Measurement and Analysis of the VoIP Capacity in IEEE 802.11 WLAN

We measured the capacity for VoIP traffic in an IEEE 802.11b wireless testbed and compared it with the theoretical capacity and our simulation results. We identified factors that have been commonly overlooked in past studies but affect experiments and simulations. We found that in many papers, the capacity for VoIP traffic has been measured via simulations or experiments without considering these factors, showing different capacity in each paper. After these corrections, simulations and experiments yielded a capacity estimate of 15 calls for 64 kb/s CBR VoIP traffic with 20 ms packetization interval and 38 calls for VBR VoIP traffic with a 0.39 activity ratio. Furthermore, we measured the capacity for VoIP traffic using each access category introduced in the 802.11e standard and the effect of the TCP traffic on VoIP traffic. We found that while the 802.11e standard can protect the QoS of VoIP against TCP traffic, it does not improve the capacity due to the significant retransmissions during TXOP.