otherwise made to the last fiber in the loop and further testing is performed a more extensive explanation of testing is as follows first the near end launch cord end harness 30 and far end tail cord end loopback harness 32 together but without a fiber under test to identify loopback fiber lengths and any events within the loopbacks used to uniquely identify each one this step can employ a jumper cable to mate the two ends of the loopback harnesses together if the mpo connectors are polarized in such a way that they do not physically mate each of the fibers in this jumper cable should suitably be chosen to be very close to the same length to each other within 0 5 meters for a duplex fiber embodiment the near end harness may be implemented as a breakout of the two fibers into a launch and tail cord next existing analysis software can be used to identify the events over the entire length each loopback segment is expected to be at least a minimum length that is beyond the deadzone of the tester the jumper cable may be shorter than this which can be preferred to distinguish these segments from the loopback fibers alternatively the jumper cable may be longer than the longest loopback segment if the length of each loopback segment is unique and has no internal events then the median length of all segments longer than the minimum length can provide an estimate of the typical loopback segment length the number of segments found should be approximately the total length minus any jumper cables and minus the first launch segment divided by the median length or the number can be a value that the user provides if the longest loopback lengths is built so.