From: Robert Slaski (robin@atm.com.pl)
Date: Tue Dec 10 2002 - 19:09:15 GMT-3
Larson, Chris wrote:
> 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.
>
I generally agree with your and P729's thoughts but WRED (you can forget
'W', for RED to work the traffic does not have to be classified or
weighted) helps TCP windowing and slow start mechanisms to obtain best
throughput. With 100:1 ratio of incoming to outgoing traffic output
buffers on a switch will be continuously filled-up so packets will be
dropped out from queue randomly. So you'll get 10Mbps of traffic but
only few Mbps (maximum) of usefull traffic as the rest would be
retransmissions. Enabling WRED and setting drop thresholds such that
output queues never become 100% filled up and they can accomodate TCP
bursts before policers start cutting traffic. This will help you obtain
most of required 10Mbps.
Sprint may police traffic in their POPs but to ensure that customers
won't exceed the bandwidth they pay for - in fact most ISPs do this. But
on the other hand I saw networks where ordinary policing from 10Mbps to
2Mbps was made on their ISP link and this caused the whole network to
shut down while the link utilization did not exceed 200kbps. This is
what I meant by "disaster". Enabling shaping, WRED or some fancy
queueing helped there a lot.
mikrobi,
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