JP2015033125A - Packet transmission device and program therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a packet transmission device for preventing unwanted reduction in congestion window size in a delay-based congestion control method.SOLUTION: A packet transmission device 1 comprises: round-trip delay time (RTT) measurement means 141 for measuring the RTT of a packet; minimum RTT update means 171 for successively updating a minimum RTT; variation amount calculation means 161 for calculating and successively updating a reference RTT variation amount resulting from smoothing a variation amount of the RTT; RTT increase determination means 172 which determines that the RTT is increased, when the RTT becomes longer than a time length resulting from adding the minimum RTT and the reference RTT variation amount, and determines that the RTT is not increased, when the RTT is equal to or shorter than the time length; and congestion window control means 15 which controls the congestion window size so as to decrease the congestion window size in the case where it is determined that the RTT is increased, and to increase the congestion window size in the case where it is determined that the RTT is not increased.

Description

  The present invention relates to a packet transmission device that transmits data by packet communication and a program thereof.

  In a best effort type IP (Internet Protocol) network in which quality is not guaranteed, a transmission packet is discarded (packet loss) due to a buffer leak in a network device, a bit error during transmission, or the like. Therefore, conventionally, TCP (Transmission Control Protocol) has been widely used as a protocol for confirming delivery for reliably transmitting data on an IP network (see Non-Patent Document 1).

  In this TCP, when a receiving device receives a packet, it notifies the transmitting device of the number of the packet to be transmitted next as a report indicating that it has been received. Then, the transmission device confirms that the packet has normally reached the reception device based on the report notified from the reception device. In addition, when the transmission device detects a packet loss in the report notified from the reception device, the transmission device retransmits the packet, and congestion indicating the number of packets (number of segments) that can be transmitted at a time until a delivery confirmation response is received. Adjust the window size (CWND: Congestion Window Size). For example, the transmission device increases CWND when a packet is normally received, and decreases CWND when a packet loss is detected.

This method of adjusting CWND is generally called a congestion control method, and can be classified into a loss-based method and a delay-based method depending on how the occurrence of congestion is determined.
The loss-based method regards occurrence of packet loss as a congestion signal, decreases CWND, and increases CWND when there is no packet loss. As this loss-based congestion control method, NewReno (see Non-Patent Document 2), CUBIC (see Non-Patent Document 3), and CTCP (see Non-Patent Document 4) are known.

On the other hand, the delay-based method regards an increase in transmission delay as a congestion signal, decreases CWND, and increases CWND when there is no increase in transmission delay. As this delay-based congestion control method, Vegas (see Non-Patent Document 5) and YeAH TCP (see Non-Patent Document 6) are known. For example, Vegas determines whether congestion has occurred based on the minimum value of transmission delay measured during communication, and performs CWND control.
Further, as a delay base method, a method of changing the change width of CWND according to the size of transmission delay based on Vegas (fixed to “1” in Vegas) is disclosed (see Patent Document 1).

Japanese Patent No. 4249049

“RFC: 793 TRANSMISSION CONTROL PROTOCOL September 1981”, [online], [searched July 29, 2013], Internet <URL: http://www.ietf.org/rfc/rfc793.txt> “RFC: 6582 The New Reno Modification to TCP's Fast Recovery Algorithm April 2012”, [online], [searched July 29, 2013], Internet <URL: http://www.ietf.org/rfc/rfc6582.txt > “CUBIC: A New TCP-Friendly High-Speed TCP Variant”, Sangtae Ha, Injong Rhee and Lisong Xu (ACM SIGOPS Operating System Review, Volume 42, Issue 5, July 2008) “A Compound TCP Approach for High-speed and Long Distance Networks,” kun Tan, Jingmin Song, Qian Zhang and Murari Sridharan (IEEE Infocom, April 2006) “TCP Vegas: End to End Congestion Avoidance on a Global Internet”, Lawrence S. Brakmo, Larry L. Peterson (IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS, Vol.13 No.8 pp.1465-1480, Oct. 1995)

  The above loss-based approach increases CWND until packet loss occurs. However, in the loss-based method, when data exceeding the usable bandwidth is transmitted, the excess data is not discarded immediately, but temporarily stored in a memory provided in the network device. In the loss-based method, the accumulated data is read from the memory and transmitted when the network bandwidth becomes available.

As described above, in the loss-based method, CWND is increased until packet loss occurs, that is, until data overflows from the memory. Therefore, an increase in queuing delay due to accumulation of data in the memory occurs.
Many network devices in recent years are equipped with a memory, and the increase in queuing delay is large, and the loss-based method has a problem of reducing the response of data communication.

On the other hand, the delay-based method described above reduces CWND by using an increase in queuing delay (transmission delay) as a congestion signal, thereby suppressing an increase in the amount of data stored in the memory in the network device, that is, an increase in transmission delay. Can do.
However, in a wireless network, retransmission is performed for packet loss due to a temporary deterioration in wireless quality due to fading, interference, and the like, and transmission delay occurs regardless of congestion. In addition, for example, in the delay-based method such as Vegas, since the presence or absence of congestion is determined based on the minimum value of transmission delay measured during communication, an increase in delay due to a temporary decrease in radio quality unrelated to congestion is also congested. Is mistakenly determined.

Therefore, the conventional delay-based method has a problem that the CWND is reduced more than necessary in an environment in which delay variation that is not a queuing delay is likely to occur, as in a wireless network, and the throughput is significantly reduced.
In the method described in Patent Document 1, the amount of change in CWND is changed depending on the magnitude of the transmission delay, but the problem is not solved because the determination of congestion is simply performed based on the transmission delay.

  The present invention has been made in view of such problems, and in the delay-based congestion control method, it is possible to prevent an unnecessary decrease in the congestion window size (CWND) due to a transmission delay unrelated to the congestion. It is an object of the present invention to provide a possible packet transmission device and a program thereof.

  In order to solve the above-described problem, a packet transmission device according to the present invention is a packet transmission device that controls a congestion window size indicating the number of packets that can be transmitted at one time until a delivery confirmation response is received according to a transmission delay of the packet. The RTT measuring unit, the minimum RTT updating unit, the reference RTT fluctuation amount calculating unit, the RTT increase determining unit, and the congestion window control unit are provided.

In such a configuration, the packet transmission device uses the RTT measurement means to determine the round trip time RTT (Round Trip Time) of the packet from the transmission time of the packet corresponding to the received delivery confirmation response and the reception time of the delivery confirmation response. ). With this RTT, the load state of the network can be recognized.
Then, the packet transmission apparatus updates the minimum RTT sequentially measured by the RTT measurement unit by the minimum RTT update unit and stores it in the storage unit. Further, the packet transmission device calculates a variation amount obtained by smoothing the measured variation amount of the RTT by the reference RTT variation amount calculation means, and sequentially updates the variation amount as the reference RTT variation amount.

Then, the packet transmission device determines that the RTT has increased when the measured RTT is longer than the time length obtained by adding the minimum RTT and the reference RTT fluctuation amount by the RTT increase determination means, and is less than the time length. In this case, it is determined that the RTT has not increased.
This is because if the RTT fluctuates within the range of the smoothed reference RTT fluctuation amount, the fluctuation can be regarded as occurring due to a delay in a network-specific environment.

The packet transmission device reduces the congestion window size when the congestion window control means determines that the RTT has increased by the RTT increase determination means, and determines that the RTT does not increase when the RTT increases. Control the congestion window size to increase the window size.
As a result, even if the RTT increases, if the fluctuation amount is within the range of the reference RTT fluctuation amount, the packet transmission apparatus has a delay that is not related to congestion, that is, a network-specific The congestion window size is not reduced.

  The packet transmission apparatus according to the present invention includes a computer of the packet transmission apparatus, a data input unit, a data transmission unit, a delivery response confirmation reception unit that measures RTT, a flow control unit, a minimum RTT update unit, and a reference RTT fluctuation amount calculation. And a packet transmission program for functioning as means, RTT increase determination means, and congestion window control means.

