Question 93

Explanation

The TCP/IP model, which is the foundation of the Internet Protocol suite, does not include a layer called "physical." Instead, the TCP/IP model has four layers: [1] Application layer (Determines the protocols for the Transport layer); [2] Transport layer (Allows for data to move among devices); [3] Internet layer (Creates and inserts packets); [4] Network Interface Layer (Governs how data will move through the network) (for more on this, see ISC2 Study Guide, Domain 4).

The physical layer is a component of the Open Systems Interconnection (OSI) model, which is another seven-layer model developed to help vendors and network administrators understand and standardize network technologies (for more on this, see ISC2 Study Guide, Domain 4).

A side-by-side illustration of the layers of the two network stack models

The figure shows the layer correspondence between the OSI model and the TCP/IP model. In the lower layers, the TCP/IP model does not distinguish between a physical layer and a data link layer (layers 1 and 2). The upper layers of the OSI model correspond to the Application layer of the TCP/IP model.

The remaining options, Application, Transport, and Internet, are actually layers within the TCP/IP model. The Application layer includes protocols that applications use to communicate over the network, such as HTTP for web browsing and SMTP for email. The Transport layer is responsible for providing communication services directly to application processes running on different hosts. It includes protocols such as Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) that help manage data transmission. The Internet layer is responsible for sending packets across potentially multiple networks and uses protocols such as IP (Internet Protocol) to route the packets to the correct destination. These layers are integral to the TCP/IP model, so they are not the correct answer to the question of which layer is not part of the TCP/IP model.