EXFO FTB-8510B Guia Del Usuario página 778

Summary Tabs
Test Summary
Through: When enabled, indicates that the RX signal is looped to the
TX port.
OTN Intrusive and SONET/SDH Intrusive are mutually exclusive.
When enabled, indicates that the RX signal is looped to the TX port
with limited TX overwrite capabilities (For SONET/SDH Intrusive: OH
and alarm/error generation). SONET/SDH Intrusive and OTN
Intrusive are not available on FTB-8105/FTB-8115.
Test Description: The test description is used to describe the test case.
A maximum of 64 ASCII characters are allowed.
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FTB-8100 Series Transport Blazer