2B1Q Line Coding
2B1Q coding is the standard used in North America and in Italy. 2B1Q means that two bits are combined to form a single Quaternary line state (symbol). 2B1Q combines two bits at a time to be represented by one of four signal levels on the line. The signal rate, therefore, is 80 kilobaud and the line rate 160 kbit/s. It operates with a maximum frequency range (bandwidth) of 40 kHz.
2B1Q coding is defined in ANSI T1.601 and ETR 080, Annex A. It can operate at distances up to about 18,000 feet (5.5 km) with loss up to 42dB. An internal termination impedance of 135 ohms is presented to the line at each end of the U-interface. Echo cancellation techniques allow full-duplex operation on the line.
2B1Q transmission can be simply described as an amplitude modulation scheme for DC pulses.
Read more about this topic: Basic Rate Interface
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