Virtualization, in which application and operating system software are essentially abstracted from the computer hardware on which they run, is a well-established practice in the world of IT. But now the discipline is being applied to process control and automation systems—even control room operator stations and collaborative displays.
A guided tour of this increasingly virtualized world, encompassing everything from thin clients to bus extenders, was conducted by Katrin Kerber, account manager at Matrox Electronic Systems, in her presentation, "Combining Workstation Virtualization with Control Room Process Visualization and Collaboration," this week at ABB Automation & Power World 2012 in Houston.
"Virtualization is one concept of separating the host from the operator interface by using bus extension technologies, KVM-extender solutions, virtualization-over-IP, and compression/decompression technologies," said Kerber.
The oldest of these separation technologies is thin computing, which joins a host computer to a client appliance via TCP/IP communications. "Its communication protocols are responsible for separating application logic from user interfaces, and only key strokes, mouse movements and screen updates travel network to the server," said Kerber. "But the latency caused by its separation means it can't function in real time."
More recently, virtualized computing over IP has provided a more modern approach to thin-client computing. "It's easier to deploy and more powerful. It has more intelligent software, and it's made big steps overcoming challenges in network latency," added Kerber. "And there are new software solutions on the market that accelerate its standard protocols and reduce packet losses, but performance is still not real-time."
I/O compression/decompression methods also link a host to a client via TCP/IP, but use algorithms to compress graphics from the host system and extend them. "There are limits to resolution and performance, depending on assured network bandwidth. For example, using multiple monitors at high resolution requires significantly more assured network bandwidth," explained Kerber. "I/O compression schemes are proprietary architectures, requiring back-end and front-end equipment from the same manufacturers. And compression necessarily implies manipulation of pixel data, even though most of these algorithms claim to be mathematically ‘lossless.' "
Meanwhile, keyboard, video and mouse (KVM) extenders describe a range of black boxes that alter the basic host/client arrangement by instead going from the host through a KVM transmitter unit via an analog Cat 5 or fiber-optic extension cable to a KVM receiver that exposes display and I/O data to operators. "In this case, a display compression scheme takes rendered outputs of graphics data and combines then with an I/O extension mechanism for keyboard and mouse," added Kerber. "This necessarily implies manipulation of pixel data with a strong potential of affecting display quality. Also, I/O extensions for keyboard and mouse are limited by their native protocols, which can involve latency over longer distance. And asymmetric graphics quality and performance can occur, depending on what equipment is contained in the main workstation."
Likewise, bus extenders go from a host computer through a hardware bus transmitter card via a digital extension medium like fiber-optic cable to a client appliance that again exposes the display and I/O data to operators. "Extenders such as PCI or PCI-Express bus are serialized to an appliance, and only bus commands are transferred over the link. This renders uncompressed graphics locally on the operator's appliance," said Kerber.
"Bus extenders have a finite transmission distance, but usually it is adequate. Also, the computing session requires the link between the appliance on the operator side and the main system in the computer room to be available at all times," said Kerber. "But in general, bus extension is the most reliable and robust virtualization method, and it provides true real-time performance because the bus itself is communicating with the display."