1. 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

2. 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

3. Fabrizio Granelli (granelli@disi.unitn.it)
Motivation
IEEE (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

4. 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

5. 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 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

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

7. Fabrizio Granelli (granelli@disi.unitn.it)
IEEE 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

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
December 03, 2009
Fabrizio Granelli

9. Performance evaluation
Simulation Setup
Ns2 simulator with RDQM module
IEEE b 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

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

11. Performance results (1)
Network with flows
Throughput Vs. Buffer size
Drop-Tail
RDQM
December 03, 2009
Fabrizio Granelli

12. Performance results (2)
Multiple flows scenario
Maximum throughput difference between all flows
December 03, 2009
Fabrizio Granelli

13. Performance results (3)
Jain’s index
Coefficient of variance
December 03, 2009
Fabrizio Granelli

14. 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

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

16. 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

17. 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