The International Organization for Standardization (ISO) has formulated the OSI model, which defines the interconnection standards of different computers and is the basic framework for designing and describing computer network communication.
OSI model divides the work of network communication into seven layers, namely, physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer.
This is a protocol that was actually eliminated by the TCP/IP 4 layer model. There is no large-scale use in the world today.
OSI features: the lower layer is invisible to the upper layer, and the lower layer serves the upper layer.
The TCP/IP model is actually a simplified version of the OSI model, which has only four levels:
1. application layer, corresponding to OSI application layer, presentation layer, session layer and data segment.
2. Transport layer, corresponding to OSI transport layer, data packet.
3. Network layer, corresponding to OSI network layer, data frame.
4. Network interface layer, corresponding to the data link layer and physical layer of OSI.
A very powerful TCP/IP diagram A very powerful TCP/IP diagram The network layer of the OSI model supports both connection-oriented and connectionless communication, but the transport layer only supports connection-oriented communication. The network layer of TCP/IP model only provides connectionless services, but the transport layer provides two communication modes at the same time.
The data segment of application layer is encapsulated into data packet after adding TCP/UDP header, encapsulated into data frame after adding IP header, and finally converted into bit data after adding MAC, which is transmitted in physical layer.
Simulation diagram of data packaging process simulation diagram of data packaging process