分层模型---OSI

7 ········ 应用层 ················ 为应用提供网络服务

6 ········ 表示层 ················ 数据格式化、加密、解密

5 ········ 会话层 ················ 建立、维护、管理会话连接

4 ········ 传输层 ················ 建立、维护、管理端到端连接

3 ········ 网络层 ················ IP寻址和路由选择

2 ········ 数据链路层 ················ 控制网络层与物理层之间通信

1 ········ 物理层 ··············· 比特流传输

分层模型---TCP/IP

四层模型：

4 ········ 应用层

3 ········ 传输层

2 ········ 网络层

1 ········ 网络接口层

五层模型：

5 ········ 应用层

4 ········ 传输层

3 ········ 网络层

2 ········ 数据链路层

1 ········ 物理层

数据包结构