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We demonstrate that the impairment on optical time-domain reflectometer (OTDR) noise floor when testing a fiber in the presence of traffic signals can be reduced by using a tunable narrow-bandwidth OTDR combined with an optical bandpass filter. By this technique, we observed that the OTDR penalty caused by the spontaneous Raman scattering generated by the traffic signals was significantly reduced. Moreover, we found that it is advantageous to monitor online fiber with a counterpropagation scheme. The simulations and experimental results will be discussed.