FA (Fuse Alarm) - An
alarm designation representing a distribution fuse or circuit breaker failure.
Fabric - A switch
fabric provides the physical interconnection architecture that redirects the
data from an incoming port to another outgoing port.
Fairness - As
related to Generic Flow Control (GFC), fairness is defined as meeting all of
the agreed quality of service (QoS) requirements by controlling the order of
service for all active connections.
Fair Queuing -
Developed to ensure fairness and prevent bursty flows from interfering with
other flows. Fair Queuing sets up firewalls between each flow. Each flow is
allocated its own dedicated queue.
Fallback to Primary Path
- Mechanism in which Marconi switches revert back to the original path once the
failed link has been restored.
Farad - The derived
SI unit of capacitance: the capacitance of a capacitor between the plates where
there is a potential difference of 1 volt when charged by a quantity of
electricity of 1 coulomb. This is a very large unit; microfarads (10 -6 ) and
picofarads (10 -12 ) are most commonly used.
Far-End - In a
relationship between two devices in a circuit, the far-end device is the one
that is remote.
Fault - A
malfunction in a circuit.
Fault to Ground -
Fault due to the failure of insulation and the consequent establishment of a
direct path to ground from a part of the circuit which should not normally be
FC - Designation
for fiber optic connector designed by Nippon Telegraph and Telephone which
features a movable anti-rotation key allowing good repeatable performance
despite numerous mating. Normally referred to as Fiber Connector, FC actually
stands for Face Contact and sometimes linked with PC (Point Contact),
designated as FC or FC-PC verses ST or SC.
FCC - A board of
commissioners appointed by the President under the Communications Act of 1934,
with the authority to regulate all interstate telecommunications originating in
the United States, including transmission over phone lines.
FCC Part 68 - The
FCC rules regulating the direct connection of non-telephone company provided
equipment to the public telephone network.
FCC Registration Number
- A number assigned to specific telephone equipment registered with the FCC, as
set forth in FCC docket 19528, part 68. The presence of this number affixed to
a device indicates that the FCC has approved it as a compatible device for
direct connection to telephone line facilities.
FCS (Frame Check Sequence)
- In bit-oriented protocols, a 16-bit field that contains transmission error
checking information, usually appended to the end of the frame.
FDDI (Fiber Distributed Data
Interface) - High-speed data network that uses fiber-optic as the
physical medium. Operates in similar manner to Ethernet or Token Ring, only
FDM (Frequency Division
Multiplexing) - A method of dividing an available frequency range into
parts with each having enough bandwidth to carry one channel.
FEBE (Far End Block Error)
- An error detected by extracting the 4-bit FEBE field from the path status
byte (G1). The legal range for the 4-bit field is between 0000 and 1000,
representing zero to eight errors. Any other value is interpreted as zero
FEC (Forward Error
Correction) - A technique used by a receiver for correcting errors
incurred in transmission over a communications channel without requiring
retransmission of any information by the transmitter; typically involves a
convolution of the transmitted bits and the appending of extra bits by both the
receiver and transmitter using a common algorithm.
FECN (Forward Explicit
Congestion Notification) - Bit set by a Frame Relay network to inform
data terminal equipment (DTE) receiving the frame that congestion was
experienced in the path from source to destination . DTE receiving frames with
the FECN bit set can request that higher-level protocols take flow control
action as appropriate.
Feedback - Refers
to the specific method used in ABR to tell a transmitting end station to slow
down due to congestion in the network.
Feeder Cable -
Large cable leaving a central office to serve a specific area. Also called main
or primary cable.
FERF (Far End Receive
Failure) - A line error asserted when a 110 binary pattern is detected
in bits 6, 7, 8 of the K2 byte for five consecutive frames. A line FERF is
removed when any pattern other than 110 is detected in these bits for five
Ferrule - (1) The
metal cap on the end of a cartridge fuse tube which is used as a contact for
the fuse; and (2) a mechanical fixture, generally a rigid tube, used to confine
the stripped end of a fiber bundle or a fiber.
FGD (Frame Ground) -
Frame Ground is connected to the equipment chassis and thus provides a
protective ground. Frame Ground is usually connected to an external ground such
as the ground pin of an AC power plug (earth ground).
Fiber - Fine glass
strands, the thickness of a human hair. Coherent light systems which now can be
modulated to carry broadband telecommunications multiplexing can be routed on
these glass fibers.
Fiber Connection Area
- An area of the frame above the switching chassis allocated fro a generic
panel used to interconnect the fiber optic cables coming from the ASX-4000.
Fiber Optics (FO) -
Thin filaments of glass through which light beams are transmitted over long
distances and which can carry enormous amounts of data. Modulating l ight on
thin strands of glass produces major benefits in high bandwidth, relatively low
cost, low power consumption, small space needs, total insensitivity to
electromagnetic interference, and great insensitivity to being bugged.
Field Programmable -
The ability of a system to have changes made in its program while it is
installed, without having to be returned to the factory.
FIFO (First-In, First-Out)
- A method of coordinating the sequential flow of data through a buffer.
Filter - (1) A
network that passes desired frequencies but greatly attenuates other
frequencies; and (2) a device for use on power or signal lines, specifically
designed to pass only selected frequencies and to attenuate substantially all
other frequencies. There are two basic types of filters: active filters which
require the application of power for the utilization of their filtering
properties; and passive filters which use inductance-capacitance components and
do not require the application of power for the utilization of their filtering
Filtering - The
action of allowing the passage of electrical energy at frequencies within one
or more bands and preventing the passage of all other frequencies.
