DEIS - Università di Bologna - L I A - Laboratorio d'Informatica Avanzata

Papers from L I A

bar

Individual paper's pages: Bellavista, P., Denti, E., Foschini, L., Omicini, A., Stefanelli, C.

bar

     
BibTeX E. Lamma, P. Mello, M. Milano
A Distributed Constraint-Based Scheduler for Railway Traffic
Will appear on Artificial Intelligence in Engineering, Elsevier Applied Science.
Abstract. This paper presents the design and implementation of a distributed advisor system which helps human experts in the management and control of traffic within railway stations and along railway branches. Our approach enables a whole railway line to be managed in a modular, expandable, and scalable way. The scheduling of trains along a railway line is performed by several modules each one controlling a certain number of resources. These modules solve the scheduling of trains by interacting and communicating with each other. Each module has to deal with temporal constraints, priority between trains and constraints due to the structure of the station and railway branches. Our approach is based on the Constraint Logic Programming (CLP) paradigm for solving the constraints involved in the scheduling problem, and shows the adequacy and versatility of the CLP approach for problems of this type.
     
BibTeX E. Lamma, P. Mello, M. Milano
Temporal Constraint Handling in Scheduling Problems
Will appear in Proceedings of The Annual Meeting of the International Institute for Advanced Studies in System Research and Cybernetics, InterSymp'95, Baden Baden, Germany, August 1995. The International Institute for Advanced Studies in Systems Research and Cybernetics.
Abstract. Scheduling deals with the allocation of resources to activities over time. It can be solved, among others, with a constraint-based approach where a planner takes decisions on the allocation of resources and a constraint manager propagates constraints and checks for the consistency of the solution proposed. In scheduling problems, every constraint can be stated as a temporal relation. Therefore, the constraint manager can be a temporal reasoner or a temporal module tailored on the application. Two main approaches are discussed in this paper: a task-based approach focusing on events and a resource-based approach focusing on resource availability.

Keywords: Scheduling, Temporal Reasoning, Constraint Processing, Constraint Satisfaction Problems

     
BibTeX E. Lamma, P. Mello, M. Milano
Combining Constraint Solvers in a Meta Constrait Logic Programming Architecture
Frontiers of Combining Systems, F. Baader, K.U. Schulz (eds.). Kluwer Academic Publisher, New York, USA, 1996. Pages 179-195. Proceedings of the First International Workshop "Frontiers of Combining Systems", FroCoS'96, Munich, Germany, March 26-29, 1996.
Abstract. We present a general technique for the combination and the integration of different Constraint Logic Programming solvers. The main idea behind the work concerns the possibility of building meta CLP architectures by adding CLP solvers in a natural and effective manner.
In the meta architecture, levels are constraint solvers each reasoning on constraints of the underlying system. The architecture presented starts from a meta Constraint Logic Programming general scheme. A distinguishing feature of the architectural scheme concerns its operational semantics which can be seen as a general combination method for data and control of two constraint solvers. A set of linking rules define how systems exchange data, while a set of transition rules define how systems combine their control flow.
We propose, as an example, a specialization of a meta CLP architecture on finite domains. The specialization concerns the possibility of combining qualitative and quantitative reasoning in a CLP framework. This combination can be useful, for example, in the field of temporal reasoning.
     
BibTeX E. Lamma, P. Mello, M. Milano
A Multi-Level CLP Architecture for Consistency Techniques
1995. Submitted for publication. Available from the authors
Abstract. In this paper we focus on Constraint Logic Programming on finite domains, CLP(FD). We consider a method of handling constraints over finite domains based on the notion of k-consistency. CLP solvers have an embedded consistency algorithm which cannot be changed by the user in accordance with the application to be solved. In this paper, we propose a multi-level CLP architecture that gains in expressivity and flexibility by adding CLP solvers as meta levels reasoning on the underlying object system constraints.
The framework will benefit, on one hand, of the efficiency of the CLP paradigm and, on the other hand, of the modularity, expressivity and flexibility of meta programming.
We provide a general scheme which can be specialized on different domains and applications that require a consistency check different by that provided by the constraint solver.
We propose a specialization of the meta CLP scheme. Each level is a CLP on finite domains solver performing its own propagation algorithm. The architecture reaches whatever degree of consistency not by changing the usual constraint solver propagation algorithm, but by adding several constraint solvers each performing its own propagation algorithm.
     
BibTeX E. Lamma, P. Mello, M. Milano
Temporal Reasoning in a Meta Constraint Logic Programming Architecture
Temporal Representation and Reasoning, Chittaro, Goodwin, Hamilton, Montanari (eds.) IEEE Computer Society Press, 1996. Pages 128-135. Proceedings of 3rd International Workshop on Temporal Representation and Reasoning, TIME96, Key West (FL), May 19-20, 1996.
ISBN 0-8186-7528-4
Abstract. Constraint Logic Programming (CLP) is a powerful programming paradigm combining the advantages of Logic Programming and the efficiency of constraint solving. However, CLP presents some limitations in dealing with temporal reasoning. First, it uses an "arc consistency" propagation algorithm which cannot be changed by the user and it is too weak in many temporal frameworks. Second, CLP is not able to deal with qualitative temporal constraints.
In this paper, we show how to overcome these limitations. In particular, we present a way of performing a path-consistency check without changing the propagation algorithm of the constraint solver. In addition, we show how to integrate qualitative and quantitative temporal reasoning by using a two module meta CLP architecture.
Each module is a finite domain constraint solver (CLP(FD)). The object system (extended with the path-consistency algorithm) performs quantitative reasoning, while the meta-level reasons on constraints of the underlying system thus performing qualitative reasoning.
In this way, we can benefit by the efficiency of the constraint handling mechanism of CLP and the modularity, flexibility and expandibility of meta-architectures.
Finally, in order to show the behavior of the resulting architecture, the paper presents a simple example where qualitative and quantitative temporal reasoning are integrated.
     
BibTeX V. Brusoni, L. Console, E. Lamma, P. Mello, M. Milano, P. Terenziani
Resource-based vs.Task-based approaches for Scheduling Problems
Will appear in the Proocedings of the 9th International Symposium on Methodologies for Intelligent Systems (ISMIS96), LNCS Series, Springer Verlag.
Abstract. Scheduling deals with the allocation of resources to activities over time, and can be interpreted as a Constraint Satisfaction Problem. Two main types of approaches, both based on constraint satisfaction, can be adopted to formulate a scheduling problem. The first type is resource-based: resources are associated with temporal domains of feasibility which describe and maintain the evolution of their state; the second type is task-based: the assignments of resources to activities are considered as temporally constrained events. This paper shows the use of the two approaches to a case study, the Train Scheduling Problem. The two approaches are then compared.
     
BibTeX A. Corradi, L. Leonardi, F. Zambonelli
A Scalable Tuple Space Model for Structured Parallel Programming
Proceedings of the Conference on Massively Parallel Programming Models, IEEE CS Press, Berlin, Germany, October 1995. Pages 25-32.
Abstract. The paper proposes and analyses a scalable model of an associative distributed shared memory for massively parallel architectures. The proposed model is hierarchical and fits the modern style of structured parallel programming. If parallel applications are composed of a set of modules with a well-defined scope of interaction, the proposed model can induce a memory access latency time that only logarithmically increases with the number of nodes. Experimental results show the effectiveness of the model with a transputer-based implementation.
     
BibTeX A. Corradi, L. Leonardi, F. Zambonelli
Load Balancing Strategies for Massively Parallel Architectures
Parallel Processing Letters, Vol. 2, No. 2, September 1992.
Abstract. The paper explores the viability of object migration for massively parallel architectures. The aim is the comparison between the global and the local perspectives in migration policies. The paper reports several implemented migration algorithms and the obtained performance. The main result is that local migration policies are more viable than global ones as soon as the system size goes up.
     
BibTeX F. Zambonelli, M. Pugassi, L. Leonardi, N. Scarabottolo
Experiences on Porting a Parallel Objects Environment from a Transputer Network to a PVM-based System
Proceedings of the Fourth Euromicro Workshop on Parallel and Distributed Processing, IEEE CS Press, Braga, Portugal, January 1996. Pages 367-374.
Abstract. Parallel Objects is a powerful model for distributed/parallel Object-Oriented programming. Goal of this paper is to present the approach adopted in porting the support of the Parallel Objects environment, originally implemented for a massively parallel architecture, onto the PVM environment, which is nowadays a de-facto standard in the design of distributed applications on heterogeneous networks of computers.
     
BibTeX A. Corradi, L. Leonardi, F. Zambonelli
High-Level Directives to Drive the Allocation of Parallel Object-Oriented Applications
Workshop on High-Level Programming Models and Supportive Environments, International Parallel Processing Symposium, Geneva (CH), April 1997, IEEE CS Press.
Abstract. The paper presents the Abstract Configuration Language (ACL) implemented within the Parallel Objects object-oriented parallel programming environment. ACL defines a set of directives that allow users to specify the allocation needs of his/her application components without being aware of the architectural details. ACL directives drive the allocation decisions of the run-time support, by adapting its general-purpose behaviour to follow applications particular allocation needs. The effectiveness of the ACL approach in increasing the performances of parallel applications is confirmed by a testbed application.
     
BibTeX A. Corradi, L. Leonardi, F. Zambonelli
Multiple Tuple Spaces onto Massively Parallel Architectures: a Hierarchical Approach
5th EUROMICRO Workshop on Parallel and Distributed Processing, London (UK), January 1997, IEEE CS Press.
Abstract. The paper proposes a tuple space implementation model suited for massively parallel architectures. The model achieves scalability by organising the system in a hierarchical way and by encouraging the presence of multiple tuple spaces with a constrained scope. The effectiveness of the model is evaluated onto a transputer-based architecture.
     
BibTeX A. Corradi, L. Leonardi, F. Zambonelli
Integrating Automated and User-Driven Tools toward Efficient Parallel Objects Allocation
High-Performance Computing and Networking Conference, Vienna (A), April 1997, Lecture Notes in Computer Science, Springer-Verlag.
Abstract. Automated allocation tools do not achieve the same efficiency for all kinds of applications. A parallel programming environment should integrate high-level tools to permits users to easily adapt the behaviour of the automated allocation tools to the peculiar application needs. The paper faces this problem and presents the approach adopted by the Parallel Objects object-oriented parallel programming environment. Parallel Objects introduces high-level directives to specify the allocation needs of the application components in an architecture-independent way. These directives drive the allocation decisions of the run-time support, by tuning its general-purpose behaviour to the peculiar application needs. The effectiveness of the presented approach is validated by a testbed application.
     
BibTeX G. Cabri, A. Corradi, F. Zambonelli
Experience of Adaptive Replication in Distributed File Systems
22nd EUROMICRO Conference, Prague (CZ), September 1996, IEEE CS Press.
Abstract. The paper focuses on distributed file systems and presents a system to transparently manage file replication through a network of workstations. The system integrates an adaptive file replication policy that is capable of reacting to changes in the patterns of access to the file system by dynamically creating or deleting replicas. The paper evaluates the efficiency of the system in several situations and shows its effectiveness.
     
BibTeX F. Esposito, E. Lamma, D. Malerba, P. Mello, M. Milano, F. Riguzzi, G. Semeraro
Learning Abductive Logic Programs
Notes of the Workshop on Abductive and Inductive Reasoning, European Conference on Artificial Intelligence, ECAI96, Budapest, Hungary, August 12, 1996, Pages 23-30.
Abstract. We propose an approach for the integration of abduction and induction in Logic Programming. In particular, we show how it is possible to learn, by induction, an abductive logic program. Abducibles and integrity constraints can be specified by the user as content of the background knowledge or can be generated by the abductive/inductive process. We ground our framework on the generalized stable model semantics defined for abductive logic programs, and its associated proof procedure. By integrating Inductive Logic Programming with Abductive Logic Programming we can learn in presence of incomplete knowledge, take into account negative examples and generate exceptions to (possibly induced) rules, in an incremental way.
     
BibTeX R. Barruffi, E. Lamma, P. Mello, M. Milano,
Application of planning techniques for system configuration tasks
Proceedings of the 4th Workshop of the OpenView University Association (OVUA '97).
ETSI Telecomunicacion. Ciudad Universitaria, Madrid, Spain, April 2-4, 1997.
Abstract. The management of networked computer systems is rapidly growing in complexity due to the advent of Internet and Intranets. The paradigm has shifted from management of single systems to the management of complex domains, where an increasing number of machines are interconnected. In this context the traditional approach to performing configuration tasks, which consists of writing procedural applications, becomes inadequate. Planning techniques allow to dynamically synthesize action plans by using basic building blocks, coded with pre and post conditions. This approach is much more flexible in fact it's possible to manage unexpected situations and updating of the system without changing the set of basic actions. As far as software for system management is concerned planning techniques almost represent a novel approach. In fact past efforts that we are aware of, though providing remarkable results, only tackled a limited subset of the problem. In order to solve complex configuration problems we need to build a powerful planner which intertwines the creation of partial plans (each corresponding to the achievement of a subgoal) with the resolution of threats among them (deriving from the interference among subgoals). The aim of this paper is to show the power and the limits of the application of an already existing planner to configuration tasks so as to understand which features are needed by a planner suitable for computer systems. We chose UCPOP, a regressive non-linear planner. As a case study, we have applied UCPOP to a typical configuration problem: an example of disk management on an HPUX system. It consists of a non trivial goal which requires a multilevel plan of basic action. We need to fill the gap between the classical assumptions of a planning algorithm and the handling of a real system.
Future work will concern the study of how to overcome these limits and the investigation on how to use Constraint Satisfaction techniques in order to increase the efficiency of the planner.
     
BibTeX R. Barruffi, E. Lamma, P. Mello, M. Milano,
Interactive Constraint Satisfaction for Information Gathering in Planning
Proceedings of the 5th Workshop of the OpenView University Association (OVUA '98).
ENST Bretagne, Rennes, France, April 19-21, 1998.
Abstract. Many modern Artificial Intelligence planners are based on Constraint Satisfaction (CS) techniques. The basic idea is to introduce constraints which must be satisfied during the plan construction in order to have a consistent solution. CS techniques allow the search space to be pruned during the planning process thanks to constraint propagation. However, classical CS approaches need all the information on variable domains at the beginning of the computation. This is not the case in a typical networked environment where the knowledge is not completely defined at the beginning, but has to be dynamically acquired during the computational process. A possible solution to this problem is to introduce in the current plan sensing actions devoted to knowledge acquisition. An alternative approach is based on the idea of allowing a CSP (Constraint Satisfaction Problem) to deal with incomplete knowledge and to interactively acquire new consistent information. In this paper, we define an Interactive CSP framework where constraints are posted on variables ranging on partially or completely undefined domains. The basic idea is to use constraints both for maintaining the consistency of the current plan, and for performing knowledge acquisition when needed. A more interesting feature of this framework concerns the possibility of driving the knowledge acquisition by means of interactive constraints in order to retrieve only consistent information for the planner.
     
BibTeX R. Barruffi, C. Bartolini,
Information models for management: an object-oriented logic-based approach
Proceedings of the 5th Workshop of the OpenView University Association (OVUA '98).
ENST Bretagne, Rennes, France, April 19-21, 1998.
Abstract. The use of knowledge-based systems to deal with management tasks is becoming increasingly popular. These systems usually consist of reasoning engines that infer a solution by making use of a declarative description of the managed objects. The central aspect of these problem-solving techniques is the selection of the knowledge representation language. This involves the ability to model the information concerning the system configuration, i.e., managed objects, their attributes, the relations among them, and the actions that can be performed on them. Such a language requires a very powerful grammar, embedding the declarative paradigm and, at the same time, capable to express the complexity of the modelled objects. We have chosen an object-oriented approach, based on Java, that promises to meet these requirements. In this paper we will present the main features of this solution with particular reference to the syntax used to express actions, their prerequisites (pre-conditions) and their effect (post-conditions). We will also discuss how this approach is a suitable criterion for designing supportable code, which is an important prerequisite to effectively troubleshoot software problems.
     
BibTeX R. Barruffi, E. Lamma, P. Mello, M. Milano,
Planning with Incomplete and Dynamic Knowledge through Interactive Constraint Satisfaction
Proceedings of the AIPS Workshop on Integrating Planning, Scheduling and Execution in Dynamic and Uncertain Environments,
AAAI Technical Report WS-98-02, Pittsburg, USA, 1998.
Abstract. Planning activity needs to deal with the problem of incomplete and dynamic knowledge. In a typical real environment, knowledge has to be dynamically acquired during the computational process, while traditional planners reason by assuming that the world is closed and static. We deal with this problem by defining the planning problem as a constraint satisfaction problem (CSP) in which variables range on partially or completely unknown domains. While typical CSPs work exclusively with completely known variable domains, in our solution, some constraints, called Interactive Constraints (IC), may result in a knowledge acquisition and a consequent propagation Knowledge acquisition can be guided by ICs in order to retrieve only consistent information for the planner. We present a hybrid approach to planning which exploits this framework both in the generative and reactive phase.
     
