TCP IP Topmost Layer Explained | Generated by AI

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Question: In the TCP/IP reference model, which consists of 4 layers, what is the topmost layer from bottom to top: network interface layer, internet layer, transport layer, and the fourth layer?

A. Presentation layer
B. Session layer
C. Physical layer
D. Application layer

Answer:

D. Application layer

The TCP/IP model (also called the Internet protocol suite or DoD model) is a 4-layer practical network model. From bottom to top, the layers are:

  1. Network Interface Layer (or Link Layer / Network Access Layer)
    → Corresponds roughly to the Physical + Data Link layers of the OSI model

  2. Internet Layer (or Network Layer)
    → Main protocol: IP (Internet Protocol)

  3. Transport Layer
    → Main protocols: TCP and UDP

  4. Application Layer
    → The topmost layer, includes all protocols that directly provide services to applications (HTTP, HTTPS, FTP, SMTP, DNS, SSH, Telnet, etc.)

Common mistake explanation:
Many people confuse the TCP/IP model with the OSI 7-layer model. In the OSI model:

But the question is clearly asking about the TCP/IP 4-layer model, not OSI. Therefore the correct answer is Application layer (D), not Physical layer (C).

Your previous answer (C) was incorrect because the physical layer is actually part of the bottom layer (Network Interface Layer) in TCP/IP, not the top layer.

References:

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