From: Kenneth Wygand (KWygand@customonline.com)
Date: Sun May 23 2004 - 13:46:42 GMT-3
Joe,
Can you provide a basic configuration example illustrating your
question?
Kenneth E. Wygand
Systems Engineer, Project Services
CISSP #37102, CCNP, CCDP, ACSP, Cisco IPT Design Specialist, MCP, CNA,
Network+, A+
Custom Computer Specialists, Inc.
"The only unattainable goal is the one not attempted."
-Anonymous
-----Original Message-----
From: Joe Chang [mailto:changjoe@earthlink.net]
Sent: Sunday, May 23, 2004 12:34 PM
To: Kenneth Wygand; ccielab@groupstudy.com
Subject: Re: Traffic Shaping question
You are absolutely correct, policing either marks or drops
non-conforming
traffic. I guess the idea behind traffic shaping is either 1) to make
sure
the upstream network never has to contend with "too much" traffic or 2)
give
the network all traffic but let it know which packets it can preferrably
drop.
However my question concerns traffic shaping - which does not mark (set
the
IP precedence) of overrun traffic. It's my fault - I didn't make that
clear
in the body of my question.
----- Original Message -----
From: "Kenneth Wygand" <KWygand@customonline.com>
To: "Joe Chang" <changjoe@earthlink.net>; <ccielab@groupstudy.com>
Sent: Sunday, May 23, 2004 1:55 AM
Subject: RE: Traffic Shaping question
> Joe,
>
> There are two strategies you can employ, and your statements mesh two
of
them together in a way that it doesn't make logical sense, so in that
way,
you are correct!
>
> When you use the token bucket (policing in this case) algorithm, each
packet passing through the algorithm is considered to "conform",
"exceed" or
"violate" the restrictions (depending on which form of policing you are
using - "rate-limit" uses only the "conform" and "exceed" actions while
"class-based policing" uses all three of the restrictions.)
>
> For arguments sake, lets say you are using the "rate-limit" command so
all
traffic can either "conform" or "exceed" the traffic contract you
configure.
For the traffic that exceeds, there are two strategies you can employ;
you
can send the traffic at a lower priority or you can drop the traffic
completely. The first method, sending traffic at a lower priority,
_will_
allow you to exceed the CIR, but will ensure that all traffic that does
exceed the CIR has its priority marked down. This way, if congestion
occurs
at a later router, that router will know which traffic has already
exceeded
a particular traffic contract and can selectively drop that traffic
first.
>
> The other option, simply dropping the traffic completely, will always
conform to the CIR, but will never send unconforming traffic.
>
> Hope this helps!
> Ken
>
> -----Original Message-----
> From: nobody@groupstudy.com on behalf of Joe Chang
> Sent: Sat 5/22/2004 7:35 PM
> To: ccielab@groupstudy.com
> Cc:
> Subject: Traffic Shaping question
>
>
>
> QoS is a real popular topic here!
>
> Does anyone know what happens to packets that are queued as a result
of
being
> rejected by the token bucket algorithm? At what point are these
packets
> forwarded onto the transmit ring? Two streams result from the token
bucket
> function - one that conforms and one that doesn't. How and when can
the
> unconforming stream be sent without defeating the objective of traffic
shaping
> - keeping the average rate under the CIR?
>
> TIA
>
>
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