TCP Congestion Control

• slow start (cwnd < ssthresh)

Multiplicative Increase Multiplicative Decrease

cwnd initialized with 1

for every ACK received, add 1 to cwnd

• congestion avoidance (cwnd > ssthresh)
  Additive Increase Multiplicative Decrease
  

for every ACK received, add 1/cwnd to cwnd

Two phases:

cwnd – congestion window (dynamic)

ssthresh – slow start threshold

Go back n protocol

Packet loss: ssthresh = cwnd / 2

cwnd = cwnd / 2

Timeout: ssthresh = cwnd / 2

cwnd = 1

[Jacobson 88]

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