GATE 2020 CS – Question 65

Computer Networks · TCP: Flow Control, Congestion Control, Socket API · 2 marks · Numerical answer

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 $t=0$. Assume that there are no timeouts and errors during transmission. Then the size of the congestion window (in KB) at time $t+60$ ms after all acknowledgements are processed is ______.

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Correct answer: 44 to 44

Explanation

t = 60 ms is 10 RTTs. Slow start gives cwnd = 2, 4, 8, 16, 32 KB, reaching the threshold after 4 RTTs. Then congestion avoidance adds 2 KB per RTT for the next 6 RTTs: 32 + 12 = 44 KB (below the 50 KB receiver window).