EXFO FTB-800 Series for FTB-1 - Manual (Page 219)

Test Setup - Test Configurator, Timer, and System
NetBlazer 209
Signal - Signal Configuration (DSn/PDH)

Modify Loop Codes button
Allows the configuration of 10 DS1 loop code pairs. Configure each
loop code name, Loop-Up and Loop-Down values.
The name field allows up to 16 characters long. Loop-Up and
Loop-Down range is from 3 to 16 bits (000 to 1111111111111111).
The default DS1 loop codes correspond to the DS1 In-Band loop
codes (Loop-Up=10000, and Loop-Down=100).