# Encoding Schemes you need to know about this

NRZ-L | Non-Return-to-Zero Level "One" is represented by one level "Zero" is represented by another level lower the one but not zero. |

NRZ-M | Non-Return-to-Zero Mark "One" is represented by a change in level "Zero" is represented by no change in level. |

NRZ-S | Non-Return-to-Zero Space "One" is represented by no change in level "Zero" is represented by change in level. |

NRZ-I | Non-Return-to-Zero Inverse "One" is represented by no change in level "Zero" is represented by change in level. |

Bi-Phase-L | Bi-Phase Level (Split Phase) Level change occurs at the beginning of every bit period "One" is represented by a "One" level with transition to the "Zero" level "Zero" is represented by a "Zero" level with transition to the "One" level. |

Bi-Phase-M | Bi-Phase Mark Level change occurs at the beginning of every bit period "One" is represented by a midbit level change "Zero" is represented by no midbit level change. |

Bi-Phase-S | Bi-Phase Space Level change occurs at the beginning of every bit period "One" is represented by no midbit level change "Zero" is represented by a midbit level change. |

DBi-Phase-M | Differential Bi-Phase Mark Level change occurs at the center of every bit period "One" is represented by no level change at the beginning of the bit period "Zero" is represented by a level change at the beginning of the bit period. |

DBi-Phase-S | Differential Bi-Phase Space Level change occurs at the center of every bit period "One" is represented by a level change at the beginning of the bit period "Zero" is represented by no level change at the beginning of the bit period. |

# BiPolar AMI

AMI stands for Alternate Mark Inversion. This means a logical one is transmitted as energy and a logical zero is not. This reduces the actual bandwidth with a factor 2. The Bipolar fact adds the benefit of no DC components and transformer coupling. This all results in a reduction of signal loss

# BnZS

Bipolar with n Zero Substitution: This means when there are more than n zeros in a data string this "All Zero"-condition is replaced by a special BnZS code.

# B8ZS (BiPolar with Eight Zero Substitution)

B8ZS is a Bell Labs method to solve 0's density in data transmission. It replaces an all 0 condition with a special B8ZS code containing specific violations to the bipolar bit coding format (AMI).

# 2B1Q (2 Binary 1 Quarternary)

Defined in detail in 1988 ANSI spec. T1.601. Defines 2 bits in a baud.

Bits | Quaternary Symbol | Voltage Level |

00 | -3 | -2.5 |

01 | -1 | -0.833 |

10 | +3 | +2.5 |

11 | +1 | +0.833 |