[Linux-ham] FSK over VoIP

[Alessandro Carminati]

Hello,
I'm working over the idea of an IP tunnel over a voip call.
This because I have the need to reach isolated Asterisk IP PBX,  that for
various reasons do not have any IP connectivity to the internet.
I thought I may use an FSK modulation over the VoIP call to reach the PBX.

My thoughts are oriented in using Amateur Radio "soundmodem" connected to
the alsa aloop and the Asterisk chan_alsa.

|<------------------------------------------------------- IP Tunnel
----------------------------------------------------------->|
|
|
[soundmodem] <----> [alsa loopback] <----> [asterisk] <--VoIP RTP stream-->
[asterisk] <----> [alsa loopback] <----> [soundmodem]



Idea seemed work at the beginning, but at last I got stuck to the fact that
soundmodem seems do not receive any signal, and therefore produces no
packets, and it's not clear to me if this is happening because it does not
receive the audio, or because the audio is not good enough to let it find
any bit inside it.
I wonder if anyone of you can indicate me a way to debug the soundmodem
received audio, if there's any, to see if my problem is have no audio, or
worse the audio received is too bad to make any connection.

here's my confs
[soundmodem.conf]
<?xml   version="1.0"?>
<modem>
<configuration name="AX25">
<chaccess txdelay="250" slottime="100" ppersist="40" fulldup="1"
txtail="100"/>
<audio type="alsa" device="plughw:Loopback,0,0" halfdup="0"
capturechannelmode="Mono"/>
<ptt file="none" hamlib_model="" hamlib_params="" gpio="0"/>
<channel name="sm0">
<mod mode="afsk" bps="1200" f0="1200" f1="2200" diffenc="1" inlv="8"
fec="1" tunelen="32" synclen="32"/>
<demod mode="afsk" bps="1200" f0="1200" f1="2200" diffdec="1" inlv="8"
fec="3" mintune="16" minsync="16"/>
<pkt mode="MKISS" ifname="sm0" hwaddr="HQH1" ip="23.0.0.1"
netmask="255.255.255.0" broadcast="23.0.0.255" file="/dev/soundmodem0"
unlink="1"/>
</channel>
</configuration>
</modem>

[axports]
sm0     HQH1            1200    255     2       prova

Consider my newbe status in the hamradio world, so please do not assume in
that field I know what I'm doing.

any help would be really appreciated.
Regards.
Alessandro
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