ND-45383 (E) CHAPTER 2Page 25Revision CD 1.05. LOOP-BACK FUNCTION TESTLoop-back tests are executed to verify the normality of the installed DRU, to perform fault localization in anevent of occurrence of a line fault. The DRU loops back all the signals (all of voice, data, control signal links)between the DLI and the DRU. The types of loop-back test are shown below. Note that there is no loop-backtest on each telephone set basis.• Local Loop-Back Check• Remote Loop-Back Check• Remote Loop-BackThe loop-back test method is as per the switch setting on the DLI card and on the DRE card in the DRU.5.1 Local Loop-Back CheckThis test loops back the signals inside the line at the line interface portion of the self office (DLI itself, DRUitself) and thus verifies the normality of the self office. During this loop-back test, the self office sends ablue signal to the associated remote office to notify that a local loop-back is in progress at the self office.Figure 2-14 Local Loop-Back CheckDLINEAX2400 IMSDRUBlue SignalBlue SignalLine Interface
