JPH0630017A - Atm cell flow converter - Google Patents

Abstract

PURPOSE:To provide a burst cell flow which is suited to be accurately evaluated by providing a means to store the inputted ATM cell flow and reading out this cell flow as a burst cell flow to control it. CONSTITUTION:An ATM cell flow 10 is inputted to a valid cell selecting circuit 1 and only a valid cell 11 is selected and stored in a cell buffer 2. When the buffer 2 becomes empty, a buffer empty signal 14 is generated. Then a counter 4 is reset and the transmission of the cell 11 is discontinued from the buffer 2. When the buffer 2 is filled, a buffer full signal 16 is generated. Then a counter 3 is reset and the cell 11 is transmitted from the buffer 2. In this method, however, a burst cell flow may possibly be excluded out of the setting. Then the generating states of the random number generating circuits 7 and 8 are set so that the burst generating probability is secured in accordance with the generating probability of the input cell flow 10. Thus the preceding problem can be evaded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an AT which converts an input ATM cell stream into a cell stream having a burst property and outputs it.
The present invention relates to an M cell flow converter, and more particularly to an ATM cell flow converter suitable for creating a cell flow input to an ATM communication system for burst traffic characteristics and performance evaluation of congestion control.

[0002]

2. Description of the Related Art Recently, a broadband ISDN (B-ISDN: Broad-Band Integ) capable of unifying and handling communication information from various media such as voice, data and images.
ratedServices Digital Network) is attracting attention.
In this B-ISDN, research is currently underway in the direction of using an ATM (asynchronous transfer mode) communication system.

Since the ATM communication system is an asynchronous transfer in which information is placed in a cell and transmitted every time information is generated in a terminal, the information is not a CBR (Constant Bit Rate) but a network at random timing. Sent to. In particular, when high bit rate information such as image information is transmitted, ATM cells are expected to occur in bursts and a so-called congestion state such as cell collision occurs. Such a congestion state is a major problem because it causes cell discard in the ATM exchange. Controlling the congestion state and minimizing cell discard will improve the performance of the exchange. From this, it is the AT that creates the burst condition, which is considered to be the largest cause of congestion.
It is considered to be important for evaluating the M communication system.

However, a conventional cell generator for evaluating an ATM communication system uses a method of manually inputting a cell generation pattern of a certain fixed period, or performs only cell generation according to a cell generation probability according to Poisson distribution. I can't. In such a conventional cell generator, it is not possible to generate a burst cell flow, in particular, a cell flow in which both the burst generation timing and the burst length, which are performed in a simulation of a burst state, have a generation probability according to Poisson distribution. Can not. This means that when an experimental machine for an ATM switching system is manufactured, it is necessary to evaluate the switching system such as the cell loss rate due to the burst cell flow, and to accurately evaluate the effect of congestion control. It can be said that this is a big problem when comparing the simulation results of burst traffic control, which is currently being subjected to many simulations, with the actual measurement results.

Furthermore, in order to create a burst cell flow suitable for proper evaluation of such an ATM communication system,
If a burst cell flow generator is configured to include a cell generator that generates cells with a cell generation probability according to the Poisson distribution, the cell generator is complicated, resulting in an extremely large overall circuit scale.

[0006]

As described above, in the conventional ATM cell generator, when evaluating the ATM communication system, the cell discard rate due to the burst cell flow, the effect of congestion control, and the burst traffic control are evaluated. There is a problem that a burst cell flow suitable for comparing the simulation result with the actual measurement result cannot be generated with a simple configuration.

It is an object of the present invention to provide an ATM cell flow converter capable of generating a burst cell flow suitable for proper evaluation of an ATM communication system with a simple structure.

[0008]

In order to solve the above problems, an ATM cell flow converter according to the present invention comprises a storage means for storing an input ATM cell flow and an ATM cell stored in the storage means. The basic feature is that the control means is provided for controlling the flow to be read as a burst cell flow.

According to one aspect of the present invention, the control means comprises first and second random number generating means, and first and second random number generating means.
First and second counting means for respectively counting the clocks synchronized with the ATM cell stream, the first counting means corresponding to the first random number value of the clocks. The reading of the cells from the storage means is started every time the counting is performed, and from the time when the reading is started, the second counting means counts the number of clocks corresponding to the second random number value from the storage means. The cell reading is completed.

According to another aspect of the present invention, the control means includes first and second random number generating means and first and second random number values generated from the first and second random number generating means. And a first and second counting means for counting a clock synchronized with the ATM cell stream, the first counting means counting a number of the clocks corresponding to a first random number value. The cells are read from the storage means during the period of 1, and the second counting means counts the number of the clocks corresponding to the second random number value after the end of the first period. Pause reading of cells from the means.

