Network Protocols: TCP/IP, HTTP, HTTPS, FTP, SMTP, POP3, PPP, Telnet and VoIP

Hello students, welcome to Kwickprep. A phone made in Korea opens a website stored on a computer in America, in less than a second. How do two machines that have never met understand each other? They follow the same rules, called protocols. Today we will learn the main protocols: T C P I P, HTTP, HTTPS and FTP. We will also meet SMTP, P O P three, PPP, Telnet and voice over I P. And we will learn the layers that hold them together.

First, a new term. A protocol is a set of rules that devices follow when they communicate. It fixes the format of the data, so both sides read it the same way. It fixes the order and timing, so both sides know who speaks when. It also says what to do when data is lost or damaged.

Think of a cricket match. Both teams follow the same rule book, so the game works. Networks are the same, because devices come from many different companies. A Windows laptop and an Android phone must still understand each other. Both sides must also agree on how to find and fix errors. And each job, like web pages, files or email, has its own protocol.

The most important pair of protocols is TCP/IP, and the Internet runs on it. TCP stands for Transmission Control Protocol. TCP breaks the data into small pieces called packets, numbers them, and makes sure all of them arrive correctly. IP stands for Internet Protocol. IP puts the sender and receiver addresses on each packet and helps it find a route across the networks.

Let us follow a photo sent to a friend. TCP splits the photo into numbered packets. IP adds the address of the sender and of the receiver to each packet. Routers pass each packet along, and packets may travel by different roads. At the other end, TCP checks, did every packet arrive? If yes, it puts them back in order and rebuilds the photo. If some are missing, the receiver asks for them again, and they are sent again.

Now the protocols we use every day. HTTP means HyperText Transfer Protocol, and HTTPS means HTTP Secure. Both carry web pages from a web server to your browser. The big difference is encryption, which means scrambling data so only the right receiver can read it. HTTP sends plain text, so browsers mark it Not secure, while HTTPS shows a site settings icon, once a padlock. Always use HTTPS for passwords, UPI and online payments.

Next, three protocols for files and email. FTP, the File Transfer Protocol, moves files between two computers, for example uploading a website to a server. SMTP, the Simple Mail Transfer Protocol, sends email from your app to the mail server and between mail servers. POP3, Post Office Protocol version three, downloads email from the server to one device, and usually deletes it from the server. IMAP is its modern cousin, which keeps mail on the server so your phone and laptop stay in sync.

A common exam question asks which protocol sends email and which receives it. Asha writes an email on her phone. SMTP pushes it to her mail server. SMTP then carries it across to Ravi's mail server, where it waits. When Ravi opens his mail app, POP3 or IMAP pulls it down to his laptop. So remember, SMTP sends, and POP3 or IMAP receives.

Three more protocols appear in exams. PPP, the Point-to-Point Protocol, connects exactly two devices over one direct link, like a computer and an Internet provider over a phone line. Telnet lets you log in to a distant computer and type commands on it, as if you were sitting in front of it. VoIP, Voice over Internet Protocol, turns your voice into packets, so calls travel over the Internet, like a WhatsApp or Google Meet call.

Here are a few extra facts that often earn marks. PPP can check the user name and password before it opens the link. Telnet is not safe, because it sends everything, even passwords, as plain text. That is why today we use SSH, Secure Shell, for remote login instead. VoIP calls cost very little, but the voice breaks up when the Internet connection is slow.

Some courses teach protocols as a layered model, like the four-layer TCP/IP model. A layer is one group of related jobs, stacked on top of other groups. The application layer talks to apps, using HTTP, FTP and SMTP. The transport layer splits data into packets and checks them, using TCP or UDP. The internet layer adds IP addresses and chooses routes. The link layer sends the bits over the cable or Wi-Fi.

Watch data move down the layers when you open a web page. The application layer writes an HTTP request. The transport layer cuts it into TCP packets. The internet layer adds the IP addresses. The link layer turns it into a Wi-Fi or cable signal. At the web server, the data climbs back up the same four layers, in reverse order.

Why split the work into layers at all? Each layer does one job, and only passes its result to the next layer. So a layer can change without touching the others, for example Wi-Fi replacing a cable. Different companies can make different layers, and they still fit together. And when something breaks, engineers can check one layer at a time.

Here is a question for you. Suppose your home switches from a cable to Wi-Fi. Which of the four layers changes? Pause the video, then look: only the link layer changes, because the others do not care how the signal travels.

Let us revise what we learned today. A protocol is a set of agreed rules so that devices understand each other. TCP splits data into packets and checks them, while IP addresses and routes them. HTTPS is HTTP with encryption, and FTP moves files. SMTP sends email, and POP3 or IMAP receives it. PPP joins two nodes, Telnet gives remote login, and VoIP carries calls over the Internet. Also remember the four layers: application, transport, internet and link.