F

failover

The automatic switching from one device or system to another. Servers can be configured in a failover configuration so that if the primary server fails, the secondary server takes over automatically.

Fast Ethernet

The IEEE 802.3 specification for data transfers of up to 100Mbps over twisted-pair cable.

See also [100BaseFX]

See also [100BaseTX]

See also [100BaseT]

See also [100BaseT4]

fault tolerance

The capability of a component or system to endure a failure.

FDDI (Fiber Distributed Data Interface)

A high-speed data transfer technology that is designed to extend the capabilities of existing LANs by using a dual-ring topology and a token-passing access method.

FDM (Frequency-Division Multiplexing)

A technology that divides the output channel into multiple smaller-bandwidth channels, each of which uses a different frequency range.

fiber-optic cable

Also known as fiber optics or optical fiber, a physical medium that is capable of conducting modulated light transmissions. Compared with other transmission media, fiber-optic cable is more expensive, but it is not susceptible to EMI or crosstalk, and it is capable of very high data rates.

fibre channel

A technology that defines full gigabit-per-second data transfer over fiber-optic cable.

firewall

A program, system, device, or group of devices that acts as a barrier between one network and another. Firewalls are configured to allow certain types of traffic to pass while blocking others.

FireWire

A high-speed serial bus technology that allows up to 63 devices to be connected to a system. FireWire provides sufficient bandwidth for multimedia operations and supports hot swapping and multiple speeds on the same bus.

fixed wireless

A technology that provides data communication capabilities between two fixed locations. Fixed wireless can be used as a private networking method but is also becoming increasingly common as an Internet access method.

flow control

A method of controlling the amount of data that is transmitted within a given period of time. There are different types of flow control.

See also [dynamic window, static window]

FQDN (fully qualified domain name)

The entire domain name that specifies the name of the computer as well as the domain in which it resides and the top-level DNS domain (for example, www.quepublishing.com).

fragment-free switching

A fast-packet-switching method that uses the first 64 bytes of a frame to determine whether the frame is corrupted. If this first part is intact, the frame is forwarded.

frame

A grouping of information that is transmitted as a unit across the network at the data-link layer of the OSI model.

FCS (Frame Check Sequence) field

A field of a packet that holds a CRC value to ensure that all of the frame's data arrives intact.

Frame Length field

In a data frame, the field that specifies the length of a frame.

Frame Relay

A high-speed data-link layer switching protocol that is used across multiple virtual circuits of a common carrier to give the end user the appearance of a dedicated line.

Frame Type field

In a data frame, the field that names the protocol that is being sent in the frame.

frequency

The number of cycles of an alternating current signal over a unit of time. Frequency is expressed in Hertz.

FTP (File Transfer Protocol)

A protocol that provides for the transfer of files between two systems. FTP is part of the TCP/IP protocol suite.

full backup

A backup in which files, regardless of whether they have been changed, are copied to the backup media. In a full backup, the archive bits of the files are reset.

full-duplex

A system in which data is transmitted in two directions simultaneously. Compare with half-duplex.