Computer Network

A computer network is a collection of interconnected computers and other devices that can communicate with each other to share resources, information, and services.

Types of Network

A network can be generally classified according to its size , distance and structure.

PAN (Personal Area Network)
- It is used for communication among devices located close to one person.
- It typically covers a range of about 10 meters (33 feet), although it can extend up to 100 meters (330 feet) with certain technologies.
- It is often used for connecting personal devices, such as smartphones, laptops, & tablets, to each other or to external networks, such as the internet.
- Example: Connecting devices via Bluetooth and Personal Hotspot

LAN (Local Area Network)
- It is like a small neighborhood of computers and devices that are connected together in a limited area, such as a home, office building, or school.
- LANs are typically set up using Ethernet cables or Wi-Fi routers, and they enable users to easily share information and collaborate within the same location.
- Example: Connection of school computers and other devices through Ethernet or WiFi, WiFi at our home.

MAN (Metropolitan Area Network)
- It is like a bigger version of a Local Area Network (LAN), covering a larger geographical area such as a city or metropolitan area.
- It connects multiple LANs and other network devices across a wide area, typically using high-speed connections like fiber optics or wireless links.
- Example: TV cables, Telecom, TashiCell

WAN (Wide Area Network)
- It is like a superhighway that connects computers and devices over a large geographic area, such as across cities, countries, or even continents.
- It is used to link together Local Area Networks (LANs) and Metropolitan Area Networks (MANs) across long distances, typically using technologies like leased lines, fiber optics, or satellite connections.
- Example: The Internet, Telecommunication network, StarLink

Networking Devices

Networking devices are hardware components used to facilitate communication and data exchange between computers and other devices within a network.

These devices help establish and maintain connections, manage network traffic, and ensure the efficient transmission of data.

1. Router

A router is a crucial networking device that forwards data packets between computer networks.

It connects different networks, such as a local area network (LAN) to the internet, and determines the best path for data to travel.

2. Switch

A switch is used to connect multiple devices within a local area network (LAN).

It operates at the data link layer (Layer 2) of the OSI model and forwards data to the appropriate destination based on the MAC addresses of connected devices.

3. Hub

Hubs are basic networking devices that connect multiple devices in a LAN.

Unlike switches, hubs broadcast data to all connected devices, which can lead to network congestion and reduced performance.

4. Network Interface Card(NIC)

A network interface card, also known as a network adapter or LAN adapter, is a hardware component that allows a computer or device to connect to a network.

It provides a physical connection (such as Ethernet or Wi-Fi) between the device and the network.

5. MODEM

A modem ( modulator-demodulator) is used to convert digital data from a computer into analog signals for transmission over telephone lines or cable systems.

It also converts incoming analog signals back into digital data.

6. Access Point

An access point (AP) is used to extend a wired network by providing wireless connectivity to devices.

It allows devices like smartphones, laptops, and tablets to connect to a wireless network (Wi-Fi) within its range.

Network Connection

A network connection in a computer enables communication with other devices or networks, facilitating data exchange, internet access, and resource sharing.

It allows users to interact with the broader digital world and collaborate effectively within a networked environment.

Wire Connection(Ethernet)

Ethernet is a type of wired network connection that uses twisted pair cables to transmit data between devices within a local area network (LAN).
Its features include high-speed data transfer, reliability, and low latency.
Ethernet is commonly used for connecting computers, printers, routers, and other devices in homes, offices, and data centers.
Its purpose is to facilitate communication and data exchange between devices, enabling resource sharing, internet access, and collaboration within the network.

Wireless Connection(WiFi)

Wi-Fi enables network access without physical cables.
Offers easy and flexible connectivity.
Supports mobility, allowing device use while moving within range.
Connects multiple devices simultaneously.
Used for internet browsing, file sharing, and device-to-device communication.
Commonly connects smartphones, laptops, tablets, and smart home gadgets.
Facilitates seamless online access and real-time collaboration.

