Is it slow?

keep alive & timeout

is it slow?

TCP Fast Open

Congestion Control

receive window – rwnd

How wide window can be?

Length === 16bit

2**16 === 65 535

Scale of window

Linux

• $> sysctl net.ipv4.tcp_window_scaling
• $> sysctl -w net.ipv4.tcp_window_scaling=1

Slow-Start

cwnd

data without ack: Math.min(rwnd, cwnd)

Slow-Start Restart (don't use too long)

How fast can file be downloaded?

275% faster

Head-of-line blocking

What to do?

Use another protocol

UDP, QUIC and others

Questions?