BibTeX R. Barruffi, E. Lamma, P. Mello, M. Milano,
Planning with Incomplete and Dynamic Knowledge via Interactive Constraint Satisfaction
Proceedings of the 6th Conference of the Italian Association of Artificial Intelligence,
University of Padova, September 23-25, 1998
     
BibTeX R. Barruffi, M. Milano,
Interactive Constraint Satisfaction for Information Gathering in Planning
Proceedings of the the 13th European Conference on Artificial Intelligence, ECAI'98,
Brighton, UK, 1998.
Abstract. Constraint Satisfaction techniques allow the search space to be pruned during the planning process thanks to the propagation of constraints. However, classical CS approaches need all the information on variable domains at the beginning of the computation. This is not the case in a typical real environment where knowledge has to be dynamically acquired during the computational process. Thus, we define an Interactive CSP framework where variables range on partially defined domains. Constraints on those variables may result in a knowledge acquisition and a consequent propagation. Knowledge acquisition can be guided by interactive constraints in order to retrieve only consistent information for the planner.
     
BibTeX R. Barruffi, E. Lamma, P. Mello, M. Milano, R. Montanari,
Constraint-based Knowledge Acquisition and Verification for Planning
Proceedings of the 18th Annual International Conference of the British Computer Society Specialist Group on Expert Systems, ES'98
Cambridge, UK, 1998.
Abstract. Many Artificial Intelligence applications can be solved by knowledge-based systems They are based on a modelled description of the real world representing the application domain. For instance as far as automatic planning activity is concerned, traditional planners build goal-oriented plans of actions by reasoning on a representation of the handled objects; this representation is assumed to be complete and static. On the other hand planning applied to real environments needs to deal with the problem of incomplete and dynamic information. There is need for a mechanism to dynamically acquire knowledge during the computational process. Our approach is based on a definition of the planning problem as a Constraint Satisfaction Problem (CSP). We extended the CSP paradigm in order to deal with incomplete knowledge. Traditional CSPs work exclusively with completely known variable domains, while, in our solution, some variables can range on partially or completely unknown domains. The acquisition of those domain values is performed by means of Interactive Constraints (IC), during their propagation. It is worth noting that only consistent information for the planner is retrieved so as to simplify further propagation steps.
     
BibTeX R. Barruffi, M. Milano, R. Montanari,
Planning for Security Management
Proceedings of AAAI'99 Workshop on AI for Distributed Information Networking, AiDIN'99,
AAAI Press, Orlando, FLORIDA, USA, 1999.
Abstract. Security Management is a key issue in distributed computer systems. Resources and data need to be protected against unauthorized access, manipulation and malicious intrusions that render a system unreliable or unusable. The complexity of the task calls for the design of intelligent support systems that aid system administrators in the detection and/or prevention of intrusions. For this purpose, Intrusion Detection Systems (IDS) have been deeply investigated. IDSs are aimed at identifying intrusions and triggering consequent repair and/or reconfiguration actions. In general, these recovery procedures are statically defined by a system administrator. An alternative approach relies on a planner that dynamically computes the action chain (plan) for reconfiguring/repairing an attacked system. Using planning techniques greatly increases IDS flexibility, since statically defined countermeasures are not always the most appropriate and can be excessive (or even wrong) in some situations. In this paper, we discuss the design and implementation of a constraint-based planner that acts as a reacting module in an IDS.
     
BibTeX R. Barruffi, M. Milano, P. Torroni,
Interactive Constraints for Plan Construction and Execution
Proceedings of the Workshop of the UK Planning and Scheduling Special Interest Group,
Manchester, UK, 1999
Abstract. An off-line planner is a goal-driven component which dynamically synthesises the sequence of actions (plan) to be executed in order to achieve a given goal. Traditional planners need a complete representation of the initial state of the environment they are acting on. In complex and dynamics settings, however, the data describing the state of the environment can be too big to be efficiently stored and updated, and change frequently. Thus the representation the planner has of the real world it is acting on can become obsolete during or after plan construction. The corresponding off-line plan execution can fail. We propose a solution where a planner and an executing component interact in order to face dynamic changes. They are able to retrieve knowledge on the environment only when needed, thus delaying as much as possible data acquisition and minimizing, at the same time, data to be managed. They exploit the Interactive Constraint Satisfaction framework. This framework represents an extension of the constraint satisfaction framework based on Interactive Constraints (hereinafter referred to as ICs). ICs are declarative relations stated among variables whose domain is partially (or fully) unknown. In presence of incomplete knowledge, ICs act both as classical constraints, in order to prune inconsistent information, and as sensing modules to the environment, in order to retrieve necessary (and consistent) information. We exploit ICs in planning both for acquiring knowledge about the environment during plan construction and for testing the (possibly changed) environment during plan execution. In particular, the plan is refined at execution time by retrieving new consistent values when those available are no longer consistent. In this setting, both planning and execution can be seen as search processes in the space of partial plans. Since execution produces side effects on the environment, a backup and recovery mechanism should be provided in order to allow backtracking at execution time. A case study in the field of computer system management shows the advantages of the proposed solution.
     
BibTeX R. Barruffi, E. Lamma, P. Mello, M. Milano,
Least Commitment on Variable Binding in presence of Incomplete Knowledge
Proceedings of the 5th European Conference on Planning, ECP'99,
Lecture Notes in Artificial Intelligence, Springer Verlag, Durham, UK, 1999.
Abstract. Constraint Satisfaction techniques have been recognized to be effective tools for increasing the efficiency of least commitment planners. We focus on least commitment on variable binding. A constraint based approach for this issue has been previously proposed by Yang and Chan. In this setting, the planning problem is mapped onto a Constraint Satisfaction Problem. Its variables represent domain objects and are defined on a finite domain of values; constraints remove inconsistent values from variable domains through constraint propagation. In many applications, however, it is not always convenient, if possible at all, to know in advance all objects belonging to variable domains. Thus, domain values should be retrieved during the plan construction only when needed. The interesting point is that data acquisition for each variable can be guided by the constraint (or the constraints) imposed on the variable itself, in order to retrieve only consistent values. For this purpose, we have extended a Partial Order Planner performing least commitment on variable binding. This extension can cope with incomplete knowledge. We use the Interactive Constraint Satisfaction framework in order to exploit the efficiency deriving from constraint propagation and the possibility of acquiring the domain knowledge during the plan construction. Experimental results and comparisons with related approaches show the effectiveness of the proposed technique.
     
BibTeX M. Boari, A. Corradi, L. Leonardi, C. Stefanelli
Adaptive Routing Strategies for Dynamic Applications in Massively Parallel Architectures
IEEE Parallel & Distributed Technology, Vol. 3, No. 1, 1995, IEEE Computer Society.
Abstract. The paper presents two adaptive routing algorithms supporting communications in massively parallel architectures where the allocation of processes to nodes is unknown. This situation is typical of dynamic environments where processes may be created and terminated dynamically or can move from one node to another according to load balancing requirements. One of the properties of these algorithms is the ability to limit the number of hops in the source-destination path by reducing the occurrence of loops in it, so as to achieve a better response time. Other properties are the complete independence of the network topology and the use of neighborhood information in the choice of the output link for the message. Deadlock freedom is ensured by the adoption of a deadlock prevention method. The paper shows the performance figures of the two adaptive routing algorithms implemented for one massively parallel architecture.
     
BibTeX A. Corradi, C. Stefanelli
A Deadlock Prevention Strategy for Adaptive Routing Systems
Microprocessors and Microsystems, Vol. 20 No. 2, April 1996, Elsevier Science Publisher B.V, (North-Holland), Amsterdam (N).
Abstract. A fundamental issue in the design and implementation of adaptive routing algorithms is deadlock treatment, either avoidance, prevention, or recovery. In case of store-and-forward networks, the resources that can cause deadlock are the buffers used to store messages in intermediate nodes. In this paper, we present a deadlock prevention mechanism that reserves a very limited number of additional buffers specially handled by the routing system. The considered routing system is adaptive and uses message misrouting. The main advantages of this approach are intrinsic locality without need of synchronisation between neighbouring nodes, and low intrusion on the routing system.

     
BibTeX M. Boari, A. Corradi, L. Leonardi, C. Stefanelli
A Routing Strategy for Object-oriented Applications in Massively Parallel Architectures
Parallel Processing Letters, Vol. 7 No. 3 (1997), World Scientific Publishing. July 1996.
Abstract. Parallel object-oriented environments have a high degree of dynamicity and need specialised support to achieve efficiency of execution. Static strategies are not suitable for these environments: any prediction before execution can only roughly estimate the real behaviour. In object-oriented environments, the decision to create/destroy objects is usually taken at run-time and object allocation can change during the execution. The requirement of dynamicity should be considered in the design of every component of the support. The routing system, for instance, must ensure delivery even in case of object dynamic allocation/reallocation. The paper argues that routing algorithms for parallel object-oriented environments in massively parallel architectures should be both adaptive and efficient. We adopted a routing strategy designed to be effective in case of objects dynamically created/destroyed and capable of moving during the execution. Our adaptive strategy does not assume any knowledge of both object allocation and system topology configuration.

     
BibTeX A. Corradi, L. Leonardi, C. Stefanelli
Programming Heterogeneous Distributed Architecture: The Integration of Massive Parallel Architecture and UNIX Distributed Systems
EUROMICRO Workshop on Parallel and Distributed Processing, Gran Canaria, Spain, January 1993, IEEE Computer Society Press.
Abstract. The resources of massive parallel architectures can be allocated and used via special-purpose interfaces, but the development phases are generally available via a host machine. The massive parallel architectures and their hosting systems represent heterogeneous architectures. The paper describes the Meiko Computing Surface, a transputer-based architecture that uses UNIX as host environment and offers a library called CSTools to help users in expressing process creation and communication. A user can adopt CSTools as the uniform interface to write applications that run on the heterogeneous global architecture:CSTools need to be enhanced to solve the problems of process definition and their dynamic creation in UNIX machines. The extensions described in the paper achieve portability of CSTools. Following this approach, applications can run, in a first stage in the UNIX distributed (host) environment for a rapid prototype phase, and, then, on the target massively parallel architecture.

     
BibTeX A. Corradi, L. Leonardi, C. Stefanelli
Software monitoring in a Transputer-based architecture
AICA93 International Section, Lecce, Italy, September 1993.
Abstract. The paper faces the issue of monitoring applications running on a massively parallel architecture. The programming model we refer to is a general process model. Our target architecture is a transputer-based system, the Computing Surface of the MEIKO. The paper shows a monitor implementation that acts at low-level. The monitor information can be used not only for post-mortem analysis but also to have a run-time feed-back on the application. In particular, the implemented monitor furnishes information used in adaptive routing strategies. Several routing strategies, all depending on the monitoring of execution, are examined and compared.

     
BibTeX M. Boari, A. Corradi, L. Leonardi, C. Stefanelli
Hot-Spot-Avoiding: an Adaptive Strategy for Transputer Routing
Transputers'94, Besancon, France, September 1994, IOS Press.
Abstract. This paper presents an adaptive and allocation independent routing system for massive parallel architectures. The idea is to route messages in such a way that scalability can be achieved even for applications with a very dynamic behaviour, i.e., where process allocation can change often and the consequent propagation of changes could be unacceptable. The proposed routing algorithm (Hot-Spot-Avoiding) exploits Transputer synchronous communications to avoid bottlenecks and is capable of working in critical conditions. The paper deals also with deadlock and livelock; the latter is the key problem of allocation independent packet-switching routing algorithms.

     
BibTeX A. Corradi, C. Stefanelli
HOLMES: a Tool for Monitoring Heterogeneous Architectures
IEEE HiPC'97 High Performance Computing Bangalore, India, December 1997, IEEE Computer Society.
Abstract. Monitoring tools are necessary components in the support of distributed applications and can be used to provide dependability, debugging and testing, to enhance the performance and to make possible the run-time steering of applications. These tools are needed to exploit in the best way all the available high performance computing resources of a heterogeneous environment. This paper describes HOLMES, an on-line monitoring system designed to support dynamic management of resources that requires run-time measurement. HOLMES identifies the evolving system state and provides the necessary information to any dynamic policy to assign resources by following application evolution. HOLMES makes possible to control and steer an application even distributed across heterogeneous architectures, from parallel machines to clusters of workstations and PCs.

     
BibTeX M. Boari, A. Corradi, R. Montanari, C. Stefanelli
Network Security in Academic Environments: a Case Study
AICA 97, Milan, Italy, September 1997.
Abstract. A large number of organisations faces the problem of interconnecting their local area network to access Internet services. This connectivity, however, presents many risks from the security point of view. The introduction of firewalls is a way to protect local networks against the insecurity of Internet. In this paper, we discuss how we have solved the security problem in our academic environment: the paper presents the design of the security policy that reflects our specific security and functionality requirements. We have implemented the security policy by using two different firewall configurations with different trade off between security and functionality. Finally, the performance of the firewalls configuration in terms of throughput and processing capacity are shown.

     
BibTeX A. Ciampolini, E. Lamma, P. Mello, C. Stefanelli
Some experimental results in implementing a logic language with multi-head clauses on a transputer architecture
Roy Dyckhoff Ed., Lecture Notes in Artificial Intelligence No.798, Springer-Verlag 1993, Proceedings of the Fourth International Workshop, ELP'93, St. Andrews, U.K., March 1993.
Abstract. We focus on the distributed implementation of an extended logic language (called ROSE) based on multi-head clauses which can be useful to implement parallel logic objects where state change is performed by unification and recursion. Distinguishing features of ROSE are OR-parallelism with committed-choice behaviour and the AND-parallel execution of subgoals which do not share variables. We present the real implementation of ROSE on a Transputer-based architecture, and discuss some experimental results obtained by considering different allocation policies for processes. These allocation policies correspond to forms of inter- and intra-object parallelism when objects with state are implemented as ROSE programs. Obtained figures help in understanding which is the optimal allocation policy to adopt on the basis of an estimation of the time necessary for performing the distributed unification and the guard and body evaluation.

     
BibTeX A. Ciampolini, E. Lamma, P. Mello, C. Stefanelli
Implementing Unification in a Distributed Environment
AICA93 International Section, Lecce, Italy, September 1993.
Abstract. In this paper, we discuss the distributed implementation of a simple parallel logic language with OR parallelism and focus on how the unification is performed in a distributed environment. The main problem we face is how and when to access remote data structures to perform the distributed unification. In order to reduce the amount of the inter-node communication, we introduce in put and get WAM instructions different levels of copying which can be adopted depending on the particular program and architecture. Experimental results are obtained by implementing the resulting language on a transputer-based architecture.

     
BibTeX A. Ciampolini, E. Lamma, P. Mello, C. Stefanelli
Distributed Logic Objects: A fragment of Rewriting Logic and its Implementation
Electronic Notes in Theoretical Computer Science (ETCS), Elsevier Science Publisher B.V, (North-Holland), Amsterdam (N), September 1996.
Abstract. This paper presents a logic language (called Distributed Logic Objects, DLO for short) that supports objects, messages and inheritance. The operational semantics of the language is given in terms of rewriting rules acting upon the (possibly distributed) state of the system. In this sense, the logic underlying the language is Rewriting Logic. In the paper we discuss the implementation of this language on distributed memory MIMD architectures, and we describe the advantages achieved in terms of flexibility, scalability and load balancing. In more detail, the implementation is obtained by translating logic objects into a concurrent logic language based on multi-head clauses, taking advantage from its distributed implementation on a massively parallel architecture. In the underlying implementation, objects are clusters of processes, objects' state is represented by logical variables, message-passing communication between objects is performed via multi-head clauses, and inheritance is mapped into clause union. Some interesting features such as transparent object migration and intensional messages are easily achieved thanks to the underlying support. In the paper, we also sketch a (direct) distributed implementation supporting the indexing of clauses for single-named methods.

     
BibTeX A. Ciampolini, E. Lamma, P. Mello, C. Stefanelli
Distributed Logic Objects
Computer Languages, Vol. 22, No.4, Pergamon Press, New York, 1997.
Abstract. This paper presents a language based on the logic programming paradigm that supports objects, messages and inheritance. The object-oriented extension is fairly simple: objects are clusters of processes, objects' state is represented by logical variables, message-passing communication between objects is performed via multi-head clauses, and inheritance is mapped into clause union. The language implementation is obtained by translating logic objects into a concurrent logic language based on multi-head clauses, taking advantage from its distributed implementation on a massive parallel architecture. The runtime support achieves some interesting features such as transparent object migration and intensional messages.

     
BibTeX A. Ciampolini, E. Lamma, P. Mello, C. Stefanelli
Blackboard- and Object-based systems via multi-head clauses
Computers and Artificial Intelligence, No. 4/97, October 1997, SAP-Slovak Academic Press Ltd.
Abstract. This paper presents a distributed architecture based on a concurrent logic language, that can be suitably used for supporting and integrating multi-agent models both blackboard- and object-based. The logic language is based on multi-head clauses with committed-choice behaviour and restricted AND parallelism. A blackboard based application is mapped into a set of multi-head clauses representing logic agents which communicate via a common (distributed) working memory. Objects are clusters of processes, objects' state is represented by logical variables, message-passing communication between objects is performed via multi-head clauses and inheritance is mapped into clauses subsumption. Thanks to the parallel nature of the underlying concurrent language, we obtain a distributed implementation where parallelism is highly exploited.

