KR100241768B1 - Method for improving virtual scheduling algorithm in atm switching system - Google Patents

Abstract

1. TECHNICAL FIELD OF THE INVENTION

ATM switchboard.

2. The technical problem to be solved by the invention

Accurate measurement of CDV (Cell Delay Variation) for all cells in order to calculate the problem and tolerance of the operation speed drop by using TRT obtained through multiple iterations in VSA for conventional UPC function as a reference point for cell discarding and buffering It is to solve the problem that the operation speed is reduced by causing the overall performance degradation.

3. Summary of Solution to Invention

When the cell enters the ingress point of the exchange, comparing the negotiated maximum cell rate (PCR) between the user and the network and the average cell rate (ACR), which is the ratio of all cells transmitted during the channel connection duration (ST1) (ST2). Wow; Comparing the average cell rate (ACR) with an MSCR for guaranteeing a minimum interval between two consecutive cells when the maximum cell rate (PCR) is greater than the average cell rate (ACR); When the average cell rate (ACR) is greater than the MSCR, buffer the arrived cell; when the average cell rate (ACR) is less than the MSCR, the value obtained by adding an error limit value (ET) to the average cell rate (ACR) and the MSCR Comparing the values (ST6); Buffering the arriving cell when the addition value (ACT + ET) obtained in the step is larger than the MSCR, and discarding the arriving cell when the addition value is smaller than the MSCR (ST5) (ST3). It is.

4. Important uses of the invention

It is applied to traffic control in ATM switch.

Description

Improving Virtual Scheduling Algorithm of ATM Switching System

In general, an ATM switch has a UPC function for traffic control, and a typical VSA is an algorithm for providing such a UPC function. UPC is a function that monitors whether traffic that has already been negotiated for use band and communication quality through the functions such as Call Admission Control (CAC) conforms to already negotiated parameters such as maximum cell rate and average cell rate when entering the network. .

In other words, if a traffic violates the reported traffic parameters, it refers to a traffic management technique for minimizing damage to other normal traffics by discarding and tagging cells of a corresponding source and managing them separately.

A typical algorithm used for such traffic management is VSA, the operation principle of which is as shown in FIG.

Here, T denotes the minimum transmission interval between cells negotiated between the user and the network during call setup, and τ denotes a tolerance introduced to improve functional degradation due to CDV (Cell Delay Variation). Here, the cell arrival time t is managed by the reference point, Theoretical Re-emission Time (TRT), and if t is greater than X = TRT + T, the cell is buffered; otherwise, the value of t plus tolerance τ is greater than X. Only when small is the cell discarded.

The three variables used in the above VSA are as follows.

1) Theoretical Re-emission Time (TRT); This is to ensure the minimum spacing between two consecutive years when cell buffering occurs and the cell cannot be transmitted before TRT.

2) Atual Re-emission Time (ART); It means the time that can be actually transmitted after TRT. ART is actually transmitted in units such as time slots.

3) Last Re-emission Time (LRT); Variable used to connect Space controller.

In other words, the cells entering the network through the exchange are buffered while maintaining the minimum spacing between cells obtained by the spacing controller running the spacing algorithm. Since each virtual channel (VC) has a limited buffer size that can be allocated, cells that arrive are discarded if network resources do not meet the negotiated maximum cell rate or if jitter is very significant. do. If a collision occurs during buffering, the TRT does not perform the next operation, and ART allocates the next possible slot to perform the channel connection function. The cell spacing algorithm is added to the initial VSA that used only one TRT.

However, the conventional VSA operating as described above has a problem in that the operation speed decreases by using the TRT obtained through several iterations as a reference point for cell discarding and buffering.

In addition, in order to calculate the tolerance, the conventional VSA requires accurate measurement of the cell delay variation (CDV) of all cells, thereby reducing the computation speed and causing the overall performance degradation.

Accordingly, the present invention has been proposed to solve various problems that occur when using the VSA, which is a typical algorithm used as the conventional traffic controller method, and an object of the present invention is a UPC (Usage Parameter Control) function, which is a traffic control function of an ATM switch. To improve the virtual scheduling algorithm (VSA) among the algorithms to control the operation at high speed, while reducing the computation time and overhead to provide an improved virtual scheduling algorithm of the ATM switch.

