1. Five layer network model

give an example ：

1. Five layer network model

From top to bottom is ： application layer 、 Transport layer 、 The network layer 、 Data link layer 、 The physical layer . When sending a message , Messages are packaged from top to bottom , Each layer will add packages on the basis of the previous layer , And when receiving messages , Unpack from bottom to top , Finally get the original information .
among ：

The application layer is mainly for application scenarios in the Internet , Such as web pages 、 mail 、 File center, etc , Its representative agreements are http、smtp、pop3、ftp、DNS wait

The transport layer is mainly oriented to the transmission process , such as TCP The protocol is to ensure reliable transmission , and UDP The protocol is a connectionless broadcast , They provide different transmission modes

The network layer mainly solves the problem of how to locate the target and how to find the optimal path , such as IP wait

The function of the data link layer is to store data in a subnet （ Broadcast area ） Internal effective transmission ,MAC Address 、 Switches belong to this layer

The physical layer is to solve the problem of conversion between binary data and signals , A hub 、 Twisted pair 、 Coaxial cables are covered devices