Chapter 11: Data Communication

CBSE Unit: Unit 2, Computer Networks (10 marks shared with Ch 10, 12) Marks Weightage: ~3-4 marks Priority: HIGH, theory questions on protocols, transmission media, switching techniques

Key Concepts

11.1 Concept of Communication

Data Communication = exchange of data between two or more networked/connected devices, Data can be text, image, audio, video, multimedia, Devices must be capable of sending and receiving data over a communication medium

11.2 Components of Data Communication

Component	Description	Examples
Sender	Device that sends data	Computer, mobile phone, smartwatch, walkie-talkie
Receiver	Device that receives data	Computer, printer, laptop, mobile phone, TV
Message	Data/information to be exchanged	Text, number, image, audio, video, multimedia
Communication Media	Path through which message travels	TV cable, telephone cable, Ethernet cable, satellite link, microwaves
Protocols	Set of rules for successful communication	Ethernet, HTTP, TCP/IP

Sender and receiver are called nodes in a network

11.3 Measuring Capacity of Communication Media

Bandwidth, Range of frequencies available for data transmission through a channel

Higher bandwidth = higher data transfer rate
Measured in Hertz (Hz)
1 KHz = 1000 Hz, 1 MHz = 1000 KHz = 1,000,000 Hz

Data Transfer Rate (Bit Rate), Number of bits transmitted per second, Measured in bits per second (bps)

Units:
1 Kbps = 2^10 bps = 1024 bps
1 Mbps = 2^20 bps = 1024 Kbps
1 Gbps = 2^30 bps = 1024 Mbps
1 Tbps = 2^40 bps = 1024 Gbps
MBps = Megabytes per second; Mbps = Megabits per second (8 times different)

11.4 Types of Data Communication

Mode	Direction	Simultaneous?	Example
Simplex	One way only	N/A	Keyboard to computer, remote to TV, IoT controlling appliances
Half-duplex	Both ways	NOT at same time	Walkie-talkie (push-to-talk)
Full-duplex	Both ways	YES, simultaneously	Mobile phone, landline telephone

Simplex Communication

Unidirectional, sender sends, receiver receives, no reverse, Entire capacity used for one-direction transmission, Like a one-way street

Half-Duplex Communication

Bidirectional but NOT simultaneous
Like a narrow one-way bridge (traffic alternates), Walkie-talkie: push-to-talk enables transmitter, disables receiver

Full-Duplex Communication

Bidirectional and simultaneous
Like a two-way road, Uses either two separate simplex lines OR shared capacity of single channel, Mobile phones, landline telephones

11.5 Switching Techniques

Circuit Switching

Dedicated path established between sender and receiver before communication starts, All packets follow the same path
Example: Traditional telephone call (physical path established end-to-end)

Packet Switching, Message broken into smaller pieces called packets

Packets transmitted independently through the network, Different packets may take different routes
Each packet has: header (destination address + info) + message part (actual data), Packets reassembled at destination, Channel occupied only during transmission (available to others when done)

Feature	Circuit Switching	Packet Switching
Path	Dedicated path for entire communication	No dedicated path; different routes possible
Efficiency	Less efficient (channel reserved)	More efficient (channel shared)
Example	Traditional telephone call	Internet data transfer

11.6 Transmission Media

Classification

Communication Media
|-- Wired (Guided)
|   |-- Twisted Pair Cable
|   |-- Coaxial Cable
|   |-- Optical Fibre Cable
|-- Wireless (Unguided)
    |-- Radio Waves
    |-- Microwaves
    |-- Infrared Waves

Wired Transmission Media

(A) Twisted Pair Cable

Two copper wires twisted together (DNA helical structure), Both wires insulated with plastic covers, Twisting minimizes electrical interference
Cheapest and most commonly used, Used in telephone lines and LANs, Types:
UTP (Unshielded Twisted Pair), no metal shield
STP (Shielded Twisted Pair), has metal shield for extra protection

(B) Coaxial Cable

Copper wire core surrounded by insulator, outer conductor (copper mesh), plastic cover
Better shielded and higher bandwidth than twisted pair, Carries signals of higher frequencies to longer distances, Used in cable TV

(C) Optical Fibre Cable

Carries data as light (not electrical signals), Structure: glass core --> cladding (less dense glass) --> outer jacket (PVC/Teflon), Uses refraction to direct light through the media, Advantages: lightweight, highest bandwidth, longest distance, immune to electromagnetic noise
Disadvantages: expensive, unidirectional (two cables needed for full duplex), Used in backbone networks

Feature	Twisted Pair	Coaxial	Optical Fibre
Signal Type	Electrical	Electrical	Light
Cost	Cheapest	Moderate	Most expensive
Bandwidth	Lowest	Medium	Highest
Interference	Susceptible	Better shielded	Immune
Distance	Short	Medium	Long

Wireless Transmission Media

Electromagnetic spectrum for wireless: 3 KHz to 900 THz

(A) Radio Waves (3 KHz, 1 GHz)

Omni-directional (travel in all directions), Can travel long distances (300 KHz, 30 MHz range), Can penetrate walls (3, 300 KHz range), Susceptible to interference, Used in: AM/FM radio, television, cordless phones

(B) Microwaves (1 GHz, 300 GHz)

Unidirectional (one direction only)
Cannot penetrate solid objects (walls, hills, mountains), Requires line-of-sight propagation (both antennas must face each other), Used in: point-to-point communication, radar, satellite communication, Provides very large information-carrying capacity

(C) Infrared Waves (300 GHz, 400 THz)

