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SAMPLE CALCULATION QUESTIONS
a) Calculate the number of bits per second that would be generated by a
webcam having a screen resolution of 150 x 100 pixels that transmits 10 frames
per second using 16 bit colour. You may ignore factors such as coding and
protocol overheads. (6 marks)
b) A token ring network consists of 81 stations and each link between stations is 20
meters long. Each station introduces a delay of 1 bit time. If a station is
transmitting at 16MBS, what is the longest message which can be transmitted if
the whole message must be contained within the ring (the speed of electricity
in wire is 2 X 1010 cm/sec) (4 marks)
c) When sending an animated GIF each image is transmitted sequentially. If the
sequence contains 12 frames and the image is 160 X 320 pixels, calculate the
bit rate required to transmit this image in less than 2 seconds. Mathematical
analysis of the GIF compression ratio for the animated gives 0.07 bytes per
pixel. You may assume 10% network overhead. (6 marks)
d) A Geo-stationary satellite orbiting at 3574 km above the earth's surface is used
to provide a communication link between two sites, A and B, on the earth's
surface. Given that microwave signals travel at the speed of light (3 x 105
km/sec), calculate the total propagation delay incurred in sending a signal
from site-A to the satellite and then from the satellite to site-B. comment briefly
on how would you expect this to compare with the propagation delay over a
2000 km terrestrial (wire) link, with a propagation speed of 2 x 105 km/sec.
(5 marks)
e) An encyclopedia of medicine is to be published on CD. The printed version
consists of about 50 million words. An analysis of the text shows that the
average length of a word is 8.4 letters
i. How many letters are there in the encyclopedia, including spaces?
ii. Allowing an extra 5% punctuation marks and similar overheads, how
many bits are there in total?
iii. Ignoring protocol overheads, how long does it take to transmit the
whole book over a T1 line (1.544mbs)?
iv. If a CD can hold 600 Mbytes of useful data (ignoring storage overheads)
, how many CDs are required to accommodate the whole book?

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f) When sending an animated GIF each image is transmitted sequentially. If the
sequence contains 12 frames and the image is 160 X 320 pixels, calculate the
bit rate required to transmit this image in less than 2 seconds. Mathematical
analysis of the GIF compression ratio for the animated gives 0.07 bytes per
pixel. You may assume 10% network overhead. (5 marks)
g) Calculate the number of bits per second that would be generated by a
webcam having a screen resolution of 150 x 100 pixels that transmits 10 frames
per second using 16 bit colour. You may ignore factors such as coding and
protocol overheads. (5 marks)
h) When sending an animated GIF each image is transmitted sequentially. If the
sequence contains 12 frames and the image is 160 X 320 pixels, calculate the
bit rate required to transmit this image in less than 2 seconds. Mathematical
analysis of the GIF compression ratio for the animated gives 0.07 bytes per
pixel. You may assume 10% network overhead. (4 marks)
PROPAGATION DELAY AND TRANSMISSION DELAY
Formulas:
i. Propagation delay = (Distance/length (m))/(NVP x Speed of Light)
ii. Propagation delay = (Distance/length (m))/(Speed of data in that media
(ms-1))
iii. Round Trip = (Propagation Delay) /( Transmission delay)
iv. Transmission Delay = (No. of Bits to be transmitted )/ (Link but rate (bitss-1))
i) Calculate THE Propagation delay of a 500 m coaxial cable with an NVP of 0.9
j) A satellite link with a length of 72000 km from the earth and back is used to
communicate. It has an NVP of 0.9. Calculate the propagation delay
k) A 1000 bit block of data is to be transmitted between 2 DTEs . Determine the
ratio of propagation delay to the transmission delay(Round Trip) for the
following types of data link
i. 1000 m twisted pair wire at a transmission arte of 10 kilo bits per second
ii. 10 km of coaxial cable at a transmission speed of 1mbs
iii. 50,000 km of free space link at a transmission rate of 10mb/s
Assume that the velocity of propagation of signal within each type of cable
is 2.0 x 188 ms-1 and that of free space is 3.0 x 108ms-1