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From: karn@petrus.UUCP (Phil R. Karn)
Newsgroups: net.ham-radio.packet
Subject: Re: IP/TCP bumps and grinds
Message-ID: <645@petrus.UUCP>
Date: Tue, 15-Oct-85 11:37:05 EDT
Article-I.D.: petrus.645
Posted: Tue Oct 15 11:37:05 1985
Date-Received: Wed, 16-Oct-85 05:43:30 EDT
References: <78@mit-eddie.UUCP> <10663@ucbvax.ARPA>
Organization: Bell Communications Research, Inc
Lines: 26

> I may have missed the point, but why bother running IP over X.25, when
> IP (as a pure datagram protocol) is ideally suited to packet-radio?

I couldn't agree with you more! The problem is that "AX.25" is a very poor
term to describe the protocol run by the amateur packet radio community.
What we call "AX.25" is really just LAPB (the link layer of X.25) with a
prepended datagram header consisting of amateur callsigns (with optional
source routing through a bunch of digital repeaters, or "digipeaters".) It
does NOT have the Packet Layer from X.25 (as of yet, anyway...and I am
determined to do everything in my power to prevent that from happening.)

It is possible to use "AX.25" in "datagram mode", i.e., by bypassing the
connection-oriented LAPB layer and sending raw packets prepended by the
link-level amateur callsigns.  However, amateur packet radio is one
of those few places where link level acknowledgments make sense, because
the links are so unreliable that the chances of a packet making it
successfully down a long chain of them approaches zero asymptotically.

My view of a real amateur packet network involves IP gateways speaking
to their neighbors over AX.25 point-to-point links. If they have excellent
quality RF links, with few collisions, they default to AX.25 unconnected
mode; otherwise they use the link level connect facilities of AX.25 to
increase the chances of each datagram making it to the next node.  The
users, of course, speak TCP, and this may be the biggest challenge of all...

Phil