JP6417225B2 - Packet transmission apparatus, communication terminal and slow start control method in packet communication - Google Patents

Description

  The present invention relates to a technique for transmitting data by packet communication, and more particularly to a packet transmission device, a communication terminal, and a slow start control method for determining a congestion window size based on delivery confirmation and performing slow start control related to packet transmission.

  In a best effort type IP (Internet Protocol) network whose quality is not guaranteed, a transmission packet is discarded due to a buffer overflow in a network device, a bit error during transmission, or the like. For this reason, TCP (Transmission Control Protocol) is widely used as a protocol for confirming delivery for reliably transmitting data (see, for example, Non-Patent Document 1).

  For example, as illustrated in FIG. 12, in communication terminals 10 and 20 that perform mutual communication connection using TCP, the communication terminal 10 is provided with a packet transmission device 11 and a packet reception device 12, and the communication terminal 20 includes a packet. A transmitter 22 and a packet receiver 21 are provided. The packet transmission device 11 and the packet reception device 21, the packet transmission device 22 and the packet reception device 12 have the same functions, respectively, and will be described by paying attention to the packet transmission device 11 and the packet reception device 21 as representatives. When the packet transmission device 11 transmits a data transmission packet to the packet reception device 21 via a predetermined communication path, the packet reception device 21 transmits a delivery confirmation response packet to the packet transmission device 11 as a report indicating that the packet has been received. To do.

  More specifically, in TCP, when the packet reception device 21 receives a packet, the packet transmission device 11 is notified of the number of the packet to be transmitted next as a report indicating that the packet has been received. Then, the packet transmission device 11 confirms that the packet has normally reached the packet reception device 21 based on the report notified from the packet reception device 21. The packet transmission device 11 adjusts a congestion window size (cwnd: congestion window size) indicating the number of packets that can be transmitted without a delivery confirmation response based on the report notified from the packet reception device 21. For example, cwnd is expanded when a packet is normally received, and cwnd is reduced when a packet loss is detected.

  This technique for adjusting cwnd is called a congestion control technique, and the control technique is switched depending on the state of communication. Phases such as “slow start phase” generally applied at the start of communication or after timeout, “congestion avoidance phase” applied when communication is stable, and “loss recovery phase” to retransmit lost packets The congestion control technique is switched according to the situation. RFC5681 describes a congestion control technique used by a general TCP (for example, see Non-Patent Document 2). In the operation of the slow start phase described in RFC5681, when cwnd is less than the slow start threshold value (ssthresh), cwnd is expanded by Expression (1). ssthresh is a threshold value that determines switching between the slow start phase and the congestion avoidance phase.

       cwnd = min (N, MSS) (1)

  N is the number of bytes newly confirmed for delivery, and MSS is the maximum number of bytes of data included in the packet. When cwnd exceeds ssthresh or packet loss occurs, the operation in the slow start phase ends.

  Various TCPs such as TCP CUBIC (for example, see Non-Patent Document 3) and CTCP (for example, see Non-Patent Document 4) have been proposed, but the operation in the “slow start phase” is the same as that of RFC5681, and “congestion” A unique congestion control algorithm is incorporated in the “avoidance phase”.

  As an example of the operation in the slow start phase, Limited Slow-Start has been proposed (see Non-Patent Document 5, for example). In RFC5681, cwnd is expanded by Equation (1) until cwnd becomes larger than ssthresh. However, Limited Slow-Start introduces a new threshold value max_ssthresh, and when cwnd becomes larger than max_ssthresh, one round trip delay time (rtt: Round Trip) Cwnd increasing around (Time) is limited to max_ssthresh / 2.

Hystart has been proposed as an operation in the slow start phase of another example (see, for example, Non-Patent Document 6). Hystart defines two new conditions for the slow start end condition in addition to RFC5681. One is ended when the time taken to transmit a packet sequence transmitted during one round-trip delay time (rtt) exceeds a threshold value. The other is that rtt _min , which is the minimum rtt measured by the first few packets of the packet sequence transmitted during a predetermined measurement period, is greater than the threshold value than the rtt _base, which is the minimum rtt measured so far. Exit if it is larger. Here, the rtt _base is the minimum rtt measured from the start of communication until the present time.

  In addition, a technique for performing a unique band measurement before the slow start phase has been proposed (see, for example, Patent Document 1). With this technique, a predetermined number of packets are sent at the start of communication, regardless of the TCP congestion window size, and the result is fed back to the TCP congestion control method, allowing the congestion window size to be increased more quickly. It is said.

  To summarize packet transmitting apparatuses based on RFC5681 and RFC3742 of the prior art to which operations relating to these slow start phases can be applied, a schematic configuration of the packet transmitting apparatus 11 is shown in FIG. Note that the packet transmission device 11 shown in FIG. 13 illustrates only functional blocks related to comparison with the present invention described later, and other necessary functions as a packet transmission device of the packet communication method for performing delivery confirmation are as follows: It can be set as the structure similar to the known technique conventionally known, The detailed description is abbreviate | omitted. 13 includes a transmission time writing unit 111, a packet transmission unit 112, a delivery confirmation response reception unit 113, a packet loss determination unit 114, and a packet transmission control unit 115, and includes packet transmission control. The unit 115 includes a loss retransmission operation unit 116, a loss recovery operation unit 117, a congestion avoidance operation unit 118, and a slow start operation unit 119.

  The transmission time writing unit 111 records the transmission time at the time of packet transmission. This transmission time can be recorded together with the packet number in an internal memory (not shown) of the packet transmission device 11. Alternatively, recording can be performed using a TCP time stamp option.

  The packet transmission unit 112 transmits a packet toward the packet reception device 21. Thereafter, when receiving the delivery confirmation response packet notified from the packet receiving device 21, the delivery confirmation response receiving unit 113 starts the next process.

  When the delivery confirmation response receiving unit 113 receives the delivery confirmation response packet, the delivery confirmation response reception unit 113 calculates an rtt required from the packet transmission from the packet transmission unit 112 to the reception of the delivery confirmation response packet. The calculation of rtt can be the difference between the transmission time and the reception time recorded in the internal memory. Alternatively, a TCP timestamp option can be used. After calculating rtt, the delivery confirmation response receiving unit 113 notifies the packet loss determination unit 114 of the delivery confirmation response packet and rtt.

When the packet loss determination unit 114 receives the delivery confirmation response packet and the rtt from the delivery confirmation response unit 113, the packet loss determination unit 114 updates the rtt _base and determines whether or not a packet loss has occurred. When a packet loss has occurred, the packet loss determination unit 114 notifies the loss retransmission operation unit 116 of the delivery confirmation response packet and the rtt, and executes a predetermined packet loss retransmission operation. If no packet loss occurs, the packet loss determination unit 114 confirms the delivery to the loss recovery operation unit 117 when the current operation phase is the loss recovery phase, and to the congestion avoidance operation unit 118 when the current operation phase is the congestion avoidance phase. Notify the response packet and rtt. Further, in the slow start phase, the packet loss determination unit 114 notifies the slow start operation unit 119 of a predetermined slow start operation instruction related to the equation (1).

  The loss retransmission operation unit 116 executes transmission packet retransmission processing based on the delivery confirmation response packet and the rtt.

