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Glossary
102 ISU 512 User Manual 61202.086L1-1
interface
A common boundary between two systems over which the inter-system commu-
nication occurs.
ISDN
Integrated services 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.
leased line
A telecommunication facility or link reserved for the exclusive use of one custom-
er. Also called a dedicated line.
leased service
The exclusive use of any channel or combination of channels designated to a sub-
scriber.
local loop
In telephony the wire pair that connects a subscriber to a phone company end of-
fice, typically containing two wires. Four-wire local loops are common, however,
especially with leased voice grade circuits.
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 signaling.
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