What is FEC and Basic Working Principle

Date 01/03/2025

This article explains what FEC is and how it works in principle, helping you understand how it can help you solve the packet loss problem caused by signal degradation, so that you can solve signal degradation when deploying your network.

As a key technology to ensure the quality of signal transmission, FEC is a proven and very effective means as people's demand for bandwidth increases and their tolerance for errors and delays decreases. It can be used to achieve efficient and high-quality signal transmission on noisy signal channels, and as the amount of data transmission increases and the transmission distance increases, FEC is also being used more and more widely. This article will help you to understand what FEC is and how it is used in 100G transmission.

What is FEC

FEC is a digital signal processing technology for error detection and correction, which is used to enhance data reliability. It adds redundant information to the transmitted or stored data, allowing the receiving end to detect and correct data errors that occur during the transmission process, ensuring the data integrity in the communication channel without requesting the sender to retransmit the data. By using the FEC function, the network transmission efficiency can be effectively improvedand the delay can be reduced, making the network more efficient.

How Does FEC Work

During the signal transmission process, signal attenuation is usually accompanied, which will cause errors at the receiving end, resulting in data errors or failure to receive. The working principle of FEC technology is to add redundant information during the data transmission process, which can enable the receiving end to automatically detect and correct errors.

When the transmitter sends data, the FEC encoder processes the original data and adds redundant information through FEC encoding algorithms such as Hamming Code or Reed-Solomon Code. They are used to detect and correct errors that may occur during the transmission process.

When the receiving end receives the transmitted data, it will use the same FEC decoding algorithm as the transmitter to detect whether the received data has errors such as bit flipping or loss, and try to correct these errors. However, it should be noted that although FEC can correct some errors, if it exceeds the range of FEC correction, the receiving end cannot fully restore the original data, and data loss or retransmission will occur.

In addition, FEC can ensure error correction of data under different network conditions by using different modes. For example, in-band FEC inserts error correction code directly into the transmitted data, transmits it to the receiving end, and detects and corrects it. Out-of-band FEC uses a separate channel for transmission. You can choose how to transmit based on network bandwidth and performance requirements.

Forward Error Correction Types and Characteristics

In systems such as SDH and DWDM, common FEC technologies include in-band FEC (coding gain of 3-4dB), out-of-band FEC (coding gain of 5-6dB), and enhanced FEC (EFEC). These technologies can reduce errors in data transmission, extend signal transmission range, and effectively reduce system power requirements.

FEC improves system reliability by introducing redundant check bits, reduces data retransmission caused by noise interference, and thus improves data throughput. Although redundant check bits increase the amount of data transmitted, the FEC function can still effectively improve system efficiency and improve the reliability of data at the receiving end by automatically correcting data errors.

In 100G networks and higher-speed networks, FEC is a critical component. It mainly relies on two error correction mechanisms: hard decision and soft decision. The hard decision method is simple to implement, but its error correction capability is weak, while the soft decision can provide stronger error correction capability, especially in the case of poor signal quality.

The use of FEC can not only effectively extend the transmission distance (for example, the transmission distance of a 100G link can be increased by 30-40% when SD-FEC is used), but also reduce data loss and avoid retransmission of data, thereby saving bandwidth and improving overall network performance. However, since the implementation of FEC requires the transmission of additional redundant information, this may cause delays. In order to implement the FEC function, it is also necessary to ensure that the sender and receiver use the same type of FEC to ensure success, which may increase the complexity of configuration when using equipment from multiple vendors. Despite this, FEC remains a key technology to ensure the stability and reliability of high-speed data transmission.

QSFPTEK 100G Optical Module With FEC

Transceiver Type	Description	FEC Support
QT-QSFP28-SR4	QSFP28,100Gbps, 850nm, MMF, 100M, DDM, MPO Connector, 0°C to +70°C	Yes
QT-QSFP28-LR4	QSFP28,100Gbps, 1310nm ,SMF, 10KM, DDM, LC connector, 0°C to +70°C	Yes
QT-QSFP28-IR4	100G QSFP28 CWDM4 Transceiver, LAN WDM, LC Connector, 2km, 0°C to +70°C	Yes
QT-QSFP28-CWDM-LR4	QSFP28,100Gbps, 1271~1331nm ,SMF, 10KM, DDM, LC connector, 0°C to +70°C	Yes
QT-QSFP28-ER4	QSFP28,100Gb/s, 1310nm, SMF, 40KM DDM, LC Connector, 40km, 0°C to +70°C	Yes

Application of FEC in 100G Network

Cloud Computing

In cloud computing applications, 100G networks are responsible for carrying high-speed data traffic from different servers, storage devices, switches and other devices. In such a huge transmission volume, frequent data errors and retransmissions will cause server downtime or increased delays. At this time, the automatic error correction function of FEC can improve the reliability of data transmission, avoid packet loss or errors caused by noise and signal attenuation, thereby improving network reliability and avoiding delays.

Telecom Service Providers

Since telecom service providers need to provide large-scale data transmission services through long-distance optical fiber links, 100G optical fiber links are the most common solution. In long-distance transmission spanning hundreds or thousands of kilometers, signal attenuation and noise are much higher than short-distance transmission. At this time, FEC technology is needed to correct error codes, ensure transmission reliability, avoid retransmission and network interruption risks, and provide better services. At the same time, it can also reduce the need for signal amplification and reduce the overall cost of optical fiber links.

Conclusion

Forward Error Correction (FEC) is an important technology to ensure reliable and efficient data transmission, especially in high-speed networks such as 100G. By adding redundant information to the transmitted data, FEC can improve data integrity, reduce errors and improve overall network performance. It is crucial for applications such as cloud computing, telecommunications services and long-distance fiber transmission because it can correct errors without retransmitting data, avoiding bandwidth waste and increased latency, making FEC an indispensable function for improving network stability and efficiency.