University of the Aegean
Cultural Technology and Communication
Mobile Agents (MAs) have been proposed as a solution for distributed Network Management (NM). However, most MA-based infrastructures exhibit scalability limitations when data intensive management applications are considered. Therefore, we... more
Mobile Agents (MAs) have been proposed as a solution for distributed Network Management (NM). However, most MA-based infrastructures exhibit scalability limitations when data intensive management applications are considered. Therefore, we present three novel applications, tailored to transfers of bulk network monitoring data, in which MAs are used to perform data aggregation, acquire atomic SNMP table views and support selective retrieval of SNMP table objects that meet specific selection criteria. The proposed applications are supported by a lightweight management framework described in previous work. A quantitative evaluation, in terms of bandwidth usage, shows that these applications surpass SNMP-based polling performance. ᭧
The use of Mobile Agent technology to distribute and delegate management tasks promises to overcome the scalability and flexibility limitations of the centralised Network Management paradigm. An efficient, lightweight infrastructure based... more
The use of Mobile Agent technology to distribute and delegate management tasks promises to overcome the scalability and flexibility limitations of the centralised Network Management paradigm. An efficient, lightweight infrastructure based on Mobile Agents is described, which addresses these issues by distributing management operations amongst managed devices and hence reducing processing load and bandwidth usage. A Mobile Agent Generator that facilitates the creation of new mobile agents for additional services is also presented. Our infrastructure is shown to outperform SNMP both in terms of polling response time and bandwidth consumption when considering data intensive operations.
Several distributed management architectures, incorporating mobile agent (MA) technology, have been recently proposed to answer the scalability limitations of centralised models and the flexibility problems of static hierarchical... more
Several distributed management architectures, incorporating mobile agent (MA) technology, have been recently proposed to answer the scalability limitations of centralised models and the flexibility problems of static hierarchical frameworks. Yet, although agent-based management frameworks have recently started evolving from the early 'flat' models to hierarchical structures, they cannot efficiently cope with the dynamically changing traffic and topological characteristics of modern networks. This is mainly due to the limited use of agent mobility (employed either through mid-level manager entities or between static mid-level managers and managed devices) and lack of appropriate policies enabling automatic calibration of the management system based on network conditions. This paper presents a hierarchical agent-based infrastructure, suitable for the management of large-scale enterprise networks that addresses these issues. The transition to hierarchical agent-based management is achieved through a mid-level manager that being a MA itself, operates at an intermediary level between the manager and the legacy systems and takes full control of managing a given network segment. These entities make the system more adaptive to changing networking conditions, while localising the traffic associated with bandwidth-intensive monitoring applications. A quantitative evaluation, in terms of the overall management cost, confirms that this architecture outperforms both centralised approaches and MA-based 'flat' management models. Ó
Mobile tourism'' represents a relatively new trend in the field of tourism and involves the use of mobile devices as electronic tourist guides. While much of the underlying technology is already available, there are still open challenges... more
Mobile tourism'' represents a relatively new trend in the field of tourism and involves the use of mobile devices as electronic tourist guides. While much of the underlying technology is already available, there are still open challenges with respect to design, usability, portability, functionality and implementation aspects. Most existing ''mobile tourism'' solutions either represent of-theshelf applications with rigidly defined content or involve portable devices with networking capabilities that access tourist content with the requirement of constant airtime, i.e., continuous wireless network coverage. This paper presents the design and implementation issues of a ''mobile tourism'' research prototype, which brings together the main assets of the two aforementioned approaches. Namely, it enables the creation of portable tourist applications with rich content that matches user preferences. The users may download these personalized applications (optimized for their specific device's model) either directly to their mobile device or first to a PC and then to a mobile terminal (through infrared or bluetooth). Thereafter, network coverage is not further required as the applications execute in standalone mode and may be updated when the user returns online. The dynamically created tourist applications also incorporate a ''push model'', wherein new tourist content is forwarded to the mobile terminal with minimal user intervention as soon as it is added or updated by the administrator. Our prototype has been developed on the top of Java 2 Micro Edition (J2ME) which offers an ideal platform for the development of full-fledged, interactive and portable applications tailored for resourceconstrained mobile devices. The paper presents our development experiences with J2ME and highlights its main advantages and shortcomings in relation to the implementation of such kind of applications. Finally, an empirical evaluation of user experience with the mobile application prototype is presented.
