# what happens when input the URL into the browser

Since web page consists of objects,
Objects can be HTML files, JPEG image, java applet, audio file,...
Web page consists of base HTML-file, which includes several referenced objects,
each object is addressable by a URL
e.g.  www. someschool.edu/somedep/pic.gif
host name: www. someschool.edu/
path name: somedep/pic.gif

HTTP: hypertext transfer protocol
-1- web's application layer protocol
-2- client/server model
    a) client: browser that requests, receives, displays web objects
    b) web server sends objects in response to the request
CheckGdoc

Notes::: from <www.superuser.com/questions/157408>

First URL stands for Uniform Resource Locator. It will be very difficult to remember an IP address. Instead of remembering the IP addresses URL came like www.intrepidkarthi.com. Url normally contains three parts. For example http://intrepidkarthi.com/index.php. Here "http" refers to the protocol it uses. Then the server name and then the requested file name.
Here I have enlisted the flow of working mechanism behind your browser The flow of work

• Your browser communicates with a name server to translate the server name "www.intrepidkarthi.com" into an IP Address, which it uses to connect to the server machine. * So your browser will see if it already has the appropriate IP address cached away from previous visits to the site. If not, it will make a DNS query to your DNS server (might be your router or your ISP's DNS server). DNS stands for Domain Name Server - For example if you want to get karthik's phone number then you will look into your telephone directory. Likewise your computer doesn't know intrepidkarthi.com's IP address . So it looks into DNS.
• The browser then formed a connection to the server at that IP address on port 80. HTTP protocol uses port number 80
• The browser sends a GET request to the server, asking for the file "http://www.google.com/karthikeyan.htm". The web server then returns the requested page and your browser renders it to the screen.
• The firewall will control connections to & from your computer. For the most part it will just be controlling who can connect to your computer and on what ports. For web browsing your firewall generally won't be doing a whole lot.
• Your router essentially guides your request through the network, helping the packets get from computer to computer and potentially doing some NAT (Network Address Translate) to translate IP addresses along the way (so your Internet LAN request can be transitioned onto the wider Internet and back).

A DNS lookup must first be performed, in order to obtain an IP address. HTTP then uses TCP/IP to open a connection, by default on port 80. After establishing the connection, it'll send a HTTP GET request for some content. The server will respond in some way, hopefully w/ an existing page and not some error. That will then be displayed by the browser. (Note, I'm not detailing what occurs on both ends. On the server end, it's basically backwards. An IP packet comes in, the TCP packet is pulled out. The TCP packet's contents is the HTTP request. That is then handled by the a web server.)
Pure routers will only be interested in the IP protocol. Your typical home router, which employs NAT to allow multiple devices to use one external IP, will also be interested in TCP traffic as most NAT routers modify the ports as part of connection management.
http://en.wikipedia.org/wiki/TCP/IP_model

A nice short tutorial :: How Does the Internet Work?
http://www.theshulers.com/whitepapers/internet_whitepaper/index.html 




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http://superuser.com/questions/157408/what-happens-when-you-enter-a-url-in-your-browser