OSI Seven layer model

Preface ： Model

OSI Seven layer model ：

1. application layer
2. The presentation layer
3. The session layer
4. Transport layer
5. The network layer
6. Data link layer
7. The physical layer

TCP Five layer model ：

1. application layer
2. Transport layer
3. The network layer
4. Data link layer
5. The physical layer

1： The physical layer

The physical layer defines the relationship between the device and the transmission medium . Such as copper cable 、 optical cable 、 voltage 、 Cable specification 、 A hub 、 Repeater 、 Network adapter, etc .

Main functions of physical layer ： Establish connection or disconnection with the communication medium ; flow control ; Signal modulation or conversion between different equipment .

2： Data link layer

Data link layer ： Main detection and correction The physical layer Possible errors .

3： The network layer

The network layer ： Transmit variable length data sequences from source hosts on one network to target hosts on different networks , At the same time, ensure the request quality of the transport layer .

4： Transport layer

Transport layer ： Provide services for communication between two host processes . Applications use this service to transport application layer messages .

5： The session layer

The session layer ： Control the dialog connection between computers , establish 、 Manage and terminate connections between local and remote applications .

6： The presentation layer

The presentation layer ： Enable communication applications to interpret the meaning of exchanged data . The service provided is data compression 、 Data encryption and data description .

7： application layer

application layer ： Defines the interaction rules between application processes , Provide services for different network applications through different application layer protocols . Such as HTTP agreement ,SMTP agreement .