Glossary - F


Facilities Based Private Switched Network Services

Facilities Based Private Switched Network Services is a private network for which LECs and IXCs dedicate physical switching and transmission facilities for the exclusive use of a particular customer.

Fast Ethernet

Any of the three versions of 100Mbps Ethernet competing to become an IEEE standard. Grand Junction Networks Inc., HP, and a consortium of vendors (including 3Com Corp., SynOptics Communications Inc., LAN Media, Intel Corp., and Sun Microsystems Inc.) are proposing solutions for the 100Mbps Ethernet standard.

Fax Preference Service (FPS)

A service established by the Direct Marketing Association to help reduce the chances of customers receiving unsolicited advertising communications via fax. It operates along similar lines to the Telephone Preference Service.

Federation of Communication Services (FCS)

The industry body for the mobile telecommunications industry.

File Transfer Protocol (FTP)

Provides a basic service for the reliable transfer of files from one machine to another.

Fixed link telephony operators

Operators providing fixed as opposed to mobile telephony services.

Foreign Exchange (FX)

FX is a service that provides a circuit(s) between a user station, a PBX, or a Centrex switch, and a central office other than the one that normally serves the caller.

Foreign Exchange (FX)

FX is a service that provides a circuit(s) between a user station, a PBX, or a Centrex switch, and a central office other than the one that normally serves the caller.


See Fax Preference Service.


In time division multiplexing systems, Frame is a sequence of time slots each containing a sample from one of the channels carried by the system. The frame is repeated at regular intervals, (normally the sampling rate used in analog-to-digital conversion processes for signals being multiplexed) and each channel usually occupies the same sequence position in successive frames.

Frame Relay

Frame relay is a network interface protocol defined in CCITT Recommendation 1.122 "Framework for additional packet mode bearer services," as a packet mode service. In effect it combines the statistical multiplexing and port sharing of X.25 packet switching with the high speed and low delay of time division multiplexing and circuit switching. Unlike X.25, frame relay implements no layer 3 protocols and only the so-called core layer 2 functions. It is a high-speed switching technology that achieves ten times the packet throughput of existing X.25 networks by eliminating two-thirds of the X.25 protocol complexity The basic units of information transferred are variable length frames, using only two bytes for header information. Delay for frame relay is lower than for X.25, but it is variable and larger than that experienced in circuit switched networks. This means that currently frame relay is not suitable for voice and video applications where excessive and variable delays are unacceptable. High speed transmission method, switching packets of data through its network to their destination. Access to the network is via Frame Relay Access Devices (FRADs) which translate the data (eg Ethernet, Token Ring) into frame relay packets. The network sets up a virtual circuit which is a path to the destination. Frame relay is more popular in the US than in Europe, but the main European carriers offer frame relay service. Frame relay can operate at speeds of up to 45 Mbps, since it is a lightweight system without error correction, relying on the integrity of the fibre optic hardware.


Automated reversed charge mechanism whereby caller pays nothing while company receiving call pays all call charges and associated costs (line rental, enhanced services).

Freephone number

A number which can be reached free of charge to the caller often beginning 0800 or 0500.

Freephone helplines

Helplines run on a not for profit basis providing access to advice, information, listening support, befriending, counselling and/or referral in the fields of health and social welfare where calls are free of charge to the caller.

Freephone Services

Telephone services offered by network operators and service providers for which there is generally no charge to the caller.


Frequency is acoustic waves and electrical signals might be made up of only a single tone, like a single note on a piano. In this case the signal waveform is made up of repeating identical "cycles" and is said to be of a single frequency, equal to the number of cycles that occur in one second of time. In communications, frequency was traditionally expressed in cycles per second, but is now expressed in hertz (Hz), still equal to one cycle per second. Thus, one thousand cycles per second is equal to one thousand hertz, or a kilohertz (kHz).

Frequency Division Multiplexing (FDM)

FDM divides the frequency bandwidth (spectrum) of a broadband transmission circuit into many subbands, each capable of supporting a single, full time communications channel on a non- interfering basis with other multiplexed channels. FDM multiplexing is generally suitable for use with analog carrier transmission systems.


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