Detecting VoIP calls hidden in web traffic

Peer-to-peer (P2P) voice over IP (VoIP) applications (e.g. Skype or Google Talk) commonly use Web TCP ports (80 or 443) as a fallback mechanism to delude restrictive firewalls. This strategy renders this kind of traffic quite difficult to be detected by network managers. To deal with this issue, we propose and evaluate a method to detect VoIP calls hidden in Web traffic. We validate our proposal considering both Skype and Google Talk generated traffic by using real-world experimental data gathered at a commercial Internet Service Provider (ISP) and an academic institution. Our experimental results demonstrate that our proposed method achieves a performance of around 90% detection rate of VoIP calls hidden in Web traffic with a false positive rate of only 2%, whereas a 100% detection rate is achieved with a false positive rate limited to only 5%. We also evaluate the feasibility of applying our proposal in real-time detection scenarios.