This read-only octet string (up to 32 characters) stores the operator-identifying trail trace text that an OTUC3 (300 Gb/s-class flexible OTU) trunk port expects from the far end, distinct from the shorter SAPI/DAPI codes. An administrator uses it to verify that only frames from the correct carrier or operator are accepted on this facility, guarding against accidental misconnection to another operator's equipment during turn-up. For example, this field might be set to a string like 'ACME-NETOPS' so that OTUC3 can be checked against whatever operator text actually arrives from the far end.