OSI seven layer model

The layer number	layered	Function
7	application layer	Define source host 、 Between destination hosts , send out / receive data , Provide services directly to users
6	The presentation layer	Responsible for data format conversion , Convert the information processed by the application into a format suitable for network transmission , Or convert the data from the next layer into a format that the upper layer can process
5	The session layer	Establish and manage communication between applications
4	Transport layer	Provide end-to-end interfaces , Ensure the reliability of network data transmission ( Security ）
3	The network layer	Address management and routing （ To use MAC Address ）
2	Data link layer	① Receive data in the form of bitstreams from the physical layer , And encapsulate it into frames , Send to the next level ; Again , The data frame of the upper layer , Data in the form of bitstream is forwarded to the physical layer ② Error detection function , Turn the physical channel with large errors into error free 、 A data link that can reliably transmit data frames ;
1	The physical layer	Transmit bitstreams （ In binary data 0,1 Photoelectric signal transmits data ）