JP4249049B2 - COMMUNICATION SYSTEM, COMMUNICATION DEVICE, PROGRAM, AND COMMUNICATION METHOD - Google Patents

Description

  The present invention relates to a communication system, a communication device, a program, and a communication method.

  As a congestion control method in TCP (Transmission Control Protocol), there are a reactive congestion control method such as TCP Reno and a proactive congestion control method such as TCP Vegas. In TCP Reno, the transmission terminal gradually increases the transmission rate of data packets until packet loss due to network congestion occurs, and greatly reduces the transmission rate when a packet loss is detected. For this reason, TCP-Reno has a drawback in that congestion eventually occurs and the network cannot be used effectively.

  In TCP Vegas, the transmission terminal uses an increase in round trip time (Round Trip Time, hereinafter referred to as “RTT”) between the transmission terminal and the reception terminal for congestion detection. Specifically, when the network starts to congest, the queuing delay due to the increase in the amount of stored packets that are stored in the routers on the network and enter the queue increases, and the RTT starts to increase. Therefore, the transmission terminal suppresses the transmission rate of the data packet when the RTT starts to increase. Therefore, in TCP Vegas, congestion can be prevented and the network can be used effectively (see, for example, Non-Patent Document 1 and Non-Patent Document 2).

  In TCP Vegas, after shifting to the Congestion Avoidance Phase, the transmission terminal uses the following Expressions (1) and (2) for each RTT, and the Congestion Window Size (hereinafter “cwnd”) is used. And the congestion control is performed.

When Queued_packet <α,
cwnd_next = cwnd + 1 data packet (1)
When Queued_packet> β,
cwnd_next = cwnd-1 data packet (2 formulas)

In Equations (1) and (2), “Queued_packet” is the amount of accumulated packets, “cwnd” is the current cwnd, and “cwnd_next” is the cwnd when the next data packet is transmitted. α and β are constants. The default value of α is 1 data packet, and the default value of β is 3 data packets.
Charalampos (Basis) Samios and Mark K. Vernon, “Modeling the Throughput of TCP Vegas”, Proceedings of the 2003 ACM SIGMETRICS international conference on Measurement and modeling of computer systems, volume 31 Issue 1, June 2003 Takeshi Hasegawa, Kenji Kurata, Masayuki Murata, “Improvement method of TCP Vegas considering fairness between versions”, IEICE Technical Report (SSE2000-31), May 2000

  However, in the congestion control method in the conventional TCP Vegas, cwnd can be increased or decreased by one data packet every RTT, and the change amount of cwnd is fixed. That is, the change speed of cwnd is only one data packet per RTT, and is fixed. For this reason, the conventional congestion control method cannot sufficiently follow a rapid change in the traffic state of the network.

  Specifically, as shown in FIG. 7 (a), when other terminal devices are also communicating during the communication of the transmission terminal 210, the transmission terminal traffic 201a by the transmission terminal 210 and other terminals are placed on the network. Other traffic 201b by the device exists. In the transmission buffer 231 of the router 230 on the network, data packets 201 from the transmission terminal 210 and other terminal devices are accumulated and queued.

  In FIG. 7A, it is assumed that there is little other traffic 201b, or other terminal devices are not communicating and there is no other traffic 201b. At this time, as shown in FIG. 7B, when the amount of data packets transmitted by other terminal devices increases or when other terminal devices start communication, the other traffic 201b increases and the network is congested. Begin to. Then, a large amount of data packets 201 starts to be accumulated in the transmission buffer 231 of the router 230. In this case, according to the conventional congestion control method, cwnd can be reduced by only one data packet every 1 RTT, and the transmission rate decreases slowly. Therefore, the transmission rate of the data packet of the transmission terminal 210 or another terminal device is slow. Cannot be quickly suppressed. As a result, the data packet 201 overflows from the transmission buffer 231 and packet loss occurs.

  On the other hand, in FIG. 7A, it is assumed that some other traffic 201b exists. At this time, as shown in FIG. 7C, when the other terminal device ends the communication, the other traffic 201b disappears and only the transmitting terminal traffic 201a exists. Then, data packets are not accumulated in the transmission buffer 231 of the router 230, and a vacant network communication band is generated. In this case, in the conventional congestion control method, cwnd can be increased only by one data packet for each RTT, and the transmission speed is not improved rapidly. Therefore, the data packet transmission speed of the transmission terminal 210 is quickly increased. I can't. As a result, the network communication band cannot be used effectively.

  In view of the above, an object of the present invention is to enable transmission of a data packet following a change in the traffic situation of a network.

