Core Internet Technologies

TCP/IP and OSI Model

Learning Outcome

The importance of IP addressing in networks

How errors can be identified using layers

The role of each layer in communication

Why networking is divided into 7 layers

How data travels from one device to another step-by-step

“Ever wondered what happens in a few seconds when you open a website?”

Your request is prepared for the system

It is secured for safe transfer

The connection with the website is managed

Data is split into smaller parts

An address is added for delivery

The best internet path is selected

It travels through Wi-Fi or cables

All parts are collected

Combined back together

Processed by the website

Finally displayed as a webpage

Suppose you are sending a message to friend

Scene 2: Using HTTPS (Secure)

Riya sends a message in a locked envelope

Message travels securely (encrypted)

No one can read or change it

HTTPS = SECURE & ENCRYPTED✅

Arjun receives the message safely

Use of OSI Model

Helps understand how data moves between devices step by step

Breaks complex networking into smaller, easy-to-manage parts

Makes it easier to identify and fix network problems

Ensures different devices and systems can work together properly

Helps in designing and improving network communication systems

Provides a standard structure for learning and understanding networking

How It Works?

HTTPS stands for HyperText Transfer Protocol Secure

HTTPS is a secure communication protocol that protects data using encryption while it travels between your browser and a website.

What is HTTPS?

EXAMPLE

HTTP can be compared to sending a postcard, where you write your message openly without any protection. As it travels from you to the destination, it passes through multiple systems and networks, and anyone handling it along the way can easily read or even modify the information.

HTTPS can be compared to sending a message in a sealed and locked envelope, where your information is protected before it is sent. As it travels from you to the destination through multiple systems and networks, even if someone handles it along the way, they cannot read or modify the contents because it is locked. Only the intended receiver, who has the correct key, can open the envelope and access the original message.

HTTP – Not Secure

HTTPS – Secure

Enable communication between a client (browser) and a server to request and receive web resources

Define how data is sent and received using the request–response model

HTTPS ensures secure communication by encrypting data and protecting it from interception

Use of HTTP and HTTPS Protocols

Difference between HTTP and HTTPS

HTTP (Not Secure)	HTTPS (Secure)
HTTP is like sending a postcard. The message is visible to anyone while it travels from you to the website.	HTTPS is like sending a sealed and locked envelope. Only the intended receiver can open and read it.
Data is sent in plain text (no encryption).	Data is encrypted before it is sent.
Information passes through multiple systems and networks.	It travels through multiple systems and networks safely.
Anyone along the way can read the data (hackers, network admins, attackers).	Even if someone intercepts it, they cannot read the data (it looks like random code).
Data can be easily modified or tampered with during transmission.	Data cannot be easily modified or tampered with during transmission.
No way to verify if the website is real or fake.	The website’s identity is verified using a digital certificate.
Ideal for non-sensitive information only. (e.g., reading public news)	Safe for sensitive information like passwords, banking, payments, etc.

How Web Communication Works (Request & Response)?

Step 1: You type a URL in the browser

Example: https://google.com
Your browser doesn’t know where Google lives
It first needs to find the IP address of that website using DNS
So before anything else: Browser → DNS → “Where is this website?”

Step 2: Browser sends HTTP/HTTPS Request

Once the IP is found: Browser sends a request to the server
This request includes:
1. Method (GET, POST, etc.)
2. URL/path (/search)
3. Headers (extra info like browser type)
4. Sometimes body (data like login info)
Basically: “Hey server, give me this page or do this action”

Step 3: Server receives and processes request

Now the server: Understands what you asked
Runs code (backend logic)
May talk to a database
Example:
1. You open Instagram → server fetches your feed data
This is where the “real work” happens

Step 4: Server sends HTTP Response

Server sends back:
1. Status code (200, 404, 500)
2. Data (HTML, JSON, images)
Example:
1. 200 → “Here’s your page”
2. 404 → “Doesn’t exist”
3. 500 → “We messed up”

Step 5: Browser receives and renders

Browser: Reads the response
Converts HTML, CSS, JS into a visible webpage
This is what you actually see on screen

We have successfully understood how HTTP and HTTPS communication works, including how data is transmitted securely over the network through encryption and protected connections.

HTTP methods tell the server what action you want to perform on data.

HTTP Methods

GET (Read / Fetch Data)

Used to retrieve data from the server
Does not change anything on the server
Data is usually sent in the URL
Example:
1. Opening a website
2. Searching on Google
Important: Should be safe (no side effects)

POST (Create / Send Data)

Used to send data to the server
Usually creates new data
Data is sent in the body (hidden from URL)
Example:
1. Signup form
2. Uploading a file
Important: Used when data is sensitive or large

PUT (Update Completely)

Used to update an existing resource fully
Replaces the entire data
Example:
1. Updating full user profile
2. Replacing a document
Important: If data doesn’t exist, sometimes it can create it

DELETE (Remove Data)

Used to delete a resource from the server
Example:
1. Deleting a post
2. Removing an account
Important: Action is permanent (usually no undo)

HTTP Status Codes

A status code is a number sent by the server that tells the result of the request, such as success (200), not found (404), or server error (500).

Status Code	Status Text	Use / Description
100	Continue	The server has received the request headers; the client should proceed to send the request.
101	Switching Protocols	The server is switching protocols as requested by the client.
102	Processing	The server has received and is processing the request, but no response is available yet.
103	Early Hints	The server is likely to send a final response; used to return some response headers early.

