Setting this write-only object to startTest (1) initiates V.54 loopback test 2, which loops the signal at the remote modem's digital side; noTest (2) leaves it inactive. This isolates faults to the digital interface of the far-end modem specifically, distinguishing it from a purely local test or from a test of the modem's analog side. For example, if the local loop (cdx6500NMV54LocalLoop) passes but this remote digital-side loop fails, the problem is narrowed to the remote modem's digital circuitry rather than the transmission line itself.