PREVIOUS YEAR SOLVED PAPERS - July 2016 Paper 3

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26. Given the following statements:
(A) Frequency Division Multiplexing is a technique that can be applied when the bandwidth of a link is greater than combined bandwidth of signals to be transmitted.
(B) Wavelength Division Multiplexing (WDM) is an analog multiplexing Technique to combine optical signals.
(C) WDM is a Digital Multiplexing Technique.
(D) TDM is a Digital Multiplexing Technique.
Which of the following is correct?

Answer
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Option : D
Explanation :
Frequency Division Multiplexing is a technique that can be applied when the bandwidth of a link is greater than combined bandwidth of signals to be transmitted.Correct
Wavelength Division Multiplexing (WDM) is an analog multiplexing Technique to combine optical signals.Correct
WDM is a Digital Multiplexing Technique IncorrectIt is wavelength-division multiplexing
TDM is a Digital Multiplexing Technique.Correct

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27. A pure ALOHA Network transmits 200 bit frames using a shared channel with 200 Kbps bandwidth. If the system (all stations put together) produces 500 frames per second, then the throughput of the system is ______.

Answer
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Option : B
Explanation : Throughput(S) in pure aloha is G * e^-2G: It is maximum when G = 1 / 2. i.e. S = 1 / 2 * (2.71)^{-2 * 1 / 2}=1 / 2 * (2.71)^-1 = 0.184. So, option (B) is correct.

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28. Match the following:

(a) Line coding	(i) A technique to change analog signal to digital data.
(b) Block coding	(ii) Provides synchronization without increasing number of bits.
(c) Scrambling	(iii) Process of converting digital data to digital signal.
(d) Pulse code modulation	(iv) Provides redundancy to ensure synchronization and inherits error detection.

	(a)	(b)	(c)	(d)
(1)	(iv)	(iii)	(ii)	(i)
(2)	(iii)	(iv)	(ii)	(i)
(3)	(i)	(iii)	(ii)	(iv)
(4)	(ii)	(i)	(iv)	(iii)

Answer
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Option : B
Explanation :
- Line coding is a Process of converting digital data to digital signal.
- Block coding provides redundancy to ensure synchronization and inherits error detection.
- Scrambling provides synchronization without increasing number of bits.
- Pulse code modulation is a technique to change analog signal to digital data.
So, option (B) is correct.

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29. Assume that we need to download text documents at the rate of 100 pages per minute. A page is an average of 24 lines with 80 characters in each line and each character requires 8 bits. Then the required bit rate of the channel is _____.

Answer
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Option : B
Explanation :
100 pages , each page contain 24 line, each line have 80 character and each character weighted 8 bit, we have to download 100 pages per minute. i.e. 100 * 24 * 80 * 8 / 60 = 25.6 kbps. So, option (D) is correct.

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30. Encrypt the plain text Message “EXTRANET” using Transposition cipher technique with the following key : Using ‘Z’ as bogus character.

3	5	2	1	4	(Cipher text)
1	2	3	4	5	(Plain text)

Answer
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Option : A
Explanation :
According to given question and key , Z is a bogus character Encrypted message will be:Plain text
E X T R A N E T Z Z
1 2 3 4 5 1 2 3 4 5

Cipher text
T A X E R T Z E N Z
1 2 3 4 5 1 2 3 4 5

So, option (A) is correct.

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July 2016 Paper 3

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