Modern distributed applications utilize a rich variety of distributed services. Due to the computation-centric notions of modern machines, application-level implementations of these services are problematic for applications requiring high data transfer rates, for reasons that include the inability of modern architectures to efficiently execute computations with communication. Conversely,network-level implementations of services are limited due to the network's inability to interpret application-level data or execute application-level operations on such data. The emergence of programmable network processors capable of high-rate data transfers, with flexible interfaces for external reconfiguration, has created new possibilities for movement of processing into the network infrastructure. This thesis explores the extent to which programmable network processors can be used in conjunction with standard host nodes, to form enhanced computational host-ANP (Attached Network Processor) platforms that can deliver increased efficiency for variety of applications and services. The main contributions of this research are the creation of SPLITS, a Software architecture for Programmable LIghtweighT Stream handling, and its key abstraction stream handlers. SPLITS enables the dynamic configuration of data paths through the host-ANP nodes, and the dynamic creation, deployment and reconfiguration of application-level processing applied along these paths. With SPLITS, application-specific services can be dynamically mapped to the host, ANP, or both, to best exploit their joint capabilities. The basic abstraction used by SPLITS to represent instances of application-specific activities are stream handlers - parameterizable, lightweight, computation units that operate on data headers as well as application-level content. Experimental results demonstrate performance gains of executing various application-level services on ANPs, and demonstrate the importance of the SPLITS host-ANP nodes to support dynamically reconfigurable services, and to deal with the resource limitations on the ANPs.

Middleware has become a key enabler for the development of distributed applications. Unfortunately, conventional middleware technologies do not yet offer sufficient functionality to make them suitable for mobile environments. This dissertation proposes a novel middleware approach termed opportunistic overlays and its dynamically reconfigurable support framework for building efficient mobile applications. Specifically, we address the inefficiency of content delivery introduced by node mobility and by dynamically changing system loads, in the context of publish/subscribe systems. In response to changes in physical network topology, in nodes' physical locations, and in network node behaviors, the opportunistic overlay approach dynamically adapts event dissemination structures (i.e., broker overlays) with the goal of optimizing end-to-end delays in event delivery. Adaptation techniques include the dynamic construction of broker overlay networks, runtime changes of mobile clients' assignments to brokers, and dynamic broker load balancing. Essentially, opportunistic overlays implement a middleware-level analogue of the networking routing protocols used in wireless communications (i.e., Mobile IP, AODV, DSR and DSDV). By thus coordinating network- with middleware-level routing, opportunistic overlays can attain substantial performance improvements over non-adaptive event systems. Such improvements are due to their use of shorter network paths and better balancing of loads across event brokers. Opportunistic overlays and the adaptive methods they use are realized by a set of distributed protocols implemented in a Java-based publish/subscribe infrastructure. Comprehensive performance evaluations are performed via simulation, emulation, and with two representative applications on actual networks. Experimental results demonstrate that the opportunistic overlay approach is practically applicable and that the performance advantages attained from the use of opportunistic overlays can be substantial, in both infrastructure-based mobile environments and mobile ad hoc networks.