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Tlcm 211:Telecommunications Fundamentals March 2011 Question Paper
Tlcm 211:Telecommunications Fundamentals March 2011
Course:Bachelor Of Science In Telecommunications
Institution: Kabarak University question papers
Exam Year:2011
KABARAK UNIVERSITY
UNIVERSITY EXAMINATIONS
2010/2011 ACADEMIC YEAR
FOR THE DEGREE OF BACHELOR OF SCIENCE IN
TELECOMMUNICATIONS
COURSE CODE: TLCM 211
INSTRUCTIONS:
Answer ALL questions in PART ONE and THREE questions from PART TWO.
Question One (20 marks)
a. Explain using a diagram what is meant by the “energizing sequence” of an electro mechanical
crossbar switch, and why it is needed. (3 marks)
b. Explain using diagrams how the number of cross points in a crossbar switch can be reduced
while at the same time keeping it non blocking. (2 marks)
c. What does common control facilitate in a multi exchange telephone network? (2 marks)
d. How many group selector stages does a 6 digit Strowger switch have? Explain your answer.
(1 mark)
e. A time slot interchanger (TSI) switch has 10 inputs and 10 outputs. Each of the inputs to
the switch is transmitting at a rate of 5000 bps. The time slot duration is 10 milliseconds.
Calculate
i. The minimum number of memory locations required on the TSI
ii. The size of each memory location. (2 marks)
f. A TST (time-space-time) multistage switch has the following characteristics
100 inlets and 100 outlets
10 switches in the first stage (time stage)
One crossbar switch in the second stage (space stage)
10 switches in the third stage (time stage)
i. Calculate the percentage reduction in cross points as compared to if a single crossbar
switch was used (2 marks)
ii. Calculate the percentage reduction in time delay as compared to if a single time slot
interchanger switch was used. (2 marks)
g. Using a diagram explain how a time division multiplex (TDM) bus switch works (2 marks)
h. What is the advantage of using intelligent networks on a telecommunication network? (2 marks)
i. What is a Softswitch? How is the Softswitch mainly used in telecommunication networks?
(2 marks)
Question Two (10 marks)
a. Give the main reason why implementation of time division multiplexing is more difficult
than frequency division multiplexing. (1 mark)
b. 10 digital signals, each with a bit rate of 2000 bps, are time division multiplexed. The number
of bits per timeslot is 32 bits. 8 framing bits are added to each frame. Calculate the bit rate
of the time division multiplexed signal (2 marks)
c. What is meant by bit padding and when is it used in time division multiplexing. (1 mark)
d. An analog signal is sampled every 10 micro seconds. It is then quantized using a quantizer
with 70 quantization levels.
i. Calculate the bit rate of the resultant digital signal. (2 marks)
ii. What is meant by quantization noise? (1 mark)
iii. How can the accuracy and quality of the resultant digital signal be improved? (1 mark)
e. How many analog signals each with frequency components between 345Hz and 899Hz
can be frequency division multiplexed using a guard band of 56Hz on a transmission
medium with a bandwidth of 10000Hz? (2 marks)
Question Three (10 marks)
a. Describe how twisted pair technology helps in reducing noise affecting an electrical signal
transmitted on it. (1 mark)
b. Why is coaxial cable more suitable than twisted pair cable in connecting a radio transmitter
and its antenna? (1 mark)
c. Describe two uses of the cladding found in a fiber optic cable. (1 mark)
d. Describe two advantages of wavelength division multiplex (1 mark)
e. Using energy band diagrams explain the following processes that occur in a laser diode.
i. Photon absorption
ii. Spontaneous emission
iii. Stimulated emission (3 marks)
f. Explain why laser diodes are referred to as threshold devices? (1 mark)
g. Using a diagram explain the operation of an avalanche photo diode. (2 marks)
Question Four (10 marks)
a. Describe
i. How ionospheric waves are propagated
ii. What is meant by the skip distance and skip zone in ionospheric wave propagation.
(2 marks)
b. In wireless communications what is meant by
i. Omni-directional and uni-directional wave propagation. (1 mark)
ii. How do the above affect the positioning of transmitting and receiving antennas? (1 mark)
c. Describe
i. Two advantages of microwave transmission as compared to radio wave transmission.
(1 mark)
ii. Two advantages of radio wave transmission as compared to microwave wave transmission.
(1 mark)
d. In a cellular network what is the function of a;
i. Base transceiver subsystem (1 mark)
ii. Base controller subsystem (1 mark)
e. Describe how a base station can be sectorised. (1 mark)
f. Describe how capacity is increased on a cellular network even though only limited frequency
bands are available for transmission. (1 mark)
Question Five (10 marks)
a. What is the minimum number of geosynchronous satellites needed to provide “global coverage”.
How are they positioned? (1 mark)
b. In relation to a geosynchronous satellite network;
i. Why is it necessary to point a ground (earth) station?
ii. Describe the two angles needed for pointing the earth station
iii. What three parameters are required to calculate these two angles? (3 marks)
c. Briefly explain how automatic repeat request error control schemes work. Why are they
not suitable for satellite communications, and which error control scheme is suitable for
satellite communications?. (2 marks)
d. Describe the four main functions perfumed by a VOIP codec. (2 marks)
e. The quality of service of a VOIP call can be adversely affected by congestion on an IP network.
Describe four methods that can used to improve the quality of VOIP calls on a private network.
(2 marks)
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