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

TCP/IP Key Applications and Application Protocols 1 Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs): Overview, History, Significance and Standards

The Internet consists of millions of interconnected servers, each of which is capable of providing useful information to Internet users who request it. The more information a network has, the richer it is, but the more difficult it becomes to locate. In order to use information, we need to be able to find it, and that requires at a minimum that we employ some means for labeling each file or object.

For this purpose, TCP/IP has defined a system of Uniform Resource Identifiers (URIs) that can be used both on the Internet and on private TCP/IP networks. Each URI uniquely specifies how a client can locate a particular resource and access it so it can be used. URIs are subdivided into Uniform Resource Locators (URLs) and Uniform Resource Names (URNs), which serve a similar purpose but work in different ways.

In this section I describe the system of addressing used on the Internet to identify files, objects and resources. I begin with an overview, which introduces the concept of Uniform Resource Identifiers (URIs), and explains the differences between URIs, URLs and URNs. At the present time, URLs are used much more often than URNs. Therefore, I have included a full subsection with several topics that cover in detail the syntax of URLs, as well as important issues related to how they are used. I also have a summary topic that gives a summary overview of URNs and their role in Internet addressing.

TCP/IP Key Applications and Application Protocols 1 Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs): Overview, History, Significance and Standards