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What Are FEF and LFP on Media Converter

August 9, 2016

Ethernet media converters are usually used in pairs to allow copper-based networks to communicate in a copper-fiber topology, thus extending the transmission distance. However, in such a paired media converter network, if the fiber or copper link on one side fails, the device on the other side will continue to work even though no data transmitted, and will not report an error to the system administrator. FEF and LFP function on media converter perfectly solve this problem.Normal Operation of Paired Media Converters.jpg

Figure 1: Normal Operation of Paired Media Converters

FEF on Fiber Media Converter

The FEF represents Far End Fault. It is a protocol compliant with IEEE 802.3u standard to sense remote data link errors in a network. With the FEF function on media converter, it is very easy for the network administrator to detect the faults on the fiber media converter links. When a fiber link error is detected, the media converter on this side will transmit the far end fault signal over a fiber connection to inform the other media converter at the far end that the fault has occurred. Then, both copper links connected to the fiber link will be automatically disconnected. By using the FEF media converter, the fault on the link can be detected and troubleshoot immediately, preventing data from being transmitted to a failed link by cutting down the failed link and sending a far end fault to the media converter.

Operation of FEF on Media Converter

1. If there is a fault occurs in the RX end of fiber connection, FEF Media Converter A will detect the fault.a fault occurs in the RX end of fiber connection.jpg

2. Then Media Converter A sends a far end fault to Media Converter B to inform that a fault has occurred in the RX end, which will disable the transmission of the TX fiber of Media Converter A.Media Converter A sends a far end fault to Media Converter B.jpg

3. Fiber Media Converter A takes down its copper link. On the corresponding Ethernet switch, the LED indicator shows a link disconnected status.

Media Converter.jpg

4. On the other side, Media Converter B takes down its copper link, too. The connected switch LED indicator shows a link downstate.

media converter A.jpg

LFP on Media Converter

The LFP (Link Fault Pass Through) means the link fault of media converter on one side (local side) will be passed to the media converter on the other side (remote side). It is used for monitoring the copper links connected to the media converters from the local device. When one copper link fails, the media converter will pass the fail state on throughout the link taking down the middle fiber link and the copper link on the opposite end. Thus the LFP function on media converter can immediately alarm network administrators the problem of the link and offer an efficient solution to monitor the network, which can minimize the loss caused by the link problem.

Operation of LFP on Media Converter

1. Copper cable to Media Convert A gets failed.Copper cable to Media Convert A gets failed..jpg

2. LFP Media Converter A notifies Media Converter B of the copper link failure and disables the fiber connection to Media Converter B.

LFP Media Converter A notifies Media Converter B.jpg

3. Media Converter B disables its copper connection, the switch on the right will display the link down state on the corresponding LED indicator.

Media Converter B disables its copper connection.jpg


  • If you intend to enable the FEF and LFP function on media converter, be sure to use Ethernet-to-fiber media converters as a pair and both devices must support FEF and LFP. In addition, remember to select the same brand and model for the two sides of the connection.

  • Test the functions you intend to use before actually implementing the functions on a working network.

  • Be sure to seek expert advice from your system vendor.

  • Conclusion

    Both FEF and LFP functions on media converter are of vital importance. FEF and LFP media converters do network administrators a great favor in diagnosing and troubleshooting network outages, thus promote the normal operation of the whole link.


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