Transport Layer is NOT part of the TCP/IP model.

Explanation:
The TCP/IP model is a network protocol suite that provides a set of rules and guidelines for communication between devices on a network. It consists of four layers, namely the Network Layer, Internet Layer, Transport Layer, and Application Layer. Each layer has its own specific functions and protocols.

1. Network Layer:
The Network Layer is responsible for routing packets across different networks. It handles tasks such as addressing, routing, and fragmenting data packets. The protocols used in this layer include IP (Internet Protocol) and ICMP (Internet Control Message Protocol).

2. Internet Layer:
The Internet Layer is responsible for the transmission of packets across the network. It encapsulates data packets into IP packets and adds the necessary addressing information. The most commonly used protocol in this layer is the IP (Internet Protocol).

3. Transport Layer:
The Transport Layer is responsible for the reliable delivery of data between hosts. It provides services such as segmentation, flow control, and error recovery. The main protocols used in this layer are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

4. Application Layer:
The Application Layer is the topmost layer of the TCP/IP model. It interacts directly with the end-user and provides services such as email, file transfer, and web browsing. Protocols like HTTP, FTP, SMTP, and DNS operate in this layer.

From the given options, the Session Layer is not part of the TCP/IP model. The Session Layer is part of the OSI model, which is another widely used networking model. It is responsible for establishing, maintaining, and terminating sessions between applications. The TCP/IP model does not explicitly include a separate Session Layer, as the functionality of session management is typically handled by the Application Layer protocols.

In summary, the correct answer is option 'B' - Session Layer, as it is not part of the TCP/IP model.