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Functions of OSI and TCP/IP Layers Q.65

0. Consider an instance of TCP’s Additive Increase Multiplicative Decrease (AI MD) algorithm where the windows size at the start of the slow start phase is 2 MSS and the threshold at the start of the first transmission is 8 MSS. Assume that a time-out occurs during the fifth transmission. Find the congestion window size at the end of the tenth transmission.

  • Option : C
  • Explanation : Window size for 1st transmission = 2 MSS
    Window size for 2nd transmission = 4 MSS
    Window size for 3rd transmission = 8 MSS
    Threshold reached, increase linearly (according to AIMD)
    Window size for 4th transmission = 9 MSS
    Window size for 5th transmission = 10 MSS
    Time out occurs, resend 5th with window size starts with as slow start.
    Window size for 6th transmission = 2 MSS
    Window size for 7th transmission = 4 MSS
    Threshold reached, now increase linearly (according to AIMD)
    Additive Increase: 5 MSS (since 8 MSS isn’t permissible anymore)
    Window size for 8th transmission = 5 MSS
    Window size for 9th transmission = 6 MSS
    Window size for 10th transmission = 7 MSS

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