JPH1056457A - Congestion detecting method and exchange device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve efficiency in transmission while suppressing the discrimination frequency of a congestion state by determining a threshold value to be used for congestion discrimination corresponding to the quantity of information to flow into a buffer memory and detecting the presence/absence of congestion generation based on that threshold value. SOLUTION: At a cell exchange device for exchanging ATM cells, its section related to congestion control is composed of a cell queue 1, cell flow-in amount monitoring means 2, threshold value determining means 3, cell amount monitoring means 4 and congestion avoiding means 5. The cell queue 1 outputs cells, which are inputted from an input line and written, from an output terminal to an output line in the order of inputs. The cell flow-in amount monitoring means 2 monitors the flow-in of cells and sets the threshold value corresponding to its amount. When the amount of cells exceeds the threshold value for determining the congestion state, the cell amount monitoring means 4 judges the cells fall into the congestion state, and the congestion avoiding means 5 is operated for suppressing recovery from congestion or influences upon another connection to a minimum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching device for exchanging information transmitted in, for example, an asynchronous transfer mode (ATM) and a congestion detecting method used in the switching device.

[0002]

2. Description of the Related Art In ATM transmission, information that is decomposed into fixed-length packets (cells) at a transmitting terminal is transferred to a destination terminal via an asynchronous transfer network, and the original information is restored again at the receiving terminal. Done in steps.

However, since normal transfer operation cannot be expected if congestion or failure occurs during transfer, a method of detecting a network state and a method of controlling network traffic according to the state have been studied.

For example, as a method of detecting congestion in the asynchronous transfer mode, there is a method of monitoring the amount of cells in a cell waiting queue (for example, a buffer memory composed of a FIFO memory) provided at the output stage of the switching device. This method is a method of determining that the network is in a congested state when the number of cells accumulated in the cell waiting queue exceeds a predetermined threshold.

[0005] As a method of controlling traffic according to the state of the network, if the switching device determines that the network is in a congested state, the congestion avoiding means controls the switching device until the congested state of the network is avoided. There are methods such as reducing the amount of cells flowing in and preventing cells from being discarded due to buffer overflow.

Heretofore, communication quality has been ensured by actually using these methods.

[0007]

However, in the conventional system described above, if the threshold used for detecting congestion is increased, the time lag from the detection of congestion by the congestion avoiding means to the reduction of the cell inflow by control is reduced. During this period, the buffer becomes full and the probability of cell discarding increases. For this reason, there was a problem that the required quality declared in advance could not be satisfied.

On the other hand, if the threshold value is reduced in order to suppress the cell loss rate, the rate of determination as a congestion state increases. For example, congestion avoidance means such as suppressing transmission of cells from an exchange located upstream on the network. Work, and the transmission efficiency of the cell deteriorates.

However, since it is necessary in the asynchronous transfer mode to satisfy the required quality negotiated at the time of setting up a call, it is necessary to set a small threshold which is safe even if the transmission efficiency is sacrificed. Is the current situation.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and a congestion detection method capable of improving the transmission efficiency as compared with the prior art while suppressing the frequency of judging the congestion state, and an exchange device having these functions. It is intended to propose.

[0011]

In order to solve the above-mentioned problems, a congestion detecting method in a switching system for transmitting information in an asynchronous transfer mode is characterized as follows.

That is, a threshold used for congestion determination is determined according to the amount of information flowing into the buffer memory, and the presence or absence of occurrence of congestion is detected based on the threshold.

[0013] Further, the switching device in the switching system is characterized as follows.

That is, (1) a buffer memory configured to accumulate cell data input from an input line in an input order and read out the cell data in an earlier input order; and (2) monitor an amount of cells flowing into the buffer memory. Inflow monitoring means;
(3) determining means for determining a threshold used for congestion determination based on the monitoring result of the inflow amount monitoring means, (4) data amount monitoring means for monitoring the amount of data stored in the buffer memory, 5) A determination means for comparing the data amount detected by the data amount monitoring means with a threshold value and determining whether or not congestion has occurred is provided.

