From: Pavel Bykov (slidersv@gmail.com)
Date: Thu Mar 26 2009 - 17:59:35 ART
Pretty much, yeah.
The idea is that fragmentation would be almost unberable.
The default value of Bc will never be less than 8000 actually.
But do not be alarmed. 64K is really slow, so you shouldn't expect 10ms
under any circumstance other than lab scenario...
Bc of 640 will allow 80-byte packets at most, and could cause quite some
problems. There is a shaping deficit when a larger packet would come.
In case of 1500-byte packet and 100Mbps interface with this policy map
applied, this setting would mean to send 1500-byte packet really fast (at
line rate, which is 100Mbps, because interfaces can never send bits at any
other speed than that which they are set to - that's why it's called
interface speed), and then shaper would wait for 188ms because of all the
stacked up deficit, and only then would be able to send any packet again.
So you see, even if setting Bc to such a low value would be possible,
because of deficit and average packet size being larger than 80 Bytes, the
actual Tc would be still larger, and effective Bc that would be
retro-calculated from this would be larger than 640.
On Thu, Mar 26, 2009 at 12:19 PM, Groupstudy @ CrespoNetworks <
groupstudy@cresponet.com> wrote:
> GS,
>
> I am getting a pretty humorous error message when I try to enter values
> for a MQC Peak Shaper task. It is basically asks to shape peak traffic
> to 128Kbps with Bc and Be based off of 10ms. So, of course, I enter:
>
> class-map match-all HTTP
> match protocol http
> !
> !
> policy-map SHAPE_PEAK
> class HTTP
> shape peak 64000 640 640
> less than 1000 bits in an interval doesn't make sense <----- :-)
> (basically, you're an idiot)
>
> So the answer is supposed to be:
>
> policy-map SHAPE_PEAK
> class HTTP
> shape peak 64000 6400 6400
>
> but that gives us a Tc of 100ms...
>
> The lowest Tc I can get is 15ms using a value of 1000. Does this mean
> we cannot shape at a Tc of 10ms with values less that 100K? Any insight
> on this would be appreciated.
>
> Thanks
>
> J
>
>
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-- Pavel Bykov ---------------- Don't forget to help stopping the braindumps, use of which reduces value of your certifications. Sign the petition at http://www.stopbraindumps.com/Blogs and organic groups at http://www.ccie.net
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