Congestion Control

1
Congestion Control

• Jain, Delay Based Approach..
• Brakmo et. al, TCP-Vegas.., SIGCOMM 94
• Hengartner, TCP-Vegas revisted, Infocomm 2000

2
End-to-end Congestion Control

• Delay and/or Throughput
• Based Congestion Control

3
Network As Black Box
Network
Round trip time, And/Or Throughput
Window Size Or Rate
4
Delay Based Approach

• Jain, Delay Based Approach.., 1989
• Based on the idea that the network responds to
  congestion window size changes as on the figure
  ci-contre

5
Delay Based ApproachThe Scheme

• NDG Normalized Delay Gradient
• Rationale if a change in congestion window size
  produce a change in RTT, then I am beyong the
  knee

6
Throughput Based Approach(Wang and Crowcroft)

• NTG Normalized Throughput Gradient

7
Throughput Based Approach(Wang and Crowcroft) (2)

• Scheme
• Measure throughput with the first packet sent
  (T1)
• If you increase your window size by one, and you
  do not get an increase of throughput of at least
  ½ T1, then you are beyond the knee..

8
TCP-Vegas Congestion ControlBrakmo et. Al
(Section 6.4 Textbook)

• Basically Improved Wangs scheme
• Scheme
• Maintain smallest RTT (BaseRTT)
• Expected Throughput WindowSize/BaseRTT
• Actual Throughput WindowSize/RTT
• Diff Expected Actual
• If Diff lt a then increase linearly window size
• If Diff gt b then decrease linearly window size