Computer Networks Practical #1

Practical exercises #1

Most of the tutorials in the subject will have one or more of these at the end. They are intended for you to do in your own time (ie, out of formal tutorial time), and are generally designed to further illustrate some aspect of the tutorial material.

An Initial Prac Task

If you're a Unix user (and you're on campus) give yourself a shell on one of the Unix systems and type the following command:

telnet www.latrobe.edu.au 80

Once you get the "connected" message, type the following (note uppercase):

    GET /home/index.html

Can you explain what happens? Don't worry -- later on you will!

More on the Initial Prac Task

To succeed in this prac task, you don't have to use Unix -- it's perfectly do-able on a Windows PC or a Mac. You do need to have a version of "telnet" on your computer. There are many versions of telnet which are freeware and widely distributed, as well as a few commercial ones.

Start up telnet. On some systems you can do this from within Netscape (or another browser such as IE) by doing an "Open Location" (under the "File" menu) and entering a URL of the form:

telnet://www.latrobe.edu.au:80
If that doesn't work, try typing "telnet" at a DOS prompt, or if you're on a Mac, do a "Find File" for "telnet" and double click it. Once you've got telnet up and running, select the "Open Connection" menu item and enter: "www.latrobe.edu.au 80" (without the quote marks). This should pop up a "terminal" (command line) window containing nothing at all. At this point it might be useful to look for a "Preferences" option to turn on "Local Echo", so you can see what you're typing. Some versions of telnet are clever enough to do this where appropriate, others have to be told...

This should be a connection to the WWW server on www.latrobe.edu.au -- that is, you should be able to type "GET /home/index.html" in the window and get a pile of HTML sent back to you.
The window will probably disappear immediately (it's usually a "Preferences" option to have them stick around after close), but you'll have seen the protocol in action.
The object of this prac exercise, incidentally, is twofold:

To observe the HTTP protocol - stuff like the "GET" operation, and the returned HTML file.
To notice that Port 80 is the "well known" port for the WWW - see the next lecture.

If It Doesn't Work
It's not really an important thing, so don't worry if you can't get it to work.
If it doesn't, it may not be your fault anyway -- one of the more recent technologies that can block access is a firewall, so if you're connected to an Internet Provider outside La Trobe University, this could be what's happening. We'll see later how the protocol works when firewalls are in use.
This set of practical exercises accompanies Tutorial #1.
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Copyright © 2000 by Phil Scott, La Trobe University.