[hylafax-devel] Re: My RH6.2 RPM hack & Q: Failure to train at2400 bps or +FMINSP value

[Robert Hardy <rhardy@webcon.net>]

With all this said (thanks for the explanation), the next obvious question
is why is there only 1 "recommended" class 1 fax modem (Digicom Scout+
well... + AT&T Dataport 14.4 too). Since we should only need to "get it
right" once in Hylafax, it sounds like almost any class 1 should work. After
that it should simply be a matter of blacklisting modems (or handling the
exceptions caused by them) which haven't been implemented properly.

I think I probably read the section below and assumed class 1 was bad news
and went on to trying to get class 2 support working. Perhaps much of this
thread/email should be put in the FAQ?

http://www.hylafax.org/class1.html

That CAVEAT EMPTOR certainly made me think I was going to have problem
with class 1.

Regards,
Rob

--
----------------"Linux the choice of a GNU Generation!"-----------------
Robert Hardy                                          C.E.O. Webcon Inc.
rhardy@webcon.net      PGP Key available by finger        (613) 276-6206


On Fri, 19 May 2000, Harald Pollack wrote:
> On Thu, 18 May 2000 15:35:55 -0400 (EDT), Robert Hardy wrote:
> >Will attempting class 1 w/ the same modem in this case make any difference?
> 
> If your fax software is well implemented, than of course. An 'well
> implemented' means, that programmer of faxsoftware KNOWs meaning of each
> single bit in a DIS/DCS frame ... but can be read in ITU-T.30 :-)
> 
> >You will excuse my ignorance on this topic. I have never found a good
> >explanation of class 1 vs. class 2/2.0
> 
> The difference is ONLY the protocol (the language level) between the fax
> program itself and the modem.
> 
> Timing consideration are of less importance, because the are in the
> magnitude of several seconds (in contrary to class 2/2.0, where often some
> milliseconds decide for death or alive :-)
> 
> All the timing assumption which are related to fax are under control of
> faxprogram in class 1. In class 2/2.0, the programmer of the fax firmware
> has done all timing and the faxprogram in class 2 does not realy know,
> which timings are meaningfull (can only guess and fail :-)
> 
> Class 2/2.0 makes a kind of mystery of fax. class 1 is clear and straight
> forward and has the advantage, that faxprogram 'knows' really ALL
> neccessary parameters of a fax connection and can handle each misbehaviour
> in the right way (in class 2/2.0, you can only hope or pray, that
> developer has done its homework well).
> 
> CLass 1 faxsoftware with open source is like to have sourcecode of modem
> firmware :-)
>
> >They are ok if your computer isn't doing alot of other things while you
> >are using it
> 
> keep in mind, that real fax machine have Z80 (or 8085) type CPU with some
> (4 - 10) MHz ...
> 
> It is in practice possible to have a slow 386 based PC (eg IBM PS/2 model
> 56) where class 1 fax is possible with 2 faxmodems (one sends, the other
> receives) and incoming fax is shown in REALTIME on (graphic) screen!
> 
> >or if you have a real time operating system which can guarantee enough
> >time to the modem
> 
> There is really NO DIFFERENCE, if you use class 1 or class 2/2.0, because
> you deliver the SAME faxdata over the SAME serial line interface.
> Difference is only in HOW you are 'speaking' to your modem (and HOW the
> modems responses) BETWEEN the single pages, and in this state, timing is
> (in class 1) no real problem, because the T.30 protocol is sooo tolerant
> (but NOT your modem, if you 'speak' in class 2/2.0).
> 
> Worst case in class 1 (which is also true for two fax machines) between
> two pages is in the dimension of 15 to 20 seconds! Try such large times in
> class 2/2.0 (you will never deliver one single page :-)



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