Layers of the OSI Model

OSI (Open Systems Interconnection) model is a conceptual framework that standardizes how different network protocols communicate across a computer network. It was developed by the International Organization for Standardization (ISO) in 1984 to provide a universal set of rules for network communication.

7 Layers of the OSI Model
The OSI model is organized into 7 distinct layers, each with specific responsibilities. Data flows from the top layer (Application) down to the bottom layer (Physical) when sending, and from bottom to top when receiving.
🔝 Layer 7: Application Layer
What it does: Interface between user applications and the network
    Examples: HTTP/HTTPS, FTP, SMTP, DNS, DHCP
    Function: Provides network services directly to applications
    Real-world example: When you browse a website, your browser uses HTTP/HTTPS protocols

📋 Layer 6: Presentation Layer
What it does: Data translation, encryption, and compression
    Examples: SSL/TLS, JPEG, GIF, ASCII, EBCDIC
    Function: Ensures data is readable by the receiving system
    Real-world example: Encrypting your password when logging into a website

🔗 Layer 5: Session Layer
What it does: Manages communication sessions between applications
    Examples: NetBIOS, RPC, SQL sessions
    Function: Establishes, maintains, and terminates connections
    Real-world example: Maintaining your login session on a website

🚚 Layer 4: Transport Layer
What it does: Reliable data transfer and error correction
    Examples: TCP, UDP
    Function: Ensures complete data transfer with error checking
    Real-world example: TCP ensures all parts of a file download arrive correctly

🗺️ Layer 3: Network Layer
What it does: Routing and logical addressing
    Examples: IP (IPv4/IPv6), ICMP, OSPF, BGP
    Function: Determines the best path for data across multiple networks
    Real-world example: Routers use IP addresses to forward data packets

🔌 Layer 2: Data Link Layer
What it does: Node-to-node delivery and error detection
    Examples: Ethernet, Wi-Fi (802.11), PPP
    Function: Handles communication between directly connected devices
    Real-world example: Your computer communicating with your router via Ethernet or Wi-Fi

⚡ Layer 1: Physical Layer
What it does: Raw data transmission over physical medium
    Examples: Cables, fiber optics, radio waves, electrical signals
    Function: Transmits raw bits over the physical medium
    Real-world example: Electrical signals traveling through an Ethernet cable

🔄 How Data Flows Through the OSI Model
Sending Data (Top to Bottom)
    Application → User creates data (email, web request)
    Presentation → Data is encrypted/compressed
    Session → Session is established
    Transport → Data is segmented and prepared for reliable delivery
    Network → Routing information is added
    Data Link → Frame headers are added for local delivery
    Physical → Data becomes electrical/optical signals