Lecture 16 Extra: The TCP Congestion Game

Tom Anderson, CSE/EE 461 Winter 2002.

These are the rules of the game by which we simulate TCP:

 

Stop and Wait.

Simulate this as a warm-up exercise.

Graph:

Notice

 

Slow-Start

Blow out the queue until there is loss. Each ack causes congestion window to be increased by one i.e., 2 packets to be sent.

Add graph for

Notice that

 

AIMD

Go through a couple of rounds of the sawtooth. Each successful ack triggers a send; every time a complete window is sent the window increases by one (ack triggers two sends). After a loss, congestion window drops by factor of 2. Carry a special object to signal each RTT round and hence congestion window increase.

Notice