busy tone signal

例句：

1. 1. The busy tone signal is a common indicator of network congestion.
   繁忙的信号是网络拥塞的常见指示器。
2. 2.In this case, the busy tone signal is used to indicate that the line is currently occupied.
   在这种情况下，繁忙信号被用来表示线路当前被占用。
3. 3.The busy tone signal is often used to alert users to potential issues with the network.
   繁忙信号通常用于提醒用户可能存在的网络问题。