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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?

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    "If a collision still happens, then the devices waits a random interval before attempting to send again." No, that is CSMA/CD. Wi-Fi devices sending a frame cannot detect a collision (CD) because the cannot both send and receive at the same time, so they try to avoid collisions (CA). – Ron Maupin Mar 23 at 15:00
  • @RonMaupin I see. It can't detect collisions, but it still assumes they happen, waits, and retransmits. According to the Wikipedia on CSMA/CA, "If such acknowledgement does not arrive in a timely manner, it assumes the packet collided with some other transmission, causing the node to enter a period of binary exponential backoff prior to attempting to re-transmit." Either way, I think the spirit of my question still stands. – Guy4444 Mar 23 at 15:11
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    The point is that a collision may not have happened in sending the frame. The frame may have gone through just fine, but something could have happened to the acknowledgement. The sending node has no way to know if there was a collision. – Ron Maupin Mar 23 at 15:24

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