Understanding Network Devices
A netwok is a group of connected computers that are able to send data to each others .
Are you ever think about how internet reaches our home or offices ??
Actually internet is connected to all over the world by opical fiber cables.. yaah literally by optical fibres which can carry terabits of data per seconds. Almost 99% of all international data travels through undersea cables ,not satellites( which are too low slow and have high latency)
Undersea cables are laid by special ships that slowly place fiber optic cables along the ocean floor after carefully planning safe routes.
Who owns Undersea Internet Cables?
These are not owned by single company . These are owned by private companies ,mainly:
Telecom companies (like Airtel, Tata Communications, etc)
Big tech companies (Google, Meta, Microsoft, etc)
Group of companies called consortium.
Note: No single country owns the undersea internet cables. Countries only control the cable landing points within their borders.
What is ISP (Internet Service Provider)
An ISP is a company that provides internet access to users, like JIO, AIRTEL, BSNL, etc.
An ISP doesn't own the internet.
It either buys or shares bandwidth from the global internet backbone (which owns undersea fiber optic cables) or from an IXP (Internet Exchange Point where different networks meet and exchange data, making the internet faster and cheaper).
There are various ways the ISP delivers internet to your home.
- Digital Subscriber Line (DSL):
Utilizes existing telephone lines to transmit data
Allows simultaneous data and voice transmission over the same line
Data speeds vary based on distance from the central office
- Cable
Uses coaxial copper cable to deliver high-speed internet.
Works on the same infrastructure used for cable television.
Provides faster speeds than DSL.
Each home's bandwidth fluctuates depending on how many neighbors are online at the same time.
- Fiber-optics
Fastest and most reliable
Each home gets its own dedicated fiber, which is why it is faster than others.
- Wireless Connections
Examples include Wi-Fi, satellite, or cellular networks.
Provides internet where wired connections are not feasible or economically viable.
Uses radio waves to transmit and receive data, allowing remote areas to access the internet.
What is Modem and how it connects your network to internet?
A modem (modulator - demodulator ) is a device which converts
digital data signals (0s and 1s) from your device into analog /transmission signals or
incoming analog/ transmission signals back into digital data signals (0s and 1s) that can be travel on ISP line
Note:
The ISP lines are the physical or wireless path used by ISP which delivers internet to you .
Fiber-optics carry light signals.
DSL and cable carry electrical signals.
Wireless connections like Wi-Fi, cellular networks, and satellite carry radio signals.
Why do we need a modem if both the sending and receiving devices use digital signals?
We need a modem because the path between the two devices (ISP lines) cannot carry raw digital signals directly. These roads don’t understand 0s and 1s directly. A modem does signal conversion.
The ISP lines are the physical or wireless path used by ISP which delivers internet to you .
Fiber-optics carry light signals.
DSL and cable carry electrical signals.
Wireless connections like Wi-Fi, cellular networks, and satellite carry radio signals.
Note: ISP uses special signals because they travel long distances ,can be amplified and repeated, survive noise and interference
Router= Traffic Police and how it directs traffic ?
A router is like the internet's traffic police, deciding the best path for data to take to reach its destination. It connects your home or office network to the internet. A router checks the destination IP address of each data packet and figures out which path to send it on. It finds the right path by looking into its routing table, then sends the data to the next router (usually your ISP’s router). The data doesn't go directly to its destination in one jump; it passes through many routers, each acting like traffic police at different junctions.
At every junction Each router reads destination IP, chooses best next road and forwards the packet .This continues until the packet reaches the destination server.
Response comes back with the same way by sending responses to correct device.
Simple real example
Your phone requests YouTube.
DNS converts youtube.com to 142.xxx.xxx.xxx.
Data packet now includes:
Source IP: your phone
Destination IP: YouTube server
Router reads the destination IP.
Router forwards the packet toward the internet.
Another Example
You type google.com on your phone.
The router receives the request.
The router forwards it to the internet.
Google's response comes back.
The router sends it only to your phone, not to others.
