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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