Establish peer-to-peer connection from behind NAT

Question

I need to make some general way for my own peer-to-peer UDP or TCP communication between my own clients over internet, without creating own server.

I cannot just use XMPP for the communication because file transmit are necessary.

Do I understand the possible sequence of actions correctly?

• Connect to some (or any?) XMPP server, using prepared existing XMPP account
• Search for another my own client connected to XMPP and connect to it.
• Resolve an unique public global internet (IP?) address or ID for each client (how?)
• Exchange these addresses between clients
• Make direct connection possible by some actions with clients' NATs
• Connect clients directly p2p to each other using received unique addresses
• Disconnect from XMPP server
• Communicate via my own p2p connection

If the sequence is correctly, what specific actions do I need to do to resolve unique addresses, and to make an UDP or TCP connection then? How that can be done on c++?

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Edit.

I've found nice answer here: Programming P2P application

Answer 1

Your situation is close to WebRTC: peers need a way to 1) discover each other ("signaling"), 2) set up a direct connection through NAT if needed. (STUN/TURN)

See this WebRTC infrastructure overview for a start, and ask more specific follow-up questions later.