Ask HN: How does FaceTime do NAT Traversal?

#1

Post by gr3g » Sat, Mar 26, 2011, 12:19 PM UTC

I've been researching on several NAT Traversal algorithms for project I'm working on. I tried FaceTime on several routers with different NAT configurations and it seemed to work great but couldn't figure out the algorithm. Any help will be much appreciated.

Re: Ask HN: How does FaceTime do NAT Traversal?

#2

Post by DanWaterworth » Sat, Mar 26, 2011, 12:51 PM UTC

The usual technique is 'UDP hole punching'.

Re: Ask HN: How does FaceTime do NAT Traversal?

#3

Post by mryan » Sat, Mar 26, 2011, 1:38 PM UTC

STUN and TURN are listed in the open source protocols used by FaceTime [1], so it is probably one or both of those. There are probably a few more methods too, and it will just keep trying until it finds one that works on the current network.

[1] http://blog.imtc.org/index.php/2010/06/09/the-technology-beh...

Re: Ask HN: How does FaceTime do NAT Traversal?

#4

Post by rycs » Sat, Mar 26, 2011, 2:28 PM UTC

DanWaterworth wrote: post #2

The usual technique is 'UDP hole punching'.

yeah, same thing Skype does, I would not be surprised if FaceTime does exactly that.

Re: Ask HN: How does FaceTime do NAT Traversal?

#5

Post by st3fan » Sat, Mar 26, 2011, 2:49 PM UTC

STUN and TURN were already mentioned.

There is also Apple's own NAT-PMP which is more like UPnP but simpler. It can directly ask your (Apple) router to open a port and redirect it incoming traffic to a specific IP address on your local network.

https://secure.wikimedia.org/wikipedia/en/wiki/NAT_Port_Mapp...

I bet Apple also supports UPnP these days.