Physical Sciences and Mathematics Commons^™

Mobile-Agent Versus Client/Server Performance: Scalability In An Information-Retrieval Task, Robert S. Gray, David Kotz, Ronald A. Peterson, Joyce Barton, Daria Chacon, Peter Gerken, Martin Hofmann, Jeffrey Bradshaw, Maggie Breedy, Renia Jeffers, Niranjan Suri

Dartmouth Scholarship

Building applications with mobile agents often reduces the bandwidth required for the application, and improves performance. The cost is increased server workload. There are, however, few studies of the scalability of mobile-agent systems. We present scalability experiments that compare four mobile-agent platforms with a traditional client/server approach. The four mobile-agent platforms have similar behavior, but their absolute performance varies with underlying implementation choices. Our experiments demonstrate the complex interaction between environmental, application, and system parameters.

Solar: Towards A Flexible And Scalable Data-Fusion Infrastructure For Ubiquitous Computing, Guanling Chen, David Kotz

Dartmouth Scholarship

As we embed more computers into our daily environment, ubiquitous computing promises to make them less noticeable and to avoid information overload. We see, however, few ubiquitous applications that are able to adapt to the dynamics of user, physical, and computational context. The challenge is to allow applications flexible access to these sources, and yet scale to thousands of devices and sensors. In this paper we introduce our proposed infrastructure, Solar. In Solar, information sources produce events. Applications may subscribe to interesting sources directly, or they may instantiate and subscribe to a tree of operators that filter, transform, merge and …

Differential Elastic Image Registration, Senthil Periaswamy, Hany Farid

Computer Science Technical Reports

We have applied techniques from differential motion estimation to the problem of automatic elastic registration of medical images. This method models the mapping between images as a locally affine but globally smooth warp. The mapping also explicitly accounts for variations in image intensities. This approach is simple and highly effective across a broad range of medical images. We show the efficacy of this approach on several synthetic and clinical images.

Detecting Steganographic Messages In Digital Images, Hany Farid

Computer Science Technical Reports

Techniques and applications for information hiding have become increasingly more sophisticated and widespread. With high-resolution digital images as carriers, detecting the presence of hidden messages has also become considerably more difficult. It is sometimes possible, nevertheless, to detect (but not necessarily decipher) the presence of embedded messages. The basic approach taken here works by finding predictable higher-order statistics of ``natural'' images within a multi-scale decomposition, and then showing that embedded messages alter these statistics.

Write Once, Move Anywhere: Toward Dynamic Interoperability Of Mobile Agent Systems, Arne Grimstrup, Robert Gray, David Kotz, Thomas Cowin, Greg Hill, Niranjan Suri, Daria Chacon, Martin Hofmann

Computer Science Technical Reports

Mobile agents are an increasingly popular paradigm, and in recent years there has been a proliferation of mobile-agent systems. These systems are, however, largely incompatible with each other. In particular, agents cannot migrate to a host that runs a different mobile-agent system. Prior approaches to interoperability have tried to force agents to use a common API, and so far none have succeeded. Our goal, summarized in the catch phrase ``Write Once, Move Anywhere,'' led to our efforts to develop mechanisms that support dynamic runtime interoperability of mobile-agent systems. This paper describes the Grid Mobile-Agent System, which allows agents to migrate …

Securing Web Servers Against Insider Attack, Shan Jiang, Sean Smith, Kazuhiro Minami Dartmouth College

Computer Science Technical Reports

Too often, ``security of Web transactions'' reduces to ``encryption of the channel''---and neglects to address what happens at the server on the other end. This oversight forces clients to trust the good intentions and competence of the server operator---but gives clients no basis for that trust. Furthermore, despite academic and industrial research in secure coprocessing, many in the computer science community still regard ``secure hardware'' as a synonym for ``cryptographic accelerator.' This oversight neglects the real potential of COTS secure coprocessing technology to establish trusted islands of computation in hostile environments---such as at web servers with risk of insider attack. …

Web Spoofing 2001, Yougu Yuan, Eileen Zishuang Ye, Sean Smith Dartmouth College

Computer Science Technical Reports

The Web is currently the pre-eminent medium for electronic service delivery to remote users. As a consequence, authentication of servers is more important than ever. Even sophisticated users base their decision whether or not to trust a site on browser cues---such as location bar information, SSL icons, SSL warnings, certificate information, response time, etc. In their seminal work on web spoofing, Felten et al showed how a malicious server could forge some of these cues---but using approaches that are no longer reproducible. However, subsequent evolution of Web tools has not only patched security holes---it has also added new technology to …

