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Priority Queuing

Priority Queuing. Achieving Flow ‘Fairness’ in Wireless Networks. Thomas Shen Prof. K.C. Wang SURE 2005. Wireless Mesh Networks. Similar to ad-hoc networks Characteristics Cheaper deployment Connectivity Redundancy Current Technologies Hardware 802.11b Proprietary Software

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Priority Queuing

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  1. Priority Queuing Achieving Flow ‘Fairness’ in Wireless Networks Thomas Shen Prof. K.C. Wang SURE 2005

  2. Wireless Mesh Networks • Similar to ad-hoc networks • Characteristics • Cheaper deployment • Connectivity Redundancy • Current Technologies • Hardware • 802.11b • Proprietary • Software • Proprietary • Open Source • Open Challenges • Security • No standard yet – 802.11s

  3. Internet Motivation • Multiple user access causes contention for network access • MAC layer governs individual node access • Network layer governs flows • Study network layer queuing methods • Implement packet assignment to control flows for QoS

  4. 802.11 – MAC layer • Carrier Sense Multiple Access / Collision Avoidance (CSMA/CA) • Optional RTS/CTS • Random Backoff

  5. Queue Queue 0 Queue 1 Queue 2 Flow 0 If packets in queue else Flow 1 If packets in queue else Flow 2 Priority Assignment Methods • Strict Priority Queuing • FIFO

  6. Queue 0 Queue 1 Queue 2 Flow 0 Probability 0.1 Flow 1 Probability 0.2 Flow 2 Probability 0.7 Priority Assignment Methods • Weighted Fair Queuing

  7. Service packets with combination of strict priority and weighted fair queuing Multiple queues Categorize packets according to type and source Controllable weights Routing Packets Queue 0 Own Packets Queue 1 Others’ Packets Queue 2 Our Queuing Strategy Enqueue

  8. MAC layer If packets exist else Queue 0 Queue 1 Queue 2 If packets exist Probability 1- p If packets exist Probability p Our Queuing Strategy Dequeue • Routing packets always serviced first • Modify p to change weights • Threshold = probability of choosing others’ packet over own packet

  9. ns-2 • The Network Simulator ns-2 • Event driven • Open source • Network Animator NAM • http://www.isi.edu/nsnam/ns/

  10. Simulations • Types of traffic • Constant Bit Rate traffic over UDP • UDP is unreliable, one way traffic. • FTP traffic over TCP • TCP is reliable, two way traffic with flow control. • Metrics • Calculate end-to-end throughput for TCP • Calculate end-to-end success rate for UDP • Simulation time of 1000s • Random starting time between 1~2s • Assumed error-free transmission • Five trials each

  11. Triple Chain 3 1 T I 0 2 Nodes in range connected by dashed lines

  12. One hop Two hop Triple Chain UDP Dashed – Original Solid - Priority 200KBps CBR traffic

  13. One hop Two hop Triple Chain TCP Dashed – Original Solid - Priority

  14. 2 1 0 T2 T1 I Quad Chain Each 200Kbps CBR traffic

  15. Flow 0 Original Flow 0 New Flow 1 Original Flow 2 Original Flow 2 New Flow 1 New Quad Chain UDP Results

  16. Flow 0 New Flow 2 New Flow 1 New Quad Chain UDP Results

  17. Quad Chain TCP • TCP throughput for 3-hop flow was terrible • Lack of MAC access prevents packets from being sent • With few packets, queuing method has no effect • 802.11 not efficient for multi-hop networks as documented in literature

  18. Small Mesh I 0 3 1 2 2 5 4 100Kbps CBR traffic

  19. One hop Flow 4/5 Original Two hop Flow 2 Original Three hop Small Mesh UDP Results

  20. Conclusion • Results show throughput is unbalanced using FIFO • Priority queuing allocates bandwidth among flows • In our simulations, thresholds of 0.5 to 0.7 distributed throughput most equally

  21. Future Work • Implement different priority assignment strategies • Identify potential objectives to guide priority assignment • Ensure throughput regardless of route length by categorizing packets according to number of hops taken • Ensure throughput of certain users by categorizing packets according to source • Ensure throughput of certain applications by categorizing according to packet type • Static vs. dynamic priority assignment • Devise a performance criteria to evaluate fairness

  22. Acknowledgement • Professor K.C. Wang • Professor D. Noneaker • Professor X.B. Xu • Clemson University • NSF

  23. References • Acharya, Misra, and Bansal. Design and Analysis of a Cooperative Medium Access Scheme for Wireless Mesh Networks • Akyildiz, Wang, and Wang. Wireless Mesh Networks: A Survey • Corson, Macker and Batsell. Architectural Considerations for Mobile Mesh Networking • Jun and Sichitiu. The Nominal Capacity of Wireless Mesh Networks • Kanodia, Li, Sabharwal, Sadeghi, and Knightly. Distributed Multi-Hop Scheduling and Medium Access with Delay and Throughput Constraints • Karrer, Sabharwal, and Knightly. Enabling Large-scale Wireless Broadband: The Case for TAPs • Kurose and Ross. Computer Networking: A Top-down Approach Featuring the Internet • Raniwala and Chiueh. Architecture and Algorithms for an IEEE 802.11-Based Multi-Channel Wireless Mesh Network • Peterson and Davie. Computer Networks • Schwartz. Mobile Wireless Communications • Tsai and Chen. IEEE 802.11 MAC Protocol over Wireless Mesh Networks: Problems and Perspectives • Wang and Ramanathan. End-to-end Throughput and Delay Assurances in Multihop Wireless Hotspots • Yin, Zeng, and Agrawal. A Novel Priority based Scheduling Scheme for Ad Hoc Networks

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