Part I of Cisco Networking Simplified

Cisco Press

TCP/IP and IP Addressing

Internet Applications

How Computers Communicate

Networking Fundamentals

Before we begin talking about specific networking technologies and applications, it's worth taking a few pages to go over some networking fundamentals. Networks exist for the sole purpose of sharing information between people or machines. However, to share information, rules must be followed to ensure that the myriad combinations of devices, transports, hardware, and software can communicate smoothly.

In "How Computers Communicate," we cover the most basic aspects of computer networking, starting with the OSI model. This communication model is the basis for all other topics discussed in this book, so it's a great place to start.

In "TCP/IP and IP Addressing," we explore how two of the most popular protocols in use today work. TCP/IP is the communication protocol that drives the Internet as well as most corporate traffic. We then go a bit deeper into the Internet Protocol with a discussion of IP addressing, the concept that allows shared information to reach its intended destination. We end the chapter with an overview of IPv6. The addressing scheme discussed here (known as IPv4) has been in service for years. However, there has been some concern in recent years that Internet has grown beyond the current IP addressing scheme's ability to serve an ever-growing demand. Changing addressing schemes this far into networking's history provides some interesting challenges, which we will also explore.

"Internet Applications" provides a look at two of the most common applications—e-mail and web browsing. This chapter provides some background on how these applications came about and provides a summary of how they work. This should be helpful, because you probably use these applications every day.

The OSI Model

At some point, everyone involved with networking comes across a reference to the Open Systems Interconnection (OSI) seven-layer model. Because this model provides the architectural framework for all of network and computing communication, it's a good place to start. Even if you don't ever plan on setting up your own network, being familiar with this model is essential to understanding how it all works.

The OSI seven-layer model describes the functions for computers to communicate with each other. The International Organization for Standardization (ISO) published this model in 1984 to describe a layered approach for providing network services using a reference set of protocols called OSI. The basis of the definition is that each of the seven layers has a particular function it must perform, and each layer needs to know how to communicate with only the layers immediately above and below it.

The advantages of the OSI approach may not be readily apparent. But this simple concept of having layers understand only those adjacent to themselves allows communications systems to be easily adapted and modified as technologies evolve. For example, as new technologies are introduced in a lower layer, such as Layer 1, upper layers do not necessarily need to be changed. Instead, the adaptations at Layer 2 allow the layers above to use the new technologies transparently. Imagine if all web browsers and e-mail programs had to be replaced every time a new wireless network standard were introduced.

When the OSI networking model was defined, there was little standardization among network equipment manufacturers. Customers generally had to standardize on a particular vendor's often proprietary hardware and software to have devices communicate with each other. As a result of the ISO's and other standardization efforts, networking customers can mix and match hardware when running open-standards protocols, such as Internet Protocol (IP).

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