1. Simulation based analysis of FAST TCP using OMNET++ Umair ul Hassan

2. Outline TCP Congestion Control Variations FAST TCP OMNET++

3. TCP Congestion Control Retransmission Timer Management Jacobson’s Algorithm Exponential RTO Backoff Karn’s Algorthim Window Management

4. Slow Start Increase cwnd by 1 for each ACK Exponential Increase Dynamic Window Sizing on Congestion Reset cwnd on packet loss and restart slow start Linear increase after threshold

5. Window Management Fast Retransmit On receiving out-of-order segment send an ACK for last in-order segment. Sender should wait atleast 3 duplicate ACKs before retransmission FAST Recovery Set cwnd = ssthreshold + 3 Increase by 1 on each duplicate ACK Set cwnd = ssthreshold on ACK

6. TCP Tahoe and Reno MeasureTahoeReno Slow Start  Dynamic Window Sizing on Congestion  Fast Retransmit  Fast Recovery 

7. Problems with TCP Reno Packet Level Slow additive increase and Fast Multiplicative decrease Oscillations due to binary congestion singal Flow Level Very small loss probability required Instability because of oscillations

8. TCP Vegas Delay Based Congestion Control New Retransmission Mechanism On duplicate ACK retransmit if RTT > RTO, don’t wait till 3 DACKs Congestion Aviodance Diff = Expected – Actual Modified Slow Start Alow exponential growth every other RTT

9. Congestion Window Update TCP Vegas cwnd + 1 if Diff<α Cwnd = cwnd – 1 if Diff>β cwnd otherwise TCP FAST cwnd + γ(α – Diff) if Diff<α Cwnd = cwnd – γ(Diff - α) if Diff>α cwnd otherwise

10. Implementation Per ACK

11. Implementation Per RTT

12. Problems Fairness when used with other variations Priority Queues

13. OMNET++ Discrete Event Simulation System NED language Atomic Modules Compound Modules Message based communication

14. INET Framework Internet Protocols (IP, TCP, UDP, PPP, ARP) TCPBaseAlg TCPReno and TCPTahoe TCPFast

15. Q & A