Glossary - F

FAI

French equivalent of ISP and/or IAP.

FAQ

Frequently Asked Questions
A list of the most common questions and their responses.

Fast LAN

Term given to two emerging standards; IEEE 802.3u (called Fast Ethernet) for Ethernet operating at 100 Mbps over CAT-3 or CAT-5 UTP, and IEEE 802.12 (called 100VG-AnyLAN) for Ethernet or Token Ring operating at 100 Mbps over CAT-3/4/5 UTP, STP or optic fiber.

Fault Management

The ability of a network to deal with isolated faults and reroute traffic in case a span is lost.

Fault Tolerance

System capability to perform fault management and continue operations in the event of a system failure.

FC

Face Contact (physical layer)

FCC

Federal Communications Commission (communications, network)

FCS

Frame Check Sequence (communications, network)
Any mathematical formula which derives a numeric value based on the bit pattern of a transmitted block of information and uses that value at the receiving end to determine the existence of any transmission errors.

FDDI

Fiber Distributed Data Interface (network)
An ANSI-defined standard for implementing a high-speed (100 Mbps) LAN over fiber. FDDI is a fault-tolerant dual counter-rotating-ring design.

FDM

Frequency Division Mutliplexing (network)
The simultaneous transmission of multiple separate signals through a shared medium (such as a wire, optical fibre or light beam) by modulating, at the transmitter, the separate signals into separable frequency bands, and adding those results linearly either before transmission or within the medium. While thus combined, all the signals may be amplified, conducted, translated in frequency and routed toward a destination as a single signal, resulting in economies which are the motivation for multiplexing. Apparatus at the reciever separates the multiplexed signals by means of frequency passing or rejecting filters, and demodulates the results individually, each in the manner appropriate for the modulation scheme used for that band or group.
Bands are joined to form groups, and groups may then be joined into larger groups; this process may be considered recursively, but such technique is common only in large and sophisticated systems and is not a necessary part of FDM.
Neither the transmitters nor the recievers need be close to each other; ordinary radio, television, and cable service are examples of FDM. It was once the mainstay of the long distance telephone system. The more recently developed time division multiplexing in its several forms lends itself to the handling of digital data, but the low cost and high quality of available FDM equipment, especially that intended for television signals, make it a reasonable choice for many purposes.
A technique that allows for the channel bandwidth of a circuit to be subdivided into many little channels (one per traffic stream).

FDMA

Frequency Division Multiplexing Access (communications, network)

FEBE

Far End Block Error (physical layer)

FEC

Forward Error Correction (ATM)
An error correction technique where there are no retransmissions and therefore the receiver is responsible for correcting any errors in the packets. FEC takes advantage of the sequence number contained in an ATM AAL (ATM adaptation layer) 1 protocol data unit to detect cell loss and prevent unnecessary transmission of cells belonging to faulty packets. A recent proposal to the ATM Forum advocates the use of FEC to address problems of data loss and packet delay on shared constant bit rate ATM links. According to studies conducted by several ATM Forum member companies, using FEC to detect cell loss allows multiple ATM devices to share the same virtual circuit for real-time audio and video transmission with minimal added overhead (approximately 3 percent) and only slight performance degradation.

FECN

Forward Explicit Congestion Notification (network)
A bit in the frame relay header. The bit is set by a congested network node in any frame which is traveling in the same direction as the congestion (in frame relay, a node can be congested in one direction of frame flow but not in the other). See BECN, EFCI.

FERF

Far End Receive Failure (physical layer, error)

Finger (network, Internet)

A protocol, defined in RFC 1288, that allows information about a system or user on a system to be retrieved.
Finger also refers to the commonly used Internet software tool for locating people on other Internet sites.
Finger is also sometimes used to give access to non-personal information, but the most common use is to see if a person has an account at a particular Internet site. Some sites consider finger to be a security risk and have either disabled it, or replaced it with a simple message.