[0011]

According to the present invention, the input ATM cell flow is once accumulated and converted into a burst cell flow when reading out. That is, a cell flow or the like generated with a cell generation probability according to the Poisson distribution sent from a cell generation device for evaluating an ATM communication system is directly used as an input signal source and converted into a burst cell flow. Therefore, a burst cell flow suitable for more accurately evaluating the ATM communication system can be obtained with a simple configuration without newly preparing an apparatus for generating the burst cell flow.

Further, by controlling the read operation of the accumulating means by using two random number generating means and two counting means respectively, the burst generation timing (burst period or burst interval) and burst length are set according to an arbitrary probability distribution. Various types of burst cell streams are available. Therefore, by inputting this burst cell flow into the ATM communication system, it becomes possible to compare and examine the effect of the congestion control expected by the calculation in the simulation and the evaluation result by the experiment using the actual system. More accurate system evaluation and simulation evaluation can be performed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of an ATM cell flow converter according to an embodiment of the present invention. This ATM cell flow converter includes a valid cell selection circuit 1 that selects and outputs a valid cell 11 from an input ATM cell flow 10, a cell buffer 2 that stores the cell 11 from the valid cell selection circuit 1, and a cell buffer 2. For controlling the first and second counters 3, 4,
The delay circuit 6 and the first and second random number generators 7 and 8 are used.

Next, the operation of this embodiment will be described. First, as an initial state, the random number values 17 and 18 generated from the random number generators 7 and 8 are loaded into the counters 3 and 4 by the initial setting signal 19. ATM cell flow 10 input
Is a cell flow generated according to a Poisson probability distribution of 60% from a cell generator (not shown), an example of which is shown in FIG. This ATM cell stream 10 is input to the valid cell selection circuit 1, where only valid cells 11 are selected and stored in the cell buffer 2.

When the first cell of the ATM cell stream 10 arrives, the cell clock CCK causes the counters 3 and 4 to start counting down. The contents of counter 3 are all "0"
Then, when the counter 3 counts the number of cell clocks CCK corresponding to the random number value 17, the burst cycle setting signal 15 is supplied from the counter 3 to the cell buffer 2. When the read operation of the cell buffer 2 is started by the burst cycle setting signal 15, the cells accumulated in the cell buffer 2 are read at the timing of the cell clock CCK and sent to the output as a burst cell stream 12. It

When the contents of the counter 3 become all "0", the delay circuit 6 is driven after the random number generator 7 is driven.
The random number value 17 generated from the random number generator 7 is loaded into the counter 3 via the, and the counter 3 starts counting down again. That is, every time the counter 3 counts the number of cell clocks CCK corresponding to the random number value 17, the reading of cells from the cell buffer 2 is started.

When the contents of the counter 3 become all "0", the random number value 18 generated from the random number generator 8 is simultaneously loaded into the counter 4 and the counter 4 starts counting down. Then, when the contents of the counter 4 become all “0”, that is, when the counter 4 counts the number of cell clocks CCK corresponding to the random number value 18, the counter 4
Then, the burst length setting signal 13 is supplied to the cell buffer 2, the reading of the cells from the cell buffer 2 is completed, and the counter 4 is in the hold state. That is, every time the counter 4 counts the number of cell clocks CCK corresponding to the random number value 18 from the start of reading, the reading from the cell buffer 2 ends.

By such an operation, as shown in FIG. 2, the burst cycle setting signal 1 generated by the first counter 3 is generated.
Burst period t _B (i) (i = 1, 2,
, And has a burst length t _L (i) (i) determined by the burst length setting signal 13 generated by the second counter 4.
= 1, 2, ...) is read from the cell buffer 2 and sent to the output.

At this time, since the cell flow sent to the output is assumed to be a burst cell flow, it is sent for each cell. However, if the cell sending timing can also be set from the outside, during the burst generation period. It is possible to arbitrarily set the cell interval of the cell flow such that one cell is transmitted every two cell clocks CCK arrive, or the cell generation during the burst generation period is made to be a cell generation probability according to Poisson distribution. is there.

Here, when the cell in the cell buffer 2 becomes empty while the counter 4 is counting down, or conversely, when the cell buffer 2 is full when the counter 4 is in the hold state. The problem is that. As a countermeasure, in the present embodiment, when the cell buffer 2 becomes empty, the cell buffer 2 is caused to generate a buffer empty signal 14 to that effect, and the counter 14 is reset by the signal 14 to reset the cell buffer 2. From the cell buffer 2 by stopping the cell transmission from the cell buffer 2 and generating a buffer full signal 16 from the cell buffer 2 when the cell buffer 2 is full and resetting the counter 3 by the signal 16. It is designed to send cells. In this method, the burst cell flow 12 sent to the output may be out of the setting, but the random number generators 7 and 8 are set so that the burst occurrence probability matches the cell occurrence probability of the input ATM cell flow 10. Such a problem can be avoided by a method such as setting the random number generation state of.

