cmHSSILoopback is a read-only enumeration reporting the current loopback state of the HSSI port's DTE side, such as local-line, remote-line, or local-digital, or none when the port is passing normal traffic. An administrator checks this to confirm a loopback left over from earlier testing was actually cleared, since a stuck loopback would explain why a HSSI circuit appears down for real traffic. For example, if a HSSI link is failing and cmHSSILoopback still shows local-line(2), the operator would clear the leftover test loopback before further troubleshooting the circuit.