     
BibTeX A. Ciampolini, E. Lamma, P. Mello, C. Stefanelli
Multi-Level Copying for Unification in Parallel Architectures
EUROMICRO Workshop on Parallel and Distributed Processing, Malaga, Spain, January 1994, IEEE Computer Society Press.
Abstract. We discuss how to implement unification in a distributed environment. The main problem we face is how and when to access remote data structures to perform the distributed unification. In order to reduce the amount of the inter-node communication, in our framework different levels of copying for data structures can be explicitly specified in the compiled code. We point out two different mechanisms which can be adopted in implementing the requested level of copying. Comparisons between the two mechanisms are drawn through some experimental results obtained on a transputer-based architecture. In order to evaluate the cost of distributed unification, we isolate two basic time parameters which depend on the chosen architecture.

     
BibTeX A. Ciampolini, E. Lamma, P. Mello, C. Stefanelli
A Distributed Architecture for Logic Agents
AIMSA94, Sixth International Conference on Artificial Intelligence: Methodology, Systems, Applications, Sofia, Bulgary, September 1994, World Scientific Publishing.
Abstract. We present an architecture, based on a concurrent logic language that can be suitably used for supporting and integrating multi-agent models both blackboard- and object-based. The logic language is characterised by multi-head clauses with committed-choice behaviour and restricted AND parallelism. Thanks to the parallel nature of the language, we obtain a distributed implementation on a Transputer-based architecture both for blackboard- and object-based systems where parallelism is highly exploited.
     
BibTeX E. Lamma, P. Mello, C. Stefanelli, P. Van Hentenryck
Improving Distributed Unification through Type Analysis
Euro-Par'97, Passau, Germany, August 1997, Lecture Notes in Computer Science LNCS 1300, Springer-Verlag.
Abstract. In distributed implementations of logic programming, data structures are spread among different nodes and unification involves sending and receiving messages to access them. Traditional implementations make remote data structures accessible to other processes by sending messages which carry either the overall data structure (infinite-level copying) or only remote references to these data structures (zero-level copying). These fixed policies can be far from optimal on various classes of programs and may induce substantial overhead. The purpose of this paper is to present an implementation scheme for distributed logic programming which consists of tailoring the copying level to each procedure. The scheme is based on a consumption specification which describes the way the procedure ``consumes'' its arguments locally. The consumption specification (or an approximation of it) can be automatically obtained through a static analysis inspired by traditional type analyses. The paper also describes a high-level distributed implementation that uses the consumption specification to avoid unnecessary copying and to request data structures globally. Experimental results for a network of workstations show the potential of the approach.

     
BibTeX A. Ciampolini, E. Lamma, P. Mello, C. Stefanelli
A Coordination Protocol for Abductive Logic Agents
IEEE ICIPS'97, Bejing, October 1997, IEEE Computer Society.
Abstract. In this work, we show how abduction can be introduced in a (logic) multi-agent environment by presenting a basic coordination protocol among agents. In particular, we define and implement a distributed protocol to coordinate the reasoning of all the abductive agents in the system, inspired to the basic algorithm for abductive reasoning presented by Kakas and Mancarella. In the implementation we use a logic-programming parallel and distributed language with multi-head guarded clauses and committed-choice behavior.

     
BibTeX A. Ciampolini, C. Stefanelli
Extending PVM to a Massively Parallel Architecture
Future Generation Computer Systems. Vol. 12 n. 1, May 1996, Elsevier Science Publisher B.V, (North-Holland), Amsterdam (N).
Abstract. Heterogeneous computing is one of the key issues for reaching high performances with limited costs. In this area, PVM is a wide-spread programming environment supported by a collection of architectures, ranging from Unix workstations to various kinds of parallel machines. We have enriched this set of architectures with the Meiko Computing Surface, a multicomputer architecture based on the transputer technology. The paper describes how the porting has been implemented. The resulting environment allows a user to distribute any application partly on 'traditional' PVM nodes, and partly on transputer ones. The advantages deriving from the inclusion of the Meiko Computing Surface in the PVM environment are particularly evident with fine-grained parallel applications: as an example, we show the experimental results obtained for a computational vision application.
     
A. Corradi, C. Stefanelli, F. Tarantino
How to employ Mobile Agents in Systems Management
Proceedings of the Third International Conference on The Practical Applications of Intelligent Agents and Multi-Agent Technology (PAAM'98), London, UK, March 23-25, 1998. Pages 17-26.
Abstract. The mobile agents technology is suited to express the management of distributed systems, by overcoming the limits of the traditional manager/agent model. In addition, mobile agents can easily integrate with the Internet scenario and the Web. The paper describes the MAMAS (Mobile Agents for Management Applications and Systems) tool implemented with a mobile agent technology. MAMAS has been developed with the goal of designing monitoring tools for the whole system and of introducing automatically correction actions. In addition, one operator can decide to dynamic modify the predefined management strategies. MAMAS has been implemented in a mobile agent framework, capable of modelling the Internet world composed of interconnected networks, each of them with its peculiar policies (for administrative, management and security purposes). MAMAS and the supporting framework has been implemented in Java.  

Keywords: Multi-agents, Monitor and management applications, Mobile Agent Architecture, Information Agent on the Internet.
     
A. Corradi, M. Cremonini, C. Stefanelli 
Melding Abstractions with Mobile Agents
CIA '98, Paris, France, July 1998, Cooperative Information Agents II, Lecture Notes in Artificial Intelligence LNAI, Springer-Verlag. 
Abstract. Mobile Agents (MA) seems to be the most suitable technology for distributed systems to integrate the Internet in a synergic way. One of the problems that should be faced when considering MA models for distributed applications is the lack of a thorough model capable of describing the Internet world composed of interconnected networks, each of them with its peculiar policies (for administrative, management and security purposes). We propose a Mobile Agent system based on a model designed to consider and favour aggregations of abstract and protected (network) domains: the use of this model makes easy the development of Internet applications. The paper describes the MAMA system (Melding Abstractions and Mobile Agents) and its implementation in the Java language. An application for distributed monitoring provides the results achieved within the MAMA system.
     
A. Corradi, M. Cremonini, C. Stefanelli 
Locality Abstractions and Security in a Mobile Agent Environment
WET ICE '98, Stanford University, California, USA, June 1998, Collaboration in Presence of Mobility, Conference Proceedings, IEEE Computer Society Press.
Abstract. Mobile Agents have achieved wide interest for distributed applications because of their flexibility and capacity of adapting to very different scenarios, a common situation over the Internet. The rapid growth of the area has forced to focus more on rapid prototyping than on other aspects that are still only partially faced. The paper addresses two main concepts connected with the Mobile Agent model: locality abstractions and security. We propose a Mobile Agent environment that introduces the idea of locality to achieve the enforcement of both abstraction and security. The use of this model permits to develop Internet applications that answer both requirements in an integrated way. The paper describes the MA environment and presents some results of its implementation in the Java language. An application for distributed monitoring is an example of the capacity of rapid prototyping.
     
P. Bellavista, A. Corradi
Learning Effectively as in Presence (LEAP): an Internet-Based Integrated Environment for Distance Learning
Proceedings of the Seventh World Conference on Continuing Engineering Education (WCCEE '98 ): "The Knowledge Revolution, the Impact of Technology on Learning", Turin, Italy, pp. 56-61, May 10-13, 1998.
Abstract. Based on modern educational principles, LEAP is a virtual interaction environment for Distance Learning (DL). We have implemented it as a framework to help authors to enrich Web-standard hypertexts with DL-specific tools. The basic guideline is to provide multiple interaction channels, according to three different directions: hypermediality, collaborative work, information metalevels. HTML modalities of interaction are rigid; we have enriched them with executing resources, both on server (Common Gateway Interface for low interactivity services) and on client side (Java Applets for real-time interaction). Object-oriented programming represents the technical solution to reach the goal of portability, expandability, fast-prototyping, standardization and openness.
     
P. Bellavista, A. Corradi
Standard and Emerging Technologies for Distributed Applications in Internet-Based Distance Learning
Proceedings of the Ninth Conference of the European Association for Education in Electrical and Information Engineering (EAEEIE '98 ): "Enhancement of Education in Electrical and Information Engineering through Industry Co-operation and Research", Lisbon, Portugal, pp. 233-238, May, 1998.
Abstract. We have implemented LEAP, a virtual interaction environment for Distance Learning (DL) based on the most recent educational principles. LEAP provides an integrated programming framework to facilitate authors in designing interactive and cooperative courseware in which Web-standard hypertexts are enhanced with DL-specific tools. The basic guideline is to provide multiple interaction channels, according to three different directions: hypermediality, collaborative work, information metalevels. LEAP permits to transparently integrate the traditional HTML modalities of interaction with all types of executing resources available in open distributed systems: server-side ones (Common Gateway Interface), client-side ones (Java Applets) and "distributed" ones (inspired to the Mobile Agents paradigm). LEAP is realized in Java, and its work of implementation has shown how Object-oriented programming can achieve the goal of portability, simple expandability, rapid prototyping, standardization and openness.

     
P. Bellavista, A. Corradi, C. Stefanelli
A Secure and Open Mobile Agent Programming Environment
Proceedings of the Fourth International Symposium on Autonomous Decentralized Systems (ISADS '99), Tokyo, Japan, March 21-23, 1999, pages 238-245, Conference Proceedings , IEEE Computer Society Press.
Abstract. The Mobile Agent technology is suitable for applica-tions in open, distributed and heterogeneous environ-ments such as the Internet and the Web, because it can overcome some limits of traditional approaches. The paper describes a Secure and Open Mobile Agent (SOMA) programming environment with two main design objectives that are security and interoperability. On the one hand, SOMA is based on a thorough security model and provides a wide range of tools and mechanisms to build and enforce flexible security policies. On the other hand, the SOMA framework can interoperate with differ-ent application components designed with different pro-gramming styles. SOMA grants interoperability by closely considering compliance with CORBA, the most diffused standard in the area of Object-Oriented components. SOMA has been adopted as a platform to develop several distributed applications in the area of network and sys-tems management, CSCW, and distributed and heteroge-neous information systems.

     
P. Bellavista, A. Corradi, C. Stefanelli
An Open Secure Mobile Agent Framework for Systems Management
Journal of Network and Systems Management (JNSM) , Special Issue on "Mobile Agent-based Network and Service Management", Vol. 7, No. 3, pp. 323-339, September 1999.
Abstract. The Mobile Agent (MA) technology is gaining importance in the distributed manage-ment of networks and services for heterogeneous environments. MA-based management systems could represent an interesting alternative to traditional tools built upon the client/server model, either SNMP- or CMIP- based. The acceptance of MA solutions for management is currently limited by two main requirements: the need of interoperability and the request for security. Without security, management systems can not suit global untrusted environment, such as the Internet; without interoperability, they can not in-teract with existing tools and legacy systems. The paper describes an MA-based man-agement system which considers security and interoperability as the two main design objectives. It is an open management framework that grants interoperability by provid-ing compliance with CORBA, the most diffused standard in the area of Object-Oriented components. In addition, it is based on a thorough security model and provides a wide range of tools and mechanisms to build and enforce flexible security policies.

     
M. Cremonini, A. Corradi, R.Montanari , C. Stefanelli
Mobile Agents and Security: Protocols for Integrity
Proceedings of the Second IFIP WG 6.1 International Working Conference on Distributed Applications and Interoperable Systems (DAIS'99), June 28 - July 1, 1999 Helsinki, Finland.
Abstract. The Mobile Agent paradigm seems to be a promising and innovative technology for developing applications in open, distributed and heterogeneous environments because it can overcome some of the limits of traditional Client/Server approaches. Many application areas, such as e-commerce, mobile computing, network management and information retrieval can benefit from the application of the MA technology. The widespread use of mobile agents is currently mainly limited by the lack of security, a requirement that should be faced when dealing with the Internet untrusted environment. The paper focuses on the problem of ensuring the integrity of agents in these environments and presents a range of solution strategies. In particular, it describes and compares two different approaches to achieve agent integrity. The first one makes use of a Trusted Third Party entity, while the second one is based on a distributed protocol that does not assume any secure collaborating entity. The two solutions suite different areas, and we have integrated them in a flexible support for a wide range of applications, called Secure and Open Mobile Agent (SOMA).

     
P. Bellavista, A. Corradi, R. Montanari, C. Stefanelli
An Integrated Environment for the Management of Network Resources and Services
Proceedings of the 6th Workshop of the OpenView University Association (OVUA '99), Bologna, Italy, June 13-15, 1999.
Abstract. The increasing complexity of the network management problem is due to both technological and human factors. Heterogeneity and globalization of network resources on the one hand, increasing user expectations for flexible and easy-to-use environments on the other hand, force to consider new approaches to the management issue. In the paper, we describe MESIS (Management Environment for Secure and Interoperable Services) for the integrated management of both network resources and services. MESIS permits the design and the implementation of new services for open, global, and untrusted scenarios, such as the Internet. The principal part of MESIS is a distributed processing environment composed of a wide set of facilities that can be exploited for building services at the application layer. The paper focuses on two crucial facilities: interoperability and security. The Interoperability Facility allows MESIS services to interwork with all resources and services, even provided by legacy systems. In particular, it considers interoperability with other management systems via compliance with CORBA. The Security Facility provides to MESIS the safe and protected operations necessary in global untrusted environments. MESIS permits authentication of principals, communication integrity and privacy, accountability, and secure interoperation with CORBA-compliant systems. MESIS is implemented in terms of mobile agents, to facilitate delegation and management automation, and to achieve efficiency and scalability through local access to managed entities.

     
P. Bellavista, A. Corradi, C. Stefanelli, F. Tarantino
Mobile Agents for Web-based Systems Management
Internet Research, MCB University Press, Vol. 9, No. 5, pp. 360-371, November 1999.
Abstract. The increasing dimension and heterogeneity of global Web systems make increasingly difficult their management with tools based on the client/server model. The Mobile Agent technology overcomes the limits of traditional approaches and proposes solutions suitable for the management of distributed and heterogeneous Internet-based systems. The paper describes the MAMAS (Mobile Agents for the Management of Applications and Systems) environment and its implementation with a Mobile Agent technology. MAMAS can adapt to organizations with very different interconnected architectures and with different policies for administration and management. The environment has the goal of monitoring the whole system, of introducing dynamic corrective actions and of modifying system policies at run-time. MAMAS achieves these goals by answering both the security guideline necessary in untrusted environments such as the Internet and the guideline of compliance to standards. The choice of Java as implementation language has permitted to achieve portability, to employ the language security features, and to provide Web accessibility. The CORBA framework has allowed interoperability with other existing management platforms.

     
P. Bellavista, C. Cavallari, A. Corradi, C. Stefanelli
Mobile Agents for Internet Services: Directions of Standardization and their Implementation in SOMA
Proceedings of the 37th Conference of the Associazione Italiana per l'Informatica ed il Calcolo Automatico (AICA'99), Abano Terme, Italy, pp. 19-31, September 27-29, 1999.
Abstract. One of the main directions in the recent evolution of information systems has certainly been the expansion of the Internet and the diffusion of the Web technology for the realization of distributed applications. The traditional models for designing, deploying and managing distributed services, based on the client/server paradigm, are not suitable to face the new types of problems raised by the globality of the Internet: open, global and heterogeneous environments force to reconsider scalability, fault-tolerance and service adaptability to on-line system properties and to dynamically specified user requirements. This scenario has justified the interest for programming paradigms based on code mobility, and in particular for the Mobile Agent (MA) one. To accelerate and facilitate the acceptance and development of MA-based commercial services, it is necessary that the several proposed MA platforms overcome their heterogeneous barriers to interoperability, by providing mechanisms and tools to permit the interaction between different MA systems and the interworking between agents and legacy resources. The paper describes our guidelines to make an MA platform interoperable via compliance with the OMG standards CORBA (Common Object Request Broker Architecture) and MASIF (Mobile Agent System Interoperability Facility). In particular, it presents which design and implementation choices have been made to obtain this compliance in SOMA. Finally, the paper reports some performance measures that permit to evaluate the costs of interoperability mechanisms if compared with the corresponding proprietary ones.

     
P. Bellavista, A. Corradi, C. Stefanelli
A Mobile Agent Infrastructure for Terminal, User and Resource Mobility
Proceedings of the IEEE/IFIP Network Operations and Management Symposium (NOMS 2000): "The Networked Planet: Management Beyond 2000", Honolulu, Hawaii, April 10-14, 2000.
Abstract. The telecommunication and the Internet scenarios have pointed out the possibility of accessing resources and services while moving in open distributed global systems. Mobility should allow users to access services and to maintain their preferred work-ing environment independently of their current point of attachment, and has moti-vated the investigation of new models and solutions. The mobile agent technology is intrinsically suitable to describe, model and implement mobility. The paper describes how a mobile agent framework, called SOMA, can provide an infrastructure to sup-port not only the traditional concepts of terminal and user mobility but also the mo-bility of resources in general. SOMA permits terminal mobility by introducing the mobile place abstraction that represents a mobile host for agent execution, and user mobility by supporting the virtual home environment service. SOMA supports re-source mobility via the resource discovery service that can preserve client/server re-lationships among SOMA resources and users independently of current positions. The paper gives also experimental results about the costs associated with the main mechanisms for supporting terminal, user, and resource mobility.

