Deterministic networking allows carrying data flows with low data-loss rates and with bounded latency. A typical usecase is the convergence of Operational Technology (OT) with Information Technology (IT), also known as the Industrial Internet. Wireless networks operate on a shared communication medium where the potential external interference along with multi-path fading impact data packet delivery. By employing diversity in the time, frequency and spatial domains, wireless technologies with scheduled transmissions, such as IEEE Std 802.15.4-2015 Time Slot Channel Hopping (TSCH), can mitigate those effects and provide Reliable and Available Wireless (RAW) communications that approach determinism. Nevertheless, a radio link operating in the ISM band still needs to handle collisions and possibly re-transmission. Therefore, It takes redundant links and paths to provide both the high availability and the near consistent reliability that industrial applications require. In this paper, we present the Packet Automatic Repeat reQuest (ARQ), Replication and Elimination (RE), and Overhearing (PAREO) functions to further increase the Quality of Service (QoS) in industrial networks, even when implemented on top of best-effort traffic in a shared network. The results show that PAREO provides up to approximately 6 times lower Packet Error Rate (PER) and up to approximately 10% higher energy consumption than the default RPL implementation with 7 retransmissions, while keeping jitter and latency as low as default RPL with 1 retransmission.

IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) is a distance vector routing protocol especially designed for the Internet of Things (IoT). RPL uses broadcast DODAG Information Object (DIO) messages to build a Destination Oriented Directed Acyclic Graph (DODAG) toward a root. Each node selects a parent node toward the root using a common Objective Function (OF). However, the use of a single route can affect the network reliability and the end-to-end latency. In this study, we propose to employ the Packet Replication and Elimination (PRE) principles to use parallel paths toward the DODAG root, over the IEEE 802.15.4 Time-Slotted Channel Hopping (TSCH) as a medium access. To this aim, we propose number of algorithms to select the second or the alternative parent in RPL. Furthermore, we study the advantages of using overhearing feature over correlated paths. Our simulation campaign conducted over Cooja, the simulator of Contiki OS, demonstrate that the use of overhearing in conjunction with PRE in RPL considerably improves the robustness of a wireless network by providing greater opportunity to a packet to reach its destination.

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The Internet of Things (IoT) has become ubiquitous due to its flexibility, ease-of-use, and reduced cost. As a consequence, the industry is adopting these systems in its transformation into Industry 4.0. However, the strict Quality of Service (QoS) requirements of the industry are not met with the default best-effort provisions of the IoT. Most industrial applications require strict guarantees in terms of end-to-end network reliability and latency. For instance, consecutive packet losses can lead to communication disruptions in supply chain systems. Therefore, adaptations are being made to fulfill these requirements with the IEEE Std 802.15.4-2015 Time slotted Channel Hopping (TSCH) link-layer standard and the IPv6 Routing Protocol for Low-Power and Lossy Networks (RPL) standard at the Internet Engineering Task Force (IETF). However, even by employing such industrial protocols, it is still difficult to achieve the expected QoS levels. Considering that RPL constructs and maintains a single-path from a source to a destination if there are potential issues on this path (e.g., queue overflow, variable wireless link quality) packets may suffer unexpected delays and even drops. If we consider a multi-path implementation where each node can replicate a packet into several paths, the transmission reliability improves since each packet copy is used to forward the packet information. However, uncontrolled replication can lead to network flooding, resulting in excessive power consumption. In this article, we present On-Demand Selection (ODeSe), a novel multi-path routing algorithm, which improves our previous work, the Common Ancestor (CA) algorithms, by selecting the most suitable upward forwarders. Moreover, we use the Packet Automatic Repeat reQuest, Replication and Elimination, and Overhearing (PAREO) functions in order to improve network reliability and availability. In order to control the number of relay nodes during a transmission, ODeSe forces each node of the same relay level to select the same Preferred Parent (PP) and the same Alternative Parent (AP). Thus, we address the trade-off between the total number of traversed nodes in the network and high reliability. Using the Cooja network simulator running the Contiki OS, we compare ODeSe against single-path RPL and multi-path RPL with different alternative parent selection algorithms. The results demonstrate that ODeSe outperforms single-path RPL in terms of reliability, and multi-path RPL in terms of energy consumption while maintaining a 99.14% packet delivery ratio.

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