The present invention has the following excellent effects.
According to the packet transmission apparatus of the present invention, in the delay-based congestion control method, a transmission delay that is not related to congestion can be estimated based on the reference RTT fluctuation amount, and a congestion window size (CWND) due to a delay other than congestion can be estimated. ) Can be prevented.
That is, according to the packet transmission apparatus according to the present invention, while adopting a delay-based congestion control method capable of keeping transmission delay low compared to the loss-based congestion control method, it is further possible to prevent unnecessary reduction of CWND. By doing so, it is possible to suppress a decrease in communication speed and maintain a high network throughput.

It is a block block diagram which shows the structure of the packet transmission apparatus which concerns on 1st Embodiment of this invention. It is a graph for demonstrating the outline | summary of the method of determining the increase in the transmission delay used as the signal of congestion in the packet transmitter which concerns on 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the packet transmitter which concerns on the 1st-4th embodiment of this invention. FIG. 4 is a flowchart illustrating an operation of updating a minimum RTT in FIG. 3. FIG. 4 is a flowchart illustrating an operation of the packet transmission device according to the first embodiment of the present invention, which is an operation of estimating the reference RTT fluctuation amount of FIG. 3. It is a flowchart which shows the operation | movement of the process at the time of packet loss generation | occurrence | production of FIG. It is a block block diagram which shows the structure of the packet transmission apparatus which concerns on 2nd Embodiment of this invention. It is a graph for demonstrating the time interval which estimates the reference | standard RTT variation | change_quantity in the packet transmitter which concerns on 2nd Embodiment of this invention. It is a flowchart which shows the operation | movement of the reference | standard RTT variation | change_quantity estimation of FIG. 3 among operation | movement of the packet transmission apparatus which concerns on 2nd Embodiment of this invention. It is a block block diagram which shows the structure of the packet transmitter which concerns on 3rd Embodiment of this invention. It is a flowchart which shows the operation | movement of the reference | standard RTT fluctuation amount estimation of FIG. 3 among operation | movement of the packet transmission apparatus which concerns on 3rd Embodiment of this invention. It is a block block diagram which shows the structure of the packet transmitter which concerns on 4th Embodiment of this invention. It is a flowchart which shows the operation | movement of the reference | standard RTT variation | change_quantity estimation of FIG. 3 among operation | movement of the packet transmission apparatus which concerns on 4th Embodiment of this invention. It is a block block diagram which shows the structure of the packet receiver which concerns on embodiment of a reference example.

Embodiments of the present invention will be described below with reference to the drawings.
<< First Embodiment >>
[Configuration of packet transmitter]
First, the configuration of the packet transmission device 1 according to the first embodiment of the present invention will be described with reference to FIG.

The packet transmission device 1 transmits data (packet data) input from a data transmission device or the like (not shown) to the packet reception device 2 by controlling the data transmission amount by a window control method.
The packet transmission device 1 is connected to the packet reception device 2 in a congestion window size (CWND: Congestion Window Size, hereinafter simply referred to as the number of packets (number of segments) that can be transmitted at a time until a delivery confirmation response is received. CWND) is controlled, and flow control is performed according to the CWND, thereby adjusting the number of packets to be transmitted (data amount).
Further, the packet transmission apparatus 1 regards an increase in packet transmission delay as a congestion signal and decreases CWND. If there is no increase in transmission delay, the packet transmission apparatus 1 performs delay-based congestion control to increase CWND.

Here, with reference to FIG. 2, an outline of a method for determining an increase in transmission delay that becomes a congestion signal in the delay-based congestion control performed by the packet transmission device 1 will be described.
In the graph shown in FIG. 2, the horizontal axis represents time, and the vertical axis represents packet round trip time (RTT), and shows how the RTT varies with time.
At this time, the packet transmitting apparatus 1 sets the moving average of the jitter of the RTT that sequentially changes as the reference RTT fluctuation amount c. The packet transmission device 1 transmits a congestion signal when the RTT fluctuates (increases) exceeding the reference RTT fluctuation amount c with respect to the minimum RTT (r) measured at a certain time t1. It is determined that the delay has increased.

In the example of FIG. 2, when the RTT fluctuates exceeding the reference RTT fluctuation amount c at time t2 (A in the figure), the packet transmission device 1 determines that the transmission delay has increased. However, even if the RTT increases, the packet transmission device 1 does not determine that the transmission delay is increased unless the variation exceeds the reference RTT variation c (B in the figure).
The configuration of the packet transmission apparatus 1 that performs such delay-based congestion control will be described in detail with reference to FIG.

  As shown in FIG. 1, the packet transmission apparatus 1 includes a data input means 10, a data buffer (temporary storage means) 11, a flow control means 12, a data transmission means 13, a delivery confirmation response reception means 14, and a congestion. A window control unit 15, a reference RTT variation estimation unit 16, an RTT variation analysis unit 17, and a storage unit 18 are provided.

  The data input means 10 is for inputting data (packet data) to be transmitted to the packet receiving device 2 from the outside. This packet data is, for example, an IP packet. The data input means 10 sequentially stores the input packets in the data buffer 11 and notifies the flow control means 12 that the packets have been input.

  The data buffer (temporary storage means) 11 temporarily stores packet data input via the data input means 10 and is a storage medium such as a semiconductor memory. The packet data stored in the data buffer 11 is read by the data transmission unit 13. That is, the data buffer 11 functions as a first-in first-out (FIFO).

  The flow control means 12 performs flow control according to CWND controlled by the congestion window control means 15. That is, the flow control unit 12 controls the number of packets transmitted from the data transmission unit 13 by a general window control method.

Specifically, the flow control unit 12 instructs the data transmission unit 13 to transmit the packet stored in the data buffer 11. Then, when the flow control means 12 receives the delivery confirmation response (ACK) for the transmitted packet from the delivery confirmation response receiving means 14, the flow control means 12 sets the transmission number (sequence number) of the packet to be transmitted next in the data buffer 11. Update. At this time, the flow control means 12 may instruct the data transmission means 13 to transmit at a time without receiving ACK up to the number of CWND packets stored in the storage means 18 (18 ₁ ). it can.
As described above, the flow control unit 12 controls the number of packets transmitted to the packet reception device 2 at a time by the CWND controlled by the congestion window control unit 15.

The data transmission unit 13 transmits a packet stored in the data buffer 11 to the packet reception device 2 via a communication line in response to an instruction from the flow control unit 12. The packet data describes the destination of the packet, and the data transmission means 13 transmits the packet to the destination. For example, when the packet is an IP packet, the destination IP address is described in the IP header.
Here, the data transmission unit 13 includes a transmission time writing unit 131.

The transmission time writing means 131 acquires the time at which a packet is transmitted from a timer (not shown) and writes it in the header area of the packet. For example, the transmission time writing unit 131 writes the transmission time in the TCP time stamp of the option area in the TCP header. This transmission time is used as a reference time for measuring the round trip time (RTT) of the packet.
Further, for example, the transmission time writing unit 131 may write the transmission time in the storage unit 18 in association with the sequence number of the packet without directly writing the transmission time in the packet.

The delivery confirmation response receiving unit 14 receives a delivery confirmation response (ACK) corresponding to the packet transmitted via the data transmission unit 13 from the destination packet receiving device 2 via the communication line. .
In addition, here, the delivery confirmation response receiving unit 14 includes an RTT measuring unit 141.

  The RTT measuring unit 141 measures the round trip delay time (RTT) of the packet transmitted from the data transmitting unit 13 and confirmed for delivery. For example, when the transmission time writing unit 131 writes the transmission time in the header area of the packet, the RTT measurement unit 141 receives a delivery confirmation response including the transmission time, and acquires the current time acquired from a timer (not shown). The RTT is calculated by taking the difference from (reception time).

For example, when the transmission time writing unit 131 writes the transmission time in the storage unit 18 in association with the sequence number of the packet, the RTT measurement unit 141 uses the packet corresponding to the sequence number notified by the delivery confirmation response. RTT is calculated by reading the transmission time from the storage unit 18 and taking the difference from the current time (reception time).
The delivery confirmation response receiving unit 14 outputs the received delivery confirmation response (ACK) to the flow control unit 12 and the congestion window control unit 15, and further outputs RTT to the congestion window control unit 15.