     
P. Bellavista, A. Corradi, A. Tomasi
The Mobile Agent Technology to Support and to Access Museum Information
Proceedings of the 2000 ACM Symposium on Applied Computing (SAC 2000), Como, Italy, March 19-21, 2000.
Abstract. The global scenario put together by communication networks determines new opportunities towards the realization of Internet-based distributed services in many complex and composite application areas, such as the access to museum information. Solution complexity mainly stems from the heterogeneous representation formats of data, their geographical distribution, the large number of data sources involved, and the user requirements for personal customization and optimization of the accessed service. The paper claims that flexible museum information access services require a middleware-level approach and the implementation of a distributed support infrastructure. Within the MOSAICO project, we have realized the VM (Virtual Museum) framework on top of the SOMA (Secure and Open Mobile Agent) programming environment. Mobile agents have been chosen for their intrinsic properties of autonomy, asynchronicity, dynamicity of distribution and behavior, adaptability to available system resources. We have designed the VM to accommodate different usage scenarios: VM users can play different roles with different expertise levels; they can ask the VM infrastructure for differently complex features, from simple Web accessibility to user accounting for data resource consumption, from data customization via user profiling to automatic update of subscripted query results. The first prototype, apart from the feasibility of the approach, has already shown the potential and the flexibility of the mobile agent infrastructure to adapt to both different user requirements and different resource availability

     
P. Bellavista, A. Corradi, C. Stefanelli
A Mobile Agent Infrastructure for the Mobility Support
Proceedings of the 2000 ACM Symposium on Applied Computing (SAC 2000), Como, Italy, March 19-21, 2000.
Abstract. The mobility of terminals and users is a crucial issue in the open global sys-tem represented by the Internet. Supporting terminal and user mobility re-quires a middleware infrastructure capable of efficiently answering the needs of scalable resource discovery, of security and interoperability, of Quality of Service (QoS) monitoring and adaptation. Some proposals address mobility at the network level and some others focus on application-level solutions. By following the latter approach, the paper proposes the adoption of the mobile agent technology to model and implement mobility. In particular, the paper concentrates on the components and modules implemented in the SOMA mo-bile agent programming framework to specifically support terminal and user mobility. The SOMA tracing and discovery system extends the SOMA basic naming service to identify and keep track of all mobile entities in the environ-ment. The SOMA QoS adaptation support exploits the functionality of the SOMA monitoring tools and permits to dynamically adjust service provision in response to the changing network and nodes conditions. These features are integrated in a mobility add-on module that pursues also the goals of security and interoperability when moving users and roaming terminals.

     
P. Bellavista, A. Corradi, C. Stefanelli
An Integrated Management Environment for Network Resources and Services
IEEE Journal on Selected Areas in Communication, Special Issue on "Recent Advances in Network Management and Operations", Vol. 18, No. 5, pages 676-85, May 2000.
Abstract. Technological and human factors have contributed to increase the complexity of the network management problem. Heterogeneity and globalization of network resources on the one hand, increasing user expectations for flexible and easy-to-use environments on the other hand, suggest to face the management problem in entirely novel ways. Several research efforts recognize the need for integrated solutions to manage both network resources and services in open, global and untrusted environments. In addition, these solutions should permit the coexistence of different management models and should interoperate with legacy systems. In the paper, we define a general architecture based on a Distributed Processing Environment (DPE) that offers a large set of facilities to the application level. We have developed the MESIS management environment shaped after the above architecture and its DPE facilities with the mobile agents technology. MESIS handles in a uniform way both resources and services, and focuses on two crucial properties: interoperability to overcome heterogeneity, and security to grant users safe and protected operations. The Agent Interoperability Facility supports compliance with CORBA-based management systems and with MASIF agent platforms. The Agent Security Facility provides authentication, integrity, privacy, authorization, and secure interoperation with CORBA systems.

     
P. Bellavista, A. Corradi, C. Stefanelli
Protection and Interoperability for Mobile Agents: A Secure and Open Programming Environment
IEICE Transactions on Communications, IEICE/IEEE Special Issue on "Autonomous Decentralized Systems", Vol. E83-B, No. 5, pages 961-972, May 2000.
Abstract. The Mobile Agent technology helps in the development of applications in open, distributed and heterogeneous environments such as the Internet and the Web, but it has to answer to the requirements of security and interoperability to achieve wide acceptance. The paper focuses on security and interoperability, and describes a Secure and Open Mobile Agent (SOMA) programming environment where both requirements are main design objectives. On the one hand, SOMA is based on a thorough security model and provides a wide range of mechanisms and tools to build and enforce flexible security policies. On the other hand, the SOMA framework permits to interoperate with different application components designed with different programming styles. SOMA grants interoperability by closely considering compliance with the OMG CORBA and MASIF standards. SOMA has already shown the feasibility and effectiveness of the approach for the development of flexible and adaptive applications in several areas, particularly in network and systems management.

     
P. Bellavista, A. Corradi, R. Montanari, C. Stefanelli
How a Secure and Open Mobile Agent Framework Suits Electronic Commerce Applications
Proceedings of the Italian Workshop "From Objects to Agents: Evolutionary Trends in Software Systems", Joint Workhop of the Italian Association for Artificial Intelligen (AI*IA) and the Italian Association for Advanced Technologies based on Object-Oriented Concepts (TABOO), Parma, Italy, pp.13-18, May 29-30, 2000.
Abstract. The Mobile Agent (MA) paradigm seems able to support effectively distributed applications in open and heteroge-neous environments, and application areas such as e-commerce appear to be of particular interest. However, MA technology has to answer to the requirements of security and interoperability to achieve wide deployment, especially in e-commerce applications. The paper focuses on security and interoperability, and describes a Secure and Open Mobile Agent (SOMA) programming envi-ronment where both requirements are main design objec-tives. On the one hand, SOMA is based on a thorough security model and provides a wide range of mechanisms and tools to build and enforce flexible security policies. On the other hand, the SOMA framework permits to interoperate with different application components de-signed with different programming styles. SOMA grants interoperability by closely considering compliance with the OMG CORBA and MASIF standards. In particular, the paper presents a SOMA-based e-marketplace that stresses to the limit the security and interoperability issues and that has served as a testbed for the validation of SOMA security and interoperability support.

     
P. Bellavista, T. Magedanz
Middleware Technologies: CORBA and Mobile Agents
Invited Chapter in the Book "Coordination for Internet Agents - Models, Technologies, and Applications ", A.Omicini, F.Zambonelli, M.Klusch, R.Tolksdorf (eds.), Springer-Verlag, ISBN 3-540-41613-7, pages 110-152, March 2001.
Abstract. The design, implementation and provision of services in the Internet scenario are forcing both the traditional area of client/server distributed systems and the emerging sector of agent technology towards the definition of a common distributed middleware, i.e., a set of basic facilities that can be ubiquitously accessed by any distributed component as an integrated part of the enhanced communication infrastructure. This middleware should not only be the basis where designers start for the realization and deployment of their services, but also be flexible enough to permit the easy and rapid extension of the common infrastructure to accommodate evolving system/service requirements and expectations of final users. Among the technologies for middleware implementation, the chapter describes the state-of-the-art of two approaches: the Common Object Request Broker Architecture (CORBA) technology and the Mobile Agent (MA) one, which are different from several points of view (interoperability and location transparency vs. mobility and location awareness). However, in contrast to using them separately, the chapter claims that an integration of both middleware technologies represents the most promising solution to achieve the maximum flexibility in the implementation of an open service infrastructure. In this context CORBA-based MA platforms demarcate an important evolution step into the direction of mobile and interoperable object systems, on which Internet services could be realized through dynamically distributed and reusable object-based components.

     
P. Bellavista, A. Corradi, C. Stefanelli
Java-based On-line Monitoring of Heterogeneous Resources and Systems
Proceedings of the 7th Workshop of the Hewlett-Packard OpenView University Association (HP OVUA '00), Santorini, Greece, June 12-14, 2000.
Abstract. The diffusion of Web-based multimedia services and the emerging competition among service providers require to enrich the Internet infrastructure with mechanisms to manage and control service quality and availability. These goals require monitoring mechanisms that ascertain the state of resources and applications in the global distributed system, and that should be a core functionality of any infrastructure for Web service provision. The paper describes the design and the implementation of a Java-based Application Programming Interface (API) to monitor uniformly heterogeneous resources and systems over the Internet. The monitoring tool operates at different levels of abstraction. On the one hand, it can instrument the Java Virtual Machine (JVM) to handle several types of events produced by Java applications. On the other hand, it can inspect the state of machine specific information (e.g., CPU and memory utilization) typically hidden by the JVM, and available via platform-dependent modules (currently developed for WindowsNT, Solaris and Linux). The implemented monitoring tool can be integrated in any Java-based Web service infrastructure and is currently part of the SOMA mobile agent platform.

     
P. Bellavista, A. Corradi, C. Stefanelli
CORBA Solutions for Interoperability in Mobile Agent Environments
Proceedings of the 2nd International Symposium on Distributed Objects & Applications (DOA'00), Antwerp, Belgium Sept. 21-23, 2000.
Abstract. The Mobile Agent (MA) paradigm proposes several attractive solutions to deal with the problems of network-centric programming. Despite the availability of several MA platforms, there are still only a few MA-based distributed services. Apart from the security issues raised by code mobility, we claim that the lack of interoperability is one of the major obstacles to the large-scale diffusion of the MA paradigm. In the paper, we discuss solutions to permit the interworking between heterogeneous MA frameworks and other systems, whether MA-based or not, via compliance with ei-ther accepted or emerging interoperability standards. In particular, we focus on compliance with CORBA, the accepted standard for OO components, but also with MASIF and FIPA, respectively, the OMG specification for the support of agent mo-bility and management, and the framework for standard languages and protocols in agent communication. In addition to interoperability, other features such as secu-rity, portability, fast prototyping and easy integration with the Web are important for MA platforms, and provided a guideline in the design and implementation of our SOMA programming framework. The paper also reports performance results of CORBA-based interoperability in SOMA: the presented costs, measured for a sys-tems management application, show the feasibility of the adopted interoperability solutions.

     
P. Bellavista, A. Corradi, R. Montanari, C. Stefanelli
Security in Programmable Network Infrastructures: the Integration of Network and Application Solutions
Proceedings of the 2nd International Working Conference on Active Networks (IWAN'00), Tokyo, Japan, October 2000.
Abstract.Programming the network infrastructure significantly enhances its flexibility and favors fast deployment of new protocols, but also introduces serious security risks. It is crucial to protect the whole distributed infrastructure, especially its availability in case of denial-of-service attacks. A security framework for programmable networks may provide security solutions at different levels of abstraction. Active networks mainly propose a network-layer approach, by extending the packet format to include security information. Mobile code technologies tend to provide security tools at the application layer to integrate with standard external infrastructures, such as public key ones. The paper describes the security frameworks of several programmable network proposals and points out the dis/advantages related to the adopted abstraction level. This comparison suggests to consider an integrated security framework capable of choosing the service-specific balance between application-layer flexibility and network efficiency. To this purpose, the paper presents the architecture of a Programmable Network Component (PNC) that integrates security solutions at different layers and that has been implemented by using a mobile agent programming environment.

     
A. Corradi, R. Montanari, C. Stefanelli
Mobile Agents Integrity in E-commerce Applications
Proceedings of the 19th IEEE International Conference on Distributed Computing Systems Workshop (ICDCS'99), IEEE Computer Society Press, Austin, Texas, May 1999.
Abstract.The Mobile Agent (MA) paradigm seems able to support effectively distributed applications in open and hetero-geneous environments, and application areas such as e-commerce appears to be of particular interest. Mobility, autonomy and easy personalization are distinguished properties of the MA paradigm that can support e-commerce transactions by helping in information gathering, filtering, and negotiation. However, MA systems, despite these offered advantages, experience a limited usage because they lack of a comprehensive security framework. Only a full answer to the requirement of protection for both execution sites and mobile shopping agents can permit the adoption of MA solutions in the electronic market. This paper describes an MA environment, called Secure and Open Mobile Agent (SOMA), that supports secure and open e-commerce applications. In particular, the paper focuses on how mobile shopping agents can be protected from malicious behavior of execution sites and describes a distributed multiple-hops integrity protocol integrated in SOMA.

     
A. Corradi, R. Montanari, C. Stefanelli
Mobile Agents Protection in the Internet Environment

Proceedings of the International Conference COMPSAC'99, IEEE Computer Society Press, Phoenix, October '99.
Abstract.The Mobile Agent (MA) paradigm seems to be a promis-ing technology for developing applications in open, distributed and heterogeneous environments, such as the Internet. Mobile agents can overcome some of the limits of the traditional Client/Server model and can easily integrate with the web to improve application accessibil-ity. Many application areas, such as electronic com-merce, mobile computing, network management and information retrieval can benefit from the application of the MA technology. However, a wider diffusion of MA is currently limited by the lack of a comprehensive security framework. Answering to the requirement of protection for both execution sites and mobile agents can boost the acceptance of the MA paradigm in the Internet environ-ment. This paper describes an MA environment, called Secure and Open Mobile Agent (SOMA), that is based on a thorough security model and provides a wide range of tools and mechanisms to build and enforce flexible secu-rity policies. In particular, we focus on the problem of how mobile agents can be protected from malicious behavior of execution sites and we propose a distributed multiple-hops integrity protocol for mobile agent protec-tion, fully integrated in SOMA.

     
A. Corradi, R. Montanari, C. Stefanelli
Security Issues in Mobile Agent Technology

Proceedings of the 7th IEEE Workshop on Future Trends of Distributed Computing Systems (FTDCS'99), IEEE Computer Society Press, Cape Town, South Africa, December 99.
Abstract.The Mobile Agent (MA) paradigm seems to be a promis-ing technology for developing applications in open, distributed and heterogeneous environments, such as the Internet. Many application areas, such as electronic commerce, mobile computing, network management and information retrieval can benefit from the application of the MA technology. The exploitation of mobile agents offer several peculiar advantages, such as reduction of network latency, asynchronous execution, robust and fault tolerant behavior. However, a wider diffusion of MA is currently limited by the lack of a comprehensive secu-rity framework that can address the security concerns arising in mobile agent applications providing efficiency at the same time. This paper describes an MA environ-ment, called Secure and Open Mobile Agent (SOMA), that offers a wide range of security tools and mechanisms aimed at protecting both execution sites and agents against reciprocal malicious behavior. In particular, SOMA integrates several possible solutions to ensure agent integrity. The paper presents an electronic market-place prototype based on SOMA where we have validated the efficiency and scalability of our security framework.

     
D. Berbecaru, A. Corradi, A. Lioy, F. Maino, R. Montanari, C. Stefanelli
A Flexible Management Framework for Certificate Status Validation

Proceedings of the 15th International Conference on Information Security (SEC'00), Kluwer Academic Publisher, Beijing, August 00.
Abstract. Public key cryptography is widely recognised as the technology to develop effective authentication, integrity, confidentiality and non-repudiation services. The provision of public key-based security services for complex and large scale organisations requires a Public Key Infrastructure (PKI) in charge of securely managing cryptographic keys/certificates. An essential PKI service is the certificate status validation (CSV) system that supports the publishing and the consistent usage of certificate status information for wide range of applications. Several CSV solutions, such as Certificate Revocation Lists or the On-line Certificate Status Protocol, are available, but none can meet the requirements for all applications, in particular of timeliness and performance. The lack of a comprehensive CSV solution calls for the development of a flexible framework that can integrate all available validation mechanisms and permit the selection of alternative validation strategies, depending on application requirements. The paper describes this framework that provides PKI users with a flexible, dynamic and transparent CSV support. In addition, the paper claims that the framework flexibility, dynamicity and transparency can greatly benefit from the adoption of the Mobile Agent (MA) technology because it exhibits the same intrinsic features, by presenting an MA-based prototype for CSV.

     
A. Corradi, E. Lupu, R. Montanari, M. Sloman, C. Stefanelli
A Flexible Access Control Service for Java Mobile Code

Proceedings of the 16th Annual Computer Security Applications Conference, (ACSAC00), IEEE Computer Society, PressNew Orleans, Luisiana, Dicember 00.
Abstract. Mobile Code (MC) technologies provide appealing solutions for the development of Internet applications. For instance, Java technology facilitates dynamic loading of application code from remote servers into heterogeneous clients distributed all over the Internet. However, executing foreign code that has been loaded from the network raises significant security concerns which limit the diffusion of these technologies. Substantial work has already been done to provide security solutions for protecting both hosting nodes and mobile code. For example, the Java security architecture evolved from a rigid sandbox model to a more flexible solution where downloaded code can perform any kind of operations, depending on its source location and signature. However, the most widespread security solutions for MC platforms today do not support the sophisticated security policies required in modern inter-organisational environments. This requires expressive languages to specify the policy and flexible mechanisms for policy implementation which cater for code mobility. This paper shows how access control policies for MC based applications can be specified in a concise and declarative language called Ponder and how these policies can be implemented within the Java security architecture.

