Nicolò Facchi

Gaining insight on friendly jamming in a real-world IEEE 802.11 network

Frequency jamming is the fiercest attack tool to disrupt wireless communication and its malicious aspects have received much attention in the literature. Yet, several recent works propose to turn the table and employ so-called friendly jamming for the benefit of a wireless network. For example, recently proposed friendly jamming applications include hiding communication channels, injection attack defense, and access control. This work investigates the practical viability of friendly jamming by applying it in a real-world network. To that end, we implemented a reactive and frame-selective jammer on a consumer grade IEEE 802.11 access point. Equipped with this, we conducted a three weeks real-world study on the jammers performance and side-effects on legitimate traffic (the cost of jamming) in a university office environment. Our results provide detailed insights on crucial factors governing the trade-off between the effectiveness of friendly jamming (we evaluated up to 13 jammers) and its cost. In particular, we observed -- what we call the power amplification phenomenon -- an effect that aggravates the known hidden station problem when the number of jammers increases. However, we also find evidence that this effect can be alleviated by collaboration between jammers, which again enables effective and minimally invasive friendly jamming.

An Innovative Rate Adaptation Algorithm for Multicast Transmissions in Wireless LANs

Rate adaptation represents a key functionality of the 802.11 MAC protocol for performance enhancement. Several solutions have been proposed for improving the transmission rate of unicast communications using frame receptions/losses, BER (Bit Error Rate) and SNR (Signal to Noise Ratio) measurements. Nevertheless, rate adaptation for multicast transmissions represents a more challenging tasks due to the complexity of estimating the reception correlation of wireless links. This paper presents a novel scheme for selecting the best transmission rate for multicast communications using the packet reception correlation of the links established among the nodes of the multicast group with the access point. The proposed algorithm has been evaluated on a real-life testbed using commercial wireless cards. The results show that our solution accurately estimates the reception correlation of wireless links, thus considerably increasing the performance of multicast transmissions up to 3x and 5x in terms of throughput and delay, respectively.

Friendly Jamming on Access Points: Analysis and Real-World Measurements

Frequency jamming is known as an efficient attack tool to disrupt wireless communication. This efficiency can also be exploited for the benefit of a network-an idea often referred to as friendly jamming. A prominent application case is the blocking of unauthenticated or malicious communication, such as injection attacks. In this paper, we propose access points as a natural place to implement friendly jamming functionality. We analyze this proposal using simulations, introduce an implementation on customer-grade access points, and report measurement results from the first real-world study of friendly jamming in an IEEE 802.11 campus network. We discover a fundamental tradeoff between the effectiveness of friendly jamming and the orthogonal aspect of having minimal side-effects to the campus networks traffic. In particular, we observed what we call the power amplification phenomenon. This effect aggravates the known hidden station problem when the number of jammers increases. We also find evidence that the collaboration between jammers can enable friendly jamming, which is both effective and minimally invasive.

Optimized P2P streaming for wireless distributed networks

Abstract The future Internet will support pervasive applications and communications models that require end-nodes cooperation, such as fog computing and machine-to-machine communications. Among the many applications, also video streaming can be provided with a cooperative and peer-to-peer approach. Cooperative distribution requires building a distribution overlay on top of the physical topology (the underlay). This work proposes an optimized, cross-layer approach to build this overlay minimizing the impact on the underlay. We design an optimal strategy, which is proven to be NP-complete, and thus not solvable with a distributed, lightweight protocol. The optimal strategy is relaxed exploiting the knowledge on the betweenness centrality of the nodes in the underlay topology, obtaining two easily implementable solutions applicable to any link-state protocol for distributed wireless mesh networks. The additional introduction of heuristic improvements further optimizes the performance in real network scenarios. Extensive simulation results support the theoretical findings using three different network topologies. They show that the relaxed implementations are reasonably close to the optimal solution, and provide vast gains compared to the traditional overlay topologies that peer-to-peer applications build.

When is the right time to transmit in multi-hop White-Fi?

