iMcV-LIM
12
FEF versus FA
FEF is preferred when the devices at both ends of the fiber can interpret the
FEF signal. This allows FEF to be turned on at both ends, which will engage
the FEF regardless of which direction the fault occurs. (Please refer to
diagram on previous page) For example if a fault should occur on segment 2
in the direction of segment 1 to 3, FEF would be engaged on the iMcV-LIM
between segment 2 and 3. This would then send a signal back to the iMcV-
LIM between segment 1 and 2. If the iMcV-LIM between segment 1 and 2 is in
a managed chassis, the chassis would send a trap that the port is down.
Alternatively, if the iMcV-LIM is not in a managed chassis, FXLL could be
engaged to propagate the fault onto the copper port; this would cause
segment 1 to show no link on both ends.
FA is used when connecting to a device that does not support FEF. If an FEF
signal is sent to a device that does not support FEF, the device acts as if there
is still a good connection. The FEF signal is mistaken for data. FA works
similar to FEF, in that when there is a fault in one direction of the fiber, it acts
on the fiber in the opposite direction. But unlike FEF, FA sends no signal.
Because of this, FA can not be enabled on both ends. If it is enabled and a
fault occurs, FA will turn signal off in the opposite direction; the device on the
other side of the fiber will see the loss of signal and engage FA, turning off
signal. The net result will be the signal turned off in both directions, even after
the fault has been repaired.
It is highly recommended that only one is chosen, either FEF or FA. If both are
selected FA will take precedence over FEF.
AUTO NEGOTIATION ON IMCV-LIM
iMcV-LIM modules include the feature Auto Negotiation. When Auto
Negotiation is enabled, the module negotiates as a 100 Mbps full-duplex
device. If the connected device can operate at 100 Mbps full-duplex, a link is
established. Auto Negotiation (DIP Switch #1) is enabled by default.
If the `twisted-pair port on the other device does not have the ability to Auto
Negotiate or if the 100 Mbps half-duplex connection is desired, then Auto
Negotiation must be disabled. Half- and full-duplex settings must be set
manually and match on does devices.
The following diagram shows a typical application and with three possible
configurations.
