WRED Mark Probability Denominator (MPD) in Byte-Based Mode

Weighted Random Early Detection (WRED) uses what is known as a Mark Probability Denominator (MPD). The MPD is the fraction of packets dropped when the average queue size is at the maximum threshold. It defines the likelihood of marking or dropping packets when they exceed the minimum threshold but do not reach the maximum threshold.

WRED can be configured in byte-based mode, where the queue depth is configured using bytes as units instead of packets. In a byte-based WRED configuration, the MPD value translates to "1 out of X bytes," meaning that the probability revolves around the flow of bytes through the queue. Thus, while you can't mark or drop specific bytes, the packet containing the 1 out of X bytes is either marked or dropped, aligning actions based on a byte calculation rather than a packet calculation.

This method provides finer granularity in traffic handling, which is useful in environments with packets of varying sizes. Byte-based WRED ensures that larger packets have a proportionally higher chance of being marked or dropped compared to smaller ones, promoting fairer traffic management.

https://networklessons.com/quality-of-service/wred-weighted-random-early-detection