Editing Optical time-domain reflectometer (section)

==OTDR data format==
In the late 1990s, OTDR industry representatives and the OTDR user community developed a unique data format to store and analyze OTDR fiber data. This data was based on the specifications in GR-196, Generic Requirements for Optical Time Domain Reflectometer (OTDR) Type Equipment. The goal was for the data format to be truly universal, in that it was intended to be implemented by all OTDR manufacturers. OTDR suppliers developed the software to implement the data format. As they proceeded, they identified inconsistencies in the format, along with areas of misunderstanding among users.

From 1997 to 2000, a group of OTDR supplier software specialists attempted to resolve problems and inconsistencies in what was then called the “Bellcore” OTDR Data Format. This group, called the OTDR Data Format Users Group (ODFUG), made progress. Since then, many OTDR developers continued to work with other developers to solve individual interaction problems and enable cross use between manufacturers.
 
In 2011, Telcordia decided to compile industry comments on this data format into one document entitled Optical Time Domain Reflectometer (OTDR) Data Format. This Special Report (SR) summarizes the state of the Bellcore OTDR Data Format, renaming it as the Telcordia OTDR Data Format.<ref name= "Telecordia July 2011">{{Citation| first =Terry | last = Donovan| title = Optical Time Domain Reflectometer (OTDR) Data Format| publisher = Telcordia (Ericsson Inc)| date = Jul 2011 | url = https://technologg.com/otdr-testing/| access-date = 15 April 2015}}</ref>
 
The data format is intended for all OTDR-related equipment designed to save trace data and analysis information. Initial implementations require standalone software to be provided by the OTDR supplier to convert existing OTDR trace files to the SR-4731 data format and to convert files from this universal format to a format that is usable by their older OTDRs. This file conversion software can be developed by the hardware supplier, the end user, or a third party. This software also provides backward compatibility of the OTDR data format with existing equipment.

The SR-4731 format describes binary data. While text information is contained in several fields, most numbers are represented as either 16-bit (2-byte) or 32-bit (4-byte) signed or unsigned integers stored as binary images. Byte ordering in this file format is explicitly low-byte ordering, as is common on [[Intel]] processor-based machines. String fields are terminated with a zero byte “\0”. OTDR waveform data are represented as short, unsigned integer data uniformly spaced in time, in units of decibels (dB) times 1000, referenced to the maximum power level. The maximum power level is set to zero, and all waveform data points are assumed to be zero or negative (the sign bit is implied), so that the minimum power level in this format is -65.535 dB, and the minimum resolution between power level steps is 0.001 dB. In some cases, this will not provide sufficient power range to represent all waveform points. For this reason, the use of a scale factor has been introduced to expand the data point power range.