Using Mobile Agents For Analyzing Intrusion In Computer Networks, Jay Aslam, Marco Cremonini, David Kotz, Daniela Rus

Dartmouth Scholarship

Today hackers disguise their attacks by launching them form a set of compromised hosts distributed across the Internet. It is very difficult to defend against these attacks or to track down their origin. Commercially available intrusion detection systems can signal the occurrence of limited known types of attacks. New types of attacks are launched regularly but these tools are not effective in detecting them. Human experts are still the key tool for identifying, tracking, and disabling new attacks. Often this involves experts from many organizations working together to share their observations, hypothesis, and attack signatures. Unfortunately, today these experts have …

Approximation Techniques For Average Completion Time Scheduling, Chandra Chekuri, Rajeev Motwani, Balas Natarajan, Clifford Stein

Dartmouth Scholarship

We consider the problem of nonpreemptive scheduling to minimize average ( weighted) completion time, allowing for release dates, parallel machines, and precedence constraints. Recent work has led to constant-factor approximations for this problem based on solving a preemptive or linear programming relaxation and then using the solution to get an ordering on the jobs. We introduce several new techniques which generalize this basic paradigm. We use these ideas to obtain

improved approximation algorithms for one-machine scheduling to minimize average completion time with release dates. In the process, we obtain an optimal randomized on-line algorithm for the same problem that beats …

Webalps Implementation And Performance Analysis: Using Trusted Co-Servers To Enhance Privacy And Security Of Web Interactions, Shan Jiang

Dartmouth College Master’s Theses

The client-server model of the Web poses a fundamental trust issue: clients are forced to trust in secrecy and correctness of computation occurring at a remote server of unknown credibility. The current solution for this problem is to use a PKI (Public Key Infrastructure) system and SSL (Secure Sockets Layer) digital certificates to prove the claimed identity of a server and establish an authenticated, encrypted channel between the client and this server. However, this approach does not address the security risks posed by potential malicious server operators or any third parties who may penetrate the server sites. The WebALPS (Web …

A Directory Infrastructure To Support Mobile Services, Ammar Khalid

Dartmouth College Undergraduate Theses

Traditional Voice-over-IP applications such as Microsoft NetMeeting assume that the user is on a machine with a fixed IP address. If, however, the user connects to the Internet, via a wireless network, on a handheld device, his IP address frequently changes as he moves from one subnet to another. In such a situation, we need a service that can be queried for the most current IP address of a person whom we wish to contact. In this project, we design and implement such a directory service. The service authenticates all callers and callees, is robust against most host failure, and …

Smartreminder: A Case Study On Context-Sensitive Applications, Arun Mathias

Dartmouth College Undergraduate Theses

Designing context-sensitive applications is challenging. We design and implement SmartReminder to explore designing context-sensitive applications and to demonstrate how the SOLAR system can be used in developing such applications. SmartReminder is an application that reminds the user based on contextual information. Current appointment-reminder applications remind the user about their appointments at an arbitrarily specified time. For instance, they might remind the user ten minutes before each appointment. SmartReminder, on the other hand, uses contextual information, like location, to better estimate the appropriate reminder time for each appointment. It reminds the user based on where they are, where they need to …

Measuring Early Usage Of Dartmouth's Wireless Network, Pablo Stern

Dartmouth College Undergraduate Theses

In Spring 2001, Dartmouth College installed a campus-wide 802.11b wireless network. To understand how that network is used, we examined the usage characteristics of the network over a five-week period. We monitored access points to determine user behavior, and user and network traffic characteristics. Because our study coincided with the deployment of the access points, our analysis captures the growth of a wireless network. The results of this study help understand the behavior of mobile users and provide a reference to network engineers wishing to deploy and expand similar wireless networks.

An Empirical Study Of Training And Testing Error In Boosting, David D. Latham

Dartmouth College Undergraduate Theses

Bounds have been proven for both training and testing error for the boosting algorithm AdaBoost, but in practice neither seem to produce a particularly tight bound. In this paper we share some observations of these bounds from empirical results, and then explore some properties of the algorithm with an eye towards finding an improved bound for the performance of AdaBoost. Based on our empirical evidence, the error of a hypothesis which labels examples probabilistically based upon the confidence of the vote of the weak hypotheses forms a tighter bound for the training error.

