Guest access with external hotspot

Normally, public guest wi-fi is monetized only when users connect to the network and pay for the usage. In Airports. Malls, Rail-stations, etc. what normally we have seen is there would be a free option for 30-45 minutes and once you complete the free usage, the paid option is available to continue browsing. 

We can monetize the guest wi-fi multiple ways. one, when the user connects to the paid option, another we coerce the user to watch a video/ad (of the company who want to put their adds on this guest wi-fi SSID) for a few minutes before proceeding to the free wi-fi access. 

Explaining how the flow of traffic and what needs to be done on the external web server(where login/self signup page is hosted) to achieve this.