Q: How does upstream and downstream port channel work in 802.11ac APs and clients?
A: AP support 802.3ad (LACP) as well as Static Port channel.
Downstream:
Packets are sprayed from Controller to both Ethernet ports of AP.
AP re-orders packets and delivers to wireless clients (in-order delivery) made possible by per-STA per-TID sequencing in GRE header for data packets from Controller.
Upstream:
Packets spraying based on Destination MAC of packet (hashed to 2 buckets statically).