Chapter 5. Diagnostics
191
Dual Channel Bank: Line Loopback
Line loopback is set in response to receiving a Line Loop Set code on a span's input. PCM
arriving at the input is looped back to the opposite span's output. The LIUs are not in the PCM
path. T1 line receivers and line buildouts are kept in the PCM loop to maintain the proper T1 line
levels. In line loopback, the PCM is looped before reaching the LIUs
Dual Channel Bank: T1-1 Line Loopback
Line Loop Set code received on the input of span B causes PCM to be looped back out
the output of span A. Output PCM from LIU B is sent to the output of span B. PCM from
the input of span A and the output of LIU A are blocked. See Figure 5-19 for detail.
Figure 5-19. Dual Channel Bank: T1-1 Line Loopback
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