Networking (SCN) extends Information-Centric Networking (ICN) from content to services, enabling clients to request services without having them coupled to specific servers. This brings new authentication challenges, since legacy authentication techniques do not apply. We propose and evaluate three generic SCN use cases and their corresponding authentication methods.

Equipped with state-of-the-art smartphones and mobile devices, today's highly interconnected urban population is increasingly dependent on these gadgets to organize and plan their daily lives. These applications often rely on current (or preferred) locations of individual users or a group of users to provide the desired service, which jeopardizes their privacy; users do not necessarily want to reveal their current (or preferred) locations to the service provider or to other, possibly untrusted, users. In this paper, we propose privacy-preserving algorithms for determining an optimal meeting location for a group of users. We perform a thorough privacy evaluation by formally quantifying privacy-loss of the proposed approaches. In order to study the performance of our algorithms in a real deployment, we implement and test their execution efficiency on Nokia smartphones. By means of a targeted user-study, we attempt to get an insight into the privacy-awareness of users in location-based services and the usability of the proposed solutions.

The ever increasing popularity of apps stems from their ability to provide highly customized services to the user. The flip side is that in order to provide such services, apps need access to very sensitive private information about the user. This leads to malicious apps that collect personal user information in the background and exploit it in various ways. Studies have shown that current app vetting processes which are mainly restricted to install time verification mechanisms are incapable of detecting and preventing such attacks. We argue that the missing fundamental aspect here is a comprehensive and usable mobile privacy solution, one that not only protects the user's location information, but also other equally sensitive user data such as the user's contacts and documents. A solution that is usable by the average user who does not understand or care about the low level technical details. To bridge this gap, we propose privacy metrics that quantify low-level app accesses in terms of privacy impact and transforms them to high-level user understandable ratings. We also provide the design and architecture of our Privacy Panel app that represents the computed ratings in a graphical user-friendly format and allows the user to define policies based on them. Finally, experimental results are given to validate the scalability of the proposed solution.

ABSTRACT We present a system for real‐time traffic support in infrastructure andad hocIEEE 802.11 networks. The proposed elastic MAC (E‐MAC) protocol provides a distributed transmission schedule for stations with real‐time traffic requirements, while allowing a seamless coexistence with standard IEEE 802.11 clients, protecting best‐effort 802.11 traffic from starvation by means of admission control policies. Our scheduling decisions are based on an ‘elastic’ transmission opportunity (TXOP) assignment which allows for efficient wireless resource usage: whenever a real‐time station does not use the assigned TXOP, the other real‐time stations can take over the unused access opportunity, thus preventing the well‐known inefficiencies of static time division multiple access (TDMA) schemes. Unlike other TDMA‐based solutions for 802.11, E‐MAC does not require a tight synchronization among the participating clients, thus allowing its implementation on commodity WLAN hardwareviaminor software changes at the client side, and no changes at the access points (APs). We studied the performance of our mechanismvians‐2 simulations and a mathematical model, showing that it outperforms IEEE 802.11e in terms of throughput, delay, and jitter. We finally provide a proof of concept through the results obtained in a real testbed where we implemented the E‐MAC protocol. Copyright © 2011 John Wiley & Sons, Ltd.

Progress in mobile wireless technology has resulted in the increased use of mobile devices to store and manage users' personal schedules. Users also access popular context-based services, typically provided by third-party providers, by using these devices for social networking, dating and activity-partner searching applications. Very often, these applications need to determine common availabilities among a set of user schedules. The privacy of the scheduling operation is paramount to the success of such applications, as often users do not want to share their personal schedules with other users or third-parties. Previous research has resulted in solutions that provide privacy guarantees, but they are either too complex or do not fit well in the popular user-provider operational model. In this paper, we propose practical and privacy-preserving solutions to the server-based scheduling problem. Our novel algorithms take advantage of the homomorphic properties of well-known cryptosystems in order to privately compute common user availabilities. We also formally outline the privacy requirements in such scheduling applications and we implement our solutions on real mobile devices. The experimental measurements and analytical results show that the proposed solutions not only satisfy the privacy properties but also fare better, in regard to computation and communication efficiency, compared to other well-known solutions.

