Page 198 - DCAP207_NETWORKS_DCAP406_COMPUTER_NETWORKS

Unit 12: Application Layer

12.3.2 Browser Architecture Notes

A web browser is composed of three parts. They are controller, client programs and interpreters.
Controller: The controller obtains input from the keyboard or the mouse to access web-pages
with the help of client program. After accessing the webpages, the controller uses one of the
interpreters to display the web pages on the host screen.
Client Programs: They are used to establish TCP session with the web server or proxy server.
The client programs use HTTP, FTP, Gopher or Telnet.
Interpreters: They are used to display the webpages on the web user’s screen. The interpreters,
which are used to translate web pages on the client’s screen, are HTML, CGI or JAVA. They
depend on the type of document. The HTML, which is a markup language and allows browser to
change the format of the webpages, is used scripting web pages. The HTML also enables to store
instructions with the text so that any browser can read the instructions and format the text
according to the host machine being used.
Documents in the World Wide Web are classified into three types. They are static, dynamic and
active documents.

Static Webpage: They are fixed content documents and always provides the same information in
response to all download requests from all web users. Static documents are stored in a web
server to be accessed by the web client. The web client while requesting a webpage gets a copy
of it. The contents of the file are determined when it is created and not when it is used. However,
the webpages can be modified in the server but the web user does not have right to alter them.
Thus, the static webpages displays the same information for all web users from all contexts and
provides hypertext links to perform navigation through static documents. The advantages of
using static web pages are that they are cachet friendly in which one copy can be displayed to
many people and provide ease to put them quickly even by someone who does not have much
experience. However, they become difficult to maintain when a site gets large and difficult to
keep consistent and up to date.

Dynamic Webpage: They provide interactive web navigation and enable to modify the content
like text, images, form fields, etc. on a webpage based on different contexts or conditions. The
dynamic web pages use two types of interactivity:
1. Client side scripting: It us used to modify interface behaviors within a specific web page
based on the mouse or keyboard actions or at specified timing events. The dynamic
behavior happens within the presentation. The presentation technologies like JavaScript
or ActionScript for dynamic HTML (DHTML) and Flash for media types of the presentation
are used. The client side scripting also enables use of remote scripting in which the DHTML
page requests additional information from a server. The content is generated on the web
client’s machine in which the web browser retrieves a page from the server and processes
the code embedded in the webpage so that the contents of the retrieved can be displayed
to web user. In the client-side dynamic pages, some web browsers do not support the
language or they do not support some of the commands of the scripting language.
2. Server side scripting: It is used to modify the requested webpage source between pages to
either adjust the sequence or reload of the web pages delivered to the browser. Server
responses are based on certain conditions like data in a posted HTML form, parameters in
the URL, the type of browser being used, the passage of time or a database or server state.
Server side scripting dynamic webpages are designed with the help of server-side languages
like PHP, Perl, ASP, JSP, etc.

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