From: Huan Pham (huan.pham@valuenet.com.au)
Date: Thu Jan 10 2008 - 01:32:40 ARST
Hi Abdul
> 1. what does my average queue length represent:
Queue length influences how heavily we should randomly drop packets in the
queue. It should have indication of the "future" congestion, rather than
just the past congestion status.
More specifically, average queue length is the estimated value of the queue
lenght over the next time interval, calculated based on the queue length
value in the last time interval and the current interval.
Depending on the value of exponential-weighting-constant, the estimated
average can be over-reactive or under-reactive to the short-term burstiness.
Value of 1 is the value most "reactive" to the short-term congestion.
> 2. why should packet be drop when my average queue lenght equals the
> Min-threshold and not just when it equal the Max threshold for that
> precedence.
The WRED randomly drop packets already in the queue, with the probability
increasing from 0% (when average queue size = Min threshold) to
mark_probability_denominator when average queue size reaches Max threshold.
The queue size between Min threshold and Max threshold is subject of WRED
dropping. The purpose of WRED is to drop packets early, to prevent
congestion (due to TCP synchronization), in stead of fixing the congestion
which already exists.
I believe that when the average queue size exceeds the Max threshold, the
packets are not subject to WRED anymore, but only subject to tail dropping
only (i.e. when queue is full).
Cheers,
Huan
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
abdul muhammed
Sent: Wednesday, 9 January 2008 10:38 PM
To: Cisco certification
Subject: Need Explanation on WRED
Hi,
in configuring WRED using Random-detect interface command based on IP
precedence where the Precedence, Min-threshold, Max-threshold and
Mark-prob--denominator parameters are deployed.
1. what does my average queue length represent:
2. why should packet be drop when my average queue lenght equals the
Min-threshold and not just when it equal the Max threshold for that
precedence.
I need explanation on this.
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