Let's
say that you are sitting at your computer, surfing the Web, and you
get a call from a friend who says, "I just read a great article!
Type in this URL and check it out! It's at http://www.byronbayonline.com.au".
So you type that URL in to your browser and press return. And magically,
no matter where in the world that URL lives, the page pops up on your
screen!
At
the most basic level possible, the following diagram shows the steps
that brought that page to your screen:
Your
browser formed a connection to a Web server, requested a page and
received it. If you want to get into a bit more detail, here are the
basic steps that occurred behind the scenes:
The
browser broke the URL into 3 parts:
• The protocol ("http")
• The server name ("www.byronbay0nline.net")
• The file name ("internet.html")
• The browser communicated with a name server to translate the
server name "www.byronbayonline.net" into an IP
Address, which it uses to connect to the server machine.
• The browser then formed a connection to the server at that
IP address on port 80.
• Following the HTTP protocol, the browser sent a GET request
to the server, asking for the file "http://www.byronbayonline.net/internet.html".
• The server then sent the HTML text for the Web page to the
browser.
• The browser read the HTML tags and formatted the page onto
your screen.
The
complex process
The
secret of the Net is a network protocol called TCP/IP--that is, a
kind of coding system that lets computers electronically describe
data, like the contents of this story, to each other over the network.
The
term actually refers to two separate parts: the transmission control
protocol (TCP) and the Internet protocol (IP). Every computer that
hooks to the Internet understands these two protocols and uses them
to send and receive data from the next computer along the network.
TCP/IP
creates what is called a packet-switched network, a kind of network
intended to minimize the chance of losing any data that is sent over
the wires.
First,
TCP breaks down every piece of data--such as an email message or instructions
from a Java applet--into small chunks called packets, each of which
is wrapped in an electronic envelope with Web addresses for both the
sender and the recipient. The IP protocol then figures out how the
data is supposed to get from point A to point B by passing through
a series of routers--sort of like regular mail passes through several
post offices on its way to a remote location.
Each
router examines the destination addresses of the packets it receives
and then passes the packets on to another router as they make their
way to their final destination. If your email was broken into ten
packets, then each of those may have traveled a completely separate
route. But you'll never know it, because as the packets arrive, TCP
takes over again, identifying each packet and checking to see if it's
intact. Once it has received all the packets, TCP reassembles them
into the original. (See Figure.)
TCP/IP
is the most important of a long list of Internet protocols. It is
sometimes used as a global term to describe additional protocols,
including simple mail transfer protocol (SMTP), file transfer protocol
(FTP), and Telnet protocol.
