JPH09224025A - Congestion control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a congestion control method for suppressing the spread of congestion and recoverying from a congestion state while maintaining the high throughput of the entire network. SOLUTION: A data receiving/holding part 1 receives data from an upstream node and holds them in a buffer, a data transmission part 2 takes out the data from the buffer and transmits them to a downstream node and a transmission rate reception part 3 receives a specified rate from the downstream node. A congestion detection part 6 detects the congestion based on the calculated result of a free capacity estimation part 7 and the free capacity estimation part 7 estimates the free capacity of the buffer after RTT(round trip time) time from the free capacity at present, a maximum data amount from the upstream node and a data amount to the downstream node. A specified rate calculation part 8 adds a rate proportional to the free capacity to the specified rate from the downstream node and calculates the specified rate to the upstream node.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention allows each network node to specify a data transmission rate of a network node (hereinafter, referred to as an upstream node) for transmitting data to the network node so that the congestion state of the network node can be reduced. The present invention relates to a congestion control method for solving the problem.

[0002]

2. Description of the Related Art The following two methods have been considered as conventional congestion control methods. 1. Congestion adaptive control method 2. Congestion Avoidance Control Method Method 1 detects the occurrence of congestion by increasing the queue length of a buffer provided in the network node, and performs operations such as suppressing data transfer. That is, it is a method of performing control after the network becomes congested. The method 2 judges whether or not congestion may occur by accepting the call when the call occurs, and rejects the acceptance of the call that may cause congestion, so that the network is congested. It is a method of controlling so that it does not fall into.

[0003]

However, method 1
According to the above, since the operation is performed without using network wide information, there is an advantage that the operation / device is relatively simple and small in scale, but it does not consider the influence of each network node on other network nodes. In addition, since the judgment is made based on the status of the own node, congestion of other nodes may be caused to spread the congestion state and reduce the throughput of the entire network.

According to the method 2, at the time of accepting a call, it is necessary to judge whether or not congestion occurs due to acceptance of the call. For that purpose, information on the entire network or a part of the current network is required. Therefore, it is necessary to use these to perform complicated calculations such as estimation of free bandwidth and probability of congestion, and in order to increase the throughput of the entire network, a highly accurate estimation method is required.

When the speed of the network is increased, the method 1 has a problem that the control delay becomes large and the control cannot be performed in time, and the method 2 has a problem that the network state is maintained while collecting the information necessary for the determination. However, there is a problem in that the reliability of the result of the judgment may change and the meaning may be meaningless.

In order to solve the above problems, the present invention provides
Providing a congestion control method for suppressing the spread of congestion and recovering from congestion by specifying the transmission rate of upstream nodes while considering the control delay between network nodes while maintaining high overall network throughput The purpose is to do.

[0007]

In order to solve the above problems, the present invention provides means for designating the sending rate of the upstream node of the own node based on the sending rate of the own node to the downstream node, and means for each node. Control delay time RTT
(Round Trip Time) The free space of the buffer after the time,
In addition to the current free space in the buffer, the maximum amount of data that flows in from the upstream, a means to estimate from the amount of data that is currently flowing out to the downstream, and use it during a period shorter than the control delay time Means for specifying ± α minutes, and the free space of the buffer after the RTT time when the specified rate from the downstream is narrowed to the minimum, the current free space of the buffer, the maximum amount of data flowing from the upstream, and the current downstream. Means to detect the congestion state by estimating it from the amount of data flowing out to, and periodic rate update for effective use of the network and rate update for recovery from the congestion state when the congestion state is detected And means of.

According to the first aspect of the present invention, each network node designates the upstream transmission rate of the own node based on the downstream transmission rate of the own node in addition to the queue length of the own node. It is characterized by recovering from the congestion state.

The invention according to claim 2 is a congestion control method in a high-speed network, wherein RTT is a control delay.
(Round Trip Time) The control amount of congestion control is determined by estimating the free capacity of the buffer after the time.