The intrinsic limitations of traditional centralised Network Management (NM), such as information bottlenecks and lack of flexibility, have encouraged a trend towards distributed management intelligence. Although several distributed NM... more
The intrinsic limitations of traditional centralised Network Management (NM), such as information bottlenecks and lack of flexibility, have encouraged a trend towards distributed management intelligence. Although several distributed NM architectures, exploiting the advantages of Mobile Agents (MA) have been recently proposed, when considering Network Performance Management (NPM) they fail to address scalability problems. In this paper, we describe a secure and fault-tolerant management framework based on MAs, which addresses these limitations by introducing two efficient, lightweight polling modes. Both real-time and off-line NM data acquisition is considered. An in-depth performance analysis of the introduced polling modes, in a data-intensive NPM application is also undertaken. The two modes are shown to outperform SNMP-based polling both in terms of response time and bandwidth consumption.
- by Damianos Gavalas and +1
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- Mobile Agent, Information Bottleneck
The rapid developments in the area of communication and data networks require highperformance and reliable Network and Systems Management (NSM). Due to the deficiencies of the traditional manager-agent paradigm and the resulting... more
The rapid developments in the area of communication and data networks require highperformance and reliable Network and Systems Management (NSM). Due to the deficiencies of the traditional manager-agent paradigm and the resulting scalability and flexibility limitations of centralisation, it is now commonly agreed that a transition to distributed management is required. There are many new trends in NSM that try to address this requirement. In general, these trends make use of well-established techniques from other computing fields, e.g. distributed objects, Java and Web technologies, adapted to NSM problems. In addition, management distribution aspects have also been incorporated in both the Internet and OSI-SM management architectures. However, it has been shown that distribution alone is not enough. Due to the high frequency of changes in networking environments, it is imperative that management systems are flexible, i.e. they can dynamically adapt to those changes and allow on-the-fly customisation of management services. In that context, Management by Delegation (MbD) paradigm has been identified as the first promising approach towards management distribution and flexibility.
- by Damianos Gavalas
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This paper introduces the concept of dynamic hierarchical management, enabled by Mobile Agent (MA) technology. The proposed framework addresses the scalability limitations of the centralised paradigm and the poor flexibility of static... more
This paper introduces the concept of dynamic hierarchical management, enabled by Mobile Agent (MA) technology. The proposed framework addresses the scalability limitations of the centralised paradigm and the poor flexibility of static hierarchical management architectures to changing networking conditions. The increased adaptability of our framework is enabled by a novel management entity, termed Mobile Distributed Manager (MDM). MDMs, being MAs themselves, can dynamically migrate to an assigned network domain (given that certain requirements are met) and undertake its management responsibility, operating at an intermediary level between the central manager and SNMP agents, localising the associated management traffic. The paper also focuses on the design decisions and implementation experiences of the proposed architecture.
- by Damianos Gavalas and +1
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- IT Management, Mobile Agent
The mobile agent (MA) technology has been proposed for the management of networks and distributed systems as an answer to the scalability problems of the centralized paradigm. Management tasks may be assigned to an agent, which delegates... more
The mobile agent (MA) technology has been proposed for the management of networks and distributed systems as an answer to the scalability problems of the centralized paradigm. Management tasks may be assigned to an agent, which delegates and executes management logic in a distributed and autonomous fashion. MA-based management has been a subject of intense research in the past few years, reflected on the proliferation of MA platforms (MAPs) expressly oriented to distributed management. However, most of these platforms impose considerable burden on network and system resources and also lack of essential functionality, such as security mechanisms, fault tolerance, strategies for building network-aware MA itineraries and support for user-friendly customization of MA-based management tasks. In this paper, we discuss the design considerations and implementation details of a complete MAP research prototype that sufficiently addresses all the aforementioned issues. Our MAP has been implemented in Java and optimized for network and systems management applications. The paper also presents the evaluation results of our prototype in real and simulated networking environments.
In this paper, we develop a batch fuzzy learning vector quantization algorithm that attempts to solve certain problems related to the implementation of fuzzy clustering in image compression. The algorithm's structure encompasses two basic... more
In this paper, we develop a batch fuzzy learning vector quantization algorithm that attempts to solve certain problems related to the implementation of fuzzy clustering in image compression. The algorithm's structure encompasses two basic components. First, a modified objective function of the fuzzy c-means method is reformulated and then is minimized by means of an iterative gradient-descent procedure. Second, the overall training procedure is equipped with a systematic strategy for the transition from fuzzy mode, where each training vector is assigned to more than one codebook vectors, to crisp mode, where each training vector is assigned to only one codebook vector. The algorithm is fast and easy to implement. Finally, the simulation results show that the method is efficient and appears to be insensitive to the selection of the fuzziness parameter.
