The 2B1Q line code for the local loop: genesis and transceiver implementation

Abstract

The genesis of the 2B1Q line code for ISDN basic rate access over metallic pair local loops is described. The reasons why 2B1Q was chosen for the emerging American National Standards Institute (ANSI) interface standard are outlined and the impact of the standard specification on transmission performance and the implementation complexity of transceivers is discussed. 2B1Q provides excellent performance with potentially low complexity of implementation.