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Encoding Schemes

Code NameBinary CodeCode Definition
NRZ-L NRZ-L Picture 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 NRZ-M Picture Non-Return-to-Zero Mark
"One" is represented by a change in level
"Zero" is represented by no change in level.
NRZ-S NRZ-S Picture Non-Return-to-Zero Space
"One" is represented by no change in level
"Zero" is represented by change in level.
NRZ-I NRZ-I Picture 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-L Picture 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-M Picture 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-S Picture 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 DBi-Phase-M Picture 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 DBi-Phase-S Picture 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

AMI Picture

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.

BitsQuaternary SymbolVoltage Level
00-3-2.5
01-1-0.833
10+3+2.5
11+1+0.833

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