Network model is a very basic but important basic knowledge of network . It's often said now OSI Seven layer model and TCP/IP Four layer model and five layer protocol model .

OSI Seven layer model

Generally called OSI(Open System Interconnection)
Model or seven layer model . He is international standardization (ISO) A standard system for interconnection between computers or communication systems . The protocol divides the computer network architecture into 7 layer .

Each layer implements its own functions and protocols , And complete the interface communication with adjacent layers . The services provided by each layer are completed by the cooperation of this layer and its lower layers .

Hierarchy OSI Model interpretation
7 application layer (Application Layer) An interface between network services and end users
6 Presentation layer (Presentation Layer) Data formatting , transformation , encryption
5 Session layer (Session Layer) Build between different machines , Administration , Terminate session
4 Transport layer (Transport Layer) Defines the protocol port number for transmitting data , Flow control and error checking
3 network layer (Network Layer) Logical address addressing , Realize the path selection between different networks
2 data link layer (Data Link Layer) Provides media access and link management
1 physical layer (Physical Layer) establish , maintain , Disconnect the physical connection that transmits binary data
TCP/IP Four layer model and five layer protocol model

actually ICP/IP It's a four tier model , But later, for the convenience of understanding the network principle , Integrate the seven layer model and the four layer model , A five layer model came out . The five layer model is only the network interface layer in the four layer model
It is divided into two layers: data link layer and physical layer

Hierarchy ICP/IP Model interpretation
4 The application layer provides users with various services they need
3 The transport layer provides end-to-end communication functions for application layer entities , It ensures the sequential transmission of data packets and the integrity of data
2 The network layer mainly solves the problem of host to host communication
1 The network interface layer is responsible for monitoring the exchange of data between the host and the network
Analogy of three models

TCP/IP Four layer model TCP/IP Four layer model OSI Model
Application layer application layer application layer
Presentation layer
Session layer
Transport layer transport layer transport layer
Network layer network layer network layer
Network interface layer data link layer data link layer
Physical layer
Same point

* OSI and TCP/IP All models adopt the concept of hierarchy
* Both can provide connection oriented and connectionless communication service mechanisms .

* TCP/IP The network interface layer of the reference model is not really defined , Just some conceptual descriptions . and OSI The reference model is not only divided into two layers , And the functions of each layer are very detailed .
* OSI The model is designed before protocol development , Universal .TCP/IP First there is the protocol set, and then the model is established , Not applicable to non TCP/IP network

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