1XX Informational Status Codes

Status Code	Status Text	Use / Description
200	OK	The request was successful, and the server returned the requested resource.
201	Created	The request was successful, and a new resource was created.
202	Accepted	The request has been accepted for processing, but the processing is not complete.
203	Non-Authoritative Information	The request was successful, but the returned information is from another source.
204	No Content	The request was successful, but there is no content to return.
205	Reset Content	The request was successful, and the client should reset the document view.
206	Partial Content	The server is delivering only part of the resource due to a range header.
207	Multi-Status	The response contains multiple status codes for multiple operations.
208	Already Reported	The members of a DAV binding have already been enumerated in a previous response.
226	IM Used	The server has fulfilled the request using instance manipulation.

2XX Success Codes Complete Guide

Status Code	Status Text	Use / Description
300	Multiple Choices	The request has multiple possible responses; the user can choose one.
301	Moved Permanently	The requested resource has been permanently moved to a new URL.
302	Found	The requested resource is temporarily located at a different URL.
303	See Other	The server is redirecting to a different URL, typically with a GET request.
304	Not Modified	The resource has not been modified since the last request.
307	Temporary Redirect	The requested resource is temporarily located at a different URL; method should not change.
308	Permanent Redirect	The requested resource has been permanently moved; method should not change.

3XX Redirect Codes and Their Uses

Status Code	Status Text	Use / Description
400	Bad Request	The server could not understand the request due to invalid syntax.
401	Unauthorized	Authentication is required, and the client has not provided valid credentials.
402	Payment Required	Reserved for future use; payment is required to access the resource.
403	Forbidden	The server understood the request but refuses to authorize it.
404	Not Found	The requested resource could not be found on the server.
405	Method Not Allowed	The requested method is not supported for the requested resource.
406	Not Acceptable	The server cannot produce a response matching the client’s acceptable content.
407	Proxy Authentication Required	Authentication with a proxy is required to complete the request.
408	Request Timeout	The server timed out waiting for the client’s request.
409	Conflict	The request could not be completed due to a conflict with the current state.
410	Gone	The requested resource is no longer available and will not be available again.

4XX Client Error Codes Reference

Status Code	Status Text	Use / Description
411	Length Required	The server requires the request to specify the Content-Length header.
412	Precondition Failed	The request’s precondition headers are not met by the server.
413	Payload Too Large	The request payload is larger than the server is willing or able to process.
414	URI Too Long	The request URI is longer than the server is willing to interpret.
415	Unsupported Media Type	The server does not support the media type in the request.
416	Range Not Satisfiable	The requested range is not satisfiable.
417	Expectation Failed	The server cannot meet the requirements of the Expect request-header field.
418	I’m a Teapot	A playful error code defined in RFC 2324; the server refuses to brew coffee.
421	Misdirected Request	The request was directed at a server that is not able to produce a response.
422	Unproccessable Entity	The server understands the request but cannot process it.
423	Locked	The resource is locked and cannot be accessed.
424	Failed Dependency	The request failed due to the failure of a previous request.

Status Code	Status Text	Use / Description
425	Too Early	The server is unwilling to risk processing a request that might be replayed.
426	Upgrade Required	The client must upgrade to a different protocol.
428	Precondition Required	The server requires the request to be conditional.
429	Too Many Requests	The client has sent too many requests in a given amount of time.
431	Request Header Fields Too Large	The server is unwilling to process the request because header fields are too large.
451	Unavailable For Legal Reasons	The resource is unavailable due to legal reasons.

Status Code	Status Text	Use / Description
500	Internal Server Error	The server encountered an unexpected condition that prevented it from fulfilling the request.
501	Not Implemented	The server does not support the functionality required to fulfill the request.
502	Bad Gateway	The server, while acting as a gateway or proxy, received an invalid response.
503	Service Unavailable	The server is currently unable to handle the request due to overload or maintenance.
504	Gateway Timeout	The server, while acting as a gateway or proxy, did not receive a timely response.
505	HTTP Version Not Supported	The server does not support the HTTP protocol version used in the request.
506	Variant Also Negotiates	The server has an internal configuration error: variant negotiation loop.
507	Insufficient Storage	The server is unable to store the representation needed to complete the request.
508	Loop Detected	The server detected an infinite loop while processing the request.
510	Not Extended	Further extensions to the request are required for the server to fulfill it.
511	Network Authentication Required	The client needs to authenticate to gain network access.

5XX Server Error Codes Explained

HTTP Response code

HTTP response code are standard status codes returned by a server to indicate the result of client request

Headers (info about the response)

Headers are additional pieces of information sent with the request or response that describe details like content type, browser info, or how the data should be handled.
Headers give more context about the request.

Body (actual data: webpage, JSON, images)

The body is the actual data being sent in the request or response, such as a webpage (HTML), JSON data, images, or form inputs.
Used mainly in POST, PUT requests.
This is actual data you are sending to the server (login forms, signup data, etc.)

HTTP response also includes

HTTP response also includes

SSL/TLS Basics (Encryption concept)

What is SSL/TLS? (Basics)

SSL (Secure Sockets Layer) and TLS (Transport Layer Security) are protocols used to secure communication over the internet by encrypting data.

SSL is the older version
TLS is the newer, more secure version (what we actually use today)
Provide Security through Encryption:- They encrypt data so no one can read it while it’s being transmitted.
Ensure Data Integrity:- They make sure data is not modified or tampered with during transfer.
Authenticate the Website :- They verify that you are connecting to the real server using digital certificates.

Feature	SSL (Secure Sockets Layer)	TLS (Transport Layer Security)
Version	Older protocol	Newer, improved version
Security	Less secure (has vulnerabilities)	More secure and stronger encryption
Usage Today	Deprecated (not used anymore)	Widely used in HTTPS
Performance	Slower	Faster and more efficient
Support	Not supported by modern browsers	Fully supported