The emergence of low-power processors, intelligent wireless networks, low-power sensors, and "big data analytics" has sparked considerable interest in the Industrial Internet of Things (IoT). In short, combining these technologies allows for the placement of a vast array of sensors anywhere: not just where communication and power infrastructure is located, but anywhere that can collect critical information about an object's behavior, location, or content. Equipping machines, pumps, pipes, train carriages, and other objects with sensors is nothing new in industry. Numerous dedicated sensors and networks are deployed across a wide range of industrial environments, from refineries to production lines. Historically, these operational technology (OT) systems operated as standalone networks, maintaining high standards of network reliability and security that consumer technologies simply could not meet. By selecting suitable technologies based on these high standards, the most appropriate technologies for mission-critical Industrial IoT applications are ultimately chosen. In particular, the way these sensors are networked determines whether they can be deployed securely, reliably, and cost-effectively in the harsh environments of industrial applications. This white paper explores some of the key requirements that differentiate Industrial Wireless Sensor Networks (WSNs).
Reliability and safety are of utmost importance
For consumer applications, cost is often the most important consideration, while industrial applications generally prioritize reliability and security. According to an ON World survey of global industrial WSN users, reliability and security were the two most important issues they cited. A company's profitability, the quality and efficiency of worker production, and worker safety often depend on these networks. This is why reliability and security are essential for industrial wireless sensor networks.
1 Industrial Wireless Sensor Networks: Trends and Development
Figure 1. Sensors are everywhere. Low-power wireless sensor nodes powered by energy harvesting systems (such as this wireless temperature sensor from ABB, driven by harvested thermal energy) can be placed in suitable locations to obtain more data about industrial environments.
A general principle for improving network reliability is to provide redundancy, setting up fault recovery mechanisms to address potential problems and enable the system to resume operation without data loss. In wireless sensor networks, redundancy is utilized in two ways. The first is the concept of spatial redundancy, where each wireless node can communicate with at least two other nodes, and the routing mechanism allows data to be forwarded to either of the two nodes while still reaching the intended final destination. In a well-designed mesh network, each node can communicate with two or more adjacent nodes; if the first path becomes unavailable, it automatically switches to another path to transmit data. Therefore, mesh networks have higher reliability compared to point-to-point networks. The second type of redundancy can be achieved using multiple available channels in the RF spectrum. Channel hopping refers to the concept that paired nodes can use different channels each time they transmit data. Therefore, in the constantly changing and harsh RF environments faced by industrial applications, a temporary problem with any given channel will not affect data transmission. In the IEEE 802.15.4 2.4GHz standard, 15 spread spectrum channels are available for frequency hopping, giving channel hopping systems greater resilience than non-frequency hopping (single-channel) systems. Several wireless mesh network standards employ this spatially and channel-redundant Time Slotted Channel Frequency Hopping (TSCH) technology, including IEC 62591 (WirelessHART) and the upcoming IETF 6TiSCH standard.<sup>2</sup> These mesh network standards utilize wireless frequencies in the globally available unlicensed 2.4 GHz spectrum. This stems from the work of Analog Devices' SmartMesh team, which pioneered the application of the TSCH protocol to low-power, resource-constrained devices starting with SmartMesh products in 2002.
While TSCH (Transmission Switching) is fundamental to ensuring data reliability in harsh RF environments, the way a mesh network is built and maintained is also crucial for achieving years of continuous, trouble-free operation. Industrial wireless networks often need to operate for many years and will face a variety of different RF challenges and data transmission requirements throughout their lifespan. Therefore, to achieve the same reliability as wired networks, they must be equipped with intelligent network management software. This type of software can dynamically optimize network topology, continuously monitor link quality, cope with interference and changes in the RF environment, and maximize throughput.
Security is another key characteristic of industrial wireless sensor networks (WSNs). The main goal of achieving security in WSNs is:
Confidentiality: Data transmitted over a network cannot be read by anyone other than the intended recipient.
Completeness: Confirm that any received information is completely consistent with the sent information, without any additions, deletions, or modifications.
Authenticity: Asserts that information from a given source actually comes from that source. Authenticity can also protect information from being recorded and replayed if time is included as part of the verification process.
Key security technologies that must be incorporated into WSNs to achieve the above objectives include: strong encryption algorithms (such as AES128) and reliable key and key management; cryptographic-level random number generators to prevent retransmission attacks; message integrity checks (MICs) for each message; and explicit access control lists (ACLs) that allow or deny access to specific devices. These advanced wireless security technologies can be easily integrated into many devices used in today's WSNs; however, not all WSN products and protocols employ all security technologies. Note that the connection between a secure WSN and an insecure gateway is another vulnerability, and end-to-end security must be considered in the system design.
Industrial IoT is not installed by wireless experts
Mature industries mostly add Industrial IoT products and services to traditional products. These customers' deployment environments contain both legacy and new equipment. The intelligence embodied in Industrial WSNs must make Industrial IoT products easy to use, enabling a seamless transition and allowing existing field personnel to easily use new Industrial IoT products. The network should be able to quickly self-build, so installers can deliver a stable network; it should avoid service interruptions through self-healing when connectivity is weak or lost; it should provide self-reporting and diagnostics when service interruptions occur; and generally, after deployment, it should require little or no maintenance, thus avoiding the high costs of on-site maintenance. The success of many applications depends in part on deployment in hard-to-reach or hazardous areas; therefore, IoT devices must rely on batteries and generally need to operate continuously for more than 5 years.
