A TCP sender starts with cwnd = 1 MSS and ssthresh = 16 MSS. If no loss occurs, what is cwnd (in MSS) at the end of the 6th RTT?

Explanation

Slow start doubles cwnd each RTT (2, 4, 8, 16) up to ssthresh; then congestion avoidance adds 1 MSS per RTT (17, 18), so cwnd = 18 after 6 RTTs.