Seungwok Han

CALM: an intelligent agent-based middleware for community computing

The applications for ubiquitous system require to effectively use the resources distributed in the environment for providing customized services to the users. In this paper we propose a middleware architecture displaying high scalability with event-based multi-agent platform, which allows dynamic creation of community for service oriented computing. It consists of event-based communication platform implemented by extending omniORB, agent platform, and various frameworks. The effectiveness of the proposed architecture is demonstrated using a ubiquitous office service scenario

Modeling and Analysis of Time-Critical Context-Aware Service Using Extended Interval Timed Colored Petri Nets

A context-aware system handling time-critical applications must satisfy explicit end-to-end time constraints which are highly dependent on the correlation between the dynamically changing contexts. To effectively deal with the timing constraints of context-aware systems, a methodology must be developed specifying the causal relationship between the contexts and timing aspect. To date, this issue has not yet been adequately addressed. In this paper, we propose a new modeling methodology which effectively represents the timing variation of contexts by extending interval timed colored Petri net. We also propose a technique determining if a service is able to satisfy the timing requirement. The effectiveness of the proposed approach is demonstrated using a collision avoidance service provided to moving vehicles.

Hierarchical P2P Networking and Two-Level Compression Scheme for Multi-agent System Supporting Context-Aware Applications

Ubiquitous computing requires an intelligent environment where the users do not need to be involved in the operation. The agent technology allows effective implementation of ubiquitous system, while agent platform provides efficient and stable interaction between the agents. In this paper we propose a hierarchical P2P networking approach where the messages are combined inside the agent platform and then compressed in two levels. The proposed approach capitalizes the static nature of the messages of typical context-aware applications. Experiment with an actual multi-agent system reveals that the response time and throughput are significantly improved compared to the existing scheme.

Context-based Dynamic Channel Management for Efficient Event Service in Pervasive Computing

In pervasive computing environment a number of distributed applications asynchronously exchange data using the event-based mechanism. The OMG defined CORBA Event Service for asynchronous messaging, which provides a flexible channel for asynchronous communication among the distributed and collocated objects. In the existing Event Service channels are created manually by the developers or users to process and disseminate the events. Also, the channel management is static which may cause bottleneck in some channels. In this paper, thus, we propose a dynamic context-based channel management scheme by efficiently combining name service with event service. It is embedded in the CALM(Component- based Autonomic Layered Middleware) developed by us, which has been implemented based on ORB. Computer simulation reveals that the proposed approach significantly reduces the event delivery and processing time of the existing omni Event Service and TIBCO.

An Efficient Dynamic Load Balancing Scheme for Multi-agent System Reflecting Agent Workload

In ubiquitous computing the multi-agent system can provide intelligent services to the users by effectively utilizing the resources distributed in the environment. The traditional load balancing approach based on the load condition of the nodes is not suitable to the multi-agent system (MAS). In this paper we propose an efficient load balancing scheme for MAS employing the models formulated to identify the condition of the agents and the relevant policies required for dynamic load balancing. The proposed scheme significantly reduces the response time by migrating some agents to balance the loads of the system. An experiment verifies this property by comparing it with the existing scheme. We also propose a MAS architecture effectively supporting the registration, modification, and deletion of agent-based services, and easy retrieval and provisioning of registered services for the users like web service.

Efficient and Dynamic Location-based Event Service for Mobile Computing Environments

In mobile computing the location information of the objects is an important factor in providing customized services to the users. The location-based service (LBS) is one of the technologies providing the services adoptively according to the changed user position. The existing filtering technology employed in the typical pub/sub model has some drawbacks such as useless connection and wasted queue space. In this paper we propose an efficient and dynamic location- based event service solving these problems. It is achieved by employing location monitor which dynamically manages the event channel. Performance evaluation shows that the proposed scheme provides much higher performance than the existing scheme when the number of suppliers is larger than six.

Modeling the contexts without distracting the perspectives of the agents in distributed reasoning

Context-awareness service is one of the key features of ubiquitous paradigm. To intelligently and sensitively deal with the dynamic environment, a methodology effectively enabling the agent-based distributed reasoning needs to be developed. The existing modeling approaches focus on scenario-based acquisition, management, and representation of context. However, they are difficult to be adapted to agent-based distributed reasoning. In this paper we propose a modeling approach for distributed reasoning which permits merging of different perspectives of context models without the distraction of individual aspects. Moreover, a context-awareness engine is developed to support agent-based context-awareness service. The effectiveness of the proposed methodology is verified by computer simulation which reveals that the proposed approach allows much more accurate and stable reasoning than the earlier scheme.

Efficient category-based service discovery on multi-agent platform

Today, multi-agent technologies are widely used for realizing prevalent ubiquitous computing applications, in which service discovery is a critical task for finding a particular service instance. While JADE is a popular system for multi-agent applications, its directory facilitator (DF) used for service discovery employs a sequential search approach, which shows degraded performance when the number of registered services becomes large. This paper proposes a new DF scheme employing the category-based classification and search approach. It greatly reduces the search space and allows accurate matchmaking. The DF implemented with the proposed approach and JADE-DF are compared in terms of query response time and memory space requirement. It demonstrates that the proposed DF allows faster query processing than JADE-DF and requires smaller memory space, especially for a large number of services and queries of multiple parameters.

Agent platform-based directory facilitator for efficient service discovery

Today, multi-agent technologies are important in realizing upcoming ubiquitous environment, in which service discovery is a critical task for finding a particular service instance. While JADE is the most popular system for multi-agent applications, its directory facilitator (DF) employs the sequential search method causing inefficiency in various aspects. This paper proposes a new DF scheme which is registered as an agent and employs category database. The DFs are compared with regards to query response time and memory space requirement using the test agent we implemented. The results demonstrate that the proposed DF requires much smaller memory space requirement and allows faster query processing than JADE-DF, especially for large number of services and queries of multiple parameters.

Enhanced Packet Buffering for DiffServ in Fast Handover Mobile IP

The packets in the Internet are classified by edge router according to the traffic conditioning agreement (TCA) in differentiated services (DiffServ) domain. The core routers forward the packets in different fashion according to the PHB(Per Hop-Behavior). Currently, the QoS during handover is not guaranteed since packet buffering does not consider PHB during the handover in DiffServ domain. To solve the problem, we propose an enhanced packet buffering scheme where the packets are buffered by the predefined rule in the new access point during handover. We analyze the loss probability of each type PHB packet with the enhanced packet buffering, and it validates its performance by computer simulation. It reveals that QoS is supported while reducing the packet loss rate significantly compared to the existing scheme.