This page assumes that you've already downloaded and compiled Asterisk
and Zaptel. If you've been linked to this page from a walkthrough
installation page, you already have! Here we're downloading and
installing the spandsp rxfax and txfax applications, along with the Newman Telecom's 'nvfaxdetect' applcation.

Download the required files:
Note: Due to long URL's on this page, be careful when copying and pasting - everything in bold is one command.

root@dhcp1 ~# cd /usr/src

root@dhcp1 src# wget http://www.soft-switch.org/downloads/spandsp/old/spandsp-0.0.2pre26.tar.gz

root@dhcp1 src# tar zxf spandsp-0.0.2pre26.tar.gz

root@dhcp1 src# cd spandsp-0.0.2

root@dhcp1 spandsp-0.0.2# ./configure --prefix=/usr && make && make install

That installs 'spandsp', a very powerful DSP package that can, as
one of it's many things, emulate a Fax machine. If you're interested in
what else spandsp can you, you can read the technical documentation here.

Download and install the txfax and rxfax applications

root@dhcp1 src# cd /usr/src/asterisk/apps

root@dhcp1 apps# wget http://www.soft-switch.org/downloads/spandsp/spandsp-0.0.2pre26/asterisk-1.2.x/app_rxfax.c

root@dhcp1 apps# wget http://www.soft-switch.org/downloads/spandsp/spandsp-0.0.2pre26/asterisk-1.2.x/app_txfax.c

root@dhcp1 apps# wget http://www.newmantelecom.com/download/asterisk/faxdetect/1.0.6/app_nv_faxdetect.c

root@dhcp1 apps# wget http://aussievoip.com/makefile.patch

root@dhcp1 apps# patch < apps_makefile.patch

root@dhcp1 apps# cd ..

root@dhcp1 asterisk# make upgrade

That will build and install the three new modules, app_rxfax,
app_txfax and app_nv_faxdetect. You will need to restart asterisk to
load these modules:

root@dhcp1 apps# asterisk -rx 'restart when convenient'