Why TCP Congestion Control Makes Networks Slower After Loss
When a network is slow, bandwidth is often the first thing people check.
Bandwidth looks sufficient, but HTTPS downloads are slow. Cellular throughput jumps up and down. Wi-Fi signal looks acceptable, but API calls occasionally time out. Packet captures show retransmissions, duplicate ACKs, RTOs, and then the sending rate drops. The server CPU is fine and the application did not change, but TCP suddenly becomes conservative.
Congestion control is often the reason.
Read More