 The system would monitor all channels in a given system and, if it detected a mobile attempting to acquire a second channel, that user would be invalidated on that channel (dumped), and immediately afterwards a 2-tone signaling sequence would begin on the original channel, bringing the lost unit into the original conversation.This could be highly annoying to users already in a conversation, as the very audible collect and group tones would interrupt the conversation, and if the invalidated user persisted in attempting to bring up a channel rather than waiting for the system to signal him, the collect and group tones would continue to be sent out on the working channel repeatedly on each channel attempt.A modern trunked system with a control channel is more costly and complicated, but sends continual messages for all in-progress conversations.