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Computer Science: Class 12 — Chapter 11: Data Communication

11.1 Concept of Communication

The term Data Communication comprises two words: Data and Communication.

11.2 Components of Data Communication

Data communication relies on five essential components to establish a connection and exchange information successfully.

Core Computer Science Concept Technical Definition / Operational State Structural Parameters & Specifications Computational Function & System Purpose
Sender A computer or device capable of sending data over a network. Can be a personal computer, mobile phone, smartwatch, walkie-talkie, or video recorder. Initiates the communication process by converting information into transmittable signals.
Receiver A computer or device capable of receiving data from the network. Can be a computer, printer, laptop, mobile phone, or television. Known as a node in the network. Accepts incoming signals and converts them back into readable data for the user.
Message The actual data or information that needs to be exchanged. Formats include \text, numbers, images, audio, video, and multimedia files. Represents the payload or content being transmitted between source and destination.
Communication Media The physical or virtual path through which the message travels. Classified as wired (guided) or wireless (unguided). Examples: coaxial cable, fiber-optic, air. Provides the physical or electromagnetic channel to propagate signals from sender to receiver.
Protocols A set of standard rules followed by communicating parties. Examples include Ethernet, HTTP, FTP, TCP/IP. Ensures successful, reliable, and standardized data exchange across diverse systems.
11.3 Measuring Capacity of Communication Media

The transmission medium is also known as a channel . Its capacity is measured using two primary metrics:

11.3.1 Bandwidth

The range of frequencies available for transmission of data through a channel. Higher bandwidth allows for a higher data transfer rate.

  • Definition: The difference between the maximum and minimum frequency contained in composite signals.
  • Unit: Measured in Hertz (Hz).
  • Conversion Units:
    • 1 KHz = 1000 Hz
    • 1 MHz = 1000 KHz = 1,000,000 Hz
11.3.2 Data Transfer Rate

The number of bits transmitted between source and destination in one second. Also known as bit rate .

  • Unit: Measured in bits per second (bps).
  • Higher 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
  • Note: MBps stands for Megabyte per second, whereas Mbps stands for Megabit per second.

Example 11.1: A user wants to upload a \text document at the rate of 10 pages per 20 seconds. What will be the required data rate of the channel? (Assume that 1 page contains 1600 characters and each character is of 8 bits).

Socio-Technical Analysis & Core Systemic Impact:

  • Total characters to transmit: 10 pages * 1600 characters/page = 16,000 characters
  • Total bits to transmit: 16,000 characters * 8 bits/character = 128,000 bits
  • Time duration: 20 seconds
  • Required data rate calculation: Required data rate = (10 * 1600 * 8) / 20 = 6400 bps = 6.25 Kbps
11.4 Types of Data Communication

Data communication between different devices is broadly categorized into three transmission modes:

11.4.1 Simplex Communication

A one-way or unidirectional communication where one device acts solely as the sender and the other as the receiver.

  • Characteristics: Devices utilize the entire capacity of the link to transmit data in a single direction.
  • Examples: Data entered through a keyboard, audio sent to a speaker, or controlling smart home appliances (fans, lights, fridge) via IoT.
11.4.2 Half-duplex Communication

A two-way or bidirectional communication where both devices can send and receive data, but not at the same time.

  • Characteristics: While one device is transmitting, the other must receive, and vice-versa. It is analogous to sharing a one-way narrow bridge.
  • Examples: Walkie-talkies, where pressing the "push-to-talk" button enables the transmitter and disables the receiver on that device.
11.4.3 Full-duplex Communication

A two-way or bidirectional communication where both devices can send and receive data simultaneously.

  • Characteristics: The capacity of the transmission link is shared between signals traveling in both directions. This can be achieved using two physically separate simplex lines or by sharing the capacity of a single channel.
  • Examples: Mobile phones and landline telephone networks.
11.5 Switching Techniques

In large networks, establishing dedicated physical connections (like mesh or star topologies) between every pair of devices is highly expensive. Switching provides an alternative by routing data through various intermediate nodes to form temporary paths.

11.5.1 Circuit Switching

Technical Profile: Circuit Switching

  • Architecture Layer / Tier: Physical and Data Link Layer routing.
  • Operational Mechanics & Syntax: Establishes a dedicated, continuous physical path (connected sequence of links) between sender and receiver before communication begins. All data packets follow this exact same path.
  • System Trade-offs & Failures: High resource reservation overhead; the channel remains occupied even during idle periods, leading to inefficient bandwidth utilization.