  A communication system and a communication device according to the present invention include an acquisition unit that acquires a traffic state of a network, a window size control unit that determines a window size change amount based on the traffic state, and a window size change amount. And transmission control means for controlling transmission of the data packet.

  According to such a communication system and communication apparatus, it is possible to acquire the traffic situation and dynamically change the window size change amount according to the acquired traffic situation. And a communication system and a communication apparatus can transmit a data packet using the window size changed dynamically based on the change amount of the window size changed dynamically. Therefore, the communication system and the communication device can transmit data packets following changes in the traffic situation of the network.

  Further, it is preferable that the acquisition unit calculates the amount of stored data packets stored in a router on the network as a traffic situation, and the window size control unit calculates the amount of change based on the amount of stored packets. According to this, the communication system and the communication apparatus can easily determine an appropriate change amount of the window size by calculating the change amount using the accumulated packet amount. Therefore, the communication system and the communication device can transmit the data packet more appropriately and easily following the change in the traffic situation of the network.

  The program according to the present invention includes an acquisition unit for acquiring a network traffic status from a computer, a window size control unit for determining a window size change amount based on the traffic status, and a data based on the window size change amount. A program for causing a packet to function as a transmission control unit that controls transmission of a packet. According to such a program, the communication system and the communication device can be realized. The communication method according to the present invention acquires a traffic state of a network, determines a change amount of a window size based on the traffic state, and controls transmission of a data packet based on the change amount of the window size. And

  As described above, according to the present invention, it is possible to transmit a data packet following a change in the network traffic situation.

  As illustrated in FIG. 1, the communication system 100 includes a transmission terminal 10, a reception terminal 20, a plurality of routers 30 a and 30 b, and a network 40. In the communication system 100, TCP Vegas is used as a congestion control method. The transmission terminal 10 and the reception terminal 20 are communication devices connected to the network 40. The transmission terminal 10 transmits the data packet 1 to the reception terminal 20 via the network 40. When receiving the data packet 1, the receiving terminal 20 transmits an acknowledgment (Acknowledge, hereinafter referred to as “Ack”) 2 to the transmitting terminal 10 via the network 40.

  The routers 30 a and 30 b are provided on the network 40 between the transmission terminal 10 and the reception terminal 20. The router 30 a transfers the data packet 1 from the transmission terminal 10 to the reception terminal 20. The router 30 a includes a transmission buffer 31. The router 30a receives the data packet 1 from the transmission terminal 10, accumulates it in the transmission buffer 31, and puts it in a queue. The router 30 a extracts the data packet 1 from the transmission buffer 31 and transfers it to the receiving terminal 20. Similarly to the router 30a, the router 30b includes a transmission buffer. The router 30b receives Ack2 from the receiving terminal 20 and transfers it to the transmitting terminal 10.

  Next, the transmission terminal 10 will be described in detail. The transmission terminal 10 includes a transmission buffer 11, a transmission control unit 12, a communication interface 13, a transmission record table 14, a clock unit 15, a packet amount calculation unit 16, and a window size control unit 17.

  The communication interface 13 acquires a data packet from the transmission control unit 12. The communication interface 13 transmits a data packet to the receiving terminal 20 in accordance with an instruction from the transmission control unit 12. The communication interface 13 receives Ack from the receiving terminal 20. The communication interface 13 inputs the received Ack to the transmission control unit 12 and the packet amount calculation unit 16. The transmission buffer 11 holds a data packet transmitted from the transmission terminal 10. The transmission record table 14 stores the transmission status of data packets by the transmission terminal 10. The transmission record table 14 stores the sequence number of the data packet transmitted by the transmission terminal 10 and the transmission time at which the data packet is transmitted in association with each other as the transmission status.

  The packet amount calculation unit 16 is an acquisition unit that acquires the traffic status of the network 40. The packet amount calculation unit 16 calculates the stored packet amount of the data packet stored in the router 30a on the network 40 as the traffic state, and acquires the traffic state. The packet amount calculation unit 16 is on the data packet transfer path from the transmission terminal 10 to the reception terminal 20 among the routers on the network 40, accumulates the data packets in the transmission buffer 31, and is a bottleneck for data packet transfer. The accumulated packet amount of the router 30a is calculated. The packet amount calculation unit 16 may calculate, as the accumulated packet amount, the packet amount that the transmission terminal 10 accumulates in the bottleneck router 30a, excluding data packets transmitted by terminal devices other than the transmission terminal 10. .

