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 atypical 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

A technological overview of the guifi.net community network

This work presents a technological analysis of guifi.net, a free, neutral, and open-access community network. Guifi.net consists of more than 27,000 operational nodes, which makes it the world’s largest community network in terms of the number of nodes and coverage area. This paper describes the characteristics of the network, the link level topology, its growth over a decade, and its resilience in terms of availability and reachability of network nodes. Our study is based on open data published by guifi.net regarding its nodes and wireless links, monitoring information, community database, and its web portal. The data includes historical information that covers the lifetime of the network. The scale and diversity of the network requires a separate analysis of the subsets of the entire dataset by area or by separating the core from the leaf nodes. This shows some degree of diversity in local characteristics caused by several demographic, geographic, technological, and network design factors. We focus on the following aspects: technological network diversity, topology characteristics, evolution of the network over time, analysis of robustness, and its effect on networking service availability. In addition, we analyse how the community, the technology used, the geographical region where the network is deployed, and its self-organised structure shape the network properties and determine its strengths and weaknesses. The study demonstrates that the guifi.net community network is diverse in technological choices for hardware, link protocols, and channels and uses a combination of routing protocols yet provides a common private IP network. The graph topology follows a power- law distribution for links in regions up to a few thousand Km 2 , limited to the scope of wireless links. Network growth has two aspects: a geographic growth of the network core using long distance links with wireless or fibre, and the local growth in density with leaf low-cost leaf nodes. The resilience of the network derived from the nodes’ uptime and the structure of the graph varies across different regions with more fragile leafs than core nodes and diverse degrees of graph resilience to random failures or coordinated attacks, such as natural causes, depending on the network planning, structure, and maturity. The guifi.net community network results from a loosely coupled and decentralised organic growth that exhibits large local differences, diverse growth, and maturity under a common community license and social network.Peer ReviewedPostprint (author's final draft

Enabling individually entrusted routing security for open and decentralized community networks

Routing in open and decentralized networks relies on cooperation. However, the participation of unknown nodes and node administrators pursuing heterogeneous trust and security goals is a challenge. Community-mesh networks are good examples of such environments due to their open structure, decentralized management, and ownership. As a result, existing community networks are vulnerable to various attacks and are seriously challenged by the obligation to find consensus on the trustability of participants within an increasing user size and diversity. We propose a practical and novel solution enabling a secured but decentralized trust management. This work presents the design and analysis of securely-entrusted multi-topology routing (SEMTOR), a set of routing-protocol mechanisms that enable the cryptographically secured negotiation and establishment of concurrent and individually trusted routing topologies for infrastructure-less networks without relying on any central management. The proposed mechanisms have been implemented, tested, and evaluated for their correctness and performance to exclude non-trusted nodes from the network. Respective safety and liveness properties that are guaranteed by our protocol have been identified and proven with formal reasoning. Benchmarking results, based on our implementation as part of the BMX7 routing protocol and tested on real and minimal (OpenWRT, 10 Euro) routers, qualify the behaviour, performance, and scalability of our approach, supporting networks with hundreds of nodes despite the use of strong asymmetric cryptography.Peer ReviewedPostprint (author's final draft

Experimenting with commodity 802.11 hardware: overview and future directions

The huge adoption of 802.11 technologies has triggered a vast amount of experimentally-driven research works. These works range from performance analysis to protocol enhancements, including the proposal of novel applications and services. Due to the affordability of the technology, this experimental research is typically based on commercial off-the-shelf (COTS) devices, and, given the rate at which 802.11 releases new standards (which are adopted into new, affordable devices), the field is likely to continue to produce results. In this paper, we review and categorise the most prevalent works carried out with 802.11 COTS devices over the past 15 years, to present a timely snapshot of the areas that have attracted the most attention so far, through a taxonomy that distinguishes between performance studies, enhancements, services, and methodology. In this way, we provide a quick overview of the results achieved by the research community that enables prospective authors to identify potential areas of new research, some of which are discussed after the presentation of the survey.This work has been partly supported by the European Community through the CROWD project (FP7-ICT-318115) and by the Madrid Regional Government through the TIGRE5-CM program (S2013/ICE-2919).Publicad

