Cisco PPP DS-3 limitations - 42.9Mbpbs?

Wed Feb 20 21:28:22 UTC 2002

On Wed, 20 Feb 2002, Jon Mansey wrote:

> OMG! Arent we missing the point here? What about never running links above
> 60% or so to allow for bursts against the 5 min average, and <shudder>
> upgrading or adding capacity when we get too little headroom.

> And here we are, nickel and diming over a few MBps near to 45M on a DS3...

And why not? Obviously there is a reason why they're not upgrading,
because there is plenty of traffic to fill up a second or faster circuit
if packets are being dropped because of congestion. (Which has not been
confirmed so far.)

There shouldn't be any problems pushing a DS3 well beyond 99% utilization,
by the way. With an average packet size of 500 bytes and 98 packets in the
output queue on average, 99% only introduces a 9 ms delay. The extra RTT
will also slow TCP down, but not in such a brutal way as significant
numbers of lost packets will. Just use a queue size of 500 or so, and
enable (W)RED to throttle back TCP when there are large bursts.