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Hand-eye coordination in switched KVM systems

Mark Hempel

Head of Product Management

Processing speed in KVM systems is crucial for ergonomic operation

The concept of TRUE KVM unites 5 key performance areas for Keyboard – Video – Mouse systems. Ergonomic Operation, Efficient Signal Management, Secure Transmissions, Modular Design and Hybrid Sources Connectivity. Today, I wanted to shed some light on Ergonomic Operation, what it means, how you can easily assess the performance of a solution and why it is important.

The core task of a KVM system is to allow the operator desk with keyboard, video, mouse or other devices such as drawing or touchscreen tablets to be physically separated over longer distances from the PC or server running the software application. The intention is to provide the operator with a user experience equivalent to a direct port by port connection of a PC located at the operator desk.

For today´s whiteboard session, I have laid out the signal flow initiated at the user desk. A dual head implementation supporting two monitors for standard software applications like process control or scheduling tasks driven keyboard and mouse. Additionally, the user desk has third monitor of different size/resolution performance to allow for creative work also employing a drawing tablet.

Ergonomic operation primarily refers to hand-eye coordination. Whenever the operator presses a key, moves the mouse or the tablet pen, the visualization of the action on the display is expected to be instantaneous. Especially high resolution displays can quickly create a challenge, since the overall system is designed to balance multiple additional requirements such as efficient one line cabling between user station, KVM switch and target PCs, pristine video quality and very low latency to enable ergonomic operation.

The round trip delay from hand movement to visual acknowledgement can be broken down into 12 steps. They are all delaying the visual presentation on the screen. In step 1, USB signals are traveling to the CON unit at the operator desk, where keyboard and mouse inputs are multiplexed (2) together with KVM system information required for On-Screen-Display and hotkey control commands (3). The KVM switch (4) transparently routes signals to the destination port (5) connected to the PC unit (6), which demultiplexes the signals and passes them in their recreated native format to the target PC (7).

The PC processes the keyboard input, mouse/cursor movement or the data representing the line drawn on the tablet and embeds the results into the numerical representation of the video and sends that to the graphics port of the PC. Depending on screen resolution, framerate, color depth and graphics port standard (HDMI, DVI, Displayport), the PC unit (8) takes the video signal and passes it through at line rate or encodes the video for the connection to the KVM switch (9). The switch routes (10) the signal to its destination port towards the CON unit (11) where the signal is demultiplexed and decoded if necessary. On the target graphic port of the CON unit (12) the DVI, HDMI or Displayport signal is sent to the monitor.

The resulting round-trip delay time for the signal can be broken down into 6 main parts. 1) Multiplexing/Demultiplexing in the CON and PC units. 2) Propagation delay on the lines between CON/PC unit and KVM switch. 3) Routing in the KVM switch. 4) Processing time in the target PC. 5) Video encoding and decoding. 6) When distances between KVM switch and CON/PC units are longer, electrical signals require conversion to and from optical signals which allow a much greater cable length.

Before looking at these contributors in more detail, lets establish some benchmark criteria for adequate hand-eye coordination. In case a monitor displays at a framerate of 30 Hz every 33 milliseconds a new image is displayed. If the display is set to 60 Hz, every 16.6 milliseconds a new image is displayed. Images change at these increments in time at the system level. In case the processing times 1) to 6) are lower than half of the frame display time (in the examples 33 or 16.6 milliseconds) the change in cursor position or a typed key will display in the next frame.

The biggest impact on delay is coming from the video coding. While broadcast or TV encoders can use optimized algorithms for viewer perceived quality, KVM manufacturers must ensure equal encoding quality across the entire image. The quality and speed of the encoding algorithm is a key determining factor for the ergonomic response of the system.

One key application to consider is virtual reality. While most people associate it with consumer customer gaming, it offers tremendous opportunity for design applications. Even early trials for control rooms suggest a work environment without physical screens, multi-user interactive. To avoid motion sickness, round trip delay needs to meet single digit millisecond limits to leave enough headroom for the more complex PC application processing.

In a dedicated KVM system the ergonomic response is predictable and repeatable and ensures a consistent user experience. IP based KVM systems can produce quite different results depending on the system implementation. While IP systems using a fully dedicated infrastructure (cabling and switches) achieve a good performance in lower port count implementations, the original advantage of reduced infrastructure invest actually completely disappears. However, when using a shared network, packet delay times can rise in an unpredictable way leading to a poor user experience. Even in high port count solutions in a dedicated IP KVM system, buffers add up quickly to introduce significant unwanted delays for connections affected by multiple IP switching stages.

Currently, the best hand-eye coordination performance is achieved with a dedicated KVM system using superior video encoding algorithms.

If you find this information useful, please leave a comment or like/share – or, even better, reach out to me to discuss. IHSE will continue to lead the way in KVM and we are here to help architect your next solution or explore how we can grow our businesses together.


Mark Hempel

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