Specifications

December 2008 Page C–3
Appendix C — Glossary
nization and signaling associated with a particular
channel. In voice channels, Frames 6 and 12 use
the eighth bit of each DS0 voice channel to carry
voice signaling information. Twelve D4 frames
are also referred to as a Superframe.
E&M Signaling A signaling arrangement charac-
terized by the use of separate paths for the voice
and signaling. The M (derived from mouth) lead
provides -48 VDC to the distant end of the circuit
for the active state and an open condition for the
inactive state. Incoming signals are received on
the E (derived from ear) lead.
EMI (Electromagnetic Interference) Extraneous
power caused or generated in a circuit by electro-
magnetic radiation energy coupling.
Electronic Industries Association (EIA) A
standards setting body comprised primarily of
manufacturers. (See RS-232, RS-449, etc.)
T1 Refers to the AT&T standard for 1.544 Mbps
transmission used in Europe.
Far-end Cross Talk (FEXT) Crosstalk that is
propagated in the same direction as the propaga-
tion of the signal.
FDL (Facility Data Link) A communication
mode using the sync bit, provided by ESF,
between terminals.
FOCUS An acronym for Fiber Optic
Communications for Utilities Systems.
Frame A set of consecutive digit time slots in
which the position of each digit time slot can be
identified by reference to a sync pulse.
Framing The process of delimiting the bit
groupings representing one or more channels from
a continuous stream of bits.
Full-duplex Transmission between two points in
both directions simultaneously.
Guard To maintain a continuous watch for an
input.
Half-duplex A transmission path capable of trans-
mitting in only one direction at a time.
Handshake Amethod of error control in which
transmitted data is returned back and checked with
the stored data originally transmitted.
HDB3 High density bipolar 3. A bipolar coding
method that does not allow more than three
consecutive zeros.
Hot Standby A second pair of Optical Fibers
using an alternate path. Used when the normal
routing is unavailable. It is the same origin and
destination, but preferably a different path than
the primary.
Index of Refraction The ratio of the velocity of
light in a vacuum to the velocity of light in the
transmission medium.
Key Input to interface module from external
source. On focus , a voltage in a range from 38-
300Vdc
Link A physical interconnection between two
nodes in a network that operates at an T1/E1 rate.
(See T1 Aggregate link.)
Local Loop Wires that run from the user’s phone
set, PBX, or key system to a telephone company’s
central office.
Lock Chassis configuration can not be changed.
Loop Back Test where transmission signal is
directly returned. Does not effect transmission
signal.
Loop Current The current from a battery at a
central office switch formed by the closure of the
phone hook switch. It is the presence or absence
of the current that enables the automatic
equipment in the central office to observe the
phone sets operation status.
Loop Start The most commonly used method of
signaling an off-hook condition between an
analog phone set and a switch. Picking up the
receiver closes a wire loop, allowing DC current
to flow, which is detected by a PBX or local
exchange, and interpreted as a request for service.
Major Alarm A designation for an alarm indi-
cating a problem affecting a large portion of an
entire chassis.
Map Area where DS0 time slots assignments are
made.
Master The terminal that is designated by the user
as the timing reference for the entire network. It