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Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!lll-winken!uunet!mcvax!tuvie!hpuviea!mah
From: mah@hpuviea.UUCP (Michael Haberler)
Newsgroups: comp.protocols.tcp-ip,comp.dcom.lans
Subject: Re: Super Cheap IP router (< $1000)
Message-ID: <877@hpuviea.UUCP>
Date: 8 Apr 89 10:20:29 GMT
References: <9817@orstcs.CS.ORST.EDU>
Organization: Hewlett-Packard Vienna,Austria
Lines: 29

We're using KA9Q as a 'super cheap' IP router for about a year now at the
University of Economics at Vienna. It's an AT clone bridging a NetBIOS
IBM PC Network (broadband - the early works from IBM & Sytek) and the
campus ethernet. Also, it has a permanent SLIP connection to a remote
PC Network running with 19200 baud. We also experimented with two KA9Q's 
and dialup SLIP for bridging two distant Ethernets.

This worked flawless as long as traffic is low; given the average dumb
PC hardware it's easy to lose interrupts when traffic is coming in from
more than one side. Especially the Slip connection deteriorated badly
under high load. The Ethernet card we use (3c501 - yes I know) keeps
the CPU busy with interrupts disabled too long so the serial port just is
overrun. The Netbios/slip route actually works better, probably due
to less latency of the Netbios driver. 

I think that a bridge able to sustain higer traffic would need interface
cards with substantial on-board buffering. The one-interrupt-per-character
scheme for slip would need to be replaced with at least DMA, or better an
own CPU on the card. 

Remember: this all is due to the !@*&^% PC hardware having lousy
real-time performance. KA9Q never gave us a problem (Kudos, Phil!).

Michael Haberler & Gustaf Neumann (neumann@awiwuw11.bitnet)
-- 
Michael Haberler		mah@hpuviea.uucp 
Hewlett-Packard Austria GmbH, 	...mcvax!tuvie!hpuviea!mah
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