JP4915415B2 - Communication terminal, communication system, congestion control method, and congestion control program - Google Patents

Description

  The present invention relates to a communication terminal, a communication system, a congestion control method, and a congestion control program, and in particular, a communication terminal, a communication system, a congestion control method, and a congestion control program that perform low-delay communication using a broadband line. About.

  In order to perform low-latency communication between transmitting and receiving terminals in communication via a network, it is required to shorten the delay time due to queue delay in the network. The minimum value of the delay between the transmission / reception terminals is the propagation delay time between the transmission / reception terminals, and it is considered that communication with a shorter delay is not possible. When congestion occurs in the network, a queue for waiting for packet output is created at the node where the congestion has occurred, and the delay between the transmitting and receiving terminals increases by the time that passes through this queue. Further, when the queue becomes long and exceeds the buffer capacity of a congested node, packet discarding occurs, so that the delay time between the transmitting and receiving terminals greatly increases by the amount related to packet retransmission. Thus, in order to perform low-latency communication, it is required to reduce the queue delay in the nodes in the network.

  The most effective method for reducing the queue delay is a method for preferentially outputting a packet by storing only a low-delay communication in a queue having a particularly high priority at a node in the network. For example, a method based on Differentiated Service (Internet Engineering Task Force, Request For Comments 2475) can be mentioned. However, this scheme requires a special mechanism in the nodes in the network, and a queue delay still occurs when a plurality of low-delay communications are performed simultaneously.

  As another method, there is a method of explicitly notifying congestion information from a node in the network to a transmitting terminal. As this method, as in ECN (Explicit Congestion Notification, Internet Engineering Task Force, Request For Comments 3168) method, the node congestion degree is entered in the packet header and notified to the transmitting terminal, or non-patent document 1 shows. There is a method of calculating an optimal transmission band for each communication at a node and notifying this to a transmission terminal. However, these systems also require a special mechanism in the nodes in the network, and costs such as replacing existing nodes.

  As a technique different from each of the above-described methods, there is a technique described below that realizes low-delay communication through congestion control between transmitting and receiving terminals.

  The first conventional technique is a technique for setting the maximum value of the transmission band according to the line capacity of the network. In this technique, unnecessary queue delay and packet discard can be prevented by preventing an excessive transmission band from being set exceeding the line capacity. For example, in the method disclosed in Patent Document 1, an optimum communication bandwidth is estimated during TCP communication, and congestion control is performed so that the transmission bandwidth does not exceed this bandwidth, thereby preventing unnecessary congestion and data transfer delay time. To shorten.

  The second conventional technique is a technique for determining a transmission band based on a one-way delay time or a round-trip delay time measured by a transmission terminal. In this technique, when the delay time increases, the transmission band is decreased, thereby performing congestion control at the transmission terminal so as to keep the queue delay short. For example, TCP-FAST (From Theory to Experiments, C. Jin, DX Wei, SH Low, G. Buhrmaster, J. Bunn, DH Choe, RLA Cottrell, JC Doyle, W. Feng, O. Martin, H. Newman, F. Paganini, S. Ravot, S. Singh. IEEE Network, 19 (1): 4-11, January / February 2005) measures the round-trip propagation delay time of the network, and the difference between the minimum value and the current value. Is multiplied by the current transmission band (this value corresponds to the amount of communication data waiting in the queue in the node), and this value is guided to a predetermined target value. By controlling this, the transmission band is controlled to the optimum band.

As technologies related to the present invention, there are Patent Literature 2, Patent Literature 3, Patent Literature 4, and Patent Literature 5.
JP 2006-279283 A JP 2000-295286 A JP 2004-153776 A JP 2006-340078 A JP 2005-517330 A "Processor Sharing Flows in the Internet" (Nandita Dukkipati, Masayoshi Kobayashi, Rui Zhang-Shen, Nick McKeown, Thirteenth International Workshop on Quality of Service (IWQoS))

  The problem with the first prior art is that when there are multiple sessions, even if the bandwidth limit of each session is less than the line capacity, the total bandwidth limit of those sessions will exceed the line capacity. is there. Therefore, when there are multiple sessions, the queue delay becomes long.

