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Washington University in St. Louis

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Articles 391 - 420 of 733

Full-Text Articles in Computer Engineering

Performance Of Deferred Reservations In Data Networks, Samphel Norden, Jonathan Turner Jan 2001

Performance Of Deferred Reservations In Data Networks, Samphel Norden, Jonathan Turner

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This paper studies the performance of deferred resource reservation in data networks. Conventional resource reservation protocols, such as PNNI and RSVP adopt an all-or-nothing approach, where partially acquired resources must be released if resources are not available at all links on the chosen path. During periods of high network load, this leads users to retry requests repeatedly, adding control traffic at exactly the time when the network's capacity to process that control traffic is exhausted. Deferred REServation (DRES) can significantly improve performance by reducing the overall call rejection probability, allowing more traffic to be carried, using the same resources. Call …

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An Efficient Quality Scalable Motion-Jpeg2000 Transmission Scheme, Ruibiao Qiu, Wei Yu Jan 2001

An Efficient Quality Scalable Motion-Jpeg2000 Transmission Scheme, Ruibiao Qiu, Wei Yu

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Video application over the Internet are getting increasingly popular because of the explosive growth of the Internet. However, video packets loss due to network congestions can degrade the video quality substantially. In this paper, we propose a transmission scheme for Motion-JPEG2000. It can be implemented in an active network environment efficiently. Our simulation shows that our scheme gracefully adapts to network congestion and improves the quality of video transmission in congested IP networks.

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Embedding Images In Non-Flat Spaces, Robert Pless Jan 2001

Embedding Images In Non-Flat Spaces, Robert Pless

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Multi-dimensional scaling is an analysis tool which transforms pairwise distances between points to an embedding of points in space which are consistent with those distances. Two recent techniques in statistical patter recognition, locally linear embedding (LLE) and Isomap, give a mechanism for finding the structure underlying point sets for which comparisons or distances are only meaningful between nearby points. We give a direct method to extend the embedding algorithm to new topologies, finding the optimal embedding of points whose geodesic distance on a surface mathes the given pairwise distance measurements. Surfaces considered include spheres, cylinders, tori, and their higher dimensional …

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A Termination Detection Protocol For Use In Mobile Ad Hoc Networks, Gruia-Catalin Roman, Jamie Payton Jan 2001

A Termination Detection Protocol For Use In Mobile Ad Hoc Networks, Gruia-Catalin Roman, Jamie Payton

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As computing devices become smaller and wireless networking technologies improve, the popularity of mobile computing continues to rise. In today's business world, many consider devices such as cell phones, PDAs, and laptops as essential tools. As these and other devices become increasingly independent of the wired infrastructure, new kinds of applications that assume an ad hoc network infrastructure will need to be deployed. Such a setting poses new challenges for the software developer, e.g., the lack of an established network topology, bandwidth limitations, and frequent disconnections. In this paper, we begin to explore design strategies for developing applications over ad …

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Parbit: A Tool To Transform Bitfiles To Implement Partial Reconfiguration Of Field Programmable Gate Arrays (Fpgas), Edson L. Horta, John W. Lockwood Jan 2001

Parbit: A Tool To Transform Bitfiles To Implement Partial Reconfiguration Of Field Programmable Gate Arrays (Fpgas), Edson L. Horta, John W. Lockwood

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Field Programmable Gate Arrays (FPGAs) can be partially reconfigured to implement Dynamically loadable Hardware Plugin (DHP) modules. A tool called PARBIT has been developed that transforms FPGA configuration bitfiles to enable DHP modules. With this tool it is possible to define a partial reconfigurable area inside the FPGA and download it into a specified region of the FPGA device. One or more DHPs, with different sizes can be implemented using PARBIT.

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Relying On Safe Distance To Ensure Consistent Group Membership In Ad Hoc Networks, Qingfeng Huang, Christine Julien, Gruia-Catalin Roman, Ali Hazemi Jan 2001

Relying On Safe Distance To Ensure Consistent Group Membership In Ad Hoc Networks, Qingfeng Huang, Christine Julien, Gruia-Catalin Roman, Ali Hazemi

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The design of ad hoc mobile applications often requires the availability of a consistent view of the application state among the participating hosts. Such views are important because they simplify both the programming and verification tasks. Essential to constructing a consitent view is the ability to know what hosts are within proximity of each other, i.e., form a group in support of the particular application. In this paper we propose a protocol that allows hosts within communication range to maintain a consistent view of the group membership despite movement and frequent disconnections. The novel features of this protocol are its …

