Date: Mon, 4 May 1998 11:58:27 -0500 (CDT) From: Jim Bryant <jbryant@unix.tfs.net> To: louie@TransSys.COM (Louis A. Mamakos) Cc: freebsd-current@FreeBSD.ORG Subject: Re: Infrared ? (a simple experiment for laptop owners...) Message-ID: <199805041658.LAA06135@unix.tfs.net> In-Reply-To: <199805041603.MAA04864@whizzo.TransSys.COM> from "Louis A. Mamakos" at "May 4, 98 12:03:57 pm"
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In reply: > > Did anyone see my last posting on this topic? > > > > These ports are ideal for AX.25! HDLC/LAPB type protocols are well > > documented. IP can be tunneled easily, as a matter of fact there are > > half-duplex TCP/IP networks all over the world using these protocols. > > AX.25 does a very simple CSMA channel access algorithm, but there > is no collision detection done (or possible). AX.25 exhibits worse that is the purpose of the ack/nak sequences [rr] frames... a level of pre-transmit collision prevention is done by monitoring the squelch line or the tone detector for channel activity. > yet you'll interfere with his transmission.) The original implementations > didn't do an exponential backoff (and I suspect many still don't) which > produces a very entertaining congestive collapse of loaded channels. exponential backoff has been pretty much de-facto standard since the mid-eighties or so. > There have been some attempts to improve the scheme - using full duplex VERY expensive [$3000+ per node] given the nature of the communications... > > If anyone is interested, if I remember correctly, I have a copy of the > > AX.25 protocol available at my web page [see .sig]... I can also > > supply the LAPB docs. > > Implement an AX.25 if you want to talk to the existing RF systems, but > you can do much better than this starting with a clean slate. AX.25 was > an experiment that escaped from the lab, and now the Amateur Radio I can think of a few better [?] ways of doing things myself. The problem at hand right now is a similar one, how to take a half-duplex serial link, and do something useful with it. there seems to be no point at this point to ask why they didn't specify a WDM/TDM solution to provide full-duplex communications in the IrDA standard. We are stuck with half-duplex. HDLC should be a common factor here, in amateur radio tcp/ip, only the HDLC layer is used, with IP directly on top of that. If async is not desired, then mebbe a TDM method would be more appropiate, nice for a finite number of nodes... jim -- All opinions expressed are mine, if you | "I will not be pushed, stamped, think otherwise, then go jump into turbid | briefed, debriefed, indexed, or radioactive waters and yell WAHOO !!! | numbered!" - #1, "The Prisoner" ------------------------------------------------------------------------------ Inet: jbryant@tfs.net AX.25: kc5vdj@wv0t.#neks.ks.usa.noam grid: EM28pw voice: KC5VDJ - 6 & 2 Meters AM/FM/SSB, 70cm FM. http://www.tfs.net/~jbryant ------------------------------------------------------------------------------ HF/6M/2M: IC-706-MkII, 2M: HTX-212, 2M: HTX-202, 70cm: HTX-404, Packet: KPC-3+ To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
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