This is part of the book "Introduction to Networking" at www.net-intro.com
So far we have spent all of our time describing the four-layer model used to design and implement the TCP/IP protocols and applications that make up the Internet. However, the TCP/IP model is not the only model we can use to help us understand how networks work. The other model commonly used to make sense of network design is called the Open System Interconnection (OSI) model. While the TCP/IP model was designed and evolved as the TCP/IP protocols were developed, deployed, and changed, the OSI model was the result of a careful design process by many networking experts who worked to develop a general approach to network models.