Principles Digital Communication System & Computer Networks (Charles River Media Computer Engineering)
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23.2 MULTIPURPOSE INTERNET MAIL EXTENSION (MIME)
MIME is defined in RFC 1521 and 1522. The specifications include:
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Five new message header fields that provide information about the body of the message.
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A number of content formats to support multimedia mail.
The five header fields are:
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MIME Version 1.0 (conforms to RFC 1521 and 1522).
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Content type that describes data contained in the body.
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Content transfer encoding that indicates the type of transformation that has been used to represent the body of the message.
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Content ID to uniquely identify MIME content types.
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Content description: plain text description of object, such as audio, text, or video clip.
Some of the MIME content types are listed here.
| Type | Subtype | Description |
|---|---|---|
| Text | Plain | |
| Multipart | Mixed | To be presented to the user in the order they appear. |
| Parallel | No order is required. | |
| Alternative | Alternative version, best to be displayed. | |
| Digest | Similar to mixed, but RFC 822. | |
| Message | RFC822 | |
| Partial | Fragment | Large mails. |
| External body | Pointer to object | |
| Image | JPEG | |
| GIF | ||
| Video | MPEG | |
| Audio | Basic | 8-bit at 8kHz |
| Application | PostScript | |
| Octet stream | Binary data with 8-bit types. |
An example MIME header looks like this:
From: kvkk.prasad@ieee.org To: kvravi@ece.nus.sg Sub: demo MIME Version 1.0 Content type: multipart/mixed Content type: video/MPEG
MIME is an extension to SMTP to provide multimedia message content to e-mails. In addition to plain text, images, executable files, audio, and video clips can be attached to the e-mail. MIME is defined in RFCs 1521 and 1522.
Hence, MIME is an extension to the SMTP to provide multimedia support in the message of the mail using the various MIME types.
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