vgetty, rockwell, and incoming data calls: a FAQ?

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Hi!

Gardner Cohen wrote:
> It's been suggested on the mailing list that the originating modem could
> send a '1' DTMF to interrupt the incoming message and get a data carrier,
> but in my experience (vgetty 0.8.0 / 18Mar98; mgetty 1.1.12-Jan27, as well
> as the latest version) all that gets me is the modem's useless data/fax
> discrimination cycle (see screamfest described in the first paragraph).

This is true. In the current implementation any received DTMF number will
result in an attempt to establish a data _or_ fax connection.

> 06/08 11:41:47 yS2    Rockwell: VCON
> 06/08 11:41:47 yS2    vgetty: trying data and fax connection
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> I'd like to have it report "trying data connection" in this case.
> 06/08 11:41:47 yS2   voice command: 'AT#CLS=2' -> 'OK'
> 
> Looking at vgetty/answer.c, I see that if I'd implemented a call_program
> script, I could have it return an exit status to select data, fax, or
> data+fax.

True.

> The file doc/Readme.voice_shell states (when describing the default behavior):
> 
>   If vgetty detects a single number only, it stops playing, then tries to 
>   make a data connection with the remote end, if it doesn't succeed, then 
>   it tries a fax connection with the remote end. 
> 
> which is not the case, which you can verify by looking at event.c.

This formulation is a bit misleading. Thanks for pointing this out. The
truth is the following (which is ment by the above formulation):

You have three possibilities to answer a fax/data call:

1.) send a data carrier, thus dropping fax connections
2.) send a fax carrier, thus dropping data connections
3.) let the modem decide, what it is and establish a connection

Vgetty currently uses #3. The interesting question is, if there are fax
machines or modems, that do _not_ produce a fax calling tone. My personal
experience is, that all fax machines _do_ send a fax calling tone. If this
is true, we could simply change vgettys behaviour to use #1 instead of #3.
Can somebody with a lot of fax traffic comment about this?

Another simple solution would be to map the DTMF number received to the
above list. So Sending a DTMF 1 would result in a data carrier from the
modem and so on. This is also esay to do, but it is still the question, what
to do, if there is only silence on the line. The current implementation
catches theoretically all possibilities, but it relies of course on a
working implementation of the auto detect for data/fax of the modem. It's
the old question: Should we support a broken modem by dropping support for
other cases? I think, I will add a new option to the voice.conf file:
answer_mode_silence with default voice:fax:data. Please keep in mind, that
the order of the entries doesn't have _any_ meaning. That way every user can
make this decision for her/his own system.

> One can enable data-only reception after a single digit DTMF with this patch:

Yes, the change is simply.

> But for my purpose, the data calling tone is the cleaner solution.

Fax and data calling tones are in any case the recommended method.

Bye,
Marc
_______________________________________________________________________________

Email: Marc.Eberhard@Poseidon.ThPhy.Uni-Duesseldorf.DE
WWW:   http://Poseidon.ThPhy.Uni-Duesseldorf.DE/~marc/
PGP:   http://Poseidon.ThPhy.Uni-Duesseldorf.DE/~marc/Marc_PGP.key

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