OT: Shaping and extended burst

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

Blogs and organic groups at http://www.ccie.net
Received on Sat Mar 05 2011 - 15:34:05 ART