Firmware - Programs
kept in semi-permanent storage, such as various types of read only memory.
Software is “burned in” on the memory device so that it is non-volatile (will
not be lost when power is shut off).
Flag - In
bit-oriented communications, a bit pattern of six binary "1"s bounded by a
binary "0" at each end (forms a 0111 1110 or Hex "7E"). It is used to mark the
beginning and/or end of a frame.
Non-volatile memory used as a re-writable, general purpose mass storage device
for the switch. Information stored on the flash file my include bootable code
images, configuration files, call record information, etc. Switch software
supports user-initiated reading/writing from/to the flash (via TFTP protocol),
allowing file backup/restore operations to a remote server.
Float - To operate
a power load such as a telephone central office on a mains-driven rectifier in
parallel with a low impedance storage battery which is kept fully charged by
the rectifier and is itself only called upon to provide power during temporary
and short-duration peaks for which the rectifier output is insufficient.
Floating - A
circuit or device that is not connected to any source of potential or to
Floating Battery -
A low impedance battery, fully charged, connected across the output of central
office rectifiers to smooth the output and serve as standby source of power
during peak load periods or faults.
Float Voltage - The
optimum voltage level at which a battery string gives maximum life and full
Floppy Disk - A
disk memory based on interchangeable, flexible plastic disks, usually with a
moveable head able to access many read/write tracks.
Flow Control - The
way in which information is controlled in a network to prevent loss of data
when the receiving buffer is near its capacity.
Foil Capacitor -
Capacitor made with thin metallic foil coating on insulating surfaces;
sometimes plastic film or thin paper sheets are used rather than foil.
Footprint - The
dimensions of a particular piece of equipment; used in computing floor loading
and completing floor plan requirements.
forearea - The ID
of the area in Marconi's hierarchy support to which this node belongs.
Foreign Address -
An address that does not match any of a given node's summary addresses.
forelevel - The
level of the area used in Marconi's hierarchy support.
Form A - A set of
contacts consisting of a make connection.
Form B - A set of
contacts consisting of a break connection.
Form C - A relay
contact set description consisting of a make, break and a common connection.
Also called a set of transfer contacts.
Fractional T1 - The
use of bandwidth in 64K bps (DS0) increments up to 1.544M bps from a T1
Frame - A variable
length group of data bits with a specific format containing flags at the
beginning and end to provide demarcation.
Frame Discard -
Sometimes call Intelligent Packet Discard is a means of increasing throughput
by the discard of an entire frame rather than individual cells that comprise
the packet to prevent or relieve congestion. Examples include EPD and PPD.
Frame Relay - A
fast packet switching protocol based on the LAPD protocol of ISDN that performs
routing and transfer with less overhead processing than X.25.
Frame Synchronization Error
- An error in which one or more time slot framing bits are in error.
Framing - A
protocol that separates incoming bits into identifiable groups so that the
receiving multiplexer recognizes the grouping.
Frequency - The
number of times per second that the voltage wave (or current wave) goes through
a complete cycle, expressed in hertz (Hz).
Frequency Reuse -
The ability to use the same frequencies repeatedly within a single system, made
possible by the basec design approach for cellular. Since each cell is designed
to use radio frequencies only within its boundaries, the same frequencies can
be reused in other cells not far away with little potential for interference.
The reuse of frequencies is what allows a cellular system to handle a huge
number of calls with a limited number of channels.
Front Contacts -
The make contacts of a relay.
FRS (Frame-Relay Service)
- A connection oriented service that is capable of carrying up to 4096 bytes
FT-PNNI (ForeThought PNNI)
- A Marconi routing and signaling protocol that uses private ATM (NSAP)
addresses; a precursor to ATM Forum PNNI (see PNNI).
FTP (File Transfer Protocol)
- A TCP/IP protocol that lets a user on one computer access, and transfer data
to and from, another computer over a network. ftp is usually the name of the
program the user invokes to accomplish this task.
Full Float or Floating
Battery - A storage battery connected permanently in parallel with
another power source. The battery normally handles only small charging or
discharging currents, but takes over the entire load upon failure of the main
(commercial power) supply.
- Both positive and negative half-cycles of the incoming AC signal are
rectified to produce a unidirectional (DC) current through the load.
Functional Block Diagram
- Diagram illustrating the definition of a problem on a logical and functional
FUNI (Frame-Based UNI)
- An ATM switch-based interface which accepts frame-based ATM traffic and
converts it into cells.
Fuse - An
overcurrent protection device with a circuit-opening fusible part which is
heated and severed by the passage of overcurrent through it.
Fuse Alarm Lamp - A
lamp which shows that a fuse in the indicated panel or bay has operated.
Fuse Block - A unit
on which fuses are mounted.
Fuse Size Determination (in
DC plants) - The proper fuse rating is 150 percent of peak load
current. Peak load is defined as 133 percent of the busy hour value for
variable loads and equal to the busy hour value for constant loads. (These
loads are classified at list 2 current drains.) The fuse rating is used to
determine the minimum capacity of the power used in the circuit.
Fusible Link - That
part of a fuse which is designed to melt when the rated current is exceeded.
Fusing - Devices
which protect circuits against damage from excessive current flowing in them by
melting of a fuse element. The fuse comprises all the parts that form the