FOLDOC Słownik terminów komputerowych
T-carrier systems
A restored polar signal, wideband data loop
digital transmission facility for use with 303-type data
stations, for serial signals synchronized to clock rates of
19.2, 40.8, 50.0, 230.4 or 460.8 kilobits per second. In its
originally intended use, the 1.544 megabit per second T1
line bit stream carried 24 pulse-code modulated, time-division
multiplexed speech signals each encoded in 64 kilobit per
second streams, leaving 8 kilobits per second of framing
information which facilitates the synchronisation and
demultiplexing at the receiver.
Asynchronous signals can be transmitted via a standard which
encodes each change of level into three bits; two which
indicate the time (within the current synchronous frame) at
which the transition occurred, and the third which indicates
the direction of the transition. Although wasteful of line
bandwidth, such use is usually only over small distances.
T1 lines are made free of direct current signal components by
in effect capacitor coupling the signal at the transmitter and
restoring that lost component with a "slicer" at the receiver,
leading to the description "restored polar".
Contrast DS1.
[Telecommunications Transmission Engineering, Vol. 2,
Facilities, AT&T, 1977].
(1996-03-21)
