Capacity of an IEEE 802.11b wireless LAN supporting VoIP

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.