Current approaches for determining and identifying whether a correct length of fiber cable is installed between network elements configured to communicate using specific lengths of cable require manual inspection. Such manual inspection may include the use of markers used for visual inspection of cables matching corresponding network elements. An embodiment of the present invention utilizes identifiers unique to cables of various lengths to determine whether a correct length of cable has been installed. Further, embodiments of the present invention determine whether the unique identifier is received by a network device according to a channel mapping corresponding to a unique physical mapping associated with cables of various lengths. The use of the identifiers and channel mappings enable automatic discovery of lengths of cable that are installed between network devices.