Which of the following statements about congestion avoidance is correct?
A.
When the number of packets exceeds the early drop threshold, packets are randomly dropped to avoid queue congestion without affecting services.
B.
Early drop and tail drop cannot coexist.
C.
Early drop indicates that packets are dropped before the number of packets reaches the preset threshold of packet numbers. This prevents queue congestion.
D.
The random drop probability in weighted early drop is related to the upper and lower thresholds.
WRED (weighted early drop) uses lower and upper thresholds to determine a probabilistic drop curve; the drop probability scales with the average queue length between these thresholds—therefore D is correct.
A is incorrect because early dropping inevitably affects services to some extent; it’s designed to trade small, controlled loss for stability.
B is incorrect; devices use early drop before buffers fill, and when full, tail drop still applies—both mechanisms coexist.
C is imprecise in Huawei’s terminology; early drop begins when the average queue depth crosses the lower threshold and increases up to the upper threshold, not simply “before a preset threshold” without that two-threshold relationship.
[Reference: HCIP-Access V2.5 – WRED thresholds and probability model; coexistence of early drop and tail drop., , ]
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