Currently there is a growing interest to support Quality of Service(QoS) for multimedia application delivery over bandwidth limited and varying wireless network. Existing work either only focus at network level QoS via MAC scheduling or provide application level QoS via per-application admission control. Due to the lack of application information, the former may not meet the specific QoS requirements of different applications, while the latter results in poor scalability. In light of the limitations of existing approaches, we present a novel QoS architecture, which incorporates a two-level design. At the network level, the cross-layer scheduling and queue management provide service differentiation for wireless network. At the middleware level, a monitor maintains a global view of the application performance over the whole network, and an adaptor coordinates service adaptation to achieve the required QoS for multimedia applications. In this paper, we present the whole QoS architecture, with a focus on the middleware design, which adopts a control-based adaptation model. To validate our design, applications with different QoS requirements are built on top of the middleware. Experimental results show that, the specific QoS levels for multimedia applications can be successfully achieved in IEEE 802.11-based wireless environment.