As described above, since the threshold value is determined based on the amount of cells flowing in, the threshold value is set high when the amount of flowing in is small to reduce the frequency of determining the congestion state, and Efficiency can be increased. Further, when the inflow amount is large, the threshold value is set low to effectively operate the congestion control, and the cell loss rate can be further suppressed.

[0016]

DETAILED DESCRIPTION OF THE INVENTION

(A) First Embodiment An embodiment of a cell switching apparatus for exchanging ATM cells will be described below with reference to the drawings. It is assumed that the information transferred as the ATM cell is multimedia information such as audio, video, data, and the like. Also, the length of each cell is
It has a fixed length of 53 bytes, of which 5 bytes are the header,
48 bytes shall be information.

(A-1) Configuration of First Embodiment (A-1-1) Overall Configuration FIG. 1 is a block diagram schematically showing the configuration of such a cell switching device. As shown in FIG. 1, the cell switching apparatus includes a cell waiting queue 1 and a cell inflow monitoring means 2.
, Threshold value determining means 3, cell amount monitoring means 4, and congestion avoiding means 5. FIG. 1 shows only a portion related to congestion control in the cell switching apparatus, and other functional blocks such as a self-routing switch are omitted.

Hereinafter, the configuration and function of each block shown in FIG. 1 will be described.

The cell waiting queue 1 is a buffer memory composed of a FIFO memory. The cell queuing queue 1 outputs cells input from the input line and once written to the output line from the output end in the order of input.

The cell inflow monitoring means 2 is located between the input line and the cell waiting queue 1 and monitors the amount of cells passing through the input line. The cell inflow monitoring means 2 monitors the time during which cells per unit flow into the cell waiting queue 1, and sets a threshold value of a threshold determination means 3 described later based on the inflow amount.

The threshold value determining means 3 is a means for determining a threshold value which gives a criterion for determining whether or not the network is in a congestion state based on the cell amount of the cell waiting queue 1. It should be noted that the threshold value determining means 3 shown in this embodiment comprises a first threshold value used when the amount of cell flowing into the input line increases, and a threshold value used when the amount of cell flowing into the input line decreases. A second threshold to be used,
The threshold is appropriately switched based on the monitoring result of the cell inflow monitoring means 2 at the preceding stage. By the way, the first
Is relatively smaller than the second threshold.

The cell amount monitoring means 4 is a means for monitoring the amount of cells stored in the cell waiting queue 1. The cell amount monitoring means 4 determines that the cell has entered a congestion state when the cell amount exceeds a threshold value for determining the congestion state.

The congestion avoiding means 5 is a means for performing various controls for avoiding a congested network from the congested state. For example, the congestion avoiding unit 5 operates so as to minimize the recovery from congestion and the influence on other connections by stopping acceptance of a new connection or discarding a low priority cell.

(A-1-2) Configuration of Cell Inflow Monitoring Unit 2 Next, the detailed configuration of the cell inflow monitoring unit 2 is shown in FIG. As shown in FIG. 2, the cell inflow monitoring means 2 includes a cell inflow counter 2A, a cell unit number memory 2B, a first comparison circuit 2C, a timer 2D, and a threshold (TH).
in) Memory 2E, second comparison circuit 2F, control circuit 2
G.

The cell inflow counter 2A is a means for counting the number of cells passing through the input line. The counting result of the cell inflow counter 2A is given to the comparison circuit 1.

The cell unit number memory 2B is a memory for recording a unit number that provides a reference when measuring the cell inflow time. Therefore, if a large value is set as this value, the average increase / decrease of the cell amount can be measured as time, and if a small value is set as this value, the instantaneous increase / decrease of the cell amount can be measured as time.

