How does WISP's differentiate users?

This maybe a little off-topic but I'm posting it anyways..
As the title says, I always wonder how actually does Wireless ISP's differentiate users, as far as I can think of, they work somehow like local Wi-fi networks in which we are connected to the same router. In our home networks, our router differentiates the users/clients with their MAC address and internal IP addresses.

But, this must be different for Wireless ISP's as we can use different PC's any time. Can anyone enlighten me please?

The same way that public hotspots at Starbucks, hotels & airports do. Through Captive Portal. Majority of the WISP's use pfSense as their back end. There is a WISP forum over at dslreports.com. Wireless Internet service provider - Wikipedia, the free encyclopedia

Okay, thanks alot