Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!hayes!tnixon From: tnixon@hayes.uucp Newsgroups: comp.dcom.fax Subject: Re: Fax Quality Message-ID: <3871.27e60601@hayes.uucp> Date: 19 Mar 91 12:37:21 GMT References: <3833.27d6468f@hayes.uucp> <1526@integow.uucp> <3842.27da8a2f@hayes.uucp> <427@paralogics.UUCP> Organization: Hayes Microcomputer Products, Norcross, GA Lines: 58 In article <427@paralogics.UUCP>, shaw@paralogics.UUCP (Guy Shaw) writes: > As long as changes are being made, the people who introduce new technology > and/or a new standard must overcome the inertia of all the existing fax modems. > So, then, why shouldn't this be the time to just switch to V.32 for fax? > What does V.29+V.17 have that couldn't be done with V.32? A lot of people in the _modem_ industry agree with you. In general, we believe that the performance of Group 3 fax could be significantly improved by switching to a high-speed full duplex modem (like V.32bis), and staying with it, rather than constantly switching between modulation schemes during the call. It's pretty ridiculous to send synchronous data using V.21 FSK modulation anyway, and to do it at 300bps -- arghhh! But there's a lot of inertia in the fax world. The best argument for sticking with half-duplex modulation schemes seems to be "we've always done it that way"!! It's unfortunate, but political squabbles and "egos" (which standards committee knows best how to send a fax) often get in the way. Proponents of half-duplex transmission also argue that echo cancellation is expensive (was, but isn't any more), and that half-duplex modems work better on poor circuits than full duplex (hasn't been demonstrated in a repeatable way). > Am I wrong in these assumptions: > 1) the only reasons that fax modems and computer modems are different are > purely historical, and > 2) if the proliferation of cheap personal computers had arrived earlier, > fax would just be some standard encoding format (a la uuencode) and > not have modem technology of its own. I think you're forgetting that the purpose of a fax modem is to be compatible with standalone fax MACHINES, not with computers. Group 3 fax predates PCs by a good bit. Faxes were using 9600bps transmission when the "standard" PC modem was still a 300bps Bell 103. When Group 3 standards were developed, there WASN'T a standard for dial-up, full duplex data modems above 1200bps. In fact, V.29 isn't even standardized for dial-up use; CCITT Study Group VIII (the fax standards committee) kludged it into the fax application without any cooperation from Study Group XVII (the modem standards committee). PC fax modems were definitely an afterthought, and had to be compatible with the (by then) huge installed base of fax machines; compatibility with high-speed data modems wasn't even a consideration. Study Groups VIII and XVII are now working on even faster modems ("V.fast") that will modulate at up to 24,000bps. XVII wants VIII to consider using the modem in a full-duplex mode, but nevertheless is developing a half-duplex mode if VIII decides to hold their ground. -- 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