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