As IP telephony becomes more widely deployed and used, tele-marketers or other spammers are bound to start using SIP-based calls and instant messages as a medium for sending spam. As is evident from the fate of email, protection against spam has to be built into SIP systems otherwise they are bound to fall prey to spam. Traditional approaches used to prevent spam in email such as content-based filtering and access lists are not applicable to SIP calls and instant messages in their present form. We propose Domain-based Authentication and Policy-Enforced for SIP (DAPES): a system that can be easily implemented and deployed in existing SIP networks. Our system is capable of determining in real time, whether an incoming call or instant message is likely to be spam or not, while at the same time, supporting communication between both known and unknown parties. DAPES includes the deployment of reputation systems in SIP networks to enable real-time transfer of reputation information between parties to allow communication between entities unknown to each other.
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