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Comp 207: Data Communications Question Paper

Comp 207: Data Communications

Course:Computer Science

Institution: Chuka University question papers

Exam Year:2013

CHUKA

UNIVERSITY

UNIVERSITY EXAMINATIONS

SECOND YEAR EXAMINATION FOR THE AWARD OF DEGREE
OF BACHELOR OF SCIENCE IN COMPUTER SCIENCE

COMP 207: DATA COMMUNICATIONS
STREAM: BSC IN COMPUTER SCIENCE - Y2S2 TIME: 2 HOURS

DAY/DATE: THURSDAY 8/8/2013 11.30 A.M – 1.30 P.M.
CANDIDATE’S INSTRUCTIONS
INSTRUCTIONS
1. Answer question ONE and any other TWO questions
2. Marks are awarded for clear and concise answers
QUESTION ONE (COMPULSORY) [30 MARKS]
(a) State Nyquist sampling theorem [2 marks]
(b) A speech signal has approximate bandwidth of 4000 HZ. If this is sampled at the Nyquist sampling rate by an 8-bit A/D converter. What is the data rate of the data generated by A/D converter. [4 marks]

(c) Give TWO disadvantages of terrestrial microwave communication. [2 marks]

(d) Give TWO differences between coaxial cable and Optic fibre. [4 marks]

(e) What is the relationship between;

(i) Frequency and bandwidth [2 marks]

(ii) Bandwidth and error rate [2 marks]

(iii) Radio communication and optical communication [2 marks]

(f) While describing what virtual circuit switching is, give TWO of its disadvantages.
[4 marks]

(g) Using diagrams briefly describe the following;

(i) Time division multiplexing [2 marks]

(ii) Frequency division multiplexing [2 marks]

(h) While giving an example in each differentiate between recognition and flagging and recognition and forward error correction in relation to error control in data communications. [4 marks]

QUESTION TWO [20 MARKS]

(a) Using appropriate diagrams, explain the following Time division multiplexing techniques

(i) Asynchronous TDM [4 marks]

(ii) Synchronous [4 marks]

(b) Why is it that packet length in asynchronous system is short [2 marks]

(ii)What is the main difference between synchronous and asynchronous transmission. [2 marks]

(c) Why is it important to encrypt messages during transmission [3 marks]

(d) (i) Briefly describe the operation of Bus topology using diagrams [3 marks]

(ii) What is the role of terminators at the end of Bus cable [2 marks]

QUESTION THREE [20 MARKS]

(a) While giving examples, differentiate between even and odd parity [4 marks]

(b) In a transmission system using checksum error detection mechanism, the following bit stream was sent: 10111001 11111110 01001100 11111111 10100000
(i) Compute the checksum value that will be sent together with this data [2 marks]
(ii) Briefly explain how the transmission that utilizes checksum such as this operates at both the sender side and the receiver side [6 marks]
(c) Using timing diagrams show how 101100111 will be encoded in Manchester phase encoding. [3 marks]
(d) A submarine telephone fibre cable connects Europe with North America. This cable comprises four fibre pairs. Each pair provides a full duplex communication link with one fibre carrying data from Europe to North America and the other carrying data from North America to Europe. Each individual fibre supports up to 16 different wavelengths of light with each wavelength being able to operate at 10 Gbps:. What is the total carrying capacity of this cable in bps. [3 Marks]

( ii) Assuming that a full duplex call requires a continuous data rate of 64 Kbps, determine the maximum number of simultaneous voice calls that can be carried by the sub-marine per second [2 Marks]
QUESTION FOUR [20 MARKS]
(a) Briefly describe the following modulation schemes
(i) Amplitude modulation [3 marks]

(ii) Frequency modulation [3 marks]
(iii) Phase code modulation [3 marks]
(b) List the 7 Layers of OSI model in correct order [7 marks]
(c) VSAT satellites are geostationary satellites at a height 35,785 km above the equator. Suppose one person 90 km away from the equator sends data to a destination 200 km away. Suppose the sender has an option of using fibre or satellite. Show that fibre data arrives earlier than satellite data under ideal network conditions. [4 marks]

QUESTION FIVE [20 MARKS]

(a) Give THREE reasons why digital systems are being preferred to analogue ones in the telecommunications industry. [3 marks]
(b) Differentiate between;
(i) Dumb and intelligent terminal [2 marks]
(ii) Sliding window and Stop and wait protocols [2 marks]
(iii) Connection oriented and connectionless protocols [2 marks]
(c) Using a timing diagram, describe what Non-return to zero (NRZ) encoding is [2 Marks]
(d) What is the wavelength of an electromagnetic wave traveling at 2.4 GHZ [2 marks]

(e) Consider a voice grade telephone line operating at a frequency of 300 -3400 HZ. The S/N ratio is 30 Db. Using Shannon’s law, compute the maximum data rate/Channel capacity of this telephone line. [4 marks]
(f) Suppose you are using a safaricom modem on your laptop and that the connection speed of the modem is 56Kbps.How long will it take you to download a movie from the internet if the size of the movie is 1024 MB assuming there are no interruptions until the movie fully downloads [3 marks]

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Comp 207: Data Communications Question Paper

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