We study the gathering problem requiring a team of mobile agents to gather at a single node in arbitrary networks. The team consists of k agents with unique identifiers (IDs), and f of them are weakly Byzantine agents, which behave arbitrarily except falsifying their identifiers. The agents move in synchronous rounds and cannot leave any information on nodes. If the number of nodes n is given to agents, the existing fastest algorithm tolerates any number of weakly Byzantine agents and achieves gathering with simultaneous termination in O(n4·|Λgood|·X(n)) rounds, where |Λgood| is the length of the maximum ID of non-Byzantine agents and X(n) is the number of rounds required to explore any network composed of n nodes. In this paper, we ask the question of whether we can reduce the time complexity if we have a strong team, i.e., a team with a few Byzantine agents, because not so many agents are subject to faults in practice. We give a positive answer to this question by proposing two algorithms in the case where at least 4f2+9f+4 agents exist. Both the algorithms assume that the upper bound N of n is given to agents. The first algorithm achieves gathering with non-simultaneous termination in O((f+|&Lambdagood|)·X(N)) rounds. The second algorithm achieves gathering with simultaneous termination in O((f+|&Lambdaall|)·X(N)) rounds, where |&Lambdaall| is the length of the maximum ID of all agents. The second algorithm significantly reduces the time complexity compared to the existing one if n is given to agents and |&Lambdaall|=O(|&Lambdagood|) holds.

We propose two algorithms for the gathering of k mobile agents in asynchronous Byzantine environments. For both algorithms, we assume that graph topology is arbitrary, each node is equipped with an authenticated whiteboard, agents have unique IDs, and at most f weakly Byzantine agents exist. Here, a weakly Byzantine agent can make arbitrary behavior except falsifying its ID. Under these assumptions, the first algorithm achieves a gathering without termination detection in O(m+fn) moves per agent (m is the number of edges and n is the number of nodes). The second algorithm achieves a gathering with termination detection in O(m+fn) moves per agent by additionally assuming that agents on the same node are synchronized, $f

In this paper, we consider the partial gathering problem of mobile agents in arbitrary networks. The partial gathering problem is a generalization of the (well-investigated) total gathering problem, which requires that all the agents meet at the same node. The partial gathering problem requires, for a given positive integer g, that each agent should move to a node and terminate so that at least g agents should meet at each of the nodes they terminate at. The requirement for the partial gathering problem is no stronger than that for the total gathering problem, and thus, we clarify the difference on the move complexity between them. First, we show that agents require Ω(gn+m) total moves to solve the partial gathering problem, where n is the number of nodes and m is the number of communication links. Next, we propose a deterministic algorithm to solve the partial gathering problem in O(gn+m) total moves, which is asymptotically optimal in terms of total moves. Note that, it is known that agents require Ω(kn+m) total moves to solve the total gathering problem in arbitrary networks, where k is the number of agents. Thus, our result shows that the partial gathering problem is solvable with strictly fewer total moves compared to the total gathering problem in arbitrary networks.

We propose an algorithm for the gathering problem of mobile agents in arbitrary networks (graphs) with Byzantine agents. Our algorithm can make all correct agents meet at a single node in O(fm) time (f is the upper bound of the number of Byzantine agents and m is the number of edges) under the assumption that agents have unique ID and behave synchronously, each node is equipped with an authenticated whiteboard, and f is known to agents. Here, the whiteboard is a node memory where agents can leave information. Since the existing algorithm achieves gathering without a whiteboard in Õ(n9λ) time, where n is the number of nodes and λ is the length of the longest ID, our algorithm shows an authenticated whiteboard can significantly reduce the time for the gathering problem in Byzantine environments.

This paper provides a mobile agent based distributed variational Bayesian (MABDVB) algorithm for density estimation in sensor networks. It has been assumed that sensor measurements can be statistically modeled by a common Gaussian mixture model. In the proposed algorithm, mobile agents move through the routes of the network and compute the local sufficient statistics using local measurements. Afterwards, the global sufficient statistics will be updated using these local sufficient statistics. This procedure will be repeated until convergence is reached. Consequently, using this global sufficient statistics the parameters of the density function will be approximated. Convergence of the proposed method will be also analytically studied, and it will be shown that the estimated parameters will eventually converge to their true values. Finally, the proposed algorithm will be applied to one-dimensional and two dimensional data sets to show its promising performance.

