S oftware engineers who want to migrate existing applications from fully connected environments to mobile environments face a significant problem in obtaining and maintaining network connectivity. In fully connected environments, connectivity is static and permanently established through wired networks. Applications simply "assume" that they are online continuously. This assumption is clearly invalid in mobile environments that use wireless connections. While decreases in computer size and cost have made it more practical to use a portable computer as a mobile workstation, and advances in wireless technologies have made it possible to access networks outside the reach of wired connections, the development of software for use in a mobile environment has lagged behind these technologies. In general, support for mobile computing is poorly integrated in operating systems and network software.In this article, we discuss some of these problems. We then describe a wireless design of a communication layer for mobile computing and a prototype based on that design. Our work was part of AMIGOS (Advanced Mobile Integration in General Operating Systems), a col-