TCP Congestion Control: Slow Start & AIMD

Every TCP connection regulates how much data it puts on the wire using a congestion window (cwnd) that grows and shrinks according to a well-defined state machine (RFC 5681). This simulator renders that state machine in 3D: a client and server node are joined by a link, and one packet sphere is spawned per unit of the current congestion window every round trip. Watch cwnd double each RTT during slow start, switch to a slower linear climb once it passes the slow-start threshold (ssthresh), and collapse — via fast recovery or a full timeout, your choice — the moment a simulated packet loss occurs. Live readouts track the window size, threshold, elapsed round trips and effective throughput, with a running graph of cwnd over time.