JP4435817B2 - Communication terminal, communication control method, and communication control program - Google Patents

Description

  The present invention relates to a communication terminal, a communication control method, and a communication control program, and is particularly suitable for application to a congestion control method in TCP (Transmission Control Protocol).

Currently, in TCP widely used in the Internet, congestion control is performed using a congestion window (CWND) when transmitting a segment in order to avoid network congestion.
Generally, in the congestion control algorithm of TCP, a congestion window (CWND) is set as follows.

1. When ACK (Acknowledgement) is received 1.1. At Slow Start, CWND (n + 1) = CWND (n) + a × MSS is set.
1.2. Cpndition Avoidance CWND (n + 1) = CWND (n) + a / CWND (n).
2. When packet loss occurs CWND (n + 1) = (1-b) × CWND (n).

However, MSS (Maximum Segment Size) is the maximum segment size that can be transmitted by the transmitting side. CWND (CONGESTION WINDOW) is a TCP state variable that limits the TCP transmittable size.
In normal TCP, a = 1 and b = 0.5 are used.
In this TCP congestion control algorithm, CWND is decreased and triggered by segment loss, and congestion control is performed. Therefore, CWND continues to increase unless segment loss occurs. For this reason, unless a segment loss occurs, CWND increases, and an increase in the utilization rate of the reception buffer of the relay node causes an increase in RTT (Round Trip Time).

For example, in Non-Patent Document 1, taking into account the slow start on the transmitting side, the receiving side informs the transmitting side twice the number of bytes (rcv_bytes) read into the application during 1 RTT, and the transmitting side transmits the segment. A method for preventing transmission of an extra segment by limiting the amount to rcv_bytes × 2 is disclosed.
FIG. 7 is a diagram illustrating a conventional RTT measurement method. Assuming that each segment has 10 bytes of data, the first sequence number of each segment is represented as seq in the figure.

In FIG. 7, the TCP receiving side 32 uses the advertisement window (rcv_wnd) to
ck (acknowledge number) + rcv_wnd seq (sequence
nce number) -1 from the TCP transmission side 31 can be set to 1 RTT.
For example, when ack = 210 and rcv_wnd = 60, the TCP reception side 32 can set the time from seq = 210 to seq = 269 (ack + rcv_wnd−1) from the TCP transmission side 31 to 1 RTT.
Dynamic Right-Sizing in TCP Mike Fish and W. Feng 2nd Annual Los Alamos Computer Science Institute Symposium (LACSI2001), Snta Fe, New Mexico, October 2001

However, in the method disclosed in Non-Patent Document 1, RTT measurement and rcv_byte are performed.
Since the calculation of s is performed on the TCP receiving side 32, there is a problem in that the measurement accuracy of RTT is deteriorated and excessive segments are transmitted.
FIG. 8 is a diagram showing a problem of a conventional RTT measurement method.
In FIG. 8, when CWND is smaller than rcv_wnd, RTT is measured longer than usual, and rcv_bytes increases, so that an excessive segment is transmitted. For example, when ack = 210, rcv_wnd = 60, and CWND = 40, seq = 2
The interval between the time when 30 is transmitted and the time when seq = 240 is transmitted increases. For this reason, in the TCP receiving side 32, since the time from receiving seq = 210 to seq = 269 is set to 1 RTT, RTT is measured longer than usual.

Further, in the method disclosed in Non-Patent Document 1, twice the number of rcv_bytes is transmitted to the transmission side as an advertisement window, and the maximum value of the measured rcv_bytes is used. Compared to the ideal case of “the number of bytes received during the period”, an excessive number of segments are transmitted.
Accordingly, an object of the present invention is to provide a communication terminal, a communication control method, and a communication control program capable of effectively suppressing transmission of an excessive segment to a network.

