” to “ACK SEQ = 3” and then returns the data packet “Data, SEQ = 3”. 5 ”is received and the data packet“ Data, SEQ = 4 ”is not received. Therefore, when the data packet“ Data, SEQ = 5 ”is received, the Duplicate ACK packet“ ACK SEQ = 3 ”is transmitted. The Duplicate ACK packet “ACK SEQ = 3” is also transmitted at each reception of Data, SEQ = 6 ”to“ Data, SEQ = 8 ”. As a result, the transmitting apparatus Tn retransmits the data packet “Data, SEQ = 4” by Fast Retransmit when receiving the Duplicate ACK packet “ACK SEQ = 3” twice, and adjusts the timeout time (above Step S2 and subsequent processes are started. That is, the transmitting apparatus Tn that retransmits the data packet “Data, SEQ = 4” Fast Retransmits obtains the sequence number 4 as the sequence number X and the sequence numbers 4 to 8 as the range of the UnACKed sequence number (steps S2 and S3). The timeout time of each UnACKed data packet is adjusted according to the packet to be transmitted / received (steps S3 to S7).

  In FIG. 8, the time-out time calculated at the time of Fast Retransmit retransmission is 10, and the worst value so far (the maximum increase in time-out time up to that point) is 3, and the data packet “Data, SEQ = The elapsed time from the transmission of “4” and the timeout time during the measurement of the data packet “Data, SEQ = 4” are shown together. As shown in the elapsed time and time-out time during counting, for the retransmitted data packet “Data, SEQ = 4”, the time-out time 10 is set at the time of Fast Retransmit retransmission, and the Duplicate ACK packet when the elapsed time 3 is reached. When “Data, SEQ = 3” is received, the worst-time value 3 is added to the time-out timeout time (10-3), so the time-out time-out time becomes 10. If the Duplicate ACK packet “Data, SEQ = 3” is received again after time 4 has elapsed and time 7 has elapsed, the worst-case value 3 is added to the time-out time (10-4) during timekeeping. The timeout time is 9.

  Then, the transmission device Tn receives the ACK packet “ACK SEQ = 8” when the time 5 passes and the elapsed time 12 is reached. The ACK packet “ACK SEQ = 8” is transmitted from the reception device Rn to the retransmission data. Since the ACK number of the ACK number that is received and returned after receiving the packet “Data, SEQ = 4” is 4 or more, the timeout time control process ends. At this time, the time-out timeout during counting is (9- (12-7)), and the remaining time is 4, so that time-out retransmission does not occur. That is, the initially set timeout time 10 has already elapsed before the reception of the ACK packet “ACK SEQ = 8” (elapsed time 12), but the transmitting device Tn performs Fast Retransmit by the above-described timeout time control. The time-out time is not timed out from occurrence to completion. As a result, the transmission device Tn can perform data packet transmission / reception with the reception device Rn without performing unnecessary time-out retransmission that overlaps when Fast Retransmit retransmission is performed. Although not shown in FIG. 8, the transmitting device Tn transmits data packets “Data, SEQ = 5” to “Data, SEQ = 8” and Fast Retransmit retransmission and before receiving the ACK packet “ACK SEQ = 8”. The same time-out adjustment is performed for data packets as described above, and unnecessary time-out retransmission is also prevented for these data packets.

  According to the timeout time control of the transmission device Tn, unnecessary retransmissions due to TCP can be reduced as described above even in a situation where a delay occurs in a data packet or an ACK packet for some reason. This also makes it possible to suppress a decrease in the size of cwnd, which is the amount of data packets that can be transmitted at one time. That is, the transmitting apparatus Tn performs the above-described timeout control only when Fast Retransmit retransmission actually occurs, and corrects the timeout time only for UnACKed data packets such as the retransmission data packet. It is possible to increase efficiency, prevent unnecessary communication, and improve TCP throughput. If timeout retransmission actually occurs, the communication situation is quite bad, so it is unlikely that the retransmitted data packet has arrived, and there is often no benefit of adjusting the timeout time. Tn can improve the retransmission efficiency by adjusting the timeout time only when Fast Retransmit retransmission is performed.

