Leandro Navarro

A case for research with and on community networks

Community Networks are large scale, self-organized and decentralized networks, built and operated by citizens for citizens. In this paper, we make a case for research on and with community networks, while explaining the relation to Community-Lab. The latter is an open, distributed infrastructure for researchers to experiment with community networks. The goal of Community-Lab is to advance research and empower society by understanding and removing obstacles for these networks and services.

Topology patterns of a community network: Guifi.net

This paper presents a measurement study of the topology and its effect on usage of Guifi.net, a large-scale community network. It focuses on the main issues faced by community network and lessons to consider for its future growth in order to preserve its scalability, stability and openness. The results show the network topology as an a typical high density Scale-Free network with critical points of failure and poor gateway selection or placement. In addition we have found paths with a large number of hops i.e. large diameter of the graph, and specifically long paths between leaf nodes and web proxies. The usage analysis using a widespread web proxy service confirms that these topological properties have an impact on the user experience.

Catallaxy-based Grid markets

Grid computing has recently become an important paradigm for managing computationally demanding applications, composed of a collection of services. The dynamic discovery of services, and the selection of a particular service instance providing the best value out of the discovered alternatives, poses a complex multi-attribute n:m allocation decision problem, which is often solved using a centralized resource broker. To manage complexity, this article proposes a two-layer architecture for service discovery in such Application Layer Networks (ALN). The first layer consists of a service market in which complex services are translated to a set of basic services, which are distinguished by price and availability. The second layer provides an allocation of services to appropriate resources in order to enact the specified services. This framework comprises the foundations for a later comparison of centralized and decentralized market mechanisms for allocation of services and resources in ALNs and Grids.

The catallaxy approach for decentralized economic-based allocation in Grid resource and service markets

Efficient resource allocation in dynamic large-scale environments is one of the challenges of Grids. In centralized economic-based allocation approaches, the user requests can be matched to the fastest, cheapest or most available resource. This approach, however, shows limitations in scalability and in dynamic environments. In this paper, we explore a decentralized economic approach for resource allocation in Grid markets based on the Catallaxy paradigm. Catallactic agents discover selling nodes in the resource and service Grid markets, and negotiate with each other maximizing their utility by following a strategy. By means of simulations, we evaluate the behavior of the approach, its resource allocation efficiency and its performance with different demand loads in a number of Grid density and dynamic environments. Our results indicate that while the decentralized economic approach based on Catallaxy applied to Grid markets shows similar efficiency to a centralized system, its decentralized operation provides greater advantages: scalability to demand and offer, and robustness in dynamic environments.

Decentralized resource allocation in application layer networks

Application-layer networks (ALN) are software architectures that allow the provisioning of services requiring a huge amount of resources by connecting large numbers of individual computers. The ALN simulation project CATNET evaluates a decentralized mechanism for resource allocation in ALN, which is based on the economic paradigm of the Catallaxy, against a centralized mechanism using an arbitrator object. In both versions, software agents buy and sell network services and resources to and from each other. The economic model is based on self-interested maximization of utility and self-interested cooperation between agents. This article describes the design of money and message flows for centralized and decentralized coordination in both versions and shows preliminary results.

Community-lab: Architecture of a community networking testbed for the future internet

Community networks are an emerging and successful model for the Future Internet across Europe and far beyond. The CONFINE project complements existing FIRE (Future Internet Research and Experimentation) infrastructures by establishing Community-Lab, a new facility for experimentally-driven research built on the federation of existing community IP networks constituted by more than 20,000 nodes and 20,000 Km of links. In this paper we present the benefits of having such testbed for the research community as well as the improvement and evolution of community networks themselves. This paper presents i) the challenges and requirements for Community-Lab, ii) the resulting testbed architecture, iii) the current state of implementation and iv) the integration of the testbed with existing community networks.

Decentralized vs. centralized economic coordination of resource allocation in grids

Application layer networks are software architectures that allow the provisioning of services requiring a huge amount of resources by connecting large numbers of individual computers, like in Grid or Peer-to-Peer computing. Controlling the resource allocation in those networks is nearly impossible using a centralized arbitrator. The network simulation project CATNET will evaluate a decentralized mechanism for resource allocation, which is based on the economic paradigm of the Catallaxy, against a centralized mechanism using an arbitrator object. In both versions, software agents buy and sell network services and resources to and from each other. The economic model is based on self-interested maximization of utility and self-interested cooperation between agents. This article describes the setup of money and message flows both for centralized and decentralized coordination in comparison.

An evaluation of BMX6 for community wireless networks

Nowadays, a growing number of communities of citizens build, operate and own open IP-based community wireless networks with thousands of low capacity nodes actively participating in routing the data traffic. This article focuses on one of their concerns, routing and its scalability, by presenting BatMan-eXperimental Version 6 (BMX6) and evaluating its performance. BMX6 is a low overhead and scalable mesh network routing protocol inspired by human networks. Its performance is evaluated in comparison with OLSR in terms of overhead and convergence time as networks grow in number of nodes and diameter. The results show that the convergence time and protocol overhead per node in BMX6 is not significantly affected by the addition of new nodes in contrast with OLSR, where both parameters can grow super-linearly. This confirms the excellent scalability of BMX6.

Clouds of small things: Provisioning infrastructure-as-a-service from within community networks

Community networks offer a shared communication infrastructure where communities of citizens build and own open networks. While the IP connectivity of the networking devices is successfully achieved, the number of services and applications available from within the community network is typically small and the usage of the community network is often limited to providing Internet access to remote areas through wireless links. In this paper we propose to apply the principle of resource sharing of community networks, currently limited to the network bandwidth, to other computing resources, which leads to cloud computing in community networks. Towards this vision, we review some characteristics of community networks and identify potential scenarios for community clouds. We simulate a cloud computing infrastructure service and discuss different aspects of its performance in comparison to a commercial centralized cloud system. We note that in community clouds the computing resources are heterogeneous and less powerful, which affects the time needed to assign resources. Response time of the infrastructure service is high in community clouds even for a small number of resources since resources are distributed, but tends to get closer to that of a centralized cloud when the number of resources requested increases. Our initial results suggest that the performance of the community clouds highly depends on the community network conditions, but has some potential for improvement with network-aware cloud services. The main strength compared to commercial cloud services, however, is that community cloud services hosted on community-owned resources will follow the principles of community network and will be neutral and open.

Research: CSCW requires open systems

Applications designed to support the work of groups will becoming increasingly important to future distributed systems. This paper considers the role of distributed systems within the development of cooperative systems. In particular we focus on the need to provide open Computer Supported Cooperative Work (CSCW) systems and their impact on distributed systems. The work currently being undertaken in Open Distributed Processing (ODP) is used to highlight significant trends for future open CSCW systems. It is shown that the CSCW and ODP community share mutual interests and have complementary aims and goals that are being developed from different perspectives. Within the paper we provide a brief introduction to CSCW, highlighting the requirements CSCW places on distributed systems. The development of an environment to support open CSCW systems is introduced and briefly described. Finally, the relationships between requirements and models for Open CSCW systems and the Basic Reference Model of ODP are discussed.