Voice and Data transmission over an 802.11 Wireless network

This paper analyzes the transmission of voice and data over an 802.11 Wireless Local Area Network (WLAN). The data is transmitted in a contention based access period, while the voice samples are transmitted during a contention free period, based on a polling scheme. Because statistical multiplexing can be utilized, speech may be outdated when a poll arrives. The portion of outdated speech is then clipped to decrease the load on the channel. We analyze the quality of the voice conversations in terms of the percentage of bits clipped as well as the throughput of the data for various parameters. We show the boundary conditions involved in the transmission of voice over the WLAN and demonstrate the impact of a time-bounded service on the throughput during the contention period. The results show that the high overhead introduced by the 802.11 WLAN standard results in a low number of possible voice conversations. It can also be concluded that the cooperation of the contention based and contention free periods results in a poor performance. Further, variation of the maximum payload size reveals that the largest possible maximum payload size must be selected to minimize the percentage of clipped bits and maximize the throughput. Finally, we show that a larger Superframe length provides the opportunity for more voice conversations or a higher data throughput, but requires increasing the Time To Live for the speech bits to retain an acceptable quality.