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PREVIOUS YEAR SOLVED PAPERS - August 2016 Paper 3

Avatto > > UGC NET COMPUTER SCIENCE > > PREVIOUS YEAR SOLVED PAPERS > > August 2016 Paper 3

26. Consider the following statements :
A. High speed Ethernet works on optic fiber.
B. A point to point protocol over Ethernet is a network protocol for encapsulating PPP frames inside Ethernet frames.
C. High speed Ethernet does not work on optic fiber.
D. A point to point protocol over Ethernet is a network protocol for encapsulating Ethernet frames inside PPP frames.
Which of the following is correct ?

  • Option : A
  • Explanation :
  • High speed Ethernet works on optic fiber Correct
  • A point to point protocol over Ethernet is a network protocol for encapsulating PPP frames inside Ethernet frames not for encapsulating Ethernet frames inside PPP frames.Correct.
    • So, option (A) is correct.
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27. In CRC checksum method, assume that given frame for transmission is 1101011011 and the generator polynomial is G(x) = x4 + x + 1. After implementing CRC encoder, the encoded word sent from sender side is _____.

  • Option : A
  • Explanation :
    Given frame for transmission is 1101011011 and generator polynomial is G(x) = x4 + x + 1 i.e. 10011. We have to append 4 0's (1 0's less then divisor according to CRC):

    We have to append 1110 to the frame. Now our frame for transmission is 11010110111110. So, option (A) is correct.
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28. A slotted ALOHA network transmits 200 bits frames using a shared channel with 200 kbps bandwidth. If the system (all stations put together) produces 1000 frames per second, then the throughput of the system is _______.

  • Option : C
  • Explanation :
    For pure aloha Throughput(S) = Ge-2G.
    For Slotted aloha Throughput(S) = Ge-G.
    (it is maximum at G = 1). i.e. S = 1 * e-1.
    S = 1 / e.
    S = 1 / 2.71
    S = 0.368.
    So, option (C) is correct.
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29. An analog signal has a bit rate of 8000 bps and a baud rate of 1000. Then analog signal has _____ signal elements and carry _____ data elements in each signal.

  • Option : A
  • Explanation : Analog signal has a bit rate of 8000 bps and a baud rate of 1000. So, each signal will clearly carry bit rate / baud rate bits. i.e. 8000 / 1000 = 8 bits and 28 = 256 signal. So, option (A) is correct.
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30. The plain text message BAHI encrypted with RSA algorithm using e = 3, d = 7 and n = 33 and the characters of the message are encoded using the values 00 to 25 for letters A to Z. Suppose character by character encryption was implemented. Then, the Cipher Text message is _____.

  • Option : B
  • Explanation :
    RSA algorithm using e = 3, d = 7 and n = 33 and text message BAHI(using the values 00 to 25 → A(00), B(01), C(02),............). for
    B → [m = cd mod n]
    i.e. m = 17 mod 33
    m = 1 mod 33.
    m = 1 → B
    A → 07 mod 33
    m = 0 mod 33.
    m = 0 → A
    m = 77 mod 33
    m = 13 → N
    m = 87 mod 33
    m = 17 → R
    Message will be BANR (using the values 00 to 25 → A(00), B(01), C(02),............). No option is matching. But if we use the values 01 to 26 → A(01), B(02), C(03)....... Then
    B → [m = cd mod n]
    i.e. m = 27 mod 33
    m = 8 mod 33.
    m = 8 → H
    A → 17 mod 33
    m = 1 mod 33.
    m = 1 → A
    m = 87 mod 33
    m = 17 → Q
    m = 97 mod 33
    m = 3 → C
    Message will be HAQC.
    So, option (B) is correct.
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