BE Computer Engineering (IOE, TU) Data Communication (IOE, CT 604 / ENCT 253) Question Paper 2079
This is the official BE Computer Engineering (IOE, TU) Data Communication (IOE, CT 604 / ENCT 253) question paper for 2079, as set in the regular annual examination. It carries 80 full marks and a time allowance of 180 minutes, across 13 questions. On Kekkei you can attempt this Data Communication (IOE, CT 604 / ENCT 253) past paper online with a timer, get instant AI feedback and step-by-step solutions, and track the topics where you lose marks — completely free. Whether you are revising for your BE Computer Engineering (IOE, TU) Data Communication (IOE, CT 604 / ENCT 253) exam or solving previous years' question papers, this 2079 paper is a great way to practise under real exam conditions.
Section A: Long Answer Questions
Attempt all / any as specified.
(a) Distinguish between data rate and signal rate (baud rate), and explain how the number of signal levels affects the relationship between them. [4]
(b) A telephone line has a bandwidth of 3 kHz. Using the Nyquist theorem, calculate the maximum bit rate if the signal is encoded using (i) 2 levels and (ii) 8 levels. [4]
(c) The same channel now has a signal-to-noise ratio (SNR) of 30 dB. Use the Shannon capacity formula to find the theoretical maximum channel capacity, and comment on why the practical achievable rate is lower than this value. [4]
(a) With the help of neat waveform diagrams, explain the three digital-to-analog modulation techniques ASK, FSK and PSK, and state one practical application of each. [6]
(b) Draw the constellation diagram for QPSK and 8-PSK, and explain how the constellation determines the bandwidth efficiency and the susceptibility to noise. [4]
(c) Why is QAM preferred over pure PSK at higher data rates? [2]
(a) Differentiate between FDM, TDM and WDM, clearly stating the type of signal each is suited for and where guard bands or guard times are required. [6]
(b) Four channels, each requiring a data rate of 1 Mbps, are multiplexed using synchronous TDM with a frame containing one bit per channel. Determine the (i) output frame rate, (ii) output frame duration and (iii) output data rate of the link. [4]
(c) Explain how statistical TDM improves link utilisation compared with synchronous TDM. [2]
(a) Compare circuit switching, datagram packet switching and virtual-circuit packet switching with respect to setup phase, addressing overhead, resource reservation and suitability for bursty traffic. [7]
(b) With a labelled timing/space diagram, explain the three phases of a circuit-switched connection. [3]
(c) Describe one scenario in modern networks where virtual-circuit switching is still used. [2]
Section B: Short Answer Questions
Attempt all / any as specified.
Compare guided and unguided transmission media. For guided media, briefly explain the construction and one suitable application of twisted-pair cable, coaxial cable and optical fibre.
Given the data word 1101011011 and the generator polynomial G(x) = x^4 + x + 1 (i.e. divisor 10011), use the CRC technique to compute the transmitted code word. Show the binary division steps clearly.
(a) State the relationship between the Hamming distance of a code and the number of errors it can detect and correct. [2]
(b) Design a Hamming code for a 7-bit data word 1001101 (using even parity) and show the positions of the redundant bits in the transmitted code word. [4]
A 1 Mbps satellite link has a one-way propagation delay of 270 ms and uses frames of 1000 bits. Calculate the link efficiency for (a) Stop-and-Wait ARQ and (b) Go-Back-N ARQ with a window size of 7. Comment on which protocol is more suitable for this link.
Explain the steps involved in Pulse Code Modulation (PCM) with a block diagram. State the sampling rate required for a voice signal band-limited to 4 kHz and justify it using the sampling theorem.
With suitable waveforms, explain the NRZ-L, NRZ-I, Manchester and Differential Manchester line-coding schemes, and state which of these provide self-synchronization.
Explain the three main types of transmission impairment — attenuation, distortion and noise. If a signal travels through a medium and its power is reduced from 10 mW to 2.5 mW, calculate the attenuation in decibels (dB).
Explain the sliding-window flow control mechanism. Differentiate between the sender window and receiver window, and state the maximum window size permitted in Go-Back-N and Selective-Repeat ARQ for an m-bit sequence number.
Explain the concept of spread spectrum. Differentiate between Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS).