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Articles 421 - 450 of 683
Full-Text Articles in Computer Engineering
Router Plugins: A Modular And Extensible Software Framework For Modern High Performance Integrated Services Routers, Dan Decasper, Zubin Dittia, Guru Parulkar, Bernhard Plattner
Router Plugins: A Modular And Extensible Software Framework For Modern High Performance Integrated Services Routers, Dan Decasper, Zubin Dittia, Guru Parulkar, Bernhard Plattner
All Computer Science and Engineering Research
Present day routers typically employ monolithic operating systems which are not easily upgraded and extensible. WIth the rapid rate of protocol development it is becoming increasingly important to dynamically upgrade router software in an incremental fashion. We have designed and implemented a high performance, modular, extended integrated services router software architecture in the NetBSD operating system kernel. This architecture allows code modules, called plugins, to be dynamically added and configured at run time. One of the novel features of our design is the ability to bind different plugins to individual flows; this allows for distinct plugin implementations to seamlessly coexist …
Terabit Burst Switching Progress Report (12/97-2/98), Jonathan S. Turner
Terabit Burst Switching Progress Report (12/97-2/98), Jonathan S. Turner
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This report summarizes progress on the Terabit Burst Switching Project at Washington University for the period from December 15, 1997 through March 15, 1998. Efforts during this period have concentrated on working out details of the burst switch architecture, evaluating a variety of implementation alternatives and developing the physical design of the 160 Gb/s ATM switch to allow demonstration of the burst switch within a realistic network context.
Integrating A Constraint Mechanism With The Javabeans Model, William M. Shapiro
Integrating A Constraint Mechanism With The Javabeans Model, William M. Shapiro
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The JavaBeans component model allows users to plug together software components to create Java applications by specifying simple relationships between component events and properties. This paper describes work on augmenting the simple JavaBeans model with a multi-way constraint mechanism that allows users to graphically specify more complex multi-way contraints, resolve cyclical constraints between bean properties and graphically layout bean components. We also discuss weaknesses in the JavaBeans model and Java Abstract Windowing Toolkit (AWT) that were discovered while integrating a constraint mechanism with JavaBeans.
Lime: Linda Meets Mobility, Gian Pietro Picco, Amy L. Murphy, Gruia-Catalin Roman
Lime: Linda Meets Mobility, Gian Pietro Picco, Amy L. Murphy, Gruia-Catalin Roman
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LIME is a system designed to assist in the rapid development of dependable mobile applications over both wired and ad hoc networks. Mobile agents reside on mobile hosts and all communication takes place via transiently shared tuple spaces distributed across the mobile hosts. The decoupled style of computing characterizing the Linda model is extended to the mobile environment. At the application level, both agents and hosts perceive movement as a sudden change of context. The set of tuples accessible by a particular agent residing on a given host is altered transparently in response to changes in the connectivity pattern among …
Tcp Dynamic Acknowledgment Delay: Theory And Practice, Daniel R. Dooly, Sally A. Goldman, Stephen D. Scott
Tcp Dynamic Acknowledgment Delay: Theory And Practice, Daniel R. Dooly, Sally A. Goldman, Stephen D. Scott
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We study an on-line problem that is motivated by the networking problem of dynamically adjusting delays of acknowledgments in the Transmission Control Protocol (TCP). The theoretical problem we study is the following. There is a sequence of n packet arrival times A = and a look-ahead coefficient L. The goal is to partition A into k subsequences sigma1, sigma2, ...,sigmak (where a subsequence end is defined by an acknowledgment) that minimizes a linear combination of the cost for the number of acknowledgments sent and the cost for the additional latency introduced by delaying acknowledgments. At each arrival, an oracle provides …
The Playground Mediator: Visual Tool For Configuring And Debugging Distributed Applications, T. Paul Mccartney
The Playground Mediator: Visual Tool For Configuring And Debugging Distributed Applications, T. Paul Mccartney
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The Mediator is a visual configuration tool for use with The Programmers' Playground distributed programming environment. With the Mediator, one can interactively launch distributed application modules, configured communication among the modules, observe communication patterns, interactively control module communication, kill running modules, and receive imported applications from a separate World Wide Web interface. This manual describes how to use the Mediator both as a stand-alone configuration tool and as a visual interface to the Playground Application Management System.
