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

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
Blogs and organic groups at http://www.ccie.net