Furthermore, since the Industrial Internet of Things (IIoT) widely adopted by end users often spans the entire company, the system should be available for global deployment and require multi-site standardization. Fortunately, international industry wireless standards that understand and meet these requirements are already in place, including IEEE 802.15.4e TSCH.
Sensors are everywhere
For Industrial Internet of Things (IIoT) applications, accurate placement of sensors or control points is crucial. While wireless technology promises to enable wireless communication, the deployment costs are prohibitive and impractical if wireless nodes need to be powered every few hours or months by plugging them into a power outlet or recharging them. For example, equipping rotating equipment with sensors to monitor its operation is not feasible using wired connections. However, by obtaining relevant information from monitoring operating equipment, customers can perform predictive maintenance on critical equipment, thus avoiding unnecessary and costly downtime.
To ensure flexible and cost-effective deployment, each node in an industrial WSN should be able to operate on batteries for at least five years. This provides users with significant flexibility and expands the reach of industrial IoT applications. As an example of an industrial TSCH WSN, Analog Devices' SmartMesh products typically operate at a current well below 50 µA, allowing them to run for many years on just two AA batteries. If there is ample energy storage available in the surrounding environment, the wireless nodes can also achieve continuous operation through energy storage (see Figure 1).
Figure 2. Network Visibility – Important information related to the health of the wireless network can be viewed through network management software, such as Emerson Process Management's SNAP-ON software utility.
2 6TiSCH Wireless Industrial Networks: Deterministic Compliance with IPv6 Standards: Maria Rita Palattella1, Pascal Thubert2, Xavier Vilajosana3,4, Thomas Watteyne4,5, Qin Wang4,6, Thomas Engel1 Published in: IEEE Communications Magazine (Vol. 52, No. 12).
3 Protecting Wireless Sensor Networks from Attacks, Kristofer Pister and Jonathan Simon
Time issue
Industrial monitoring and control networks are mission-critical. These networks support systems that impact the fundamental costs of goods production, making data timeliness crucial. Over the past decade, deterministic TSCH WSN systems have been field-proven in various monitoring and control applications. These time-slotted systems (such as WirelessHART) provide timestamped, time-constrained data transmission. In these networks, nodes requiring more data transmission opportunities will automatically allocate more time slots, and low-latency transmission can be achieved by configuring multiple time slots on consecutive paths within the network. This data transmission coordination capability also significantly enhances the ability to deploy dense networks with frequent data transmissions. Without a timetable, a flood of uncontrolled wireless traffic can overwhelm non-TSCH wireless networks.
Furthermore, each data packet in the TSCH network contains accurate timestamp information indicating the time the packet was sent, and each node has access to a unified network-wide time, enabling coordination of control signals within the WSN node network when needed. Because timestamped data is provided, data can be correctly ordered even if it is not received in sequence. In industrial applications where information from multiple sensors must be coordinated, timestamped data is helpful in diagnosing the exact cause and impact.
Visibility of network operations is crucial.
Industrial networks need to operate continuously for many years; however, no matter how robust a network is, problems can still occur. Even if a network functions well at installation, its quality can still be affected by various environmental factors throughout its operational lifespan. Providing appropriate early warnings for such problems is crucial for any industrial network, and the ability to quickly diagnose and resolve issues is key to high-quality service. Regarding visibility into network management metrics, not all wireless sensor networks have the same requirements. However, at a minimum, the management system for industrial wireless networks should provide visibility into the following aspects:
• Wireless link quality as measured by signal strength index (RSSI)
• End-to-end data packet transmission success rate.
• Mesh quality, highlighting nodes that do not have enough backup paths to maintain network reliability.
• Node status and battery life (where applicable).
In optimized industrial applications employing intelligent networks, the aforementioned issues can be addressed by automatically retransmitting data along alternative paths while continuously updating the network topology to maximize connectivity (see Figure 2).
Intelligent "everything" should have an intelligent network.
While there is considerable interest in enhancing the intelligence of "everything," the "intelligence" in Industrial Internet of Things (IIoT) applications extends beyond this. IIoT networks should employ intelligent endpoints and provide network and security management capabilities to showcase the technological advantages of an enterprise's IT and operations departments. The network should be highly configurable to meet specific application needs. For example, to meet the low-power requirements for extended battery life, it should have the ability to autonomously determine available network power and employ intelligent routing to optimize overall network power consumption. Furthermore, the network should automatically adapt to changes in the RF environment; dynamically changing the topology in such cases may be more advantageous. Analog Devices' SmartMesh Network Manager not only enables network security, management, and routing optimization but also allows users to reconfigure nodes via wireless networks as needed, providing a pathway for future upgrades to meet evolving customer requirements.
The Internet of Things (IoT) is largely an industrial phenomenon that can drive business growth and deliver excellent ROI. In these business-critical applications, industrial wireless sensor networks must meet high standards of intelligent, secure, and reliable wireless operation, supporting continuous operation for many years. These stringent requirements can be met through existing and emerging wireless mesh network standards, which will become key building blocks for the Industrial IoT, helping industrial customers transform their businesses and services in the era of the Industrial IoT (see Figure 3).
Figure 3. Driving Change – Software analytics, such as Brains.App software from IntelliSense.io, leverages data from industrial wireless sensor networks to streamline factory operations and optimize output and improve safety.
Analog Devices (ADI) believes the information provided is accurate and reliable. However, ADI assumes no responsibility for the use of the data, nor for any infringement of third-party patents or other rights arising from the use of such data. Specifications are subject to change without notice. This does not constitute an implied or other form of license to ADI's patents or patent rights.
