GCS-MA: A group communication system for mobile agents

Reliable messaging is a key component necessary for mobile agent systems. Current researches focus on reliable one-to-one message delivery to mobile agents. But how to implement a group communication system for mobile agents remains an open issue, which is a powerful block that facilitates the development of fault-tolerant mobile agent systems. In this paper, we propose a group communication system for mobile agents (GCS-MA), which includes totally ordered multicast and membership management functions. We divide a group of mobile agents into several agent clusters, and each agent cluster consists of all mobile agents residing in the same sub-network and is managed by a special module, named coordinator. Then, all coordinators form a ring-based overlay for interchanging messages between clusters. We present a token-based algorithm, an intra-cluster messaging algorithm and an inter-cluster migration algorithm to achieve atomicity and total ordering properties of multicast messages, by building a membership protocol on top of the clustering and failure detection mechanisms. Performance issues of the proposed system have been analysed through simulations. We also describe the application of the proposed system in the context of the service cooperation middleware (SCM) project.     

防止移动Agent通信失效的方法

通信机制是移动代理系统研究的关键技术之一,但是由于Agent具有移动性,使得Agent在通信过程中会引起通信失效问题.在比较了几种防止通信失效的方法后,结合集中式控制和本地通信,提出了一种新的防止移动Agent通信失效的方法,在有效控制通信开销的同时,保证了消息传递的可靠性.     

移动代理人编程技术与移动用戶管理系统探讨

有自我控制与辨别身份能力的移动代理人编程技术,不但能够在网路上移动,也能够与其他代理人编程沟通及执行任务.由于移动代理人常常运作于异质的网路或作业系统(operating system)环境下,因此,一个具有整体逻辑性操作界面来存取实体结构的管理系统就显得越发重要.提出了一个能够追踪和维持移动代理人的管理系统,并且应用于远距教学(distance learning).此系统的主要目的在于提供移动代理人通用的存取环境.为了能使此系统完全运作,论述了移动代理人通信网路模组、移动代理人演化阶段来支援管理代理人与用户端代理人.另外,也将移动代理人所使用的工具编程整合成为角色扮演(role-setting)物件;此角色扮演物件是符合所谓应用编程驱使元件(application-driven component)的,因此,此系统也能够符合专业化利益的使用者的需求.     

移动Agent安全措施与实现

移动Agent的应用日益广泛,移动Agent系统的安全问题突出,如何解决移动Agent安全问题是非常关键的。本文提出了基于密码学和计算机网络安全的移动Agent的安全措施,同时给出了实现的方法,并提出可以采用的其他新型的安全措施。这些措施的核心问题是既要保证移动Agent通信的安全和移动Agent执行环境的安全,同时又要保证移动Agent能够应用的更为广泛。     

CONNECTING MIGRATION METHOD IN A MOBILE AGENT SYSTEM

Connecting migration in mobile agent systems is to support continuous and transparent communication operations between mobile agents. This article presents the design and implementation of a reliable connecting migration mechanism that provides exactly one delivery for all transmitted data during agent migration. We implemented this mechanism and named it AgentSocket in a VPNAgent system used in the VPN security mechanism. It is a pure middleware implementation, without requiring modification of Java virtual machines.     

移动Agent通信技术的研究与分析

本文研究和分析了移动Agent系统中常见的四个通信技术问题。这四个问题分别是:移动Agent的命名,移动Agent的定位,移动Agent的消息处理及移动Agent通信可靠性。     

一种改进的移动Agent通信算法

如何实现远程Agent通信的位置透明性，保证消息不会因为目标Agent迁移而丢失，一直是移动Agent通信所面临的难题，在现有的很多移动Agent系统中都没有得到解决，作者在Mogent系统中提出的通信算法初步实现了通信的位置透明和可靠的消息传输，该文在原有处的基础上提出了一种改进的适于多种迁移和通信模式的移动Agent通信算法，进一步减少了Agent的地址注册开销和迁移受到的限制，并给出了一种避免地址欺骗攻击的解决方案。     

移动Agent系统通信失效问题研究

The Mobile Agent is thought to be the popular computing model for the next generation's distributed sys-tem. The mobile agent has the following key features: autonomy, collaboration, security and especially mobility. Agood communication model for mobile agents cooperation is also necessary. In this article, after describing the maincommunication mechanisms, we analyze the methods to solve Agent Tracking and Communication Failure and make classification. We also propose a reliable and efficient mechanism named MEFS which uses Detecting methods and then analyze its performance by giving the experimental data at the end.     

