From: Scott Morris (smorris@internetworkexpert.com)
Date: Fri Jan 02 2009 - 13:20:58 ARST
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 <http://www.ccie.net/>
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