Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!uunet!hayes!tnixon From: tnixon@hayes.uucp Newsgroups: comp.dcom.modems Subject: Re: CODEX V.32bis Modems: Experiences? Message-ID: <3824.27d23d97@hayes.uucp> Date: 4 Mar 91 12:29:11 GMT References: <6894.27CDE028@zswamp.fidonet.org> Organization: Hayes Microcomputer Products, Norcross, GA Lines: 38 In article <6894.27CDE028@zswamp.fidonet.org>, root@zswamp.fidonet.org (Geoffrey Welsh) writes: > I disagree strongly! The standards are more complex than ever, and > marginal compliance, i.e. modems which follow the basic standard but only > connect well with certain other modems, is more commonplace than ever. I should also point out that "marginal compliance" is not the only reason one sees variations between modems from different manufacturers. CCITT modulations standards quite purposely and specifically defined ONLY the TRANSMITTER of the modem; the operation of the receiver is left of to the skills of the implementer. This makes sense; the purpose of the standard is to insure that the modems put the signal on the line properly, not to constrain the technology used to demodulate the signal. You also see considerable differences in the performance of V.42 and V.42bis between modems. The standards specify the encoding of the protocol and compressed data on the phone line, but don't (and shouldn't) specify the type or speed of microprocessor to use, the amount of memory available, the quality of firmware code that is written to implement the protocols, or much of anything else! _Connectivity_ should be accomplished if both implementations are compliant, but _performance_ may vary widely between compliant implementations! Actually testing is necessary to determine how various modems will perform. The trade press reviews devices and publishes tests, but the testing methods vary so widely and the results are so different that you really can't depend on what you read in the press to help make a decision on which modem to buy. It's truly a matter of luck which modem comes out on top in a particular magazine's article. -- 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