Information about how Continuity communicates

As a paranoid person, I'm curious how Continuity is able to implement SMS/Phone relay and handoff under various circumstances.

I was under the impression that these features only work when your on the same WiFi network and AP isolation is not enabled on the router, and both devices have bt enabled. However over the past few weeks I've noticed that it works in a lot of circumstances where I wouldn't expect it to work. For example, today at Starbucks, my phone was on LTE, wifi and bt enabled but not connected to anything, and my laptop was on public wifi with OpenVPN tcp method activated, bt enabled. Yet I could send SMS messages from iMessage.

I've read some articles, and I know that both bt and wifi work in tandem somehow to implement continuity, but can someone here explain better at what layer/level are the devices communicating? Does disabling either wifi or bt break the communication? Can it do it with just one protocol or the other? I figure it can't be just bt alone because the range is pretty limited, yet phone relay works when my phone is upstairs in my room and I'm downstairs way on the other end of the house.

I guess from a security perspective I'm concerned about weather this communication is limited to the lan I'm on/is device to device, or is there transmission over the internet going on here? I know I have to be signed in to iCloud on both devices, so maybe yes. Not sure.

Insights?

 

Connect your iPhone, iPad, iPod touch, and Mac using Continuity - Apple Support

 

Thanks, I did see that page. It tells me how to enable it and the pieces involved, but I was looking for something a bit more detailed/technical which describes how it actually works, which features use which connections (bt and/or wifi), and what data is actually sent and how iCloud ties into it all. The most informative thing I've found so far is this:

Explaining Continuity: The tech tying iOS 8 and OS X Yosemite together | Ars Technica

But I was looking for something deeper.

 

Isn't continuity just a Wifi thing? I don't think that you can use bluetooth with it.