CCNA Cisco Certified Network Associate Study Guide - FTP Server

FIGURE 1.3 Layer functions
The OSI Reference Model 7
Figure 1.3 shows the functions defined at each layer of the OSI model. The
following pages discuss this in detail.
The Application Layer
The Application layer of the OSI model is where users communicate to the
computer. The Application layer is responsible for identifying and establishing
the availability of the intended communication partner and determining
if sufficient resources for the intended communication exist.
Although computer applications sometimes require only desktop
resources, applications may unite communicating components from more
than one network application; for example, file transfers, e-mail, remote
access, network management activities, client/server processes, and information
location. Many network applications provide services for communication
over enterprise networks, but for present and future internetworking,
the need is fast developing to reach beyond their limits. Today, transactions
and information exchanges between organizations are broadening to require
internetworking applications like the following:
World Wide Web (WWW) Connects countless servers (the number
seems to grow with each passing day) presenting diverse formats. Most
are multimedia and include some or all of the following: graphics, text,
video, and even sound. Netscape Navigator, Internet Explorer, and other
browsers like Mosaic simplify both accessing and viewing Web sites.