In TCP slow-start, what pattern describes the congestion window?

• A. A steady linear increase
• B. A fixed window
• C. An initial rapid growth of the congestion window with a small initial window, followed by ramp-up
• D. A decrease in cwnd

Answer: (C)

Slow-start drives the congestion window up very quickly from a small starting value. It begins with a tiny window (often one MSS), and for each ACK received during this phase, cwnd increases, causing the amount you can send in the next round trip to grow rapidly. This rapid growth is why the window roughly doubles each RTT in slow-start. Once cwnd reaches the slow-start threshold, the mechanism transitions to congestion avoidance, where growth becomes slower and more linear rather than exponential. So the described pattern—an initial rapid increase from a small window, followed by a ramp-up—is exactly what slow-start looks like. The other patterns describe different behaviors: linear growth is what happens during congestion avoidance, a fixed window means no growth at all, and a decrease in cwnd occurs in response to loss rather than as the normal startup pattern.