Mobile Netw Appl (2009) 14:523–538 DOI 10.1007/s11036-009-0157-6 VoIP over Wi-Fi Networks: Performance Analysis and Acceleration Algorithms Yeonsik Jeong · Sandeep Kakumanu · Cheng-Lin Tsao · Raghupathy Sivakumar Published online: 10 February 2009 © Springer Science + Business Media, LLC 2009 Abstract The expected VoIP call capacity in a one hop IEEE 802.11b network with G.711 voice codec is about 85 simultaneous calls, but the actual observed capacity is only 5 calls even at the highest data rate and under zero loss conditions. In this paper we an- alyze the reasons behind this inferior performance of VoIP traffic. We also present algorithms at the me- dium access control layer to improve the observed call An earlier version of this paper was published in the IEEE Conference on Broadband Communications, Networks, and Systems (BroadNets) 2007 [1]. This work was supported in part by the National Science Foundation under grants CNS-0519733 and CNS-0721296, and the Georgia Tech Broadband Institute. Yeonsik Jeong was also supported under the Korea Research Foundation Grant KRF-2005-214-D00362 funded by the Korean Government (MOEHRD). This work was performed when Y. Jeong was a research scientist in the GNAN research group at Georgia Institute of Technology. Y. Jeong (B ) Department of Multimedia System Engineering, SungKongHoe University, Seoul, Korea e-mail: ysjeong@mail.skhu.ac.kr, ysjeong@ece.gatech.edu S. Kakumanu · C.-L. Tsao · R. Sivakumar School of Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, GA, USA S. Kakumanu e-mail: ksandeep@ece.gatech.edu C.-L. Tsao e-mail: cltsao@ece.gatech.edu R. Sivakumar e-mail: siva@ece.gatech.edu capacity. Using ns-2 based simulations, we evaluate the algorithms and show that performance improvements of more than 300% can be achieved. Finally, using a testbed implementation of one of the proposed al- gorithms, we show its feasibilty in real world VoIP implementations. Keywords VoIP · Wi-Fi networks · call capacity · ACK aggregation · frame aggregation · link adaptation 1 Introduction Voice over IP (VoIP) services have been significantly gaining prominence over the last few years because of a number of impressive advantages over their traditional circuit-switched counterparts including but not limited to high bandwidth efficiency, low cost, and flexibility of using various compression strategies. Simultaneously, the use of wireless networks has also grown tremen- dously over the past years. Wireless LAN (WLAN) so- lutions, armed with better physical layer technologies, now promise high data rates of more than 100 Mbps such as IEEE 802.11n. In this context, recent efforts have focused on mar- rying the potential benefits of VoIP and WLANs to provide wireless telephone services. A natural ques- tion that then arises is how well does VoIP perform over WLAN environments? The answer to this question is counter-intuitive. Even though the WLANs boast very high data rates and a typical VoIP call carries only 128 Kbps of bidirectional data (using G.711 voice codec), the number of VoIP calls supported by these