📈

TCP Window Scaling & High-BDP Networks

Medium

Free preview · 2 of 5 steps

The window bottleneck

TCP's flow control uses a receive window — the amount of unacknowledged data allowed in flight. The 16-bit window field in the TCP header limits this to 65,535 bytes (64KB).

On a 10 Gbps link with 140ms RTT (San Francisco to London), the Bandwidth-Delay Product is 175MB — the amount of data that must be in flight to saturate the link. With only 64KB in flight, you use 0.037% of available bandwidth.

Packets in motion — click to inspect:

1 / 2

Space to play/pause · ← → to step