From: WorkerBee (ciscobee@gmail.com)
Date: Wed Oct 25 2006 - 05:35:26 ART
With either shape average or shape peak, the Tc calculation is fixed.
Shape average - CIR = Bc / Tc
Shape peak - CIRpeak = CIR (1 + Be/Bc)
= Bc/Tc + Be/Tc
= 1/Tc (Bc + Be) note : Tc is constant
Use shape average if the CIR must always maintained.
Use shape peak if your network allows you to burst above CIR.
Be value range from 0 to (Access Rate - Bc).
Hence, both commands are meant for different meaning, should not
just view it from a mathematically view. It does not work that way.
On 10/25/06, Vincent Mashburn <vmashburn@fedex.com> wrote:
> It is my understanding that Be only gets transmitted only if excess
> bandwidth is available, even in shape peak. So, if your transmitted
> traffic totally saturates the entire token bucket at a particular
> interval (Tc), then there is no room to use the Be, so the transmitted
> Be is 0 (the entire Bc is used). However, if the Bc did not take the
> entire bucket for that interval, the Be is allowed to be used until the
> excess bandwidth is used up. Now for Shape average, this Be is
> calculated based on the previous intervals (Tc) information whereas the
> shape peak allows the Be to transmitted based on the current intervals
> (Tc) information. This is how I understand it. Please add any
> additional info to this that you can.
> Thanks
> Vince Mashburn
> Voice / Data Engineer
> 901-263-5072
> CCVP, CCNP, CCDA,Network +
> Cisco IP Telephony Support Specialist
> Cisco IP Telephony Operations Specialist
>
> -----Original Message-----
> From: Alexei Monastyrnyi [mailto:alexeim@orcsoftware.com]
> Sent: Tuesday, October 24, 2006 12:47 PM
> To: Vincent Mashburn
> Cc: Cagri Yucel; Group study
> Subject: Re: Shape average and shape peak
>
> Hi Wincent.
>
> When adding to Bc we definitely increase Tc with the same CIR... but
> under the hood... Odom in DQOS Guide says "shape average" behavior is
> the same as normal GTS behavior, i.e spending Be after "a long period of
>
> inactivity" during which Be is being accumulated, whereas "shape peak"
> spends tokens from Be on every Tc.
>
> If we spend tokens from Be at each and every Tc and our traffic profile
> is not lower than conform rate, i.e >=CIR all the time, where do we get
> Be accumulated from?
>
> I have a feeling that this Be is not the same as normal traffic-shaping
> Be... It is just a sort of extra credit we've got to be able to burst
> more at each Tc ... without increasing a Tc...
>
> Does it make any sense?
>
> A.
>
>
> Vincent Mashburn wrote:
> > This is a common question. To answer the question, refer back to the
> > formula: CIR = bc/tc.
> >
> > For shape peak, bc + be is sent every interval, but the formula is
> still
> > CIR = bc / tc. For shape average, bc is sent every interval, and the
> > formula is still CIR = bc / tc.
> >
> > So, say you have a CIR of 64000, bc = 8000 and be = 16000.
> > Using shape average:
> >
> > 64000 = 8000 / tc ==> tc = 125ms.
> >
> > Using shape peak:
> >
> > 64000 = 8000 / tc ==> tc = 125ms
> >
> > Using shape average by setting bc = bc + be
> >
> > 64000 = 24000 / tc ==> tc = 375ms.
> >
> > So, as you can see, it is different.
> > Hope this helps.
> >
> > Vince Mashburn
> > Voice / Data Engineer
> > 901-263-5072
> > CCVP, CCNP, CCDA,Network +
> > Cisco IP Telephony Support Specialist
> > Cisco IP Telephony Operations Specialist
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> > Cagri Yucel
> > Sent: Tuesday, October 24, 2006 4:49 AM
> > To: Group study
> > Subject: Shape average and shape peak
> >
> > I am sure I am missing a bit here but on the Cisco Doc it says
> >
> > shape average sends Bc bits in each interval
> > shape peak sends Bc+Be bits in each interval
> >
> > So what's the point of having a different command ? Isn't it the same
> > thing
> > if I set shape average with a Bc equal to Bc+Be of shape peak ?
> >
> > Thanks
>
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