John Oden. It is difficult to have a conversation about network without hearing someone refer at this or that layer. If you talk for more time, you will soon hear someone refer to this device as Layer X or Layer Y. These conversations are often started with the assumption that everyone is familiar with the layers and how they relate.
The other day, I was guilty of discussing network layers in a blog post. I assumed that everyone would understand what I meant. This post is intended to correct my mistakes and help you understand the importance of layering in networking.
Why layer?
There are two main reasons to organize data networks into layers. First, it is difficult to have an application on one computer communicate with another application on another computer over a network. From the moment you open your Web browser, type an address into it and wait for the desired Web page to appear on your screen, imagine all that must happen.
This involves multiple pieces and operating systems on both the host computers as well as software. It also includes the entire network infrastructure that connects computers, including routers switches, firewalls and telecommunication service provider providers. Without a framework to organize our thoughts, it would be difficult to understand and analyze all this information simultaneously.
The structure of networking into layers that are dedicated to a specific set of functions provides a framework for understanding, analyzing, and discussing these concepts better than if we were to attempt to understand it all. This organization also makes troubleshooting much easier.
Vendor interoperability is the second reason networks are organized into layers. It is currently impossible to source all components required to build a computer network from one vendor. Each layer of networking is organized into layers. Each layer acquires services from the lower layer and exposes a consistent interface to the layer above. These protocols and standards are shared among vendors to ensure consistency. We can replace a device that operates at one layer with another vendor’s device without affecting other layers because of the consistent implementation.

Figure 1 The ISO OSI Reference Model
The ISO OSI Reference Model
The International Organization for Standards (ISO), realizing the need for a standard framework for computer networking, developed the Open Systems Interconnection model (Figure 1). This model covers everything from the lowest level of networking, which is the media that carries the optical or electrical signals, to the highest level nearest to the user. The protocols used by user-facing programs such as email programs and Web browsers are at the highest level.
Figure 1 shows two sets of seven layers in an OSI model. This is to show one computer communicating with another. Each computer has its own set layers. This is a very simple network with only two computers connected together. There will be many different types of devices connected to any network implementation. A network would typically consist of many devices connected together by a variety intermediary networking devices, such as routers, switches, firewalls and routers. Each device in the network has its own set of layers. Each layer is assigned a Protocol Data Unit (PDU), which allows data to be characterized as it passes through them. T