  The loss recovery operation unit 117 performs adjustment processing for increasing or reducing the value of cwnd so as to recover the communication state after occurrence of packet loss based on the delivery confirmation response packet and the rtt.

  The congestion avoiding operation unit 118 updates the value of cwnd so as to avoid congestion of the communication path based on the delivery confirmation response packet and the rtt.

  However, the loss retransmission operation unit 116, the loss recovery operation unit 117, and the congestion avoidance operation unit 118 may be configured to execute a rate control process based on a known congestion control technique including general TCP. Further details of the operation are omitted.

  The slow start operation unit 119 updates the value of cwnd to be enlarged based on Expression (1) while no packet loss occurs.

  In this way, the packet transmission control unit 115 executes rate control based on various operation phases according to whether or not packet loss has occurred.

Japanese Patent No. 4367505

“RFC793-Transmission Control Protocol”, [online], formulated in September 1981, DARPA INTERNET PROGRAM PROTOCOL SPECIFICATION, [searched on December 19, 2014], Internet <URL: http: // www. rfc-base.org/txt/rfc-793.txt> “RFC5681-TCP Congestion Control”, [online], formulated in September 2009, Network Working Group, [searched on December 19, 2014], Internet <URL: http: //tools.ietf. org / search / rfc5681> Sangtae Ha, Injong Rhee and Lisong Xu, “CUBIC: A New TCP-Friendly High-Speed TCP Variant,” [online], ACM SIGOPS Operating System Review, Volume 42, Issue 5, July 2008, [December 19, 2014 Day search], Internet <URL: http://dl.acm.org/citation.cfm?id=1400105> kun Tan, Jingmin Song, Qian Zhang and Murari Sridharan, “A Compound TCP Approach for High-speed and Long Distance Networks,” [online], INFOCOM 2006. 25th IEEE International Conference on Computer Communications. Proceedings, April 2006, [Heisei 26 December 19th]], Internet <URL: http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=4146841&url=http%3A%2F%2Fieeexplore.ieee.org%2Fxpls%2Fabs_all. jsp% 3Farnumber% 3D4146841> “RFC3742-Limited Slow-Start for TCP with Large Congestion windows”, [online], formulated in March 2004, Network Working Group, [searched on December 19, 2014], Internet <URL: https : //tools.ietf.org/html/rfc3742> Sangtae Ha and Injong Rhee, “Hybrid slow start for high-bandwidth and long-distance networks,” [online], PFLDnet, 2008, [searched on December 19, 2014], Internet <URL: http: // netsrv. csc.ncsu.edu/export/hybridstart_pfldnet08.pdf>

  In RFC5681, it is recommended that ssthresh be set to a sufficiently large value (for example, the maximum value that can be taken) at the start of communication. As a result, the slow start phase continues until a packet loss occurs. Since cwnd is expanded rapidly and packets are sent to the network until packet loss occurs, other traffic is affected. In addition, when packet loss occurs, it is necessary to resend the lost packet, so that its own communication efficiency also decreases.

  Thus, the above problem can be solved by shifting from the slow start phase to the congestion avoidance phase without causing packet loss. However, the Limited Slow-Start disclosed in Non-Patent Document 5 avoids many packet losses at once by reducing the increase rate of cwnd before the loss occurs, but it is slow until the packet loss occurs. Since the start phase does not end, packet loss eventually occurs. Further, the value of max_ssthresh is unknown at the start of communication, and there is a problem that the behavior is the same as RFC5681.

  In addition, Hystart disclosed in Non-Patent Document 6 presents a technique of using the rtt of a packet transmitted in the slow start phase and shifting to the congestion avoidance phase by detecting congestion before packet loss occurs. . However, Hystart assumes an environment in which propagation delay is stable like a wired network, and performs congestion detection using only the first few samples of rtt measured during each rtt period. In a network in which the propagation delay changes regardless of congestion as described above, a transition to the congestion avoidance phase may occur before cwnd expands.

  Also, with the technique disclosed in Patent Document 1, since a predetermined load is applied while the line status is unknown at the start of communication, there is a possibility of causing congestion and lowering the line quality.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to suppress packet loss at the start of communication even in an environment in which delay fluctuation is likely to occur in packet communication for confirming delivery. Then, it is providing the packet transmitter in the packet communication which enables high-speed communication, a communication terminal, and the slow start control method.

  The packet transmission device according to the present invention is configured to determine the upper limit value of the congestion window size from the packet transmission / reception result in the slow start phase and use it for the end determination of the slow start phase.

  That is, the packet transmission device of the present invention is a packet transmission device that determines the congestion window size based on the delivery confirmation and performs slow start control related to packet transmission, and is a delivery confirmation response packet notified as a delivery confirmation of packet transmission. A delivery confirmation response receiving means for calculating a round trip delay time based on the delivery confirmation of the packet transmission from the difference between the transmission time of the packet transmission and the reception time of the delivery confirmation response packet, and a congestion window from the start of communication Congestion determination is performed while increasing the size, and when it is determined that there is congestion, a slow start control means that operates to transition from the slow start phase to the congestion avoidance phase, the slow start control means, in the slow start phase During operation, the minimum round-trip delay measured continuously for the round-trip delay time. Time, the maximum value of the congestion window size that is updated based on a predetermined update formula each time the congestion window size is updated, and the packet group received at the most recent time relative to the received acknowledgment packet Congestion window upper limit calculation means for determining an upper limit value of the congestion window size for each measurement period related to a predetermined packet delay amount based on the transmission time and the reception time, and immediately before receiving the delivery confirmation response packet The congestion window size is expanded by a predetermined width below the upper limit value of the congestion window size determined when one measurement period elapses, and the upper limit value of the congestion window size and the increased congestion window size for each measurement period When the expanded congestion window size is greater than or equal to the upper limit value of the congestion window size, And having a congestion window increasing means which operates to transition from over-start phase to the congestion avoidance phase.

  In the packet transmission device according to the present invention, the congestion window upper limit calculation unit may determine that the transmission rate of the transmission packet corresponding to the delivery confirmation response packet is equal to the congestion window size each time the delivery confirmation response packet is received. First determination means for determining whether the transmission rate is equal to or higher than a transmission rate obtained from the maximum value, and each time the delivery confirmation response packet is received, it is determined whether the packet is included in the recently received packet group. When satisfying the determination of both the second determination means and the first determination means and the second determination means, the number of bytes confirmed by the delivery confirmation response packet is added to the number of received bytes of the recently received packet group. When the number of received bytes is determined and the determination of either one of the first determination means and the second determination means is not satisfied, A congestion window that calculates a congestion window size based on a reception rate of a packet group received at the latest time required, updates the window every measurement period, and determines the updated congestion window size as an upper limit value of the congestion window size And an upper limit determining means.

  In the packet transmission apparatus of the present invention, the maximum value of the congestion window size is a value that is twice the updated congestion window size or twice the updated congestion window size as the predetermined update formula. The value is updated with the smaller value of the congestion window size determined at the time of the immediately preceding one measurement period.