The congestion window control means 15 controls the congestion window size (CWND) when the flow control means 12 performs flow control according to the load state of the network. The congestion window control unit 15 detects a packet loss by an acknowledgment response (ACK) input from the acknowledgment response receiving unit 14 and decreases CWND or increases the RTT input from the RTT fluctuation analyzing unit 17. Control to increase or decrease CWND is performed according to the determination result.
Here, the congestion window control unit 15 includes a packet loss detection unit 151, a loss generation CWND processing unit 152, and an RTT fluctuation CWND processing unit 153.

The packet loss detection unit 151 detects a packet loss based on a delivery confirmation response (ACK) input from the delivery confirmation response reception unit 14.
The packet loss detecting means 151 may detect the packet loss by a general method, for example, assuming that a loss has occurred when three consecutive ACKs having the same sequence number are received.

When detecting the packet loss, the packet loss detecting unit 151 notifies the loss generating CWND processing unit 152 that the packet loss has occurred. Further, when the packet loss detection unit 151 detects a packet loss, the RTT input from the delivery confirmation response reception unit 14 and the fact that a packet loss has occurred (loss notification) is indicated by the reference RTT variation estimation unit 16 and the RTT variation. Output to the analysis means 17.
On the other hand, when no packet loss is detected, the packet loss detecting unit 151 outputs the RTT input from the delivery confirmation response receiving unit 14 to the RTT fluctuation analyzing unit 17.

The loss-generating CWND processing means 152 reduces CWND when a packet loss occurs. Here, the loss-generating CWND processing unit 152 stores a value obtained by reducing the CWND in the storage unit 18 (18 ₁ ) when the packet loss detection unit 151 is notified that the packet loss has been detected. Update CWND.
For example, when a packet loss occurs, the loss-generating CWND processing unit 152 sets ₁ to 0.5 times, 0.7 times, or the like with respect to the current CWND stored in the storage unit 18 (18 ₁ ). Multiply by a smaller predetermined value to reduce CWND.

The RTT fluctuation CWND processing means 153 decreases the CWND if the RTT is in an increased state according to the determination result indicating whether the RTT fluctuation analysis means 17 has exceeded the reference RTT fluctuation amount or increased. Otherwise, CWND is increased.
Here, the RTT fluctuation CWND processing unit 153, when notified from the RTT fluctuation analysis unit 17 that the RTT has increased as a determination result, decreases the CWND to prevent the occurrence of congestion. For example, when the RTT increases, the RTT variation CWND processing unit 153 decreases the CWND stored in the storage unit 18 (18 ₁ ) by a predetermined number (eg, “1”).

On the other hand, when the RTT fluctuation analyzing means 17 notifies the RTT fluctuation analyzing means 17 that the RTT fluctuation has not increased (not increased) as a determination result, the CWND processing means 153 increases the number of packets to be transmitted at one time. increase. For example, if the RTT has not increased, the RTT variation CWND processing unit 153 increases the CWND stored in the storage unit 18 (18 ₁ ) by a predetermined number (eg, “1”).

The reference RTT fluctuation amount estimation means 16 smoothes the RTT fluctuation amount measured by the RTT measurement means 141, and estimates a reference RTT fluctuation quantity that serves as a reference for RTT increase determination. If the RTT fluctuates within the range of the reference RTT fluctuation amount, even if the RTT increases, it occurs due to a delay in a network-specific environment (such as a wireless environment) that is not related to congestion. Can be regarded as
Here, the reference RTT fluctuation amount estimation means 16 includes a fluctuation amount calculation means 161.

The fluctuation amount calculation means (reference RTT fluctuation amount calculation means) 161 is an RTT (current RTT) measured by the delivery confirmation response (ACK) received this time and the delivery confirmation received immediately before the TCP connection establishment. By calculating the moving average of the difference (jitter) from the RTT measured in response (ACK) (previous RTT), the RTT smoothed fluctuation amount (reference RTT fluctuation amount) is calculated and updated. is there. Here, for example, the fluctuation amount calculation means 161 can recognize whether or not the connection is being established by notifying the data transmission means 13 that the TCP connection establishment or termination sequence has been completed. it can.
Here, the reference RTT fluctuation amount estimation means 16 (fluctuation amount calculation means 161) inputs RTT via the RTT fluctuation analysis means 17. This is because the RTT for calculating the reference RTT fluctuation amount by the reference RTT fluctuation estimation means 16 is synchronized with the RTT for the RTT fluctuation analysis means 17 determining the increase in RTT.

Specifically, the fluctuation amount calculation means 161 includes the RTT (current RTT) measured by the delivery confirmation response (ACK) received this time and the previously calculated reference RTT stored in the storage means 18 (18 ₂ ). From the fluctuation amount and the RTT (previous RTT) measured by the previously received acknowledgment (ACK), the fluctuation amount is smoothed by the following equation (1) and updated as a new reference RTT fluctuation amount.

Reference RTT fluctuation amount ← Reference RTT fluctuation amount * (1-α)
+ (The absolute value of the difference between the previous RTT and the current RTT) * α (1)

Here, α is a predetermined smoothing parameter (0 <α <1). For example, as α, a value “1/8” used for smoothing RTT in TCP, a value “1/4” used for smoothing dispersion of RTT, and the like can be used.
The fluctuation amount calculating means 161 updates the reference RTT fluctuation amount by storing the calculated new reference RTT fluctuation amount in the storage means 18 (18 ₂ ), and also updates the new reference RTT fluctuation amount to the RTT fluctuation analyzing means 17. Output to. In addition, the fluctuation amount calculation unit 161 stores the RTT (current RTT) measured by the delivery confirmation response (ACK) received this time in the storage unit 18 (18 ₂ ) as the previous RTT.

Note that the fluctuation amount calculation means 161 does not calculate the reference RTT fluctuation amount when the packet loss detection means 151 inputs that the packet loss has occurred (loss notification) and the RTT, and does not calculate the reference RTT fluctuation amount (this time). RTT) is stored in the storage means 18 (18 ₂ ) as the previous RTT.

The RTT fluctuation analyzing means 17 analyzes whether or not the RTT measured this time is in an increasing tendency from a reference RTT fluctuation amount estimated by the reference RTT fluctuation amount estimating means 16 beyond a certain reference. . Here, it is assumed that the RTT fluctuation analysis means 17 uses RTT via the congestion window control means 15. This is because the processing of the RTT fluctuation analyzing means 17 differs depending on the presence or absence of packet loss.
Here, the RTT fluctuation analysis unit 17 includes a minimum RTT update unit 171 and an RTT increase determination unit 172.

The minimum RTT update means 171 sequentially updates the minimum value of RTT measured so far. Here, the minimum RTT updating unit 171 determines the RTT measured by the RTT measuring unit 141 notified via the congestion window control unit 15 when the minimum RTT is not stored in the storage unit 18 (18 ₂ ). Write to the storage means 18 (18 ₂ ). The minimum RTT update unit 171, if the minimum RTT in the storage unit 18 (18 ₂₎ is stored, the smaller the current RTT than its minimum RTT, stored in the storage unit 18 (18 ₂₎ The minimum RTT is updated with the current RTT.

The RTT increase determination means 172 determines whether or not the RTT has increased by a fluctuation amount exceeding the reference RTT fluctuation amount.
The RTT increase determination unit 172 notifies the reference RTT fluctuation amount estimation unit 16 of the RTT notified from the congestion window control unit 15, and acquires the reference RTT fluctuation amount from the reference RTT fluctuation amount estimation unit 16. Then, the RTT increase determination means 172 determines whether or not the RTT has increased based on the minimum RTT stored in the storage means 18 (18 ₂ ) and the reference RTT fluctuation amount.

  More specifically, the RTT increase determination means 172 uses the determination formula as shown in the following formula (2) to determine the currently received delivery confirmation response (ACK) from the time length obtained by adding the minimum RTT and the reference RTT fluctuation amount. If the RTT measured at (the current RTT) is longer, it is determined that the RTT has increased. Further, the RTT increase determination means 172 determines that the RTT has not increased if the time length obtained by adding the minimum RTT and the reference RTT fluctuation amount is equal to or greater than the RTT measured this time.

if (minimum RTT + reference RTT fluctuation <current RTT)
then RTT has increased otherwise RTT has not increased ... Formula (2)

The RTT increase determination unit 172 outputs the determination result to the congestion window control unit 15.
When the RTT increase determination means 172 inputs from the packet loss detection means 151 that a packet loss has occurred (loss notification) and RTT, the RTT increase determination means 172 is stored in the storage means 18 (18 ₂ ) according to the input RTT. Only the minimum RTT that is present is updated. This is because when a packet loss occurs, the loss-generating CWND processing unit 152 of the congestion window control unit 15 decreases the CWND regardless of the increase or decrease of the RTT.