Is Router and Modem same?
Modem= Internet Translator (Modem is just like translator that translates foreign language into local language and local language into foreign language )
Router =Internet Traffic Police (Router is the traffic police inside the city ,directing vehicles to correct streets)
Switch Vs Hub :
Switch
A network switch connects devices in a local network (LAN) and sends data only to the correct device.
Note: “A switch learns which device is connected to each port and forwards data only to that device using MAC addresses (unique hardware identity). It stores this information in a MAC address table.”
Hub (Loudspeaker in the street)
A hub is basic networking device that connects multiple computers in local network and send data to all of them
Note: “A hub does not think — it just copies and broadcasts data to every connected device. “
How a Hub Works :
A computer sends data to the hub.
The hub receives the data.
The hub broadcasts the same data to all ports.
Every device receives it.
Only the correct device accepts it; others ignore it.
Hub doesn’t check MAC address & IP address
Note: Hub Is Called a ”DUMB Device “ because it has No memory ,No MAC table ,No decision making , No filtering. It works like a wire extender.
how local network actually work?
A local network lets nearby devices (like your phone ,laptop, printer ) talk to each other using a switch or wi-fi ,without needing the internet. All the devices are now part of the same local network
Every device has MAC address (fixed, hardware) and IP address (given by router).This helps devices identify each other.
Step by step process
Device wants to send data
Example: Laptop → Printer
Laptop says: “I want to send data to this printer.”
LAN finds the correct device
Laptop asks: “Who has this IP?” (broadcast)
Printer replies with its MAC address
Laptop now knows where to send data
Switch delivers the data
Laptop sends data
Switch forwards it only to the printer
Other devices are not disturbed
Communication happens
Printing
File sharing
Playing local games
Accessing local server
🚫 Internet not needed
If Internet is needed
Data goes to router
Router sends it to ISP
Reply comes back → LAN → your device
What is Firewall (Security Guard)?
A firewall is a security guard for your network or computer. It checks all incoming and outgoing data and decides it has to allow it or bock it based on security rules
How Firewall works
Data comes from the internet
Firewall inspects it
Compares it with the security rules
Allows safe data
Blocks harmful or unknown data
why security lives here?
Because every network connection must pass through the firewall which blocks hackers ,stops malware traffic ,prevent unauthorized access , and control which app can use the internet
What is Load Balancer ( Traffic Manager)
A load balancer is a traffic manager that distributes incoming requests across multiple servers.
Instead of sending all users to one server, it spreads the load.
Note
A load balancer shares work between servers so no single server gets overloaded.
How Load Balancer Works (Step-by-Step)
User sends request (opens a website)
Request first reaches load balancer
Load balancer checks:
Which server is free
Which is healthy
Forwards request to that server
Server responds → user
User never knows which server handled the request.
why scalable systems need it
Handles more users – distributes traffic across multiple servers
Prevents overload – no single server gets too much traffic
Improves performance – faster response time
High availability – keeps system running even if one server fails
Easy scaling – add or remove servers without downtime
Smooth maintenance – update servers without affecting users
How all these devices work together in real-world setup?
🌐 Real-World Flow (Step by Step)
User opens website on laptop
Router receives request ,knows it’s for internet so it sends to modem
Modem converts signal and sends to ISP and from ISP to website server
Website server responds and comes back through modem and through modem it goes to router
If company website has multiple servers, load balancer directs the request to a free server
Firewall checks traffic and it blocks malicious requests
Inside LAN, switch sends internal packets to correct device (like printer or local server)
Hub, if present, would broadcast to all (less efficient, rarely used now)
Simple Analogy
Imagine a city where cars (requests) want to reach shops (servers).
The traffic police (router) directs cars inside town or to the city gate (modem) for the highway.
At intersections, smart intersections (switches) send cars to the right building.
Security checkpoints (firewalls) stop unsafe cars.
Big malls with multiple entrances use load balancers to send customers to free entrances.
Older loudspeakers (hubs) just shout directions to everyone.
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