4.1 Device Set Introduction

4.1 Device Set Introduction

4.1.1 The Device Set Concept

The KoiosLT platform allows certain protocols to be configured for high-availability connections to communication devices by combining the Devices Instances into a Device Set.  For example, an owner's site may have two or more OPC-UA servers available for serving system tags. The KoiosLT platform can easily be configured to link all of the available OPC-UA servers together in a Device Set.  The Device Set will establish a primary device to link all internal tag communications too so long as a timeout or loss of communication to the selected Device Instance has not occurred.  If a loss of communication is experienced, the KoiosLT will then automatically transfer, in a round-robin style attempt (refer to 4.1.3 Understanding Round Robin, to the next available Device Instance within the Device Set.  Should a backup properly establish communication, the primary status will be transferred to that Device instance.  Tag status' and Model status' associated with the Device Set are not affected during this transfer, allowing for a robust communication architecture for high-availability.  Manual transfer within the Device Set is also possible.  Should the primary Device Instance have to go down for updating or patching, the primary control can be transferred to the next available Device Instance in the Device Set.

4.1.2 Understanding Active Selection

There are two (2) ways to affect the currently connected device.

• Manual: A user can manually select the active device, from the set of devices
• Automatically:By default, the device set will always try and connect to any available device in the device set.  An automatic swap over of the active device will if any of the following occur:
  • Active Device Timeout, refer to 3.4 Device Timeouts
  • Active Device Disabled by User, refer to 3.2 Device Detail

4.1.3 Understanding Round Robin Attempts

The device set can be configured with as many device instances as required.  Each device instance is given a priority number in the stack.  In the event the active device requires an automatic swap over, the device set will attempt connect to the next highest number on the priority stack.  If the device instance is the highest number on the stack, it will revolve back to the lowest number on the stack as next available device in the set.  The order can be manually set by the user, but by default stacks the devices in the order at which they were added to the device set, refer to 4.3 Device Set Detail