The random number generators 7 and 8 generate random number values 17 and 18, respectively, according to a probability distribution function preset by an external input. FIG. 4 shows an example of this probability distribution function. By using such a function, the burst period t _B (i) and the burst length t _L (i) can be randomly changed as shown in FIG.

The present invention is not limited to the configuration as shown in FIG. 1. For example, the time when a cell of the burst cell flow is transmitted, the time when the cell is not transmitted, or the cell occurrence probability according to the Poisson distribution. It is also possible to configure to generate a burst cell flow of a pattern different from that described above by determining the two times of the cells to be generated by the two counters and the random number generator.

FIG. 6 shows the relationship between the cell generation timing of the burst cell flow and the values of the first and second counters in this case. That is, in this example, the burst length t _L (i) (i = 1, 2,
, And the burst interval t _N (i) (i = 1, 2, ...) Of the burst cell flow is determined by the second counter. In this case, the first period (t) in which the first counter counts the number of cell clocks CCK corresponding to the first random number value
(Corresponding to _L (i)), the cell is read from the cell buffer 2, and after the end of the first period, the second counter is set to the second
During the second period (corresponding to t _N (i)) of counting the number of cell clocks CCK corresponding to the random number value of 1, the reading of cells from the cell buffer 2 may be suspended.

A cell generator may be provided instead of the cell buffer 2 shown in FIG. In that case, the device of FIG. 1 is not a cell flow converter but a burst cell flow generator. Further, if only the first counter 3 is operated in FIG. 1 and the load value of the second counter 4 is always set to 1, the device of FIG. 1 has a cell generation probability according to a normal Poisson distribution. Can also occur. Other,
The present invention can be implemented with various modifications.

[0025]

As described above, according to the present invention, the input ATM cell flow is all burst cell flow or only a part of the cell flow is burst cell flow with a simple structure. It becomes possible to appropriately evaluate congestion control and burst traffic characteristics, which have been major problems in ATM communication systems. In addition, by simply setting the probability distribution function for random number generation from the outside, it becomes easy to compare and study with the simulation results of the burst cell flow that is currently popular, so a more accurate evaluation of the ATM communication system as a whole is possible. Is possible.

[Brief description of drawings]

FIG. 1 is a block diagram of an ATM cell flow converter according to an embodiment of the present invention.

FIG. 2 is a diagram showing a burst cell flow output from the ATM cell flow converter of FIG.

3 is an AT input to the ATM cell flow converter of FIG.
Diagram showing M-cell flow

4 is a diagram showing a probability distribution function for setting a random number value generated by the random number generator of FIG.

5 is a diagram showing a probability distribution function for setting a random number that determines the ATM cell flow of FIG. 1;

FIG. 6 is a diagram showing an example of a burst cell flow output in another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Effective cell selection circuit 2 ... Cell buffer (storage means) 3 ... 1st counter 4 ... 2nd counter 5 ... Gate circuit 6 ... Delay circuit 7 ... 1st random number generator 8 ... 2nd random number generator 10 ... Input ATM cell flow 11 ... Effective cell 12 ... Burst cell flow 13 ... Burst length setting signal 14 ... Burst empty signal 15 ... Burst period setting signal 16 ... Burst full signal 17 ... First random number value 18 ... Second random number Numerical value 19 ... Initial setting signal

Claims (3)

[Claims] 1. An ATM cell comprising: an accumulating means for accumulating an inputted ATM cell flow; and a control means for controlling to read out the ATM cell flow accumulated in the accumulating means as a burst cell flow. Flow converter. 2. The control means includes first and second random number generating means, first and second counting means for counting clocks synchronized with the ATM cell flow, and first and second counting means.
Means for loading the first and second random number values generated from the random number generating means into the first and second counting means, respectively, and the first counting means corresponds to the first random number value. Each time the number of the clocks is counted, the reading of the cells from the storage means is started, and the second counting means counts the number of the clocks corresponding to the second random number value from the reading start time. 2. An ATM cell flow converter according to claim 1, wherein reading of cells from the storage means is completed. 3. The control means includes first and second random number generating means, first and second counting means for counting clocks synchronized with the ATM cell stream, and the first and second counting means.
Means for loading the first and second random number values generated from the random number generating means into the first and second counting means, respectively, and the first counting means corresponds to the first random number value. During the first period of counting the number of clocks, the cells are read from the storage means, and after the end of the first period, the second counting means counts the number of clocks corresponding to the second random number value. 2. An ATM cell flow converter according to claim 1, wherein reading of cells from said storage means is suspended during the second period of time.