NetNews Usenet Archive 1992 #19/NN_1992_19.iso/spool/comp/dcom/modems/12915

Internet Message Format | 1992-09-03 | 3.2 KB

Path: sparky!uunet!hayes!tnixon
From: [e-mail]
Newsgroups: comp.dcom.modems
Subject: Re: ?'s about Class 1 & Class 2 fax
Message-ID: <[e-mail]>
Date: 3 Sep 92 12:14:39 EDT
References: <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]>
Organization: Hayes Microcomputer Products, Norcross, GA
Lines: 53

In article <[e-mail]>,
[e-mail] (Jerry Wallace) writes:

> I understand that the Class 1 spec we've all heard about is quite old
> and that there is a Class 2 document available, but where would a
> revised Class 1 put us?  Why do you feel that the newer Class 1 would
> be better (in 500 words or less :^)?

TR-29.2 is going to do a "clean up" of the existing Class 1
document -- basically an editorial revision to make necessary
corrections, but without adding to or changing technical
requirements.  This will be "TIA-578-A", will still be known as
Class 1, and all existing Class 1 devices will continue to be in
compliance with it.

TR-29.2 is also working on an exhanced, extended Class 1 standard,
which is known variously as "Class 1-A", "Class 1.1", etc.  The
major problem with the existing Class 1 standard is that AT command
set interactions must take place at extremely critical places in the
Group 3 fax protocols -- there are times when the devices must
change modulation schemes in less than 80 milliseconds, and if there
is any delay whatsoever in the processing on the PC, you've lost it!
Class 2 solves this by moving control of the Group 3 T.30 protocol
out into the modem, but at the expense of flexibility: you have to
upgrade the modem ROMs to fix a bug or to implement new features
(and CCITT is continually adding new features to Group 3).

The extensions to Class 1 will retain the flexibility of having the
software in the PC, but eliminate these critical timing
dependencies.  We're still nailing down the exact syntax; the
current debate is whether we should have specific "macro"-style
commands tied to Group 3 procedures, or whether we should have a
more flexible scheme which simply allows any Class 1 functions to be
chained together on a single command line (Microsoft supports the
later, and I'm leaning that way).  Since it is almost always
possible to anticipate the next series of operations to be done, and
since the critical modulation changes are always in a well-defined
sequence, this relatively simple extension will make Class "1.1"
usable in many environments not currently supported (OS/2, Unix,
Windows, across LANs, etc.).  We also hope to make Class 1.1 less
fax-specific, so that if someone decided to use the same modulation
schemes for other applications (e.g., dial-up MHS), you'd be able to
use a Class 1.1 modem for it.3

The next meeting of the committee is the first week of October in
Dallas.

--
Toby Nixon, Principal Engineer      | Voice   [phone]  Telex 401243420
Hayes Microcomputer Products, Inc.  | Fax     [phone]  CIS   70271,404
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