Rongdi Chen crd02@csnet1.cs.tsinghua Network Research Center

1. Performance Optimization in Wireless Mesh Networks Based on Mesh Point Priority Mechanism Rongdi Chen crd02@csnet1.cs.tsinghua.edu.cn Network Research Center Tsinghua Univ. Beijing, P.R.China

2. Background Performance degradation in WMN Mesh Point Priority Mechanism distinguish transmit priority of mesh points from two perspectives Performance evaluation Future works Conclusions Outline

3. Internet Internet Gateway Extend coverage Facilitate deployment Background Internet Internet Gateway

4. Background Cont.

5. Several mesh network solutions Nortel WMN Tropos MetroMesh Azalea MSR MeshDynamics Structured Mesh …… More real application scenarios Wireless campus Wireless city: Philadelphia, New York, Kaohsiung, Taibei …… Solutions state-of-the-art? No! The use of standard 802.11 MAC protocol Not suitable for the backhaul networking in WMN: media sharing and the weakness of CSMA/CA Performance deteriorates significantly: when the number of WMNs hops or the number of competing stations increases, especially for single radio single channel situation Current Status of WMN

6. Performance degradation: single radio single channel Performance Degradation in Wireless Mesh Network Effective system throughput: the total quantity of UDP payload received by all the destinations within a second

7. Degradation by number of hops: increase radios Use two or more radios dedicated for backhaul Degradation by number of competing stations: adjust 802.11 protocol parameters Bianchi: CWmin has great influence on the system performance Performance evaluation and enhancement of the CSMA/CA MAC protocol for 802.11 wireless LANs IEEE 802.11-saturation throughput analysis Hui Ma: Optimize multiple competing stations throughput degradation in WLAN (1 hop) situation by adjusting CWmin values Range estimation and performance optimization for IEEE 802.11 based on filter Does it work well in multihop situation? Question to be answered in our paper How to solve these problems?

8. WMN: backhaul networking, packet transmit in hop by hop fashion Mesh Access Point VS Normal station Same access opportunityto wireless medium Different contribution to effective system throughput the data transmitted by MAPs contribute more to effective system throughput than by normal stations, as the data should be transmitted by MAPs before they arrive at the destination Among different hop MAPs, the contribution to effective system throughout is also different We should distinguish these differences and guarantee the priority How to?: give MAP higher sending probability by adjusting CWmin and CWmax Analysis

9. MPPM distinguishes transmit priority of mesh points from two perspectives: The MAPs should have higher priority than the normal stations due to their outstanding contribution to effective system throughput. The priority among the MAPs should be adjusted according to the topology and traffic load of the wireless mesh network. Change the priority by adjusting the MAC protocol parameters: CWmin & CWmax Smaller contention window represents higher sending probability We can set smaller CWmin and CWmax for MAPs to get higher priority Mesh Point Priority Mechanism (MPPM)

10. Performance Evaluation • NS2 simulator with the CMU wireless extensions and NOAH routing protocol • Simulation parameters accord with IEEE 802.11b network specification • Ideal channels • RXThresh_: 5.844e-9, 125m • CSThresh_: 3.652e-10, 250m • dataRate: 11Mbps • UDP packet size: 1500 bytes • Simulation time: 400s • Saturated data source

11. Simulation results (1) • All the stations associated to 2 Hop MAP • Simulation runs for 400s • Calculate effective system throughput within each second • Use the steady data set to calculate Trimmed Mean throughput • Illustrated with MATLAB • By using MPPM the effective system throughput is greatly improved especially when the number of competing stations increases 2833.3Kbps 12.9%↑ 2403.87Kbps 2510.5Kbps 138.4%↑ 1008.17Kbps 2 Hop Throughput

12. Simulation results (2) • All the stations associated to 3 Hop MAP • Simulation runs for 400s • Calculate effective system throughput within each second • Use the steady data set to calculate Trimmed Mean throughput • Illustrated with MATLAB • By using MPPM the effective system throughput is greatly improved especially when the number of competing stations increases 1552.3Kbps 1150.0Kbps 80%↑ 862.4Kbps 180.3%↑ 410.3Kbps 3 Hop Throughput

13. Simulation results (3) • One station is associated to 2 Hop MAP and sends UDP flow to Server S at the rate 6 Mbps • The other stations are associated to 3 Hop MAP • Simulation runs for 400s • Calculate effective system throughput within each second • Use the steady data set to calculate Trimmed Mean throughput • Illustrated with MATLAB • By using MPPM the effective system throughput is greatly improved especially when the number of competing stations increases 1855.6Kbps 1413.0Kbps 92.0%↑ 140.8%↑ 966.8Kbps 586.7Kbps 3 Hop Throughput Case 1

14. The situation that many stations are associated to both 2 Hop MAP and 3 Hop MAP is also considered. The simulation result shows that MPPM still functions well. So in WMN, the MPPM can gain much higher throughput than standard IEEE 802.11 MAC If we dynamically adjust the CWmin and CWmax for both MAPs and stations based on the topology and traffic load of WMN, the more throughput gains would be achieved. Simulation results

15. More precise way to map the priority to the parameter value Ideal adaptive optimization mechanism Consider the fairness issue in WMN Achieve relative fairness by adjusting the protocol parameters Future works

16. Wireless Mesh Networks: a promising broadband wireless access infrastructure but suffers performance degradation problem Degradation when the number of hops increases Degradation when the number of competing stations increases Mesh Point Priority Mechanism Distinguish transmit priority of mesh points from two perspectives by adjusting the parameters of IEEE 802.11 MAC protocol Optimize effective system throughput Simple but effective Some future works Ideal adaptive optimization mechanism Consider fairness issues in Wireless Mesh Metworks Conclusions

17. Thank you! Any idea or other suggestions?