Internet and Web

Computer networks and the web: PAN, LAN, MAN and WAN, network devices and topologies, the Internet, URLs and the WWW, e-mail, chat and VoIP, websites, web servers, hosting and browsers.

Key ideas

• A network joins devices to share data and resources; by area, PAN (around one person) < LAN (a room or building) < MAN (a city) < WAN (countries; the Internet is one).
• A modem converts digital signals to analog and back; a repeater regenerates a weak signal; a hub sends data to every port, a switch only to the port it is meant for.
• A router finds the best path between networks and links a LAN to the Internet; a gateway joins networks that use different protocols.
• Star: every device joins a central switch or hub, so a broken cable cuts off one computer but a failed centre stops all; bus: one shared backbone; mesh: every pair joined directly; tree: star networks joined in levels.
• The World Wide Web is the set of linked web pages reached over the Internet with a browser; e-mail waits in the inbox, chat is instant and VoIP carries voice calls over the Internet.
• A URL is protocol://domain name/path/file; https is the secure, encrypted form of http, and the top-level domain is the last part of the domain name.
• A website is a set of linked pages under one domain, stored on a web server; web hosting rents that space; a static page is the same for everyone, a dynamic page is made when it is requested.
• A cookie is a small text file a website stores in the browser to remember a visitor; add-ons and plug-ins extend what a browser can do.

Remember

Watch out

• Using n(n − 1) for mesh cables: each cable joins two computers, so halve it.
• Calling the whole URL the domain name: the domain is only the part between // and the next /.
• Mixing up a hub with a switch, or a router with a gateway.

Worked example