ℹ WHAT IS THE OSI MODEL? INTRO

The OSI (Open Systems Interconnection) model is a conceptual framework that standardizes network communication into seven distinct layers. Each layer has specific functions and communicates with adjacent layers to enable reliable data transmission.

Layered Architecture

Each layer has specific responsibilities and communicates with adjacent layers.

Standardization

Provides a common framework for understanding network communication.

Modularity

Allows independent development and modification of each layer.

📊 7-LAYER MODEL — CLICK ANY LAYER! INTERACTIVE

↑ Highest layer (closest to user)    ↓ Lowest layer (closest to hardware)

7
🌐 Application Layer
User interface and network services
HTTP HTTPS FTP SMTP DNS SSH

Functions

  • User interface to network services
  • File transfer, email, web browsing
  • Network transparency
  • Resource sharing

Protocols & Examples

  • HTTP, HTTPS
  • FTP, SMTP, POP3
  • DNS, DHCP
  • Telnet, SSH
6
🔐 Presentation Layer
Data translation, encryption, compression
SSL/TLS JPEG ASCII Unicode MPEG

Functions

  • Data translation
  • Encryption/decryption
  • Data compression
  • Character encoding

Protocols & Examples

  • SSL/TLS
  • JPEG, GIF, PNG
  • ASCII, Unicode
  • MPEG, AVI
5
🤝 Session Layer
Session management and dialog control
NetBIOS RPC SQL PPTP

Functions

  • Session establishment
  • Session maintenance
  • Session termination
  • Dialog control

Protocols & Examples

  • NetBIOS
  • RPC (Remote Procedure Call)
  • SQL
  • PPTP
4
🚚 Transport Layer
End-to-end communication and reliability
TCP UDP SCTP DCCP

Functions

  • End-to-end communication
  • Error detection and recovery
  • Flow control
  • Segmentation and reassembly

Protocols & Examples

  • TCP (Transmission Control Protocol)
  • UDP (User Datagram Protocol)
  • SCTP
  • DCCP
3
🗺 Network Layer
Routing and logical addressing
IP ICMP ARP OSPF BGP

Functions

  • Logical addressing
  • Routing
  • Path determination
  • Packet forwarding

Protocols & Examples

  • IP (Internet Protocol)
  • ICMP, ARP
  • OSPF, BGP
  • RIP
2
🔗 Data Link Layer
Physical addressing and error detection
Ethernet WiFi PPP HDLC

Functions

  • Physical addressing (MAC)
  • Error detection and correction
  • Frame synchronization
  • Flow control

Protocols & Examples

  • Ethernet
  • WiFi (802.11)
  • PPP, HDLC
  • Frame Relay
1
⚡ Physical Layer
Physical transmission of data bits
Cables Fiber Wireless Bluetooth

Functions

  • Physical transmission
  • Signal encoding
  • Bit synchronization
  • Physical topology

Protocols & Examples

  • Ethernet cables
  • Fiber optic
  • Wireless (WiFi)
  • Bluetooth
📦 DATA ENCAPSULATION PROCESS HOW IT WORKS

As data travels down from Application to Physical layer, each layer adds its own header (and sometimes trailer) — this is called encapsulation. On the receiving side, each layer strips its header — this is decapsulation.

→ Application Data (HTTP Request)
→ + Presentation Header (SSL/TLS encryption)
→ + Session Header (NetBIOS)
→ + Transport Header (TCP: ports, seq nums)
→ + Network Header (IP: source & dest addresses)
→ + Data Link Header (Ethernet: MAC addresses)
→ Transmitted as Physical Bits (electrical/optical signals)
📋 OSI vs TCP/IP MODEL COMPARISON
OSI Layer TCP/IP Layer Protocols
Application (7)ApplicationHTTP, FTP, SMTP, DNS
Presentation (6)ApplicationSSL/TLS, JPEG, MPEG
Session (5)ApplicationNetBIOS, RPC
Transport (4)TransportTCP, UDP
Network (3)InternetIP, ICMP, ARP
Data Link (2)Network AccessEthernet, WiFi
Physical (1)Network AccessCables, Wireless