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