Lorenzo Vita

MAP: design and implementation of a mobile agents' platform

Abstract The recent development of telecommunication networks has contributed to the success of applications such as information retrieval and electronic commerce, as well as all the services that take advantage of communication in distributed systems. In this area, the emerging technology of mobile agents aroused considerable interest. Mobile agents are applications that can move through the network for carrying out a given task on behalf of the user. In this work we present a platform called MAP (Mobile Agents Platform) for the development and the management of mobile agents. The language used both for developing the platform and for carrying out the agents is Java. The platform gives the user all the basic tools needed for creating some applications based on the use of agents. It enables us to create, run, suspend, resume, deactivate, reactivate local agents, to stop their execution, to make them communicate each other and migrate.

Dynamic SLAs management in service oriented environments

The increasing adoption of service oriented architectures across different administrative domains, forces service providers to use effective mechanisms and strategies of resource management in order for them to be able to guarantee the quality levels their customers demands during service provisioning. Service level agreements (SLA) are the most common mechanism used to establish agreements on the quality of a service (QoS) between a service provider and a service consumer. The WS-Agreement specification, developed by the Open Grid Forum, is a Web Service protocol to establish agreements on the QoS level to be guaranteed in the provision of a service. The committed agreement cannot be modified during service provision and is effective until all activities pertaining to it are finished or until one of the signing party decides to terminate it. In B2B scenarios where several service providers are involved in the composition of a service, and each of them plays both the parts of provider and customer, several one-to-one SLAs need to be signed. In such a rigid context the global QoS of the final service can be strongly affected by any violation on each single SLA. In order to prevent such violations, SLAs need to adapt to any possible needs that might come up during service provision. In this work we focus on the WS-Agreement specification and propose to enhance the flexibility of its approach. We integrate new functionality to the protocol that enable the parties of a WS-Agreement to re-negotiate and modify its terms during the service provision, and show how a typical scenario of service composition can benefit from our proposal.

Fast and accurate edge-based segmentation with no contour smoothing in 2-D real images

In this paper we propose an edge-based segmentation algorithm built on a new type of active contour which is fast, has a low computational complexity and does not introduce unwanted smoothing on the retrieved contours. The contours are always returned as closed chains of points, resulting in a very useful base for subsequent shape representation techniques.

Active Monitoring in Grid Environments Using Mobile Agent Technology

Monitoring distributed computational resources effectively is a crucial factor for high-performance distributed computation. Performance analysis and tuning, scheduling strategies, fault detection, are only some of the activities that require monitoring facilities. In this paper we present a mobile agent-based monitoring architecture. After explaining the reasons why this technology is adequate to cope with Grid systems’ heterogeneity, a description of the basic components of the system designed is provided. We also present some considerations on the high degree of flexibility t hat can be reached with the proposed approach.

On the use of mobile code technology for monitoring Grid system

Grid systems are becoming the underlying infrastructure for many high-performance distributed scientific applications. Resources in these systems have heterogeneous features, are connected by potentially unreliable networks, and are often under different administrative management domains. These remarks show how a new generation of techniques, mechanisms and tools need to be considered that can cope with the complexity of such systems and provide the performance suitable for scientific computing applications. In this paper an architecture for monitoring services in Grid environments based on mobile agent technology is presented. One of the most interesting aspects of the proposed approach is the possibility of customizing the parameters to be monitored. After describing the general framework where agents will execute, an application for improving the capabilities of traditional network monitoring paradigms is presented.

Resource and service discovery in SOAs: A P2P oriented semantic approach

Resource and service discovery in SOAs: A P2P oriented semantic approach An intense standardization process is favouring the convergence of grids and Service Oriented Architectures (SOAs). One of the benefits of such technological convergence is that grid resources and applications can be virtualized by services and offered through the SOA paradigm. In the broad and interoperable scenarios enabled by the SOA, involving the participation of several grid infrastructures across many administrative domains, service discovery can be a serious issue. In this paper we present a P2P-based infrastructure that leverages semantic technologies to support a scalable and accurate service discovery process. The key concept of the presented idea is the creation of an overlay network organized in several semantic groups of peers, each specialized in answering queries pertaining to specific applicative domains. Groups are formed by clustering together peers offering services that are semantically related. The architecture details of the proposed solution are presented. A system prototype has also been implemented and validated through a case study deployed on the PlanetLab testbed.

Research: Monitoring performance in distributed systems

Continuous monitoring of computer network performance is probably the only solution which allows prompt identification of anomalous functioning conditions and provides knowledge of parameters on which to base recovery interventions. A number of tools for performance management already exist, but their effectiveness is limited as they are essentially inserted inside owner network management solutions. In this paper we describe the realization of PMt, a platform for the development of performance management applications for the control and real-time management of a heterogeneous computer network. PMt uses an object-oriented approach in managing the various elements in the distributed system, and defines a methodology for the design of applications to monitor performance. The methodology is mainly destined for use on distributed systems, and provides the user with a set of tools and services that can be used to develop management applications.

Concurrent Generalized Petri Nets

We extend the class of Markov Regenerative Stochastic Petri Nets* (MRSPN*s), removing the restriction that at most one generally distributed timed transition can be enabled in any marking. This new class of Petri Nets, which we call Concurrent Generalized Petri Nets (CGPNs) allows simultaneous enabling of immediate, exponentially distributed and generally distributed time transitions, under the hypothesis that the latter are all enabled at the same instant. The stochastic process underlying a CGPN is shown to be still an MRGP. We evaluate the kernel distribution of the underlying MRGP and define the steps required to generate it automatically.

P2P over Manet: a comparison of cross-layer approaches

Mobile ad-hoc networks (Manet) and peer-to-peer (P2P) systems are recently emerged technologies which share a common underlying decentralized networking paradigm. However, the two fields have been mainly investigated by different research communities, without catching several cross-cutting issues. Both systems share some common issues and relevant differences: however, similarities could be exploited in a more synergic way when coupling the two systems. In particular, very recently, some cross-layer approaches have appeared, trying to improve the overall performance of a P2P-Manet system: in this paper, we analyze them in order to identify some common guidelines and the most promising approaches. Indeed, since many combinations of Manet routing algorithm and P2P overlay network building are possible, our analysis also aims to minimize common pitfalls in designing such kind of applications.

Design and evaluation of a multimedia storage server for mixed traffic

Abstract. The relative simplicity of access to digital communications nowadays and the simultaneous increase in the available bandwidth are leading to the definition of new telematic services, mainly oriented towards multimedia applications and interactivity with the user. In the near future, a decisive role will be played in this scenario by the providers of interactive multimedia services of the on-demand type, which will guarantee the end user a high degree of flexibility, speed and efficiency. In this paper, some of the technical aspects regarding these service providers are dealt with, paying particular attention to the problems of storing information and managing service requests. More specifically, the paper presents and evaluates a new storage technique based on the use of disk array technology, which can manage both typical multimedia connections and traditional requests. The proposed architecture is based on the joint use of the partial dynamic declustering and the information dispersal algorithm, which are employed for the allocation and retrieval of the data stored on the disk array. We also define efficient strategies for request management in such a way as to meet the time constraints imposed by multimedia sessions and guarantee good response times for the rest of the traffic. The system proposed is then analyzed using a simulation approach.