  A problem of the second prior art is that a packet having a set data amount stays in the queue constantly, and the fluctuation of the delay time is severe because the number of staying packets greatly oscillates. In order to perform low-delay communication, it is necessary to reach the optimal transmission band at an early stage. For this purpose, it is necessary to set a large increase in the transmission band. However, if a large increase in the transmission bandwidth is set, a large amount of packets arrive at the network node in a short period of time, so the queue length increases significantly in a short period of time, but congestion is notified to the transmitting terminal due to an increase in queue delay. It takes longer to complete. As a result, when the transmission bandwidth is suddenly increased, the time from the occurrence of congestion until the transmission bandwidth is reduced correspondingly becomes longer, and as a result, the queue length becomes unstable. In addition, the first conventional technique has a problem that the number of packets constantly staying in the queue increases linearly as the number of sessions increases.

  Therefore, a first object of the present invention is to suppress the total bandwidth to a line capacity or less even when there are a plurality of sessions, and as a result, to shorten the delay time between transmitting and receiving terminals.

  The second object of the present invention is to converge the queue delay to a small value without oscillating even when the increase width of the transmission band is increased or when the number of sessions is large. Is to shorten the delay time.

In order to achieve the above object, a communication terminal of the present invention is a communication terminal used for a communication system for setting a communication session between a plurality of communication terminals via a network and transmitting and receiving data,
Means for measuring a round trip delay time between the communication terminals performing transmission and reception based on the received data; and a measurement means for measuring a reception band in the receiving terminal among the plurality of communication terminals based on the received data. ,
Correction means for correcting the value of the round-trip delay time using at least the reception band;
Determining means for determining a transmission band according to the round trip delay time corrected by the correcting means;
Means for measuring the amount of data being transmitted,
The correcting means uses a value obtained by dividing the amount of data being transmitted by the reception band as a corrected value of the round trip delay time .

The communication terminal of the present invention is a terminal used for a communication system that sets a communication session between a plurality of communication terminals via a network and transmits and receives data.
A means of measuring the amount of data being transmitted;
Measuring means for measuring a reception band in a receiving terminal among the plurality of communication terminals based on the received data;
An estimation means that takes a value obtained by dividing the measured amount of data being transmitted by the reception band as a round-trip delay time ;
And having a determination means for determining a transmission band by said round trip time estimated by the estimating means.

The congestion control method of the present invention is a congestion control method in a communication terminal of a communication system that performs communication transmission and reception by setting a communication session between a plurality of communication terminals via a network,
A first step of measuring a round trip delay time between the communication terminals performing transmission and reception based on the received data and measuring a reception band in the reception terminal of the plurality of communication terminals;
A second step of correcting the value of the round-trip delay time using at least the reception band;
A third step of determining a transmission band based on the round trip time corrected in the second step;
A fourth step of measuring the amount of data being transmitted;
In the second step, a value obtained by dividing the amount of data being transmitted by the reception band is used as a corrected value of the round trip delay time .

The congestion control method of the present invention is a congestion control method in a communication terminal of a communication system for setting a communication session between a plurality of communication terminals via a network and transmitting and receiving data,
A first step of measuring the amount of data being transmitted;
A second step of measuring a reception band in a receiving terminal among the plurality of communication terminals based on the received data;
A third step in which a value obtained by dividing the measured amount of data being transmitted by the reception band is a round-trip delay time ;
And a fourth step of determining a transmission band based on the round trip delay time.

  According to the present invention, the following effects are achieved.

  First, in response to the increase in queue delay, the total amount of bandwidth is kept below the line capacity even when there are multiple sessions by reducing the amount of queued data. The delay time between the transmitting and receiving terminals can be shortened.

    Second, because the transmission bandwidth can be controlled faster than the measured RTT changes, the queue delay can be converged to a small value without oscillating, and as a result, the delay time between the transmitting and receiving terminals is shortened. be able to.

    Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[Embodiment 1]
A first embodiment of the present invention will be described with reference to the drawings.

(Description of configuration)
FIG. 1 is a block diagram showing a configuration of a communication terminal 1 according to the present embodiment. A communication terminal 1 serving as a transmission terminal includes a data generation unit 1-1 that generates transmission data, a packet transmission unit 1-2 that outputs communication data to a network, and another communication terminal (reception terminal) that communicates with the communication terminal 1 A packet reception unit 1-3 for receiving a response confirmation packet (ACK packet) from the packet, and a congestion control unit 1-4 for instructing a transmission band to the packet transmission unit 1-2.

    Congestion control unit 1-4 measures round trip time RTT (Round Trip Time) 1-6 every time an ACK packet is received, transmission band measurement unit 1-8 measures the transmission band, and measures the reception band Reception band measurement unit 1-9, RTT correction unit 1-7 that corrects the RTT measured using the values of the transmission band and the reception band, and a transmission band determination unit 1-5 that determines the transmission band based on the RTT Is done. Here, RTT refers to the time required for one packet to go from the source to the destination and back again in network communication.

