Hack the Route Start free Open app TCP performance
Window and bandwidth-delay product
How much data may be unacknowledged at once; to fill a path it must reach bandwidth × round trip.
A sender moves at most one window per round trip, so throughput ≈ window ÷ RTT. At 20 Mbit/s and 40 ms the pipe holds 100 KB; a smaller window leaves it idle. Window scaling, agreed in the handshake, lifts the original 64 KB limit.