一个基于UDP的ping程序，使其产生4个报文，发送这些报文并对应答计时，通过这种方法来测量它们之间的RTT,用来测试目的主机的可达性。-UDP based on the ping process to produce 4 message, send these messages and response time, through this method to measure their RTT, used for testing purposes Reachability host.