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

Hi

I, ok so I was one of the below until a few days ago:

*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.*

but after reading emails on GS I have come to understand that I do not
really understand this aswell as I should.

Carlos, I answered a question on traffic shaping the other day in which it
stated "allow burst up to port speed if credit has been accumulated"
You replied to the same thread saying that because Be was not Tc related the
question should state how long Be applies for.
In the question in this thread the question states that bursting is possible
for 30 seconds.

My question is how does stating how long we can burst up to line rate affect
the Be?

e.g if AIR=128k CIR=64k Bc=8000

if we can Be to port speed for 1 second the Be will be 8000, if we can Be to
port speed for 30 seconds the Be will be 8000.
Doesn't this all just depend on how much credit is accumulated?

Thanks in advance

On 25 April 2010 22:56, Carlos G Mendioroz <tron_at_huapi.ba.ar> wrote:

> I would second the move to understand it.
> Bc is Tc related. Tc is your clock, Bc is how much credit you get
> at every tick to transmit.
> Be is not Tc related, so can be much larger than Bc, or even 0.
> And it is how much credit you can save as long as you spend (transmit)
> less than your Bc bits. You can not spend all of it at once, since
> no matter how much credit you have, AR is a hard limit on the speed
> of the link.
>
> Now Bc/Tc is a base rate that is accounted (CIR). If you want to rev up,
> your only need credit for the part over CIR up to AR. Hence the AR-CIR
> count.
>
> -Carlos
>
> Ladee Geek @ 25/04/2010 16:10 -0300 dixit:
> > 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.
> >
>
> --
> Carlos G Mendioroz <tron_at_huapi.ba.ar> LW7 EQI Argentina
>
>
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Received on Sun Apr 25 2010 - 23:53:33 ART