(Description of operation)
The operation of this embodiment will be described with reference to FIGS. FIG. 2 is a flowchart showing the operation of the communication terminal 1.

    When transmission data is generated in the data generation unit 1-1 (step S11), the packet transmission unit 1-2 packetizes the transmission data according to the transmission band specified by the transmission band determination unit 1-5 of the congestion control unit 1-4. (Step S12). At that time, the transmission band measuring unit 1-8 measures the transmission band (step S12). This may be, for example, a value obtained by dividing the amount of data transmitted in a fixed time by the reception time as in the following equation.

Measurement transmission bandwidth = (Amount of data transmitted between time t1 and time t2) / (t2-t1)
Further, as shown in the following expression, a measured transmission band calculated by taking an exponential average every time a packet is transmitted may be used.

Measured transmission band = (previously calculated transmission band x coefficient) + ((data amount transmitted this time) / (current packet transmission time-previous packet transmission time)) x (1-coefficient)
The transmission band measuring unit 1-8 may use the value of the transmission band obtained by the transmission band determining unit 1-5 instead of the measured transmission band.

    When the ACK packet for the transmitted packet arrives at the packet receiving unit 1-3, the RTT measuring unit 1-6 measures the round-trip delay time (RTT) related to the packet and its minimum value (RTTmin) from the start of transmission (RTTmin) ( Step S13).

    In this embodiment, a round trip delay time (RTT) is used as a delay, but a one way delay time may be used instead. As a method for deriving the one-way delay time, for example, the transmission terminal writes the transmission time in the packet header at the time of packet transmission, and the reception terminal receiving this packet calculates the difference between the transmission time and the packet reception time as a one-way delay, A method of writing the calculated value in an ACK packet and notifying the transmitting terminal can be used.

    The reception band measuring unit 1-9 measures the reception band at the receiving terminal from the amount of data confirmed to be received by the ACK packet (step S13). This may be, for example, a value obtained by dividing the amount of data confirmed to be received in a certain time by the reception time as in the following equation.

Receive band = (Amount of data confirmed to be received between time t1 and time t2) / (t2-t1)
Further, as shown in the following expression, a reception band calculated by taking an exponential average every time an ACK packet is received may be used.

Receive Band = (Receive Band Calculated Previously x Coefficient) + ((Amount of Data Acknowledged by Current ACK Packet) / (Current ACK Packet Arrival Time-Previous ACK Packet Arrival Time)) x (1-Coefficient)
Next, the RTT correction unit 1-4 corrects the RTT based on the balance between the measured transmission band and the reception band (step S14). For example, what is necessary is just to obtain | require like the following formula | equation.

Correction RTT = max (Measurement RTT × (Measurement transmission bandwidth / Reception bandwidth), Measurement RTTmin)
That is, the correction RTT is a larger value of measurement RTT × (measurement transmission band / reception band) and measurement RTTmin.

    Moreover, you may obtain | require with the following formula | equation.

Correction RTT = max (Measurement RTT × (Measurement transmission bandwidth / Reception bandwidth), Measurement RTT)
That is, the correction RTT is a larger value of the measurement RTT × (measurement transmission band / reception band) and the measurement RTT.

    Here, the latest measured values are used for the measured transmission band and the received band, respectively, but the measured transmission band and the measured time of the received band for the same packet can be obtained by using the measured value of the measured transmission band for 1 RTT. May be combined.

    The transmission band determining unit 1-5 controls the transmission band using the corrected RTT value (step S15). The controlled transmission band becomes the transmission band designated in step S12. The transmission bandwidth control method is arbitrary as long as it is a control method using RTT. For example, it may be calculated by the following formula.

Transmission band = Transmission band of the previous calculation +
(α / RTT − (RTT-RTTmin) / RTT × transmission bandwidth of previous calculation) × time constant
As the time constant, for example, a value such as (time calculated this time−time calculated last time) * RTT is used. The value of α is a parameter that determines the increase rate of the transmission band. The above formula can be obtained by using the following formula. Note that “*” in the above expression means “×” (that is, “*” in the above expression means multiplication). The same applies to the following equations.

Transmission band = Transmission band of the previous calculation +
(α / RTT-(previous transmission bandwidth-reception bandwidth)) x time constant In the above, the congestion control method by controlling the transmission bandwidth has been described. However, the above method is a window flow such as TCP (Transmission Control Protocol). It can also be applied to a congestion control method based on control. In this case, the transmission band calculation formula is changed as follows.