The scope of mobile phones has skyrocketed in recent years to such an extent that smartphone sales are expected to surpass those of PCs by the end of 2011. Equipped with relatively powerful processors and fairly large memory and storage capabilities, smartphones can accommodate increasingly complex interactive applications. As a result, the growing amount of sensitive information shared by smartphone users raises serious privacy concerns and motivates the need for appropriate privacy-preserving mechanisms. In this paper, we present a novel architecture geared for privacy-sensitive applications where personal information is shared among users and decisions are made based on given optimization criteria. Specifically, we focus on two application scenarios: (i) privacy-preserving interest sharing, i.e., discovering shared interests without leaking users' private information, and (ii) private scheduling, i.e., determining common availabilities and location preferences that minimize associate costs, without exposing any sensitive information. We propose efficient yet provably-private solutions, and conduct an extensive experimental analysis that attests to the practicality of the attained privacy features.

Pervasive social networks extend traditional social networking by enabling users to share information in a peer-to-peer fashion using their wireless mobile devices. Contrary to traditional online social networks, privacy protection in such networks depends heavily on users' context (time, location, activity, etc.) and their sensitivity to the shared data and context. Existing privacy-preserving mechanisms do not adapt well to different data, context and user sensitivities. In this work, we follow a fresh approach for privacy preservation, called privacy-triggered communications; it allows users in such pervasive networks to dynamically regulate their communications based on their context and on the evolution of their privacy in that context. Our initial results show that this is a feasible strategy for privacy management in pervasive social networking scenarios.

Interference management is one of the most critical operations for CSMA/CA protocols. In this paper we investigate how specific PHY-layer operations, designed to mitigate the effect of interference, can cause the radio-receiver circuitry to over-estimate the channel occupation status, thus unnecessarily limiting the overall spatial reuse or impeding the synchronization to incoming frames. We individuated the root of this problem in the surprising effectiveness of the overall packet detection procedure of WLAN PHY, which allows for the demodulation of strongly attenuated 802.11 frames. The transmit spectrum mask for the IEEE 802.11 standard allows limited power leakage over adjacent channels. Such a low power signal from adjacent channels nowadays can be correctly recognized by recent OFDM/CCK receive circuitry, which has an important impact on WLAN performance. A receiver may miss the reception of packets destined to it, whenever a frame capture of a transmission on a partially overlapping channel occurs. A similar effect occurs in the transmit phase. In carrier sense mode, the OFDM/CCK receiver of the WLAN device is capable of synchronizing to the preamble of low SNR signals, thus unnecessarily deferring the channel access in case of transmissions on partially overlapping channels.

Rate adaptation based on signal-to-noise ratio (SNR) measurements is a common channel adaptation scheme to increase throughput in wireless communication systems. To use rate adaptation efficiently in cooperative wireless networks, an adaptation algorithm must consider multiple channels (source- destination, source-relays, and relays-destination) to select modulation and code rates that maximize throughput. In this paper we analyze the potential gains that combining cooperation with rate adaptation brings in three steps: (1) We derive the theoretical capacity bounds for ideal rate adaptation schemes for typical topologies. (2) We propose an offline heuristic for computing SNR thresholds aimed at reaching the derived bounds. (3) Using this heuristic, we compare rate adaptation for maximal ratio combining (MRC), where links are equally adapted, with soft-bit MRC (SBMRC), where links are individually adapted. We find that adapting the rate per link is superior in terms of throughput.

Interference limits throughput in wireless networks. To protect themselves against interference, many wireless protocols create areas around receivers in which no node is allowed to transmit. If such an exclusion area is small, more transmissions can proceed simultaneously but observe higher interference, creating a tradeoff between network capacity and link capacity.

Cooperative relaying has been shown to provide diversity gains which can significantly improve the packet error rate (PER) in wireless transmissions. In ad hoc wireless routing where packets may travel over a number of hops before reaching the destination, hop-wise cooperative relaying may severely reduce network capacity. This approach was mainly addressed in literature so far. In this paper, we efficiently apply cooperative relaying along a complete path and over multiple hops at the same time. We use information from the routing layer to improve the medium access control (MAC) layer's performance. Simulations and testbed implementation show appealing gains through diversity resulting in up to 66% better PER performance and up to 148% goodput increase compared to conventional approaches.

