CS601 Data Communication Assignment 3 Solution Spring 2013

Question 1: (5 Marks)


Assume that you are working as an assistant network administrator in a company and assisting your network administrator in creating and maintaining networks for the company. You are assigned a task to analyze three different types of network media i.e. twisted pair cable, coaxial cable and fiber optic cable. You are required to fill the following table on the basis of your analysis.


Cables Attenuation (Less /High) Bandwidth (Hz) Distance (Limited / Long / Very Long )
Twisted pair
Coaxial cable
Fiber optic



Question 2: (5 Marks)


According to the propagation of signals there are two types of signals i.e. Omni directional waves/signals and unidirectional waves/signals. In your opinion what is the difference between unidirectional and Omni directional waves and write at least two examples of unidirectional and Omni directional
Solution: Omnidirectionalwaves are propagated in all directions; unidirectional waves are propagated in one direction.

Omnidirectional Antennas. The omnidirectional antenna radiates or receives
equally well in all directions. It is also called the “non-directional” antenna because it does
not favor any particular direction. Figure 1 shows the pattern for an omnidirectional antenna,
with the four cardinal signals. This type of pattern is commonly associated with verticals,
ground planes and other antenna types in which the radiator element is vertical with respect
to the Earth’s surface.
The key factor to note is that for receivers all four signals (or signals from any
direction, for that matter) are received equally well. For transmitters, the radiated signal has
the same strength in all directions. This pattern is useful for broadcasting a signal to all
points of the compass (as when calling “CQ”), or when listening for signals from all points.

Directional Antennas. Gain and directivity are intimately related in antennas. The
directivity of an antenna is a statement of how the RF energy is focussed in one or two
directions. Because the amount of RF energy remains the same, but is distributed over less
area, the apparent signal strength is higher. This apparent increase in signal strength is the
antenna gain. The gain is measured in decibels over either a dipole (dBd) or a theoretical
construct called an isotropic radiator (dBi). The isotropic radiator is a spherical signal
source that radiates equally well in all directions. One way to view the omnidirectional
pattern is that it is a slice taken horizontally through the three dimensional sphere

Question 3: (5 Marks)


Consider the following network in which a signal travels from point A to point G. At point A, the signal power is 100 W and at point G, the power is 80 W. You are required to calculate the decibel (dB) and identify whether the signal received at point G is attenuated or amplified?


Given data;

pt. A=P1=100W

at pt. G=P2=80W


dB = 10 log10 (P2/P1)

Substituting the values of P1 and P2 we get;

dB =10Log10 (80W/100W)


=10*(-0.09691)                 (Since: Log 0.8= -0.09691)

dB = -0.9691

Question 4: (5 Marks)


Some of the popular transmission applications/devices are given below. You are required to categorize these applications according to their respective wireless transmission waves.


Applications              Radio waves/ Micro waves/ Infrared waves
FM Radio  Radio waves
Satellite networks Micro waves
Television  Radio waves
Remote control  Infrared waves
Cordless phones   Infrared waves