In order to solve the above-described problem, according to the communication terminal according to claim 1, the received byte number calculating unit that calculates the number of bytes of the segment that has reached the receiving side within a certain period on the transmitting side, and the received byte number based on the number of bytes of segments calculated by calculation unit, and a transmission segment control unit for controlling the target is the number of transmission segment, the transmission segment control unit is space is a predetermined set value, the communication If the cwnd, which is a variable that limits the data size that can be transmitted on the protocol, and the minimum value of rcv wnd, which is the data size that can be received at one time, are below the minimum value, a segment is transmitted according to space, When the target is large, the space is set to the maximum segment size that can be transmitted by the transmission side every time an ACK is received. Set the value obtained by doubling the MSS that is equal to the value added to the space, and if the space is greater than the target, set the space to the same value as the target, or receive the ACK for the space Each time, the MSS is subtracted from the space, and when the number of ACKed bytes can be calculated, if the target is larger than the space, the space is set to the space every time an ACK is received. If the number of ACKed bytes is set, and the space is larger than the target, the space is set to the same value as the target, or the space is set from the space every time an ACK is received. by setting the ACK value obtained by subtracting the half of the number of bytes And features.
According to the communication terminal of claim 2, the minimum time measuring unit that measures the minimum value of RTT, and the segment that has reached the receiving side within the period of the minimum value of RTT measured by the minimum time measuring unit A received byte number calculating unit that calculates the number of bytes on the transmission side, a transmission segment control unit that controls a target that is the number of transmission segments based on the number of bytes of the segment calculated by the received byte number calculating unit, The transmission segment control unit includes a space having a predetermined setting value of cwnd, which is a variable that limits a data size that can be transmitted on a communication protocol, and rcv wnd, which is a data size that can be received at a time by the receiving side. If below the minimum value, send the segment according to space, and if the target is greater than the space, the sp For each ACK received, ace is set to a value obtained by adding MSS, which is the maximum segment size that can be transmitted by the transmitting side, to twice the space, and when the space is larger than the target, the space is set to the target Or the space is set to a value obtained by subtracting the MSS from the space every time an ACK is received, and the number of ACKed bytes can be calculated, the target is more than the space. If it is larger, the space is set to a value obtained by adding the number of bytes ACKed to the space every time an ACK is received. If the space is larger than the target, the space is set to the same value as the target. Alternatively, the space is set to the spa every time an ACK is received. and setting a value obtained by subtracting the half of the number of bytes ACK e. From

Further, according to the communication terminal of claim 3, the minimum time measurement unit is configured such that when the segment is not transmitted for a predetermined time or more, or when the congestion window is smaller than the initial window size, or for a predetermined measurement time. If the RTT below the value specified by the minimum value of the RTT is not measured over the period, the minimum value of the RTT is reset. According to the communication terminal of claim 4 , the congestion window or the slow start threshold value at the time of ACK reception or packet loss occurrence can be set without considering the number of bytes of the segment calculated by the received byte number calculation unit. It further comprises a congestion window calculation unit for calculating, wherein the transmission segment control unit performs segment transmission control based on a congestion window or a slow start threshold calculated by the congestion window calculation unit .

According to the communication control method of claim 5, the step of calculating the number of bytes of the segment that has reached the receiving side within a certain period on the transmitting side, and the number of bytes of the segment calculated on the transmitting side are transmitted. And controlling based on the maximum segment size that can be transmitted or the number of bytes that have been ACKed, and the step of controlling the transmission of a predetermined set value based on a communication protocol. When the variable is smaller than the minimum value of cwnd, which is a variable that limits the possible data size, and rcv wnd, which is the data size that can be received at one time, the segment is transmitted according to space, and the target is larger than the space , The maximum segment size that can be transmitted by the transmission side every time an ACK is received The value obtained by doubling the MSS is set to the value added to the space. If the space is larger than the target, the space is set to the same value as the target, or the space is set for each ACK received. In addition, if the MSS is subtracted from the space and the number of ACKed bytes can be calculated, and the target is larger than the space, the space is ACKed to the space every time an ACK is received. If the space is larger than the target, the space is set to the same value as the target, or the space is acknowledged from the space every time an ACK is received. Japanese to be set to the value obtained by subtracting the half of the number of bytes To.

