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OSI ModelIt is a standardization system developed by the International Organization for Standardization (ISO) for the interconnection of computer or communication systems. It is mainly divided into 7 levels:

• Physical Layer
• data link layer
• Network layer
• Transport Layer
• Session Layer
• Presentation Layer
• Application Layer

Although the OSI model is more comprehensive in theory, the TCP/IP model is more practical in actual network communications. TCP/IP is divided into four layers:

• Application Layer
• Transport Layer
• Internet Layer
• Network Interface Layer

Application Layer：This layer corresponds to the "application layer, presentation layer, session layer" of the OSI model, provides an interface that directly interacts with user programs, and provides services for various applications on the network, such as email, web browsing, etc.

Transport Layer：This layer corresponds to the "transport layer" of the OSI model, providing end-to-end data transmission and reliable connectionless transmission services. The main transmission protocols are TCP and UDP. TCP provides reliable data transmission to ensure the correctness and integrity of data. UDP is connectionless and suitable for transmission that does not require reliability, such as real-time audio and video streaming.

Internet Layer:This layer corresponds to the "network layer" of the OSI model and provides routing and forwarding of data packets. The main protocol is IP, which transmits data from the source host to the destination host by selecting the best path.

Network interface layer:This layer corresponds to the "data link layer, physical layer" of the OSI model and is responsible for the transmission of physical transmission media, such as Ethernet, WIFI, etc.