Anna University Coimbatore 2009 B.E Electronics

Checksum is based on the concept of redundancy.
13. elaborate the steps followed in checksum generator?
The sender follows these steps
a) The units are divided into k parts every of n bits.
b) All parts are added together using 2's complement to get the sum.
c) The sum is complemented and become the checksum.
d) The checksum is sent with the data.
14. List out the steps followed is checksum checker side.
The receiver must follow these steps
a) The unit is divided into k part every of n bits.
b) All parts are added together using 1's complement to get the sum.
c) The sum is complemented.
d) If the outcome is zero.
15. Write short notes on fault correction.
It is the mechanism to accurate the errors and it can be handled in two ways.
a) When an fault is discovered, the receiver can have the sender
retransmit the entire data unit.
b) A receiver can use an fault correcting coder, which automatically
corrects certain errors.
16. Mention the kinds of fault correcting methods.
There are two error-correcting methods.
a) Single bit fault correction
b) Burst fault correction.
17. What is the purpose of hamming code?
A hamming code can be designed to accurate burst errors of certain lengths. So the
simple strategy used by the hamming code to accurate single bit errors must be redesigned
to be applicable for multiple bit correction.
18. describe flow control.
Flow control refers to a set of procedures used to restrict the amount of data. The
sender can send before waiting for acknowledgment.
19. What is a buffer?
every receiving device has a block of memory called a buffer, reserved for storing
incoming data until they are processed.
20. Mention the categories of flow control.
There are two methods have been developed to control flow of data across
communication links.
a) Stop and wait- send 1 from at a time.
b) Sliding window- send several frames at a time.
21. What is the function of stop and wait flow control?
In this method, the sender sends 1 frame and waits for an acknowledgement
before sending.
22. Mention the advantage and disadvantage of stop and wait flow control.
Advantage: simplicity
Disadvantage: inefficiency.
23. describe ARQ.
fault control in the data link layer is based on Automatic repeat request (ARQ),

Earning:   Approval pending.