The storage means 18 (18 ₁ , 18 ₂ ) stores information that is sequentially updated by the packet transmission device 1, and is a storage medium such as a semiconductor memory.
The storage means 18 stores CWND, reference RTT fluctuation amount, previous RTT, and minimum RTT. Here, the CWND is updated by the congestion window control unit 15 and is referred to by the flow control unit 12. The reference RTT fluctuation amount and the previous RTT are updated by the reference RTT fluctuation amount estimation means 16 (fluctuation amount calculation means 161), and the minimum RTT is updated by the RTT fluctuation analysis means 17 (minimum RTT update means 171). .
The reference RTT fluctuation amount is set to “0” as an initial value.
In FIG. 1, it is illustrated separately storing unit 18 in the storage unit 18 ₁ and the storage means 18 _2, may be the same storage medium.

By configuring the packet transmission device 1 as described above, the packet transmission device 1 estimates the amount of RTT variation (reference RTT variation) that occurs regardless of congestion, and sets the reference RTT variation amount to the minimum RTT. The delay increase is dynamically determined using the added value as a threshold value.
As a result, the packet transmission device 1 can accurately detect an increase in RTT, which is a congestion signal, and perform CWND control according to the network environment.

[Operation of packet transmission device]
Next, the operation of the packet transmission apparatus 1 according to the first embodiment of the present invention will be described with reference to FIGS.
Note that the description of a general delay-based congestion control method is omitted here, and an increase in transmission delay that becomes a congestion signal is controlled based on the round-trip delay time (RTT) of the packet, which is a feature of the present invention. The operation of performing CWND control by making a determination will be mainly described. That is, here, data transmission means 13 (mainly transmission time writing means 131), delivery confirmation response reception means 14 (mainly RTT measurement means 141), congestion window control means 15, reference RTT fluctuation amount estimation means 16 and RTT The operation of the fluctuation analysis means 17 will be described.

As illustrated in FIG. 3, the packet transmission device 1 receives a delivery confirmation response (ACK) corresponding to a packet transmitted via the data transmission unit 13 (not illustrated) as a step by the delivery confirmation response reception unit 14. (Step S1).
The packet transmission device 1 calculates the RTT by taking the difference between the packet transmission time and the current time (reception time) by the RTT measurement unit 141 (step S2).

Then, the packet transmission device 1 detects whether or not a packet loss has occurred by the delivery confirmation response (ACK) received in step S1, by the packet loss detection unit 151 of the congestion window control unit 15 (step S3). .
Here, if a packet loss is not detected (No in step S3), the packet transmitting apparatus 1 proceeds with the operation after step S4.
That is, the packet transmitting apparatus 1 updates the minimum RTT by the minimum RTT updating unit 171 of the RTT fluctuation analyzing unit 17 (step S4).
The operation in step S4 will be described with reference to FIG.

As shown in FIG. 4, the packet transmitting apparatus 1 uses the minimum RTT update unit 171 to determine the minimum RTT up to the present time stored in the storage unit 18 (18 ₂ ) and the ACK received this time calculated in step S2. The corresponding RTT (current RTT) is compared (step S41).

If the minimum RTT is larger than the current RTT (Yes in step S41), the minimum RTT update unit 171 updates the minimum RTT stored in the storage unit 18 (18 ₂ ) with the current RTT. (Step S42). If the minimum RTT is equal to or less than the current RTT (No in step S41), the minimum RTT update unit 171 does not update the minimum RTT.
Returning to FIG. 3, the operation of the packet transmission device 1 will be described.

After step S4, the packet transmitting apparatus 1 estimates the reference RTT fluctuation amount by the reference RTT fluctuation amount estimating means 16 (step S5).
The operation in step S5 will be described in detail with reference to FIG.

As shown in FIG. 5, the packet transmission device 1 determines whether or not the previous RTT is stored in the storage unit 18 (18 ₂ ) by the fluctuation amount calculation unit 161 (step S51).
Here, when the previous RTT is stored in the storage unit 18 (18 ₂ ) (Yes in step S51), the fluctuation amount calculation unit 161 calculates the previous RTT and the current RTT according to the equation (1). The moving average of the difference (jitter) is calculated.

That is, the fluctuation amount calculating means 161 first calculates the absolute value of the difference between the previous RTT and the current RTT as the RTT difference (step S52). Then, the fluctuation amount calculation unit 161 calculates the reference RTT fluctuation amount stored in the storage unit 18 (18 ₂ ) and the RTT difference calculated in step S52 at a predetermined ratio [(1-α): α. ] To calculate a new reference RTT fluctuation amount (step S53). The new reference RTT fluctuation amount calculated in step S53 is stored in the storage means 18 (18 ₂ ) by the fluctuation amount calculation means 161.

Then, the fluctuation amount calculating means 161 stores the current RTT as the previous RTT in the storage means 18 (18 ₂ ) (step S54).
In step S51, when the previous RTT is not stored in the storage unit 18 (18 ₂ ) (No in step S51), the fluctuation amount calculation unit 161 performs only the operation of step S54.
Returning to FIG. 3, the operation of the packet transmission device 1 will be described.

After step S5, the packet transmission device 1 determines whether or not the RTT has increased by a fluctuation amount exceeding the reference RTT fluctuation amount by the RTT increase determination means 172 of the RTT fluctuation analysis means 17 (step S6).
Here, if the current RTT is longer than the time length obtained by adding the minimum RTT stored in the storage unit 18 (18 ₂ ) and the reference RTT fluctuation amount estimated in step S5, the RTT increase determination is performed. The means 172 determines that the RTT is increasing. Further, if the current RTT is equal to or shorter than the time length obtained by adding the minimum RTT and the reference RTT fluctuation amount, the RTT increase determination unit 172 determines that the RTT has not increased.

When it is determined that the RTT has increased (Yes in step S6), the packet transmitting apparatus 1 decreases the CWND (for example, −1) by the RTT fluctuation CWND processing unit 153 of the congestion window control unit 15. (Step S7). On the other hand, when it is determined that the RTT has not increased (No in step S6), the packet transmission device 1 increases the CWND (for example, +1) by the RTT variation CWND processing unit 153 (step S8).
If a packet loss is detected in step S3 (Yes in step S3), the process at the time of packet loss occurrence in step S9 is performed.
The operation in step S9 will be described with reference to FIG.

As shown in FIG. 6, when a packet loss occurs, the packet transmission device 1 reduces the CWND (0.5 times, 0.7 times, etc.) by the loss generation CWND processing means 152 of the congestion window control means 15. (Step S91).
In addition, the packet transmission device 1 does not perform the RTT increase determination in the RTT fluctuation analysis unit 17 and only updates the minimum RTT by the minimum RTT update unit 171 (step S92). This step S92 is the same as the operation described in FIG.
Further, the packet transmission device 1 does not calculate the reference RTT fluctuation amount in the fluctuation amount calculation means 161 of the reference RTT fluctuation amount estimation means 16, and stores the current RTT in the storage means 18 (18 ₂ ) as the previous RTT. (Step S93).

  By configuring and operating the packet transmission device 1 as described above, the packet transmission device 1 maintains the merit of delay-based congestion control that keeps the transmission delay low, and is related to congestion such as a wireless environment. Even in an environment where there is no delay increase, an unnecessary decrease in CWND can be suppressed and the throughput can be maintained at a high level.

<< Second Embodiment >>
[Configuration of packet transmitter]
Next, the configuration of the packet transmission device 1B according to the second embodiment of the present invention will be described with reference to FIG.

The packet transmission device 1B performs packet transmission by delay-based congestion control, and basically has the same function as the packet transmission device 1 described in FIG.
The packet transmission device 1 described with reference to FIG. 1 has a configuration in which the moving average of RTT jitter is used as a reference RTT fluctuation amount, and the reference RTT fluctuation amount is sequentially updated at the timing when the RTT is measured.
However, the packet transmission device 1B updates the reference RTT fluctuation amount using the moving average of the maximum value of the RTT jitter in a predetermined time interval as the reference RTT fluctuation amount.

