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...

Comments

  • 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

  •  

     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

  • Tox,

    This isn't quite what I was asking, although, I genuinely appreciate you taking the time to write it all down. Smile

    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 [;)]

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