Re: Shaping and calculating Be value for a 30 second burst

hey guys

i wanted to know how to prepare for CCIE SP OEQ's?

Raghava

On Fri, Apr 30, 2010 at 12:21 PM, Kambiz Agahian <kagahian_at_ccbootcamp.com>wrote:

> Jack,
>
> Math, bloody math and aah you goddamn math! Again we can blame this
> (so-called) science...I loved it when I was a student though.
>
> First off, thanks for chasing this up, I hate yes/no candidates and I'm
> so glad to see someone like you in here who's interested in "WHY's" more
> than just "HOW's".
>
> Actually, Odom is one of the greatest Cisco press authors and accidently
> he's a QoS specialist more than a routing/switching guy. He's also well
> known for his nice examples in his classes...
>
> Anyway, let's go back to the Cisco's certification guide v4, page 597
> and see what's going on. You're absolutely right it's not probably the
> best way to represent a numeric value but let's take a closer look; that
> equation includes 3 parts; the Bc itself which is what we're after, then
> a bit of stuff in the middle and that odd thing at the end.
>
> You see the second part? { CIR*0.25 second } ; what is the "unit" of the
> output of this statement? { Bit/sec * sec } ; so it yields "bits" hence
> you can perfectly and safely divide it by 32 and say hey it's my Bc.
>
> Odom however has done a better job in his QoS book and I strongly
> recommend that you spend some time on that precious book well before
> your lab date.
>
> If you still need more clarification on how to "prove" the nature of Bc
> (from a math's point of view) I have enough time to draw something and
> get it to you...
>
> Please let me know if you have any other issues with this.
>
>
> --------------------------
> Kambiz Agahian
> CCIE (R&S)
> CCSI, WAASSE, RSSSE
> Technical Instructor
> CCBOOTCAMP - Cisco Learning Solutions Partner (CLSP)
> Email: kagahian_at_ccbootcamp.com
> Toll Free: 877-654-2243
> International: +1-702-968-5100
> Skype: skype:ccbootcamp?call
> FAX: +1-702-446-8012
> YES! We take Cisco Learning Credits!
> Training And Remote Racks: http://www.ccbootcamp.com
> OEQ Voice Waiver: http://www.ccbootcamp.com/noeqvoice.html
> OEQ R&S Waiver: http://www.ccbootcamp.com/noeqrs.html
> OEQ Commercial: http://www.ccbootcamp.com/noeq.mpg
>
>
>
>
>
>
>
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> Jack Router
> Sent: Thursday, April 29, 2010 10:06 PM
> To: ccielab_at_groupstudy.com
> Subject: RE: Shaping and calculating Be value for a 30 second burst
>
> Kambiz,
>
> I totally agree with you. However, I must say that Cisco itself is the
> main
> source of the confusion. As an example just look in the Cisco's
> certification guide v4, page 597. In the key topics they say
> "Bc=CIR/32".
> This is totally insane. At the top of the same page they even manage to
> provide a "proof"!!! The "formula" Bc=CIR/32 clearly implies that units
> are
> the same at each side of the equation, which is not the case! I learned
> in
> the elementary school not to compare apples and oranges but this is
> exactly
> what Cisco does here.
>
> For me personally, there is only one formula "Bc=CIR*Tc". It is as
> obvious
> as distance=speed*time. In the example above all you need to remember is
> that Tc=0.25 second. With *understanding* of the principle anyone should
> be
> able to figure out the rest. No need for confusing Cisco explanations.
>
>
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> Kambiz Agahian
> Sent: 25-Apr-10 15:44
> To: Ladee Geek; CCIE Study Group
> Subject: RE: Shaping and calculating Be value for a 30 second burst
>
> Hi Ladee,
>
> I guess you need to revise some parts of your understanding and take a
> fresh
> look at the example - I never give a YES/NO answer but I want you to
> *understand* it:
>
> Fact: Be is not AIR-CIR. Why? Because Be basically represents a
> "quantity"
> and
> not a "rate". Both AIR and CIR are sort of rates (say bit/s) and the
> output
> of
> a subtraction operation won't change the "units".
>
> If you ask legendary network engineers (60+ y.o!) they'd say "Bc is CIR
> per
> TC
> and Be is AIR-CIR per Tc". Actually their training was simple and
> effective...hence again you can say both Bc and Be are referring to the
> number
> of bits and not rates. Technically it's true to say my Bc or my Be is
> 32000
> bits but it's not true when people say hey the Bc is now 32Kbps.
>
> Many of my students just try to memorize things like Bc=CIR*Tc etc. but
> when
> you ask them "WHY?" they're always like "ummm hang on...it was..that
> was..."
> Why? because no one had enough time to draw a simple primary school-like
> diagram to prove it. Would you like to be different? spend a couple of
> hours
> and take a "math look" at the QoS formulas.
>
> Problem?
> That bloody bucket!!! whenever we start from "the bucket" after 2-3 mins
> students stop learning! but if you think about the math behind the
> scene,
> it's
> just a piece of cake.
>
> You might wish to see these:
> http://www.cisco.com/en/US/tech/tk543/tk545/technologies_q_and_a_item091
> 86a0<http://www.cisco.com/en/US/tech/tk543/tk545/technologies_q_and_a_item091%0A86a0>
> 0
> 800cdfab.shtml
> http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a
> 0080
> 0
> a3a25.shtml
>
>
>
>
> --------------------------
> Kambiz Agahian
> CCIE (R&S)
> CCSI, WAASSE, RSSSE
> Technical Instructor
> CCBOOTCAMP - Cisco Learning Solutions Partner (CLSP)
> Email: kagahian_at_ccbootcamp.com
> Toll Free: 877-654-2243
> International: +1-702-968-5100
> Skype: skype:ccbootcamp?call
> FAX: +1-702-446-8012
> YES! We take Cisco Learning Credits!
> Training And Remote Racks: http://www.ccbootcamp.com
> OEQ Voice Waiver: http://www.ccbootcamp.com/noeqvoice.html
> OEQ R&S Waiver: http://www.ccbootcamp.com/noeqrs.html
> OEQ Commercial: http://www.ccbootcamp.com/noeq.mpg
>
>
>
> -----Original Message-----
> From: nobody_at_groupstudy.com on behalf of Ladee Geek
> Sent: Sun 4/25/2010 12:10 PM
> To: CCIE Study Group
> Subject: Shaping and calculating Be value for a 30 second burst
>
> I have a question about determining the Be for generic traffic shaping.
> I've looked through the QoS exam guide, QoS configuration guide, the doc
> cd
> and haven't seen enough to be able to figure this one out.
>
> AR - 1.544 mb
> Cir - 768k
> Tc - 125 ms
> burst for 30 sec up to line rate
>
> I understood Be to be AR - Cir.
>
> The answer key for this task states that the Be is calculated by taking
> the line rate and multiplying it by 30 sec?
>
> 1544000bps*30s = 46320000bits
>
> There's just no way to put that many bits on the wire in 1 sec. Or is
> the
> Be the number of tokens to be replenished in 1 sec ( same as 5790000
> bits/Tc)
>
> And while I am at it, if you've found a good reference please pass it
> on.
>
> --
> r/
> LG
>
>
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-- 
Regards,
Raghava Rao T.V
Mumbai
Blogs and organic groups at http://www.ccie.net