OSI is the abbreviation of Open Systems Interconnection Model, which is used to define the way two computers communicate in a network.
The first layer is the physical layer, which is closely related to physical signals, such as electrical signals, radio, and optical signals.
It is the hardware layer of OSI, such as signal intensifiers and routers all work on this layer, and the RS232 protocol is also defined in this layer.
data link layer.
Responsible for the encoding and decoding of electrical signal encoding to bit stream.
Manage errors at the physical layer.
Convert electrical signals to frame structure.
It also has two layers, one is the media access control layer MAC and the other is the logical link control layer LLC. MAC controls how the computer gains access to the network. LLC is responsible for frame synchronization, flow control, and error checking. The switch actually works at this layer.
The third layer is the network layer.
Route the data to the destination.
Responsible for data forwarding.
Congestion control, error handling.
The router works on this layer.
Establish a logical connection between any two devices in the world. Protocols such as TCP/IP work at this layer.
Transport layer.
This is the fourth floor.
Responsible for direct data transmission between two endpoints.
Responsible for data flow control and recovery between two endpoints.
Responsible for complete data transmission.
Network protocols such as UDP and TCP work at this layer.
Session layer.
Responsible for establishing and closing the connection between the two endpoints.
Such as NFS, RPC, SQL work in this layer.
Presentation layer.
Responsible for the data presentation on the screen.
Encryption and decryption of data.
The semantics and syntax of the data.
Such as encryption and decryption, ASCII, GIF, JPEG, MPEG work in this layer.
Application layer.
Support applications, user programs.
Quality of Service (QOS)
Responsible for file transfer, mail sending and receiving, etc.
Such as Telnet, HTTP, FTP work in this layer.