IP多播

代码说明：

  在局域网中，管理员常常需要将某条信息发送给一组用户。如果使用一对一的发送方法，虽然是可行的，但是过于麻烦，也常会出现漏发、错发。为了更有效的解决这种组通信问题，出现了一种多播技术（也常称为组播通信），它是基于IP层的通信技术(In a LAN, administrators often need to send a certain message to a group of users. If one to one transmission method is used, it is feasible, but it is too troublesome, and often there will be missed and wrong hair. In order to solve this kind of communication problem more effectively, there is a multicast technology (often called multicast communication). It is a communication technology based on the IP layer.)