# Understanding Networks Everwondered how YouTube open in your device and how when you search a particular video it appears to you ? Looks pretty simple from outside but it is much more deep and interesting from inside. So if you are interested in knowing the inner mechanism of all this than this blog is for you lets start our journey. First we’ll start with understanding what is a network and what is a internet. ### Network : A **network** is a group of **two or more devices** (computers, mobiles, printers, etc.) **connected together** so they can **share data and resources**. Like for an example your TV , Mobile , Printer all these are connected to your home network which is to your WiFi router. They can: * Share internet * Send files * Use the same printer ### Internet : The **Internet** is a **global network of networks**. It connects **millions of smaller networks** all over the world. And here we will discuss our YouTube example , how actually it works? : ## Step 1: Your Device joins a **Network** * Your **mobile phone** connects to your **home Wi-Fi router** * This Wi-Fi router connects: * Your phone * Laptop * TV This group is a **LOCAL NETWORK (LAN)** --- ## Step 2: Router connects to ISP (Another Network) * Your Wi-Fi router is connected to an **ISP** (Internet Service Provider) * Example: Jio, Airtel, BSNL ISP also has **its own large network** Now: * Your home network * ISP network are **connected together** --- ## Step 3: ISP connects to YouTube’s Network * YouTube is stored on **Google’s servers** * These servers are part of **Google’s private network** * ISP connects to Google’s network through **high-speed global cables** Now **multiple networks are connected** This **collection of connected networks** is called the **Internet** --- ## Step 4: Request–Response (Very Important Concept) ### Request When you tap **Search** on YouTube: * Your phone sends a **request** > “Give me this video” This request travels: Phone → Home Network → ISP Network → Google Network --- ### Response * Google’s server finds the video * Sends data back in **small packets** Google Network → ISP → Home Network → Your Phone Video starts playing **So we understanded how all this works but many of you will ask how the internet itself reaches our home so lets discuss this also :** ## Step 1: Internet Exists on Big Servers (Far Away) * Websites like Google, YouTube, WhatsApp live on **huge servers** * These servers are placed in **data centers** * Data centers are connected by **very high-speed cables** --- ## Step 2: Global Connection Using Cables (Backbone of Internet) * Countries are connected using: * **Undersea fiber-optic cables** * **Land fiber cables** These cables carry data as **light signals** This forms the **global internet backbone** --- ## Step 3: Internet Comes to Your City (ISP Level) * Internet enters your city through **ISP (Internet Service Provider)** * ISP examples (for understanding): Jio, Airtel, BSNL ISP has: * Huge routers * Fiber cables * Control centers ISP **buys internet** from global providers ISP **distributes internet** to homes --- ## Step 4: Internet Reaches Your Local Area From ISP office: * Internet is sent through: * **Fiber-optic cable** (most common now) * Copper cable (older) * Mobile towers (for mobile data) This cable reaches **your street / building** --- ## Step 5: Internet Enters Your Home A cable enters your house and connects to a device: ### Modem / ONT * Converts light/electrical signals into data * Acts as a **translator** Without modem → internet is useless to your devices --- ## Step 6: Router Creates Your Home Network * Router takes internet from modem * Creates: * **Wi-Fi** * **LAN ports** All devices connect to this router Now **internet has reached your home** ![My home network setup in 2024 :: Bruno Antunes — Thoughts, rants ...](https://blog.nootch.net/img/post/my-home-network-setup-in-2024/home_network.png align="left") **Looks interesting , let us now understand how our network connects to the internet.** **So for this we need to understand few things like modem , routers , hub , switch , etc.** A modem and router are two of the most frequent components in a home network configuration. A router establishes a local area network (LAN), whereas a modem connects to an internet service provider (ISP). For a home network to work, both devices are necessary. ## Modem : [**Modem**](https://www.geeksforgeeks.org/techtips/how-to-install-a-modem/) [stand](https://www.geeksforgeeks.org/techtips/how-to-install-a-modem/)s for Modulator/Demodulator. The modem is defined as a [**networking device**](https://www.geeksforgeeks.org/computer-networks/network-devices-hub-repeater-bridge-switch-router-gateways/) [that is used to c](https://www.geeksforgeeks.org/computer-networks/network-devices-hub-repeater-bridge-switch-router-gateways/)onnect devices connected in the network to the [**internet**](https://www.geeksforgeeks.org/computer-science-fundamentals/internet-and-its-services/). [The main](https://www.geeksforgeeks.org/computer-science-fundamentals/internet-and-its-services/) function of a modem is to convert the [**analog signals**](https://www.geeksforgeeks.org/digital-logic/analog-signal/) [that come from](https://www.geeksforgeeks.org/digital-logic/analog-signal/) telephone