This selects the format of the SONET Path Trace (J1 byte) identifier used on this path -- options visible in the syntax include no trace, a 64-byte string, a 64-byte string with a CR/LF terminator, and a 16-byte string. An admin picks this to match what the far-end equipment expects, since SONET path trace format has to agree between both ends of a circuit for the trace-mismatch detection (comparing the expected trace against the received trace) to work correctly rather than reporting a false mismatch. Setting this to the 16-byte option on a path connecting to older equipment that only supports the shorter J1 format ensures the transmitted trace string's first 16 bytes get sent instead of the full 64-byte string.