WRED

Term WRED = Weighted Random Early Detection (algorithm)

(Wiki) Weighted random early detection (WRED) is a queue management algorithm with congestion avoidance capabilities.^[1] It is an extension to random early detection (RED) where a single queue may have several different queue thresholds. Each queue threshold is associated to a particular traffic class.

For example, a queue may have lower thresholds for lower priority packet. A queue buildup will cause the lower priority packets to be dropped, hence protecting the higher priority packets in the same queue. In this way quality of service prioritization is made possible for important packets from a pool of packets using the same buffer.^[2]

It is more likely that standard traffic will be dropped instead of higher prioritized traffic.

Functional Description

WRED proceeds in this order when a packet arrives:

§  Calculation of the average queue size.

§  The arriving packet is queued only if the average queue size is below the minimum queue threshold.

§  Depending on the packet drop probability the packet is either dropped or queued if the average queue size is between the minimum and maximum queue threshold.

§  The packet is automatically dropped if the average queue size is greater than the maximum threshold.