TCP Congestion Control
Slow-start, congestion avoidance, fast recovery
TCP does not know how fast your network is. It guesses, crashes, guesses again. Watch the congestion window ramp, collapse on loss, and settle into a sawtooth — then compare Reno, CUBIC, and BBR on the same channel to see how differently they read the same signal.
RTT80 ms
Packet loss0.10%
Bottleneck50 Mbps
current cwnd
1.3
avg throughput
0.15 Mbps
link utilization
0.3%
The sender never observes bandwidth directly. It infers capacity from loss (Reno, CUBIC) or from delay gradients (BBR), and that inference is what you see oscillate.