An Effective NAT Traversal Mechanism for SIP/IMS Services in SDN-Enabled All-IP Mobile Networks

Network Address Translation (NAT) is the major solution to ease the IP address shortage problem and support the upcoming demands of huge IP address from the Machine-to-Machine communications and Internet of Things . However, NAT breaks the peer-to-peer communications and blocks the Internet-oriented requests. In order to resolve the problems, lots of NAT traversal solutions such as Session Traversal Utilities for NAT, Universal Plug-and-Play, Traversal Using Relay NAT, Application-Layer Gateway (ALG) and Interactive Connectivity Establishment have been proposed. Among the NAT traversal solutions, the 3rd Generation Partnership Project adopts the ALG solution for SIP/IMS multimedia services in the mobile networks. The ALG solution does not require modifications to the clients (e.g., User Equipments). However, the ALG solution utilizes the Real-time Transport Protocol (RTP) proxy to translate the RTP packets, and thus this solution produces extra delay and packet loss possibility to the RTP packets. In this paper, we integrate Software-defined networking (SDN) to the All-IP mobile networks and propose a solution to improve the ALG solution in the SDN-enabled All-IP mobile networks. We derive the analytic models for analyzing the ALG solution and the proposed solution, and compare these two solutions in terms of the throughput, loss rate and delay.