  Also, since the value added to the timeout value in the timeout adjustment is the maximum increase amount of the previous timeout value, the amount to increase the timeout time changes using the delay occurring in the line as an index. Thereby, it is possible to increase the timeout time by an amount necessary for avoiding duplicate retransmission as appropriate. In order to increase the timeout time by a necessary amount in this way, not only the maximum increase in the timeout value described above, but also any index indicating the delay occurring in the communication line when Fast Retransmit occurs is used. For example, other indices such as the maximum increase in RTT can be used.

  Further, in the data packet transmission / reception by the transmission device Tn and the reception device Rn described above, only the transmission device Tn performs a specific process, and the reception device Rn only needs to be able to perform normal data packet reception by the TCP. As long as normal data transmission by TCP is possible. Therefore, since the data packet communication similar to the above can be performed without requiring any special function other than the device on the transmission side, the data packet with the timeout time control can be easily used even in an existing communication system using the Internet. Transmission and reception can be realized.

(iv) Other Timeout Adjustment Algorithm The transmitting device Tn may perform the process in step S4 using a timeout adjustment algorithm other than the timeout adjustment algorithm described above. Examples are given below.

-Other timeout adjustment algorithm A
Each time a Duplicate ACK packet with the same sequence number is returned, the timeout value measurement is reset to the original timeout value. As described above, the timeout time is manipulated every time the transmitting apparatus Tn receives a Duplicate ACK packet with the same ACK number. This is because that the Duplicate ACK packet with the same ACK number is returned from the receiving side indicates that the retransmitted data packet has not yet arrived at the receiving side. Therefore, as another timeout adjustment algorithm A, every time a Duplicate ACK packet is received, measurement of the timeout time of each UnACKed data packet is stopped, and the timeout value is reset to the originally set timeout value. In particular,
(a) In the first adjustment when Fast Retransmit occurs, the timeout value of each UnACKed data packet is cleared, and the timeout time (such as the above timeout time RTO) calculated at the time of Fast Retransmit occurrence is cleared. Each UnACK
Set to timeout value of ed data packet.
(b) In the second and subsequent adjustments, reset the timeout value during timing of each UnACKed data packet.
However, when a new UnACKed data packet is added in the second and subsequent adjustments (when a new data packet is transmitted), the time-out value calculated at that time is set to the timeout value of the UnACKed data packet. The time-out value of other UnACKed data packets is maintained as it is, and the adjustment of (b) is performed for each UnACKed data packet including the UnACKed data packet in the subsequent adjustments.

  FIG. 9 is a diagram showing an example of a data packet transmission / reception sequence performed by the transmission device Tn and the reception device Rn when the timeout time control is performed by the other timeout adjustment algorithm A. In the transmission / reception sequence example of FIG. 9, as in FIG. 8, the transmission of the data packets “Data, SEQ = 1” to “Data, SEQ = 8”, the loss of the data packet “Data, SEQ = 4”, the ACK packet “ACK SEQ = 1 ”to“ ACK SEQ = 3 ”, and the receiving device Rn receives the Duplicate ACK packet“ ACK SEQ = 3 ”when receiving the data packet“ Data, SEQ = 5 ”to“ Data, SEQ = 8 ”. The transmission device Tn retransmits the data packet “Data, SEQ = 4” by Fast Retransmit, and starts the processing from step S2 onward.

  In FIG. 9, the time-out time calculated at the time of Fast Retransmit retransmission is 10, and the elapsed time and the time-out time during data packet “Data, SEQ = 4” are shown together as in FIG. As shown in the elapsed time and time-out time during counting, for the retransmitted data packet “Data, SEQ = 4”, the time-out time 10 is set at the time of Fast Retransmit retransmission, and the Duplicate ACK packet when the elapsed time 3 is reached. When “Data, SEQ = 3” is received, the timeout time is reset and the time-out timeout time is set to 10. When the Duplicate ACK packet “Data, SEQ = 3” is received again when the elapsed time 7 is reached, the timeout time is reset again and the time-out timeout time is set to 10.

