Post on 21-Mar-2017
WELCOME
DETECTION
Presented By
Anika OhabID:142-15-3568
Abul HasnathID:142-15-3532
Shahinur Rahman ID: 142-15-3606
Umme HabibaID: 142-15-3677
Introduction
kinds
redundancy
Block coding
Parity check
LRC
CRC
checksum
Contents
ERROR DETECTION
In networking, error detection refers to the techniques used to detect noise or other impairments introduced into data while it is transmitted from source to destination.
Error detection minimizes the probability of
passing incorrect frames to the destination, known as undetected error probability
Types of Error
Error
Burst Error
Single-Bit
Error
If the signal is carrying binary encoded data, such changes can alter the meaning of the data. These errors can be divided into two types-
In a single-bit error, only one bit in the data unit has changed.
Note:
Single-Bit Error
A burst error means that 2 or more bits in the data unit have changed.
Note:
Burst Error
Error detection uses the concept of redundancy, which means adding
extra bits for detecting errors at the destination.
Redundancy
Redundancy
Popular techniques are:
Block Coding
Parity Check
LONGITUDINAL REDUNDANCY CHECK
Cyclic Redundancy Check (CRC)
Checksum
Block coding
Data Words
CodeWards
00 000
01 011
10 101
11 110
k=2,n=3
Simple Parity Checking
Even Parity:1 is added to the block if it contains an odd number of 1’s and 0 is added if it contains an even number of 1’s.
Even-parity concept
Two-dimensional parity
Simple parity check can detect all single-bit errors. It can detect burst
errors only if the total number of errors in each data unit is odd.
Note:
LONGITUDINAL REDUNDANCY CHECKLRC
LRC 10101010
Data plus LRC
11100111 11011101 00111001 10101001
10101001001110011101110111100111
11100111 11011101 00111001 10101001 10101010
CRC encoder and decoder
The last error detection method we discuss here is called the checksum. The checksum is used in the Internet by several protocols although not at the data link layer.
However, we briefly discuss it here to complete our discussion on error checking.
Checksum
We can make the job of the receiver easier if we send the negative (complement) of the sum, called the checksum.
In this case, we send (7, 11, 12,0,6, -36). The receiver can add all the numbers received (including the checksum).
If the result is 0, it assumes no error; otherwise, there is an error.
Checksum
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