We don't really know if the HR encoding is compatible with other
equipment, but it _should_ follow Chapter 5.2 of ETSI TS 101 318.
Please note that RFC5993 also specifies a way to encode GSM-HR into RTP,
we do not try to be compatible with that. The only difference seems to
be one additional TOC octet at the beginning of the payload field.
Using osmo-bts-sysmo and this code, it is now possible to do FR and AMR
based voice calls on TCH/F.
A lot of CPU is wasted in the conversion between the RTP formats and the
L1 specific formats for the codec frames. All data needs to be shifted
by four bits, and the order of bits needs to be reversed in every byte.
This only implements creating, binding, connecting and free'ing RTP
sockets, not yet anything regarding receiving or transmitting codec
frames on them.
You will need the rtp branch of libosmocore for libosmotrau
This is not full encrpytion support, the bts-model part still
needs to detect the ENCR CMD when de-queueing from LAPDm and enable
the de-ciphering, detect the arrival of the first encrypted frame,
etc, enable en-ciphering, ...