According to the communication control program of claim 6, the step of calculating the number of bytes of the segment that has reached the receiving side within a certain period on the transmitting side, and the number of bytes of the segment calculated on the transmitting side are transmitted. And controlling based on the maximum segment size that can be transmitted or the number of bytes that have been ACKed, and the step of controlling the transmission of a predetermined set value based on a communication protocol. When the variable is smaller than the minimum value of cwnd, which is a variable that limits the possible data size, and rcv wnd, which is the data size that can be received at one time, the segment is transmitted according to space, and the target is larger than the space , The maximum segment that the transmitting side can transmit for each ACK received A value obtained by doubling the size MSS is set to the value added to the space, and if the space is larger than the target, the space is set to the same value as the target, or the space is received by ACK. Each time, the MSS is subtracted from the space, and when the number of ACKed bytes can be calculated, if the target is larger than the space, the space is set to the space every time an ACK is received. If the number of ACKed bytes is set, and the space is larger than the target, the space is set to the same value as the target, or the space is set from the space every time an ACK is received. Set to a value obtained by subtracting 1/2 of the number of bytes that were acknowledged. And characterized by causing a computer to execute the.

  As described above, according to the present invention, by calculating the number of bytes of the segment that has reached the receiving side on the transmitting side, the number of bytes of the segment that has reached the receiving side can be transmitted while considering the circumstances on the transmitting side. Therefore, it is possible to effectively suppress transmission of an excessive segment to the network.

Hereinafter, a communication terminal according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of a transmission terminal according to the first embodiment of the present invention.
In FIG. 1, the transmission terminal 11 is measured by a segment receiving unit 12 that receives a segment sent via a network such as the Internet, a minimum time measuring unit 13 that measures a minimum value of RTT, and a minimum time measuring unit 13. Based on the number of bytes of the received segment calculated by the received byte number calculating unit 14 and the received byte number calculating unit 14 for calculating the number of bytes of the segment that has reached the receiving side within the period of the minimum value of the RTT The target calculation unit 15 that calculates a target used for segment transmission control, the transmission segment control unit 16 that performs segment transmission control based on the target calculated by the target calculation unit 15, and a network such as the Internet A segment transmission unit 17 for transmitting a segment is provided.

Then, the minimum time measuring unit 13 can measure the RTT in the same manner as the method performed by TCP. That is, when the Timestamp Option is available, the minimum time measurement unit 13 can set (current time) − (Timestamp Echo) as an RTT when receiving an ACK (Acknowledgement).
On the other hand, when the Timestamp Option cannot be used, the minimum time measurement unit 13 can set (current time)-(time at which the acked segment is transmitted) as the RTT when ACK is received.

Then, the minimum time measuring unit 13 continuously performs RTT measurement while the segment is being transmitted, and updates the RTT minimum value (rtt_min) every time the RTT minimum value (rtt_min) is measured. , The minimum value of RTT (rtt_min) can be used to calculate the number of bytes (rcv_bytes) of the received segment.
In consideration of the case where the RTT changes greatly due to route switching or movement of the receiving terminal, the minimum value (rtt_min) of the RTT can be reset in the following cases.

(1) When segment transmission is not performed for a time longer than 1 RTT.
In this case, as 1 RTT, in addition to the minimum value of RTT (rtt_min), TCP
RTO (Retransmission Timeout) calculated from RTT can be used.
(2) When CWND falls below the initial window size.
(3) When the following RTT is not measured over several RTTs: rtt_min × (target / rcv_bytes + 1) (target will be described later). Here, as the measurement period, 1 RTT for measurement of rcv_bytes, and 1 RTT for controlling the number of transmission segments based on the measured value are set to 2 RTT or more.

