Class A Testing . This is done by the vendor and local telco , They test the cable pairs from your Dmarc back to CO .The tech wil most likly start testing from the termination inside the CO and work there way to your location , testing the signal acr...
A bad CSU/DSU won't cause the line to be looped , What I have found is during the night your circuit may have taken a hit and your vendor starts testing the circuit,but fogets to remove the looped. Any alarms on the CSU/DSU ? if so have your vendor t...