In the super channel mode, it seems the BTS transmits one byte in each
timeslot, accross the entire link.
This basically means that if you have a 10 byte long signalling message
to be sent, its first byte will be in TS1 up until the tenth byte in
TS10.
As we are reading in 160 byte chunks from the E1 timeslots, we build a
matrix with 160 columns (for each byte) and 24/30 rows (timeslots). So
we write 24 times 160 bytes into the matrix.
Once we have completed all timeslots, we start to read the matrix by
reading byte 0 of each timeslot (in incrementing TS order), next byte 1
of each timeslot, ... until we end up having read 160 times 24 bytes
from the matrix.
The resulting bitstream needs to be HDLC-synchronized and the resulting
messages passed up for further decoding.
The SIGN mode implies that LAPD instances are bound to the timeslots, which is
of course not what we want in a pure capturing/recording scenario.
Instead, use the new E1INP_TS_TYPE_HDLC mode, which allows us to capture
any HDLC framed messages on E1/T1 timeslots, whether LAPD or e.g. MTP.
Harald Welte