EXFO FTB-800 Series for FTB-1 - Manual (Page 227)

Test Setup - Test Configurator, Timer, and System
NetBlazer 217
Signal - Signal Configuration (SONET/SDH)
VT/TU Path (SONET/SDH LOP)
The following diagram shows a test case data path that is terminated at
the SONET/SDH low order path. The remaining STS-1 or AU-3 timeslot
not involved in the test case are filled with background traffic of STS-1
or AU-3 level depending on the interface being SONET or SDH. At the
low order path level, the data path not involved in the data path
defined in the test case are filled with a background traffic equivalent
to the VT Group (VTG) or Tributary Unit Group (TUG) type defined by
the traffic selected in the data path. Further, the remaining VTG or TUG
within the high order path, selected in the test case, are respectively
filled with traffic of equivalent rate for SONET and SDH data paths.