Final answer:
The service used by both client stations and AP stations as specified in the 802.11-2016 standard is the Distribution service. It plays a pivotal role in managing the delivery of frames across the wireless network.
Step-by-step explanation:
The 802.11-2016 standard is part of the IEEE set of protocols for implementing wireless local area network (WLAN) computer communication. When addressing which service is used by both client stations (often referred to as stations) and AP stations (Access Points), the correct answer is the Distribution service. This service is responsible for managing the delivery of frames between stations and between a station and the distribution system that could be part of a local area network (LAN).
Distribution service operates within the context of a Basic Service Set (BSS) and is vital for maintaining communication among devices that are part of the wireless network regardless if they are client stations or Access Points. This service distinguishes between intra-BSS and inter-BSS communications, delivering data accordingly.