A third aspect of the present invention is a congestion control method in a high speed network, wherein RTT is a control delay.
(Round Trip Time) The congestion state is detected by estimating the free space of the buffer after a lapse of time, and the control is activated.

According to a fourth aspect of the present invention, flow control in which a downstream node periodically specifies a transmission rate of an upstream node in a high speed network, and each network node has a minimum downstream transmission rate. The upstream transmission rate is updated when a congestion state is detected by estimating the free space of the buffer after the assumed RTT time, and the rate specified in both cases is the transmission rate of the upstream node of the own node. It is characterized in that it is specified based on the transmission rate of the own node to the downstream node and the estimated buffer capacity after the RTT time of the own node.

[0012] The invention according to claim 5 is flow control in which a downstream node periodically specifies a transmission rate of an upstream node in a high-speed network, and each network node has a minimum downstream transmission rate. The free space of the buffer after the assumed RTT time was estimated from the current free space of the buffer and the maximum amount of data arriving within the RTT time, and the estimated free space of the buffer was a negative value. Occasionally, if a congestion condition is detected, the upstream transmission rate is updated in addition to the periodic rate update. The specified rate is specified by the sending rate ± α to the downstream node of the own node, and it is assumed that the sending rate to the downstream node of the own node is constant for this ± α. Estimating the buffer capacity of the self-node after the RTT time, characterized in that it specify that the zero rate update period is a period for periodically update the rate the estimated buffer capacity.

[0013]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a network node having a congestion control method according to an embodiment of the present invention. In this figure, the data receiving / holding unit 1 receives data from an upstream node and holds the data in a buffer provided in the receiving / holding unit 1 (see FIG. 4). The data sending unit 2 takes out the data from the buffer and sends the data to the downstream node.

The sending rate receiving unit 3 receives a designated rate from the downstream node (that is, a value designating a sending rate of data to the downstream node). Designated rate transmitter 4
Sends a specified rate to the upstream node (that is, a value that specifies the data transmission rate from the upstream node). The designated rate history holding unit 5 holds the past history of the designated rate transmitted by the designated rate transmission unit 4. The congestion detection unit 6 detects the occurrence of congestion based on the calculation result of the free space estimation unit 7.

The free space estimation unit 7 estimates the free space of the buffer after the RTT time. In a high-speed network, there is a propagation delay that cannot theoretically be ignored, so
It takes a finite time from when the notification signal of the designated rate is sent to the upstream node until the notification signal reaches the upstream node and its influence returns (that is, the control starts to take effect). Here, the above time is set to RTT (= Roun
d Trip Time).

The designated rate calculation unit 8 calculates a designated rate for the upstream node. The designated rate transmission timer 9 monitors the timing of transmitting the designated rate to the upstream node. The network node 10 includes a data receiving / holding unit 1, a data sending unit 2, a sending rate receiving unit 3, a designated rate transmitting unit 4, a designated rate history holding unit 5, a congestion detecting unit 6, a free space estimating unit 7, and a designation. Rate calculator 8,
It is composed of a designated rate sending timer 9.

FIG. 2 is a block diagram showing an example of a network constructed by using a plurality of the network nodes shown in FIG. The network shown in this figure is composed of network nodes 11 to 13 and terminals 14 and 15. The configurations of the network nodes 11 to 13 are the same as those of the network node 10 shown in FIG.

Next, the operation of the congestion control method having the above configuration will be described. FIG. 3 is a flowchart showing an operation example of a network node provided with the congestion control method according to this embodiment. Here, in the network shown in FIG. 2, the network node 11 is an upstream node, and
The operation of the network node 12 when the network node 13 is the downstream node will be described.

