Achieving Flow Isolation in 802.11 Networks with the DTT Scheduler
Though the IEEE 802.11 standard has reached wide acceptance, its main access function, the Distributed Coordination Function (DCF), still suffers from some relevant problems coming from the specific features of the wireless channel. By means of simulation, we analyse the performance anomaly and the “inter-flow blocking” problems, highlighting the mechanisms that generate them. Starting from these insights, we propose a simple centralized channel aware scheduling algorithm, named Deficit Transmission Time (DTT). The basic principle under the DTT is measuring the channel quality in terms of frame transmission times. This measurement is then used to take scheduling decisions that guarantee each downlink flow an equal time share of the channel. The proposed scheduler has been developed and deployed in a Linux-based prototype AP to experimentally evaluate its performance. The results clearly show the improvements introduced by the DTT in terms of flow isolation and reduction of the effects of the performance anomaly.
KeywordsMedium Access Control Access Point Distribute Coordination Function Medium Access Control Layer Channel Quality
Unable to display preview. Download preview PDF.
- 1.ANSI/IEEE Std 802.11, 1999 Edition. Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specificationsGoogle Scholar
- 2.Pilosof, S., Ramjee, R., Raz, D., Shavitt, Y., Sinha, P.: Understanding TCP Fairness over Wireless LAN. In: Proc. of IEEE Infocom 2003, San Francisco (April 2003)Google Scholar
- 3.Jiang, L.B., Liew, S.C.: Proportional Fairness in Wireless LANs and Ad Hoc Networks. In: IEEE Wireless Communications and Network Conference (March 2005)Google Scholar
- 4.Heusse, M., Rousseau, F., Berger-Sabbatel, G., Duda, A.: Performance Anomaly of 802.11b. In: Proc. of IEEE Infocom 2003, San Francisco (April 2003)Google Scholar
- 6.Bhagwat, P., Krishna, A., Tripathi, S.: Enhancing throughput over wireless LANs using channel state dependent packet scheduling. In: Proc. of InfoCom 1996, March 1996, pp. 1133–1140 (1996)Google Scholar
- 8.The OMNeT++ discrete event simulation system, Available at: http://www.omnetpp.org
- 9.The Mobility Framework for OMNeT++, Available at: http://mobility-fw.sourceforge.net/hp/index.html
- 10.Garroppo, R.G., Giordano, S., Lucetti, S., Russo, F.: IEEE 802.11b Performance Evaluation: Convergence of Theoretical, Simulation and Experimental Results. In: Networks 2004, Wien, vol. 1, pp. 405–410 (2004)Google Scholar
- 12.Adamson, B., Greenwald, H.: MGEN User’s and Reference Guide (2004), Available at: http://mgen.pf.itd.nrl.navy.mil/mgen.html
- 14.Garroppo, R.G., Giordano, S., Lucetti, S., Tavanti, L.: A measurement-based channel aware scheduler to lessen VoIP capacity degradation in 802.11 networks, submitted to ICC 2006 and available at: http://netgroup-serv.iet.unipi.it/reports/dtt-voip-icc06.pdf