使用图表非常系统介绍了TCP和UDP的区别
https://blog.fundebug.com/2019/03/22/differences-of-tcp-and-udp/
举了一个TCP/IP通讯的例子，发送/接收邮件
https://blog.csdn.net/freekiteyu/article/details/72236734
介绍了socket和TCP/IP的关系
https://cloud.tencent.com/developer/article/1347105
ROS使用TCP/IP进行通讯
