OSI Layers 1–3 Explained Simply | Generated by AI
Question: In the OSI Reference Model, the physical layer, data link layer, and network layer are collectively called
A. End-to-end layers
B. Node-to-end layers
C. Node-to-node layers
D. Intermediate system layers
Your answer: D
Correct answer: C
Answer:
The correct answer is C. Node-to-node layers.
Explanation:
In the OSI Reference Model (OSI/RM), the seven layers are divided into two major groups based on their scope of communication:
- Node-to-node layers (also called point-to-point layers or hop-by-hop layers):
These layers are responsible for communication between adjacent network devices (one hop at a time).- Physical layer (Layer 1)
- Data Link layer (Layer 2)
- Network layer (Layer 3)
→ These three layers together are called node-to-node layers (or point-to-point layers / 结点到结点层 in Chinese).
- End-to-end layers (also called host-to-host layers):
These layers are responsible for communication from the source host to the destination host, regardless of how many intermediate devices (routers, switches) are crossed.- Transport layer (Layer 4)
- Session layer (Layer 5)
- Presentation layer (Layer 6)
- Application layer (Layer 7)
→ These four layers together are called end-to-end layers (端到端层).
Why not D (Intermediate system layer)?
“Intermediate system” is a term mainly used in ISO terminology to refer to routers (devices that operate at Layer 3 — the network layer). It is not the standard name for the group of layers 1–3 in OSI teaching materials or textbooks.
Summary table:
| Group | Layers involved | Scope of responsibility | Chinese name |
|---|---|---|---|
| Node-to-node | Physical + Data Link + Network | Between adjacent nodes (one hop) | 结点到结点层 |
| End-to-end | Transport + Session + Presentation + Application | From source host to destination host | 端到端层 |
So the physical layer, data link layer, and network layer are correctly called node-to-node layers → answer C.
References:
- None (standard OSI model knowledge; widely consistent across textbooks and certification materials such as CCNA, CompTIA Network+, and Chinese computer network textbooks)