While Western societies are becoming increasingly connected, many developing regions lack basic Internet connectivity, primarily due to the high costs associated with infrastructure deployment and maintenance. Potential exists for the TV white-space (TVWS) wireless technology to bridge this digital divide, though efficient channel access mechanisms suited to multi-hop networks that operate in sub-gigahertz bands are yet to be developed. Using a small test bed, we demonstrate a prototype implementation of a medium access protocol that learns appropriate transmission opportunities in such settings, achieving pseudo-scheduled behaviour ex tempore and providing substantial gains over the de facto IEEE 802.11af protocol.

Imola: A decentralised learning-driven protocol for multi-hop White-Fi

In this paper we tackle the digital exclusion problem in developing and remote locations by proposing Imola, an inexpensive learning-driven access mechanism for multi-hop wireless networks that operate across TV white-spaces (TVWS). Stations running Imola only rely on passively acquired neighbourhood information to achieve scheduled-like operation in a decentralised way, without explicit synchronisation. Our design overcomes pathological circumstances such as hidden and exposed terminals that arise due to carrier sensing and are exceptionally problematic in low frequency bands. We present a prototype implementation of our proposal and conduct experiments in a real test bed, which confirms the practical feasibility of deploying our solution in mesh networks that build upon the IEEE 802.11af standard. Finally, the extensive system level simulations we perform demonstrate that Imola achieves up to 4× more throughput than the channel access protocol defined by the standard and reduces frame loss rate by up to 100%.

Making a case for flexible 802.11 architectures

In the past years, researchers have been advocating for flexible 802.11 devices that dynamically adapt to the varying network conditions, looking for efficient alternatives to the 802.11 standard MAC. In this work we demonstrate that this flexibility is readily available at the MAC level, and its operation can be tuned by re-programming the firmware inside the wireless chipsets that are built on relatively generic hardware modules. We show this by implementing the new amendment IEEE 802.11aa in legacy equipments by simply coding the frame exchange schemes at the firmware level. Nevertheless, we claim that the lack of flexibility in the way these modules interact results in a bottleneck that severely degrades performance. In our work, we prove this inefficiency of the 802.11 hardware architecture that hinders high throughput features, as in our case study of 802.11aa reliable multicast. To solve this problem, we provide new directions for the revision of the current hardware architecture and propose a new vision for the future design of wireless chipsets.

Rate adaptation algorithms for reliable multicast transmissions in wireless LANs

The widespread utilization of wireless local area networks (WLANs) as the leading technology for delivering multimedia streams pushed IEEE to ratify the new 802.11aa amendment that enables reliable multicast transmissions over the air. The new feedback-based Group Addressed Transmission Services (GATS) also allows the development of innovative rate adaptation algorithms for multicast traffic; though not explicitly contemplated by the 11aa document, they are crucial in order to improve the overall network throughput. Nonetheless, their performance analysis on large-scale wireless networks results is impractical due to the lack of a unified simulation framework. To this end, we introduce in this chapter new extensions to Network Simulator (NS-2) for implementing GATS and we design a novel application programming interface (API) that permits us to seamlessly integrate new multicast rate adaptation mechanisms by exploiting GATS feedback. We first review the relevant literature on rate adaptation for multicast wireless networks. Then, we describe our unified framework integrated within NS-2 for simulating these algorithms in realistic network scenarios, detailing its internal architecture as well as the reference API. Finally, we provide some multicast rate adaptation algorithms developed using our framework and present their comparative evaluation, which demonstrates the validity of our solution.

Enabling cognitive-radio paradigm on commercial off-the-shelf 802.11 hardware

Cognitive Radio paradigm (CR) is recognized as key enabler for next generation wireless networking: accessing the limited radio spectrum in an opportunistic manner allows secondary users to boost their transmission performance without interfering with existing primary networks. Full testing and experimenting with this paradigm, however, is still a tough task, given either the i) limited capabilities above the PHY layer of cheap SDR solutions, or the ii) heavy investment required for setting up multi-node testbeds powered by FPGAs. In this demo we show how we leveraged our Wireless MAC Processor architecture to tackle the two issues at the same time, providing a highly reconfigurable cognitive solution for wireless local area networks on top of commercial off-the-shelf (COTS) 802.11 devices. We demonstrate a typical CR use case where local and network-wide cognitive loops interact for configuring secondary users real time channel switching in reaction to channel state mutation. We also prove the flexibility of our Wireless MAC Processor (WMP) architecture for extensive testing of the CR paradigm.