Implementing A Database Information System For An Electronic Baseball Scorecard, Tiffany M. Wong

Dartmouth College Undergraduate Theses

We present our design and implementation of a database system of information storage and retrieval for an electronic baseball scorecard. The program uses the relational MySQL database to hold information and a Tcl API to handle interactions between the database and the user interface code. This paper discusses the inner workings of how information storage was broken down inside the database, how queries were internally constructed in accordance with the user's input, and how statistics for players and teams were calculated and returned to the user. Finally, we discuss some limitations attached to our current implementation of the program and …

A System For Audio Personalization With Applications On Wireless Devices, David Marmaros

Dartmouth College Undergraduate Theses

We present and analyze a system for dynamically tailoring discrete audio content for numerous users based on aggregate data and intuitive feedback mechanisms. The framework for this system utilizes a flexible client-server architecture to facilitate audio dissemination, with particular attention to distribution over wireless networks. We discuss the requirements and specifications of such a system. We further analyze the algorithms and protocols required for its operation. Finally, we outline and provide data from a demonstration of this application.

An Armored Data Vault, Alex Iliev

Dartmouth College Undergraduate Theses

We consider the problem of secure long-term archiving of network traffic, an instance of the problem of storing data securely. We approach the problem using secure hardware, which enables the enforcement of flexible access policy. The policy cannot be circumvented by anyone, even insiders, and so we are assured that access to the data is as originally intended. The policy can be expressed as any feasible computation, as it will be checked inside the secure hardware without possibility of interference. We discuss our design of a device to perform such network data archiving and have implemented a prototpe device. We …

Optimizing The Dimensional Method For Performing Multidimensional, Multiprocessor, Out-Of-Core Ffts, Jeremy T. Fineman

Dartmouth College Undergraduate Theses

We present an improved version of the Dimensional Method for computing multidimensional Fast Fourier Transforms (FFTs) on a multiprocessor system when the data consist of too many records to fit into memory. Data are spread across parallel disks and processed in sections. We use the Parallel Disk Model for analysis. The simple Dimensional Method performs the 1-dimensional FFTs for each dimension in term. Between each dimension, an out-of-core permutation is used to rearrange the data to contiguous locations. The improved Dimensional Method processes multiple dimensions at a time. We show that determining an optimal sequence and groupings of dimensions is …

Ecomrisk.Org : A Site To Classify And Organize The Risks Of Performing Business On The Internet, Aidan Stanley Marcuss

Dartmouth College Undergraduate Theses

As the use of the Internet and other computer networks to transact business grows, there is an ever increasing need for those taking part in those transactions to understand the risks of doing so. While there are many web sites that have created valuable databases of specific vulnerabilities for certain types of hardware and software, there is a lack of focus on attempting to analyze the interaction of businesses, their systems, computer networks, and their customers and the risks that are created by either intended or unattended interactions. EcomRISK.org is a web site that presents a clear taxonomy to classify …

Efficient Compression Of Generic Function Dispatch Tables, Eric Kidd

Dartmouth College Undergraduate Theses

A generic function is similar to an overloaded operator, but provides a way to select an appropriate behavior at run-time instead of compile-time. Dujardin and colleagues have proposed an algorithm for building and compressing generic function dispatch tables. We present several modifications to their algorithm, including an improvement to Pseudo-Closest-Poles and two new algorithms for compressing pole tables. The two new compression algorithms are simple and fast, and one produces smaller output than the original.

Dassfnet: An Extension To Dassf For High-Performance Network Modeling, Mehmet Iyigun

Dartmouth College Undergraduate Theses

Scalable Simulation Framework (SSF) is a discrete-event simulation framework providing a unified programming interface geared towards network simulation. Dartmouth SSF (DaSSF) is a C++ implementation of SSF, designed for simulating very large-scale multi-protocol communication networks. As of the latest release, DaSSF lacks many features present in SSF and this prevents it from achieving mainstream use. To alleviate this shortcoming we designed and implemented DaSSFNet which extends DaSSF to the levels of functionality found in SSF. In this paper, we show that DaSSFNet and SSFNet are identical in operation given the same input. We also show that DaSSFNet is about twice …

Fastab: Solving The Pitch To Notation Problem, Jeremy I. Robin

Dartmouth College Undergraduate Theses

I have always been frustrated with the length of time necessary to notate a piece of music. Computers have simplified so many other aspects of our lives, it seems that they should be able to simplify this task as well. In fact, there are already two distinct ways that engineers have attempted to attack this problem. The first analyzes the waveform generated by microphone input and relies on Fourier Analysis and other similar methods. The other examines the analog signal generated by a electric guitar-like pickup placed beneath the strings. The method used by Fastab relies much less on the …

