DATA
COMMUNICATION
Lecture-33
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Error, Detection Techniques - Data Communication - Lecture Slides, Slides of Data Communication Systems and Computer Networks
Error Detection Techniques, Types of Errors, Redundancy, Types of Redundancy Checks, Single Bit Error, Vertical Redundancy Check, Performance of VRC are points you can learn these slides.
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DATA
COMMUNICATION
Lecture-
Recap of Lecture 32
T-Lines in Analog Transmission
Fractional T-Lines
E-Lines
Fiber To The Curb (FTTC)
Error Detection and Correction
Types of Errors
Single-Bit Error
Only one bit of a given data unit is changed
The least likely type of error in serial transmission
Single-bit error can happen in parallel transmission
Burst Error
Two or more bits in the data unit are changed
Most likely to happen in a serial transmission
Number of bits affected depends on the data rate and duration of noise
Burst Error
Redundancy
Detection Methods
Four types of redundancy checks
VRC, LRC, and CRC: For use in the data link layer
Checksum: Used by upper layers
Vertical Redundancy Check
Often called a Parity Check
A parity bit is added to every data unit
Even-parity checking or odd-parity checking
Vertical Redundancy Check
Example 9.
Suppose “world” is received by the receiver without being corrupted:
Receiver counts the 1’s and passes it 1110111 w 1110111 0 6 1101111 o 1101111 0 6 1110010 r 1110010 0 4 1101100 l 1101100 0 4 1100100 d 1100100 1 4
Example 9.
Suppose “world” is received by the receiver corrupted:
Receiver counts the 1’s and rejects it 1110111 w 1111111 0 7 1101111 o 1101111 0 6 1110010 r 1110110 0 5 1101100 l 1101100 0 4 1100100 d 1100100 1 4
Performance of VRC
We have an Even Parity data unit where the total number of 1’s including the parity bit is ‘6’ : 1000111011
If 3 bits change value resulting parity will be odd and an error will be detected: 1111111011: 1’s = 9
Performance of VRC
If 2 bits change value resulting parity will still be even and error will not be detected: 1110111011: 1’s = 8
VRC cannot detect errors when the total number of bits changed are even