Joy Weiss, Ross Yu, Linear Corporation
introduction
The emergence of low-power processors, smart wireless networks and low-power sensors, and "big data" analysis has led to a surge in interest in the Industrial Internet of Things. In short, the combination of these technologies allows a large number of sensors to be placed anywhere: not only where the communications and electrical infrastructure exist, but also wherever valuable information needs to be collected. This information relates to how the “object†behaves. , where or what. The practice of equiping “objects†such as machines, pumps, pipelines, train cars, etc. is nothing new in the industry. From refineries to production lines, custom sensors and networks already exist in a variety of industrial environments. In the past, this type of operating technology (Operations Technology, OT for short) system was operating as a separate network, maintaining high standards of network reliability and security, and using consumer technology simply could not meet such high requirements. Following these high standards to filter available technologies, what remains is the most suitable technology for business-critical IoT applications. In particular, the networking of these sensors determines whether the sensors are safe and cost-effective to deploy in the harsh environments typical of industrial applications. This article discusses some of the key requirements that make Industrial Wireless Sensor Networks (WSN) unique.
Reliability and safety are the most important
For consumer applications, where cost is often the most important system attribute, industrial applications generally place reliability and security at the top of the list. According to OnWorld's survey of global industrial WSN users, reliability and security are the two most important issues they mentioned (see Reference 1). The profitability of a company, the quality and efficiency of the goods produced by the workers, and the personal safety of the workers often depend on these networks. If this comes to mind, the above findings will not be surprising. This is why reliability and security are essential for industrial wireless sensor networks.
A general principle to improve network reliability is to use redundant methods. In the case of redundancy, failure mechanisms that may cause problems can allow the system to recover without data loss. In wireless sensor networks, there are two basic opportunities for exploiting redundancy. The first is the concept of spatial redundancy. That is, each wireless node can communicate with at least two other nodes, and the routing mechanism allows data to be forwarded to any of the two nodes but still be able to reach the intended final destination. In a mesh network, each node can communicate with two or more neighboring nodes. An appropriately constructed mesh network is more reliable than a point-to-point network, because in such a mesh network, if When the first path is unavailable, it automatically sends data on the other path. The second type of redundancy can be implemented using multiple available channels in the RF spectrum. The concept of channel hopping refers to the fact that pairs of nodes can use different channels each time data is transmitted, so any temporary channel problems in a constantly changing harsh RF environment will not affect data transfer. The harsh RF environment is Typical environment for industrial applications. In the IEEE 802.15.4 2.4 GHz standard, there are 15 spread-spectrum channels that can be used for frequency hopping so that channel-hopping systems have much greater flexibility than non-hopping (single-channel) systems. There are several wireless mesh network standards that use both spatial redundancy and channel redundancy. These standards are called Time Slot Frequency Hopping (TSCH), which includes IEC62591 (WirelessHART) and the upcoming IETF 6TiSCH standard ( See reference 2). These meshed network standards use the wireless frequency of the unlicensed 2.4 GHz spectrum available globally and evolved based on the work done by Linear Technology's Dust Networks® department. Starting from SmartMesh® products in 2002, Dust Networks took the lead. Apply the TSCH protocol to low-power, resource-constrained devices.
Although in the harsh RF environment, TSCH is an indispensable basic component for realizing data reliability, but for years of continuous and trouble-free operation, the establishment and maintenance of mesh networks is also critical. Industrial wireless networks often have to operate for many years and will face a variety of different RF challenges and data transfer requirements throughout their lives. Therefore, the last element needed to achieve the same reliability as a wired network is the intelligent network management software that dynamically optimizes the network topology and continuously monitors the link quality to maximize the presence of interference and changes in the RF environment. Throughput.
Security is another key attribute of industrial wireless sensor networks. The main goals for implementing security in WSN are:
Confidentiality - Data transmitted over the network cannot be read by anyone other than the intended recipient.
Integrity - All received messages are acknowledged, completely sent, with no additions, deletions, or modifications to the content.
Authenticity - claims that information from a given source actually came from that source. If you use time as part of the verification method, authenticity also protects the information from being recorded and played back.
Key security technologies that must be incorporated into the WSN to achieve these goals include strong cryptographic algorithms (such as AES128) and robust key and key management, password-level random number generators that block replay attacks, and information for each piece of information. Integrity check (MIC), and access control list (ACL) that specifically allows or prohibits access to a specific device. These latest wireless security technologies can easily be incorporated into many of the devices used in existing WSNs, but not all WSN products and protocols include all security technologies (see Reference 3). Please note that the connection between the secure WSN and the insecure gateway is another weakness, 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 based on traditional products. Customers in these industries have both old and new equipment. The intelligence in the industrial WSN must be embodied in the ease of use of industrial IoT products, enabling existing field workers to seamlessly transition to new industrial IoT products. The network should be formed quickly so that the installer can leave the site with a stable network; when the connection is weak or disconnected, the service interruption is prevented through self-repair; when the service is actually interrupted, self-service reporting and diagnosis are performed; After the deployment is complete, little or no maintenance is required to avoid the high costs of on-site maintenance. For many applications, its success depends in part on whether it can be deployed in difficult-to-reach or very dangerous areas, so IoT devices must run on batteries, typically for more than five years.
In addition, since the industrial IoT widely used by end users often covers the whole company, the system should be available for global deployment and multi-site standardization is needed. Fortunately, international industry wireless standards that understand and meet this requirement are in place, including the IEEE 802.15.4e TSCH.
