Network models define a set of network layers (also known as a stack) and how those layers (protocols) interact with one another. There are two commonly used network models in use today, TCP/IP (Transmission Control Protocol/Internet Protocol) and OSI (Open Systems Interconnection). By using network models we enable devices using the same network model to communicate with one another more effectively and we’re better equipped to understand how the network works.

TCP/IP Model
The TCP/IP model is by far the most widely used model in existence today. Just about every modern networking device supports the TCP/IP model including computers, mobile devices, and even a few appliances. This model is also known as the DoD model and the Internet model. It was created by the efforts of the U.S. Department of Defense and various universities in the 1970s.

The TCP/IP model defines an enormous collection of protocols that are governed by their respective Request For Comments (RFC). It is human nature to categorize anything and everything to help us understand and remember. The TCP/IP model is no exception. It separates these protocols into four layers (or categories) to make it easier to understand how these layers (protocols) interact with one another. The four layers of the TCP/IP model are the Application, Transport, Internet, and Network Access layers with each layer providing a service to the layer above it.

The Application layer is the layer most of us will interact with on a daily basis whether we realize it or not. The protocols used in the Application layer provide services to the software running on a computer, such as retrieving the web page of your favorite website. The Application layer doesn’t care what the application looks like, what new features it has, what language it’s written in, or what you think of it. The Application layer defines what services the software might need, such as HTTP (web browsing) or POP3 and SMTP (e-mail). There are many protocols supported within the Application layer, such as HTTP, SMTP, POP3, FTP, Telnet, IRC, IMAP, SSL, PPP, etc. Continue reading..