Re: Policing and Tc

The answer as usual is "it depends". I would have to double check but I believe it uses the lower of the two values.

It will be the minimum of either the Bc or the interval based token bucket based on the CIR and packet arrival time

Regards,

Joe Astorino CCIE #24347 (R&S)
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-----Original Message-----
From: Garth Bryden <hacked.the.planet.on.28.8k.dialup_at_gmail.com>
Date: Tue, 2 Mar 2010 11:56:00
To: karim jamali<karim.jamali_at_gmail.com>
Cc: Cisco certification<ccielab_at_groupstudy.com>
Subject: Re: Policing and Tc

So what are you saying here that Policing uses a scheduler for single rate
polcing but a packet based approach for dual rate policing?

Cheers,

Garth

On Tue, Mar 2, 2010 at 1:20 AM, karim jamali <karim.jamali_at_gmail.com> wrote:

> 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,

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Received on Tue Mar 02 2010 - 04:06:02 ART