GFSK modulation uses a bit rate of 1152 kbit/s, with a frame of 10 ms (11520 bits) which contains 24 time slots. Each slots contains 480 bits, some of which are reserved for physical packets and the rest is guard space. Slots 0–11 are always used for downlink (FP to PP) and slots 12–23 are used for uplink (PP to FP).