Network Plus Course: OSI Model Overview

Introduction to the OSI Model

• OSI Model: Open Systems Interconnection Reference Model.
  • Describes data traversal in networks.
  • Not a detailed protocol suite, but works with many protocols, especially TCP/IP.
• Purpose: Provides a universal language for IT professionals to discuss network processes.
  • Enables clear communication across organizations.

OSI Model Layers

• Layer 7: Application Layer

  • Interaction with the application.
  • Examples: HTTP, HTTPS, FTP, DNS, POP3.
  • Represents the user interface.

• Layer 6: Presentation Layer

  • Data formatting for user interpretation.
  • Functions: Character encoding, application encryption/decryption.
  • Works closely with the application layer.

• Layer 5: Session Layer

  • Manages communication sessions between systems.
  • Functions: Initiating, maintaining, terminating sessions.
  • Involves control protocols and tunneling.

• Layer 4: Transport Layer

  • Responsible for reliable data transfer across the network.
  • Protocols: TCP (Transmission Control Protocol), UDP (User Datagram Protocol).
  • Manages data segmentation and reassembly.

• Layer 3: Network Layer

  • Handles routing of data between devices.
  • Main elements: IP addressing, subnetting, fragmentation.
  • Key component in routing traffic.

• Layer 2: Data Link Layer

  • Transfers data between adjacent network nodes.
  • Key feature: MAC addresses (Media Access Control).
  • Regarded as the "switching layer" for network traffic.

• Layer 1: Physical Layer

  • Concerns the physical transmission of signals.
  • Involves cables, connectors, and wireless signals.
  • Troubleshooting often includes checking cables and signals.

Real-World Application

• Physical Layer (Layer 1): Focus on physical connections like cables and fiber optics.
• Data Link Layer (Layer 2): Focus on hardware addresses (MAC) and data frames.
• Network Layer (Layer 3): Focus on IP addresses and routing.
• Transport Layer (Layer 4): Focus on TCP/UDP port numbers.
• Session Layer (Layer 5): Focus on session management protocols.
• Presentation Layer (Layer 6): Focus on encryption/decryption processes.
• Application Layer (Layer 7): Focus on applications and user interaction.

Wireshark and OSI Model

• Wireshark: A tool for analyzing network protocol traffic.
  • Displays data at different layers.
  • Helps visualize the OSI model in practice:
    • Physical layer: Signal details.
    • Data link layer: MAC addresses.
    • Network layer: IP addresses.
    • Transport layer: TCP/UDP ports.
    • Higher layers: Encryption and application data.

Conclusion

• Importance of OSI Model: Provides a structured approach to understanding network communications.
• Communication: Helps IT professionals discuss network issues effectively by referencing specific OSI layers.