The T-BERD 107A is a full-featured, hand-held T1 Test Set designed for field testing. The T-BERD 107A can be used during circuit installation, acceptance testing, and fault isolation. The T-BERD 107A can monitor a T1 circuit without interrrupting service, generate and receive test patterns during out-of-service circuit testing, and emulate a network device, such as a Network Interface Unit (NIU) or Channel Service Unit (CSU).