  The packet amount calculation unit 16 acquires Ack from the communication interface 13. When acquiring Ack, the packet amount calculation unit 16 refers to the clock unit 15 and acquires the reception time of Ack. The clock unit 15 provides the current time. Ack includes the sequence number of the data packet received by the receiving terminal 20. The packet amount calculation unit 16 searches the transmission record table 14 based on the sequence number included in Ack, and acquires the transmission time of the data packet at which the transmission terminal 10 received Ack. The packet amount calculation unit 16 deletes the transmission status of the data packet that received Ack from the transmission record table 14. The packet amount calculation unit 16 calculates the accumulated packet amount using the Ack reception time and the data packet transmission time. The packet amount calculation unit 16 inputs the accumulated packet amount obtained by the calculation to the window size control unit 17.

  The window size control unit 17 is a window size control unit that determines a change amount of the window size based on the traffic situation. The window size control unit 17 calculates the change amount using the accumulated packet amount as the traffic state. The window size control unit 17 acquires the accumulated packet amount as the traffic amount from the packet amount calculation unit 16.

  A control cycle for controlling the window size in the communication system 100 is represented as “Round”. A period from immediately after the window size is controlled until the next window size is controlled is a control period (Round). The window size control unit 17 determines a window size change amount for each control period (Round). Specifically, the window size control unit 17 determines the amount of change in the window size every 1 RTT. Therefore, the length of the control cycle (Round) is 1 RTT. The window size control unit 17 determines the change amount of cwnd as the window size.

  The window size control unit 17 determines the window size using the determined window size change amount. The window size control unit 17 may determine any control cycle (Roundnd) as long as it is a variation amount and window size of a control cycle (Round) after the current control cycle (Round). Therefore, the window size control unit 17 may determine a variation amount and window size of the next control cycle (Round), and may further determine a change amount and window size of the subsequent control cycle (Round). The window size control unit 17 inputs the determined window size to the transmission control unit 12. Further, the window size control unit 17 may input the window size change amount to the transmission control unit 12 without determining the window size.

  The transmission control unit 12 is a transmission control unit that controls the transmission of the data packet based on the window size change amount. The transmission control unit 12 acquires the window size or the window size change amount from the window size control unit 17. When acquiring the window size change amount, the transmission control unit 12 first determines the window size using the change amount.

  The transmission control unit 12 acquires the data packet having the window size determined or acquired from the transmission buffer 11. Then, the transmission control unit 12 inputs the acquired data packet to the communication interface 13 and designates a control period (Round) to transmit a window size data packet.

  The transmission control unit 12 records the transmission status of the data packet in the transmission record table 14. The transmission control unit 12 refers to the clock unit 15 when instructing the communication interface 13 to transmit a data packet, and acquires the transmission time of the data packet. The transmission control unit 12 records the sequence number of the data packet in association with the transmission time in the transmission record table 14. Further, the transmission control unit 12 acquires Ack from the communication interface 13. The transmission control unit 12 instructs the communication interface 13 to retransmit a data packet that cannot receive an Ack after a certain period of time.

  Next, the change amount of the window size and the method for determining the window size will be described in detail. Hereinafter, the order of the control cycle (Round) is represented as “#i”, and the “#i” -th control cycle is represented as “Round (#i)”. The first control cycle (Round) after the start of communication is “Round (# 1)”. In Round (#i), cwnd is expressed as “cwnd (#i)”, and the change amount of cwnd is expressed as “V (#i)”. Further, the sequence number of the data packet is represented by “Si”, the data packet having the sequence number “Si” is represented by “data packet (Si)”, and the Ack for the data packet having the sequence number “Si” is represented by “Ack (Si)”. . Furthermore, RTT between the transmission terminal 10 and the reception terminal 20 when the network 40 is not congested is defined as “RTTbase”. An example of data packet transmission / reception between the transmission terminal 10 and the reception terminal 20 after transition to the congestion avoidance phase in TCP Vegas will be described with reference to FIGS.

  First, as shown in FIG. 3, in Round (#i), the transmitting terminal 10 sends a data packet of cwnd (#i), a data packet (S4) 1a, a data packet (S5) 1b, a data packet (S6) 1c, The data packet (S7) 1d is transmitted to the receiving terminal 20. Note that the data packets (S1) to (S3) in Round (#i) have already been transmitted. At this time, the transmission control unit 12 of the transmission terminal 12 records the transmission times of all transmitted data packets in the transmission record table 14. The transmitting terminal 10 receives from the receiving terminal 20 Ack (S1) 2a, Ack (S2) 2b, and Ack (S3) 2c for the data packet already transmitted in Round (#i).

