T Carrier

In telecommunications, T-carrier, sometimes abbreviated as T-CXR, is the generic designator for any of several digitally multiplexed telecommunications carrier systems originally developed by Bell Labs and used in North America, Japan, and Korea.The basic unit of the T-carrier system is the DS0, which has a transmission rate of 64 kbit/s, and is commonly used for one voice circuit.The E-carrier system, where 'E' stands for European, is incompatible with the T-carrier and is used at most places in the world outside of North America, Japan, and Korea. It typically uses the E1 line rate and the E3 line rate. The E2 line rate is less commonly used. See the table below for bandwidth comparisons.
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The generic designator for any of several digitally multiplexed telecommunications carrier systems. Note 1: The designators for T-carrier in the North American digital hierarchy correspond to the designators for the digital signal (DS) level hierarchy. See the table on the following page. Note 2: T-carrier systems were originally designed to transmit digitized voice signals. Current applications also include digital data transmission. (188 ) Note 3: If an "F" precedes the "T", a fiber optic cable system is indicated at the same rates. Note 4: The table below lists the designators and rates for current T-Carrier systems. Note 5: The North American and Japanese hierarchies are based on multiplexing 24 voice-frequency channels and multiples thereof, whereas the European hierarchy is based on multiplexing 30 voice-ifrequency channels and multiples thereof. See table below. T-Carrier Systems North American Japanese European (CEPT) Level zero (Channel data rate) 64 kb/s (DS0) 64 kb/s 64 kb/s First level 1.544 Mb/s (DS1) (24 user channels) 1.544 Mb/s (24 user channels) 2.048 Mb/s (30 user channels) (Intermediate level, North American Hierarchy only) 3.152 Mb/s (DS1C) (48 Ch.) - - Second level 6.312 Mb/s (DS2) (96 Ch.) 6.312 Mb/s (96 Ch.), or 7.786 Mb/s (120 Ch.) 8.448 Mb/s (120 Ch.) Third level 44.736 Mb/s (DS3) (672 Ch.) 32.064 Mb/s (480 Ch.) 34.368 Mb/s (480 Ch.) Fourth level 274.176 Mb/s (DS4) (4032 Ch.) 97.728 Mb/s (1440 Ch.) 139.268 Mb/s (1920 Ch.) Fifth level 400.352 Mb/s (5760 Ch.) 565.148 Mb/s (7680 Ch.) 565.148 Mb/s (7680 Ch.) Note 1: The DS designations are used in connection with the North American hierarchy only. Note 2: There are other data rates in use, e.g. , military systems that operate at six and eight times the DS1 rate. At least one manufacturer has a commercial system that operates at 90 Mb/s, twice the DS3 rate. New systems, which take advantage of the high data rates offered by optical communications links, are also deployed or are under development.

<communications> A series of wideband digital data transmission formats originally developed by the Bell System and used in North America and Japan.
The basic unit of the T-carrier system is the DS0, which has a transmission rate of 64 Kbps, and is commonly used for one voice circuit.
Originally the 1.544 megabit per second T1 format 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. T2 and T3 circuits channels carry multiple T1 channels multiplexed, resulting in transmission rates of up to 44.736 Mbps.
The T-carrier system uses in-band signaling or bit-robbing, resulting in lower transmission rates than the E-carrier system. It uses a restored polar signal with 303-type data stations.
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".
[Telecommunications Transmission Engineering, Vol. 2, Facilities, AT&T, 1977].
(2001-04-08)