Physical Sciences and Mathematics Commons^™

Group-Aware Stream Filtering For Bandwidth-Efficient Data Dissemination, Ming Li, David Kotz

Dartmouth Scholarship

In this paper we are concerned with disseminating high-volume data streams to many simultaneous applications over a low-bandwidth wireless mesh network. For bandwidth efficiency, we propose a group-aware stream filtering approach, used in conjunction with multicasting, that exploits two overlooked, yet important, properties of these applications: 1) many applications can tolerate some degree of “slack” in their data quality requirements, and 2) there may exist multiple subsets of the source data satisfying the quality needs of an application. We can thus choose the “best alternative” subset for each application to maximize the data overlap within the group to best benefit …

Quality-Managed Group-Aware Stream Filtering, Ming Li, David Kotz

Dartmouth Scholarship

We consider a distributed system that disseminates high-volume event streams to many simultaneous monitoring applications over a low-bandwidth network. For bandwidth efficiency, we propose a group-aware stream filtering approach, used together with multicasting, that exploits two overlooked, yet important, properties of monitoring applications: 1) many of them can tolerate some degree of “slack” in their data quality requirements, and 2) there may exist multiple subsets of the source data satisfying the quality needs of an application. We can thus choose the “best alternative” subset for each application to maximize the data overlap within the group to best benefit from multicasting. …

Scalability In A Secure Distributed Proof System, Kazuhiro Minami, David Kotz

Dartmouth Scholarship

A logic-based language is often adopted in systems for pervasive computing, because it provides a convenient way to define rules that change the behavior of the systems dynamically. Those systems might define rules that refer to the users' context information to provide context-aware services. For example, a smart-home application could define rules referring to the location of a user to control the light of a house automatically. In general, the context information is maintained in different administrative domains, and it is, therefore, desirable to construct a proof in a distributed way while preserving each domain's confidentiality policies. In this paper, …

Improving Data Access For Computational Grid Applications, Ron Oldfield, David Kotz

Dartmouth Scholarship

High-performance computing increasingly occurs on “computational grids” composed of heterogeneous and geographically distributed systems of computers, networks, and storage devices that collectively act as a single “virtual” computer. A key challenge in this environment is to provide efficient access to data distributed across remote data servers. Our parallel I/O framework, called Armada, allows application and data-set providers to flexibly compose graphs of processing modules that describe the distribution, application interfaces, and processing required of the dataset before computation. Although the framework provides a simple programming model for the application programmer and the data-set provider, the resulting graph may contain bottlenecks …

Secure Context-Sensitive Authorization, Kazuhiro Minami, David Kotz

Dartmouth Scholarship

There is a recent trend toward rule-based authorization systems to achieve flexible security policies. Also, new sensing technologies in pervasive computing make it possible to define context-sensitive rules, such as “allow database access only to staff who are currently located in the main office.” However, these rules, or the facts that are needed to verify authority, often involve sensitive context information. This paper presents a secure context-sensitive authorization system that protects confidential information in facts or rules. Furthermore, our system allows multiple hosts in a distributed environment to perform the evaluation of an authorization query in a collaborative way; we …

Policy-Driven Data Dissemination For Context-Aware Applications, Guanling Chen, David Kotz

Dartmouth Scholarship

Context-aware pervasive-computing applications require continuous monitoring of their physical and computational environment to make appropriate adaptation decisions in time. The data streams produced by sensors, however, may overflow the queues on the dissemination path. Traditional flow-control and congestion-control policies either drop data or force the sender to pause. When the data sender is sensing the physical environment, however, a pause is equivalent to dropping data. Instead of arbitrarily dropping data that may contain important events, we present a policy-driven data dissemination service named PACK, based on an overlay-based infrastructure for efficient multicast delivery. PACK enforces application-specified policies that define how …

Design And Implementation Of A Large-Scale Context Fusion Network, Guanling Chen, Ming Li, David Kotz

Dartmouth Scholarship

In this paper we motivate a Context Fusion Network (CFN), an infrastructure model that allows context-aware applications to select distributed data sources and compose them with customized data-fusion operators into a directed acyclic information fusion graph. Such a graph represents how an application computes high-level understandings of its execution context from low-level sensory data. Multiple graphs by different applications inter-connect with each other to form a global graph. A key advantage of a CFN is re-usability, both at code-level and instance-level, facilitated by operator composition. We designed and implemented a distributed CFN system, Solar, which maps the logical operator graph …

Dependency Management In Distributed Settings (Poster Abstract), Guanling Chen, David Kotz

