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Abstract

A method and apparatus for smoothing the rate of packet discards for random early detection ('RED') in a communication device such as an ATM switch is described. The ATM switch includes a plurality of class of service queues. An accumulated discard probability is stored independently for each class of service queue. With the arrival of each packet (frame), an instantaneous discard probability is calculated. The sum of the instantaneous discard probability and the accumulated discard probability becomes the effective probability for discard. If the effective discard probability is greater than (or equal to) a random number, the cell is discarded, and the accumulated discard probability is cleared. Otherwise, the sum is stored back as the new value for the accumulated discard probability. The accumulated discard probability may optionally be cleared if a class of service queue's current cell count is zero. Additionally, if the instantaneous discard probability caused the accumulated discard probability to increase too fast, causing too many discards, a programmable accumulation factor may be multiplied by the instantaneous discard probability.

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First Claim