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Data Communication – Class 12 Computer Science notes, important questions and MCQs

NCERT Class 12 Computer Science, chapter 11. Notes, key terms, important questions with answers and MCQs.

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Chapter overview

Data communication is the exchange of data between two or more devices through a transmission medium. Its components are sender, receiver, message, transmission medium and protocol. Communication can be simplex, half-duplex or full-duplex, and uses circuit switching or packet switching. Transmission media may be wired (guided) or wireless (unguided), and protocols such as HTTP, FTP, SMTP, POP3 and TCP/IP govern communication. Mobile telecommunication has evolved from 1G to 5G.

Components, modes and switching

  • Components: sender, receiver, message, communication (transmission) medium and protocol (set of rules).
  • Bandwidth is the range of frequencies a channel can carry, measured in hertz; data transfer rate is the number of bits transmitted per second (bps, Kbps, Mbps, Gbps).
  • Modes: simplex (one direction only, such as a radio broadcast), half-duplex (both directions but one at a time, such as walkie-talkie) and full-duplex (both directions at once, such as a telephone call). Circuit switching sets up a dedicated path before communication (telephone); packet switching breaks data into packets that travel independently (internet).

Media and protocols

  • Wired media: twisted pair cable (telephone and LAN), coaxial cable (cable TV) and optical fibre (light signals, very high bandwidth, immune to electromagnetic interference).
  • Wireless media: radio waves (3 kHz–3 GHz, omnidirectional, used in FM radio and Wi-Fi), microwaves (3–300 GHz, line of sight, used in satellite and mobile communication) and infrared (300 GHz–400 THz, short range, used in remote controls); Bluetooth and Wi-Fi are wireless technologies.
  • Protocols: HTTP (web pages), FTP (file transfer), SMTP (sending email), POP3 (receiving email), PPP (point-to-point link), TCP/IP (reliable delivery and addressing on the internet). Mobile generations: 1G analog voice, 2G digital voice and SMS, 3G mobile internet, 4G high-speed broadband, 5G very high speed and low latency.

Key terms

Protocol
a set of rules governing data communication
Bandwidth
the range of frequencies a channel can carry
Full-duplex
communication in both directions at the same time
Packet switching
dividing data into packets that travel independently
Optical fibre
a cable that transmits data as light signals

Important questions with answers

Distinguish between circuit switching and packet switching.2 marks

In circuit switching, a dedicated path is established between sender and receiver for the entire communication, as in traditional telephone calls. In packet switching, data is broken into packets that travel independently through the network and are reassembled at the destination, as on the internet; it uses bandwidth efficiently.

Compare twisted pair cable, coaxial cable and optical fibre.3 marks

Twisted pair cable is cheap and easy to install but has low bandwidth and is affected by interference; it is used in telephone lines and LANs. Coaxial cable has better shielding and higher bandwidth, used in cable TV. Optical fibre transmits light, has very high bandwidth, low loss and immunity to electromagnetic interference, but is costly and difficult to install.

Explain the commonly used communication protocols.5 marks

A protocol is a set of rules that determines how data is transmitted, formatted and received between devices. HTTP (HyperText Transfer Protocol) is used to transfer web pages between web servers and browsers; its secure version, HTTPS, encrypts the data, which is important for logins and payments. FTP (File Transfer Protocol) is used to upload and download files between a client and a server. SMTP (Simple Mail Transfer Protocol) is used to send email from a client to a server and between mail servers, while POP3 (Post Office Protocol version 3) is used to download email from a mail server to the user's device. PPP (Point-to-Point Protocol) establishes a direct connection between two devices, such as a computer and an internet service provider over a telephone line. TCP/IP (Transmission Control Protocol/Internet Protocol) is the fundamental protocol suite of the internet: IP handles addressing and routing of packets to the correct destination, while TCP breaks data into packets, ensures they arrive correctly and in order, and requests retransmission of lost packets. Together, these protocols allow different devices and networks to communicate reliably, regardless of their hardware or operating systems.

Quick revision

  • Components of data communication.
  • Bandwidth and data transfer rate.
  • Simplex, half-duplex, full-duplex; switching.
  • Wired and wireless media; protocols; 1G to 5G.

Exam tips

  • Remember: SMTP sends, POP3 receives email.
  • Simplex = one way; half-duplex = both ways one at a time; full-duplex = both ways together.

Practice MCQs

  1. A set of rules that governs data communication is a

    1. medium
    2. protocol
    3. bandwidth
    4. packet
    Show answer

    Answer: (b) protocol. Example: HTTP.

  2. Television broadcast is an example of

    1. simplex
    2. full-duplex
    3. half-duplex
    4. packet switching
    Show answer

    Answer: (a) simplex. Data flows one way.

  3. The protocol used to send email is

    1. SMTP
    2. POP3
    3. FTP
    4. HTTP
    Show answer

    Answer: (a) SMTP. Simple Mail Transfer Protocol.

  4. A walkie-talkie is an example of

    1. simplex
    2. half-duplex
    3. full-duplex
    4. circuit-free mode
    Show answer

    Answer: (b) half-duplex. Both can talk, but not at the same time.

  5. The transmission medium that uses light signals is

    1. twisted pair
    2. coaxial cable
    3. optical fibre
    4. radio waves
    Show answer

    Answer: (c) optical fibre. It offers very high bandwidth.

  6. The internet mainly uses

    1. packet switching
    2. circuit switching
    3. message broadcasting only
    4. analog switching
    Show answer

    Answer: (a) packet switching. Packets may take different routes.

  7. Which wireless medium requires line-of-sight and is used for satellite communication

    1. radio waves
    2. microwaves
    3. infrared over long distances
    4. Bluetooth only
    Show answer

    Answer: (b) microwaves. Microwaves travel in straight lines.

  8. Data transfer rate is measured in

    1. hertz
    2. bytes per page
    3. metres
    4. bits per second
    Show answer

    Answer: (d) bits per second. Bandwidth is measured in hertz.

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.