Posted by: Bernhard Wiegel on August 23, 2017
What do preprogrammed robots on a factory floor have in common with driverless trains and metro systems? A uniquely advanced degree of automation.
Automation is transforming lives at an unprecedented rate. In the railway industry, for example, technological innovation is taking the shape of futuristic offerings, like driverless cars and trains. And now these same innovations are coming to other transportation applications and the factory floor.
System operators depend on strong, reliable wireless connections to efficiently operate the network that supports these developments and keep passengers and employees safe. Interruptions to communication due to slow or unreliable roaming in these mission-critical situations puts any company at risk of financial and reputational damage.
Fast roaming significantly reduces these risks. With its long communication ranges and high transmission speeds, the technology allows mobile clients to roam continuously throughout a wireless network, seamlessly sending packets of information between control bases, access points and end devices. This permits continuous connectivity onboard trains and other vehicles that rely on wireless communication to operate. Without fast roaming, the mobility, reliability and security required by industrial systems, especially those that operate autonomously, would not be possible.
Railway networks use fast roaming technologies to boost industrial WiFi performance, guaranteeing end-to-end packet delivery and arrival.
The use of wireless to expand communication throughout factory and transportation networks provides teams with simple implementation processes and reduced application costs, in addition to:
Fast roaming enhances AGV communication by extending transmission ranges across multiple access points.
To optimize the capabilities of industrial WiFi networks, there are a couple of technologies employed that typically lead to higher roaming speeds, while continuing to maintain thorough network security. A solution providing only one or the other would not be sufficient.
1. Fast roaming with highest WiFi security: Mobile clients move through the transmission range of several different access points, which means the reliability of the communication and available bandwidth must be guaranteed at all times. Fast roaming works to optimize communication and bandwidth by automatically allowing clients to connect to access points with the greatest signal, frequently achieving interruptions of less than 50 ms. When a mobile client is in motion and wants to change its current connection to a different access point, the client triggers a procedure to enact a fast Basic Service Set (BSS) transition as defined in the IEEE 802.11 standard. A secure transition can only take place when a client connects to and authenticates the target access point by providing a valid key for encrypted data packets. To consistently safeguard and ensure fast roaming, a network might also adopt any of the four following techniques: Pre-Master Key (PMK) Caching, Pre-Authentication, Opportunistic Key Caching (OKC) and the IEEE 802.11r standard. These techniques are applied to fast roaming technology to optimize network roaming while continuing to deliver consistent security.
2. Fast roaming through reduced scan times: When a railway operator wants to know whether a track is available at an upcoming station, he or she typically sends a flicker or alarm to find out if the space is already occupied or not. A train sending wireless signals would also follow the same procedure to scan a channel or frequency to identify if an upcoming trackside access point is busy or not, looking to avoid packet interruptions at all costs. The active method to locate available frequencies of available access points is through repetitive, quick channel scans of wireless local area networks (WLANs). If an access point responds to a train’s “Who’s there?” query with “Me!”, the client can actively and efficiently make note of potential roaming target points and their surrounding company.
If channels that require radar detection are also used, such as in outdoor operation within 5 GHz, this poses a further challenge. For these channels, clients are not allowed to actively search for access points by sending probe requests (“Who’s there?”), but they must first determine if the channel has a primary user, such as a radar station. Since this determination must be repeated and requires one minute of passive listening, this is not an option for fast roaming outdoors. Therefore, the client is obliged to sequentially listen to all existing channels until the access points make themselves known. With access points and clients specially optimized for fast roaming, the timings of periodic announcements and waiting times are configurable. Thus, very fast roaming can be facilitated, especially in outdoor operation in the less congested 5 GHz band.
Though created to work in sync, the technologies above should be considered as methods to optimize industrial WiFi, not in place of standard network security measures. Incorporating these technologies ensures throughput requirements are met and increases reliability and communication range while reducing packet latency and interruption. All of these benefits result in a seamless handover of information between end devices, giving railway operators and passengers constant and trustworthy connectivity.
Fast roaming is undoubtedly critical to the success of industrial transportation and manufacturing applications. As automation continues to transform industrial equipment and settings, fast roaming will grow in navigational and operational importance.
Teams need to consider how this technology will reduce financial, reputational and safety risks and bring their networks forward. With fast roaming capabilities, teams will have the know-how to set their industrial WiFi networks up for success today and in the future.
Interested in reading more on the topic? This Belden white paper outlines which fast roaming technologies can ensure your network requirements are consistently met: IEEE 802.11 – Technologies for Fast Roaming.
Tobias Heer | Email Tobias
Future Technologies, R&D, Belden, Inc.
Tobias Heer has been with Belden since 2012 and specializes in topics that revolve around security and wireless in industrial control systems. He is a professor for IT Security at the University of Applied Science in Albstadt-Sigmaringen, Germany. He received his doctoral degree in 2011 and worked as a postdoctoral researcher at the Chair of Communication and Distributed Systems at RWTH Aachen University. His focus areas are network protocol design, security and wireless communication. Heer was involved in the development and standardization of secure Internet protocols in the Internet Engineering Task Force (IETF).