[1] VoIP systems, like e-mail and other Internet applications, are susceptible to abuse by malicious parties who initiate unsolicited and unwanted communications, such as telemarketers and prank callers.
VoIP calling rates are cheap, and the technology provides convenient, often free tools, such as Asterisk and other applications.
The primary underlying technology driving this threat is the Session Initiation Protocol (SIP),[2] which is a standard for VoIP telecommunications.
The vast amount of work on spam detection in emails does not directly apply here because of the real-time nature of the voice calls.
A statistical analysis of the signaling traffic and in particular the call frequency can be used to detect anomalies, to observe and finally to black-list suspicious callers.
SymRank[9] adapts of the PageRank algorithm and computes the reputation of subscribers based on both incoming and outgoing calls.
Some recent smartphone vendors are incorporating notification of possible spam for incoming calls, such as Google in its Nexus Android devices[14] and Apple in its iOS 10 release.
Commercial VoIP software for communication service providers may include a behavioral analysis, e.g. Acme Packet Palladion.