Comcast effectively has 2 modern day routers in their home computer devices, so the communications are completely disparate among the customer's ISP account and the xfinitywifi public hotspot. Usually someone would either have to pay a big fee or have a device associated by MAC address to their own Comcast account to use the xfinitywifi hotspots, but I found a way around that, which I discovered by accident after using MAC spoofing to get unlimited 1 hour (though some are now 30 minutes) free trials over and over again.