In fiber systems, dynamic range is one of the most important characteristics of an OTDR that determines the maximum observable length of a fiber and, therefore, the OTDR suitability for analyzing any particular network. The higher the dynamic range, the higher the signal to noise ratio (SNR) and the better the trace will be, with better event detection.

Depending on the noise level reference, there are many definitions of dynamic range, each providing different values not immediately comparable. Among them:

• IEC Dynamic Range (introduced by Bellcore) The upper level of the noise is taken as the upper limit of a range, which contains at least 98% of all noise data points. This definition was endorsed by the International Electro-technical Commission (IEC) in document IEC 61746.
• RMS Dynamic Range. The root mean square, also termed SNR=1, dynamic range corresponds to the difference between the extrapolated point of the backscatter trace at the near end of the fiber (taken at the intersection between the extrapolated trace and the power axis) and the RMS noise level.