Routers are expected to play an important role in the IPbased wireless data network. Although a substantial number of techniques have been proposed to improve wireless network performance under dynamic wireless channel conditions and host mobility, a system support framework is still missing. In this paper, we describe DIRAC, a software-based router system that is designed for wireless networks to facilitate the implementation and evaluation of various channeladaptive and mobility-aware protocols. DIRAC adopts a distributed architecture that is composed of two parts: a Router Core (RC) shared by the wireless subnets, and a Router Agent (RA) at each access point/base station. RAs expose wireless link-layer information to the RC and enforce the control commands issued by the RC. This approach allows the router to make adaptive decisions based on linklayer information feedback. It also permits the router to enforce its policies (e.g., policing) more effectively through underlying link-l...