Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uunet!hayes!tnixon From: tnixon@hayes.uucp Newsgroups: comp.dcom.modems Subject: Re: comp.dcom.modems lexicon Message-ID: <3832.27d4dcf9@hayes.uucp> Date: 6 Mar 91 12:13:45 GMT References: <1991Mar5.225546.6672@panix.uucp> <19552@cbmvax.commodore.com> Organization: Hayes Microcomputer Products, Norcross, GA Lines: 55 With regard to the discussion on "duplex" vs. "full duplex", etc.: I serve on the Vocabulary Special Rapporteur's Group in Study Group XVII, and so try to pay attention to these things. I sometimes point out, particularly when people are _already_ confused about word meanings, what the current practice is in the CCITT and other standards committees. For example, we've officially abandoned the term "baud", because of widespread misuse, and instead use "symbols per second". "Full duplex" never has been an official term, so we couldn't abandon it, but we avoid using it. It gets used pretty often in discussion, but never in printed documents. Personally, I don't see any real harm in saying "full duplex" when you mean "duplex", in terms of two-way simultaneous transmission on the phone line. There's really no confusion here. I would prefer that glossaries and lexicons mention that the correct term is simply "duplex". I _do_, however, object to the use of "half duplex/full duplex" when, from context, the meaning seems to be "local echo/no local echo"; that is a serious misapplication of the terminology. The issue of "duplex" vs. "simplex" is interesting. The standards committees generally use "simplex" when the modem is truly capable of only transmission OR reception, and "half-duplex" when it is capable of alternating between transmission and reception, but not performing both at the same time. I suppose we could call it "alternating simplex". We've also adopted "asymmetrical duplex" when the modem transmits and receives simultaneously, but at different rates (either symbol rates or data rates), and the two channels are always flowing in opposite directions. If the two channels are not linked but are instead independent with regard to direction, then this is a "half-duplex modem with secondary channel", not an asymmetrical modem. In article <19552@cbmvax.commodore.com>, grr@cbmvax.commodore.com (George Robbins) writes: > The opposite of duplex is simplex, i.e. able to transmit one way, over > on set of wires, period. Given this, and the fact that half-duplex > technology probably preceeded full duplex, and the full was added to > to make the distinction, I think it's still a meaningful modifier. Actually, the first modems standardized by the CCITT were V.21 (300 baud duplex) and V.23 (600 or 1200 baud forward channel with 75 baud backward channel). V.23 can be implemented with or without the reverse channel, and the direction of transmission on the reverse channel can be either linked or not linked to the forward channel direction. -- Toby Nixon, Principal Engineer | Voice +1-404-840-9200 Telex 151243420 Hayes Microcomputer Products Inc. | Fax +1-404-447-0178 CIS 70271,404 P.O. Box 105203 | UUCP uunet!hayes!tnixon AT&T !tnixon Atlanta, Georgia 30348 USA | Internet hayes!tnixon@uunet.uu.net