A security protocol for mobile agents based upon the cooperation of sedentary agents

Despite its many benefits, mobile agent technology results in significant security threats from agents and hosts. This paper presents a protocol which protects mobile agents from malicious hosts. This protocol combines four concepts: the cooperation between a mobile agent and a sedentary agent; the reference execution (reliable platforms which shelter our cooperating sedentary agents); the cryptography and the digital signature to ensure safe inter-agent communication and time-limited execution (timeout). A dynamic approach which makes use of a timer to make it possible to detect a mobile agent's code re-execution was used. The attack on agent permanent modification was also dealt with. Moreover, the protocol is sufficiently robust so that it is durable and fault tolerant.     

一种改进的移动Agent通信算法

通信机制是移动Agent技术研究的重要课题,目前提出的多种Agent通信机制都尚未满足要求或存在缺陷,该文结合多种传统的Agent通信机制,提出了一种改进的移动Agent通信算法,实现了通信的位置透明性、高可靠性、高效性,极大地减少了迁移受到的限制和迁移引起的地址注册(或更改)开销。该算法在网络主机数目多的Agent系统中,其优点更为明显。     

Design and Implementation of a Hybrid Agent Platform

This paper presents IMAP, a hybrid agent platform composed of several cooperating intelligent agents and mobile agents. IMAP is implemented in Java and Prolog. Java is used to implement the framework of the system, and in particular for supporting the communication between agents and mobility of agent, while Prolog is used to implement both adduction and derivation mechanisms. IMAP intends to independently employ the underlying derivation/adduction and mobility mechanism. In IMAP, intelligent agent and mobile agent can not only fully exploit individual virtue, but also cooperate to perform a task under a uniform platform. Intelligent agents in IMAP are equipped with hypothetical reasoning capabilities, performed by means of adduction: if the knowledge available to an agent is insufficient to solve a query, the agent could adduce new hypotheses. Each intelligent agent can accept queries from mobile agents by means of the interface module, each query is passed to the reasoning module of intelligent agent which performs a derivation and adduction in order to get an answer for mobile agent. IMAP also provides mobile agents a flexible and efficient coordination mechanism and a reliable migration mechanism, and supports persistence of agent state and agent security. Mobile agent's coordination mechanism exploits the advantages of the XML language and Linda-like coordination. This programmable Linda-like coordination mechanism suits the mobility and openness of the Internet application, XML standard for Internet data representation may guarantee a high-degree of interoperability between heterogeneous environments. The design and implementation key technologies of IMAP are described in this paper. An Internet based auction application example shows the suitability and the effectiveness of the IMAP, and its performance evaluation is also made. Finally, some conclusions and remarks are given.     

一种基于域的可靠移动Agent通信机制

移动Agent间的通信机制是开发移动Agent系统的基础,但目前的通信机制均无法适用于规模庞大的Internet环境。把整个系统按域划分,将移动Agent名字解析机制与改进的邮箱消息传递机制相结合,提出一种高效可靠的移动Agent通信模型,并较好地支持了移动Agent的离线运行能力。经模拟验证表明,该模型在节点数目和消息条数众多的情况下,尤为有效。     

J-SEAL2—A Secure High-Performance Mobile Agent System

Even though the advantages of mobile agents for distributed electronic commerce applications have been highlighted in numerous research works, mobile agent applications are not in widespread use today. For the success of mobile agent applications, secure, portable, and efficient execution platforms for mobile agents are crucial. However, popular mobile agent systems do not meet the high security requirements of electronic commerce applications, are not portable, or cause high overhead. Currently, the majority of mobile agent platforms is based on Java. These systems simply rely on the security model of Java, although it is not suited to protect agents and service components from each other.In contrast, J-SEAL2 is a mobile agent system designed to meet the high security, portability, and performance requirements of large-scale electronic commerce applications. J-SEAL2 extends the Java environment with a model of strong protection domains. The core of the system is a micro-kernel fulfilling the same functions as a traditional operating system kernel: protection, communication, domain termination, and resource control. For portability reasons, J-SEAL2 is implemented in pure Java. This paper focuses on the design of the new communication model in J-SEAL2, which allows convenient, efficient, and mediated communication in a hierarchy of strong protection domains.     

