Underwater sensor networks represent an important and promising field of research due to the large diversity of underwater ubiquitous applications that can be supported by these networks, e.g., systems that deliver tsunami and oil spill warnings, or monitor submarine ecosystems. Most of these monitoring and warning systems require real-time communication in wide area networks that have a low density of nodes. The underwater communication medium involved in these networks is very harsh and imposes strong restrictions to the communication process. In this scenario, the real-time transmission of information is done mainly using acoustic signals, since the network nodes are not physically close. The features of the communication scenario and the requirements of the communication process represent major challenges for designers of both, communication protocols and monitoring and warning systems. The lack of models to represent these networks is the main stumbling block for the proliferation of underwater ubiquitous systems. This paper presents a real-time communication model for underwater acoustic sensor networks (UW-ASN) that are designed to cover wide areas with a low density of nodes, using any-to-any communication. This model is analytic, considers two solution approaches for scheduling the real-time messages, and provides a time-constraint analysis for the network performance. Using this model, the designers of protocols and underwater ubiquitous systems can quickly prototype and evaluate their solutions in an evolving way, in order to determine the best solution to the problem being addressed. The suitability of the proposal is illustrated with a case study that shows the performance of a UW-ASN under several initial conditions. This is the first analytic model for representing real-time communication in this type of network, and therefore, it opens the door for the development of underwater ubiquitous systems for several application scenarios.
Dimogerontakis, E.; Neto, J.; Meseguer, R.; Navarro, L.; Veiga, L. IFIP/IEEE International Symposium on Integrated Network Management p. 377-385 DOI: 10.23919/INM.2017.7987301 Data de presentació: 2017-05 Presentació treball a congrés
Citizens develop Wireless Mesh Networks (WMN) in many areas as an alternative or their only way for local interconnection and access to the Internet. This access is often achieved through the use of several shared web proxy gateways. These network infrastructures consist of heterogeneous technologies and combine diverse routing protocols. Network-aware state-of-art proxy selection schemes for WMNs do not work in this heterogeneous environment. We developed a client-side gateway selection mechanism that optimizes the client-gateway selection, agnostic to underlying infrastructure and protocols, requiring no modification of proxies nor the underlying network. The choice is sensitive to network congestion and proxy load, without requiring a minimum number of participating nodes. Extended Vivaldi network coordinates are used to estimate client-proxy network performance. The load of each proxy is estimated passively by collecting the Time-to-First-Byte of HTTP requests, and shared across clients. Our proposal was evaluated experimentally with clients and proxies deployed in guifi.net, the largest community wireless network in the world. Our selection mechanism avoids proxies with heavy load and slow internal network paths, with overhead linear to the number of clients and proxies.
Dimogerontakis, E.; Meseguer, R.; Navarro, L.; Ochoa, Sergio F.; Veiga, L. IEEE International Conference Networking, Sensing and Control p. 299-304 DOI: 10.1109/ICNSC.2017.8000108 Data de presentació: 2017-05 Presentació treball a congrés
In several community scenarios, people share benevolently their spare broadband Internet access connectivity with other people who cannot afford it. Although laudable, this sharing process can negatively affect the service received by the primary users, thus jeopardizing the continuity of this community service. In this paper we propose the use of a gateway that separates the traffic of the primary users from that of the secondary users, the beneficiaries of this sharing. We analyze the impact and behavior of several mechanisms for using this gateway, to determine how to maximize network utilization, use of the excess network capacity, and minimize the impact on the primary traffic. As a result we present a set of lessons learned and recommendations. Particularly, some strategies that use tunneling for managing the primary and secondary traffic achieve the best performance isolation for the primary user, while the secondary user obtains the spare capacity equivalent to non-differentiated best effort, with a limited penalty (around 20%). Combined with complementary queueing techniques (instead of FIFO), other important flows for the user experience (such as DNS or ICMP) can be practically unaffected.
Global access to the Internet for all requires a dramatic reduction in Internet access costs particularly in developing areas. This access is often achieved through several proxy gateways shared across local or regional access networks. These proxies allow individuals or organisations to share the capacity of their Internet connection with other users. We present a measurement study of a crowdsourced Internet proxy service in the guifi.net community network that provides free Web access to a large community with many small proxy servers spread over the network. The dataset consists of Squid proxy logs for one month, combined with network topology and traffic data. Our study focuses on a representative subset of the whole network with about 900 nodes and roughly 470 users of the web proxy service. We analyse the service from three viewpoints: Web content traffic from users, performance of proxies and influence of the access network. We find clear daily patters of usage, excess capacity and little reuse of content which makes caching almost unnecessary. We also find variations and small inefficiencies in the distribution of traffic load across proxies and the access network, related to the locality and manual proxy choice. Finally, users experience an overall usable Internet access with good throughput for a free crowdsourced service.