This CoriantTypesEnableSwitch (default disabled) turns loopback testing on or off for the coherent optical channel (och-os) on the line side of a pluggable transceiver. An administrator enables it during maintenance or fault isolation to loop the signal back at this facility and determine whether a suspected problem lies in the local equipment or further out in the network. For example, a technician suspecting a faulty transceiver would enable loopback on och-os, then check whether locally generated test traffic returns correctly before deciding whether the fault is local or downstream.