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Computer Networks – Class 12 Computer Science notes, important questions and MCQs

NCERT Class 12 Computer Science, chapter 10. Notes, key terms, important questions with answers and MCQs.

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Chapter overview

A computer network is a group of interconnected computers and devices that share data and resources. Networks are classified by size as PAN, LAN, MAN and WAN. Network devices such as modems, hubs, switches, routers, gateways and repeaters connect and manage networks. Topologies describe the arrangement of devices. The internet is the global network of networks, and every device has an IP address and websites have domain names resolved by DNS.

Types and devices

  • PAN (Personal Area Network) covers a few metres, such as Bluetooth devices; LAN (Local Area Network) covers a building or campus; MAN (Metropolitan Area Network) covers a city, such as a cable TV network; WAN (Wide Area Network) covers countries, the internet being the largest WAN.
  • Devices: a modem converts digital signals to analog and back (modulation-demodulation); an Ethernet card (NIC) connects a computer to a network and has a unique MAC address; a repeater regenerates weak signals; a hub broadcasts data to all ports; a switch sends data only to the intended device; a router forwards data between networks; a gateway connects networks using different protocols.
  • The internet connects millions of networks; the World Wide Web (WWW), invented by Tim Berners-Lee in 1989, is a system of interlinked web pages accessed through browsers using HTTP.

Topologies and identification

  • Topologies: bus (single backbone cable, failure of the backbone affects all), star (all devices connected to a central hub or switch, easy to manage), ring, mesh (each node connected to many others, highly reliable) and tree (hierarchical combination of star and bus).
  • A MAC address is a 48-bit physical address burnt into the NIC; an IP address identifies a device on a network, IPv4 being 32-bit (for example 192.168.0.1) and IPv6 128-bit.
  • The Domain Name System (DNS) translates domain names such as ncert.nic.in into IP addresses; a URL is the complete address of a web resource.

Key terms

Network
interconnected computers sharing data and resources
LAN
a network covering a small area such as a building
Router
a device that forwards data packets between networks
Topology
the arrangement of devices in a network
DNS
the system that converts domain names into IP addresses

Important questions with answers

Distinguish between a hub and a switch.2 marks

A hub is a simple device that broadcasts incoming data to all connected devices, causing unnecessary traffic. A switch is an intelligent device that sends data only to the device for which it is intended, using MAC addresses, making the network faster and more secure.

What is the difference between a MAC address and an IP address?3 marks

A MAC address is a 48-bit physical address permanently assigned to a network interface card by the manufacturer and identifies the device on a local network. An IP address is a logical address assigned to a device on a network, which can change, and is used to route data across networks; IPv4 is 32-bit and IPv6 is 128-bit.

Explain any four network topologies with their advantages and disadvantages.5 marks

Network topology is the physical or logical arrangement of nodes in a network. In a bus topology, all devices are connected to a single cable called the backbone, with terminators at both ends. It is simple, cheap and uses less cable, but if the backbone fails the entire network stops, and performance drops as more devices are added. In a star topology, each device is connected to a central hub or switch. It is easy to install, manage and troubleshoot, and failure of one cable affects only one device, but if the central device fails the whole network fails, and it needs more cable than bus. In a mesh topology, each node is connected to several or all other nodes, providing multiple paths for data. It is highly reliable and robust, since data can be rerouted if a link fails, but it is expensive and complex because of the large amount of cabling, so it is used in critical networks. In a tree topology, groups of star networks are connected to a bus backbone in a hierarchical structure. It is scalable and suitable for large organisations, allowing easy expansion, but failure of the backbone or a higher-level node affects the networks below it. A ring topology connects each node to two neighbours in a closed loop, in which a single break can disrupt the network. The choice depends on cost, reliability and size.

Quick revision

  • Need and evolution of networks.
  • PAN, LAN, MAN, WAN.
  • Network devices.
  • Topologies; MAC, IP, DNS, URL.

Exam tips

  • PAN < LAN < MAN < WAN by area.
  • Hub broadcasts; switch sends to the specific device.

Practice MCQs

  1. A network covering a building or campus is a

    1. WAN
    2. LAN
    3. MAN
    4. PAN
    Show answer

    Answer: (b) LAN. Local Area Network.

  2. The device that converts digital signals into analog and vice versa is a

    1. modem
    2. router
    3. hub
    4. switch
    Show answer

    Answer: (a) modem. Modulator-demodulator.

  3. The system that converts domain names into IP addresses is

    1. DNS
    2. HTTP
    3. FTP
    4. URL
    Show answer

    Answer: (a) DNS. Domain Name System.

  4. In which topology are all devices connected to a central device

    1. bus
    2. mesh
    3. ring
    4. star
    Show answer

    Answer: (d) star. The central device is a hub or switch.

  5. A device that sends data only to the intended recipient port is a

    1. switch
    2. hub
    3. repeater
    4. modem
    Show answer

    Answer: (a) switch. Hubs broadcast to all ports.

  6. An IPv4 address is

    1. 16 bits
    2. 32 bits
    3. 48 bits
    4. 128 bits
    Show answer

    Answer: (b) 32 bits. Written as four decimal numbers.

  7. A MAC address is

    1. a logical address that changes with each network
    2. a 48-bit physical address assigned to the network card
    3. a website name
    4. a 128-bit IP address
    Show answer

    Answer: (b) a 48-bit physical address assigned to the network card. It is fixed by the manufacturer.

  8. Which topology offers the highest reliability because of multiple paths between nodes

    1. bus
    2. star
    3. mesh
    4. tree
    Show answer

    Answer: (c) mesh. But it needs more cabling.

All chapters of Class 12 Computer Science

Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.