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Articles 451 - 480 of 683
Full-Text Articles in Computer Engineering
Cappucino: An Extensible Planning Tool For Constraint-Based Atm Network Design, Inderjeet Singh, Jonathan S. Turner
Cappucino: An Extensible Planning Tool For Constraint-Based Atm Network Design, Inderjeet Singh, Jonathan S. Turner
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Cappuccino is a planning tool for topological design of ATM networks. It uses a novel constraint-based approach to ATM network design. Extensibility of the tool is a basic design goal and the tool provides an open interface to incorporate new algorithms.
An Architecture For Monitoring Visualization And Control Of Gigabit Networks, Guru Parulkar, Douglas Schmidt, Eileen Kraemer, Jonathan Turner, Anshul Kantawala
An Architecture For Monitoring Visualization And Control Of Gigabit Networks, Guru Parulkar, Douglas Schmidt, Eileen Kraemer, Jonathan Turner, Anshul Kantawala
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We propose a network monitoring, visualization and control system (NMVC) that ensures adequate quality of service to network users while maintaining high network resource utilization. The main components of our system are a network probe, an endsystem probe, software network management agents that provide extensible multi-attribute event filtering for highly scalable data/event collection, network operation centers (NOCs) which can remotely install and (re)configure these agents, efficient online event ordering algorithms that can help synthesize and display a consistent view of network health, status and performance and a View Choreographer that allows management applications and administrators to specify the mapping of …
Enhancements To 4.4 Bsd Unix For Efficient Networked Multimedia In Project Mars, Milind M. Buddhikot, Xin Jane Chen, Dakang Wu, Guru M. Parulkar
Enhancements To 4.4 Bsd Unix For Efficient Networked Multimedia In Project Mars, Milind M. Buddhikot, Xin Jane Chen, Dakang Wu, Guru M. Parulkar
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Cluster based architectures that employ high performance inexpensive Personal Computers (PCs) interconnected by high speed commodity interconnect have been recognized as a cost-effective way of building high performance scalable Multimedia-On-Demand (MOD) storage servers [4, 5, 7, 9]. Typically, the PCs in these architectures run operating systems such as UNIX that have traditionally been optimized for interactive computing. They do not provide fast disk-to-network data paths and guaranteed CPU and storage access. This paper reports enhancements to the 4.4 BSD UNIX system carried out to rectify these limitations in the context of our Project Massively-parallel And Real-time Storage (MARS) [7]. We …
Replication Of The First Controlled Experiment On The Usefulness Of Design Patterns: Detailed Description And Evaluation, Lutz Prechelt, Barbara Unger, Douglas Schmidt
Replication Of The First Controlled Experiment On The Usefulness Of Design Patterns: Detailed Description And Evaluation, Lutz Prechelt, Barbara Unger, Douglas Schmidt
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Advocates of software design patterns claim that using design patterns improves communication between software developers. The controled experiment that we describe in this report tests the hypothesis that software maintainers of well-structured, well-documented software containing design patterns can make changes (1) faster and (2) with less errors if the use of patterns is explicitly documented in the software. The experiment was performed with 22 participants of a university course on C++ and design patterns; it is similar to a previous experiment performed in Karlsruhe. For one of the two experiment tasks the experiment finds that both hypotheses appear to be …
Computational Detection Of Cpg Islands In Dna, Eric C. Rouchka, Richard Mazzarella, David J. States
Computational Detection Of Cpg Islands In Dna, Eric C. Rouchka, Richard Mazzarella, David J. States
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Regions of DNA rich in CpG dinucleotides, also known as CpG islands, are often located upstream of the transcription start side in both tissue specific and housekeeping genes. Overall, CPG dinucleotides are observed at a density of 25% the expected level from base composition alone, partially due to 5-methylcytosine decay (Bird, 1993). Since CpG dinucleotides typically occur with low frequency, CpG islands can be distinguished statistically in the genome. Our method of detecting CpG islands involves a heuristic algorithm employing classic changepoint methods and log-likelihood statistics. A Java applet has been created to allow for user interaction and visualization of …
An Algorithm For Message Delivery In A Micromobility Environment, Amy L. Murphy, Gruia-Catalin Roman, George Varghese
An Algorithm For Message Delivery In A Micromobility Environment, Amy L. Murphy, Gruia-Catalin Roman, George Varghese
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With recent advances in wireless communication and the ubiquity of laptops, mobile computing has become an important research area. An essential problem in mobile computing is the delivery of a message from a source to either a single mobile node, unicast, or to a group of mobile nodes, multicast. Standard solutions proposed for macromobility (Mobile IP) and micromobility (cellular phones) for the unicast problem rely on tracking the mobile node. Tracking solutions scale badly when mobile nodes move frequently, and do not generalize well to multicast delivery. Our paper proposes a new message delivery algorithm for micromobility based on a …
An Introduction To Mobile Unity, Gruia-Catalin Roman, Peter J. Mccann
