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 CCE 484 - Computer Networks 5/22/2019

Types of Encoding 5/22/2019 CCE 484 - Computer Networks

Digital-to-Digital Encoding CCE 484 - Computer Networks 5/22/2019

Unipolar Uses only one level of value (polarity) Pros: simple and inexpensive Cons: DC component and synchronization 0 1 0 0 1 1 1 CCE 484 - Computer Networks 5/22/2019

Polar Uses two levels of amplitude CCE 484 - Computer Networks 5/22/2019

Non-Return to Zero (NRZ) 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) NRZ-Inverted: The signal is inverted if a 1 is encountered Less DC-component and more synchronization than Unipolar CCE 484 - Computer Networks 5/22/2019

NRZ 0 1 0 0 1 1 1 0 NRZ-L NRZ-I CCE 484 - Computer Networks 5/22/2019

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 CCE 484 - Computer Networks 5/22/2019

RZ 0 1 0 0 1 1 1 0 CCE 484 - Computer Networks 5/22/2019

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. CCE 484 - Computer Networks 5/22/2019

Biphase 0 1 0 0 1 1 1 0 Manchester Differential Manchester 0 1 0 0 1 1 1 0 Manchester Differential Manchester CCE 484 - Computer Networks 5/22/2019

Bipolar Uses three signal levels: positive, zero, and negative Zero level represents binary 0 Positive and negative levels represent alternating 1s CCE 484 - Computer Networks 5/22/2019

Bipolar Encoding Bipolar AMI B8ZS HDB3 CCE 484 - Computer Networks 5/22/2019

Alternate Mark Inversion (AMI) Zero voltage represents binary 0. Binary 1s are represented by alternating positive and negative signals. 0 1 0 0 1 1 1 0 CCE 484 - Computer Networks 5/22/2019

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: 000+-0-+ if the previous polarity is negative: 000-+0+- CCE 484 - Computer Networks 5/22/2019

High-Density Bipolar 3 (HDB3) Adopted in Europe and Japan. + 0 0 0 0 - 0 0 0 0 + 0 0 0 + - 0 0 0 - Number of 1s since last substitution is odd + 0 0 0 0 - 0 0 0 0 + - 0 0 - - + 0 0 + Number of 1s since last substitution is even CCE 484 - Computer Networks 5/22/2019