  When Round (# i + 1) is started, the receiving terminal 20 transmits Ack (S4) 2d and Ack (S5) 2e for the data packet transmitted in Round (#i) to the transmitting terminal 10, as shown in FIG. . The packet amount calculation unit 16 of the transmission terminal 10 uses the sequence number of Ack (S4) and Ack (S5) received by the transmission terminal 10 from the transmission record table 14 to transmit the data packet (S4) at the transmission time t4. The transmission time t5 of the packet (S5) is acquired.

  The packet amount calculation unit 16 calculates the RTTs of all data packets transmitted in Round (#i) using the Ack reception time and the data packet transmission time. That is, the packet amount calculation unit 16 calculates the time from when the transmitting terminal 10 transmits a data packet until it receives the Ack as the RTT between the transmitting terminal 10 and the receiving terminal 20. For example, the packet amount calculation unit 16 calculates the difference between the transmission time t4 of the data packet (S4) and the reception time of Ack (S4), and calculates the RTT of the data packet. In this way, the packet amount calculator 16 measures the RTT by always calculating it. Then, the packet amount calculation unit 16 uses the smallest RTT among the measured RTTs as the RTT base.

  Immediately after the start of Round (# i + 1), the data packet (S6) 1c and the data packet (S7) 1d transmitted by the transmitting terminal 10 in Round (#i) are as shown on the arrow B side from the dotted line A in FIG. The terminal 20 has not yet been reached. Further, in Round (# i + 1), the transmitting terminal 10 transmits a data packet of cwnd (# i + 1) to the receiving terminal 20. Therefore, as shown on the arrow C side from the dotted line A in FIG. 4, transmission of the data packet (S8) 1e and data packet (S9) 1f in Round (# i + 1) is started. Note that the window size control unit 17 of the transmission terminal 10 uses cwnd (# 1) as it is as cwnd (# 2) in Round (# 2) immediately after the transition to the congestion avoidance phase.

  As shown in FIG. 5, the transmitting terminal 10 transmits a data packet (S11) 1g, a data packet (S12) 1h, a data packet (S13) 1i, and a data packet (S14) 1j to the receiving terminal 20, and a Round (# When all the data packets in i + 1) are transmitted and Round (# i + 1) ends, the transmitting terminal 10 finishes receiving Ack of all the data packets transmitted in Round (#i) from the receiving terminal 20. Then, the receiving terminal 20 starts to transmit Ack (S8) 2f, Ack (S9) 2g, and Ack (S10) 2h to the transmitting terminal 10 for the data packet transmitted in Round (# i + 1).

The packet amount calculation unit 16 of the transmission terminal 10 calculates an average value of RTTs of all data packets transmitted in Round (#i). Then, the packet amount calculation unit 16 calculates the accumulated packet amount using the following equation (3). The accumulated packet amount in “Round (#i)” is represented as “Queued_packet (#i)”, and the average RTT value of data packets transmitted in Round (#i) is represented as “RTT_ave (#i)”.
Queued_packet (#i) = (cwnd (#i) / RTT_ave (#i)) × (RTT_ave (#i) −RTTbase) (3)

Next, the window size control unit 17 calculates V (# i + 2) in Round (# i + 2) using the obtained accumulated packet amount and the following expressions (4) and (5).
When Queued_packet (#i) <α or Queued_packet (#i)> β,
V (# i + 2) = ε (δ−Queued_packet (#i)) (Formula 4)
When α ≦ Queued_packet (#i) ≦ β,
V (# i + 2) = 0 Formula (5)

Then, the window size control unit 17 calculates cwnd (# i + 2) in Round (# i + 2) using the obtained V (# i + 2) and the following equation (6).
cwnd (# i + 2) = cwnd (#i) + V (# i + 2) (6)

Alternatively, the window size control unit 17 directly calculates cwnd (# i + 2) based on the amount of change in the window size using the obtained accumulated packet amount and the following equations (7) and (8). Also good.
When Queued_packet (#i) <α or Queued_packet (#i)> β,
cwnd (# i + 2) = cwnd (#i) + ε (δ−Queued_packet (#i)) (Expression 7)
When α ≦ Queued_packet (#i) ≦ β,
cwnd (# i + 2) = cwnd (#i) (8) Formula

  In the equations (4) to (8), α, β, and ε are constants. δ = (α + β) / 2. The constants α and β are constants for determining whether the window size can be changed. When the amount of stored packets is small and there is a vacancy in the communication band of the network, it is necessary to increase the data packet transmission speed quickly and effectively use the communication band of the network. Therefore, as the constant α, a lower limit value of the accumulated packet amount for determining whether or not the window size can be changed is set so that the window size can be changed appropriately when the accumulated packet amount is small. In addition, when there is a large amount of accumulated packets and congestion occurs, it is necessary to quickly suppress the data packet transmission rate and suppress congestion. Therefore, an upper limit value of the accumulated packet amount for determining whether or not the window size can be changed is set as the constant β so that the window size can be appropriately changed when the accumulated packet amount is large.

