An Introductory Guide for Link Fault Pass-Through (LFPT) in Media Converters

Media converters are the devices that enable the conversion of data from one form to another. Generally, in hybrid networks comprising copper-fiber transmission media, these devices are of great significance. These media converters convert the electronic signals into optical pulses and vice versa. The media converters can translate and transmit data over different transmission protocols like Ethernet, Internet Protocol (IP), Transmission Control Protocol (TCP), and Power over Ethernet (PoE), etc. Owing to the high-end compatibility of media converters with several transmission protocols, these devices are used in high-capacity networks. These devices are often exposed to high data traffic, return losses, etc which can abruptly damage the converter, and eventually, the network may fail. To reduce the chances of data loss during such conditions, Link Fault Pass-Through (LFPT) function is adopted in modern, high-capacity fiber media converters. The main purpose of adopting the link pass-through function in the media converters is to constantly monitor the copper and fiber links and prevent data loss by taking an action on an incident of link failure.

Link Fault Pass Through (LFPT)

Commonly, the link fault pass-through function is introduced to overcome the potential drawbacks of conventional paired media converters connections. However, before introducing link fault pass-through (LFPT) function in the media converters connections, it is essential to understand different aspects of the same. This post introduces the link fault pass-through (LFPT) function, its importance in media converters, its operating principle, etc.

Link fault pass-through (LFPT) is the function of media converters. This function prevents data loss in case of link failure. The media converters feature a pair of hetero links, such as a pair of copper links and fiber links. In cases of high data traffic, return losses, etc, the copper or fiber link may fail. If one link fails, and its successive link remains active, the data is lost between the link gaps. Sometimes, if the link on the transmitter end fails, the data transmission may terminate at the moment of link failure. To prevent certain issues, the link pass-through function is adopted. This function terminates the successive link if the link on the transmitting end fails. This terminates the transmission of data in case of a link failure on any end.

This function also enables continuous monitoring of the transmission links connected to the media converters. This way, the network administrators can monitor, survey, troubleshoot, repair, and maintain the networks by using the continuous monitoring capability of link fault pass-through (LFPT). This function informs network administrators’ link failure.
Let us discuss how exactly this link pass-through function operates.

Construction and Operation of Link Pass-Through

In order to understand the operation, the construction of link pass-through (LFT) integrated media converter and network must be understood. The construction of the LFT-integrated media converter is as follows.

Construction of Link Pass-Through

The link pass-through (LFT) is an integrated, built-in function in media converters. The construction of the LFT-integrated network is as follows.

  • A pair of hetero transmission links defined as Link A- Copper Link and Link B- Fiber Link.
  • A media converter with LFT function is introduced between Link A and Link B.
  • The extreme ends of Link A and Link B are paired with network switches through which the data is routed.
  • In case of electro-optical conversion, Link A-Media Converter (LFT)-Link B type of construction may suffice. However, if reverse signal translation i.e.; optical to electric signal conversion is required, this combination is successively extended with a reverse version of the combination by using an additional media converter. In case of forward and reverse conversion, the construction is Link A (Copper)-Media Converter 1 (LFT)-Link B (Fiber)-Media Converter 2 (LFT)-Link C (Copper). In this case, Link B (Fiber) becomes a middle or intermediate fiber.

Operation of Link Pass-Through

The operation of the Link Pass-Through function highly depends on the type of connection or networking layout. Let us discuss the operation of Link Fault Pass-Through (LFPT) for Link A (Copper)-Media Converter 1 (LFT)-Link B (Fiber)-Media Converter 2 (LFT)-Link C (Copper) type of connection.
The operation of the link pass-through (LFT) function is detailed below.

  • If Link A (Copper) fails, the link pass-through (LFT) function of the first media converter monitors or detects the link failure.
  • On failure of Link A, the access fiber gear is terminated, which sends the indication to middle or intermediate fiber is indicated for fiber failure.
  • As Link B (Fiber) fails, the consecutive media converter 2 indicates Link C (Copper) for the failure of Link B. This terminates the signal transmission to the further link.
  • However, if the copper link works fine but the fiber link (Link 2) fails, then the Far-End Fault (FEF) feature is activated. This feature notifies both ends of a fiber link in case of any fault or failure in the fiber link.
  • As the links fail, the network administrators are notified via monitoring and control software tools.  The software tool operates based on Simple Network Management Protocol (SNMP).

In hybrid (Copper-Fiber) networks, Far-End Fault (FEF) is as important as the link pass-through (LFT) function, let us discuss it too.


Far-End Fault

Ideally, it is a function integrated into media converters in compliance with IEEE802.3u standards. It is designed and integrated to detect link faults while assisting fiber gear. In execution of this feature, on the failure of fiber link, the failed end of the fiber optic cable sends a far-end fault signal to another fiber end. This way, the transmitter understands the fiber link has failed and terminates the transmission of signals.
On the termination of transmission activity, both the copper links attached to both ends of the fiber Link Are taken down automatically.
Once copper links and fiber links are terminated, Simple Network Management Protocol (SNMP) function takes charge and indicates the network administrators about the failure of copper and fiber links.

Note: This function complements the network monitoring and controlling software tools, therefore, it works well for remote operations of the Ethernet or IP networks. This feature of media converters contributes to the remote troubleshooting, maintenance, management, and operational configuration of copper-fiber networks. 


Media converters are a crucial part of hybrid networks comprising fiber optics and copper cables as transmission media. These media converters translate the electronic signals to the optical pulses and vice versa for the convenience of compatible transmission media. However, as the networks are becoming demanding, a high amount of data is being transmitted through the networks and eventually, through the media converters, networks are susceptible to link failure. If the media converter does not recognize the failed link, data loss occurs. To prevent data loss, Link Fault Pass-Through (LFPT) function is introduced in the media converter. This function notifies the successive links about the failed links and the successive links are taken down automatically to prevent data loss. Further to identify fiber link failure, a far-end fault (FEF) function is introduced.

This white paper discusses the LFPT and FEF functions of media converters and their operational fundamentals. To know more about media converters with LFPT and FEF functions, please visit