Apple has been granted a patent (number 9,654,551) for an “apparatus and method for inviting users to online sessions” such as peer-to-peer sessions. Peer-to-peer SIP (P2P-SIP) is an implementation of a distributed voice over Internet Protocol (VoIP) or instant messaging communications method in which no central servers are required.
In the patent, Apple notes that lLarge public networks, such as the Internet, frequently have connections to smaller private networks, such as those maintained by a corporation, Internet service provider, or even individual households. By their very nature, public networks must have a commonly agreed upon allocation of network addresses, i.e., public addresses.
For a variety of reasons, maintainers of private networks often choose to use private network addresses for the private networks that are not part of the commonly agreed upon allocation. For network traffic from the private network to be able to traverse the public network, some form of private/public network address translation ("NAT") is required.
Here’s a (kinda technical) summary of Apple’s patent: “An invitation service performs a series of transactions to enable P2P communication between two or more mobile data processing devices. Prior to attempting to establish a P2P network communication channel, the invitation service may first collect network information for each of the mobile devices and use the network information to determine if a direct P2P network communication channel is feasible.
“If a direct connection is feasible, then the invitation service provides for direct P2P communication, pushing the necessary network information to each of the mobile devices. If a direct connection is infeasible, or an attempted direct connection fails, then the invitation service may identify network information associated with a relay service. The network information may then be used by any pair of mobile devices to establish a connection through the relay service. The invitation service can perform its functions without maintaining per-connection state information for the mobile devices.”
Of course, Apple files for — and is granted — lots of patents by the U.S. Patent & Trademark Office. Many are for inventions that never see the light of day. However, you never can tell which ones will materialize in a real product.