Abstract-In this paper we evaluate the capacity of an IEEE 802.11b network carrying voice calls in a wide range of scenarios, including varying delay constraints, channel conditions and voice call quality requirements. We consider both G.711 and G.729 voice encoding schemes and a range of voice packet sizes.We first present an analytical upper bound and, using simulation, show it to be tight in scenarios where channel quality is good and delay constraints are weak or absent. We then use simulation to show that capacity is highly sensitive to the delay budget allocated to packetization and wireless network delays. We also show how channel conditions and voice quality requirements affect the capacity. Selecting the optimum amount of voice data per packet is shown to be a trade-off between throughput and delay constraints: by selecting the packet size appropriately given the delay budget and channel conditions, the capacity can be maximized.Unless a very high voice quality requirement precludes its use, G.729 is shown to allow a capacity greater than or equal to that when G.711 is used, for a given quality requirement.

In this paper we study the ability of an IEEE 802.11g WLAN to support video-conferencing and data applications. We evaluate the number of simultaneous video-conference calls that can be supported, subject to user perception-based quality requirements, and compare the performance of two MAC protocols: the default Distributed Coordination Function (DCF) protocol and the Enhanced Distributed Channel Access (EDCA) protocol. We also assess the effect of the presence of data traffic generated by web browsing and file transfer applications and the physical size of the network on the number of video conference calls that can be supported.The analysis of the network is carried out by means of simulation; great care is taken to accurately represent the applications and the network, requiring several modifications and additions to the widely-used ns-2 network simulator. At the application layer, traffic is generated using realistic models or real traces, and user perception-based quality metrics (for example, the Mean Opinion Score for voice) are used to assess the network's performance. Within the network, we use accurate representations of the MAC protocols, and use a wireless channel model which incorporates the effect of frequency-selective fading.We find that the presence of data traffic does not reduce the number of video-conference calls that can be supported when EDCA is used; this is not the case with DCF. Furthermore, the performance of both data applications considered is slightly improved by the use of EDCA. 1324 0-7803-8938-7/05/$20.00 (C) 2005 IEEE