Re: Policing and Tc

Thanks for the input Guys but I'm still not convinced.

I have not been able to find any reference to this Scheduler based approach
anywhere :|

In my view here, I can't see any benefit here of having a token bucket
smaller than 1second of the CIR!

This is because say for example you had a 64kbps line which equates to 8000
bytes per second, if you configure your token bucket in an interval of
.125ms which is 1000 bytes say you had a heap of packets burst through your
router and your token bucket is empty, then 1 second later a new 1500byte
packet passes through the policer, wouldn't the policer then look fill up
the token bucket, to it's maximum of 1000 bytes and consider the 1500 byte
packet to be violating (presuming a Be of 0) instead of conforming?

Where as if the bucket could hold up to 8000 bytes it would be considered
conforming!

Excuse me if I am totally off track here but I am just trying to really get
my head around it.

Thanks heaps,

Garth

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

> Hi Garth,
>
> 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.
>
> Best Regards,
>
> Karim Jamali
>
>
> On Tue, Mar 2, 2010 at 7:06 AM, Joe Astorino <jastorino_at_ipexpert.com>wrote:
>
>> 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)
>> Sr. Technical Instructor - IPexpert
>> Mailto: jastorino_at_ipexpert.com
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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,
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
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>>
>>
>>
>>
>>
>>
>>
>
>
> --
> KJ

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Received on Wed Mar 03 2010 - 15:27:02 ART