Subject: RE: Setting up a T1 and email
To: 'Johnny Billquist' <bqt@Update.UU.SE>
From: Alex Barclay <>
List: port-vax
Date: 07/15/1998 16:29:35
On Wednesday, July 15, 1998 1:56 PM, Johnny Billquist [SMTP:bqt@Update.UU.SE] 
> On Wed, 15 Jul 1998, Jacob Suter wrote:
> > Rick Copeland wrote:
> > >
> > > Johnny,
> > >
> > > I would like to know how I could use a 386 netbsd box as a router between
> > > the CSU/DSU (from a T1) and the web/email server which is a uVax3600.
> > > Could you post directions?
> >
> > a 386 (even a DX/40) is WAAAAAAAAAAAY to slow to route a T1.  Get a
> > 486DX2/66 or something.  I used to drag my 386DX/40 down with just a
> > 33.6k modem w/ FreeBSD.
> It all depends on what you expect. A dedicated 286 box will work just fine
> as a router, with dedicated software.
> A 386 will work just fine, it's just that it gets swamped easily, and then
> it will throw away some data. Nobody will die because of it, and nothing
> ought to break.
> It's all a question of what performance you expect. If it is going to
> route for a uVAX behind, than machine will hardly swamp very much
> anyway...

I fully agree. You need to remember that the serial ports on PeeCees are
terrible from an efficiency point of view. The machine is getting swamped
with interrupts. I have used a 486/33 as a fine IP router between two ethernets
and that was 10MB. Ethernet cards place far less load on the CPU than a
serial port. In the same way a decent T1 board will place a small load because
it should be doing stuff via DMA.

There was a paper in the early days of UNIX talking about the efficiency of
devices on a VAX or PDP (I think it was Kernighan, Thompson or Ritchie
who wrote it) Anyway they were saying that to run 50 terminals off a machine
at 9600 baud at 1 interrupt per char would be 48000 interrupts/sec. This
would bring the machine to its knees. An alternative would be to have
the serial ports have some intelligence. The main processor only polls
every 50Hz and gets every character since last time.

I think that their paper directly parallels the Ethernet/T1 to serial case on


Alex Barclay                    E-mail:
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