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Encoding Schemes

Code Name	Binary Code	Code Definition
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

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