Re: OT: Shaping and extended burst

Aaron,
> What I am confused about is the fact that more than the CIR rate can
> actually be sent over the initial lets say 1 second ...

Now think about it, it's only the *first* second. When did it happen in
an actual implementation ? :)

It's called *burst* for a reason. And doing the analysis from the math
is not going to help you understand it, IMHO.

It's there to compensate the jitter in the packets, because your
line rate is/may be way faster than your CIR, and your "small window
perception" (aka Tc) of the rate may not be accurate.

As far as I see it, this is not OT at all.

-Carlos

Aaron Riemer @ 05/03/2011 04:34 -0300 dixit:
> Hi Guys,
>
>
>
> I am just reading up on the token bucket principles with shaping in
> particular with the use of Bc and Be (extended burst capability).
>
>
>
> I have read that when Be is configured the token bucket maximum size will
> equal Bc + Be. Therefore initially (Let's say the first Time Period Tc) Bc +
> Be packets will be taken from the bucket.
>
>
>
> Does this mean that when Be is configured you can initially send more than
> the actual shaped rate?
>
>
>
> Take this example:
>
>
>
> I enable traffic shaping and set the shaped rate to 64kbps over a 128kbps
> serial link. I stick with the default Tc and therefore calculate Bc to be
> 8000bits (64000 * .125). I enable Be to be 8000bits as well.
>
>
>
> Going by the token bucket logic the shaper will take (Bc+Be) from the bucket
> (the bucket is full to start with). This means 16000 bits are taken
> effectively allowing the burst to 128kbps for the first Tc of .125ms.
>
>
>
> What I am confused about is the fact that more than the CIR rate can
> actually be sent over the initial lets say 1 second of transfer (8 * Tc). I
> calculate this to be 72k bits for the first second of transfer and then 64k
> bits for every subsequent second assuming full load over one second.
>
>
>
> Is this correct? I am just trying to get my head around it and understand
> this completely.
>
>
>
> Any comments welcome as always.
>
>
>
>
>
> Thanks guys,
>
>
>
> -Aaron
>
>
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-- 
Carlos G Mendioroz  <tron_at_huapi.ba.ar>  LW7 EQI  Argentina
Blogs and organic groups at http://www.ccie.net