Re: Token buckets question

Depends on if you are talking about a shaper or a policer. With a shaper,
tokens are added to the bucket usually based on a set static amount of time
called Tc. This is where we get the popular formula Tc = Bc/CIR. For
instance, with FRTS our Tc is 1/8 seconds so every 1/8th of a second we get
bc tokens into the bucket. With a policer, the logic is different and
tokens are added to the bucket based on packet arrival time, not some static
Tc as in shaping. With a policer, basically it looks at the CIR and it looks
at the last time that you received a packet, and it prorates you some amount
of tokens based on those things. So if your CIR was 100,000 bits/second and
the last time you received a packet was .5 seconds ago you would
instantaneously get 50,000 tokens. That is a little simplified because
typically policers specify the token bucket in terms of bytes, not bits.

HTH

On Tue, Oct 11, 2011 at 11:22 PM, Jacek <q.192.168.1.0_at_gmail.com> wrote:

> Hello Experts,
>
> I have a question, how often tokens are added to token buckets?
> Different docs give different explenations:
>
> 1.
> Cisco book End-to-end QOS network design says:
> "policer has two separate buckets that are filled EACH SECOND with two
> separate token rates."
> If I understand correctly, buckets are refilled only one time per
> second. It does not look very often to me.
>
> 2.
> RFC 2698 ( http://tools.ietf.org/html/rfc2698 ) says: " token count Tc
> is incremented by one CIR times per second up to CBS."
> Does this mean that if CIR=100,000bps then 100 tokens are put into the
> bucket every millisecond ? Just curious, can router count tokens that
> fast ?
>
> Can someone please explain ?
>
> Thanks
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>

-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
Blogs and organic groups at http://www.ccie.net