University of Anbar
College of Engineering computer network
Dept. of Electrical Engineering adnan salih
ERRORS, DETECTION & CORRECTION
OBJECTIVE
Understand error classification
Types of error
Understand concept redundancy
Hamming code concept
CRC concept
Checksum technic
7.1 INTRODUCTION: Errors in the data are basically caused due to the various
impairments that occur during the process of transmission. When there is an imperfect
medium or environment exists in the transmission it prone to errors in the original data.
Errors can be classified as follows: Attenuation Noise Distortion
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7.2 ERRORS CLASSIFICATION Following are the categories of the errors: 1.
Attenuation: As signal travels through the medium, its strength decreases as distance
increases, as shown in the figure 7.1, the example is voice, it becomes weak over the
distance and loses its contents beyond a certain distance. As the distance increases
attenuation also increases.
Strength Distance Figure 7.1 2. Noise: Noise is defined as an unwanted data. When some
electromagnetic signal gets inserted during the transmission, it is generally called as a
Noise. Due to Noise it is difficult to retrieve the original data or information. 3. Distortion:
When there is an interference of the different frequencies who travel across the medium
with the different speed, Distortion occurs. So it is important to have a space (guard space)
between the different frequencies. 7.3 TYPES OF ERRORS: If the signal comprises of
binary data there can be two types of errors which are possible during the transmission: 1.
Single bit errors 2. Burst Errors
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Figure 7.2 1. Single-bit errors: In single-bit error, a bit value of 0 changes to bit value 1 or
vice versa. Single bit errors are more likely to occur in parallel transmission. Figure 7.3 (a)
2. Burst errors: In Burst error, multiple bits of the binary value changes. Burst error can
change any two or more bits in a transmission. These bits need not be adjacent bits. Burst
errors are more likely to occur in serial transmission. Figure 7.3 (b)
Original data Received data
0
1
0
0
1
1
0
1
1
1
0
0
0
0
1
1
0
1
1
1
Figure 7.3 (a) Single bit error
Original data Received data
0
1
0
0
1
1
0
1
1
1
