[asterisk-users] T38modem in loopback mode does not work on asterisk 1.4.20.1

[David Backeberg]

On Tue, Apr 14, 2009 at 10:46 AM, Lee Howard <faxguy at howardsilvan.com> wrote:
> David Backeberg wrote:
>> It may be possible to use hylafax, but
>> I don't know how or why you would.
>
> The reason *why* is generally due to support issues.

What I was specifically getting at in the context of that response was
a comparison of dynamic modem pool versus fixed-size modem pool. When
faced with the choice between a fixed-size modem pool or one that
would grow or shrink dynamically with demand, I think the dynamic is a
better choice. That is my opinion, based on my particular style of
usage, and I am certainly grateful for the existence of Hylafax.

The other thing I was getting at was complexity of a multi-layer
software stack in loopback mode when it comes to trying to figure out
where the problem could be. One of my suggestions was to separate the
sender and receiver to separate machines, and my other suggestion was
to reduce the layers of software involved. As you know from having
written Hylafax, it's designed for hardware modems and does things
like letting you take your fax device online/offline, as well as
taking it down for five seconds post-fax to do a reset on the line.
These things are all documented, they all have debugging tools, and
ways to view modem state. But for a beginning person trying to set up
a fax for the first time I feel like it adds complexity to what can
already be a complex task. Thus I suggested trying without.

As I've been debugging faxes it seems more and more like fax failures
are due to poorly-thought-through enterprise voip implementations, or
intermittent line noise, or poor implementations of fax protocols in
proprietary fax machine hardware. I think the Hylafax versus app_fax
thing is really six of one versus a half-dozen of the other, but both
are useful data points in debugging a failing fax configuration.