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GATE CSE 2020 Q65: TCP congestion window after 60 ms with slow start and AIMD

Question

Consider a TCP connection between a client and a server with the following specifications: the round trip time is 6 ms, the size of the receiver advertised window is 50 KB, slow-start threshold at the client is 32 KB, and the maximum segment size is 2 KB. The connection is established at time t=0t = 0. Assume that there are no timeouts and errors during transmission. Then the size of the congestion window (in KB) at time t+60t + 60 ms after all acknowledgements are processed is _______.

Try it: numerical answer: type the value

Numerical answer. No negative marking.
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Answer: 44 (official GATE 2020 final answer key)

Concept used: Slow start doubles the window each RTT up to the threshold; congestion avoidance then adds one MSS per RTT.

First step: 60 ms is 10 RTTs. Starting at 2 KB, the window doubles to 4, 8, 16, 32 KB, then grows by 2 KB per RTT.

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Source: official GATE 2020 CS question paper and final answer key, organised by IIT Delhi. Question paper · Answer key

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