A vehicular ad hoc network (VANET) consists of vehicles (mobile nodes) and road side units which are equipped with the wireless devices such as wireless LANs. Mobile nodes exchange information messages with each other so that VANETs are configured in a self-organized manner. As one of network service scenarios in VANETs, there is a network service to provide the parking spaces in the city central to vehicles (mobile nodes). In this scenario, the road side units (source nodes) which are deployed at the parking spaces periodically disseminate the number of available parking spaces to mobile nodes. Therefore, in this paper, we propose a mobile agent-based information dissemination scheme using location information of mobile nodes and source nodes in the VANET environment. In addition, we conduct simulation experiments in the VANET environment to evaluate the proposed mobile agent-based information dissemination scheme. We confirmed that it could disseminate information messages with lower overhead because mobile agents migrate among mobile nodes by using the location information.

In recent years, society has experienced several changes in its ways and methods of consuming. Nowadays, the diversity and the customization of products and services have provoked that the consumer needs continuously change. Hence, the database systems support e-business processes are required to be timeliness and adaptable to the changing preferences. Autonomous Decentralized Database System (ADDS), has been proposed in order to satisfy the enhanced requirements of current on-line e-business applications. Autonomy and decentralization of subsystems help to achieve short response times in highly competitive situations and an autonomous Coordination Mobile Agent (CMA) has been proposed to achieve flexibility in a highly dynamic environment. However, a problem in ADDS is as the number of sites increases, the distribution and harmonization of product information among the sites are turning difficult. Therefore, many users cannot be satisfied quickly. As a result, system timeliness is inadequate. To solve this problem, a self configuration technology is proposed. This technology can configure the system to the evolving situation dynamically for achieving high response. A simulation shows the effectiveness of the proposed technology in a large-scale system. Finally, an implementation of this technology is presented.

In tree-based wireless sensor networks (WSNs), multihop sensor nodes require a longer time frame to send sensed data to a sink node as the number of hops increases. The time taken for delivery of sensed data becomes a critical issue when a large WSN is deployed. This paper proposes a new data collection scheme with rapid data delivery that utilizes the so-called mobile agent technique. The proposed scheme achieves high data collection efficiency while not relying on route optimization unlike conventional data collection techniques. Simulation results show that the larger the size or the maximum hops of the network, the more effective the proposed scheme becomes. Effectiveness of the proposed scheme is also confirmed through field experiments with actual sensor devices.

We consider the exploration problem with a single agent in an undirected graph. The problem requires the agent starting from an arbitrary node to explore all the nodes and edges in the graph and return to the starting node. Our goal is to minimize both the number of agent moves and the memory size of the agent, which dominate the amount of communication during the exploration. We focus on the local memory called the whiteboard of each node. There are several exploration algorithms which are very fast (i.e. the exploration is completed within a small number of agent moves such as 2m and m+3n) and do not use whiteboards. These algorithms, however, require large agent memory because the agent must keep the entire information in its memory to explore a graph. We achieve the above goal by reducing the agent memory size of such algorithms with using whiteboards. Specifically, we present two algorithms with no agent memory based on the traditional depth-first traversal and two algorithms with O(n) and O(nlog n) space of agent memory respectively based on the fastest algorithms in the literature by Panaite and Pelc [J. Alg., Vol.33 No.2, 1999].

We have already proposed a service discovery scheme using mobile agents for mobile ad hoc networks where node positions in the network and the network topology change frequently. Mobile agents autonomously migrate among nodes and then perform a given task at a node. In the service discovery scheme using mobile agents, mobile agents collect and disseminate services in the network so it is most important how the mobile agents migrate in the network. Therefore, we propose two types of mobile agent migration mechanisms in this paper. One is that mobile agents migrate to the nodes at which other mobile agents do not stay, the other is that mobile agents migrate to the nodes to which mobile agents can disseminate a lot of service information. Finally, we conducted simulation experiments to investigate the performance of the proposed migration mechanisms with respect to the service dissemination time and rate.