     
P. Bellavista, A. Corradi, D. Cotroneo, S. Russo
Integrating Mobile Agent Infrastructures with CORBA-based Distributed Multimedia Applications
Proceedings of the 9th Euromicro Workshop on Parallel and Distributed Processing (PDP 2001), Mantova, Italy, February 7-9, 2001, pages 121-128, IEEE Computer Society Press.
Abstract.The increased computing power and the enhanced con-nectivity of current open computing systems are encour-aging the deployment of new classes of services both centered around dynamically changing user requirements and based on the exploitation of the Internet infrastruc-ture. Distributed Multimedia Applications (DMAs) are a typical class of services with challenging requirements in terms of resource demand, dynamicity and QoS adapta-tion. The paper claims that distributed objects and mobile agents can complement each other to provide a flexible middleware for DMAs, and describes the case study of MADAMA (Mobile Agent-based Distributed Architecture for Multimedia Applications). MADAMA adopts mobile agents to simplify the distribution of service control and to provide location-aware adaptability. In addition, MADAMA is compliant with CORBA to achieve large ac-cessibility and interoperability.

     
P. Bellavista, A. Corradi, C. Stefanelli
Mobile Agent Middleware for Mobile Computing
IEEE Computer magazine, Vol. 34, No. 3, pages 73-81, March 2001.
Abstract.Telecommunication systems and the Internet are converging toward an integrated scenario to permit the development and the access to mobile computing services. Mobility permits users to connect to the Internet from ubiquitous and heterogeneous access points while preserving their personal preferences (user mobility), and allows to connect/disconnect portable computing devices (terminal mobility). A still open issue is to provide mobile users and terminals with the access to local/remote re-sources and services, independently of current location (mobile access to resources). These mobility issues require an integrated middleware that can significantly benefit from a Mobile Agent (MA) implementation. The paper describes the three services needed to support user mobility, terminal mobility and mobile access to resources, termed respectively User Virtual Environment, Mobile Virtual Terminal and Virtual Resource Management. We have implemented these services as add-on modules in a general-purpose middleware for MA-based Internet services.

     
P. Bellavista, A. Corradi, C. Stefanelli
Middleware Services for Interoperability in Open Mobile Agent Systems
Microprocessors and Microsystems, Elsevier Science, Vol. 25, No. 2, pages 75-83, May 2001.
Abstract.Despite the design and implementation of several Mobile Agent (MA) platforms, widely diffused services based on the MA pro-gramming paradigm are still lacking. Apart from the security chal-lenges imposed by the MA technology, the paper claims that interoperability between mobile agents, legacy systems and hetero-geneous MA platforms is a major obstacle to the MA diffusion. The paper discusses solutions to permit the interworking between MA platforms and other systems, even non MA-based, via compli-ance with either accepted or emerging interoperability standards. In particular, it focuses on compliance with CORBA, the accepted standard for object-oriented components, but also with MASIF and FIPA, respectively, the OMG specification for the support of agent mobility and management, and the framework for standard agent platforms and communication languages. The discussed solutions have guided the design and implementation of the middleware interoperability service in the SOMA (Secure and Open Mobile Agents) programming framework. The SOMA interoperability service is structured in a layered and modular way: its components can be dynamically distributed and installed only where and when needed. The paper also presents an application scenario in the area of network, systems and service management, where the interoperability components permit the interworking of SOMA agents, SNMP-compliant elements, legacy resources, and non-SOMA MA platforms.

     
P. Bellavista, A. Corradi, C. Stefanelli
Monitor and Control of Mobile Agent Applications
ACM OOPSLA Workshop on Experiences with Autonomous Mobile Objects and Agent Based Systems, Minneapolis, USA, Oct. 2000.
Abstract.Mobile agents raise significant security concerns that have been the focus of several research activities. However, some security-related issues, such as the protection against denial of service attacks and the accounting of agent resource consumption, still need further investigation. Solutions to these problems require monitoring the resource state during agent execution, in order to control and possibly limit resource usage. The paper presents solution guidelines for the on-line monitoring and control of Java-based mobile agents. In particular, it describes the implementation of MAPI, an on-line monitoring component integrated in the SOMA mobile agent platform. MAPI exploits the JVMPI and JNI technologies to achieve full visibility of the state of both Java and platform-dependent resources from within the Java Virtual Machine.

     
P. Bellavista, A. Corradi, S. Vecchi
How to Prevent Denial-of-Service Attacks of Mobile Agents: a Solution for Java-based Platforms
Proceedings of the 39th Conference of the Associazione Italiana per l'Informatica ed il Calcolo Automatico (AICA'01), pp. 445-456, Como, Italy, September 19-21, 2001.
Abstract.The Mobile Agent (MA) technology has already demonstrated its suitability in several application domains, from mobile computing to network, systems and service management. However, a problem that still limits MA diffusion in commercial environments is how to control and limit dynamically the operations that either malicious or badly programmed agents are entitled to perform. It is necessary not only to rule the MA access to resources but also to control resource usage of admitted agents during execution, for instance to protect against possible denial-of-service attacks on hosting execution resources. The paper presents an on-line distributed monitoring tool that gives information about the state of mobile agents and their use of resources, thus permitting to enforce the required management policies on MA resource consumption. The tool is a key component of the Java-based SOMA programming framework and achieves visibility of monitoring information at different levels of abstraction. The experimental measurements about overhead and reaction time of the on-line control of SOMA agent execution show the feasibility of the approach that does not modify the standard Java Virtual Machine.

     
F. Baschieri, P. Bellavista, A. Corradi
Mobile Agents for QoS Tailoring, Control and Adaptation over the Internet: the ubiQoS Video on Demand Service
Proceedings of the 2nd IEEE International Symposium on Applications and the Internet (SAINT'02), pp. 109-118, Nara, Japan, January 28-February 1, 2002, IEEE Computer Society Press.
Abstract.Service provision over the Internet has to address the issues of differentiated Quality-of-Service (QoS) and ubiquitous accessibility. Internet services should take into consideration the user QoS desiderata together with the various properties of servers providing replicated/partitioned services and of different access devices/points, from workstations over high-capacity ATM links to personal digital assistants over packet-switched 3G mobile phone. The major paper claim is that the provision over best-effort networks of services with negotiated and controlled QoS requires a distributed support infrastructure consisting of intermediate active nodes along the path between clients and servers. The paper deals with the Mobile Agent (MA) technology as suitable for implementing this active infrastructure and, in particular, presents the MA-based design and implementation of the ubiQoS Video on Demand (VoD) middleware. At negotiation time, ubiQoS establishes an active path between the requesting client and the proper VoD server to tailor the quality of VoD flow depending on user profile and device characteristics. At provision time, ubiQoS dynamically controls the offered QoS level to adapt locally when and where network resource availability changes.

     
P. Bellavista, A. Corradi, R. Montanari, C. Stefanelli
An Active Middleware to Control QoS Level of Multimedia Services
Proceedings of the 8th IEEE Workshop on Future Trends of Distributed Computing Systems (FTDCS'01), pp. 126-132, Bologna, Italy, October 31-November 2, 2001, IEEE Computer Society Press.
Abstract.The provision of novel Internet services has both to specify and to maintain differentiated Quality-of-Service (QoS) levels. Services should tailor to different user QoS preferences together with the differentiated quality prop-erties deriving from servers and access points and de-vices, from workstations connected with high-capacity networks to wearable devices exploiting limited-capacity wireless links. The paper claims that service provision with negotiated and controlled QoS over best-effort net-works calls for a support infrastructure that activates in-termediate nodes along the path between clients and serv-ers. In fact, the paper proposes MASQ, an active middle-ware solution for the QoS management of Video-on-Demand (VoD) streaming. At negotiation time, MASQ ex-ploits code mobility to establish an active path between the requesting client and the VoD server chosen to tailor VoD flows based on user profiles and device properties. At provision time, MASQ dynamically controls the offered QoS level to adapt locally when and where network re-source availability changes. MASQ significantly benefits from dynamic and flexible programmability stemming from the employment of high-level policies.

     
P. Bellavista, A. Corradi, C. Stefanelli
How to Monitor and Control Resource Usage in Mobile Agent Systems
Proceedings of the 3rd International Symposium on Distributed Objects & Applications (DOA'01), pp. 126-132, Rome, Italy, September 18-20, 2001, IEEE Computer Society Press.
Abstract.The Mobile Agent technology has already shown its advantages, but at the same time has already remarked new problems currently limiting its diffusion in commercial environments. A key issue is to control the operations that foreign mobile agents are authorized to perform on hosting execution environments. It is necessary not only to rule the MA access to resources but also to control resource usage of admitted agents at execution time, for instance to protect against possible denial-of-service attacks. The paper presents a solution framework for the on-line monitoring and control of Java-based MA platforms. In particular, it describes the design and implementation of MAPI, an on-line monitoring component that we have integrated within the SOMA system. The paper shows how to use MAPI as the building block of a distributed monitoring tool that gives application- and kernel-level information about the state of mobile agents and their resource usage, thus enabling the enforcement of management policies on MA resource consumption.

     
P. Bellavista, A. Corradi
How to Support Internet-based Distribution of Video on Demand to Portable Devices
Proceedings of the 7th IEEE International Symposium on Computers and Communications (ISCC'02), Taormina, Italy, pages 126-132, July 1-4, 2002, IEEE Computer Society Press.
Abstract. The increasing diffusion of mobile computing and of portable devices with wireless connectivity identifies new challenging scenarios for service provisioning. The access from devices with limited heterogeneous capabilities to traditional and novel Internet services requires new infra-structures capable of integrating with the fixed network and of supporting service tailoring/adaptation. The paper presents a mobile agent-based middleware for the distri-bution of Video on Demand (VoD) to portable devices. Mobile agents can act as device proxies over the fixed network, can negotiate the proper QoS level and can dy-namically tailor VoD flows depending on profiles of ter-minal characteristics and user preferences. The paper also describes the design and implementation of a movie-info service prototype, built on top of the proposed mid-dleware. The prototype shows the feasibility of distribut-ing movie trailers ubiquitously even to portable devices with strict constraints on computing power and visualiza-tion capabilities, e.g., Palm personal digital assistants hosting the Java KVM/CLDC/MIDP software suite.

     
P. Bellavista, A. Corradi, S. Vecchi
Mobile Agent Solutions for Accounting Management in Mobile Computing
Proceedings of the 7th IEEE International Symposium on Computers and Communications (ISCC'02), Taormina, Italy, pages 753-760, July 1-4, 2002, IEEE Computer Society Press.
Abstract. The convergence of mobile telecommunications and the Internet global system forces to reconsider traditional cli-ent/server solutions for network and systems management. The paper claims that accounting in the mobility-enabled Internet requires support infrastructures hosted in the fixed network. These infrastructures should monitor, con-trol and register resource consumption locally within the domains where users/terminals dynamically move to, without requiring continuous connectivity with remote and centralized accounting home managers. In addition, the paper shows that the Mobile Agent (MA) technology is suitable to overcome the limits of traditional accounting solutions in several mobility-enabled usage scenarios. MAs can maximize locality in accessing monitoring data, can enable accounting even in case of temporary discon-nection, can install new monitoring/control behavior dy-namically, and can support session-dependent solutions. The paper finally presents the design and implementation of the MA-based Middleware for Mobility Accounting Management (MAM2), together with some use cases show-ing the advantages of the MA adoption.

     
P. Bellavista, A. Corradi, C. Stefanelli
The Ubiquitous Provisioning of Internet Services to Portable Devices
IEEE Pervasive Computing, IEEE Computer Society Press, Vol. 1, No. 3, pages 81-87, July-Sep. 2002.
Abstract. Advances in mobile telecommunications and device miniaturization call for the provision of standard Internet services to mobile clients. In addition, mobility sug-gests new classes of services that take into account the client location and that adapt to the limited capabilities of portable access devices. Service provisioning requires not only ubiquitous device connectivity but also novel infrastructures to support location tracking, automatic resource discovery in the device locality, ser-vice management during device disconnection and roaming, and service tailoring to heterogeneous device characteristics. The Mobile Agent (MA) properties of mobility, dynamicity, asynchronicity and autonomy make the MA programming paradigm peculiarly suitable for the development of novel middlewares for mobil-ity-enabled services. The paper presents a middleware where MAs act as mobile proxies for portable devices over the fixed network and dynamically adapt service provisioning to fit the specific characteristics of their companion devices.

     
P. Bellavista, A. Corradi, C. Stefanelli
Java for On-line Distributed Monitoring of Heterogeneous Systems and Services
The Computer Journal, Oxford University Press, Vol. 45, No. 6, pages 595-607, November 2002.
Abstract. The control and management of Web-based service quality require the extension of the Internet infrastructure with monitoring functions to ascertain dynamically the state of networked resources. The paper describes the design and implementation of the Monitoring Application Programming Interface, a Java-based tool for the on-line monitoring of Internet heterogeneous resources, which provides monitoring indicators at different levels of abstraction. At the application level, it instruments the Java Virtual Machine to notify several different types of events triggered during the execution of Java applications, e.g., object allocation and method calls. At the kernel level, MAPI inspects system-specific information generally hidden by the JVM, e.g., CPU usage and incoming network packets, by integrating with SNMP agents and platform-dependent monitoring modules. MAPI is the core part of a portable tool for distributed monitoring, control and management in the Internet environment. The tool is implemented in terms of mobile agents that move close to the monitored resources to enforce distributed management policies autonomously, with a significant reduction in both reaction time and traffic overhead.

     
P. Bellavista, A. Corradi
A Mobile Agent-activated Middleware for Internet Video on Demand
IPSJ Journal, Information Processing Society of Japan Press, Vol. 43, No. 11, pages 3301-3315, November 2002.
Abstract. The widening of user requirements and the enlargement of terminal heterogeneity force to address the issues of differentiated Quality-of-Service (QoS) and ubiquitous accessibility in Internet services. The paper claims that the provision of services with negotiated and controlled QoS over best-effort networks is achievable via distributed support infrastructures that activate some of the nodes along the network path between clients and servers. The paper proposes Mobile Agents (MAs) as the activation technology to implement the needed active infrastructures and presents the MA-based design and implementation of the ubiQoS middleware for Video on Demand. At the negotiation time, ubiQoS establishes an active path of intermediate nodes capable of tailoring multimedia flow QoS depending on profiles of user preferences and of device characteristics. At the provision time, ubiQoS moni-tors the offered quality and promptly react to changes in resource availability by locally performing management operations, such as flow transcoding/downscaling and resource preemption, when and where needed.

     
P. Bellavista (guest editor)
Middleware Solutions for QoS in Distributed Multimedia Services (guest editorial)
Microprocessors and Microsystems, Special Issue on "Middleware Solutions for QoS in Distributed Multimedia Services", Elsevier Science, Vol. 27, No. 2, pages 43-44, March 2003.
Abstract. The special issue is willing to introduce the readers to the up-to-date research results in the area of QoS-aware middleware for multimedia, by trying to span the most relevant different aspects involved in such a challenging scenario. It starts with a contribution entitled "Total Quality of Service Provisioning in Middleware and Ap-plications" that has the duty of introducing the general aspects of static and dynamic QoS provisioning. The pa-per illustrates how standard component-based middle-ware solutions should be enhanced for both static QoS tailoring and dynamic service adaptability and how to put together these capabilities to provide an integrated middleware solution for total QoS for distributed real-time and embedded systems. The following paper from the University of Naples focuses on the architectural issues related to the design and implementation of multimedia servers over real-time operating systems. In particular, it discusses how it is possible to provide differentiated QoS levels in multi-media distribution while adopting the Rate Monotonic scheduling algorithm. If the two first contributions reflect the significant re-sults achieved by extending and specializing traditional middleware approaches coming from the research areas of real-time distributed components and operating sys-tems, the following two articles from the University of Illinois at Urbana-Champaign and from the University of Bologna explore innovative approaches based on the dis-tributed collaboration of dynamically deployed infra-structure peers. "QoS-aware Middleware Support for Collaborative Multimedia Streaming and Caching Ser-vice" concentrates on collaborative techniques for streaming, scheduling and pre-fetching when provisioning multimedia services to heterogeneous client devices. "Active Middleware for Internet Video on Demand: the QoS-aware Routing Solution in ubiQoS" presents an in-frastructure of mobile agent proxies that dynamically in-stall where needed to compose an active path for tailor-ing/adaptation of Video on Demand. In particular, the paper details how the active path is dynamically deter-mined by exploiting a completely decentralized and QoS-aware peer-to-peer discovery. Finally, the two last contributions from University of Messina and from the Liverpool John Moores University address some of the new challenging requirements com-ing from the distribution of multimedia flows in mobile networks. "QoS Management for MPEG-4 Flows in Wireless Environment" investigates the issues of a middleware architecture to allow mobile wireless devices to access multimedia services offered by the wired Internet. Finally, "MNPA: A Basis for Privacy-Enhanced QoS in Mobile Networks" proposes solutions for supporting the full privacy of users who negotiate the preferred QoS levels in mobile networks.

     
P. Bellavista, A. Corradi
Active Middleware for Internet Video on Demand: the QoS-aware Routing Solution in ubiQoS
Microprocessors and Microsystems, Special Issue on "Middleware Solutions for QoS in Distributed Multimedia Services", Elsevier Science, Vol. 27, No. 2, pages 73-83, March 2003.
Abstract. Several factors are forcing to address the issues of differentiated Quality-of-Service (QoS) and ubiquitous accessibility in Internet ser-vices, from growing user requirements to the increasing heterogeneity of access devices, from the competition of service providers to the severe constraints of resource availability in emerging wireless envi-ronments. The paper claims that the provision of services with nego-tiated and controlled QoS over best-effort networks is achievable via distributed support infrastructures that activate some of the nodes along the network path between clients and servers. The paper proposes Mobile Agents (MAs) as the activation technology to implement the needed active infrastructure and the MA-based design and implementation of the ubiQoS middleware for Video on Demand. At the starting of the service session, ubiQoS establishes an active path of intermediate nodes capable of tailoring multimedia flow QoS de-pending on profiles of user preferences and of device characteristics; at provision time, ubiQoS monitors the offered quality and promptly react to changes in resource availability by locally performing multimedia transcoding/downscaling and resource preemption. In par-ticular, the paper focuses on how it is possible to determine dynami-cally a QoS-aware active path between clients and servers, discusses alternative solutions, and evaluates the performance results of the completely decentralized peer-to-peer implementation of the active path determination in ubiQoS.