An Introduction To Mobile Unity, Gruia-Catalin Roman, Peter J. Mccann
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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 …
Terabit Burst Switching, Jonathan S. Turner
Terabit Burst Switching, Jonathan S. Turner
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This report summarizes the results of an architectural study on Terabit Burst Switching. The purpose of this study was to explore alternative architectures for very high performance switching for data communication, using a combination of optical and electronic technologies. We explore two alternative implementations of the burst switching concept in detail, one using a hybrid architecture with an electronic core, and an integrated architecture using an all optical data path. We also briefly discuss an approach using optical TDM. Our results show that using the hybrid architecture, it is feasible to construct systems with aggregate capacities of tens of terabits …
Compositional Programming Abstractions For Mobile Computing, Peter J. Mccann, Gruia-Catalin Roman
Compositional Programming Abstractions For Mobile Computing, Peter J. Mccann, Gruia-Catalin Roman
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Recent advances in wireless networking technology and the increasing demand for ubiquitous, mobile connectivity demonstrate the importance of providing reliable systems for managing reconfiguration and disconnection of components. Design of such systems requires tools and techniques appropriate to the task. Many formal models of computation, including UNITY, are not adequate for expressing reconfiguration and disconnection and are therefore inappropriate vehicles for investigating the impact of mobility on the construction of modular and composable systems. Algebraic formalisms such as the pi-calculus have been proposed for modeling mobility. This paper addresses the question of whether UNITY, a state-based formalism with a foundation …
Design And Implementation Of A New Connection Admission Control Algorithm Using A Multistate Traffic Source Model, Robert Engel
Design And Implementation Of A New Connection Admission Control Algorithm Using A Multistate Traffic Source Model, Robert Engel
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This report develops a practical method for connection admission control in ATM networks. The method is based on a virtual cell loss probability criterion, is designed to handle heterogeneous traffic types and allows each traffic source to be described by an individual finite-state model with as many states as are needed to describe the source traffic. To make connection admission decisions with respect to individual links, an aggregate finite state model is computed from the individual models and used to estimate the virtual cell loss probabilities. To reduce the computational requirements for maintaining the aggregate traffic model, the aggregate model …
The Design And Performance Of A Real-Time Corba Event Service, Timothy H. Harrison, David L. Levine, Douglas C. Schmidt
The Design And Performance Of A Real-Time Corba Event Service, Timothy H. Harrison, David L. Levine, Douglas C. Schmidt
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The CORBA Event Service provides a flexible model for asynchronous communication among objects.However, the standard CORBA Event Service specification lacks important features required by real-time applications. For instance, operational flight programs for fighter aircraft have complex real-time processing requirements. This paper describes the design and performance of an object-oriented, real-time implementation of the CORBA Event Service that is designed to meet these requirements. This paper makes three contributions to the design and performance measurement of object-oriented real-time systems. First, it illustrates how to extend the CORBA Event Service so that it is suitable for real-time systems. These extensions support periodic …
An Error Control Scheme For Large-Scale Multicast Applications, Christos Papadopoulos, Guru Parulkar, George Varghese
An Error Control Scheme For Large-Scale Multicast Applications, Christos Papadopoulos, Guru Parulkar, George Varghese
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Retransmission based error control for large scale multicast applications is difficult because of two main problems: request implosion and lack of local recovery. Existing schemes (SRM, RMTP, TMTP, LBRRM) have good solutions to request implosion, but only approximate solutions (e.g., based on scoped multicast) for the local recovery problem. Our scheme achieves finer grain fault recovery by exploiting new forwarding services that allow us to create a dynamic hierarchy of receivers. We use a new paradigm, where routers provide a more refined form of multicasting (that may be useful to other applications), that enables local recovery. The new services, however, …
The Programmers' Playground Application Management System User Guide, William M. Shapiro, T. Paul Mccartney, E.F. Berkley Shands
The Programmers' Playground Application Management System User Guide, William M. Shapiro, T. Paul Mccartney, E.F. Berkley Shands
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Application Management permits the advertising, launching, and configuring of distributed applications created using the Programmers' Playground. Applications can be documented and made available to end-users through the use of application pages on the World Wide Web. The launching and configuring of applications is performed by a brokerage system consisting of an applicatoin broker and one or more hierarchies of module launchers. This document describes how to setup and use the components of the Application Management system.
