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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            9  TCP/IP Application Layer Addressing: Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs)

TCP/IP Application Layer Addressing: Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs) 1 2 3 Uniform Resource Locators (URLs)

URI Standards

A number of Internet standards published in the 1990s describe the syntax and basic use of URIs, URLs and URNs. The first was RFC 1630, Universal Resource Identifiers in WWW, which was published in 1994 and is still a good overview of the topic. In December 1994 a pair of documents, RFCs 1737 and 1738, provided more specific information about URNs and URLs respectively. RFC 1808 describes how to define and use relative URLs, while RFC 2141 provides more information on URN syntax.

RFC 2396, Uniform Resource Identifiers (URI): Generic Syntax, was published in August 1998 to revise and replace some of the information in many of the previous RFCs just mentioned. It is probably the definitive standard on URIs at the present time, though RFCs continue to be published discussing issues related to URIs. This is especially true of URNs, which as I said before, are still in active development.

The base documents such as RFC 2396 describe how URLs can be specified for a number of common protocols (called schemes in URL-speak, as we will see when we look at URLs more closely). To provide flexibility, a mechanism was also defined to allow new URL schemes to be registered. This is described in RFC 2717, Registration Procedures for URL Scheme Names, and RFC 2718, Guidelines for new URL Schemes. There are also a few RFCs that describe specific URL schemes for different protocols, including RFCs 2192 (IMAP), 2224 (NFS), 2368 (e-mail) and 2384 (POP).

TCP/IP Application Layer Addressing: Uniform Resource Identifiers, Locators and Names (URIs, URLs and URNs) 1 2 3 Uniform Resource Locators (URLs)