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Chapter 1

Internetworking

Financial transaction services

Target the financial community. They

gather and sell information pertaining to investments, market trading,
commodities, currency exchange rates, and credit data to their subscribers.

The Presentation Layer

The Presentation layer gets its name from its purpose: It presents data
to the Application layer and is responsible for data translation and code
formatting.

This layer is 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 one.

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 too. 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 stan-
dards to us.

Other standards guide movies and sound:

MIDI The Musical Instrument Digital Interface is used for digitized
music.

MPEG The Moving Picture Experts Group's standard for the compres-
sion 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.

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