When querying the FEC_BEF_COR_ER on NMS, the value displayed is over 18dB while the value queried using Navigator is 0. The NMS version is U2000 V1R5C00SPC603.
FEC_BEF_COR_ER = Over 18dB
When U2000 display FEC_BEF_COR_ERR as over 18dB, can assume that the value is 0.
From R&D’s explanation, in U2000 V1R5C00SPC603, the FEC_BEF_COR_ER uses the Q factor (unit is dB). Q factor is a parameter that directly reflects the quality of a optical signal which measures the propagation impairments caused by optical noise, non-linear effects, polarization effects and dispersion. As the Q factor measurement is with respect to analog signal, if assuming that signal impairment follows a stochastic distribution, there exist a one-to-one relationship between the Q factor and BER.
Also, the higher the Q-factor, the better the quality of optical signal. Thus, a Q factor of over 18dB corresponds to having BER of smaller than 1E-16, which in this case the FEC_BEF_COR_ER will be 0 on navigator as well as older NMS versions.