The World  Wide Web HTTP

The Hyper text Transfer Protocols( HTTP) is a protocols  used mainly to  access data on the world  wide  web. HTTP functions as a carbonation of FTP( File  Transfer Protocols) and SMTP ( Simple  Mail Transfer Protocols). HTTP is  implemented in two programs a  client program  and a server program. The  client program  and server program executing on different end systems talk to each other by  exchanging. HTTP message HTTP defines the structure of these  message  and how  the client and server exchange  the messages.

HTTP defines  how web  clients (f or  example browser ) request  web  page from web  servers and  how servers transfer web page to client. In  figure 3.3 when a user requests a web  page (f or  e, g, clicks on a hyperlink) the  browse sends HTTP request messages for the objects  ( an  objects  is simply a file such as an HTML file a JPEG image are GIF image java applet an audio clip and so on in the page to the server.

HTTP uses TCP (Transmission control  protocols) is  its  underlying transport protocol.  Because TCP provides a reliable data transfer services to HTTP. HTTP consists  of two  types  of massage format request  and response.

                                                                   figure HTTP request response behavior

The HTTP client first  initiates a TCP connection with  the server. Once the connection is established the browser and the server process access TCP through their socket interface. On  the client  side the socket interface is the door between  the client process and the TCP connection on  the server side it is the door  between  into its  socket interface and receives HTTP response message from  its socket interface. Similarly  the HTTP server receives request message from its  socket interface and sends response message  into its socket interface. Once  the client sends  a message  into its  socket  interface the  message  is out  of the  clients  hands  and is  in the bands of TCP.

HTTP need not worry  about  lost data  or the details of  how TCP recovers from loss  or reordering of data within  the network. That is the job of TCP and the  protocols in the  lower layers  of the protocols stack. It  is important to note  that the server sends  requested files to client without storing any state information about the client. If  a particular client asks for  the same object twice in a period of a few  seconds the server does not  respond by saying that it just  served the object  t the client instead the server resends the objects as it has completely forgotten what  the server  has sent earlier because on HTTP server mantas no information  about  clients HTTP is said  to be  as tasteless protocols.