  In the packet transmission apparatus of the present invention, the slow start control means monitors the fluctuation amount of the round-trip delay time for each received acknowledgment packet and monitors the maximum fluctuation amount of the packet sequence of successive round-trip delay packets. And a delay fluctuation amount estimating means for calculating a moving average value of the maximum fluctuation amount for each measurement period as an average fluctuation amount of a round-trip delay time, and the congestion window upper limit calculating means includes the average fluctuation A means for determining the upper limit value of the congestion window in consideration of the amount, and the congestion window increasing means is a value obtained by adding the average fluctuation amount to the minimum round-trip delay time continuously measured for the round-trip delay time. And the minimum round-trip delay time in the measurement period measured as the minimum value in the immediately preceding measurement period, the minimum round-trip delay time in the measurement period It further has means for operating to transition from the slow start phase to the congestion avoidance phase when exceeding the value obtained by adding the average fluctuation amount to the minimum round-trip delay time continuously measured for the delay time. .

  Furthermore, the communication terminal of the present invention is characterized by including the packet transmission device of the present invention.

  Furthermore, the slow start control method of the present invention is a slow start control method for determining a congestion window size based on delivery confirmation and performing slow start control related to packet transmission, and transmitting packet transmission during operation in the slow start phase. The minimum round-trip delay time continuously measured for the round-trip delay time based on the delivery confirmation of the packet transmission based on the difference between the time and the reception time of the delivery confirmation response packet, and predetermined every time the congestion window size is updated A packet delay determined in advance based on the maximum value of the congestion window size updated based on the update formula and the transmission time and reception time of the packet group received at the latest time with respect to the received acknowledgment packet Determining an upper limit value of the congestion window size for each measurement period relating to the amount; Each time an acknowledgment packet is received, the congestion window size is expanded by a predetermined width below the upper limit value of the congestion window size determined at the time of the immediately preceding measurement period, and the congestion window size is increased for each measurement period. A step of comparing an upper limit value with the expanded congestion window size and operating to transition from the slow start phase to the congestion avoidance phase when the expanded congestion window size is equal to or greater than the upper limit value of the congestion window size. It is characterized by including these.

  In packet communication that confirms delivery, suppress false detection of congestion due to delay unrelated to congestion that can occur in environments where delay fluctuations are likely to occur, such as wireless networks, and suppress occurrence of bursty packet loss, As a result, the transition to the congestion avoidance phase prior to increasing the congestion window size in the slow start phase at the start of communication can be efficiently suppressed, thus enabling high-speed communication.

It is a block diagram in the packet transmitter of one Embodiment by this invention. It is a flowchart which shows the process of the delivery confirmation response receiver in the packet transmitter of one Embodiment by this invention. It is a flowchart which shows the process of the packet loss determination part in the packet transmission apparatus of one Embodiment by this invention. (A), (B) is explanatory drawing of the measurement period regarding the packet delay amount which concerns on the packet transmitter of one Embodiment by this invention. It is a block diagram which shows the structure of the slow start operation | movement part of Example 1 in the packet transmission apparatus of one Embodiment by this invention. It is a flowchart which shows the congestion window increase process of the slow start operation | movement part of Example 1 in the packet transmitter of one Embodiment by this invention. It is a flowchart which shows the congestion window upper limit calculation process of the slow start operation | movement part of Example 1 in the packet transmitter of one Embodiment by this invention. It is a block diagram which shows the structure of the slow start operation | movement part of Example 2 in the packet transmission apparatus of one Embodiment by this invention. It is a flowchart which shows the congestion window increase process of the slow start operation | movement part of Example 2 in the packet transmitter of one Embodiment by this invention. It is a flowchart which shows the delay variation calculation process of the slow start operation | movement part of Example 2 in the packet transmitter of one Embodiment by this invention. It is a flowchart which shows the congestion window upper limit calculation process of the slow start operation | movement part of Example 2 in the packet transmitter of one Embodiment by this invention. It is a figure explaining the network connection example of the communication terminal which performs mutual communication connection using TCP. It is a block diagram in the packet transmitter based on a prior art.

  Hereinafter, a packet transmission device, a communication terminal, and a slow start control method according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram of a packet transmission device 11a according to an embodiment of the present invention. The packet transmission device 11a is a device provided in the communication terminal 10 shown in FIG. 12 in place of the packet transmission device 11 shown in FIG. Similarly, the communication terminal 20 can be replaced with the packet transmission device 22 and provided with the same configuration as the packet transmission device 11a. Therefore, as shown in FIG. 12, in the communication terminals 10 and 20 that perform mutual communication connection using TCP, the packet transmission device 11a transmits the data transmission packet to the packet reception device 21 via a predetermined communication path. Then, the packet reception device 21 transmits a delivery confirmation response packet to the packet transmission device 11a as a report indicating that the packet has been received. Note that the packet transmission device 11a shown in FIG. 1 illustrates only the functional blocks according to the present invention, and other necessary functions as a packet transmission device of a packet communication method for confirming delivery have been conventionally known. The configuration can be the same as that of the known technology, and detailed description thereof is omitted.

  As shown in FIG. 1, the packet transmission device 11a of the present embodiment includes a transmission time writing unit 111, a packet transmission unit 112, a delivery confirmation response reception unit 113, a packet loss determination unit 114, and a packet transmission control unit 115. The packet transmission control unit 115 includes a loss retransmission operation unit 116, a loss recovery operation unit 117, a congestion avoidance operation unit 118, and a slow start operation unit 119a. Compared with the packet transmission device 11 shown in FIG. 13, the packet transmission device 11a of this embodiment is different in that it includes a slow start operation unit 119a instead of the slow start operation unit 119. Components are given the same reference numbers.

  The transmission time writing unit 111 records the transmission time when transmitting the data transmission packet. This transmission time can be recorded together with the packet number in an internal memory (not shown) of the packet transmission device 11. Alternatively, recording can be performed using a TCP time stamp option.

  The packet transmission unit 112 transmits a packet toward the packet reception device 21. Thereafter, when receiving a delivery confirmation response packet (hereinafter referred to as “ACK packet”) notified from the packet reception device 21, the delivery confirmation response receiving unit 113 starts the next process.

  When receiving the ACK packet, the delivery confirmation response receiving unit 113 calculates a round trip delay time (rtt) required from the packet transmission from the packet transmission unit 112 to the reception of the ACK packet. The calculation of rtt is expressed as the transmission time (hereinafter referred to as “sndtime”) of the transmission packet corresponding to the ACK packet recorded in the internal memory and the reception time (hereinafter referred to as “rcvtime”) of the ACK packet. ) Difference. Alternatively, a TCP timestamp option can be used instead of recording in the internal memory. After calculating rtt, the delivery confirmation response receiving unit 113 notifies the packet loss determination unit 114 of the ACK packet and the rtt, sndtime, and rcvtime. More specifically, as shown in FIG. 2, when receiving the ACK packet (step S11), the delivery confirmation response receiving unit 113 calculates the round-trip delay time (rtt) from the difference between the transmission time (sndtime) and the reception time (rcvtime). ) (Step S12), and after calculating rtt, the packet loss determination unit 114 is notified of the ACK packet and the rtt, sndtime, and rcvtime (step S13).

