Data Communication Notes – Class 12 CS (083) | Computer Networks Revision
Class 12 Data Communication Notes (083) with CBSE-aligned topics, diagrams, and pointwise explanations for quick revision and board exams.
According to the latest CBSE syllabus, Unit 3: Computer Networks of Class 12 Computer Science is organized into two chapters in the NCERT textbook, which we will study one by one.
- Chapter 10 – Computer Networks
- Chapter 11 – Data Communication
We have already covered Computer Networks, where we learned about the evolution of networking, network devices, network topologies, network types, network protocols, and web services. If you haven’t studied that chapter yet, you can check it out using the link provided below.
Computer Networks Notes – Class 12 CS | NCERT Chapter-10
Now, it’s time to move on to Data Communication—the second and equally important part of Unit 3. Every topic is presented in an easy-to-understand manner, making the notes ideal for concept building, quick revision, and board exam preparation. So, let’s get started!
Concept of Communication
- Data communication refers to the exchange of data between two or more connected devices over a network.
- Data can be in the form of text, images, audio, video, or multimedia files.
- Communication means sending and receiving this data between devices.
- The devices involved must be capable of transmitting and receiving data, such as computers, laptops, and mobile phones.
- These devices are connected through a communication medium (like cables or wireless signals) that carries data from one device to another.
Components of Data Communication
Data communication consists of five main components:
- Sender: A sender is a device that sends data over a network. It can be a computer, mobile phone, smartwatch, walkie-talkie, video recording device, etc.
- Receiver: A receiver is a device that receives data from a network. It can be a computer, printer, laptop, mobile phone, television, etc. Both sender and receiver are called nodes in a network.
- Message: It is the data or information that is exchanged between the sender and receiver. It can be in the form of text, numbers, images, audio, video, or multimedia.
- Communication Media: It is the path or channel through which the message travels from sender to receiver. It can be wired (like telephone or Ethernet cables) or wireless (like satellite or microwave signals).
- Protocols: These are a set of rules that both sender and receiver must follow to ensure proper, reliable, and successful communication. Examples include Ethernet and HTTP.
Measuring Capacity of Communication media
Bandwidth
- Bandwidth is the range of frequencies available for transmitting data through a communication channel.
- It is calculated as the difference between the maximum and minimum frequencies in a signal.
- Bandwidth is measured in Hertz (Hz).
- 1 KHz = 1000 Hz
Data Transfer Rate
- Data transfer rate is the number of bits transmitted from source to destination in one second.
- It is also called bit rate.
- It is measured in bits per second (bps).
- 1 Kbps = 2¹⁰ bps = 1024 bps
- 1 Mbps = 2²⁰ bps = 1024 Kbps
- 1 Gbps = 2³⁰ bps = 1024 Mbps
- 1 Tbps = 2⁴⁰ bps = 1024 Gbps
Identifying nodes In a networked communication
Each device (node) in a network must have a unique identity so that the sender and receiver can be identified. The following are the types of addresses used for this purpose:
- MAC Address
- IP Address
MAC Address
• MAC stands for Media Access Control. It is a unique hardware (physical) address assigned to a network adapter (NIC).
• It is permanently stored in the NIC at the time of manufacturing and generally cannot be changed.
• It helps in uniquely identifying a device on a network.
• A MAC address is a 12-digit hexadecimal number (48 bits).
• The first 6 digits (24 bits) represent the manufacturer’s ID, known as the Organisational Unique Identifier (OUI).
• The last 6 digits (24 bits) represent the unique serial number assigned by the manufacturer.
• Example of a MAC address: 00:1A:2B:3C:4D:5E
IP Address
• An IP address (Internet Protocol address) is a unique address used to identify a device on a network.
• It is assigned to each device that uses the Internet Protocol for communication.
• With an IP address, a device can communicate with other devices anywhere in the world.
• Unlike a MAC address, an IP address can change when a device connects to a different network.
