Stands for "Protocol Data Unit." A PDU is a specific block of information transferred over a network. It is often used in reference to the OSI model, since it describes the different types of data that are transferred from each layer. The PDU for each layer of the OSI model is listed below.
- Physical layer – raw bits (1s or 0s) transmitted physically via the hardware
- Data Link layer – a frame (or series of bits)
- Network layer – a packet that contains the source and destination address
- Transport layer – a segment that includes a TCP header and datra
- Session layer – the data passed to the network connection
- Presentation layer – the data formatted for presentation
- Application layer – the data received or transmitted by a software application
As you can see, the protocol data unit changes between the seven different layers. The resulting information that is transferred from the application layer to the physical layer (and vice versa) is not altered, but the data undergoes a transformation in the process. The PDU defines the state of the data as it moves from one layer to the next.
NOTE: PDU also stands for "Power Distribution Unit." A typical power distribution unit looks like a power strip with multiple outlets, but includes electrical components that ensure equal voltage is distributed to each outlet. They are commonly used in data centers to provide consistent power to connected servers. These type of PDUs are often rack mountable, meaning they can be placed in a 1U rack space like a server.