Here, an example of a time interval for estimating the reference RTT fluctuation amount of the packet transmission device 1B will be described with reference to FIG. Here, it is assumed that the predetermined time interval is from the last update of the reference RTT fluctuation amount until the minimum RTT time elapses.
In the graph shown in FIG. 8, the horizontal axis represents time and the vertical axis represents packet round-trip delay time (RTT), and shows how the RTT varies with the passage of time.

  Here, it is assumed that the packet transmission device 1B updates the reference RTT fluctuation amount at time t1. At this time, when the minimum RTT measured so far is r1, the packet transmission device 1B receives the acknowledgment (ACK) after the elapse of r1 from the time t1, and at the timing (here, the time t2), the reference Update the RTT fluctuation amount.

In the example of FIG. 8, the minimum RTT is r1 at time t2, but when the minimum RTT is updated to r2 during the time measurement from t2, the packet transmission device 1B has passed r2 from time t2. Later, the reference RTT fluctuation amount is updated at the timing (here, time t3) when the delivery confirmation response (ACK) is received. Of course, the reference RTT fluctuation amount may be updated after elapse of r1, which is the initial minimum RTT from time t2.
In the second embodiment, the predetermined time interval is described as the minimum RTT. However, the predetermined time interval does not need to be the minimum RTT as long as it indicates the packet transmission delay time. For example, an RTT that is sequentially measured may be used.

This packet transmission device 1B prevents the reference RTT fluctuation amount from becoming excessively low when used in an environment where the transmission rate is increased and packet transmission / reception occurs in bursts, or in an environment where the frequency of delay increases other than congestion is low. Therefore, the update frequency of the reference RTT fluctuation amount is reduced. By using a time interval based on the transmission delay time as a reference for the update frequency, update suitable for the network can be performed.
In this way, the configuration of the packet transmission device 1B that updates the reference RTT fluctuation amount in a predetermined time interval will be described in detail with reference to FIG.

  As shown in FIG. 7, the packet transmission apparatus 1B includes a data input means 10, a data buffer (temporary storage means) 11, a flow control means 12, a data transmission means 13, a delivery confirmation response reception means 14, and a congestion. A window control unit 15, a reference RTT variation estimation unit 16 </ b> B, an RTT variation analysis unit 17, and a storage unit 18 are provided.

  Since the configuration other than the reference RTT variation estimation means 16B is the same as that of the packet transmission device 1 described in FIG. 1, the same reference numerals are given and description thereof is omitted. Note that the storage unit 18 stores more content than the packet transmission device 1. Since the content is updated by the reference RTT fluctuation amount estimation means 16B, it will be described in the description of the reference RTT fluctuation amount estimation means 16B.

  The reference RTT fluctuation amount estimation means 16B smoothes the RTT fluctuation amount measured by the RTT measurement means 141, and estimates the reference RTT fluctuation amount that serves as a reference for the RTT increase determination. Here, the reference RTT fluctuation amount estimation unit 16B includes a fluctuation amount calculation unit 161B and a time interval determination unit 162.

  The fluctuation amount calculating means (reference RTT fluctuation amount calculating means) 161B received the RTT (current RTT) measured by the delivery confirmation response (ACK) in a predetermined time interval and immediately before the TCP connection establishment. By calculating the moving average of the maximum value of the difference (jitter) from the RTT (previous RTT) measured by the acknowledgment response (ACK), the fluctuation amount obtained by smoothing the maximum value of the RTT is calculated, and the reference RTT It is updated as a fluctuation amount. Here, the reference RTT fluctuation amount estimation means 16B (fluctuation amount calculation means 161B) inputs the RTT via the RTT fluctuation analysis means 17.

The fluctuation amount calculation means 161B inquires of the time interval determination means 162 whether or not a predetermined time interval has elapsed since the previous update of the reference RTT fluctuation amount, and when the time interval has elapsed, Update the RTT fluctuation amount.
Specifically, variation calculation means 161B after a predetermined time interval has elapsed, the reference RTT variation previously calculated stored in the storage unit 18 (18 _2), stored in the storage unit 18 (18 ₂₎ From the maximum variation amount of the RTT measured in the predetermined time interval (current interval maximum variation amount), the variation amount is smoothed by the following equation (3) to calculate a new reference RTT variation amount.

Reference RTT fluctuation amount ← Reference RTT fluctuation amount * (1-α)
+ Maximum fluctuation amount for the current section * α (3)

Here, α is a predetermined smoothing parameter (0 <α <1). For example, similarly to the reference RTT variation estimation means 16 (see FIG. 1), as α, a value “1/8” used for smoothing the RTT in TCP and a value “1 /” used for smoothing the dispersion of RTT. 4 ″ or the like can be used.
In addition, the maximum fluctuation amount of the current section includes the RTT measured by the delivery confirmation response (ACK) in the time section determined by the time section determination unit 162 (current RTT) and the delivery confirmation response (ACK) received immediately before the RTT. This is the maximum value of the difference (jitter) from the RTT (previous RTT) measured in (1).
The fluctuation amount calculating unit 161B updates the reference RTT fluctuation amount by storing the calculated new reference RTT fluctuation amount in the storage unit 18 (18 ₂ ).

In addition, when the reference RTT fluctuation amount is updated, the fluctuation amount calculation unit 161B notifies the time interval determination unit 162 of the fact, and outputs the updated reference RTT fluctuation amount to the RTT fluctuation analysis unit 17. In addition, when the reference RTT fluctuation amount is not updated, the fluctuation amount calculation unit 161B outputs the reference RTT fluctuation amount stored in the storage unit 18 (18 ₂ ) to the RTT fluctuation analysis unit 17 as it is.
When the reference RTT fluctuation amount is updated, the fluctuation amount calculating unit 161B initializes (sets to “0”) the current zone maximum fluctuation amount stored in the storage unit 18 (18 ₂ ).

The variation amount calculation means 161B each time it receives the RTT, the storage means 18 the absolute value of the difference between the previous RTT stored in (18 ₂₎ is calculated, and the storage unit 18 (18 ₂₎ in the storage If it is larger than the current maximum fluctuation amount of the current section, the current maximum section fluctuation amount is updated with the current RTT fluctuation amount. It is assumed that the current section maximum fluctuation amount stored in the storage means 18 (18 ₂ ) is set to “0” as an initial value in advance.

Further, the fluctuation amount calculating unit 161B stores the RTT (current RTT) measured by the delivery confirmation response (ACK) received this time in the storage unit 18 (18 ₂ ) as the previous RTT.
Note that the fluctuation amount calculation means 161B does not calculate the reference RTT fluctuation amount when the packet loss detection means 151 inputs that the packet loss has occurred (loss notification) and the RTT, and does not calculate the reference RTT fluctuation amount (this time). RTT) is stored in the storage means 18 (18 ₂ ) as the previous RTT.

The time interval determination means 162 determines whether or not a predetermined time has elapsed from the time when the reference RTT fluctuation amount is updated until the next time when the reference RTT fluctuation amount is updated.
The time interval determination unit 162 starts timekeeping when it is notified from the fluctuation amount calculation unit 161B that the reference RTT fluctuation amount has been updated. In addition, the time interval determination unit 162 receives the inquiry from the variation calculation unit 161B as to whether or not the predetermined time interval has elapsed, and stores the elapsed time since the reference RTT variation was updated. It is determined whether or not the minimum RTT stored in 18 (18 ₂ ) has been exceeded.
The time interval determination unit 162 outputs the determination result to the fluctuation amount calculation unit 161B.

By configuring the packet transmission device 1B as described above, the packet transmission device 1B is configured so that the reference RTT fluctuation amount estimation unit 16B performs the reference RTT at a timing when at least a predetermined time interval (here, the minimum RTT) has elapsed. The amount of change can be updated.
Here, the time interval for estimating (updating) the reference RTT fluctuation amount is the minimum RTT, but the time interval is not limited to this time interval as long as it is a time interval based on the RTT.