  Furthermore, if the fluctuation of the queuing delay becomes large, the window size and the amount of stored packets may not converge to a constant value and vibration may occur. Therefore, it is preferable to determine the constants α and β so that the transmission rate of the data packet can be appropriately suppressed and improved by changing the window size and vibration is not generated. Specifically, the constants α and β are set so that the interval between the constants α and β is increased to such an extent that no vibration is generated, and the stable region where the window size is not changed is increased.

  The constant ε is preferably set in the range of 0 <ε <2. For example, it is assumed that N transmitting terminals transmit data packets via a router 30a that is a bottleneck. The router 30a pays attention to the transmitting terminal to which the data packet is transferred nth, cwnd in Round (#i) of the transmitting terminal is “cwnd_n (#i)”, and RTT between the transmitting terminal and the receiving terminal is “ By substituting RTT_n ”and RTTbase as“ RTTbase_n ”into equation (7), the following equation (9) is obtained.

cwnd_n (# i + 2)
= Cwnd_n (#i) + ε (δ−Queued_packet (#i))
= Cwnd_n (#i) + ε {δ− [cwnd_n (#i) × D / (RTTbase_n + D)]}
= {1- [εD / (RTTbase_n + D)]} × cwnd_n (#i) + εδ (9)

From equation (9), it is necessary to satisfy equation (10) so that cwnd_n (# i + 2) does not diverge.
| {1− [εD / (RTTbase_n + D)]} | <1
0 <{εD / (RTTbase_n + D)} <2 (10)

  “D” is a queuing delay time of the data packet by the router 30a which is a bottleneck. The queuing delay time D varies depending on the situation of the network 40 or the like. Therefore, by setting the constant ε within the range of 0 <ε <2, the expression (10) can be satisfied regardless of the value of the queuing delay time D.

For example, when the constants α, β, and ε are set to α = 1, β = 3, and ε = 1, and the window size is determined using the equations (7) and (8), the following (7 ′ ) And (8 ′).
When Queued_packet (#i) <1 or Queued_packet (#i)> 3,
cwnd (# i + 2) = cwnd (#i) + 1 × (2-Queued_packet (#i)) (7 ′) When Expression 1 ≦ Queued_packet (#i) ≦ 3,
cwnd (# i + 2) = cwnd (#i) (8 ′) Formula

  By determining the window size variation amount and the window size using the equations (4) to (6) or the equations (7) and (8), the accumulated packet amount Queued_packet and the constant α, The larger the deviation from β, the larger the window size change amount for each control cycle. Therefore, if the amount of stored packets is small, the network communication bandwidth is vacant, and its usage efficiency is low, or if the amount of stored packets is large and congestion occurs, the window size change amount for each control cycle is increased. it can. Furthermore, if the amount of change in the window size is too large, the window size and the amount of stored packets do not converge to a constant value, causing vibration and the network 40 becoming unstable. However, when the window size variation and the window size are determined using the equations (4) to (6), or the equations (7) and (8), the network 40 is configured as shown below. The window size can be controlled within a stable range. When the equation (9) is modified, the equation (11) is obtained.

cwnd_n (# i + 2)-{δ (RTTbase_n + D) / D}
= {1- [εD / (RTTbase_n + D)]} × {cwnd_n (#i)-[δ (RTTbase_n + D) / D]} (11) where a = 1− {εD / (RTTbase_n + D)}, b = When δ (RTTbase_n + D) / D is set, equation (12) is obtained.
cwnd_n (# i + 2) −b = a (cwnd_n (#i) −b) (12)

When the queuing delay time D does not vary greatly, a and b do not vary greatly. Further, from the formula (10), | a | <1. Therefore, as time passes, cwnd_n (# i + 2) approaches b. Therefore, the following expression (13) is obtained.
cwnd_n (# i + 2) → δ (RTTbase_n + D) / D
D × cwnd_n (# i + 2) / (RTTbase + D) = Queued_packet (#i) → δ (13)

  Thus, the accumulated packet amount Queued_packet (#i) approaches δ. Therefore, the transmission terminal 10 determines the amount of variation in the window size and the window size using the equations (4) to (6) or the equations (7) and (8), so that the accumulated packet amount is constant. It is possible to prevent divergence without converging on the value. Therefore, the transmission terminal 10 can control the window size within a stable range in which the network 40 does not diverge the accumulated packet amount.

