1. What is a Computer Network?
A computer network is a collection of two or more interconnected devices (computers, servers, printers, etc.) that can communicate and share resources such as data, files, applications, and hardware (e.g., printers, storage).
Purpose: Enable communication, resource sharing, and collaboration across distances.
2. Key Components of a Network
| Component | Description |
|---|---|
| Nodes | Devices connected to the network (e.g., PCs, laptops, smartphones, servers). |
| Links | Physical (cables) or wireless (radio waves) connections between nodes. |
| Network Interface Card (NIC) | Hardware that allows a device to connect to a network (has a unique MAC address). |
| Switch | Connects devices within a local network and forwards data efficiently. |
| Router | Connects different networks (e.g., your home network to the internet); directs traffic using IP addresses. |
| Modem | Modulates and demodulates signals to connect to the internet via telephone, cable, or fiber lines. |
| Protocols | Rules governing data communication (e.g., TCP/IP, HTTP, FTP). |
3. Types of Networks (Based on Geography)
| Type | Full Form | Range | Use Case |
|---|---|---|---|
| PAN | Personal Area Network | < 10 meters | Bluetooth, USB tethering (e.g., phone to laptop) |
| LAN | Local Area Network | Up to 1 km (e.g., office, home) | File sharing, printer access |
| MAN | Metropolitan Area Network | City-wide (5–50 km) | Cable TV networks, city-wide Wi-Fi |
| WAN | Wide Area Network | National/Global | Internet, corporate networks across countries |
Note: The Internet is the largest WAN in the world.
4. Network Topologies
Describes the physical or logical layout of devices in a network:
| Topology | Description | Pros | Cons |
|---|---|---|---|
| Bus | All devices connected to a single backbone cable | Simple, low cost | Single point of failure; hard to troubleshoot |
| Star | All devices connected to a central hub/switch | Easy to manage; failure of one node doesn’t affect others | Central hub failure brings down entire network |
| Ring | Devices connected in a circular fashion | Equal access; predictable performance | Failure of one node disrupts whole network |
| Mesh | Every device connected to every other (full mesh) or some (partial) | Highly reliable; redundant paths | Expensive; complex cabling |
| Hybrid | Combination of two or more topologies | Flexible, scalable | Complex design |
5. Types of Network Architectures
A. Client-Server
- Centralized model: Clients request services; Server provides resources (e.g., file server, web server).
- Advantages: Centralized security, backup, and management.
- Used in: Organizations, websites, databases.
B. Peer-to-Peer (P2P)
- All devices (peers) act as both clients and servers.
- Advantages: Easy setup, no dedicated server needed.
- Disadvantages: Less secure, harder to manage at scale.
- Used in: Small offices, file-sharing apps (e.g., BitTorrent).
6. Basic Networking Concepts
IP Address
- A unique numerical label assigned to each device on a network (e.g.,
192.168.1.10). - IPv4: 32-bit (e.g., 192.0.2.1) – ~4.3 billion addresses.
- IPv6: 128-bit (e.g., 2001:db8::1) – virtually unlimited addresses.
MAC Address
- A unique hardware identifier burned into the NIC (e.g.,
00:1A:2B:3C:4D:5E). - Used at the data link layer for local network communication.
DNS (Domain Name System)
- Translates human-readable domain names (e.g.,
www.google.com) into IP addresses.
Bandwidth
- Maximum data transfer rate of a network (measured in bps, Mbps, Gbps).
Latency
- Time delay between sending and receiving data (lower = better).
7. Wired vs. Wireless Networks
| Feature | Wired | Wireless |
|---|---|---|
| Medium | Ethernet cables (Cat5e, Cat6) | Radio waves (Wi-Fi, Bluetooth) |
| Speed | High (up to 10 Gbps+) | Moderate (up to 9.6 Gbps with Wi-Fi 7) |
| Security | More secure (physical access needed) | Less secure (signals can be intercepted) |
| Mobility | Limited | High |
| Installation Cost | Higher (cabling) | Lower |
8. Common Network Protocols
| Protocol | Function |
|---|---|
| TCP/IP | Core protocol suite of the internet (ensures reliable data delivery) |
| HTTP/HTTPS | Transfers web pages (HTTPS = secure with encryption) |
| FTP | File transfer between client and server |
| SMTP/POP3/IMAP | Email sending and receiving |
| DHCP | Automatically assigns IP addresses to devices |
9. Importance of Networking
- Resource Sharing: Printers, files, internet connections.
- Communication: Email, video conferencing, instant messaging.
- Data Backup & Recovery: Centralized storage (e.g., NAS, cloud).
- Scalability: Easy to add new users or devices.
- Cost Efficiency: Shared infrastructure reduces expenses.
Types of Networks (Based on Geographic Area)
Networks are classified primarily by their size and coverage:
| Type | Full Name | Description | Typical Range |
|---|---|---|---|
| PAN | Personal Area Network | Connects devices around a single person (e.g., Bluetooth devices). | Up to 10 meters (33 ft) |
| LAN | Local Area Network | Connects devices in a small, localized area (e.g., a home, office building, or school). | Up to 2 km |
| MAN | Metropolitan Area Network | Connects multiple LANs across a city or large campus. | 5 km to 50 km |
| WAN | Wide Area Network | Connects networks over large geographic areas (e.g., states, countries, or the entire world, like the Internet). | Above 50 km |
Network Architecture Models
To enable different technologies to communicate, networking uses layered models:
The OSI Model (Open Systems Interconnection)
This is a conceptual model that standardizes the functions of a communication system into seven abstract layers. The layers work together to pass data from an application on one host to an application on another.
| Layer | Name | Function |
|---|---|---|
| 7 | Application | Provides the interface for applications to access network services (e.g., HTTP, DNS). |
| 6 | Presentation | Handles data formatting, encryption, and compression. |
| 5 | Session | Manages communication sessions (opening, closing, and managing connections). |
| 4 | Transport | Provides reliable (TCP) or unreliable (UDP) data transfer between hosts. |
| 3 | Network | Handles logical addressing (IP) and routing of data packets across different networks. |
| 2 | Data Link | Handles physical addressing (MAC) and error control for data transfer between adjacent nodes. |
| 1 | Physical | Transmits raw binary data over a communication medium (cables, radio waves). |
The TCP/IP Model (Transmission Control Protocol/Internet Protocol)
This is a more practical, four-layer model that forms the basis of the Internet. It essentially consolidates the seven layers of the OSI model:
- Application Layer (OSI Layers 5, 6, 7)
- Transport Layer (OSI Layer 4)
- Internet Layer (OSI Layer 3)
- Network Access Layer (OSI Layers 1, 2)