COMPUTER NETWORK - UNIT IV
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Error :- An error occurs when the output information does not match the input information.
The interfaces can change the shape of a signal and such changes can alter the meaning
of data.
An error is a situation when data received at the destination ma...
An error occurs when the output information does not match the input information.
The int erfaces can change t he shape of a signal and such changes can alt er t he meaning
of data.
An error is a sit uat ion when data received at t he dest inat ion machine is not the same as
data t hat is actually sent by t he source machine.
Types of Errors
Basically, t here are two t ypes of errors t hat can occur during t he transmission of data.
The t ypes of errors are as follows.
o Single Bit Error: The term single bit error means t hat only one bit of a data unit is
changed from 1 to 0 or from 0 to 1.
o Burst Error: The term burst error means t he two or more two bit s of t he data unit is
changed from 1 to 0 or vice versa.
There may be three types of errors:
Single bit error
In a frame, there is only one bit, anywhere though, which is corrupt.
Multiple bits error
Frame is received with more than one bits in corrupted state.
Burst error
Frame contains more than1 consecutive bits corrupted.
Error control mechanism may involve two possible ways:
Error detection
Error correction
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, COMPUTER NETWORK - UNIT IV
Error Detection
When a message is sent, it may be jumbled by noise or the data may be damaged.
To avoid this, we employ error-detecting codes, which are bits of extra data appended to a digital
message to assist us detect whether an error occurred during transmission.
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 ensures reliable delivery of data across vulnerable networks.
The oldest method of error correction involves using parity. It works by adding an additional bit to each
character word transmitted.
The state of the bit is determined by a number of factors such as the type of parity and the number of
logic-one bits in the data character.
Error Detecting Codes (Implemented either at Data link layer or Transport Layer of OSI Model)
Whenever a message is transmitted, it may get scrambled by noise or data may get corrupted.
To avoid this, we use error-detecting codes which are additional data added to a given digital message
to help us detect if any error has occurred during transmission of the message.
Basic approach used for error detection is the use of redundancy bits, where additional bits are added
to facilitate detection of errors.
Some popular techniques for error detection are:
1. Simple Parity check
2. Two-dimensional Parity check
3. Checksum
4. Cyclic redundancy check
1. Simple Parity check : -
It is also known as a parity check.
It has a cost-effective mechanism for error detection.
In this technique, the redundant bit is known as a parity bit. It is appended for every data unit. The
total number of 1s in the unit should become even, which is known as a parity bit.
This scheme makes the total number of 1’s even, that is why it is called even parity checking.
2. Two-dimensional Parity check
Parity check bits are calculated for each row, which is equivalent to a simple parity check bit.
Parity check bits are also calculated for all columns, then both are sent along with the data.
At the receiving end these are compared with the parity bits calculated on the received data.
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