How Does The Internet Work?

The Internet is the backbone of the Web, the technical infrastructure that makes the Web possible. At its most basic, the Internet is a large network of computers which communicate all together.

The history of the Internet is somewhat obscure. It began in the 1960s as a US-army-funded research project, then evolved into a public infrastructure in the 1980s with the support of many public universities and private companies. The various technologies that support the Internet have evolved over time, but the way it works hasn’t changed that much: Internet is a way to connect computers all together and ensure that, whatever happens, they find a way to stay connected.

It is made up of a massive network of specialized computers called routers. Each router’s job is to know how to move packets along from their source to their destination. A packet will have moved through multiple routers during its journey. When a packet moves from one router to the next, it’s called a hop.

What’s a protocol?

A protocol is a set of rules specifying how computers should communicate with each other over a network. For example, the Transport Control Protocol has a rule that if one computer sends data to another computer, the destination computer should let the source computer know if any data was missing so the source computer can re-send it. Or the Internet Protocol which specifies how computers should route information to other computers by attaching addresses onto the data it sends.

What’s a packet?

Data sent across the Internet is called a message. Before a message is sent, it is first split in many fragments called packets. These packets are sent independently of each other. The typical maximum packet size is between 1000 and 3000 characters. The Internet Protocol specifies how messages should be packetized.

Networking Infrastructure

So now you know how packets travel from one computer to another over the Internet. But what’s in-between? What actually makes up the Internet? Let’s look at another diagram:

Here we see Diagram 1 redrawn with more detail. The physical connection through the phone network to the Internet Service Provider might have been easy to guess, but beyond that might bear some explanation.

The ISP maintains a pool of modems for their dial-in customers. This is managed by some form of computer (usually a dedicated one) which controls data flow from the modem pool to a backbone or dedicated line router. This setup may be refered to as a port server, as it ‘serves’ access to the network. Billing and usage information is usually collected here as well.

After your packets traverse the phone network and your ISP’s local equipment, they are routed onto the ISP’s backbone or a backbone the ISP buys bandwidth from. From here the packets will usually journey through several routers and over several backbones, dedicated lines, and other networks until they find their destination, the computer with address

Where did these Internet routers come from? Who owns them?

These routers originated in the 1960s as ARPANET, a military project whose goal was a computer network that was decentralized so the government could access and distribute information in the case of a catastrophic event. Since then, a number of Internet Service Providers (ISP) corporations have added routers onto these ARPANET routers.

There is no single owner of these Internet routers, but rather multiple owners: The government agencies and universities associated with ARPANET in the early days and ISP corporations like AT&T and Verizon later on.

Asking who owns the Internet is like asking who owns all the telephone lines. No one entity owns them all; many different entities own parts of them.

How does the router know where to send a packet? Does it need to know where all the IP addresses are on the Internet?

Every router does not need to know where every IP address is. It only needs to know which one of its neighbors, called an outbound link, to route each packet to. Note that IP Addresses can be broken down into two parts, a network prefix and a host identifier. For example, can be broken down into

Network Prefix: 129.42
Host Identifier: 13.69

All networked devices that connect to the Internet through a single connection (ie. college campus, a business, or ISP in metro area) will all share the same network prefix.

Routers will send all packets of the form 129.42.*.* to the same location. So instead of keeping track of billions of IP addressesrouters only need to keep track of less than a million network prefix.

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