ct both the strengths and limitations of receiver without further discussion with the the original Ethernet MAC. transmitting station: this is known as forward error The IEEE 802 working group deals with standards for correction. Interleaving is the process of redistributing wired LANs and MANs. IEEE 802.3 is the formal stan- bits into an effectively random order to guard dardization of the Ethernet wired LAN. The IEEE de- against bursts of errors or interference destroying cided to incorporate WLANs as part of the 802 working all the neighboring bits and thus defeating the group and created the 802.11 activity, culminating in the ability of the codes to correct local errors. first release in 1997 of the 802.11 standard. In recent Packet construction: Data packets get preambles years, in addition to various elaborations of the 802.11 prepended onto them. The preambles typically standards, which are discussed below, other working contain synchronization sequences that allow the groups have formed within 802 to consider related ap- receiving station to capture the timing of the plications of wireless data links. (In practice, WPANs transmitter and, in the case of more sophisticated are also included as part of the 802.15 activity.) modulations, may also allow the receiver to The 802.11 standard actually allowed three physical determine the carrier phase and frequency. The layers: an infrared link, a frequency-hopping (FH) radio preambles also contain digital information specific to link, and a direct-sequence spread-spectrum (DSSS) radio the wireless medium. link. These links supported data rates of 1 to 2 Mbps. The Modulation and demodulation: The resulting packets infrared link physical layer has had little commercial must then be modulated onto the carrier, transmitted significance (in fact, the author has been unable to find on the wireless medium, and received, amplified, and any evidence of any commercial product using this pro- converted back into bits. tocol ever having been manufactured). Commercial produc