Opportunistic Relaying (OR) and Selection Decode-and-Forward (SDF) cooperation protocols can both substantially improve the performance of wireless networks but fundamentally differ in utilized redundancy, relays, and channel knowledge. To analyze when SDF or OR improves error and data rate, we (1) derive their general outage probability and capacity for arbitrary relay configurations, (2) systematically benchmark both approaches in two-hop configurations, (3) study how often beneficial configurations occur in large networks, and, finally, condition our capacity results by this occurrence probability. Our results clearly show that OR maximizes the outage capacity at high acceptable error rate while SDF succeeds if a low error rate is required. SDF performs best if even the relays can cooperate among themselves, supported frequently in networks with more than three neighbors. Consequently, cooperating relays, adapting between OR and SDF, and joining these two approaches should be the focus of future protocol design. To this end, our paper provides a theoretical basis, adaptation rules, and design guidelines.

In this paper a cooperative retransmission scheme for 802.11 WLANs is proposed. The mechanism allows stations with good channel to the access point to retransmit packets on behalf of other stations with worse channel. The cooperative partner selection is carried out in a completely opportunistic and distributed way that is compatible with 802.11. Simulations performed in a realistic WLAN scenario with adaptive modulation show that the system provides considerable gains in terms of goodput and packet error rate in comparison with legacy 802.11.

To overcome the lack of strict QoS guarantees in existing hotspots, in this paper we present a system for realtime traffic support in 802.11 networks that works in either infrastructure or ad-hoc mode. The proposed mechanism, called elastic MAC (E-MAC) protocol, helps stations with real-time traffic to organize and establish a transmission schedule in a distributed manner, while coexisting with standard 802.11 stations. This distributed scheduling guarantees very short delays and a minimum reserved data rate for real-time stations, while protecting best-effort 802.11 traffic from starvation. Another feature of our mechanism is time-slot reuse, which improves the network efficiency by allowing other real-time stations to take over unused slots (e.g., in case of using voice codecs with silence suppression). We evaluate the performance of our system using a testbed implementation, ns-2 simulations and a mathematical model, and show how it outperforms other QoS schemes (e.g., 802.11e) in terms of throughput, delay, and jitter.

Vehicular networks (VNs) are emerging, among civilian applications, as a convincing instantiation of the mobile networking technology. However, security is a critical factor and a significant challenge to be met. Misbehaving or faulty network nodes have to be detected and prevented from disrupting network operation, a problem particularly hard to address in the life-critical VN environment. Existing networks rely mainly on node certificate revocation for attacker eviction, but the lack of an omnipresent infrastructure in VNs may unacceptably delay the retrieval of the most recent and relevant revocation information; this will especially be the case in the early deployment stages of such a highly volatile and large-scale system. In this paper, we address this specific problem. We propose protocols, as components of a framework, for the identification and local containment of misbehaving or faulty nodes, and then for their eviction from the system. We tailor our design to the VN characteristics and analyze our system. Our results show that the distributed approach to contain nodes and contribute to their eviction is efficiently feasible and achieves a sufficient level of robustness.

Protocols for beamforming antennas usually direct the beam toward the respective communication partner. This requires significant coordination between nodes and results in frequent changes of the beam direction. In this paper, we present much simpler algorithms that instead aim at improving connectivity and robustness of routing. A node computes the optimal beam direction using aggregate information about its neighborhood such as the number of neighbors in each beam direction. We analyze the performance of such algorithms in terms of number of paths to a destination, mutual interference, and route lifetime in mobile networks, and show that they are a promising alternative to existing beamforming schemes

IEEE 802.11 works properly only if the stations respect the MAC protocol. We show in this paper that a greedy user can substantially increase his share of bandwidth, at the expense of the other users, by slightly modifying the driver of his network adapter. We explain how easily this can be performed, in particular, with the new generation of adapters. We then present DOMINO (detection of greedy behavior in the MAC layer of IEEE 802.11 public networks), a piece of software to be installed in or near the access point. DOMINO can detect and identify greedy stations without requiring any modification of the standard protocol. We illustrate these concepts by simulation results and by the description of a prototype that we have recently implemented

