TCP for Application Engineers: The Bits That Actually Bite

You don't need to memorize the TCP state machine. But you do need to know why a paused process leaves connections in CLOSE_WAIT, why your service times out only on long-lived connections, and why Nagle's algorithm secretly added 200ms to your latency. The application bugs that look like 'the network is broken' are almost always TCP doing exactly what it was designed to do.