Cellular Network Infrastructure » Radio Access Network » OsmoPCU

When a MS has active TBF, any CS paging is delivered via the PCU interface from the BTS to the PCU, and the PCU is sending it on the PACCH to the MS.

This appears to be working fine if the paging is by TMSI. Hoewver, if the paging is by IMSI, the paging is failing.

One of the sysmocom customers has reported that there's an encoding error in this case.

I have received this somewhat garbled diff:

if ((identity[0] & 0x07) == 4) {
bitvec_write_field(dest, &wp,0x0,1);  // TMSI
identity++;
len--;
} else {
-- bitvec_write_field(dest, &wp,0x0,1);  // MI
++ bitvec_write_field(dest, &wp,*0x1*,1);  // MI
bitvec_write_field(dest, &wp,len,4);  // MI len
}
while (len) {
bitvec_write_field(dest, &wp,*identity++,8);  // MI data
len--;
}
bitvec_write_field(dest, &wp,chan_needed,2);  // CHANNEL_NEEDED
bitvec_write_field(dest, &wp,0x0,1);  // No eMLPP_PRIORITY

return wp;
}

Please investigate this referring to the spec (3GPP TS 44.060 Section 11.2.10). If possible, write an unit test (osmo-trx/tests directory) that covers both IMSI and TMSI scenario, as well as a fix for the apparently broken IMSI case.