Send window = Send window of previous calculation +
(α − (RTT-RTTmin) / RTT × previous calculation transmission window) / previous calculation transmission window
When the degree of network congestion increases, the reception band temporarily becomes smaller than the transmission band. Further, when the transmission band becomes larger than the optimum value, the transmission band temporarily becomes larger than the reception band. Thus, when it is necessary to lower the transmission band, the ratio between the transmission band and the reception band temporarily changes, and then the queuing delay starts to increase and the RTT increases. That is, since the change in the ratio appears as a phenomenon prior to the change in RTT, by performing congestion control with the change in the ratio, or by correcting the RTT value with the change in the ratio, Control can be performed earlier.

[Embodiment 2]
A second embodiment of the present invention will be described with reference to the drawings.

(Description of configuration)
FIG. 3 is a block diagram showing the configuration of the communication terminal 2 according to the present embodiment. The difference from the first embodiment is that a transmitting data amount measuring unit is provided instead of the transmission band measuring unit.

    The communication terminal 2 includes a data generation unit 2-1 that generates transmission data, a packet transmission unit 2-2 that outputs communication data to the network, and a packet reception unit 2- that receives a response confirmation packet (ACK packet) from the reception terminal. 3. Consists of a congestion control unit 2-4 for instructing the transmission bandwidth to the packet transmission unit 2-2.

    Congestion control unit 2-4, RTT measurement unit 2-6 that measures the round-trip delay time every time an ACK packet is received, Transmitting data amount measurement unit 2-8 that measures the amount of transmitting data that has not yet been received, and reception Reception band measurement unit 2-9 that measures the band, RTT correction unit 2-7 that corrects the RTT measured using the value of the reception band and the amount of data being transmitted, and a transmission band determination unit that determines the transmission band based on the RTT Consists of 2-5.

(Description of operation)
The operation of this embodiment will be described with reference to FIGS.

    FIG. 4 is a flowchart showing the operation of the communication terminal 2.

    When transmission data is generated in the data generation unit 2-1 (step S11), the packet transmission unit 2-2 packetizes the transmission data according to the transmission band specified by the transmission band determination unit 2-5 of the congestion control unit 2-4. (Step S22). At that time, unlike the first embodiment, the transmission band is not measured. When the ACK packet corresponding to the transmitted packet arrives at the packet receiving unit 2-3, the RTT measuring unit 2-6 measures RTT and RTTmin, and the receiving band measuring unit 2-9 measures the receiving band (step S23). In addition, the data amount measuring unit 2-8 during transmission obtains the amount of data being transmitted from the difference between the sequence number of the last transmitted packet and the sequence number confirmed to be received by ACK (step S23).

    Next, the RTT correction unit 2-7 corrects the RTT using the amount of data being transmitted and the transmission band (step S24). For example, what is necessary is just to obtain | require like the following formula | equation.

Correction RTT = max (Amount of data being sent / Receive band), Measurement RTTmin)
Moreover, you may obtain | require with the following formula | equation.

Correction RTT = max (Amount of data being sent / Receive band, Measurement RTT)
Here, the latest measured values are used for the data amount being transmitted and the reception band, respectively, but the measurement value of the data amount being transmitted is used as the measurement time of the data amount being transmitted for the same packet by using the measured value of 1 RTT past. The measurement time of the reception band may be adjusted.

    The transmission band determining unit 2-5 controls the transmission band using the value of the correction RTT (Step S15). The control method is arbitrary as long as it is a control method using RTT. For example, it may be calculated by the following formula.

Transmission band = Transmission band of the previous calculation +
(α / RTT − (RTT-RTTmin) / RTT × transmission bandwidth of previous calculation) × time constant
The above formula can be obtained by using the following formula.

Transmission band = Transmission band of the previous calculation +
(α / RTT − (data amount during transmission / RTTmin − reception band)) × time constant [Third embodiment]
A third embodiment of the present invention will be described with reference to the drawings.

(Description of configuration)
FIG. 5 is a block diagram showing the configuration of the terminal 3 according to the present embodiment. The communication terminal 3 has a configuration in which a transmission band increase width changing unit 3-10 is added to the configuration of the communication terminal 1 according to the first embodiment.

    The communication terminal 3 includes a data generation unit 3-1 that generates transmission data, a packet transmission unit 3-2 that outputs communication data to the network, and a response confirmation packet (ACK packet) from another communication terminal that communicates with the communication terminal 3. ) And a congestion control unit 3-4 for instructing the transmission band to the packet transmission unit 3-2.