Compare and write down the differences between Wire Connection(Ethernet) and Wireless Connection(WiFi).

Network Protocols

Packets

A packet refers to a unit of data that is transmitted over a network.
It includes:

Header – for addressing and control info (like sender/receiver address)

Payload – the actual data being transferred

Packets are the fundamental building blocks of network communication and are used to efficiently transmit data between devices within a network.
They travel through the network from the source to the destination, where they are reassembled into the original data.
This packet-switching method allows for flexible and reliable data transmission across various network topologies and technologies.

Protocols

Network protocols are sets of rules and conventions that govern communication between devices in a network.
These protocols define how data is formatted, transmitted, routed, and received across the network.
They ensure that devices can understand and interpret data exchanged between them, regardless of differences in hardware, software, or operating systems.

TCP (Transmission Control Protocol)
- Ensures reliable, ordered, and error-checked delivery of data between applications.
- Used for web browsing, email, and file transfers where data integrity is critical.
IP (Internet Protocol)
- Handles addressing and routing of data packets across networks.
- Works with TCP (as TCP/IP) to deliver data to the correct destination.
SMTP (Simple Mail Transfer Protocol)
- Manages the sending and routing of email messages between mail servers.
FTP (File Transfer Protocol)
- Facilitates file transfers between a client and a server on a network.
HTTP (Hypertext Transfer Protocol)
- The foundation of data communication for the World Wide Web.
- Used for loading web pages and transmitting web content.
DNS (Domain Name System)
- Translates human-readable domain names (e.g., www.google.com) into IP addresses.
- Essential for navigating the internet without memorizing numerical IP addresses.

Basic Network Commands

These commands help diagnose and troubleshoot network issues such as connectivity problems, slow speed, DNS errors, and more. Use them in Command Prompt (CMD) or PowerShell.

💡 Shortcut to open CMD: Press Win + R, type cmd, and hit Enter.

1. ping

Purpose: Tests if a remote device/server is reachable.
How it Works: Sends ICMP packets and waits for a reply.
Command: ping google.com
Use Cases:
- Check if a website or server is online.
- Detect packet loss or network delay.

2. ipconfig

Purpose: Displays your computer’s IP address, gateway, DNS, etc.
Useful Variations:
- ipconfig /all → Detailed info (MAC address, DHCP, etc.)
- ipconfig /release & ipconfig /renew → Reset IP address

Command: ipconfig

Use Cases:
- Troubleshoot "No Internet" problems.
- Check if you have a valid IP configuration.

3. tracert (Trace Route)

Purpose: Shows the path data takes to reach a destination.
How it Works: Lists all routers (hops) along the way.

Command: tracert google.com

Use Cases:
- Find out where a connection fails.
- Detect slow or lagging network points.

4. nslookup

Purpose: Queries DNS to resolve domain names to IP addresses.
Common Uses:
- nslookup google.com → Find IP of a website
- nslookup 8.8.8.8 → Reverse lookup (IP to domain)

Command: nslookup google.com

Use Cases:
- Test if DNS is working.
- Verify website IPs.

5. netstat

Purpose: Shows active network connections and open ports.
Useful Options:
- netstat -a → All connections
- netstat -b → Show apps using connections
- netstat -ano → Show ports with PID

Command: netstat -ano

Use Cases:
- Detect suspicious activity.
- Find which ports are being used.

6. pathping

Purpose: Combines ping and tracert for detailed analysis.

Command: pathping google.com

Use Cases:
- Check each hop for latency or packet loss.
- Monitor network stability over time.

🧠 When to Use Which?

Issue Command to Use

Can't connect to website ping

No internet access ipconfig

Website is too slow tracert or pathping

DNS not resolving nslookup

Suspicious network activity netstat

🛠️ Bonus Quick Fixes

Flush DNS cache (if DNS is not working):

ipconfig /flushdns

Reset network settings (if internet isn’t working):

netsh int ip reset

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