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Current Industrial Internet of Things (IoT) requires high-reliability, guaranteed performance and low-power consumption in order to allow mission-critical infrastructures monitoring and control in harsh environments with a battery lifetime of years. 6TiSCH is a promising Industrial IoT technology that aims to provide these requirements by combining the TSCH mode of the IEEE 802.15.4e standard with an IPv6-enabled upper stack that connects the IoT network to the Internet. Since 6TiSCH is based on TSCH, it has the capability of allocating a specific amount of bandwidth per node in a quasi-deterministic manner and at the same time, is able to minimize the radio duty cycle to reduce energy consumption. Additionally, the channel hopping technique addresses unreliability issues caused by factors such as multi-path fading and narrow-band external interference. However Industrial IoT networks and also 6TiSCH networks, are still facing major challenges. First, the current exponential growth of the IoT is also being experienced in the Industrial IoT. This calls for more scalable solutions that can cope with current and future demand. Second, Industrial IoT requires also to be flexible and programmable in order to be further tailored to the actual dynamic industrial automation needs. This is of most importance since Industrial IoT networks are expected to not only cope with a dynamic external environment that alters the available resources over time, but also to cope with variable demands and QoS policies that have different optimization goals over the time. Consequently, in order to achieve an effective and end-to-end QoS compliance, this programmability should be present in all the industrial network domains, including the IoT network. These challenges currently remain as open questions. On one hand, intradomain scalability largely depends on how network resources are shared and distributed. Although TSCH itself does not specify how these resources have to be scheduled, 6TiSCH provides the upper layers with minimal distributed scheduling capabilities that ensure communication between nodes. However, as we will later study in this book, limitations may appear when 6TiSCH networks scale up. On the other hand, flexibility and programmability are currently absent in 6TiSCH networks. In 6TiSCH, distributed protocols make static decisions over the routing (RPL) and scheduling (6P), and configuring the network dynamically is problematic. Alternatively, the proposed centralized SDN-based approaches provide operators with the required flexibility, but seem to be prone to high control overhead, and inherently, to be low scalable. On top of this, current Industrial IoT solutions are usually isolated in network silos, which hinders a complete end-to-end control in a multi-domain hierarchical architecture, which is typically required to scale the network up with QoS guarantees. This PhD book addresses these research questions. It first studies intradomain scalability in 6TiSCH networks, from a theoretical point of view and through extensive simulations. Then, it identifies the existing scalability problems and proposes a new scheduling mechanism in order to try to overcome them. Secondly, it proposes an innovative technique to flexibly control Industrial IoT networks (in our case 6TiSCH) in an efficient but yet scalable manner. We analyze our new approach in depth, discussing its possibilities and comparing it with other alternative approaches. Subsequently, we integrate it in a widely used open-source SDN framework to support multi-domain scalable end-to-end control in Industrial IoT networks. This means to allow a controller to be able to globally and jointly control,in a hierarchical manner, the wired and wireless network segments involved in a real Industrial IoT network. Finally, this PhD book also includes two complementary studies on 6TiSCH. First, we study the open-source simulator for 6TiSCH that allows benchmarking and fast-prototyping. The simulator is validated with current state-of-the-art hardware and software and is proven to be a useful tool to not only study scalability in 6TiSCH networks, but also the performance of different networks scenarios (topologies, traffic patterns, etc.), scheduling functions and routing algorithms. Secondly, in order to further discuss the potential and possibilities of Industrial IoT networks, this PhD book also includes a report on a cycling use case that leverages 6TiSCH to monitor athletes using a long-range multihop highly dynamic network. This use case, which may open new interesting research paths, shows that applications that intuitively would not have been the target for 6TiSCH at first sight, can also take advantage from 6TiSCH industrial performance.

The Industrial Internet of Things is a challenge for wireless sensor networks, where ultrareliability, guaranteed performance, and ultralow-power consumption are mandatory requirements to enable critical IoT applications. The time-slotted channel hopping (TSCH) mode of the IEEE 802.15.4e standard is one of the most promising technologies to accomplish these requirements by yielding guaranteed performance and, simultaneously, efficiently combating external interference and multipath fading. One of the challenges in TSCH networks is to build an efficient schedule for managing the access of the nodes to the timeslots and channels. Several scheduling algorithms have been proposed. Currently, the Scheduling Function Zero SFx is one of the proposed scheduling algorithms for 6TiSCH, the ongoing standard for an IPv6-enabled stack working over TSCH. SFx is based on random resource allocation according to the traffic demand, which makes it inadequate for large-scale and dense deployments due to internal collisions. This paper has two main goals. First, we extensively investigate the performance of SFx for large-scale and dense scenarios, analyze its scalability, and identify its scheduling limitations. Second, we present a new TSCH-based scheduling function, ie, the distributed broadcast-based scheduling (DeBraS) algorithm, a scheduling solution designed for dense deployments based on sharing scheduling information between nodes to reduce collisions proactively. We show, through extensive and large-scale simulations, that DeBraS supports much larger densities than state-of-the-art scheduling functions, outperforming the current distributed 6TiSCH algorithm SFx up to 1.61 times in terms of throughput for large network sizes, at the expense of an increase in power consumption.

The Time-Slotted Channel Hopping (TSCH) mode of the IEEE 802.15.4e amendment aims to improve reliability and energy efficiency in industrial and other challenging Internet-of-Things (IoT) environments. This paper presents an accurate and up-to-date energy consumption model for devices using this IEEE 802.15.4e TSCH mode. The model identifies all network-related CPU and radio state changes, thus providing a precise representation of the device behavior and an accurate prediction of its energy consumption. Moreover, energy measurements were performed with a dual-band OpenMote device, running the OpenWSN firmware. This allows the model to be used for devices using 2.4 GHz, as well as 868 MHz. Using these measurements, several network simulations were conducted to observe the TSCH energy consumption effects in end-to-end communication for both frequency bands. Experimental verification of the model shows that it accurately models the consumption for all possible packet sizes and that the calculated consumption on average differs less than 3% from the measured consumption. This deviation includes measurement inaccuracies and the variations of the guard time. As such, the proposed model is very suitable for accurate energy consumption modeling of TSCH networks.