Anna University Coimbatore 2009 B.E Electronics

Single bit error: The term single bit fault means that only 1 bit of a provided data
unit (such as byte character/data unit or packet) is changed from one to 0 or from 0 to 1.
Burst error: Means that two or more bits in the data unit have changed from one to 0
from 0 to 1.
4. What is redundancy?
It is the fault detecting mechanism, which means a shorter group of bits or extra
bits may be appended at the destination of every unit.
5. List out the available detection methods.
There are four kinds of redundancy checks are used in data communication.
a) Vertical redundancy checks (VRC).
b) Longitudinal redundancy checks (LRC).
c) Cyclic redundancy checks (CRC).
d) Checksum.
6. Write short notes on VRC.
The most common and lowest expensive mechanism for fault detection is the
vertical redundancy check (VRC) often called a parity check. In this technique a
redundant bit called a parity bit, is appended to every data unit so, that the total number
of 0's in the unit (including the parity bit) becomes even.
7. Write short notes on LRC.
In longitudinal redundancy check (LRC), a block of bits is divided into rows and
a redundant row of bits is added to the whole block.
8. Write short notes on CRC.
The 3rd and most powerful of the redundancy checking techniques is the cyclic
redundancy checks (CRC) CRC is based on binary division. Here a sequence of
redundant bits, called the CRC remainder is appended to the end of data unit.
9. Write short notes on CRC generator.
A CRC generator uses a modulo-2 division.
° In the 1st step, the 4-bit divisor is subtracted from the 1st four bit of the
dividend.
° every bit of the divisor is subtracted from the corresponding bit of the
dividend without disturbing the next higher bit.
10. Write short notes on CRC checker.
A CRC checker functions exactly like a generator. After receiving the data
appended with the CRC it does the identical modulo-2 division. If the remainder is all 0's the
CRC is dropped and the data accepted. Otherwise, the received stream of bits is discarded
and the dates are resent.
11. provide the essential properties for polynomial.
A polynomial should be opted to have at lowest the subsequent properties.
a) It should not be
b) It should be divisible by(x+1).
12. describe checksum.
The fault detection method used by the higher layer protocol is called checksum.

Earning:   Approval pending.