Synchronous and Concurrent Transmissions for Consensus in Low-Power Wireless

With the emergence of the Internet of Things, autonomous vehicles and the Industry 4.0, the need for dependable yet adaptive network protocols is arising. Many of these applications build their operations on distributed consensus. For example, UAVs agree on maneuvers to execute, and industrial systems agree on set-points for actuators.Moreover, such scenarios imply a dynamic network topology due to mobility and interference, for example. Many applications are mission- and safety-critical, too.Failures could cost lives or precipitate economic losses.In this thesis, we design, implement and evaluate network protocols as a step towards enabling a low-power, adaptive and dependable ubiquitous networking that enables consensus in the Internet of Things. We make four main contributions:- We introduce Orchestra that addresses the challenge of bringing TSCH (Time Slotted Channel Hopping) to dynamic networks as envisioned in the Internet of Things. In Orchestra, nodes autonomously compute their local schedules and update automatically as the topology evolves without signaling overhead. Besides, it does not require a central or distributed scheduler. Instead, it relies on the existing network stack information to maintain the schedules.- We present A2 : Agreement in the Air, a system that brings distributed consensus to low-power multihop networks. A2 introduces Synchrotron, a synchronous transmissions kernel that builds a robust mesh by exploiting the capture effect, frequency hopping with parallel channels, and link-layer security. A2 builds on top of this layer and enables the two- and three-phase commit protocols, and services such as group membership, hopping sequence distribution, and re-keying.- We present Wireless Paxos, a fault-tolerant, network-wide consensus primitive for low-power wireless networks. It is a new variant of Paxos, a widely used consensus protocol, and is specifically designed to tackle the challenges of low-power wireless networks. By utilizing concurrent transmissions, it provides a dependable low-latency consensus.- We present BlueFlood, a protocol that adapts concurrent transmissions to Bluetooth. The result is fast and efficient data dissemination in multihop Bluetooth networks. Moreover, BlueFlood floods can be reliably received by off-the-shelf Bluetooth devices such as smartphones, opening new applications of concurrent transmissions and seamless integration with existing technologies

Concurrent Transmissions for Multi-hop Bluetooth 5

Bluetooth is an omnipresent communication technology, available on billions of connected devices today.While it has been traditionally limited to peer-to-peer and star network topology, the recent Bluetooth 5 standard introduces new operating modes to allow for increased reliability and Bluetooth Mesh supports multi-hop networking based on message flooding.In this paper, we present BlueFlood.It adapts concurrent transmissions, as introduced by Glossy, to Bluetooth.The result is fast and efficient network-wide data dissemination in multi-hop Bluetooth networks.Moreover, we show that BlueFlood floods can be reliably received by off-the-shelf Bluetooth devices such as smart phones, opening new applications of concurrent transmissions and seamless integration with existing technologies. We present an in-depth experimental feasibility study of concurrent transmissions over Bluetooth PHY in a controlled environment.Further, we build a small-scale testbed where we evaluate BlueFlood in real-world settings of a residential environment.We show that\ua0BlueFlood achieves 99% end-to-end delivery ratio in multi-hop networks with a duty cycle of 0.13% for 1-second intervals

Paxos Made Wireless: Consensus in the Air

Many applications in low-power wireless networks require complex coordination between their members. Swarms of robots or sensors and actuators in industrial closed-loop control need to coordinate within short periods of time to execute tasks. Failing to agree on a common decision can cause substantial consequences, like system failures and threats to human life. Such applications require consensus algorithms to enable coordination. While consensus has been studied for wired networks decades ago, with, for example, Paxos and Raft, it remains an open problem in multi-hop low-power wireless networks due to the limited resources available and the high cost of established solutions.This paper presents Wireless Paxos, a fault-tolerant, network-wide consensus primitive for low-power wireless networks. It is a new flavor of Paxos, the most-used consensus protocol today, and is specifically designed to tackle the challenges of low-power wireless networks. By building on top of concurrent transmissions, it provides low-latency, high reliability, and guarantees on the consensus. Our results show that Wireless Paxos requires only 289 ms to complete a consensus between 188 nodes in testbed experiments. Furthermore, we show that Wireless Paxos\ua0stays consistent even when injecting controlled failures

Paxos Made Wireless: Consensus in the Air

Many applications in low-power wireless networks require complex coordination between their members. Swarms of robots or sensors and actuators in industrial closed-loop control need to coordinate within short periods of time to execute tasks. Failing to agree on a common decision can cause substantial consequences, like system failures and threats to human life. Such applications require consensus algorithms to enable coordination. While consensus has been studied for wired networks decades ago, with, for example, Paxos and Raft, it remains an open problem in multi-hop low-power wireless networks due to the limited resources available and the high cost of established solutions.This paper presents Wireless Paxos, a fault-tolerant, network-wide consensus primitive for low-power wireless networks. It is a new flavor of Paxos, the most-used consensus protocol today, and is specifically designed to tackle the challenges of low-power wireless networks. By building on top of concurrent transmissions, it provides low-latency, high reliability, and guarantees on the consensus. Our results show that Wireless Paxos requires only 289 ms to complete a consensus between 188 nodes in testbed experiments. Furthermore, we show that Wireless Paxos\ua0stays consistent even when injecting controlled failures

