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How the Internet actually works

To most people, the Internet is the place to which everyone plugs in their computer and views webpages and sends e-mail. That's a very human-centric viewpoint, but if we're to truly understand the Internet, we need to be more exact:

The Internet is THE large global computer network that people connect to by-default, by virtue of the fact that it's the largest. And, like any computer network, there are conventions that allow it to work.

This is all it is really - a very big computer network. However, this article will go beyond explaining just the Internet, as it will also explain the 'World Wide Web'. Most people don't know the difference between the Internet and Web, but really it's quite simple: the Internet is a computer network, and the Web is a system of publishing (of websites) for it.

Computer networks

And, what's a computer network? A computer network is just two or more of computers connected together such that they may send messages between each other. On larger networks computers are connected together in complex arrangements, where some intermediary computers have more than one connection to other computers, such that every computer can reach any other computer in the network via paths through some of those intermediary computers.

Computers aren't the only things that use networks - the rail network is very similar to computer networks, just that transports people instead of information.
Trains operate on a certain kind of track - such a convention is needed, because otherwise the network could not effectively work. Computers in a network have conventions too, and we usually call these conventions 'protocols'.

There are many kinds of popular computer network today. The most conventional by far is the so-called 'Ethernet' network that physically connects computers together in homes, schools and offices. However, WiFi is becoming increasingly popular for connecting together devices so that cables aren't required at all.

Connecting to the Internet

When you connect to the Internet, you're using networking technology, but things are usually a lot muddier. There's an apt phrase, "Rome wasn't built in a day" because neither was the Internet. The only reason the Internet could spring up so quickly and cheaply for people was because another kind of network already existed throughout the world - the phone network!

The pre-existence of the phone network provided a medium for ordinary computers in ordinary people's homes to be connected onto the great high-tech military and research network that had been developed in years before. It just required some technological mastery in the form of 'modems'. Modems allow phone lines to be turned into a mini-network connection between a home and a special company (an 'ISP') that already is connected up to the Internet. It's like a bridge joining up the road networks on an island and the mainland - the road networks become one, due to a special kind of connection between them.

The Internet

The really amazing about the Internet isn't the technology. We've actually had big Internet-like computer networks before, and 'The Internet' existed long before normal people knew the term. The amazing thing is that such a massive computer network could exist without being built or governed in any kind of seriously organised way. The only organisation that really has a grip on the core computer network of the Internet is a US-government-backed non-profit company called 'ICANN', but nobody could claim they 'controlled' the Internet, as their mandate and activities are extremely limited.

What I have described so far is probably not the Internet as you or most would see it. It's unlikely you see the Internet as a democratic and uniform computer network, and to an extent, it isn't. The reason for this is that I have only explained the foundations of the system so far, and this foundation operates below the level you'd normally be aware of. On the lowest level you would be aware of, the Internet is actually more like a situation between a getter and a giver - there's something you want from the Internet, so you connect up and get it. Even when you send an e-mail, you're getting the service of e-mail delivery.

Being a computer network, the Internet consists of computers - however, not all computers on the Internet are created equal. Some computers are there to provide services, and some are there to consume those services. We call the providing computers 'servers' and the consuming computers 'clients'. At the theoretical level, the computers have equal status on the network, but servers are much better connected than clients and are generally put in place by companies providing some kind of commercial service. You don't pay to view a web site, but somebody pays for the server the website is located on - usually the owner of the web site pays a 'web host' (a commercial company who owns the server).

Making contact

I've established how the Internet is a computer network: now I will explain how two computers that could be on other sides of the world can send messages to each other.

Imagine you were writing a letter and needed to send it to someone. If you just wrote a name on the front, it would never arrive, unless perhaps you lived in a small village. A name is rarely specific enough. Therefore, as we all know, we use addresses to contact someone, often using: the name, the house number, the road name, the town name, the county name, and sometimes, the country name. This allows sending of messages on another kind of network - the postal network. When you send a letter, typically it will be passed between postal sorting offices starting from the sorting office nearest to the origin, then up to increasingly large sorting offices until it's handled by a sorting office covering regions for both the origin and the destination, then down to increasingly small sorting offices until it's at the sorting office nearest the destination - and then it's delivered.

In our postal situation, there are two key factors at work - a form of addressing that 'homes in' on the destination location, and a form of message delivery that 'broadens out' then 'narrows in'. Computers are more organised, but they actually effectively do exactly the same thing.

Each computer on the Internet is given an address ('IP address'), and this 'homes in' on their location. The 'homing in' isn't done strictly geographically, rather in terms of the connection-relationship between the smaller computer networks within the Internet. For the real world, being a neighbour is geographical, but on a computer network, being a neighbour is having a direct network connection.

Like the postal network with its sorting offices, computer networks usually have connections to a few other computer networks. A computer network will send the message to a larger network (a network that is more likely to recognise at least some part of the address). This process of 'broadening out' continues until the message is being handled by a network that is 'over' the destination, and then the 'narrowing in' process will occur.

An example 'IP address' is '69.60.115.116'. They are just series of digit groups where the digit groups towards the right are increasingly local. Each digit group is a number between 0 and 255. This is just an approximation, but you could think of this address meaning:

• A computer 116
• in a small neighbourhood 115
• in a larger neighbourhood 60
• controlled by an ISP 69
• (on the Internet)

The neighbourhoods, the ISP, and the Internet, could all be consider computer networks in their own right. Therefore, for a message to the same 'larger neighbourhood', the message would be passed up towards one of those intermediary computers in the larger neighbourhood and then back down to the correct smaller neighbourhood, and then to the correct computer.