A study of mobile VoIP performance in wireless broadband networks

Voice service is to date still the killer mobile service and the main source for operator revenue for years to come. Additionally, voice service will evolve from circuit switched technologies towards packet based Voice over IP (VoIP). However, using VoIP over wireless networks different from 3GPP cellular technologies makes it also a disruptive technology in the traditional telecommunication sector. The focus of this dissertation is on determining mobile VoIP performance in different wireless broadband systems with current state of the art networks, as well as the potential disruption to cellular operators when mobile VoIP is deployed over different access networks. The research method is based on an empirical model. The model and experiments are well documented and based on industry standards for voice quality evaluation. The evaluation provides results from both experiments in a controlled laboratory setup as well as from live scenarios. The research scope is first, evaluate each network technology independently; second, investigate vertical handover mobility cases; third, determine other aspects directly affecting end user experience (e.g., call setup delay and battery lifetime). The main contribution of this work is a systematic examination of mobile VoIP performance and end user experience. The research results point out the main challenges for achieving call toll quality, and how derive the required changes and technological performance roadmap for improved VoIP service. That is, investigate how the performance and usability of mobile VoIP can eventually be improved to be a suitable substitute for circuit switched voice. In addition, we evaluate the potential disruption to cellular operators that mobile VoIP brings when deployed over other access networks. This research extends the available knowledge from simulations and provides an insight into actual end user experience, as well as the challenges of using embedded clients in handheld devices. In addition, we find several issues that are not visible or accounted for in simulations in regard to network parameters, required retransmissions and decreased battery lifetime. The conclusion is that although the network performance of several wireless networks is good enough for near toll quality voice in static scenarios, there are still a number of problems which make it currently unfeasible to use as a primary voice service. Moreover, under mobility scenarios performance is degraded. Finally, there are other issues apart from network performance such as energy consumption, hardware limitations and lack of supporting business models (e.g., for WiFi mesh) that further limit the possibility of rolling out mobile VoIP services

Internet sharing in community networks

Cotutela Universitat Politècnica de Catalunya i Instituto Superior TécnicoThe majority of the world's population does not have any or adequate Internet access. This implies that the Internet cannot provide universal service, reaching everyone without discrimination. Global access to the Internet for all requires the expansion of network infrastructures and a dramatic reduction in Internet access costs especially in less developed geographical regions. Local communities come together to build their own network infrastructures, known as Community Networks, and provide accessible and affordable local and Internet inter-networking. Sharing resources, such as infrastructure or Internet access, is encouraged at all levels, in order to lower the cost of connectivity and services. Communities can develop their own network infrastructures as a commons, using several interconnected sub-networks when the scale requires it, and sharing several Internet gateways among their participants. Shared Internet access is offered through web proxy gateways, where individuals or organisations share the full or spare capacity of their Internet connections with other participants. However, these gateway nodes may be overloaded by the demand, and their Internet capacity may degrade due to lack of regulation. This thesis investigates whether shared Internet access in community networks can be utilized to provide universal Internet access. As a first step in this direction, in this thesis we explored characteristics, limitations and usability of a concrete shared Internet Web proxy service in community networks. Based on our findings we studied and proposed mechanisms to improve the user experience and fairness of Internet sharing Web proxy services in community networks, without introducing significant overhead to the network and other services. More specifically, we proposed a scalable client-side Internet gateway selection mechanism suitable for heterogeneous environments such as community networks. Finally, we studied and proposed techniques for sharing spare Internet capacity without deteriorating the contributors' performance.La mayoría de la población mundial no tiene ningún o un adecuado acceso a Internet. Esto implica que Internet no puede prestar un servicio universal, llegando a todos sin discriminación. El acceso global a Internet para todos requiere una drástica reducción de los costos de acceso a Internet, especialmente en zonas geográficas y poblaciones menos desarrolladas. Las comunidades locales se organizan para construir sus propias infraestructuras de red, conocidas como redes comunitarias, y proporcionan interconexión local y con Internet de forma accesible y asequible. Se fomenta la compartición de recursos, como la infraestructura o el acceso a Internet, para reducir el coste de la conectividad y los servicios. Las comunidades pueden desarrollar sus propias infraestructuras de red como un recurso común, utilizando varias subredes interconectadas dado su tamaño, y compartiendo varias pasarelas de Internet entre sus participantes. El acceso compartido a Internet se ofrece a través de pasarelas que son proxy web, donde los participantes o las organizaciones comparten la capacidad total o excedente de su conexión a Internet con otros participantes. Sin embargo, estas pasarelas pueden saturarse por la demanda, y su capacidad de acceso a Internet se puede degradar debido la falta de regulación. Esta tesis investiga si las redes comunitarias se pueden utilizar para proporcionar acceso universal a Internet. Como primer paso en esta dirección, exploramos las características, limitaciones y usabilidad de un servicio concreto de acceso compartido a Internet con proxies web en una red comunitaria. Sobre la base de nuestros hallazgos, estudiamos y proponemos mecanismos para mejorar la experiencia del usuario y la equitatividad de la compartición, sin introducir una sobrecarga significativa en la red y a otros servicios. Más específicamente, proponemos un mecanismo escalable de selección de pasarela a Internet del lado del cliente, adecuado para entornos heterogéneos como las redes comunitarias. Además, estudiamos y proponemos técnicas para compartir la capacidad de Internet sin deteriorar el desempeño de los participantes que contribuyen.Postprint (published version