Further, by calculating the accumulated packet amount using the expression (3), as shown below, the packet amount calculating unit 16 causes the transmitting terminal 10 to accumulate the accumulated packet amount in the bottleneck router 30a. The amount of packets can be calculated. When the queuing delay time D occurs, the RTT increases as shown in the equation (14).
RTT = RTTbase + D (14) Thus, the queuing delay time D can be measured from the variation of the RTT. Substitute equation (14) into equation (3). At this time, the transmission rate of the data packet of the transmission terminal 10 is “T”. T = cwnd (#i) / RTT_ave (#i).

Queued_packet (#i)
= (Cwnd (#i) / RTT_ave (#i)) × (RTT_ave (#i) −RTTbase)
= {(Cwnd (#i) / RTTbase) − (cwnd (#i) / (RTT_ave (#i))} × RTTbase
= {(Cwnd (#i) / RTTbase)-[cwnd (#i) / (RTTbase + D)]} × RTTbase
= (Cwnd (#i) / RTT_ave (#i)) × D
= T × D (15) Formula

  The queuing delay time D is determined by the amount of all traffic including data packets transmitted by terminal devices other than the transmitting terminal 10. However, the transmission terminal 10 that has established the TCP connection always transmits the data packet at the transmission speed T. For this reason, it is considered that all data packets from the transmission terminal 10 are accumulated in the transmission buffer 31 during the queuing delay time D, transmitted after entering the queue. Therefore, in the end, Queued_packet (#i) indicated by T × D corresponds to the accumulated packet amount accumulated in the transmission buffer 31 by the transmission terminal 10.

  When the transmission control unit 12 becomes Round (# i + 2), the transmission control unit 12 transmits the data packet to the receiving terminal 20 according to cwnd (# i + 2) determined by the window size control unit 17. Thereafter, similarly, the packet amount calculation unit 16 and the window size control unit 17 calculate the accumulated packet amount Queued_packet (# i + 1) and determine cwnd (# i + 3). Thereafter, the packet amount calculation unit 16 and the window size control unit 17 calculate the accumulated packet amount Queued_packet (# i + 2) and determine cwnd (# i + 4), so that the accumulated packet amount in the previous cycle control is calculated. Used to determine the window size change amount and window size.

  Note that the window size control unit 17 preferably controls cwnd so that the amount of packets stored in the transmission buffer 31 of the router 30a serving as a bottleneck can be maintained at 1 to 3 packets. In addition, when the transmission control unit 12 obtains the window size change amount from the window size control unit 17, the transmission control unit 12 can determine the window size using Equation (6).

  Such a transmission terminal 10 includes, in the computer, an acquisition unit that acquires a network traffic state, a window size control unit that determines a window size change amount based on the traffic state, and a window size change amount. This can be realized by executing a program for functioning as transmission control means for controlling transmission of data packets. Such a program is stored in a recording medium, and the computer reads the program from the recording medium and executes it.

  Next, a communication method using the communication system 100 will be described. As shown in FIG. 6, in Round (#i), the transmission terminal 10 transmits a data packet using cwnd (#i) (S101). At this time, the transmission terminal 10 records the transmission time of each data packet (S102). When it becomes Round (# i + 1), the transmitting terminal 10 transmits a data packet by cwnd (# i + 1) (S103). Furthermore, the transmission terminal 10 receives the Ack of the data packet transmitted in Round (#i). Then, the transmission terminal 10 calculates the RTT of each data packet transmitted in Round (#i) using the transmission time recorded in step (S102) (S104).

  When the transmitting terminal 10 receives all the Ack of the data packet transmitted in Round (#i), it calculates the average value of RTT, RTT_ave (#i) in Round (#i) (S105). Then, the transmitting terminal 10 calculates the accumulated packet amount Queued_packet (#i) in Round (#i) using RTT_ave (#i) (S106). Further, the transmission terminal 10 calculates cwnd (# i + 2) in Round (# i + 2) using the accumulated packet amount Queued_packet (#i), and determines the window size based on the window size change amount (S107). When the transmission terminal 10 becomes Round (# i + 2), the transmission terminal 10 transmits a data packet using cwnd (# i + 2) (S108).

