These slides explain more about types of errors in Data communication, issues of parity check , and redundancy . also it includes some solutions of questions based on data communication

1. DATA COMMUNICATION
NOTES

2. TABLE OF CONTENTS
 COVER PAGE………………………….slide 01
 NAMES OF PARTICIPANTS…………. slide 03
 TYPES OF ERRORS………………….. Slide 04
 REDUNDANCY………………………. Slide 05
 ERROR DETECTION AND CORRECTION slide 06

3. TYPES OF ERRORS
1) SINGLE BIT ERROR
The term single-bit error means that only 1 bit of a
given data unit (such as a byte, character, or packet) is
changed from 1 to 0 or from 0 to 1.

4. TYPES OF ERRORS cont…
BURST ERROR
The term burst error means that 2 or more bits in the
data unit have changed from 1 to 0 or from 0 to 1.

5. REDUNDANCY
The central concept in detecting or correcting errors.
 To be able to detect or correct errors, we need to
send some extra bits with our data.
 These redundant bits are added by the sender and
removed by the receiver.
 Their presence allows the receiver to detect or
correct corrupted bits.

6. ERROR DETECTION AND ERROR
CORRECTION
ERROR DETECTION
is the process of monitoring data transmission and
determining when errors have occurred. Error-
detection techniques neither correct errors nor identify
which bits are in error they indicate only when an
error has occurred.
ERROR CORRECTION
Is the process of recovering or removing errors in
transmitted signal of information. This is mainly done
at the receiver.

7. BLOCK CODING
 The message is divided into blocks
 Each block is k-bits size, called dataword add r
redundant bits to each block
 The resulting n-bit blocks are called codewords.
 n = k + r
 2^n – 2^k (illegal or invaild codewords)

8. BLOCK CODING cont……
 An error-detecting code can detect only the types of
errors for which it is designed; other types of errors
may remain undetected.

9. PARITY CHECK
Parity Check
The simplest error-detecting scheme is to append a
parity bit to the end of a block of data. A typical
example is character transmission, in which a parity
bit is attached to each 7-bit IRA character. The value of
this bit is selected so that the character has an even
number of 1s (even parity) or an odd number of 1s
(odd parity).

10. HAMMING DISTANCE
 Is the number of difference between the
corresponding bits. d(x,y)
 The minimum Hamming distance is the smallest
Hamming distance between all possible pairs in a set
of words.
 Any coding scheme needs at least three parameters

11. HAMMING DISTANCE cont…..
(i)Code word size n
(ii)Data word size k
(iii)d min
 The hamming distance between the sent and
received code words is the number of bits affected
 To guarantee the detection of up to s errors in all
cases, the minimum
 Hamming distance in a block code must be dmin= s
+ 1.

12. CYCLIC REDUNDANCY CHECKING
One of the most common, and one of the most
powerful, error-detecting codes is the cyclic
redundancy check (CRC), which can be described as
follows. Given a k-bit block of bits, or message the
transmitter generates an (n-k) bit sequence, known as
a frame check sequence (FCS), such that the resulting
frame, consisting of n bits, is exactly divisible by some
predetermined number. The receiver then divides the
incoming frame by that number and, if there is no
remainder, assumes there was no
Error.

13. CHECKSUM
 CHECKSUM is another relatively simple form of
redundancy error checking where each character has
a numerical value assigned to it. The characters
within a message are combined together to produce
an error-checking character (checksum), which can
be as simple as the arithmetic sum of the numerical
values of all the characters in the message.

14. FORWARD ERROR CORRECTION
Forward error correction (FEC) is the only error-
correction scheme that actually detects and corrects
transmission errors when they are received without
requiring a retransmission.
With FEC, redundant bits are added to the message
before transmission. When an error is
detected, the redundant bits are used to determine
which bit is in error