The traditionally separate technologies of the Internet and mobile computing have now started to converge, bringing promises for seamless wireless Internet access through portable devices. This article represents a comprehensive review of... more
The traditionally separate technologies of the Internet and mobile computing have now started to converge, bringing promises for seamless wireless Internet access through portable devices. This article represents a comprehensive review of the main technological, architectural and business issues related to the current state-of-the-art wireless web technologies: WAP, i-mode and J2ME. A brief review of relevant application development platforms and authoring tools is also included, covering Microsoft solutions with emphasis on the Microsoft .Net platform for the Mobile Web and the Macromedia Flash Lite. The article also presents a critical analysis of the main assets and weaknesses of these technologies as well as their current status and the trends that will affect their market share and customer base in the foreseeable future.
Several distributed Network Management (NM) architectures, exploiting the advantages of Mobile Agents (MA), have been recently proposed to answer some of the limitations intrinsic to client-server based centralised NM, such as information... more
Several distributed Network Management (NM) architectures, exploiting the advantages of Mobile Agents (MA), have been recently proposed to answer some of the limitations intrinsic to client-server based centralised NM, such as information bottlenecks and lack of flexibility. However, when considering network performance management, they fail to address scalability problems. In this paper, we introduce two efficient, lightweight polling modes based on MAs that address these limitations. Both real-time and off-line NM data acquisition is considered. The introduced modes are shown to outperform SNMPbased polling both in terms of response time and bandwidth consumption.
In this article, we consider the problem of calculating an appropriate number of near-optimal (subject to a certain routing objective) routes for mobile agents (MAs) that incrementally fuse the data as they visit the nodes in a... more
In this article, we consider the problem of calculating an appropriate number of near-optimal (subject to a certain routing objective) routes for mobile agents (MAs) that incrementally fuse the data as they visit the nodes in a distributed sensor network. We propose an improved heuristic algorithm which computes an approximate solution to the problem by suggesting an appropriate number of MAs and constructing near-optimal itineraries for each of them. The performance gain of our algorithm over alternative approaches both in terms of cost and task completion latency is demonstrated by a quantitative evaluation and also in simulated environments through a Java-based tool.
- by Damianos Gavalas and +1
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- Mobile Agents, Mobile Agent, Heuristic algorithm
Clustering for mobile ad hoc networks (MANETs) offers a kind of hierarchical organization by partitioning mobile hosts into disjoint groups of hosts (clusters). However, the problem of changing topology is recurring and the main challenge... more
Clustering for mobile ad hoc networks (MANETs) offers a kind of hierarchical organization by partitioning mobile hosts into disjoint groups of hosts (clusters). However, the problem of changing topology is recurring and the main challenge in this technique is to build stable clusters despite the host mobility. In this paper, we present a novel clustering algorithm, which guarantees longer lifetime of the clustering structure in comparison to other techniques proposed in the literature. The basis of our algorithm is a scheme that accurately predicts the mobility of each mobile host based on the stability of its neighborhood (i.e., how different is its neighborhood over time). This information is then used for creating each cluster from hosts that will remain neighbors for sufficiently long time, ensuring the formation of clusters that are highly resistant to host mobility. For estimating the future host mobility, we use provably good information theoretic techniques, which allow on-line learning of a reliable probabilistic model for the existing host mobility.
This paper explores requirements that authoring tools and development platforms should satisfy for the development of cultural applications tailored for deployment on Personal Digital Assistants (PDAs) and mobile phones. To effectively... more
This paper explores requirements that authoring tools and development platforms should satisfy for the development of cultural applications tailored for deployment on Personal Digital Assistants (PDAs) and mobile phones. To effectively determine such requirements the paper reviews the use of mobile technologies in the context of cultural organizations and tourism and examines three 'real world' case studies that focus on the use of PDAs and mobile phones for providing cultural and tourist information, keeping the visitors' interest and attention, as well as promoting various cultural organizations and tourist facilities. This approach allows the extraction of a set of PDA and mobile phone application requirements, the implementation of which is based on the apparatus offered by authoring tools and development platforms. The paper reviews and evaluates the design and development facilities provided by state-of-the-art multimedia application development tools for PDAs and mobile phones: Macromedia Flash Lite, Navipocket, Java 2 Micro Edition and Microsoft .Net platform for the Mobile Web. The paper concludes with a set of recommendations related to the way authoring tools and development platforms should be exploited in order to gratify application and designer needs for developing cultural and tourist applications.
