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While the 7-layer OSI model is a fantastic theoretical tool for learning and standardizing network communications, the actual Internet does not strictly follow it. Instead, the Internet runs on the TCP/IP Protocol Suite, which was developed prior to the OSI model by the United States Department of Defense (DoD) for ARPANET.
The TCP/IP model condenses the 7 OSI layers into 4 simpler, highly pragmatic layers.
The TCP/IP Application layer is equivalent to the combined Application, Presentation, and Session layers of the OSI model.
Directly maps to the OSI Transport Layer. It is responsible for providing communication services directly to the application processes.
Directly maps to the OSI Network Layer. Its primary responsibility is to route packets across multiple independent networks from the source to the destination.
ping), ARP (Address Resolution Protocol).Combines the OSI Data Link and Physical layers. It deals with the physical hardware and the lowest-level framing of data.
The most critical concept in layered networking is Encapsulation. As data moves down the TCP/IP stack from the application to the physical wire, each layer adds its own control information in the form of a "Header".
Imagine sending an Email:
The Frame is then converted into raw electrical signals (or light pulses) and transmitted over the physical wire. When it reaches the destination computer, the process is reversed (Decapsulation), stripping off the headers one by one as the data moves back up the stack to the receiving email client.