    Congestion control unit 3-4, RTT (Round Trip Time) measurement unit 3-6 that measures the round trip delay time every time an ACK packet is received, transmission band measurement unit 3-8 that measures the transmission band, and measurement of the reception band Receiving band measuring unit 3-9, RTT correcting unit 3-7 for correcting RTT measured using values of transmission band and receiving band, transmission band determining unit 3-5 for determining transmission band based on RTT, measurement The transmission band increase width changing unit 3-10 changes the transmission band increase width based on the RTT.

(Description of operation)
The operation of this embodiment will be described with reference to FIGS. FIG. 6 is a flowchart showing the operation of the communication terminal 3. Here, the same operations as those in FIG. 2 are denoted by the same reference numerals, and the description of the operations is omitted.

    The operation at the time of packet transmission (steps S11 and S12) is the same as in the first embodiment.

    The operation at the time of packet reception is the same as that in the first embodiment until the corrected RTT is calculated (steps S13 and S14).

    Also in the present embodiment, the method for calculating the transmission bandwidth is based on the following conventional general method.

    In general, in a congestion control method using a queue delay in a network as a control index, the amount of data stored in the queue is estimated, and the transmission bandwidth is controlled based on this amount of data. In other words, if the amount of data stored in the queue is larger than the target value set in advance, it is determined that the network is congested and the transmission bandwidth is reduced. Conversely, the amount of data stored in the queue is If it is less, it is determined that the network is not congested and the transmission bandwidth is increased.

    Generally, the amount of data stored in the queue can be estimated as follows. The measured minimum value of RTT (RTTmin) is the delay time when no data is stored in the queue in the network, which can be regarded as the physical propagation delay time on the network line. . If the measured RTT is larger than this value, the difference, that is, (RTT-RTTmin) can be regarded as the time that has been waited in the queue. The amount of data stored in the queue is the amount of data stored in the queue, because (RTT-RTTmin) x transmission bandwidth is the amount of time spent waiting in the queue multiplied by the transmission bandwidth. Can be estimated.

    If the target of the amount of data stored in the queue is α, and the longer the RTT, the smaller the control gain and the more stable control is taken into account, the congestion control method uses the queue delay in the network as a control index. Can generally be represented by the following equations.

Transmission band = Transmission band of the previous calculation +
(α / RTT-(RTT-RTTmin) / RTT x previously calculated transmission bandwidth) x time constant
In the above method, since the queue delay increases as the target value α of the data amount stored in the queue increases, the value of α needs to be set appropriately in order to reduce the queue delay. On the other hand, if the value of α is small, there is a problem that the increase rate of the transmission band becomes slow.

    Therefore, in this embodiment, optimal control is performed by dynamically changing the value of α in accordance with the network conditions, instead of setting the value of α to a fixed value. In order to reduce the queue delay, it is sufficient to use a function that reduces the value of α as the queue delay increases. Therefore, the value of α is dynamically changed based on the measured RTT value or the corrected RTT value. To do. Therefore, in this embodiment, the value of α is defined as a decreasing function with respect to (RTT−RTTmin). For example, the following function is used.

(Equation 1) α = 1 / e ^{(RTT-RTTmin) × a} , or
(Equation 2) α = 1 / e ^{(RTT-RTTmin) / (maximum RTT-RTTmin) x b} , or
(Equation 3) α = max (c-(RTT-RTTmin) * d, e), or
(Equation 4) α = f * B / e ^{(RTT-RTTmin) × a} , or
(Equation 5) α = f * B / transmission band / e ^{(RTT-RTTmin) × a} , or
(Equation 6) α = f * B / Transmission band * RTT / e ^{(RTT-RTTmin) × a} , or
(Equation 7) α = f * B / Transmission band * RTTmin / e ^{(RTT-RTTmin) × a}
Here, a, b, c, d, e, and f are constants of 0 or more, respectively. B is a value of the line bandwidth, and uses a preset value or a value obtained by using an estimation method disclosed in Japanese Patent Application No. 2005-027684. Here, when Equation (1) and Equation (2) use an exponential decrease function of the queue delay as the target value α, Equation (3) shows an equation (4) when using a linear decrease function of the queue delay. When the target value is multiplied by the line bandwidth, Equation (5) is multiplied by the target value divided by the line bandwidth and the transmission bandwidth, Equation (6) is when Equation (5) is multiplied by the round-trip delay time Equation (7) represents the case where Equation (5) is multiplied by the minimum value of the round-trip delay time.