Exact Learning Of Discretized Geometric Concepts, Nader H. Bshouty, Paul W. Goldberg, Sally A. Goldman, H. David Mathias
Exact Learning Of Discretized Geometric Concepts, Nader H. Bshouty, Paul W. Goldberg, Sally A. Goldman, H. David Mathias
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We first present an algorithm that uses membership and equivalence queries to exactly identify a discretized geometric concept defined by the unioin of m axis-parallel boxes in d-dimensional discretized Euclidean space where each coordinate can have n discrete values. This algorithm receives at most md counterexamples and uses time and membership queries polynomial in m and log(n) for any constant d. Furthermore, all equivalence queries can be formulated as the union of O(mdlog(m)) axis-parallel boxes. Next, we show how to extend our algorithm to efficiently learn, from only equivalence queries, any discretized geometric concept generated from any number of halfspaces …
Dynamic Flow Switching: A New Communication Service For Atm Networks, Qiyong Bian, Kohei Shimoto, Jonathan Turner
Dynamic Flow Switching: A New Communication Service For Atm Networks, Qiyong Bian, Kohei Shimoto, Jonathan Turner
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This paper presents a new communication service for ATM networks that provides one-way, adjustable rate, on-demand communication channels. The proposed dynamic flow service is designed to operate within a multi-service cell switched network that supports both conventional switched virtual circuits and IP packet routing and is designed to complement those services. It is particularly well suited to applications that transmit substantial amounts of data (a few tens of kilobytes or more) in fairly short time periods (up to a few seconds). Much of the current world-wide web traffic falls within this domain. Like IP packet networks, the new service permits …
Sequence Assembly Validation By Restriction Digest Fingerprint Comparison, Eric C. Rouchka, David J. States
Sequence Assembly Validation By Restriction Digest Fingerprint Comparison, Eric C. Rouchka, David J. States
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DNA sequence analysis depends on the accurate assembly of fragment reads for the determination of a consensus sequence. Genomic sequences frequently contain repeat elements that may confound the fragment assembly process, and errors in fragment assembly, and errors in fragment assembly may seriously impact the biological interpretation of the sequence data. Validating the fidelity of sequence assembly by experimental means is desirable. This report examines the use of restriction digest analysis as a method for testing the fidelity of sequence assembly. Restriction digest fingerprint matching is an established technology for high resolution physical map construction, but the requirements for assembly …
Reducing Web Latencies Using Precomputed Hints, Girish P. Chandranmenon, George Varghese
Reducing Web Latencies Using Precomputed Hints, Girish P. Chandranmenon, George Varghese
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Current network technology is bandwidth-rich but latency-poor; thus round-trip delays will dominate access latency for web traffic. We describe four new techniques that reduce the round-trips needed for web accesses. The techniques are based on the paradigm of preprocessing a web page to collect information about links and inline data in the page. Stored Address Binding almost always eliminates the DNS lookup (which can cost seconds) at the start of a transaction. In Informed Server Proxying, a server tells its client that it has cached pages referenced in a page the client just retrieved; this allows the client to retrieve …
An Algorithm For Message Delivery To Mobile Units, Amy L. Murphy, Gruia-Catalin Roman, George Varghese
An Algorithm For Message Delivery To Mobile Units, Amy L. Murphy, Gruia-Catalin Roman, George Varghese
All Computer Science and Engineering Research
With recent advances in wireless communication and the ubiquity of laptops, mobile computing has become an important research area. An essential problem in mobile computing is the delivery of a message from a source to either a single mobile node, unicast, or to a group of mobile nodes, multicast. Standard solutions used in Mobile IP and cellular phones for the unicast problem rely on tracking the mobile unit. Tracking solutions scale badly when mobile nodes move frequently, and do not generalize well to multicast delivery. Our paper proposes a new message delivery algorithm for micromobility based on a modification of …
Bringing Real-Time Scheduling Theory And Practice Closer For Multimedia Computing, R. Gopalakrishnan, Guru M. Parulkar
Bringing Real-Time Scheduling Theory And Practice Closer For Multimedia Computing, R. Gopalakrishnan, Guru M. Parulkar
