This read-write object specifies the type of end device and the type of loopback (latching, nonlatching, or polynomial) to be used for the BERT test, such as different OCU or CSU loopback variants. It configures exactly how the far-end device should be looped for the test to be meaningful. An admin testing through a specific type of channel service unit would select the matching device/loopback combination here so the loop command is compatible with that hardware.