Next, the received byte count calculation unit 14 causes the minimum time measurement unit 13 to use the minimum value of RTT (rtt_
min)), the ACK received within the time of the minimum value of RTT (rtt_min)
Alternatively, the number of bytes (rcv_bytes) of the received segment is calculated from information of SACK (Selective Acknowledgment).
FIG. 2 is a block diagram illustrating a measurement point of the number of bytes of a reception segment according to an embodiment of the present invention in comparison with a conventional example.

In FIG. 2, a segment 24 is sent from the TCP transmission side 21 to the TCP reception side 22 via the network 23. The segment 24 received by the TCP receiving side 22 is held in the reception buffer 26 and read into the application 25 via the reception buffer 26.
Here, in the method of FIG. 5, the number of bytes of the segment 24 at the time point P2 read by the application 25 is used for congestion control. For this reason, when the segment is retransmitted, the number of segments at the time point P2 read into the application 25 is underestimated / overestimated, and accurate control cannot be performed.

On the other hand, in this embodiment, by using the number of bytes of the segment 24 at the time point P1 received for congestion control, it is possible to effectively suppress the transmission of excessive segments to the network.
FIG. 3 is a diagram illustrating a method for measuring the number of bytes of a received segment according to an embodiment of the present invention.
In FIG. 3, the TCP transmission side 21 determines the number of bytes (rcv__) of the received segment from the ACK information received from the TCP reception side 22 within the time of the minimum RTT value (rtt_min).
bytes) is calculated.

Specifically, the number of bytes (rcv_bytes) of the received segment can be measured as follows.
-When SACK Option is supported.
When the measurement is started from the maximum sequence number (rcv_ack) notified to the receiving terminal by the ACK received within the time of the minimum value of RTT (rtt_min), the AC
A value obtained by subtracting the number of sequence numbers (drs_snd_una) of the first segment not receiving K can be used.

In addition, during segment retransmission, in order to consider the total number of bytes of segments retransmitted within the time of the minimum value of RTT (rtt_min), the total number of bytes of segments notified by the SACK Option of the received ACK ( sack_end)
A value obtained by subtracting the total number of bytes (sack_start) of the segment notified by the SACK Option when the measurement is started is added to the first value.
That is, rcv_bytes = rcv_ack−drs_snd_una + (sack_
end-sack_start).

If no segment loss occurs, both sack_end and sack_start are 0, so rcv_bytes = rcv_ack−drs_snd_una. Further, when the segment loss is resolved within the time of the minimum value of RTT (rtt_min), the suck_end becomes 0 and only the suck_start is valid.
-SACK Option is not supported.
In this case, the number of bytes (rcv_bytes) of the received segment can be calculated in consideration of the number of duplicate ACKs (rcv_ack is equal to or less than the smallest segment (snd_una) for which ACK has not been received).

That is, the sequence of the first segment that has not received ACK when measurement is started from the sequence number (rcv_ack) notified to the receiving terminal by the last received ACK within the time of the minimum value of RTT (rtt_min) A value obtained by subtracting the number (drs_snd_una) can be used.
Also, during segment retransmission, in order to consider the total number of bytes of the retransmitted segment, the number of duplicate ACKs received within the time of the minimum value of RTT (rtt_min) × MSS
From (dack_end), the number of duplicate ACKs received at the start of measurement × MSS (da
The value obtained by subtracting (ck_start) is added to the first value.

That is, rcv_bytes = rcv_ack−drs_snd_una + (dack_
end-dack_start).
When the number of received segment bytes (rcv_bytes) increases from the previously calculated number of received segment bytes (rcv_bytes), the value may be updated every time an ACK is received.

Further, when no segment loss occurs, both dack_end and dack_start are 0.
Here, when a queuing delay also occurs for the ACK path, the number of received segment bytes (rcv_bytes) may not be accurately measured depending on the situation.
Therefore, by using the ACK transmission time, the influence of the ACK path queuing delay is eliminated, and the number of bytes (rcv_bytes) of the received segment can be accurately measured.

