Hi JD, I’ll try to answer all your questions.
1. The priorities during TCH assignment are vendor specific and as I don’t have Ericsson experience I am not sure about your case. There are some features in assignment priorities to have some more loaded and less loaded frequencies or your BSS may use pseudo-random assignment sequence. Refer to your vendor’s documentation for this.
2. The BCCH is ALWAYS located on timeslot 0 on the TRX which carries the BCCH frequency (not mandatory to be TRX 1).
3. As SDCCH has very important role during call setup and all assignment procedures, it should use the most clean of interferences frequency as is a frequency from the BCCH set. Normaly the timeslots are 1, 2, etc. in case of combined BCCH/CCCH. In case of bigger cells you can spread SDCCHs of the other TRXs, using timeslots 0, 1, etc.
4. When you are using base-band hopping and the assigned timeslot is different than 0 then normaly you are hopping over all available frequencies. In case of timeslot 0 – the hopping list is all the frequencies except the BCCH freq. BCCH does not hop!
5. In case of BCCH TRX failure, depending on the vendor’s software release there is a possibility for the cell to continue operation in degraded mode. After detection of such failure the structure of the BCCH frequency is transfered to the second TRX and all the calls in this cell are released. Normaly this procedure takes from 30 sec. up to 2 min. (depending on the vendor and the load of the BSC)
I hope that this answers all your questions.