What are the two most common industry-standard protocols used to transport data from an AP...

CAPWAP (Control and Provisioning of Wireless Access Points):Modern standard protocol for tunneling management and data frames between APs and WLCs.

GRE (Generic Routing Encapsulation):Sometimes used by vendors as an alternative tunneling method, especially for data transport.

From CWDP-305:

“CAPWAP is the most widely used protocol for communication between access points and controllers. GRE is also utilized in some vendor implementations for tunneling user data.”

— Reference: CWDP-305 Official Study and Reference Guide, Chapter on Infrastructure Design