  Then, the transmitting apparatus Tn receives the ACK packet “ACK SEQ = 8” when the time 5 has passed and the elapsed time 12 has been reached, and the ACK number of the ACK packet “ACK SEQ = 8” is 4 or more. The timeout time control process ends. At this time, the time-out time during counting is (10- (12-7)) and the remaining time is 5, so that time-out retransmission does not occur. That is, the initially set timeout time 10 has already passed before the reception of the ACK packet “ACK SEQ = 8” (elapsed time 12). However, in the transmission apparatus Tn, the timeout time is set every time a Duplicate ACK packet is returned. The time-out time is not timed out from the occurrence of Fast Retransmit until the completion. As a result, the transmission device Tn can perform data packet transmission / reception with the reception device Rn without performing unnecessary time-out retransmission that overlaps when Fast Retransmit retransmission is performed. Although omitted in FIG. 9, the transmitting apparatus Tn transmits the data packets “Data, SEQ = 5” to “Data, SEQ = 8” and the Fast Retransmit retransmission and before receiving the ACK packet “ACK SEQ = 8”. The same time-out adjustment is performed for data packets as described above, and unnecessary time-out retransmission is also prevented for these data packets.

・ Other timeout adjustment algorithm B
Each time a Duplicate ACK packet with the same sequence number is returned, a predetermined value is added to the timeout value. Since the timeout period is operated every time the transmitting apparatus Tn receives a Duplicate ACK packet with the same ACK number, the timeout period of each UnACKed data packet is increased by a predetermined amount each time. In particular,
(a) In the first adjustment when Fast Retransmit occurs, the timeout value of each UnACKed data packet is cleared, and the timeout time (such as the above timeout time RTO) calculated at the time of Fast Retransmit occurrence is cleared. Each UnACK
Set to timeout value of ed data packet.
(b) In the second and subsequent adjustments, a predetermined constant value is added to the time-out value during timing of each UnACKed data packet.
However, when a new UnACKed data packet is added in the second and subsequent adjustments (when a new data packet is transmitted), the time-out value calculated at that time is set to the timeout value of the UnACKed data packet. The time-out value of other UnACKed data packets is maintained as it is, and the adjustment of (b) is performed for each UnACKed data packet including the UnACKed data packet in the subsequent adjustments.

  FIG. 10 is a diagram illustrating an example of a data packet transmission / reception sequence performed by the transmission device Tn and the reception device Rn when the timeout time control is performed by the other timeout adjustment algorithm B. In the transmission / reception sequence example of FIG. 10, as in FIG. 8, the transmission of the data packets “Data, SEQ = 1” to “Data, SEQ = 8”, the loss of the data packet “Data, SEQ = 4”, the ACK packet “ACK SEQ = 1 ”to“ ACK SEQ = 3 ”, and the receiving device Rn receives the Duplicate ACK packet“ ACK SEQ = 3 ”when receiving the data packet“ Data, SEQ = 5 ”to“ Data, SEQ = 8 ”. The transmission device Tn retransmits the data packet “Data, SEQ = 4” by Fast Retransmit, and starts the processing from step S2 onward.

  In FIG. 10, the timeout time calculated at the time of Fast Retransmit retransmission is set to 10, and a predetermined fixed addition amount is set to 5. As in FIG. 8, the elapsed time and the time-out timeout time of the data packet “Data, SEQ = 4” are measured. Is also shown. As shown in the elapsed time and time-out time during counting, for the retransmitted data packet “Data, SEQ = 4”, the time-out time 10 is set at the time of Fast Retransmit retransmission, and the Duplicate ACK packet when the elapsed time 3 is reached. When “Data, SEQ = 3” is received, the time-out timeout time is set to 12 by adding the addition amount 5 to the time-out timeout time (10-3). When the Duplicate ACK packet “Data, SEQ = 3” is received again when the elapsed time 7 is reached, the time-out timeout period is set to 13 by adding the addition amount 5 to the time-out timeout period (12-4).

