1. Physical layer: it mainly defines physical equipment standards, such as interface type of network cable, interface type of optical fiber, transmission rate of various transmission media, etc. Its main function is to transmit the bit stream (that is, 1 0 is converted into current intensity for transmission, and then converted into 1 0 at the destination, also known as analog-to-digital conversion and digital-to-analog conversion). This layer of data is called bits.

2. Data link layer: it mainly encapsulates and decapsulates the MAC address (address of network card) of the data received from the physical layer. This layer of data is usually called a frame. The equipment working at this level is a switch, through which data is transmitted.

3. Network layer: IP address that mainly encapsulates and decapsulates the data received from the lower layer (for example, 192 4438+068.0. 1). The device working at this layer is a router, and the data at this layer is usually called a packet.

4. Transport layer: Some protocols and port numbers (WWW port 80, etc.) are defined. ) is used to transmit data, such as TCP (transmission control protocol, low transmission efficiency and high reliability, used to transmit high reliability data) and UDP (user datagram protocol, contrary to TCP, used to transmit low reliability and small data, such as QQ chat data). It mainly transmits the data received from the lower layer in segments, and then reassembles it after reaching the destination address. This layer of data is usually called a segment.

5. Session layer: establish data transmission path through the transport layer (port number: sending port and receiving port). Initiate a session or accept a session request between your systems (devices need to know each other, which can be IP, MAC or hostname).

6. Presentation layer: it mainly interprets, encrypts and decrypts, compresses and decompresses the received data (that is, converts what the computer can recognize into what the human can recognize (such as pictures and sounds).

7. The application layer is mainly some terminal applications, such as FTP (downloading various files), WEB (browsing), QQ, etc. (you can understand what we see on the computer screen, that is, terminal applications).