SPAM over Internet Telephony and how to deal with it
  In our modern society telephony has developed to an omnipresent service. People are available at anytime and anywhere. Furthermore the Internet has emerged to an important communication medium. These facts and the raising availability of broadband internet access has led to the fusion of these two services. Voice over IP or short VoIP is the keyword, that describes this combination. The advantages of VoIP in comparison to classic telephony are location independence, simplification of transport networks, ability to establish multimedia communications and the low costs. Nevertheless one can easily see, that combining two technologies, always brings up new challenges and problems that have to be solved. It is undeniable that one of the most annoying facet of the Internet nowadays is email spam. According to different sources email spam is considered to be 80 to 90 percent of the email traffic produced. The threat of so called voice spam or Spam over Internet Telephony (SPIT) is even more fatal, for the annoyance and disturbance factor is much higher. As instance an email that hits the inbox at 4 p.m. is useless but will not disturb the user much. In contrast a ringing phone at 4 p.m. will lead to a much higher disturbance. From the providers point of view both email spam and voice spam produce unwanted traffic and loss of trust of customers into the service. In order to mitigate this threat different approaches from different parties have been developed. This paper focuses on state of the art anti voice spam solutions, analyses them and reveals their weak points. In the end a SPIT producing benchmark tool will be introduced, that attacks the presented anti voice spam solutions. With this tool it is possible for an administrator of a VoIP network to test how vulnerable his system is. 
Andreas U. Schmidt, Nicolai Kuntze, Rachid El Khayari