Docker swarm in a public nic

Is the communication among the machines secure? For joining to a swarm i need a token , so i suppose at least there is a authentication control. But the channel for communication is encrypted? In addition i read i can add ecryption when i add a docker network. I suppose these channels are completely separated by control stream so they are 2 concept completely different. I d like to receive a little clarification about how to secure swarm data&control streams