Black Box Explains...Link loss..
Media converters solve the problem of connecting different media types in mixed-media networks. In order to comply with IEEE standards, they implement IEEE data-encoding rules and the Link Integrity Test.
For a twisted-pair segment, a link is a signal sent by the converters when the cable is in use. If no Link Integrity Test signal is received, the connected device assumes that the link is lost.
With fiber cable, a connected device checks a line by monitoring the Link Integrity Test signal from the converter and the power of the light being received. If the light’s power drops below a certain threshold, the link is lost. In either case, link loss usually results from a broken cable, which is the cause of approximately 70% of all LAN problems.
Link loss is often indicated by an LED on a connected network device. You can also monitor a link with network-management software, such as SNMP, which sends a TRAP (alert) to the management workstation when the link is lost.
Media converters actually function as two separate Multistation Access Units (MAUs). For example, one monitor is a twisted-pair segment and one monitor is a fiber segment. If a fiber cable is broken and the link is lost, a network manager on the twisted-pair end wont know there’s a problem until users on the fiber side report it.
To solve this problem, Black Box® Modular Media Converters feature a unique Link-Loss capability. This enables the link status on one segment to reflect the link status of the other segment. So if the link is lost on the fiber side, the link is disabled on the UTP segment as well. And the converters will send an SNMP TRAP indicating the loss of link to the management workstation.