From: ccie2be (ccie2be@nyc.rr.com)
Date: Fri Dec 24 2004 - 12:07:29 GMT-3
Mani,
I don't know if that's right.
Tc is computed differently for policing compared to shaping.
With policing Tc is based on how much time has elasped since the last packet
and then tokens
are added to the bucket on a pro-rata basis.
So, for example, if 1 full second has elasped since the last packet, then all
Bc tokens are added to the bucket.
If only 1/2 second has elasped, then .5 x Bc is added to the bucket.
With shaping Tc = Bc/CIR
Check out the new 2nd edition of Odom book, Cisco QoS.
On a related topic, do you know when Be is really equal to Bc + Be and when Be
just equals Be?
There's seems to be inconsistencies on when which value for Be should be
used.
Tim
----- Original Message -----
From: mani poopal
To: ccie2be ; ccielab@groupstudy.com
Sent: Friday, December 24, 2004 9:42 AM
Subject: Re: QOS- CAR rate-limit statement's normal/extended burst
Hi Tim,
Thanks for getting back to me. Look at the example form cisco press lab
practise guide(lab5 QOS), In the example average is given as 20mbps.
I would calculate bc as follows:
20 mbps=20,000,000bps
20000000*(1/8)=2500000bits (tc is assumed as defualt 1/8sec or 125ms)
2500000/8=312500bytes(bits to byte conversion)
EXAMPLE GIVEN IN THE DEBRIEF SECTION::
rate-limit output access-group 101 20000000 24000 32000 conform-action
set-prec-transmit 5 exceed-action set-prec-transmit 0
So if it is either MQC police command or rate-limit command I would use
312500 for both bc and be. But the example uses:24000 and 32000 bytes. I am
not sure how the author came up with 24000 byts and 32000 bytes for normal and
extended burst values. I think we have to get it right because even in the
exam we have to type right numbers.
Mani
ccie2be <ccie2be@nyc.rr.com> wrote:
Mani,
Off-hand, I don't know the answer to your question but here are a couple
thoughts:
1) Given that's there's nothing that can be done using the rate-limit
command that can NOT be done
using the police MQC, and Cisco's direction is to do all QoS with MQC, I
would doubt that you would
ever need to use the rate-limit command in the lab.
2) Does the command (either rate-limit or police) require that a value
for
Bc is entered? I'm not sure, but I think
it's possible that you don't need to enter a Bc value and therefore, you
can
let IOS compute that value.
3) If the Bc must be entered, just use the same value but converted to
bytes.
HTH, Tim
----- Original Message -----
From: "mani poopal"
To:
Sent: Friday, December 24, 2004 8:07 AM
Subjec! t: QOS- CAR rate-limit statement's normal/extended burst
> Hi Guys,
>
> In the rate limit statement or question if only rate is given(assue
20mbps), how do we arrive at values for extended and normal burst sizes.
I
know this has been discussed earlier but any help is appreciated.
> eg:
> rate-limit output access-group 101 20000000 24000 32000 conform-action
set-prec-
> transmit 5 exceed-action set-prec-transmit 0
>
> ps:
> 20000000- in bits per second
> 24000----bytes
> 32000----bytes
> How do they arrive at 24000 and 32000 values.
>
> thanks
>
> Mani
>
>
>
> B.ENG,A+,CCNA,CCNP,CCNP-VOICE, CSS1,CNA,MCSE
> (416)431 9929
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>
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