OSI Model Guide

Open Systems Interconnection - 7-Layer Network Model

What is the OSI Model?

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.

OSI Model - 7 Layers

Data Flow Through OSI Layers

Layer Details

🌐

Layer 7: Application Layer

User interface and network services

Functions
  • β€’ User interface to network services
  • β€’ File transfer, email, web browsing
  • β€’ Network transparency
  • β€’ Resource sharing
Protocols & Examples
  • β€’ HTTP, HTTPS
  • β€’ FTP, SMTP, POP3
  • β€’ DNS, DHCP
  • β€’ Telnet, SSH
πŸ”

Layer 6: Presentation Layer

Data translation, encryption, compression

Functions
  • β€’ Data translation
  • β€’ Encryption/decryption
  • β€’ Data compression
  • β€’ Character encoding
Protocols & Examples
  • β€’ SSL/TLS
  • β€’ JPEG, GIF, PNG
  • β€’ ASCII, Unicode
  • β€’ MPEG, AVI
🀝

Layer 5: Session Layer

Session management and dialog control

Functions
  • β€’ Session establishment
  • β€’ Session maintenance
  • β€’ Session termination
  • β€’ Dialog control
Protocols & Examples
  • β€’ NetBIOS
  • β€’ RPC (Remote Procedure Call)
  • β€’ SQL
  • β€’ PPTP
🚚

Layer 4: Transport Layer

End-to-end communication and reliability

Functions
  • β€’ End-to-end communication
  • β€’ Error detection and recovery
  • β€’ Flow control
  • β€’ Segmentation and reassembly
Protocols & Examples
  • β€’ TCP (Transmission Control Protocol)
  • β€’ UDP (User Datagram Protocol)
  • β€’ SCTP
  • β€’ DCCP
πŸ—ΊοΈ

Layer 3: Network Layer

Routing and logical addressing

Functions
  • β€’ Logical addressing
  • β€’ Routing
  • β€’ Path determination
  • β€’ Packet forwarding
Protocols & Examples
  • β€’ IP (Internet Protocol)
  • β€’ ICMP, ARP
  • β€’ OSPF, BGP
  • β€’ RIP
πŸ”—

Layer 2: Data Link Layer

Physical addressing and error detection

Functions
  • β€’ Physical addressing (MAC)
  • β€’ Error detection and correction
  • β€’ Frame synchronization
  • β€’ Flow control
Protocols & Examples
  • β€’ Ethernet
  • β€’ WiFi (802.11)
  • β€’ PPP, HDLC
  • β€’ Frame Relay
⚑

Layer 1: Physical Layer

Physical transmission of data bits

Functions
  • β€’ Physical transmission
  • β€’ Signal encoding
  • β€’ Bit synchronization
  • β€’ Physical topology
Protocols & Examples
  • β€’ Ethernet cables
  • β€’ Fiber optic
  • β€’ Wireless (WiFi)
  • β€’ Bluetooth

Data Encapsulation Process

OSI Model vs TCP/IP Model

OSI Model TCP/IP Model Protocols
Application (7) Application HTTP, FTP, SMTP, DNS
Presentation (6) Application SSL/TLS, JPEG, MPEG
Session (5) Application NetBIOS, RPC
Transport (4) Transport TCP, UDP
Network (3) Internet IP, ICMP, ARP
Data Link (2) Network Access Ethernet, WiFi
Physical (1) Network Access Cables, Wireless