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Path: euryale.cc.adfa.oz.au!newshost.carno.net.au!harbinger.cc.monash.edu.au!munnari.OZ.AU!news.mel.connect.com.au!news.syd.connect.com.au!news.bri.connect.com.au!corolla.OntheNet.com.au!news From: Tony Griffiths <tonyg@OntheNet.com.au> Newsgroups: comp.unix.bsd.freebsd.misc Subject: Re: FreeBSD and ATM NICs Date: Tue, 10 Sep 1996 11:42:01 +1000 Organization: On the Net (ISP on the Cold Coast, Australia) Lines: 44 Message-ID: <3234C769.5025@OntheNet.com.au> References: <MPG.c968e4b64c0acd7989680@netnews.ntc.nokia.com> <50q98v$fvb@dworkin.wustl.edu> <32321B46.167EB0E7@FreeBSD.org> <32336F13.7017@tidepool.com> Reply-To: tonyg@OntheNet.com.au NNTP-Posting-Host: swanee.nt.com.au Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 3.0 (WinNT; I) To: Charles Smith <shadow1@tidepool.com> Charles Smith wrote: > > I have been reading somethings about ATM. What is ATM, and where could > I find more info about it. Does it run under a stand phone line, or is > it via coxal cable? > Thanks. > -Charles Smith ATM == Asynchronous Transfer Method Basically a way of muxing multiple VCs (Virtual Connections) down wires (or fibre or <some serial comms path>). Each VC gets 53 bytes (48 data + 5 VC header). The 48 is a compromise between the voice people who wanted 32 and the data people who wanted 64 !!! Multiple VC 'cells' forms a larger ATM packet although each VC cell has it's own "routing" (in a ATM switch sense, not IP-type routing) info in it's header. ATM will run at different bit rates, but 45 Mbps and 155 Mbps are most frequently mentioned. Now ATM is a protocol designed by the Telecoms people so it is CONS (Connection-Oriented Networking Service) based, unlike IP or OSI routing which is CLNS (Connection-Less Networking Service). The fact that ATM is CONS means that it doesn't work too well with TCP/IP (CLNS), so they came up with LANE (LAN Emulation!!!) to make ethernet-type broadcast/multicast packets work in a point-to-point ATM network. Ipsilon have come up with an alternative to LANE, namely IP Switching. What they do is basically 'look' at the TCP/IP packet header and try to recognise a "flow". The definition of a "flow" is a PERSISTENT connection between two host systems. Once a "flow" has been recognised, the cells (ie. the IP packets of n-bytes has by this time been broken down into multiple 48+5 byte cells) can be forwarded by the ATM switch without the management processor getting in the way! Does all this sound like it's getting out of hand? Sure does to me... What is really needed is TCP0/2 (ala OSI's TP0/2)... eg. TCP over a CONS network. Then we wouldn't need LANE or IP Switching. Just open up an ATM VC between the two hosts that want to talk to each other and spit data! Tony