[rf6647]

I do not know the correct technical terminology for this question. Frame this question around using a smartphone application to remotely control or monitor your home thermostat or security system or lost iPad (no cell). What is involved in making that connection?  On the home network, the Smart Thermostat connects to the Wifi router. This step shares a dynamic IP and/or MAC ID for my cable modem (gateway to Internet) with my app (maybe)? After that it is all guessing. Is there some type of polling over the Internet seeking the device to respond to make a connection? Another possibility has the device register with a designated server to memorize the routing to the device.  Is this a form a DNS routing for private networks?  

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Keep In mind that your smartphone has two different internal hardware circuitry that allows it to access a cellphone tower and a WiFi network. Therefore, since your smartphone has access to both any app you install it would also (potentially) have access to both. So, when you're out and about somewhere your smartphone is connected to your cellphone provider, who is also connected to the internet. Bingo, your phone knows what's on your home network and can now access it through your cellphone provider.

[SpywareDr]

Keep In mind that your smartphone has two different internal hardware circuitry that allows it to access a cellphone tower and a WiFi network. Therefore, since your smartphone has access to both any app you install it would also (potentially) have access to both. So, when you're out and about somewhere your smartphone is connected to your cellphone provider, who is also connected to the internet. Bingo, your phone knows what's on your home network and can now access it through your cellphone provider.

[rf6647]

I am not comfortable with your answer.  Initiate the app, connects mobile to a server. My login ID relates to a MACID for the smart thermostat connected to wifi on the home network. One option is that the smart thermostat is periodically checking in with the server. When the app is connected, the server is in the middle. Each side of the connection uses standard Internet protocols & messages flow with the server acting as a relay.  Another option is like playing the kids game "marco polo" with the server broadcasting 'macro' and waiting for the reply 'polo'.  This option imagines a direct connection is made after invoking the app.

 

When you bring the cellular network into the picture, that seems to complicate matters in this connected world. However, I doubt that the smartphone uses any knowledge of the home network when remotely connected.

[SpywareDr]

<shrug> Okay.