The GATE Grind

GATE 2023 CS – Question 50

Computer Networks · TCP: Flow Control, Congestion Control, Socket API · 2 marks · Multiple select

Suppose you are asked to design a new reliable byte-stream transport protocol like TCP. This protocol, named myTCP, runs over a 100 Mbps network with Round Trip Time of 150 milliseconds and the maximum segment lifetime of 2 minutes. Which of the following is/are valid lengths of the Sequence Number field in the myTCP header?

  1. 30 bits
  2. 32 bits
  3. 34 bits
  4. 36 bits

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Correct answer: (B) 32 bits; (C) 34 bits; (D) 36 bits

Explanation

In one MSL (120 s) at 100 Mbps, 12.5 MB/s × 120 s = 1.5×10⁹ bytes are sent. The sequence space must not wrap within an MSL, so 2ⁿ > 1.5×10⁹ needs n ≥ 31. So 32, 34 and 36 bits are valid, but 30 is not.