From: Petr Lapukhov (petr@internetworkexpert.com)
Date: Mon Jul 03 2006 - 08:15:10 ART
It's even driven, I suppose.
When a new packet is scheduled into queue, AQD is calculated,
based on "current queue depth+1" and previous AQD value.
HTH
-- Petr Lapukhov, CCIE #16379 petr@internetworkexpert.comInternetwork Expert, Inc. http://www.InternetworkExpert.com Toll Free: 877-224-8987 Outside US: 775-826-4344
2006/7/3, Martin Dean <mdean@diatac.co.uk>: > > Great info. > Do you happen to know how the AQD is calculated? > There is a constant n (default=9) when used to calculate the AQD, which is > based on the old AQD and the real FIFO Q size. > But how often is this calculated? > All the formula I have seen just shows Qavg(t+1) without declaring the > interval period. > Any ideas of the interval period? > > Martin > > ----- Original Message ----- > From: "Petr Lapukhov" <petr@internetworkexpert.com> > To: "Victor Cappuccio" <cvictor@protokolgroup.com> > Cc: "Cisco certification" <ccielab@groupstudy.com> > Sent: Monday, July 03, 2006 7:45 AM > Subject: Re: MDP .- WRED > > > > Oh, I see your point now :) > > > > Now, let's take a look how it works: > > > > MDP is just a *probablity* of drop, when you reach the upper limit. > > > > RED tracks "smoothed" average queue depth (AQD). Queue is > > FIFO, so scheduler basically just takes the first packet and sends > > it, _or_ drops it, depending on AQD and thresholds. > > > > When AQD reaches low-threshold, you have drop probability of zero. > > That is, no packets are dropped here, first packet in FIFO queue > > is always sent. > > > > When AQD grows from low to high threshold, drop probability is > > linearly interpolated: > > > > drop_prob = (AQD-min_thresh)/(max_thresh-min_thresh)*MDP > > > > Finally, when you reach high threshold, approx every 1 of MDP > > packets in queue head will be dropped, and every other is sent. > > Above that threshold, every packet is dropped by scheduler > > > > You see, MDP is a value to calculate drop_prob, and make a > > "decision" for scheduler - send upper packet in FIFO queue, or > > drop it. > > > > HTH > > -- > > Petr Lapukhov, CCIE #16379 > > petr@internetworkexpert.com > > > > Internetwork Expert, Inc. > > http://www.InternetworkExpert.com > > Toll Free: 877-224-8987 > > Outside US: 775-826-4344 > > > > 2006/7/3, Victor Cappuccio <cvictor@protokolgroup.com>: > > > > > > Petr, that was very informative. > > > > > > > > > > > > But I'm looking for the formula here. > > > > > > > > > > > > So if the Theory Says that the MPD is the fraction of packets drops, > how > > > many packets are dropped using that Config that you posed ? 512 of > 20? > > > > > > 0,0390625 when the Average Q Depth is 20? > > > > > > Thanks > > > > > > > > > > > > > > > > > > _____ > > > > > > De: petrsoft@gmail.com [mailto:petrsoft@gmail.com] En nombre de Petr > > > Lapukhov > > > Enviado el: Lunes, 03 de Julio de 2006 01:36 a.m. > > > Para: Victor Cappuccio > > > CC: Cisco certification > > > Asunto: Re: MDP .- WRED > > > > > > > > > > > > Victor, > > > > > > It may be set separately for precedence or dscp value. > > > There are some basic default, at the same time. > > > > > > e.g. > > > > > > Rack1R6(config-if)#random-detect > > > Rack1R6(config-if)#random-detect precedence 0 10 20 512 > > > > > > 0 - precedence value > > > 10 - min thresh > > > 20 - max thresh > > > 512 - MPD > > > > > > -- > > > Petr Lapukhov, CCIE #16379 > > > petr@internetworkexpert.com > > > > > > Internetwork Expert, Inc. > > > http://www.InternetworkExpert.com > > > Toll Free: 877-224-8987 > > > Outside US: 775-826-4344 > > > > > > 2006/7/3, Victor Cappuccio <cvictor@protokolgroup.com>: > > > > > > Hi guys, > > > > > > I just can not get what they are trying to say > > > > > > > > http://www.cisco.com/en/US/products/sw/iosswrel/ps1831/products_configuratio > > > > > > n_guide_chapter09186a00800c60d9.html#1000915 > > > > > > The mark probability denominator is the fraction of packets dropped > when > > > the > > > average queue depth is at the maximum threshold. For example, if the > > > denominator is 512, one out of every 512 packets is dropped when the > > > average > > > > > > queue is at the maximum threshold. > > > > > > But then the MAX-TH of the Q depth is set to what number? 512?? > > > > > > I think that they forgot to tell that > > > > > > Opinions? > > > > > > Thanks > > > Victor.- > > > > > > > _______________________________________________________________________ > > > Subscription information may be found at: > > > http://www.groupstudy.com/list/CCIELab.html > > > > > > > _______________________________________________________________________ > > > Subscription information may be found at: > > > http://www.groupstudy.com/list/CCIELab.html > > > > _______________________________________________________________________ > > Subscription information may be found at: > > http://www.groupstudy.com/list/CCIELab.html > > > > > > -- > > No virus found in this incoming message. > > Checked by AVG Free Edition. > > Version: 7.1.394 / Virus Database: 268.9.8/380 - Release Date: > 30/06/2006 > > _______________________________________________________________________ > Subscription information may be found at: > http://www.groupstudy.com/list/CCIELab.html
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