Cisco DS3 Questions..

Thu Feb 21 18:46:44 UTC 2002

Since the topic exploded, what are your opinions on encapsulation of leased
line DS3s.  We currently use Frame Relay for out Point to Point DS3
connections.  Personally, I don't know why we use FR as our encapsulation,
and so the question to all.  If you are running Cisco to Cisco, would it be
wise to run HDLC or PPP?  Our DS3s' here are hardly maxed out, 15% or so, so
I'm not complaining about the few extra bits I can squeeze out them but
maybe that 15% can shrink to 10% with less overhead.  Opinions or examples
of life appreciated.  

Thanks

shawn  

-----Original Message-----
From: Iljitsch van Beijnum [mailto:iljitsch at muada.com] 
Sent: Wednesday, February 20, 2002 4:28 PM
To: Jon Mansey
Cc: nanog at merit.edu
Subject: Re: Cisco PPP DS-3 limitations - 42.9Mbpbs?

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.