What is the function FEC of 100G optical module?
882 2022-01-06
Two important trends of optical modules are to increase transmission rate and extend transmission distance, but with the increase of transmission rate, the signal transmission distance will be limited by many factors, such as chromatic dispersion, nonlinear effects, polarization mode dispersion, etc. These factors will limit the transmission rate and transmission distance to increase at the same time. To reduce the impact of these unfavorable factors, industry experts have proposed the Forward Error Correction function, referred to as FEC (Forward Error Correction).
FEC is a kind of error correction technology, which emerged to solve the problem that the optical signal at the transmitting end is partially scrambled during transmission, resulting in misjudgment at the receiving end. When the optical signal is scrambled during transmission, the receiver may misjudge the "1" signal as a "0" signal, or the "0" signal as a "1 " signal. Therefore, the FEC function is used to improve the quality of the signal by forming the information code into a code with certain error correction capability on the channel coder at the transmitter, and decoding the received code by the channel decoder at the receiver, so that if the number of errors generated in transmission is within the error correction capability (discontinuous errors), the decoder will locate and correct the errors. Usually when this function is turned on, the transmission distance of the high speed rate optical module will be longer than when the FEC function is not turned on.
100G optical modules generally have the FEC function, although the FEC function has two advantages: forward error correction and increased transmission distance, but in the process of correcting the error code will inevitably cause some packet delay, so not all high-speed optical modules are recommended to open this function. For example, when using 100G QSFP28 LR4 optical module, it is not recommended to turn on the FEC function.
100G optical module mainly relies on the device side of the configuration of the FEC function to achieve error correction, so the switch also needs to support the FEC function, usually there is support for the FEC function of the switch is enabled by default FEC function. It should also be noted that if the FEC function is enabled on the A-side optical module, the B-side optical module should also be enabled, otherwise the interface is not Up.