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The vision behind the Internet of Things (IoT) revolves around creating a connected ecosystem where devices, people, and systems collaborate seamlessly, unlocking new possibilities, improving efficiency, and enhancing our daily lives. IoT encloses many device classes, including low-power wireless devices that rely on batteries or energy harvesting. Due to the low-power nature and the instability of the wireless links, networks comprising these IoT devices are commonly known as Low-power and Lossy Networks (LLNs).

Several network-wide flooding-based communication primitives that employ synchronous transmissions have emerged as an alternative to traditional multi-hop routing, thereby creating a new dimension of LLN research. While these primitives have demonstrated superior performance in terms of latency and reliability, they have received little attention regarding network security. In this dissertation, we study the effectiveness of several attacks that strive to disrupt synchronous transmission-based protocols. Based on the findings from this work, we examine the security requirements and propose encryption and lightweight flood verification methods to protect synchronous transmission-based flooding protocols from these attacks.

Realising the IoT's vision demands employing well-established communication technologies like the Internet Protocol (IP) suite protocols to ensure interoperability. However, the IP suite protocols are not explicitly designed for low-power networks; hence using them in LLNs encounters numerous challenges. Some of my work included in this dissertation focuses on the performance issues of two widely used IP suite protocols: Transmission Control Protocol (TCP) and Datagram Transport Layer Security (DTLS). We propose to replace the conventional link layer protocols of the LLN  stacks with a synchronous transmission-based protocol to enhance the reliability that TCP expects in lower layers, thereby improving the TCP performance. We introduce novel header compression mechanisms to reduce the size of DTLS messages without violating end-to-end security. Reducing the size of DTLS messages lowers the transmission overhead, improving its performance in LLNs.

Optical Wireless Communication (OWC) is a complementary technology to radio frequency communication. Specifically, visible light communication (VLC) has proven its capability to offer higher data transfer rates, enabling faster and more efficient communication. The last work of this dissertation draws inspiration from synchronous transmissions in LLNs and presents an OWC-based time synchronisation system for high-speed VLC access points to synchronise their transmissions. This time synchronisation system has a considerably lower synchronisation jitter than the widely-used Precision Time Protocol (PTP).