Simulation basedanalysis of FAST TCP     using OMNET++          Umair ul Hassan
Outline TCP  Congestion Control Variations FAST TCP OMNET++
TCP Congestion Control Retransmission   Timer Management    Jacobson’s Algorithm    Exponential RTO Backoff    Karn’s ...
Window Management Slow   Start    Increase cwnd by 1 for each ACK    Exponential Increase Dynamic    Window Sizing on ...
Window Management Fast   Retransmit    On receiving out-of-order segment send an ACK     for last in-order segment.    ...
TCP Tahoe and Reno  Measure                    Tahoe   Reno  Slow Start                                         Dynamic ...
Problems with TCP Reno Packet   Level    Slow additive increase and Fast Multiplicative     decrease    Oscillations du...
TCP Vegas Delay   Based Congestion Control New   Retransmission Mechanism    On duplicate ACK retransmit if RTT > RTO, ...
Congestion Window Update TCP   Vegas               cwnd + 1    if Diff<α    Cwnd =     cwnd – 1    if Diff>β          ...
Implementation              ___________________________________________              For earh source i : Per   ACK     1....
Implementation Per   RTT              ___________________________________________              For each source i, on comp...
Problems Fairness  when used with other variations Priority Queues
OMNET++ DiscreteEvent Simulation System NED language Atomic Modules Compound Modules Message based communication
INET Framework Internet        Protocols (IP, TCP, UDP, PPP, ARP) TCPBaseAlg TCPReno and TCPTahoe TCPFast
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04030038 proposal presentation

  1. 1. Simulation basedanalysis of FAST TCP using OMNET++ Umair ul Hassan
  2. 2. Outline TCP Congestion Control Variations FAST TCP OMNET++
  3. 3. TCP Congestion Control Retransmission Timer Management  Jacobson’s Algorithm  Exponential RTO Backoff  Karn’s Algorthim Window Management
  4. 4. Window Management 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. 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. 6. TCP Tahoe and Reno Measure Tahoe Reno Slow Start   Dynamic Window Sizing on Congestion   Fast Retransmit   Fast Recovery 
  7. 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. 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. 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. 10. Implementation ___________________________________________ For earh source i : Per ACK 1. Initialization : count i = wi and fastOni = 1 2. On arrival of each ACK of packet l (a) RTTi (l ) = CurrentTime − TimeStampi (l )  3 1 (b) ρ = min  ,   w 8  i  (c) ARTTi (l ) = (1 − ρ ) ARTTi (l ) + ( ρ ) RTTi (l ) (d) If fastOni = 1 :  wi (l )  i. Calculate ∆wi = γ  d i + α i − wi   ARTTi (l )  ii. If ∆wi > β : wi = wi + 1 iii. If ∆wi < − β : wi = wi − 1 (e) count i = counti − 1 (f) If counti ≤ 0 : (One RTT is finished) i. fastOni = 1 − fastOni ii. count i = wi iii. Call Fine Tuning Algorithm ___________________________________________
  11. 11. Implementation Per RTT ___________________________________________ For each source i, on completetion of each RTT  wi (l )  1. Calculate ∆wi = γ  d i + α i − wi   ARTTi (l )  2. If ∆wi ≥ 1 : wi = wi + 1 3. If ∆wi ≤ −1 : wi = wi − 1 ___________________________________________
  12. 12. Problems Fairness when used with other variations Priority Queues
  13. 13. OMNET++ DiscreteEvent Simulation System NED language Atomic Modules Compound Modules Message based communication
  14. 14. INET Framework Internet Protocols (IP, TCP, UDP, PPP, ARP) TCPBaseAlg TCPReno and TCPTahoe TCPFast
  15. 15. Q&A

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