Loopback fiber patch cord (Loopback fiber cable) provides a media of return path for a signal, whether the signal is for testing purposes or due to network restoration. Loopback fiber patch cord can be regarded to be the two connectors on the same piece of simplex fiber optic patch cable put together, thus it forms a loop. In the case of testing, the loopback signal is used for diagnosing a problem. Sending a loopback test to network equipment, one at a time, is a technique for isolating a problem. Its performance is as good as that of a general patch cord.