What a network is

A network is two or more devices connected so they can exchange data. That one idea explains why you can print from your laptop, open a shared document, stream a film and message a friend in another country. Networks exist to share resources (files, printers, software, an internet connection), to communicate, and to let work be done on a different machine from the one you are sitting at.

Networks are sorted by how far they reach, because distance decides almost everything else about them. Four characteristics are worth comparing every time: bandwidth (how much data per second), latency (how long one piece takes to arrive), range, and who owns and controls the network.

A PAN connects the devices around one person: phone, earbuds, watch, tablet. It reaches about 10 metres, is almost always wireless (Bluetooth, Wi-Fi Direct) and is built for low power, because most of the devices on it run on tiny batteries. Its purpose is simple: let your own gadgets talk to each other without cables.

A LAN connects devices in one place: a home, a school, an office, a hospital. There is no strict limit, but think of up to about a kilometre. Because the distances are short, a LAN has high bandwidth and low latency (typically 100 Mb/s up to 10 Gb/s), and it is owned and controlled by one organisation. Most LANs mix wired Ethernet with wireless; the wireless part is a WLAN. The main purpose of a LAN is sharing: files, printers, applications and the route out to the internet.

A WAN connects networks, usually LANs, across a large area: between cities, countries or continents. It is how a company links its offices, or a government links its services to citizens everywhere. WANs use long-distance links such as leased lines (a dedicated, fixed-bandwidth link rented from a telecoms company), fibre, satellite, or the public internet with a VPN on top. Compared with a LAN they have lower data rates and higher latency, and they usually depend on other companies' infrastructure. The internet itself is the largest WAN.

A VPN is not a different size of network but a different way of using one. It builds an encrypted tunnel across the public internet so that a remote device behaves as if it were plugged into the private network. A VPN can work over any distance. It is used for remote workers reaching company files, for joining office networks into a cheap WAN, and by people who want to hide their traffic or IP address on public Wi-Fi. A VPN protects the data in the tunnel; it does not make the device itself safe, and it adds a little delay.