The emphasis of research projects in the field of mobile agent (MA) technology has been mainly put on identifying applications where the employment of MAs is preferable compared to centralised or alternative distributed computing models.... more
The emphasis of research projects in the field of mobile agent (MA) technology has been mainly put on identifying applications where the employment of MAs is preferable compared to centralised or alternative distributed computing models. Very little has been done though on examining how MA platforms design could be optimised so as to minimise the network traffic and latency associated with MA transfers. The work presented herein addresses these issues by investigating the effect of several optimisation ideas applied on our MA platform prototype. Furthermore, we discuss the results of a set of timing experiments aiming at offering a better understanding of the agent migration process and suggesting ways for reducing MA transfers delay.
The rapid advances in WDM technology are expected to bring about tremendous growth in the size of optical cross connects (OXCs). In this context, multigranular OXCs (MG-OXCs) have been suggested as a means of reducing the amount of... more
The rapid advances in WDM technology are expected to bring about tremendous growth in the size of optical cross connects (OXCs). In this context, multigranular OXCs (MG-OXCs) have been suggested as a means of reducing the amount of equipment required. Here we expand the concept of MG-OXCs to include optical packet granularity and review the key building blocks for the advent of MG-OXCs. A single-layer MG-OXC is suggested that offers enhanced flexibility with respect to other single-layer concepts, conversion capability, and good physical performance. Concatenation performance is analytically investigated.
- by Christina Politi and +1
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- Optics, Medical Imaging, Fiber Optics, Optical Networking
Organization, scalability and routing have been identified as key problems hindering viability and commercial success of mobile ad hoc networks. Clustering of mobile nodes among separate domains has been proposed as an efficient approach... more
Organization, scalability and routing have been identified as key problems hindering viability and commercial success of mobile ad hoc networks. Clustering of mobile nodes among separate domains has been proposed as an efficient approach to address those issues. In this work, we introduce an efficient distributed clustering algorithm that uses both location and energy metrics for cluster formation. Our proposed solution mainly addresses cluster stability, manageability and energy efficiency issues. Also, unlike existing active clustering methods, our algorithm relieves the network from the unnecessary burden of control messages broadcasting, especially for relatively static network topologies. This is achieved through adapting broadcast period according to mobile nodes mobility pattern. The efficiency, scalability and competence of our algorithm against alternative approaches have been demonstrated through simulation results.
Distributed network management (NM) architectures exploiting the advantages of mobile agents (MA) promise to relieve some of the limitations intrinsic to client-server based centralised NM, such as lack of scalability, interoperability... more
Distributed network management (NM) architectures exploiting the advantages of mobile agents (MA) promise to relieve some of the limitations intrinsic to client-server based centralised NM, such as lack of scalability, interoperability and flexibility. However, the use of MAs alone could impose an unnecessary transmission overhead if mobile code were to be used for trivial tasks. Hence, an infrastructure based on a hybridisation of centralised and distributed approaches is proposed, which maintains the lightweight nature of centralised NM for trivial management tasks, whilst adopting a distributed MA-based scheme as task complexity and suitability changes. Remote processing and compression of NM data issues are investigated in order to reduce the bandwidth usage. Security enhancements are also considered.
- by Damianos Gavalas and +1
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- Mobile Code, Mobile Agent
Mobile Agent (MA) technology has been proposed for Network & Systems Management (N&SM) as an answer to the scalability limitations of centralised models and the flexibility problems of static hierarchical frameworks. Yet, much still need... more
Mobile Agent (MA) technology has been proposed for Network & Systems Management (N&SM) as an answer to the scalability limitations of centralised models and the flexibility problems of static hierarchical frameworks. Yet, much still need to be done to deploy MA-based management frameworks that efficiently cope with the dynamically changing traffic and topological characteristics of modern networks. This paper starts with an extensive review of the research approaches on MA-based management. Then, we propose a highly adaptive and dynamic hierarchical MAbased framework for N&SM that is based on appropriate policies to enable automatic calibration of the management system depending on network conditions. The applicability of the introduced framework is tested in realistic management scenarios and three applications on network monitoring are proposed.
We propose a categorical data fuzzy clustering algorithm to classify web documents. We extract a number of words for each thematic area (category) and then, we treat each word as a multidimensional categorical data vector. For each... more
We propose a categorical data fuzzy clustering algorithm to classify web documents. We extract a number of words for each thematic area (category) and then, we treat each word as a multidimensional categorical data vector. For each category, we use the algorithm to partition the available words into a number of clusters, where the center of each cluster corresponds to a word. To calculate the dissimilarity measure between two words we use the Hamming distance. Then, the classification of a new document is accomplished in two steps. Firstly, we estimate the minimum distance between this document and all the cluster centers of each category. Secondly, we select the smallest of the above minimum distance and we classify the document in the category that corresponds to this distance.