Layers

Application

The application layer exchanges messages to implement some application service using services of the transport layer

Transport

The transport layer protocol transfers messages from one process to another

It encapsulates application-layer messages with the transport layer header to createa a transport layer segment.

Network Layer

The network layer protocol transfers transport-layer segments from one host to anohter, using the link layer

It encapsulates the transport layer segment with a network layer header to create a network layer datagram

The link layer protocol encapsulates network datagrams with link-layer headers to create link-layer frames

Physical Layer

This is a wire, or the air sometimes