Congestion Control In Multicast Transport Protocols, Rajib Ghosh, George Varghese
Congestion Control In Multicast Transport Protocols, Rajib Ghosh, George Varghese
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We discuss congestion control mechanisms in multicast transport protocols and we propose TCP-M - a TCP-friendly Multicast transport protocol. TCP-M uses IP multicast to deliver data packets and acknowledgements to provide reliability. Ack implosion at the source is prevented by fusing acknowledgements at some intermediate routers. TCP-M reacts to network congestion exactly like TCP by having the sender emulate a TCP sender.
Search And Tracking Algorithms For Rapidly Moving Mobiles, Amy L. Murphy, Gruia-Catalin Roman, George Varghese
Search And Tracking Algorithms For Rapidly Moving Mobiles, Amy L. Murphy, Gruia-Catalin Roman, George Varghese
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With the advent of wireless technology and laptops, mobility is an important area of research. A fundamental problem in this area is the delivery of messages to a moving mobile. Current solutions work correctly only for slowly moving nodes that stay in one location long enough for tracking to stabilize. In this paper we consider the problem of message delivery to rapidly moving mobile units. With these algorithms, we introduce a new method for designing algorithms based on the paradigm of considering a mobile unit as a message, and adapting traditional message passing algorithms to mobility. Our first algorithm is …
Algorithms For Message Delivery In A Micromobility Environment, Amy L. Murphy, Gruia-Catalin Roman, George Varghese
Algorithms For Message Delivery In A Micromobility Environment, Amy L. Murphy, Gruia-Catalin Roman, George Varghese
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As computing components get smaller and people become accustomed to having computational power at their disposal at any time, mobile computing is developing as an important research area. One of the fundamental problems in mobility is maintaining connectivity through message passing as the user moves through the network. This is usually accomplished in one of two ways: search or tracking. In search, an algorithm hunts the mobile unit through the network each time a message is to be delivered, while in tracking, a specific home keeps up to date information about the current location of the mobile unit. Our paper …
Optimizing The Performance Of The Corba Internet Inter-Orb Protocol Over Atm, Aniruddha Gokhale, Douglas C. Schmidt
Optimizing The Performance Of The Corba Internet Inter-Orb Protocol Over Atm, Aniruddha Gokhale, Douglas C. Schmidt
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The Internet Inter-ORB Protocol (IIOP) enables heterogeneous CORBA-compliant Object Request Brokers (ORBs) to interoperate over TCP/IP networks. The IIOP uses the Common Data Representation (CDR) transfer syntax to map CORBA Interface Definition Langauge (IDL) data types into a bi-canonical wire format. Due to the excessive marshaling/demarshaling overhead, data copying, and high-levels of function call overhead, conventional implementation of IIOP protocols yield poor performance over high-speed networks. To meet the demands of emerging distributed multimedia applications, CORBA-compliant ORBs must support both interoperable and highly efficient IIOP implementations. This paper provides two contributions to the study and design of high performance CORBA …
Expressing Code Mobility In Mobile Unity, Gian Pietro Picco, Gruia-Catalin Roman, Peter J. Mccann
Expressing Code Mobility In Mobile Unity, Gian Pietro Picco, Gruia-Catalin Roman, Peter J. Mccann
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Advancements in network technology have led to the emergence of new computing paradigms that challenge established programming practices by employing weak forms of consistency and dynamic forms of binding. Code mobility, for instance, allows for invocation-time binding between a code fragment and the location where it executes. Similarly, mobile computing allows hosts (and the software they execute) to alter their physical location. Despite apparent similarities, the two paradigms are distinct in their treatment of location and movement. This paper seeks to uncover a common foundation for the two paradigms by exploring the manner in which stereotypical forms of code mobility …
Symmetrical Routes And Reverse Path Congestion Control, Rajib Ghosh, George Varghese
Symmetrical Routes And Reverse Path Congestion Control, Rajib Ghosh, George Varghese
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We describe new mechanisms to deal with asymmetries that arise in routing protocols. We show how to avoid route asymmetries (due to non-unique shortest paths) by adding random integer link costs. We show in detail how RIP can be modified to avoid route asymmetry with high probability, without affecting either its efficiency or performance metrics such as convergence time. Symmetrical intra-domain routing also makes possible a new form of congestion control that we call Reverse Path Congestion Control (RPCC). We show, using simulations, that RPCC can augment existing TCP congestion control mechanisms to improve start up behavior and to avoid …