Getting the message across

Now that we are able to deliver messages the hard part is over. All we need to do is to put stuff in our messages in a certain way such that it makes sense at the other end.

Letters we send in the real world always have stuff in common - they are written on paper and in a language understood by both sender and receiver. I've discussed before how conventions are important for networks to operate, and this important concept remains true for our messages.

All parts of the Internet transfer messages written in things called 'Packets', and the layout and contents of those 'packets' are done according to the 'Internet Protocol' (IP). You don't need to know these terms, but you do need to know that these simple messages are error prone and simplistic.
You can think of 'packets' as the Internet equivalence of a sentence - for an ongoing conversation, there would be many of them sent in both directions of communication.

Reliable message transfer on the Internet is done via 'TCP'. IP is fundamental to the Internet, but TCP is not - there are in fact other 'protocols' that may be used that I won't be covering.

Names, not numbers

When most people think of an 'Internet Address' they think of something like 'www.ocportal.com' rather than '69.60.115.116'. People relate to names with greater ease than numbers, so special computers that humans need to access are typically assigned names ('domain names') using a system known as 'DNS' (the 'domain name system').

All Internet communication is still done using IP addresses (recall '69.60.115.116' is an IP address). The 'domain names' are therefore translated to IP addresses behind the scenes, before the main communication starts.

At the core, the process of looking up a domain name is quite simple - it's a process of 'homing in' by moving leftwards through the name, following an interrogation path. This is best shown by example - 'www.ocportal.com' would be looked up as follows:

• Every computer on the Internet knows how to contact the computers (the 'root' 'DNS servers') responsible for things like 'com', 'org', 'net' and 'uk'. There are a few such computers and one is contacted at random. The DNS server computer is asked if they know 'www.ocportal.com' and will respond saying they know which server computer is responsible for 'com'.
• The 'com' server computer is asked it knows 'www.ocportal.com' and will respond saying they know which server computer is responsible for 'ocportal.com'.
• 'The 'ocportal.com' server computer is asked if it knows 'www.ocportal.com' and will respond saying that it knows the corresponding server computer to be '69.60.115.116'.

Note that there is a difference between a server computer being 'responsible' for a domain name and the domain name actually corresponding to that computer. For example, the 'ocportal.com' responsible DNS server might not necessarily be the same server as 'ocportal.com' itself.

Meaningful dialogue

I've fully covered the essence of how messages are delivered over the Internet, but so far these messages are completely raw and meaningless. Before meaningful communication can occur we need to layer on yet another protocol (recall IP and TCP protocols are already layered over our physical network).

There are many protocols that work on the communications already established, including:

• HTTP - for web pages, typically read in web browser software
• POP3 - for reading e-mail
• SMTP - for sending e-mail

I'm not going to go into the details of any of these protocols because it's not really relevant unless you actually need to know it.

The information transferred via a protocol is usually a request for something, or a response for something requested. For example, with HTTP, a client computer requests a certain web page from a server via HTTP and then the web server, basically, responds with the file embedded within HTTP.

Each of these protocols operates on more or more so-called 'ports', and it is these 'ports' that allow the computers to know which protocol to use. For example, a web server (special computer software running on a server computer that serves out web pages) uses a port of number '80', and hence when the server receives messages on that port it passes them to the web server software which naturally knows that they'll be written in HTTP.

The World Wide Web

I've explained how the Internet works, but not yet how the web works. The web is the publishing system that most people don't realise is distinguishable from the Internet itself.
The Internet uses IP addresses (often found via domain names) to identify resources, but the web has to have something more sophisticated as it would be silly if every single page on the Internet had to have it's own 'domain name'. The web uses 'URLs' (uniform resource locators), and I'm sure you know about these as nowadays they are printed all over the place in the real world.

A typical URL looks like this: :///

For example: http://www.ocportal.com/index.php

HTTP is the core protocol for the web. This is why URLs usually start 'http://'.

Typically the 'resource identifier' is simply a file on the server computer. For example, 'mywebsite/index.html' would be a file on the server computer of the same path, stored underneath a special directory.

We now have three kinds of 'Internet Address', in order of increasing sophistication:

• IP addresses
• Domain names
• URLs

If a URL were put into web browser software by a prospective reader then the web browser would send out an appropriate request (usually, with the HTTP protocol being appropriate) to the server computer identified by the URL. The server computer would then respond and typically the web browser would end up with a file. The web browser would then interpret the file for display, much like any software running on a computer would interpret the files it understands.

An 'HTML' file is the kind of file that defines a web page. It's written in plain text, and basically mixes information showing show to display a document along with the document itself.

I've explained how typical web pages are just files on the disk of a server computer. Increasingly, things are slightly less direct. When you visit something like eBay you aren't just reading files. You're actually interacting with computer software, and the web pages you receive are generated anew by that software every time a request is made. These kinds of systems are known as 'web applications' and are becoming increasingly prevalent.

About the Author

Chris Graham is Managing Director of ocProducts (http://ocproducts.com/), a company specialising in advanced website solutions, via the ocPortal website engine (http://ocportal.com/). ocPortal allows the creation of interactive and dynamic websites with great ease; advanced websites that anybody can create, run and manage.

I'm using an Apple airport express router with a DSL modem. When I use bridge mode I lose internet. Advice?

If I don't use bridge mode, I get a double NAT error. But when I use bridge mode to solve the double NAT, I lose internet. Is there anything I can do to fix both problems?
Yeah, I saw that FAQ as well. Unfortunately, it doesn't address this issue. Any other ideas?

This FAQ doc from Apple Support might help
http://support.apple.com/kb/HT1515

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