The method for achieving the object of the present invention comprises the steps of comparing the average cell rate, which is the ratio of the maximum cell rate negotiated between the user and the network upon arrival of the cell and the total cells transmitted during the channel connection duration; Comparing the average cell rate with an MSCR for guaranteeing a minimum spacing between two consecutive cells if the maximum cell rate is greater than the average cell rate; Buffering the arrived cell when the average cell rate is greater than the MSCR, and comparing the MSCR value with a value obtained by adding an error threshold to the average cell rate when the average cell rate is less than the MSCR; If the addition value obtained in the step is larger than the MSCR, the arrived cell is buffered; otherwise, if the addition value is smaller than the MSCR, the arrived cell is discarded.

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

1 is a flowchart showing a virtual scheduling algorithm of a conventional ATM switch.

2 is a schematic block diagram of an apparatus for controlling traffic of an ATM switch to which the present invention is applied.

3 is a flowchart illustrating a method for improving a virtual scheduling algorithm (VSA) of an ATM switch system according to the present invention.

* Explanation of symbols for main parts of the drawings

1: Traffic Source 2: UPC (Usage Parameter Control)

3: buffer

2 is a schematic block diagram of a traffic control device of an ATM switch to which the present invention is applied.

As shown in the drawing, when a traffic source 1 providing a traffic source and a cell transmitted from the traffic source 1 arrive, a maximum cell rate, an average cell rate, and an MSCR are selectively compared to determine whether the cell is buffered and discarded. The use parameter control part 2 which determines, and the buffer part 3 which buffers and outputs the cell obtained by the said use parameter control part 2 are comprised.

3 is a flowchart illustrating a method for improving a virtual scheduling algorithm (VSA) of an ATM switch system according to the present invention.

As shown in the drawing, when the cell arrives, comparing the maximum cell rate (PCR) and the average cell rate (ACR) (ST2), and when the maximum cell rate (PCR) is larger than the average cell rate (ACR), the average cell rate (ACR) ) And comparing the mean square cell rate (MSCR) to ensure the minimum spacing between two consecutive cells (ST4), and if the average cell rate (ACR) is larger than the MSCR (buffer the arrived cell (ST5)). ), When the average cell rate (ACR) is smaller than the MSCR, comparing the MSCR value with the value obtained by adding the error limit value (ET) to the average cell rate (ST6), and the addition value (ACR + obtained in the step) If ET) is larger than the MSCR, the arriving cell is buffered (ST5); otherwise, if the addition value is smaller than the MSCR, the arriving cell is discarded (ST3).

Referring to the accompanying drawings, a method for improving a virtual scheduling algorithm (VSA) of an ATM switch according to the present invention is as follows.

First, when a cell transmitted from the traffic source 1 arrives at the usage parameter controller 2 (ST1), the usage parameter controller 2 uses the mean square cell rate (MSCR) obtained by applying a stochastic estimation technique as a reference point. Determine whether to buffer and discard the arrived cell. In order to calculate the tolerance, the conventional VSA required accurate measurement of the cell delay variation (CDV) for all cells. However, in the present invention, the tolerance is determined by probabilistic calculation by changing the value of t, which determines the reliability. It speeds up the operation and reduces the hardware overhead.

A method for achieving the subject matter of the present invention described above is shown in FIG. 3, wherein the parameters used are as follows.

1) Peak Cell Rate (PCR); Concept standardized by the ITU-U as the maximum cell rate negotiated between the user and the network during call setup.

2) Average Cell Rate (ACR); It means the average cell rate, which means the ratio of total cells transmitted during the channel connection duration, a concept standardized by ITU-T.

3) Error Tolerant (ET); Error limit considering cell rate fluctuation that may be caused by delay change.

4) Mean Square Cell Rate (MSCR); It is a new reference value proposed to replace the function of TRT used as a reference point in the conventional VSA.

A method of processing a cell transmitted in actual call setup using the above-described parameters will be described below.

When the cell transmitted from the traffic source 1 arrives (ST1), the maximum cell rate (PCR) and the average cell rate (ACR) are compared (ST2), and when the maximum cell rate (PCR) is smaller than the average cell rate (ACR) Discard the transmitted cell (ST3). On the contrary, when the maximum cell rate (PCR) is larger than the average cell rate (ACR) and the mean square cell rate (MSCR) newly proposed in the present invention in order to ensure the minimum interval between two consecutive cells and the average cell rate (ACR) and Is compared (ST4).