Market-Based Control Of Mobile-Agent Systems, Jonathan L. Bredin

Dartmouth College Ph.D Dissertations

Modern distributed systems scatter sensors, storage, and computation throughout the environment. Ideally these devices communicate and share resources, but there is seldom motivation for a device's owner to yield control to another user. We establish markets for computational resources to motivate principals to share resources with arbitrary users, to enforce priority in distributed systems, to provide flexible and rational limitations on the potential of an application, and to provide a lightweight structure to balance the workload over time and between devices. As proof of concept, we implement a structure software agents can use to discover and negotiate access to networked …

An Implementation Of Object-Oriented Program Transformation For Thought-Guided Debugging, Tiffany M. Wong

Dartmouth College Undergraduate Theses

This paper presents our design and implementation of program transformation for C++ that will be used in the context of a thought-guided debugging system. The program uses a lexical analyzer written in Flex and a grammar written in Bison that work in conjunction to scan the inputted C++ code for function definitions and class definitions. The code is then transformed to produce trace information for each defined function, while the original functionality of the code is left untouched. We also implement two additional data structures that are used for information storage during the course of the program.

Mobile Voice Over Ip (Mvoip): An Application-Level Protocol, Ayorkor Mills-Tettey

Dartmouth College Undergraduate Theses

Current Voice over Internet Protocol (VOIP) protocols require participating hosts to have fixed IP addresses for the duration of a VOIP call. When using a wireless-enabled host, such as a tablet computer on an 802.11 wireless network, it is possible for a participant in a VOIP call to roam around the network, moving from one subnet to another and needing to change IP addresses. This address change creates the need for mobility support in VOIP applications. We present the design of Mobile Voice over IP (MVOIP), an application-level protocol that enables such mobility in a VOIP application based on the …

Tcp/Ip Implementation Within The Dartmouth Scalable Simulation Framework, Michael G. Khankin

Dartmouth College Undergraduate Theses

This paper discusses TCP/IP networking, and in particular, the DaSSF implementation of TCP/IP. The paper reviews the protocols, outlines the implementation design, and demonstrates some tests. In addition, some performance and memory usage analysis is performed. We find DaSSF TCP/IP to be a viable option to the existing SSF. DaSSF TCP/IP is faster and uses less memory so we can simulate larger, more complex, models.

Supporting Adaptive Ubiquitous Applications With The Solar System, Guanling Chen, David Kotz

Computer Science Technical Reports

As we embed more computers into our daily environment, ubiquitous computing promises to make them less noticeable and help to prevent information overload. We see, however, few ubiquitous applications that are able to adapt to the dynamics of user, physical, and computational context. We believe that there are two challenges causing this lack of ubiquitous applications: there is no flexible and scalable way to support information collection and dissemination in a ubiquitous and mobile environment, and there is no general approach to building adaptive applications given heterogeneous contextual information. We propose a system infrastructure, Solar, to meet these challenges. Solar …

Improving A Brokering System For Linking Distributed Simulations, Thomas B. Stephens

Dartmouth College Undergraduate Theses

The Agent Based Environment for Linking Simulations (ABELS) is a software framework designed to provide disparate simulations with dynamically updated data sources. It allows simulations and other agents to join a "cloud" of interacting producers and consumers of data. Once they have joined the cloud, they can publish services to other members and use methods published by others. This paper presents the initial design of a set of matchmaking components for the ABELS framework. These components dictate how services describe their abilities and requirements to ABELS. Furthermore, they help ABELS successfully match data producing services to the requests of data …

Outbound Authentication For Programmable Secure Coprocessors, S W. Smith

Computer Science Technical Reports

A programmable secure coprocessor platform can help solve many security problems in distributed computing. These solutions usually require that coprocessor applications be able to participate as full-fledged parties in distributed cryptographic protocols. Thus, to fully enable these solutions, a generic platform must not only provide programmability, maintenance, and configuration in the hostile field---it must also provide outbound authentication for the entities that result. A particular application on a particular untampered device must be able to prove who it is to a party on the other side of the Internet. To be effective, a secure outbound authentication service must closely mesh …

Mobile-Agent Versus Client/Server Performance: Scalability In An Information-Retrieval Task, Robert S. Gray, David Kotz, Ronald A. Peterson Jr, Peter Gerken, Martin Hofmann, Daria Chacon, Greg Hill, Niranjan Suri

Computer Science Technical Reports

Mobile agents are programs that can jump from host to host in the network, at times and to places of their own choosing. Many groups have developed mobile-agent software platforms, and several mobile-agent applications. Experiments show that mobile agents can, among other things, lead to faster applications, reduced bandwidth demands, or less dependence on a reliable network connection. There are few if any studies of the scalability of mobile-agent servers, particularly as the number of clients grows. We present some recent performance and scalability experiments that compare three mobile-agent platforms with each other and with a traditional client/server approach. The …