  When the packet loss determination unit 114 receives the ACK packet and the rtt, sndtime, and rcvtime from the delivery confirmation response unit 113, the packet loss determination unit 114 performs the packet loss determination based on the delivery confirmation number (also referred to as “ACK number”) in the ACK packet. . When a packet loss has occurred, the packet loss determination unit 114 notifies the loss retransmission operation unit 116 of the ACK packet and rtt. If no packet loss has occurred, the packet loss determination unit 114 notifies the loss recovery operation unit 117 of the ACK packet and rtt if the current operation phase is the loss recovery phase, and congestion avoidance if the current operation phase is the congestion avoidance phase. The ACK packet and rtt are notified to the operation unit 118, and in the slow start phase, the ACK packet and rtt, sndtime, and rcvtime are notified to the slow start operation unit 119a. More specifically, as shown in FIG. 3, when the packet loss determination unit 114 receives a delivery confirmation response packet and rtt from the delivery confirmation response reception unit 113 (step S21), whether or not a packet loss has occurred. Is determined (step S22). For example, the packet loss may be determined when a packet having the same ACK number included in the ACK packet is received three times.

  When packet loss has occurred (step S22: Yes), the packet loss determination unit 114 notifies the loss retransmission operation unit 116 of the ACK packet and rtt, and executes a predetermined packet loss retransmission operation (step S23). ). If no packet loss has occurred (step S22: No), the packet loss determination unit 114 proceeds to the loss recovery operation unit 117 (steps S24 and S25) if the current operation phase is the loss recovery phase (step S24, S25). In this case, the ACK packet and rtt are notified to the congestion avoiding operation unit 118 (steps S24 and S26). In the slow start phase, the packet loss determination unit 114 notifies the slow start operation unit 119a according to the present invention of the ACK packet and the rtt, sndtime, and rcvtime (steps S24 and S27).

  The packet transmission control unit 115 executes rate control based on various operation phases according to whether or not packet loss has occurred. The loss retransmission operation unit 116, the loss recovery operation unit 117, and the congestion avoidance operation unit 118 may be configured to execute rate control processing based on a known congestion control technique including general TCP. Further details of the operation are omitted. In particular, the packet transmission control unit 115 includes a slow start phase in which the congestion window size is increased at a relatively high speed by the slow start operation unit 119a, and a congestion avoidance phase in which the congestion window size is adjusted relatively slowly by the congestion avoidance operation unit 118. It operates to execute rate control while transitioning.

As will be described in detail later, the slow start operation unit 119a according to the first embodiment of the present invention uses an rtt _base which is the minimum rtt measured from the start of communication until the present time, and compares and monitors this rtt _base. On the other hand, an upper limit value of the congestion window size (hereinafter referred to as “cwnd _limit ”) is determined from the packet transmission / reception result, and is used for determining the end of the slow start phase. In addition, the slow start operation unit 119a according to the second embodiment of the present invention determines a predetermined 1 for the rtt _base that is the minimum rtt measured from the start of communication until the present time and the rtt corresponding to the received ACK packet. Calculate and update rtt _min , which is the minimum rtt among all the rtts measured for each measurement period, compare and monitor this rtt _base and rtt _min , and send and receive packets in consideration of the amount of packet delay variation An upper limit value (cwnd _limit ) of the congestion window size is determined from the result, and is used to determine the end of the slow start phase. It should be noted that the rtt _{min according} to the present invention is different from the minimum rtt (rtt _min ) in Hystart disclosed in Non-Patent Document 6.

  Here, the “measurement period” will be described. For example, as shown in FIG. 4A, the data transmission packets D1, D2, and D3 transmitted continuously by the communication terminal 10 are transmitted to the communication terminal 20, and the data transmission packets D1, D2, and D3 are transmitted. Considering the case of receiving ACK packets ACK1, ACK2, and ACK3 corresponding to each of the packets, one measurement period is a delivery to a packet that is first transmitted by the communication terminal 10 (packet transmission apparatus 11a) from the start of measurement of the measurement period Until an acknowledgment (ACK) arrives.

Alternatively, as shown in FIG. 4B, one measurement period is from the start of measurement in the measurement period until a predetermined time has elapsed (for example, until the minimum rtt (rtt _min ) has elapsed in the immediately preceding measurement period), It can be. The measurement period may be continuously determined for IP data flow, may be determined intermittently, rtt _min as determined by the measurement period is maintained until obtaining a rtt _min at least the next measurement period configured as, to update such cwnd using rtt _min to allow use rtt _min holding at that update time.

(Slow start operation part of Example 1)
First, the slow start operation unit 119a according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 5 is a block diagram illustrating a configuration of the slow start operation unit 119a according to the first embodiment of the present invention. FIG. 6 is a flowchart showing the congestion window increasing process of the slow start operation unit 119a according to the first embodiment of the present invention. FIG. 7 is a flowchart illustrating the congestion window upper limit calculation process of the slow start operation unit 119a according to the first embodiment of the present invention.

  As illustrated in FIG. 5, the slow start operation unit 119a according to the first embodiment includes a congestion window increasing unit 1191 that executes a congestion window increasing process and a congestion window upper limit calculating unit 1192 that executes a congestion window upper limit calculating process.

  First, the congestion window increasing process by the congestion window increasing unit 1191 will be described with reference to FIG.

When the congestion window increasing unit 1191 receives the ACK packet and the rtt, sndtime, and rcvtime from the packet loss determining unit 114 (step S31), the congestion window increasing unit 1191 updates the rtt _{base according} to the equation (2) (steps S32 and S33). rtt _base is the minimum value of rtt measured during communication from the start of communication. The initial value at the start of rtt _base communication can be a certain value such as the maximum possible value.

if rtt _base > rtt (2)
then rtt _base = rtt

Next, the congestion window increasing unit 1191 notifies the congestion window upper limit calculating unit 1192 of the ACK packet and the rtt _base , sndtime, rcvtime, and cwnd _max (step S34). cwnd _max is a value used by the congestion window upper limit calculation unit 1192 to calculate the upper limit value (cwnd _limit ) of the congestion window size. The calculation method (update method) of the cwnd _max value and the calculation procedure of the upper limit value (cwnd _limit ) of the congestion window size will be described later.

Subsequently, when the congestion window increasing unit 1191 receives the cwnd _limit from the congestion window upper limit calculating unit 1192 (step S35), the congestion window increasing unit 1191 determines whether one measurement period has elapsed (step S36). As a determination method for one measurement period, for example, as shown in FIG. 4 described above, for example, a method in which a delivery confirmation response to a packet transmitted first after starting measurement in one measurement period is received, or start of one measurement period There is a method in which a predetermined time has elapsed from the time. When this one measurement period has elapsed (step S36: Yes), the congestion window increasing unit 1191 determines whether or not to end the slow start phase (steps S38 to S40). This determination is made by comparing the current congestion window size (cwnd) and the upper limit value (cwnd _limit ) of the congestion window size, that is, by equation (3).

if cwnd ≧ cwnd _limit (3)
then end the slow start phase,
else Continue the slow start phase.

  When the slow start phase is finished (step S38: Yes), the process shown in the equation (4) is performed (step S40).

ssthresh = cwnd (4)
cwnd = cwnd + MSS

  On the other hand, when the slow start phase is continued (step S38: No), the processing shown in the equation (5) is performed (step S39).

cwnd = min (cwnd + γ, cwnd _limit ) (5)

  γ is the size of the congestion window size (cwnd) that is increased by receiving one ACK packet, and can be MSS or the number of bytes that have been acknowledged by the ACK packet received this time.

