-to- peer or ad-hoc mode (q.v.). Initialisation Vector (IV): An initialisation vector is part of the key used in an encryption algorithm, and is typically changed for each data packet. The IV is added to a secret key, such as a 40-bit key derived from a WEP passphrase, to obtain the full key used in the encryption algorithm. The IV is transmitted with the encrypted message and the receiving station, know- ing the secret key, can determine the full encryption key. The IV prevents the occurrence of patterns in the encrypted data that would otherwise make it easier for a hacker to determine the secret key. Chapter Sixteen Internet Protocol (IP): Internet Protocol is the Network layer protocol that provides addressing and routing functions on the Internet. The current version is IPv4. IP Address: A number that uniquely identifies a device on the Internet SO that other devices can communicate with it. IPv4 uses 32-bit addresses, while IPv6 addresses will be 128-bit. IP addresses are used by protocols at Layer 3 and above, and are translated into MAC addresses by the address resolution protocol (ARP) for use at Layer 2 and below. ISM (Industrial, Scientific and Medical): The ISM bands are three radio bands at 900 MHz, 2.4 and 5.8 GHz that were originally reserved for licence exempt use in industrial, scientific and medical applications, but are now also home to the main wireless networking PHY layer tech- nologies. Isochronous: An isochronous service requires data to be delivered within certain time constraints. Multimedia streams require an isochronous transport service to ensure that data frames are delivered as fast as they are displayed. The requirements of an isochronous service are not as rigid as those of a synchronous service, but are also not as lenient as an asynchro- nous service (q.v.). Jitter: Jitter refers to the variability in latency of individual transmitted packets, and is particularly important in determining quality of service for isochronous data services such as streaming video. Latency: The time 