  For example, the time interval from when the reference RTT fluctuation amount is last updated until the delivery response confirmation (ACK) for the packet to be transmitted next arrives by the packet transmission apparatus 1B, that is, the RTT after the reference RTT fluctuation amount is updated. It is good.

In this case, the data transmission means 13 notifies the reference RTT fluctuation amount estimation means 16B of the sequence number of the transmission packet. In addition, the congestion window control means 15 (packet loss detection means 151) notifies the RTT fluctuation analysis means 17 of the ACK number included in the delivery confirmation response together with the RTT. Then, the RTT fluctuation analyzing means 17 (RTT increase determining means 172) notifies the reference RTT fluctuation amount estimating means 16B of the ACK number together with the RTT.
Then, the reference RTT fluctuation amount estimation means 16B (time interval determination means 162) uses the reference RTT fluctuation from the sequence number notified from the data transmission means 13 and the corresponding ACK number notified from the RTT fluctuation analysis means 17. A time interval corresponding to the RTT of the transmission packet after the amount update is determined.

[Operation of packet transmission device]
Next, the operation of the packet transmission device 1B according to the second embodiment of the present invention will be described with reference to FIGS.
Note that the operation of the packet transmission device 1B shown in FIG. 3 is the same as that of the packet transmission device 1 (see FIG. 1) except for step S5B, and thus the description thereof is omitted here. In other words, the operation of the packet transmission device 1B is merely that step S5 of the packet transmission device 1 is replaced with step S5B.
Here, the operation of step S5B will be described in detail with reference to FIG.

As shown in FIG. 9, the packet transmission device 1B uses the time interval determination unit 162 of the reference RTT fluctuation amount estimation unit 16B to store the time measured from the previous update of the reference RTT fluctuation amount in the storage unit 18 (18 ₂ ). It is determined whether or not the stored minimum RTT (predetermined time interval) has elapsed (step S51B). Here, the time interval determination unit 162 determines that a predetermined time interval has elapsed when the reference RTT fluctuation amount has not been updated yet.

Here, when a predetermined time interval has elapsed (Yes in step S51B), the fluctuation amount calculation means 161B of the reference RTT fluctuation amount estimation means 16B is stored in the storage means 18 (18 ₂ ) by the above equation (3). The new reference RTT fluctuation amount is calculated by adding the reference RTT fluctuation amount and the current section maximum fluctuation amount at a predetermined ratio [(1-α): α] (step S52B). The new reference RTT fluctuation amount calculated in step S52B is stored in the storage means 18 (18 ₂ ) by the fluctuation amount calculation means 161B.

Then, the fluctuation amount calculating means 161B initializes (“0”) the current section maximum fluctuation amount stored in the storage means 18 (18 ₂ ) (step S53B).
In addition, the time interval determination unit 162 resets the time interval measurement in response to the update notification of the reference RTT variation amount from the variation amount calculation unit 161B, and starts the time interval measurement again (not shown as a step). .

Thereafter, or when the time interval has not elapsed in step S51B (No in step S51B), the fluctuation amount calculating means 161B determines whether or not the previous RTT is stored in the storage means 18 (18 ₂ ). (Step S54B).
When the previous RTT is stored in the storage unit 18 (18 ₂ ) (Yes in step S54B), the fluctuation amount calculating unit 161B determines the absolute value of the difference between the previous RTT and the current RTT (RTT difference). ) Is calculated (step S55B).

Then, if the RTT difference calculated in step S55B is larger than the current section maximum fluctuation amount stored in the storage means 18 (18 ₂ ) (Yes in step S56B), the fluctuation amount calculating means 161B determines the current section maximum fluctuation. The amount is updated with the RTT difference calculated in step S55B (step S57B).

Then, the fluctuation amount calculating unit 161B stores the current RTT in the storage unit 18 (18 ₂ ) as the previous RTT (step S58B).
In step S54B, when the previous RTT is not stored in the storage means 18 (18 ₂ ) (No in step S54B), or in step S56B, the RTT difference is equal to or smaller than the current section maximum fluctuation amount (step S56B). No), the fluctuation amount calculating means 161B performs only the operation of step S58B.

  By configuring and operating the packet transmission device 1B as described above, the packet transmission device 1B can determine the predetermined time interval after the reference RTT fluctuation amount is updated by the time interval determination unit 162. Even in an environment where the transmission rate increases and packet transmission / reception occurs in bursts with respect to its own time resolution, or in an environment where the frequency of delay increases other than congestion is low, the reference RTT fluctuation amount is excessively low Can be prevented. That is, the packet transmission device 1B can prevent an excessive decrease in CWND and maintain high throughput.

«Third embodiment»
[Configuration of packet transmitter]
Next, the configuration of a packet transmission device 1C according to the third embodiment of the present invention will be described with reference to FIG.

The packet transmission device 1C performs packet transmission by delay-based congestion control, and has basically the same function as the packet transmission device 1 described in FIG.
That is, the packet transmission device 1C sequentially updates the reference RTT fluctuation amount at the timing when the RTT is measured, using the moving average of the RTT jitter as the reference RTT fluctuation amount.
However, the packet transmission device 1C does not update the reference RTT variation when the packet transmission time interval is longer than a predetermined time length.

This is due to the following reason.
In general, when the packet transmission time interval is long, it is highly possible that the state of the network through which two packets pass has changed. Here, when the RTT is considered to be composed of “queuing delay (variable) + processing / propagation delay (fixed) + delay unrelated to congestion such as retransmission (variable)”, the state of the network (for example, There is a possibility that the queuing delay will be different if the degree of congestion) is different. In this case, the amount of delay unrelated to congestion cannot be estimated.
Therefore, the packet transmission device 1C excludes such RTT from the sample when the packet transmission time interval is long.

  As shown in FIG. 10, the packet transmission apparatus 1C includes a data input means 10, a data buffer (temporary storage means) 11, a flow control means 12, a data transmission means 13, a delivery confirmation response reception means 14, and a congestion. A window control unit 15, a reference RTT variation estimation unit 16 </ b> C, an RTT variation analysis unit 17, and a storage unit 18 are provided.

  Since the configuration other than the reference RTT variation estimation unit 16C is the same as that of the packet transmission device 1 described in FIG. 1, the same reference numerals are given and the description thereof is omitted. Note that the storage unit 18 stores more content than the packet transmission device 1. Since the content is updated by the reference RTT fluctuation amount estimation means 16C, it will be described in the description of the reference RTT fluctuation amount estimation means 16C.

The reference RTT fluctuation amount estimation unit 16C smoothes the RTT fluctuation amount measured by the RTT measurement unit 141, and estimates the reference RTT fluctuation amount that serves as a reference for the RTT increase determination. Here, the reference RTT variation estimation unit 16C includes a variation calculation unit 161C and a transmission time determination unit 163.
The reference RTT fluctuation amount estimation unit 16C uses the transmission time of the packet whose delivery has been confirmed for the update determination of the reference RTT fluctuation amount. The transmission time is associated with the RTT, and the delivery confirmation response reception unit 14 ( It is obtained from the RTT measurement means 141) via the congestion window control means 15 (packet loss detection means 151) and the RTT fluctuation analysis means 17 (RTT increase determination means 172).

  Fluctuation amount calculation means (reference RTT fluctuation amount calculation means) 161C, during the establishment of the TCP connection, RTT (current RTT) measured by the delivery confirmation response (ACK) received this time and the delivery confirmation received immediately before By calculating the moving average of the difference (jitter) from the RTT (previous RTT) measured by the response (ACK), the smoothed fluctuation amount of the RTT is calculated and updated as the reference RTT fluctuation amount. . This function is the same as that of the fluctuation amount calculation means 161 described in FIG.

  However, the fluctuation amount calculation means 161C inquires of the transmission time determination means 163 whether or not the packet transmission time interval is longer than a predetermined time length, and only as a new reference RTT fluctuation amount when the transmission time interval is short. Update.

