[Freeswitch-users] What would happen if a selected rtp port is used?

Hi, I'm running more than one FS on a server, just want to know, how does FS chose a free rtp port? If a rtp port selected by one FS already used by another FS or another process, can it pick another free one automatically? Another option I know would be limit the rtp port range for each FS instance or bind to different address. But definitely need more configuration. Thanks.