In FIG. 3, first, the operation of the network node 12 proceeds to step S1. In step S1, it is determined whether new data has arrived from the upstream node (= network node 11). When this determination result is “YES”, the data receiving / holding unit 1 receives the arrived data, stores it in the buffer, and notifies the free space estimation unit 7 of the new state of the buffer caused by the storage. , And proceeds to step S7. In step S7,
The free space estimation unit 7 estimates the free space of the buffer after the RTT time, and proceeds to step S8.

On the other hand, the determination result of step S1 is "NO".
In the case of, it progresses to step S2. In step S2,
It is determined whether the specified rate is notified from the downstream node (= network node 13). The result of this determination is “YE
In the case of "S", the process proceeds to step S5. In step S5,
The sending rate receiving unit 3 updates the sending rate of the present network node 12 by notifying the data sending unit 2 and the free space estimating unit 7 of the specified rate, and step S7
Proceed to. In step S7, the free space estimation unit 7 determines that the RT
The free space of the buffer after T time is estimated, and the process proceeds to step S8.

On the other hand, the determination result of step S2 is "NO".
In the case of, it progresses to step S3. In step S3,
The network node 12 itself determines whether or not it is time to send data to the downstream node (= network node 13). If the result of this determination is "YES", then the operation proceeds to step S6. In step S6, the data sending unit 2 fetches the data from the buffer in the data receiving / holding unit 1, and the downstream node (= network node 1
3). Since the state of the buffer changes due to the transmission, the data receiving / holding unit 1 notifies the free space estimating unit 7 of the new state of the buffer, and proceeds to step S7. In step S7, the free space estimation unit 7 estimates the free space in the buffer after the RTT time,
Proceed to 8.

Now, the operation of the free space estimating section 7 (calculation of free space) in step S7 will be described. As described above, since there is a propagation delay that cannot be ignored in a high speed network, the free space estimation unit 7 according to the present embodiment estimates the free space of the buffer after RTT described above.

The free space estimating unit 7 receives the current queue length Q (t) from the data receiving / holding unit 1, the designated rate f (t) from the sending rate receiving unit 3, and the designated rate history holding unit 5. History of specified rate R (t) ~ R (t-RT
T) respectively, and the free space X (t + T) of the buffer after T time is calculated by the following equation (1).

[Equation 1]

Here, the designated rate f (t) is the current designated rate notified from the downstream node (= network node 13). Also, the history records R (t) to R (t-RT
T) is the past history of the designated rate notified to the upstream node (= network node 11), in other words,
It shows the maximum amount of data that arrives from the upstream node (= network node 11) from the present time to RTT time. L is the buffer capacity excluding the margin, and Q
(T) is the queue length at time t (see FIG. 4).

Equation (1) is the current free space L of the buffer.
The maximum amount of data that arrives at the network node 12 in the RTT from Q (t)

[Equation 2] And the difference between the estimated f (t) T of the amount of data transmitted from the network node 12 within the RTT.

As a result, the minimum value of the free space of the buffer after RTT, that is, the maximum amount of data that does not exceed the specified rate notified to the upstream node (= network node 11) is the upstream node (= network node 1).
The free space of the buffer when it is sent from 1) is estimated. However, this value is a value under the assumption that the designated rate notified from the downstream node (= network node 13) is constant.

As described above, the calculation by the equation (1) is based on the assumption that the designated rate notified from the downstream node (= network node 13) is constant, and therefore the RTT is calculated based on the calculation. Free space after (X
Even if (t + T)) is estimated, when the designated rate notified from the downstream node (= network node 13) is narrowed down, the amount of data transmitted from the network node 12 to the downstream node (= network node 13) decreases. Therefore, the queue length of the buffer in the network node 12 may increase more than expected and data may overflow from the buffer.

Therefore, it is assumed that the transmission rate notified from the downstream node (= network node 13) is the minimum value (= 0), and the free space (Y (t + T)) after RTT under the assumption is Similar to the equation (1), it is calculated by the following equation (2).

