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Telecommunications Question Paper
Telecommunications
Course:Bachelor Of Science In Information Technology
Institution: Kca University question papers
Exam Year:2010
UNIVERSITY EXAMINATIONS: 2010/2011
FIRST YEAR STAGE EXAMINATION FOR THE DEGREE OF BACHELOR
OF SCIENCE IN INFORMATION TECHNOLOGY
BIT 4302: TELECOMMUNICATIONS
DATE: DECEMBER 2010 TIME: 2 HOURS
INSTRUCTIONS: Answer question ONE and any other TWO questions
QUESTION ONE
a) Explain briefly why optical fiber cable has greater data carrying capacity than copper-based media.
[3 Marks]
b) “Modern business operations will be damaged substantially in the absence of telecommunications
facilities”. Support this statement. [5 Marks]
c) A T1 carrier can support 24 simultaneous voice calls. Show that the aggregate data rate of the T1
carrier is 1.544 Mbps. [7 Marks]
d) Briefly compare and contrast GEO and LEO satellites [4 Marks]
e) Radio antennas often work best when the diameter of the antenna is equal to the wavelength of the
radio wave. Reasonable antennas range from 1 cm to 5 meters in diameter. What frequency range
does this cover? [5 Marks]
f) “Multiple access” is a phrase commonly used with communication systems. Define multiple access
and differentiate between the following types of multiple access: FDMA and TDMA. [6 Marks]
QUESTION TWO
a) With the aid of a simple diagram, show the basic structure of the Public Switched Telephone
Network (PSTN) and state the function of each component highlighted. [8 Marks]
2
b) Show the basic structure of international telephone numbers. [2 Marks]
c) A simple telephone system consists of two end offices and a single toll office to which each end
office is connected by a 1-MHz full-duplex trunk. The average telephone is used to make four calls
per 8-hour workday. The mean call duration is 6 min. Ten percent of the calls are long-distance
(i.e., pass through the toll office). What is the maximum number of telephones an end office can
support? (Assume 4 kHz per circuit.) [10 Marks]
QUESTION THREE
a) A switching network could be packet switched or circuit switched. Highlight the fundamental
features of each type of switching network. [8 Marks]
b) Fig. Q3(b) below shows time division multiplexing (TDM) frames as used in the GSM
communications standard. GSM uses a frame structure in which each frame consists of time slots,
each time slot contains 156.25 bits, and data are transmitted at 270.833 kb/s over the channel. The
data carried can be circuit switched or packet switched.
890.2 MHz
890.4 MHz
914.4 MHz
935.2 MHz
935.4 MHz
959.8 MHz
1
2
124
1
2
124
Base
To
Mobile
Channels
Mobile
To
Base
channels
TDM Frame Channel
Fig. Q3(b).
Frequency
Time
Find:
i. The time duration of a bit
ii. The time duration of a slot
iii. The time duration of a frame [6 Marks]
3
c) Compare the delay in sending an x-bit message over a k-hop path in a circuit-switched network and
in a (lightly loaded) packet-switched network. The circuit setup time is s sec, the propagation delay
is d sec per hop, the packet size is p bits, and the data rate is b bps. Under what conditions does the
packet network have a lower delay? [6 Marks]
QUESTION FOUR
a) Mobile phone communications networks have been established rapidly over the last two decades
and significant developments continue to emerge in the sector.
i. Give your understanding of a 2G mobile phone network [2 Marks]
ii. Show a well-labeled diagram that represents the basic architecture of the GSM-based 2G
mobile phone network. [4 Marks]
iii. Give a function for each principal database component in the basic GSM architecture.
[4 Marks]
b) In the 2G mobile phone network, a user engaged in a conversation has an outgoing message on one
channel in the uplink band and an incoming message on another channel in the downlink band.
i. State the uplink frequency band, downlink frequency band, channel bandwidth and the number of
conversations per channel for the GSM900 system used in Kenya. [4 Marks]
ii. A user is communicating on channel 890.2 MHz uplink channel. Determine the downlink channel.
[2 Marks]
iii. State how the access part of a mobile phone network differs from the access loop of the public
switched telephone network (PSTN). [2 Marks]
QUESTION FIVE
a) Fig. Q5 shows a typical Integrated Services Digital Network (ISDN) setup:
4
2 wires to central office
(local loop)
TE2 TA
TE1
R interface
S interface U interface
S NT2 T NT1 U
Service p rovider
network
R
T interface
Fig. Q5. ISDN Elements
i. State FOUR benefits of bringing digital connectivity through ISDN to the local site. [4 Marks]
ii. State TWO disadvantages of ISDN as a WAN design solution. [2 Marks]
iii. Explain the terms: TE1, TE2, TA, NT1 and NT2. [5 Marks]
b) Digital Subscriber Line is a new high-speed (broadband) data service to homes and small offices.
Using suitable diagram(s), describe the operation of this service. [8 Marks]
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