CSMA/CA protocols rely on the random deferment of packet transmissions. Like most other protocols, CSMA/CA was designed with the assumption that the nodes would play by the rules. This can be dangerous, since the nodes themselves control their random deferment. Indeed, with the higher programmability of the network adapters, the temptation to tamper with the software or firmware is likely to grow; by doing so, a user could obtain a much larger share of the available bandwidth at the expense of other users. We use a game-theoretic approach to investigate the problem of the selfish behavior of nodes in CSMA/CA networks, specifically geared towards the most widely accepted protocol in this class of protocols, IEEE 802.11. We characterize two families of Nash equilibria in a single stage game, one of which always results in a network collapse. We argue that this result provides an incentive for cheaters to cooperate with each other. Explicit cooperation among nodes is clearly impractical. By applying the model of dynamic games borrowed from game theory, we derive the conditions for the stable and optimal functioning of a population of cheaters. We use this insight to develop a simple, localized and distributed protocol that successfully guides multiple selfish nodes to a Pareto-optimal Nash equilibrium.

Significant progress has been made towards making ad hoc networks secure and DoS resilient. However, little attention has been focused on quantifying DoS resilience: Do ad hoc networks have sufficiently redundant paths and counter-DoS mechanisms to make DoS attacks largely ineffective? Or are there attack and system factors that can lead to devastating effects? In this paper, we design and study DoS attacks in order to assess the damage that difficult-to-detect attackers can cause. The first attack we study, called the JellyFish attack, is targeted against closed-loop flows such as TCP; although protocol compliant, it has devastating effects. The second is the Black Hole attack, which has effects similar to the JellyFish, but on open-loop flows. We quantify via simulations and analytical modeling the scalability of DoS attacks as a function of key performance parameters such as mobility, system size, node density, and counter-DoS strategy. One perhaps surprising result is that such DoS attacks can increase the capacity of ad hoc networks, as they starve multi-hop flows and only allow one-hop communication, a capacity-maximizing, yet clearly undesirable situation.

The proliferation of hotspots based on IEEE 802.11 wireless LANs brings the promise of seamless Internet access from a large number of public locations. However, as the number of users soars, so does the risk of possible misbehavior; to protect themselves, wireless ISPs already make use of a number of security mechanisms, and require mobile stations to authenticate themselves at the Access Points (APs). However, IEEE 802.11 works properly only if the stations also respect the MAC protocol. We show in this paper that a greedy user can substantially increase his share of bandwidth, at the expense of the other users, by slightly modifying the driver of his network adapter. We explain how easily this can be performed, in particular with the new generation of adapters. We then present DOMINO (System for Detection Of greedy behavior in the MAC layer of IEEE 802.11 public NetwOrks), a piece of software to be installed in the Access Point. DOMINO can detect and identify greedy stations, without requiring any modification of the standard protocol at the AP and without revealing its own presence. We illustrate these concepts by simulation results and by the description of our prototype.

The IEEE 802.11 medium access control (MAC) protocol provides a contention-based distributed channel access mechanism for mobile stations to share the wireless medium, which may introduce a lot of collisions in case of overloaded active stations. Slow contention window (CW) decrease scheme is a simple and efficient solution for this problem. In this paper, we use an analytical model to compare the slow CW decrease scheme to the IEEE 802.11 MAC protocol. Several parameters are investigated such as the number of stations, the initial CW size, the decrease factor value, the maximum backoff stage and the coexistence with the RequestToSend and ClearToSend (RTS/CTS) mechanism. The results show that the slow CW decrease scheme can efficiently improve the throughput of IEEE 802.11, and that the throughput gain is higher when the decrease factor is larger. Moreover, the initial CW size and maximum backoff stage also affect the performance of slow CW decrease scheme.

The IETF is currently working on service differentiation in the Internet. However, in wireless environments where bandwidth is scarce and channel conditions are variable, IP differentiated services are sub-optimal without lower layers' support. We present three service differentiation schemes for IEEE 802.11. The first one is based on scaling the contention window according to the priority of each flow or user. The second one assigns different inter-frame spacings to different users. Finally, the last one uses different maximum frame lengths for different users. We simulate and analyze the performance of each scheme with TCP and UDP flows.

The IETF is currently working on service differentiation for the Internet. However service differentiation at the IP layer is useless without support of lower layers. This support is even more critical in wireless environments because of the dynamism of the channel conditions and of the network topology. We present a service differentiation support for the IEEE 802.11. The idea is to scale the contention window according to the priority of each flow or user. Preliminary simulation results are shown when using this mechanism with TCP and UDP.