Question 1

a) List the layers of the OSI model and briefly explain the function of each layer.

b) List the three key elements of a protocol. Give a brief explanation of each of these key elements.

c) Describe the concept of half duplex transmission.

d) Describe the bus topology. Give an advantage and a disadvantage of the topology

Question 2

a) Describe the term periodic signal and give an example of a periodic analog signal.

b) A digital signal has ten levels. How many bits are needed per level to represent the signal?

c) A signal has a spectrum with frequencies between 1500 and 3500 Hz. A medium allows frequencies from 4000 to 6000 Hz to pass through it. Describe if the signal will faithfully pass through this medium?

d) Describe the term distortion.

e) The attenuation of a signal is -20dB. What is the final signal power if the original signal was 10W?

f) Suppose a channel with a bandwidth of 10MHz. Evaluate the channel capacity if the signal to noise ratio is 60dB.

Question 3

a) Show this sequence 011010 using

i. Unipolar NRZ
ii. Manchester coding
iii. Differential Manchester coding

b) List two advantages and two disadvantages of Manchester coding.

c) State the Nyquist Sampling theorem.

d) What is the Nyquist sampling rate for each of the given signals?

i. A low-pass signal with a bandwidth of 300 KHz
ii. A band-pass signal with bandwidth of 200 KHz if the lowest frequency is 200 KHz

e) Describe the occurrence of quantization error.

f) What is serial transmission? Give one advantage of serial transmission over parallel transmission.

Question 4

a) Differentiate between signal rate and data rate.

b) Two sets of constellation points are given below. The numbers in parentheses define the values of I and Q respectively.

• Four points at (1,1), (-1,1), (-1,-1) and (1,-1).
• Two points (0,3) and (0,-3).

For each case,

i. Show  the constellation diagram.
ii. find the peak amplitude value.
iii. explain the type of modulation.

c) What is the required bandwidth for the subsequent cases if we need to send 2400 bps? Let d=1.

i. QPSK
ii. 16-QAM

d) What is crosstalk? How is it minimized in the case of twisted-pair of wire?

e) List four advantages and two disadvantages of optical fibre.