FIG. 4 is a diagram showing another example of a method for measuring the number of bytes of a received segment according to an embodiment of the present invention.
In FIG. 4, when the same Timestamp Option as that on the TCP transmission side 21 side is added to the ACK, by referring to the transmission time of the ACK transmitted within the time of the minimum value (rtt_min) of RTT, Number of bytes (rcv_byte
es) can be measured. However, when the granularity of Timestamp Option used on the receiving side and the transmitting side is different, it is necessary to correct the ACK transmission time on the transmitting side.

FIG. 5 is a diagram illustrating an example in which the transmission time of the ACK is corrected on the transmission side.
In FIG. 5, ts represents the segment transmission time, and ts_echo represents Timestamp Echo. On the transmission side, when ACK is received, measurement is performed for a certain period, and the increase in ts and ts_echo of ACK received during that period is calculated and used for correction. In FIG. 5, the increase amount of ts_echo is 60, whereas the increase amount of ts is 6. Therefore, rcv_bytes is the time until the time when 1/10 of rtt_min is added to the transmission time of ACK when transmission is started. Calculated by ACK.

Next, the target calculation unit 15 in FIG. 1 calculates a target based on the number of bytes of the received segment calculated by the received byte number calculation unit 14.
Here, as the target calculation method, the following six methods can be considered.
(1) The number of received segment bytes (rcv_by) measured by the received byte number calculating unit 14
tes) using the maximum value × 2.
(2) Number of received segment bytes measured by the received byte number calculation unit 14 (rcv_by)
tes) × 2 method.
(3) A method of using the average of the number of bytes (rcv_bytes) of the last two received segments measured by the received byte count calculator 14.
(4) Number of bytes of the received segment measured by the received byte number calculation unit 14 (rcv_by
a method using twice the weighted average of tes).

For example, target = (average number of received segment bytes (rcv_bytes) measured so far (av_rcv_bytes) × 7/8 + (rcv_bytes) × 1/8) × 2.
(5) A method using an arbitrary constant α.
For example, rcv_bytes + α × MSS ≧ cwnd
If cwnd <Slowstart Threshold (ssthresh), then target = rcv_bytes × 2.

Otherwise,
target = rcv_bytes + α × MSS.
(6) The number of received segment bytes (rcv_by) measured by the received byte number calculation unit 14
tes) using a weighted average and a weighted average deviation.
For example, the weighted average of the number of bytes in the received segment (rcv_bytes) (avg_rcv_bytes) = (avg_rcv_bytes) × 7/8 + (rcv_bytes) × 1/8, and the weighted average deviation of the number of bytes in the received segment (rcv_bytes) _var_rcv_ = (Var_rcv_bytes) × 7/8 + | rcv_bytes−avg_rcv_bytes | × 1/8, and using the obtained var_rcv_bytes, target = avg_rcv_bytes + var_rcv_bytes can be set to 4 × 4.

The constant α can be arbitrarily set according to the network conditions. At least, the constant α is set to be equal to or greater than the value of cwnd that increases to the maximum during 1 RTT when cwnd ≧ ssthresh (1MSS for TCP). can do.
Further, an arbitrary constant β can be used so that the target does not become a predetermined value or less, and β × MSS can be used as the lower limit value of the target. The constant β can be arbitrarily set, but for example, an initial window size can be used.

  Next, the transmission segment control unit 16 in FIG. 1 performs segment transmission control based on the target calculated by the target calculation unit 15. Note that the transmission segment control unit 16 can limit the actual segment transmission by using the value “space” in order to prevent the segment from being transmitted in bursts when the target increases rapidly. .

Here, the space can be set as follows.
If space <target.
It is assumed that space = space + 2MSS every time an ACK is received.
In the case of space> target, the following two methods are conceivable.
(1) A method of setting space = target.
(2) A method of setting space = space-MSS every time an ACK is received.