(Equation 3) As a result, the downstream node (= network node 13)
The free space of the buffer after RTT is calculated, assuming that the transmission rate notified from the minimum value (= 0).

When the free space of the buffer is estimated by the above method, the free space estimating section 7 determines the free space of the buffer X (t + T) calculated by the equation (1) as the designated rate calculating section 8.
The free space Y of the buffer calculated by equation (2)
(T + T) is notified to the congestion detection unit 6, and the process proceeds to step S8. Above, the operation | movement description of the free space estimation part 7 in step S7 is complete | finished.

In step S8, the congestion detection unit 6 determines whether or not to fall into the congestion state based on the free space Y (t + T). As described above, when the designated rate notified from the downstream node (= network node 13) is narrowed down, the queue length in the network node 12 may increase more than expected and data may overflow from the buffer. The congestion detection unit 6 determines the congestion based on the free capacity (Y (t + T)) after RTT, assuming that the specified rate notified by the downstream node (= network node 13) has reached the minimum value (= 0). Judge whether or not to fall into a state. Here, when Y (t + T) ≧ 0, R
It is estimated that there is still free space in the buffer after the TT time, so the process proceeds to step S4.

On the other hand, the determination result of step S3 is "NO".
Also in case of, it progresses to step S4. The designated rate sending timer 9 holds a cycle (designated rate update cycle W) for updating the designated rate notified to the upstream node (= network node 11). Therefore, in step S4, the elapsed time from the previous notification of the designated rate is constantly measured, and it is determined whether or not the designated rate update period W has elapsed. If the result of this determination is "YES", then the operation proceeds to step S9.

On the other hand, in the judgment of step S8, Y
If (t + T) <0, buffer capacity L after RTT time
Since it is estimated that (see FIG. 4) will be used up, the congestion detection unit 6 notifies the designated rate sending timer 9 of the fact that congestion has been detected, and proceeds to step S9.

In step S9, the designated rate calculation unit 8
From the free space estimation unit 7 to the free space (X (t
+ T)) and the current sending rate,
A new designated rate to be notified to the upstream node (= network node 11) is calculated. Then, the designated rate calculation unit 8 notifies the designated rate transmission unit 4 of the calculated designated rate and issues an instruction to transmit the new designated rate to the upstream node (= network node 11), and step S10. Go to.

The operation of the designated rate calculation unit 8 in step S9 (calculation of the designated rate notified to the upstream node) will be described below. The designated rate R (t) notified to the upstream node (= network node 11) is equal to the designated rate f (t) notified from the downstream node (= network node 13) to the free capacity X after the RTT of the network node 12. We will add a rate proportional to (t + T).

Since it is impossible to always send the notification signal of the designated rate, the designated rate update cycle W (> T)
Then, the network node 12 notifies the upstream node (= network node 11) of the designated rate at intervals of the designated rate update cycle W. The designated rate update cycle W is held by the designated rate calculation unit 8 and the designated rate sending timer 9.

As a result, the designated rate calculation unit 8 calculates the designated rate by the following equation (3) so that the free space X (t + T) estimated by the free space estimation unit 7 is consumed within the designated rate update period W. To do. R (t) = f (t) + {X (t + T) / W} (3) However, the specified rate R (t) is within the bandwidth of the link.

In step S10, the designated rate transmission unit 4
Receives an instruction to send the designated rate from the designated rate transmission timer 9, the new designated rate received from the designated rate calculation unit 8 is sent to the upstream node (= network node 11).
To step S11. At this time, the designated rate history holding unit 5 stores the designated rate as a history. In step S11, the timer that counts the elapsed time after the notification of the designated rate is reset, and in step S1
Return to On the other hand, even when the result of the determination in step S4 is "NO", the process returns to step S1. This is the end of the description of the operation of the congestion control method according to the above configuration.

