OSI Model & TCP/IP Model

describe OSI model like I am 10

Imagine you want to send a letter to your friend who lives far away. The OSI Model is like a team of 7 helpers, where each helper has one special job to make sure your letter gets to your friend correctly.

7. Application Layer (The "You" Layer)

  • This is where you use an app like a web browser, email, or a game.

  • It starts the process of sending your message.

Example: You type "Hi!" in a chat app.

6. Presentation Layer (The "Translator")

  • Makes sure both computers understand the message.

  • It can:

    • Change the message into a format both computers understand.

    • Compress it to make it smaller.

    • Encrypt it to keep it secret.

Example: Like translating English into Spanish so your friend can understand.

5. Session Layer (The "Conversation Manager")

  • Starts, keeps, and ends the conversation between two computers.

Example: Like saying:

  • "Hello!"

  • Talking.

  • "Goodbye!"

4. Transport Layer (The "Delivery Helper")

  • Breaks big messages into smaller pieces.

  • Makes sure every piece arrives.

  • If a piece gets lost, it asks for it again.

Example: Like sending a 100-piece puzzle through the mail and checking that all 100 pieces arrive.

3. Network Layer (The "GPS")

  • Decides the best path for your message to travel.

  • Uses IP addresses to know where to send it.

Example: Like using Google Maps to find the fastest route to your friend's house.

2. Data Link Layer (The "Neighborhood Mail Carrier")

  • Moves data between devices on the same local network.

  • Checks for small errors.

  • Uses MAC addresses to know which nearby device should get the message.

Example: Like delivering mail to the correct house on your street.

1. Physical Layer (The "Road")

  • Sends the actual 1s and 0s as electrical signals, light, or radio waves.

  • Includes cables, Wi-Fi signals, and network hardware.

Example: Like the roads your mail truck drives on.

Easy Way to Remember the Layers

From top to bottom:

  1. Application – You use an app.

  2. Presentation – Translates and protects data.

  3. Session – Starts and ends conversations.

  4. Transport – Delivers every piece safely.

  5. Network – Finds the best route.

  6. Data Link – Delivers to the correct nearby device.

  7. Physical – Sends the signals.

Super Simple Story

Imagine you write a birthday card:

  • 🎉 Application: You write the card.

  • 🌍 Presentation: Someone translates it if needed.

  • 🤝 Session: You start talking to your friend.

  • 📦 Transport: The card is packed safely.

  • 🗺 Network: The post office chooses the best route.

  • 🏠 Data Link: The local mail carrier finds the right house.

  • 🚚 Physical: The truck drives the card there.

Each layer has one job, and together they make sure your message gets from your computer to someone else's computer safely.


same for TCP/IP Model

Imagine the TCP/IP Model as a team of 4 helpers that work together to send your message across the internet. It's like the OSI Model, but it combines some of the jobs into fewer layers.

4. Application Layer (The "You" Layer)

  • This is where you use apps like:

    • Web browsers

    • Email

    • Online games

    • Video calls

  • It gets your message ready to send.

Example: You type "Hello!" in a chat app.

3. Transport Layer (The "Delivery Helper")

  • Makes sure your message gets where it needs to go.

  • Splits big messages into smaller pieces.

  • Checks that all the pieces arrive.

  • If a piece is missing, it sends it again (when using TCP).

Example: Like mailing a 100-piece puzzle and making sure every piece arrives.

2. Internet Layer (The "GPS")

  • Finds the best path across the internet.

  • Uses IP addresses to know where to send your message.

Example: Like using GPS to find the fastest way to your friend's house.

1. Network Access Layer (The "Road")

  • Sends the actual data using cables, Wi-Fi, or other network hardware.

  • Moves data to the next device on the network.

Example: Like the roads that a mail truck drives on.

Easy Way to Remember the Layers

From top to bottom:

  1. Application – You use an app.

  2. Transport – Delivers your message safely.

  3. Internet – Finds the best route.

  4. Network Access – Sends the data over cables or Wi-Fi.

Super Simple Story

Imagine you're sending your friend a birthday card:

  • 🎉 Application: You write the card.

  • 📦 Transport: You pack it safely so nothing gets lost.

  • 🗺 Internet: The post office chooses the best route.

  • 🚚 Network Access: The mail truck drives on the roads to deliver it.

