Date: Mon, 4 May 1998 23:21:28 +0200 From: Thomas Zenker <thz@tuebingen.netsurf.de> To: "Louis A. Mamakos" <louie@TransSys.COM> Cc: freebsd-current@FreeBSD.ORG Subject: Re: Infrared ? (a simple experiment for laptop owners...) Message-ID: <19980504232127.62419@tuebingen.netsurf.de> In-Reply-To: <199805041603.MAA04864@whizzo.TransSys.COM>; from Louis A. Mamakos on Mon, May 04, 1998 at 12:03:57PM -0400 References: <199805041546.KAA06041@unix.tfs.net> <199805041603.MAA04864@whizzo.TransSys.COM>
next in thread | previous in thread | raw e-mail | index | archive | help
On Mon, May 04, 1998 at 12:03:57PM -0400, Louis A. Mamakos wrote: > > > 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. > > It may be true that AX.25 "works" (for some definition of working) over > a half duplex channel, but that's no reason to cripple another medium > with badly though-out network architecture. > > LABP protocols were intended to be used over full duplex, point-to-point > links. Early experimentation took advantage of USRT parts and Bell 202 > modems that happened to be available. Unfortunately, it persists today, > more than a decade later. It is astonshing to me, as a networking > professional, that you would make a deliberate choice to misapply one > kind of technology into a completely different problem domain. Sure, as > an experiment... This is true, LAPB is a full duplex protocol, really what is called HDLC/TWS by ECMA (two way synchronous), bad for RF or IR. AX.25 adopted it, don't know why. But for this kind of transmission you need a half duplex protocol, with controlled access. Collision detection alla ethernet doesn't work with RF and IMHO neither with IR. > AX.25 does a very simple CSMA channel access algorithm, but there > is no collision detection done (or possible). AX.25 exhibits worse AX.25 uses this algorithm because the rf amateurs don't have uniform fixed network, it is somewhat in flow all the time. We used therefore in our radio network (all on a single frequency) a kind of token passing, which passes the token around within the network. The radio modem which has the token is the primary and has the right to initiate transfers or has to pass the token along. In case of a single transmission line this is actually superflous, should be enough leaving the lines sending RRs if nothing to transmit. Thomas Zenker To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?19980504232127.62419>