Creating Peer to Peer connections using intermedia

Question

I want to connect two clients (via TCP/IP sockets). The clients can discover each other using an intermediate server. Once the clients discover each other, there should not be any involvement of the server.

I made some study about this and found many people suggesting JXTA. But I'd like to create the protocol myself from scratch (because in future I might have to implement the same using WebSockets as well (when my client is a Browser)). Currently, my clients can be Desktop applications or mobile applications.

My questions are:

1. How will clients discover each other at the server? If the server sends the global IP address of the clients to each other, will that information be enough to create a peer-to-peer connection? What if the clients are on the same LAN network and the server is on a different WAN?

2. Client have dynamic IP address. Can their IP change all of a sudden even if it has an active socket?

3. Is peer-to-peer connection is reliable for transfer of non-continuous data (like in chat application)?

[NOTE: by peer-to-peer connection I mean establishing a client-server TCP/IP socket connection (using Java) by making one of the client as temporary socket-server]

Thanks in advance.

Answer 1

1) When the clients connect to the server they will have to notify the server of the port number they will keep open for incoming connections from other clients. The server will know client's IP address. Then the server will need to communicate/send these details to the other party/client. The actual location of the clients does not make any difference. If two clients are on the same network the network routers will find them and make their communication paths shorter.

2) Dynamic IP address can NOT change during active connection - if it does the connection will be dropped and both clients will have to re-initiate the connection through the server in 1)

3) Yes