From: Bob Sinclair (bsin@cox.net)
Date: Sat May 22 2004 - 22:35:14 GMT-3
Tom,
It helps to remember that shaping creates a software queue or queues which
feed the interface output queue. The shaping queue feeds the interface
output queue at the shaped rate. This is true whether or not there is
congestion on the interface queue.
The interface could be T3 with no traffic. If you are shaping to 64k, then
a burst of 192k will be buffered. Shaping "creates congestion" between the
software shaping queue and the interface output queue.
Wendell Odom as an excellent explanation in Cisco DQOS.
HTH,
Bob Sinclair
CCIE #10427, CISSP, MCSE
www.netmasterclass.net
----- Original Message -----
From: "Tom Rogers" <cccie71@yahoo.com>
To: "Richard Dumoulin" <richard.dumoulin@vanco.es>; "Ahmed Mustafa"
<ahmed.mustafa@sbcglobal.net>
Cc: <ccielab@groupstudy.com>
Sent: Saturday, May 22, 2004 9:26 PM
Subject: RE: QoS Shape Vs Police
> Richard and Ahmed,
>
> So I take that shape is a congestion, command right ?
>
> If so, that means if I I have shape average 96000 ===> Only during
congestion class XXX is shaped to 96 kbps and if there is no congestion I ll
send full e0 speed out, right?
>
> Rx(e0)------------------------(e0)ISP
> policy-map TEST
> class xxx
> shape 96000
> int e0/0
> service-policy out TEST
>
> Thats what I thought. So if ISP only wants 96kbps to come in, should'nt we
be using police keyword instead of shape on Rx ?
>
> But the DQoS book is using shape keyword (ISBN#1-58720-058-9, page 364, Eg
5-5)
> It says Provider is policing at 96kbps and adjust your traffic
accordingly.
>
> Thanx
> Tom
>
> Richard Dumoulin <richard.dumoulin@vanco.es> wrote:
>
> Tom, it is precisely traffic shaping that creates congestion. When the
packet rate approach the CIR then they are enqueued in the pvc queues and
shaped.
>
>
> --Richard
>
> -----Original Message-----
> From: Tom Rogers [mailto:cccie71@yahoo.com]
> Sent: domingo, 23 de mayo de 2004 0:40
> To: Ahmed Mustafa
> Cc: ccielab@groupstudy.com
> Subject: Re: QoS Shape Vs Police
>
>
> Ahmed,
> Thank you for your explanation. My confision is still not clear. I
understand that in shape the graph is like a plateau ie packets re held as
long long as they can and transmitted at a certain threshold say 96kbps in
this book example.
>
>
> What I want to know is, is this only during the CONGESTION ?
> Or no matter what, whether congestion or not... like in policing.
>
> Is this shape independendent of congestion ?
>
> Thanx in advance
>
> Tom
>
> Ahmed Mustafa <ahmed.mustafa@sbcglobal.net> wrote:
> 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"
> To:
> 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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