Solution:
Line Build Out ensures that pulses hit the first repeater with the appropriate amplitude. Pulses that are too big or too small will not be processed correctly and might even be reflected at jacks. For smart jacks, LBO should usually be set to 0 dB.
Check with the telco technician who installed the line for the exact value.
Short Haul Build Out (Line Equalization) is balanced for the signal loss due to the cable length between the external CSU and the Perle.
Long Haul Build Out is balanced for the signal originating from the repeaters used by the Telco (or the smart jack). Most smart jacks generate a full-strength signal and thus a 0dB LBO setting.
Incorrect LBO can also cause a Yellow Alarm on the T1 card, and can also cause problematic connections/handshakes. Usually seen as poor modem handshakes and frequent disconnects during modem connection attempts.