A computer network is a setup where two or more computers communicate with each other. The connection between the computers is some kind of electrical connection, whether it be copper wire, fiber optic or radio waves. You might not have though about it before, but networks are everywhere. When you watch TV, you are getting data over a network. When you are talking on the telephone, you are using a network. When you are on the internet, you are using a network.
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These networks are obviously very large and this book is not intended to go in depth into any of these types of networks. The type of network you are likely to be using is smaller and is usually terms a Local Area Network (LAN). A LAN is a network of computers which are located close to one another – usually in the same building or house. In contrast, the internet is considered a wide area network (WAN). A WAN is an interconnected network of smaller LANs. So, take everybody’s LAN and link them up and you have a WAN. That’s all the internet is.
A LAN is a single set of computers in a network. A WAN is many LANs connected together.
The Absolute Essentials
Any LAN has to have computers on it. Each computer must be equipped with a network interface card (or NIC). Sometimes, the NIC is a separate expansion card installed into the computer. Many modern PCs have the NIC integrated right in with the motherboard. The NIC acts as a gateway for the computer to “talk” with the network.
Plugged into each NIC is a network cable. The cables are what connect each of the computers together. The connections are not usually direct computer-to-computer.
Some LANs do not use wires but instead use wireless Ethernet. A wireless network uses radio waves to allow the computers to “talk” to each other. Wireless networks provide more freedom of movement because the computer does not need to sit where the network cabling is. It uses to be that Wifi networks were expensive, slow and unreliable. But, modern technologies as well as agreement on standards means wireless networks today are pretty reliable.
The most simplistic LAN would be a direct computer to computer connection. In this case, the network cable would simply directly connect two computers, with each end of the network cable being plugged into an NIC. However, this type of network is not all that useful because it only allows two computers and does not have any internet capability. In order to add more computers to the network, you will need to install a Switch on your network. A switch acts as a splitter for the Ethernet signal. Routers can also be used to share your single internet connection. The difference between a router and a switch is that a switch controls traffic within a network. A router acts as a bridge between one network and another network and controls incoming traffic to the network. Most routers today have built-in switches, so your router can connect your network internally as well as control traffic to and from your network to the outside (the internet in most cases). More on this will be discussed later in the book.
The last major component of the network is the software itself. Later in this book I will discuss the underlying technologies, however at this point just know that each computer on a network does not natively know how to communicate over a network. After all, the computer is just a lump of circuitry at it’s bare essential. So, software is required to make the computers “talk” to each other. This software does the equivalent of teaching a child to talk. Fortunately, in the case of your computer, the operating system usually takes care of all of this for you. All versions of Windows from Windows 98 onward have built-in networking capability. Mac OS/X and Linux also have such capability built-in.
Placing any computer on a network opens it up to potential attack. Most home networks are connected to the internet via a router and a cable/DSL modem. The internet is a very large network and you don’t know everybody on it. You need to make sure you guard your network against attack from the outside. This is where a firewall comes in. A firewall acts as a wall of protection between your own network and outside networks. Out-going connections are usually allowed through as if nothing is there (unless you specify otherwise) however incoming connections are subject to a set of rules on what to allow and what to block.
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