Bandwidth Calculations
Does anyone have a good way to remember all of the bandwidth calculations required for the exam (in your head or with some quick paper scratch)? For instance, calculating the required bandwidth for a G729 call for LBCAC vs. RSVP vs. GK vs. LLQ, etc. And for G711 as well...
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write it down. The best way I know to memorize something is to write it down over and over again from short term memory till it goes into long term memory.
I'm doing that with QOS formulae .
Takes 10 minutes > immediately upon waking write them down.
I figure about 2 weeks of doing it and then once every now and then i'll have em down.
HTH
Tox!
Tox,
Thanks for the advice. I agree, it's best to use repetition. But what are you writing down?
-Brandon
you just gave me a reason for a quick review
for WFQ >>
Virtual Scheduling time = Queue Tail time + (packet size X weight)
Queue Tail time = Previous virtual scheduling time
weight = 32384/(IP precedence +1)
For Random early Detect.
New average queue depth = Old average Queue depth X (1 - 2 ^ -N) + Current Queue depth ( 2 ^ -N)
N = exponential weighting constant = 9 by default
the smaller the value of N the more closely the Average Q depth resembles the actual queue depth and vice versa.
When queue depth is above min threshold but below max threshold
drop probability = (Average Q depth - mim queue depth)/ (max - min) X (1 / Mark probability demonimator)
When q depth is above Max threshold you drop at 1/Mark probability deminimator
For Flow based RED
you get the average q depth for each flow by dividing total Q size by number of flows
Avg depth = Queue size/ # of flows
As long as
Current Flow Q size < Average Q Queue Depth X scaling factor we are good
if current flow Q size gets larger than the Scaled Average then decrease max threshold to
New max threshold = min threshold + (max-min)/2
For now those are it....i think....
Edit<i just re read this and i've misspelled DENOMINATOR 6 different ways it seems...for the record..i do know how to spell that particular word...i just dont know how to type!>
Tox!
edit / add
cisco doc however says that once you get over max threshold you do a Full drop not at mark probability
the above furmulae are from WB1 for RnS
Tox!
Tox,
This isn't quite what I was asking, although, I genuinely appreciate you taking the time to write it all down. [:)]
I'm looking more for CUCM LBCAC vs. Gatekeeper vs. RSVP bandwidth utilization. Does that make sense?
-Brandon
a review is a review regardless
in anycase as i said before..i'm studying for the RnS ...what i didn't say is..i know nothing about VOIP except how to interleave it and sent it along a priority Q!
sorry man...my advice about writing it down works but as to the WHAT to write down of the matter, I have no clue [*-)]
Tox!
Understood. Very good information though [;)]