Historical Example: Early telephone systems, where switching equipment established a physical copper path from the caller's home to the receiver's telephone.

11.5.2 Packet Switching

Technical Profile: Packet Switching

  • Architecture Layer / Tier: Network Layer routing.
  • Operational Mechanics & Syntax: Messages are broken down into smaller pieces called packets . Each packet contains a header (with destination address and routing info) and the payload. Packets travel independently and can take different routes based on network availability, being reassembled at the destination.
  • System Trade-offs & Failures: Highly efficient bandwidth utilization as channels are occupied only during packet transmission. However, packets may arrive out of order or experience variable latency (jitter).
11.6 Transmission Media

Transmission media are the physical or virtual links that carry signals or data between a transmitter (source) and a receiver (destination). They are broadly classified into guided (wired) and unguided (wireless) media.

11.6.1 Wired (Guided) Transmission Media

Physical links made of wires or cables through which electromagnetic or optical signals propagate between nodes.

Technical Profile: Twisted Pair Cable

  • Architecture Layer / Tier: Physical Layer (Wired).
  • Operational Mechanics & Syntax: Consists of two insulated copper wires twisted together in a helical structure (similar to DNA). Twisting minimizes electrical interference and crosstalk from adjacent pairs.
  • System Trade-offs & Failures: Inexpensive and easy to install, but has limited bandwidth and is susceptible to external noise over long distances. Available as Unshielded Twisted-Pair ( UTP ) and Shielded Twisted-Pair ( STP ).

Technical Profile: Coaxial Cable

  • Architecture Layer / Tier: Physical Layer (Wired).
  • Operational Mechanics & Syntax: Features a central solid copper core surrounded by an insulating layer, which is wrapped in an outer conductor (braided copper mesh) and covered by a protective plastic jacket.
  • System Trade-offs & Failures: Better shielding and higher bandwidth than twisted pair, allowing high-frequency signal transmission over longer distances. However, it is bulkier and less flexible.

Technical Profile: Optical Fibre Cable

  • Architecture Layer / Tier: Physical Layer (Wired / High-Speed Backbone).
  • Operational Mechanics & Syntax: Transmits data as light pulses through a thin strand of glass (core) using the principle of total internal reflection. The core is surrounded by a less dense glass layer called cladding , protected by an outer PVC or Teflon jacket.
  • System Trade-offs & Failures: Extremely high bandwidth, lightweight, and completely immune to electromagnetic interference (EMI). However, it is expensive, fragile, and unidirectional (requiring two separate fibers for full-duplex communication).
11.6.2 Wireless (Unguided) Transmission Media

Data travels through the air in the form of electromagnetic waves using antennas. The electromagnetic spectrum ranging from 3 KHz to 900 THz is utilized for wireless communication.

Transmission Wave Type Frequency Range Key Properties & Operational Characteristics Common Applications
Radio Waves 3 KHz to 1 GHz Omni-directional (propagates in all directions); can penetrate solid walls; susceptible to interference. AM/FM radio, television broadcasting, cordless phones.
Microwaves 1 GHz to 300 GHz Unidirectional (line-of-sight propagation required); cannot penetrate solid obstacles like walls or mountains; high information-carrying capacity. Radar, satellite communication, point-to-point terrestrial links.
Infrared Waves 300 GHz to 400 THz Very high frequency; strictly short-distance; cannot penetrate solid walls (provides high security against eavesdropping). TV remote controls, wireless keyboards/mice, mobile-to-mobile short-range transfers.
11.6.3 Wireless Technologies
  • Bluetooth: A short-range wireless technology operating in the unlicensed 2.4 GHz frequency band. It builds a Personal Area Network ( PAN ) called a piconet using a master-slave configuration (1 master can communicate with up to 7 active slaves simultaneously, supporting up to 255 total connected devices). Range is typically up to 10 meters with speeds of 1-2 Mbps.
  • Wireless LAN (Wi-Fi): Standardized under IEEE 802.11 . Uses Access Points ( APs ) connected to a wired network to allow mobile devices to communicate wirelessly within a local area.
  • WiMax: Worldwide Interoperability for Microwave Access. Unlike Wi-Fi (which forms small WLANs), WiMax uses a larger spectrum to deliver high-speed connections over a much larger area, making it suitable for Metropolitan Area Network ( MAN ) applications.
11.7 Mobile Telecommunication Technologies