    In equations (6)-(7), the value of α is multiplied by the round-trip delay time, but as an alternative, instead of multiplying the value of α by the round-trip delay time, the estimated amount of data is divided by the round-trip delay time. May be. That is, the following equation is obtained.

Transmission band = Transmission band of the previous calculation +
(α / RTT-(RTT-RTTmin) / RTT x transmission band of previous calculation / RTT) x time constant transmission band = transmission band of previous calculation +
(α / RTT-(RTT-RTTmin) / RTT x previous transmission band / RTTmin) x time constant Also, in the above formula, the term (RTT-RTTmin) / RTT x previous transmission band is (RTT-RTTmin) / Constant g × Transmission bandwidth of previous calculation may be used.

    Furthermore, the time constant in the above formula may also be dynamically changed according to the amount of data queued in the network. This is because it is judged that the congestion state becomes more severe as the amount of data increases, and the congestion is quickly eliminated by greatly changing the time constant. Therefore, the time constant may be defined as an increasing function with respect to the absolute value of the difference. For example, the following function is used.

Time constant = max (f × | A |, g)
Here, f and g are constants of 0 or more, A is the difference value, and | A | is its absolute value.

    The calculation of α and the transmission bandwidth increase width, that is, / RTT− (RTT−RTTmin) / RTT × transmission bandwidth of the previous calculation) × time constant are performed by the transmission bandwidth increase width changing unit.

    When there are multiple sessions, the queue delay becomes longer. By setting the target value to a smaller value as the queue delay increases, the amount of data queued in each session decreases, and the overall The amount of data queued in the session is reduced.

[Embodiment 4]
A fourth embodiment of the present invention will be described with reference to the drawings.

(Description of configuration)
FIG. 7 is a block diagram showing the configuration of the communication terminal 4 according to the present embodiment. The communication terminal 4 includes a data generation unit 4-1 that generates transmission data, a packet transmission unit 4-2 that outputs communication data to the network, and a packet reception unit 4- that receives a response confirmation packet (ACK packet) from the reception terminal. 3. Consists of a congestion control unit 4-4 for instructing the transmission bandwidth to the packet transmission unit 4-2.

    The congestion control unit 4-4 includes a transmission data amount measurement unit 4-8 that measures the amount of transmission data that has not been received by an ACK, a reception band measurement unit 4-9 that measures a reception band, a reception band and a transmission data amount. An RTT estimation unit 4-7 that estimates an RTT using a value and a transmission band determination unit 4-5 that determines a transmission band based on the RTT.

(Description of operation)
The operation of this embodiment will be described with reference to FIGS. FIG. 8 is a flowchart showing the operation of the communication terminal 4.

    Since processing at the time of packet transmission (steps S11 and S22) is the same as that of the second embodiment, description thereof is omitted here.

    When the ACK packet corresponding to the transmitted packet arrives at the packet receiving unit 4-3, the reception band measuring unit 4-9 measures the reception band (step S23). The data amount measuring unit 4-6 during transmission obtains the amount of data being transmitted from the difference between the sequence number of the last transmitted packet and the sequence number confirmed to be received by ACK (step S23).

    Next, the RTT estimator 4-4 estimates the RTT using the data amount being transmitted and the transmission band (step S44). For example, what is necessary is just to obtain | require like the following formula | equation.

Estimated RTT = amount of data being transmitted / reception band RTTmin is determined as the minimum estimated RTT.

    Next, the transmission band is controlled based on the obtained RTT (step S45). Since the method is the same as in the second embodiment, the description thereof is omitted here.

[Embodiment 5]
A fifth embodiment of the present invention will be described with reference to the drawings.

(Description of configuration)
FIG. 9 is a block diagram showing the configuration of the communication terminal 5 according to the present embodiment. The communication terminal 5 includes a data generation unit 5-1 that generates transmission data, a packet transmission unit 5-2 that outputs communication data to the network, and a response confirmation packet (ACK packet) from another communication terminal that communicates with the communication terminal 5. ) And a congestion control unit 5-4 that instructs the packet transmission unit 5-2 on the transmission band.

    The congestion control unit 5-4 includes an RTT (Round Trip Time) measurement unit 5-6 that measures a round trip delay time every time an ACK packet is received, a reception band measurement unit 5-9 that measures a reception band, and a value of the reception band The RTT correction unit 5-7 corrects the RTT measured by using the RTT, and the transmission band determination unit 5-5 determines the transmission band based on the RTT. Compared with the congestion control unit 1-4 in the first embodiment, the transmission band measurement unit 1-8 is not provided, and the others are the same.

