Establishing TCP connections between hosts behind NATs

Firewalls and Network Address Translation (NAT) devices are becoming increasingly prevalent, and they pose a significant problem for connection establishment for peer-to-peer protocols. This paper proposes novel mechanisms to create direct TCP connections between two hosts behind NATs with minimal help from a third-party. We implement two of these solutions on common hardware within a common environment. Once this connection is established, the applications can communicate with each other using a standard TCP implementation with no further external help.