From: CiSco Champ (cischamp2009@gmail.com)
Date: Fri Jan 02 2009 - 14:12:51 ARST
thats what i wanted to know. Now it clear to me.
Thanks
On Fri, Jan 2, 2009 at 7:20 PM, Scott Morris <smorris@internetworkexpert.com
> wrote:
> AR is 768k which is purely informational, or for us to give our max
> values.
>
>
>
> So let's look at 768000. Then look at the Tc we want to use (125ms or
> 1/8sec). 768000 / 8 = 96000. That means that AT the AR (max value) you can
> send 96000 bits per Tc. So if your Be is equal to the max @ AR, then you'll
> have problems. Once you define your Bc, you SUBTRACT it from the max
> allowed.
>
>
>
> At AR, max bits per Tc is 96000. Minus the 48000 for Bc defined, that
> leaves you a maximum of 48000 leftover without causing mathematical issues.
>
>
>
> HTH,
>
>
>
> Scott
>
>
>
>
>
> *From:* CiSco Champ [mailto:cischamp2009@gmail.com]
> *Sent:* Friday, January 02, 2009 9:41 AM
>
> *To:* smorris@internetworkexpert.com
> *Cc:* ccielab@groupstudy.com
> *Subject:* Re: QOS Formulas
>
>
>
> Sorry may be i am confusing but see AR is 768000 and CIR is 384000 so Bc =
> 48000. assume Be 96000 per interval so it will try to burst upto AR not more
> then that. means 384000 x 2. how you write 384000 x 3 ?
>
>
>
> Regards
>
> On Fri, Jan 2, 2009 at 6:24 PM, Scott Morris <
> smorris@internetworkexpert.com> wrote:
>
> That Be would be wrong. In the rate-limit policer, the excess-burst is
> INCLUSIVE of normal-burst (so overlapping values) but in traffic shaping
> they are ADDITIVE values.
>
>
>
> So with Bc 48000 and Be 96000, then the AR will be presumed (attempted by
> the router) to be 384000 x 3, or 1,152,000bps.
>
>
>
> You'll run into problems (output drops) as the router tries to cram 1.1M
> worth of traffic through a .7M circuit. :) But it wil try!
>
>
>
> Scott
>
>
>
>
>
> *From:* CiSco Champ [mailto:cischamp2009@gmail.com]
> *Sent:* Friday, January 02, 2009 8:40 AM
> *To:* smorris@internetworkexpert.com
> *Cc:* ccielab@groupstudy.com
> *Subject:* Re: QOS Formulas
>
>
>
> Thanks Scott, well explained the concept behind that. So when ever i need
> to calculate bc and be for traffic shaping i will use
>
>
>
> Bc = CIR * Tc/1000 and to calculate Be is Be = (AR - CIR) * Tc/1000
>
>
>
> and calculation for rate limit will be with below formulas
>
>
>
> normal burst = configured rate * (1 byte)/(8 bits) * 1.5 seconds
> extended burst = 2 * normal burst
>
>
>
> I am confuse because i feel like anyone of two formulas to calculate Bc can
> be used for taffic shaping based on task requirement and vice virsa.
>
>
>
> In an example of a workbook
>
>
>
> AR = 768000bps
>
> CIR = 384000bps
>
> Tc = 125ms
>
>
>
> so Bc = CIR x Tc/1000 = 48000
>
> and Be = (AR-CIR) x Tc/1000 = 48000
>
>
>
> but in his calculation Be = 96000, it means he used rate-limit formula i,e,
> Be = 2 x Normal Burst
>
> Please correct me.
>
> Regards
>
>
>
>
> On Fri, Jan 2, 2009 at 5:12 PM, Scott Morris <
> smorris@internetworkexpert.com> wrote:
>
> The rate-limit command isn't tied to a time interval in the same fashion
> that traffic-shaping it. In traffic shaping, your CIR and Bc are used to
> derive the interval (moving target).
>
> In the rate-limit command, samples are taken every one second and averaged
> over a 5-second period of time. So it's more of a statistical analysis
> than
> any interval-based specific function.
>
> HTH,
>
> Scott
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> CiSco Champ
> Sent: Friday, January 02, 2009 6:33 AM
> To: ccielab@groupstudy.com
> Subject: QOS Formulas
>
> Hi,
>
> Qos parameters calculation like Bc and Be, are there different formulas to
> calculate for FRTS and rate-limit. I am confused like one formula to
> calculate Bc is
>
> Bc = CIR * Tc/1000 and to calculate Be is Be = (AR - CIR) * Tc/1000
>
> other formula i can see on cisco doc is
>
> normal burst = configured rate * (1 byte)/(8 bits) * 1.5 seconds
> extended burst = 2 * normal burst
> Can somene explain when to use one and when other formula, I really
> appreciate
>
> Regards
>
> Blogs and organic groups at http://www.ccie.net
>
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