End-User Visualization And Manipulation Of Distributed Aggregate Data, T. Paul Mccartney, Kenneth J. Goldman
End-User Visualization And Manipulation Of Distributed Aggregate Data, T. Paul Mccartney, Kenneth J. Goldman
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Aggregate visualization and manipulation enables the viewing and interaction of dynamically changing data sets in a graphically meaningful way. However, off-the-shelf applications typically provide only limited ways to view static aggregates and generally to not support manipulation of aggregate data through the resulting visualization. To be fully dynamic, an aggregate visualization should be customizable to suit the individual's needs and should allow end-users to modify the data through direct manipulation. This paper describes a software system that empowers end-users to create interactive aggregate visualizations through a visual language interface. Included are mechanisms for specifying how aggregate data is processed from …
Reasoning About Code Mobility With Mobile Unity, Gian Pietro Picco, Gruia-Catalin Roman, Peter J. Mccann
Reasoning About Code Mobility With Mobile Unity, Gian Pietro Picco, Gruia-Catalin Roman, Peter J. Mccann
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Advancements in network technology have led to the emergence of new computing paradigms that challenge established programming practices by employing weak forms of consistency and dynamic forms of binding. Code mobility, for instance, allows for invocation-time binding between a code fragment and the location where it executes. Similarly, mobile computing allows hosts (and the software they execute) to alter their physical location. Despite apparent similarities, the two paradigms are distinct in their treatment of location and movement. This paper seeks to uncover a common foundation for the two paradigms by exploring the manner in which stereotypical forms of code mobility …
Using Snapshot Streams To Support Visual Exploration, Delbert Hart, Eileen Kraemer, Gruia-Catalin Roman
Using Snapshot Streams To Support Visual Exploration, Delbert Hart, Eileen Kraemer, Gruia-Catalin Roman
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The non-determinism, complexity, and size of distributed software systems present significant difficulties for designers and maintainers. Visualization can help alleviate these difficulties through interactive exploratory tools that allow both novice and experienced users to investigate a distributed computation using a common tool set. Essential to the success of a visual exploration tool is the ability to provide accurate representations of global states. This paper is concerned with the use of snapshots in support of interactive visual exploration of distributed computations. The nature of the visualization process requires snapshots that (1) are consecutive, thus facilitating smooth animation of state changes, (2) …
Mobile Unity: A Language And Logic For Concurrent Mobile Systems, Peter J. Mccann, Gruia-Catalin Roman
Mobile Unity: A Language And Logic For Concurrent Mobile Systems, Peter J. Mccann, Gruia-Catalin Roman
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Traditionally, a distributed system has been viewed as a collection of fixed computational elements connected by a static network. Prompted by recent advances in wireless communications rechnology, the emerging field of mobile computing is challenging these assumptions by providing mobile hosts with connectivity that may change over time, raising the possibility that hosts may be called upon to operate while only weakly connected to or while completely disconnected from other hosts. We define a concurrent mobile system as one where independently executing coponents may migrate through some space during the course of the computation, and where the pattern of connectivity …
Architectural Choices In Large Scale Atm Switches, Jonathan Turner, Naoaki Yamanaka
Architectural Choices In Large Scale Atm Switches, Jonathan Turner, Naoaki Yamanaka
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The rapid development of Asynchronous Transfer Mode technology in the last 10-15 years has stimulated renewed interest in the design and analysis of switching systems, leading to new ideas for system designs and new insights into the performance and evaluation of such systems. As ATM moves closer to realizing the vision of ubiquitous broadband ISDN services, the design of switching systems takes on growing importance. This paper seeks to clarify the key architectural issues for ATM switching system design and provides a survey of the current state-of-the-art.
