A large-scale volunteer computing system is a type of distributed system in which contributors volunteer their computing resources, such as personal computers or mobile devices, to contribute to a larger computing effort. Volunteer resources are connected over the Internet and together form a powerful computing system capable of providing a service without depending on a service provider. Volunteer network resource allocation is the process of assigning computing tasks or services to a network of volunteer resources. The allocation process includes identifying the needed resources, selecting appropriate volunteers, and assigning tasks or services based on their capabilities. Volunteer computing systems consist of a large number of heterogeneous resources - in terms of processing power, storage, and availability - belonging to different authorities - users or organizations - and exhibiting uncertain behavior in terms of connection, disconnection, capacity, and failure. All of this makes resource allocation a challenging task in terms of ensuring a minimum quality of service, requiring complex algorithms and optimization techniques to ensure that services are efficiently allocated while respecting the constraints of the available resource. This paper introduces the Network-Aware Resource Allocation mechanism, which leverages the location, connectivity, and network latency of volunteer nodes to minimize the time a service runs with degraded quality of service and aims to deal with the energy consumption resulting from data replication requirements. This resource allocation mechanism applies to both the initial deployment of the service in the network and to the reallocation of nodes in the event that one of the allocated nodes fails or becomes unavailable. Our method has been validated in a simulation environment of a realistic volunteer system. The analysis of the results shows how our mechanism meets the quality requirements of users while minimizing the synchronization and replication times of service data replicas, as well as the time that services run with degraded quality of service, reducing the times by more than 70% in the service deployment phase and by more than 60% in the service execution phase. It also helps to reduce overall energy consumption.

Online Social Networks (OSNs) have gained enormous popularity in recent years. They provide a dynamic platform for sharing content (text messages or multimedia) and for facilitating communication between friends and acquaintances. Microblogging services are a popular form of OSNs. They allow sending small messages in a one-to-many messaging model so that users can communicate with their favorite celebrity, brand, politician, or other regular users without the obligation of a pre-existing social relationship. A chain of privacy-related scandals linked to questionable data handling practices in microblogging services has arisen in the last past few years. Most current microblogging service providers offer centralized services and their business model is based on monitoring, analyzing, and selling users’ activity and patterns. In the end, the personal information shared by the users to benefit from the free-of-charge services is used for the underlying payment in such systems. In this paper, we present Garlanet, a privacy-aware censorship-resistant microblogging social network that does not rely on a centralized service provider as all data is hosted in computers voluntarily contributed by the users of the system. Garlanet provides microblogging functionalities while protecting privacy and preserving the confidentiality and integrity of users and data. It ensures that users’ identities and their social graphs are hidden from the system and adversaries and it provides availability and scalability of the services. We also evaluate the privacy level of Garlanet and we compare it with the privacy level of eight other microblogging systems.

Online courses heavily relying on programming skills tend to be difficult and time-consuming for students, who may get frustrated when stuck in an assignment. Obviously, this may increase drop-out rate and decrease academic performance as well as students’ satisfaction with the course and the institution in general. In this context, we propose a notification, recommendation and monitoring system which is integrated into an automatic assessment tool with the aim to enhance the learning process in virtual classrooms. In particular, notifications, recommendations and visualization reports are used to show the activity, progress and performance of all students. The system is implemented in a distributed computing course in an online university. A quantitative analysis method used to collect and analyze data of students’ perceptions regarding the system showed that: (1) notifications helped students organize their time and encourage them to work more effectively; (2) recommendations allowed students to receive useful and timely scaffolding for coping with their problems and completing their assignment; and (3) visualization reports provided valuable insights toward monitoring the learning process. Moreover, the analysis of correlations showed that the reception of recommendations and the visualization reports is related to encourage students to do more executions and to start earlier the assignments. Finally, this study seeks to contribute to online teachers’ endeavor to enhance students’ engagement, performance and learning in the field of programming (and not only).

