The most threatening attacks for VoIP service providers and enterprises are those that can degrade the quality of voice, thus rendering the service useless. The simplest way to achieve voice quality degradation is through Denial of Service (DoS) and Distributed Denial of Service (DDoS) attacks. VoIP communication brings another dimension into the security challenge by introducing both control (signaling) and content (voice) parallel channels which together form the VoIP service. The dependence of these channels on one another drastically increases the risk that VoIP service can be damaged, as each one of the channels has its own vulnerabilities. It doesn’t matter which vulnerability is exploited because the attack renders the whole service uselss.