     
P. Bellavista, A. Corradi, S. Vecchi
Mobile Agents for Usage-based Accounting in Wireless Ubiquitous Environments
Proceedings of the Italian Workshop "From Objects to Agents: From Information to Knowledge" (WOA'02), Joint Workhop of the Italian Association for Artificial Intelligen (AI*IA) and the Italian Association for Advanced Technologies based on Object-Oriented Concepts (TABOO), Milano, Italy, ISBN 88-371-1363-3, November 18-19, 2002, Pitagora Editrice Bologna.
Abstract. Mobile communications and device miniaturization are enabling pervasive ubiquitous scenarios where a plethora of heterogeneous wireless devices are expected to access both traditional and location-dependent services. Within this usage perspective, the intrinsic limitation in resource availability and the widening market of final users make crucial to enable the usage-based accounting of consumed resources. Usage-based charging not only can represent an important revenue for service providers and network operators but also can force users to a more informed resource consumption and leverage the provisioning of services with differentiated quality levels. The paper claims that the accounting of pervasive services requires extending the fixed Internet infrastructure, where and when needed, with mobility-enabled monitoring, processing, pricing and charging functions. The proposed middleware solution evolves dynamically depending on the mobility patterns of portable client devices and can operate locally to them without requiring continuous connectivity with remote centralized home managers. The paper presents an accounting infrastructure based on the Mobile Agent (MA) technology with an example service of city guide assistance. MAs can effectively support session-dependent usage-based accounting, can install new monitoring and charging behavior dynamically, can maximize locality in the access to monitoring data, and can enable accounting even in case of temporary network partitioning.

     
P. Bellavista, A. Corradi, R. Montanari, C. Stefanelli
Policy-driven Binding to Information Resources in Mobility-enabled Scenarios
Proceedings oft the 4th International Conference on Mobile Data Management (MDM'03), Melbourne, Australia, pages 212-229, January 21-24, 2003, Springer-Verlag Lecture Notes on Computer Science (LNCS 2574).
Abstract. The widespread diffusion of mobile computing and of portable devices with wireless connectivity identifies new challenging scenarios for the Internet provisioning of information services. The possible mobility of users, terminals, and even middleware/service components requires so-lutions to handle properly the links to information resources in response to the mobile entity migration. Binding decisions may depend on dynamic deployment conditions, e.g., local availability of resources, user preferences, and terminal hardware/software characteristics, and should be determined at service provision time. There is the need for novel middlewares capable of supporting mobility-enabled resource binding and of cleanly separating the application logic from binding strategies. The paper presents a middleware, called SCaLaDE, that supports the acces-sibility of mobile users/terminals to information services. SCaLaDE provides mobile clients with mobile agent-based proxies that can follow the user/terminal roaming and have their re-source references transparently accommodated by the middleware depending on policy-driven binding strategies expressed in a high-level specification language and separated from the application logic. This separation of concerns is crucial to reduce the complexity and leverage the development of mobility-enabled information services.

     
P. Bellavista, A. Corradi, S. Vecchi
QoS-aware Accounting in Mobile Computing Scenarios
Proceedings of the 11th Euromicro Conference on Parallel Distributed and Network-based Processing (PDP'03), Genoa, Italy, pages 537-543, February 5-7, 2003, IEEE Computer Society Press.
Abstract.The enlarging market of portable devices and wireless networks stimulates the provisioning of mobility-enabled Internet services with differentiated levels of Quality of Service (QoS). The finally supplied QoS level can greatly differ from the negotiated one because of the very variable availability of network resources. This significantly impacts on the pricing policies and, consequently, on the definition and realization of fair accounting strategies. The paper claims the need of middleware solutions able to evolve dynamically depending on user/terminal mobility to monitor, control and register the finally supplied QoS level directly within the network localities where users/terminals move to. The paper presents the design and implementation of the Active middleware for Quality-aware Accounting of Mo-bile services (AQuAM) that is capable of accounting final users for the QoS level finally supplied during service provisioning, in contexts of user/terminal mobility.

     
P. Bellavista, A. Corradi, R. Montanari, C. Stefanelli
Dynamic Binding in Mobile Applications: a Middleware Approach
IEEE Internet Computing, Special Issue on "Mobile Applications", Vol. 7, No. 2, pages 34-42, Mar.-Apr. 2003.
Abstract. Mobile computing raises new challenges for Internet service provisioning. In par-ticular, mobility of users, terminals, and service components requires novel solu-tions to handle properly the set of bindings to needed resources. We propose a middleware approach to support dynamic binding strategies that can be defined and modified at service provision time, depending on dynamic conditions, e.g., local resource availability, user preferences, and terminal hardware/software char-acteristics. The proposed middleware cleanly separates binding concerns from ap-plication logic ones, and automatically updates resource bindings depending on different metadata, from high-level management policies specified by system ad-ministrators and service providers to user/terminal/resource profiles and resource co-locality constraints. This permits the adaptation of mobile applications to run-time changing environments without any intervention on the application logic.

     
P. Bellavista, A. Corradi, S. Vecchi
Application Domain Accounting for Roaming Services
Proceedings of the 8th IEEE Workshop on Future Trends of Distributed Computing Systems (FTDCS'03), Puerto Rico, May 28-30, 2003, IEEE Computer Society Press.
Abstract. Wireless portable devices and ubiquitous service ac-cess points are enabling pervasive scenarios where a plethora of different client terminals expect to access services while roaming from a network locality to another one and between different local service providers. Within this usage perspective, there is the need for extending accounting functions to include also the possi-bility to charge clients for application-level resource consumption, i.e., application domain accounting. The paper claims that application domain accounting of roaming services requires extending the fixed Internet in-frastructure, where and when needed at service provisioning time, with mobility-enabled monitoring, processing, pricing and charging functions. We propose an accounting middleware solution capable of evolving dynamically in dependence of the exhibited mobility patterns of Wi-Fi client devices. The presented solution is based on the Mobile Agent (MA) implementation technology, on portable mechanisms for quality monitoring, and on portable mechanisms for achieving the visibility of IEEE 802.11b client roaming at the middleware level to automatically trigger the migration of the needed middleware components.

     
P. Bellavista, A. Corradi, E. Magistretti
Proxy-based Middleware for Service Continuity in Mobile Ad Hoc Networks
Proceedings of the Italian Workshop "From Objects to Agents: Intelligent Systems and Pervasive Computing" (WOA'03), Joint Workhop of the Italian Association for Artificial Intelligen (AI*IA) and the Italian Association for Advanced Technologies based on Object-Oriented Concepts (TABOO), Cagliari, Italy,September 10-11, 2003.
Abstract. Advances in device miniaturization and wireless technologies are stimulating novel kinds of networks (Mobile Ad hoc NETworks - MANET) capable of autonomous peer-to-peer organization without the need of a statically deployed support infrastructure. MANET are specifically characterized by high mobility of network nodes and frequent changes of direct visibility. High dynamicity affects the design and implementation of distributed applications by significantly increasing their complexity, to consider not only routing and node configuration issues, but also the possible mobility of software components and the loss of direct connectivity during service provisioning. The paper proposes a highly dynamic and flexible middleware to support service continuity over MANET, i.e., to enable the continuous provisioning of a service, based on the client/server model of interaction, even if clients/servers move at runtime. The middleware is based on application-transparent proxies that act as decoupling intermediaries between the moving clients and servers. The proxy role is assigned dynamically in a completely decentralized way. Proxies exploit code mobility to install only when and where needed. The paper aims to show how the middleware facilitates the development of applications with service continuity, by describing the design and implementation of a file transfer case study. First experimental results demonstrate the feasibility and effectiveness of our approach at the application level and point out the suitability of mobile code programming paradigms in highly dynamic MANET environments.

     
P. Bellavista, A. Corradi, S. Vecchi
Pervasive Accounting of Resource Consumption for Wireless Services with Adaptive QoS
Proceedings of the 6th IFIP/IEEE International Conference on Management of Multimedia Networks and Services (MMNS'03), Belfast, Northern Ireland, September 7-10, 2003, Springer-Verlag Lecture Notes on Computer Science.
Abstract. Wireless communications and device miniaturization are enabling pervasive scenarios where the limited resource availability and the wide heterogeneity of access terminals make crucial to provide mechanisms and tools for the dynamic adaptation of Quality of Service (QoS). Particularly in case of very resource-consuming services QoS levels should be downscaled to fit the specific characteristics of the provisioning environment and of the current access device. In this context, a challenging aspect is to account clients not only for the generated network traffic, but also for the distributed resources involved in the dynamic QoS adaptation. The paper presents an accounting middleware solution that extends the traditional Internet where and when needed, depending on the mobility patterns of the wireless client devices, by introducing flexible mobile components for metering and charging. The middleware exploits the Mobile Agent (MA) technology to achieve dynamicity in metering/charging behavior, locality in the access to metering data, and to enable session-dependent accounting, even in case of temporary network partitioning.

     
P. Bellavista, A. Corradi
Mobile Middleware Solutions for the Adaptive Management of Multimedia QoS to Wireless Portable Devices
To be presented at the 9th IEEE International Workshop on Object-oriented Real-time Dependable Systems (WORDS 2003F), Capri, Italy, October 1-3, 2003, IEEE Computer Society Press.
Abstract. New challenging service scenarios are integrating wireless portable devices with limited and heterogeneous capabilities. They are expected to access both traditional and novel (context-dependent) Internet services. This not only calls for novel infrastructures to support the integration of mobile access devices with the fixed network, where and when needed, but also stresses the necessity of negotiation-time tailoring and provision-time adaptation of Quality of Service (QoS). The paper presents a highly flexible and dynamic middleware for the management of multimedia QoS to wireless portable devices that can roam during service provisioning. The middleware exploits mobile agents that act as device shadow proxies over the fixed network to transparently follow the device movements between wireless localities, to negotiate the proper QoS level, and to dynamically tailor/adapt multimedia flows depending on device profiles and user preferences. In particular, the paper focuses on how the middleware achieves the on-line visibility of the device change of locality in a portable way over different implementations of different wireless technologies, i.e., IEEE 802.11 and Bluetooth. The first experimental results show that, notwithstanding the application-level approach, the middleware reorganization time is compatible with the requirements imposed by the addressed multimedia scenario.

     
P. Bellavista, A. Corradi, S. Vecchi
An Integrated Resource Management Architecture for Wireless Smart Environments
Proceedings of the Italian Workshop "From Objects to Agents: Intelligent Systems and Pervasive Computing" (WOA'03), Joint Workhop of the Italian Association for Artificial Intelligence (AI*IA) and the Italian Association for Advanced Technologies based on Object-Oriented Concepts (TABOO), Cagliari, Italy, ISBN 88-371-1413-3, September 10-11, 2003.
Abstract. Pervasive and ubiquitous computing is enabling the implementation of "smart environments", i.e., environments where applications support and enhance the abilities of their occupants in executing tasks. To provide the appropriate behavior, these applications must be able to acquire and manage information about the resources populating the smart environment. We propose an integrated resource management solution targeted to highly dynamic and heterogeneous smart environments. The proposed middleware is based on the Java Management Extensions (JMX) and on the Mobile Agent (MA) technology. JMX provides a unifying interface to different monitoring/management mechanisms, thus simplifying the integration with very heterogeneous distributed resources. MAs simplify the processing and the aggregation of raw management data to dynamically consider and achieve application-specific management goals, thus providing the flexibility and the level of abstraction needed in the addressed scenario.

     
P. Bellavista, R. Montanari, D. Tibaldi
COSMOS: a Context-centric Access Control Middleware for Mobile Environments
Proceedings of the 5th IEEE/IFIP International Workshop on Mobile Agents for Telecommunication Applications (MATA'03), Marrakech, Morocco, October 8-10, 2003, Springer-Verlag Lecture Notes on Computer Science.
Abstract. User/terminal mobility during service provisioning and high heterogeneity of wireless portable devices identify novel challenges for service delivery in ubiquitous pervasive environments. An emerging architecture solution in the wireless Internet is to have middleware components (mobile proxies) over the fixed network that follow the movements and act on behalf of the limited wireless clients. It is crucial that mobile proxies have full visibility of their context, i.e., the set of available and relevant resources depending on access control rules, client location, user preferences, privacy requirements, terminal characteristics, and current state of hosting environments. The paper presents the design and implementation of a context-centric access control middleware, called COSMOS, for the wireless Internet. COSMOS dynamically determines the contexts of mobile proxies, and effectively rules the access to them, by taking into account different types of metadata (user profiles and system/user-level authorization policies), expressed at a high level of abstraction and cleanly separated from the service logic. The paper also shows how COSMOS facilitates the development of articulated access control strategies in the case study of a context-dependent movie-info service deployed over IEEE 802.11 network localities.

     
P. Bellavista, A. Corradi, R. Montanari, C. Stefanelli
Context-aware Middleware for Resource Management in the Wireless Internet
IEEE Transactions on Software Engineering, Special Issue on "Wireless Internet", Vol. 29, No. 12, pages, Dec. 2003.
Abstract. The provisioning of Web services over the wireless Internet introduces novel challenging issues for service design and implementation: from user/terminal mobility during service execution, to wide heterogeneity of portable access devices and unpredictable modifica-tions in accessible resources. In this scenario, there are frequent provision-time changes in the context, defined as the logical set of accessible resources depending on client location, access terminal capabilities, and system/service management policies. The development of context-dependent services requires novel middlewares with full context visibility. We pro-pose a middleware for context-aware resource management, called CARMEN, capable of supporting the automatic reconfiguration of wireless Internet services in response to context changes without any intervention on the service logic. CARMEN determines the context on the basis of metadata, which include declarative management policies and profiles for user preferences, terminal capabilities, and resource characteristics. In addition, CARMEN ex-ploits the mobile agent technology to implement mobile middleware components that fol-low the provision-time movement of clients to support locally their customized service ac-cess. The proposed middleware shows how metadata and mobile agents can favor compo-nent reusability and automatic service reconfiguration, by reducing the develop-ment/deployment complexity.

     
P. Bellavista, A. Corradi, C. Stefanelli
Application-level QoS Control and Adaptation for Video on Demand
IEEE Internet Computing, Vol. 7, No. 6, pages 16-24, Nov.-Dec. 2003.
Abstract. The increasing number of Internet users with different service requirements and the heterogeneity of wired/wireless access devices suggest differentiated quality levels in service provisioning. In particular, services with response time constraints, such as Video on Demand (VoD), require the differentiation, control and dynamic adaptation of Quality of Service (QoS). This paper discusses the guidelines of middleware solutions to support differentiated QoS in VoD services over best-effort networks. Novel VoD middlewares should take advantage of location awareness, to make possible effective distributed management operations, and should support dynamic adaptability, to enable VoD services to adapt to dynamic changes in resource availability and service conditions. This paper presents the ubiQoS middleware for Internet VoD: at service negotiation, ubiQoS supports QoS tailoring depending on user preferences and terminal properties; at provision time, it promptly reacts to modifications in resource availability via QoS-aware management operations on the provided VoD flows. ubiQoS exploits the Mobile Agent technology to achieve autonomous deployment and dynamic extensibility. ubiQoS components migrate at runtime depending on the location of client requests and on the possible congestion of network resources, with no need of any static pre-installation.

     
P. Bellavista, D. Bottazzi, A. Corradi, R. Montanari, S. Vecchi
Mobile Agent Middlewares for Context-aware Applications
Invited chapter in the book "Handbook of Mobile Computing", I. Mahgoub, M. Ilyas (eds.), ISBN 0-84931-971-4, CRC Press, Dec. 2004.
Abstract. Wireless communications and the Internet are converging towards an integrated scenario where both traditional and novel services should be ubiquitously accessible, independently of the mobility of users, terminals, resources and service components. Mobility-enabled service provisioning introduces several challeng-ing issues to address: from client/server location change at provision time, to wide heterogeneity of access terminals, and to unpredictable modifications in accessible resources. In this complex scenario, two main guidelines are recently emerging: the need for novel middleware solutions to support service development and deployment, and the necessity of full visibility of the context, intended as the logical set of accessible resources depending on client location, access terminal capabilities, and system/service management policies, to adapt service provisioning to specific runtime conditions. The chapter discusses and motivates the suitability of the Mobile Agent (MA) technology to implement novel context-aware middlewares for mobile computing, mainly because of the MA properties of mobility, asynchronicity, decentralization, and location awareness. In addition, the chapter gives an extensive overview of the state-of-the-art research activities about MA-based supports for mobile computing, and especially about context-aware ones, in order to point out, through system/prototype exemplifications, the main lessons learned and the primary directions of the on-going research work.

