Networking

Introduction

In the space of just a few decades, computer networking has gone from being a curiosity involving screeching modems to being the primary reason for having a computer. Many modern laptops and smartphones aren’t much more than an interface to the Internet. Using a computer without an Internet connection feels so limited that it’s hard to believe that the first version of Windows 95 didn’t even ship with Internet Explorer!

A large amount of modern day software development involves at least some web work. For this reason, it’s absolutely critical that you have a firm understanding of computer networking, the Internet and the associated web technologies. In this chapter we’ll develop a conceptual model of networking using stacked layers of protocols. We’ll then use that model to study the Internet, its major protocols and the web.

What is a network?

Let’s begin by getting our terminology straight. Computers can be connected together to form a network. A host is any device connected to a network. Hosts on a network are able to exchange information. The network might involve physical connections using cables (so retro!) or, more likely these days, wireless connections using WiFi or Bluetooth. Either way, there will be a component in each host known as the network interface card (NIC) that is responsible for encoding and decoding messages to and from whatever physical signals the network uses.

If you want to call someone, you need to know their phone number. It uniquely identifies the phone you’re calling out of all of the phones connected to the phone network. It’s the same for computer networks. Each host on the network has a unique identifying address determined by the NIC. One host can talk to another by using its NIC to broadcast across the network a message addressed to the NIC of the receiving host. The receiving host’s NIC will listen to all the messages on the network. Whenever it detects a message addressed to it, the NIC will excitedly read the message into the computer’s memory and notify the OS using the interrupt system we saw in the OS chapter.

If a network only allows machines to communicate with other machines on the same network, then it is referred to as an intranet because all of the communication stays within (intra) the bounds of the network. Lots of businesses run their own private intranets, accessible only to computers within the office, to share access to storage, printers and so on.

Some networks include machines that are