  According to the communication system 100, the transmission terminal 10, and the program and the communication method for realizing the transmission terminal 10, the traffic situation of the network 40 is acquired, and the window size change amount is dynamically changed according to the acquired traffic situation. Can change. And the communication system 100 and the transmission terminal 10 can transmit a data packet using the window size dynamically changed based on the change amount of the dynamically changed window size. Moreover, the communication system 100 and the transmission terminal 10 can easily determine an appropriate window size change amount by calculating the change amount using the accumulated packet amount. Therefore, the communication system 100 and the communication apparatus 10 can appropriately follow the change in the traffic status of the network 40 and transmit the data packet.

  More specifically, the communication system 100 and the communication device 10 can dynamically change the increase / decrease amount of cwnd for each control period (Round) having a length of 1 RTT according to the traffic situation. Therefore, the communication system 100 and the communication apparatus 10 can improve the followability with respect to the change of a traffic condition. Therefore, the communication system 100 and the communication device 10 can quickly relieve the congestion when congestion occurs, and can effectively use the free communication band when the network communication band becomes empty.

  In addition, this invention is not limited to the said embodiment, A various change is possible. For example, a control device that controls the window size may be provided in the communication system as the communication device. Then, the control device may control the transmission of the data packet by acquiring the traffic status of the network 40, determining the change amount of the window size and the window size based thereon, and notifying each transmitting terminal. For example, the packet amount calculation unit 16, the window size control unit 17, and the transmission control unit 12 may be provided in different communication devices.

It is a figure which shows the structure of the communication system which concerns on the 1st Embodiment of this invention. It is a block diagram which shows the structure of the transmission terminal which concerns on the 1st Embodiment of this invention. It is a figure which shows the condition of the communication system in Round (#i) which concerns on the 1st Embodiment of this invention. It is a figure which shows the condition of the communication system at the time of Round (# i + 1) start which concerns on the 1st Embodiment of this invention. It is a figure which shows the condition of the communication system at the time of Round (# i + 1) completion | finish which concerns on the 1st Embodiment of this invention. It is a flowchart which shows the procedure of the communication method which concerns on the 1st Embodiment of this invention. It is a figure which shows the conventional congestion control method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Communication system 10,210 Transmission terminal 11 Transmission buffer 12 Transmission control part 13 Communication interface 14 Transmission recording table 15 Clock part 16 Packet amount calculation part 17 Window size control part 20 Receiving terminal 30a, 30b, 230 Router 31 and 231 Transmission buffer 40 network

Claims (7)

