The Media Level Redundancy Plug-In supports two types of redundancy: Communications Path Redundancy and Device Pair Redundancy. Communications Path Redundancy is used to communicate with the same device over multiple communications methods. For example:

• A device supporting communications via TCP as well as RS-485/RS-232 serial ports. The device could be to set up with a primary communications path via TCP but then fall back to RS-485 if there are issues with the Ethernet network.
• A PC/machine with multiple Ethernet cards communicating with a single device can establish primary communications through a primary Ethernet card and fall back to the secondary Ethernet card.
• A PC/machine supporting multiple RS-485/RS-232 serial ports and a device with multiple RS-485/RS-232 serial ports. The RS-485/RS-232 Port 1 of PC and device could be set up as the primary and fall back to Port 2 of PC and device.

Device Pair Redundancy is used to communicate with two identical devices configured as a redundant unit (each running the same logic). For example:

• Two devices are on the same RS-485 network monitoring the same process condition. Client monitoring software must be able to receive information from at least one of these devices to maintain the information integrity.

See Also: Media Level Redundancy Plug-In