How the Internet Works.

Course notes to the second in a series of three sessions.

When you connect your computer to the Internet you are connecting to a gigantic Network.

A network is a collection of computers connected together one to the other.

There are varieties of Networks. Theres a bus Net work Every thing gets on the bus and portions are identified as they get around Ethernet. Token Ring network And then the Packet Switched network. The Internet is simply the biggest network in the world with millions of computers connected to it.

The Internet is a packet switching network because instead of each computer being permanently and directly linked to each other they are linked only to the Network.

Nothing happens until your computer sends a packet addressed to another computer or receives one addressed to it.

The biggest value in a packet switched Network is what iot does not do.

When any address is idle its still connected but its costing nothing.

A packet switched network is different to say the normal idea of a network such as a point to point network where things on the network are connected directly to each other all the time.

Telephones connect to a point to point network. When you call a friend in Madrid you establish a connection across the network which will be open while your call is in progress.

Your communication is point to point.

Only you and your friend can use that connection.

Your connection stops everyone else using that particular point to point connection. Since voice does not use all the bandwidth, the capacity of the connection it is wasteful of resources. Its expensive.

To understand a packet switched network think of a railway station on a network of tracks. Your message is split into small packages - like tiny railroad carriages - and pushed out onto the network of rails.

Imagine trillions of tiny railroad carriages rushing to and fro along this network. Each little carriage carries a packet of data, perhaps a chunk of an email message, or a request for a web page.

On the front of each packet is a "header", a label saying where the packet, the rail roadcar is going to. Every time it reaches a computer hooked to the Internet a "Router", literally a device the routes packets to where they are supposed to go to, reads the label, the header and routes the packet further towards its destination.

Its extremely efficient. Any "dead" time, or band width can be used up by pushing more packets along the system. In the milliseconds between your package trundling along the rails millions of other packages can get "in between" and use up the full capacity of the system.

Take for instance sending an email. First the text is divided into many different packets or chunks.

Then each packet gets a label, a header, an address. And then its put into the network among the trillions of other packets winging their way through the network. Parts of the e-mail may go via Alaska, some by Santiago, Chile and others by Singapore.

The routers direct the packets along the large "trunk roads" the fibre optic cables known as the backbone of the internet to their destinations.

The packets take whatever route is open and in a series of hops the message crosses the world.

The world wide Web operates in a similar fashion. When you ask for a page to be downloaded from the Internet a message divided into the small packages is sent to the addresses where the page resides. The messages arrive at the computer or web site which has the page in its system.

Of the page is assembled and once again divided into small packages which make their way from a router to router through the various network connections between computers connected to the Internet or over the world.

If you are interested in seeing how a message has arrived to your computer there are a few software packages such as Neo trace which will show you where the message originated from and the number of hops it has taken across the world to reach your computer.

The interesting thing about this network of computers willing to accept internet traffic and pass it on to where it wishes to go is that nobody owns it.

There is no central control.

There are a number of corporations, societies and working groups who get together and agree on its architecture, the protocols and standards they will use. But nobody controls content, or what application can be connected.

Thats what is amazing.

What Happens at your ISP.

Its all down to routers. Things get routed. A message from you is routed. To where ever it goes. They have mail servers, file servers they may hot the files that make an internet site HTML code for browsers. Hosting a Site Internet sites are hosted on servers. There are several kinds of these but basically they serve files. An Browsers are fairly simple to use.
Each site on the Internet world Wide Web has a specific address, a Domain Name System allocated to it by the Internet Domain Name Allocation.

An Internet Protocol address (IP address) is constructed of a four level string of numbers and dots,
Your Internet Providers address is something like 234.342.77.345

If you wanted to tell your browser to get you the site for your local library you would probably have to type in a number like that.
Easier to type in
The last two letters of an internet address refer to the country. nz, is of course new Zealand. de is Germany. Other parts of the address give you a clue as to whether it is a Government Department or a commercial company. There is one exception to the rule that the last two letters. If it doesn't have a country ending its either from the United States or from anywhere. Simple really. To go to a site enter the name
That will take you to google one of the finest search engines about.

Searching on the Web
There are sites on the Internet that provide you with searching facilities.
You go to the site and type in the item you want to Search for.

My favorite is Google.


is much like C++ but with a further accent on the object orientated style of program. It was invented at Sun Labs.

Object orientated programs are an attempt to get over the fact that often programmers invent the wheel again and again in the course of designing a suite of programs. In Java the actions of the program is to execute a series of objects or modules.

For instance there might be an object or class of program lines that address a letter. Get the address from the data base and send the data to a printer that prints out the address in the prescribed lines.

Once that class or object has been written there is no need to write it again. Any time a programmer needs to print envelopes all that is needed is to place that object into the program and the results will follow.

Javascript is different. The language is similar to Java but it performs a different function. Java script is a language which operates from the web page that you download from the Internet.

