Two-binary, one-quaternary (2B1Q) is a physical layerencoding used for Integrated Services Digital Network (ISDN) basic rate interface. 2B1Q uses four signal levels, which are -450 mV, -150 mV, 150 mV and 450 mV, each (1Q) equivalent to two bits (2B). A competing encoding technique, also used for ISDN basic rate interfaces, is 4B3T.
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