If the number of ACKed bytes can be calculated,
If space <target.
It is assumed that every time ACK is received, space = space + ACK number of bytes.
In the case of space> target, the following two methods are conceivable.
(1) A method of setting space = target.
(2) A method in which space = space−number of bytes ACKed / 2 for each ACK received.
If the ACK is a duplicate ACK, it is treated as 1 MSS. If the number of bytes ACKed when the space is reduced is less than 1 MSS, the space is decreased until the number of ACKed bytes is 1 MSS or more. I won't let you.

Next, the segment transmission unit 17 in FIG. 1 transmits the segment whose transmission control is performed by the transmission segment control unit 16. Specifically, the segment can be transmitted according to the minimum values of space, cwnd, and rcv_wnd, and the segment can be transmitted according to the space when the value of space is lower than the minimum values of cwnd and rcv_wnd.
This makes it possible to suppress segment transmission based on the number of received segment bytes (rcv_bytes) calculated on the transmission side, and effectively suppress excessive segment transmission to the network. Become.

In addition, in order not to disturb the communication speed when cwnd is small, when the number of bytes of the received segment (rcv_bytes) is equal to or less than cwnd + α (constant) at the time of measuring the number of bytes of the received segment (rcv_bytes), space It is also possible not to perform control using.
Furthermore, in order to maintain fairness with TCP that is not controlled by space at the time of retransmission, when ACK is received or packet loss occurs using the value of CWND obtained by not performing control using space CWND and SSTHRESH may be set.

FIG. 6 is a block diagram showing a schematic configuration of a transmission terminal according to the second embodiment of the present invention.
6, in addition to the configuration of FIG. 1, the transmission terminal 111 is provided with a congestion window calculation unit 18 for calculating CWND and SSTHRESH when an ACK is received or when a packet loss occurs.
Here, the congestion window calculation unit 18 can calculate CWND and SSTHRESH when ACK is received or when packet loss occurs as follows.

That is, when packet loss occurs, SSTHRESH and CWND are determined using WND (Window) as follows.
WND = Max (CWND, CWND_est)
Here, CWND_est is a value of CWND that would be obtained when control using space is not performed.

2.1. FF (Fast Retransmit & Fast Recovery: Fast Retransmission and Fast Recovery) SSTHRESH = (1-b) × WND
Set so that CWND = SSTHRESH.
2.2. When RTO (Retransmission Timeout) occurs SSTHRESH = (1-b) × WND
CWND = 1 × MSS is set.

However, if the number of received segment bytes (rcv_bytes) is less than or equal to cwnd + α (constant) at the time of measuring the number of received segment bytes (rcv_bytes), it is determined that there is no packet loss due to congestion and CWND and SSTHRESH are not decreased. You can also.
MSS (Maximum Segment Size) is the maximum segment size that can be transmitted by the transmission side. CWND (CONGESTION WINDOW) is a TCP state variable that limits the TCP transmittable size. SSTHRESH (SLOWSTART THRESHOLD) is a slow start threshold value.
In normal TCP, a = 1 and b = 0.5 are used.

  When control using space is not performed, the congestion window calculation unit 18 calculates CWND and SSTHRESH when ACK is received or when packet loss occurs according to the above formula. Then, the transmission segment control unit 16 transmits the segment via the segment transmission unit 17 while performing transmission control of the segment based on the CWND and SSTHRESH calculated by the congestion window calculation unit 18.

Note that the minimum time measuring unit 13, the received byte number calculating unit 14, and the target calculating unit 15 can be realized by causing a computer to execute a program in which an instruction for performing processing performed by these means is executed.
If this program is stored in a storage medium such as a CD-ROM, the minimum time measuring unit 13, the number of received bytes is installed by installing the storage medium in the computer of the transmission terminal 11 and installing the program in the computer. The processing performed in the calculation unit 14 and the target calculation unit 15 can be realized. Moreover, this program can be easily spread by downloading this program via a network.

