• Star: every device has its own cable to a central switch. One broken cable affects one device; a failed switch stops everything. n devices need n cables.
• Mesh: devices are linked to several others, so data can take another route if a link fails. A full mesh links every device to every other: n devices need n(n - 1) ÷ 2 links, which gets expensive fast. The internet is a partial mesh of routers.
• Bus: every device has a short drop cable to one shared main cable, the backbone, with a terminator at each end to absorb the signal. It is cheap (little cable, no switch), but all data shares one cable, so collisions grow as traffic grows, and a break in the backbone stops the whole network.

The internet is a worldwide network of networks. The World Wide Web is the collection of pages reached over it.

1. You type a URL. The browser asks a DNS server for the IP address of the domain name.
2. The DNS server looks it up (asking other DNS servers if it must) and sends the IP address back.
3. The browser sends a request to the web server at that IP address.
4. The server sends the page back.

Web hosting stores a website on a server connected to the internet. The cloud is remote servers that store data and run services: reachable anywhere, but you need a connection and someone else holds your data.

• IPv4: 32 bits, written as four denary numbers 0 to 255, such as 192.168.4.17. Used to route packets between networks; can change when a device moves.
• IPv6: 128 bits, written as eight groups of hex digits, because IPv4 ran out of addresses.
• MAC address: 48 bits, six pairs of hex digits such as 3C:22:FB:9A:01:7E, fixed into the NIC when it is made; used on the local network.