Due to the increasing popularity of P2P systems and their contribution to overall Internet traffic, it is essential to understand how content, which is the main attraction in P2P systems, is fed. The main goal of this talk is to identify and characterize those communities of users that are primarily responsible for publishing/feeding content in BitTorrent. For this purpose we have performed two large scale measurement studies that collectively identify the feeders of more than 30k torrents. Out of these measurements we conclude that a significant part of the BitTorrent’s content (40%) is fed by two different groups: (i) users concentrated min a few IP addresses of Hosting Service Providers. In particular, there is a single Hosting Provider in this community that alone is responsible of feeding 25% of the content published in the current major BitTorrent Portal. (ii) A large number of regular BitTorrent users spread across the networks of big ISPs. In addition, we characterize how the feeders of both communities behave, finding out that the typical Hosting Providers feeder (i) publishes a larger number of torrents that become more popular and (ii) seeds longer its torrents than regular users acting as feeders. Our findings suggest that a small group of users in Hosting Providers effectively leverage BitTorrent to publish content. Therefore, their presence is essential for the livelihood of BitTorrent.

The steadily raising energy costs and the increasing number of evidences of climate changes induced by high levels of CO2 in the atmosphere have brought the issue of a sustainable use of energy to the attention of governments and of people all over the world. The need for a more responsible use of energy has emerged in all sectors, together with the awareness that a decrease in carbon emissions is vital to ensuring a future to mankind. The ICT sector, which has brought deep transformations and a rapid increase in productivity in many domains in the last decades, is at the center of this transformation. In all fields of communications, researchers have started to investigate approaches to reduce energy consumption, both by designing new devices, and by exploring new network architectures. In particula r, dynamic network planning, which implies decreasing the power consumption of those network resources which are underutilized, is seen as one of the most promising techniques to improve the energy efficiency of networks.

Already a popular application in the Internet, IPTV is becoming, among the service providers, a preferred alternative to conventional Broadcasting technologies. Since many of the existing deployments have been done within the safe harbor of telcos own networks, IP multicast has been the desired streaming solution. However, previous studies showed that the popularity of the TV channels follows the Pareto principle, with the bulk of TV channels being watched only by a small fraction of viewers. Recognizing the potential scalability issues, we believe that multicast streaming approach may not be desirable for unpopular TV channels, especially when there are many such channels in the provider's service package. For this reason, the peer-to-peer content distribution paradigm is seen as an alternative, in particular for non-popular content. In order to analyze its viability, in this paper we perform a comparative analysis between IP multicast and a peer-to-peer overlay using unicast connections as streaming approaches, in the context of channels with different degrees of popularity. Our findings show that while multicast is always more efficient in terms of bandwidth utilization, peer-to-peer has a comparable performance for unpopular channels with a low number of viewers.

The GeoNet consortium invites you to attend its final workshop as a unique opportunity to learn more about IPv6 geonetworking and the link between IPv6 geonetworking and the related ITS development in CAR 2 CAR Communication Consortium, CVIS implementation and ETSI TC ITS standardization. During the workshop you will get information through communications and posters and also see the system working in real cars. Please find the program in attachment with practical details (exact place, registration procedure…).

A lot of attention has been given to multihop wireless networks lately. This attention has motivated an increase in the number of 802.11-based deployments, both indoor and outdoor, used to perform measurement studies to analyze WLAN performance by means of wireless sniffers that passively capture transmitted frames. In this talk talk we will introduce some of the major issues that systems researchers have to address when performing such measurements: i) on one hand, the testbed itself requires a significant amount of resources during both its deployment and its maintenance, and they require a "calibration" phase before running the experiments given that as off-the-shelf devices have recently been shown to deviate from the expected behavior–in this talk we summarize a few lessons learned from the deployment of a 28-node wireless testbed; ii) on the other hand, little attention has been given to the fidelity of an individual device, i.e., the ability of a given sniffer to capture all frames that could have been captured by a more faithful device. We assess this fidelity by running controlled experiments, and show that it varies significantly across sniffers, both quantitatively and qualitatively.

Energy consumption in Computer Networks is an issue that is gaining increasing attention. In this talk we will review the issue of energy consumption in Computer Networks to then focus on Ethernet where a new standard is being developed to improve energy efficiency. We will discuss some of the alternatives that were considered during the Energy Efficient Ethernet standardization process and describe the solution adopted in the standard. Then we will present some results of an initial performance evaluation of the standard that shows the potential savings for different scenarios. We will conclude the talk by outlining the implications that Energy Efficient Ethernet will have on different aspects of the LANs.

The Theory of Computing is almost a hundred year old now. Its roots can actually be traced to the Entscheidungsproblem posed by David Hilbert in 1928. Another concrete theory in Physics called the Quantum Mechanics had its inceptions almost two hundred years ago (with Thomas Young's Double Slit Experiment in 1803) but actually started in the late 19th century. Today, Quantum Mechanics is proven to be the most successful theory of Physics. So the natural question to ask was that while the statement of Church-Turing Thesis is seen to be a statement of physics (laws of nature), then it should be compatible with the theory of Quantum Mechanics!

The problem is interesting for two reasons. First, the cost function closely models the energy consumption of some network elements and network-wide optimization is a well-motivated but under-explored direction for energy minimization. Second, it brings light to a challenging combinatorial optimization problem. We will present positive and negative results for polynomial functions and polynomial functions with startup cost. For the latter, techniques to accomplish better-than-polynomial approximation ratios independent of demands and cost function remains a challenging problem.

Many delay-based congestion protocols have been proposed. Some recent studies have questioned the validity of congestion prediction at end hosts Based on measurement studies. In this talk, we show that end-host based delay prediction can be more accurate than previously characterized. We propose PERT (Probabilistic Early Response TCP) to mitigate the uncertainties in end-host based congestion prediction. PERT emulates the behavior of AQM/ECN in the end hosts' response to congestion.

This talk addresses the problem of providing throughput guarantees in heterogeneous wireless mesh networks. As a first step, it proposes a novel model to represent the capacity region of a wireless link that, by linearizing this region, has the fundamental property of being very simple while providing a good approximation to the entire region. In a second step, this model is mapped to two of the most prominent wireless technologies nowadays, namely Wireless LAN and WiMAX. The last step addresses the issue of finding optimal routing strategies, which is done by solving an optimization problem subject to the constraints imposed by the linearized capacity region. The performance of the proposed approach has been compared against traditional routing metrics in mesh networks, such as ETT and ETX, and shown to overperform them by approximately a factor of 2.