Network Plus Course: OSI Model Overview

Introduction to OSI Model

• OSI Model: Open Systems Interconnection Reference Model
  • Describes data process traversal in networks
  • Not a detailed protocol suite; it's a broad overview
  • Compatible with many protocols, including TCP/IP
• Purpose:
  • Provides a common understanding among IT professionals
  • Facilitates communication, irrespective of organization

OSI Model Layers

• Layer 7: Application Layer
  • Interaction with applications
  • Examples: HTTP, HTTPS, FTP, DNS, POP3
• Layer 6: Presentation Layer
  • Data formatting and encryption/decryption
  • Character encoding
• Layer 5: Session Layer
  • Manages communication sessions
  • Initiates, maintains, and terminates sessions
• Layer 4: Transport Layer
  • Data transportation
  • Protocols: TCP (Transmission Control Protocol), UDP (User Datagram Protocol)
• Layer 3: Network Layer
  • Routing of data via IP addresses
  • Handles IP addressing and fragmentation
• Layer 2: Data Link Layer
  • Communication between network devices
  • MAC addresses (Media Access Control)
  • Referred to as the switching layer
• Layer 1: Physical Layer
  • Physical signal transmission
  • Involves cables, fibers, and wireless signal integrity

Detailed Explanation of Layers

• Physical Layer (Layer 1)
  • Focuses on hardware transmission
  • Issues could involve cables, fibers, wireless interference
  • Testing involves loopback tests, checking adapters
• Data Link Layer (Layer 2)
  • MAC address-oriented
  • Switch operations
  • Extended Unique Identifiers (EUI)
• Network Layer (Layer 3)
  • Utilizes IP addresses for routing
  • Concerns with subnet masks and routing
• Transport Layer (Layer 4)
  • Uses TCP/UDP ports for data transport
  • Manages data packetization and delivery
• Session Layer (Layer 5)
  • Manages sessions and tunneling protocols
  • Starts and ends sessions
• Presentation Layer (Layer 6)
  • Encrypts and decrypts application data
  • SSL/TLS operations
• Application Layer (Layer 7)
  • User interaction with software
  • Example interactions include email and web browsing

Real-World Application of OSI Model

• Using Tools Like Wireshark
  • Analyze captured data to view different OSI layers
  • Example: Frame 88 breakdown in Wireshark
    • Layer 1: Frame bytes (Physical Layer)
    • Layer 2: Ethernet (Data Link Layer)
    • Layer 3: IP addresses (Network Layer)
    • Layer 4: TCP ports (Transport Layer)
    • Higher layers: SSL encapsulation (Session, Presentation, Application)
• Summary: OSI model enables clear communication among IT professionals
  • Easily diagnose network issues at specific OSI layers
  • Enhances understanding of network operations