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 b Proprietary Software Proprietary Open Source Open Challenges Security No standard yet – s

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

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

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

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

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

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

ns-2 The Network Simulator ns-2 Event driven Open source Network Animator NAM

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

Triple Chain I T Nodes in range connected by dashed lines

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

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

Quad Chain I T1 T Each 200Kbps CBR traffic

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

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

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 not efficient for multi-hop networks as documented in literature

Small Mesh 100Kbps CBR traffic I

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

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

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

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

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