George Samaras

Locating objects in mobile computing

In current distributed systems, the notion of mobility is emerging in many forms and applications. Mobility arises naturally in wireless computing since the location of users changes as they move. Besides mobility in wireless computing, software mobile agents are another popular form of moving objects. Locating objects, i.e., identifying their current location, is central to mobile computing. We present a comprehensive survey of the various approaches to the problem of storing, querying, and updating the location of objects in mobile computing. The fundamental techniques underlying the proposed approaches are identified, analyzed, and classified along various dimensions.

WebExpress: a client/intercept based system for optimizing Web browsing in a wireless environment

This paper describes an application model and software technology that makes it possible to run World Wide Web applications in wide area wireless networks. Web technology in conjunction with todays mobile devices (e.g., laptops, notebooks, personal digital assistants) and the emerging wireless technologies (e.g., digital cellular, packet radio, CDPD) offer the potential for unprecedented access to data and applications by mobile workers. Yet, the limited bandwidth, high latency, high cost, and poor reliability of todays wireless wide-area networks greatly inhibits (to the point of infeasibility) supporting such applications over wireless networks. This paper presents the Client/Intercept computational model that makes it possible to run such distributed applications efficiently in wide area wireless networks. Furthermore, it presents WebExpress, a client/intercept based system for optimizing Web browsing, that reduces data volume and latency of wireless communications by intercepting the HTTP data stream and performing various optimizations including: file caching, forms differencing, protocol reduction, and the elimination of redundant HTTP header transmission. This paper describes these optimizations and presents some experimental results.

Mobile agents for World Wide Web distributed database access

The popularity of the Web as a universal access mechanism for network information has created the need for developing Web-based DBMS client/server applications. However, the current commercial applet-based approaches for accessing database systems offer limited flexibility, scalability, and robustness. We propose a new framework for Web-based distributed access to database systems based on Java-based mobile agents. The framework supports lightweight, portable, and autonomous clients as well as operation on slow or expensive networks. The implementation of the framework using the aglet workbench shows that its performance is comparable to, and in some case outperforms, the current approach. In fact, in wireless and dial-up environments and for average size transactions, a client/agent/server adaptation of the framework provides a performance improvement of approximately a factor of ten. For the fixed network, the gains are about 40 percent and 30 percent, respectively. We expect our framework to perform even better when deployed using different implementation platforms as indicated by our preliminary results from an implementation based on Voyager.

Mobile agents for WWW distributed database access

The popularity of the Web as a universal access mechanism for network information has created the need for developing Web based DBMS client/server applications. However, the current commercial applet based methodologies for accessing database systems offer limited flexibility, scalability and robustness. We propose a new framework for Web based distributed access to database systems based on Java based mobile agents. The framework supports lightweight, portable and autonomous clients as well as operation on slow or expensive networks. The implementation of the framework shows that its performance is comparable to, and in some cases outperforms, the current approach. In fact, in wireless and dial-up environments and for average size transactions, a client/agent/server adaptation of the framework provides a performance improvement of approximately a factor of ten. For the fixed network, the gains are about 40% and 30% respectively.

Mobile Agents for Wireless Computing: The Convergence of Wireless Computational Models with Mobile-Agent Technologies

Wireless mobile computing breaks the stationary barrier and allows users to compute and access information from anywhere and at anytime. However, this new freedom of movement does not come without new challenges. The mobile computing environment is constrained in many ways. Mobile elements are resource-poor and unreliable. Their network connectivity is often achieved through low-bandwidth wireless links. Furthermore, connectivity is frequently lost for variant periods of time. The difficulties raised by these constraints are compounded by mobility that induces variability in the availability of both communication and computational resources. These severe restrictions have a great impact on the design and structure of mobile computing applications and motivate the development of new software models. To this end, a number of extensions to the traditional distributed system architectures have been proposed [26]. These new software models, however, are static and require a priori set up and configuration. This in effect limits their potential in dynamically serving the mobile client; the client cannot access a site at which an appropriate model is not configured in advance. The contribution of this paper is twofold. First, the paper shows how an implementation of the proposed models using mobile agents eliminates this limitation and enhances the utilization of the models. Second, new frameworks for Web-based distributed access to databases are proposed and implemented.

