Please Whitelist This Site?

I know everyone hates ads. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. And I have a family to support, just like you. :)

If you like The TCP/IP Guide, please consider the download version. It's priced very economically and you can read all of it in a convenient format without ads.

If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. To do so, just open the Adblock menu and select "Disable on tcpipguide.com". Or go to the Tools menu and select "Adblock Plus Preferences...". Then click "Add Filter..." at the bottom, and add this string: "@@||tcpipguide.com^$document". Then just click OK.

Thanks for your understanding!

Sincerely, Charles Kozierok
Author and Publisher, The TCP/IP Guide


NOTE: Using software to mass-download the site degrades the server and is prohibited.
If you want to read The TCP/IP Guide offline, please consider licensing it. Thank you.

The Book is Here... and Now On Sale!

The whole site in one document for easy reference!
The TCP/IP Guide

Custom Search







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 Electronic Mail System: Concepts and Protocols (RFC 822, MIME, SMTP, POP3, IMAP)
                     9  TCP/IP Electronic Mail Message Formats and Message Processing: RFC 822 and MIME
                          9  TCP/IP Enhanced Electronic Mail Message Format: Multipurpose Internet Mail Extensions (MIME)

Previous Topic/Section
MIME Basic Structures and Headers
Previous Page
Pages in Current Topic/Section
1
2
345
Next Page
MIME Composite Media Types: Multipart and Encapsulated Message Structures
Next Topic/Section

MIME Content-Type Header and Discrete Media: Types, Subtypes and Parameters
(Page 2 of 5)

Discrete Media Types and Subtypes

As I mentioned in the preceding topic, MIME supports two basic structures: simple or complex. A simple message carries only one media type, such as a piece of text, a picture or an executable file. These are called discrete media types in MIME. A complex message carries a composite media type, which may incorporate multiple body parts. Each body part in turn carries data corresponding to one of the discrete media types. The top-level media type indicates whether the whole message carries a discrete media type or a composite type; I will describe the discrete media types here; the composite types are discussed in the next topic.

The RFC 2046 standard (part two of the set of five standards that describes MIME) defines five discrete top-level media types: text, image, audio, video and application; they each represent one of the major classes of data commonly transmitted over TCP/IP. Each of these has one or more subtypes, and some also have parameters that are used to provide more information about them.

The creators of MIME recognized that the standard could not describe every media type, and that new ones would be created in the future. RFC 2048 (part four of the five-standard MIME set) describes the process by which new media types, subtypes and parameters can be described and registered with the Internet Assigned Numbers Authority (IANA).

Thus far, only one new top-level media type has been created; this is the model top-level type, defined for CAD modeling files and similar uses, as described in RFC 2077. However, many dozens of new subtypes have been created over the years, some specified in RFCs and others just registered directly with IANA. This includes many “vendor-specific” subtypes, which are usually identified by either the prefix “x-” or “vnd.” in the subtype name.

On The Web: You can find a complete list of MIME media organized by top-level media type, on IANA's web site: http://www.iana.org/assignments/media-types/index.html


Key Concept: The MIME Content-Type header specifies what sort of data is encoded in a MIME message. The header indicates the general form of the message’s content through a top-level media type, and the more specific nature of the data through the specification of a subtype. It may also contain optional parameters that provide still more information about the content.



Previous Topic/Section
MIME Basic Structures and Headers
Previous Page
Pages in Current Topic/Section
1
2
345
Next Page
MIME Composite Media Types: Multipart and Encapsulated Message Structures
Next Topic/Section

If you find The TCP/IP Guide useful, please consider making a small Paypal donation to help the site, using one of the buttons below. You can also donate a custom amount using the far right button (not less than $1 please, or PayPal gets most/all of your money!) In lieu of a larger donation, you may wish to consider purchasing a download license of The TCP/IP Guide. Thanks for your support!
Donate $2
Donate $5
Donate $10
Donate $20
Donate $30
Donate: $



Home - Table Of Contents - Contact Us

The TCP/IP Guide (http://www.TCPIPGuide.com)
Version 3.0 - Version Date: September 20, 2005

© Copyright 2001-2005 Charles M. Kozierok. All Rights Reserved.
Not responsible for any loss resulting from the use of this site.