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The Presentation layer gets its name from its purpose: It presents data to the Application layer. Itís essentially a translator and provides coding and conversion functions. A successful data transfer technique is to adapt the data into a standard format before transmission. Computers are configured to receive this generically formatted data and then convert the data back into its
native format for actual reading (for example, EBCDIC to ASCII). By providing translation services, the Presentation layer ensures that data transferred from the Application layer of one system can be read by the Application layer of another host.
The OSI has protocol standards that define how standard data should be formatted. Tasks like data compression, decompression, encryption, and decryption are associated with this layer. Some Presentation layer standards are involved in multimedia operations. The following serve to direct graphic and visual image presentation:
PICT This is picture format used by Macintosh or PowerPC programs for transferring QuickDraw graphics.
TIFF The Tagged Image File Format is a standard graphics format for high-resolution, bitmapped images.
JPEG The Joint Photographic Experts Group brings these photo standards to us.
Other standards guide movies and sound:
MIDI The Musical Instrument Digital Interface is used for digitized music.
MPEG The Moving Picture Experts Groupís standard for the compression and coding of motion video for CDs is increasingly popular. It provides digital storage and bit rates up to 1.5Mbps.
QuickTime This is for use with Macintosh or PowerPC programs; it manages audio and video applications.
ol Protocol (DNA SCP) Is a DECnet Session-layer protocol.