In telecommunications, a Protocol Data Unit (PDU) is a single unit of information transmitted among peer entities of a computer network. It is composed of protocol-specific control information and user data. In the layered architectures of communication protocol stacks, each layer implements protocols tailored to the specific type or mode of data exchange.
Protocol-Specific PDUs
Each protocol in a communication stack defines its own PDU format:
- Transmission Control Protocol (TCP): Uses segments as PDUs for connection-oriented transfer mode.
- User Datagram Protocol (UDP): Uses datagrams as PDUs for connectionless communication.
- Internet Layer: Uses packets as PDUs, irrespective of its payload type.
Structure of a PDU
A PDU consists of two main parts:
- Control Information: Protocol-specific headers and trailers that manage the data transfer.
- User Data: The actual payload being transmitted.