实现组播，模拟简单的开会场景，点击进入会议，就可以开始发言，点击退出会议室，就没有办法发言了，进入会议室的人都可以接收到讲的内容。-Multicast simulation of a simple meeting scene, click into the conference, you can begin to speak, Click to exit the conference room, there is no way to speak into the conference room