This field set the TUG-3 #2 Trails Pass Through (hexadecimal number). It used by the NMS to indicate that a trail is not 'ended' on this ADM, but it is the last in the configuration chain. the lsb 4 bits set VC12=0 or VC3=1 structure to the TUG-3 #2. for VC12 structure the next 21 bits (for SDH) or 28 bits (for SONET) set each of the VC12 to be blocked (bit is 0) or unblocked (bit is 1). if it is VC3 only one more bit indicates if it is Pass-Through disabled (0, default) or Pass-Through enabled (1). if it is VC12, the 21 or 28 bits order is as folwed (from lsb to msb direction): first 7 bits for M=1 (from KLM index), the next 7 bits for M=2, the next for M=3, and the last (only for SONET) for M=4.