OSI reference model network layering

(1) physical layer

The main function of the physical layer is to complete the original bit stream transmission between adjacent nodes (that is, from 1, 0 to current strength for transmission, and to 1, 0 after arriving at the destination), to establish, maintain and disconnect the physical connection. Its main concern is how to use physical signals to represent data 1 and 0, whether data transmission can be carried out in two directions at the same time, how to establish and terminate connections with both sides of communication, and the characteristics of physical interface.

(2) data link layer

The main purpose of the data link layer is to encapsulate the upper data into data frames to connect the source and destination MAC addresses (which are used to represent the physical address of the network card) and to check errors.

(3) Network layer

The network layer is responsible for the transmission of data from the source to the destination, encapsulates the upper data into data packets, establishes an IP address connection, and selects the best transmission path according to the address.

(4) Transport layer

The transport layer is used to complete the communication of processes between different users, from end to end, using TCP (security protocol) / UDP (efficiency protocol) protocol to select different user processes according to different data.

(5) session layer

The session layer establishes and manages session communication between users.

(6) presentation layer

The presentation layer defines the syntax and semantics of delivery messages, encoding and decoding, compression and decompression, encryption and decryption.

(7) Application layer

The application layer provides an interface with the user