The Community for Technology Leaders
RSS Icon
Issue No.08 - August (2009 vol.8)
pp: 1063-1076
An Chan , University of California, Davis, Davis
Soung Chang Liew , The Chinese University of Hong Kong, Hong Kong
IEEE 802.11 WLAN has high data rates (e.g., 11 Mbps for 802.11b and 54 Mbps for 802.11g), while voice streams of VoIP typically have low-data-rate requirements (e.g., 29.2 Kbps). One may, therefore, expect WLAN to be able to support a large number of VoIP sessions (e.g., 200 and 900 sessions in 802.11b and 802.11g, respectively). Prior work by one of the authors, however, indicated that 802.11 is extremely inefficient for VoIP transport. Only 12 and 60 VoIP sessions can be supported in an 802.11b and an 802.11g WLAN, respectively. This paper shows that the bad news does not stop there. When there are multiple WLANs in the vicinity of each other—a common situation these days—the already low VoIP capacity can be further eroded in a significant manner. For example, in a {5 \times 5}, 25-cell multi-WLAN network, the VoIP capacities for 802.11b and 802.11g are only 1.63 and 10.34 sessions per AP, respectively. This paper investigates several solutions to improve the VoIP capacity. Based on a conflict graph model, we propose a clique-analytical call admission scheme, which increases the VoIP capacity by 52 percent from 1.63 to 2.48 sessions per AP in 802.11b. For 11g, the call admission scheme can also increase the capacity by 37 percent from 10.34 to 14.14 sessions per AP. If all the three orthogonal frequency channels available in 11b and 11g are used to reduce interferences among adjacent WLANs, clique-analytical call admission scheme can boost the capacity to 7.39 VoIP sessions per AP in 11b and 44.91 sessions per AP in 11g. Last but not least, this paper expounds for the first time the use of coarse-grained time-division multiple access (CoTDMA) in conjunction with the basic 802.11 CSMA to eliminate the performance-degrading exposed-node and hidden-node problems in 802.11. A two-layer coloring problem (which is distinct from the classical graph coloring problem) is formulated to assign coarse time slots and frequency channels to VoIP sessions, taking into account the intricacies of the carrier-sensing operation of 802.11. We find that CoTDMA can further increase the VoIP capacity in the multi-WLAN scenario by an additional 35 percent, so that 10 and 58 sessions per AP can be supported in 802.11b and 802.11g, respectively.
VoIP, multiple WLANs, CSMA, coarse-grained time-division multiple access, clique-analytical call admission control.
An Chan, Soung Chang Liew, "Performance of VoIP over Multiple Co-Located IEEE 802.11 Wireless LANs", IEEE Transactions on Mobile Computing, vol.8, no. 8, pp. 1063-1076, August 2009, doi:10.1109/TMC.2008.176
[1] W. Wang, S.C. Liew, and V.O.K. Li, “Solutions to Performance Problems in VoIP over 802.11 Wireless LAN,” IEEE Trans. Vehicular Technology, vol. 54, no. 1, pp. 366-384, Jan. 2005.
[2] W. Wang, S.C. Liew, Q.X. Pang, and V.O.K. Li, “A Multiplex-Multicast Scheme That Improves System Capacity of Voice-over-IP on Wireless LAN by 100%,” Proc. Ninth IEEE Symp. Computers Comm., June 2004.
[3] D.P. Hole and F.A. Tobagi, “Capacity of an IEEE 802.11b Wireless LAN Supporting VoIP,” Proc. IEEE Int'l Conf. Comm. (ICC '04), vol. 1, pp. 196-201, June 2004.
[4] F. Anjum et al., “Voice Performance in WLAN Networks—An Experimental Study,” Proc. IEEE Global Comm. Conf. (GLOBECOM '03), vol. 6, pp. 3504-3508, Dec. 2003.
[5] S. Garg and M. Kappes, “An Experimental Study of Throughput for UDP and VoIP Traffic in IEEE 802.11b Networks,” Proc. IEEE Wireless Comm. and Networking Conf. (WCNC '03), vol. 3, pp. 1748-1753, Mar. 2003.
[6] H. Wu et al., “SOFTMAC: Layer 2.5 Collaborative MAC for Multimedia Support in Multihop Wireless Networks,” IEEE Trans. Mobile Computing, vol. 6, no. 1, pp. 12-25, Jan. 2007.
[7] D. Niculescu et al., “Performance of VoIP in a 802.11 Wireless Mesh Network,” Proc. IEEE INFOCOM, Apr. 2006.