Sensors are everywhere
For industrial IoT applications, accurate placement of sensors or control points is critical. The promise of wireless technology is to communicate without wires, but if you need to power the wireless nodes by plugging in or recharging them every few hours or months, deployment costs can be daunting, and it's impractical to do so. . For example, adding sensors to a rotating device to monitor the operating conditions of the device makes it impossible to use a wired connection, but the information obtained by monitoring the running device enables the customer to anticipate maintenance of critical devices, thereby avoiding undesired and expensive expenses. The wingman.
To ensure flexible and cost-effective deployments, each node in the industrial WSN should be able to run on batteries for at least five years, providing users with ultimate flexibility to expand the reach of industrial IoT applications. As an example of an industrial TSCH WSN, Linear Technology's SmartMesh products typically operate at much less than 50μA, so they can run on two AA batteries for many years. If the surrounding environment has a wealth of energy that can be collected, then the wireless node can still operate continuously by energy collection (see Figure 1).
Figure 1: Sensors everywhere – Low-power wireless sensor nodes that are continuously powered by the collected energy. This wireless temperature sensor, for example, from ABB's collection of heat, can be placed in the best location for more industrial environment data.
Time problem
Industrial surveillance and control networks are mission-critical. This network consolidates the systems that affect the basic costs of commodity production, and the timeliness of its data is crucial. Over the past 10 years, deterministic TSCH WSN systems have been field tested in a variety of surveillance and control applications. Time-slot systems of this type (for example, WirelessHART) have their data transfer time stamped and time-limited. In such networks, more time slots are automatically configured for nodes that require more data transmission opportunities, and low latency transmissions can be achieved in such networks by configuring multiple time slots on successive paths in the network. This data transfer coordination capability also greatly enhances the deployment of frequent, dense data transfer networks. Without a timetable, the flood of disorderly influx of wireless traffic could crash non-TSCH wireless networks.
In addition, each packet in the TSCH network contains accurate timestamp information indicating the time the packet was sent, and each node can obtain a uniform time across the entire network to coordinate control signals across WSN nodes when needed. Since timestamp data is provided, data can be correctly sequenced even if the data is not received in order. In the face of industrial applications that must coordinate information from multiple sensors, timestamp data is helpful in diagnosing exact causes and effects. .
Visibility of network operations is key
Industrial networks require continuous operation for many years, but no matter how robust a network is, problems may still occur. Even though the network is performing well during installation, the network quality may be affected by various environmental factors during its operating life. Prompt early warning of such issues is important for any industrial network, and the ability to quickly diagnose and resolve problems is also key to high quality service. When it comes to providing visibility into network management metrics, not all wireless sensor networks must be treated equally. However, at a minimum, the management systems of industrial wireless networks should provide visibility into the following areas:
• Wireless link quality as measured by signal strength (RSSI)
• End-to-end packet delivery success rate
• Grid quality, highlighting nodes with insufficient backup paths to maintain network reliability
• Node status and battery life (where applicable)
In the deployment of the best industrial applications using intelligent networks, the solution to this type of problem is to automatically resend data on alternate paths while continuously updating the network topology to maximize connectivity (see Figure 2).
Figure 2: Network Visibility - Network management software provides critical visibility into the health of wireless networks such as the SNAP-ON utility software tool from Emerson Process Management
Smart "objects" should have intelligent networks
People are concerned about improving the intelligence of “objectsâ€, but in industrial Internet of Things applications, this is not the only place of “intelligenceâ€. Industrial IoT networks should use both intelligent terminal nodes and the best network and security management functions that must be provided by enterprise IT and operational technology departments. The network should be highly configurable to meet specific application needs. For example, to meet the low power requirements for extended battery life, you should have the ability to self-learn the available power of the network and use intelligent routing to maximize the power consumption of the entire network. In addition, the network should automatically adapt to changes in the RF environment. When this change occurs, it can be more advantageous to be able to dynamically change the topology. Linear Technology's SmartMesh Network Manager (SmartMesh Network Manger) not only implements network security, management, and route optimization, but also allows users to reconfigure nodes over the air when needed to provide a functional upgrade path that adapts to future customer demand changes .
in conclusion
The Internet of Things is largely an industrial phenomenon with clear business drivers and compelling return on investment. In business-critical applications, industrial wireless sensor networks must meet high standards of intelligence and security, and can reliably run without wires for many years. Existing and emerging wireless mesh network standards can meet these stringent requirements, which will become key building blocks for industrial IoT and help industrial customers realize business and service changes in the era of industrial Internet of Things (see Figure 3).
Figure 3: Promoting change - Software analysis (eg Brains.App software from IntelliSense.io) uses data from industrial wireless sensor networks to simplify plant operations, optimize production, and increase safety.
reference:
1. Industrial Wireless Sensor Networks: Trends and Developments https://#sthash.cl3G9ze5.dpuf
2. 6TiSCH Wireless Industrial Networks: Determinism Meets IPv6: Maria Rita Palattella, Pascal Thubert, Xavier Vilajosana, Thomas Watteyne, Qin Wang, and Thomas Engel. Published in IEEE Communications Magazine (Vol. 52, No. 12)
3. Secure Wireless Sensor Networks Against Attacks, Kristofer Pister and Jonathan Simon, http://electronicdesign.com/communications/secure-wireless-sensor-networks-against-attacks
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