From: Ivan (ivan@iip.net)
Date: Thu Mar 09 2006 - 12:07:33 GMT-3
Principal difference between shaping and policing is when tokens add to the
bucket. Both shaping and policyng use concept of token bucket. Shaping add
token at pre-defined Tc interval. But policyng add token at traffic arrive.
As You wrote to forward packet need 2 condition
- Bc must be greater than packet size
- enough time elasped after previous packet was forwarded.
Target rate affect on time tocken add to the bucket. Base formula for policing
count token=(t-t1)*target rate.
> After long and useless reading of all kinds of books, white papers, docCDs
> and other I can say that policing is still a mistery for me. Please help.
>
> I think I understand very clearly shaping and the idea of Bc, Be and tokens
> around it. But in policing it is a little different.
>
> Let me tell you how I understand the things and tell me where my mistake
> is.
>
> When I configure this command under policy-map
>
> Police 128000 bc 1000 conform-acion transmit exceed-action drop,
>
> As I understand the fundamentals a packet will be forwarded if:
> - the packet is smaller than the Bc bucket or smaller than 1000 bytes in
> this case (otherwise fragmentation will be a good idea) - enough time has
> elapsed after the previous packet was forwarded and the token bucket is
> filled enough to serve our packet
>
> Other things I think are right
> - if I have Bc=1000 this is my tocken bucket size and no matter how big
> the policed rate (in my case 128000) is, the tocken bucked cannot have more
> than 1000 tockens in it refilled? Tha major thing I don't understand is If
> the above is right, what meaning does this policed rate has. What will be
> the difference if I put 256000 instead of 128000 ? Maybe the bucket will be
> refilled in smaller time with more tokens ?
>
>
> And if I load the router with constant traffic let's say around 512 Kbit/s
> what output rate will be expected on the interface ?
>
>
>
> You can see in what mess I am.
> At least someone tell me if I am on the right path, and some more
> clarification about Policing will be very helpful.
>
> Thanks,
> Nick
>
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-- Ivan
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