HTTP

                   Before rushing to what is HTTP and what is HTTPS, lets proceed with the basic details and the derivation of HTTPS in the field of  Data Communication in Information Technology.

                     Communication is an essential factor for human existence. Since the past, different types of communications among humans has brought them a so far of a distance as present. Below figure shows different kinds of communications among humans.

In Human Communication, they convey their ideas to each other. And with the ideas taken from others, humans process them inside their heads in order to reach a final decision. 

   

                                Heads in humans are equivalent to the Computers in Information Technology.  Furthermore, Computers can be known as the foundation element in IT. Thus.... 

                
             Have you ever thought of communication in IT ...?

So the communication in IT takes place through the main unit of Computers. Message receive, message processing, message output delivering is done by Computers. Here the word 'message ' refers to a collection of data. Below figure shows the five main components involved in the communication process in 

                     

• Message is a collection of data in a chosen format
• Sender and Receiver are two computers communicating 
• Medium can be a cable medium or a wireless medium
• Protocol is a set of rules and instructions to be used in the communication procedure by its endpoints

HTTP is another Protocol

What exactly is HTTP?

                            As mentioned earlier, HTTP....,  abbreviation for Hyper Text Transfer Protocol is a Protocol..., that is a set of instructions describing a data communication procedure. It allows to transfer various data formats between the sender and receiver such as 

                                                                                 - Plaintext

- Hypertext
- Images
- Video
- Sound

In brief it is the foundation of data communication in the World Wide Web.

The environment in which this data communication occurs and all the data communication components(sender, receiver, message document) resides is known as World Wide Web(Web). In the Web the documents and resources like computers are identified by URLs(something like an address given for each item in the Web)

Features of HTTP...

1)  It is a request-response protocol in the client-server computing        modal

 A web browser, for example, may be the client and an application running on a computer hosting a web site may be the server.

The client submits an HTTP request message to the server.

The server,  returns a response message to the client. 

The response contains the requested message body, status information about the response

2)  It is an Application Layer Protocol

                     For the purpose of vivid explanation and understanding of the  data communication, common frame of reference was introduced. OSI (Open Systems Interconnect Reference Mode) was the first reference model to discuss the data communication. It contains 7 layers and each layer describes the function performed when data is transferred between two applications. From below link can get more of a understanding on the functionalities of each layer.

http://www.diablotin.com/librairie/networking/tcpip/ch01_02.htm

     After the OSI model, TCP/IP model was introduced with an abstraction of layers. It consists of only 4 layers and the data communication is described in terms of 4 layers. Out of these 4 layers, HTTP is an Application Layer Protocol.Below figure shows the layered architecture description for data communication.

The protocols in the Application layer is responsible for process-to-process  communication/ application-to-application communication.  This layer is responsible only for standardizing the communication. To perform host-to-host communication, this Application layer protocols  depend on the Transport Layer protocols like TCP.

3)  It is media independent

As mentioned earlier any type of data can be sent over HTTP protocol such as plain text, hypertext, images, videos etc.

4)  It is a stateless protocol

This means that the HTTP protocol treats each request  as an independent transaction and is not related to any of the previous requests.  This makes the communication to consist of unique request-response pairs. 

This stateless design makes the server design simple, since there is no need of dynamically allocating



HTTP  URLs (Uniform Resource Locater)

• A URL is used to uniquely identify a resource over the web.

Syntax :

    protocol://hostname:port/path-and-file-name\

http://xxx.myplace.com:80/cgi-bin/t.html

protocol (http, ftp, smtp,dns,news..etc)

host name (name.domain name)

port (usually 80 but many on 8080)

directory path to the resource

resource name

 How HTTP works......

•  Client wants to visit        http://www.yahoo.com

• Request is sent to the DNS Server. It converts the domain name and send the Server IP

• The IP address is sent to the web server make the connection

•  Requested web page is sent by the server after establishing the connection

 HTTP Request Message 

 

 HTTP Response Message

 

 HTTP Redirection

when a web page is visited at a certain URL, it changes to a different URL

eg :

a person visits "website.com/page-a" in their browser 

                     But it is redirected to                          

                      "website.com/page-b" instead

• A redirected URL would open up a page with another URL

• The server specifies the redirection by returning 3xx status code (set aside for redirects)

Few Applications of Http Redirect

• if the company is migrating to a new web site, all requests can be redirected from the old to the new website
• when the domain name is misspelled by users, organisations register likely misspelled domains and redirect them to the correct location 
• redirection is used by URL shortening services  

 Cookies

• method of maintaining states between HTTP requests

• small piece of data sent from website and stored in the user’s web browser at the first time user visits that web site

• Every other time the user visits the same web site, the browser sends the cookie back to the server to notify the website about user’s previous activity

eg: Amazon

                       The more you use the site, the more Amazon understands what kind of products you

                    search for and buy.    

                    make recommendations of products you might like

                    help prevent extensive searching in such a big store

Web Caching

• Is a technology that significantly enhance the web browsing experience

• Web cache is the temporary storage place for web documents (HTML pages,images etc) requested from the internet

• After the original request, further requests for the same file are returned from the cache in the LAN

• Advantages

                - users experience a fast download

                - bandwidth usage is extensively reduced and free for another delivery

                - content available during network interruptions