An Effective NAT Traversal Mechanism for IMS Applications in 3GPP Networks

Network Address Translation (NAT) is the major solution to solve IP address shortage. However, NAT breaks the peer-to-peer communications and the Internet-oriented requests. In order to resolve this problem, lots of NAT traversal solutions such as Session Traversal Utilities for NAT (STUN), Universal Plug-and-Play (UPnP), Traversal Using Relay NAT (TURN), Application-Layer Gateway (ALG) and Interactive Connectivity Establishment (ICE) have been proposed. The 3rd Generation Partnership Project (3GPP) adopts the ALG solution, which does not require modifications to the clients, to resolve the NAT traversal problems. The ALG solution utilizes the RTP proxy to translate the RTP packets, and RTP packets increases extra delay and packet loss possibility. This paper proposes a solution to improve the ALG solution for IMS applications in 3GPP environments. We derive the analytic models for analyzing the ALG and the proposed solutions and compare these two solutions in terms of in throughput and delay.