利用UDP通信时，服务器端的程序有一个线程不停地监听客户端发来的数据报，等待客户的请求，服务器只有通过客户发来的数据报中的信息才能得到客户端的地址及端口-A thread stop to listen for client datagram using UDP traffic, the server-side program, wait for the customer' s request, the datagram server sent only through the information to get the address and port of the client