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Telecommunications And Computers Question Paper
Telecommunications And Computers
Course:Bachelor Of Computer Science (It Telecommunication)
Institution: Kabarak University question papers
Exam Year:2010
Page 1 of 4
KABARAK UNIVERSITY
UNIVERSITY EXAMINATIONS
2010/2011 ACADEMIC YEAR
FOR THE DEGREE OF BACHELOR OF COMPUTER SCIENCE
COURSE CODE: COMP 222
COURSE TITLE: TELECOMMUNICATIONS AND
COMPUTERS
STREAM: Y2S2
DAY: TUESDAY
TIME: 2.00 – 4.00 P.M.
DATE: 07/12/2010
INSTRUCTIONS:
• Answer ALL the questions in PART ONE and any TWO questions in PART TWO.
PLEASE TURNOVER
Page 2 of 4
PART ONE
QUESTION ONE (30 MARKS)
a. Describe three impairments that a signal undergoes as it is transmitted along a
transmission medium (3 marks)
b. Describe three advantages that digital transmission has over analog transmission
(3 marks)
c. In pulse code modulation;
i. How can the digital reproduction of an analog signal be improved with regard to
precision and accuracy? (2 marks)
ii. What is meant by the term quantization noise? (1 marks)
d. An analog signal with frequency components between 300 Hz and 3400 Hz is sampled
at a rate of 4000 samples per second. It is then quantized with a quantizer using 64
quantization levels. The quantized samples are then binary encoded.
i. Calculate the Nyquist sampling rate of the analog signal (1 mark)
ii. Calculate the bit rate of the resultant digital signal. (2 marks)
e. What are the two main disadvantages of the unipolar line coding scheme. (2 marks)
f. Briefly describe
i. Return to zero code (2 marks)
ii. Manchester code (2 marks)
g. Give one disadvantage of return to zero code as compared to Manchester code
(2 marks)
h. Describe
i. Quadrature amplitude modulation (4 marks)
ii. 4PSK (phase shift keying) (4 marks)
i. A transmission medium has a bandwidth of 3400 Hz. Calculate the maximum bit rate
achievable on the medium if FSK, using frequencies 1700 Hz and 2400 Hz for
modulation is used. (2 marks)
Page 3 of 4
PART TWO
QUESTION TWO (20 MARKS)
a. Describe multiplexing and demultiplexing. What is the main advantage of using these
techniques? (3 marks)
b. Five signals have the following bit rates.
Signal 1 240 bps
Signal 2 720 bps
Signal 3 480 bps
Signal 4 240 bps
Signal 5 960 bps
The signals are time division multiplexed. Calculate the number of time slots per frame
and the duration of a frame given that 6 bits are transmitted per timeslot. (3 marks)
c. How many signals, each with a bandwidth of 770 Hz, can be frequency division
multiplexed using a guard band of 40 Hz onto a transmission link with a bandwidth of
11500 Hz. (2 marks)
d. Name the two main circuit switching techniques. (2 mark)
e. Using a diagram describe how a time slot interchanger switch works. (4 marks)
f. A multistage crossbar switch is designed using the following information.
• 50 inputs and 50 outputs
• 3 stages
• 5 crossbar switches in the first stage
• 3 crossbar switches in the second stage
• 5 crossbar switches in the third stage
Calculate the number of crosspoints the multistage switch has? (4 marks)
g. Describe the main disadvantage of a multistage crossbar switch (2 marks)
Question Three (20 marks)
a. Explain what the number of bits affected by a burst error depends on. (3 marks)
b. Explain why the checksum error detection method does not detect all errors involving
even number of bits. (3 marks)
c. What is the code rate and distance for the simple parity check error detection scheme?
(2 marks)
Page 4 of 4
d. Two communicating devices A and B communicate over a noisy transmission medium.
The use the (7, 4) hamming code for error correction. Device B receives the following
data from device A which is transmitted from left to right (first bit to be received is
binary 1).
0010101000110110000001101111
Determine if any errors occurred during transmission. Use the following information
about the (7,4) hamming code. (6 marks)
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
e. Describe the stop and wait ARQ method (3 marks)
f. Describe two disadvantages of the stop and wait ARQ method. (3 marks)
QUESTION FOUR (20 MARKS)
a. What is the difference between random access and controlled access methods?
(3 marks)
b. Describe the
i. ALOHA multiple access method. (3 marks)
ii. Token passing access method (3 marks)
c. Describe the composition of;
i. Coaxial cable
ii. Unshielded twisted pair cable (3 marks)
d. Describe three advantages of fiber optic cable as compared to coaxial cables
(3 marks)
e. What are the two main disadvantages of satellite communications? (2 marks)
f. Name the three random access methods that are used in cellular communication
(3 marks)
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