In the slow start phase of the TCP congestion control algorithm, the size of…
2008
In the slow start phase of the TCP congestion control algorithm, the size of the congestion window
- A.
does not increase
- B.
increases linearly
- C.
increases quadratically
- D.
increases exponentially
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Correct answer: D
Answer: The congestion window increases exponentially during slow start.
Why: In slow start the sender increases the congestion window (cwnd) by one maximum segment size (MSS) for each acknowledgement received. Because each newly sent packet can produce further acknowledgements within the same round-trip time (RTT), the total cwnd roughly doubles every RTT, producing exponential growth.
When slow start stops: Slow start continues until the congestion window reaches the slow start threshold (ssthresh) or a loss is detected. After that TCP transitions to congestion avoidance, where the window increases approximately linearly.
Example start: cwnd = 1 MSS.
After one RTT: cwnd ≈ 2 MSS (each packet acknowledged allows sending another).
After two RTTs: cwnd ≈ 4 MSS, and so on (doubling each RTT in ideal conditions).
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