[comp.dcom.fax] Why FAX send-only?

logajan@ns.network.com (John Logajan) (01/28/91)

Forgive me if this has been discussed before, but what is the reason
behind these computer FAX modems / software that are advertized as
send-only.  What is the technical difficulty in producing send/receive?

The more technical your answer, the better. :-)

Thanks.

-- 
- John Logajan @ Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428
- logajan@ns.network.com, 612-424-4888, Fax 612-424-2853

vaisanen@joyds2.joensuu.fi (Jarmo Vaisanen) (01/28/91)

> The more technical your answer, the better. :-)

This is not going to be technical at all...

I have got the impression that the reason for this is that FAX-standards
don't specify any way to address the recipient (person specific) other than
FAX-number (site specific).  Future Group 4 (?) standard should bring more
advanced addressing methods for us.  (When is this going to happen?)

Jarmo Vaisanen

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wallach@motcid.UUCP (Cliff H. Wallach) (01/29/91)

In article <1991Jan27.195313.25909@ns.network.com> logajan@ns.network.com (John Logajan) writes:
-
-Forgive me if this has been discussed before, but what is the reason
-behind these computer FAX modems / software that are advertized as
-send-only.  What is the technical difficulty in producing send/receive?
-
-The more technical your answer, the better. :-)
-
-Thanks.


It is much easier to build a transmit only fax modem.  Modulating the
the signal can be done with an 8-bit controller, while a DSP chip is
needed to demodulate.  I believe that Sierra sells a V22.bis + sendfax
chipset.


Cliff Wallach				...uunet!motcid!wallach

oeschi@netmbx.UUCP (Johann Deutinger) (01/30/91)

In article <1991Jan28.141246.700@ujocs.joensuu.fi> vaisanen@joyds2.joensuu.fi (Jarmo Vaisanen) writes:
>> The more technical your answer, the better. :-)
>This is not going to be technical at all...
>I have got the impression that the reason for this is that FAX-standards
>don't specify any way to address the recipient (person specific) other than
>FAX-number (site specific).  Future Group 4 (?) standard should bring more
>advanced addressing methods for us.  (When is this going to happen?)

The reason to have many modems with fax send-only is that there are some
quite cheap modem chips (mainly from Sierra) that implement sending
faxes at 4800 bps (V27ter) only. Receiving faxes at high speed is
much more difficult than sending them. This makes the price difference.

Don't expect too much from Group 4. Sub-addressing is not included there
(but may be easily; it could also be included in Group 3 from the technical
point of view. The problem here is that there are too many fax machines
already installed that could not learn new protocol features)


-- 
oeschi@netmbx.UUCP     | Johann Deutinger
voice +49 30 396 50 21 | Ferrari electronic GmbH (.. no, we don't sell cars)
fax   +49 30 396 80 20 | Beusselstr. 27  -  1000 Berlin 21  -  FRG

logajan@ns.network.com (John Logajan) (01/30/91)

oeschi@netmbx.UUCP (Johann Deutinger) writes:
>The reason to have many modems with fax send-only is that there are some
>quite cheap modem chips (mainly from Sierra) that implement sending
>faxes at 4800 bps (V27ter) only. Receiving faxes at high speed is
>much more difficult than sending them. This makes the price difference.

Thanks to the many people who have confirmed this.  The latest issue of
Byte magazine also discusses the different aspects of FAX and concurs
that the send-only FAXes do indeed get by by using available cheaper
parts for the send circuit, for which no comparable cheap components
exist for the receive circuit.

The upshot of all of this is that you can't (in my opinion) buy a send-only
FAX in the hope that some software upgrade in the future will make it
a send/receive FAX.  It would require a hardware replacement.

-- 
- John Logajan @ Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428
- logajan@ns.network.com, 612-424-4888, Fax 612-424-2853