  Then, the transmitting apparatus Tn receives the ACK packet “ACK SEQ = 8” when the time 5 has passed and the elapsed time 12 has been reached, and the ACK number of the ACK packet “ACK SEQ = 8” is 4 or more. The timeout time control process ends. At this time, since the time-out time during counting is (13- (12-7)) and the remaining time is 8, no time-out retransmission occurs. That is, the initially set timeout time 10 has already passed before the reception of the ACK packet “ACK SEQ = 8” (elapsed time 12). However, in the transmission apparatus Tn, the timeout time is set every time a Duplicate ACK packet is returned. The time-out time is not timed out from the occurrence of Fast Retransmit until the completion. As a result, the transmission device Tn can perform data packet transmission / reception with the reception device Rn without performing unnecessary time-out retransmission that overlaps when Fast Retransmit retransmission is performed. Although not shown in FIG. 10, the transmitting apparatus Tn transmits data packets “Data, SEQ = 5” to “Data, SEQ = 8” and Fast Retransmit retransmission and before receiving the ACK packet “ACK SEQ = 8”. The same time-out adjustment is performed for data packets as described above, and unnecessary time-out retransmission is also prevented for these data packets.

  According to the other timeout adjustment algorithms A and B as described above, the amount of increase in the timeout time is slightly increased. However, when a Fast Retransmit retransmission is actually performed, an UnACKed data packet such as a retransmission data packet is transmitted. Since the timeout period is corrected only for the target, it is possible to improve retransmission efficiency, prevent unnecessary communication, and improve TCP throughput.

It is the figure which showed the structure of the communication system provided with transmitter Tn which is a data transmitter by one Embodiment of this invention. It is the figure which showed the transmission / reception sequence of the data packet accompanying Fast Retransmit between the transmitter tn and the receiver Rn. It is the figure which showed the transmission / reception sequence of the data packet accompanying timeout retransmission between the transmission apparatus tn and the receiving apparatus Rn. It is the figure which showed the fluctuation | variation of cwnd when there was Fast Retransmit and timeout retransmission. It is the figure which showed the example of the transmission / reception sequence of the data packet in which the duplicate resending has generate | occur | produced. It is a figure showing the example of the application range of the timeout adjustment algorithm of transmitter Tn. It is the flowchart which showed the processing procedure of timeout time control which transmitter Tn performs. It is the figure which showed the example of a transmission / reception sequence of the data packet by the transmitter Tn and the receiver Rn at the time of implementing timeout time control of FIG. It is the figure which showed the example of the transmission / reception sequence of the data packet by the transmitter Tn and the receiver Rn at the time of performing timeout time control by the other timeout adjustment algorithm A. It is the figure which showed the example of the transmission / reception sequence of the data packet by the transmitter Tn and the receiver Rn at the time of implementing timeout time control by the other timeout adjustment algorithm B. FIG.

Explanation of symbols

Tn transmitter NW communication network Rn receiver

Claims (6)

A data transmission device that performs data packet transmission by TCP,
When the Fast Retransmit retransmission of data packets in response to a retransmission request from the receiving side, per previously transmitted data packet acknowledgment of receipt is not from the receiving side, the data at the time of the retransmission of the reception side A data transmission device that adjusts the elapsed time for a time-out retransmission due to the lapse of time of the already transmitted data packet based on a packet transmission / reception state. A past maximum increase in time-out value that is dynamically calculated based on the time between the transmission time of the data packet and the reception time of the ACK packet for the data packet is set as the time count when the retransmission request for the same data packet is received. The data transmission device according to claim 1, wherein the time measurement is adjusted in addition to the time until the time- out retransmission shown. The data transmission device according to claim 1, wherein when the retransmission request for the same data packet is received, the time until the time- out retransmission indicated by the timing is reset to the initial time when the timing is started, and the timing is adjusted. The data transmission device according to claim 1, wherein, when receiving a retransmission request for the same data packet, the time is adjusted by adding a certain time to a time- out retransmission indicated by the time measurement. A data transmission method for transmitting a data packet by TCP,
When the Fast Retransmit retransmission of data packets in response to a retransmission request from the receiving side, per previously transmitted data packet acknowledgment of receipt is not from the receiving side, the data at the time of the retransmission of the reception side A data transmission method for adjusting the elapsed time for time-out retransmission due to the lapse of time of the already transmitted data packet based on a packet transmission / reception state. A data transmission program for data packet transmission by TCP,
When the Fast Retransmit retransmission of data packets in response to a retransmission request from the receiving side, per previously transmitted data packet acknowledgment of receipt is not from the receiving side, the data at the time of the retransmission of the reception side A data transmission program for causing a computer to realize a function of adjusting the elapsed time for time-out retransmission due to the lapse of time of the already transmitted data packet based on a packet transmission / reception state.

Images