(Description of operation)
The operation of the present embodiment will be described with reference to FIGS. FIG. 10 is a flowchart showing the operation of the communication terminal 5. In the following, the derivation of the corrected RTT in this embodiment will be described, and the other operations are the same as those in the first embodiment, and the description thereof will be omitted.

    In the present embodiment, the RTT is corrected using only the reception band without measuring the transmission band. The RTT correction unit 5-7 uses the current reception band and the reception band measured in the past, and corrects the RTT according to the ratio (step S54). For example, what is necessary is just to obtain | require like the following formula | equation.

Correction RTT = max (Measured RTT x (Received bandwidth measured in the past / Current received bandwidth), RTTmin)
[Embodiment 6]
A sixth embodiment of the present invention will be described with reference to the drawings.

(Description of configuration)
FIG. 11 is a block diagram showing the configuration of the system according to this embodiment. This system includes a communication terminal 6-1 serving as a transmission terminal, a communication terminal 6-2 serving as a reception terminal, and a network 6-3. Since the configuration of the communication terminal 6-1 is the same as that of the communication terminal 1 in the first embodiment, the description is omitted here. Any of the communication terminals shown in the second to fifth embodiments can be used. The communication terminal 6-2 includes a data reconfiguration unit 6-5 that reconfigures communication data from the received packet, a data reception unit 6-4 that receives and processes the reconfigured data, and generates an ACK packet to generate the communication terminal 6 ACK generation unit 6-6 that returns to -1.

(Description of operation)
The operation of this embodiment will be described with reference to FIG.

    The packet transmitted from the transmission terminal 5-1 arrives at the reception terminal 5-3 via the network 5-3.

    The data reconstruction unit 6-5 extracts data from the received packet, reconstructs the original data, and sends it to the data reception unit 6-4. The data receiving unit 6-4 processes the received data by various receiving applications.

    The data reconstruction unit 6-5 notifies the ACK generation unit 6-6 of the number of the data that has been received. Then, the ACK generation unit 6-6 generates an ACK packet based on the number and transmits it to the communication terminal 6-1. The number of the data notified by the ACK packet is the number of the data confirmed by the communication terminal 6-2, and this number and data before this number are surely received by the communication terminal 6-2. . Therefore, when the communication terminal 6-1 receives the ACK packet, the data up to the number written in the packet is not retransmitted, so that the data may be discarded on the communication terminal 6-1 side. When packet discard occurs on the transmission path, the communication terminal 6-2 writes the same data number to multiple ACKs to notify the communication terminal 6-1 that data after this number has not been received. And prompts for retransmission. As another method, a NACK (Negative ACK) indicating that a packet is explicitly discarded may be transmitted from the communication terminal 6-2 side to the communication terminal 6-1 side.

    Although the communication terminal of each embodiment described above can be configured by hardware using a dedicated IC or the like, it can be realized by software using a computer. That is, for example, the communication terminal shown in FIG. 1, FIG. 3, FIG. 5, FIG. 7, or FIG. The function of the communication terminal can be realized by a program describing any one of the flows. The program describing any of the flows in FIGS. 2, 4, 6, 8, and 10 is stored in a disk device 103 such as a hard disk device or a storage device such as a ROM (here, the disk device is shown). The CPU 105 executes a program for realizing the function of the communication terminal. The input unit 102 is an input device such as a keyboard. The transmission / reception unit 101 corresponds to a packet transmission unit and a packet reception unit. An LCD (Liquid Crystal Display) 107 displays information processing status and determination results. Reference numeral 104 denotes a bus such as a data bus, and 106 denotes a memory such as a DRAM that stores information necessary for information processing by the CPU 105.

    The present invention relates to a communication terminal, a communication system, a congestion control method, and a congestion control program, and in particular, a communication terminal, a communication system, a congestion control method, and a congestion control program that perform low-delay communication using a broadband line. Applicable to.

It is a block diagram which shows the structure of the terminal by the 1st Embodiment of this invention. It is a flowchart which shows operation | movement of the communication terminal by 1st Embodiment. It is a block diagram which shows the structure of the terminal by the 2nd Embodiment of this invention. It is a flowchart which shows operation | movement of the communication terminal by 2nd Embodiment. It is a block diagram which shows the structure of the terminal by the 3rd Embodiment of this invention. It is a flowchart which shows operation | movement of the communication terminal by 3rd Embodiment. It is a block diagram which shows the structure of the terminal by the 4th Embodiment of this invention. It is a flowchart which shows operation | movement of the communication terminal by 4th Embodiment. It is a block diagram which shows the structure of the terminal by the 5th Embodiment of this invention. It is a flowchart which shows operation | movement of the communication terminal by 6th Embodiment. It is a block diagram which shows the structure of the system by one Embodiment of this invention. It is a block diagram which shows an example of a structure of a computer.

