What does "OSI" mean? What's the full name?

OSI is the abbreviation of Open System Interconnection, which means Open System Interconnection. The International Organization for Standardization (ISO) has formulated the OSI model, which defines the interconnection standards of different computers and is the basic framework for designing and describing computer network communication.

OSI model divides the work of network communication into seven layers, namely, physical layer, data link layer, network layer, transport layer, session layer, presentation layer and application layer.

1. Physical layer

Physical layer is the most important and basic layer in OSI hierarchical structure system. Based on the transmission medium, it plays the role of establishing, maintaining and canceling the physical connection, and realizes the physical interface between devices. The physical layer only receives and sends a string of bit streams, regardless of the meaning and structure of the information.

2. Data Link Layer (Data Link Layer)

Based on the bit stream service provided by the physical layer, the bit information is encapsulated into a data frame, which plays the role of establishing, canceling, identifying logical links and link multiplexing and detecting errors on the physical layer. Use the hardware address or physical address of the receiving system for addressing.

3. Network layer

Network layer, also known as communication subnet layer, is the interface layer between high-level protocols, which is used to control the operation of communication subnet and the interface between communication subnet and resource subnet. There may be many data links and many communication subnets between two computers communicating in a computer network.

4. Transport layer

The transport layer is established between the network layer and the session layer, which is essentially the interface layer between the upper layer and the lower layer in the network architecture. Use the addressing mechanism to identify a specific application (port number). The transport layer is not only a single structural layer, but also the core of the whole layered system protocol. Without the transport layer, the whole layered protocol is meaningless.

5. Conversation layer

This layer can also be called conference layer or dialogue layer. At the higher level above the session layer, the unit of data transmission is no longer named separately, and is collectively called message. Session layer does not participate in specific transmission, but provides a mechanism to establish and maintain communication between applications, including access verification and session management. If the server verifies the user login, it is done by the session layer.

6. Presentation layer

The presentation layer provides services to the application layer upwards and receives services from the session layer downwards. The presentation layer is a service that provides a representation method for information transmitted between application processes, and it only cares about the syntax and semantics of information.

7. Application layer

The network application layer is a window between communication users, providing users with services such as network management, file transfer and transaction processing. It contains several independent and universal service protocol modules. The network application layer is the highest layer of OSI, which provides special programs for communication between network users.

Extended data:

1. People can easily discuss and understand the specification details of the protocol.

2. The standard interface between layers is beneficial to engineering modularization.

3. Create a better interconnection environment.

4. Reduce the complexity, make the program easier to modify and the product development speed faster.

5. It is easier for each layer to remember the function of each layer by using the service of the next layer.

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