Further, when the slow start phase is continued (step S38: No), cwnd _max is also updated (step S39). cwnd _max is a value used by the congestion window upper limit calculation unit 1192 to calculate the upper limit value (cwnd _limit ) of the congestion window size, more specifically, the maximum value of the congestion window that can be taken until the next slow start phase end determination. The initial value of cwnd _max can be the maximum value that can be taken at the start of communication. In addition, when the slow start threshold (ssthresh) is used to switch between the slow start phase and the congestion avoidance phase after the start of communication, the initial value of cwnd _max used for the current slow start phase is set to the slow start threshold (ssthresh) Value.

The cwnd _max is updated based on a predetermined update formula every time cwnd is updated in the current slow start phase. As an example of a more specific update formula, the congestion window increasing unit 1191 updates, for example, cwnd _max Is the smaller of the updated value of cwnd, the updated value of cwnd, and the upper limit value cwnd _limit of the congestion window size determined at the end of the previous measurement period. Determined as the value of.

  If it is determined that one measurement period has not elapsed (step S36: No), the congestion window increasing unit 1191 performs the process shown in equation (5) (step S37).

  Next, a congestion window upper limit calculation process performed by the congestion window upper limit calculation unit 1192 will be described with reference to FIG.

When the congestion window upper limit calculation unit 1192 receives the ACK packet and the rtt _base , sndtime, rcvtime, and cwnd _max from the congestion window increase unit 1191 (step S41), the congestion window upper limit calculation unit 1192 calculates the upper limit value cwnd _limit of the congestion window size according to the following procedure. . The cwnd _limit is an upper limit value when the congestion window size is increased during the current slow start phase, and the reception rate is calculated from the ACK packet and calculated. The initial value of cwnd _limit can be a predetermined maximum value assumed in advance (the maximum value that can be taken).

The upper limit value cwnd _limit of the congestion window size is calculated every time an ACK packet is received. First, the transmission rate obtained from cwnd _max is compared with the transmission rate of the transmission packet corresponding to the ACK packet received this time. (Step S42).

When the transmission rate of the transmission packet corresponding to the ACK packet received this time is equal to or higher than the transmission rate obtained from cwnd _max (step S42: Yes), subsequently, the packet group ( That is, it is determined whether or not the packet is included in an ACK packet group regarded as corresponding to a series of transmission packets (step S43). This determines whether or not an ACK packet received with delay variation due to congestion that can occur during the slow start phase in an environment where delay variation is likely to occur, such as a wireless network, is handled as a series of transmission packets. . For this determination, the following two determination methods are effective.

The determination method of the first example is performed by equation (6). Note that sndtime _last is the transmission time of the transmission packet corresponding to the ACK packet received immediately before.

if sndtime−sndtime _last ≦ (MSS / cwnd _max ) × rtt _base (6)
then included in the recently received packet group.
else Not included in recently received packets.

The determination method of the second example is performed by Expression (7). Rcvbyte is the number of bytes received in the recently received packet group (that is, the ACK packet group regarded as corresponding to a series of transmitted packets), and sndtime _first corresponds to the first ACK packet of the recently received packet group. This is the transmission time of the transmission packet to be transmitted.

if sndtime−sndtime _first ≦
((rcvbyte + delivery confirmation byte count) / cwnd _max ) x rtt _base (7)
then included in the recently received packet group.
else Not included in recently received packets.

When the transmission rate of the transmission packet corresponding to the ACK packet received this time is not equal to or higher than the transmission rate obtained from cwnd _max (step S42: No), and the packet group (that is, a series of packets received recently) ACK packet group that is regarded as corresponding to the transmission packet of No. (step S43: No), the packet group received recently (from the record of the packet group received recently) according to equation (8) ( That is, a congestion window size cwnd _est that satisfies this reception rate is calculated on the basis of the reception rate of an ACK packet group that is regarded as corresponding to a series of transmission packets (step S45).

cwnd _est = rcvbyte x rtt _base / (rcvtime _last -rcvtime _first ) (8)

Here, rcvbyte is the number of bytes received in the recently received packet group (that is, the ACK packet group regarded as corresponding to a series of transmission packets), rcvtime _last is the last ACK packet in the recently received packet group Rcvtime _first is the time when the _first ACK packet was received among the group of packets received recently.

Further, in order to prevent the measurement state required for calculating the congestion window size from continuing for 1 rtt or more, in order to calculate the congestion window size periodically at less than 1 rtt, Equation (9) As shown in FIG. 5, even when the continuous transmission period (sndtime-sndtime _first ) for the transmission packet corresponding to the ACK packet received this time exceeds a predetermined threshold value (rtt _base / 2 in this example) The congestion window size cwnd _{est according} to 8) is calculated.

if sndtime-sndtime _first > rtt _base / 2 (9)
Then, the congestion window size is calculated by equation (8).

When cwnd _est is calculated, the maximum value cwnd _limit-tmp of cwnd _{est in} one measurement period is updated by equation (10) (steps S46 and S47). The initial value of cwnd _limit-tmp is cwnd _limit-tmp = 0.

if cwnd _limit-tmp <cwnd _est (10)
then cwnd _limit-tmp = cwnd _est

  Further, each variable is reset as shown in Expression (11) in order to determine in step S44 regarding the ACK packet to be received next and to calculate the congestion window size (step S48).

rcvbyte = 0 (11)
sndtime _first = sndtime
rcvtime _first = rcvtime

The transmission rate of the transmission packet corresponding to the ACK packet received this time is equal to or higher than the transmission rate obtained from cwnd _max (step S42: Yes), and the ACK packet received this time is the group of packets received recently (that is, a series of transmissions). (ACK packet group regarded as corresponding to a packet)) (step S43: Yes), that is, it is regarded as a continuous packet sequence based on the determination based on the transmission interval, and a predetermined number of transmission packets related to the continuous packet sequence If the transmission period does not exceed a predetermined threshold, the number of received bytes of the continuous packet sequence is updated by equation (12) (step S44).

      rcvbyte = rcvbyte + delivery confirmation byte count (12)

Next, it is determined whether or not one measurement period has elapsed (step S49). When it is determined that one measurement period has elapsed (step S49: Yes), is cwnd _limit-tmp being updated? It is determined whether or not (step S50).

When the cwnd _limit-tmp is updated (step S50: Yes), the cwnd _limit is updated by the equation (13) (step S51).

if cwnd _limit-tmp > 0 (13)
then cwnd _limit = cwnd _limit-tmp ,
cwnd _limit-tmp = 0

When it is determined that one measurement period has not elapsed (step S49: No) and when cwnd _limit-tmp is not updated (step S50: No), cwnd _limit remains the previous value.

