A Provider-Level Reputation System for Assessing the Quality of SPIT Mitigation Algorithms

The prevention of Spam over IP telephony (SPIT) is one of the greatest challenges for future large-scale deployments of VoIP telephony solutions. Some useful information for detecting SPIT calls is only available at the caller's VoIP provider. Recent approaches therefore suggest the signalling of such information among providers. However, there is currently no way for a receiving provider to assess the trustwortiness or the semantics of SPIT-related information received. Our approach tackles this problem by applying a provider-level reputation system, based on SPIT tags assigned to outgoing SIP messages by the caller's provider. The system provides an incentive to tag outgoing calls correctly, and it translates tags with arbitrary semantics into meaningful SPIT probabilities. We show analytically that our system significantly improves the receiving provider's assessment of SPIT tags.