Dialogue And Deliberation, Ronald P. Loui, Diana M. Moore
Dialogue And Deliberation, Ronald P. Loui, Diana M. Moore
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Formal accounts of negotiation tend to invoke the strategic models of conflict which have been impressively developed by game theorists in this half-century. For two decades, however, research on artificial intelligence (AI) has produced a different formal picture of the agent and of the rational deliberations of agents. AI's models are not based simply on intensities of preference and quantities of probability. AI's models consider that agents use language in various ways, that agents use and convey knowledge, that agents plan, search, focus, and argue. Agents can choose their language, apply their knowledge, change their plans, continue their search, shift …
Noise-Tolerant Parallel Learning Of Geometric Concepts, Nader H. Bshouty, Sally A. Goldman, H. David Mathias
Noise-Tolerant Parallel Learning Of Geometric Concepts, Nader H. Bshouty, Sally A. Goldman, H. David Mathias
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We present several efficient parallel algorithms for PAC-learning geometric concepts in a constant-dimensional space. The algorithms are robust even against malicious classification noise of any rate less than 1/2. We first give an efficient noise-tolerant parallel algorithm to PAC-learn the class of geometric concepts defined by a polynomial number of (d-1)-dimensional hyperplanes against an arbitrary distribution where each hyperplane has a slope from a set of known slopes. We then describe how boosting techniques can be used so that our algorithms' dependence on {GREEK LETTER} and {DELTA} does not depend on d. Next we give an efficient noise-tolerant parallel algorithm …
Alchourron's Defeasible Conditionals And Defeasible Reasoning, Fernando Tohme, Ronald P. Loui
Alchourron's Defeasible Conditionals And Defeasible Reasoning, Fernando Tohme, Ronald P. Loui
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No abstract provided.
Eliding The Arguments Of Cases, Ronald P. Loui, Jeff Norman
Eliding The Arguments Of Cases, Ronald P. Loui, Jeff Norman
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No abstract provided.
End-User Visualization And Manipulation Of Aggregate Data, T. Paul Mccartney, Kenneth J. Goldman
End-User Visualization And Manipulation Of Aggregate Data, T. Paul Mccartney, Kenneth J. Goldman
All Computer Science and Engineering Research
Aggregate visualization and manipulation enables the viewing and interaction of dynamically changing data sets in a graphically meaningful way. However, off-the-shelf applications generally provide only limited ways to view aggregates. To be truly effective to the end-user, an aggregate visualization should be customizable to suit the individual's needs. This paper describes a software system that empowers end-users to create interactive aggregate visualizations through direct manipulation. Included are mechanisms for specifying how aggregate data is processed from multiple sources, providing functionality similar to project, select, join, and cross product of relational databases. Visualization of distributed data sets is emphasized.
Euphoria Reference Manual, T. Paul Mccartney, Kenneth J. Goldman
Euphoria Reference Manual, T. Paul Mccartney, Kenneth J. Goldman
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EUPHORIA is a user interface management system that enables end-users to create direct manipulation graphical user interfaces (GUIs) through interactive drawing. Used in conjunction with The Programmers' Playground, a distributed programming environment, end-users can dynamically create and associate GUI components with an underlying application without programming, This document describes EUPHORIA's functionality.
