Asynchronous file transfer in ASP.Net Chat Application (peer to peer)

I've developed a chat application using WCF/ASp.net. I want to asynchronously transfer a file from one chat user to another chat user. What is best approach for this?

here are my insights/doubts

1. Do i need a central server between two users to assist the file transfer?
2. Can i create a direct channel without a central server?
3. Do i need to store/upload it anywhere for file transfer?
4. How should i开发者_开发问答 make the file transfer reliable?

I found that it is virtually impossible to do the file transfer by establishing a channel between the two clients directly without a server. So a central server should exist to server the file transfer. I also i found that WCF offers excellent support for file transfer in terms of different bindings and chunking-mechanism.