     
P. Bellavista, A. Corradi, C. Federici, R. Montanari, D. Tibaldi
Security for Mobile Agents: Issues and Challenges
Invited chapter in the book "Handbook of Mobile Computing", I. Mahgoub, M. Ilyas (eds.), ISBN 0-84931-971-4, CRC Press, Dec. 2004.
Abstract.

     
P. Bellavista, A. Corradi
A QoS Management Middleware based on Mobility Prediction for Multimedia Service Continuity in the Wireless Internet
Proceedings of the 9th IEEE International Symposium on Computers and Communications (ISCC'04), Alexandria, Egypt, June 29-31, 2004, pages 531-538, IEEE Computer Society Press.
Abstract. New challenging service scenarios are integrating mobile wireless devices with limited and heterogeneous capabilities. This not only calls for novel solutions to support different forms of mobility and connectivity in wired-wireless integrated networks, but also stresses the necessity of Quality of Service (QoS) tailoring and adaptation, especially in resource-consuming applications such as multimedia distribution. The paper presents Mobile ubiQoS, a Mobile Agent (MA) middleware to manage the QoS provisioning of multimedia content to client devices that roam in the wireless Internet. In particular, the paper focuses on how Mobile ubiQoS provides a portable solution to predict inter-cell mobility, without any external global positioning system. Mobility prediction permits to migrate personalized MAs, which tailor/adapt multimedia contents to both device profiles and user preferences, by anticipating user movements. This is crucial to proactively rearrange personalized sessions by maintaining service continuity. The adopted prediction solution is lightweight and decentralized, by exploiting the client-side monitoring information about the received signal strength of IEEE 802.11 base stations in a completely portable way. Both simulation and experimental results show that, notwithstanding the portable application-level approach, our middleware can predict the next user cell location enough in advance to support continuous multimedia services for the wireless Internet.

     
P. Bellavista, A. Corradi, L. Foschini
MUM: a Middleware for the Provisioning of Continuous Services to Mobile Users
Proceedings of the 9th IEEE International Symposium on Computers and Communications (ISCC'04), Alexandria, Egypt, June 29-31, 2004, pages 498-505, IEEE Computer Society Press.
Abstract. Advances in wireless solutions and portable devices are enabling new challenging service scenarios where mobile users are willing to access ubiquitous and continuous services. This calls for novel middleware capable of tailoring service contents to client characteristics and of following client movements at provision time. The paper proposes MUM, a dynamic and flexible middleware to support continuous services to mobile users in ubiquitous scenarios. MUM performs service configuration by dynamically distributing middleware components to intermediate nodes along the client-server path and provides service session continuity by automatically migrating the session state in response to user movements during service provisioning. MUM exploits mobile agents to move both middleware components and session state, where and when needed, while it allows service developers to continue using the traditional client/server model for MUM-based application components. In addition, the paper presents the implementation of a Video-on-Demand service on top of MUM, with the goal of verifying the feasibility of our approach when applied to the very challenging multimedia area. First experimental results show that, notwithstanding the application-level approach, the MUM configuration/session migration times are compatible even with the strict requirements imposed by multimedia distribution over the best-effort Internet.

     
P. Bellavista, A. Corradi, C. Stefanelli
Policy-based Access Control for Context-aware Services over the Wireless Internet
Peer-reviewed Chapter in the book "Advances in Security and Payment Methods for Mobile Commerce", Wen-Chen Hu, Chung-wei Lee, and Weidong Kou (eds.), ISBN 1-59140-345-6, Idea Group, Dec. 2004.
Abstract. The spreading wireless accessibility to the Internet stimulates the provisioning of mobile commercial services to a wide set of heterogeneous and limited client terminals. This requires novel programming methodologies to support and simplify the development of innovative service classes. In these novel services, results and offered quality levels should depend on both client location and locally available resources (context). In addition, it is crucial to manage the frequent modifications of resource availability due to wireless client movements during service provisioning. Within this perspective, the chapter motivates the need for novel access control solutions to flexibly control the resource access of mobile clients depending on the currently applicable context. In particular, it discusses and exemplifies how innovative middlewares for access control should support the determination of the client context on the basis of high-level declarative directives (profiles and policies) and distributed on-line monitoring.

     
P. Bellavista, C. Stefanelli, M. Tortonesi
The ubiQoS Middleware for Audio Streaming to Bluetooth Devices
Proceedings of the Annual International Conference on Mobile and Ubiquitous Systems: Networking and Services (Mobiquitous'04), Boston, USA, Aug. 2004, pages 138-145, AAAI, IEEE Computer Society, ACM SIGMOBILE and European Union's IST program.
Abstract. The full and seamless integration of wireless devices with traditional fixed networks is more and more important to foster the mobile and ubiquitous access to the Internet. In particular, the heterogeneity and resource limitations of wireless devices motivate novel support infrastructures that can facilitate the wired-wireless integration and can provide service tailoring depending on client characteristics. The paper presents an application-level portable middleware, called ubiQoS, for QoS-enabled audio streaming to Bluetooth clients. ubiQoS exploits support proxies for QoS tailoring and for managing the QoS over the last segment of the audio distribution path towards the clients, by using different types of Bluetooth links. Proxies execute at the wired-wireless network edges and can even migrate to follow the device movements, where and when needed. The reported experimental results show the feasibility of the application-level approach in the challenging case of QoS-enabled audio streaming to resource-limited Bluetooth devices.

     
P. Bellavista, A. Corradi, E. Magistretti
Lightweight Code Mobility for Proxy-based Service Rebinding in MANET
Proceedings of the International Symposium on Wireless Communication Systems (ISWCS'04), Mauritius, Sep. 2004, IEEE Computer Society Press.
Abstract. Advances in device miniaturization and wireless technologies are stimulating Mobile Ad-hoc NETworks (MANET) where mobile nodes can autonomously organize in a peer-to-peer mode, without requiring a statically deployed network infrastructure. Because of node mobility, the set of service components that MANET clients have at one-hop distance changes often during service provisioning. That continuous change in locally accessible services significantly increases the complexity of designing and implementing effective MANET applications. The paper claims the need of dynamic middleware supports for MANET, not only to address routing/configuration issues, but also to automate the re-qualification of service bindings at provision time. It presents COMMAND, a flexible middleware solution, based on code mobility, for transparent service rebinding in MANET. COMMAND exploits dynamically elected proxies that act as intermediaries to decouple mobile clients and needed service components. In particular, the paper focuses on how COMMAND implements a lightweight MANET-specific solution for effective code distribution to deploy the needed proxy behavior only when and where required. Finally, the paper shows the implementation of a COMMAND-based forum distributed application, together with its related performance, to point out how the proposed middleware can help service development in MANET.

     
P. Bellavista, A. Corradi, C. Giannelli
Mobility Prediction for Mobile Agent-based Service Continuity in the Wireless Internet
Proceedings of the 1st International Workshop on Mobility Aware Technologies and Applications (MATA'04), Florianopolis, Brazil, Oct. 2004, pages 1-12, Sprinter-Verlag Lecture Notes on Computer Science.
Abstract. New challenging deployment scenarios are integrating mobile devices with limited and heterogeneous capabilities that roam among wireless access localities during service provisioning. This calls for novel middleware solutions not only to support different forms of mobility and connectivity in wired-wireless integrated networks, but also to perform personalized service reconfiguration/adaptation de-pending on client characteristics and in response to changes of wireless access lo-cality. The paper proposes the adoption of Mobile Agent (MA) proxies working at the wired-wireless network edges to support the personalized access of limited wireless clients to their needed resources on the fixed network. In particular, the paper focuses on how to predict device mobility between IEEE 802.11 cells in a portable lightweight way, with no need of external global positioning systems. In fact, we claim that mobility prediction is crucial to maintain service continuity: MA-based proxies can migrate in advance to the wireless cells where mobile clients are going to reconnect to, in order to anticipate the local rearrangement of personalized sessions. The paper proposes and evaluates different mobility prediction solutions based on either client-side received signal strength or Ekahau positioning, all integrated in the SOMA platform. Both simulation and experimental results show that SOMA can predict the next visited cell with a very limited overhead and enough in advance to maintain service continuity for a large class of wireless Internet services.

     
A. Corradi, R. Montanari, D. Tibaldi
Context-based Access Control Management in Ubiquitous Environment
Proceeding of the 3rd IEEE International Symposium on Network Computing and Applications (IEEE NCA04), , IEEE Computer Society Press, Cambridge, MA, USA, August 30 - September 1, 2004.
Abstract. Wireless connectivity and the the widespread diffusion of portable devices of portable devices with wireless connectivity raise new challenges for ubiquitous service provisioning. Mobility of users determinescauses frequent and unpredictable changes in the user location and consequently in consequently available resources.; Access controlling to resources is crucial to leverageage the provision of ubiquitous services and calls for novel solutions that controlling the access to resources dependingbased on various context information, e.g., user location, device properties, user needs, local resource visibility. This paper presents a novel access control model that proposes the adoption of context as a first-class design principle for governing to rule the access to resources. The paper proposes a context-centric access control middleware, called UbiCOSM, that dynamically determines the contexts of mobile users and effectively rules the access to them, by taking into account different types of metadata: user profiles and system/user-level authorization policies. The paper also presents a context-dependent movie-info service to evaluate the functioning of UbiCOSM.

     
P. Bellavista, C. Stefanelli, M. Tortonesi
Middleware-level QoS Differentiation in the Wireless Internet: the ubiQoS Solution for Audio Streaming over Bluetooth
Proceedings of the 1st International Conference on Quality of Service in Heterogeneous Wired/Wireless Networks (QShine'04), Dallas, USA, October 2004, pages 172-180, IEEE Computer Society Press.
Abstract. The ultimate goal of mobile and ubiquitous Internet accessibility is not only the seamless integration of wireless devices with traditional fixed networks but also the dynamic differentiation of the provided levels of Quality of Service (QoS) depending on client characteristics. In this context, the paper presents the provisioning of audio streaming with different QoS levels in the application-level ubiQoS middleware. In particular, it focuses on how ubiQoS manages the QoS over the last segment of the audio distribution path towards Bluetooth clients by allocating different types of Bluetooth communication channels (unicast connection-oriented or broadcast connectionless) depending on the differentiated QoS requirements of different user classes. To this purpose, we have designed and implemented a library that extends the JSR82 standard specification with the support of Ac-tive Slave Broadcast, thus simplifying the Java-based management of Bluetooth communications. The reported experimental results show the feasibility of our application-level middleware approach in the challenging case of audio streaming with differentiated QoS to resource-limited Bluetooth devices.

     
A. Corradi, R. Montanari, D. Tibaldi
Context-based Access Control for Ubiquitous Service Provisioning
Proceedings of the 28th Annual International Computer Software and Applications Conference (COMPSAC 2004), Hong Kong, September 28 - 30, 2004, pages 444-501, Conference Proceedings, IEEE Computer Society Press.
Abstract. Pervasive user mobility, wireless connectivity and the widespread diffusion of portable devices raise new challenges for ubiquitous service provisioning. In particular, mobility of users/devices causes frequent and unpredictable changes in physical user location and in consequently available resources and services. Users can also change portable access devices, with different capabilities, even at runtime and during the same service session, thus forcing us to consider very dynamic aspects even due to client heterogeneity. Access control to resources is crucial to leverage the provision of ubiquitous services and calls for novel solutions based on various context information, e.g., user/device location, device properties, user needs, local resource visibility. This paper presents a novel access control model built upon the concept of context as the first-class design principle to rule access to resources. As key features, this model allows to associate access control permissions with contexts where users operate and users acquire/lose their permissions when entering/leaving a specific context. Unlike traditional access control solutions where user identity/role triggers policy evaluation when requesting resource access, this model exploits the user context to fully determine the set of available permissions. In addition, the proposed model allows to express context-based access control policies at a high level of abstraction cleanly separate from service logic implementation, thus promoting dynamic policy modification with no impact on the service code. The paper shows the implementation of the proposed model in the UbiCOSM framework and presents a mobile office service provisioning scenario.

     
A. Corradi, R. Montanari, D. Tibaldi, A. Toninelli
A Context-centric Security Middleware for Service provisioning in Pervasive Computing
Proceedings of the IEEE/IPSJ International Symposium on Applications and the Internet (SAINT2005), Trento, Italy, January 31 - February 4, 2005, IEEE Computer Society Press.
Abstract. Pervasive user mobility, wireless connectivity and the widespread diffusion of portable devices raise new challenges for ubiquitous service provisioning. An emerging architecture solution in the wireless Internet is based on mobile proxies (implemented as mobile agent-based middleware components) over the fixed network that follow the movements and act on behalf of the limited wireless clients. It is crucial that mobile proxies have full visibility of their context, i.e., the set of available and relevant resources, depending on access control rules, client location, user preferences, privacy requirements, terminal characteristics, and current state of hosting environments. The paper presents the design and implementation of a context-centric security middleware, called UbiCOSM, for MA-based service provisioning in pervasive computing. UbiCOSM dynamically determines the contexts of mobile proxies, and effectively rules the access to them, by taking into account different types of metadata (user profiles and authorization policies), expressed at a high level of abstraction and cleanly separated from the service logic. The paper also shows the functioning of UbiCOSM in the design and the development of a mobile context-centric airport business assistant.

     
A. Corradi, R. Montanari, D. Tibaldi
A Context-driven Adaptation of Trust Relationships in Pervasive Collaborative Environments
Proceedings of the IEEE/IPSJ International Symposium on Applications and the Internet (SAINT2005) Workshop on Context-aware Adaptation and Personalization for the Mobile Internet, Trento, Italy, January 31, 2005, IEEE Computer Society Press.
Abstract. The growing diffusion of portable devices with wireless connectivity and the integration of telecommunication systems and the Internet enable users to benefit from anytime and anywhere impromptu collaboration. Security is crucial to ensure secure sharing of information, but calls for novel solutions capable of establishing trust relationships on-the-fly among previously unknown entities. Traditional trust solutions seem to be inappropriate in dynamic mobile environments. They typically rely on centralised trust certification authorities and assign to entities levels of trust that depend on static entity attributes, such as entity identity or role. However, entity identities/roles are often either not sufficiently informative or too limited to take adequate collaborative decisions. This paper presents a novel trust model that rules the assignment of trust to entities based on various dynamic context information, e.g., user/device location, device properties, user needs, local operating conditions. As key features, this model allows to determine, to associate and to adapt entity levels of trust depending on the contexts where users operate and users acquire/lose a level of trust when entering/leaving a specific context. The proposed model facilitates the update of trust relationships as relevant changes in context information occur. The paper also shows the implementation of the proposed model in the COMITY framework that provides support facilities for defining and enforcing context-based trust policies.

     
A. Corradi, R. Montanari, A. Toninelli
Adaptive Semantic Support Provisioning in Mobile Internet Environments
Proceedings of the IEEE/IPSJ International Symposium on Applications and the Internet (SAINT2005) Workshop on Context-aware Adaptation and Personalization for the Mobile Internet, Trento, Italy, January 31, 2005, IEEE Computer Society Press.
Abstract. The Mobile Internet scenario encourages the design and development of context-aware applications that provide results depending on context information, such as the relative position of users, user preferences, device capabilities and available resources. A key requirement for the provisioning of context-aware applications is to give computer systems the ability to understand context information. Semantic languages are well suited to leverage the possibility to express, process and reason about context information and to facilitate knowledge sharing and interoperability among previously unknown entities accessing services from heterogeneous devices. However, the exploitation of semantic languages for the design and deployment of context-aware applications raises new challenges, mainly due to the high degree of heterogeneity that mobile devices exhibit in terms of computing power, memory, operating system, and supported software. Semantic languages require complex and heavyweight support facilities, e.g. metadata interpreters, reasoning engines and ontology repositories, that may not fit the capabilities of all user access devices, especially of the resource-limited ones. Novel solutions are required that are capable of transparently and dynamically adapting semantic support functionalities to the properties of the different user access devices. The paper proposes a novel middleware solution that exploits the visibility of two kinds of metadata, user/device profiles and policies, to tailor semantic support functionalities and that offers a wide set of mechanisms for providing on demand appropriate semantic support to mobile portable devices.

     
P. Bellavista, A. Corradi, L. Foschini
MUMOC: an Active Infrastructure for Open Video Caching
Proceedings of the First International Conference on Distributed Frameworks for Multimedia Applications (DFMA'05), Besançon, France,
February 6-9, 2005, IEEE Computer Society Press.
Abstract. Advances in networking and content delivery systems are enabling new challenging provisioning scenarios where a growing number of users access Video on Demand (VoD), possibly while moving among different points of attachment to the Internet and using different access terminals. This calls for novel middlewares capable of supporting personalized VoD access by dynamically activating intermediate nodes between VoD servers and clients. The paper proposes MUMOC, a dynamic and flexible overlay infrastructure for the distributed caching of both VoD prefixes and VoD metadata. To achieve openness and easy interoperability with legacy VoD services, MUMOC adopts standard XML-based formats, based on both Dublin Core and MPEG7, to represent VoD metadata. First experimental results show that MUMOC significantly reduces bandwidth utilization and user perceived delays. In addition, notwithstanding the dynamic building of the overlay network and the application-level approach, the introduced overhead is compatible with the strict requirements imposed by multimedia distribution over the best-effort Internet.

