osmo-isdntap is a small stand-alone [daemon] program that you can run to create recordings of ISDN calls.
It is part of the retronetworking project.
The program works by passively decoding the ISDN D-channel, specifically the Q.931 call control protocol. Whenever a call is being set up, it starts to capture the B-channel
timeslot allocated to that call. It creates two files, one for each of the two directions of the call. The files contain the raw transparent binary B-channel data.
Currently the only supported ISDN hardware/driver interface is DAHDI.
Currently, only PRI (primary rate) ISDN interfaces are supported.
You can clone from the official osmo-isdntap.git repository using
git clone https://gitea.osmocom.org/retronetworking/osmo-isdntap
There is a web interface at <https://gitea.osmocom.org/retronetworking/osmo-isdntap>
Converting recordings to audio¶
If you'd like to convert any of the recorded files to audio, you can use the following example
command to do so:
sox --channels 1 --type raw --rate 8000 -e a-law isdntap-03012342111-03012343038-20221016-212558-8-tx.raw output.wav
The generated `output.wav` file can then be played back with any standard audio player.