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consider that a company's profitability, the quality and efficiency with which they produce goods and worker safety often rely on these networks. This is why reliability and security are essential for industrial wireless sensor networks. One general principle in designing a network for reliability is redundancy, where failover mechanisms for likely problems enable systems to recover without data loss. In a wireless sensor network, there are two basic opportunities to harness this redundancy. First is the concept of spatial redundancy, where every wireless node has at least two other nodes with which it can communicate, and a routing scheme that allows data to be relayed to either node, but still reach the intended final destination. A properly formed mesh network—one in which every node can communicate with two or more adjacent nodes—enjoys higher reliability than a point-to-point network by automatically sending data on an alternate path if the first path is unavailable. The second level of redundancy can be achieved by using multiple channels available in the RF spectrum. The concept of channel hopping is that pairs of nodes can change channels on every transmission, thereby averting temporary issues with any given channel in the ever changing and harsh RF environment typical of industrial applications. Within the IEEE 802.15.4 2.4GHz standard, there are fifteen spread spectrum channels available for hopping, affording channel hopping systems much more resilience than non-hopping (single channel) systems. There are several wireless mesh networking standards that include this dual spatial and channel redundancy known as Time Slotted Channel Hopping (TSCH), including IEC62591 (WirelessHART) and the forthcoming IETF 6TiSCH standard. These mesh networking standards, which utilize radios in the globally available unlicensed 2.4GHz spectrum, evolved out of work by Analog Devices' SmartMesh team, who pioneered the use of TSCH protocols on low power, resource constrained devices starting in 2002 with SmartMesh products. While TSCH is an essential building block for data reliability in harsh RF environments, the creation and maintenance of the mesh network is key for continuous, problem-free multiyear operation. An industrial wireless network often must operate for many years and over its lifetime will be subject to vastly different RF challenges and data transmission requirements. Therefore, the final ingredient required for wire-like reliability is intelligent network management software that dynamically optimizes the network topology, continuously monitoring link quality to maximize throughput despite interference or changes to the RF environment. Security is the other critical attribute of industrial wireless sensor networks. The primary goals for security within the WSN are: Confidentiality: Data transported in the network cannot be read by anyone but the intended recipient. Integrity: Any message received is confirmed to be exactly the message that was sent, with out additions, deletions, or modifications of the content. Authenticity: A message that claims to be from a given source is, in fact, from that source. If time is used as part of the authentication scheme, authenticity also protects a message from being recorded and replayed. The critical security technologies that must be incorporated into a WSN to address these goals include strong encryption (e.g., AES128) with robust keys and key management, crypto- graphic-quality random number generators to deter replay attacks, message integrity checks (MIC) in each message, and access control lists (ACL) to explicitly permit or deny access to specific devices. These state-of-the-art wireless security technologies may be readily incorporated in many of the devices used in today's WSNs, but not all WSN products and protocols incorporate all measures. Note that connecting a secure WSN to an insecure gateway is another point of vulnerability, and end-to- end security must be considered in system design. Industrial IoT Is Not Installed by Wireless Experts For the most part, established industries are adding IIoT products and services to their legacy products, and their customers are deploying in environments with a mix of old and new equipment. The intelligence embodied in industrial WSN must confer an ease of use to IIoT products that make transitions seamless to the existing field personnel. Networks should rapidly self-form so that the installer can leave the site with a stable running network, avoid service interruptions by repairing themselves when connections are weak or lost, self- report and diagnose when service interruptions do occur, and avoid costly onsite visits by requiring little or no maintenance once deployed. For many applications, their success relies in part on being deployable in areas that are difficult or dangerous to reach, so the IoT devices must operate on batteries, typically for more than five years. Also, systems should be available for global deployment since the widespread adoption of IIoT by end users is often company wide, and requires multisite standardization. Fortunately, international industry radio standards that comprehend and fulfill this requirement are in place, including IEEE 802.15.4e TSCH. Sensors Anywhere For IIoT applications, the precise placement of a sensor or control point is critical. Wireless technology offers the promise of no-wires communication, but if you need to power a wireless node by plugging it in, or recharge it every few hours or even months, the cost and impracticality of deployment become prohibitive. For example, adding sensors to rotating equipment 25 IoT

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