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Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!uflorida!haven!umbc3!wolf.umbc.edu!alex
From: alex@wolf.umbc.edu (Alex Crain)
Newsgroups: unix-pc.general,comp.sys.att
Subject: TCP for the unix-pc
Summary: what to do?
Keywords: 3b1 7300 TCP SLIP Appletalk network
Message-ID: <1892@umbc3.UMBC.EDU>
Date: 10 Apr 89 00:19:35 GMT
Sender: newspost@umbc3.UMBC.EDU
Reply-To: alex@wolf.umbc.edu.UUCP (Alex Crain)
Organization: University of Maryland Baltimore Co.
Lines: 81


			CALL FOR DISCUSSION

		Topic: Serial line networking of unix-pc's.

	As my efforts to produce a working socket driver for the
unix-pc are generating positive results (it works), The looming
question of how to interconnect machines is becomming more pertenant.
like many people, I bought a large machine and later a small machine
as a future parts doner, and getting the two of them to talk would be
right nice. I'm running a uucp network now, but I'd really like some
kind of packet base protocol. With the TCP driver taking shape, the
idea is becomming more attractive.

	For myself, I would like to run a bus network around my house,
consisting of a single serial line. I will probably purchase a mac as
a game machine/graphics engine/word processor for my wife in the next
year or so, and I would like to pick up a nice printer, an maybe a
trailblazer. Also, I never want to buy a peripheral from apple! (nobody
has that much money)

	So I'm figureing my network to be:

		HARDWARE

	1) a bi-directional bus network, or some kind of fault-tolerant ring
	that can tell when a host goes down. No star networks. I only want to 
	have to deal with one port per machine, and I want to be able to splice
	in devices.

	2) RS232 or simular hardware speeds and voltage levels. ($$$)

	3) hardware support for packet acceptance/rejection, and queueing of
	data so that the machines don't die.

		SOFTWARE

	1) support for virtual circuits and datagrams, with out-of-band 
	facilities.

	2) reasonable efficency with in packet overhead.

	3) gateway/forwarding capability, for dealing with modems and printers.
	This means machine addresses and ports.

	4) virtual files, as in some kind of restricted NFS.

I think that some kind of minimal hardware support is going to be
required for speed, but I'd like to make that an option, so that poor
folks can use the existing RS232. I envision a card that watches the
net and screens packets against their address. I would also like at
least 16 bytes of buffer space with a timeout, to limit interrupts.

I'd also like to use an existing protocol, custom protocols are a drag
unless they catch on, even free ones. The two protocols that come to
mind are SLIP and Appletalk. SLIP would be in keeping with tradition,
but I'm worried about the overhead. I don't know anything about
Appletalk, but the fact that its built around a serial line suggests
that its optimized for speed. The fact that I'm looking at a mac also
makes Appletalk more desireable :-).

Also, Appletalk hardware is pretty close to what I'm looking for,
although I don't know much about it. Appletalk also supports some kind
of disk sharing that works over a serial line.

I will probably add the code for SLIP anyway, since much of the code
is free and available. I'm looking into a protocol developed at CMU
thats built around Appletalk, and if the code is free, I'll look into
adding that to, if only for my future mac.

So what does everybody think? I want to write something thats going to
be *used*, although I won't be charging for it. What are your needs? I
don't know diddly about hardware, so I would like to here from the
hardware guys regarding the interface. Optimally we would see the same
deal as the hard disk upgrade, namely a "lenny and gil do it yourself"
model and a "custom PAL on a special board for $$" version.

					:alex
Alex Crain
Systems Programmer			alex@umbc3.umbc.edu
Univ Md Baltimore County		umbc3.umbc.edu!nerwin!alex