EXFO FTB-800 Series for FTB-1 - Manual (Page 218)

Test Setup - Test Configurator, Timer, and System
208 FTB-700G/800 Series
Signal - Signal Configuration (DSn/PDH)
Loopback button
The Loopback feature generates a code that is interpreted by the DUT.
The DUT interprets the command and implements the loopback.
Select the type of loopback that will be used to overwrite the traffic that
will be generated. Choices are listed in the following table in addition
with 10 predefined Loop Codes (see Modify Loop Codes button on
page 209).

Loop-Up injects the selected loop up code. The loop code will be
generated continuously for a maximum of 10 seconds or until the
loopback is confirmed. After 10 seconds, if the loopback has failed,
a Loop-Down command is sent. A pop-up window appears
indicating the loop code injection progress and result. The text box
next to the Loop-Up button indicates the selected loop up code.

Loop-Down injects the selected loop down code. The loop code
will be generated continuously for a maximum of 10 seconds or
until the loopback is confirmed. After 10 seconds, if the loopback
has failed, a Loop-Down command is sent. A pop-up window
appears indicating the loop code injection progress and result. The
text box next to the Loop-Down button indicates the selected loop
down code.
Loopback Type
Command
Loop-Up Loop-Down
CSU (10000/100) 10000 (default) 100
NIU FAC1 (1100/1110) 1100 1110
NIU FAC2 (11000/11100) 11000 11100
NIU FAC3 (100000/100) 100000 100