The first comparison circuit 2C is a means for constantly comparing the value of the cell inflow amount counter 2A with the value of the cell unit number memory 2B. When the value of the cell inflow counter 2A is greater than the value of the cell unit number memory 2B. When this happens, a timer is notified.

The timer 2D includes a cell inflow counter 2
A means for measuring the elapsed time since A was reset,
The time required for a predetermined number of cells to flow after the reset is measured.

The threshold (THin) memory 2E is a memory for recording the threshold THin of the timer 2D.

When the second comparing circuit 2F receives the notification of the elapsed time from the timer 2D, the second comparing circuit 2F compares the elapsed time with the value of the threshold value THin, and determines the inflow time of the cells per unit number by the timer. This is a means for determining whether or not the threshold value (THin) is larger than the threshold value (THin).

The control circuit 2G resets the timer 2D and the cell inflow counter 2A at the same time when receiving the notification of whether the value is larger from the second comparison circuit 2F, and sends the comparison result to the threshold value determination means 3. It is a means to notify. The control of the threshold value by the control circuit 2G makes it possible to set the threshold value according to the cell inflow amount.

(A-2) Operation of First Embodiment The operation procedure of the cell exchange having the above configuration will be described with reference to FIG.

The cell switching device sequentially accumulates cells input via an input line in a cell waiting queue 1, and monitors the amount of cells passing through the input line by means of a cell inflow amount monitoring means 2.

At this time, the cell inflow monitoring means 2 counts the number of cells passing through the input line by the cell inflow counter 2A (step SP1), and compares the count value with a threshold (step SP2). This comparison operation
This is repeated until it is determined in step SP3 that the number of cells has exceeded the threshold value.

When it is determined that the number of cells passing through the input line has exceeded a predetermined threshold value, the elapsed time required to exceed the threshold value and the threshold value (THi) are determined.
n) Compare with the threshold value THin stored in the memory 2E (step SP4), and determine whether the current inflow is large or small (step SP5).

Here, when the cell inflow time per unit number is less than the threshold value THin (that is, at step S
If a positive result is obtained in P5), the control circuit 2G proceeds to step SP6 and notifies the threshold value determining means 3 of a cell inflow amount increase signal.

In this case, the threshold value deciding means 3 outputs a threshold value changing signal to the cell amount monitoring means 4 so as to switch the criterion to the first threshold value having a relatively small value (step S1). SP7).

On the other hand, if the cell inflow time per unit number is equal to or longer than the threshold value THin (ie, if a negative result is obtained in step SP5), the control circuit 2
G proceeds to step SP8 and notifies the threshold value determining means 3 of a cell inflow amount decrease signal.

In this case, the threshold value determining means 3 outputs a threshold value changing signal to the cell amount monitoring means 4 so as to switch the criterion to the second threshold value having a relatively large value (step). SP9).

When the threshold value setting process according to the inflow amount of the cell amount is completed, the cell amount monitoring unit 4 sets the new threshold value notified from the threshold value determining unit 3 to the new threshold value. , And the monitoring of the cell amount of the cell combination queue 1 is continued (step SP1).
0).

Here, the cell amount monitoring means 4 compares the updated threshold value with the cell amount stored in the cell waiting queue 1, and executes the next operation according to the comparison result (step). SP11).

That is, when the cell amount stored in the cell waiting queue 1 is larger than the updated threshold value, the cell amount monitoring means 4 determines that the network has entered a congestion state, and sends a congestion signal to the network. This is sent to the avoidance means 5 (step SP12). At this time, the congestion avoiding means 5
The congestion signal is received, and appropriate control for avoiding network congestion is performed.

On the other hand, if the cell amount stored in the cell waiting queue 1 is smaller than the updated threshold value, the cell amount monitoring means 4 determines whether the network congestion state has been avoided or The congestion release signal is sent to the congestion avoiding means 5 (step SP13).
At this time, the congestion avoiding unit 5 receives the congestion release signal and stops the control for avoiding network congestion.

The above operation is repeated every time the cell inflow counter 2A and the timer 2D are reset.

