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From: Luigi Rizzo <luigi@labinfo.iet.unipi.it>
Message-Id: <199610141429.PAA13506@labinfo.iet.unipi.it>
Subject: Re: ppp over vty possible ?
To: exidor@nimbus.superior.net (Christopher Masto)
Date: Mon, 14 Oct 1996 15:29:34 +0100 (MET)
Cc: question@freebsd.org, isp@freebsd.org
In-Reply-To: <199610141332.JAA16872@nimbus.superior.net> from "Christopher Masto" at Oct 14, 96 09:32:14 am
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> Luigi Rizzo writes:
> > When I use ppp from home (14.4 modem) with telnet (and possibly
> > other apps, I haven't checked), the RTT is suspiciously close to
> > 200 ms (within 10ms; I have a modified kernel which prints the
> > current RTT and bandwidth on every connection). As you can imagine,
> > typing this way is not the most pleasant thing in the world.
> 
> That doesn't sound very suprising to me.  I typically see 200-300ms
> ping times over a modem running PPP.  There's a lot of turnaround
> latency in 14.4/28.8 modems.

Can you give more details ? The same problem does not occur when
I use a plain connection (e.g. using the "term" mode of ppp). Now,
for sure it might be something in the modem, e.g. it sees a burst
of bytes coming in and decides it is worth waiting for a sufficiently
large block to attempt compression. But -- apart for this being a
symptom of poor design in the modem -- what is intriguing me is
the delay -- 200ms -- so close to what is a TCP_FASTTIMEOUT.

	Luigi
====================================================================
Luigi Rizzo                     Dip. di Ingegneria dell'Informazione
email: luigi@iet.unipi.it       Universita' di Pisa
tel: +39-50-568533              via Diotisalvi 2, 56126 PISA (Italy)
fax: +39-50-568522              http://www.iet.unipi.it/~luigi/
====================================================================