Linux Fax Stack Setup (HylaFax & SIP)

• This guide is WIP
• Ubuntu 20.04 LTS VM (VirtualBox, LXC?)
• TODO: Test on Debian / RockPi / RaspberryPi
• TODO: Test on Eventphone Infra

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Setup t38modem

• TODO: Package t38modem with service files and config

Opal

• http://wiki.opalvoip.org/index.php?n=Main.HomePage
• Don't use libavformat-dev -> Compile error in Opal
• https://sourceforge.net/projects/opalvoip/files/
• Version 3.18.6
• TODO: Test out other versions
• .tar.bz2 files for *nix

Build PTLib

• Version 2.18.6

• Dependency of Opal, bundled with Opal source code (SourceForge)

• http://wiki.opalvoip.org/index.php?n=Main.BuildingPTLibUnix

• Wiki outdated:

  • libssl1.0-dev -> libssl-dev

• TODO: Remove dependencies, most of them are optional

sudo apt install \
	g++ git make autoconf libpcap-dev libexpat-dev libssl-dev libsasl2-dev libldap-dev \
	unixodbc-dev liblua5.3-dev libv8-dev libncurses-dev libsdl2-dev \
	libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev

• PTLib will be installed in the /usr/local tree -> set PKG_CONFIG_PATH to be findable (compile time)
• Set LD_LIBRARY_PATH to find PTLib at compile and run time
• Set PTLIBPLUGINDIR (compile and run time)
• (To compile as static library: ./configure --disable-shared)

export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig # compile time
export LD_LIBRARY_PATH=/usr/local/lib # compile and run time
export PTLIBPLUGINDIR=/usr/local/lib/ptlib-x.y.z # compile and run time
 
cd ptlib-x.y.z/
./configure
make
sudo make install

Build Opal

• Version 3.18.6
• http://wiki.opalvoip.org/index.php?n=Main.BuildingOpalUnix
• Wiki outdated:
  • libsrtp-dev -> libsrtp2-dev
  • Dont use capiutils, we are not using ISDN capable cards
  • Dont use libavcodec-dev -> Compile error
• TODO: Remove dependencies, most of them are optional

sudo apt install \
	lisrtp2-dev libgsm1-dev libspeex-dev libopus-dev libx264-dev \
	libvpx-dev libtheora-dev libspandsp-dev dahdi

• (To compile as static library: ./configure --disable-shared)

export PKG_CONFIG_PATH=/usr/local/lib/pkgconfig # compile time
export LD_LIBRARY_PATH=/usr/local/lib # compile and run time
export PTLIBPLUGINDIR=/usr/local/lib/ptlib-x.y.z:/usr/local/lib/opal-a.b.c # compile and run time

cd opal-a.b.c/
./configure
make
sudo make install

t38modem

• https://github.com/hehol/t38modem, Version 4.6.2
  • Could also use https://github.com/T38Modem/t38modem, not as maintained
• If you are getting error about -1 not being able to be casted to a long unsigned int due to -Wnarrowing inside dle.cxx, you can add -Wno-narrowing to the CPPFLAGS in the Makefile to disable this error

cd t38modem-x.y.z/
make
sudo cp ./t38modem /usr/local/bin

• t38modem can only find Opal if LD_LIBRARY_PATH and PTLIBPLUGINDIR are environment variables to the program

Init script

• To automatically start t38modem, you need to create Systemd services, as well as start and stop scripts
• init.d script is adapted from https://web.archive.org/web/20111231021042/https://www.foriamroot.org/hylafax-6-0-debian-or-ubuntu-t38modem-1-0-asterisk-1-6/

#!/bin/bash
# /etc/init.d/t38modem

export LD_LIBRARY_PATH=/usr/local/lib
export PTLIBPLUGINDIR=/usr/local/lib/ptlib-x.y.z:/usr/local/lib/opal-x.y.z # Adjust lib versions!

case "$1" in
	start)
		. /etc/t38modem/config
		# defines
		# - T38MODEM_SIP_USERNAME
		# - T38MODEM_SIP_PASSWORD
		# - T38MODEM_SIP_SERVER

		COMMAND="t38modem -u 'T38modem' --ptty +/dev/ttyT38-1 --sip-proxy '${T38MODEM_SIP_USERNAME}:${T38MODEM_SIP_PASSWORD}@${T38MODEM_SIP_SERVER}' --sip-register '${T38MODEM_SIP_USERNAME}@${T38MODEM_SIP_SERVER},${T38MODEM_SIP_PASSWORD}' --sip-listen udp\$:5060 --route 't38:.*=sip:<dn>@${T38MODEM_SIP_SERVER}' --route 'sip:.*=t38:<dn>'"
		exec $COMMAND > /dev/null 2>&1 &
		PID=$!
		echo "Starting t38modem with pid $PID (pidfile /run/t38modem.pid)"
		echo $PID > /run/t38modem.pid
	;;
	stop)
		if [ ! -f "/run/t38modem.pid" ]; then
			echo "t38modem is not running! (/run/t38modem.pid does not exist)"
			exit 1
		fi

		echo -n "Stopping t38modem pid: "
		PID=`cat /run/t38modem.pid`
		kill -9 $PID
		rm /run/t38modem.pid
		echo "${PID} Done"
	;;
	*)
		echo "Usage: $0 {start|stop}"
		exit 1
	;;
esac

exit 0

sudo chmod +x /etc/init.d/t38modem

• -t enables debugging
  • More t's is deeper debugging (e.g. -tttt)
• You can of course run the t38modem command without this init script
• If t38modem says it was able to create the virtual modem but /dev/ttyT38-1 is not available, you do not have sufficient permissions
• Configuration is specified in /etc/t38modem/config

# /etc/t38modem/config
T38MODEM_SIP_USERNAME="USERNAME"
T38MODEM_SIP_PASSWORD="PASSWORD"
T38MODEM_SIP_SERVER="voip.example.com"

• Give only root access to the config

sudo chown root:root /etc/t38modem
sudo chmod 700 /etc/t38modem

• You can now communicate with your modem /dev/ttyT38-1 , just as if it was a real Hayes compatible modem (https://www.computerhope.com/atcom.htm)
• Test using minicom, configure it to point to our modem. Each command is initiated by a Return
  • Dial a number:
    • Get the attention of the modem: at -> OK
    • Dial: atd0123456789
    • If all works correctly you should be able to answer the phone and hear a single beep
  • Answer a call:
    • Get the attention of the modem: at -> OK
    • Call the number of your modem
    • -> RING
    • Answer the call: ata -> CONNECT
    • You should now hear your modem "talking" to you
• Pitfalls:
  • If you are already connected to your SIP server it may not give proper response codes. My provider returns 500 Internal Server Error
  • Test the command before running the init script!

systemd service

# /etc/systemd/system/t38modem.service
[Unit]
Description=t38modem
After=network.target

[Service]
Type=simple
ExecStart=/etc/init.d/t38modem start
ExecStop=/etc/init.d/t38modem stop
PIDFile=/run/t38modem.pid
KillMode=none

[Install]
WantedBy=multi-user.target

• Enable the service:

sudo systemctl daemon-reload
sudo systemctl enable t38modem.service
sudo systemctl start t38modem.service

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HylaFax

• TODO