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. Programs that use mobility as a mechanism to adapt to resource changes have three requirements that are not shared with other mobile programs. First, they need to monitor the level and quality of resources in their operating environment. Second, they need to be able to react to changes in resource availability. Third, they need to be able to control the way in which resources are used on their behalf (by libraries and other support code). In this chapter, we describe the design and implementation of Sumatra, an extension of Java that supports resourceaware mobile programs. We also describe the design and implementation of a distributed resource monitor that provides the information required by Sumatra programs. 1 Introduction Mobile programs can move an active thread of control from one site to another during execution. This flexibility has many potential advantages. For example, a program that searches distributed data repositories can improve its performance by migrating to the re...

This paper presents the architecture for a Base, a clustered environment for building and executing highly available, scalable, but exible and adaptable infrastructure services. Our architecture has three organizing principles: addressing all of the dicult service faulttolerance, availability, and consistency problems in a carefully controlled environment, building that environment out of a collection of execution environments that are receptive to mobile code, and using dynamically generated code to introduce run-time-generated levels of indirection separating clients from services. We present a prototype Java implementation of a Base called the MultiSpace, and talk about two applications written on this prototype: the Ninja Jukebox (a cluster based music warehouse), and Keiretsu (an instant messaging service that supports heterogeneous clients). We show that the MultiSpace implementation successfully reduces the complexity of implementing services, and that the platform is conducive...

Hive is a distributed agents platform, a decentralized system for building applications by networking local system resources. This paper presents the architecture of Hive, concentrating on the idea of an "ecology of distributed agents" and its implementation in a practical Java based system. Hive provides ad-hoc agent interaction, ontologies of agent capabilities, mobile agents, and a graphical interface to the distributed system. We are applying Hive to the problems of networking "Things That Think," putting computation and communication in everyday places such as your shoes, your kitchen, or your own body. TTT shares the challenges and potentials of ubiquitous computing and embedded network applications. We have found that the flexibility of a distributed agents architecture is well suited for this application domain, enabling us to easily build applications and to reconfigure our systems on the fly. Hive enables us to make our environment and network more alive.

In this paper, we investigate network-aware mobile programs, programs that can use mobility as a tool to adapt to variations in network characteristics. We present infrastructural support for mobility and network monitoring and show how adaptalk, a Java-based mobile Internet chat application can take advantage of this support to dynamically place the chat server so as to minimize response time. Our conclusion was that on-line network monitoring and adaptive placement of shared data-structures can significantly improve performance of distributed applications on the Internet. 1

Security is an important issue for the widespread deployment of applications based on software agent technology. It is generally agreed that without the proper countermeasures in place, use of agent-based applications will be severely impeded. However, not all applications require the same set of countermeasures, nor can they depend entirely on the agent system to provide them. Instead, countermeasures are applied commensurate with the anticipated threat profile and intended security objectives for the application. While countermeasures typically include any action, device, procedure, technique, or other measure that reduces the vulnerability of or threat to a system, our focus here is specifically on technical mechanisms, as opposed to procedural or non-technical measures. Such countermeasures can be integrated directly into an agent system, or incorporated into the design of an agent to supplement the capabilities of an underlying agent system. This paper gives an overview of the t...

Abstract. Mobile-agent systems must address three security issues: protecting an individual machine, protecting a group of machines, and protecting an agent. In this chapter, we discuss these three issues in the context of D’Agents, a mobile-agent system whose agents can be written in Tcl, Java and Scheme. (D’Agents was formerly known as Agent Tcl.) First we discuss mechanisms existing in D’Agents for protecting an individual machine: (1) cryptographic authentication of the agent’s owner, (2) resource managers that make policy decisions based on the owner’s identity, and (3) secure execution environments for each language that enforce the decisions of the resource managers. Then we discuss our planned market-based approach for protecting machine groups. Finally we consider several (partial) solutions for protecting an agent from a malicious machine. 1

A process is an operating system abstraction representing an instance of a running computer program. Process migration is the act of transferring a process between two machines during its execution. Several implementations

JavaSeal is a secure mobile agent kernel that provides a small set of abstractions for constructing agent applications. This paper describes the design of these abstractions and their implementation. We address the limitations of the Java security model that had to be overcome, and then present a medium-sized e-commerce application that runs over JavaSeal. 1

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 con guration 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.