[8] S. Ganguly et al., “Performance Optimizations for Deploying VoIP Services in Mesh Networks,” IEEE J. Selected Areas in Comm., vol. 24, no. 11, pp. 2147-2158, Nov. 2006.
[9] The Network Simulator—ns2,, 2007.
[10] Cisco System, Data Considerations and Evolution of Transmission Network Design, optical/ps5724/ps2006prod_white_ paper0900aecd803faf8f_ps2001_Products_White_Paper.html , 2009.
[11] A. Sfairopoulou, C. Macián, and B. Bellalta, “VoIP Codec Adaptation Algorithm in Multirate 802.11 WLANs: Distributed vs. Centralized Performance Comparison,” Dependable Adaptable Networks Services, pp. 52-61, Springer, 2007.
[12] M.S. Gast, 802.11 Wireless Networks: Definitive Guide. O'Reilly, 2002.
[13] L.B. Jiang and S.C. Liew, “Hidden-Node Removal and Its Application in Cellular WiFi Networks,” IEEE Trans. Vehicular Technology, vol. 56, no. 5, pp. 2641-2654, Sept. 2007.
[14] Cisco System, Extending the Reach of a LAN, http://www. , 2009.
[15] L.B. Jiang and S.C. Liew, “Improving Throughput and Fairness by Reducing Exposed and Hidden Nodes in 802.11 Networks,” IEEE Trans. Mobile Computing, vol. 7, no. 1, pp. 34-49, Jan. 2008.
[16] Clique, 29 , 2009.
[17] Maximal Clique, , 2009.
[18] IEEE Std. 802.11e, Part 11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications. Amendment 8: MAC Quality of Service Enhancements, IEEE, Nov. 2005.
[19] J. Snow, W. Feng, and W. Feng, “Implementing a Low Power TDMA Protocol over 802.11,” Proc. IEEE Wireless Comm. and Networking Conf. (WCNC '05), vol. 1, pp. 75-80, Mar. 2005.
[20] S. Sharma et al., “Implementation Experiences of Bandwidth Guarantee on a Wireless LAN,” Proc. ACM/SPIE Multimedia Computing and Networking, Jan. 2002.
[21] T. Chiueh and C. Venkatramani, “Design, Implementation, and Evaluation of a Software-Based Real-Time Ethernet Protocol,” ACM SIGCOMM Computer Comm. Rev., vol. 25, no. 4, pp. 27-37, 1995.
[22] K.M. Sivalingam et al., “Design and Analysis of Low-Power Access Protocols for Wireless and Mobile ATM Networks,” Wireless Networks, vol. 6, no. 1, pp. 73-87, Feb. 2000.
[23] F.N. Ali et al., “Distributed and Adaptive TDMA Algorithms for Multiple-Hop Mobile Networks,” Proc. IEEE Military Comm. Conf. (MILCOM '02), pp. 546-551, Oct. 2002.
[24] A. Kanzaki, T. Hara, and S. Nishio, “An Adaptive TDMA Slot Assignment Protocol in Ad Hoc Sensor Networks,” Proc. ACM Symp. Applied Computing (SAC '05), Mar. 2005.
[25] Z. Cai and M. Lu, “SNDR: A New Medium Access Control for Multi-Channel Ad Hoc Networks,” Proc. IEEE Vehicular Technology Conf. (VTC '00), May 2000.
[26] D.J.A. Welsh and M.B. Powell, “An Upper Bound for the Chromatic Number of a Graph and Its Application to Timetabling Problems,” Computer J., vol. 10, pp. 85-86, 1967.
[27] G. Bianchi, “Performance Analysis of the IEEE 802.11 Distributed Coordination Function,” IEEE J. Selected Areas in Comm., vol. 18, no. 3, pp. 535-547, Mar. 2000.
[28] O. Tickoo and B. Sikdar, “Modeling Queuing and Channel Access Delay in Unsaturated IEEE 802.11 Random Access MAC Based Wireless Networks,” IEEE/ACM Trans. Networking, vol. 16, no. 4, pp. 878-891, Aug. 2008.
[29] C. Hoene et al., “Measuring the Impact of Slow User Motion on Packet Loss and Delay over IEEE 802.11b Wireless Links,” Proc. IEEE Conf. Local Computer Networks (LCN '03), 2003.
23 ms
(Ver 2.0)

Marketing Automation Platform Marketing Automation Tool