FIFO

First In First Out
A queue. A data structure or hardware buffer from which items are taken out in the same order they were put in. Also known as a "shelf" from the analogy with pushing items onto one end of a shelf so that they fall off the other. A FIFO is useful for buffering a stream of data between a sender and receiver which are not synchronised - i.e. not sending and receiving at exactly the same rate. Obviously if the rates differ by too much in one direction for too long then the FIFO will become either full (blocking the sender) or empty (blocking the receiver). A Unix pipe is a common example of a FIFO.
The opposite of a FIFO is a LIFO (last in first out) which is the same as a stack.

FIORL

Fiber Optic Inter-Repeater Link (network)
Fiber-optic signaling methodology based on the IEEE 802.3 fiber-optic specification.

Firewall (network, security)

A dedicated gateway machine with special security precautions on it, used to service outside network, especially Internet, connections and dial-in lines. The idea is to protect a cluster of more loosely administered machines hidden behind it from crackers. The typical firewall is an inexpensive microprocessor-based Unix machine with no critical data, with modems and public network ports on it, but just one carefully watched connection back to the rest of the cluster. The special precautions may include threat monitoring, call-back, and even a complete iron box keyable to particular incoming IDs or activity patterns. Firewalls often run proxy gateways.

Flow control

A method used in networking for congestion avoidance and traffic regulation. There are three techniques:

• window-based control, where a sliding window is used to determine how many cells can be transmitted during a predefined period,
• rate-based control, where the rate at which the source can transmit is monitored and controlled,
• credit-based control, where a source can transmit a cell if there is a credit available.

CAC is also part of the flow control. See also Congestion control.

FM

Facilities Management

FMBS

Frame Mode Bearer Service

FOIRL

Fiber Optic Inter-Repeater Link (communications)
A fiber optic signaling method based on the IEEE 802.3 and implemented over two fiber links, transmit and receive, in a point-to-point link. This medium may be up to 500m and 1 kilometer(3,280 ft.) long depending on the number of repeaters in the network.
It has been replaced by 10BASE-FL.

Fragmentation

Breaking a packet into smaller units when transmitting over a network medium that cannot support the original size of the packet.

Frame

1. networking: a datalink layer "packet" which contains the header and trailer information required by the physical medium. That is, network layer packets are encapsulated to become frames. See also datagram, encapsulation, packet.
2. programming: activation record.
3. hardware: One complete scan of the active area of a display screen. Each frame consists of a number N of horizontal scan lines, each of which, on a computer display, consists of a number M of pixels. N is the vertical resolution of the display and M is the horizontal resolution. The rate at which the displayed image is updated is the refresh rate in frames per second.

FR

Frame Relay (network)
A packet-switching technology to provide a very reliable packet delivery over virtual circuits (VC). Some of the concepts used in frame relay have been incorporated in ATM networks.

Frame Relay Forum

A voluntary organization composed of Frame Relay vendors, manufacturers, service providers, research organizations and users. Similar in purpose to the ATM Forum. (see SIG).
Web site: http://www.frforum.com/.

Freeware (software)

Free software available for example on the Internet that can be freely used and redistributed.

FRM

Fast Resource/Reservation Management
A form of network management for allocating resources (buffers, bandwidth) dynamically.

FRS

Frame-Relay Service (network)

FTAM

File Transfer Access and Management (network)
Name given by the ISO to a layer 7 standard used to transfer and manage remote files.

FTP

File Transfer Protocol (network, Internet)
A TCP/IP Internet application and protocol used for transferring files between different machines across a network over TCP/IP services.

FT-PNNI

ForeThought PNNI (ATM)

Full Duplex (communications)

LAN Technique for transmitting full duplex between a LAN station and the wiring hub. Supports 10 Mbps in each direction (20 Mbps) for Ethernet and 16 Mbps in each direction (32 Mbps) for Token Ring. Only supports single stations, not LAN segments.

FUNI

Frame-based UNI (ATM)

FYI (standard, Internet)

For Your Information (standard, Internet)
A subseries of RFCs that are not technical standards or descriptions of protocols. FYIs convey general information about topics related to TCP/IP or the Internet.
See also STD.

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