Integrating mobile agents into the mobile middleware

Mobile agents are a new paradigm for distributed computing that is especially well suited for mobile computing over global wireless networks. This paper describes the approach taken in the ACTS On TheMove project to integrate a mobile agent system into the Mobile Application Support Environment (MASE), a middleware for mobile computing. In this project, an existing mobile agent system was adapted for the requirements of mobile computing. We present the changes that had to be made to the agent system to adapt it to the wireless communication. We also present some of the application areas where a mobile agent system is suitable for mobile communication. We describe an agent based pre-fetcher application where an agent operaes disconnected from the user on the fixed network and prepares web pages for the anticipated next connection of the user using the Quality-of-Service trading functions available in MASE.     

Reliable Communication for Highly Mobile Agents

The provision of a reliable communication infrastructure for mobile agents is still an open research issue. The challenge to reliability we address in this work does not come from the possibility of faults, but rather from the mere presence of mobility, which complicates the problem of ensuring the delivery of information even in a fault-free network. For instance, the asynchronous nature of message passing and agent migration may cause situations where messages forever chase a mobile agent that moves frequently from one host to another. Current solutions rely on conventional technologies that either do not provide a solution for the aforementioned problem, because they were not designed with mobility in mind, or enforce continuous connectivity with the message source, which in many cases defeats the very purpose of using mobile agents.In this paper, we propose an algorithm that guarantees delivery to highly mobile agents using a technique similar to a distributed snapshot. A number of enhancements to this basic idea are discussed, which limit the scope of message delivery by allowing dynamic creation of the connectivity graph. Notably, the very structure of our algorithm makes it amenable not only to guarantee message delivery to a specific mobile agent, but also to provide multicast communication to a group of agents, which constitutes another open problem in research on mobile agents. After presenting our algorithm and its properties, we discuss its implementability by analyzing the requirements on the underlying mobile agent platform, and argue about its applicability.     

Mailbox-based scheme for mobile agent communications

In various situations, mobile agents at different hosts must cooperate with one another by sharing information and making decisions collectively. To ensure effective interagent communication, communication protocols must track target agent locations and deliver messages reliably. Researchers have proposed a wide range of schemes for agent tracking and reliable message delivery. However, each scheme has its own assumptions, design goals, and methodology. As a result, no uniform or structured methods exist for characterizing current protocols, making it difficult to evaluate their relative effectiveness and performance. The authors propose a mailbox-based scheme for designing mobile agent communication protocols. This scheme assigns each agent a mailbox to buffer messages, but decouples the agent and mailbox to let them reside at different hosts and migrate separately.     

The mobile groups approach for the coordination of mobile agents

We present the concept of mobile groups as a basic mechanism for the reliable coordination of mobile agents. Analogously to traditional group systems, mobile groups also provide message delivery guarantees and virtual synchrony. Furthermore, they make agent mobility not only visible for the group, but also consistently ordered with other group actions (such as crashes, joins, leaves, and other migrations). The mobile groups approach represents a novel mobility support mechanism, which can be used to handle reliability of mobile agents required at both, the application and system level (e.g., for coordinating distributed agents and for reliable agent migration, respectively). In this paper, we discuss the motivations for the mobile groups approach, formally define their properties, and present a membership protocol for such groups. We also discuss some implementation issues and related performance data, and present the advantages of mobile groups against mechanisms commonly employed for the coordination of mobile agents.     

All-to-all communication with cellular automata agents in 2d grids: topologies,streets and performances

Solving the all-to-all communication task in the cyclic triangulate and square grids in shortest time with mobile agents was the objective of this work. In order to solve the problem, the multi-agent system is modeled by cellular automata with synchronous updating and the agents’ behavior by an embedded finite state machine (FSM). Agents can move or stay, and turn to any direction. An agent is able to leave a trace by setting a color flag on its site. Colors allow indirect communication similar to pheromones, speed up the task and contribute to a better reliability. More reliable agents are found using different initial control states for the agent’s FSMs. A simple genetic procedure based on mutation is used to evolve near optimal FSMs for both grids. Agents in the triangulate grid can solve the task in around 2/3 of the time compared with the square grid. The communication time depends also on the density of agents in the field, e.g., agents with density 4/(16 \(\times \) 16) turned out to be the slowest.