(A-3) Effect of First Embodiment As described above, according to the first embodiment, the first embodiment is used for congestion detection in accordance with the ratio of the amount of cells flowing into the cell waiting queue 1. Since the threshold has been changed,
Appropriate congestion control according to the amount of inflow into the cell waiting queue 1 becomes possible.

That is, when the ratio of the amount of cells flowing into the cell waiting queue 1 is small, the threshold value is increased, and the frequency of determination of the congestion state is reduced, thereby reducing the frequency of operation of the congestion avoiding means. This makes it possible to increase the cell transfer efficiency in the network.

When the ratio of the amount of cells flowing into the buffer cell waiting queue 1 is large, the threshold value is reduced, and the congestion avoiding means is activated quickly and effectively. Even if a time lag is considered, the cell discard rate can be effectively suppressed, and the required quality of the call can be always satisfied.

(B) Other Embodiments (B-1) In the above-described embodiment, the first and second threshold values are prepared in the threshold value determining means 3 and input to the input line. Although the case where these two thresholds are properly used according to the cell inflow amount has been described, the third, fourth,... Thresholds are prepared in accordance with the cell inflow amount, and these are set to the cell inflow amount. The switching may be appropriately performed each time according to the amount.

(B-2) In the above embodiment,
Threshold value TH for determining the amount of cells flowing into the input line
Although the value of in is set to an appropriate fixed value, it may be changed to an appropriate value in accordance with parameters such as the cell discard rate and the use frequency of the cell waiting queue.

(B-3) Further, in the above-described embodiment, the number of observations when observing the inflow time per unit number of cells is fixed, but in the present invention, the number of observations of these cells is appropriately adjusted. It may be changed to an appropriate value.

[0051]

As described above, according to the present invention, the threshold value is changed to an appropriate threshold value in accordance with the amount of cells flowing in, so that a congestion detection method capable of achieving both communication quality and transfer efficiency. And a switching device.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a cell switching device according to a first embodiment.

FIG. 2 is a block diagram showing a configuration of a cell inflow monitoring unit.

FIG. 3 is a flowchart illustrating an operation procedure of the cell switching device according to the first embodiment.

[Explanation of symbols]

1 ... cell waiting queue, 2 ... cell inflow monitoring means,
2A: Cell inflow counter, 2B: Cell unit number memory, 2C, 2F: Comparison circuit, 2D: Timer, 2E: Threshold memory, 2G: Control circuit, 3: Threshold determination means, 4: Cell amount monitoring Means 5, congestion avoidance means.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Ryohei Onuma 1-7-12 Toranomon, Minato-ku, Tokyo Oki Electric Industry Co., Ltd.

Claims (5)

[Claims] 1. A method for detecting congestion in a switching system for transmitting information in an asynchronous transfer mode, comprising: determining a threshold used for determining congestion in accordance with an amount of information flowing into a buffer memory; A congestion detection method, comprising detecting the occurrence of congestion. 2. The congestion detection method according to claim 1, wherein the amount of information flowing into the buffer memory is obtained by monitoring a flow time per unit number of cells. 3. The congestion detection method according to claim 1, wherein the threshold value is selected from a plurality of preset values. 4. A buffer memory configured to accumulate cell data input from an input line in an input order and read out the cell data in an earlier input order, and an inflow amount monitoring means for monitoring an amount of cells flowing into the buffer memory. Determining means for determining a threshold value used for determining congestion based on the monitoring result of the inflow amount monitoring means; data amount monitoring means for monitoring the amount of data stored in the buffer memory; A switching unit for comparing the amount of data detected by the unit with the threshold value to determine whether or not congestion has occurred. 5. The inflow amount monitoring means obtains an amount of cells flowing into the buffer memory from a comparison result between an inflow time per unit number of cells flowing into the buffer memory from an input line and a predetermined threshold value. 5. The switching device according to claim 4, wherein: