N6Windows and flow control

The problem

1 s on screen = 100 ms

The line is fast, so why does sending a big file still crawl?

Send one, wait for its answer

Sender has 100 messages a second for a receiver 25 ms away, and sends each only after the last one's answer.

Live metrics for each version of the scene
One at a time	A window	Flow control
0/s	0/s	0/s
—	—	—
—	—	—
1	12	12

N6Windows and flow control

Waiting for each ack before sending the next leaves the pipe empty. A window keeps several messages in flight.