Date: Sat, 02 May 1998 11:46:06 -0700 From: Bill Trost <trost@cloud.rain.com> To: current@FreeBSD.ORG Subject: Re: Infrared ? (a simple experiment for laptop owners...) Message-ID: <4719.894134766@cloud.rain.com> In-Reply-To: Your message of Sat, 02 May 1998 19:31:37 %2B0200. <9297.894130297@critter.freebsd.dk> References: <9297.894130297@critter.freebsd.dk>
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One concern I have (before getting into the nitty-gritty) is that
anything "we" do (and I might go dig up an IR transceiver for my desktop
just to help) be compatible with whatever else might be in use. Tekram
(www.tekram.com) makes an IPX IR bridge, and Mac laptops run AppleTalk
over their IrDA ports. I would expect the you might actually be able to
get something out of Apple about what their machines do.
Poul-Henning Kamp writes:
>Example: one side (the 'client' ppp) acts as a master, the other
>one as a slave. The protocol is governed by the master, and the
>slave can only send a packet right after a pkt coming from the
>master.
On the other hand, IP isn't very well suited to half-duplex, and to
get a decent performance you probably need to flip though Tanenbaums
book and see if you can find some old stuff from Hawai to use...
Slotted ALOHA is probably overkill for this task. You probably do not
want to try more than two nodes in the infrared network. The reason
is that IRdA ports have a fairly narrow beam width (30 degrees, as
I recall), and not that great a range (3 feet +/- 3 feet). As soon
as you add a third node, you will probably start running into hidden
transmitter problems. ALOHA would deal with that in the simple case,
but you more or less have to "know" that one node can reach all the
other nodes in the network.
Actually, in a two-node system, ALOHA more or less degenerates into
the protocol Luigi described anyhow, so this seems like an on-track
proposal. If you do try to go to three nodes, you may be better off
with the PPP server acting as the master, as it is more likely to be the
"fixed" system.
Finally, I think cellphone systems like GSM use an ALOHA-like protocol
as well, so that will provide a more recent literature reference. Note
that cellphone systems have a known "master", however (the cell tower).
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