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 across each B box . So if the CO is 3 miles from your location there
could be 10 to 15 termination points . A signal is sent between each terminating point to isolate
the problem .