OpenBSC + LCR + Asterisk = half sided calls in one

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Sipos Csaba dchardware at gmail.com
Mon Oct 28 19:57:35 UTC 2013


Hey Peter,

> I'd suggest to make LCR use SIP for communcation with Asterisk. See
> http://stuge.se/lcr.txt for a minimal example of LCR configuration.

Do you have some more example configuration files for the Asterisk end
of the SIP trunk?

> Since you're using bridging you might also want to try rtp-bridge
> between GSM and SIP, which could allow GSM phones and SIP phones to
> negotiate codec directly, avoiding any transcoding. (But maybe it
> only works with Abis over IP and not over ISDN? I'm not sure.)

I am almost sure that RTP bridge can only be used with IP based BTSes
which I don't have. My units are connecting via E1 dahdi.

> You can of course continue to debug the LCR-Asterisk module but I
> would suggest moving to SIP since I think working with SIP on both
> legs makes debugging a bit easier.

My problem is that I made test calls an analyzed the logs at both LCR
and Asterisk end, and there is no difference between a good and a half
sided call. First, I forced the GSM phones to use TCH/F FR only, then
I forced LCR and Asterisk SIP clients to use Alaw only (SIP clients
are not supporting any GSM codec). Transcoding obviously happens
between TCH/F FR and Alaw, but how on earth is possible that the
direction of the call can affect that this transcoding is going to
be a success or not? If its a transcoding failure it shouldn't work in
any direction. If its a call routing problem, then the call shouldn't
make its way to the called party. But none of this is what happens.

So I really don't know where to look, or how to debug this problem.

BR,
Csaba





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