Performance modelling and evaluation of heterogeneous wired / wireless networks under Bursty Traffic. Analytical models for performance analysis of communication networks in multi-computer systems, multi-cluster systems, and integrated wireless systems.

Computer networks can be classified into two broad categories: wired networks and wireless networks, according to the hardware and software technologies used to interconnect the individual devices. Wired interconnection networks are hardware fabrics supporting communications between individual processors in highperformance computing systems (e.g., multi-computer systems and cluster systems). On the other hand, due to the rapid development of wireless technologies, wireless networks have emerged and become an indispensable part for people¿s lives. The integration of different wireless technologies is an effective approach to accommodate the increasing demand of the users to communicate with each other and access the Internet. This thesis aims to investigate the performance of wired interconnection networks and integrated wireless networks under the realistic working conditions. Traffic patterns have a significant impact on network performance. A number of recent measurement studies have convincingly demonstrated that the traffic generated by many real-world applications in communication networks exhibits bursty arrival nature and the message destinations are non-uniformly distributed. Analytical models for the performance evaluation of wired interconnection networks and integrated wireless networks have been widely reported. However, most of these models are developed under the simplified assumption of non-bursty Poisson process with uniformly distributed message destinations. To fill this gap, this thesis first presents an analytical model to investigate the performance of wired interconnection networks in multi-computer systems. Secondly, the analytical models for wired interconnection networks in multi-cluster systems are developed. Finally, this thesis proposes analytical models to evaluate the end-to-end delay and throughput of integrated wireless local area networks and wireless mesh networks. These models are derived when the networks are subject to bursty traffic with non-uniformly distributed message destinations which can capture the burstiness of real-world network traffic in the both temporal domain and spatial domain. Extensive simulation experiments are conducted to validate the accuracy of the analytical models. The models are then used as practical and cost-effective tools to investigate the performance of heterogeneous wired or wireless networks under the traffic patterns exhibited by real-world applications

Contribution to the improvement of the performance of wireless mesh networks providing real time services