The success of peer-to-peer overlay networks depends on cooperation among participating peers. In this paper, we investigate the degree of cooperation among individual peers required to induce globally favorable properties in an overlay network. Specifically, we consider a resource pricing problem in a market-oriented overlay network where participating peers sell own resources (e.g., CPU cycles) to earn energy which represents some money or rewards in the network. In the resource pricing model presented in this paper, each peer sets the price for own resource based on the degree of cooperation; non-cooperative peers attempt to maximize their own energy gains, while cooperative peers maximize the sum of own and neighbors' energy gains. Simulation results are presented to demonstrate that the network topology is an important factor influencing the minimum degree of cooperation required to increase the network-wide global energy gain.

This paper presents an agent-based system for building and operating context-aware services in public spaces, including museums. The system provides users with agents and detects the locations of users and deploys location-aware user-assistant agents at computers near the their current locations by using active RFID-tags. When a visitor moves between exhibits in a museum, this dynamically deploys his/her agent at the computers close to the exhibits by using mobile agent technology. It annotates the exhibits in his/her personalized form and navigate him/her user to the next exhibits along his/her routes. It also introduces user movement as a natural approach to interacting between users and agents. To demonstrate the utility and effectiveness of the system, we constructed location/user-aware visitor-guide services and experimented them for two weeks in a public museum.

This paper presents a fault-tolerance scheme based on mobile agents for the reliable mobile computing systems. Mobility of the agent is suitable to trace the mobile hosts and the intelligence of the agent makes it efficient to support the fault tolerance services. This paper presents two approaches to implement the mobile agent based fault tolerant service and their performances are evaluated and compared with other fault-tolerant schemes.

Input/Output (I/O) automata and the Temporal Logic of Actions (TLA) are two well-known techniques for the specification and verification of concurrent systems. Over the past few years, they have been extended to the so-called dynamic I/O automata and, respectively, Mobile TLA (MTLA) in order to be more appropriate for mobile agent systems. Dynamic I/O automata is just a mathematical model, whereas MTLA is a logic with a formally defined language. In this paper, therefore, we investigate how MTLA could be used as a formal language for the specification of dynamic I/O automata. We do this by writing an MTLA specification of a travel agent system which has been specified semi-formally in the literature on that model. In this specification, we deal with always existing agents as well as with an initially unknown number of dynamically created agents, with mobile and non-mobile agents, with I/O-automata-style communication, and with the changing communication capabilities of mobile agents. We have previously written a TLA specification of this system. This paper shows that an MTLA specification of such a system can be more elegant and faithful to the dynamic I/O automata definition because the agent existence and location can be expressed directly by using agent and location names instead of special variables as in TLA. It also shows how the reuse of names for dynamically created and destroyed agents within the dynamic I/O automata framework can be specified in MTLA.

The steady approach of advanced nations toward realization of ubiquitous computing societies has given birth to rapidly growing demands for new-generation distributed computing (DC) applications. Consequently, economic and reliable construction of new-generation DC applications is currently a major issue faced by the software technology research community. What is needed is a new-generation DC software engineering technology which is at least multiple times more effective in constructing new-generation DC applications than the currently practiced technologies are. In particular, this author believes that a new-generation building-block (BB), which is much more advanced than the current-generation DC object that is a small extension of the object model embedded in languages C++, Java, and C#, is needed. Such a BB should enable systematic and economic construction of DC applications that are capable of taking critical actions with 100-microsecond-level or even 10-microsecond-level timing accuracy, fault tolerance, and security enforcement while being easily expandable and taking advantage of all sorts of network connectivity. Some directions considered worth pursuing for finding such BBs are discussed.