A communication system in which a transmission terminal, a router, and a reception terminal are connected to each other via a network, and a data packet transmitted from the transmission terminal in a predetermined transmission unit is transferred to the reception terminal by the router. And
Traffic status calculation means for calculating the amount of data packets stored in the router;
Window size control means for determining a window size that is the transmission unit of data packets to be transmitted to the network based on the accumulated packet amount calculated by the traffic status calculation means;
Transmission control means for controlling transmission of data packets based on the window size determined by the window size control means,
The traffic condition calculation means includes:
Each time a response signal indicating that the data packet transmitted to the network is received by the receiving terminal is received, a reception time of the response signal, a transmission time of a data packet corresponding to the response signal, and From the above, it has an accumulated packet amount calculation means for calculating a round trip time of the data packet,
While the data packet of the second transmission unit following the one transmission unit is being transmitted by the transmission control means, the response signal for the data packet transmitted in the one transmission unit is received from the network,
From the received response signal, the accumulated amount of data packets included in the one transmission unit accumulated in the router is expressed as an average value of actually measured round trip times with respect to the round trip time of the data packets when there is no congestion. Calculate as the product of the ratio value and the current window size,
The window size control means includes:
A change amount of the window size is determined based on a difference between a predetermined threshold value and the accumulated packet amount calculated by the traffic condition calculation means, and then the data is determined based on the current window size and the change amount. Determine the window size when sending packets,
The transmission control means includes
A communication system, wherein data packets of three transmission units following the second transmission unit are transmitted with the window size determined by the window size control means.   The storage unit according to claim 1, further comprising: a storage unit that associates and stores sequence numbers of all data packets transmitted from the transmission terminal toward the network and transmission times of all the data packets. Communications system.   The accumulated packet amount calculating means calculates a round trip time in a case where there is no congestion in the one transmission unit as a minimum round trip time among round trip times calculated for each data packet transmitted in one transmission unit. The communication system according to claim 1, wherein time is set.   The accumulated packet amount calculation means sets an average value of round trip times calculated for all data packets transmitted in the one transmission unit as an average value of the actually measured round trip times. Item 12. The communication system according to Item 1. A communication device that is connected to each other via a network, transmits a data packet in a predetermined transmission unit to another terminal via a router connected to the network, or receives the data packet from the network,
Traffic status calculation means for calculating the amount of data packets stored in the router;
Window size control means for determining a window size that is the transmission unit of data packets to be transmitted to the network based on the accumulated packet amount calculated by the traffic status calculation means;
Transmission control means for controlling transmission of data packets based on the window size determined by the window size control means,
The traffic condition calculation means includes:
Each time a response signal indicating that the data packet transmitted to the network is received by the receiving terminal is received, a reception time of the response signal, a transmission time of a data packet corresponding to the response signal, and From the above, it has an accumulated packet amount calculation means for calculating a round trip time of the data packet,
While the data packet of the second transmission unit following the one transmission unit is being transmitted by the transmission control means, the response signal for the data packet transmitted in the one transmission unit is received from the network,
From the received response signal, the accumulated amount of data packets included in the one transmission unit accumulated in the router is expressed as an average value of actually measured round trip times with respect to the round trip time of the data packets when there is no congestion. Calculate as the product of the ratio value and the current window size,
The window size control means includes:
A change amount of the window size is determined based on a difference between a predetermined threshold value and the accumulated packet amount calculated by the traffic condition calculation means, and then the data is determined based on the current window size and the change amount. Determine the window size when sending packets,
The transmission control means includes
The communication apparatus transmits a data packet of three transmission units following the second transmission unit with the window size determined by the window size control means. A program that causes a computer to function as a communication device that transmits a data packet in a predetermined transmission unit to another terminal via a router connected to the network or receives the data packet from the network,
Traffic status calculation means for calculating the amount of data packets stored in the router;
Window size control means for determining a window size that is the transmission unit of data packets to be transmitted to the network based on the accumulated packet amount calculated by the traffic status calculation means;
Transmission control means for controlling transmission of data packets based on the window size determined by the window size control means,
The traffic condition calculation means includes:
Each time a response signal indicating that the data packet transmitted to the network is received by the receiving terminal is received, a reception time of the response signal, a transmission time of a data packet corresponding to the response signal, and From the above, it has an accumulated packet amount calculation means for calculating a round trip time of the data packet,
While the data packet of the second transmission unit following the one transmission unit is being transmitted by the transmission control means, the response signal for the data packet transmitted in the one transmission unit is received from the network,
From the received response signal, the accumulated amount of data packets included in the one transmission unit accumulated in the router is expressed as an average value of actually measured round trip times with respect to the round trip time of the data packets when there is no congestion. Calculate as the product of the ratio value and the current window size,
The window size control means includes:
A change amount of the window size is determined based on a difference between a predetermined threshold value and the accumulated packet amount calculated by the traffic condition calculation means, and then the data is determined based on the current window size and the change amount. Determine the window size when sending packets,
The transmission control means includes
A program that transmits data packets of three transmission units following the second transmission unit with the window size determined by the window size control means. In a communication system in which a transmitting terminal, a router, and a receiving terminal are connected to each other via a network, a communication method for transferring a data packet transmitted by the transmitting terminal in a predetermined transmission unit to the receiving terminal by the router There,
A traffic status calculation step of calculating the amount of stored data packets stored in the router;
A window size control step of determining a window size that is the transmission unit of the data packet to be transmitted to the network based on the accumulated packet amount calculated in the traffic situation calculation step;
A transmission control step for controlling transmission of data packets based on the window size determined in the window size control step, and
The traffic situation calculation step includes:
Each time a response signal indicating that the data packet transmitted to the network is received by the receiving terminal is received, a reception time of the response signal, a transmission time of a data packet corresponding to the response signal, and From the accumulated packet amount calculation step of calculating the round trip time of the data packet,
While the data packet of two transmission units following one transmission unit is being transmitted by the transmission control step, the response signal for the data packet transmitted in the one transmission unit is received from the network,
From the received response signal, the accumulated amount of data packets included in the one transmission unit accumulated in the router is expressed as an average value of actually measured round trip times with respect to the round trip time of the data packets when there is no congestion. Calculate as the product of the ratio value and the current window size,
The window size control step includes:
A change amount of the window size is determined based on a difference between a predetermined threshold value and the accumulated packet amount calculated by the traffic situation calculation step, and then data is determined based on the current window size and the change amount. Determine the window size when sending packets,
The transmission control step includes
A communication method of transmitting data packets of three transmission units following the second transmission unit with the window size determined by the window size control step.

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