From: Leah Lynch (leah_lynch@xxxxxxxxxx)
Date: Tue Feb 12 2002 - 17:25:55 GMT-3
That's pretty close:
Short answer:
CAR is a DiffServ packet marking/classification application based on value
in TOS header. It is very configurable and allows you to change the value of
the IP precedence bit or DSCP value based on conform or exceed statements
which are configurable.
WRED is based on RED (that goes based on Nagle algorithm) where WRED uses
the value of TOS header to drop packet proactively based on their weight
(kind of like WFQ) WRED will drop a percentage of packets once congestion
has been detected on the interface. WRED is used to avoid congestion by
forcing TCP flows to backoff using TCP windowing.
This doc explains a lot about the differences between the two.
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/fqos
_c/qcfintro.htm
This is also covered in Cisco IOS Quality of Service and the Configuration
guide but a lot has changed since that was written (and since IOS 12.2). I
personally like the Documentation CD contents best.
Hope that helps.
Leah Lynch
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Ahmed Mamoor Amimi
Sent: Tuesday, February 12, 2002 11:42 AM
To: ccielab@groupstudy.com
Subject: CAR and WRED
my thinking about CAR and WRED :
CAR
By CAR u can set normal and max burst then tell if the rate drop from
normal then apply precedence or drop or ATM-CLP or QoS or trasmit.
General assumption:
set min xxx
max xxx
if min<flow of packet
then
drop or clp or prec or qos or transmit
end
WRED
Use the random-detect command to enable WRED, which randomly discards
packets during congestion based on IP precedence settings
General assumption:
if RED<flow of packet
then
{(set precedence 0-7) and (threshold 1-4096)}
or
set precedence to rsvp packets
my thinking is that they both are some what same but CAR is more flexible as
it gives u the upper and lower bond of limit
to traffic.
-Mamoor
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