Nowadays, people expectations for ubiquitous connectivity is continuously growing. Cities are now moving towards the smart city paradigm. Electricity companies aims to become part of smart grids. Internet is no longer exclusive for humans, we now assume the Internet of everything. We consider that Wireless Mesh Networks (WMNs) have a set of valuable features that will make it an important part of such environments. WMNs can also be use in less favored areas thanks to their low-cost deployment. This is socially relevant since it facilitates the digital divide reduction and could help to improve the population quality of life. Research and industry have been working these years in open or proprietary mesh solutions. Standardization efforts and real deployments establish a solid starting point.We expect that WMNs will be a supporting part for an unlimited number of new applications from a variety of fields: community networking, intelligent transportation systems, health systems, public safety, disaster management, advanced metering, etc. For all these cases, the growing needs of users for real-time and multimedia information is currently evident. On this basis, this thesis proposes a set of contributions to improve the performance of an application service of such type and to promote the better use of two critical resources (memory and energy) of WMNs.For the offered service, this work focuses on a Video on Demand (VoD) system. One of the requirements of this system is the high capacity support. This is mainly achieved by distributing the video contents among various distribution points which in turn consist of several video servers. Each client request that arrives to such video server cluster must be handled by a specific server in a way that the load is balanced. For such task, this thesis proposes a mechanism to appropriately select a specific video server such that the transfer time at the cluster could be minimized.On the other hand, mesh routers that creates the mesh backbone are equipped with multiple interfaces from different technologies and channel types. An important resource is the amount of memory intended for buffers. The quality of service perceived by the users are largely affected by the size of such buffers. This is because important network performance parameters such as packet loss probability, delay, and channel utilization are highly affected by the buffer sizes. An efficient use of memory for buffering, in addition to facilitate the mesh devices scalability, also prevents the problems associated with excessively large buffers. Most of the current works associate the buffer sizing problem with the dynamics of TCP congestion control mechanism. Since this work focuses on real time services, in which the use of TCP is unfeasible, this thesis proposes a dynamic buffer sizing mechanism mainly dedicated for such real time flows. The approach is based on the maximum entropy principle and allows that each device be able to dynamically self-configure its buffers to achieve more efficient memory utilization. The proper performance of the proposal has been extensively evaluated in wired and wireless interfaces. Classical infrastructure-based wireless and multi-hop mesh interfaces have been considered. Finally, when the WMN is built by the interconnection of user hand-helds, energy is a limited and scarce resource, and therefore any approach to optimize its use is valuable. For this case, this thesis proposes a topology control mechanism based on centrality metrics. The main idea is that, instead of having all the devices executing routing functionalities, just a subset of nodes are selected for this task. We evaluate different centralities, form both centralized and distributed perspectives. In addition to the common random mobility models we include the analysis of the proposal with a socially-aware mobility model that generates networks with a community structure.Actualmente las expectativas de las personas de una conectividad ubicua están creciendo. Las ciudades están trabajando para alcanzar el paradigma de ciudades inteligentes. Internet ha dejado de ser exclusivo de las personas y ahora se asume el Internet de todo. Las redes inalámbricas de malla (WMNs) poseen un valioso conjunto de características que las harán parte importante de tales entornos. Las WMNs pueden utilizarse en zonas menos favorecidas debido a su despliegue económico. Esto es socialmente relevante ya que facilita la reducción de la brecha digital y puede ayudar a mejorar la calidad de vida de la población. Los esfuerzos de estandarización y los despliegues de redes reales establecen un punto de partida sólido.Se espera entonces, que las WMNs den soporte a un número importante de nuevas aplicaciones y servicios, de una variedad de campos: redes comunitarias, sistemas de transporte inteligente, sistemas de salud y seguridad, operaciones de rescate y de emergencia, etc. En todos estos casos, es evidente la necesidad de disponer de información multimedia y en tiempo real. En base a estos precedentes, esta tesis propone un conjunto de contribuciones para mejorar el funcionamiento de un servicio de este tipo y promover un uso eficiente de dos recursos críticos (memoria y energía) de las WMNs.Para el servicio ofrecido, este trabajo se centra en un sistema de video bajo demanda. Uno de los requisitos de estos sistemas es el de soportar capacidades elevadas. Esto se consigue principalmente distribuyendo los contenidos de video entre diferentes puntos de distribución, los cuales a su vez están formados por varios servidores. Cada solicitud de un cliente que llega a dicho conjunto de servidores debe ser manejada por un servidor específico, de tal forma que la carga sea balanceada. Para esta tarea, esta tesis propone un mecanismo que selecciona apropiadamente un servidor de tal manera que el tiempo de transferencia del sistema sea minimizado.Por su parte, los enrutadores de malla que crean la red troncal están equipados con múltiples interfaces de diferentes tecnologías y tipos de canal. Un recurso muy importante para éstos es la memoria destinada a sus colas. La calidad de servicio percibida por los usuarios está altamente influenciada por el tamaño de las colas. Esto porque parámetros importantes del rendimiento de la red como la probabilidad de pérdida de paquetes, el retardo, y la utilización del canal se ven afectados por dicho tamaño. Un uso eficiente de tal memoria, a más de facilitar la escalabilidad de los equipos, también evita los problemas asociados a colas muy largas. La mayoría de los trabajos actuales asocian el problema de dimensionamiento de las colas con la dinámica del mecanismo de control de congestión de TCP. Debido a que este trabajo se enfoca en servicios en tiempo real, en los cuales no es factible usar TCP, esta tesis propone un mecanismo de dimensionamiento dinámico de colas dedicado principalmente a flujos en tiempo real. La propuesta está basada en el principio de máxima entropía y permite que los dispositivos sean capaces de auto-configurar sus colas y así lograr un uso más eficiente de la memoria. Finalmente, cuando la WMN se construye a través de la interconexión de los dispositivos portátiles, la energía es un recurso limitado y escaso, y cualquier propuesta para optimizar su uso es muy valorada. Para esto, esta tesis propone un mecanismo de control de topología basado en métricas de centralidad. La idea principal es que en lugar de que todos los dispositivos realicen funciones de enrutamiento, solo un subconjunto de nodos es seleccionado para esta tarea. Se evalúan diferentes métricas, desde una perspectiva centralizada y otra distribuida. A más de los modelos aleatorios clásicos de movilidad, se incluye el análisis de la propuesta con modelos de movilidad basados en información social que toman en cuenta el comportamiento humano y generan redes con una clara estructura de comunidade