     
P. Bellavista, A. Corradi, E. Magistretti
REDMAN: a Decentralized Middleware Solution for Cooperative Replication in Dense MANETs
To be published in the proceedings of the 2nd International Workshop on Middleware Support for Pervasive Computing (PerWare'05), Kauai, USA, March 8, 2005, in conjunction with the Thrid IEEE International Conference on Pervasive Computing and Communications (PerCom'05), IEEE Computer Society Press.
Abstract. The mass market of wireless devices is pushing towards service provisioning over dense Mobile Ad-hoc NETworks (MANETs), i.e., limited spatial regions, such as university campuses, airports and shopping malls, where many mobile wireless peers autonomously cooperate, without the need of statically deployed support infrastructures. Dense MANETs can take advantage of high node population to replicate resources of common interest to increase their availability overcoming unpredictable node movements. The paper proposes a lightweight application-level middleware, called REDMAN, to manage, retrieve and disseminate replicas of data and service components transparently from the point of view of service developers, thus facilitating the realization of scalable distributed applications for dense MANETs. REDMAN proposes novel lightweight solutions, specific for and effective in dense MANETs, to determine dense region boundaries, to perform resource cloning/distribution/ retrieval, and to approximately maintain the desired resource replication degree.

     
A. Toninelli, A. Corradi, R. Montanari,
Semantic Discovery for Context-Aware Service Provisioning in Mobile Environments
Proceedings of the First International Workshop on Managing Context Information in Mobile and Pervasive Environments (MCMP'05), Agya Napa, Cyprus, May 9, 2005, in conjunction with the Sixth International Conference on Mobile Data Management (MDM'05), CEUR-WS.
Abstract. Advances in telecommunication and wireless systems together with the increasing diffusion of portable devices are enabling a pervasive and ubiquitous computing infrastructure for service provisioning, where mobile users expect to access the needed data from ubiquitous attachment points and require context-aware services, i.e., services that can adapt provided results to changing context information, such as variations in user relative position, in user requirements, and in locally available resources. A crucial requirement for the provisioning of context-aware services is the dynamical retrieval and interaction with local resources, i.e., discovery. Traditional discovery solutions, which are essentially based on the exact matching of syntactic patterns, like for instance identifiers, interfaces or keywords, cannot be flexible enough to effectively deal with the heterogeneity typical of mobile and pervasive environments. Recent research efforts that exploit semantic, i.e., meaning-based, techniques for the discovery of services have emerged and proved to be able to overcome this kind of limitations. However, semantic-enabled discovery solutions still seem to be underestimated within the pervasive community. In this paper we propose a middleware that supports the intelligent discovery of context-aware services for mobile users, by providing an automatic tool that enable users to specify service queries at a high level of abstraction and a semantics-based matching functionality.

     
P. Bellavista, A. Corradi, L. Foschini
Java-based Proactive Buffering for Multimedia Streaming Continuity in the Wireless Internet
Poster paper in the proceedings of the First IEEE International Symposium on a World of Wireless, Mobile and Multimedia Networks (WoWMoM'05), Taormina, Italy, June 13-16, 2005, IEEE Computer Society Press.
Abstract. New challenging deployment scenarios are accommodating portable devices with limited and heterogeneous capabilities that roam among wireless access localities during service provisioning with session continuity requirements, such as in multimedia streaming. The paper proposes an original two-level buffering strategy to maintain streaming continuity independently of client roaming at provision time. In particular, it focuses on a specific component of the proposed support infrastructure, i.e., the pure Java buffering component, which has shown to outperform the standard Java Media Framework in both streaming initialization time and imposed overhead.

     
R. Montanari, A. Toninelli, J.M. Bradshaw
Context-based Security Management for Multi-Agent Systems
Proceedings of the IEEE Symposium on Multi-Agent Security and Survivability (MAS&S'05), Philadelphia, USA, August 30, 2005, IEEE Conference Proceedings.
Abstract. Policies are being increasingly used for controlling the behavior of complex multi-agent systems. The use of poli-cies allows administrators to specify both agent permis-sions and duties without changing source code or requiring the consent or cooperation of the agents being governed. However, policy-based control can encounter difficulties when applied to agents that act in pervasive environments characterized by frequent and unpredictable changes. In this case, policies cannot be all specified a priori to face any operative run time situation, but require continuous adjustments to allow agents to behave in a contextually appropriate manner. Current approaches to policy repre-sentation have been restrictive in many ways, as they typi-cally follow a subject-centric model, which assigns agent permissions and obligation on the basis of agent role/identity information. However, in the new pervasive scenario the roles/identities of interacting agents may not be known a-priori and most important, may not be informative or sufficiently trustworthy. We claim that the design of policy-based agent systems for pervasive environments requires a paradigm shift from subject-centric policy mod-els to context-centric ones. This paper discusses some is-sues concerning the specification and enforcement of con-text-driven policies and presents a novel context-based policy approach that considers context as a first-class principle to guide both policy specification and enforce-ment. In this perspective, “context” explicitly appears in the specification of security policies and context changes trigger the evaluation process of applicable agent permis-sions and obligations.

     
P. Bellavista, A. Corradi, L. Foschini
Application-level Middleware to Proactively Manage Handoff in Wireless Internet Multimedia
Proceedings of the 8th International Conference on Management of Multimedia Networks and Services (MMNS'05), Barcelona, Spain, October 24-26, 2005, Springer Verlag.
Abstract. New deployment scenarios tend to consider the requirement of session continuity for service provisioning, especially multimedia streaming, to limited heterogeneous portable devices roaming among wireless localities. In particular, multimedia streaming should not experience any interruption while clients roam in wired-wireless integrated networks based on the standard best-effort Internet. The paper proposes an application-level middleware approach to proactively overcome Wi-Fi handoff and maintain multimedia session continuity in the wireless Internet by exploiting mobile proxies running on the wired network. Mobile middleware proxies locally support resource-limited clients, avoid packet losses during handoffs, prefetch local buffers with multimedia contents before handoff occurrence, and possibly reconfigure/renegotiate ongo-ing sessions after handoffs. Experimental results show that, notwithstanding the application-level implementation, mobile proxies can avoid streaming discontinuities with good efficiency in wireless-wired integrated networks even if their pro-activity is based on simple and lightweight handoff prediction techniques.

     
A. Toninelli, J.M. Bradshaw, L. Kagal, Rebecca Montanari
Rule-based and Ontology-based Policies: Toward a Hybrid Approach to Control Agents in Pervasive Environments
Pproceedings of the Semantic Web and Policy Workshop (SWPW'05), Galway, Ireland, November 7, 2005, in conjunction with the Fourth International Semantic Web Conference (ISWC'05).
Abstract. Policies are being increasingly used for controlling the behavior of complex multi-agent systems. The use of policies allows administrators to regulate agent behavior without changing source code or requiring the consent or cooperation of the agents being governed. However, policy-based control can sometimes encounter difficulties when applied to agents that act in pervasive environments characterized by frequent and unpredictable changes. In such cases, we cannot always specify policies a priori to handle any operative run time situation, but instead require continuous adjustments to allow agents to behave in a contextually appropriate manner. To address these issues, some policy approaches for governing agents in pervasive environments specify policies in a way that is both context-based and semantically-rich. Two approaches have been used in recent research: an ontology-based approach that relies heavily on the expressive features of Description Logic (DL) languages, and a rule-based approach that encodes policies as Logic Programming (LP) rules. The aim of this paper is to analyze the emerging directions for the specification of semantically-rich context-based policies, highlighting their advantages and drawbacks. Based on our analysis we describe a hybrid approach that exploits the expressive capabilities of both DL and LP approaches.

     
P. Bellavista, M. Cinque, D. Cotroneo, L. Foschini
Integrated Support for Handoff Management and Context Awareness in Heterogeneous Wireless Networks
Proceedings of the 3rd International Workshop on Middleware for Pervasive Ad-Hoc Computing (MPAC'05), held in conjunction with Middleware 2005, Grenoble, France, Novermber 28-December 2, 2005, ACM Press.
Abstract. The overwhelming success of mobile devices and wireless communications is stressing the need for the development of mobility-aware services. Device mobility requires services adapting their behavior to sudden context changes and being aware of handoffs, which introduce unpredictable delays and intermittent discontinuities. Heterogeneity of wireless technologies (Wi-Fi, Bluetooth, 3G, …) complicates the situation, since a different treatment of context-awareness and handoffs is required for each solution. This paper presents a middleware architecture designed to ease mobility-aware service development. The proposed architecture hides technology-specific mechanisms and offers a set of facilities for context awareness and handoff management. The architecture prototype works with Bluetooth and Wi-Fi, which today represent two of the most widespread wireless technologies. In addition, the paper discusses motivations and design details in the challenging context of mobile multimedia streaming applications.

     
P. Bellavista, A. Corradi, L. Foschini
Proactive Management of Distributed Buffers for Streaming Continuity in Wired-Wireless Integrated Networks
Proceedings of the 10th IEEE/IFIP Network Operations and Management Symposium (NOMS'06), Vancouver, Canada, April 3-7, 2006, IEEE Computer Society Press.
Abstract. New challenging deployment scenarios are accommodating limited and heterogeneous portable devices that roam among wireless access localities during service provisioning with session maintenance and continuity requirements, such as in multimedia streaming. That calls for novel middlewares able to dynamically personalize service quality, with no interruptions while clients move in wired-wireless integrated networks at provision time. The paper proposes a middleware-level proactive buffering solution for streaming continuity based on mobile proxies. Mobile proxies execute in the wired network locally to their wireless clients and proactively migrate to maintain co-locality with associated roaming devices. In addition, apart from traditional client-side buffering, mobile proxies proactively manage pre-fetching buffers of multimedia contents by dynamically adapting buffer size to the current context such as handoff probability, client/streaming characteristics, and user service class. Experimental results show that, notwithstanding portable Java-based implementation, our context-aware proactive and adaptive buffering does not experience streaming interruptions in most common wireless Internet deployment scenarios.

     
P. Bellavista, A. Corradi, L. Foschini
SIP-Based Proactive Handoff Management for Session Continuity in the Wireless Internet
Proceedings of the 2nd IEEE International Workshop on Services and Infrastructure for the Ubiquitous and Mobile Internet (SIUMI'06), held in conjunction with the 26th International Conference on Distributed Computer Systems (ICDCS'06), Lisboa, Portugal, July 4-7, 2006, IEEE Computer Society Press.
Abstract. New challenging deployment scenarios are accom-modating limited and heterogeneous portable devices that roam in wired-wireless best-effort networks with session maintenance and continuity requirements. In particular, continuous services, e.g., multimedia streaming, should not experience any interruption while clients roam between different wireless access localities during service provisioning. The paper de-scribes how to exploit the Session Initiation Protocol (SIP) to build a middleware for session continuity, also by integrating with our novel context-aware SIP notifi-cation package. In particular, the proposed middle-ware makes use of SIP notifications to update session information and to proactively activate session recon-figuration for roaming clients. Experimental results show that, notwithstanding the portable Java-based implementation, our SIP-based solution is feasible in most common wireless Internet deployment scenarios and achieves good scalability.

     
P. Bellavista, A. Corradi, L. Foschini
Middleware for Handoff Management in Wireless Intenet Mobile Multimedia
To be published as chapter (from open call) in the book "Broadband Mobile Multimedia: Techniques and Applications", Yan Zhang, Shiwen Mao, Laurence T. Yang, Thomas Chen (eds), Taylor&Francis, Dec. 2007.
Abstract. Advances in wireless networking and content delivery systems are enabling new challenging scenarios where access to multimedia services as audio and video streaming should be provided to a growing number of users that move between different points of attachment to the Internet, possibly with different connectivity technologies (Wi-Fi, Bluetooth, and 3G cellular). That calls for novel middlewares capable of dynamically personalizing service provisioning to the characteristics of client environments, in particular to achieving service continuity during handoff and consequent discontinuities in wireless resource availability. This chapter proposes a general framework starting from main handoff-related problems and requirements, to identify main handoff management design guidelines, and ends proposing an extensive survey of state-of-art middlewares for handoff management; the chapter completes by sketching current industry handoff standardization directions and open research issues.

     
P. Bellavista, A. Corradi, L. Foschini
Context-Aware Multimedia Middleware Solutions for Counteracting IEEE 802.11 Performance Anomaly
Proceedings of the 1st International Conference on Multimedia and Ubiquitous Engineering (MUE'07), Seoul, Korea, April 26-28, 2007, IEEE Computer Society Press.
Abstract. Multimedia provisioning over Wi-Fi networks is a complex task that should consider also novel issues stemming from the specific behavior of IEEE 802.11 protocols. In particular, we claim the need for visibility of context data about the IEEE 802.11 performance anomaly, i.e., the situation where even a single node located at the borders of the coverage area of a Wi-Fi access point produces a relevant degradation in the connectivity quality of all other nodes in the area. The paper proposes a novel application-level middleware that counteracts IEEE 802.11 anomaly without imposing any modification in standard Wi-Fi protocols, thus permitting to maintain the current wide base of installed equipment. Our middleware portably detects anomaly situations via decentralized standard mechanisms available at clients; anomaly awareness is used to promptly react with application-level management operations (flow quality downscaling and traffic shaping) that both preserve the goodput at nodes in well-covered areas and minimize quality degradations at clients generating the anomaly. The reported experimental results point out the feasibility of application-level middleware approaches also in the challenging multimedia area.

     
P. Bellavista, A. Corradi, L. Foschini
Context-Aware Handoff Middleware for Transparent Service Continuity in Wireless Networks
Accepted for publication in the Elsevier Pervasive and Mobile Computing Journal, Sep. 2007.
Abstract. Advances in wireless networking and content delivery are enabling new challenging provisioning scenarios where a growing number of users access continuous services, e.g., audio/video streaming, while moving among dif-ferent points of attachment to the Internet, possibly with different connec-tivity technologies, e.g., Wi-Fi, Bluetooth, and cellular 3G. That calls for novel middlewares capable of dynamically personalizing service provision-ing to the characteristics of client environments, in particular to discontinui-ties in wireless resource availability due to handoffs. The paper proposes a novel middleware solution, called Mobile agent-based Ubiquitous multi-media Middleware (MUM), that performs effective and context-aware handoff management to transparently avoid service interruptions during both horizontal and vertical handoffs. MUM exploits the full visibility of wireless connections available and their handoff implementations (handoff awareness), of service quality requirements and handoff-related quality de-gradations (QoS awareness), and of network topology and local resource availability (location awareness); that visibility enables MUM to provide original solutions for handoff prediction, multimedia continuity via adap-tive data buffering/pre-fetching, and proactive re-addressing/rebinding.

     
P. Bellavista, A. Corradi, L. Foschini
The MUM Middleware to Counteract IEEE 802.11 Performance Anomaly in Context-aware Multimedia Provisioning
Accepted for publication in the International Journal of Multimedia and Ubiquitous Engineering, SERSC Publisher, July 2007.
Abstract. Multimedia provisioning over Wi-Fi networks is a complex task that should consider also novel issues stemming from the specific behavior of IEEE 802.11 protocols. In particular, we claim the need for visibility of context data about the IEEE 802.11 performance anomaly, i.e., the situation where even a single node located at the borders of the coverage area of a Wi-Fi access point produces a relevant degradation in the connectivity quality of all other nodes in the area. The paper proposes a novel application-level middleware that counteracts IEEE 802.11 anomaly without imposing any modification in standard Wi-Fi protocols, thus permitting to maintain the current wide base of installed equipment. Our middleware portably detects anomaly situations via decentralized standard mechanisms available at clients; anomaly awareness is used to promptly react with application-level management operations (flow quality downscaling and traffic shaping) that both preserve the good-put at nodes in well-covered areas and minimize quality degradations at clients generating the anomaly. The reported experimental results point out the feasibility of application-level middleware approaches also in the challenging multimedia area.

     
P. Bellavista, A. Corradi, M. Fanelli, L. Foschini
A Survey of Context Data Distribution for Mobile Ubiquitous Systems
Accepted for publication in ACM Computing Surveys (CSUR), ACM Press, expected to appear in Vol. 45, No. 1, Mar. 2013, pages 1-49.
Abstract. The capacity to gather and timely deliver to the service level any relevant information that can characterize service-provisioning environment, such as computing resources/capabilities, physical device location, user preferences, and time constraints, usually defined as context-awareness, is widely recognized as a core function for the development of modern ubiquitous and mobile systems. Much work has been done to enable context-awareness and to ease the diffusion of context-aware services; at the same time, several middleware solutions have been designed to transparently implement context management and provisioning in the mobile system. However, to the best of our knowledge, an in-depth analysis of the context data distribution, namely the function in charge of distributing context data to interested entities, is still missing. Starting from the core assumption that only effective and efficient context data distribution can pave the way to the deployment of truly context-aware services, this paper aims at putting together current research efforts to derive an original and holistic view of the existing literature. We present a unified architectural model and a new taxonomy for context data distribution, by considering and comparing a large number of solutions. Finally, based on our analysis, we draw some of the research challenges still unsolved and we identify some possible directions of future work.

About this Server
About this Server		 Mail to DocMaster
DocMaster		 Mail to WebMaster
LIA WebMaster
 
[LIA Home] [LIA Research] [DEIS Research] [DEIS Home] [Alma Mater Home]