OSI Model Overview

Introduction

• OSI Model: Open Systems Interconnection reference model
  • Describes data processes in network systems
  • Not a protocol suite but applicable to many protocols
  • Works with TCP/IP protocols
• Purpose: Universal framework to discuss and understand network processes
• Layers: Each layer may operate with multiple protocols

Importance of the OSI Model

• Facilitates communication and understanding across different IT teams and organizations
• Aids in troubleshooting by categorizing network functions and problems

The Layers of the OSI Model

Layer 7: Application Layer

• Function: Interface for end-user applications
• Examples: HTTP, HTTPS, FTP, DNS, POP3

Layer 6: Presentation Layer

• Function: Data translation and encryption/decryption
• Role: Ensures data is in a readable format for the application layer
• Examples: Character encoding, application encryption (SSL, TLS)

Layer 5: Session Layer

• Function: Manages sessions between applications
• Role: Session initiation, maintenance, termination
• Use Cases: Control protocols, tunneling protocols

Layer 4: Transport Layer

• Function: Provides reliable or unreliable delivery
• Protocols: TCP (Transmission Control Protocol), UDP (User Datagram Protocol)
• Roles: Segmentation and reassembly of data

Layer 3: Network Layer

• Function: Routing and forwarding of packets
• Role: IP Addressing, packet fragmentation
• Examples: IP Protocol, Subnet Masks

Layer 2: Data Link Layer

• Function: Node-to-node data transfer
• Role: MAC addressing, switching
• Examples: Ethernet, MAC addresses, EUI-48, EUI-64

Layer 1: Physical Layer

• Function: Physical transmission of data
• Role: Cables, signals, wiring
• Troubleshooting: Cable issues, signal interference

Practical Application: Wireshark Protocol Analysis

• Wireshark: Tool to capture and analyze network data
• Frame Analysis:
  • Layer 1: Physical (Electrical signals)
  • Layer 2: Data Link (Ethernet frames, MAC addresses)
  • Layer 3: Network (IP addresses)
  • Layer 4: Transport (TCP/UDP ports)
  • Layers 5-7: Session, Presentation, Application (SSL/TLS encryption, Application data)

Conclusion

• Application: OSI model applies to most network communication
• Communication: Helps IT professionals discuss and resolve network issues effectively
• Real-world relevance: Useful for troubleshooting, understanding network operations