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Scheduling Processing Resources In Programmable Routers, Prashanth Pappu, Tilman Wolf Jan 2001

Scheduling Processing Resources In Programmable Routers, Prashanth Pappu, Tilman Wolf

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To provide flexibility in deploying new protocols and services, general-purpose processing engines are being placed in the datapath of routers. Such network processors are typically simple RISC multiprocessors that perform forwarding and custom application processing of packets. The inherent unpredictability of execution time of arbitrary instruction code poses a significant challenge in providing QoS guarantees for data flows that compete for such processing resources in the network. However, we show that network processing workloads are highly regular and predictable. Using estimates of execution times of various applications on packets of given lengths, we provide a method for admission control and …

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Design Of Wavelength Converting Switches For Optical Burst Switching, Jeyashankher Ramamirtham, Jonathan Turner Jan 2001

Design Of Wavelength Converting Switches For Optical Burst Switching, Jeyashankher Ramamirtham, Jonathan Turner

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Optical Burst Switching (OBS) is an experimental network technology that enables the construction of very high capacity routers, using optical data paths and electronic control. In this paper, we study two designs for wavelength converting switches that are suitable for use in optical burst switching systems and evaluate their performance. Both designs use tunable lasers to implement wavelength conversion. One is strictly nonblocking design, that also requires optical crossbars. The second substitutes Wavelength Grating Routers (WGR) for the optical crossbars, reducing cost, but introducing some potential for blocking. We show how the routing problem for the WGR-based switches can be …

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Local Search And Encoding Schemes For Soft Constraint Minimization Problems, Michael P. Moran, Weixiong Zhang Jan 2001

Local Search And Encoding Schemes For Soft Constraint Minimization Problems, Michael P. Moran, Weixiong Zhang

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Soft constraint minimization problems (SCMPs) contain hard constraints that cannot be violated and soft constraints that may be violated but carry penalties if not satisfied. In this paper, we first extend local search, WalkSAT in particular, to SCMPs and study the existing SAT encoding schemes for SCMPs. We propose a general encoding method called k-encoding. We then investigate the effects of local search neiborhood structures introduced by encoding schemes and analyze the anytime performance of extended WalkSAT using different encoding methods. Our experimental results on various graph coloring problems show that a direct extension of WalkSAT is most effective, and …

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Aggregated Hierarchical Multicast For Active Networks, Tilman Wolf, Sumi Y. Choi Jan 2001

Aggregated Hierarchical Multicast For Active Networks, Tilman Wolf, Sumi Y. Choi

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Active Networking is the basis for a range of new and innovative applications that make use of computational resources inside network routers. One such application is Aggregated Hierarchical Multicast, which aims at implementing efficient many-to-many communication. In certain scenarios it is possible to transmit less accurate, aggregated data and thus achieve better scalability. Using Active Networks, this aggregation computation can be done transparently by network routers without end system support. We present how aggregated data streams can be structured in a hierarchical fashion to allow easy access of data at the desired aggregation level. We introduce two application examples to …

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A Distributed Annotation System, Robin Dowell Jan 2001

A Distributed Annotation System, Robin Dowell

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One goal of any genome project is the elucidation of hte primary sequence of DNA contained within a given species. While the availability ot the primary sequence itself is valuable, it does not reach its full potential until i has been annotated. Generally defined, annotation is descriptive information or commentary added to text, in this case genomic sequence. Without a mechanism for collecting, recording, and disseminating community-based annotation, a valuable source of information is severely diminshed. In this report I outline the design and implementation of a Distributed Annotation System (DAS). DAS allowes sequence annotations to be decentralized among multiple …

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Phase Transitions And Backbones Of Constraint Minimization Problems, Weixiong Zhang Jan 2001

Phase Transitions And Backbones Of Constraint Minimization Problems, Weixiong Zhang

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Many real-world problems involve constraints that cannot be all satisfied. The goal toward an overconstrained problem is to find solutions minimizing the total number of constraints violated. We call such a problem constraint minimization problem (CMP). We study the behavior of the phase transitions and backbones of CMP. We first investigate the relationship between the phase transitions of Boolean satisfiability, or precisely 3-SAT (a well-studied NP-complete decision problem), and the phase transitions of MAX 3-SAT (an NP-hard optimization problem). To bridge the gap between the easy-hard-easy phase transitions of 3-SAT, in which solutions of bounded quality, e.g., solutions with at …

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A Proposal For A Scalable Internet Multicast Architecture, Sherlia Shi Jan 2001

