1. CS433 - Data Communication and 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
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

2. CS433 - Data Communication and Computer Networks
Types of Encoding
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

3. Digital-to-Digital Encoding
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

4. CS433 - Data Communication and Computer Networks
Unipolar
Uses only one level of value (polarity)
Pros: simple and inexpensive
Cons: DC component direct current component with zero frequency) and synchronization (occur whenever the data stream includes a long uninterrupted series of 1’s and 0’s the solution is another line carrying a clock pulse allow the receiver to resynchronize its timer but cost is high)
Digital Transmission systems work by sending voltage pulses along a medium
Polarity: weather the pulse is negative or positive 1’s are positive values 0’s are 0 values
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

5. CS433 - Data Communication and Computer Networks
Polar
Uses two levels of amplitude
Each bit consists of both positive and negative voltage
Dc component is totally eliminated
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

6. Non-Return to Zero (NZR)
The level of the signal is always either positive or negative
NRZ-Level : the level of the signal is dependent on the state of the bit (ex. +  1 and –  0) a problem arises when long stream of 0’s and 1’s in the data so the receiver receives a continuous voltage and cannot determine number of bits its clock cannot synchronize with sender clock.
NRZ-Inverted: The signal is inverted if a 1 is encountered supirur to
Less DC-component and more synchronization than Unipolar
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

7. CS433 - Data Communication and Computer Networks
NRZ
NRZ-L
NRZ-I
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

8. CS433 - Data Communication and 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
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

9. CS433 - Data Communication and Computer NetworksRZ
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

10. CS433 - Data Communication and 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.
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

11. CS433 - Data Communication and Computer Networks
Biphase
Manchester
Differential Manchester
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

12. CS433 - Data Communication and Computer Networks
Bipolar
Uses three signal levels: positive, zero, and negative
Zero level represents binary 0
Positive and negative levels represent alternating 1s
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

13. CS433 - Data Communication and Computer Networks
Bipolar Encoding
Bipolar
AMI
B8ZS
HDB3
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

14. Alternate Mark Inversion (AMI)
Zero voltage represents binary 0.
Binary 1s are represented by alternating positive and negative signals.
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

15. Digital signal encoding formats
Unipolar
NRZL
NRZI RZ
Manchester
Differential Manchester
Bipolar-AMI
Pseudoternary
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

16. 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:
Dr. Shawakfa
CS433 - Data Communication and Computer Networks

17. 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
Dr. Shawakfa
CS433 - Data Communication and Computer Networks