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CHAPTER 4. TEST and DIAGNOSTICS Main E1 local digital loop back Main E1 local digital loop back is performed by connecting the main link receive signal to the output of the transmit path in the digital mode. This loop back test checks the performance of the local ETU02A-MUX, the remote ETU02A-MUX and the connections between them, as shown in Figure 4-2. LOCAL ETU02A-MUX User DTE CH1 CSU CH2 E1 Transmission CH3 CH4 MAIN LINK SUB LINK Figure 4-2. Main E1 local digital loop back Main E1 remote loop back Main E1 remote loop back is performed by sending the remote loop back code to the remote CSU/DSU. The remote then enters digital loop back mode and the link is returned to the local unit. This loop back test checks the performance of the local ETU02A-MUX, the remote unit and the connections between them, as shown in Figure 4-3. LOCAL ETU02A-MUX CH1 REMOTE ETU02A-MUX CSU CSU CH1 CH2 CH2 CH3 CH3 E1 Link CH4 SUB LINK MAIN LINK CH4 MAIN LINK SUB LINK Figure 4-3. Main E1 remote loop back 29 ETU02A MAY 2000
