The core problem here is not what program to use for transferring files, but rather how one device can reach the other. With all the firewalls, proxies, NATs, a

The core problem here is not what program to use for transferring files, but rather how one device can reach the other. With all the firewalls, proxies, NATs, and whatnot, it's quite difficult to establish a direct connection between two devices without using an intermediary server. If you can make the connection simple, such as in your LAN, files exchange becomes trivial.