When the value of cwnd _limit is determined through step S50, sndtime _last and rcvtime _last are updated by equation (14) (step S52). In the first embodiment, sndtime _last is used only in the case of Expression (6).

sndtime _last = sndtime (14)
rcvtime _last = rcvtime

Finally, the congestion window upper limit calculation unit 1192 notifies the congestion window increase unit 1191 of cwnd _limit (step S53). Accordingly, the congestion window upper limit calculation unit 1192 receives the sum of the number of bytes received confirmed by the ACK packet received this time to the number of received bytes of the packet group received at the latest time when both determinations of step S42 and step S43 are satisfied. If the number of bytes is determined (step S44) and one of the determinations of step S42 and step S43 is not satisfied, the congestion window size based on the reception rate of the packet group received at the latest time obtained from the number of received bytes ( cwnd _limit-tmp ) is calculated and updated every measurement period, and the congestion window size (cwnd _limit-tmp ) updated every measurement period is determined as the upper limit value (cwnd _limit ) of the congestion window size. Then, every time an ACK packet is received, the congestion window increasing unit 1191 increases the congestion window size (cwnd) by a predetermined width below the cwnd _limit determined when one measurement period has elapsed, and for each measurement period, one measurement period. The transition from the slow start phase to the congestion avoidance phase is determined by comparing the cwnd _limit determined when elapses with the expanded cwnd.

  As described above, the slow start operation unit 119a of the first embodiment including the congestion window increasing unit 1191 and the congestion window upper limit calculating unit 1192 is configured and included in the packet transmission device 11a, thereby suppressing occurrence of bursty packet loss. As a result, the transition to the congestion avoidance phase prior to increasing the congestion window size in the slow start phase at the start of communication can be efficiently suppressed, thus enabling high-speed communication.

(Slow start operation part of Example 2)
Next, the slow start operation unit 119a according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a block diagram illustrating a configuration of the slow start operation unit 119a according to the second embodiment of the present invention. FIG. 9 is a flowchart showing the congestion window increasing process of the slow start operation unit 119a according to the second embodiment of the present invention. FIG. 10 is a flowchart showing the delay variation calculation processing of the slow start operation unit 119a according to the second embodiment of the present invention. FIG. 11 is a flowchart illustrating the congestion window upper limit calculation process of the slow start operation unit 119a according to the second embodiment of the present invention. In FIG. 8, the same reference numerals are assigned to the same components as those in the first embodiment.

  As illustrated in FIG. 8, the slow start operation unit 119a according to the second embodiment includes a congestion window increasing unit 1191 that performs a congestion window increasing process, a congestion window upper limit calculating unit 1192 that performs a congestion window upper limit calculating process, and congestion. Includes a delay variation estimation unit 1193 for estimating an irrelevant delay variation.

In the second embodiment, the delay variation estimation unit 1193 monitors the variation amount of the rtt for each received ACK packet, measures the maximum variation amount of the packet sequence of consecutive ACK packets, and calculates the maximum variation for each measurement period. A moving average value of the fluctuation amount is calculated as the average fluctuation amount of the rtt. Then, the congestion window upper limit calculation unit 1192 determines the upper limit value (cwnd _limit ) of the congestion window in consideration of the average fluctuation amount of the rtt. The congestion window increasing unit 1191 then adds a value obtained by adding the average fluctuation amount to the minimum rtt (rtt _base ) measured from the start of communication until the present time, and rtt within the measurement period in the immediately preceding measurement period. The slow start end determination is performed by comparison with the measured minimum rtt (rtt _min ), and when it is determined to end, the transition is made from the slow start phase to the congestion avoidance phase. Therefore, the second embodiment is different from the first embodiment in that the end determination of the slow start phase can be performed in consideration of the average fluctuation amount of the rtt.

  First, the congestion window increasing process by the congestion window increasing unit 1191 will be described with reference to FIG.

When the congestion window increasing unit 1191 receives the ACK packet and the rtt, sndtime, and rcvtime from the packet loss determining unit 114 (step S61), the congestion window increasing unit 1191 updates the rtt _{min according} to the equation (15) (steps S62 and S63). rtt _min is the minimum value of rtt determined in the immediately preceding one measurement period. Note that the value of rtt _min before the elapse of one measurement period from the start of communication can be set to the same value as the rtt _base which is the minimum rtt measured from the start of communication to the present time. Note that the initial value at the start of communication of the rtt _base can be a certain value such as the maximum possible value. In addition, the first measured rtt from the start of one measurement period is substituted for rtt _min regardless of the size.

if (rtt first measured in one measurement period) or (rtt _min > rtt) (15)
then rtt _min = rtt

When rtt _min is updated by equation (15) (step S63), the rtt _base is updated by equation (2) (steps S64 and S65). rtt _base is the minimum value of rtt measured during communication. At the start of communication, it can be initialized to a certain value such as the maximum possible value.

Next, the congestion window increasing unit 1191 notifies the delay variation estimation unit 1193 of the ACK packet and the rtt and sndtime (step S66), and receives jitter _ave from the delay variation estimation unit 1193 (step S67). Jitter _ave is a delay fluctuation amount unrelated to congestion, and a calculation method thereof will be described later with reference to FIG.

Next, the congestion window increasing unit 1191 notifies the congestion window upper limit calculating unit 1192 of the ACK packet and the rtt _base , jitter _ave , sndtime, rcvtime, cwnd _max (step S68). cwnd _max is a value used by the congestion window upper limit calculation unit 1192 to determine a transmission packet used to calculate the upper limit value (cwnd _limit ) of the congestion window size. The calculation method (updating method) of the cwnd _max value is the same as that of the first embodiment, and the calculation procedure of the upper limit value (cwnd _limit ) of the congestion window size will be described later.

Subsequently, when the congestion window increasing unit 1191 receives the cwnd _limit from the congestion window upper limit calculating unit 1192 (step S69), the congestion window increasing unit 1191 determines whether one measurement period has elapsed (step S70). When the one measurement period has elapsed (step S70: Yes), the congestion window increasing unit 1191 determines whether or not to end the slow start phase (step S72). This determination is made according to equation (16).

if rtt _min > rtt _base + jitter _ave (16)
then end the slow start phase,
else Shift to the end of the slow start phase by Equation (3).

The end of the slow start phase is determined by the expression (3) by comparing the current congestion window size cwnd with the upper limit value (cwnd _limit ) of the congestion window size (step S73), and the slow start phase is ended (step S72). : Yes, or step S73: Yes), the process shown by Formula (4) is performed similarly to Example 1 (step S75).

  On the other hand, when the slow start phase is continued (step S72: No, and step S73: No), the processing shown in Expression (5) is performed as in the first embodiment (step S74).

When the slow start phase is continued (step S72: No, and step S73: No), cwnd _max is also updated, and rtt _min is initialized with the minimum value of rtt determined in the immediately preceding one measurement period (step S74).

  If it is determined that one measurement period has not elapsed (step S70: No), the congestion window increasing unit 1191 performs the process shown in equation (5) (step S71).

  Next, the delay variation calculation processing by the delay variation estimation unit 1193 will be described with reference to FIG.

  When the delay variation estimation unit 1193 receives the ACK packet and the rtt and sndtime from the congestion window increase unit 1191 (step S81), the delay variation estimation unit 1193 continues to the recently received packet group (packet sequence of the ACK packet) according to the equation (17). It is determined whether or not it is a packet (step S82).

if sndtime−sndtime _last ≦ β (17)
then consecutive packets,
else Packets that are not consecutive.

sndtime _last is the transmission time of the transmission packet corresponding to the ACK packet received immediately before, and β is a constant. β can be an integral multiple of the minimum time that can be measured by the packet transmission device 11a or an integral multiple of the time required for the packet transmission device 11a to transmit one TCP packet having a length of 1 MSS.

