TRX means transreceiver which is used to call processing , one TRX supports 8 channels each of 25 Khz(200 KHZ career is devided in to 8 timeslots).
BCCH provides broadcast information,
actually ACCESS GRANT CHANNEL IS USED TO KNOW WEITHER THE TRX CHANNELS/TIMESLOTS ARE FREE OR NOT
AFTER THAT IT WILL SEND AN ACK THEN THE CALL WILL BE PROCEESED
THNXS