Presentation Layer
The presentation layer provides a variety of coding and conversion
functions that are applied to application layer data. These functions ensure
that information sent from the application layer of one system will be readable
by the application layer of another system. Some examples of presentation-layer
coding and conversion schemes include common data representation formats,
conversion of character representation formats, common data compression schemes,
and common data encryption schemes.
Common data representation formats, or the use of standard image, sound, and
video formats, enable the interchange of application data between different
types of computer systems. Conversion schemes are used to exchange information
with systems by using different text and data representations, such as EBCDIC
and ASCII. Standard data compression schemes enable data that is compressed at
the source device to be properly decompressed at the destination. Standard data
encryption schemes enable data encrypted at the source device to be properly
deciphered at the destination. Presentation-layer implementations are not
typically associated with a particular protocol stack. The following serve
to direct graphic and visual image presentations:
PICT
-Picture format used by Mac and PowerPC programs for transferring Quick
draw graphics.
TIFF
-Tagged Image File Format, a standard graphics format for high-resolution
bitmapped images.
JPEG
-Joint Photographic Experts Group standards.
MIDI
-Musical Instrument Digital Interface, used for digitized music.
MPEG
-Moving Picture Experts Group, standard for compression and coding of
motion video. Digital storage and bit rates up to 1.5 Mbps.
Quicktime
-Mac and PowerPC audio and video applications.
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