Lorenzo Bracciale

Performance Assessment of an Epidemic Protocol in VANET Using Real Traces

Abstract Many vehicular ad-hoc network protocols have been validated using complex urban mobility simulators or by means of the few publicly available real mobility traces. This work presents an extensive measurement campaign of the positions of a fleet of 370 taxi cabs moving around the city of Rome, Italy. Due to its street network and its traffic conditions, Rome presents a characteristic mobility pattern representative of an ancient city with heavy road congestion, and therefor provides a valuable test case to experiment VANET protocols. We exploit these traces to run a set of experiments to assess the performance of a simple epidemic protocol that we compare with the basic random waypoint model in order to quantify how far the performance metrics are from this baseline. The results show the possible outcomes of implementing data dissemination through an opportunistic network that uses taxi cabs as an information vector.

A push-based scheduling algorithm for large scale P2P live streaming

this paper, we present a chunk scheduling algorithm for a mesh-based peer-to-peer live streaming system and we evaluate it by simulations over large-scale networks. Literature papers typically design chunk scheduling algorithms by considering the chunk delivery ratio as performance metric. We propose a push-based algorithm, which not only tries to maximize the chunk delivery ratio but it also takes into account and tries to minimize the delivery delay of chunks at the peer nodes. This is an important requirement, when dealing with realtime multimedia flows. Another important contribution of this paper is the design and implementation of a simulator able to evaluate the performance of large scale P2P networks (tens of thousands peers). The importance of this contribution lies in the fact that existing simulators and performance studies handle at most hundreds or few thousands of peers, while real-life P2P streaming systems aim at distributing contents to several hundreds of thousands, if not millions, of users. The performance evaluation study aims at providing a comprehensive view of what performance can be expected for mesh-based peer-to-peer streaming systems, both in terms of chunk delivery ratio and delay, for a large range of the number of users. The individual effect of a variety of system parameters, and especially number of partner nodes in the mesh, constrained link bandwidth, node heterogeneity, and network size, has been analyzed. Our results show that performances of the proposed push-based solution are already quite effective even with severely bandwidth constrained large scale networks.

Streamline: An Optimal Distribution Algorithm for Peer-to-Peer Real-Time Streaming

In this paper, we propose and evaluate an overlay distribution algorithm for P2P, chunk-based, streaming systems over forest-based topologies. In such systems, the stream is divided in chunks; chunks are delivered by each node in a store-and-forward way. A relaying node starts distributing a chunk only when it has completed its reception from another node. Peers are logically organized in a forest of trees, where each tree includes all peers. The source periodically distributes different chunks to each tree for their delivery. Our key idea consists in employing serial transmission: for each tree, and thus, for each chunk, the source node sends the chunk to its children in series; the same holds for each peer node of the tree, excluding the leaves. Besides this basic idea, the contributions of this paper are: 1) we demonstrate the feasibility of serial transmission over a forest of trees, which is not a trivial problem, unlike the case of parallel transmission; 2) we derive an analytical model to evaluate the system performance; 3) we derive a theoretical bound for the number of nodes reachable in a given time interval or equivalently for the time required to reach a given number of nodes; 4) we prove the optimality of our approach in terms of its capability to reach such bound; and 5) we develop a general simulation package for P2P streaming systems and use it to compare our solution to literature results. Finally, we stress that this paper is focused on the theoretical properties and performance understanding of the proposed distribution algorithm, rather than on its practical implementation in a real system. However, we also briefly describe a practical workable implementation of our algorithm.

Better than nothing privacy with bloom filters: to what extent?

Bloom filters are probabilistic data structures which permit to conveniently represent set membership. Their performance/memory efficiency makes them appealing in a huge variety of scenarios. Their probabilistic operation, along with the implicit data representation, yields some ambiguity on the actual data stored, which, in scenarios where cryptographic protection is unviable or unpractical, may be somewhat considered as a better than nothing privacy asset. Oddly enough, even if frequently mentioned, to the best of our knowledge the (soft) privacy properties of Bloom filters have never been explicitly quantified. This work aims to fill this gap. Starting from the adaptation of probabilistic anonymity metrics to the Bloom filter setting, we derive exact and (tightly) approximate formulae which permit to readily relate privacy properties with filter (and universe set) parameters. Using such relations, we quantitatively investigate the emerging privacy/utility trade-offs. We finally preliminary assess the advantages that a tailored insertion of a few extra (covert) bits achieves over the commonly employed strategy of increasing ambiguity via addition of random bits.

The Sleepy Bird Catches More Worms: Revisiting Energy Efficient Neighbor Discovery

Neighbor discovery is a primary enabling ability for many emerging mobile applications. Due to its significant impact on the energy budget of battery equipped devices, energy preserving solutions have been investigated for a longtime, often introducing duty cycling. Ultimately, these solutions settle for trade-offs between energy and performance, leaving the final decision on how much energy to allocate to neighbor discovery in the hands of application developers or system engineers. In other words, someone must decide if an improvement in the quality of the discovery (e.g. better discovery latency) is worth an increase in energy consumption. In this paper, we devise a different approach in order to answer the following basic question: how many contacts can a smartphone discover using its battery energy budget? The answer clearly depends on the adopted discovery algorithm, on the mobility conditions, and on the stochastic characteristics of the encounters. However, we demonstrate that there is a natural optimum duty cycle that maximizes the number of discovered contacts in almost every real application scenario. This optimum is natural in the sense that it does not depend on any system level parameter or performance requirements. It depends uniquely on the stochastic characteristics of the meeting process between the nodes. We present an analytic analysis and devise a practical algorithm that dynamically adapts the duty cycle length to the time-varying context, without the need to make assumptions on (or predict) the distribution of the contact duration. The findings presented in the paper are validated against data coming from real human mobility traces and implemented on a mobile application.