Dartmouth Scholarship

Ubiquitous-computing environments are heterogeneous and volatile in nature. Systems that support ubicomp applications must be self-managed, to reduce human intervention. In this paper, we present a general service that helps distributed software components to manage their dependencies. Our service proactively monitors the liveness of components and recovers them according to supplied policies. Our service also tracks the state of components, on behalf of their dependents, and may automatically select components for the dependent to use based on evaluations of customized functions. We believe that our approach is flexible and abstracts away many of the complexities encountered in ubicomp environments. In …

Computational Markets To Regulate Mobile-Agent Systems, Jonathan Bredin, David Kotz, Daniela Rus, Rajiv T. Maheswaran, Cagri Imer, Tamer Başar

Dartmouth Scholarship

Mobile-agent systems allow applications to distribute their resource consumption across the network. By prioritizing applications and publishing the cost of actions, it is possible for applications to achieve faster performance than in an environment where resources are evenly shared. We enforce the costs of actions through markets where user applications bid for computation from host machines. \par We represent applications as collections of mobile agents and introduce a distributed mechanism for allocating general computational priority to mobile agents. We derive a bidding strategy for an agent that plans expenditures given a budget and a series of tasks to complete. We …

Context-Sensitive Resource Discovery, Guanling Chen, David Kotz

Dartmouth Scholarship

This paper presents the “Solar” system framework that allows resources to advertise context-sensitive names and for applications to make context-sensitive name queries. The heart of our framework is a small specification language that allows composition of “context-processing operators” to calculate the desired context. Resources use the framework to register and applications use the framework to lookup context-sensitive name descriptions. The back-end system executes these operators and constantly updates the context values, adjusting advertised names and informing applications about changes. We report experimental results from a prototype, using a modified version of the Intentional Naming System (INS) as the core directory …

Solar: An Open Platform For Context-Aware Mobile Applications, Guanling Chen, David Kotz

Dartmouth Scholarship

Emerging pervasive computing technologies transform the way we live and work by embedding computation in our surrounding environment. To avoid increasing complexity, and allow the user to concentrate on her tasks, applications in a pervasive computing environment must automatically adapt to their changing \em context, including the user state and the physical and computational environment in which they run. Solar is a middleware platform to help these “context-aware” applications aggregate desired context from heterogeneous sources and to locate environmental services depending on the current context. By moving most of the context computation into the infrastructure, Solar allows applications to run …

Armada: A Parallel I/O Framework For Computational Grids, Ron Oldfield, David Kotz

Dartmouth Scholarship

High-performance computing increasingly occurs on “computational grids” composed of heterogeneous and geographically distributed systems of computers, networks, and storage devices that collectively act as a single “virtual” computer. One of the great challenges for this environment is to provide efficient access to data that is distributed across remote data servers in a grid. In this paper, we describe our solution, a framework we call Armada. Armada allows applications to flexibly compose modules to access their data, and to place those modules at appropriate hosts within the grid to reduce network traffic.

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 …

A Market-Based Model For Resource Allocation In Agent Systems, Jonathan Bredin, David Kotz, Daniela Rus

Dartmouth Scholarship

In traditional computational systems, resource owners have no incentive to subject themselves to additional risk and congestion associated with providing service to arbitrary agents, but there are applications that benefit from open environments. We argue for the use of markets to regulate agent systems. With market mechanisms, agents have the abilities to assess the cost of their actions, behave responsibly, and coordinate their resource usage both temporally and spatially. \par We discuss our market structure and mechanisms we have developed to foster secure exchange between agents and hosts. Additionally, we believe that certain agent applications encourage repeated interactions that benefit …

A Formal Semantics For Spki, Jon Howell, David Kotz

Dartmouth Scholarship

We extend the logic and semantics of authorization due to Abadi, Lampson, et al. to support restricted delegation. Our formal model provides a simple interpretation for the variety of constructs in the Simple Public Key Infrastructure (SPKI), and lends intuition about possible extensions. We discuss both extensions that our semantics supports and extensions that it cautions against.

End-To-End Authorization, Jon Howell, David Kotz

Dartmouth Scholarship

Many boundaries impede the flow of authorization information, forcing applications that span those boundaries into hop-by-hop approaches to authorization. We present a unified approach to authorization. Our approach allows applications that span administrative, network, abstraction, and protocol boundaries to understand the end-to-end authority that justifies any given request. The resulting distributed systems are more secure and easier to audit. \par We describe boundaries that can interfere with end-to-end authorization, and outline our unified approach. We describe the system we built and the applications we adapted to use our unified authorization system, and measure its costs. We conclude that our system …

Trading Risk In Mobile-Agent Computational Markets, Jonathan Bredin, David Kotz, Daniela Rus