A Proposal For A Scalable Internet Multicast Architecture, Sherlia Shi

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We propose a new network and system architecture for multicast in the Internet. Our main objectives are to find a cost-effective way to scale to a large number of multicast groups whose members are geographically dispersed, and to enable small and less capable devices to participate in group communications. In order to preserve the efficiency of data distribution gained by multicast, while avoiding the control complexity previously exhibited by IP multicast, we propose the use of an overlay network for multicast services. We construct "virtual" multicast trees, which consist of unicast connections joining multicast servers in the network. These servers …

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Indra: A Distributed Approach To Network Intrusion Detection And Prevention, Qi Zhang, Ramaprabhu Janakiraman Jan 2001

Indra: A Distributed Approach To Network Intrusion Detection And Prevention, Qi Zhang, Ramaprabhu Janakiraman

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While advances in computer and communications technology have made the network ubiquitous, they ahve also rendered networked systems vulnerable to malicious attacks orchestrated from a distance. These attacks, usually called cracker attacks or intrusions, start with crackers infiltrating a network through a vulnerable host and then going on to launch further attacks. Crackers depend on increasingly sophisticated techniques like using distributed attack sources. On the other hand, software that guards against them remains rooted in traditional centralized techniques, presenting an easily-targetable single point of failure. Scalable, distributed network intrusion prevention software is sorely needed. We propose Indra - a distributed …

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Formal Specification And Design Of Mobile Systems, Gruia-Catalin Roman, Christine Julien, Qingfeng Huang Jan 2001

Formal Specification And Design Of Mobile Systems, Gruia-Catalin Roman, Christine Julien, Qingfeng Huang

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Termination detection, a classical problem in distributed computing, is revisited in the new setting provided by the emerging mobile computing technology. A simple solution tailored for use in ad hoc networks is employed as a vehicle for demonstrating the applicability of formal requirements and design strategies to the new field of mobile computing. The approach is based on well understood techniquest in specification refinement, but the methodology is tailored to mobile applications and helps designers address novel concerns such as the mobility of hosts, transient interactions, and specific coordination constructs. The proof logic and programming notation of Mobile UNITY provide …

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Rad Module Infrastructure Of The Field-Programmable Port Extender (Fpx) Version 2.0, David E. Taylor, John W. Lockwood, Naji Naufel Jan 2001

Rad Module Infrastructure Of The Field-Programmable Port Extender (Fpx) Version 2.0, David E. Taylor, John W. Lockwood, Naji Naufel

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The Field-programmable Port eXtender (FPX) provides dynamic, fast, and flexible mechanisms to process data streams at the ports of the Washington University Gigabit Switch (WUGS-20). In order to facilitate the design and implementation of portable hardware modules for the Reprogrammable Application Device (RAD) on the FPX board, infrastructure components have been developed. These components abstract application module designers from device-specific timing specifications of off-chip memory devices, as well as processing system-level control cells. This document describes the design and internal functionality of the infrastructure components and is intended as a reference for future component revisions and additions. Application module designers …

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Relationship Between Two Generalized Images For Discrete And Differential Camera Motions, Robert Pless Jan 2001

Relationship Between Two Generalized Images For Discrete And Differential Camera Motions, Robert Pless

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The recent popularity of catadioptic and multi-camera imaging systems indicates a need to create formal models for general, non-perspective camera geometries. Development of algorithmic tools for interpreting images from a generalized camera model will lead to a better understanding of how to design camera systems for particular tasks. Here we define the corollary to epi-polar constraints for standard cameras - the relationship between two images of a scene taken by generalized cameras from viewpoints related by discrete or differential motions.

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Legends As A Device For Interacting With Visualizations, Mihail E. Tudoreanu, Eileen Kraemer Jan 2001

Legends As A Device For Interacting With Visualizations, Mihail E. Tudoreanu, Eileen Kraemer

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Users and developers of visualization tools must deal with the problem of specifying what information to show and how to represent it. Typically, the user's focus of interest will change over time, and the specifications must change with the user's interests. Techniques for the simple, direct, and intuitive creation and refinement of these specifications can be useful. In this paper we show how legends, a natural element of graphical displays, may be used as a direct and unobstrusive interaction device through which users may interactively specify new visualizations and animations.