The MSCR calculation used in the proposed VSA is as follows.

When all k-th calls transmit n cells, it is assumed that the mean square of the cell rate is a random variable X _k . If we assume that the entire arc is a population, we can obtain the sample variance S ² from Equation (1) below by using the population mean μ and the variance σ ² .

The sample MSCR (mean square cell rate) can be obtained by the above formula (1) as shown in the following formula (2).

Assuming that the number of calls is quite large, the central limit theorem shows that the distribution of transmission cells follows a normal distribution with σ ² / n variance. If the variance σ ² is unknown, assuming that the number of calls is quite large, we can use S instead of σ because S is the consistent estimator of σ. In this case, the interval estimation formula can be obtained as shown in Equation (3) below.

That is, the tolerance was determined by the reliability t (S / √n) in order to set a lower limit that determines whether to discard cells that do not reach the average cell speed.

Referring to FIG. 3 again, when the maximum cell rate PCR is greater than the average cell rate ACR, the average cell rate ACR is compared with the MSCR obtained above (ST4). As a result of the comparison, when the average cell rate (ACR) is larger than the MSCR, the arrived cell is transmitted to the buffer unit 3 to be buffered and then transmitted (ST5) .In contrast, when the average cell rate (ACR) is smaller than the MSCR, Next, the average cell rate is compared with the value obtained by adding the error limit value ET (ACR + ET) to the MSCR value (ST6). As a result of the comparison, when the addition value (ACR + ET) is larger than the MSCR, the arriving cell is buffered (ST5). Otherwise, when the addition value is smaller than the MSCR, the arriving cell is discarded (ST3).

As described in detail above, the present invention has an effect of enabling high-speed computation by controlling traffic of a cell using an MSCR obtained by applying a probabilistic estimation technique as a reference point.

In addition, there is an advantage that the load of the exchange can be reduced by reducing the amount of computation, and since the execution speed of the UPC function is increased by the high-speed computation, the overall communication quality is also improved.

The present invention improves a typical virtual scheduling algorithm (hereinafter, abbreviated as " VSA ") among algorithms for controlling the UPC (Usage Parameter Control) function, which is a traffic control function of an ATM switch, to operate at high speed. The purpose of this paper is to provide a method for improving virtual scheduling algorithm of ATM switch which can reduce overhead.

Claims (3)

A traffic control method of an ATM exchange employing a virtual scheduling algorithm to provide a UPC function, which is a traffic control function, wherein when a cell enters an ingress point of the exchange, a maximum cell rate negotiated between a user and a network and a channel connection duration Comparing the average cell rate (ACR), which is the ratio of all cells transmitted during the time period (ST1) (ST2); Comparing the average cell rate (ACR) with an MSCR for guaranteeing a minimum interval between two consecutive cells when the maximum cell rate (PCR) is greater than the average cell rate (ACR); When the average cell rate (ACR) is greater than the MSCR, buffer the arrived cell; when the average cell rate (ACR) is less than the MSCR, the value obtained by adding an error limit value (ET) to the average cell rate (ACR) and the MSCR Comparing the values (ST6); Buffering the arrived cell if the addition value (ACT + ET) obtained in the step is larger than the MSCR, and discarding the arrived cell (ST5) (ST3) if the addition value is smaller than the MSCR. A method for improving a virtual scheduling algorithm (VSA) of an ATM switch. 2. The MSCR of claim 1, wherein the MSCR calculates a sample variance S ² from a total probability sample as shown in Equation (1) below when all kth calls transmit n cells. A method for improving the virtual scheduling algorithm (VSA) of an ATM switch, comprising calculating a sample MSCR (/ X) as shown in Equation (2).

Where X _k = probability variable (mean square of cell rate), total call = population, μ = population mean, σ ² = population variance. The method of claim 2, wherein assuming that the number of calls is considerably large when the variance σ ² is unknown, S is used instead of σ, and in this case, an estimated equation such as Equation (3) is obtained. A method for improving the virtual scheduling algorithm (VSA) of an ATM switch, comprising setting a lower limit for decommissioning cells that fall short of the average cell rate.

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