# Industrial IoT Monitoring: Technologies and Architecture Proposal
## 1 Introduction  
The Internet of Things (IoT) currently makes it possible to have a world sensed by and connected to all kinds of devices. Wireless Sensor Network (WSN) technology is the key for connecting physical and virtual environments. This technology is growing up so rapidly that in 2011 Cisco-IBSG estimated that globally there would be 50 billion interconnected \"things\" by 2020 [1]. The IoT paradigm leads to an extremely large number of new opportunities and technical challenges in several fields in general, and in the industrial field in particular. In industry, wired technologies continue to be prevalent [2; 3]. Digital technologies like ModBus, ProfiBus, CanBus, HART [4], and even analogue technologies like 4-20 mA [5], are used to monitor and control most processes. Despite the high reliability of such technologies, proven over many years, wired technologies are expensive, difficult to install, time consuming, and unable to cope with the requirements of Cyber Physical Systems (CPS) and Industry 4.0. In Industry 4.0, CPSs will confer micro intelligence (namely processing and networking capabilities) to industrial objects, reducing even further today's already short production cycles [6]. Additionally, in the near future, new markets will drive CPSs to increase their level of adaptability, directly connecting customers to manufacturing facilities, using Cyber Physical Manufacturing Systems(CPMS) [7, 8]. Thus, WSNs or, more specifically, Industrial Wireless Sensor Networks (IWSN), are fundamental for meeting the requirements of Industry 4.0. IWSN characteristics like low operating costs, self-organization, self-configuration, flexibility, rapid-deployment, and easy upgrading, make them ideal to industrial scenarios. However, despite all of these favourable characteristics, the adoption of WSNs in industry requires standards, dependability, ease of use, network security, extended battery life, low cost, and IP connectivity [9]. In recent years, considerable effort was made in order to design technologies that meet these requirements, and to standardize IWSN technology. Standards like IEEE 802.15.4 [10] and IEEE 802.15.1 [11] are the technology foundation of many industrial applications for process and factory automation. IEEE 802.15.4 is the base technology for standards such as ZigBeePRO [12], WirelessHART [13], ISA100.11a [14], and WIA-PA [15]. These are widely used in process automation applications in the areas of chemical manufacturing, pulp and paper, oil and gas, and glass and mineral [16]. On the other hand, IEEE 802.15.1 is the base technology for standards such as WISA [17] and WSAN-FA [9], widely used in factory automation applications in the areas of assembly process for automotive, consumer products and electronics [18]. Nevertheless, although standards compliance is necessary, it is not enough to guarantee ISWN reliability per se. Sensor node components, either at hardware or firmware levels, and the network itself, can be at the root of a variety of faults [19]. Sensor nodes are inherently resource-constrained devices in terms of energy, processing power and memory capacity. In this respect, the Internet Engineering Task Force (IETF) recently defined three classes of devices [20]: Class 0 for devices with less than 10 KB of RAM and 100 KB of flash memory; Class 1 for devices with around 10 KB of RAM and 100 KB of flash; and Class 2 for devices that have more resources but are still quite constrained when compared to high-end devices. In addition to the device constraints mentioned, sensor, network, and application heterogeneity lead to extremely complex IWSN solutions and, consequently, to fault-proneness. These characteristics impose adequate, carefully-designed strategies in the development of sensor nodes firmware, hardware architectures, and operating systems (OSs) kernel (e.g., choosing between exokernel, microkernel, monolithic approach or hybrid approach) [21].