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Fairness Implementation and Throughput Tuning in Wireless Mesh Networks

This paper discusses the implementation of fairness and throughput tuning in wireless mesh networks, focusing on MAC layer fairness and end-to-end flow fairness. It proposes a token-based distributed scheduling method and explores solutions for achieving desired proportion and fairness in chain topologies. The results of experiments and simulations are presented to demonstrate the effectiveness of the proposed approaches.

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Fairness Implementation and Throughput Tuning in Wireless Mesh Networks

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  1. Fairness Implementation and Throughput Tuning in Wireless Mesh Networks 姓名:劉柏廷 學號:694415027 系所:電機所網路組

  2. Outline • Overview of Wireless Mesh Networks • Background and Related Work • MAC Layer Fairness Study • End-to-End Fairness Study • MAC Layer Fairness Discussion • Token-Based Distributed Scheduling • End-to-end Fairness Discussions and Solutions • Conclusion and Future Work

  3. Wireless Mesh Networks

  4. Desired Approach • Two categories of MAC layer solutions to WMNS • Extend existing MAC protocols • Multiple channels • Throughput tuning to desired proportion • Two fairness issues are studied • MAC layer fairness • End-to-end flow fairness • We focus on chain topologies

  5. N-node chain topology

  6. Unfairness of MAC Layer Throughput

  7. MAC Layer Fairness Discussion • Observe the node behavior when failure transmission occurs. • Hidden terminal problem is the major reason of packet collision • Traffic Model • CBR traffic flow to neighbor • 1024kbps • 2Mbps bandwidth

  8. End-to-end Fairness Study [JANGEUN][1]

  9. ,n=number of nodes Fairness Experiments • Avoiding hidden terminal problem is difficult to achieve • Two experiments are studied • Changing network topology from chain to ring • Increasing contention window size • Fairness Index:

  10. Experiment 1 : Ring Topology (Symmetric) (Asymmetric)

  11. Exp.1 – Successful Packets

  12. Exp.1 – Successful Packets

  13. Exp.2 – Fairness of Increasing CW 1->full fairness CW increases, fairness index increases

  14. Token-Based Distributed Scheduling • TDMA-like system • Token Concept • Concept of Cluster • Assumptions • Chain topology • Location knowledge • No-routing overhead • All nodes always have packets to send • Fixed Packet sizes

  15. Better !! Problem!! Token-Based Distributed Scheduling Round-Robin Round-Trip

  16. RTS (1,1) RTS (5,2) RTS (5,2) CTS CTS CTS Data Data Data Ack Ack RTS (2,1) RTS (2,1) CTS Data Data Ack RTS (2,1) RTS (2,1) CTS Data Data Ack RTS (2,1) RTS (2,1) CTS Data Data Ack Return,0,1 NAV Return,0,1 RTS (0,1) RTS (5,2) RTS (5,2) CTS CTS CTS Data Data Data Ack Ack Token-Based Distributed Scheduling • Node Configuration • Node (token,next,weight,type) • Node 1 (1,2,1,H) • Node 2 (1,3,1,I) • Node 3 (1,4,1,I) • Node 4 (1,1,1,T) • Node 5 (2,5,1,H) • Node type • H - Head node • T - Tail node • I - Interval node

  17. Token-based Distributed Scheduling-Throughput in Chain Topology

  18. Throughput (802.11 v.s. TDS) Better

  19. Fairness Comparison 1->full fairness

  20. Short Summary • Advantage • Fairness throughput • Can be tuned to desired proportion in 4 hops • Improve the total throughput (more than 7 hops) • Low delay and low jitter • Disadvantage • Node location must be known • Chain topology

  21. End-to-End Throughput Capacity 1142kbps in Glomosim

  22. More Simulations with 802.11 3 nodes 4 nodes

  23. Solutions • Still use TDS • Separated queues for each flow • Per flow fair queue • To achieve the per flow fairness • MAC-layer bandwidth tuning • To maximize the total throughput

  24. Separated Queues for Per Flow Single Queue Per Flow Fair Queue

  25. MAC-layer Bandwidth Tuning MAC-layer bandwidth tuning

  26. Six Case Studies for 4 Flows • 802.11 • Single FIFO queue • Per flow fair queue • TDS 1:1:1:1 • Single FIFO queue • Per flow fair queue • TDS 1:2:3:4 • Single FIFO queue • Per flow fair queue

  27. Results of MAC layer throughput Unit: Number of Packets

  28. End-to-end Flows Comparison

  29. RTS (1,1) RTS (1,1) RTS (5,2) RTS (5,2) RTS (5,2) RTS (5,2) CTS CTS CTS CTS CTS CTS Data Data Data Data Data Data Ack Ack Ack Ack RTS (2,1) RTS (2,1) CTS CTS Data Data Ack Ack RTS (2,1) RTS (2,1) CTS Data Data Ack NAV Return,0,1 Advanced TDS • Because of the direction of traffic in WMN is uni-direction to gateway. • Number of members in a Cluster change to 3.

  30. Results of MAC layer throughput for uni-direction traffic Better! Better! Unit: Number of Packets

  31. Conclusions • MAC layer • The hidden terminal problem causes serious unfairness in throughput in multi-hop networks. • The ring topology and contention window are considered to solve the unfairness problem. • Propose atoken-based distributed scheduling that can achieve the fairness result and desired proportion in four hops. • Network Layer • Analyze and solve the end-to-end unfairness

  32. Future Work • One-dimension (chain topology) • Remove four-hop limitation • Two-dimension (mesh topology) • Multi-channel implementation

  33. Reference [1] J. Jun and L. Sichitiu, “The Nominal capacity of wireless mesh networks,” IEEE Wireless Communication, pp. 8–14, October 2003.

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