The transmission time determination unit 163 determines whether or not the transmission time interval of the packet whose delivery has been confirmed is longer than a predetermined time length.
Specifically, the transmission time determination unit 163 transmits the packet from the transmission time of the confirmed delivery packet that is sequentially notified in association with the RTT, using a determination expression (if statement) as shown in the following expression (4). It is determined whether the time interval is longer than a threshold (predetermined time length). Then, the fluctuation amount calculation unit 161C acquires the determination result, and if the transmission time interval is longer than the threshold value (then), the reference RTT fluctuation amount is not updated, and if the transmission time interval is less than the threshold value (otherwise), the reference RTT fluctuation amount Update.

if (transmission time of packet confirmed to be delivered this time−transmission time of packet confirmed to be delivered last time)> β
the the reference RTT fluctuation amount is not updated. the other The reference RTT fluctuation amount is updated. Equation (4)

Here, β is a threshold value for determining whether or not to update.
This threshold value β can be set to, for example, the minimum time that can be measured by a clock on an OS (Operating System) operating on the packet transmission device 1C. Further, for example, the time required to output a transmission packet from the packet transmission device 1C (transmission packet length / transmission interface speed) can be set as the threshold value β. Further, for example, a value obtained by dividing the time length obtained by adding the minimum RTT time and the reference RTT fluctuation amount by the congestion window size (CWND) can be used. Alternatively, the maximum value of these exemplified values may be set as the threshold value β.

The transmission time determination unit 163 sets the transmission time of the packet confirmed this time delivery (current transmission time) as the transmission time of the packet confirmed last time delivery (previous transmission time) in the storage unit 18 (18 ₂ ). Remember. The transmission time determination unit 163 outputs the determination result to the fluctuation amount calculation unit 161C.

  By configuring the packet transmission device 1C as described above, the packet transmission device 1C estimates the amount of RTT variation (reference RTT variation) that occurs regardless of congestion, and dynamically determines the delay increase. It can be carried out. At this time, if the packet transmission time interval is long, the packet transmitting apparatus 1C does not update the reference RTT fluctuation amount, thereby updating the difference between the two RTTs having different queuing delays to update the reference RTT fluctuation amount. It can be excluded from the judgment sample.

[Operation of packet transmission device]
Next, the operation of the packet transmission device 1C according to the third embodiment of the present invention will be described with reference to FIGS.
The operation of the packet transmission device 1C shown in FIG. 3 is the same as that of the packet transmission device 1 (see FIG. 1) except for step S5C, and thus the description thereof is omitted here. In other words, the operation of the packet transmission device 1C is merely that step S5 of the packet transmission device 1 is replaced with step S5C.
Here, the operation of step S5C will be described with reference to FIG.
Note that steps S51C, S54C, S55C, and S57C shown in FIG. 11 are the same as the operations of steps S51, S52, S53, and S54 of the packet transmission device 1 described with reference to FIG. Omitted.

In the operation of the packet transmission device 1C, the operations of steps S52C, S53C, and S56C are newly added to the operation of the packet transmission device 1.
That is, when the previous RTT is stored in the storage unit 18 (18 ₂ ) (Yes in step S51C), the packet transmission device 1C uses the variation calculation unit 161C of the reference RTT variation estimation unit 16C to store the storage unit 18. It is determined whether (18 ₂ ) stores the transmission time (previous transmission time) of the packet confirmed to be delivered last time (step S52C).

Here, when the previous transmission time is stored in the storage unit 18 (18 ₂ ) (Yes in step S52C), the packet transmission device 1C transmits the transmission time of the packet confirmed to be delivered this time by the transmission time determination unit 163. It is determined whether or not the difference between (current transmission time) and the transmission time of the packet confirmed for the previous delivery (previous transmission time) is larger than the threshold β (step S53C).

If the difference between the current transmission time and the previous transmission time is equal to or less than the threshold β (No in step S53C), the packet transmission device 1C causes the fluctuation amount calculation unit 161C to perform the operations of steps S54C and S55C, that is, The reference RTT fluctuation amount is updated.
On the other hand, the storage means 18 (18 ₂₎ when the last RTT is not stored (No at step S51C), if the previous transmission time to the storage means 18 (18 ₂₎ is not stored (No at Step S52c) Alternatively, if the difference between the current transmission time and the previous transmission time is greater than the threshold (Yes in step S53C), the packet transmission device 1C advances the operation to step S56C.

Then, the packet transmission device 1C stores the current transmission time in the storage unit 18 (18 ₂ ) as the previous transmission time by the fluctuation amount calculation unit 161C (step S56C). Further, the packet transmitting apparatus 1C stores the current RTT in the storage unit 18 (18 ₂ ) as the previous RTT by the fluctuation amount calculating unit 161C (step S57C).

By configuring and operating the packet transmission device 1C as described above, the packet transmission device 1C has the following effects in addition to the effects of the packet transmission device 1.
That is, the packet transmitting apparatus 1C can determine whether or not the packet transmission time interval is longer than a predetermined time length by the transmission time determination unit 163, and the packet transmission time by the reference RTT fluctuation amount calculation unit. Since the RTT fluctuation amount when the interval is long and the queuing delay occurring in each of the two packets is changed is not used for estimating the reference RTT fluctuation amount, the reference RTT fluctuation amount can be estimated more accurately. Thus, the packet transmission device 1C can more appropriately control CWND, and can maintain an optimum throughput according to the network environment.

<< Fourth Embodiment >>
[Configuration of packet transmitter]
Next, the configuration of a packet transmission device 1D according to the fourth embodiment of the present invention will be described with reference to FIG.

The packet transmission device 1D transmits packets by delay-based congestion control, and has a function that combines the packet transmission device 1B described in FIG. 7 and the packet transmission device 1C described in FIG.
That is, the packet transmission device 1D uses the moving average of the maximum value of the RTT jitter in a predetermined time interval as the reference RTT variation amount, and updates the reference RTT variation amount in the time interval, but the packet transmission time interval is predetermined. When it is longer than the time length, the maximum value of the RTT jitter is not updated.

  As shown in FIG. 12, the packet transmission device 1C includes a data input unit 10, a data buffer (temporary storage unit) 11, a flow control unit 12, a data transmission unit 13, a delivery confirmation response reception unit 14, a congestion A window control unit 15, a reference RTT variation estimation unit 16 </ b> D, an RTT variation analysis unit 17, and a storage unit 18 are provided.

  The configuration other than the reference RTT variation estimation means 16D is the same as that of the packet transmission device 1 (FIG. 1), the packet transmission device 1B (FIG. 7), and the packet transmission device 1C (FIG. 10). The description is omitted.

The reference RTT fluctuation amount estimation means 16D smoothes the RTT fluctuation amount measured by the RTT measurement means 141, and estimates a reference RTT fluctuation amount that serves as a reference for RTT increase determination. Here, the reference RTT fluctuation amount estimation unit 16D includes a fluctuation amount calculation unit 161D, a time interval determination unit 162, and a transmission time determination unit 163.
The time interval determination unit 162 is the same as the packet transmission device 1B (FIG. 7), and the transmission time determination unit 163 is the same as that of the packet transmission device 1C (FIG. 10).

The fluctuation amount calculating means (reference RTT fluctuation amount calculating means) 161D has a function of combining the fluctuation amount calculating means 161B (FIG. 7) and the fluctuation amount calculating means 161C (FIG. 11).
That is, the fluctuation amount calculating unit 161D uses the maximum value of the RTT fluctuation amount measured when the packet transmission time interval is equal to or shorter than the predetermined time length during the TCP connection establishment. Update the fluctuation amount.

Specifically, the fluctuation amount calculation means 161D inquires of the time interval determination means 162 whether or not a predetermined time has elapsed, and updates the reference RTT fluctuation amount when the predetermined time has elapsed. Further, the fluctuation amount calculation means 161D inquires of the transmission time determination means 163 whether or not the packet transmission time interval is longer than a predetermined time length, and compares it with the current interval maximum fluctuation amount only when the transmission interval is short. When the RTT difference is larger than the current section maximum fluctuation amount, the update is performed.
Thus, by configuring the packet transmission device 1D, the packet transmission device 1D has both the effects of the packet transmission device 1B (FIG. 7) and the effects of the packet transmission device 1C (FIG. 10). .

