Toward Deterministic and Predictable Industrial 4.0 – TPI

Toward Multi-path Routing Strategies in Low-power Wireless Mesh Networks

In order to achieve high Quality of Service (QoS) in low-power wireless mesh networks such as high end-to-end reliability and bounded latency, without being dependent on the variability of the link quality and the availability of the selected intermediate relay nodes, we extended the de facto single-path routing protocol with multi-path strategies. Multi-path routing protocols have been a popular approach over the past years for different reasons, including to mitigate traffic load and to enhance end-to-end network reliability. Indeed, they enable multiple paths using different nodes from a source to a destination, and depending on the use case, these multiple paths can be used alternatively or simultaneously. The conducted work in this project opted for a simultaneous multi-path approach, and proposed multi-path redundant algorithms which exploit data packet replication and elimination, promiscuous overhearing, and forward error correction to combat isolated and cumulated losses, and to bound the latency in the network. The results show that reliability and predictability can be guaranteed by using multiple parallel data paths instead of retransmissions along a default single path.

During the TPI project, the team successfully proposed a series of multipath routing protocols and algorithms. The proposed algorithms, which enable the use of multiple paths in the RPL routing protocol, ensure high end-to-end network reliability and fault tolerance in the presence of temporarily unavailable nodes or sudden drops in link quality, while providing a low-latency network for industrial applications, and not only (e.g., smart street lighting, vehicle automation, real-time multiplayer gaming). More specifically, the project members were able to achieve network reliability above 99%, as well as jitter performance (i.e., latency variation) close to 15 ms. The project contributed to two IETF standards, i.e., RFC 9450 and RFC 9551 thanks to the research results. Additionally, these results have provided the opportunity to launch several new research projects with industrial partners such as Texas Instrument and Renault, who were interested in a high level of QoS on the wireless activation of the Battery Management System (BMS) in electric vehicles, and more recently with Silicon Labs, which is interested in smart lighting solutions for smart cities.

Even though many objectives have been achieved during the ANR JCJC TPI project, there are still research items that there was not enough time to tackle such as centralized approach of achieving reliable and predictable networking. In fact, we observed issues when applying a distributed multi-path routing strategies over a centralized resource allocation system. Indeed, when the nodes change their preferred parents, then there is dysfunctionality with the centralized controller to redistribute the required resources. Therefore, this subject is an essential part of our ongoing research, and, thus we continue working on addressing it over newly founded research projects. More specifically, we are investigating on introducing the proposed multi-path strategies in Software-Defined Networking (SDN) technology

Lagos Jenschke, T.; et al. ODeSe: On-Demand Selection for Multi-path RPL Networks. Ad Hoc Networks. 2021, 114, 102431.

Koutsiamanis, R.-A.; et al. “From Best-Effort to Deterministic Packet Delivery for Wireless Industrial IoT Networks«. In IEEE Transactions on Industrial Informatics. July 2018, 14, 4468-4480.

Koutsiamanis, R.-A.; et al. «A Centralized Controller for Reliable and Available Wireless Schedules in Industrial Networks«. In Proc. MSN 2020.

Koutsiamanis, R.-A.; et al. «Meet the PAREO Functions: Towards Reliable and Available Wireless Networks«. In Proc. IEEE ICC 2020.

“New communication process for an electric vehicle battery calculator system”, CIFRE: Private Contract with Renault.

“Enabling Wireless Battery Management System (BMS) in Electric Vehicles”, Contrat de Recherche : Private Contract with Texas Instrument.

To reduce the operational, automation, management and production cost and to simplify the production chain, the IoT technology is now considered in the industrial domain, also called the Industry 4.0, i.e., the 4th Industrial Revolution. The Industry 4.0 ambition is to make the factory more flexible and adaptable. The main goal is to replace the existing cables with a wireless medium, while guaranteeing network reliability above 99.999%. Furthermore, the Industry 4.0 requires robust communications, messages need to be sent securely and the communication framework must guarantee message delivery in a given delay with jitter close to 0. In addition, some environments may require a dense network, with thousand of nodes sending a large amount of messages. Scalability is thus another constraint imposed by the Industry 4.0. To reach this ambition, the wireless industrial networks must not only be reliable but also deterministic and predictable.

A deterministic network guarantees that the transported information will be carry out in a pre-defined and in a tight window of time, whatever the link quality and the network congestion. Moreover, a periodic process will be repeated identically every time. So the most important characteristic of the network is to exhibit a jitter (different on the consecutive packet inter-arrival time) close to 0. Determinism is a required property in the power grid, to ensure that high tension lines breakers can be activated within milliseconds, in public transportation to make sure that automated vehicles are operated safely for their passengers, and in industrial automation for control loops. However, the current technologies deployed for the IoT are based on best-effort packet switched network. Data are encapsulated within packets that are subject to variable delays in the network, due to retransmissions and enqueuing in intermediate nodes.

In 2016, the IEEE 802.15.4 standard was published to offer QoS for deterministic industrial-type applications. Time-Slotted Channel Hopping (TSCH) allows for competing the industrial standards. However, it does not avoid retransmissions when a data packet is lost, due to collision, or outage of one node. Moreover, the potential interferences, which lead to packet losses, with technologies operating on 2.4GHz, may decrease the reliability performance [4]. Since TSCH seems to be a good candidate solution, we propose to focus on implementing and extending the standard to bridge the gap between academia and Industry 4.0. Moreover, we propose to use distributed scheduling, multi-path routing and hybrid network to build the Industry 4.0 as presented in the following.

In this project, firstly, we plan to define algorithm and protocols for nodes to set up their network: select the “good” channel (i.e., less interfering channels) and discover their neighbor and the routes within the network. Then we will investigate in depth both the distributed and centralized scheduling solutions of 6TiSCH to identify the pros and cons, as well as their appropriateness for ultra-deterministic industrial networks. We will propose new dynamic scheduling, tightly coupled with routing algorithms over multiple interfaces. Moreover, we plan to propose isolated (dedicated) tracks to provide flow isolation, and to make the transmissions reliable and independent: each application has dedicated (i.e., reserved) bandwidth for its packets transmissions. Associating innovative and original forwarding techniques (such as duplication, overhearing, opportunism and glossy networking) and a dynamic and efficient scheduling will allow us to have a jitter close to 0, thus to fully control delays in the network. In addition to those new algorithms and protocols, we will provide a security threat analysis and provide countermeasure within our protocol to secure the network. Both simulation and experimental set up will be used to validate our work toward the Industrial IoT.