STUN-based connection sequence through symmetric NATs for TCP connection

Network Address Translation (NAT) is one of the solutions against IPv4 address shortage. They sometimes prevent the acts of Peer-to-Peer applications. Session Traversal Utilities for NATs (STUN) is one of the solutions and it is effective for many kinds of NATs. However, symmetric NAT, a kind of NAT, does not applied STUN. We implement a extension of STUN to apply it for symmetric NAT, and also measure its overhead. As a result, symmetric NAT can be traversed with our method and it causes some overhead which hardly affect to use the connections.