wire into a digital form. ## **Working of Modem** The two main components of a modem are modulation and demodulation. Where the modem can perform both tasks simultaneously. The step-by-step working of the modem is given below: **Step 1: Data Generation:** When data needs to be transmitted it is first generated. Therefore computer system generated the data which is in digital form of 0s and 1s. **Step 2: Modulation:** Modulation is defined as a process of converting digital data signals of the computer into analog data signals so that these signals can travel on the internet. The digital data is encoded onto a carrier wave. **Step 3: Transmission:** The resultant of modulation that is modulated data is transmitted over the communication line to the modem that is receiving it. **Step 4: Demodulation:** Demodulation is defined as a process in which analog data signals from the internet are converted into digital data signals so they can be understood by computer systems. In the process of demodulation the digital data from the carrier wave is decoded. **Step 5: Decoding:** The resultant of demodulation that is demodulated data is being sent to the computer systems for their further use. ## Router : A router is a networking device that forwards data packets between different computer networks. It connects multiple packet-switched networks or subnetworks, managing traffic by directing packets to their intended IP addresses. Routers allow multiple devices to share an Internet connection efficiently. It takes internet from the modem and **shares it among multiple devices**. ## **How Does a Router Work?** Routers determine the path for a packet by examining its destination IP address and consulting the routing table, which contains information on network paths. They use a set of rules to identify the most efficient route for each packet. * **Static routing:** Configured manually, suitable for small or stable networks. * **Dynamic routing:** Automatically updated based on network activity, ideal for large or changing networks. # **Difference Between Modem and Router** ![Modem vs Router: What's the Difference? - VSOL](https://www.vsolcn.com/wp-content/uploads/2025/05/modem-vs-router-en.webp align="left") The basic difference between a Modem and a Router is that a Modem takes Internet Signals from the provider and connects it with your device and a Router takes the Internet from the modem and transfers it to your wireless devices. Both Modem and Router measure the networking devices, wherever a piece of electronic equipment connects your laptop or your network to the Internet Service Provider for accessing the web. To get the internet connection for our network, we both need a modem and router either individually or integrated. We will discuss each Modem and Router in detail. ## Hub : A **hub** is a basic networking device that **connects multiple computers** in a network and **broadcasts data to all devices**. --- ### How a Hub works * Data comes in from **one computer** * Hub sends that data to **ALL connected computers** * Even devices for which the data is **not meant** receive it \*Hub is **not intelligent** ## Switch : A **switch** is a smart networking device that **forwards data only to the intended device**. --- ### How a Switch works * Switch learns **MAC addresses** of devices * Builds a **MAC address table** * Sends data **only to the correct port** Switch is **intelligent** ## Basic difference between them : A hub broadcasts data to all devices, whereas a switch forwards data only to the intended device. ![Difference between Hub, Switch and Router - GeeksforGeeks](https://media.geeksforgeeks.org/wp-content/cdn-uploads/Network_devices.jpg align="left") **Now we have seen so many thing but the question arises that there are so many thing on internet some useful thing along with some danger like malware , hackers etc. so how and what makes our device safe form danger side of internet , let us check that.** ## Firewall : ![Packet Filter Firewall and Application Level Gateway ...](https://media.geeksforgeeks.org/wp-content/uploads/1111-6.png align="left") A **firewall** is a **security gate** between your **network** and the **internet** that **monitors, allows, or blocks data** based on security rules. Think of it as: **A security guard for your network** --- ## Where is the Firewall placed? Internet ↓ Firewall ← security lives here ↓ Your Network (devices, servers) Everything entering or leaving your network **must pass through the firewall**. --- ## Why do we say **“Security lives here”**? Because the firewall is the place where: * Decisions are made: * Allow or block? * Attacks are stopped: * Malware * Hackers * Unauthorized access * Network rules are enforced If firewall fails → network is exposed. --- ## How a Firewall Works (Step-by-Step) ### 1️⃣ Data tries to enter your network * From a website * From an unknown source * From another country --- ### 2️⃣ Firewall checks rules Firewall asks: * Is this traffic allowed? * Is the IP trusted? * Is the port safe? * Is the request normal or suspicious? --- ### 3️⃣ Firewall decision * Safe → allow * Dangerous → block \*All happens in **milliseconds** **Now from our YouTube example if someone got a question about its traffic since YouTube is a very big platform and many users are there so how it holds such big traffic without crashing or slowing down , so here the concept of load balancer comes in the picture lets us see this.