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The TCP/IP Guide

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Table Of Contents  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

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HTTP Entities and Internet Media Types
(Page 3 of 3)

Other MIME Constructs Used In HTTP

In addition to media types, HTTP also borrows from MIME in several other ways. These include the notion of content codings and the use of a header to indicate the length of an entity. It’s important to recognize, however, that even though HTTP’s handling of Internet media is very similar to that of MIME, it is not identical. In fact, my understanding is that there was an early proposal that HTTP use MIME exactly as defined, but a specific decision was made not do this. We will explore a possible reason why in the next topic.

The bottom line, however, is that HTTP’s developers chose to adopt concepts from MIME that made sense, and left other parts out. As a result, HTTP messages are not MIME compliant, even though you may see several headers in HTTP messages starting with MIME’s “Content-” prefix. For example, even though HTTP has a Content-Encoding header, its use is quite different from that of MIME’s, as we will again see in the next topic. Confirmation of the difference between HTTP and MIME can be found in the fact that HTTP does not use the MIME-Version header that is required in MIME messages.

Key Concept: Even though HTTP borrows several concepts and header types from MIME, the protocol is not MIME-compliant.



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