The fast way is to —
1. Identify near end and far end of DSX circuit by inserting a patch plug into one of the MON jacks. The LED at both ends should flash for 30 seconds and then remain lit.
2. Loop near end by inserting patch cord or looping plug into OUT and IN jacks. If near end restores, then network facility and NEs are okay. The problem is probably with the far end. If near end doesn’t restore, suspect the near-end facility or a near-end NE.
3. Repeat Step 2 on the far end. If near end restores, suspect a jumper failure. If near end doesn’t restore, suspect the far-end facility or a far-end NE.
4. Visually inspect cross-connect jumper cabling, tracer connections, etc.
5. As last resort, you’ll need test equipment and a diagnostic.