Network convergence and the NAT/Firewall problems

Voice over IP technology is fueling the rapid growth on network convergence and we are seeing the successful deployment of converged networks within enterprises. However, most enterprises today sit behind firewalls and also use private IP addressing behind NATs (network address translators). These NATs and firewalls cause significant problems for multimedia over IP to work and function properly. There are presently two standards for VoIP signaling: H.323 (from ITU-T) and SIP (session initiation protocol from IETF). In this paper we present the details of the problems and issues associated with NATs/firewalls and then survey some ways to solve this problem for SIP. There is no single best solution yet. However, this paper discusses how such a simple and elegant solution can be built. This problem remains a significant obstacle for the successful adoption of convergence as security has become even more important to enterprises than adoption of emerging technologies.