Edge-Case Integration into Established NAT Traversal Techniques

Traversing Network Address Translation (NAT) is often necessary for establishing direct communication between clients. The traversal of NAT with static port translation is solved in many cases by the Session Traversal Utilities for NAT (STUN) protocol. Nevertheless, it does not cover the traversal of progressing symmetric and random symmetric NAT, which make it necessary to correctly predict opened ports. This paper presents a method for predicting (a) progressing symmetric NAT-translated ports based on a network traffic model and the Expected Value Method, and (b) random symmetric NAT-translated ports based on heuristics between monitored and opened ports across numerous traversal attempts. Tests were conducted in German cities using local cellular communication providers. Compared to established approaches, they yielded considerable improvements traversing progressing symmetric NAT and slight improvements traversing random symmetric NAT in real-world environments.