In my recent app I managed to send data (mostly audio) via UDP in my local network (WiFi) to other iPhone. And now I need to do this same but in WAN. Can You guys please point me in the right direction where to start? What I need to achieve this?
I'm using GCDAsyncSocket to manage sockets. I believe that I have to got server, where I can keep IP addresses of both devices.
Also, how can I connect to device behind NAT/Firewall? I'm guessing, that I need to have public IP address (scrapped for instance from http://checkip.dyndns.com/). And then do I need to traceroute? Or NSLookup? Or piggyback? Or do I need to use UDP hole punching?
I know it's a lot of question, but if you can just point me to the right technology, I would be very grateful.
To achieve a communication between two participants behind a NAT you could use Hole-Punching like you mentioned it. This is explained quite well here: http://en.wikipedia.org/wiki/UDP_hole_punching#Flow
Basically a Server with a Public IP and Port is used to share the Port-numbers of the iPhones. But a NAT may use a different Port for every different IP the iPhone talks to. So if iPhone1 sends data to the server the NAT uses port X, but if iPhone1 wants to send data to a different IP the NAT may choose port Y. (See http://en.wikipedia.org/wiki/Network_address_translation#Symmetric_NAT)
To overcome this problem there is a protocol called UPnP and the lesser known NAT Port Mapping Protocol.
I am not well versed in UPnP but maybe someone else can provide some information on that.
The protocol NAT-PMP enables you to dynamically request an external port to be forwarded to your device. See http://en.wikipedia.org/wiki/NAT_Port_Mapping_Protocol, RFC 6886 . This allows you to "predict" your external port and establish connections over NAT.