Dzmitry Kliazovich, Fabrizio Granelli, University of Trento, Italy GLOBECOM’09 December 03, 2009 Receiver-Driven Queue Management for 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

Fabrizio Granelli (granelli@disi.unitn.it) Outline Motivation and objectives Receiver-Driven Queue Management (RDQM) architecture RTT-fairness algorithm Performance evaluation and results Conclusions December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Fabrizio Granelli (granelli@disi.unitn.it) 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 December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Fabrizio Granelli (granelli@disi.unitn.it) 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 December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Fabrizio Granelli (granelli@disi.unitn.it) 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 December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Fabrizio Granelli (granelli@disi.unitn.it) RDQM architecture December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Fabrizio Granelli (granelli@disi.unitn.it) 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 December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

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 December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

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 December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Fabrizio Granelli (granelli@disi.unitn.it) Simulation topology December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Performance results (1) Network with flows Throughput Vs. Buffer size Drop-Tail RDQM December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Performance results (2) Multiple flows scenario Maximum throughput difference between all flows December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Performance results (3) Jain’s index Coefficient of variance December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Fabrizio Granelli (granelli@disi.unitn.it) 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. December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

Fabrizio Granelli (granelli@disi.unitn.it) Thank you! December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)

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

Fabrizio Granelli (granelli@disi.unitn.it) 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 Drop-Tail RDQM December 03, 2009 Fabrizio Granelli (granelli@disi.unitn.it)