Over the course of the last decades there has been significant growth in smartphone penetration and capacities. This trend presently complements the rise of IoT and ever complex and smarter connected devices. On balance, considerable contribution has been made to the emergence of unprecedented computing capacity at the edge of the network, which is only expected to have a long-lasting impact with the rise of connected vehicles, robots and drones. Considering the abovementioned context, computing will cease to be confined to certain devices located into large data centers or stationary edge devices, instead it will be embedded and pervasive to virtually everything. This paper provides a comprehensive framework for distributed and decentralized Edge Computing systems dynamically formed out of edge computing resources with the objective of harnessing the increasingly available computing at the edge. In order to facilitate this, we propose an architecture for this Ad-hoc Edge Computing infrastructure. Furthermore, two critical aspects for Resource Management are evaluated in the present framework: namely scalability and implications of node volatility.

Community Cloud computing is a new trend on cloud computing that aims to build service infrastructures upon Wireless Community Networks taking advantage of underused community physical resources. Service allocation protocols are a key design challenge that all cloud systems must properly address to optimize resource utilization. They are specially important when cloud services require a Quality of Service (QoS) and network stability or performance (delay, jitter, minimum bandwidth) cannot be guaranteed a-priory. This work presents a study that tries to understand how to address cloud service deployments in such scenario. In particular, we start proposing an allocation algorithm to find optimal solutions when there is a central authority that coordinates the process. These solutions optimize the communication cost in two ways: (1) minimizing the service overlay diameter and, (2) minimizing the coordination cost along the network. Based on the study of the algorithm and the experimental simulations, we study the variables that outcome optimal service allocations to the detriment of other solutions. We verify these findings using data mining techniques. Researchers can take advantage of the simulation results and our observations to design more reliable distributed algorithms able to dynamically self-adapt to network changes.

This paper presents a simple decentralized service deployment mechanism that can be used to offer services with high availability by using contributed resources with variable, possibly very low availability. It uses little information about the state of the group, and provides best-effort results. Contributory computer systems are those where users provide their own resources to be used collectively. Contributory applications are complex to build, as they have to deal with issues like unpredictable individual resource availability, heterogeneity and ease of use, as well as the complexities derived from their own functionalities. This complexity can be alleviated by creating a middleware for the creation of contributory communities that allows the use of contributed resources in a decentralized way through service deployment.

Large scale systems such as the Grid need scalable and efficient resource allocation mechanisms to fulfil the requirements of its participants and applications while the whole system is regulated to work efficiently. Economics inspired models have shown to efficiently allocate resources and services, scaling up well as they are decentralized. However most of existing implementations rely on a single market mechanism as a mean to handle resource allocation. Besides, in most of those approaches the allocation mechanism itself is neither flexible nor configurable, mostly designed for specific purposes such as scheduling one type of tasks. Nowadays, Grids are heterogeneous systems composed of multiple cohabitating resources and applications. Such heterogeneity requires complex mechanisms and usually cannot be achieved by a single type of allocation mechanism. Therefore, we aim to develop a generic approach to resource allocation in Grids able to support multiple cohabitating auctions. We claim that resource allocation frameworks may deal with heterogeneity by means of flexibility and configurability and they have to provide functionalities by which the allocation mechanism should be configured and adapted to application requirements and resource providers needs. This paper presents a configurable auction server architecture that enables dynamic configuration of markets so as to adapt them to the requirement of their initiators.

A commutative replicated data type (CRDT) is one where all concurrent operations commute. The replicas of a CRDT converge automatically, without complex concurrency control. This paper describes Treedoc, a novel CRDT design for cooperative text editing. An essential property is that the identifiers of Treedoc atoms are selected from a dense space. We discuss practical alternatives for implementing the identifier space based on an extended binary tree. We also discuss storage alternatives for data and meta-data, and mechanisms for compacting the tree. In the best case, Treedoc incurs no overhead with respect to a linear text buffer. We validate the results with traces from existing edit histories.

