1. CCE 484 - Computer Networks
Chapter 5: Encoding
Information must be encoded into signals before it can be transported across communication media
Information can be either
Digital, or
Analog
Signals can be also of two types:
Digital
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2. CCE 484 - Computer Networks
Types of Encoding
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3. Digital-to-Digital Encoding
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4. CCE 484 - Computer Networks
Unipolar
Uses only one level of value (polarity)
Pros: simple and inexpensive
Cons: DC component and synchronization
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5. CCE 484 - Computer Networks
Polar
Uses two levels of amplitude
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6. Non-Return to Zero (NZR)
The level of the signal is always either positive or negative
NZR-Level : the level of the signal is dependent on the state of the bit (ex. +  1 and –  0)
NRZ-Inverted: The signal is inverted if a 1 is encountered
Less DC-component and more synchronization than Unipolar
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7. CCE 484 - Computer Networks
NRZ
NRZ-L
NRZ-I
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8. CCE 484 - Computer Networks
Return to Zero (RZ)
Uses three signal values: positive, zero, and negative
There is a signal change for each bit (negative-to-zero for 0 and positive-to-zero for 1
Excellent synchronization
Disadvantage: It needs more bandwidth since two signal changes per bit
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9. CCE 484 - Computer NetworksRZ
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10. CCE 484 - Computer Networks
Biphase
Manchester: negative-to-positive transition represents 1 and a positive-to-negative transition represents 0.
Transition at the middle of the bit is used for both synchronization and bit representation.
Differential Manchester: a transition means 0 and no transition means 1.
Transition at the middle of the bit is used only for synchronization. Bit representation is shown by the inversion or noninversion at the beginning of the bit.
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11. CCE 484 - Computer Networks
Biphase
Manchester
Differential Manchester
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12. CCE 484 - Computer Networks
Bipolar
Uses three signal levels: positive, zero, and negative
Zero level represents binary 0
Positive and negative levels represent alternating 1s
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13. CCE 484 - Computer Networks
Bipolar Encoding
Bipolar
AMI
B8ZS
HDB3
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14. Alternate Mark Inversion (AMI)
Zero voltage represents binary 0.
Binary 1s are represented by alternating positive and negative signals.
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15. Bipolar 8-Zero Substitution (8BZS)
A convention adopted in North America to provide synchronization of long string of 0s
If eight or more consecutive 0s are encountered, enforce violations to the bipolar coding as follows:
if the previous polarity is positive:
if the previous polarity is negative:
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16. High-Density Bipolar 3 (HDB3)
Adopted in Europe and Japan.
Number of 1s since last substitution is odd
Number of 1s since last substitution is even
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