Dartmouth Scholarship

Mobile-agent systems allow user programs to autonomously relocate from one host site to another. This autonomy provides a powerful, flexible architecture on which to build distributed applications. The asynchronous, decentralized nature of mobile-agent systems makes them flexible, but also hinders their deployment. We argue that a market-based approach where agents buy computational resources from their hosts solves many problems faced by mobile-agent systems. \par In our earlier work, we propose a policy for allocating general computational priority among agents posed as a competitive game for which we derive a unique computable Nash equilibrium. Here we improve on our earlier approach …

Restricted Delegation: Seamlessly Spanning Administrative Boundaries, Jon Howell, David Kotz

Dartmouth Scholarship

Historically and currently, access control and authentication is managed through ACLs. Examples include:

• the list of users in /etc/password, the NIS passwd map, or an NT domain

• permissions on Unix files or ACLs on NT objects

• a list of known hosts in .ssh/known hosts

• a list of IP addresses in .rhosts (for rsh) or .htaccess (http)

The limitations of ACLs always cause problems when spanning administrative domains (and often even inside administrative domains). The best example is the inability to express transitive sharing. Alice shares read access to object X with Bob (but not access to …

Transportable Information Agents, Daniela Rus, Robert Gray, David Kotz

Dartmouth Scholarship

Transportable agents are autonomous programs. They can move through a heterogeneous network of computers under their own control, migrating from host to host. They can sense the state of the network, monitor software conditions, and interact with other agents or resources. The network-sensing tools allow our agents to adapt to the network configuration and to navigate under the control of reactive plans. In this paper we describe the design and implementation of the navigation system that gives our agents autonomy. We also discuss the intelligent and adaptive behavior of autonomous agents in distributed information-gathering tasks.

Transportable Agents Support Worldwide Applications, David Kotz, Robert Gray, Daniela Rus

Dartmouth Scholarship

Worldwide applications exist in an environment that is inherently distributed, dynamic, heterogeneous, insecure, unreliable, and unpredictable. In particular, the latency and bandwidth of network connections varies tremendously from place to place and time to time, particularly when considering wireless networks, mobile devices, and satellite connections. Applications in this environment must be able to adapt to different and changing conditions. We believe that transportable autonomous agents provide an excellent mechanism for the construction of such applications. We describe our prototype transportable-agent system and several applications.

Worldwide applications exist in an environment that is inherently distributed, dynamic, heterogeneous, insecure, unreliable, and unpredictable. …

Autonomous And Adaptive Agents That Gather Information, Daniela Rus, Robert Gray, David Kotz

Dartmouth Scholarship

We have designed and implemented autonomous software agents. Autonomous software agents navigate independently through a heterogeneous network of computers. They can sense the state of the network, monitor software conditions, and interact with other agents. The network-sensing tools allow our agents to adapt to the network configuration and to navigate under the control of reactive plans. In this paper we illustrate the intelligent and adaptive behavior of autonomous agents in distributed information-gathering tasks.

The Expected Lifetime Of Single-Address-Space Operating Systems, David Kotz, Preston Crow

Dartmouth Scholarship

Trends toward shared-memory programming paradigms, large (64-bit) address spaces, and memory-mapped files have led some to propose the use of a single virtual-address space, shared by all processes and processors. To simplify address-space management, some have claimed that a 64-bit address space is sufficiently large that there is no need to ever re-use addresses. Unfortunately, there has been no data to either support or refute these claims, or to aid in the design of appropriate address-space management policies. In this paper, we present the results of extensive kernel-level tracing of the workstations on our campus, and discuss the implications for …

Transportable Agents, Keith D. Kotay, David Kotz

Dartmouth Scholarship

As network information resources grow in size, it is often most efficient to process queries and updates at the site where the data is located. This processing can be accomplished by using a traditional client-server network interface, which constrains the client to the set of queries supported by the server, or requires the server to send all data to the client for processing. The former is inflexible; the latter is inefficient. Transportable agents, which support the movement of the client computation to the location of the remote resource, have the potential to be more flexible and more efficient. Transportable agents …

The Expected Lifetime Of “Single-Address-Space” Operating Systems, David Kotz, Preston Crow

Dartmouth Scholarship

Trends toward shared-memory programming paradigms, large (64-bit) address spaces, and memory-mapped files have led some to propose the use of a single virtual-address space, shared by all processes and processors. Typical proposals require the single address space to contain all process-private data, shared data, and stored files. To simplify management of an address space where stale pointers make it difficult to re-use addresses, some have claimed that a 64-bit address space is sufficiently large that there is no need to ever re-use addresses. Unfortunately, there has been no data to either support or refute these claims, or to aid in …