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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 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)
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MIME Content-Type Header and Discrete Media: Types, Subtypes and Parameters
(Page 5 of 5)
Application Media Type (application)
This media type is a catch
all for any kind of data that doesn't fit into one of the categories
above, or that is inherently application-specific. The subtype describes
the data by indicating the kind of application that uses it. This can
be used to guide the recipient's e-mail program in choosing an appropriate
application program to display it, just like how a file extension in
Windows tells the operating system how to open different kinds of files.
For example, if you have Microsoft
Excel installed on your PC, clicking a file ending with .XLS
will launch Excel automatically. Similarly, an Excel spreadsheet will
normally be sent using MIME with a media type of application/vnd.ms-excel.
This tells the recipient's e-mail program to launch Excel to read this
file.
Since there are so many applications
out there, there are over a hundred different subtypes within this top-level
type. Table 247
contains a few representative samples.
Table 247: MIME application Media Type Subtypes
type/subtype
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Description
|
Defining
Source
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application/octet-stream
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An arbitrary set of binary data
octets. See below for more details.
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RFC 2046
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application/postscript
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A Postscript
file, used for printing and for generating Adobe Acrobat (PDF) files.
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RFC
2046
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application/applefile
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Resource file information for
representing Apple Macintosh files.
|
Registration
with IANA
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application/msword
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Microsoft Word
document. Note that this does not have the vnd prefix like
most other Microsoft file types.
|
Registration
with IANA
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application/pdf
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A Portable Document Format (PDF)
file, as created by Adobe Acrobat.
|
Registration
with IANA
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application/vnd.framemaker
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An Adobe FrameMaker
file.
|
Registration
with IANA
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application/vnd.lotus-1-2-3
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A Lotus 1-2-3 file.
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Registration
with IANA
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application/vnd.lotus-notes
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A Lotus Notes
file.
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Registration
with IANA
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application/vnd.ms-excel
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A Microsoft Excel spreadsheet
file.
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Registration
with IANA
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application/vnd.ms-powerpoint
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A Microsoft
Powerpoint presentation file.
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Registration
with IANA
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application/vnd.ms-project
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A Microsoft Project file.
|
Registration
with IANA
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application/zip
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A compressed
archive file containing one or more other files, using the ZIP/PKZIP
compression format.
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Registration
with IANA
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Of these, there is one
special subtype that is worth further mention: the application/octet-stream
subtype. This is a catch all within the catch all
of the application type, and just means the file is a sequence
of arbitrary binary data. It is usually used when the sender is unsure
of what form the data takes, or cannot identify it as belonging to a
particular application. When this type is used, the recipient will usually
be prompted to just save the data to a file. He or she must then figure
out what application to use to read it.
The application/octet-stream
MIME type/subtype may even be used for images, audio or video in unknown
formats. If you try to send a multimedia document that your sending
program does not understand, it will generally encode it as application/octet-stream
for transmission. This is your e-mail program's way of saying to the
recipient I am sending you this file as-is, you figure out what
to do with it.
This application/octet-stream
type is also very often used for transmitting executable files (programs)
especially on Windows systems. Unfortunately, while convenient, this
can be a serious security hazard. In recent years, the Internet has
been subject to a steady stream of viruses and worms that spread by
sending themselves to other users through executable file attachments
in e-mail. This makes opening and running any unknown application/octet-stream
attachment potentially dangerous.
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Version 3.0 - Version Date: September 20, 2005
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