Re: OT: Shaping and extended burst

Nod. This is on topic for me.

I believe Aaron's interpretation is correct. I can understand why the
burst is needed, but I have never been able to figure out "correct"
burst size and what really happens when the burst size is too large or
small.

Chris

On 3/5/2011 8:29 AM, Aaron Riemer wrote:
> Thanks Carlos,
>
> I just wanted to know if my understanding was correct more than anything.
> When things don't add up I like to question rather than just accept an
> answer without knowing why. This I think helps to solidify my understanding.
>
> Thanks for your help again mate.
>
> Cheers,
>
> -Aaron
>
> -----Original Message-----
> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
> Carlos G Mendioroz
> Sent: Saturday, 5 March 2011 7:57 PM
> To: Aaron Riemer
> Cc: ccielab_at_groupstudy.com
> Subject: Re: OT: Shaping and extended burst
>
> Aaron,
> > What I am confused about is the fact that more than the CIR rate can
> > actually be sent over the initial lets say 1 second ...
>
> Now think about it, it's only the *first* second. When did it happen in
> an actual implementation ? :)
>
> It's called *burst* for a reason. And doing the analysis from the math
> is not going to help you understand it, IMHO.
>
> It's there to compensate the jitter in the packets, because your
> line rate is/may be way faster than your CIR, and your "small window
> perception" (aka Tc) of the rate may not be accurate.
>
> As far as I see it, this is not OT at all.
>
> -Carlos
>
> Aaron Riemer @ 05/03/2011 04:34 -0300 dixit:
>> Hi Guys,
>>
>>
>>
>> I am just reading up on the token bucket principles with shaping in
>> particular with the use of Bc and Be (extended burst capability).
>>
>>
>>
>> I have read that when Be is configured the token bucket maximum size will
>> equal Bc + Be. Therefore initially (Let's say the first Time Period Tc) Bc
> +
>> Be packets will be taken from the bucket.
>>
>>
>>
>> Does this mean that when Be is configured you can initially send more than
>> the actual shaped rate?
>>
>>
>>
>> Take this example:
>>
>>
>>
>> I enable traffic shaping and set the shaped rate to 64kbps over a 128kbps
>> serial link. I stick with the default Tc and therefore calculate Bc to be
>> 8000bits (64000 * .125). I enable Be to be 8000bits as well.
>>
>>
>>
>> Going by the token bucket logic the shaper will take (Bc+Be) from the
> bucket
>> (the bucket is full to start with). This means 16000 bits are taken
>> effectively allowing the burst to 128kbps for the first Tc of .125ms.
>>
>>
>>
>> What I am confused about is the fact that more than the CIR rate can
>> actually be sent over the initial lets say 1 second of transfer (8 * Tc).
> I
>> calculate this to be 72k bits for the first second of transfer and then
> 64k
>> bits for every subsequent second assuming full load over one second.
>>
>>
>>
>> Is this correct? I am just trying to get my head around it and understand
>> this completely.
>>
>>
>>
>> Any comments welcome as always.
>>
>>
>>
>>
>>
>> Thanks guys,
>>
>>
>>
>> -Aaron
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>>
>>
>>
>>
>>
>>
>>

-- 
Chris Proctor
--
This message was scanned by ESVA and is believed to be clean.
Blogs and organic groups at http://www.ccie.net