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Comp 222-Telecommunications And Computers Question Paper
Comp 222-Telecommunications And Computers
Course:Bachelor Of Computer Science (It Telecommunication)
Institution: Kabarak University question papers
Exam Year:2011
KABARAK UNIVERSITY
UNIVERSITY EXAMINATION
2011 ACADEMIC YEAR
FOR THE DEGREE OF BACHELOR OF COMPUTER SCIENCE
COURSE CODE: COMP 222
COURSE TITLE: TELECOMMUNICATIONS AND COMPUTERS
STREAM: Y2S2
DAY: TUESDAY
TIME: 9.00 – 11.00 A.M.
DATE: 15/03/2011
INSTRUCTIONS:
Answer ALL questions in PART ONE and two questions from PART TWO.
Question One (30 Marks)
a. What is a transducer? Give one example of a transducer used in telecommunications.(2 marks)
b. A transmission medium has a signal to noise ratio of 1000 at its output. It can transmit
frequencies between 300 Hz and 3300 Hz. Calculate the maximum capacity of the medium in
bits per second. (2 marks)
c. An analog signal is digitized using pulse code modulation. The quantizer used uses 56
quantization levels. The resultant digital signal has a bit rate of 36 kilobits per second.
i. Calculate the rate at which the analog signal was sampled. (2 marks)
ii. If the analog signal has a bandwidth of 4000 Hz, determine if the resultant digital signal is
a true representation of the analog signal. (1 mark)
d. What is meant by a self synchronizing line code? How is synchronization implemented in
a line code? (2 marks)
e. Give two disadvantages of a residual direct current (DC) component in a line code. (2 marks)
f. Describe asynchronous serial transmission. (3 marks)
g. Which of the following line codes is suitable for;
Synchronous serial transmission
Asynchronous serial transmission
i. Return to zero level
ii. Return to zero invert
iii. Return to zero
iv. Manchester
v. Alternate mark inversion
Give an explanation for your answer. (6 marks)
h. Encode the following data
110010101010001101
Using;
i. Non return to zero invert code (2 marks)
ii. Manchester code (2 marks)
iii. Return to zero code (2 marks)
i. You are given a transmission medium that can transmit frequencies between 0 Hz and 10 KHz.
Design a full duplex system with a guard band of 600 Hz and using 64QAM as the digital
modulation technique. In the design calculate
i. The carrier signal frequency used for each direction of transmission (2 marks)
ii. The transmission rate in bits per second for each direction of transmission (2 marks)
Question Two (20 Marks)
a. Ten digital signals, each with a bit rate of 1600bps are time division multiplexed. The number
of bits per time slot is 32 bits. Calculate
i. Duration of a time slot (2 marks)
ii. Frame rate of the time division multiplexed signal. (2 marks)
b. Determine the frequency components of the output signal of the following filters if the input
signal contains frequency components between 200Hz and 1578Hz.
i. Low pass filter with a cutoff frequency of 600Hz (1 mark)
ii. High pass filter with a cutoff frequency of 800 Hz (1 mark)
iii. Band pass filter with cutoff frequencies of 400Hz and 1600Hz (1 mark)
c. Use the following information;
• Number of inputs = 450
• Number of outputs = 750
• Number of stages = 3
• Number of crossbar switches in stage one = 9
• Number of crossbar switches in stage two = 5
• Number of crossbar switches in stage three = 25
To design (and draw)a multistage crossbar switch and calculate the number of crosspoints that the
switch has (5 marks)
d. Use a diagram of a multistage crossbar switch to describe what is meant by blocking. (2 marks)
e. Using a diagram describe how the time slot interchanger (TSI) switch works. (3 marks)
f. Design and draw a diagram of a time-space-time (TST) multistage switch given the following
information.
i. Number of inputs = 40
ii. Number of outputs = 40
iii. Number of time division switches in first time stage = 4
iv. Number of time division switches in last stage = 4 (3 marks)
Question Three (20 Marks)
a. Briefly describe
i. Frequency division multiple access (2 marks)
ii. Code division multiple access (2 marks)
iii. Time division multiple access (2 marks)
b. Give two examples of communication networks that use the multiple access methods given
in (a) above. (2 marks
c. Describe the main advantage and the main disadvantage of controlled access methods as
compared to random access methods. (4 marks)
d. Describe the reservation access method. (3 marks)
e. Explain why digital transmission offers better signal quality than analog transmission.(3 marks)
f. Give two advantages of twisted pair cable as compared to coaxial cable. (2 marks)
Question Four (20 marks)
a. A burst of noise with duration of 0.00001 seconds occurs on a transmission medium which is
transmitting a digital signal at a rate of 10 Megabits per second. How many bits will be
affected by the noise burst? (1 mark)
b. Describe what is meant by the code rate and distance of an error correction scheme. Explain
the significance of these two terms and how they are related. (4 marks)
c. Using examples describe;
i. How the checksum error detection scheme works (3 marks)
ii. What type of errors (odd errors , even errors) can be detected by the checksum error
detection scheme (3 marks)
d. Calculate the cyclic redundancy check (CRC) of the following block of data
1000010101010000011111111
Using a divisor of 11011 (3 marks)
e. Use the information given below about the (7,4) hamming code to locate and correct the errors
in the following received bits.
i. 1010010 (1 mark)
ii. 1000010 (1 mark)
iii. 1101001 (1 mark)
Generator Matrix =
0 0 0 1 1 1 1
0 0 1 0 1 0 1
0 1 0 0 0 1 1
1 0 0 0 1 1 0
Parity Check Matrix =
0 1 1 1 0 0 1
1 1 0 1 0 1 0
1 0 1 1 1 0 0
f. Describe the Go back to N automatic repeat request method. (3 marks)
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