  In the method of FIG. 7, rcv_bytes is determined in consideration of the status of the network 23 and the TCP receiver 22 in FIG. 2, whereas in this embodiment, rcv_bytes is determined in consideration of the status of the network 23. Is done. However, when the speed at which the application 25 reads data is extremely slow compared to the data transmission speed of the network 23, it is preferable to consider the number of bytes of the segment staying on the TCP receiving side 22.

Here, when determining the rcv_bytes, the number of bytes (buf_bytes) of the segment staying in the reception buffer 26 can be indirectly estimated from the ACK as a method of considering the state of the TCP reception side 22.
Specifically, buf_bytes = (maximum rcv_wnd received by ACK) − (current rcv_wnd).

By calculating buf_bytes when calculating rcv_bytes and subtracting buf_bytes from the target, it is possible to indirectly consider the number of bytes of the segment staying in the reception buffer 26 of the TCP reception side 22. However, if the segment is being retransmitted, the retention of the segment in the reception buffer 26 is likely to be caused by the segment waiting for the order, so that the target can be calculated without considering buf_bytes. preferable.
In the above-described embodiment, the method of performing segment transmission control based on the target calculated by the target calculation unit 15 has been described. However, the target is calculated on the reception side, and the target calculated on the reception side is calculated. The segment transmission control may be performed by transmitting to the transmission side.

It is a block diagram which shows schematic structure of the transmission terminal which concerns on 1st Embodiment of this invention. It is a block diagram which shows the measurement point of the byte number of the receiving segment which concerns on one Embodiment of this invention compared with a prior art example. It is a figure which shows the measuring method of the number of bytes of the receiving segment which concerns on one Embodiment of this invention. It is a figure which shows the other example of the measuring method of the byte number of the receiving segment which concerns on one Embodiment of this invention. It is a figure which shows the example which correct | amends the transmission time of ACK in the transmission side. It is a block diagram which shows schematic structure of the transmission terminal which concerns on 2nd Embodiment of this invention. It is a figure which shows the measuring method of the conventional RTT. It is a figure which shows the problem of the measuring method of the conventional RTT.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11, 111 Transmission terminal 12 Segment receiving part 13 Minimum time measurement part 14 Received byte number calculation part 15 Target calculation part 16 Transmission segment control part 17 Segment transmission part 18 Congestion window calculation part 21 TCP transmission side 22 TCP reception side 23 Network 24 Segment 25 Application 26 Receive buffer

Claims (6)

