From: Chris Lewis (chrlewiscsco@gmail.com)
Date: Thu Mar 09 2006 - 11:59:57 GMT-3
The previous post
http://www.groupstudy.com/archives/ccielab/200509/msg00978.html may help.
Policing calculations are done as a packet arrives, the Bc defines the depth
of teh token bucket, meaning if there are free toekns after the policing
calculation done as a packet arrives, they will be put there for later use
if needed. The CIR sets the rate that will be achieved on a continual basis.
In your case, the size of the packet is not inherently the issue. A packet
will be forwarded if [t-t1]*CIR, where t is time of packet arrival and t1 is
time of last packet arrival is greater than the number of bits to be
transmitted, so it is more a case of the time between packets being offered
for transmission as well as their size, rather than anything to do with
their size as an isolated consideration.
Chris
On 3/9/06, Popgeorgiev Nikolay <nikolay.popgeorgiev@siemens.com> wrote:
>
> Dear all,
>
> 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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