From: Jason T. Rohm (jtrohm@xxxxxxxxxxx)
Date: Tue Feb 12 2002 - 18:29:15 GMT-3
Quick and dirty answer:
DSCP replaces the use of seperate IP Precedence (3bits), Delay(1bit),
Throughput(1bit), and Reliability(1bit) sections of the IP header with a
single 6 bit QOS marker. It gives you more granularity (64 markers vs. 8) in
your QOS configurations while maintaining rough backward compatability with
systems that only understand IP Precedence. (The Delay, Throughput, and
Reliability indicators were largely unimplemented).
Jason T. Rohm
CCIE #6861
jtrohm@athenet.net (home)
jtrohm@wiretech-inc.com (work)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Ahmed Mamoor Amimi
Sent: Tuesday, February 12, 2002 2:41 PM
To: leah_lynch@lucent.com; ccielab@groupstudy.com
Subject: Re: CAR and WRED
can u explain something about DSCP value .... what is that and wat is the
value for use
-Mamoor
----- Original Message -----
From: Leah Lynch <leah_lynch@lucent.com>
To: 'Ahmed Mamoor Amimi' <mamoor@ieee.org>; <ccielab@groupstudy.com>
Sent: Wednesday, February 13, 2002 1:25 AM
Subject: RE: CAR and WRED
> 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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