A received byte count calculation unit that calculates the number of bytes of a segment that has reached the receiving side within a certain period of time,
A transmission segment control unit that controls a target that is the number of transmission segments based on the number of bytes of the segment calculated by the reception byte number calculation unit;
The transmission segment control unit
If the space that is the predetermined setting value is smaller than the minimum value of cwnd, which is a variable that limits the data size that can be transmitted on the communication protocol, and rcv wnd, which is the data size that can be received at one time, according to space Send a segment,
When the target is larger than the space, the space is set to a value obtained by adding the value obtained by doubling the MSS, which is the maximum segment size that can be transmitted by the transmitting side, to the space every time an ACK is received.
If the space is greater than the target, set the space to the same value as the target, or set the space to the value obtained by subtracting the MSS from the space for each ACK received,
If the number of ACKed bytes can be calculated,
When the target is larger than the space, the space is set to a value obtained by adding the number of bytes ACKed to the space every time an ACK is received,
If the space is greater than the target,
The communication terminal is characterized in that the space is set to the same value as the target, or the space is set to a value obtained by subtracting ½ of the number of bytes ACKed from the space every time an ACK is received . A minimum time measurement unit for measuring the minimum value of RTT;
A received byte number calculating unit that calculates the number of bytes of the segment that has reached the receiving side within the period of the minimum value of the RTT measured by the minimum time measuring unit;
A transmission segment control unit that controls a target that is the number of transmission segments based on the number of bytes of the segment calculated by the reception byte number calculation unit;
The transmission segment control unit
If the space that is the predetermined setting value is less than the minimum value of cwnd, which is a variable that limits the data size that can be transmitted on the communication protocol, and rcv wnd, which is the data size that can be received at one time, according to space Send a segment,
When the target is larger than the space, the space is set to a value obtained by adding the value obtained by doubling the MSS, which is the maximum segment size that can be transmitted by the transmitting side, to the space every time an ACK is received.
If the space is greater than the target, set the space to the same value as the target, or set the space to the value obtained by subtracting the MSS from the space for each ACK received,
If the number of ACKed bytes can be calculated,
When the target is larger than the space, the space is set to a value obtained by adding the number of bytes ACKed to the space every time an ACK is received,
If the space is greater than the target,
The communication terminal is characterized in that the space is set to the same value as the target, or the space is set to a value obtained by subtracting ½ of the number of bytes ACKed from the space every time an ACK is received .   The minimum time measurement unit is defined by the minimum value of the RTT when a segment is not transmitted for a predetermined time or more, or when the congestion window is smaller than the initial window size, or over a predetermined measurement time. The communication terminal according to claim 2, wherein when the RTT equal to or less than the value is not measured, the minimum value of the RTT is reset. Without considering the number of bytes of the segment calculated by the received byte number calculation unit, further comprising a congestion window calculation unit for calculating a congestion window or a slow start threshold at the time of ACK reception or packet loss occurrence,
4. The communication according to claim 1, wherein the transmission segment control unit performs segment transmission control based on a congestion window or a slow start threshold calculated by the congestion window calculation unit. 5. Terminal. Calculating the number of bytes of the segment that reached the receiving side within a certain period on the sending side;
Controlling the number of bytes of the segment calculated on the transmitting side while limiting based on the maximum segment size that can be transmitted by the transmitting side or the number of ACKed bytes ,
The controlling step includes
If the space that is the predetermined setting value is less than the minimum value of cwnd, which is a variable that limits the data size that can be transmitted on the communication protocol, and rcv wnd, which is the data size that can be received at one time, according to space Send a segment,
When the target is larger than the space, the space is set to a value obtained by adding the value obtained by doubling the MSS, which is the maximum segment size that can be transmitted by the transmitting side, to the space every time an ACK is received.
If the space is greater than the target, set the space to the same value as the target, or set the space to the value obtained by subtracting the MSS from the space for each ACK received,
If the number of ACKed bytes can be calculated,
When the target is larger than the space, the space is set to a value obtained by adding the number of bytes ACKed to the space every time an ACK is received,
If the space is greater than the target,
The communication control method is characterized in that the space is set to the same value as the target, or the space is set to a value obtained by subtracting 1/2 of the number of bytes ACKed from the space every time an ACK is received. . Calculating the number of bytes of the segment that reached the receiving side within a certain period on the sending side;
Controlling the number of bytes of the segment calculated on the transmitting side while limiting based on the maximum segment size that can be transmitted by the transmitting side or the number of ACKed bytes ,
If the space that is the predetermined setting value is less than the minimum value of cwnd, which is a variable that limits the data size that can be transmitted on the communication protocol, and rcv wnd, which is the data size that can be received at one time, according to space Send a segment,
When the target is larger than the space, the space is set to a value obtained by adding the value obtained by doubling the MSS, which is the maximum segment size that can be transmitted by the transmitting side, to the space every time an ACK is received.
If the space is greater than the target, set the space to the same value as the target, or set the space to the value obtained by subtracting the MSS from the space every time an ACK is received,
If the number of ACKed bytes can be calculated,
When the target is larger than the space, the space is set to a value obtained by adding the number of bytes ACKed to the space every time an ACK is received,
If the space is greater than the target,
Causing the computer to execute a process of setting the space to the same value as the target, or setting the space to a value obtained by subtracting ½ of the number of bytes ACKed from the space every time an ACK is received. A featured communication control program.

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