[Twisted-Python] Problem with NAT Traversal

[hz hanks]

Hi, All

I'm working with a small program to realize P2P file transfer.
Therefore, I have to accomplish the function of NAT traversal. From
the searching result, I know that it always requires a public server
to initialize the transfer, but I don't have one. Now, my idea is
that, we already have many communication ways such as the cell phone, so
one side of P2P file transfer program can just run a 'touch' function
to know some parameters, such as the port number and the public IP
address, and just display them to the users. And the users will
guarantee that the other side P2P file transfer program will know
these parameters. However, I don't know any function in python can
achieve the 'touch' function. Any one has some experience on this?  It
would be even better if any function in twisted can achieve that,
because most part of my program is adopted from twisted.
Really appreciated.

Best,
Hanks