Basics of Computer Networks (कंप्यूटर नेटवर्क और टोपोलॉजी)

A Computer Network is an interconnected collection of autonomous computers, servers, printers, and smart devices linked together through cables or wireless signals to share data, files, hardware resources, and internet connections.

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1. Classification of Networks by Geographical Scale

In computer networking, networks are categorized based on their geographical coverage area:

2. Network Topologies (नेटवर्क टोपोलॉजी)

Topology refers to the geometric arrangement or physical layout in which computers (nodes) and cables are connected in a network.

1. Bus Topology (बस टोपोलॉजी)

• All computers are connected to a single central communication cable called the Backbone Cable.
• Both ends of the cable must have Terminators to prevent signal reflection.
• Advantage: Simple and inexpensive to install.
• Disadvantage: If the main backbone cable breaks anywhere, the entire network collapses!

2. Star Topology (स्टार टोपोलॉजी - सबसे लोकप्रिय)

• Every computer is connected individually to a central connection device called a Hub or Switch.
• Advantage: Highly reliable! If one computer's cable fails, only that single PC disconnects; the rest of the network operates normally.
• Disadvantage: If the central Switch/Hub fails, the entire network shuts down.

3. Ring Topology (रिंग टोपोलॉजी)

• Each computer is connected to exactly two neighboring computers, forming a closed circular loop.
• Data travels in one direction using an electronic token (Token Ring).
• Disadvantage: If any single computer in the ring fails, the entire loop breaks.

4. Mesh Topology (मेश टोपोलॉजी - सबसे सुरक्षित)

• Every node has a direct dedicated point-to-point physical cable to every other node in the network.
• Number of cables required for $N$ nodes $= \frac{N(N-1)}{2}$.
• Advantage: Maximum fault tolerance and privacy.
• Disadvantage: Extremely expensive and complex wiring.

3. Essential Network Hardware Devices

• Network Interface Card (NIC): A hardware card with a unique 48-bit physical hardware address called a MAC Address (e.g. 00:1A:2B:3C:4D:5E).
• Hub: A dumb broadcast device that sends incoming data packets to all connected ports.
• Switch: An intelligent device that inspects the destination MAC address and transmits packets only to the intended recipient device.
• Router (राउटर): Connects two different networks together (e.g. connecting your local home LAN to the global Internet WAN) by inspecting IP addresses.

Multiple Choice Questions

1. Which of the following represents the largest geographical network spanning across countries and continents?

A. LAN B. MAN C. PAN D. WAN Answer: D Explanation: WAN (Wide Area Network) covers vast geographical regions such as countries, continents, or the entire globe. The Internet is the most prominent example of a WAN.

2. In which network topology are all computers connected to a central Hub or Switch?

A. Bus Topology B. Ring Topology C. Star Topology D. Mesh Topology Answer: C Explanation: In Star Topology, each network node connects directly via an independent point-to-point cable to a central connectivity hub or switch.

3. What is the permanent 48-bit physical hardware address burned into a Network Interface Card (NIC) called?

A. IP Address B. MAC Address C. URL D. Port Number Answer: B Explanation: The MAC (Media Access Control) address is a unique, permanent 48-bit (12 hexadecimal digit) hardware identifier assigned by the manufacturer to network adapters.

4. What happens in a Bus Topology if the main central backbone cable is severed?

A. Only the first computer stops working B. The entire network communication ceases completely C. The network automatically converts into a Star topology D. Communication speed doubles Answer: B Explanation: In Bus Topology, all nodes share a single transmission line. A break in the central backbone cable disrupts signal transmission across the entire network.

5. Which intelligent network device directs data packets between different networks (such as your home network and the Internet)?

A. Repeater B. Router C. Hub D. Modulator Answer: B Explanation: A Router is an intelligent networking layer device that determines the optimal path to forward data packets between distinct interconnected networks based on IP addresses.