Computer Networks

1. Introduction to Computer Networks

A computer network is a system consisting of two or more computers connected together to share resources, exchange data, and communicate. The devices in a network are called nodes and the connections between them are called links.

Key components of a network:

• Nodes: Computers, servers, printers, or any device connected to the network.
• Links: Wired or wireless connections between nodes.
• Protocols: Rules governing communication between devices.
• NIC (Network Interface Card): Hardware that connects a device to the network.
• Switch/Router: Devices that forward data within and between networks.

2. Advantages of Networking

• Resource sharing: Share hardware like printers, scanners, and storage devices.
• Data sharing: Share files and databases across multiple users.
• Communication: Enable email, instant messaging, video conferencing.
• Cost-effective: Reduce hardware costs by sharing resources.
• Centralized management: Manage data and security from a central location.
• Scalability: Add new devices easily to the network.
• Reliability: Data can be replicated across multiple servers.

3. Types of Networks

4. Network Topologies

Network topology refers to the physical or logical arrangement of devices in a network. The choice of topology affects performance, scalability, and fault tolerance.

5. Star Topology

All devices are connected to a central device (hub or switch). Data passes through the central device to reach its destination.

Advantages: Easy to install and manage; failure of one node does not affect others; easy to add or remove devices.

Disadvantages: Central device failure brings down the entire network; requires more cable than bus topology.

6. Bus Topology

All devices are connected to a single central cable called the bus or backbone. Data travels along the cable in both directions.

Advantages: Simple and cost-effective for small networks; requires less cable.

Disadvantages: Limited cable length; a break in the cable brings down the entire network; difficult to troubleshoot.

7. Ring Topology

Each device is connected to exactly two other devices, forming a circular ring. Data travels in one direction around the ring.

Advantages: Equal access for all nodes; no data collisions; predictable performance.

Disadvantages: Failure of one node can disrupt the entire network; adding/removing devices requires reconfiguration.

8. Mesh Topology

Every device is connected to every other device in the network. A full mesh has n(n-1)/2 connections for n devices.

Advantages: Highest fault tolerance; no single point of failure; excellent performance.

Disadvantages: Very expensive and complex; requires extensive cabling; difficult to maintain.

9. Tree Topology

A combination of star topology arranged hierarchically. Multiple star networks are connected to a central bus backbone.

Advantages: Scalable and easy to manage; supports hierarchical organization.

Disadvantages: Failure of backbone affects the entire network; more cable required than bus topology.

10. Hybrid Topology

A combination of two or more different topologies. Large networks often use hybrid topologies to leverage the advantages of each type.

Example: A university network may use star topology within departments and bus topology to connect different departments.

11. Network Devices

Network devices are hardware components used to connect computers and other devices in a network.

12. Hub

A hub is a simple device that connects multiple devices in a network. It broadcasts data to all connected ports.

Characteristics:

• Operates at the Physical layer (Layer 1) of the OSI model.
• Broadcasts data to all devices; no intelligent routing.
• Half-duplex communication.
• Inefficient for large networks due to collisions.

13. Switch

A switch is an intelligent device that forwards data only to the intended recipient based on MAC addresses.

Characteristics:

• Operates at the Data Link layer (Layer 2).
• Creates a dedicated connection between sender and receiver.
• Full-duplex communication.
• More efficient than a hub; reduces collisions.

14. Router

A router forwards data packets between different networks based on IP addresses.

Characteristics:

• Operates at the Network layer (Layer 3).
• Connects different networks (e.g., home network to the Internet).
• Performs path selection using routing algorithms.
• Can filter traffic using access control lists.

15. Modem

A modem (Modulator-Demodulator) converts digital signals from a computer to analog signals for transmission over telephone lines and vice versa.

Types: DSL modem, cable modem, fiber optic modem.

16. Gateway

A gateway connects two networks that use different protocols. It performs protocol conversion between the two networks.

Example: Connecting a local network to the Internet requires a gateway.

17. Transmission Media

Transmission media carry data from one device to another. They are classified into guided (wired) and unguided (wireless) media.

18. Guided/Wired Media

Unguided (Wireless) Media: Radio waves, microwaves, infrared, satellite communication.