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Services Provision In Ad Hoc Networks, Radu Handorean, Gruia-Catalin Roman Jan 2001

Services Provision In Ad Hoc Networks, Radu Handorean, Gruia-Catalin Roman

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The client-server model continues to dominate distributed computing with increasingly more flexible variants being deployed. Many are centered on the notion of discovering services at run time and on allowing any system component to act as a service provider. The result is a growing reliance on the service registration and discovery mechanisms. This paper addresses the issue of facilitating such service provision capabilities in the presence of (logical and physical) mobility exhibited by applications executing over ad hoc networks. The solution being discussed entailes a new kind of service model, which we were able to build as an adaption layer …

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Dres: Internet Resource Management Using Deferred Reservations, Samphel Norden Jan 2001

Dres: Internet Resource Management Using Deferred Reservations, Samphel Norden

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In this proposal, we consider the problem of resource reservation for Integrated Services (IntServ) and Differentiated Services (DiffServ) networks. Current approaches for resource reservation in INtegrated Service Networks adopt an all-or-nothing approach, where partially acquired resources must be released if resources are not available at all routers on the chosen path. Furthermore, under high load, end-systems must retry requests repeatedly leading to inefficient allocation and increased traffic. We propose a new approach called Deferred REServation (DERS) that substantially improves performance (reduces the overall cell rejection probability and increases link utilization) over the all-or-nothing reservation approach. Call admissibility is increased by …

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Layered Protocol Wrappers For Internet Packet Processing In Reconfigurable Hardware, Florian Braun, John Lockwood, Marcel Waldvogel Jan 2001

Layered Protocol Wrappers For Internet Packet Processing In Reconfigurable Hardware, Florian Braun, John Lockwood, Marcel Waldvogel

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The ongoing increases of line speed in the Internet backbone combined with the need for increased functionality of network devices presents a major challenge. These demands call for the use of reprogrammable hardware to provide the required flexible, high-speed functionality, at all network layers. The Field Programmable Port Extender (FPX) provides such an environment for development of networking components in reprogrammable hardware. We present a framework to streamline and simplify networking applications that process ATM cells, AAL5 frames, Internet Protocol (IP) packets and UDP datagrams directly in hardware.

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Scalable Ip Lookup For Programmable Routers, David E. Taylor, John W. Lockwood, Todd Sproull, David B. Parlour Jan 2001

Scalable Ip Lookup For Programmable Routers, David E. Taylor, John W. Lockwood, Todd Sproull, David B. Parlour

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Continuing growth in optical link speeds places increasing demands on the performance of Internet routers, while deployment of embedded and distributed network services imposes new demands for flexibility and programmability. IP adress lookup has become a significant performance bottleneck for the highest performance routers. New commercial products utilize dedicated Content Addressable Memory (CAM) devides to achieve high lookup speeds. This paper describes an efficient, scalable lookup engine design, able to achieve high-performance with the use of a small portion of a reconfigurable logic device and a commodity Random Access Memory (RAM) device. Based on Eatherton's Tree Bitmap algorithm [1] the …

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Synthesizable Design Of A Multi-Module Memory Controller, Sarang Dharmapurikar, John W. Lockwood Jan 2001

Synthesizable Design Of A Multi-Module Memory Controller, Sarang Dharmapurikar, John W. Lockwood

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Random Access Memory (RAM) is a common resources needed by networking hardware modules. Synchronous Dynamic RAM (SDRAM) provides a cost effective solution for such data storage. As the packet processing speeds in the hardware increase memory throughput can be a bottleneck to achieve overall high performance. Typically there are multiple hardware modules which perform different operations on the packet payload and hence all try to access the common packet buffer simultaneously. This gives rise to a need for a memory controller which arbitrates between the memory requests made by different modules and maximizes the memory throughput. This paper discusses the …

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Obiwan - An Internet Protocol Router In Reconfigurable Hardware, Florian Braun, Marcel Waldvogel, John Lockwood Jan 2001

Obiwan - An Internet Protocol Router In Reconfigurable Hardware, Florian Braun, Marcel Waldvogel, John Lockwood

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The ongoing exponential increase of line speed in the Internet and combined with the uncountable requests for increased functionality of network devices presents a major challenge. These demands call for the use of reprogrammable hardware to provide the required flexible high-speed functionaltiy. The Field Programmable Port Extender (FPX) provides such an environment for development of networking components in reprogrammable hardware. We present the high-speed IP routing components in reprogrammable hardware. We present the high-speed IP routing module "OBIWAN" (Optimal Binary search IP lookup for Wide Area Networks) built on top of an IP processing framework.