From the above, when the queue is expected to be smaller than the buffer capacity L (X (t + T)> 0) after the RTT time, the network node 12 sets the specified rate for notifying the upstream node (= network node 11). Move in the raising direction (R (t) = f (t) + α). Also,
When the queue is near the buffer capacity L (X (t + T) ≈0), the network node 12 has the specified rate for notifying the upstream node (= network node 11) and the specified rate for notifying from the downstream node (= network node 13). Move in the same direction (R (t) ≈f (t)).
Also, the queue exceeds the buffer capacity L (X (t + T)
At the point where <0) is expected, the network node 1
2 moves in the direction of slowly lowering the specified rate for notifying the upstream node (= network node 11) (R (t)
= F (t) -α), try to recover from the congestion state.

By the above operation, it is possible to recover from the congestion state while suppressing the spread of the congestion while keeping the throughput of the entire network high.

Although the embodiment of the present invention has been described in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and changes in the design and the like can be made without departing from the gist of the present invention. Even if there is, it is included in the present invention.

[0041]

As described above, according to the present invention, the transmission rate of the upstream node is designated based on the transmission rate to the downstream node, so that the congestion state is recovered without reducing the throughput of the entire network. it can.
Further, since the control delay is taken into consideration and the network-wide information is not used, even if the network speeds up, it is possible to recover from the congestion state without causing an inappropriate operation.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a network node equipped with a congestion control method according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an example of a network configured by using a plurality of network nodes shown in FIG.

FIG. 3 is a flowchart showing an operation example of a network node equipped with the congestion control method according to the present embodiment.

FIG. 4 is an explanatory diagram showing an example of a state of a buffer in this embodiment.

[Explanation of symbols]

1 ... Data receiving / holding unit, 2 ... Data sending unit, 3
...... Sending rate receiving unit, 4 …… Specified rate transmitting unit, 5
...... Designated rate history holding unit, 6 ...... Congestion detection unit, 7 ...
... Free space estimation section, 8 ... Designated rate calculation section, 9 ...
Specified rate sending timer, 10, 11, 12, 13 ... Network node, 14, 15 ... Terminal

Claims (5)

[Claims] 1. A network node recovers from a congestion state by designating an upstream transmission rate of its own node based on the downstream node transmission rate of its own node in addition to its own queue length. Congestion control method characterized by. 2. A congestion control method in a high speed network, which is a control delay RTT (Round Trip Time).
A congestion control method characterized in that the control amount of congestion control is determined by estimating the free capacity of a buffer after a lapse of time. 3. A congestion control method in a high-speed network, which is a control delay RTT (Round Trip Time).
A congestion control method which detects a congestion state by estimating the free space of a buffer after a lapse of time and activates the control. 4. RTT time when flow control in which a downstream node periodically specifies the transmission rate of an upstream node in a high-speed network, and each network node assumes that the downstream transmission rate is the lowest. When a congestion state is detected by estimating the free capacity of the subsequent buffer, the upstream sending rate is updated. In both cases, the specified rate is the sending rate of the upstream node of the own node, and the downstream node of the own node. A congestion control method characterized by designating based on the transmission rate to the node and the estimated buffer capacity after the RTT time of the own node. 5. A flow control in which a downstream node periodically specifies a transmission rate of an upstream node in a high-speed network, and each network node assumes that the downstream transmission rate is the lowest RTT time. The free capacity of the subsequent buffer is estimated from the current free capacity of the buffer and the maximum amount of data that arrives within the RTT time, and when the estimated free capacity of the buffer is a negative value, the congestion state is detected. In addition to the periodic rate update, the upstream sending rate is updated, and when the rate is updated regularly and congestion is detected, the new specified rate that indicates the sending rate of the upstream node of the own node is The transmission rate to the downstream node of is specified by ± α, and this ± α is after RTT time when the transmission rate of the own node to the downstream node is assumed to be constant. Congestion control method characterized by estimating the buffer capacity of its own node, and designating the estimated buffer capacity to be zero within a rate update period, which is a period for periodically updating the rate.