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Computer networks is a short unit with a lot of vocabulary, and it ends in one of the most predictable questions in the paper: a campus with several blocks, a table of distances and computer counts, and five parts asking where the server goes and what to install. This post covers the syllabus, gives a working definition for each device and protocol, and then solves a design question step by step.
What does the networks unit cover?
The CBSE Computer Science curriculum for Class XII (2026-27) gives Computer Networks 10 of the 70 theory marks. It lists the evolution of networking (ARPANET, NSFNET, the Internet), data communication terms such as bandwidth, data transfer rate, IP address and circuit and packet switching, wired and wireless media, network devices, network types and topologies, protocols, and web services such as WWW, HTML, XML, URLs and web hosting. NCERT splits this across two chapters, Computer Networks and Data Communication.
What are PAN, LAN, MAN and WAN?
PAN: devices around one person, within about 10 metres, as NCERT puts it. A phone and earbuds.
LAN: one building or campus, such as a school lab.
MAN: a city or town. NCERT's example is a cable TV or cable broadband network.
WAN: across countries. The Internet is the largest.
How do the topologies compare?
Bus: every device joins one shared cable. It is cheap and easy to maintain, but NCERT rates bus and ring topologies as less secure and less reliable.
Star: every device connects to a central hub or switch. One failed computer does not affect the rest, but if the central device fails, the whole network does.
Tree (hybrid): star or bus networks joined in a hierarchy, used to connect several LANs.
Mesh: every device linked to every other. NCERT notes it needs n(n − 1)/2 cables, so 6 computers need 6 × 5 / 2 = 15 cables. Very reliable, expensive to wire.
What does each network device do?
Modem: converts digital data to analog signals and back.
Ethernet card (NIC): connects a computer to a wired network. Each has a MAC address.
RJ45: the eight-pin plug at the end of an Ethernet cable.
Repeater: regenerates a weakened signal. NCERT says signals on a cable travel "usually about 100 m" before they need it.
Hub: sends incoming data out on every port, so data can collide.
Switch: reads the destination address and sends data only to that device.
Router: connects different networks, such as a LAN to the Internet, and can repackage data for the next network.
Gateway: the entry and exit point between an organisation's network and the outside world.
Wi-Fi card: connects a device to a wireless network.
What is each protocol for?
HTTP and HTTPS: fetching web pages. The HTTP standard, RFC 9110, sets TCP port 80 as the default for http and 443 for https. HTTPS adds encryption.
FTP: transferring files between computers.
SMTP: sending email between mail servers. RFC 5321 defines it.
POP3: downloading email from a mail server to your device. RFC 1939 has the server listen on TCP port 110.
PPP: a direct link between two devices, such as two routers, or a home computer connecting to an Internet service provider through a modem.
TCP/IP: TCP splits data into packets and delivers them reliably; IP addresses and routes them.
TELNET: logging in to a remote computer as text.
VoIP: voice calls over the Internet.
How do you answer the network design question?
The 2026-27 CBSE sample question paper gives four blocks with distances and computer counts. The marking scheme shows the reasoning examiners expect. Here is the same method on our own example.
Example. A school has four blocks: Admin (25 computers), Science (80), Library (15) and Sports (10). Distances from Science: Admin 60 m, Library 40 m, Sports 130 m.
Server: put it in Science, the block with the most computers. That is the reason the marking scheme gives, and it keeps most traffic inside one building.
Topology: a star centred on Science, which lets the whole network be managed from one place.
Repeater: between Science and Sports, because 130 m is more than the roughly 100 m a cable signal travels.
Switch: one in every block, to connect that block's computers.
Link to a distant branch: for a fast wired link to a far-off campus, the expected answer is optical fibre. For a video meeting across blocks, the protocol is VoIP.
What mistakes cost marks?
Server by distance alone. Examiners want the block with the most computers, and the reason written out.
Hub when the question wants a switch.
Repeater on every link, instead of only where the cable run is over about 100 m.
Bandwidth and data rate mixed up. NCERT measures bandwidth in hertz and data transfer rate in bits per second.
SMTP for receiving mail. SMTP sends; POP3 retrieves.
A practice routine for networks
Spreading practice over days helped across many studies in a review by Dunlosky and colleagues, which rated distributed practice and practice testing highest.
Day 1: Write one line for every device and protocol above from memory. Check against NCERT.
Day 2: Draw bus, star, tree and mesh for six computers, and write one advantage and one limitation for each.
Day 4: Solve the sample paper's design question, then mark it with the marking scheme.
Day 7: Invent your own campus with four blocks and answer all five parts.
When a concept such as packet switching needs a proper explanation, the Fermi Concept Library covers every concept in computing, each with its own lesson. Networks also connect to online safety, which our guide to cyber safety for CBSE covers.
Tonight, sketch your school's computer lab and label every device you can find.
