2.2 KiB


Software modem with sound
For burble's retro voip modem https://burble.dn42/retro/modem/
Now also for JerryXiao's own software voip modems!

Fortunately this old proprietary software modem still works :)


  • A desktop GNU/Linux distribution, livecd is also OK
  • See the original README
  • Modem without any sound isn't a real modem? No problem, pulseaudio is used to output modem sound in realtime. You must have pulseaudio dev package installed on your system to compile this software.

Step-by-step instruction

Execute these commands as a normal user:

./slmodemd/slmodemd -e ./d-modem
screen /tmp/ttySL0 115200

Inside the serial console, use the following at commands:

> OK
> OK
> CONNECT 1200

You can also connect to:

number AT+MS ATD Modulation
(42403618)361800 AT+MS=90,1 ATD361800@pbx.jerry.dn42 V.90
(42403618)361801 AT+MS=34,1 ATD361801@pbx.jerry.dn42 V.34
(42403618)361802 AT+MS=32,1 ATD361802@pbx.jerry.dn42 V.32
(42403618)361803 AT+MS=22,1 ATD361803@pbx.jerry.dn42 V.22
(42403618)361804 AT+MS=22,1 ATD361804@pbx.jerry.dn42 V.22
(42403618)361805 AT+MS=23,1 ATD361805@pbx.jerry.dn42 V.23
(42403618)361806 AT+MS=23,1 ATD361806@pbx.jerry.dn42 V.23

Now you should be connected. If you see a login prompt, go to https://burble.dn42/retro/modem/ for login username and password. Once logged in, close out of GUN Screen and execute pppd like this:

sudo pppd $(readlink /tmp/ttySL0) 1200 user dn42 noauth nodefaultroute nodetach

nodefaultroute is used here to keep your voip alive :)


If you would like a full dialup dn42 experience, try using netns:

sudo ip netns add modem
sudo ip netns exec modem pppd $(readlink /tmp/ttySL0) 1200 noauth nodefaultroute nodetach

Start a new terminal and

sudo ip netns exec modem $SHELL
unshare -m
echo > /tmp/resolv.conf
mount --bind /tmp/resolv.conf /etc/resolv.conf
ping burble.dn42

Have fun!


This code can also work as a server, no docs available though ;)
Just type ATA in the modem console and try it out first.