From: sgd@tfm.com (Stephen Diercouff)
Newsgroups: comp.dcom.modems,biz.comp.telebit,comp.dcom.fax
Subject: Re: How does WB handle incoming fax vs. data calls?
Date: 9 Jan 93 02:28:34 GMT
Organization: tfm Associates, Ltd.

ewv@craycos.com (Eric Varsanyi) writes:

Please note the cross-posting to biz.comp.telebit and comp.dcom.fax. This is
not intended as a response specifically to Eric, but addresses the
general discussion in both newsgroups.

>In article <1993Jan6.194044.1088@cmkrnl.com> jeh@cmkrnl.com writes:
>>this won't work.  No way is the remote FAX going to know how to log in to my
>>machine. 
> [...]
>>
>>How does Telebit address this???

>Telebit adresses this by vague implications that they may adress it later,
>possibly for another $xxx upgrade fee.

>This is a bug in their new Fax firmware/palware (yes, its a bug,
>V.whatever is a standard for sending AND receiving faxes, if you want
>to use the WB as a modem you can't use it as a fax as well, its one or
>the other).

First, to address your second point -- The modem can be used for data
or facsimile on outgoing calls, it needs to be one or the other for
incoming only. (I'm not saying that this is the best possible behavior).

Second, and this gets a bit long :-(, here are some quotes from the standard:

Asynchronous Facsimile DCE Control Standard -- SP-2388,
Section 8.3.2.4 -- Connection as Data modem

If configured to do so by the +FAA paramater, (8.5.4.1), the DCE may
adaptively answer as a facsimile DCE or as a data DCE. If the DCE answers
as a data DCE, it shall reset the +FCLASS paramater to 0, and issue
appropriate final result codes (e.g. CONNECT, NO CARRIER) to the DTE.

Section 8.5.4.1 --  Answer Paramater, +FAA

Write Syntax:     +FAA=<value>
Valid Values:     0 1
Default Value:    manufacturer's option
Mandatory Value:  0

+FAA=0  constrains the DCE to answer as set by +FCLASS

+FAA=1  indicates the DCE can answer and automatically
		determine whether to answer as a facsimile DCE or
		as a data modem.  If the DCE automatically switches,
		it shall modify FCLASS appropriately.

m:$ tip tbit
connected
 at+fmfr?
 Telebit

 OK
 at+fmdl?
 WorldBlazer - SA - Version LA7.01 

 OK
 at+faa=0
 OK
 ~
 [EOT]
 m:$ 

Looks like it complies with SP-2388 to me. Only at+faa=0 is _mandatory._
It would be nice if adaptive answering were implemented, but in no way
can lack of implementing an optional feature be considered a bug. (Well,
perhaps one could consider it a bug in SP-2388. Telebit have implemented
every mandatory feature in SP-2388, and several optional ones (e.g.
several of the optional T.30 Session Subparameter Codes).

On a somewhat related note, there has been much discussion about Telebit's
lack of supplied facsimile documentation. There is a basic difference
between data and facsimile modes in a modem. If I spend a few minutes
and write a simple program to open a serial port, I can get useful work
done by interactively typing AT commands to the modem. Facsimile transmission
is not an interactive process. At several stages of negotiation between
two fax modems, the session will time out before one can type in the
appropriate command. Therefore, the only way to get useful work done with
a fax modem is to use a dedicated application. Having the command set for
facsimile mode is only useful for application programmers. If an end-user
is shopping for fax applications that run with the Telebit, (s)he needs
only to tell the vendor "The Worldblazer Fax modem complies fully with
all mandatory SP-2388 features."

My copy of SP-2388 is 87 pages long. We have found it necessary to have
copies of CCITT Recommendation T.4 (Standardization of Group 3 Facsimile
Apparatus for Document Transmission) -- 26 pages, and Recommendation T.30
(Procedures for Document Facsimile Transmission in the General Switched
Telephone Network) -- 97 pages, to write and debug facsimile software.

The added expense of printing and providing this additional documentation
for the small fraction of users who would use it would certainly increase
the cost of the upgrade significantly, not to mention Telebits having to
get CCITT permission to reproduce the latter two documents.

The other data/fax modems I have worked with either provide no facsimile
documentation, or only a command summary which requires access to the
full SP-2388 document to understand. To quote a typical example:

RESPONSE	VALUE RANGE		FUNCTION
+FET:		0,1,2			Post page message response.

This is the total documentation of the +FET: result code from one
manufacturer's manual. SP-2388 fully documents this result code,
and the manual refers the reader to SP-2388 for further information.

For those who are interested, the SP-2388 draft standard is available from:

Telecommunication Industry Association
1722 Eye Street N.W., Suite 440
Washington DC 20006.

The Document is titled "Electronics Industries Association and
Telecommunications Industry Association TIA Project, Nember 2388,
Asynchronous Facsimile DCE Control Standard, Service Class 2, TR-29.2
Committee Letter Ballot".

I have not seen the electronic document available from Supra. If this is,
indeed a copy of SP-2388, perhaps someone will make it available for
anonymous ftp, and let us know where it can be had.

--Stephen
-- 
Stephen Diercouff, tfm Associates, Ltd., Bellingham WA  voice: +1 206 733 5721
Internet:  sgd@tfm.com                                    fax: +1 206 738 0630
UUCP    :  uunet!nwnexus!mtbaker!sgd
Snail   :  P.O. Box 5084/Bellingham WA 98227-5084