I started to explore the option of connecting with other using a p2p connection, so I coded a simple socket program in JAVA for android devices in which the users can share simple messages p2p (I didn&#39;t have any idea about NAT then). I got to know about NAT, so I now need to establish a TCP connection with another user which uses a server for discovery but payload is transferred p2p. I have also looked at XMPP(a very good and detailed explanation of how protocol works is [here][1]) and UPnP but I dont know how to implement them.

Another interesting question that arises is of BitTorrent because they can work on any device and even behind a NAT. I am not able to get any explanation of how BitTorrent works.

I have researched a lot but I am stuck.

My questions are:

1. A detailed explanation of BitTorrent(like [here][1], not how torrents work) and how is it able to work around NAT ?
2. Is there a way to make a NAT entry programmatically ?
3. Is socket programming sufficient for p2p ?
3. How difficult is it to create your own protocol and how can I build one ?
4. If two devices D1 and D2 want to communicate p2p and they know each other&#39;s IP. D1 sends a request to D2 and that can&#39;t get through the D2&#39;s NAT, but there should be an entry created in D1&#39;s NAT. So when D2 tries to send something D1&#39;s NAT should discover an entry with D2&#39;s IP. Then why is the packet not allowed by it ?


  [1]: http://ceit.uq.edu.au/content/how-xmpp-works-step-step

All Nat Solutions on Gang of Coders

Total of 1 Nat Solutions

Connecting P2P over NAT?