F

FDDI II
FDDI II is an incompatible extension to FDDI that provides better support for constant bit-rate applications such as voice and video transmission. FDDI II divides its 100-Mbps bandwidth into 16 circuits that can be allocated to various types of traffic; those circuits can be further divided into 96 channels per circuit.

FDDI Follow-On LAN (FFOL)
FFOL is a proposed 2.4-Gbps standard that could eventually replace FDDI.

feeder
A cable that connects a single-floor network segment to a building backbone or multistory trunk is referred to as a feeder.

Fiber Distributed Data Interface (FDDI)
A LAN standard specifying a 100-Mbps token-passing network using fiber optic cable.

Fibre Channel
Fibre Channel is a very high-speed fiber optic data transfer interface based on the ANSI FCS. FCS can carry multiple existing protocols, including IP and SCSI.

firewall
A firewall is a controlled access point between sections of the same network, designed to confine problems to one section. A firewall is also a controlled access between a private network and a public network (such as the Internet), usually implemented with a router and special firewall software.

flat address space
Flat address space refers to a system of one-part, unique addresses, not arranged into a hierarchical organization.

flat file
A flat file is the simplest type of database, which stores data in isolated tables that are not linked to each other. A box of paper file cards is essentially a flat file.

frame
A frame is a unit of information transmitted across a data link. Ethernet frames, for example, are frames generated by an Ethernet NIC.

frame check sequence (FCS)
FCS is a 4-byte CRC value used to check for damaged frames. CRC is a mathematical process used to check the accuracy of data being transmitted across a network. When a block of data is about to be transmitted, the sending station performs a calculation on the data block and appends the resulting CRC value to the end of the data block (frame). The receiving station performs the same calculation on the data. If the CRC values match, the data is transmitted without errors.

frame relay
Unit 1: A frame relay is essentially an electronic switch. Physically, it is a box that connects to three or more high-speed links and routes data traffic between them. Frame relay is intended only for data communications, not voice or video. Transmission errors are detected but not corrected (the frame is discarded).
Unit 5: Frame relay is a technology designed to move data across a WAN. Frame relay normally operates at speeds of 56 Kbps to 1.5 Mbps.

freeware
Freeware is software that does not require a license fee, because its copyright is in the public domain. In other words, the creators of the software give it away. The source code is also freely distributed, so any developer may modify or add to it (fees may be charged for those added components). Periodically, the best modifications become part of the next "official" release of the core software. Thus, freeware, or open source software, benefits from the best ideas and approaches of the worldwide software development community. The Linux OS and the Apache Web server are two of the best-known examples of freeware.

front-end processor (FEP)
A FEP is a device used in IBM mainframe networks that provides connectivity between networking devices and a mainframe. A FEP is also referred to as a communications controller.