T-carrier: 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.

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