When it is determined that the packets are continuous (step S82: Yes), the jitter (jitter) between the packets related to the ACK packet is calculated by the equation (18) (step S83). rtt _last is the rtt measured with the previously received ACK packet.

jitter = | rtt−rtt _last | (18)

After calculating jitter, the processing of equation (19) is performed to update jitter _max representing the maximum jitter during one measurement period (step S84).

if jitter _max <jitter (19)
then jitter _max = jitter

On the other hand, when it is determined that the packets are not continuous (step S82: No), or when the jitter _max representing the maximum jitter during one measurement period is not updated (step S84: No), the process proceeds to step S86.

Then, after determining the value of jitter _max , it is determined whether one measurement period has elapsed (step S86). If one measurement period has elapsed (step S86: Yes), it is assumed that the value of jitter _max is greater than zero. If it has been calculated (step S89: Yes), the average jitter (jitter _ave ) is updated by equation (20) (step S90), and the value of jitter _max is reset to 0 (step S91). When the jitter _max value is reset to 0 (step S91), and when the jitter _max value is 0 even when one measurement period has elapsed (step S89: No), the process proceeds to step S87. The initial value of jitter _ave is 0. Α is a weighting constant less than 1, and may be a predetermined value such as 0.5.

jitter _ave = (1-α) x jitter _ave + α x jitter _max (20)

Next, when it is determined that one measurement period has not elapsed when the current ACK packet is received (step S86: No), when the value of jitter _max is reset to 0 (step S91), or when one measurement period is Even when it is determined that the time has elapsed, if the value of jitter _max is 0 (step S89: No), rtt _last and sndtime _last are updated by equation (21) (step S87).

rtt _last = rtt (21)
sndtime _last = sndtime

After determining the value of jitter _ave , the delay variation estimation unit 1193 notifies the congestion window increase unit 1191 (step S88).

  Next, a congestion window upper limit calculation process performed by the congestion window upper limit calculation unit 1192 will be described with reference to FIG.

When the congestion window upper limit calculation unit 1192 receives the ACK packet and the rtt _base , jitter _ave , sndtime, rcvtime, and cwnd _max from the congestion window increase unit 1191 (step S101), the congestion window size upper limit value cwnd _limit is set as follows. Calculate with The cwnd _limit is an upper limit value when the congestion window size is increased during the slow start phase, and the reception rate is calculated from the ACK packet and calculated. The initial value of cwnd _limit can be a predetermined maximum value assumed in advance (the maximum value that can be taken). In the second embodiment, the processing of equation (6) is converted into equation (22), the processing of equation (7) is converted into equation (23), the processing of equation (8) is converted into equation (24), and equation (9). The process is the same as that of the first embodiment except that the process of (2) is changed to the expression (25).

When the ACK packet is received, the calculation operation of the congestion window size upper limit value cwnd _{limit first} compares the transmission rate obtained from cwnd _{max with} the transmission rate of the transmission packet corresponding to the ACK packet received this time (step S102).

When the transmission rate of the transmission packet corresponding to the ACK packet received this time is equal to or higher than the transmission rate obtained from cwnd _max (step S102: Yes), subsequently, the packet group ( That is, it is determined whether or not the packet is included in an ACK packet group regarded as corresponding to a series of transmission packets (step S103). As a result, whether or not an ACK packet received with delay variation due to congestion and jitter that may occur during the slow start phase in an environment where delay variation is likely to occur, such as a wireless network, is handled as a series of transmission packets. judge. For this determination, the following two determination methods are effective.

The determination method of the first example is performed according to Equation (22). Note that sndtime _last and cwnd _max are the same as those in the first embodiment.

if sndtime-sndtime _last ≤ (MSS / cwnd _max ) x (rtt _base + jitter _ave ) (22)
then included in the recently received packet group.
else Not included in recently received packets.

The determination method of the second example is performed by Expression (23). The sndtime _first is the same as that in the _first embodiment.

if sndtime−sndtime _first ≦
((rcvbyte + delivery confirmation byte count) / cwnd _max ) x (rtt _base + jitter _ave ) (23)
then included in the recently received packet group.
else Not included in recently received packets.

When the transmission rate of the transmission packet corresponding to the ACK packet received this time is not equal to or higher than the transmission rate obtained from cwnd _max (step S102: No), and the group of packets received recently (that is, a series of ACK packets received this time) ACK packet group that is regarded as corresponding to the transmission packet of No. (step S103: No), a congestion window that satisfies the reception rate according to equation (24) from the record of the recently received packet group The size cwnd _est is calculated (step S105).

cwnd _est = rcvbyte x (rtt _base + jitter _ave ) / (rcvtime _last -rcvtime _first ) (24)

Further, in order to prevent the measurement state required for calculation of the congestion window size from continuing for 1 rtt or more, in order to calculate the congestion window size periodically at less than 1 rtt, Expression (25) As shown in the above, when the continuous transmission period (sndtime-sndtime _first ) exceeds the predetermined threshold ((rtt _base + jitter _ave ) / 2 in this example) for the transmission packet corresponding to the ACK packet received this time Also, the congestion window size cwnd _est according to the equation (24) is calculated.

if sndtime-sndtime _first > (rtt _base + jitter _ave ) / 2 (25)
Then, calculation of the congestion window size by the equation (24).

When cwnd _est is calculated, the maximum value cwnd _limit-tmp of cwnd _{est in} one measurement period is updated by equation (10) (steps S106 and S107).

  Further, each variable is reset as shown in Expression (11) in order to determine step S44 regarding the ACK packet to be received next and to calculate the congestion window size (step S108).

The transmission rate of the transmission packet corresponding to the ACK packet received this time is equal to or higher than the transmission rate calculated from cwnd _max (step S102: Yes), and the ACK packet received this time is the group of packets received recently (ie, a series of transmissions). A group of ACK packets regarded as corresponding to a packet) (step S103: Yes), that is, it is regarded as a continuous packet sequence in the determination based on the transmission interval, and a predetermined number of transmission packets related to the continuous packet sequence If the transmission period does not exceed a predetermined threshold, the number of received bytes of the continuous packet sequence is updated by equation (12) (step S104).

Next, it is determined whether or not one measurement period has elapsed (step S109). When it is determined that one measurement period has elapsed (step S109: Yes), cwnd _limit-tmp is updated. It is determined whether or not (step S110).

When the cwnd _limit-tmp is updated (step S110: Yes), the cwnd _limit is updated by the equation (13) (step S111).

When the ACK packet received this time has not passed one measurement period (step S109: No), and when cwnd _limit-tmp is not updated (step S110: No), cwnd _limit remains the previous value. It is.

When the value of cwnd _limit is determined through step S110, sndtime _last and rcvtime _last are updated by equation (14) (step S112).

