The line coding technique employed in E-1. HDB3 is a bipolar transmission method that reverses the polarity of alternate marks, or 1 bits, expressing the first as a positive voltage of +3V, the second as a negative voltage of -3V, the third as +3V, and so on. Zero bits are coded as 0V. HDB3 is based on a combination of alternate mark inversion (AMI) and Bipolar with EightZeros Substitution (B8ZS) in T1 networking, but imposes a limit of three successive 0 bits. A fourth 0 bit triggers zeros suppression, substituting a known bit pattern with an intentional bipolar violation (BPV) known to the receiver, as illustrated in Figure H-1. See also AMI, bipolar, B8ZS, BPV, E-1, mark, multiplexer, polarity, and T1.