Networking - PDU (Protocol Data Unit)
A Protocol Data Unit (PDU) is a specific block of data that is passed between devices in a network. It is the name given to the data at different layers of the OSI (Open Systems Interconnection) model. Each layer of the OSI model has its own type of PDU, which helps in organizing and managing how data is transmitted across a network.
In simple terms, a PDU is like a package of data that carries not only the information being sent but also the control information needed by that specific layer (like addresses, error checks, and delivery instructions).
Here’s how the PDU changes at each layer of the OSI model:
| OSI Layer | Name of PDU | What It Contains |
|---|---|---|
| Application, Presentation, Session | Data | The actual user information (like an email message or a file) |
| Transport | Segment (TCP) or Datagram (UDP) | Data with transport information such as port numbers |
| Network | Packet | Data with logical addressing (like IP addresses) |
| Data Link | Frame | Data with physical addressing (like MAC addresses) |
| Physical | Bits | The actual electrical or optical signals transmitted over the cable or air |
You can imagine it like mailing a parcel:
-
Each layer wraps the data with its own information (like putting it in a box, adding a label, and attaching stamps).
-
When the data reaches its destination, the layers unwrap the information one by one until the original message is delivered.
In summary:
-
A PDU is the term for data at a particular OSI layer.
-
It includes both the actual data and the control information needed for that layer’s communication.
-
PDUs help ensure that data is properly formatted, transmitted, and received across networks.