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

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

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

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 0 1 0 0 1 1 1 Dr. Shawakfa CS433 - Data Communication and Computer Networks

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

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

CS433 - Data Communication and Computer Networks NRZ 0 1 0 0 1 1 1 0 NRZ-L NRZ-I Dr. Shawakfa CS433 - Data Communication and Computer Networks

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

CS433 - Data Communication and Computer Networks RZ 0 1 0 0 1 1 1 0 Dr. Shawakfa CS433 - Data Communication and Computer Networks

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

CS433 - Data Communication and Computer Networks Biphase 0 1 0 0 1 1 1 0 Manchester Differential Manchester Dr. Shawakfa CS433 - Data Communication and Computer Networks

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

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

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 Dr. Shawakfa CS433 - Data Communication and Computer Networks

Digital signal encoding formats 0 1 0 0 1 1 0 0 0 1 Unipolar NRZL NRZI RZ Manchester Differential Manchester Bipolar-AMI Pseudoternary Dr. Shawakfa CS433 - Data Communication and Computer Networks

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

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 Dr. Shawakfa CS433 - Data Communication and Computer Networks