[Operation of packet transmission device]
Next, the operation of the packet transmission device 1D according to the fourth embodiment of the present invention will be described with reference to FIGS.
The operation of the packet transmission device 1D shown in FIG. 3 is the same as that of the packet transmission device 1 (see FIG. 1) except for step S5D. That is, the operation of the packet transmission device 1D is merely the step S5 of the packet transmission device 1 replaced with step S5D.

The operation of step S5D of the packet transmission device 1D shown in FIG. 13 is basically the same as the operation of step S5B of the packet transmission device 1B (FIG. 7) described in FIG. 9 and the packet transmission device described in FIG. This is a combination of the operation of step S5C of 1C (FIG. 10).
Therefore, the description of FIG. 13 is omitted here by using the same step numbers for the same steps as the operations described in FIG. 9 and FIG.

As described above, the packet transmission device 1D has an environment in which the transmission rate is large and packet transmission / reception occurs in bursts with respect to its own time resolution, or an environment in which the frequency of delay increases other than congestion is low. However, excessive reduction of CWND can be prevented and high throughput can be maintained.
Furthermore, since the packet transmission device 1D does not use the RTT fluctuation amount when the packet transmission time interval is long and the queuing delay occurring in each of the two packets changes, for estimation of the reference RTT fluctuation amount, it is more accurate. The reference RTT fluctuation amount can be estimated. Thereby, the packet transmission device 1D can control the CWND more appropriately, and can maintain an optimum throughput according to the network environment.

  The configuration and operation of the packet transmission device according to the first to fourth embodiments have been described above. These packet transmission devices operate the computer with a program (packet transmission program) for causing the computer to function as each of the above-described means. be able to.

<< embodiments of reference examples >>
[Packet receiving device]
Finally, with reference to FIG. 14, a general packet receiver 2 that receives packet data transmitted by the packet transmitter 1 (1B, 1C, 1D) will be briefly described.
The packet receiving device 2 includes a data receiving unit 20, a data buffer (temporary storage unit) 21, a data output unit 22, a flow control unit 23, and a delivery confirmation response transmission unit 24.

  The data receiving unit 20 receives packet data transmitted from the packet transmission device 1 via a communication line. The data receiving means 20 sequentially writes the received packets in the data buffer 21 and notifies the flow control means 23 that the packets have been received.

  The data buffer (temporary storage means) 21 temporarily stores packet data received via the data receiving means 20, and is a storage medium such as a semiconductor memory. The packet data stored in the data buffer 21 is read by the data output means 22, and the data buffer 21 functions as a FIFO.

  The data output means 22 sequentially reads out the packets stored in the data buffer 21 and outputs them to the outside. The data output means 22 notifies the flow control means 23 that the packet has been read.

The flow control unit 23 performs flow control with the packet transmission device 1.
This flow control means 23 manages the maximum number of packets (reception window size) determined in advance by the capacity of the data buffer 21, and performs flow control so that the number of packets stored in the data buffer 21 does not exceed the reception window size. I do. Note that the number of packets stored in the data buffer 21 can be grasped by the number of packets received by the data receiving unit 20 and the number of packets output by the data output unit 22.
Here, for the packet received by the data receiving unit 20, the flow control unit 23 transmits a delivery confirmation response (ACK) including information indicating that the packet has been received and information specifying the next packet to be received. Output to means 24.

The delivery confirmation response transmission unit 24 transmits the delivery confirmation response (ACK) output from the flow control unit 23 to the packet transmission device 1 via the communication line.
As described above, the packet transmission apparatus 1 (1B, 1C, 1D) transmits a packet to the general packet reception apparatus 2 even if the packet transmission apparatus 1 (1B, 1C, 1D) has a CWND due to a transmission delay unrelated to congestion. The packet can be transmitted while maintaining a throughput suitable for the network environment.

1 Packet transmission device 10 Data input means 11 Data buffer (temporary storage means)
DESCRIPTION OF SYMBOLS 12 Flow control means 13 Data transmission means 131 Transmission time writing means 14 Delivery confirmation response reception means 141 RTT measurement means 15 Congestion window control means 151 Packet loss detection means 152 Loss generation CWND processing means 153 RTT fluctuation CWND processing means 16 Reference RTT fluctuation amount estimation means 161 Fluctuation amount calculation means (reference RTT fluctuation amount calculation means)
162 Time interval determination means 163 Transmission time determination means 17 RTT fluctuation analysis means 171 Minimum RTT update means 172 RTT increase determination means 18 Storage means

Claims (5)

In a packet transmission device that controls a congestion window size indicating the number of packets that can be transmitted at one time until a delivery confirmation response is received, according to the transmission delay of the packet,
RTT measuring means for measuring RTT which is a round trip delay time of the packet from the transmission time of the packet corresponding to the received delivery confirmation response and the reception time of the delivery confirmation response;
A minimum RTT update means for updating the minimum RTT of the RTT sequentially measured by the RTT measurement means and storing it in the storage means;
A reference RTT fluctuation amount calculating means for calculating a fluctuation amount obtained by smoothing the measured RTT fluctuation amount and sequentially updating the fluctuation amount as a reference RTT fluctuation amount;
When the measured RTT is longer than the time length obtained by adding the minimum RTT and the reference RTT fluctuation amount, it is determined that the RTT has increased. When the measured RTT is less than the time length, it is determined that the RTT has not increased. RTT increase determination means for
When the RTT increase determining means determines that the RTT has increased, the congestion window size is decreased, and when it is determined that the RTT has not increased, the congestion window size is increased. Congestion window control means for controlling
A packet transmission device comprising: After updating the reference RTT fluctuation amount, comprising a time interval determination means for determining whether or not a predetermined time interval has elapsed,
The reference RTT fluctuation amount calculation means stores the maximum value of the fluctuation amount in the time interval, and smoothes the reference RTT fluctuation amount and the maximum value of the fluctuation amount after the time interval has elapsed, thereby obtaining a new reference The packet transmission device according to claim 1, wherein the packet transmission device is updated as an RTT fluctuation amount. A transmission time determination means for determining whether or not the transmission time interval of the packet whose delivery has been confirmed is longer than a predetermined time length;
The reference RTT fluctuation amount calculating means does not update the reference RTT fluctuation amount when the transmission time determining means determines that the transmission time interval is longer than a predetermined time length, and the transmission time interval is predetermined. 2. The packet transmission device according to claim 1, wherein the reference RTT fluctuation amount is updated when it is determined that the time length is equal to or less than a predetermined time length. Time interval determination means for determining whether or not a predetermined time interval has elapsed after calculating the reference RTT fluctuation amount;
Transmission time determination means for determining whether or not the transmission time interval of the packet confirmed for delivery is longer than a predetermined time length,
The reference RTT fluctuation amount calculating means stores the maximum value of the fluctuation amount only when the transmission time interval is shorter than a predetermined time length in the time interval, and after the time interval elapses, The packet transmission apparatus according to claim 1, wherein the maximum value of the fluctuation amount is smoothed and updated as a new reference RTT fluctuation amount. In order to control the congestion window size indicating the number of packets that can be transmitted at one time until a delivery confirmation response is received according to the transmission delay of the packet, the computer of the packet transmission device is
Data input means for inputting packet data and storing it in a data buffer;
Data transmission means for reading out the packet data stored in the data buffer and transmitting the data via a communication line;
A delivery response confirmation receiving means for receiving the delivery confirmation response and measuring an RTT that is a round trip delay time of the packet from a transmission time of the packet corresponding to the delivery confirmation response and a reception time of the delivery confirmation response;
Flow control means for controlling the data amount of the packet to be transmitted based on the congestion window size;
A minimum RTT updating means for updating a minimum RTT of RTT sequentially measured by the delivery response confirmation receiving means and storing the updated RTT in a storage means;
A reference RTT fluctuation amount calculating means for calculating a fluctuation amount obtained by smoothing the measured RTT fluctuation amount and sequentially updating it as a reference RTT fluctuation amount;
When the measured RTT is longer than the time length obtained by adding the minimum RTT and the reference RTT fluctuation amount, it is determined that the RTT has increased. When the measured RTT is less than the time length, it is determined that the RTT has not increased. RTT increase determination means for
When the RTT increase determining means determines that the RTT has increased, the congestion window size is decreased, and when it is determined that the RTT has not increased, the congestion window size is increased. Congestion window control means for controlling
Packet transmission program to function as

Images