OSI Model vs. TCP/IP Model

OSI Model

TCP/IP Model

Job

Application

Application

Apps you use

Presentation

Application

Translates and encrypts data

Session

Application

Starts and ends conversations

Transport

Transport

Delivers data safely

Network

Internet

Finds the best route

Data Link

Network Access

Sends data on the local network

Physical

Network Access

Sends signals through cables or Wi-Fi

The biggest difference:

  • OSI Model: 7 layers (used mainly for learning and understanding networking).

  • TCP/IP Model: 4 layers (used by the real Internet every day).

Think of it this way:

  • OSI Model is like having 7 workers, each with one specific job.

  • TCP/IP Model is like having 4 workers, where some workers do multiple jobs.


How does the OSI model match to the TCP/IP model?

The OSI Model and the TCP/IP Model do almost the same jobs—they just organize them differently. The TCP/IP Model combines some of the OSI layers.

OSI Model (7 Layers)

TCP/IP Model (4 Layers)

What They Do

7. Application

Application

Apps like web browsers, email, and games.

6. Presentation

Application

Translates, compresses, and encrypts data.

5. Session

Application

Starts, manages, and ends conversations.

4. Transport

Transport

Breaks data into pieces and makes sure it arrives correctly.

3. Network

Internet

Finds the best route using IP addresses.

2. Data Link

Network Access

Sends data to the correct device on the local network.

1. Physical

Network Access

Sends data as electrical signals, light, or Wi-Fi.

Easy way to remember

OSI Model                  TCP/IP Model

7. Application   ┐
6. Presentation  ├──► Application
5. Session       ┘

4. Transport     ───► Transport

3. Network       ───► Internet

2. Data Link     ┐
1. Physical      ┘──► Network Access

Think of it like sending a package

OSI Layer

TCP/IP Layer

Mail Example

Application, Presentation, Session

Application

You write the letter, translate it if needed, and start the conversation.

Transport

Transport

You pack the letter and make sure every page is included.

Network

Internet

The post office chooses the best route to your friend's house.

Data Link, Physical

Network Access

The mail truck drives on the roads and delivers the letter to the correct house.

The main difference

  • OSI Model has 7 layers, with each layer having one specific job. It's mainly used for learning and troubleshooting.

  • TCP/IP Model has 4 layers by combining related OSI layers. It's the model that the Internet actually uses.

Simple memory trick:

  • OSI = 7 specialists (everyone has one job).

  • TCP/IP = 4 multitaskers (some workers do several jobs).


OSI Layer Addressing (Mac Addresses, IP Addresses, and Port Addresses): Which kind of address functions at layer 4: Which kind of address functions at layer 3: Which kind of address functions at layer 2:

Here's the mapping of OSI layers to their address types:

OSI Layer

Address Type

What It Identifies

Layer 4 – Transport

Port Address (Port Number)

Identifies the specific application or service (like a web browser or email).

Layer 3 – Network

IP Address

Identifies the destination device on a network or the Internet.

Layer 2 – Data Link

MAC Address

Identifies a specific network device on the local network.

Answers

  • Which kind of address functions at Layer 4?

    • Port Address (Port Number)

  • Which kind of address functions at Layer 3?

    • IP Address

  • Which kind of address functions at Layer 2?

    • MAC Address

Easy Memory Trick

  • Layer 4 = Port → "Which app?"

  • Layer 3 = IP → "Which computer?"

  • Layer 2 = MAC → "Which network card?"


OSI Layer Networking Devices: Which networking device(S) operate at OSI layer 3: Which networking device(S) operate at OSI layer 2: Which networking device(S) operate at OSI layer 1:

Here's how common networking devices map to the OSI Model:

OSI Layer

Networking Device(s)

What They Do

Layer 3 – Network

Router

Uses IP addresses to send data between different networks.

Layer 2 – Data Link

Switch, Bridge, Wireless Access Point

Uses MAC addresses to send data to the correct device on the local network.

Layer 1 – Physical

Hub, Repeater, Wireless Range Extender, Cables

Sends electrical, light, or radio signals without looking at addresses.

Answers

  • Which networking device(s) operate at OSI Layer 3?

    • Router

  • Which networking device(s) operate at OSI Layer 2?

    • Switch

    • Bridge

    • Wireless Access Point (WAP)

  • Which networking device(s) operate at OSI Layer 1?

    • Hub

    • Repeater

    • Wireless Range Extender

Easy Memory Trick

  • Layer 3 = Router = IP Address

  • Layer 2 = Switch/Bridge/WAP = MAC Address

  • Layer 1 = Hub/Repeater = Signals Only