Steve Ward

Structured Decomposition of Adaptive Applications

We describe an approach to automate certain high- level implementation decisions in a pervasive application, allowing them to be postponed until run time. Our system enables a model in which an application programmer can specify the behavior of an adaptive application as a set of open-ended decision points. We formalize decision points as goals, each of which may be satisfied by a set of scripts called Techniques. The set of Techniques vying to satisfy any goal is additive and may be extended at runtime without needing to modify or remove any existing techniques. Our system provides a framework in which Techniques may compete and interoperate at runtime in order to maintain an adaptive application. Technique development may be distributed and incremental, providing a path for the decentralized evolution of applications. Benchmarks show that our system imposes reasonable overhead during application startup and adaptation.

NuMesh: an architecture optimized for scheduled communication

The NuMesh system defines a high-speed communication substrate optimized for off-line routing. By determining possible communication paths at compile time, highly efficient hardware and software constructs can be exploited to yield superior network performance. These communication paths can be independently tuned to allow more utilized paths greater bandwidth. Although communication paths are scheduled, data need not be sent during every scheduled cycle. Flow-control protocols allow for empty communication cycles as well as for data backup in the network. Limited gate delays between NuMesh registers as well as single-cycle message transfers allow for a high clock frequency and low network latency. A highly pipelined architecture for this communication is presented and a mechanism for efficient flow-controlled communication is discussed. A unique communication protocol is presented and shown to provide single-cycle transfers between nodes. An overview of the necessary compiler support is also provided. Preliminary results and a description of the current hardware and software status are listed.

A dynamic platform for runtime adaptation

We present a middleware platform for assembling pervasive applications that demand fault-tolerance and adaptivity in distributed, dynamic environments. Unlike typical adaptive middleware approaches, in which sophisticated component model semantics are embedded into an existing, underlying platform (e.g., CORBA, COM, EJB), we propose a platform that imposes minimal constraints for greater flexibility. Such a tradeoff is advantageous when the platform is targeted by automatic code generators that inherently enforce correctness by construction. Applications are written as simple, single-threaded programs that assemble and monitor a set of distributed components. The approach decomposes applications into two distinct layers: (1) a distributed network of interconnected modules performing computations, and (2) constructor logic that assembles that network via a simple block-diagram construction API. The constructor logic subsequently monitors the configured system via a stream of high-level events, such as notifications of resource availability or failures, and consequently provides a convenient, centralized location for reconfiguration and debugging. The component network is optimized for performance, while the construction API is optimized for ease of assembly.

Three-Dimensional Network Topologies

This paper presents the derivation and performance results of several new three-dimensional topologies. Various transformations can be applied to the conventional six-neighbor mesh in order to construct these topologies, which vary both in number of neighbors (degree) and logical connectivity. Analysis shows that after normalization for constant pin-count, lower-degree topologies yield lower latencies for long messages on unloaded networks, while higher-degree topologies possess higher bandwidth capacities. Although simulation results generally verify these findings, we also observe a surprising amount of difference in the performance between distinct topologies of the same degree.

The NuMesh: a modular, scalable communications substrate

Many standardized hardware communication interfaces offer runtime flexibility and configurability at the cost of efficiency. An alternate approach is the use of a highly-efficient, minimal communication element, with as much communication decision-making as possible done at compile time. NuMesh is a packaging and interconnect technology supporting high-bandwidth systolic communications on a 3D nearest-neighbor lattice; our goal is to combine Lego-like modularity with supercomputer performance. To date, the primary focus of the project has been the class of applications whose static communication patterns can be precompiled into independent and carefully choreographed finite state machines running on each node. Several extensions of the NuMesh to more general communication paradigms have been implemented, and the issues involved are under active exploration. This paper presents an overview of our approach, as well as an introduction to our current-generation prototype. We also discuss our software environment and simulation technology, and enumerate some of the applications and programming models we have developed to make full use of the capabilities of the NuMesh.

Reducing configuration overhead with goal-oriented programming

The rapid increase in the number and variety of consumer-level electronic devices without the corresponding development of device management technology has lead to a configuration nightmare. We propose to use goal-oriented programming over a substrate of network-portable objects to help reduce the amount of configuration users must do in order to have their applications use their devices efficiently. We detail an architecture and describe a prototype system using existing pervasive computing technology that plays music on the most appropriate devices without requiring user interaction and configuration

Curl: a language for web content

We describe a language designed for the representation of a broad spectrum of web content, including formatted text, graphics, and programmed application-level function. The approach described maps conventional markup tags to underlying, more general programming constructs, and provides local extensibility of the markup language by addition of programmed objects, procedures, and macros to the underlying object-oriented programming language. An implementation strategy based on a mix of static and dynamic just-in-time compilation techniques is described. The discussion focuses on a number of specific technical challenges raised by the languages breadth and performance goals, and the impact of these issues on Curls architecture.

Cloudtop: a workspace for the cloud

Even as users rely more on the web for their computing needs, they continue to depend on a desktop-like area for quick access to in-use resources. The traditional desktop is file-centric and prone to clutter, making it suboptimal for use in a web-dominated world. This paper introduces Cloudtop, a browser plugin that offers a lightweight workplace for temporary items, optimized around the idea that its contents originate from and will ultimately return to the web. Cloudtop improves upon the desktop by 1) implementing a simple, time-based notebook metaphor for managing clutter, 2) capturing and bundling extensible metadata for web resources, and 3) providing a platform for greater interface uniformity across sites.

Chit-based remote storage

We propose a model for reliable remote storage founded on contract law. Consumers submit their bits to storage providers in exchange for a chit. A chit is a cryptographically secure, verifiable contract between a consumer and the storage provider. A user can use the chit to request the bits from the provider. In return, the provider must be able to supply the chits bits to the user according to the terms of the chit. If the storage provider cannot supply the bits, then the provider must pay a penalty. Chits make explicit the penalty for losing data, allowing users to value their data and providers to quantify the financial risk they have undertaken by storing a set of chits. We envision chit-based storage being used as a reliable mechanism for users in pervasive environments.

Message from the technical program chairs

It gives us a great pleasure to introduce the technical program of the Eighth Annual IEEE International Conference on Pervasive Computing and Communications (PerCom 2010). The 28 papers included in our program are excellent examples of the high-quality research conducted over the broad spectrum of topics related to pervasive computing.