Question

Suppose internet data in hex is 99 f5 44 27 23 96 e3 4f. Calculate internet checksum.

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Answer 1

WHY DO WE NEED CHECKSUM?

Error
Error is a condition when the receiver’s information does not match with the sender’s information. During transmission the data gets corrupted due to the noise in the path or external disturabances , That means a 0 bit may change to 1 or a 1 bit may change to 0.

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.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.

SOME COMMON APPROACHES USED FOR ERROR DETECTION ARE AS FOLLOW:-

Some popular techniques for error detection are:
1. Simple Parity check
2. Two-dimensional Parity check
3. Checksum
4. Cyclic redundancy check

DOWN HERE IS AN EXAMPLE OF HOW CHECKSUM IS CALCULATED AT THE SENDER'S AND RECIVERS'S SIDE TO CHECK FOR ERROR:--

GENERALLY WE IMPLEMENT AN 8-BIT CHECKSUM ERROR HANDLING AND SO I HAVE SOLVED THE QUESTION:-

Checksum

In checksum what we generally do is first find the checksum of the data,complement the checksum at the sender's side and then add to the IP/TCP header of the packet.At the recivers end we again find out the checksum of the recived data and check if the checksum new +old checksum ==0 .

IF their sum turns out to be 0 ,then the data is correct else it is considered to be corrupted .

This is a diagram depicting how to find out the checksum at the senders and recivers side and then match them.

NOW IS THE HANDWRITTEN SOLUTION OF THE QUESTION:--

ANSWER:--