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Embracing WLANs in the industrial market
The realization of wireless networking as a mainstream technology is now clear as a result of a myriad of products available today that satisfy the demand driven by consumer and office applications. However, the adoption of this technology by industrial device manufacturers has been limited thanks to some significant challenges and security concerns involved in deploying the technology in industrial environments such as the plant floor. In spite of this, there is no getting around the fact that significant interest in the industrial use of wireless technologies continues to be driven by its staggering advantages over cabled systems in harsh industrial environments and its use in difficult-to-wire equipment, such as those with moving parts or distributed over large areas. This, coupled with the fact that yesterday’s proprietary, closed control systems are giving way to open network architectures such as Ethernet, we see a WLAN future hurtling toward the industrial world at an incredible speed. A quick WLAN primer Typical industrial network topology
Figure 1 Office networks in an industrial facility mimic that of any typical office, supporting common functions such as database services, desktop computing, e-mail, intranet, Internet, and other communication/data services. However, the office network in this case is also connected to the rest of the plant for such purposes as sales, inventory, and maintenance operations. Operations personnel such as plant operation engineers, production managers, and batch operators use control networks for performing batch and process monitoring/control typically in areas of real-time control, which can be vital to a plant’s operation. Systems on a control network may also include SCADA (System Control and Data Acquisition, Supervisory Control and Data Acquisition, Security, Control and Data Acquisition) and M2M (Man to Machine) interfaces. In some cases, they may include many of the same computer systems found in the office and embedded devices such as redundant Ethernet switches, real-time monitoring systems with special control panels, and display devices, although the applications are different from those in an office network. Device networks are the most diverse and the most automated of the three networks, and include different specialized embedded and electrical systems such as programmable logic controllers (PLCs), fieldbus-enabled equipment for measuring flows, temperatures, vibrations, liquid and gas volumes, sensor panels, motion control, pressure, fluid, gas, and heat controllers. Several of the common open fieldbus standards, such as PROFIBUS, Modbus, DeviceNet, and CANopen have traditionally been used in industrial device networks. Trend toward standards In device networks, there still exist competing technologies including some of those used in control networks. Table 1 lists common fieldbus technologies and networks they are used in, each with its unique cabling requirements and competing open standards or organizations representing the standards. A significant issue in industrial networks used to be the connectivity between one fieldbus network standard to the next and then back to the control network, requiring the use of converters and adapters, which Ethernet has served to alleviate to a large extent as well.
Table 1 Why industrial WLANs? There are many good reasons to consider WLANs for the control network on the factory floor. In addition to the basic mobility aspects of WLANs that are such an asset to office networks, the control floor also has some unique safety issues that WLANs can help address. For example, WLANs may be used to seek out current operational data and manage a controlled shutdown procedure remotely and allow the proliferation of control points such as safety shutoff valves and other mechanisms much more conveniently than a wired network. Furthermore, the controlled equipment may also be installed near wet, moist, or corrosive materials that could damage physical wires and plugs. On device networks, too, WLANs present several unique advantages beyond those in office networks. Remote device maintenance and monitoring becomes quite convenient if a device is networked wirelessly. This is especially true for devices that are not easily reached because of their physical location in the plant (such as dangerous or harsh operating environments, or restricted areas in the plant). In addition to maintenance, basic wireless connectivity of devices located on moving parts such as in a wind tunnel, robotic, or motor-controlled system is optimal compared to physically wiring a system that can be problematic, especially in corrosive or harsh environments. In other words, WLANs can be used to untether difficult connections and allow for measurements at the source without passing through various intermediate connector devices. Last, but not the least, WLANs make it easier to come up with proof-of-concept networked systems in an industrial environment without expensive prototyping. Moving Wi-Fi to the industrial environment The wireless security problem The inherent link security problem in a WLAN stems from its very strength — its wirelessness. Since wireless technologies make use of a shared medium, in other words, airwaves, with no well-defined physical boundary that can be protected, the link is not as secure against eavesdropping as a wired one, and it is also difficult to restrict network access to a set of authorized users. The security mechanism proposed in the initial 802.11 standards was, in a moment of misplaced bluster, named Wired Equivalent Privacy (WEP) but it turned out to be flawed. Newer industry standards such as Wireless Protected Access (WPA) provide important fixes for issues that plagued the legacy WEP and at the same time maintain legacy compatibility with WEP encryption hardware. WPA2 and the recently ratified IEEE 802.11i standard add further security enhancements to WPA, including use of the Advanced Encryption Standard (AES) block cipher in the form of Counter Mode CBC-MAC Protocol (CCMP) and stronger integrity check mechanisms. Table 2 outlines the significant differences between various generations of Wi-Fi security technologies.
Table 2 In the presence of strong link security, privacy and integrity of network data are maintained, but there still exists the possibility of other attacks that may allow an intruder to act as a valid client connecting to the network, or as an evil twin access point masquerading as a valid access point to hijack client credentials (or worse). Other means of defending against attacks such as MAC filtering, which inventories valid client MAC addresses that can connect to the WLAN and denies access to all others, and access control/blocking of network nodes are required to reduce the chances of unintentional or casual access to the wireless network. Mechanisms that monitor for rogue access points are also an integral part of industrial WLAN security. Finally, secure management of devices that form the industrial WLAN and LAN infrastructure is a frequently overlooked item that can turn out to be the Achilles heel of an industrial network. Management capabilities allowing for remotely controlling the configuration, upgrades, and provisioning of the network infrastructure devices in all three types of industrial networks need to be upgraded to secure versions of protocols such as:
In many applications, strong user or device authentication requirements may necessitate the use of independent authentication mechanisms such as Kerberos or embedded digital certificates for cryptographically secure access mechanisms.
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