From: keith tokash (ktokash@hotmail.com)
Date: Sat Dec 01 2007 - 16:48:48 ART
Thanks for the insight, particularly the usage (outbound to carrier who
polices). The context makes it really easy to remember. I have Odom's QOS
book, but I've just been using it for reference. I think I'm off to a coffee
shop with that book and a highlighter/pen for the day, as I have enough QOS
cli time to actually understand the otherwise esoteric information in there.
With a few exceptions, secrecy is deeply incompatible with democracy and with
science.
--Carl Sagan
> Date: Sat, 1 Dec 2007 20:14:45 +0530
> From: pahujat@gmail.com
> To: scott_ccie_list@it-ag.com
> Subject: Re: "shape average" vs police
> CC: ktokash@hotmail.com; ccielab@groupstudy.com
>
> Keith,
> Scott brought up a very good point. Policing drops the
> packets whereas Shaping tries to buffer the packets during the time of
> congestion. Rate-limiting works well with controlling Denial of
> service attacks and other harmful applications. There isn't a good use
> for Rate-limiting as it drops a lot of packets, which makes TCP think
> there is congestion, so it slows down the flow and after a while the
> flow picks up again and then there is more packet loss. Traffic
> shaping on the other hand, just slows the packets down so TCP adapts
> to the available bandwidth.
>
> The following statistics were collected from a well documented test.
> During the test an ftp application was used to file transfer on a
> 128Kbps link. When rate limiting was used the performance was only 84
> Kpbs as appose to traffic-shaping where the performance was 121 Kps.
>
> Traffic shaping has a limitation that it can not be configured
> inbound. Therefore it is recommended to configure traffic shaping
> outbound at the customer end when conning to a Service provider using
> rate-limiting to enforce CIR. Better performance will be achieved.
>
> HTH,
> Tarun
>
> On 12/1/07, Scott Vermillion <scott_ccie_list@it-ag.com> wrote:
> > Hey Keith,
> >
> > I can't think of an article, per se, but Odom's QoS Guide is pretty much
> > required reading for CCIE candidates, IMHO. You will not have any doubts
> > about this or other such issues if you give that a good read.
> >
> > In short, just remember that shaping actually delays (buffers) exceeding
> > traffic in an attempt to "spool" it out at the CIR. Policing does not
> > perform any kind of delaying/buffering, but rather drops or remarks
traffic
> > that is out of conformance with the defined service parameters. For this
> > reason, shaping is typically done outbound while policing is typically
done
> > inbound. You would shape towards your carrier, for example, because they
> > would be policing inbound from you. Better to buffer up your outbound
> > traffic and try to spool it out during an ebb in offered load than to
have
> > the carrier deal more harshly with it inbound. As far as lab scenarios
go,
> > there are usually keywords in the task which help you to know which to
> > choose.
> >
> > But again, you will not be disappointed with your investment of both time
> > and $$ if you buy and read that book. I'm going to read it
cover-to-cover
> > once more before I attempt the lab in Feb...
> >
> > Regards,
> >
> > Scott
> >
> >
> > -----Original Message-----
> > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > keith tokash
> > Sent: Friday, November 30, 2007 9:58 PM
> > To: ccielab@groupstudy.com
> > Subject: "shape average" vs police
> >
> > Does anyone happen to know of a nice article explaining the difference
> > between
> > "shape average" and "police"? I'd like to clear this up, and my searches
> > keep
> > turning up configuration steps, which are far easier than understanding
the
> > nuances of the two.
> >
> > As I understand things, shaping allows some ebb and flow from the average
> > rate
> > you give it, queueing packets if possible, whereas policing is a hard
drop
> > at
> > the prescribed limit.
> >
> > With a few exceptions, secrecy is deeply incompatible with democracy and
> > with
> > science.
> > --Carl Sagan
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