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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 File and Message Transfer Applications and Protocols (FTP, TFTP, Electronic Mail, USENET, HTTP/WWW, Gopher)                 9  TCP/IP World Wide Web (WWW, "The Web") and the Hypertext Transfer Protocol (HTTP)                      9  TCP/IP Hypertext Transfer Protocol (HTTP)                           9  HTTP Entities, Transfers, Coding Methods and Content Management

HTTP Entities, Transfers, Coding Methods and Content Management 1 2 3 HTTP Data Transfer, Content Encodings and Transfer Encodings

The presence of the word “text” in the name “Hypertext Transfer Protocol” is a reminder of the legacy of HTTP. As I explained in my brief history of the World Wide Web, it was originally created to allow text documents to be linked together. This made sense, because at the time that the Web was being created, most computing was still being done with text. Accordingly, the first version of HTTP (HTTP/0.9) supported only one type of message body: a plain ASCII text document.

In the early 1990s, the rapid increase in computing power and networking performance transformed the world of information technology from text to multimedia. These were also the World Wide Web’s formative years, and it did not take long before many users wanted to exploit the power of the Web to share not only text files but also pictures, drawings, sound clips, movies and much more. Thus, HTTP had to evolve as well; starting with HTTP/1.0, significant changes were made to allow the protocol to transport and process much more than just text. Today, HTTP really would be better described as dealing with hypermedia than hypertext, though the name of the protocol was never changed.

One drawback of supporting many types of files in HTTP is added complexity. Where before every message recipient knew the body contained ASCII text, now any message can contain any of many kinds of data. When HTTP was expanded to support flexible media, it needed a system that would address two specific issues: encoding entities of various types into an HTTP message body, and clearly identifying the entity’s characteristics for the recipient of the message.

At the same time that HTTP was being changed to support non-text entities, another important TCP/IP application was also moving away from its decades-long role as a text-messaging medium, to one that could transport multimedia: electronic mail. This was accomplished using a technology called Multimedia Internet Mail Extensions (MIME), which define a mechanism for encoding and identifying non-text data—exactly what HTTP needed to do. Since TCP/IP developers wisely reuse technologies that work, the creators of HTTP borrowed many concepts from MIME, including many of the MIME e-mail headers that are used to identify the contents of a MIME message.

HTTP Entities, Transfers, Coding Methods and Content Management 1 2 3 HTTP Data Transfer, Content Encodings and Transfer Encodings