Page 133 - Handout Computer Network.

Computer Network 2026

The application layer is the layer closest to the end user. This determines whether
sufficient resources exist for communication between systems. Without the application layer,
there would be no network communication support.

The application layer does not provide services to any other layer, but it does provide
services to application processes lying outside the scope of the TCP/IP model, such as
spreadsheet programs, word processing programs, and banking terminal programs.
Additionally, the application layer provides a direct interface to the rest of the model for
network applications (such as browser or e-mail program) or an indirect interface for standalone
applications (such as word processors, spreadsheets, and presentation managers) with a
network redirector.
6.3.2 Direct Network Applications

Most applications that work in a networked environment are classified as client/server
applications. These applications, such as FTP clients (not protocols), web browsers, and e-mail
programs, all have two components that allow them to function:
o The client side.

o The server side.

The client side is located on the local computer and is the requestor of the services.

The server side is located on a remote computer and provides services in response to the

client’s requests.

A client/server application works by constantly repeating the following looped routine:
client request, server response; client request, server response.

For example, a web browser accesses a web page by requesting a uniform resource
locator (URL), which is resolved to an IP address on a remote web server.

After it locates the URL, the web server that is identified by that URL responds to the
request.

Then, based on the information received from the web server, the client can request
more information from the same web server or can access another web page from a different
web server.
Netscape Navigator and Internet Explorer are probably the most commonly used
network applications.
An easy way to understand a web browser is to compare it to a television remote control.

A remote control gives you the capability to directly control a TV’s functions: volume, channels,
brightness, and so on.

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