** --- ## Load Balancer : ![What is a load balancer? - IONOS](https://www.ionos.com/digitalguide/fileadmin/DigitalGuide/Schaubilder/how-load-balancing-works.jpg align="left") A **load balancer** is a system that **distributes incoming user requests across multiple servers** so that **no single server gets overloaded**. hink of it as: **A traffic police for servers** --- ## Why does the problem exist in the first place? ### Without a Load Balancer Imagine: * Only **one server** * 10,000 users suddenly open a website Result: * Server becomes slow * Requests fail * Website crashes One server **cannot handle massive traffic alone**. --- ## What does a Load Balancer do? The load balancer: * Receives **all incoming requests** * Decides **which server should handle which request** * Sends traffic in a **balanced way** --- ## How a Load Balancer Works (Step by Step) ### 1️⃣ User sends a request Example: “Open YouTube homepage” --- ### 2️⃣ Request hits the Load Balancer The load balancer checks: * Which server is free? * Which server is healthy? * Which server handled the last request? --- ### 3️⃣ Request is forwarded * User 1 → Server 1 * User 2 → Server 2 * User 3 → Server 3 Load is **shared** --- ### 4️⃣ Server responds * Server sends data back * Load balancer passes it to the user --- ## Why **Scalable Systems NEED** a Load Balancer ### 1\. **Scalability** * Traffic increases → add more servers * Load balancer automatically starts using them No need to change user-side anything. --- ### 2\. **High Availability** If Server 2 fails : * Load balancer **stops sending traffic** to it * Redirects traffic to other servers Website stays online --- ### 3\. **Better Performance** * No server is overloaded * Faster response time * Smooth user experience --- ### 4\. **Fault Tolerance** * Server crash ≠ system crash * Failures are **isolated** **Now we will conclude all this and see how all these devices works together in a real world example:** ## Step-by-Step: How Everything Works Together ### 1️⃣ **Internet → Modem** **Role: Entry point** * Internet comes from ISP (fiber/cable) * **Modem / ONT** converts ISP signals into usable data Without modem → internet cannot enter your premises --- ### 2️⃣ **Modem → Firewall** **Role: Security gate (where security lives)** * Firewall inspects **all incoming & outgoing traffic** * Blocks: * Hackers * Malware * Unauthorized access In homes, firewall is usually **inside the router** --- ### 3️⃣ **Firewall → Router** **Role: Traffic director (network creator)** * Router: * Creates your **local network** * Assigns IP addresses * Decides where traffic should go Router decides: * Internet traffic → outside * Local traffic → inside network --- ### 4️⃣ **Router → Switch** **Role: Internal network expansion** * Switch connects **many wired devices** * Used when: * One router port is not enough * Office / lab / data center Switch is fast & intelligent Hub is NOT used anymore (legacy only) --- ### 5️⃣ **Switch → End Devices** **Role: Connectivity** Connected devices: * Computers * Printers * Servers * IP phones * Cameras --- ### 6️⃣ **Load Balancer (for Large Systems only)** **Role: Scalability & reliability** Placed **in front of servers**: ![How To use Switches in Network Diagram | Network Gateway ...](https://www.conceptdraw.com/How-To-Guide/picture/Network-diagram-System-design.png align="left") > Modem brings internet, firewall secures it, router directs it, switch expands it, and load balancer scales it. ## How these are connected to backend system and production deployment ? : In real-world production deployments, backend systems do not operate in isolation; they function behind multiple networking layers that ensure security, reliability, and scalability. When a user sends a request, it first passes through the internet and reaches a firewall, which acts as the primary security boundary by inspecting and blocking malicious or unauthorized traffic. The request is then forwarded to a load balancer, which distributes incoming traffic across multiple backend servers to prevent overload and to keep the system available even if one server fails. These backend application servers run the actual business logic and APIs, and they communicate with databases, caches, and other internal services through private networks managed by routers and switches. Databases are kept deep inside this internal network and are never directly exposed to the internet, providing an additional layer of protection. Finally, the response travels back through the same path to the user. Together, devices like the modem, router, firewall, switch, and load balancer form the foundation that allows backend systems to run securely at scale, making modern production deployments fast, resilient, and reliable. **So now we are at the end of our journey hope you enjoyed knowing all these network stuff. Thankyou for giving your valuable time for reading this blog hope you get something interesting and valuable , we’ll see you in the next blog till then signing off Thankyou.**