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Application Layer
The application layer is the OSI layer closest to the end user, which means
that both the OSI application layer and the user interact directly with the
software application. This layer interacts with software applications that
implement a communicating component. Such application programs fall
outside the scope of the OSI model. Application-layer functions typically
include identifying communication partners, determining resource
availability, and synchronizing communication.
When identifying communication partners, the application layer determines the
identity and availability of communication partners for an application with data
to transmit. When determining resource availability, the application layer
must decide whether sufficient network resources for the requested communication
exist. In synchronizing communication, all communication between
applications requires cooperation that is managed by the application layer.
Two key types of application-layer implementations are TCP/IP applications
and OSI applications. TCP/IP applications are protocols, such as Telnet,
File Transfer Protocol (FTP), and Simple Mail Transfer Protocol (SMTP), that
exist in the Internet Protocol suite. OSI applications are protocols, such
as File Transfer, Access, and Management (FTAM), Virtual Terminal Protocol
(VTP), and Common Management Information Protocol (CMIP), that exist in the OSI
suite.
Internetworking Applications
WWW
-Connects countless servers presenting diverse formats: multimedia,
graphics, text, sound, and video. Applications such as Netscape
Navigator, Internet Explorer, and Mosaic simplify accessing and viewing web
sites.
EMAIL
-Versatile can use SMTP or X.400 to deliver messages between different
email applications.
Electronic Data Interchange
-Composite of specialized standards that facilitates the flow of tasks such
as accounting, shipping / receiving, and order and inventory tracking
between business.
Bulletin Boards
-Includes Internet chat rooms, and sharing public domain software.
Internet Navigation Utilities
-Includes Gopher, WAIS, and search engines, e.g. Yahoo, Excite, and Alta
Vista. Helps users locate resources and information on the Internet.
Financial Transaction Services
-They gather and sell information pertaining to investments and credit data
to their subscribers.
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