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Glossary
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ISU 2x64 Dual Port ISDN Service Unit User Manual 61200051L1-1D
ISDN
Integrated service digital network. A network architecture that enables end-to-
end digital connections. The network supports diverse services through integrat-
ed access arrangements and defines a limited set of standard, multipurpose inter-
faces for equipment vendors, network providers, and customers. Interworking
with a public switched telephone network is retained.
LATA
Local Access and Transport Area. One of 161 local telephone serving areas in the
United States, generally encompassing the largest standard statistical metropoli-
tan areas. Subdivisions established as a result of the AT&T divestiture that now
distinguish local from long distance service. Circuits with both end-points within
the LATA (intraLATA) are generally the sole responsibility of the local telephone
company, while circuits that cross outside the LATA (interLATA) are passed on to
an interexchange carrier.
Loopback
A diagnostic procedure where data is sent to the device being tested, and the out-
put of the device is fed directly back to its input, looped around, and the returning
data is checked against that which was sent.
loopback test
A test typically run on a 4-wire circuit. Two transmit leads are joined to the two
receive leads. A signal is then sent around the loop. Measuring differences be-
tween the sent and received signal is the essence of a loopback test.
master clock
The source of timing signals, or the signals themselves, which all network stations
use for synchronization.
message
The Layer 3 information that is passed between the CPE and SPCS for signalling.
multiplexing
The combining of multiple data channels onto a single transmission medium. Any
process through which a circuit normally dedicated to a single user can be shared
by multiple users. Typically, user data streams are interleaved on a bit or byte ba-
sis (time division) or separated by different carrier frequencies (frequency divi-
sion).
multipoint circuit
A circuit consisting of three or more stations connected directly electrically.