1.2 TCP/IP model

• Open Systems Interconnection Reference Model (OSI/RM)
  • In order to realize the mutual communication of various computers, the International Organization for Standardization ISO officially announced a network architecture model as an international standard in 1981, called the Open Systems Interconnection Reference Model (OSI/RM), also known as ISO/OSI.
  • "Open" means that any two systems that comply with OSI/RM can be interconnected. When one system can communicate with another system according to OSI/RM, the system is called an open system.

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• The OSI reference model defines a hierarchy to which devices in a network adhere
  • Advantages of layered structure:
  • Open standardized interface
  • Multi-vendor compatibility
  • Ease of understanding, learning and updating protocol standards
  • Realize modular engineering, reducing the complexity of development and implementation
  • Easy to troubleshoot

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• OSI Reference Model Hierarchy
  • It is divided into seven layers, also known as the seven-layer model. The seven-layer model defines different layers, and each layer has its own function.

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• Peer-to-peer communication: (any operating system and device want to communicate, must follow the OSI model)
  • The peer layers talk to each other (for example: the physical layer can only communicate with the physical layer, and the data link layer can only communicate with the data link layer)
    • no cross communication

• Each layer uses its own protocol
• Each layer communicates with the peer layer using the services provided by the lower layer

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• Data encapsulation and decapsulation

• Hierarchy of the TCP/IP Model