From: Ahmed Mustafa (ahmed.mustafa@sbcglobal.net)
Date: Sat May 22 2004 - 14:44:03 GMT-3
Tom,
The major difference between policing and shaping is when you do policing,
no matter if your link is 10MB, 100MB, 1GB, once you set the limit, and
traffic beyond that limit will be dropped or you set parameters if you don't
want the traffic to get dropped. In shapping, your intention is not to drop
the packet, but to delay the packet so the packet doesn't get dropped
Shapping is advantageous where your low end traffic will not get dropped,
and it will arrive to the destination with some latency. Shapping is never
meant to be for delay sensitive traffic such as voice and video.
The best example would be
Your router is connected to ISP. The Clock rate of your line is 1536, but
the CIR you are paying for is 128KB. ISP knows that the guranteed CIR is
128KB, but the router at your end could easily send traffic above 128KB.
The ISP router can then start policing traffic coming from your end at 128KB
at the ingress point, so no matter how fast your access rate the traffic
above 128 will get dropped.
So now at your end you could configure some shapping at the egress point
where you can shape your data traffic at certain rate, and prioritized your
low latency traffic at certain rate.
HTH,
Ahmed
----- Original Message -----
From: "Tom Rogers" <cccie71@yahoo.com>
To: <ccielab@groupstudy.com>
Sent: Saturday, May 22, 2004 7:55 AM
Subject: QoS Shape Vs Police
> Hello Every one,
>
> Can some explain me the difference beween shape and police.
> I did the research and could not find an answer.
>
> When I look at the DQoS book ISBN#1-58720-058-9
> Page 364 Example 5-5
> It says the FR provider wants to police the VCs at 96kbps and we re to
adjust our FR interfaces accordingly.
>
> I was under the impression police cir command should do it.
> But the solution has shape average.
>
> My confusion is, I thought shape average kicks in when there is a
congestion and would plateau the graph and policing no matter what we limit
or restrict traffic even if there is no congestion and would tail drop the
graph.
>
> Can some one tell me the when to use police and when use shape?
>
> I think I am lacking some concept here
>
>
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