Re: Policing and Tc

Hi Garth,

This is from a previous email I sent to groupstudy and was a result of an
explanation of Petr Lapukhov and Joe Astrino. I am truly thankful to both
for sharing their knowledge.

This is the email I sent which is sort of a summary:

Dear Gents,

I would like to thank Petr & Joe for such a wonderful knowledge sharing. The
main point of discussion as I understand is how the token bucket is updated
with policing:

1)Scheduler Approach which Petr mentioned relies on adding a number of
packets every scheduling interval (without having to do anything with the
way packets arrive and inter-arrival time).

2)Packet based approach: which relies on the inter-arrival time of packets

Specifically, the token arrival rate is calculated as follows:
(time between packets<which is equal to t-t1>* policer rate)/8 bits per byte
Looking at the formulas that Joe used from Cisco's website:

Tc(t) = min(CIR * (t-t1) + Tc(t1), Bc)
Tp(t) = min(PIR * (t-t1) + Tp(t1), Be)

It seems that the either the Packet based approach or the Scheduler based
approach could be used (based on the minimum). We are comparing the number
of tokens currently in the bucke (at time t): addition of what we have put
CIR * (t-t1) as well as what was already in the bucket at time t1. We
compare this value to the Bc. This comparison will lead to using either
packet or scheduled mode.

Once again,Petr & Joe can't thank you enough!

Best Regards,

Blogs and organic groups at http://www.ccie.net
Received on Mon Mar 01 2010 - 20:20:50 ART