HTTP

HTTP

1. Features

• Persistent TCP Connections: Remain open for multiple requests

• Partial Document Transfers: Clients can specify start and stop positions

• Conditional Fetch: Several additional conditions

• Better content negotiation

• More flexible authentication.

2. Web Browsers :

Mosaic - NCSA (Univ. of Illinois), in early 1993 First to use a GUI, led to Explosion of Web use Initially for X-Windows, under UNIX, but was ported to other platforms by late 1993

•  Browsers are clients - always initiate, servers react (although sometimes servers require responses)

• Most requests are for existing documents, using Hypertext Transfer Protocol

• (HTTP) But some requests are for program execution, with the output being

returned as a document.

Browser: A web browser is a software application for retrieving, presenting, and traversing information resources on the World Wide Web.

3. Web Servers:

-  Provide responses to browser requests, either existing documents or dynamicallyBuilt documents.

-  Browser-server connection is now maintained through more than one request- Response

cycle

-  All communications between browsers and servers use Hypertext Transfer Protocol

-  Web servers run as background processes in the operating system.

-  Monitor a communications port on the host, accepting HTTP messages when they appear All current Web servers came from either

1. The original from CERN

2. The second one, from NCSA

-  Web servers have two main directories:

1. Document root (servable documents)

2. Server root (server system software)

-  Document root is accessed indirectly by clients

-  Its actual location is set by the server Configuration file

-  Requests are mapped to the actual location

-  Virtual document trees

-  Virtual hosts

-  Proxy servers

-  Web servers now support other Internet protocols

-  Apache (open source, fast, reliable)

-  IIS

-  Maintained through a program with a GUI interface.

4. Markup Language:

Mark-up Language is used to identify elements of a page so that a browser can render that page on your computer screen.

Content to be displayed is “marked up” or tagged to tell the browser how to display it.

A markup language is a set of characters or symbols that define a document’s logical structure or how a document should be printed or displayed.

5.  Hyper Text Markup Language:

Hyper Text Mark-up Language, the language used to create documents on the World Wide Web.

·   HTML is a collection of styles (indicated by mark-up tags) that define the various elements of a World Wide Web document.

·     HTML is based on an older language called Standard Generalized Markup Language, or SGML, which defines the data in a document independently of how the data will be displayed.

· HTML document can be read and displayed by many different browsers running      on

different types of computers – platform independent!

· HTML defines the structure and layout of the elements on a Web page with a variety of tags.

· Each tag may have a set of attributes that modify the appearance or layout of the visual element contained by the tag.

· HTML is a plain-text file that can be created using a text editor like Notepad.

·  HTML is a programming language that allows you to tell the browser what you want it to display and how you want it to be displayed, in simple terms, it is a Webpage.

· HTML there are certain markers, like commands, that tell the Browser what to do, these are called tags. By using tags you can have tables, fonts, colors, pictures, links, and almost anything you can think up, and experimentation with tags can lead to some pretty cool WebPages.