From: tnixon@hayes.com
Newsgroups: comp.dcom.modems
Subject: Re: ?'s about Class 1 & Class 2 fax
Date: 27 Aug 92 10:34:49 EDT
Organization: Hayes Microcomputer Products, Norcross, GA

In article <1992Aug25.055903.460@sdf.lonestar.org>,
mo@sdf.lonestar.org (Mohit Goyal) writes: 

> Hello.  I have a couple of questions about Class 1 and Class 2 fax.
> 
> What exactly are they?

They are both extensions to the AT command set which allow software 
to control modems with fax features.  The difference between them in 
how much of the fax protocols are built into the modem as opposed to 
having to be implemented in the software.  Class 1 provides the 
minimum level of hardware support, and virtually all of the fax 
protocols are implemented in the software, which Class 2 moves most 
of the T.30 procedure handling into the modem (but the T.4 image 
handling remains in the software).

> Is it true Class 2 is not finalized and the current Class 2 modems use
> a Aug, 1991 spec. that is very different from the current spec?

You're right that Class 2 is not yet finalized.  TIA TR-29 just a 
couple of weeks ago agreed to send it out for a final, 30-day letter 
ballot, after which it will be either adopted as TIA-592 or (I
predict) abandoned if it doesn't pass.  The modems on the market
today claiming to be "Class 2" implement SP-2388, the first balloted 
version of the standard from August of _1990_; it is indeed quite 
different in details from the current spec, although in principle 
(i.e., the division of responsibilities) it is similar.  For 
example, the names of virtually all of the commands and parameters 
are different, and there are a number of new parameters in the 
latest spec; there are also some pretty significant procedural 
changes.

> If so, when will Class 2 be finalized by the CCITT?

The work is being done in technical subcommittee TR-29.2 of the 
Telecommunications Industry Association (TIA) in the USA, not in the 
CCITT.  TR-29 has contributed a fairly recent version of the spec to 
CCITT Study Group VIII for information, and SG VIII has placed 
consideration of it on their program of work for the 1993-1996 study 
period.  I suspect that if TIA-592 is adopted in the USA, the final 
document will be forwarded to CCITT forthwith, and that it won't 
take too long to have an international version of the standard.

> Can a modem and/or software support both Class 1 & 2?

Yes, both modems and software can support both, although only one is 
used at a time.

> Does the software have to support the same Class as the modem in 
> order to fax?

Yes.  They must either both be Class 1 or both be Class 2.

> Can a modem be upgraded from Class 1 to Class 2 just by changing the
> ROM? (I'm specifically interested in the Hayes Optima v32bis faxmodem)

Generally, yes, although whether or not a particular manufacturer 
offers such an upgrade is up to them.  I believe Hayes intends to do 
so, since we at one time announced our intentions to support Class 2 
after it is adopted, but no specifics have been mentioned with 
regard to the cost or method of upgrading or the products for which 
it will be available.  

-- 
Toby Nixon, Principal Engineer      | Voice   +1-404-840-9200  Telex 401243420
Hayes Microcomputer Products, Inc.  | Fax     +1-404-447-0178  CIS   70271,404
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