Which of the following is NOT a part of the TCP/IP model?

A.  Application Layer
B.  Internet Layer
C.  Business Layer
D.  Transport Layer

Answer: C
Explanation:

A. Application Layer

In the TCP/IP model, the Application layer is the top layer. It combines the functions of the OSI Model's top three layers (Application, Presentation, and Session).

• The Function: It provides the interface for applications to access network services.

• Protocols: HTTP, FTP, SMTP, DNS, and SSH operate here.

B. Internet Layer

The Internet layer is responsible for logical addressing and routing packets across different networks.

• The Function: It handles the movement of packets from source to destination.

• Protocols: The primary protocol here is IP (Internet Protocol), along with ICMP, ARP, and IGMP. It maps directly to the OSI Network Layer.

C. Business Layer

The "Business Layer" is a term often found in Enterprise Architecture (like TOGAF) or Software Design (3-tier architecture), but it has no place in a networking stack.

• Why it's the Answer: The TCP/IP model is strictly technical, focusing on the mechanics of how bits move across a wire. Business logic occurs inside the software being used, not within the protocol suite itself.

D. Transport Layer

The Transport layer provides end-to-end communication services for applications.

• The Function: It manages flow control, error correction, and data segmentation.

• Protocols: TCP (Connection-oriented, reliable) and UDP