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This paper seeks to bridge the gap between theory and practice of real-time scheduling in the domain of multimedia computer systems. We show that scheduling algorithms that are good in theory, often have practical limitations. However when these algorithms are modified based on practical considerations, existing theoretical results cannot be used as they are. In this paper we motivate the need for new scheduling schemes for multimedia protocol processing, and demonstrate their real-time performance in our prototype implementation. We then explain the observed results by analysis and measurement. More specifically, we show that using strict preemption can introduce overheads in …
New Results On Generalized Caching, Saied Hosseini-Khayat
New Results On Generalized Caching, Saied Hosseini-Khayat
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We report a number of new results in generalized caching. This problem arises in modern computer networks in which data objects of various sizes are transmitted frequently. First it is shown that its optimal solution is NP-complete. Then we explore two methods of obtaining nearly optimal answers based on the dynamic programming algorithm that we provided in [5]. These methods enable a trade-off between optimality and speed. It is also shown that LFD (the longest forward distance algorithm which is the optimal policy in the classical case), is no longer optimal but is competitive. We also prove that LRU remains …
A Usability Study Of End-User Construction Of Direct Manipulation User Interfaces, T Paul Mccartney
A Usability Study Of End-User Construction Of Direct Manipulation User Interfaces, T Paul Mccartney
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This paper describes an empirical study of end-users that tested the usability of The Programmers' Playground graphical environment. The Programmers' Playground is a software library and run-time system for constructing distributed multimedia applications. Playground's graphical environment enables end-users to create direct manipulation graphical user interfaces (GUIs) and to dynamically configure communication among distributed application components. In this study, 28 end-users with no prior experience in distributed computing or user interface construction were timed and evaluated on several tasks using our graphical environment. Tasks included the use of direct and indirect constraint relationships, visual configuration of distributed applications, and graphical user …
Design And Implementation Of A Practical Security-Conscious Electronic Polling System, Lorrie Faith Cranor, Ron K. Cytron
Design And Implementation Of A Practical Security-Conscious Electronic Polling System, Lorrie Faith Cranor, Ron K. Cytron
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We present the design and implementation of Sensus, a practical, secure and private system for conducting surveys and elections over computer networks. Expanding on the work of Fujioka, Okamoto, and Ohta, Sensus uses blind signatures to ensure that only registered voters can vote and that each registered voter only votes once, while at the same time maintaining voters' privacy. Sensus allows voters to verify independently that their votes were counted correctly, and anonymously challenge the results should their votes be miscounted. We outline seven desirable properties of voting systems and show that Sensus satisfied these properties well, in some cases …
Mobile Unity: Reasoning And Specification In Mobile Computing, Gruia-Catalin Roman, Peter J. Mccann
Mobile Unity: Reasoning And Specification In Mobile Computing, Gruia-Catalin Roman, Peter J. Mccann
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Mobile computing represents a major point of departure from the traditional distributed computing paradigm. The potentially very large number of independent computing units, a decoupled computing style, frequent disconnections, continuous position changes, and the location-dependent nature of the behavior and communication patterns present designers with unprecedented challenges in the areas of modularity and dependability. So far, the literature on mobile computing is dominated by concerns having to do with the development of protocols and services. This paper complements this perspective by considering the nature of the underlying formal models that will enable us to specify and reason about such computations. …
Distributed Stream Filtering For Database Applications, William M. Shapiro, Kenneth J. Goldman
Distributed Stream Filtering For Database Applications, William M. Shapiro, Kenneth J. Goldman
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Distributed stream filtering is a mechanism for implementing a new class of real-time applications with distributed processing requirements. These applications require scalable architectures to support the efficient processing and multiplexing of large volumes of continuously generated data. This paper provides an overview of a stream-oriented model for database query processing and presents a supporting implementation. To facilitate distributed stream filtering, we introduce several new query processing operations, including pipelined filtering that efficiently joins and eliminates duplicates from database streams and a new join method, the progressive join, that joins streams of tuples. Finally, recognizing that the stream-oriented model results in …