Finally, the congestion window upper limit calculation unit 1192 notifies the cwnd _limit to the congestion window increase unit 1191 (step S113). Therefore, in the second embodiment, the congestion window upper limit calculation unit 1192 also considers jitter that occurs regardless of congestion, and when the determinations of both step S102 and step S103 are satisfied, the received byte of the packet group received at the latest time The number of received bytes is determined by adding the number of bytes confirmed by the ACK packet received this time to the number (step S104), and if either one of the determinations of step S102 and step S103 is not satisfied, the number of received bytes calculates the congestion window size relative to the receiving rate of packets received (cwnd _limit-tmp) and updated for each measurement period during recently updated the congestion window size for each measurement period (cwnd _limit-tmp ) Is determined as the upper limit value (cwnd _limit ) of the congestion window size. Then, every time an ACK packet is received, the congestion window increasing unit 1191 increases the congestion window size (cwnd) by a predetermined width below the cwnd _limit determined when one measurement period has elapsed, and for each measurement period, one measurement period. The transition from the slow start phase to the congestion avoidance phase is determined by comparing the cwnd _limit determined when elapses with the expanded cwnd.

  As described above, the slow start operation unit 119a according to the second embodiment including the congestion window increasing unit 1191, the congestion window upper limit calculating unit 1192, and the delay variation estimating unit 1193 is configured and provided in the packet transmission device 11a, thereby causing congestion and Suppresses the occurrence of bursty packet loss in consideration of the jitter that occurs independently, thereby efficiently suppressing the transition to the congestion avoidance phase before expanding the congestion window size in the slow start phase at the start of communication. Therefore, high-speed communication is possible.

  The present invention has been described with reference to specific examples. However, the present invention is not limited to the above-described embodiments and examples, and various modifications can be made without departing from the technical concept thereof. For example, any apparatus may be used as long as it is a packet transmission apparatus that performs slow start control related to packet transmission using a delay amount based on delivery confirmation.

  According to the present invention, in packet communication for confirming delivery, it is possible to increase the communication efficiency in the slow start phase at the start of communication in an environment in which delay variation is likely to occur as in a wireless network. This is useful for applications that perform slow start control related to packet transmission.

DESCRIPTION OF SYMBOLS 10 Communication terminal 11 Packet transmission apparatus 11a which concerns on prior art Packet transmission apparatus of one Embodiment by this invention 12 Packet reception apparatus 20 Communication terminal 21 Packet reception apparatus 22 Packet transmission apparatus 111 Transmission time writing part 112 Packet transmission part 113 Delivery confirmation Response reception unit 114 Packet loss determination unit 115 Packet transmission control unit 116 Loss retransmission operation unit 117 Loss recovery operation unit 118 Congestion avoidance operation unit 119 Slow start operation unit 119a according to prior art 1191 Slow start operation unit 1191 according to the present invention Increase in congestion window Unit 1192 congestion window upper limit calculation unit 1193 delay variation estimation unit

Claims (6)

A packet transmission device that determines a congestion window size based on delivery confirmation and performs slow start control related to packet transmission,
A packet for a delivery confirmation response notified as a delivery confirmation of packet transmission is received, and a round-trip delay time based on the delivery confirmation of the packet transmission is calculated from a difference between the transmission time of the packet transmission and the reception time of the delivery confirmation response packet. A delivery confirmation response receiving means for calculating;
It comprises a slow start control means that operates to make a transition from the slow start phase to the congestion avoidance phase when determining congestion while increasing the congestion window size from the start of communication,
The slow start control means includes:
During operation in the slow start phase, the minimum round-trip delay time continuously measured for the round-trip delay time and the congestion window size updated based on a predetermined update formula each time the congestion window size is updated. Based on the maximum value and the transmission time and reception time of the recently received packet group with respect to the received delivery confirmation response packet, the upper limit value of the congestion window size for each predetermined measurement period regarding the packet delay amount A congestion window upper limit calculating means for determining
Each time the acknowledgment packet is received, the congestion window size is expanded by a predetermined width below the upper limit value of the congestion window size determined at the time of the immediately preceding one measurement period, and the congestion window is increased for each measurement period. The upper limit value of the size is compared with the expanded congestion window size, and when the expanded congestion window size is equal to or larger than the upper limit value of the congestion window size, the operation is performed so as to shift from the slow start phase to the congestion avoidance phase. Means for increasing congestion window;
A packet transmission apparatus comprising: The congestion window upper limit calculation means includes:
The first time for determining whether or not the transmission rate of the transmission packet corresponding to the delivery confirmation response packet is equal to or higher than the transmission rate obtained from the maximum value of the congestion window size each time the delivery confirmation response packet is received. A determination means;
A second determination means for determining whether or not the packet is included in the recently received packet group each time the delivery confirmation response packet is received;
When the determinations of both the first determination unit and the second determination unit are satisfied, the number of received bytes is obtained by adding the number of bytes confirmed by the delivery confirmation response packet to the number of received bytes of the recently received packet group. If the determination of either one of the first determination means and the second determination means is not satisfied, the congestion window size is calculated based on the reception rate of the packet group received at the latest time obtained from the number of received bytes. Update for each measurement period, and a congestion window upper limit determination means for determining the updated congestion window size as an upper limit value of the congestion window size;
The packet transmission device according to claim 1, comprising:   The maximum value of the congestion window size is a value that is twice the updated congestion window size or a value that is twice the updated congestion window size as the predetermined update formula, and the elapse of one measurement period immediately before. The packet transmission device according to claim 1, wherein the packet transmission device is updated with a smaller value of the upper limit value of the congestion window size determined at times. The slow start control means monitors the fluctuation amount of the round-trip delay time for each received acknowledgment packet and measures the maximum fluctuation amount of the packet sequence of successive round-trip delay time packets. A delay fluctuation amount estimating means for calculating a moving average value of the maximum fluctuation amount as an average fluctuation amount of the round trip delay time;
The congestion window upper limit calculating means includes means for determining an upper limit value of the congestion window in consideration of the average fluctuation amount.
The congestion window increasing means includes a value obtained by adding the average fluctuation amount to a minimum round-trip delay time continuously measured for the round-trip delay time, and a minimum in a measurement period measured as a minimum value in the immediately preceding measurement period. Compared with the round trip delay time, when the minimum round trip delay time within the measurement period exceeds the value obtained by adding the average fluctuation amount to the minimum round trip delay time continuously measured for the round trip delay time, the slow start The packet transmission device according to claim 1, further comprising means for operating to make a transition from the phase to the congestion avoidance phase.   A communication terminal comprising the packet transmission device according to any one of claims 1 to 4. A slow start control method for determining a congestion window size based on delivery confirmation and performing a slow start control on packet transmission,
During the operation in the slow start phase, the minimum round-trip delay time continuously measured for the round-trip delay time based on the delivery confirmation of the packet transmission from the difference between the transmission time of the packet transmission and the reception time of the delivery confirmation response packet; The maximum value of the congestion window size that is updated based on a predetermined update formula each time the congestion window size is updated, the transmission time of the packet group received recently with respect to the received acknowledgment packet, and Determining an upper limit value of the congestion window size for each measurement period related to a predetermined packet delay based on the reception time;
Each time the acknowledgment packet is received, the congestion window size is expanded by a predetermined width below the upper limit value of the congestion window size determined at the time of the immediately preceding one measurement period, and the congestion window is increased for each measurement period. The upper limit value of the size is compared with the expanded congestion window size, and when the expanded congestion window size is equal to or larger than the upper limit value of the congestion window size, the operation is performed so as to shift from the slow start phase to the congestion avoidance phase. And steps to
A slow start control method comprising: