ransmission capacity, which is a major advantage in crowded underground ducts. The fibers are immune to electrical interference, which is another advantage. Also called lightwave communi- cations, photonics, or, simply, fiber. Fibre Channel A high-speed interface, standardized by ANSI, that supports up to 800Mbps over 6.2 miles (10 km) of fiber. FIFO (first in, first out) A queuing technique in which the next item to be retrieved is the item that has been in the queue for the longest time. This ensures that cells remain in the correct sequence. file server In local networks, a station dedicated to providing file and mass data storage ser- vices to the other stations on the network. filter To selectively forward data, based on criteria specified by the network manager. firewall A system designed to prevent unauthorized access to or from a private network. Fire- walls can be implemented in both hardware and software, or a combination of both. five-nines reliability A desired level of network or system reliability that equates to 99.999% uptime (i.e., about 5 minutes of downtime per year). fixed wireless local loop A stationary installation that dramatically cuts down on the cost of installing and maintaining the local loop. It uses a fixed antenna location, so it is relatively easy to engineer. Flash-OFDM (Fast Low-Latency Access with Seamless Handoff OFDM) A WMAN standard that is a variant of 802.20. Flash-OFDM uses a technique called fast hopping, a signal- processing scheme that supports high data rates with very low packet and delay losses (i.e., latencies) over a distributed all-IP wireless network. Flash-OFDM is not compatible with 2.5G or 3G technology. flat network A network that is constructed by using bridges or Layer 2 LAN switches. This type of network is easy to configure, and it promises better performance than hierarchical net- works; it offers higher throughput and therefore also lower latencies. However, the scalability of a flat network is limited, and a flat network is subject to broadcast storms