From: Nadeem Ansari (nadeem.ansari574@gmail.com)
Date: Thu Feb 26 2009 - 06:06:18 ARST
Hi Dale,
Cisco Doc simply says that rate is exceeded to CIR whenever Queue depth
decreased from its max depth value with no BECN received, Also I did not
find any information about consecutive intervals what is that ?
Regards
Nadeem
On Thu, Feb 26, 2009 at 12:02 PM, Dale Shaw <dale.shaw@gmail.com> wrote:
> Hi all,
>
> Regarding 'shape adaptive' ..
>
> I've read the docs on this and it seems pretty straight-forward, but
> something I read in Wendell Odom's QoS book is a bit confusing.
>
> When talking about the way adaptive shaping brings the actual shaping
> rate back up to the configured shaping rate, he says:
>
> "As a reminder, after 16 consecutive intervals with no received BECNs,
> this router would start increasing the Shaping rate by 1/16 of the
> original 96-kbps shaping rate teach Tc. To do so, CB Shaping actually
> starts replenishing the token bucket with a little more each Tc,
> specifically by (Bc + Be)/16 each Tc. As a result, the rate will
> likely increase more slowly than it decreased in the presence of
> BECNs."
>
> It's the second sentence that's got me stuck. Does adaptive shaping
> cause the actual shaping rate to go up by 1/16 of the original rate
> each Tc, or by the amount specified in the formula (Bc + Be)/16 each
> Tc? Because they are not necessarily the same.
>
> Example:
>
> Configured shaping rate: 4,000,000bps (4Mbps)
> Tc: 25ms (default)
> Bc: 100,000 bits (derived from Tc)
> Be: 100,000 bits (same as Bc)
>
> 1/16 of 4,000,000 = 250,000, implying that the actual shaping rate
> increased by 250Kbps every 25ms.
>
> The second sentence implies that it would actually increase by 12,500
> (12.5Kbps) every 25ms.
>
> Which is it? Or am I just confused :-)
>
> cheers,
> Dale
>
>
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