PLANET FT-801 - Manual (Page 8)

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Link Loss Carry Forward (LLCF)
FT-80X incorporates an LLCF function for troubleshooting a
remote connection. When LFP function is enabled, the FL/TP ports
do not transmit a link signal until they receive a link signal from
the opposite port.
The diagram below shows a typical network configuration with a
good link status using FT-80X for remote connectivity.
If the connection breaks, FT-80X that link loss forward to the
switch/hub that generates a trap to the management station. The
administrator can then determine the source of the problem.
*Units are shipped with the LFP function enabled (ON).
Link Loss Return (LLR)
The fiber ports of FT-80X have been designed with an LLR function
for troubleshooting a remote connection. LLR works in conjunction
with LLCF.
When LFP function is enabled *(by default), the port’s transmitter
shuts down when its receiver fails to detect a valid receive link.
LLR should only be enabled on one end of the link and is typically
enabled on either the unmanaged or remote device.
The diagram below shows a typical network configuration with a
good link status using FT-80X for remote connectivity. Note that
LLR and LLCF are enabled as indicated in the diagram.