IPv4:
• IPv4 is a 32-bit address written as four decimal numbers separated by dots.
• Each number ranges from 0 to 255.
• Example: 192.168.0.178
IPv6:
• IPv6 is a 128-bit address introduced to overcome the limitation of IPv4 addresses.
• It is written as eight groups of hexadecimal numbers separated by colons.
• Example: 2001:CDBA:0000:0000:0000:0000:3257:9652
Switching Techniques
The two main types of switching techniques are Circuit Switching and Packet Switching.
Circuit Switching
- In circuit switching, a dedicated path is established between the sender and receiver before communication begins.
- All data travels through this fixed path during the entire communication.
- Example: Traditional telephone calls, where a complete path is set up before conversation starts.
Packet Switching
- In packet switching, a message is divided into small units called packets, which are sent independently through the network.
- Different packets of the same message may travel through different routes depending on network availability.
- Each packet contains a header (with destination address and control information) and the actual data.
- At the destination, all packets are reassembled to form the complete message.
Transmission Media
Transmission media are broadly classified into two types:
- Guided Media (Wired): Data travels through a physical path such as cables or wires (e.g., metallic cables, fibre-optic cables).
- Unguided Media (Wireless): Data travels through air in the form of electromagnetic waves using antennas.
Wired Transmission Media – Guided Media
- Wired transmission media use physical cables or wires to carry data signals between devices.
- The three commonly used types are Twisted Pair Cable, Coaxial Cable, and Optical Fibre Cable.
Twisted Pair Cable
- A twisted pair cable consists of two insulated copper wires twisted together like a helix.
- Multiple such pairs are often bundled together with a protective outer covering.
- Each twisted pair acts as a separate communication link.
- Twisting helps reduce electrical interference from nearby wires.
- It is low-cost and widely used in telephone lines and LANs.
- Types: UTP (Unshielded Twisted Pair) and STP (Shielded Twisted Pair).
Coaxial Cable
- A coaxial cable has a central copper core surrounded by an insulating layer, a metallic shield (mesh), and an outer plastic cover.
- Its shielded structure protects signals from external interference.
- It offers higher bandwidth and better performance than twisted pair cables.
- It is used for transmitting high-frequency signals over longer distances.
Optical Fibre Cable
- Optical fibre transmits data as light through thin strands of glass.
- It uses the principle of refraction to guide light signals.
- It consists of a core (glass), cladding (less dense glass), and an outer protective jacket.
- It provides very high bandwidth, faster data transfer, and supports long-distance communication.
- It is not affected by electromagnetic interference and is lightweight.
- it is expensive and generally requires two cables for full-duplex communication.
Wireless Transmission Media
- In wireless communication, data is transmitted through air in the form of electromagnetic waves without using any physical cables.
- Wireless communication uses the electromagnetic spectrum (3 KHz to 900 THz), which is divided into categories like radio waves, microwaves, infrared waves, and visible (light) waves based on their frequency.
- Examples of wireless technologies include Bluetooth, Wi-Fi, and WiMAX, which are widely used for connecting devices without wires.
Classification of Transmission Waves and Their Properties
| Transmission Waves | Properties |
| Radio Waves | Frequency range: 3 KHz – 1 GHz Omni-directional (travel in all directions)300 KHz – 30 MHz waves can travel long distances3 – 300 KHz waves can penetrate wallsProne to interferenceUsed in AM/FM radio, television, cordless phones |
| Microwaves | Frequency range: 1 GHz – 300 GHzUnidirectional (travel in one direction)Cannot penetrate solid objects (walls, hills)Require line-of-sight communicationUsed in radar, satellite communication, point-to-point linksHigh data carrying capacity |
| Infrared Waves | Frequency range: 300 GHz – 400 THzVery high frequency wavesCannot penetrate solid objectsUsed for short-distance communicationExamples: remote controls, Bluetooth devices, mobile-to-device communication |
