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Class 12 Internet and Web: cheat sheet
CBSE Informatics Practices. 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
| Mesh cables | n(n − 1) ÷ 2: 10 computers → 45 cables |
| Star cables | one per computer: n cables to the switch |
| URL parts | https://learn.example.org/notes/index.html: protocol https, domain learn.example.org, path /notes/, file index.html, top-level domain .org |
| Sizes | PAN < LAN < MAN < WAN |
| Hub or switch | to every port; only to the right port |
| Planning a campus | server in the block with the most computers; a repeater on any link longer than a cable carries well (100 m in the sheets) |
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
An office has 26 computers. (a) How many cables does a mesh topology need? (b) How many does a star topology with one switch need? (c) How many more cables does the mesh need?
Working: mesh: 26 × 25 ÷ 2; star: one per computer
Answer: (a) 325; (b) 26; (c) 299
Practise Internet and Web
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