In this paper we present a proposal of the architecture for a system which allows the deployment of services in a group of computers, connected in a peer-to-peer fashion. This architecture is divided in layers, and each of them contains some components which offer specific functions. By putting them together, we obtain a system with desirable characteristics such as scalability, decentralization, ability to deal with heterogeneity, fault tolerance, load-balancing, and self-* properties.

The paper presents a bidding specification language and support tools for Grid-oriented open resource marketplaces. The structure of bids is based on trees that permit bidders to express their preferences for Grid resources by means of logical operators. Additionally, our bidding specification reduces the complexity of existing bidding languages since it permits imprecise description of user's preferences. One important issue not addressed so far is that of flexible bidding and offer configuration in open resource marketplaces where multiple market mechanisms cohabitate. Besides, the paper presents a support tool to adapt any bid to any type of market.

In this paper we present the design of a system which allows service deployment in a small-sized group of computers distributed through the Internet. These groups are formed by users who share a common interest, and voluntarily yield their own resources for the achievement of the collaborative activities of the group. Having enough resources contributed by the members of the group, our system guarantees service availability and the fact that the deployment and execution of the services is carried out using only the resources of the group. This management is done in a completely decentralized manner, and the system is self-organized in the presence of component connections, disconnections and failures. We demonstrate its validity through the implementation of a prototype and the execution of some tests, which allow us to guarantee that the system is self-organized, always reaching a consistent state.

The goal of this paper is to explore the possibility of using CSCL component-based software under a Grid infrastructure. The merge of these technologies represents an attractive, but probably quite laborious enterprise if we consider not only the benefits but also the barriers that we have to overcome. This work presents an attempt toward this direction by developing a generic platform of CSCL components and discussing the advantages that we could obtain if we adapted it to the Grid. We then propose a means that could make this adjustment possible due to the high degree of genericity that our library component is endowed with by being based on the generic programming paradigm. Finally, an application of our library is proposed both for validating the adequacy of the platform which it is based on and for indicating the possibilities gained by using it under the Grid.

The design of distributed systems for collaborative work or learning requires that both humans and machines be organized such that the potential and limitations of the human-machine interdependence is optimized. Current distributed architectures like peer-to-peer and Grids have not yet been optimized to support the needs of collaborative applications. In this paper, we investigate the requirements of collaborative applications for groups and, discuss current Grid and P2P architectures with regards to this. need. We suggest possible extensions described in a "function dispersion architecture". Finally, we present as case study our recent work on the design of a middleware to provide services for distributed collaborative applications that has been validated by simulation and prototyping.

In this paper, the authors explore the different processes involved in constructing effective virtual collaborative learning groups, especially why, when and how these processes affect group formation and to which degree they guarantee the creation of well-functioning and successful learning groups. A student can benefit from collaborative learning only if he/she participates in supportive learning teams. For this reason, their research interest is to aid and provide the means for the configuration of learning groups that are appropriate for different learning situations. A key issue in this process is to make the educational function and structure of collaborative learning groups clear, by identifying and making explicit both the individual and group learning and social goals, as well as the relationships, interaction processes and roles that determine the nature and idiosyncrasy of the group.

Group learning at Internet scale is becoming more frequent in university courses. This complex process requires support by distributed computing learning support infrastructures.This paper describes the design of WWG (World-Wide Groups): a distributed and decentralized infrastructure with the aim of supporting distributed group learning and team work, centered on the distribution of events, so that every participant can be notified and thus be aware of the actions, changes, progress of the groups he belongs to.The design issues, requirements and the resulting architecture are presented. WWG is based on a multi-component architecture where metainformation agents are responsible for helping the events to reach the members of the group; the repository agents are responsible for the storage of group information; and user agents are responsible for the representation of users (sources and sinks of events). In this paper we tried to show that, applying events transformation policies, WWG is scalable at group level.