The IEEE 802.15.4 PHY layer specifies three bands and 27 channels. The 2.4GHz frequency offers 16 channels and functions at a data rate of 250 Kbps. The 868.3MHz frequency offers 1 channel and a data rate of 20 Kbps. The 902-928MHz frequencies provide for 10 channels and a data rate of 49 Kbps. The 2.4GHz frequency is unlicensed worldwide, opening up this frequency to engineers globally. The specification includes O-QPSK modulation, a DSSS (direct sequence spread spectrum) energy spreading scheme, -85dBm sensitivity at 1% PER, 0 dBm output power, and a minimum range of 30 meters indoors or 100 meters line of site. However, 300 meters line of site ranges are not uncommon. In these frequency ranges, the 2.4GHz range offers high data rate and accessible channels in the specified ranges.