Class 12 Computer Networks

How networks grew, PAN, LAN, MAN and WAN, network devices, bus, star, tree and mesh topologies, MAC and IP addresses, DNS, URLs and the web.

Key ideas

Networking began with ARPANET in 1969; with NSFNET it grew into the Internet, a network of networks.

By the area covered: PAN about 10 m around a person, LAN a room to a campus (about 1 km), MAN a city, WAN countries and continents.

A modem turns digital signals into analog and back; a repeater boosts a weak signal; a hub sends to every computer, a switch only to the one addressed.

A router forwards data between networks along the best path, and a gateway joins networks that use different protocols.

Topologies: bus (one backbone cable), star (a central hub or switch), tree (stars joined in a hierarchy), mesh (every node linked to every other).

A MAC address is 48 bits fixed on the network card; an IPv4 address is 32 bits, four numbers from 0 to 255, given by the network.

A URL is protocol://domain/path; DNS finds the IP address of a domain name, so the browser can reach the web server.

Remember

Links for n computers

mesh: n(n − 1)/2 (10 computers → 45); star with a switch: n; ring: n; bus: one backbone

Address sizes

MAC 48 bits (12 hex digits); IPv4 32 bits = 4 bytes; IPv6 128 bits

Valid IPv4

192.168.10.5 is valid; 192.168.300.5 is not, since 300 is above 255

URL parts

https://learn.example.com/notes/ch1.html: protocol https, domain learn.example.com, path /notes/ch1.html

Top-level domains

.com commercial; .org organisation; .edu education; .gov government; .net network; .in India

Campus layout

server in the block with the most computers; a repeater on any cable over 100 m; a switch in each block

Worked example

A school has four blocks: Junior (49 computers), Science (12 computers), Sports (25 computers), Library (38 computers). Junior is 71 m from Library, 107 m from Sports and 92 m from Science. (a) Which block should house the server, and why? (b) Suggest a topology and draw the layout in words. (c) Where would a repeater be needed if signals weaken beyond 100 m? (d) Which device in each block connects its computers? (e) What type of network is this?

Working: the server goes where most computers are; repeaters on long cables

Answer: (a) Junior, as it has the most computers (49), so most traffic stays inside it; (b) a star (or tree) topology with Junior at the centre, a cable from it to each other block; (c) on every cable longer than 100 m: Junior–Sports (107 m); (d) a switch; (e) a LAN.

Computer Networks

Key ideas

Remember

Watch out

Worked example