Building Interactive Distributed Applications In C++ With The Programmers' Playground, Kenneth J. Goldman, Joe Hoffert, T. Paul Mccartney, Jerome Plun, Todd Rogers
Building Interactive Distributed Applications In C++ With The Programmers' Playground, Kenneth J. Goldman, Joe Hoffert, T. Paul Mccartney, Jerome Plun, Todd Rogers
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The objective of The Programmers' Playground, described in this manual, is to provide a development environment and underlying support for end-user construction of distributed multimedia applications from reusable self-describing software components. Playground provides a set of software tools and a methodology for simplifying the design and construction of applications that interact with each other and with people in a distributed computer system. This manual explains how to write interactive distributed applications using Playground. The only background necessary to get started is an understanding of basic data structures and control constructs in C++. If you already know C++, then with the …
Learning With Unreliable Boundary Queries, Avrim Blum, Prasad Chalasani, Sally A. Goldman, Donna K. Slonim
Learning With Unreliable Boundary Queries, Avrim Blum, Prasad Chalasani, Sally A. Goldman, Donna K. Slonim
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We introduce a model for learning from examples and membership queries in situations where the boundary between positive and negative examples is somewhat ill-defined. In our model, queries near the boundary of a target concept may receive incorrect or "don't care" responses, and the distribution of examples has zero probability mass on the boundary region. The motivation behind our model is that in many cases the boundary between positive and negative examples is complicated or "fuzzy." However, one may still hope to learn successfully, because the typical examples that one sees to not come from that region. We present several …
Noise-Tolerant Distribution-Free Learning Of General Geometric Concepts, Nader H. Bshouty, Sally A. Goldman, H. David Mathias, Subhash Suri, Hisao Tamaki
Noise-Tolerant Distribution-Free Learning Of General Geometric Concepts, Nader H. Bshouty, Sally A. Goldman, H. David Mathias, Subhash Suri, Hisao Tamaki
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We present an efficient algorithm for PAC-learning a very general class of geometric concepts over Rd for fixed d. More specifically, let T be any set of s halfspaces. Let x = (x1,...,xd) be an arbitrary point in Rd. With each t Є T we associate a boolean indicator function It(x) which is 1 if and only if x is in the halfspace t. The concept class Cds that we study consists of all concepts formed by any boolean function over It1, ...Its for ti Є T. This class is much more general than any geometric concept class known to …
A Theoretical And Empirical Study Of A Noise-Tolerant Algorithm To Learn Geometric Patterns, Sally A. Goldman, Stephen D. Scott
A Theoretical And Empirical Study Of A Noise-Tolerant Algorithm To Learn Geometric Patterns, Sally A. Goldman, Stephen D. Scott
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Developing the ability to recognize a landmark from a visual image of a robot's current location is a fundamental problem in robotics. We describe a way in which the landmark matching problem can be mapped to that of learning a one-dimensional geometric pattern. The first contribution of our work is an efficient noise-tolerant algorithm (designed using the statistical query model) to PAC-learn the class of one-dimensional geometric patterns. The second contribution of our work is an empirical study of our algorithm that provides at least some evidence that statistical query algorithms may be valuable for use in practice for handling …
Principles For Developing And Measuring High-Performance Web Servers Over Atm, James C. Hu, Sumedh Mungee, Douglas C. Schmidt
Principles For Developing And Measuring High-Performance Web Servers Over Atm, James C. Hu, Sumedh Mungee, Douglas C. Schmidt
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High-performance Web servers are essential to meet the growing demands of the Internet. Satisfying these demands requires a thorough understanding of the key factors that affect Web server performance. This paper provides three contributions to the design, implementation, and evaluation of high-performance Web servers. First, we report the results of a comprehensive empirical study of popular high-performance Web servers (such as Apache, Netscape Enterprise, PHTTPD, and Zeus) over high-speed ATM networks. This study illustrates their relative performance and identifies their performance bottlenecks. To measure performance accurately, we developed a new benchmarking technique that subjects Web servers to varying connection frequencies. …
Costs Of Constraint Based Networks On A Sphere, Hongzhou Ma, Jonathan Turner
Costs Of Constraint Based Networks On A Sphere, Hongzhou Ma, Jonathan Turner
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This paper estimates the link costs of constraint based nonblocking ATM networks on a sphere. Analytical results are obtained when switches are uniformly distributed on the surface of a unit sphere and every switch has source and sink capacity of one, and the results are compared with simulations.
Balancing Consistency And Lag In Transaction-Based Computational Steering, Eileen Kraemer, Delbert Hart, Gruia-Catalin Roman
Balancing Consistency And Lag In Transaction-Based Computational Steering, Eileen Kraemer, Delbert Hart, Gruia-Catalin Roman
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Computational steering, the interactive adjustment of application parameters and allocation of resources, is a promising technique for higher-productivity simulation, finer-grained optimization of dynamically varying algorithms, and greater understanding of program behavior and the characteristics of data sets and solution spaces. Tools for computational steering must provide monitoring, visualization, and interaction facilities. In addition, these tools must address issues related to the consistency, latency, and scalability at each of these phases, and must consider the perturbation that results. In this paper we describe transaction-based components for a computational steering system and present an approach that guarantees consistent monitoring and displays, supports …