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COMSPHERE 3550 Series Data Service Units
Glossary-4 February 1995 3550-A2-GB20-10
errored second A performance measurement reported during Digital Test or Transmit Test Pattern
that is defined as a second in which at least one error has been detected.
facility alarm A failure condition reported to the 6700 Series NMS when there is a break in
communication with one or more tributary.
fallback Retraining of a V.32 DBM at a lower rate or speed.
FCC Federal Communications Commission. Board of commissioners that regulates all
interstate and foreign electrical communication systems that originate from the
United States.
Front-End Processor
(FEP)
A communications computer associated with a host computer that manages the
lines and routing of data through the network; it is the data terminal equipment
(DTE) at the control DSU.
generator A circuit in a DSU or in external test equipment that produces a continuous string
or stream of known data patterns.
IEC InterExchange Carrier. A company that provides inter-LATA (local exchange
carrier) telecommunication services, like AT&T, MCI , and Sprint . Access to
these services can be provided through DDS dedicated channels, T1.5 dedicated
access channel, or digital switched access (DSA) channels.
LADS Local Area Data Set (also called a limited-distance modem or LDM). This refers to
a mode of operation where the control and tributary DSUs are directly connected
but not passing through a DDS network.
Lamp Test A test to verify that all status indicators and the control panel’s LCD are operating.
LATA Local Area Transport Area. A region served by a local exchange carrier (LEC) that
consists of one or more area codes.
LCD Liquid Crystal Display. A thin sandwich of two sealed glass plates containing liquid
crystal material. When voltage is applied, the amount of light able to pass through
the glass plates is altered so that messages may be “written” on the display.
LDM Limited-Distance Modem (also called a local area data set or LADS).
LEC Local Exchange Carrier. A company that provides intra-LATA (local exchange
carrier) telecommunication services, like NYNEX or Bell South.
LED Light-Emitting Diode. A light or status indicator on the diagnostic control panel
(DCP) that glows in response to the presence of a certain condition (e.g., Alrm).
link-level address NMS communications are directed to a tributary via a link-level address. It takes
the form of control network address/tributary network address (e.g., 157/04 – DSU
control address of 157 and tributary address of 04).
Local Loopback A test used to determine whether the DSU’s DTE connection and the DSU are
operating properly. The DSU must be connected to the DTE for this loopback to be
run.
LSD The state of the received Line Signal Detect lead, also known as carrier detect.