BE Computer Engineering (IOE, TU) Data Communication (IOE, CT 604 / ENCT 253) Question Paper 2078

(a) State Nyquist's theorem and Shannon's capacity formula, clearly defining every term in each. (6)

(b) A telephone line has a bandwidth of 3000 Hz (300 Hz to 3300 Hz) and a signal-to-noise ratio of 3162 (35 dB). Compute the theoretical maximum channel capacity using Shannon's formula. Then, using the Nyquist formula for the same channel, determine the number of signal levels required to achieve a practical data rate that is close to (but not exceeding) this capacity. Comment on why the two results differ. (6)

(a) With the help of waveform diagrams, explain ASK, FSK, and PSK as digital-to-analog conversion (modulation) techniques. Compare them on the basis of bandwidth requirement and noise immunity. (8)

(b) Draw the constellation diagram for 8-QAM and explain how QAM combines amplitude and phase modulation to increase the bit rate. (4)

(c) Explain the concept of a constellation diagram and use it to distinguish between 4-PSK (QPSK) and 4-QAM. (4)

(a) Describe the Pulse Code Modulation (PCM) process with a neat block diagram, explaining the role of sampling, quantization, and encoding. (7)

(b) An analog signal carries 4 bits per signal element. If 1000 signal elements are sent per second, find the bit rate. If the highest frequency component of the analog signal is 4 kHz, determine the minimum sampling rate according to the sampling theorem and explain the consequence of sampling below this rate. (5)

(a) Explain the Sliding Window flow control protocol. With suitable timing diagrams, compare the Go-Back-N ARQ and Selective-Repeat ARQ protocols, highlighting how each handles a damaged frame and the window size restriction in each case. (8)

(b) For a Go-Back-N protocol using a 3-bit sequence number, state the maximum sender window size and justify your answer. (4)

Define transmission impairment. Explain attenuation, distortion, and noise as three causes of signal impairment, and describe two types of noise (thermal and crosstalk) that affect a transmission medium.

Compare guided and unguided transmission media. Briefly describe the construction and typical applications of twisted-pair cable, coaxial cable, and optical fibre.

(a) Given the data word 1101011011 and the divisor (generator polynomial) 10011, compute the CRC and show the transmitted frame. (5)

(b) Explain how the Hamming distance is used to detect and correct errors, and determine the error-detecting and error-correcting capability of a code with a minimum Hamming distance of 4. (3)

Differentiate between Frequency Division Multiplexing (FDM) and Time Division Multiplexing (TDM) with neat diagrams. Explain the need for guard bands in FDM and the role of framing bits in synchronous TDM.

With block diagrams, compare circuit switching, datagram packet switching, and virtual-circuit packet switching on the basis of connection setup, addressing, and resource reservation.

Draw the line-coding waveforms for the bit pattern 0101110 using NRZ-L, NRZ-I, Manchester, and Differential Manchester encoding. State one advantage of self-synchronizing (biphase) schemes over NRZ schemes.

Explain bit stuffing and byte (character) stuffing as framing techniques in data link layer protocols. Given the data 01111110 01111100, show the bit sequence after bit stuffing is applied for an HDLC-like flag of 01111110.

Define bandwidth, throughput, latency, and bandwidth-delay product. A network has a bandwidth of 1 Mbps and a round-trip propagation delay of 20 ms; calculate the bandwidth-delay product and explain its significance for the choice of sender window size.