This read-only octet string, up to 32 bytes, is the expected operator-identifier portion of the trail-trace (TTI) configured for this OTU4 (about 111.8 Gbit/s) line facility. On multi-carrier OTN paths, this lets the NE confirm the line genuinely originates from the operator it is contractually supposed to, catching a wrong-carrier hand-off automatically. For example, the OTU4 facility on slot 3 expecting a specific partner-carrier's operator code would raise a mismatch if the actually received TTI names a different operator, flagging an unexpected routing change.