A software support infrastructure for wireless access routers

Routers are expected to play an important role in the Internet protocol-based wireless data network. Although a substantial number of adaptive and intercell coordination 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 channel-adaptive 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 link-layer information feedback on both data and control planes. It also permits the router to enforce its policies (e.g., policing) more effectively through underlying link-layer mechanisms. It further enables interaccess-point coordination at the RC. As showcases, we implement under DIRAC the prototypes of three wireless network services: link-layer assisted fast handover, channel-adaptive scheduling, and link-layer enforced policing. Our implementation and experiments show that our distributed wireless router provides a flexible framework, which enables advanced network-layer wireless services that are adaptive to channel conditions and host mobility.