Detection and filtering Spam over Internet Telephony — a user-behavior-aware intermediate-network-based approach

VoIP applications have gained popularity due to largely reduced cost and wider range of advanced services, as compared to traditional telephone networks. However, SPIT (spam over Internet telephony), known as unsolicited bulk calls sent via VoIP networks, is becoming a major problem that would undermine the usability of VoIP. Unlike detection and filtering of e-mail spam, countermeasures against SPIT face great challenges on how to identify and filter SPIT in real time. In this paper, a user-behavior-aware anti-SPIT technique implemented at the router level for detecting and filtering SPIT is proposed. The rationale for the technique is that voice spammers behave significantly different from legitimate callers because of their revenue-driven motivations. The technique defines and combines three features developed from user behavior analyses to detect and filter spam calls. Compared to existing SPIT defending techniques, it is simple, fast and effective. Other advantages of our approach are that it is applicable for detecting and filtering both machine-initiated and human-initiated spam calls, better protects VoIP calls against sybil attacks and spammer behavior changes.