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Routing & Switching · Intermediate

Random Early Detection (RED)

A congestion avoidance mechanism that randomly drops packets as average queue depth rises between minimum and maximum thresholds.

Definition

Below the minimum threshold nothing is dropped; between thresholds drop probability rises linearly to the mark probability denominator; above the maximum, all new packets are dropped (full drop). Early drops signal TCP senders to slow down.

Example

random-detect

Exam tip

RED is effective for TCP; it does nothing useful for UDP voice, which should never be in a WRED queue.

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