transport protocol data unit (OSI) (TPDU)
A Transport Protocol Data Unit(TPDU) is a data set that is exchanged between different communication layers.
The TPDU is embedded in various Protocol Data Units( PDU); in the Network PDU, which in turn is embedded in the Data Link PDU.
The term Transfer Protocol Data Unit also appears in mobile networks in connection with the Short Message Service( SMS). This refers to support for sending and receiving short messages via the serial interface of the mobile station, since many mobile stations do not support input and output in plain text but expect or supply the data as a TPDU.