Learning Objectives

By the end of this chapter, you should be able to:

• Explain why the Open Systems Interconnection (OSI) model was created.
• Describe the networking problems the OSI model was designed to solve.
• Understand the concept of layered network architecture.
• Identify the seven layers of the OSI model and their high-level responsibilities.
• Explain how data moves through the layers using encapsulation and decapsulation.
• Understand why the TCP/IP model is used in practice while the OSI model remains an essential learning and troubleshooting framework.
• Appreciate why DevOps engineers, Cloud Engineers, Network Engineers, and Security Engineers still rely on the OSI model.

Introduction

Imagine trying to build a house without a blueprint.

One team starts laying bricks before the foundation is complete.

Another team installs electrical wiring without knowing where the walls will be.

The plumbing team uses different measurements than the construction team.

The result would be confusion, incompatibility, delays, and expensive mistakes.

Early computer networking faced similar challenges.

Different manufacturers built computers and networking equipment using proprietary communication methods. Systems from one vendor often could not communicate with systems from another because there was no universally accepted framework describing how devices should exchange information.

To address this challenge, the Open Systems Interconnection (OSI) Model was developed.