VoIP Spam Prevention

摘要

Like email and conventional telephony, Voice over IP telephony is subject to spam. This paper discusses the problem of spam over IP telephony and investigates techniques which use the Session Initiation Protocol (SIP) to reject likely nuisance callers. Existing techniques include content filtering, black lists, white lists, gray lists, call rate monitoring, IP/domain correlation, consent-based communications, reputation systems, address obfuscation, limited-use addresses, computational puzzles, payments at risk, legislation, circles of trust, centralized SIP providers, and authenticated identity. A new technique using a text-based Turing test is proposed and demonstrated to be compatible with the SIP protocol.