Telecom Dictionary

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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 Packet
Fast Packet is a term referring to a number of broadband switching and networking paradigms. 
Implicit is the assumption of an operating environment that includes reliable, digital, broadband, 
nearly error free transmission system.

FCC Federal Communications Commission
The FCC is a board of commissioners empowered by the U.S. Congress to regulate all interstate 
and international communications, as well as use of the radio frequency media. www.fcc.gov

FDDI 
fiber-distributed data interface

FDL 
facility data link

FDM 
frequency division multiplexing

FEP 
front-end processor

FIPS 
Federal Information Processing Standard

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.

Frame
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.

Frequency
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.

FSS 
fully separated subsidiary

FTAM 
file transfer access & management

Full Duplex
Full duplex is a transmission path capable of transmitting signals in both directions 
simultaneously.

FX 
foreign exchange