Towards fully IP-enabled IEEE 802.15.4 LR-WPANs

This extended abstract describes a poster and a proposal for demonstration. Its focus is on low rate wireless personal area networks (LR-WPANs) which use IEEE 802.15.4 physical and MAC layers at the lower layers of the protocol stack. More precisely, goal of this extended abstract is to present a real test-bed, whose main goal is to demonstrate how IEEE 802.15.4 LR-WPANs can fully inter-operate with IP networks. To this end, the protocol stack implemented at each IEEE 802.15.4 node includes the so said LoWPAN adaptation layer, which has been defined by the IETF 6LoWPAN working group. Moreover, we will present a possible practical solution for the problem of how to realize a gateway between the IEEE 802.15.4 LR-WPANs and the IP networks.

On the IP support in IEEE 802.15.4 LR-WPANs: Self-configuring solutions for real application scenarios

Due to the lack of IP support, the ZigBee protocol stack for IEEE 802.15.4 low rate wireless personal area networks (LR-WPANs) is the perfect solution for closed, ad-hoc environments. However, we can envisage also open and interconnected application scenarios, such as the Internet of Things or the integration of ZigBee/IEEE 802.15.4 nodes in mobile/smart phones, that would greatly benefit from the IP support. The LoWPAN adaptation layer proposed by the 6LoWPAN IETF working group to enable the transmission/reception of IPv6 data in IEEE 802.15.4 networks may be regarded as the first step towards the direction of IP direct support into IEEE 802.15.4 nodes. However, a fully fledged solution to be used in the scenarios outlined above still lacks the following functionality: i) self-configuring address assignment mechanism; ii) multi-hop routing protocol; iii) support of Internet-compliant transport protocols; iv) self-configuring network and service discovery. It may seem trivial to provide such functionality in an IP world, as off the shelf solutions could be adopted; however, this is not an easy task, given the very limited hardware capabilities of IEEE 802.15.4 devices. In this paper we define a complete protocol architecture and specific self-configuring mechanisms to support the aforementioned functionality over IEEE 802.15.4 devices, taking into account their hardware constraints. We also present an implemented test-bed which demonstrates the functionality of the proposed solution in a real application scenario. 1.

Human time-scale duty cycle for opportunistic WiFi based mobile networks

Despite the great interest received by the smart-phones in opportunistic networks context, the requested energy toll still remains one of the prominent inhibiting factors to the real deployment of such technology. In this paper we evaluate a on-off approach devised to provide intermittent (but synchronized) WiFi communication across opportunistically connected devices while saving energy. Differently form classical duty cycle approaches that are implemented at the protocol/network level, we devise a “human time-scale” duty cycle that can be implemented as an overlay system service at the application level. The relatively large time-scale allows to simply keep a loose synchronization between terminals, without requiring any changes in the default operating system or system internals of commercial mobile phones.With reference to Android devices, we analyze the effects of varying such duty cycle in terms of the feasibility of the synchronization requirements as well as the energy gain obtained in order to find the trade-off for the different state settings. For these values, we evaluate the loss of discovered contacts using the data coming from real human mobility traces.

A Theory-Driven Distribution Algorithm for Peer-to-Peer Real Time Streaming

Many distribution algorithms have been proposed up to now for P2P real time streaming. However, due to the lack of basic theoretical results and bounds, common sense and intuitions and heuristics have driven their design so far. The consequence is that we can find in the literature a large variety of different choices about the main aspects of a P2P system, such as overlay topology, scheduling process and upload strategy. In this situation, it is difficult to establish unambiguously the absolute goodness of a particular algorithm or even the rationale behind a particular choice or solution. In this paper we propose and evaluate a theory-driven distribution algorithm for P2P real time streaming. We take advantage from a previous theoretical study, where: i) we derived a theoretical performance bound for forest-based overlay topologies regarding the number of nodes reachable in a given time interval or equivalently the time required to reach a given number of nodes; ii) we proved the optimality of streamline, a distribution algorithm based on the serial transmission over forest-based topologies, in terms of its capability to reach such a bound. The streamline algorithm is based on some ideal assumptions that prevent its practical implementation. In this paper we remove these assumptions and present a practical and working algorithm, named operational streamline or simply O-Streamline. We also evaluate the performance of O-Streamline, comparing them with the optimal bounds of streamline.

Push Attack: Binding Virtual and Real Identities Using Mobile Push Notifications

Popular mobile apps use push notifications extensively to offer an “always connected” experience to their users. Social networking apps use them as a real-time channel to notify users about new private messages or new social interactions (e.g., friendship request, tagging, etc.). Despite the cryptography used to protect these communication channels, the strict temporal binding between the actions that trigger the notifications and the reception of the notification messages in the mobile device may represent a privacy issue. In this work, we present the push notification attack designed to bind the physical owners of mobile devices with their virtual identities, even if pseudonyms are used. In an online attack, an active attacker triggers a push notification and captures the notification packets that transit in the network. In an offline attack, a passive attacker correlates the social network activity of a user with the received push notification. The push notification attack bypasses the standard ways of protecting user privacy based on the network layer by operating at the application level. It requires no additional software on the victim’s mobile device.