Multichannel Communication in Contiki's Low-power IPv6 Stack

Vast majority of wireless appliances used in household, industry and medical field share the ISM frequency band. These devices need to coexist and thus are challenged to tolerate their mutual interference. One way of dealing with this is by using frequency hopping; where the device changes its radio channel periodically. Consequently, communications will not suffer from the same interference each time; instead, it should be fairer and more stable. This thesis investigates the aforementioned problem in the field of low power wireless sensor networks and Internet of Things where Contiki OS is used. We introduce a low-power pseudo-random frequency-hopping MAC protocol which is specifically characterized as a duty cycled asynchronous sender-initiated LPL style protocol. We illustrate two flavors of the protocol; one that does not use any dedicated channel and another which allows dedicated broadcast channels that can implement frequency-hopping as well. We implement the protocol in C for real hardware and extensively test and evaluate it in a simulated environment which runs Contiki. It proved to work with Contiki's IPv6 stack running RPL (the standardized routing protocol for low power and lossy wireless networks). We compare the performance of the implemented protocol to the singlechannel ContikiMAC with varying levels of interference. Results show a reduction down to 56% less radio-on time (1.50% vs. 3.4%) and 85% less latency (306 ms vs. 2050 ms) in the presence of noise, while keeping a good basecost in noise-free environments with 1.29% radio duty cycle when using 9 channels with no dedicated broadcast channels (vs. 0.80% for single channel) and 252 ms average latency(vs. 235 ms). Moreover, the results show that the multichannel protocol performance metrics converge to almost the same values regardless of the noise level. Therefore, it is recommended as a good alternative to single channel ContikiMAC in realworld deployments where noise presence is anticipated

Synchronous Protocols for Low-Power Wireless: Towards Reliable and Low-Latency Autonomous Networking for the Internet of Things and Wireless Sensor Networks

With the emergence of the Internet of Things, autonomous vehicles and the Industry 4.0, the need for reliable yet dynamic connectivity solutions is arising.Many of these applications build their operation on distributed consensus.For example, networked cooperative robots and UAVs agree on manoeuvres to execute, and industrial control systems agree on set-points for actuators.Many applications are mission- and safety-critical, too.Failures could cost lives or incur economic losses.Any wireless network connecting safety-critical devices must be reliable, and often energy-efficient, as many devices are battery powered and we expect them to last for years.It shall be self-forming and self-fixing as well, to allow for reliable autonomous operation; as many applications cannot afford to stop and wait for external configuration. In this context, synchronised communication has emerged as a prime option for low-power critical applications.Solutions such as Chaos or Time Slotted Channel Hopping (TSCH) have demonstrated end-to-end reliability upwards of 99.99 percent.In this thesis, we design and implement protocols to support highly reliable and low latency communication in low-power wireless settings.First, we present a standard-based solution that integrates with the 6TiSCH stack (IPv6 over TSCH) without the need of static scheduling or schedule negotiation.Second, we identify key challenges when it comes to implementing the 6TiSCH stack, and demonstrate how these challenges can be addressed.Then, we take a step beyond the standards and focus on synchronous network flooding such as Glossy and Chaos.We show how to enhance them by adding time-slotting and frequency diversity to achieve high reliability and low latency under interference.Finally, we design and realise a network stack that combines and extends ideas from TSCH and synchronous transmissions to achieve highly reliable data delivery with a loss rate lower than x and achieve network-wide consensus with a radio duty cycle of 0.5 percent.On top of this robust kernel, we enable two- and three-phase commit protocols to provide network-wide consensus.We implement our protocols, evaluate them on public testbeds of sensor nodes equipped with IEEE 802.15.4 compatible radios and compare to state-of-the-art protocols.We contribute the source code of our main protocols to the community as a step towards enabling ubiquitous connectivity in the context of the Internet of Things

Competition: Towards Low-Power Wireless Networking that Survives Interference with Minimal Latency

Low-power wireless networking needs to survive interference in order to accommodate the requirements of serious applications of Internet of Things. Synchronous transmission techniques like Glossy and Chaos perform well under normal operating conditions. However, their data delivery latency suffers under interference even when extended to use channel hopping. In this paper we discuss our techniques to enhance the robustness of synchronous flooding while keeping the latency and power consumption minimal

Competition: Towards Low-Power Wireless Networking that Survives Interference with Minimal Latency

Low-power wireless networking needs to survive interference in order to accommodate the requirements of serious applications of Internet of Things. Synchronous transmission techniques like Glossy and Chaos perform well under normal operating conditions. However, their data delivery latency suffers under interference even when extended to use channel hopping. In this paper we discuss our techniques to enhance the robustness of synchronous flooding while keeping the latency and power consumption minimal

Competition: Aggressive synchronous transmissions with in-network processing for dependable all-to-all communication

Low-power wireless networking needs to survive interference in order to accommodate the requirements of serious applications of the Internet of Things. Synchronous transmission techniques like Glossy and Chaos perform well under normal operating conditions. However, their data delivery latency suffers under interference even when extended to use channel hopping. In this paper, we discuss our techniques to enhance the robustness of synchronous flooding while keeping the latency and power consumption minimal and how to collect data from multiple sources to multiple destinations

Competition: Towards Low-Latency, Low-Power Wireless Networking Under Interference

Low latency reliable data delivery is a key challenge for mission critical applications in the Industrial Internet of Things. Chaos was shown to perform well under normal operating conditions. In this paper we discuss some techniques to enhance its robustness under strong interference