Data Communication

12 Grade 10 Computer Studies questions on Data Communication, with worked marking schemes. 12 questions are available on this topic in full.

1. Question 1

   1 mark

   Which statement best describes a digital signal used in data communication?

   A. It never becomes weaker, no matter how far it travels

   B. It varies continuously in strength as time passes

   C. It can only be transmitted along a fibre-optic cable

   D. It carries data as separate, distinct levels that represent 0s and 1s

   (1 mark)

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2. Question 2

   1 mark

   A school is comparing internet packages offered by different providers. In which unit is the rate at which data moves through the link stated?

   A. Megabits per second (Mbps)

   B. Gigabytes (GB)

   C. Dots per inch (dpi)

   D. Hertz (Hz)

   (1 mark)

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3. Question 3

   1 mark

   In asynchronous serial transmission, each character sent is enclosed by a start bit and a stop bit. State the purpose of these two bits.

   A. They convert the character into analogue form

   B. They double the speed at which the character travels

   C. They correct any bits that arrive wrongly

   D. They show the receiving device where each character begins and ends

   (1 mark)

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4. Question 4

   3 marks

   Distinguish between simplex, half-duplex and full-duplex data transmission, giving one everyday example of each.

   (3 marks)

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5. Question 5

   4 marks

   State the function of each of the following data communication devices: (a) repeater; (b) switch; (c) router; (d) wireless access point.

   (4 marks)

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6. Question 6

   4 marks

   A school is linking its administration block to a new library block about 200 metres away. Explain four factors that should be considered when choosing the transmission medium for the link.

   (4 marks)

   Marking scheme

   Award 1 mark for each factor correctly named and explained, to a maximum of 4: - Distance to be covered - ordinary twisted-pair cable is limited to about 100 metres, so a medium that carries the signal 200 metres without a repeater, such as fibre, is needed. - Cost - the price of the cable, the fittings and the labour of laying it must fit the school budget. - Required speed or bandwidth - the medium must carry the amount of data the library will need, for example for online research by many learners. - Interference in the environment - power lines, machinery or lightning affect copper cables but not fibre. - Ease of installation and the terrain between the blocks - a road, drainage channel or rocky ground may make trenching difficult and favour a wireless link. - Security of the data and future expansion needs. Accept any four.

7. Question 7

   1 mark

   A tea-processing factory in Kericho runs heavy electric motors that produce strong electromagnetic fields along the route where a network cable must pass. Suggest the most suitable transmission medium for that route.

   A. Coaxial cable

   B. Unshielded twisted-pair cable

   C. Fibre-optic cable

   D. An infrared link

   (1 mark)

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8. Question 8

   1 mark

   As data travels along a long copper cable between two farm offices, the signal steadily becomes weaker. Identify the term used for this weakening.

   A. Attenuation

   B. Multiplexing

   C. Encryption

   D. Modulation

   (1 mark)

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9. Question 9

   4 marks

   A livestock research camp in Marsabit is far from any fibre cable or mobile mast, so it connects to the internet through a satellite link. Explain two advantages and two disadvantages of using satellite transmission at this camp.

   (4 marks)

   Marking scheme

   Award 1 mark for each point correctly explained; 2 advantages and 2 disadvantages required, to a maximum of 4. Advantages: - It reaches very remote areas where no cables or masts have been laid, so the camp can be connected at all. - One satellite covers a very wide area, so other stations in the region can be linked to the same service. - Installation does not require digging trenches over long, difficult terrain. Disadvantages: - The equipment and subscription are expensive compared with terrestrial links. - There is a noticeable delay because the signal travels a very long distance up and down, which affects voice and video calls. - Heavy rain or cloud weakens the signal, so the service is unreliable during storms. - The dish needs a clear, unobstructed view of the sky and careful alignment. A point listed on the wrong side of the answer earns no mark.

10. Question 10

    3 marks

    Forty learners in a school share one internet connection. A video lesson plays smoothly early in the morning but becomes very slow at lunchtime. Account for the slowness, and suggest two measures the school could take to improve the situation.

    (3 marks)

    Marking scheme

    1 mark for the reason and 1 mark for each valid measure, to a maximum of 3: Reason: the connection has a fixed data transfer rate that is shared among all users, so when many learners are online at once each one receives a smaller share and the link becomes congested. Measures (any two): - Subscribe to a package with a higher data transfer rate. - Use bandwidth management so that each user or computer is limited to a fair share, and heavy downloads are restricted. - Timetable heavy activities such as video lessons so that classes do not all use the link at the same time. - Download or cache the lesson material in advance and play it from the school server.

11. Question 11

    2 marks

    Distinguish between serial and parallel data transmission.

    (2 marks)

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12. Question 12

    1 mark

    A home in Nyeri connects to the internet over an ordinary telephone line using a modem. State the function of the modem in this connection.

    A. It converts the computer's digital signals into analogue form for the line, and back into digital form at the other end

    B. It removes viruses from data arriving from the internet

    C. It stores web pages so that they open faster the next time

    D. It increases the number of telephone lines available to the home

    (1 mark)

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