tcp和udp的区别和联系， 1、端对端通信的概念 2、TCP提供的服务内容 3、TCP的流量控制和可靠性实现 4、UDP的协议特点和提供的服务 -the difference between tcp and udp and contact, 1, end to end communications concept 2, TCP provides services 3, TCP flow control and reliability to achieve 4, UDP pr