Explanation of symbols

1-1, 2-1,3-1,4-1,5-1 Data generator
1-2, 2-2,3-2,4-2,5-2 Packet transmitter
1-3, 2-3,3-3,4-3,5-3 Packet receiver
1-4,2-4,3-4,4-4,5-4 Congestion controller
1-5,2-5,3-5,4-5,5-5 Transmission band decision part
1-6,2-6,3-6,5-6 RTT (Round Trip Time) measurement unit
1-7,2-7,3-7,5-7 RTT correction part
4-7 RTT estimation part
1-8,3-8 Transmission band measurement part
2-8, 4-8 Transmitting data volume measurement unit
1-9,2-9,3-9,4-9,5-9 Receive Band Measurement Unit
3-10 Transmission bandwidth increase width change section
6-1,6-2 Communication terminal
6-3 Network
6-4 Data receiver
6-5 Data reconstruction unit
6-6 ACK transmitter

Claims (9)

A communication terminal used in a communication system for setting a communication session between a plurality of communication terminals via a network and transmitting / receiving data,
Means for measuring a round trip delay time between the communication terminals performing transmission and reception based on the received data;
Measuring means for measuring a reception band in a receiving terminal among the plurality of communication terminals based on the received data;
Correction means for correcting the value of the round-trip delay time using at least the reception band;
Determining means for determining a transmission band according to the round trip delay time corrected by the correcting means;
Means for measuring the amount of data being transmitted,
The communication device according to claim 1, wherein the correction means uses a value obtained by dividing the amount of data being transmitted by the reception band as a corrected value of the round-trip delay time. A terminal used in a communication system for setting a communication session between a plurality of communication terminals via a network and transmitting and receiving data,
A means of measuring the amount of data being transmitted;
Measuring means for measuring a reception band in a receiving terminal among the plurality of communication terminals based on the received data;
An estimation means that takes a value obtained by dividing the measured amount of data being transmitted by the reception band as a round-trip delay time ;
Communication terminal, comprising a determination means for determining a transmission band by said round trip time estimated by the estimating means.   A communication system comprising the communication terminal according to claim 1 and another communication terminal that transmits and receives data to and from the communication terminal.   4. The communication system according to claim 3, wherein the other communication terminal transmits a response confirmation packet in response to data transmission from the communication terminal, and the communication terminal sets the round trip delay time based on the response confirmation packet. A communication system characterized by measuring. A congestion control method in a communication terminal of a communication system for setting a communication session between a plurality of communication terminals via a network and transmitting and receiving data,
A first step of measuring a round trip delay time between the communication terminals performing transmission and reception based on the received data and measuring a reception band in the reception terminal of the plurality of communication terminals;
A second step of correcting the value of the round-trip delay time using at least the reception band;
A third step of determining a transmission band based on the round trip time corrected in the second step;
A fourth step of measuring the amount of data being transmitted;
In the second step, a value obtained by dividing the amount of data being transmitted by the reception band is used as a corrected value of the round-trip delay time. In the congestion control method according to claim 5,
In the second step, a larger value of the corrected round-trip delay time value and the measured round-trip delay time value is set as the corrected round-trip delay time. Congestion control method. In the congestion control method according to claim 5,
In the second step, the larger one of the corrected round-trip delay time value and the plurality of minimum round-trip delay time values measured each time the receiving terminal receives a response confirmation packet. Is output to the determining means as the corrected round-trip delay time. A congestion control method in a communication terminal of a communication system for setting a communication session between a plurality of communication terminals via a network and transmitting and receiving data,
A first step of measuring the amount of data being transmitted;
A second step of measuring a reception band in a receiving terminal among the plurality of communication terminals based on the received data;
A third step in which a value obtained by dividing the measured amount of data being transmitted by the reception band is a round-trip delay time ;
And a fourth step of determining a transmission band based on the round trip delay time.   9. Each of the congestion control methods according to claim 5, wherein a computer serving as a communication terminal of a communication system that performs data transmission / reception by setting a communication session between a plurality of communication terminals via a network is provided. A program for executing steps.

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