# Industrial IoT Monitoring: Technologies and Architecture Proposal
## 2 Technologies for Industrial IoT
### IWSN Standards  
This subsection analyses the characteristic features of each of the main IWSN standards, namely ZigBeePRO, WirelessHART, ISA100.11a, and WIA-PA. The analysis is done on a per-OSI-layer basis, starting with the physical layer and working up to the application layer. Table 1, below, presents a summary of the referred features, and may be used as guidance for the reader. IEEE 802.15.4 [10] is a standard for low-rate wireless personal area networks (LR-WPANs) that specifies the physical (PHY) and medium access control (MAC) layers. These layers' design was optimized for very low-power consumption, high reliability (using mesh networks), low-data rates, and low-cost. ZigBee, WirelessHART, ISA100.11a, and WIA-PA have all adopted IEEE 802.15.4 at the PHY layer. However, because WirelessHART, ISA100.11a, and WIA-PA target worldwide adoption, they've chosen to use the 2.4 GHz frequency band only, as opposed to ZigBee, which can use the 868 Mhz and 915 Mhz bands as well [18]. At the MAC layer, there are significant differences in the adoption of the IEEE 802.15.4 by each of the four standards. At this layer, networks can work in beacon or non-beacon modes of operation. When using the beacon mode, sensor nodes receive a specific message that is used to synchronize the network devices and, at the same time, to identify the network, and to describe the structure of the frame. Beacon networks are capable of detecting other beacon networks, and, for this reason, beacon networks can coexist in the same geographical area. Additionally, IEEE 802.15.4 uses a superframestructure in order to manage nodes channel access. The superframe is formed by three different parts: Contention Access Period (CAP), Contention Free Period (CFP), and inactive period. This superframe structure is used in ZigBee and WIA-PA because these two standards operate in beacon mode. On the other hand, WirelessHART and ISA100.11a do not operate in beacon-mode, as their developers considered that this mode is not good enough for industrial applications (Note: WIA-PA also shares the same view; however, its authors opted for maintaining full compatibility with IEEE 802.15.4-based networks, and implement additional features at the Data Link (DL) layer). As a result, WirelessHART and ISA100.11a implemented their own superframes [34]. WirelessHART's superframe is composed of 10 ms timeslots, while ISA100.11a can operate in any of three superframe modes (short, long, and hybrid). Finally, ZigBee can use a slotted or unslotted CSMA/CA mechanism for managing the access to the wireless medium, while the remaining standards (WirelessHART, ISA100.11a and WIA-PA) use TDMA and CSMA, providing a high and medium level of latency determinism, respectively. Neither WirelessHART or ISA100.11a implement the full IEEE 802.15.4 MAC layer, as they consider that the MAC layer of IEEE 802.15.4 is not capable of delivering the deterministic latency needed by industrial applications. As such, these standards extend and complement medium access mechanisms with functionality at the data link (DL) layer [9], namely, Time Synchronized Channel Hopping (TSCH), which then evolved to the new IEEE 802.15.4.e standard. The TSCH mechanism offers two significant improvements: the possibility to have deterministic latency (communication resources are pre-allocated); and a mechanism of channel hopping that minimizes interference with nearby devices that operate in the same frequency, such as IEEE 802.11 devices. On the other hand, the WIA-PA follows the IEEE 802.15.4 standard at the DL layer, including functionalities like time synchronization and frequency hopping techniques. Lastly, ZigBee does not implement any mechanism at this layer. It is also worthwhile mentioning that, in addition to extending/complementing MAC layer functionality, the DL layer is also used by ISA100.11a for implementing some network-related functions, specifically in what concerns routing.