ADTRAN 1203086L1, Руководство пользователя, Страница: 148 / 162

Glossary
Glossary-6 ISU 512e User Manual 61203086L1-1
leased line
A telecommunication facility or link reserved for the exclusive use
of one customer. Also called a dedicated line.
leased service
The exclusive use of any channel or combination of channels des-
ignated to a subscriber.
local loop
In telephony the wire pair that connects a subscriber to a phone
company end office, typically containing two wires. Four-wire lo-
cal loops are common, however, especially with leased voice
grade circuits.
loopback
A diagnostic procedure where data is sent to the device being test-
ed, and the output 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 between 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.
Media Access Control (MAC)
As defined by the IEEE, the lower of the two sublayers of the OSI
reference model data link layer. The MAC sublayer is concerned
with media access issues, such as whether token passing or con-
tention is used.
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 transmis-
sion medium. Any process through which a circuit normally ded-
icated to a single user can be shared by multiple users. Typically,
user data streams are interleaved on a bit or byte basis (time divi-
sion) or separated by different carrier frequencies (frequency divi-
sion).