Introduction to Computer Networks

This note covers the fundamental concepts of computer networks, exploring how devices communicate and share resources across different network topologies and protocols.

What is a Computer Network?

A computer network is a group of interconnected computers that can share resources and exchange data. Networks enable communication between devices, allowing users to share files, access remote resources, and collaborate in real-time.

Computer networks form the backbone of modern communication and information systems. They range from small home networks connecting a few devices to massive global networks like the Internet that connect billions of devices worldwide.

Key Components

Every computer network consists of several essential components:

• Nodes: Devices connected to the network (computers, servers, smartphones, IoT devices)
• Links: Physical or wireless connections between nodes
• Protocols: Rules and standards governing communication
• Network Interface Cards (NICs): Hardware that enables devices to connect to networks
• Switches and Routers: Devices that direct traffic within and between networks

Network Benefits

Computer networks provide numerous advantages:

1. Resource Sharing: Multiple users can access shared printers, storage devices, and applications
2. Data Communication: Fast and reliable exchange of information between users
3. Centralized Management: Easier administration and maintenance of resources
4. Cost Efficiency: Shared resources reduce hardware and software costs
5. Scalability: Networks can grow to accommodate more users and devices

Types of Networks

Computer networks are classified based on their size, scope, and purpose. Understanding these classifications helps in designing and implementing appropriate network solutions.

LAN (Local Area Network)

A Local Area Network connects devices within a limited geographical area, such as a home, office, or school campus. LANs are characterized by:

• High data transfer rates (typically 100 Mbps to 10 Gbps)
• Low latency and minimal data loss
• Private ownership and management
• Limited geographical scope (typically within a single building)

Common Uses: Office networks, home networks, school computer labs

WAN (Wide Area Network)

Wide Area Networks span large geographical areas, often connecting multiple LANs across cities, countries, or continents. The Internet is the largest example of a WAN.

Characteristics:

• Covers extensive geographical areas
• Lower data transfer rates compared to LANs
• Higher latency due to distance
• Often relies on third-party telecommunications providers

Applications: International corporate networks, telecommunications networks, the Internet

MAN (Metropolitan Area Network)

Metropolitan Area Networks connect devices within a city or metropolitan area, bridging the gap between LANs and WANs.

Features:

• Covers an entire city or campus
• Higher speeds than WANs but slower than LANs
• Often used by city governments and large organizations
• Can interconnect multiple LANs within a city

Other Network Types

PAN (Personal Area Network): Very small networks connecting personal devices (Bluetooth, USB connections)

CAN (Campus Area Network): Connects multiple LANs within a university campus or corporate campus

SAN (Storage Area Network): Specialized network for accessing consolidated data storage

Network Topologies

The physical and logical arrangement of nodes in a network is called its topology. Different topologies offer various advantages and trade-offs.

Bus Topology

All devices connect to a single central cable (the bus). Simple but prone to failures - if the main cable fails, the entire network goes down.

Star Topology

All devices connect to a central hub or switch. This is the most common topology in modern LANs because it’s easy to manage and troubleshoot.

Ring Topology

Devices are connected in a circular fashion, with data traveling in one direction. Each device acts as a repeater, regenerating the signal.

Mesh Topology

Each device connects to multiple other devices, providing redundancy and reliability. Common in wireless networks and critical systems.

Network Protocols

Protocols are standardized rules that govern how data is transmitted and received across networks. They ensure different devices and systems can communicate effectively.

TCP/IP Protocol Suite

The Transmission Control Protocol/Internet Protocol is the foundation of Internet communication:

• IP (Internet Protocol): Handles addressing and routing of data packets
• TCP (Transmission Control Protocol): Ensures reliable, ordered delivery of data
• UDP (User Datagram Protocol): Faster but less reliable than TCP

Other Important Protocols

• HTTP/HTTPS: Web browsing and secure communication
• FTP: File transfer between systems
• SMTP/POP3/IMAP: Email transmission and retrieval
• DNS: Domain name resolution
• DHCP: Automatic IP address assignment

Network Security

Security is crucial in modern networks to protect data and resources from unauthorized access and attacks.

Common Security Measures

1. Firewalls: Monitor and control incoming and outgoing network traffic
2. Encryption: Protects data confidentiality during transmission
3. Authentication: Verifies user identities
4. Access Control: Limits resource access based on user permissions
5. Intrusion Detection Systems (IDS): Monitor networks for suspicious activity

Summary

Computer networks are essential infrastructure in modern society, enabling communication, collaboration, and resource sharing across the globe. Understanding network types, topologies, and protocols is fundamental to working with information technology systems.

Table Example

Network Type	Geographical Scope	Typical Speed	Example
PAN	Personal space (meters)	Variable	Bluetooth devices
LAN	Building or campus	100 Mbps - 10 Gbps	Office network
MAN	City	100 Mbps - 1 Gbps	City-wide fiber network
WAN	Country/Global	Variable	The Internet