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Comment by userbinator | Hacker News Reader

I do wonder if there are patents on this, and if that has prevented other devices from adopting this kind of protocol?

WiFi has always had AdHoc mode which enables two devices to directly communicate like they were on the same Ethernet link, and I've used it a few times for a similar use-case to yours. It seems AirDrop is just a layer on top of that which facilitates the configuration required, but otherwise it would probably not be too difficult to "roll your own" similar app.

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AirDrop can also use BT. I think it decides based on file size? Either way I imagine BT is used to help negotiate everything instead of just connecting to dozens of random ad-hoc networks.

Aren’t many devices limited to one WiFi network (whether ad-hoc or infrastructure) at once? That would mean many devices couldn’t do this without breaking normal WiFi.

Doesn't Ad hoc force you to disconnect from your current Access Point? I'm under the impression that this is not the case with Air Drop.

Most cards nowadays support at least one ad-hoc and one infrastructure connection. Sometimes they have to be on the same frequency though, but it certainly wouldn't be hard for Apple to just buy one that supports multiple frequencies.

This is why AirDrop only works on some newer hardware: It requires Wi-Fi interfaces which can do Ad-Hoc and Infrastructure mode simultaneously.

Not in most cases, but it is somewhat chip (and driver) dependent).

Miracast is another example of this - In most cases you can remain connected to your main network connection via Wi-Fi but also use Wi-Fi direct to run a casting session.

Yes, unless your AP and ad hoc networks are on the same channel, you need two Wi-Fi radios to support this. AWDL "solves" this problem by quickly switching between these channels and schedules frame transmissions when the radio is tuned to the correct channel so the operation is (almost) transparent for the user (obviously, you loose some airtime for channel switching and your average latency increases).

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