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Network Abstractions For Context-Aware Mobile Computing, Gruia-Catalin Roman, Christine Julien, Qingfeng Huang Jan 2001

Network Abstractions For Context-Aware Mobile Computing, Gruia-Catalin Roman, Christine Julien, Qingfeng Huang

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Context-Aware computing is characterized by the ability of a software system to continuously adapt its behavior to a changing environment over which it has little or no control. Previous work along these lines presumed a rather narrow definition of context, one that was centered on resources immediately available to the component in question, e.g., communication bandwidth, physical location, etc. This paper explores context-aware computing in the setting of ad hoc networks consisting of numerous mobile hosts that interact with each other opportunistically via transient wireless interconnections. We extend the context to encompass awareness of an entire neighborhood within the ad …

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Implementation Of An Open Multi-Service Router, Fred Kuhns, John Dehart, Ralph Keller, John Lockwood, Prashanth Papu, Jyoti Parwatikar, Ed Spitznagel, David Richard, David Taylor, Jon Turner, Ken Wong Jan 2001

Implementation Of An Open Multi-Service Router, Fred Kuhns, John Dehart, Ralph Keller, John Lockwood, Prashanth Papu, Jyoti Parwatikar, Ed Spitznagel, David Richard, David Taylor, Jon Turner, Ken Wong

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This paper describes the design, implementation, and performance of an open, high-performance, dynamically reconfigurable Multi-Service Router (MSR) being developed at Washington University in St. Louis. This router provides an experimentation platform for research on protocols, router software, and hardware design, network management, quality of service and advanced applications. The MSR has been designed to be flexible, without sacrificing performance. It support gigabit links and uses a scalable architecture suitable for supporting hundreds or even thousands of links. The MSR's flexibility makes it an ideal platform for experimental research on dynamically extensible networks that implement higher level functions in direct support …

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Efficient Queue Management For Tcp Flows, Anshul Kantawala, Jonathan Turner Jan 2001

Efficient Queue Management For Tcp Flows, Anshul Kantawala, Jonathan Turner

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Packets in the Internet can experience large queueing delays during busy periods. Backbone routers are generally engineered to have large buffers, in which packets may wait as long as half a second (assuming FIFO service, longer otherwise). During congestion periods, these bufferfs may stay close to full, subjecting packets to long delays, even when the intrinsic latency of the path is relatively small. This paper studies the performance improvements that can be obtained by using more sophisticated packet schedulers, than are typical of Internet routers. The results show that the large buffers found in WAN routers ocntribute only marginally to …

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Routing In Overlay Multicast Networks, Sherlia Y. Shi, Jonathan S. Turner Jan 2001

Routing In Overlay Multicast Networks, Sherlia Y. Shi, Jonathan S. Turner

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Multicast servises can be provided either as a basic network service or as an application-layer service. Higher level multicast implementations often provide more sophisticated features, and since they don't require network supoprt for multicast, they can provide multicast services, where no network layer support is available. Overlay multicast networks offer an intermediate option, potentially combining the flexibility and advanced features of application layer multicast with the greater efficiency of network layer multicast. Overlay multicast networks play an important role in the Internet. Indeed, since Internet Service Providers have been slow to enable IP multicast in their networks, Internet multicast is …

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Generalized Rad Module Interface Specification Of The Field-Programmable Port Extender (Fpx) Version 2.0, David E. Taylor, John W. Lockwood, Sarang Dharmapurikar Jan 2001

Generalized Rad Module Interface Specification Of The Field-Programmable Port Extender (Fpx) Version 2.0, David E. Taylor, John W. Lockwood, Sarang Dharmapurikar

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The Field-programmable Port eXtender (FPX) provides dynamic, fast, and flexible mechanisms to process data streams at the ports of the Washington University Gigabit Switch (WUGS-20). By performing all computations in FPGA hardware, cells and packets can be processed at the full line speed of the transmission interface, currently 2.4 Gbits/sec. In order to design and implement portable hardware modules for the Reprogrammable Application Devide (RAD) on the FPX board, all modules should conform to a standard interface. This standard interface specifies how modules receive and transmit ATM cells of data flows, prevent data loss during reconfiguration, and access off-chip memory. …

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Lime: A Middleware For Physical And Logical Mobility, Gian Pietro Picco, Amy L. Murphy, Gruia-Catalin Roman Jan 2000

Lime: A Middleware For Physical And Logical Mobility, Gian Pietro Picco, Amy L. Murphy, Gruia-Catalin Roman

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LIME is a middleware supporting the development of applications that exhibit physical mobility of hosts, logical mobility of agents, or both. LIME adopts a coordination perspective inspired by work on the Linda model. The context for computation, represented in Linda by a globally accessible, persistent tuple space, is represented in LIME by transient sharing of the tuple spaces carried by each individual mobile unit. Linda tuple spaces are also extended with a notion of location and with the ability to react to a given state. The hypothesis underlying our work is that the resulting model provides a minimalist set of …

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