The Internet's role is changing dramatically, from a means of connecting together PCs and servers to a ubiquitous communications medium interconnecting mobile personal devices, environmental sensors, and Web services. As new services (voice, video, emergency response, etc.) are being deployed on the infrastructure, there have been increased demands on extending the existing Internet architecture for new capabilities, such as efficient and resilient routing among mobile and wired nodes, location of proximity-based services, and wide-area service discovery and composition.;This dissertation presents an extensible Internet architecture M OSAIC---based on declarative languages and composable views over router, network and host state at different layers---to meet the demand of the emerging network services. The proposed architecture explicitly separates logical state representation and acquisition from physical implementation, to enable more extensible and adaptive protocols and distributed systems, because programmers can focus on high-level logical operations whose implementations may be separately and transparently optimized.;The main contributions made by this dissertation are: (1) a unified network architecture (MOSAIC) under which new networks can be developed, deployed, selected, and dynamically composed according application and administrator needs; (2) a declarative programming language (Mozlog) to concisely specify high-level network protocol specifications; (3) a runtime system prototype that can translate Mozlog specifications into efficient implementations.;To validate the approach, we evaluate the work in the context of a heterogeneous, dynamic Internet environment where end hosts are connected via both wired and wireless media and have diverse application requirements. We demonstrate that in MOSAIC, new network services can be readily introduced by either concisely specifying protocols in Mozlog or dynamically selecting and composing existing network services at low overheads.
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