mPERSONA: personalized portals for the wireless user: An agent approach

The needs of the wireless and mobile user regarding information access and services are quite different than those of the desktop user. This need is not about browsing the Web but about receiving personalized services that are highly sensitive to the immediate environment and requirements of the user. Personalization appears to be the most appropriate solution to this need. It comes into aid by creating personalized portals that are specific for the wireless user, which (a) are focus on the local content and (b) directly tones down factors that break up the functionally of the Internet/wireless services when viewed through wireless devices; factors like the “click count”, user response time (the “choice” factor) and the size of the wireless network traffic. In this paper we present a flexible personalization system for the wireless user that takes into consideration user mobility, the local environment and the user and device profile. The system utilizes the various characteristics of mobile agents to support flexibility, scalability, modularity and user mobility. We present metrics appropriate to the wireless environment, and an initial performance evaluation indicating improvement ranging from 33% up to, for certain metrics, 60%.

Key issues for the design and development of mobile commerce services and applications

This paper suggests a new approach for developing m-commerce services and applications based on a scheme that divides m-applications into directory- and transaction-oriented classes, identifies mobile user requirements, and takes into consideration the constraints of current technologies for mobile and wireless computing. The efficacy of the proposed approach in a real scenario is discussed.

DBGlobe: a service-oriented P2P system for global computing

The challenge of peer-to-peer computing goes beyond simple file sharing. In the DBGlobe project, we view the multitude of peers carrying data and services as a superdatabase. Our goal is to develop a data management system for modeling, indexing and querying data hosted by such massively distributed, autonomous and possibly mobile peers. We employ a service-oriented approach, in that data are encapsulated in services. Direct querying of data is also supported by an XML-based query language. In this paper, we present our research results along the following topics: (a) infrastructure support, including mobile peers and the creation of context-dependent communities, (b) metadata management for services and peers, including location-dependent data, (c) filters for efficiently routing path queries on hierarchical data, and (d) querying using the AXML language that incorporates service calls inside XML documents.

Two-phase commit optimizations in a commercial distributed environment

An atomic commit protocol can ensure that all participants in a distributed transaction reach consistent states, whether or not system or network failures occur. The atomic commit protocol used in industry and academia is the well-known two-phase commit (2PC) protocol, which has been the subject of considerable work and technical literature for some years.Much of the literature focuses on improving performance in failure cases by providing a non-blocking 2PC that streamlines recovery processing at the expense of extra processing in the normal case. We focus on improving performance in the normal case based on two assumptions: first, that networks and systems are becoming increasingly reliable, and second, that the need to support high-volume transactions requires a streamlined protocol for the normal case.In this paper, various optimizations are presented and analyzed in terms of reliability, savings in log writes and network traffic, and reduction in resource lock time. The papers unique contributions include the description of some optimizations not described elsewhere in the literature and a systematic comparison of the optimizations and the environments where they cause the most benefit. Furthermore, it analyzes the feasibility and performance of several optimization combinations, identifying situations where they are effective.

Mobile agent platforms for Web databases: a qualitative and quantitative assessment

We present practical experiences gathered from the employment of two popular Java-based mobile-agent platforms, IBMs Aglets and Mitsubishis Concordia. We present some basic distributed computing models and describe their adaptation to the mobile-agent paradigm. Upon these models we develop a set of frameworks for distributed database access over the World Wide Web, using IBMs Aglets and Mitsubishis Concordia platforms. We compare the two platforms both quantitatively and qualitatively. For the quantitative comparison, we propose, employ, and validate an approach to evaluate and analyse mobile-agent framework performance. For the qualitative assessment, we present our observations about the programmability and robustness of, and mobility provided by, the two platforms.