PART A
PART C (JUN 2018)
QUESTION 1
a) Describe cyclic codes in error detection and correction. (4 marks)
-
Cyclic codes are a type of linear block code that has an additional
characteristic. When a code word is cyclically shifted (rotated) in a cyclic
code, the result is another code word.
b) Explain the concepts of redundancy. (4 marks)
-
Redundancy is a process through which additional or alternate instances
of network devices, equipment and communication mediums are installed
within network infrastructure. It is a method for ensuring network
availability in case of a network device or path failure and unavailability.
As such, it provides a means of network failover.
c) Given a dataword of 1010 and a divisor of 1011. By using Cyclic Redundancy Check
(CRC), show the process at the sender side in generating the codeword and also prove
the syndrome generated at the receiver assuming that there are no data corruption
during transmission. (10 marks)
- Sender site
1011
1
0
0
1
1
0
1
0
1
0
1
1
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
1
0
1
1
0
1
1
Codeword: 10010011
Syndrome: 011
-
Receiver site
0
0
0
1011
1
0
0
1
1
0
1
0
1
0
1
1
0
0
1
0
0
0
0
0
0
1
0
1
0
0
0
0
1
0
1
0
1
0
1
1
0
0
0
0
1
1
Codeword: 10010000
No syndrome
PART C (JAN 2018)
QUESTION 1
a) Explain the process of preparing the checksum for error checking. (5 marks)
-
A checksum is the outcome of running an algorithm, called a
cryptographic hash function, on a piece of data, usually a single file.
Comparing the checksum that is generated from the version of the file,
with the one provided by the source of the file, helps ensure that your copy
of the file is genuine and error free. A checksum is also sometimes called
a hash sum and less often a hash value, hash code, or simply a hash.
b) Give THREE (3) common redundancy methods in error detection and correction. (3
marks)
-
Three types of redundancy methods in error detection and correction are Parity
Check, Cyclic Redundancy Check(CRC) and Checksum.
PART C (JUL 2017)
QUESTION 1
a) Define the meaning of burst error in network communication. (2 marks)
b) Internet has been using a 16-bit checksum for error detection. Determine the steps of
calculating the internet checksum on the sender’s side before the data is sent to the
receiver. (5 marks)
c) Given a dataword 1101 and a divisor of 1011. Show the process at the sender in
generating the codeword and prove the syndrome at receiver using Cyclic Redundancy
Check (CRC). (8 marks)
- Sender site
1101
1
0
0
1
1
1
0
0
1
1
0
1
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
1
1
0
1
1
0
1
Codeword: 1001101
Syndrome: 101
0
0
0
-
Receiver site
1011
1
0
0
1
1
1
0
0
1
1
0
1
0
0
1
0
0
0
0
0
0
1
0
1
0
0
0
0
1
0
1
1
1
1
0
1
0
0
0
0
1
1
Codeword: 1001000
No syndrome
PART C (DEC 2016)
QUESTION 2
a) Explain burst error in network communication. (2 marks)
b) Describe cyclic codes in error detection and correction. (4 marks)
●
Cyclic codes are a type of linear block code that has an additional
characteristic. When a code word is cyclically shifted (rotated) in a cyclic
code, the result is another code word.
c) One host intended to send a list of five sets of four bit numbers to a receiver. The set of
numbers is (10, 2, 8, 11, and 5). Show the process to find the checksum at the sender
and receiver with the details of wrapping (if any) and complementing process. (9 marks)