The BSC/MS will send a Hello packet that includes the version number,
make LCR verify this version number and close the socket in case it
does not match a supported version.
Because EFR/AMR/HR codecs use dynamic RTP payload types, it is essential
to forward the actual media types between endpoints too. These media
types are used for negotiation of codecs. A dynamic payload type is
used as given by remote peer. Locally generated payload types are used
when offering codecs to remote peer.
In this case the frame is dropped, but audio of the last frame is repeated
with a reduced level. The level is reduced again an again until a new
valid frame is received. This way there is no silent gap in the audio
stream.
The dependency on mISDN (loopback interface) is completely removed
from GSM and SIP interfaces.
The built in bridge of LCR now forwards audio data between these
interface instances or between these instances and other instances.
Additionally both GSM BS and SIP support direct forwarding of RTP
traffic between other SIP endpoint and OpenBSC, so no traffic is
forwarded by the LCR itself. This is done by forwarding RTP peer
informations between these interface instances.
There is no linking of any osmocomBB source code required. In order
to use osmocomBB or OpenBSC, just enable the interface, as described
in defaults/interface.conf. At osmocomBB/mobile or at OpenBSC, just
use the option "-m" to enable the socket interface.
Enable GSM at LCR with "./configure --with-gsm-ms --with-gsm-bs".
Andreas Eversberg