What is a Protocol Data Unit (PDU)?

What Is a Protocol Data Unit?

A Protocol Data Unit (PDU) is the data unit used by the Network Layer of the Open System Interconnection (OSI) Model and other protocol stacks, to exchange data between connected devices. The PDU encapsulates the higher layer protocols' data into an acceptable format for transmission over the physical medium, as well as providing addressing information so that the data can be routed across the network.

PDUs are created by taking the data from a higher layer protocol, such as TCP or UDP, and adding headers and trailers. The header contains information about the source and destination of the data, as well as other control information. The trailer contains flags, checksums, and other control information necessary to ensure the accuracy of the data during transmission.

PDUs are then transmitted through the lower layers of the OSI Model with the help of data link and physical layer protocols. Once the data has been transmitted, the PDU is deconstructed and the data is delivered to its intended recipient.

Types of Protocol Data Units

The most common types of Protocol Data Units are known as PDU type 0, PDU type 1, and PDU type 2. Each type has its own header and trailer length, and is important in the proper functioning of the network.

PDU type 0 is the simplest form of PDU, used mainly for datagrams. It contains only the source and destination address. No checksum is included, as this would require additional overhead.

PDU type 1 includes a checksum in addition to the source and destination address fields. This allows for better data integrity, as the checksum can verify that the data was sent correctly.

PDU type 2 is the most complex type of PDU. In addition to the source and destination address fields, it also includes control information, the checksum, and the payload length. This type of PDU is used in applications that require more complex communication, such as streaming audio or video.