Quiz Entry - updated: 2026.07.14
What is a Protocol Data Unit (PDU) and what are the PDU names at each layer?
A PDU is the name for the data at each stage of encapsulation; going down the stack: Data → Segment → Packet → Frame → Bits.
* The PDU name at each layer, from Data down to Bits. *
Encapsulation is the process where protocols add their information to the data.
A Protocol Data Unit (PDU) is the name for data at each stage of encapsulation.
| Order | PDU Name | Layer |
|---|---|---|
| 1 | Data (Data Stream) | Application |
| 2 | Segment | Transport |
| 3 | Packet | Network/Internet |
| 4 | Frame | Data Link |
| 5 | Bits (Bit Stream) | Physical |
Memory tip: "Do Some People Fear Birthdays" (Data, Segment, Packet, Frame, Bits)
Go deeper:
Protocol data unit (PDU) — the per-layer PDU names across the OSI and TCP/IP models.- Encapsulation (networking) — how each PDU is built from the one above.