EXFO FTB-800 Series for FTB-1 - Manual (Page 469)

Test Functions
NetBlazer 459
Signaling Bits
Signaling Bits
Signaling Bits is only available for DSn/PDH BERT test with DS1 interface,
DS0 enabled, and SF, ESF, or SLC-96 framing.
From the Test menu, tap Functions and the Signaling Bits tab.
The monitoring of signaling bits of the 24 - DS0 channels is performed
when test is running. Two signaling bits (AB) are monitored for SF or
SLC-96 framing while four signaling bits (ABCD) are monitored for ESF.