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GATE CSE 2026 Session 1 Q44: When segment 2000 is sent under TCP slow start

Question

A TCP sender successfully establishes a connection with a TCP receiver and starts the transmission of segments. The TCP congestion control mechanism's slow-start threshold is set to 10000 segments. Assume that the round-trip time is fixed at 1 millisecond. Assume that the sender always has data to send, the segments are numbered from 1, and no segment is lost. Let tt denote the time (in milliseconds) at which the transmission of segment number 2000 starts.

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Answer: B (official GATE 2026 final answer key)

Concept used: In slow start the congestion window doubles every RTT: 1, 2, 4, … segments.

First step: By the start of RTT number kk (time kk ms), 2k−12^k - 1 segments have been sent; find kk with 2k−1<2000≤2k+1−12^k - 1 < 2000 \le 2^{k+1} - 1.

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Source: official GATE 2026 Session 1 CS question paper and final answer key, organised by IIT Guwahati. Question paper · Answer key

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