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Data Communication Question Paper

Data Communication 

Course:Diploma In Computer Studies

Institution: Mombasa Polytechnic question papers

Exam Year:2006



1. (a) Define the following terms as used in data communication.
(i) Real time.
(ii) Terminal
(iii) Datel. (3marks)
(b) (i) Explain "polling" as applied to data networks.
(ii) Explain how a data network can be used for:
(I) Airline reservation
(II) Track stations for space satellites. (8marks)
(c) (i) State any TWO factors to consider when selecting a network for a specific application.
(ii) With the aid of a sketch, explain the operation of a ring topology.
(iii) State why a single-mode failure in a ring is a major problem and explain how this problem can be solved. (7marks)
(d) Explain the difference between LAN and WAN. (2marks)

2. (a) (i) State the sampling theorem.
(ii) State the advantage of the store capacitor in a sample-and-hold circuit.
(iii) With the aid of a labeled block diagram, explain the operation of sample and hold circuit. (9marks)
(b) (i) Explain any THREE reasons for using digital signal transmission.
(ii) Determine the most suitable P.C.M.code length for an analogue system whose Vmax: Vmin is approximately equal to 251. (9marks)
(c) State any TWO advantages of PCM over other methods of modulation. (2marks)

3. (a) (i) Sketch a labeled block diagram of a pocket format switching network.
(ii) State any FOUR characteristics of packet switching.(8marks)
(b) With the aid of a two-level network, explain the operation of circuit switching network.(8marks)
(c) (i) Explain the operations of a TDMA switching system.
(ii) State any TWO advantages of the system in (c) (i). (4marks)
4.(a) (i) State the effect of both attenuation and phase distortion on transmission of signals
(ii) Explain why phase distortion causes the greatest problems. (3marks)
(b) (i) Distinguish between mark-differential and space-differential encoding.
(ii) With the aid of a block diagram explain the operation of a PSK detector.
State the reason why ASK is not a widely favoured keying technique. (12marks)
(c) (i) Define the term "disparity" as applied to binary codes.
(ii) Explain the effects of lack of d.c coupling between the data source and sink within the switched telephone-network.
(iii) Explain the method which can be used to prevent effects in (c)(ii).(5marks)

5.(a) (i) State the FOUR uses of control frames in BSC.(8marks)
(ii) Describe the operation of a BSC multi frame. (8marks)
(b) Explain the following data transmission modes :
(i) Normal response (NRM)
(ii) Asynchronous response (ARM)
(iii) Asynchronous balanced (ABM)
(6marks) (c) Draw a flow chart of bit stuffing in HDLC.

(6marks) 6. (a) (i) State any TWO advantages and TWO disadvantages of using light and fibre optics in data communication.
(ii) With the aid of sketches, describe the light propagating mechanisms in the following types of fibre cables.
(I) Graded index
(II) Mono mode(12marks)
(b) Explain the following types of losses which occur in optical fibres:
(i) Micro bending
(ii) Splice loss.(4marks)
(c) (i) Define the "Numerical aperture"as applied to fibre cables.
(ii) State reason why larger NA is required in optical fibre cables.
(iii) A step index core has n1=1.4 and is surrounded by cladding of n2=1.1.
Determine the cone half-angle (4marks)

7.(a) Explain the following terms as applied to digital modulation.
(i) Amplitude shift keying (ASK)
(ii) Frequency shift keying (FSK) (4marks)
(b) (i) Explain how band-limiting in a digital communication system may lead to inter symbol interference.
(ii) With the aid of a labeled block diagram, explain the operation of an FSK demodulator employing correlation detection. (9marks)
(c)(i) An FSK signal consists of bursts of frequency 999HZ and 1MHZ,the higher frequency being used to send a binary 1,The bit rate is1000bps.
Determine the bandwidth of the FSK signal.
(ii) Explain the term "frequency-hopping"(FH) as used in data communication. (7marks)

8. (a) State any TWO advantages of a digital telephony system.(2marks)
(b) With the aid of a labeled block diagram, describe the operation of a multi-level distributed multiprocessor architecture within the public network. (12marks)
(c) Explain the functions of the following with reference to digital switching network.
(i) Voice-band interface,
(ii) Data-link interface,
(iii) FDM terminal equipment. (3marks)
(d) State any THREE advantages of RS-422A (3marks)




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