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NETWORK CONCEPT |
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The Internet
The Internet is not the world wide web
- nor is it web browsing. This is a common misconception. Often people will say
such things
as, "OK, I am finished
with email. Now I want to use the Internet." Email is something you can do
over the Internet - as is web
browsing with Netscape or Internet Explorer.
In other words, the Internet is a collection of computers, networked together
throughout the world, and communicating with each
other
through a common language called TCP/IP (Transfer Control Protocol/Internet
Protocol).
The various programs you use recognize TCP/IP, and if everything is set up
correctly, and the computer is correctly connected to
the
Internet, all sorts of things can be done, including:
·
Web Crossing
·
email
·
the World Wide Web (WWW)
·
FTP
·
Internet news
All sorts of other services
IP Addresses
In order to identify all the computers and other devices
(printers and other networked peripherals) on the Internet, each connected
machine
has a unique number, called an "IP address". IP stands for
"Internet Protocol," the common language used by machines
on the Internet to share
information.
An IP address is written as a set of 4 numbers, separated by periods, as in
203.183.184.10
This representation is sometimes referred to as dotted-octet
representation of an IP address.
Here is some simple mathematics you should know! Each number
in this four-number address can range from 0 through 255. So
there are 256 different possible numbers for each part.
Since there are four parts, so there are a possible 256 X 256
X 256 X 256 = 256 to the 4th power = 4,294,967,296 different possible
machine
numbers - over four billion different possible machine numbers.
This sounds like more than enough addresses to go
around, but IP addresses are beginning to run out.
One single network, for example, might typically have all the IP addresses
starting with 203.183.184 (203.183.184.0 through
203.183.184.255). This has been a
customary way of distributing IP numbers - in chunks of 256 addresses. This is
referred to as a
"Class
C" network. If numbers are distributed as Class C networks it means
there are only a possible 256 to the 3rd power different
networks - or just 16 million networks - in the whole world.
When you say it like that it doesn't sound like so many networks, because every
office and many offices within offices have their
separate network of computers.
To make matters worse, many networks don't even use all the
256 IP addresses available to them, which means that although the
IP addresses are reserved by them they are going to waste.
To help solve this problem, networks have started being assigned with just 8 or
16 IP addresses. Some special techniques using local
IP addresses that
aren't visible to the outside world are also helping alleviate the strain.
But basically you should understand that you need a fixed,
predefined IP address assigned to each machine that acts as a server to
the
outside world. You can get an IP address assignment from your network
administrator, who receives them in turn from your
network's Internet provider.
Domains & Sub-domains
Each machine having its own unique IP address is great for machines
communicating with each other, but quite difficult for humans
to remember.
For example, the mail server at Web Crossing Harbor has an IP address
210.226.166.200. You could send email to doug@
210.226.166.200, but it isn't very convenient for a lot of reasons.
For one thing, it is difficult to remember. For another, we might
need
to move the mail server to a different machine (with a different IP address)
someday. Then we would have to tell everybody
our
new IP address in order to receive mail.
To solve this problem a system of giving easy-to-remember
names to IP addresses was created. This system is called the domain
system.
There are several top-level domains, and all other names fall under that in a
hierarchy of sub-domains.
There are two basic kinds of top-level domains - those based on type of
activity and those based on geographical location:
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Some Activity Based Domains |
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.com |
Perhaps the most well-known top-level domain. Originally it
was designated for use by companies and commercial activities. Now it can be
used by anybody for any purpose. |
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.org |
Originally designated for use by nonprofit organizations
and individuals, now it can be used for any purpose. |
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.net |
Originally designated for use by network organizations
(such as Internet providers). Now it can be used for any purpose. |
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.gov |
For governmental organizations in the United States. |
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.mil |
For military organizations in the United States. |
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.edu |
For four-year degree-granting colleges and universities
only. |
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Some Geographic Based Domains |
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.jp |
The Japan domain |
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.us |
The U.S. domain |
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.ca |
The Canada domain |
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.to |
The Tonga domain |
Some geographic domains, such as the .to (Tonga) domain, open up
their domains and make them available to anybody in the
world.
One common misconception is that ".com" is a domain
for companies located in the U.S. It isn't - any company in the world can
use a .com domain.
A "host" refers to a fully specified domain, specified completely
down to the specific machine and complete IP address. For
example, webxharbor.com is a sub-domain of the .com domain. www.webharbor.com is
the name of the web server machine
in
the webxharbor.com domain. It has a corresponding IP address, but you do not
need to know it because the domain name
system keeps track of it for you.
When the Internet first started out there was just one big
list with all the hosts in the world and their corresponding IP addresses.
But the list quickly
got too large and these days the same task is accomplished with the use of a
distributed DNS (domain name
server) system, components of which are located on most networks throughout the
world (including the Web Crossing Harbor office).
Servers
A server is just a host that serves something. Some
examples are:
·
web servers - computers that serve web pages. People connect to web servers
using browsers, such as Netscape Navigator
or Internet Explorer.
·
FTP servers - People connect to them for
file transfer, using a browser or a specialized FTP program, such as Fetch (on
a Mac)
or FTP Explorer (on Windows).
·
mail servers - People connect to them to
send and receive mail, using such programs as Eudora, Netscape Mail, Claris
Mail
and Microsoft Outlook Express.
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Web Crossing - a server that lets users
create and use online communities, including forums and chat and other services