Data Communication (Section B1)

Data Communication

DATA COMMUNICATION: COMPLETE CUET STUDY NOTES

1. Introduction to Data Communication

Concept of Communication The term “Data Communication” is a combination of two words: Data (which refers to text, images, audio, video, and multimedia files) and Communication (the act of sending or receiving this data). 

Therefore, data communication is the exchange of information between two or more networked or connected devices. These devices, such as personal computers, mobile phones, and laptops, must be capable of sending and receiving data over a specific medium.

Components of Data Communication For successful communication between two computing devices, five essential components are required:

1. Sender: The device (computer, smartphone, smartwatch, etc.) that initiates and sends the data over the network.

2. Receiver: The device (computer, printer, laptop, etc.) that is intended to receive the data from the network. In computer networks, both senders and receivers are known as nodes.

3. Message: The actual information or data to be exchanged, which can be in the form of text, numbers, images, audio, video, or multimedia.

4. Communication Media: The physical or wireless path through which the message travels from the source to the destination.

5. Protocols: A standard set of rules followed by the communicating parties to ensure reliable and successful data exchange.

2. Measuring Capacity of Communication Media

In the field of data communication, the transmission medium is often referred to as a channel. The capacity of a channel is the maximum amount of traffic or signals it can carry, measured using the following two metrics:

A. Bandwidth

• Definition: Bandwidth represents the range of frequencies available for data transmission through a channel.

• Relationship: A higher bandwidth typically results in a higher data transfer rate.

• Measurement: It is calculated as the difference between the maximum and minimum frequency in a signal and is measured in Hertz (Hz).

• Units:

  • 1 Kilohertz (KHz) = 1,000 Hz.

  • 1 Megahertz (MHz) = 1,000 KHz = 1,000,000 Hz.

B. Data Transfer Rate

• Definition: This refers to the number of bits transmitted between the source and destination in one second. It is also known as the bit rate.

• Measurement: Measured in bits per second (bps).

• Units (Note: These use base-2 for digital calculations):

1 Kbps = 210bps = 1,024 bps.

1 Mbps = 220bps = 1,024 Kbps.

1 Gbps = 230bps = 1,024 Mbps.

1 Tbps = 240bps = 1,024 Gbps.

• Crucial Distinction: MBps stands for Megabytes per second, while Mbps stands for Megabits per second.

3. Types of Data Communication

Data transfer between nodes occurs over point-to-point or multipoint channels and is categorised into three modes:

1. Simplex Communication:

   • A unidirectional (one-way) communication where one device is strictly the sender and the other is strictly the receiver.

   • Examples: Data entry via a keyboard, audio sent to a speaker, or using a smartphone to control home appliances like lights and fans via IoT.

2. Half-duplex Communication:

   • A bidirectional (two-way) communication where both devices can send and receive data, but not at the same time. While one sends, the other must receive.

   • Example: A walkie-talkie, where users must press a "push-to-talk" button to speak while the receiver is disabled in their device.

3. Full-duplex Communication:

   • A bidirectional communication where both devices can send and receive data simultaneously.

   • Example: Mobile phones and landline telephones. This is achieved either by using two separate simplex lines or by sharing the capacity of a single channel between signals moving in different directions.

4. Switching Techniques

Switching is used to route data through various nodes in a network to establish a temporary path between sender and receiver.

• Circuit Switching:

  • A dedicated physical path is established between the sender and receiver before communication begins.

  • All packets follow this same established path.

  • Example: The traditional landline telephone system.

• Packet Switching:

  • The message is broken down into smaller pieces called packets.

  • Each packet has a header (containing the destination address) and the message data.

  • Packets are transmitted independently and may take different routes depending on network availability. They are reassembled at the destination.

  • Efficiency: Unlike circuit switching, a channel is only occupied during the actual transmission of a packet, freeing it up for others immediately after.

5. Communication Media (Transmission Media)

Transmission media are classified into Guided (Wired) and Unguided (Wireless).

A. Wired Technologies (Guided Media)

These involve a physical link through which signals propagate.

• Twisted Pair Cable: Consists of two insulated copper wires twisted together to minimise electrical interference.

  • UTP (Unshielded Twisted Pair): Standard cable without extra shielding.

  • STP (Shielded Twisted Pair): Includes a metal shield for better protection against interference.

• Coaxial Cable: Features a central copper wire core surrounded by an insulator, which is then covered by a copper mesh (outer conductor) and a plastic jacket. The shielded design allows for high-speed transmission with minimal interference.

• Ethernet Cable: Used in Local Area Networks (LANs) to connect devices. It typically uses RJ45 connectors to plug into Network Interface Cards (NIC).

• Optical Fibre: Carries data as light signals through thin strands of glass. It uses the principle of refraction to direct light.

  • Pros: Light weight, high bandwidth, immune to electromagnetic noise, and can travel long distances.

  • Cons: Expensive and unidirectional (requires two cables for full-duplex).

B. Wireless Technologies (Unguided Media)

Data travels through the air as electromagnetic waves.

• Bluetooth: A short-range technology (approx. 10 metres) used for connecting devices like phones, mice, and keyboards. It uses a low-cost transceiver chip on the 2.4 GHz frequency band. It forms a small network called a piconet in a master-slave configuration.

• WLAN (Wireless LAN / Wi-Fi): Based on the IEEE 802.11 standard, it uses Access Points (APs) to connect wireless devices to a wired network infrastructure.

• Infrared: High-frequency waves used for very short-distance, line-of-sight communication.

  • Examples: TV remote controls or mobile-to-mobile data transfers.

• Microwaves: Unidirectional, high-frequency waves (1GHz - 300GHz) that require line-of-sight propagation. They are used for point-to-point communication, radars, and satellite links.

6. Mobile Telecommunication Technologies

Mobile networks allow for "on-the-go" connectivity and have evolved through several generations:

• 1G & 2G: Early generations focused on voice and basic digital services.

• 3G: Introduced around 2001, providing digital voice and faster data services (Internet access) via radio towers.

• 4G: Significantly faster than 3G, supporting interactive multimedia, high-quality video, and broadband services.

• 5G: Currently under development; expected to provide data speeds in Gbps. It is designed to be a milestone for IoT and Machine-to-Machine (M2M) communications, where devices talk to each other directly.

7. Network Protocols

What is a Protocol? A protocol is a set of standard rules that all devices (sender, receiver, and intermediate) must follow to communicate.

Need for Protocols:

• Flow Control: Manages speed mismatches between sender and receiver to prevent data loss.

• Access Control: Determines which node can use the communication link at a given time to avoid data collisions.

• Addressing: Defines how computers identify each other.

• Data Integrity: Ensures all data reaches the destination without loss and is correctly reassembled.

Key Examples of Protocols:

• HTTP (HyperText Transfer Protocol): The primary protocol for accessing the World Wide Web. It is a request-response (client-server) protocol. HTTPS is the secure version that encrypts data.

• FTP (File Transfer Protocol): Used specifically for transferring files between machines. It resolves issues like different file-naming conventions or directory structures between systems.

• IP (Internet Protocol): A unique logic address used to identify each node on a network. TCP/IP is the combined suite of rules used for the backbone of the Internet.

• PPP (Point-to-Point Protocol): Establishes a direct and dedicated connection between two devices, often used between two routers or a home computer and an ISP. It requires duplex mode and ensures data integrity.

• Electronic Mail Protocols:

  • SMTP (Simple Mail Transfer Protocol): Used to transmit emails from the sender to the destination mailbox. It handles the message header (recipients' addresses) but is not concerned with the message content.