We study algorithms for carrier and rate allocation in cellular systems with distributed components such as a heterogeneous LTE system with macrocells and femtocells.  Existing work on LTE systems often involves centralized techniques or requires significant signaling, and is therefore not always applicable in the presence of femtocells. More distributed CSMA-based algorithms (carrier-sense multiple access) were developed in the context of 802.11 systems and have been proven to be utility optimal. However, the proof typically assumes a single transmission rate on each carrier. Further, it relies on the CSMA collision detection mechanisms to know whether a transmission is feasible. In this talk we present a framework for LTE scheduling that is based on CSMA techniques. In particular we first prove that CSMA-based algorithms can be generalized to handle multiple transmission rates in a multi-carrier setting while maintaining utility optimality.  We then show how such an algorithm can be implemented in a heterogeneous LTE system where the existing Channel Quality Indication (CQI) mechanism is used to decide transmission feasibility.

Bitcoin is a decentralized peer-to-peer payments network. It is the first and most widely used example of a new kind of money known as cryptocurrency. Transactions are fast, non-repudiable and almost anonymous. Fees are extremely cheap and every single transaction is stored in a ledger called the block chain.

This unique conference will be the venue fostering dialogue among scholars and practitioners belonging to these disciplines.

The main functionality of the Internet is to provide global connectivity for every node attached to it. In light of the IPv4 address space depletion, large networks are in the process of deploying IPv6. In this paper we perform an extensive analysis of how BGP route propagation affects global reachability of the active IPv6 address space in the context of this unique transition of the Internet infrastructure. We propose and validate a methodology for testing the reachability of an IPv6 address block active in the routing system. Leveraging the global visibility status of the IPv6 prefixes evaluated with the BGP Visibility Scanner, we then use this methodology to verify if the visibility status of the prefix impacts its reachability at the interdomain level. We perform active measurements using the RIPE Atlas platform. We test destinations with different BGP visibility degrees (i.e., limited visibility - LV, high visibility - HV and dark prefixes). We show that the IPv6 LV prefixes (v6LVPs) are generally reachable, mostly due to a less-specific HV covering prefix (v6HVP). However, this is not the case of the dark address space, which, by not having a covering v6HVP is largely unreachable. When talking about the results we present in this paper a better explanation of trace route and some basic concepts of BGP will be provided.

Peer-to-peer networks have been quite thoroughly measured over the past years; however it is interesting to note that the BitTorrent Mainline DHT has received very little attention even though it is by far the largest of currently active overlay systems, as our results show. As Mainline DHT differs from other systems, existing measurement methodologies are not appropriate for studying it. In this talk we present an efficient methodology for estimating the number of active users in the network. We have identified an omission in previous methodologies used to measure the size of the network and our methodology corrects this. This omission may lead to inaccuracies of up to 40% in the number of active users. Our method is based on modeling crawling inaccuracies as a Bernoulli process. It guarantees a very accurate estimation and is able to provide the estimate in about 5 seconds. Through experiments in controlled situations, we demonstrate the accuracy of our method and show the causes of the inaccuracies in previous work, by reproducing the incorrect results. Besides accurate network size estimates, our methodology can be used to detect network anomalies, in particular Sybil attacks in the network. We also report on the results from our measurements which have been going on for almost 2.5 years and are the first long-term study of Mainline DHT.

“Destripa” un móvil, un televisor, el cuerpo humano, … con la ayuda de los investigadores de los Institutos IMDEA

Descubre la enorme cantidad de ciencia y tecnología que rodea nuestra vida, haciéndola más cómoda, fácil y segura; y conoce a quienes se dedican a que cada día una y otra continúen mejorando.

La Ciencia del Salón de tu casa es la actividad con la que los institutos IMDEA participan este año en la iniciativa europea La Noche de los Investigadores. Su principal objetivo es mostrar al público que en casi todos los objetos y servicios que nos rodean hay mucha ciencia y mucha tecnología, y hacerlo dejando que el público interactúe con el investigador y mostrando el atractivo de quienes se dedican a mejorarlos. En definitiva, lo que se persigue es analizar con la ayuda del público lo diferente que sería nuestra vida sin ellos: los objetos o servicios y los investigadores, para resaltar lo importantes que son la ciencia y la tecnología para el bienestar social y lo interesante y gratificante que es dedicarse a ellas.

Information and communication technologies (ICTs) often fail to perform well in environments and scenarios that were not envisioned at the time of the ICTs creation. Examples of such failures include poor usability of traditional WiFi networks in resource-constrained rural areas, geographically-dependent performance of centralised networked systems, and context-insensitive behaviour of ubiquitous computing devices.

Discovering services in the local broadcast domain is easy from the application point of view. However, from the network point of view, especially when wireless networks are also involved, it is wasteful, as query and response are broadcast on all access points at the lowest data rate, ignoring efficient transmission modes. It also does not scale beyond the single broadcast domain, as this would require deployment of IP multicast, which has yet to happen despite decades of trying. We introduce Stateless DNS as an efficient and broader range alternative. Stateless DNS requires no action from the network service provider, improves upon privacy and comes with incremental deployment options. While providing a well-known DNS interface to the applications, it can identify organizational boundaries and uses existing DNS caches for performance.

By tweaking the BGP configurations, the network operators are able to express their interdomain routing preferences, designed to accommodate a myriad goals. Given the complex interactions between policies in the Internet, the origin AS by itself cannot ensure that only by configuring a routing policy it can also achieve the anticipated results. Moreover, the definition of routing policies is a complicated process, involving a number of subtle tuning operations prone to errors. In this paper, we propose the BGP Visibility Scanner which allows network operators to validate the correct implementation of their routing policies, by corroborating the BGP routing information from approximately 130 independent observation points in the Internet. We exemplify the use of the proposed methodology and also perform an initial validation for the BGP Visibility Scanner capabilities through various real operational use cases.

Airbnb.com is an online community marketplace that facilitates short-term rentals of "unique spaces" around the world. Since its launch, Airbnb has grown from a few hundred bookings in 2008 to over ten million nights of cumulative bookings worldwide by the end of 2012, spanning more than 300,000 properties in 192 countries. Our work investigates the consequences of the rise of Airbnb as seen by the local economy, focusing on quantifying the impact of Airbnb's growth on the local hotel industry. To explore this question, we consider the state of Texas, where Airbnb adoption exhibits significant spatio-temporal variation across a large number of city-level markets. We leverage a dataset we collected from Airbnb.com,  comprehensively spanning the thousands of Texas properties listed on Airbnb from 2008 to 2013, which we combine with a panel of quarterly tax revenue data for all hotels in the state of Texas from 2001 to 2013. Our analysis provides evidence that the hotel industry has experienced a decrease in revenue due to the entry of Airbnb in the market. Specifically, we find that a 1% increase in the size of the Airbnb market results in a 0.05% decrease in hotel revenue. Furthermore, our results indicate that losses are unevenly distributed among hotels in different price segments, with lower-priced hotels experiencing the largest impact.