EXFO FTB-8510B Guia Del Usuario página 1189

System Tab
Default Test Preferences
SONET/SDH HOP
Allows the selection of the default high order path background
traffic. Choices are AIS, Unequipped, and Equipped (PRBS
2^23-1 pattern). The default setting is Equipped.
For SONET/SDH rates up to OC-192/STM-64: The following diagram
shows a test case data path that is terminated right after
SONET/SDH high order path. High order background traffic is
automatically adapted to the rate (STS-1, AU-4, or AU-4) signal level
for the paths that are not defined in the test case. In the situation
where the traffic pattern is replaced by GFP the background traffic
remains the same for the STS-1/AU-3/AU-4 that are not involved in
the test case data path. In the situation where contiguous
concatenation or virtual concatenation is used, the background
traffic continues to be applied on the remaining timeslots not
involved in the test case data path.
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SONET/SDH Application