From: Jonathan V Hays (jhays@jtan.com)
Date: Wed Jul 09 2003 - 20:36:53 GMT-3
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On
> Behalf Of Jim Phillipo
> Sent: Wednesday, July 09, 2003 6:48 PM
> To: ccielab@groupstudy.com
> Subject: More QOS CAR example
>
>
> This is from VEGESNA's book
>
> All traffic except HTTP over a rate of 15 Mbps is marked with
> IP Prec 4
> HTTP over 15 Mbps is marked with 0
> This is a 30 Mbps pipe from provider
>
> There answer:
>
> rate-limit input 30000000 15000 15000 conform-action continue
> exceed-action-drop
> rate-limit input access-group 101 15000000 10000 10000 conform-action
> set-prec-transmit 4 exceed-action set-prec-transmit 0
> rate-limit input 30000000 15000 15000 conform-action
> set-prec-transmit 4
> exceed-action set-prec-transmit 4
>
> access-list 101 permit tcp any any eq www
> access-list 101 permit tcp any eq www any <This is for web
> traffic leaving
> the site correct ?>
>
> How do they arrive at 15000 and 10000 respectively ?
[snip]
Good observation.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
fqos_c/fqcprt4/qcfpolsh.htm#1000977
The above reference on the Doc CD gives the CAR formula as:
<quote>
Recommended Burst Values
Cisco recommends the following values for the normal and extended burst
parameters:
normal burst = configured rate * (1 byte)/(8 bits) * 1.5 seconds
extended burst = 2 * normal burst
</quote>
Here are the calculations (commas added for readability - my apologies
to Europeans and others who don't use commas to break up the thousands
;-)
configured rate = 30,000,000 bps
normal burst = 30000000/8 * 1.5 = 5,625,000 bytes
extended burst = 2 * 5625000 = 11,250,000 bytes
configured rate = 10,000,000 bps
normal burst = 10000000/8 * 1.5 = 1,875,000 bytes
extended burst = 2 * 1875000 = 3,750,000 bytes
Vegesna is obviously *not* using this formula. Maybe there is a
saturation point or ceiling for burst size? (This is no more than a
SWAG.)
Perhaps the "experts" will chime in ...
Jonathan
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