Our paper explores the issue of how to provide appropriate quality of service mechanisms incompatible with mobility in wireless local area networks. We present a hierarchical QoS architecture that extends Differentiated Services (DiffServ) to mobile hosts in a wireless environment. Our approach is based on controlling several parameters of a wireless LAN cell: the limited geographical span to ensure the same high bit rate for all hosts, the constrained rate of traffic sources and the limited number of active hosts in each cell. We give some details of experiments to show the quality of service differentiation over the 802.11b network.