Very high frequency
Cannot penetrate solid objects, Used for short-distance point-to-point: mobile-to-mobile, remote-to-TV, Bluetooth devices

Property	Radio Waves	Microwaves	Infrared
Frequency	3 KHz, 1 GHz	1 GHz, 300 GHz	300 GHz, 400 THz
Direction	Omni-directional	Unidirectional	Point-to-point
Penetration	Can penetrate walls	Cannot penetrate solid objects	Cannot penetrate solid objects
Range	Long	Medium (line-of-sight)	Short

11.7 Wireless Technologies

Bluetooth

Short-range wireless technology (~10 metres), Uses 2.4 GHz unlicensed frequency band, Speed: 1-2 Mbps, Creates a piconet (personal area network)
Master-slave configuration: 1 master + up to 7 active slaves, Total up to 255 devices (8 active + rest inactive/waiting)

Wireless LAN (Wi-Fi), Standard number: IEEE 802.11

Uses Access Points (APs), devices that create wireless LAN by connecting to wired router/switch/hub, APs are installed in buildings/floors, Benefits: flexibility to move while connected, extends wired infrastructure, easy Internet access in public places

WiMax, Worldwide Interoperability for Microwave Access, Like Wi-Fi but for larger area with higher data transfer rate

Used in MAN applications

11.8 Mobile Telecommunication Generations

Generation	Year	Technology	Key Features
1G	~1982	Analog	Voice calls only, analog signals
2G	~1991	Digital	Digital voice, improved quality, encryption, SMS/MMS
3G	~2001	Digital voice + data	Internet access via radio towers, faster data transfer
4G	Recent	All-IP	Much faster than 3G, interactive multimedia, voice, video, wireless internet
5G	Under development	Advanced	Expected Gbps speeds, supports IoT, M2M (Machine to Machine)

11.9 Protocols

A protocol is a set of standard rules that sender, receiver, and intermediate devices must follow.

Why protocols are needed:

Flow control: Handle speed mismatch between sender and receiver
Access control: Decide which node accesses shared link at a given time, Identify computers on network, Define data format for transmission, Decide routing (forwarding to correct node), Ensure complete data delivery without loss, Rearrange and process packets at destination

Key Protocols

Protocol	Full Form	Purpose
HTTP	HyperText Transfer Protocol	Access WWW; client-server protocol over TCP; developed by Tim Berners-Lee at CERN (1989)
HTTPS	HTTP Secure	Encrypted version of HTTP; uses SSL certificate
FTP	File Transfer Protocol	Transfer files between machines; client-server model; handles file naming, format, and directory differences
PPP	Point to Point Protocol	Direct connection between two devices; authentication; used by home computers connecting to ISP via modem; requires duplex mode
SMTP	Simple Mail Transfer Protocol	Email delivery; reads message header for destination; removes from queue after successful delivery
TCP/IP	Transmission Control Protocol / Internet Protocol	IP assigns unique address to each node; TCP breaks messages into packets, ensures delivery and correct ordering; packets may take different routes

TCP/IP details:

IP: Ensures each node has a unique IP address (the "adhesive" of the Internet)
TCP: Breaks message into packets, guarantees delivery, orders packets at destination, Packets may take different routes due to redundant connection paths, Reassembled at receiver's end

Important Definitions

Data Communication: Exchange of data between two or more networked devices
Bandwidth: Range of frequencies available for transmission; measured in Hz
Data Transfer Rate: Number of bits transmitted per second; measured in bps
Simplex: One-way communication
Half-duplex: Two-way communication, not simultaneous
Full-duplex: Two-way simultaneous communication
Circuit Switching: Dedicated path established before communication
Packet Switching: Data broken into packets sent independently
Guided/Wired Media: Physical cables (twisted pair, coaxial, optical fibre)
Unguided/Wireless Media: Electromagnetic waves through air
Protocol: Set of standard rules for communication
Piconet: Personal area network formed by Bluetooth devices

Common Board Exam Question Patterns

Name the communication mode (1 mark): Given a scenario, identify simplex/half-duplex/full-duplex
Compare wired media (2-3 marks): Twisted pair vs coaxial vs optical fibre
Expand and explain protocols (2 marks): HTTP, FTP, SMTP, TCP/IP, PPP
Switching techniques (2 marks): Circuit vs Packet switching differences
Bandwidth calculation (2 marks): Given frequencies, calculate bandwidth
Data transfer rate (1-2 marks): Convert between Kbps, Mbps, Gbps
Wireless communication (2 marks): Radio waves vs Microwaves vs Infrared properties
Mobile generations (1-2 marks): Features of 1G through 5G
Components of data communication (2 marks): List and explain the 5 components
Short notes (2-3 marks): HTTP, Bluetooth, DNS, Bandwidth

Key Points Students Miss

Bandwidth is measured in Hz (Hertz); Data transfer rate in bps (bits per second), different units for different concepts
MBps (megabytes) vs Mbps (megabits), 1 MBps = 8 Mbps
Optical fibre is unidirectional, needs two cables for full duplex
Optical fibre carries light; twisted pair and coaxial carry electrical signals
Radio waves are omni-directional; microwaves are unidirectional
Microwaves need line-of-sight (both antennas must face each other)
Circuit switching = dedicated path; Packet switching = independent routes
Bluetooth uses 2.4 GHz band, range 10m, speed 1-2 Mbps
Wi-Fi = IEEE 802.11; WiMax is for larger areas (MAN)
HTTP is for web pages; FTP is for file transfer; SMTP is for email, each protocol has a specific purpose
TCP ensures delivery and ordering; IP ensures addressing, they work together
5G supports IoT and M2M (Machine to Machine) communication