HylaFAX The world's
most advanced open source fax server
Re: [hylafax-users] Difference in classes
Thanks everyone for their help. It sounds like I should stick with class 1.
I thought maybe the class was causing some of my problems, but it probably
is just the modem. I just bought a Rocketmodem II, so that will hopefully
fix some of my modem woes. Thanks again everyone.
From: Lee Howard [mailto:faxguy@xxxxxxxxxxxxxxxx]
Sent: Monday, November 03, 2003 1:12 PM
To: Matt Yeager
Cc: 'HylaFax Users Mailing List (hylafax-users@xxxxxxxxxxx)'
Subject: Re: [hylafax-users] Difference in classes
On 2003.11.03 07:55 Matt Yeager wrote:
> What's the difference exactly between class 1, class 1.0, class 2,
> class 2.0, and class 2.1 . I've looked around some online, but can't
> find any
> definative comparison.
Class 1 and 1.0 are protocols currently defined by T.31.
T.31 protocols give a low-level interface mechanism between the DTE
(software - HylaFAX) and the DCE (modem). Not all modems' firmware
implement all of the command aspects found in T.31. The basic
difference between Class 1 and Class 1.0 is V.34-fax (SuperG3)
capability. Also there are a small few effectually minor command
enhancements. Actual Class 1.0 protocol varies quite a bit from Class
1 in the DTE implementation (which is why HylaFAX doesn't support Class
Class 2.0 and 2.1 are protocols currently defined by T.32.
Back when the CCITT first began formulating the T.32 standard Rockwell
had a proposal and US Robotics had a proposal. Ultimately USR's
proposal was accepted as the standard and became Class 2.0. However,
Rockwell's proposal had been in production-use with many modems for a
long time already and was called Class 2. Class 2.0 has more commands
than Class 2, but for the most part it is not consequential to basic
faxing. Class 2 will generally lack features such as subaddressing,
extended-resolutions, and ECM... however, that is not always true as
some firmwares have customized commands which try to provide those
features in the Class 2 manner (so as to maintain compatibility with
Class 2-only software). So the effectual differences between Class 2.0
and Class 2 are very vague, sometimes... it just depends on the modem
manufacturer's customization of the firmware. The difference between
Class 2.0 and Class 2.1 is the same as between Class 1 and Class 1.0,
that is, V.34-fax capability.
Class 2/2.0/2.1 provides a high-level interface mechanism between the
DTE and the DCE. This makes it very easy to develop fax software for
the modem, but it therefore relies very heavily on the firmware for
features and proper functionality. Most faxing problems resulting in
+FHNG or +FHS errors will require the fix to come from the modem
manufacturer. Usage of Class 2 generally ensures that the modem will
function identically accross different software.
By comparison, usage of Class 1 ensures that the software will function
identically with various modems. Software that uses Class 1 has a
great deal of control over the actual faxing and it may therefore
implement Class 1 with very few features or it may implement it with a
very many features. A full-featured Class 1-supporting software can
support more faxing features than most Class 2 modems. Faxing problems
in Class 1 are generally the responsibility of the DTE software.
HylaFAX 4.1.7 has about the same feature-set in Class 1 as do most
modems' Class 2 firmware. HylaFAX CVS has a much greater feature-set
in Class 1 than do most modems' Class 2 firmware (ECM and extended
> Which one is the better one to use for faxing?
The one that works best for you. In my case, since I know fax protocol
and since I like the control I get with Class 1, I use Class 1. I
could also argue some technical aspects such as modulation control
where Class 2 will never have the capability that Class 1 can, but I
think that those arguments are irrelevant for most people's faxing
needs. Of course, if you have a problem in Class 2 you should switch
to Class 1 and report the problem to the manufacturer. If you have a
problem in Class 1 you should report the problem here (log) and you
could try Class 2.
As for buying a modem... it's advisable to choose one that supports
both Class 1 and Class 2 that is actively supported by the manufacturer.
____________________ HylaFAX(tm) Users Mailing List _______________________
To subscribe/unsubscribe, click http://lists.hylafax.org/cgi-bin/lsg2.cgi
On UNIX: mail -s unsubscribe hylafax-users-request@xxxxxxxxxxx < /dev/null
*To learn about commercial HylaFAX(tm) support, mail sales@xxxxxxxxxxxx*