The market and users' requirements have been rapidly changing and diversified. Under these heterogeneous and dynamic situations, not only the system structure itself, but also the accessible information services would be changed constantly. To cope with the continuously changing conditions of service provision and utilization, Faded Information Field (FIF) has been proposed, which is a agent-based distributed information service system architecture. In the case of a mono-service request, the system is designed to improve users' access time and preserve load balancing through the information structure. However, with interdependent requests of multi-service increasing, adaptability and timeliness have to be assured by the system. In this paper, the relationship that exists among the correlated services and the users' preferences for separate and integrated services is clarified. Based on these factors, the autonomous preference-aware information services integration technology to provide one-stop service for users multi-service requests is proposed. As compared to the conventional system, we show that proposed technology is able to reduce the total access time.

As one of the technologies for the retrieval of desired contents over large-scale networks, multi-agent systems are receiving much attention. Since there are too many contents on the network to search them all exhaustively, some applications on multi-agent systems have time constraints, that is, they must obtain a result by a given deadline. To find better results for such applications, it is important for the agents to complete their tasks on as many nodes as possible by the deadline. However, most existing agent systems using round robin scheduling disciplines do not take time constraints into account. Therefore, agents are likely to miss their deadlines on many nodes. In this paper, we propose an efficient agent-dispatching method for time-constrained applications. This method decides creation and migration of a clone agent according to the estimated value of the number of agents that would have completed their tasks by the deadline. The results of our performance evaluation show that the proposed method increases the number of agents that complete their tasks.

To meet users' multi-service requests under dynamic and heterogenous environment with high-assurance, the Autonomous Network-Based Integration System based on Faded Information Field (FIF) has been proposed, which permits to actively integrate the correlated information services according to the current situation of the system. However, the increase in the total number of users' requests and changes in users' preferences cause the unbalancing load in the system and the overload in the locality. In this paper, based on the autonomous access distribution in the locality, a new approach of autonomous correlated services access is proposed to reduce the load of the system and achieve the adaptability and timeliness of correlated services utilization. We proved the effectiveness of the proposed technology through the simulation and the results show that the system can improve the average response time not only for joint requests of correlated services, but also for separate requests of each service under changing environments.

Privacy is increasingly viewed as a key concern in multi-agent based algorithms for Distributed Constraint Satisfaction Problems (DCSP) such as the Meeting Scheduling (MS) problem. Many algorithms aim for a global objective function and as a result, incur performance penalties in computational complexity and personal privacy. This paper describes a mobile agent-based scheduling scheme called Efficient and Privacy-aware Meeting Scheduling (EPMS), which results in a tradeoff among complexity, privacy, and global utility. It also introduces a privacy loss model for collaborative computation, multiple criteria for evaluating privacy in the MS problem, and a privacy measurement metric called the Min privacy metric. We have utilized a common computational space in EPMS for reducing the complexity and the privacy loss in the MS problem. The analytical results show that EPMS has a polynomial time computational complexity. In addition, simulation results show that the obtained global utility for scheduling multiple meetings with EPMS is close to the optimal level and the resulting privacy loss is less than for those in existing algorithms.

Mobile-agent-based distributed computing is one of the most promising paradigms to support autonomic computing in a large-scale of distributed system with dynamics and diversity: mobile agents traverse the distributed system and carry out a sophisticated task at each node adaptively. In mobile-agent-based systems, a larger number of agents generally require shorter time to complete the whole task but consume more resources (e.g., processing power and network bandwidth). Therefore, it is indispensable to keep an appropriate number of agents for the application on the mobile-agent-based system. This paper considers the mobile agent population control problem in dynamic networks: it requires adjusting the number of agents to a constant fraction of the current network size. This paper proposes algorithms inspired by the single species population model, which is a well-known population ecology model. These two algorithms are different in knowledge of networks each node requires. The first algorithm requires global information at each node, while the second algorithm requires only the local information. This paper shows by simulations that the both algorithms realize self-adaptation of mobile agent population in dynamic networks, but the second algorithm attains slightly lower accuracy than the first one.