The Internet
The Internet
The Internet consists of thousands of interconnected networks incorporating hundreds of millions of computers around the world.
Underlying ideas:
Built on standard protocols:
| DNS | VoIP | ... | Telnet | FTP | HTTP | HTCPCP | ... | ||
| UDP | TCP | ... | |||||||
| IP | ... | ||||||||
Every computer connected to the Internet has a numeric IP address (e.g., 132.206.12.100).
A computer connected to the Internet may also have a
domain name
like medcor.mcgill.ca or www.medcor.mcgill.ca.
The top-level domain of ca
means Canada.
The right-most part of an Internet address is the top-level domain.
The top-level domains are controlled by the Internet Assigned Numbers Authority or, more recently, by the new Internet Corporation for Assigned Names and Numbers.
Top-level domains are either
generic names or country codes (not counting the
special domain .arpa used for Internet technical
infrastructure).
The original generic names were created in the 1980's.
Three are unrestricted but intended for specific uses:
| com | Commercial entities |
| net | Network providers, etc. |
| org | Not-for-profit organizations |
The other four are for restricted purposes:
| edu | Educational institutions (U.S.A. only) |
| gov | Government (U.S.A. only) |
| int | International treaty organizations |
| mil | Military (U.S.A. only) |
Seven new top-level domains were introduced in 2001/2002.
Four are unsponsored (operated under rules established
directly through ICANN):
| biz | Businesses |
| info | Unrestricted |
| name | Individuals |
| pro | Professionals (engineers, physicians, etc.) |
The other names are sponsored (under rules established in part
by a narrower community):
| aero | Air-transport industry |
| coop | Coöperatives |
| museum | Museums |
The following are a few of the hundreds
of
country codes
used as top-level domain names in Internet addresses:
| ad | Andorra |
| aq | Antarctica |
| be | Belgium |
| ca | Canada |
| nu | Niue (commercialised) |
| ru | Russian Federation
(su for Soviet Union no longer used)
|
| tm | Turkmenistan (commercialised) |
| to | Tonga (commercialised) |
| tv | Tuvalu (commercialised; may need to be retired?) |
| uk | United Kingdom |
| us | United States of America |
| ws | Samoa (Western) (commercialised) |
| zw | Zimbabwe |
What is the difference between ‘the Internet’ and an ‘internet’?
Hypertext is text that contains links to other texts.
Hypermedia extends this to include graphics, animations, video, sound, ...
The World Wide Web is an enormous networked collection of hypermedia information, built on top of the Internet using the HTTP protocol.
It was invented in 1990 at CERN, the European Laboratory for Particle Physics in Geneva, Switzerland, and has exploded in popularity, size, and even usefulness.
The World Wide Web is explored using a browser, that is, a client programme which knows how to locate, download and display files from Web servers.
The first widely used Web browser was Mosaic, created in 1992/1993 by Marc Andreessen and Eric Bina, students at NCSA.
Current graphical Web browsers include Netscape, Mozilla, Firefox, Opera, Galeon, Internet Explorer and others.
There are also text-only Web browsers, e.g., Lynx.
What is the difference between ‘the Web’ and a ‘web’?
The Telnet protocol is a communication standard which allows remote logins, that is, it allows a user on one computer to login on a second computer via the Internet.
You need to specify the Internet address of the remote computer,
e.g., funsan.biomed.mcgill.ca.
You usually can't login to the remote computer unless you have an account there. Use the username and password that you've been given for that computer.
Note that there may be rules about using your account.
The use of all McGill computing facilities is governed by a Code of Conduct. The main points are:
Once you have logged in, you can use whatever commands are appropriate for the operating system on the remote computer, e.g., Unix commands:
cd
cd subdir_name
cd ..
mkdir dir_name
ls
rm filename
passwd
logout
The SSH protocol, an alternative to Telnet, provides encryption. This is especially important for passwords.
Not all Telnet servers support SSH, and vice versa.
Funsan requires SSH for remote logins.
Available SSH clients include
FTP stands for
The local (client)
computer is the one you're directly connected to.
The remote (server) computer is the one that you want to
get files from or put files to.
You need to specify the Internet address of the remote computer,
e.g., audilab.bmed.mcgill.ca.
Some sites maintain archives of files for public use, permitting access using the username anonymous. Usually you are asked to enter your real e-mail address as the password. An example of such an anonymous-FTP site is the software archive at wuarchive.wustl.edu.
If a site is not using anonymous FTP, you must provide the username and password which has been assigned to you for that computer.
FTP programmes have different methods of handling
plain-text (or ASCII) files
and binary files.
The plain-text mode attempts
to correct for the different ways that different operating
systems handle line breaks in text files.
The binary mode ensures that everything is transferred without change.
HTML files are plain-text files.
Word-processing documents and images are binary files.
Different operating systems have different restrictions on filenames. When using FTP, filenames must be valid for the operating systems on both the source and destination computers.
If you're trying to find a file on an FTP server and don't seem to have the file name quite right: try specifying just the directory, and then browse through the list of files in that directory. You can even start higher up in the directory tree and follow the subdirectories that you see.
There are various FTP clients that have graphical interfaces.
Many systems provide a simple FTP client which is used from a command line.
For example, to run the built-in Windows FTP client, do
, type ftp into the
box, then click on
. An MS-DOS dialogue box should open with
the FTP client running in it.
The ftp> prompt indicates that the FTP client is
waiting for a command. Typing help will display a list of
commands. Commonly used commands are:
open
open host.name.mcgill.ca
mkdir
mkdir public_html
cd
cd public_html
ls
lcd
lcd c:\temp or lcd e:\
binary
ascii
put
put test.html
mput
mput *.html
get
get test.html
quit
Some Web browsers can also be used as FTP clients by entering
ftp://username@server.name.domain
in the browser's address bar.
In Microsoft Windows XP, both Windows Explorer and My Computer windows can also be used as FTP clients in this way.
If you are using an account for the first time, you should change your password from the one pre-assigned to one which is known to you alone.
Your new password should be at least six characters long. It should contain a mixture of upper and lower case letters, and preferably also digits. It should not consist of any of the following:
One method used to break into accounts is to systematically try all of the words in a dictionary or list of names as possible passwords for known usernames. (Some servers, but not all, will block multiple unsuccessful login attempts. Yahoo! mail server started doing so in 1999; Microsoft said there was no problem, but they'd do something about it (TCP 1999 April).)
It's a good idea to change your password periodically.
Remember to keep your password private.
You are responsible for anything done using your account.
Bad. Sometimes harmless, sometimes bothersome, sometimes very serious. Sometimes attributed to testosterone.
Viruses, worms, trojan horses, spyware, back doors, buffer overflows, ...
See, e.g., 1997 November article in Scientific American.
Many packages available. Examples:
Check whether your institution supports particular antivirus software (e.g., McGill's policy).
Last modified: Thu, 2007 Aug 16 17:50:54