As the channel is accessed randomly in IEEE 802.11 WLAN systems, it’s difficult to support Quality of Services for real time applications. To solve the issue, there are already some approaches proposed in different network layers. However, when those QoS approaches are implemented in different network environments, the performance may vary significantly. In this paper, we will compare two major classes of QoS schemes for IEEE 802.11 WLAN in MAC layer and network layer respectively. The performances are compared in both one hop and multi-hop ad hoc network environments. It’s observed that MAC layer QoS scheme is very efficient in one hop network environments, while network layer QoS schemes is only efficient for multi-hop ad hoc networks. Based on the observations, it’s necessary to design a new hybrid scheme to efficiently support QoS in IEEE 802.11 WLAN system.