The architecture of mobile networks has evolved through distinct generations, each introducing major technological advancements:

  1. First Generation (1G): Introduced around 1982. Used analog signals to transmit voice calls only.
  2. Second Generation (2G): Introduced around 1991. Shifted from analog to digital signals, improving voice quality, enabling encryption for security, and introducing SMS (Short Message Service) and MMS (Multimedia Message Service).
  3. Third Generation (3G): Developed in the late 90s and commercially introduced around 2001. Offered digital voice and high-speed data services, enabling mobile Internet access, video calling, and greater network capacity.
  4. Fourth Generation (4G): Revolutionized mobile broadband by supporting interactive multimedia, high-definition video streaming, wireless internet, and IP-based telephony (VoLTE).
  5. Fifth Generation (5G): Designed to support extremely high data transfer rates (in the Gbps range), ultra-low latency, and massive connectivity for the Internet of Things (IoT) and Machine-to-Machine ( M2M ) communications.
11.8 Protocol

A Protocol is a set of standard rules that communicating parties (sender, receiver, and intermediate devices) must follow to ensure structured and error-free data exchange.

11.8.1 Need for Protocols

Protocols are essential for managing key aspects of network communication:

  • Flow Control: Manages speed mismatches between sender and receiver. For example, if Computer A sends data at 1024 Mbps but Computer B can only receive at 512 Mbps, flow control prevents packet loss by signaling the sender to slow down.
  • Access Control: Determines which node can access a shared communication link at any given instant to prevent packet collisions and data corruption.
  • Addressing: Ensures data is delivered to the correct destination node on the network.
11.8.2 Specific Network Protocols

Technical Profile: HTTP (HyperText Transfer Protocol)

  • Architecture Layer / Tier: Application Layer.
  • Operational Mechanics & Syntax: A request-response (client-server) protocol running over TCP. Used by web browsers (clients) to request hypertext documents from web servers.
  • System Trade-offs & Failures: Stateless by default, requiring cookies or session tokens to maintain state across multiple requests.

Technical Profile: FTP (File Transfer Protocol)

  • Architecture Layer / Tier: Application Layer.
  • Operational Mechanics & Syntax: Used for transferring files between machines. Establishes a connection, handles user authentication (ID/password), and resolves differences in file naming conventions, directory structures, and data formats.
  • System Trade-offs & Failures: Transmits credentials and data in cleartext, making it insecure unless upgraded to SFTP or FTPS.

Technical Profile: PPP (Point-to-Point Protocol)

  • Architecture Layer / Tier: Data Link Layer.
  • Operational Mechanics & Syntax: Establishes a direct, dedicated connection between two communicating devices (e.g., two routers or a home computer connecting to an ISP via modem). Handles authentication, link establishment, and data integrity.
  • System Trade-offs & Failures: Requires duplex mode support on both devices; designed strictly for point-to-point links, not multi-point networks.

Technical Profile: SMTP (Simple Mail Transfer Protocol)

  • Architecture Layer / Tier: Application Layer.
  • Operational Mechanics & Syntax: Used for email transmission. Reads the message header (containing recipient addresses) and places the email in an outgoing queue. The SMTP sender program transmits it to the destination mail server, where the SMTP receiver places it in the user's mailbox.
  • System Trade-offs & Failures: Strictly a push protocol (cannot pull emails from a server; requires POP3 or IMAP for retrieval).

Technical Profile: TCP/IP (Transmission Control Protocol / Internet Protocol)

  • Architecture Layer / Tier: Transport Layer (TCP) and Network Layer (IP).
  • Operational Mechanics & Syntax:
    • IP: Assigns a unique IP address to each node on the network to identify it and routes individual packets across routers.
    • TCP: Breaks messages into smaller packets, guarantees reliable delivery to the destination IP, and reassembles packets in their correct sequence.
  • System Trade-offs & Failures: TCP introduces latency due to connection establishment (three-way handshake) and error-checking overhead, making it slower than connectionless protocols like UDP.