How does Facetime work?

The OP is on AT&T's network.

Nothing irritates me more than someone who says "it's too complicated".

This is how FaceTime works. SIP, STUN and TURN.

http://youshottheinvisibleswordsman.co.uk/2010/06/25/iphone4-facetime-and-open-s tandards/

normFL wrote:
Nothing irritates me more than someone who says "it's too complicated".

This is how FaceTime works. SIP, STUN and TURN.

To non-tech people, that means nothing, haha. Try calling (888) FACE-TIME to FaceTime with an Apple rep. I believe it only works on the weekdays though, from 8am to 8pm, EST.

Thanks to normFL for the link to my post. I was about to post it myself.

wjosten, you're correct in a sense when you say that this stuff "happens in the background". But it's worth understanding just how VOIP works, and how it doesn't rely on the traditional phone networks as we understand them.

Thanks to normFL for answering the initial question, sdstrowes for writing the answer, and marcbyron for asking the question in the first place (which I was also curious about)

No thanks to the idiots who assumed marcbyron was as idiotic as themselves, ignored his question, misinformed him, lost patience when their lack of intellect became apparent, then rubbished the actual answer when somebody was good enough to provide it.

FaceTime doesn't need a mobile signal to work, read [here|http://www.appleinsider.com/articles/10/06/29/iphone4_facetime_doesnt_need_a_mobile_signal_towork.html].

Has nobody mentioned that you can initiate a facetime call directly from your contacts list without making a cellular call first? I just tried it with my phone in airplane mode and it works just fine. So in theory if you are in different countries it should work as long as youre on wifi right? Im in the military so im really curious about this myself...

Btw...read and replied to this thread on my iphone 4 using opera, which seems to load these pages faster than my pc using internet explorer!

maybe, but he stated face time requires AT&T. This is not true. I have seen facetime used from t-Mobile Germany to another person not in Germany and not on AT&T.

That's the theory, but in checking some of the FT problem threads you will note that to activate FT a couple of SMS text messages are sent in the background between the phone and a Apple server. Not all cellular networks are passing those messages along:

http://discussions.apple.com/thread.jspa?threadID=2483442&tstart=0

However once FT is activated on a phone then it should work ?

Yes, but that's just a first step. If it's just ID exchange (or even simpler, e.g., "Are you Facetime capable?"/"Yes"), then it's a very small step in the whole process. Those details could, if implemented differently, be exchanged via any other mechanism (email is the obvious example). I wouldn't be surprised if it opened up that way, either. Consider wifi capable devices which don't have cell numbers but are otherwise Facetime capable...

But yes, once the ID to contact is known locally, it all happens over IP without any interaction on the cellular network.

Also interesting: Attempting to initiate a Facetime call with a non-FT capable handset incurs zero IP traffic. Presumably because the caller doesn't receive that initial SMS response from the receiver, and so doesn't know the SIP user to contact. No STUN packets are sent, no TURN allocations are requested, and no SIP invites are sent.

Facetime does work overseas. I'm here in Germany connected (primarily) to the Vodafone network, but I have AT&T back in the United States. I've FaceTimed my family back home; you don't even have to call them with a cellular connection initiating the conversation. I simply connected to my MacBook's shared internet Wifi hotspot, went to the contact card and clicked "FaceTime".

The ID exchange via SMS is not done each time you try to facetime someone. In my case the SMS were sent even though no one tried to facetime me and even though I did not initiate a facetime call. Instead, the SMS was sent when I first enabled Facetime in the phone's preferences.

What happens here (my guess) is that when you enable Facetime for the first time, the SMS is sent to some sort of ID database (owned by Apple?) that makes a record of it. Now whenever someone is trying to initiate a Facetime call, it asks that ID database first to find out the SIP address.

Both my wife & I have AT&T in the US and have successfully called each other using FaceTime...
I arrived in Korea (where there's no AT&T coverage) yesterday and successfully called my wife using FaceTime (Airplane Mode but with Wifi ON) using a local Wifi connection.
However, since then, FaceTime quickly fails and is unable to connect anymore... I've had my wife call me too with no luck. I also check my router settings and it doesn't seem to be the problem.

Do you think it made the first FaceTime call successfully because the iPhone had cached some info in needed the firstime?

I do want to understand it. That's why I own a PC and not a Mac. <ducks>

It only works if you own a Mac.

I'm in Afghanistan and just did a successful FaceTime call with my wife (via WiFi). It worked fine. I turned OFF roaming, turned on WiFi and connected with my wife in California via FaceTime. I noticed that there IS a cell network that my phone picked up called "O!" (I was not able to turn it off).
I then turned ON the airplane mode and connected to WiFi again. But I was NOT able to make a FaceTime call or send a text message. So here are my big questions:

1. Did I unknowingly make a 3G call and THEN connect via wifi?
2. Will I be charged from AT&T because it connected to the "O!" network in order to initially establish the call?