Shulou(Shulou.com)06/01 Report--

The OSI hierarchical model is divided into seven layers, which are arranged from the bottom up as follows:

Physical layer data link layer network layer transport layer session layer presentation layer application layer

1. Physical layer

The physical layer refers to the platform that provides data transmission media such as network cables, optical fibers, computers, etc., whose main function is to establish, maintain, and disconnect physical connections, such as connecting network cables, installing and configuring router splitters. These real operations belong to the physical layer.

two。 Data link layer

The main functions of the data link layer are the establishment of logical links, hardware addressing, error checking and other functions, which refers to the establishment and maintenance of an receiving and sending port after the completion of the physical layer configuration, that is, the process in which the switch looks for the mac address of the computer, that is, the network card. The mac address is an attribute of each computer that will no longer be changed from the factory. Equivalent to a geographical location of your family marked by latitude and longitude on the map, it is unique.

3. Network layer

The network layer carries on a logical address addressing to realize the path selection between different networks. The logical address is the IP address, which is unique in the same network segment. A computer can have multiple IP addresses, but only one valid address can be used at the same time. The data transmission between computers is the transmission from the sender to the receiver, that is, the transmission from the source port to the destination port. The IP address acts as a port, just like an address for sending and receiving express delivery. When sending data, how to choose the best path to transmit data is also carried out at the network layer.

4. Transport layer

The function of the transport layer is to define the port number of the transmitted data, as well as to control the flow and check the error of the data. The data in the transport layer is to filter the data, and each data will be assigned to its corresponding application process, just like sending a message in Tencent QQ. Other software can not receive it, so it can only use qq to receive and send it. In popular terms, the port is an application. Messages sent by one computer using the qq port can only be received by the same port qq on another computer.

5. Session layer

The function of the session layer is to establish, manage, and terminate the session. Popularly speaking, it is the process of a series of operations in which computer users use various applications to communicate, talk, and send and receive files with other computer users.

6. Presentation layer

The function of the presentation layer is the presentation, security and compression of data. All kinds of instruction operations carried out by computer users are typed into the computer system, and the computer will turn the human interface operation into data instructions that the machine can understand and execute.

7. Application layer

The application layer is a final interface between the network and computer users, which is popularly called the window interface of windows. In the application layer, it contains a large number of protocols commonly needed by people, such as HTTPS protocol, to help people use the network more conveniently and quickly.

There is no large-scale application of the OSI seven-layer model. Nowadays, the five-layer TCP/IP model is often used, which combines the session layer, the presentation layer and the application layer into one layer, that is, the application layer, and the other four layers remain unchanged.

The typical equipment in the application layer is the computer we use every day, and people use computers to manage data at this level.

The presentation layer is the process level in which the computer converts human operations, language instructions, and machine binary language to and from the application layer when the device is in use.

The session layer is the process of data transmission such as communication between a computer user and another computer user, sending and receiving files, etc.

The transport layer is the sending and receiving of data from port to port. The binary data translated by the computer will be sorted out and segmented to facilitate transmission. At this time, the data unit is segment, and the protocols used are usually TCP,UDP. TCP is secure and reliable, U is fast, but it may cause data damage. For example, Wechat messages are sometimes not accepted, and the transmission mode it uses is UDP. In network management, data is transmitted through a firewall, which is a typical device at the transmission level; it is the process of data transmission between a specific port used by computer users and the same port of another computer. Popularly speaking, the conversation layer is that people use computers to communicate with each other, and the transport layer is subdivided into the qq software used in human computers.

The typical equipment in the network layer is the router. The function of the router is to assign the IP address to each host. The data sent and received in the network should also have the IP address of the sender to ensure that the data can be sent and received correctly. So in this step, the segments of the upper layer that are sorted out and segmented will be re-sorted and given IP addresses and packaged, and the data processed in this process will be called data packets.

The typical equipment in the data link layer is the switch. in daily life, the optical cat in the telecom optical fiber broadband installation at home is the photoelectric switch. When the data is transmitted through the data link layer, the switch will assign the mac network card address to the data sent, and the network card address is also the transceiver. The typical device in the data link layer is the switch, which identifies the unique network card interface of each computer to send and receive data.

The physical layer is a variety of hardware in the computer network system and the basic platform of computer network transmission.

In the OSI model, the application layer, presentation layer and session layer are also called the upper three layers; the physical layer, the data link layer, the network layer and the transport layer are called the lower four layers; the data link layer is also commonly known as the second layer, and the related devices are also known as layer 2 devices, the network layer is commonly known as layer 3, and the related devices are also known as layer 3 devices.

The above is a personal analysis, welcome to correct.

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