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A fire wall is a gateway that restricts and controls the flow of traffic between networks, typically between an internal corporate network and the Internet. Firewalls may also provide secure gateway services between internal networks. For example, a military installation may have two networks, one for non-classified general communications and another network that is connected to strategic defense systems. A very secure firewall must be in place to ensure that only authorized users access the defense network. In some cases, no connection may be the most secure policy.

Frame relay is a metropolitan and wide area networking solution that implements data link switching techniques. Data frames are sent across permanent or switched virtual circuits that are defined within a network of frame relay switches. Frame relay networks are operated by local and long-distance carriers such as Sprint, MCI, AT&T, and most of the RBOCs (Regional Bell Operating Companies).

Full-Duplex Transmissions

The simple explanation of full-duplex mode is that it is like the telephone, where both parties can talk at the same time. In contrast, a pair of walkie-talkies operates in half-duplex mode because only one party can talk at a time. A full-duplex data transmission is one in which data flows in both directions at the same time. Two separate channels are required for full duplex—either two separate wire pairs or two multiplexed channels. In contrast, a half-duplex connection allows data to flow in only one direction at a time.

Fabric, Switched		Think of a multiconnection device in which a mesh of interconnections connects inputs on one side with outputs on the other side. Any input can be switched to any output almost instantaneously. This is a switching fabric. Now reduce it down to fit on a thumbnail-size (or smaller) chip. Switching fabrics allow fast internetwork connections between devices inLAN environments, on network backbones, or in Internet core networks.

Fast Ethernet		Fast Ethernet is traditional CSMA/CD (carrier sense multiple access / collision detection) access controlat100Mbits/secovertwisted-pairwire The original Ethernet data rate was 10Mbits/sec. During the early development of Fast Ethernet, two different groups worked out standards proposals—and both were finally approved, but under different IEEE committees .One standard became IEEE 802. 3uFast Ethernet and the other became100VG-AnyLAN,which is now governed by the IEEE 802.12 committee. The latter uses the “demand priority” medium access method instead of CSMA/CD.

Fast IP		3Com’s Fast IP is a 3Com proprietary flow-driven, cut-through routing technique designed as an overlay for layer 2 switched networks. It is one of many schemes that attempt to take advantage of fast switching in layer 2 and avoid the overhead of routing every packet on a hop-by-hop basis.

FDDI (Fiber Distributed Data Interface)		FDDI is a 100-Mbit/sec networking technology developed by the ANSI (American National Standards Institute) X3T9.5 committee. It was originally designed for fiber-optic cable, but was later modified to support copper cable over shorter distances. Before Fast Ethernet and Gigabit Ethernet came along, FDDI was commonly used in the LAN and campus environment, as well as a backbone to tie together devices on service provider networks and at exchange points on the Internet. FDDI uses a redundant dual-ring topology that supports 500 nodes over a maximum distance of 100 kilometers (60 miles). Such distances also qualify FDDI for use as a MAN (metropolitan area network).

FDM (Frequency Division Multiplexing)		Multiplexing is a technique used to combine multiple channels of information onto a single circuit or within a specific bandwidth range of a wireless system. At the other end of the circuit, the information is demultiplexed so that the individual channels can be extracted. Frequency division multiplexing allocates bands at specific frequencies for each multiplexed channel.

Fiber-Optic Cable		Fiber-optic cable employs photons for the transmission of digital signals across a strand of ultrapure silica (or plastic in some cases). Photons pass through the cable with negligible resistance. The silica is so pure that, according to Michael Coden of Codenoll Technologies Corporation, a 3-mile-thick window made of the purified silica would give you the same view as a 1/8-inch-thick glass window. As optical system requirements increase, the purity of the cable becomes even more important. The best cable from Corning and Lucent is free of all butthe smallest trace elements of iron and other metals, as well as hydroxyl ions, which are present due to water molecules in the cable.

Firewall		A fire wall is a gateway that restricts and controls the flow of traffic between networks, typically between an internal corporate network and the Internet. Firewalls may also provide secure gateway services between internal networks. For example, a military installation may have two networks, one for non-classified general communications and another network that is connected to strategic defense systems. A very secure firewall must be in place to ensure that only authorized users access the defense network. In some cases, no connection may be the most secure policy.

Frame Relay		Frame relay is a metropolitan and wide area networking solution that implements data link switching techniques. Data frames are sent across permanent or switched virtual circuits that are defined within a network of frame relay switches. Frame relay networks are operated by local and long-distance carriers such as Sprint, MCI, AT&T, and most of the RBOCs (Regional Bell Operating Companies).

Full-Duplex Transmissions		The simple explanation of full-duplex mode is that it is like the telephone, where both parties can talk at the same time. In contrast, a pair of walkie-talkies operates in half-duplex mode because only one party can talk at a time. A full-duplex data transmission is one in which data flows in both directions at the same time. Two separate channels are required for full duplex—either two separate wire pairs or two multiplexed channels. In contrast, a half-duplex connection allows data to flow in only one direction at a time.