The way it works is the routers themselves (dorys) will have two provisioned states. One is your private network and the other is the public wifi. Each is segmented from each other, will not see each other, and provide different IPs.
Each provisioned state has it's own bandwidth. It will NOT impact the subscribers data usage, bandwidth, etc.
To use teh public wifi, you must login with your comcast.net email address. If you have a valid account, it's free. if you do not have an active internet account, you can pay by the hour.