states, commonly at the middle of the bit or chip period. The transition may be between amplitude, frequency or phase states. Media Access Control (MAC) Address: The MAC address is a unique hardware address of a network interface device and is used by Layer 2 pro- tocols to address data packets to a desired destination device. MAC addresses are 48-bits long, although a 64-bit Extended Unique Identifier has been developed by the IEEE. MICHAEL (MIC): The message integrity check (MIC) is a feature of the wireless protected access (WPA) enhancement to IEEE 802.11 security, developed by the Wi-Fi Alliance as an interim improvement on WEP in advance of the IEEE 802.11i standard. Chapter Sixteen Miller Coding: Miller coding is a type of Manchester coding (q.v.) where a 1-bit is represented by a transition of some type (amplitude, frequency, phase) at the centre of the bit period and a 0-bit is represented by no tran- sition. A repeated 0-bit is represented by a transition at the start of the bit period. In modified Miller coding, each transition is replaced by a negative pulse. Modulation: Modulation is the technique used to combine a digital data stream with a transmitter's carrier signal. Modulation Index: The modulation index is defined as [A-B] / [A+B] where A and B are the maximum and minimum signal amplitudes. Multicast: A multicast message is transmitted to a subset of all stations on the network, in contrast to broadcast and unicast messages (q.v.). Multipath Interference: See Fading Multiple Input Multiple Output (MIMO): Multiple Input Multiple Output refers to wireless links with multiple transmitter and receiver antennas. Processing signals from multiple antennas can increase the available data bandwidth or reduce the average bit error rate (BER) of the link, by exploiting spatial diversity (spatial multiplexing). Network Address Translation (NAT): Network Address Translation is the replacement of a local network address with an address that can be used on an external network such as the Internet, and is perf