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The TCP/IP Guide  9  TCP/IP Application Layer Protocols, Services and Applications (OSI Layers 5, 6 and 7)

TCP/IP Remote Network Monitoring (RMON) 1 TCP/IP Application Layer Addressing: Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs)

For centuries, philosophers have struggled with this question: “what's it all about?” Needless to say, the meaning of life is a bit beyond the scope of this Guide. J However, we can examine this quandary within the scope of networking itself. What is networking for? Why do we bother creating networks anyway? What's it all about?

The simplified answer is that all of the hardware devices, software modules and layered protocols examined in this Guide are means to one real end: enabling people to use networking applications. The true power of layering is that it allows applications to be created that automatically make use of lower-level technologies to communicate without having to worry about the details of how the communication is accomplished. This frees application programmers to create a wide variety of applications that find many different ways to facilitate the exchange information.

The TCP/IP protocol suite is the foundation of modern internetworking, and for this reason, has been used as the primary platform for the development and implementation of networking applications. Over the last few decade, as the global TCP/IP Internet has grown, hundreds of new applications have been created. These programs enable a myriad of different tasks and functions to be accomplished, ranging from implementing essential business tasks to pure entertainment, by users who may be in the same room or on different continents.

It would be impossible to try to describe every possible TCP/IP application, and pointless to even try. However, of all the TCP/IP applications, there are a small number that are widely considered to be “key applications” of TCP/IP. Most have been around for a very long time—in some cases, longer than even the modern Internet Protocol itself. They are generally implemented as TCP/IP application protocols and are defined using the same RFC process and standards as other TCP/IP protocol suite components.

This section describes some of these definitive TCP/IP applications and application layer protocols. Before getting into the applications themselves, I explain the universal system set up for TCP/IP applications to use for addressing Internet resources: uniform resource identifiers (URIs), which can be either uniform resource locators (URLs) or uniform resource names (URNs). These are best known for their use on the World Wide Web, but can in fact be used by a variety of applications.

I then provide several subsections that discuss the application groups themselves. The first describes file and message transfer applications; this group is the largest, as it contains many of the applications we consider central to TCP/IP networking, such as electronic mail, file transfer and the World Wide Web. The second describes interactive and remote application protocols, which are used traditionally to allow a user of one computer to access another, or to permit the real-time exchange of information. The third discusses TCP/IP administration and troubleshooting utilities, which can be employed by both administrators and end users alike.

TCP/IP Remote Network Monitoring (RMON) 1 TCP/IP Application Layer Addressing: Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs)