Unit 2, UDP & ICMP & End-to-End Principle
UDP，相比较之下，就非常简单了。Sending self-contained message。UDP与IP干的活非常类似，the unique feature is that it allows the layer to senddata to a specific appliacation. That’s also why it is called, theUser Demultiplexing Protocal1.它自己（UDP peer层内）无法实现missing datare-tra
