Redundancy Control Options -
When Failure is Not an Option




Media Level Redundancy

PlugIn_Help_File_DkGreenStarting with V5.6 and forward, TOP Server includes support for Media-Level Redundancy capabilities for all drivers via the Media Level Redundancy Plug-In.  This powerful functionality allows redundancy of network, network type and device and is supported for most drivers - For a list of drivers not supporting Media Level Redundancy click here. If your license is covered by an active support & maintenance contract, you can install a free upgrade and add this plug-in to your installation.

CPR_Serial_ENETCommunications Path Redundancy (CPR)

Communications Path Redundancy involves establishing redundant physical connections to the same device, such as having both an Ethernet and serial connection to the same device.

Since it is possible to specify a NIC card at the channel level, CPR can also be used to enable network redundancy, as well, for Ethernet devices either supporting multiple connections or that have multiple network modules.

Communications Path Redundancy decreases the likelihood of lost communications due to the cabling or communications module of a particular device.

DPR_Different_DevicesDevice Pair Redundancy (DPR)

Device Pair Redundancy involves having two identical devices running the same logic, allowing fail over in the event that one of the devices becomes disabled.

Device Pair Redundancy decreases the likelihood of downtime caused by an issue with the actual device or controller affecting responsiveness to TOP Server requests.

These modes of redundancy can all be used together or separately to provide the level of reliability your application requires at all levels of downstream communications from TOP Server.

Starting with V5.18 and forward, Media-Level Redundancy has been enhanced to support a new Switch On Trigger mode, where the switch over for the primary to the secondary can be based on a tag value, quality, or time on inactivity. 

Available Media Level Redundancy System Tags:

Tag Name

Data Type



VT_BSTR (String)

The fully-qualified path of the active device.


VT_UI4 (DWord)

The number of seconds that the active device has been active.


VT_UI4 (DWord)

The number of seconds that the previously active device has been active.


VT_UI4 (DWord)

The number of times the active device has changed.


VT_BSTR (String)

The pair's current operating mode:
“Switch On Failure” / “Primary Only” / “Secondary Only”


VT_BSTR (String)

The current value of the "Secondary Device" parameter.


VT_BOOL (Boolean)

The current value of the "Return to Primary Connection ASAP After Failover" parameter.


VT_BSTR (String)

The current value of the "Monitor Item" parameter.


VT_UI4 (DWord)

The current value of the "Poll Monitor Item Every x Seconds" parameter.

The TOP Server also has always supported device and Network redundancy through it’s system tags which you can use to switch which device your connected to or even which Ethernet Network your connected through.  Though this functionality is still present, it is recommended to take full advantage of the redundancy capabilities now available for the best performance.

OPC Server Redundancy

With critical data it’s important to have redundant systems, when that means having redundant data gathering too.  For full redundancy, including OPC Server redundancy, you can add the OPC Redundancy Master to make this easy and transparent to your OPC DA client applications. 

Features for OPC Server Redundancy

  • RedMstrAniAutomatic switching to secondary server on failure of primary server
  • Works with any OPC Data Access Application
  • Supports multiple OPC Server pairs
  • No programming or application changes required
  • Hot, Warm, and Cold fail over modes
  • Configurable Server polling intervals
  • Trigger fail over and fallback
  • Configure multiple monitor items
  • Diagnostic and event logging
  • E-mail notifications



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