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Receiver-Driven Queue Management for achieving RTT-fairness in Wi-Fi Networks

This paper proposes a receiver-driven queue management architecture to achieve RTT-fairness in Wi-Fi networks. The architecture allows the base station to manage the shared buffer and ensure fairness between flows, addressing the RTT-fairness problem. The performance evaluation results show that the proposed algorithm improves throughput fairness in the network.

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Receiver-Driven Queue Management for achieving RTT-fairness in Wi-Fi Networks

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  1. GLOBECOM’09 December 03, 2009 Receiver-Driven Queue Managementfor achieving RTT-fairness in Wi-Fi Networks Dzmitry Kliazovich, Fabrizio Granelli, University of Trento, Italy Pedro Henrique Gomes, Nelson L. S. da Fonseca University of Campinas, Brazil

  2. Outline • Motivation and objectives • Receiver-Driven Queue Management (RDQM) architecture • RTT-fairness algorithm • Performance evaluation and results • Conclusions Fabrizio Granelli (granelli@disi.unitn.it)

  3. Motivation • IEEE 802.11 (Wi-Fi) as the de facto technology for wireless/mobile access networks • TCP as the main transport layer on the Internet • Wi-Fi in the infrastructure mode usually connects heterogeneous wired network to the last-mile wireless link • BS’s buffer plays a key role for sharing the wireless resources between all the flows • RTT-fairness problem • Flows with low RTT monopolize the BS’s buffer, achieving higher throughput than flows with high RTT Fabrizio Granelli (granelli@disi.unitn.it)

  4. Objectives • Queue management is centralized at the BS’s buffer to better share the wireless resources • Receiver-driven architecture proposed • Mobile nodes send information to Base Station throughput a feedback channel created at link layer • Base Station manages the shared buffer to ensure fairness between the flows • RTT-fairness is in the focus Fabrizio Granelli (granelli@disi.unitn.it)

  5. RDQM architecture • Receiver-Driven Queue Management • BS manages its outgoing queue of wireless interface • Mobile stations send to BS supporting information (RTT of incoming flows) encapsulating them into link layer ACK frames • Totally transparent to high-layer protocols and legacy 802.11 nodes • Incremental deployment • Easy implementation (changes only in the wireless network) • Generic framework that can be used to achieve any goal, such as RTT-fairness Fabrizio Granelli (granelli@disi.unitn.it)

  6. RDQM architecture Fabrizio Granelli (granelli@disi.unitn.it)

  7. IEEE 802.11 MAC employs stop-and-wait ARQ, requiring positive acknowledge for every packet Mobile receivers send the most recent RTT statistics through the LL-ACK packets Using 14 bits of reserved portion in the Duration field Fabrizio Granelli (granelli@disi.unitn.it)

  8. RTT-fairness algorithm • RDQM uses RTT statistics of all the flows to divide the buffer space proportionally to the RTT values • Prioritizing flows with large RTT and • Avoiding monopolization of flows with low RTT • Based on the TCP flow requirement to have at least Bandwidth-Delay Product (BDP) allocated at the bottleneck buffer for achieving 100% of utilization Fabrizio Granelli (granelli@disi.unitn.it)

  9. Performance evaluation • Simulation Setup • Ns2 simulator with RDQM module • IEEE 802.11b wireless standard • Wired-cum-wireless topology with N flows (with variable RTT) • Performance Metrics • Individual flow throughput values • Throughput variation • Throughput fairness Fabrizio Granelli (granelli@disi.unitn.it)

  10. Simulation topology Fabrizio Granelli (granelli@disi.unitn.it)

  11. Performance results (1) Drop-Tail RDQM • Network with flows • Throughput Vs. Buffer size Fabrizio Granelli (granelli@disi.unitn.it)

  12. Performance results (2) • Multiple flows scenario • Maximum throughput difference between all flows Fabrizio Granelli (granelli@disi.unitn.it)

  13. Performance results (3) Jain’s index Coefficient of variance Fabrizio Granelli (granelli@disi.unitn.it)

  14. Conclusions • RDQM: Receiver-Driven Queue Management • Improves BS’s queue management in Wi-Fi networks • Mobile nodes can assist BS queue management by sending such parameters as RTT stats using a link layer feedback channel • RTT-fairness is achieved by means of proportional buffer allocation • But not only fairness is concerned RDQM architecture is rather general solution • Future work will deal with other goals for RDQM algorithm: BDP fairness, real-time applications, etc. Fabrizio Granelli (granelli@disi.unitn.it)

  15. Thank you! Fabrizio Granelli (granelli@disi.unitn.it)

  16. Drop-Tail RDQM • Network with 5 flows • Delays of 5, 10, 20, 50 and 100 ms • Throughput Vs. Buffer size Fabrizio Granelli (granelli@disi.unitn.it) December 03, 2009

  17. Drop-Tail RDQM • Fairness allocation proportional to the Bandwidth-Delay Product (BDP) – 6 Flows • Delays of 5, 10 and 20 ms • Datarates of 11, 5.5 and 1 Mbps • Throughput Vs. Buffer size Fabrizio Granelli (granelli@disi.unitn.it) December 03, 2009

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