Please Whitelist This Site? I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :) If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads. If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK. Thanks for your understanding! Sincerely, Charles Kozierok Author and Publisher, The TCP/IP Guide

NOTE: Using software to mass-download the site degrades the server and is prohibited. If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The TCP/IP Guide  9  Networking Fundamentals       9  Fundamental Network Characteristics

Fundamental Network Characteristics 1 2 Protocols: What Are They, Anyway?

One of the reasons why many people find networking difficult to learn is that it can be a very complicated subject. One of the chief reasons for this complexity is that networks consist of so many hardware and software elements. While a network user may only perceive that he or she is using one computer program (like a Web browser) and one piece of hardware (like a PC), these are only parts of a much larger puzzle. In order for even the simplest task to be accomplished on a network, dozens of different components must cooperate, passing control information and data to accomplish the overall goal of network communication.

The best way to understand any complex system is to break it down into pieces and then analyze what they do and how they interact. The most logical approach for this is to divide the overall set of functions into modular components, each of which is responsible for a particular function. At the same time, we also need to define interfaces between these components, which describe how they fit together. This enables us to simplify the complexity of networking by approaching it in digestible chunks.

Networking technologies are most often compartmentalized in this manner by dividing their functions into layers, each of which contains hardware and/or software elements. Each layer is responsible for performing a particular type of task, as well as interacting with the layers above it and below it. Layers are conceptually arranged into a vertical stack. Lower layers are charged with more concrete tasks such as hardware signaling and low-level communication; they provide services to the higher layers. The higher layers in turn use these services to implement more abstract functions such as implementing user applications.

Dividing networks into layers this way is somewhat like the division of labor in a manufacturing facility, and yields similar benefits. Each hardware device or software program can be specialized to perform the function needed by that layer, like a well-trained specialist on an assembly line. The different modules can be combined in different ways as needed. Understanding how a network functions overall is also made much easier this way.

Fundamental Network Characteristics 1 2 Protocols: What Are They, Anyway?