Optimal Solution Of Off-Line And On-Line Generalized Caching, Saied Hosseini-Khayat, Jerome R. Cox
Optimal Solution Of Off-Line And On-Line Generalized Caching, Saied Hosseini-Khayat, Jerome R. Cox
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Network traffic can be reduced significantly if caching is utilized effectively. As an effort in this direction we study the replacement problem that arises in caching of multimedia objects. The size of objects and the cost of cache misses are assumed non-uniform. The non-uniformity of size is inherent in multimedia objects, and the non-uniformity of cost is due to the non-uniformity of size and the fact that the objects are scattered throughout the network. Although a special case of this problem, i.e. the case of uniform size and cost, has been extensively studied, the general case needs a great deal …
Extending Atm Networks For Efficient Reliable Multicast, Jonathan S. Turner
Extending Atm Networks For Efficient Reliable Multicast, Jonathan S. Turner
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One of the important features of ATM networks is their ability to support multicast communications. This facilitates the efficient distribution of multimedia information streams (such as audio and video) to large groups of receivers (potentially millions). Because ATM networks do not provide reliable delivery mechanisms, it is up to end systems to provide end-to-end reliability where it is needed. While this is straightforward for point-to-point virtual circuits, it is more difficult for one-to many and many-to-mamy virtual circuits. In this report, we propose some minimal extensions to the hardware of ATM switches that enables end systems to implement reliable multicast …
Analysis Of Mpeg Compressed Video Traffic, Jerome R. Cox Jr., O. Matthew Beal
Analysis Of Mpeg Compressed Video Traffic, Jerome R. Cox Jr., O. Matthew Beal
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This paper outlines a study of MPEG compressed video sequences and simulation of multiplexed video traffic in the ATM environment. A number of statistical characteristics including autocorrelation and variance of MPEG-1 compressed video sequences are used to characterize the 16 sample traces used in this study. From these measurements, a preliminary model is developed which utilizes basic measurements of the individual component video sequences to predict bandwidth requirements and cell loss of the multiplexed video traffic.
Design Of Nonblocking Atm Networks, J. Andrew Fingerhut, Rob Jackson, Subhash Suri, Jonathan S. Turner
Design Of Nonblocking Atm Networks, J. Andrew Fingerhut, Rob Jackson, Subhash Suri, Jonathan S. Turner
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This paper considers the problem of designing ATM networks that are nonblocking with respect to virtual circuit requests, subject to specified constraints on the traffic. In this paper, we focus on global traffic constraints that simply limit the total entering and exiting traffic at each switching system. After reviewing prior results for linear link costs, we introduce a more realistic link cost model, and develop a number of results using it. We also describe a technique for converting tree-structured networks to nonblocking hierarchical networks satisfying limits on the capacity of any single switch.
Simulation Of Asynchronous Instruction Pipelines, Chia-Hsing Chien, Mark A. Franklin
Simulation Of Asynchronous Instruction Pipelines, Chia-Hsing Chien, Mark A. Franklin
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This paper presents the ARAS simulator with which asynchronous instruction pipelines can be modelled, simulated and displayed. ARAS allows one to construct instruction pipelines by preparing various configuration files. Using these files and a number of benchmark programs, performance of the instruction pipelines can be obtained. The performance of asynchronous instruction pipelines can also be compared to synchronous case. Thus, one can decide the optimal design for instruction pipelines in asynchornous or synchronous cases and explore the deisng space of asynchronous instruction pipeline architectures.
Design Of A Gigabit Atm Switch, Tom Chaney, Andrew Fingerhut, Margaret Flucke, Jonathan S. Turner
Design Of A Gigabit Atm Switch, Tom Chaney, Andrew Fingerhut, Margaret Flucke, Jonathan S. Turner
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This report describes the design and implementation of a gigabit ATM switching system supporting link rates from 150 Mb/s to 2.4 Gb/s, with a uniquely efficient multicast switch architecture that enables the construction of systems with essentially constant per port costs for configurations ranging from 8 to 4096 ports and system capacities approaching 1- Tb.s. The system design supports many-to-one and many-to-many forms of multicast, in addition to the usual one-to-many. It also provides multicast virtual paths, constant time configuration of multicast connections and an efficient packet-level discard method, that can achieve 100% link efficiencies, without large buffers.