1. TCP with Adaptive Pacing for Multihop Wireless Networks Sherif M. EIRakabawy, Alexander Klemm, Christoph Lindemann University of Dortmund Germany Proceedings of the 6th ACM international symposium on Mobile ad hoc networking and computing 2005 Presented by JIUN-JAU CHIOU

2. Outline Introduction Motivation TCP-AP Performance – FTP-like data transfer – Variable length flows Conclusion

3. Introduction TCP with Adaptive Pacing (TCP-AP): – A congestion control algorithm for TCP over multihop IEEE 802.11 – TCP-AP provides a rate-based control by motnitoring RTTs to shrottles transmission rate to avoid congestion-related loss.

4. Motivation TCP’s window-based congestion control increase contention on 802.11. – Spatial reuse constraint of wireless channel in IEEE 802.11 – Packet loss due to hidden terminal problem. TCP identifies congestion when packet lossed. – This behavior result in increased congestion.

5. TCP-AP R max : upper bound of transmission rate Two parameters of TCP-AP to get R max – covRTT (coefficient of variation) : Quantifies the degree of contention on the network. – FHD (4-hop propagation delay): The transmitting time between Sorce node and Des node whitch lies 4 hops away.

6. cov RTT – N is number of RTT samples – /RTT is the mean of samples – RTT i denotes i-th RTT sample

7. Justify the applicability of cov RTT :

9. FHD:

10. Hidden terminal effects depend mainly on the characteristics of the network : – Interference range – Transmission range This paper consider “FHD” for the calculation of the transmission rate.

11. R max = 1 / FHD

12. TCP - Adaptive Pacing :

13. Parameter Tuning and Responsiveness: – Responsiveness: How quickly this algorithm adapts to changing network conditions. 2 parameters : – N : samples of RTT for calculation – α: averaing weight – (N, α) = (50, 0.7)

16. Performance (FTP-like) Chain topology :

17. Symmetric Parallel Chains Topology:

18. Asymmetric Parallel Chains Topology:

19. Grid Topology

20. Random Topology

21. Performance (variable length flows) Symmetric Parallel Chain Scenario:

23. Random Scenario: Pause = 1 sec

24. Conclusion Quntification of congestion by measuring the fluctuation of RTT samples using cov RTT Based on cov RTT and FHD, TCP-AP adaptively calculates the rate for pacing.