Loop Back Switch
The Loop Back Switch has three positions, Line Loop Back (LLB),
Off (reset loop back), and Data Port Loop Back (DPLB). Loop backs
initiated with the Loop Back Switch cannot be reset by commands
from a DataSMART DSU at the far end and override any previously
set loop backs from the far end.
Line Loop Back (LLB)
When Line Loop Back (LLB) is activated from the Loop Back Switch
or from the far end, the NI signal is looped back to the NI without
modification. All 1s is sent to the DTE.
When to Use
LLB is used to identify trouble in the network. During the loop back,
an all ones signal is sent out the data port to indicate service is
interrupted. LLB provides minimal penetration into the D-SERV
DSU/CSU; it does not remove BPVs or other line coding errors, so
that test signals such as Fault Locate trios pass through unaltered.
Figure 25. Line Loop Back (LLB)
Operator's Manual
38
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