My understanding of CSMA/CA is that devices listen until a Wi-Fi channel is idle before sending packets. If a collision still happens, then the devices waits a random interval before attempting to send again. I can imagine how this protocol would work with a few dozen devices in the same vicinity. However, I can't imagine how this would be workable in an area where thousands of devices are crammed together in small spaces, such as at a concert, sports game, rally, etc. How is it possible that thousands of devices can send thousands of packets over the same channel while still having normal latency? What mechanisms does CSMA/CA employ to improve scalability? Is there an upper-bound for Wi-Fi network devices?