It is often called the OSI reference model.
It is a network interconnection model studied by ISO in 1985.
At the earliest time, when the network just appeared, many large companies had network technology, and internal computers could be connected with each other. Yes, but you can't connect with other companies. Because there is no uniform specification. The information transmitted between computers is incomprehensible to the other party. So it can't be interconnected.
In order to make network applications more popular, ISO introduced OSI reference model. It means that all companies are recommended to use this specification to control the network. In this way, all companies have the same specifications and can be interconnected.
Its contents are as follows:
Layer 7 Application Layer—Provides services directly to applications and can
Changes, but including electronic information transmission.
Layer 6 presentation layer-formats data and provides a common interface for applications.
Mouth. This may include encryption services.
Session layer 5- establishes a terminal connection between two nodes. This service includes
Is the connection established in full duplex or half duplex mode?
Settings, although duplex mode can be handled at Layer 4.
Layer 4 transport layer-general data transmission-connection-oriented or connectionless. include
Full duplex or half duplex, flow control and error recovery services
Layer 3 Network Layer-This layer establishes a connection between two nodes by addressing.
It includes routing and forwarding data through the Internet.
Layer 2 Data Link Layer-This layer is responsible for data framing and flow control. This floor
Specify topology and provide hardware addressing.
Layer 1 physical layer-transmission of original bit stream, transmission of electronic signal and hardware interface.
When data is sent, it is transmitted from the seventh layer to the first layer, and the receiver is the opposite.
The upper three layers are called application layer, which is used to control software.
The next four layers, called data flow layer, are used to manage the hardware.
Data is split when it is sent to the data flow layer.
The data in the transport layer is called segment, the network layer is called packet, the link layer is called frame, and the physical layer is called bit stream. This is called PDU (Protocol Data Unit).
Each layer in OSI has its own function. For example, the network layer should manage the destination IP of the local IP. The data link layer needs to manage MAC address (media access control) and so on, so it needs to split the data at each layer and encapsulate it to complete the communication between the receiver and the computer.
If there are rules.
OSI model is widely used.
Many network devices, such as switches, hubs and routers, are designed with reference to the OSI model.
It's enough to know so much. At least that's all CCNA took.