[Asterisk-Users] Modem and Fax over VoIP

[Steven Critchfield]

On Mon, 2003-10-06 at 13:55, Eduardo Goncalves wrote:
> On Mon, 06 Oct 2003 13:43:21 -0500
> Steven Critchfield <critch at basesys.com> wrote:
> 
> > On Mon, 2003-10-06 at 10:12, Eduardo Goncalves wrote:
> > > Hello,
> > > 
> > > 	I have the fowling scenario:
> > > 
> > > fxs[asterisk1]-----iax-----[asterisk2]e1----e&m---PSTN
> 
> > 
> > If asterisk2 is your only access to the PSTN, then it doesn't make a lot
> > of sense to do fax over VoIP. Put a couple of modems on asterisk2 with
> > matching FXS ports and learn to use Hylafax. 
> 
> 	I can't. Because asterisk1 is at a remote site. And the only access
> to PSTN at this remote site is trough asterisk2.

unless you are using standalone fax units for the scanning, then you
should be able to. The scenario I laid out above was for specifically
this case. Drop a cheap flatbed scanner in to capture the image, then
send it to hylafax at asterisk2 location to hop a local modem to a FXS
port and off to the net. You can then receive incoming faxes via email
or similar and then choose what to print. 

> > performance out of the faxing and potentially lower bills. Also it is
> > more flexible. Not to mention that the bandwidth over VoIP to make data
> > quality calls is around 80k of VoIP to get flakey 9.6k. Do you need to
> > waste 10x bandwidth for sub par functionality?  
> 
> 	Is it possible to config asterisk1 to change to g.711 only when a fax
> transmission is detected?

If it is on a specific non shared port, then you can set it up in a
context that uses a different username and password to connect, and in
that definition disallow all and allow ulaw. Just know that this method
is spotty, and may not work because of problems in the fax protocol and
timing needs. search archive for very good explanations of this problem.
-- 
Steven Critchfield  <critch at basesys.com>