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Title: Data communication and networks chapter 10 error detection
Description: These notes are very help full for computer science stuents
Description: These notes are very help full for computer science stuents
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ERROR DETECTION AND
CORRECTION
By:
Inzamam Saleem
CYCLIC CODES
CYCLIC CODES
Cyclic Redundancy Check
Polynomials
Cyclic Code Encoder Using Polynomials
Cyclic Code Analysis
Advantages of Cyclic Codes
Other Cyclic Codes
Hardware Implementation
TYPES OF ERRORS
Single-bit error
Burst error
SINGLE-BIT ERROR
Whenever bits flow from one point to another, they are subject to
unpredictable changes because of interference
...
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
SINGLE-BIT ERROR
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
...
BURST ERROR
The number of bits affected depends on the data rate and
duration of noise
...
BURST ERROR
REDUNDANCY
The central concept in detecting or correcting errors is
redundancy
...
These redundant bits are added by the sender and removed by
the receiver
...
DETECTION VERSUS CORRECTION
The correction of errors is more difficult than the detection
...
The answer is a simple yes or no
...
A single-bit error is the same for us as a burst error
...
The number of errors and the size of the message are important
factors
...
CODING
Redundancy is achieved through various coding schemes
...
The receiver checks the relationships between the two sets of
bits to detect errors
...
We can divide coding schemes into two broad categories: block
coding and convolution coding
...
There are many uses for interleaving at the
system level, including:
Storage: As hard disks and other storage devices are used to store user and system data,
there is always a need to arrange the stored data in an appropriate way
...
CHUNK INTERLEAVING
Another way to achieve FEC in multimedia is to allow some small chunks to be
missing at the receiver
...
We can divide each packet into 5 chunks (normally the number is much larger)
...
In this case, each packet sent carries a chunk from
several original packets
...
COMBINING HAMMING DISTANCE AND INTERLEAVING
Hamming distance and interleaving can be combined
...
Then we interleave m rows and send the bits column by column
...
COMBINING HAMMING DISTANCE AND INTERLEAVING
Hamming distance and interleaving can be combined
...
Then we interleave m rows and send the bits column by
column
...
COMPOUNDING HIGH- AND LOW-RESOLUTION
PACKETS
Still another solution is to create a duplicate of each packet with a low-resolution
redundancy and combine the redundant version with the next packet
...
COMPOUNDING HIGH- AND LOW-RESOLUTION
PACKETS
If a packet is lost, we can use the low-resolution version from the next packet
...
In this method, if the last packet is lost, it cannot be recovered, but we use the low-resolution
version of a packet if the lost packet is not the last one
...
Title: Data communication and networks chapter 10 error detection
Description: These notes are very help full for computer science stuents
Description: These notes are very help full for computer science stuents