Chapter 6

Multiplexing and

Error Detection/Correction

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By Dr.Sukchatri P.

Contents

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•Multiplexing• Many to one/one to many• Types of multiplexing• Telephone system•Error Detection/Correction• Types of Errors• Detection• Correction

Multiplexer/Demultiplexer

Multiplexer/Demultiplexer

Multiplexing VS No Multiplexing

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Catagories of multiplexing

Type of Multiplexer

Frequency Division Multiplex (FDM)

Time Division Multiplex (TDM)

FDM Multiplexing process, Time domain

FDM Multiplexing process, Frequency domain

FDM demultiplexing process, time domian

FDM demultiplexing, frequency domain

Time-Division Multiplexing (TDM)

Synchronous TDM

Synchronous TDM, multiplexing process

Synchronous TDM, demultiplexing process

Framing bits

Data rate calculation for frames

Asynchronous TDM

Examples of asynchronous TDM frames

A.Case 1 : only three lines sending data

Examples of asynchronous TDM frames

B.Case 2 : only four lines sending data

C. Case 3 : all five lines sending data

Examples of asynchronous TDM frames

Multiplexing and inverse multiplexing

Telephone network

Catagories of Telephone service

Catagories of analog services

Analog switched service

Analog leased service

Analog hierarchy

Categories of Digital services

Switched/56 services

DDS services (Digital Data Service)

DSU : Digital Service Unit

DS hierarchy (Digital Signal)

T-1 line for multiplexing telephone lines

PCM: Plus Code Modulation :> convert analog-digital

T-1 frame structure

Fractional T-1 line

DSU : Digital Service UnitCSU : Channel Service Unit

Types of errors

Error Detection and Correction

Single-bit error

Multiple-bit error

Burst error of length five

Redundancy

Detection methods

Even parity VRC concept

Longitudinal Redundancy Check (LRC)

VRC and LRC

Cyclic Redundacy Check (CRC)

CRC generator and checker

Binary division in a CRC generator

Polynomial

A polynomial representing a divisor

Standard polynomials

Checksum

Data unit and checksum

Error Correction

Data and redundancy bits

Positions of redundancy bits in Hamming code

Redundancy bits calculation : Hamming Code

Example of redundancy bit calculation

Single-bit error

Error detection using Hamming code

Questions/Answers