From: Chris Home (clarson52@comcast.net)
Date: Tue Dec 10 2002 - 19:54:28 GMT-3
I wrote the previous post below hurriedly and didn't really read it over
before hitting the send. It was rather matter of fact and I didn't mean it
to be. I usually try to put a discrete disclaimer like "This is just MY
understanding of things but I could be totally wrong" in my post and
realized I hadn't. This is just my understanding. Enlightenment welcome!!
----- Original Message -----
From: "Larson, Chris" <CLarson@usaid.gov>
To: "'Robert Slaski'" <robin@atm.com.pl>; "P729" <p729@cox.net>
Cc: "sg p" <sgp4377@yahoo.com>; <ccielab@groupstudy.com>
Sent: Tuesday, December 10, 2002 2:51 PM
Subject: RE: Reduce the bandwidth of Gig Interface
> I would have to disagree that "policing TCP traffic would be disastrous."
It
> is done in many networks and I know Sprint does it in their Internet pops.
>
> If you have packet drop due to policing (or congestion or for any other
> reason), the source of the traffic is going to back off on it's
transmition
> rate until packets are acknowledged and not being dropped any longer.
> Tranmission will then increase in rate again until packets are again
> droppped thereby indicating congestion and the cycle repeats or the
> reciever sets an acceptable window size. This is desirable and far from
> disastrous.
> Windowing mechanism's are used regardless of whether a person uses WRED,
> Policing, Traffic shaping or anything else.
> WRED is not a cure for this behaviour, and this behaviour doesn't change
> because you use WRED. WRED simply allows a person to set what traffic gets
> dropped first. WRED does help in that it will decrease the likelyhood of
> global restarts. Where for instance congestion is detected by a whole slew
> of sources due to many packet drops thereby all of the sources backing off
> at once.
>
>
> > -----Original Message-----
> > From: Robert Slaski [SMTP:robin@atm.com.pl]
> > Sent: Tuesday, December 10, 2002 9:29 AM
> > To: P729
> > Cc: sg p; ccielab@groupstudy.com
> > Subject: Re: Reduce the bandwidth of Gig Interface
> >
> > P729 wrote:
> > > "We want to use some type of traffic policing so that the excess
traffic
> > > that arrives at our port (10Mb) doesnt get dropped due to the
> > bandwidth
> > > reduction."
> > >
> > > Herein lies one of the differences between policing and shaping. With
> > > policing, you're allowing for a certain amount of bursting such that
TCP
> > > between the end-nodes polices itself to your desired commited rate.
> > > Excessive bursting will lead to dropped (vs. delayed) frames. This is
> > > necessary to "close the window." With shaping, you begin delaying
> >
> > Policing will cause disaster with TCP traffic, especially if you discard
> > 99 out of 100 frames (1Gbps->10Mbps). But you can use tail-drop-WRED
> > available on gigabit ports of 3550 along with aggregate policing. This
> > will cause TCP traffic to be smoothed using its windowing mechanisms,
> > and policing will not allow the traffic to excess 10Mb.
> >
> > mikrobi,
> > --
> > .
> .
.
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