payload (Pl)
Payload refers to the user data in data packets that are transported between the communication partners. Alternatively, this data is also referred to as payload, user data or user data. It is information of a Protocol Data Unit( PDU) without frame limitation, i.e. without header and trailer.
Payload data is pure information data of a data packet that does not contain any control information or protocol information. The data scope of the user data depends on the protocol and is determined by the payload length. Header data for functional control is added to the user data when it passes through each protocol layer. This results in the protocol data units (PDU).
First, the user data passes through the application layer, where the application header( AH) is added. This is followed by the presentation layer in which the Presentation Header(PH) is added. Then the Session Header( SH) from the communication control layer. This covers the application-oriented layers.
The protocol data unit already includes the SH header, the PH header, the AH header and the payload. The transport-oriented layers follow. The Transport Header( TH) of the transport layer is inserted before the SH header, the Network Header (NH) of the network layer and the Data Link Header( DLH) of the data linklayer. And the lowest layer is the physical layer, which also adds a header.