Nested among the the Data is a small script or set of instructions telling the browser to perform a small program. This might be for instance to display the date or the current time or to run a banner with certain information across the top of the site.

Java scripts are useful in that they do not depend on the server I. E. the ISP or the source of the web page to carry out the action.

The action that is commanded by the script is performed on your computer.

If you want to see a Java script use your browser to look at the source of the code.

To do this in Netscape Press View and then page source.

In Internet Explorer the command to view the page source is view and then source.


it is a mistake to believe that the material you see on the Internet is not owned by anyone.
It is.
It is just that in some cases the owner will act to protect their ownership of the copyright and in other cases some owners will not.

A large company, University, publisher or government Department may take action at law to protect their ownership. Material on a personal homepage is still owned by someone. The person who owns it may not be able to afford to take legal action to protect their ownership.

Generally it is okay to quote a small excerpt from a piece of work so long as you acknowledge the ownership of the original creator.

there is no special "Internet copyright law". The copyright law for the Internet is the same as for any where else. It is not okay to take large slabs of and other persons hard work and creativity without their permission.

If you e-mail the creator of a piece of work it is most likely they will give you permission to cite parts of it.

It has been established in some jurisdictions that placing a link to another site or material on another site is not a breach of copyright.

If you wish to chase up more material on this its easily done. simply place the words copyright on the Internet into a search engine and you'll come up with a lot of interesting material.

Topic 3

Topic 3 - Security Issues - Firewalls, Viruses, Trojan Horses Keyloggers

If you think that the Internet is a dangerous place full of hackers, lunatics, sleaziness and people trying to get your credit card number and rifle your bank account your are correct.
It is like that - in parts.

Think of it as a large city, most of it is pleasant and exciting, a small part is not.

Stay out of the bad parts.

Some of the problems and suggested solutions.

Problem - Trojan Horses and hackers.

When your computer is connected to the Internet there is a possibility that a hacker will try to access your computer directly by testing each port at your ISP. If the hacker finds a port with no barrier it is possible that they could directly interfere with your computer.

It is also possible that either a hacker or a file accompanying an e-mail could leave a Trojan horse on your computer. A Trojan horse is a program on your computer which either maliciously damages and your files and operating system or ships data from your computer to another location.


The first line of protection that you have against hackers and Trojan horses is a personal firewall.
This is a program which:

There are a number of firewalls are available on the Internet. The Norton security package contains both an antivirus component and a personal firewall. The Zone Alarm firewall is available in two versions a "lite" free version and a professional paid for version. There are others. Type "personal firewall" into the Google search engine and I am sure you will find one that will suit you.

Problem - Viruses

Viruses can come in to your computer in a number of ways. Generally they come attached to e-mail.
Your e-mail posing as a message from your ISP or some other such innocuous message will have attached a file. Most files for personal computers have dot and a 3 letter extension.

For instance the extension .doc is for a Microsoft word document. The extension .jpg is for a graphic. Viruses usually come in executable program type files.

Thus thus any file attached to an e-mail with the extensions .exe, .srn .com .pif should be regarded with the greatest suspicion.

In fact it is good practice not to open any attached file unless you know and trust the sender.


You must not connect a personal computer to the Internet without having full antivirus software installed. There are many packages available, Norton, McAfee, Penicillin, Solo, and VET are a few that come to mind.

Problem - Keyloggers

Believe it or not it is possible for a hacker to place on your personal computer a programme which captures every keystroke you make and sends this information back to their computer.

They may not be interested in your latest magnus opus. But they are very interested in the numbers you type in for your credit card. They are also interested in data on your bank accounts and passwords.


There is anti key logger software packages available. The best way to locate a suitable package is to type the phrase "anti key logger software" into a search engine like Google and make a selection of what is on offer.

A few general security hints

Do not leave your computer unattended and connected to the Internet without engaging the firewall lock.
Do not give details of your address or phone number on forms or information request unless you are confident this information will not be abused.

Remember to update your virus definitions for your antivirus software - often.

Finally a word about cookies.

A cookie is a small piece of information left on your computer by an Internet site on the World Wide Web.

In some cases it benefits you as well as the owner of the Internet site. For instance if you commonly visit a newspaper site, you may receive from the site a cookie. The next time you visit the site it will remember that you've visited the before, perhaps your name if you gave it to the site on your previous visit.

This can be helpful.

On other occasions the cookie is purely for the benefit of the site owner.

You can block cookies on your browser. Some sites are getting so arrogant that they will not let you visit unless you accept a cookie.

The Netscape 7 browser has a cookie manager under a menu item Tools.
You can examine all the cookies that are in your system. You can delete them all if you wish. You can block future cookies.

The Internet Explorer browser allows you to delete cookies - menu item - tools - Internet settings privacy - . under both general and privacy options. It is more complicated to manage than Netscape but worth coming to grips with

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